U.S. patent application number 13/797694 was filed with the patent office on 2013-07-25 for frac water heater and fuel oil heating system.
The applicant listed for this patent is Ronald L. Chandler. Invention is credited to Ronald L. Chandler.
Application Number | 20130189629 13/797694 |
Document ID | / |
Family ID | 48797501 |
Filed Date | 2013-07-25 |
United States Patent
Application |
20130189629 |
Kind Code |
A1 |
Chandler; Ronald L. |
July 25, 2013 |
FRAC WATER HEATER AND FUEL OIL HEATING SYSTEM
Abstract
An accessory heat exchanger unit for heating the fuel oil used
by the frac oil heater system of the invention prior to combustion.
The accessory heat exchanger unit receives and distributes the fuel
oil through a plurality of heat exchanger tubes prior to directing
the oil to the combustion chamber. The unit also includes an inlet
for receiving heated treatment fluid from the frac water heater
system of the present invention. The heated treatment fluid passes
over the plurality of heat exchanger tubes of the accessory heat
exchanger unit prior to being directed to the outlet of the
accessory heat exchanger unit. By heating the fuel oil prior to
combustion, the accessory heat exchanger unit greatly improves the
viscosity and flow rate of the fuel oil, thereby allowing cheaper,
less cold-tolerant grades of fuel oil to be used in extreme cold
climates with no degradation in the operation of the frac water
heater system of the present invention.
Inventors: |
Chandler; Ronald L.;
(Wichita Falls, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chandler; Ronald L. |
Wichita Falls |
TX |
US |
|
|
Family ID: |
48797501 |
Appl. No.: |
13/797694 |
Filed: |
March 12, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12352505 |
Jan 12, 2009 |
|
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13797694 |
|
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61078734 |
Jul 7, 2008 |
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Current U.S.
Class: |
431/11 ;
431/207 |
Current CPC
Class: |
F23K 5/20 20130101; F24H
1/06 20130101; F24H 1/40 20130101; F28D 7/08 20130101; F28D
2021/008 20130101; F28D 2021/0059 20130101; F28D 7/02 20130101;
F28D 7/0066 20130101; F24H 9/2035 20130101 |
Class at
Publication: |
431/11 ;
431/207 |
International
Class: |
F23K 5/20 20060101
F23K005/20 |
Claims
1. An accessory fuel oil heating system for a frac-water heating
system, comprising: a heat exchanger unit having a manifold for
receiving and distributing fuel oil through a plurality of heat
exchanger tubes prior to directing said fuel oil to the burners of
the frac-water heating system for combustion, said heat exchanger
unit having an inlet for receiving heated treatment fluid from the
frac-water heating system and directing the heated treatment fluid
over the plurality of heat exchanger tubes prior to directing the
heated treatment fluid to an outlet of said heat exchanger
unit.
2. The accessory fuel oil heating system of claim 1, wherein the
heat exchanger unit comprises a heat exchanger manifold assembly
coaxially aligned with an outer housing unit.
3. The accessory fuel oil heating system of claim 2, further
comprising at least support bracket configured around the plurality
of heat exchanger tubes, wherein the support bracket maintain the
spacing and alignment of the heat exchanger tubes and prevent the
heat exchanger tubes from contacting the outer housing unit.
4. The accessory fuel oil heating system of claim 2, wherein the
outer housing unit includes an inlet having a diameter almost twice
as large as the diameter of the outlet.
5. The accessory fuel oil heating system of claim 1, wherein the
manifold includes a passageway which extends through the manifold
for receiving the heated treatment fluid.
6. The accessory fuel oil heating system of claim 1, wherein said
manifold comprises an inlet chamber fluidly connected to an outlet
chamber by the plurality of heat exchanger tubes.
7. The accessory fuel oil heating system of claim 6, wherein the
inlet chamber is fluidly connected to a fuel tank via a fuel pump
and pressurized fuel line.
8. The accessory fuel oil heating system of claim 7, wherein the
pressurized fuel line includes an isolation valve and a by-pass
valve for bypassing heat exchanger unit when not needed.
9. The accessory fuel oil heating system of claim 1, further
comprising a pressure relief valve configured downstream of the
heat exchanger unit to allow excess heated fuel oil to be directed
back into the fuel tank.
10. The accessory fuel oil heating system of claim 1, wherein the
plurality of heat exchanger tubes are U-shaped and each has a
different length.
11. The accessory fuel oil heating system of claim 1, wherein the
inlet of said heat exchanger unit is fluidly connected to an outlet
conduit of the frac-water heating system.
12. The accessory fuel oil heating system of claim 1, wherein the
outlet of said heat exchanger unit is fluidly connected to an
outlet manifold of the frac-water heating system.
13. The method for heating fuel oil prior to combustion in a
frac-water heating system, comprising in combination: directing
fuel oil to a manifold of a heat exchanger unit, wherein said
manifold receives and distributes said fuel oil through a plurality
of heat exchanger tubes prior to directing said fuel oil to the
burners of the frac-water heating system for combustion, supplying
an inlet in the heat exchanger unit with heated treatment fluid
from the frac-water heating system; directing the heated treatment
fluid over the plurality of heat exchanger tubes prior to directing
the heated treatment fluid to an outlet of said heat exchanger
unit.
14. The method for heating fuel oil of claim 13, wherein the step
of supplying the inlet of the heat exchanger with heated treatment
fluid comprises fluidly connecting the inlet of the heat exchanger
unit to an outlet conduit of the frac-water heating system.
15. The method for heating fuel oil of claim 13, wherein the heated
treatment fluid passes over the plurality of heat exchanger tubes
in a single pass.
16. The method for heating fuel oil of claim 13, wherein said
manifold distributes the fuel oil through the plurality of heat
exchanger tubes by receiving fuel oil in an inlet chamber that is
fluidly connected to an outlet chamber by the plurality of heat
exchanger tubes.
17. The method for heating fuel oil of claim 16, wherein the step
of directing fuel oil to the manifold of the heat exchanger unit
comprises fluidly connecting the inlet chamber to a fuel tank via a
fuel pump and pressurized fuel line.
18. The method for heating fuel oil of claim 17, further comprising
allowing excess heated fuel oil to be directed back into the fuel
tank by configuring a pressure relief valve downstream of the heat
exchanger unit.
19. The method for heating fuel oil of claim 13, further comprising
fluidly connecting the outlet of the heat exchanger unit to an
outlet manifold of the frac-water heating system to direct heated
treatment fluid to a wellbore application.
20. The method for heating fuel oil of claim 13, wherein said
treatment fluid is heated from 40.degree. F. to 210.degree. F. in
ambient atmospheric temperatures below 25.degree. F. while pumping
treatment fluid through said heat exchanger unit at a volumetric
flow rate ranging from 200-250 gpm.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/352,505 filed on Jan. 12, 2009, which
claims the benefit of and priority to U.S. Provisional Patent
Application No. 61/078,734 filed Jul. 7, 2008, the technical
disclosure of which is hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to an apparatus and method for
heating fuel oil prior to combustion for subsequent use in heating
a water or petroleum based fluid for injection into an oil or gas
well or into a pipeline system. In particular, the present
invention relates to an apparatus and method for pre-heating fuel
oil prior to combustion to improve its viscosity and combustion
characteristics in cold weather.
[0004] 2. Description of the Related Art
[0005] It is common in the oil and gas industry to treat oil and
gas wells and pipelines with heated fluids such as water and oil.
For example, one such application commonly known as a hydraulic
fracturing job or "frac" job, involves injecting large quantities
of a heated aqueous solution into a subterranean formation to
hydraulically fracture it. Such frac jobs are typically used to
initiate production in low-permeability reservoirs and/or
re-stimulate production in older producing wells. Water is
typically heated to a specific temperature range to prevent
expansion or contraction of the downhole well casing. The heated
water is typically combined with a mixture of chemical additives
(e.g., friction reducer polymers which reduce the viscosity of the
water and improve its flowability so that it's easier to pump down
the well), proppants (e.g., a special grade of light sand), and a
cross-linked guar gel that helps to carry the sand down into the
well. This fraccing fluid is then injected into a well hole at a
high flow rate and pressure to break up the formation, increasing
the permeability of the rock and helping the gas or oil flow toward
the surface. As the fraccing solution cracks the rock formation, it
deposits the sand. As the fractures try to close, the sand keeps
them propped open. Frac jobs are typically performed once when a
well is newly drilled, and again after a couple of years when the
production flow rate begins to decline
[0006] Another application, commonly referred to as a "hot oil
treatment", involves treating tubulars of an oil and gas well or
pipeline by flushing them with a heated solution to remove build up
of paraffin along the tubulars that precipitate from the oil stream
that is normally pumped therethrough.
[0007] Frac jobs and hot oil treatments are typically performed at
the remote well sites and usually require less than a week to
complete. Consequently, the construction of a permanent heating
facility at the well site is not cost effective. Instead, portable
heat exchangers, which are capable of transport to remote well
sites via improved and unimproved roads, are commonly used.
[0008] In the past, such portable heat exchangers have typically
employed gas-fired heat sources using a liquefied petroleum gas
(LPG) such as propane to heat treatment fluids at remote well
sites. Such gas-fired heater units typically include a tubular coil
heat exchanger configured above one or more open flame gas burners
in an open-ended firebox housing. The tubular coil heat exchanger
typically comprises a fluid inlet in communication with a plurality
of interconnected tubes, which in turn communicate with a fluid
outlet. The plurality of tubes are typically arranged in a stacked
configuration of planar rows, wherein each tube in a row is aligned
in parallel with the other tubes. The outlet of each tube is
connected in series to the inlet of an adjacent tube in the row by
means of a curved tube or return bend. Similarly, each planar row
is connected to the adjacent rows above and below by connecting the
outlet of the outermost tube in one row with the inlet of the
outermost tube in another row by means of a curved tube or return
bend.
[0009] The one or more gas burners are typically positioned below
the tubular coil heat exchanger so as to project a vertical flame
up and through the heat exchanger. The gas burners are supplied
with gas fuel from a nearby gas storage tank (e.g., a propane
tank). Ambient air is also supplied to the burners via the
opened-ended bottom of the firebox housing. The hot flue gasses
generated from the burning of the LPG rise up and through the
tubular coil heat exchanger within the firebox housing and exhaust
via a vent at the top of the firebox housing.
[0010] While gas-fired heat sources are adequate for performing
many oil field servicing tasks, they exhibit a number of inherent
drawbacks. These inherent limitations significantly impact their
effectiveness in performing certain heating operations at remote
oil field work sites. For example, frac jobs typically require the
production of massive volumes of heated water. While gas-fired heat
sources are certainly capable of heating fluids such as water, they
are poorly suited to heating in a timely manner large volumes of
continuously flowing water in many commonly occurring climactic and
atmospheric conditions. Moreover, the logistics involved in
conducting such heating operations at remote work sites negatively
impacts the cost efficiencies of such a system.
[0011] For example, LPG (e.g., propane gas) has a relatively low
energy content and density when compared to other fuel options. For
example, diesel fuel when properly combusted typically releases
about 138,700 British thermal units (BTU) per US gallon, while
propane typically releases only about 91,600 BTU per liquid gallon,
or over 33% less. Thus, gas-fired heating units often lack
sufficient heating capacity to produce sufficient quantities of
heated water rapidly enough for the required operation to be
completed. Consequently, in order to provide sufficient quantities
of heated water on a timely basis for a typical frac job, the
treatment water must often be preheated and stockpiled in numerous
frac water holding tanks. These holding tanks range in size up to
500 bbl (i.e., approximately 21,000 gallons). It is not unusual for
a typical frac job to require 10 or even 20 frac water holding
tanks at the remote work site. The preheated water is typically
overheated so as to allow for cooling while waiting to be injected
into the well. Oftentimes, the preheated treatment water must be
reheated just prior to injection into the well head. Needless to
say, the logistics involved with providing additional holding tanks
at the remote work site and the additional costs incurred in
overheating or reheating the supply water negatively impacts the
efficiency of the overall operation.
[0012] While the technique of overheating and stockpiling supply
water can ameliorate some the shortcomings in the heating capacity
of gas-fired heat sources, in certain circumstances (e.g., severely
cold weather or high altitude) it is inadequate. This is due to a
number of reasons. First, the temperature change requirement for
the system is simply greater in colder weather. That is, in colder
weather the intake water supplied to the gas-fired heating unit is
colder while the required injection temperature remains essentially
the same. Thus, it takes longer for the gas-fired heating unit to
preheat the supply water. The problem is further compounded by the
fact that the stockpiled preheated water cools more rapidly in
colder weather. Moreover, at higher altitudes there is less oxygen
in the ambient atmosphere for combustion in the gas burner. Thus,
at higher altitudes the heating capacity of gas-fired heat sources
is further reduced.
[0013] In addition, propane gas requires large and heavy
high-pressure fuel tanks for its transport to remote sites. The
size of such high-pressure fuel tanks is, of course, limited by the
size of existing roads. Thus, a typical frac job may require the
transport of multiple large high-pressure fuel tanks to a remote
site to ensure an adequate supply of fuel to complete the
operation.
[0014] Furthermore, there are several safety concerns which must be
taken into consideration when using gas-fired heat sources. As
mentioned previously, current gas-fired heat exchangers typically
use an open flame burner, i.e., a burner which is open to the
ambient atmosphere. The fire boxes of such heat exchanger are
typically elevated above the ground and opened on the bottom. The
gas-fired burners are typically positioned near the open bottom of
the firebox and directly below the heat exchange tubing. The
gas-fired burners draw ambient air as necessary to assist in the
combustion of the propane gas. While simple and efficient in
providing air for combustion, open flame burners present a number
of safety concerns. An open flame at the well site poses a
substantial risk of explosion and uncontrolled fire, which can
destroy the investment in the rig and injure or even cost the lives
of the well operators. Moreover, open flame burners are
particularly susceptible to erratic burning or complete blow-out in
gusty wind conditions. Current U.S. government safety regulations
provide that the open flame heating of the treatment fluids cannot
take place within the immediate vicinity of the well.
[0015] While safety concerns are of overriding importance,
compliance with the no open-flame regulations requires additional
time and expense to conduct heated fluid well treatments. Thus,
there has been a long felt need for a safer and more efficient
apparatus and method of heating a treatment fluid for injecting
into the tubulars of oil and gas wells and pipelines without using
an open flame heat source in the vicinity of the treatment
location.
[0016] The present invention discloses an oil-fired heat exchanger,
which provides enhanced frac-water heating capabilities in the
field. However, operation of the present invention in extreme cold
climates has revealed a need for additional improvements. For
example, in extreme cold climates standard fuel oil (e.g., standard
diesel fuel) used for combustion by the system tends to gel
together. Moreover, paraffin (a common component of standard diesel
fuel) begins to crystallize when cold weather strikes, which
further degrades the viscosity and flow characteristics of the fuel
oil in the system of the present invention. Maintaining proper
viscosity and flow characteristics of the fuel oil in the system of
the present invention is critical to ensuring proper combustion of
the air-fuel mixture. In the past, this problem has been alleviated
by using fuel additives or switching to a more cold-tolerant grade
of fuel oil when operating in extreme cold climates. However, such
remedies often come with significant increases in operating costs.
For example, using fuel additives or switching to more
cold-tolerant grades of fuel oil noticeably increases the operating
costs on a per gallon basis. When multiplied by the large volumes
consumed by the frac-water heater of the present invention, the
costs associated with an operating cycle are significant. For
example, the frac-water heater of the present invention can easily
consume well over 8,500 gallons of fuel oil in a 24-hour operation.
Thus, a further need exists for an improved method and apparatus
for operating the present frac-water heating system in extreme cold
climates without the added expense of fuel additives or using a
more cold-tolerant grade of fuel oil.
SUMMARY OF THE INVENTION
[0017] The present invention overcomes many of the disadvantages of
prior art mobile oil field heat exchange systems by providing an
oil-fired heat exchange system. The present invention is a
self-contained unit which is easily transported to remote
locations. In one embodiment, the present invention is disposed on
a trailer rig and includes a closed-bottom firebox having a
forced-air combustion and cooling system. The rig also includes
integral fuel tanks, hydraulic and pneumatic systems for operating
the rig at remote operations in all weather environments. In a
preferred embodiment, the oil-fired heat exchanger system is used
to heat water on-the-fly (i.e., directly from the supply source to
the well head) to complete a hydraulic fracturing operation.
[0018] The present invention comprises a closed firebox that
includes a novel heat exchanger comprised of a single-pass tubular
coil configured in a highly oscillating or serpentine manner and
oriented along multiple axes so as to maximize its exposure to the
heat generated by the oil-fired burner assemblies. The design of
the heat exchanger includes a horizontal tunnel configured within a
bottom portion. The oil-fired burner assemblies are configured and
oriented in relation to the tunnel so that their flames are
initially generated in a horizontal fashion into the tunnel within
the heat exchanger.
[0019] The present invention further includes a novel forced-air
combustion and cooling system. The forced-air system is comprised
of a primary air system and a secondary air system. The primary air
system provides pressurized air directly to the oil-fired burner
assemblies to maximize atomization and combustion of the fuel oil.
The secondary air system provides pressurized air to strategic
positions within the firebox to assist in controlling the cooling
of the firebox and to maximize the combustion of the fuel/air
mixture. In addition, vents and vent passageways are formed in the
wall of the firebox and supply supplemental ambient air to front of
the burner assemblies. The vents allow the system to be operated
more safely by allowing burner access doors to be configured in a
"down" or "closed" position during operations, which significantly
reduces the operational noise created by burner assemblies when
operating. Moreover, with the burner access doors configured in the
"down" position, the danger inherent in a blowback event of the
burner assemblies is greatly reduced. The primary and secondary air
systems are powered by hydraulic pumps integral to the overall
system. The present invention also includes systems for regulating
and adjusting the fuel/air mixture within the firebox to maximize
the combustion efficiency.
[0020] The improved system of the present invention also includes
several subsystems for maximizing the safety and efficiency of the
heat exchanger system. The system includes a novel hood mechanism
attached to the exhaust stack of the firebox. In addition, the
system includes a novel intake air muffler/silencer system, which
significantly reduces the noise generated by the intake of such
large quantities of ambient air.
[0021] The system also includes novel methods for heating large
volumes of treatment fluids, such as water, in a continuously
flowing fashion so that heating operations can be performed
"on-the-fly", i.e., without the use of preheated stockpiles of
treatment fluid. For example, water at ambient conditions can be
drawn into the device of the present invention and heated so that
sufficient volumes of continuously flowing heated treatment fluid
may be supplied directly to the well head for conducting hydraulic
fracturing operations on the well. The system also includes novel
methods for controlling the heating of the treatment fluid as it
passes through the system. The system further includes novel
methods for controlling the temperature change and volume flow of
treatment fluid as it passes through the system.
[0022] The improved system of the present invention may further
include an accessory fuel oil heating system for heating the fuel
oil prior to combustion. The accessory fuel oil heating system
includes a heat exchanger unit having a manifold for receiving and
distributing the fuel oil through a plurality of heat exchanger
tubes. The unit further includes an inlet for receiving heated
treatment fluid from the frac water heater system of the present
invention. The heated treatment fluid from the frac water heater
system passes over the plurality of heat exchanger tubes of the
accessory heat exchanger unit prior to being directed to the outlet
of the accessory heat exchanger unit. The accessory fuel oil
heating system can be integral to the frac water heater system of
the present invention or comprise a separate unit which may be
selectively incorporated into an oil-fired frac water heating
system. By heating the fuel oil prior to combustion, the accessory
fuel oil heating system of the present invention greatly improves
the viscosity and flow rate of the fuel oil, thereby allowing
cheaper, less cold-tolerant grades of fuel oil to be used in
extreme cold climates with no degradation in the operation of the
system of the present invention. In addition, any preheated fuel
oil that is not sent to the burner will be returned to the fuel
tank to help preheat the fuel of in the fuel tank.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] A more complete understanding of the method and apparatus of
the present invention may be had by reference to the following
detailed description when taken in conjunction with the
accompanying drawings, wherein:
[0024] FIG. 1 is a perspective view of an embodiment of the
Oil-Fired Heat Exchanger of the present invention;
[0025] FIG. 2A is a left side elevation view of the embodiment of
the Oil-Fired Heat Exchanger of the present invention shown in FIG.
1;
[0026] FIG. 2B is a right side elevation view of the embodiment of
the Oil-Fired Heat Exchanger of the present invention shown in FIG.
1;
[0027] FIG. 2C is a close-up view of the mechanism for opening and
closing the opposing hood doors of the embodiment of the Oil-Fired
Heat Exchanger of the present invention shown in FIG. 2B;
[0028] FIG. 3 is an overhead plan view of the embodiment of the
Oil-Fired Heat Exchanger of the present invention shown in FIG.
1;
[0029] FIG. 4A is a front perspective view of an embodiment of the
heat exchanger of the Oil-Fired Heat Exchanger of the present
invention;
[0030] FIG. 4B is a back perspective view of the embodiment of the
heat exchanger shown in FIG. 4A;
[0031] FIG. 4C is a cross-sectional view of the embodiment of the
heat exchanger shown in FIGS. 4A and 4B installed in the embodiment
of the Oil-Fired Heat Exchanger of the present invention shown in
FIG. 1;
[0032] FIG. 5 is perspective view of a portion of the primary and
secondary air systems of the Oil-Fired Heat Exchanger of the
present invention;
[0033] FIG. 6 is cut-away cross-sectional view of a portion of the
secondary blower section of the secondary air system of the
Oil-Fired Heat Exchanger of the present invention;
[0034] FIG. 7 is a schematic depiction of the hydraulic, fuel, and
air supply systems of the embodiment of the Oil-Fired Heat
Exchanger of the present invention shown in FIG. 1;
[0035] FIG. 8 is an overhead view of the schematic depiction of the
hydraulic, fuel, and air supply systems of the embodiment of the
Oil-Fired Heat Exchanger of the present invention shown in FIG.
7;
[0036] FIG. 9 is a schematic depiction of an embodiment of the
accessory fuel oil heating system of the present invention;
[0037] FIG. 10 is a perspective view of an embodiment of an
accessory heat exchanger unit in the system thereof`
[0038] FIG. 11A is an overhead plan view thereof;
[0039] FIG. 11B is a partial cross-sectional view thereof;
[0040] FIG. 12 is a partial exploded view thereof;
[0041] FIG. 13A is an elevation view of the inlet end thereof;
[0042] FIG. 13B is a partial cross-sectional view of the inlet end
shown in FIG. 13A;
[0043] FIG. 14A is a cross-sectional view of the accessory heat
exchanger unit shown in FIG. 11B at line 14A-14A; and
[0044] FIG. 14B is a plan view of the support bracket shown in FIG.
14A.
[0045] Where used in the various figures of the drawing, the same
numerals designate the same or similar parts. Furthermore, when the
terms "top," "bottom," "first," "second," "upper," "lower,"
"height," "width," "length," "end," "side," "horizontal,"
"vertical," and similar terms are used herein, it should be
understood that these terms have reference only to the structure
shown in the drawing and are utilized only to facilitate describing
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0046] With reference to the Figures, and in particular to FIGS. 1
and 2A-C, an embodiment of the improved oil-fired heat exchanger
system 100 of the present invention is shown. The embodiment 100
shown in the Figures is configured to be an oil-fired frac water
heater system. As depicted, the embodiment of the frac water heater
system 100 is configured on a drop deck trailer 14 and suitable for
transport to remote oil field sites. The system 100 includes a fuel
storage and supply system, a firebox 40 containing a single heat
exchanger 50, primary 70 and secondary 80 air supply systems
connected to the firebox 40, and an auxiliary power plant 30 for
driving an accessory gearbox 32. The accessory gearbox 32, in turn,
drives multiple hydraulic pumps, which power a main fluid pump 94
and the air supply systems. The main fluid pump 94 is used to draw
fluid, such as water, from a fluid source and supply it to the
intake 51 of the heat exchanger 50. The hydraulic pressure
generated by the main fluid pump 94 effectively pumps the fluid
through the heat exchanger 50 where it is heated. As the treatment
fluid proceeds through a single pass of the heat exchanger 50 it
increases in temperature until it reaches an outlet 52 of the heat
exchanger 50 where it is directed via tubular conduits or hose to
the well head for injection into the formation. The system 100 also
includes a control quadrant 10 and control levers 12 for operating
and monitoring the system 100.
[0047] As shown in the embodiment depicted in the Figures, the
entire frac water heater system 100 is configured on a single drop
deck trailer 14 having multiple wheels 16 and connected to a
separate towing vehicle 2. It is understood that alternate
embodiments of the system of the present invention may be skid
mounted or configured integral to a single vehicle. In addition,
the subject invention may also be configured so that one or more of
the various components of the system (e.g., fuel tank 20, firebox
40, and auxiliary power plant 30) are configured on separate
trailers, vehicles or skids for transport to the remote work
site.
[0048] With reference again to the Figures, and in particular to
FIGS. 2A-2C and 3, the components of the embodiment of the improved
oil-fired heat exchanger system 100 of the present invention will
be described in greater detail. As depicted in the Figures, the
embodiment the present invention 100 is disposed on a single
trailer rig 14 and includes a firebox 40 containing a single heat
exchanger 50, primary 70 and secondary 80 air supply systems
connected to the firebox 40, a fuel system for storing and
supplying fuel to multiple burner assemblies 60 configured in the
firebox 40, and an auxiliary power plant 30, which powers multiple
hydraulic systems and assorted auxiliary systems. The firebox 40
may also include at least one vent 40b and passageway 40c which
supplies ambient air from the upper exterior of the firebox 40 to
the front of the burner assemblies 60. The vent 40b and passageway
40c enable the burner assemblies 60 to operate with the access door
40a configured in a "closed" position, which significantly reduces
the operational noise created by burner assemblies 60 when
operating. Moreover, with the burner access doors 40a configured in
the "down" position (shown in FIG. 1), the danger inherent in a
blowback event of the burner assemblies 60 is greatly reduced.
Auxiliary Power Plant & Hydraulic System
[0049] As depicted in the Figures, the auxiliary power plant 30 is
configured near the front end of the trailer 14. The auxiliary
power plant 30 provides power for driving an accessory gearbox 32
and assorted auxiliary systems (e.g., electric, pneumatic). In one
embodiment, the auxiliary power plant 30 comprises a diesel engine,
which includes an electric alternator and air compressor.
Alternatively, the electric alternator and air compressor may be
powered by the accessory gearbox 32. The electric alternator
provides electrical power to the system 100 and the pneumatic
compressor provides pneumatic pressure for controlling the system
100.
[0050] The auxiliary power plant 30 provides the primary motive
force for driving the accessory gearbox 32. The accessory gearbox
32, in turn, drives multiple hydraulic pumps that power the
hydraulic systems of the present invention. Each hydraulic pump is
used to power an independent hydraulic circuit. For example, in the
depicted embodiment, the accessory gearbox 32 powers three
hydraulic circuit systems. The first hydraulic circuit includes a
first hydraulic pump 33 that supplies pressurized hydraulic fluid
via supply/return line 33a to a first hydraulic motor 36, which
powers the first air blower system. The second hydraulic circuit
includes a second hydraulic pump 34 that supplies pressurized
hydraulic fluid via supply/return line 34a to the second hydraulic
motor 37, which powers the second air blower system. The third
hydraulic circuit includes a third hydraulic motor 35 that supplies
pressurized hydraulic fluid via supply/return line 35a to a third
hydraulic motor 38, which powers the main fluid pump 94. The three
hydraulic systems are supplied by a hydraulic reservoir 31
positioned near the accessory gearbox 32. In a preferred
embodiment, the three hydraulic pumps 33, 34, each comprise a
mechanically-driven, variable-displacement, hydraulic pump; while
the three hydraulic motors 36, 37, 38 each comprise fixed
displacement hydraulic motors. The hydraulic pumps 33, 34, 35 are
rated at 5000 psi, but typically operated at approximately
2500-3000 psi.
Treatment Fluid Supply System
[0051] The main fluid pump 94 is used to draw a treatment fluid,
such as water, from a fluid source and supply it to the inlet 51 of
the heat exchanger 50. The main fluid pump 94 is typically integral
to the system 100 and has sufficient power to both draw the
treatment fluid from a source and to pump the treatment fluid
through the heat exchanger 50 and on to the well head for
subsequent injection into the formation. In one embodiment, the
main fluid pump 94 comprises a hydraulically-powered centrifugal
fluid pump that is capable of supplying treatment fluid to the heat
exchanger 50 at a pressure of about 150 psi. The volume of
treatment fluid pumped through the heat exchanger 50 will vary with
the pump speed. In a preferred embodiment, the main fluid pump 94
is capable of pumping a maximum of 252 gpm of treatment fluid
through the heat exchanger 50.
[0052] As shown in the Figures, the fluid supply system may include
an intake 90 manifold for connecting one or more supply hose (not
shown) to the system's respective intake. The intake manifold 90
may include one or more spigots 91 for receiving supply hose in
fluid communication with the fluid source. Each inlet spigot 91 may
further include a valve mechanism 92, which selectively controls
the fluid flow through its respective inlet spigot 91. Tubular
intake conduits 93a, 93b fluidly connect the inlet of the main
fluid pump 94 with the intake manifold 90. Conduit 93c fluidly
connects the outlet of the main fluid pump 94 with the inlet 51 of
the heat exchanger 50. The hydraulic pressure generated by the main
fluid pump 94 effectively pumps the fluid through the heat
exchanger 50 where it is heated. As the treatment fluid proceeds
through a single pass of the heat exchanger 50 it increases in
temperature until it reaches an outlet 52 of the heat exchanger 50
where it is directed via tubular outlet conduit 95 and supply hose
(not shown) to the well head for injection into the formation. As
shown in the Figures, the fluid supply system may further include
an outlet manifold 96 having one or more spigots 97 for connecting
with supply hose. Each outlet spigot 97 may further include a valve
mechanism 98, which selectively controls the fluid flow through its
respective outlet spigot 97.
Fuel Supply & Control System
[0053] As shown in the Figures and schematically depicted in FIGS.
7 and 8, the fuel system includes a fuel tank 20, which is
configured near the rear or back end of the trailer 14. The fuel
tank 20 is typically unpressurized and used to store the liquid
fuel used by the multiple burner assemblies 60 configured in the
firebox 40. In the depicted embodiment 100, the fuel tank 20 is
unpressurized and can hold up to 60 bbl of diesel fuel. The fuel
system also includes an unpressurized fuel line 21, which supplies
fuel from the fuel tank 20 to the intake of a fuel pump 22. The
fuel pump 22 boosts the fuel pressure and directs it to the
multiple burner assemblies 60 by means of a pressurized fuel line
26. In one embodiment, the fuel pump 22 boosts the fuel pressure to
approximately 50-100 psi, preferably 60 psi.
[0054] The fuel system also includes a pressure relief valve 24 in
fluid communication with the pressurized fuel line 26. The pressure
relief valve 24 permits fuel to vent back into the fuel tank by
means of fuel line 25 when the fuel pressure in the pressurized
fuel line 26 exceeds a certain pressure.
[0055] The fuel system further includes a fuel pressure control
motor valve 27, which regulates the flow of fuel from the
pressurized fuel line 26. The pressurized fuel line 26 fluidly
connects the outlet of the fuel pump 22 with the inlet of a fuel
pressure control motor valve 27. The fuel pressure control motor
valve 27 controls the amount of fuel supplied to the multiple
burner assemblies 60 via pressurized metered fuel lines 28. As
depicted in the drawings, the metered fuel lines 28 may be
configured so as to supply pressurized fuel to sets of burner
assemblies, which are comprised of more than one burner assembly
60. The fuel pressure control motor valve 27 may be electrically,
pneumatically or hydraulically actuated. In a preferred embodiment,
the fuel pressure control motor valve 27 comprises a
pneumatically-actuated flow control valve.
[0056] The temperature of the treatment fluid exiting the heat
exchanger outlet 52 is a function of three variables: the
volumetric flow rate of the treatment fluid through the heat
exchanger 50; the flow rate of the pressurized secondary air; and
the heat generated by the multiple burner assemblies 60 configured
in the heat exchanger 50. The flow rate of the secondary air is
typically held constant during all operations while the volumetric
flow rate of the treatment fluid is typically constant for a given
operation. Thus, the temperature of the treatment fluid exiting the
heat exchanger outlet 52 is controlled by regulating the volume of
fuel supplied to the multiple burner assemblies 60.
[0057] An adjustable temperature controller mechanism 68 is used to
send a control signal, which causes the fuel pressure control motor
valve 27 to open or close, thereby increasing or decreasing the
volume of fuel supplied to the multiple burner assemblies 60 via
pressurized metered fuel lines 28. The control signal may comprise
an electrical, wireless, pneumatic, or hydraulic signal. For
example, in one embodiment, the adjustable temperature controller
mechanism 68 comprises a simple manual rotary or slider rheostat
device, which controls an electric signal that controls the
actuation of the fuel pressure control motor valve 27. In another
embodiment, the adjustable temperature controller mechanism 68
comprises a simple manual rotary valve, which controls a pneumatic
pressure signal that controls the actuation of the fuel pressure
control motor valve 27.
[0058] The temperature controller mechanism 68 may further includes
a thermostat mechanism, which continually monitors the temperature
of the treatment fluid exiting the heat exchanger outlet 52 and
automatically adjusts the control signal to the fuel pressure
control motor valve 27 to open or close as necessary to maintain a
set point temperature.
[0059] Thus, the fuel pressure supplied to the multiple burner
assemblies 60 is initially generated by the fuel pump 22 and
regulated by the fuel pressure control motor valve 27. For example,
in the previously noted embodiment, the fuel pump 22 boosts the
fuel pressure to approximately 50-100 psi, preferably 60 psi. The
fuel pressure is limited to a maximum pressure of 100 psi by the
pressure relief valve 24, which permits fuel to vent back into the
fuel tank by means of fuel line 25 when the fuel pressure in the
pressurized fuel line 26 exceeds 100 psi. The fuel pressure control
motor valve 27 regulates the maximum fuel pressure supplied to the
multiple burner assemblies 60 via pressurized metered fuel lines 28
to approximately 60 psi.
Firebox
[0060] As depicted in the Figures, the firebox 40 is configured
near the center of the trailer 14. The firebox 40 is a
closed-bottomed box having one or more exhaust stacks 42 configured
near the top. In a preferred embodiment, the outer shell of the
firebox 40 is constructed substantially of 3/16'' carbon steel. The
firebox 40 houses a single heat exchanger 50 and a plurality of
burner assemblies 60 for heating a treatment fluid during a single
pass through the heat exchanger 50. The closed-bottom design of the
firebox 40 ensures the plurality of burner assemblies 60 are less
susceptible to changes in ambient conditions, such as wind
direction or gustiness. The interior walls and bottom of the
firebox 40 are lined with an insulating refractory material. The
refractive lining 48 is configured between the interior walls and
bottom of the firebox 40 and the heat exchanger 50. In one
embodiment, the refractive lining 48 comprises one or more layers
of fiber-type insulation coated with a cementious refractive
compound. In a preferred embodiment, the firebox 40 further
includes at least one vent 40b and passageway 40c, which supplies
ambient air from the upper exterior of the firebox 40 to the front
of the burner assemblies 60. The vent 40b and passageway 40c enable
the burner assemblies 60 to operate with the access door 40a
configured in a "closed" position, which significantly reduces the
operational noise created by burner assemblies 60 when operating.
Moreover, with the burner access doors 40a configured in the "down"
position, the danger inherent in a blowback event of the burner
assemblies 60 is greatly reduced.
Exhaust Stacks
[0061] As previously noted, one or more exhaust stacks 42 are
configured near the top the firebox 40 providing an exhaust for
flue gases to exit the firebox 40. In the depicted embodiment, the
firebox 40 further includes a tapered hood assembly 41, which
incorporates the one or more exhaust stacks 42. The tapered hood
assembly 41 is removable so as to allow access to the heat
exchanger 50 for servicing. Each exhaust stack 42 also includes a
hood door assembly 44, which is opened when the system 100 is
operating. As depicted in FIG. 2A, each hood door assembly 44
includes two doors 44a, 44b which are pivotally mounted to opposing
sides of a respective exhaust stack 42.
Hood Door Opening Mechanism
[0062] With reference to FIG. 2B, each hood door assembly 44 may
further include a novel mechanism 46 for opening and closing the
opposing hood doors. As shown in greater detail in FIG. 2C, the
mechanism 46 comprises a series of bell crank mechanisms, which
cause the hood doors to open or close when actuated. The embodiment
in FIG. 2C depicts the hood door assembly 44 on the left side in an
opened position and the hood door assembly 44 on the right side in
a closed position. Each mechanism 46 comprises a piston 46a having
one end attached to the firebox 40 and a second end attached to a
first bell crank 46b. The first bell crank is pivotally attached to
the side of the firebox 40. When actuated, the piston 46a causes
the first bell crank 46b to rotate about its pivot point p.sub.1.
The first bell crank 46b also includes a pivotally attached push
rod linkage 46c that connects the first bell crank 46b to a second
bell crank 46d, which is fixably attached to the side edge of one
of the hood doors 44a. The second bell crank 46d is configured so
that its pivot point p.sub.2 is co-aligned with that of its
respective hood door. The second bell crank 46d also includes a
pivotally attached push rod linkage 46e that connects the second
bell crank 46d to a third bell crank 46f, which is also fixably
attached to the side edge of the other of the hood doors 44b. The
third bell crank 46f is also configured so that its pivot point
p.sub.3 is co-aligned with that of its respective hood door.
Actuating the piston 46a causes the extension or retraction of a
piston rod r.sub.p, which causes each of the three bell cranks to
rotate simultaneously about their respective pivot points. This, in
turn, causes the hood doors 44a, 44b to pivot open or closed as
desired. In a preferred embodiment, the piston 46a is a
pneumatically actuated piston.
Burner Assemblies
[0063] The firebox 40 also includes a plurality of burner
assemblies 60, which are configured in the lower side of the
firebox 40. As will be subsequently described in greater detail,
each of the burner assemblies 60 are connected to the fuel system
and a pressurized air supply. For example, as schematically
depicted in FIGS. 7 and 8, liquid fuel is supplied to each burner
assembly 60 via the metered pressurized fuel line 28. Similarly,
pressurized air for combustion is supplied to each burner assembly
60 via a primary air conduit 78c. The pressurized air and fuel are
combined in the burner assembly 60 and directed through an atomizer
nozzle 64, which projects an atomized fuel spay into the firebox 40
where it is combusted. Each burner assembly 60 is configured in the
lower side of firebox 40 so as to initially generate a
substantially horizontal combustion flow within the firebox 40.
Each burner assembly 60 includes self-contained controls for
adjusting the fuel-air mixture and an ignition mechanism for
initially igniting the fuel-air mixture. In a preferred embodiment,
the burner assembly 60 comprises a 780-Series self-proportioning,
oil-fired burner manufactured by the Hauck Manufacturing Company of
Lebanon, Pa.
Heat Exchanger
[0064] The heat exchanger 50 contained within firebox 40 is
comprised of a tubular coil which is configured in a highly
oscillating or serpentine manner and oriented along multiple axes
so as to maximize its exposure to the heat generated by the
oil-fired burner assemblies 60. The heat exchanger coil 50 includes
a single inlet 51 configured at or near the top of the heat
exchanger coil 50 and a single outlet 52 configured at or near the
bottom of the heat exchanger coil 50. Such a configuration greatly
improves the efficiency of the system 100 by minimizing the back
pressure exerted on the main fluid pump 94 by the treatment fluid
and providing a gravity assist to the flow of treatment fluid
through the heat exchanger 50. As the treatment fluid proceeds
through a single pass through of the heat exchanger coil 50 it
increases in temperature until it reaches the outlet 52 where it is
directed, via an outlet conduit 95 and supply hose (not shown), to
the well head for injection into the formation.
[0065] With reference now to FIGS. 4A-4B, an embodiment of the heat
exchanger 50 of the present invention is depicted. The heat
exchanger 50 is comprised of a tubular coil which is configured in
a highly oscillating and serpentine manner and oriented along two
axes so as to maximize its exposure to the heat generated by the
oil-fired burner assemblies 60. For example, the depicted
embodiment of heat exchanger 50 includes an upper portion 53
configured in stacked horizontal rows of tubing faked down in a
series of reversing loops oriented about a vertical axis; and a
lower portion 56 configured in a helical coil oriented about a
horizontal axis. The upper portion 53 is fluidly connected to the
lower portion 56 forming the single heat exchanger 50. In one
embodiment, the upper 53 and lower 56 portions of the tubular coil
of the heat exchanger 50 comprise approximately 1,300 ft. of 3''
seamless steel pipe with weld fittings.
[0066] Each row of the upper portion 53 of the heat exchanger 50 is
constructed of a plurality of tubes 54 aligned in parallel with
each other. The outlet of each tube 54 is connected in series with
the inlet of an adjacent tube 54 by means of an approximate
180.degree. curved tube or return bend 55. Similarly, each planar
row is connected in series to the adjacent rows above and below by
connecting the outlet of the outermost tube in one row with the
inlet of the outermost tube in another row by means of a return
bend 55a. In a preferred embodiment, each planar row is laterally
offset from the planar row above and below it so that the tubes 54
in one row are centered on the space between two adjacent tubes 54
in the rows above and below it.
[0067] Each return bend 55 may further include an alignment bolt 47
extending from the approximate exterior inflection point of the
return bend 56. The multiple alignment bolts 47 correspond to holes
formed in an alignment plate 98, which is fixably attached to the
upper portion 53 of the heat exchanger 50 by means of mechanical
fasteners 45, such as threaded nut fasteners. The alignment plate
98 maintains the alignment of the stacked planar rows of the upper
portion 53 of the heat exchanger 50 so that the adjacent rows do
not touch and space is maintained between all adjacent tubes 54,
thereby enabling the flow of heated air through the upper portion
53 of the heat exchanger 50 during operation.
[0068] The upper portion 53 is fluidly connected in series to the
lower portion 56 of the heat exchanger 50. As shown in FIGS. 4A-4B,
the lower portion 56 transitions to an angled rectangular helical
coil configuration, which is oriented about a horizontal plane and
defines a five-sided cavity/chamber or tunnel 65. As will be
described infra, the tunnel 65 serves as an effective combustion
chamber for the multiple oil-fired burner assemblies 60. The lower
portion 53 of the heat exchanger 50 comprises a tubular coil
constructed a plurality of adjacently aligned upper 57a and lower
57b lateral tubes, which are vertically spaced and connected in
series by means of quarter-bend (i.e., approximately 90.degree.
bend) tubes 58 and riser tubes 59. The outlet of each lateral tube
57 is fluidly connected in series with the inlet of the next
vertically spaced lateral tube 57 by means of a quarter-bend tube
58 followed by a riser tube 59 followed by another quarter-bend
tube 58. As shown in FIG. 4A, the outlet of the last lateral tube
57 in the tubular coil forming the lower portion 53 is fluidly
connected to the outlet 52 of the heat exchanger 50.
[0069] With reference now to FIG. 4C, a cross-sectional view of the
heat exchanger 50 shown in FIGS. 4A-4B installed in the firebox 40
of the present invention is shown. The firebox 40 includes a
refractive lining 48 configured between the interior walls and
bottom of the firebox 40 and the tubular coil of the heat exchanger
50. In a preferred embodiment, the firebox 40 may further include
at least one vent 40b and passageway 40c, which supplies ambient
air from the upper exterior of the firebox 40 to the front of the
burner assemblies 60. The passageway 40c is typically configured
between the exterior wall of the firebox housing 40 and the
refractive lining 48. The vent 40b and passageway 40c enable the
burner assemblies 60 to operate with the access door 40a configured
in a "closed" position, which significantly reduces the operational
noise created by burner assemblies 60 when operating. Moreover,
with the burner access doors 40a configured in the "down" position,
the danger inherent in a blowback event of the burner assemblies 60
is greatly reduced.
[0070] As previously described, the heat exchanger 50 is comprised
of a tubular coil which is configured in a highly oscillating and
serpentine manner and oriented along two axes so as to maximize its
exposure to the heat generated by the oil-fired burner assemblies
60. The upper portion 53 configured in tightly stacked horizontal
rows of tubing faked down in a series of reversing loops oriented
about a vertical axis; and a lower portion 56 configured in a
helical coil oriented about a horizontal axis. The upper portion 53
is fluidly connected to the lower portion 56 forming the single
heat exchanger 50. The attached alignment plate 98 maintains the
alignment of the stacked planar rows of the upper portion 53 of the
heat exchanger 50 so that the adjacent rows do not touch and space
is maintained between all adjacent tubes 54, thereby enabling the
flow of heated exhaust or flue gases 88 through the upper portion
53 of the heat exchanger 50 during operation. The lower portion 56
of the heat exchanger 50 transitions to an angled rectangular
helical coil configuration, which is oriented about a horizontal
plane and defines a five-sided cavity/chamber or tunnel 65.
[0071] The tunnel 65 serves as an effective combustion chamber for
the multiple oil-fired burner assemblies 60 configured in the lower
side of the firebox 40. Each burner assembly 60 is connected to the
fuel system and a pressurized air supply. For example, as
schematically depicted in FIGS. 7 and 8, liquid fuel is supplied
from the fuel tank 20 to each burner assembly 60 via fuel pump 22,
pressurized fuel line 26, fuel pressure control motor valve 27 and
the metered pressurized fuel line 28. Similarly, pressurized air
for combustion is supplied to a primary air inlet 62 configured on
each burner assembly 60 via a primary air conduit 78c. With
reference again to FIG. 4C, the primary air and fuel are combined
in the burner assembly 60 and directed through an atomizer nozzle
64, which projects an atomized fuel spay F.sub.A into the firebox
40 where it is combusted in the previously described cavity/chamber
or tunnel 65 formed in the heat exchanger 50. It is further noted
that each burner assembly 60 is oriented so as to initially
generate a substantially horizontal combustion flow 69 within the
firebox 40. Each burner assembly 60 includes self-contained
controls 66 for adjusting the fuel-air mixture and an ignition
mechanism for initially igniting the fuel-air mixture.
[0072] The firebox 40 depicted in FIGS. 4C, 7 and 8 further
includes ductwork 85a, 85b, which supply pressurized secondary air
to the interior of firebox 40. The pressurized secondary air
assists in directing and regulating the flow of heated flue gases
88 through the heat exchanger 50 during operation. The ductwork
85a, 85b supplies pressurized secondary air to vents 86, 87
configured on opposing sides of the firebox 40. The vents 86, 87
are typically configured so that their respective airflows F.sub.B,
F.sub.C are generally directed into the cavity/chamber or tunnel 65
formed in the heat exchanger 50. The secondary airflows F.sub.B,
F.sub.C, which are projected from their respective vents 86, 87,
assist in regulating and directing the flow of heated flue gases 88
through the heat exchanger 50 during operation.
[0073] For example, a first or front vent 86 is configured under
the burner assemblies 60 and projects a first flow of secondary
pressurized air F.sub.B into the open front portion of the
cavity/chamber or tunnel 65 formed in the heat exchanger 50. In one
embodiment, the first vent 86 comprises an individual nozzle vent
configured under each burner assembly 60. The first flow of
secondary pressurized air F.sub.B provides a thermal air barrier
that partially insulates the lateral tubes 57b on the bottom of the
heat exchanger 50 from the substantially horizontal combustion
flame 69 generated by the burner assembly 60. In addition, the
first flow of secondary pressurized air F.sub.B absorbs the heat
produced by the substantially horizontal combustion flow 69
generating a flow of heated flue gases 88, which exhausts up
through the heat exchanger 50 during operation. In a preferred
embodiment, the first vent 86 is angled at a slightly upward angle,
so that the first flow of secondary pressurized air F.sub.B
combines with the atomized fuel spay F.sub.A to effectively
supercharge the resulting combustion flow 69 with additional
air.
[0074] The second or rear vent 87 is configured on the opposing
wall or side from the first vent 86 and burner assemblies 60, and
projects a second flow of secondary pressurized air F.sub.C into
the rear portion of the cavity/chamber or tunnel 65 formed in the
heat exchanger 50. As depicted in Figures, the rear portion of the
cavity/chamber or tunnel 65 formed in the heat exchanger 50 is
partially obscured by the lateral tubes 57c traversing the tunnel
65. Thus, the second or rear vent 87 is configured so as to project
the second flow of secondary pressurized air F.sub.C through gaps
existing between adjacent lateral tubes 57. The injection of the
second flow of secondary pressurized air F.sub.C provides a thermal
air barrier that partially insulates the lateral tubes 57c
traversing the back of the heat exchanger 50. In addition, the
second flow of secondary pressurized air F.sub.C also absorbs the
heat produced by the substantially horizontal combustion flow 69
generating a flow of heated flue gases 88, which exhausts up
through the heat exchanger 50 during operation. In one embodiment,
the second vent 87 may also be angled at a slightly upward
angle.
Air Supply System
[0075] With reference again to the Figures, and in particular to
FIGS. 5 and 6 the air supply system of the present invention will
be described in greater detail. The air supply system of the
present invention a forced-air or pressurized system which is not
susceptible to changes in ambient conditions, such as wind
direction or gustiness. The air supply system of the present
invention is comprised of primary and secondary air systems. The
primary air system supplies large volumes of pressurized air to the
multiple burner assemblies 60 configured in the side of the firebox
40. The primary air system includes a high-pressure pump which
compresses ambient air and directs it to the primary air inlet 62
of each oil-fired burner assembly 60 where it is used to atomize
fuel. The secondary air system supplies large volumes of
pressurized air to strategic locations within the firebox 40 to
control and regulate the heating of the heat exchanger 50 and
firebox 40. The secondary air system includes a secondary air
blower mechanism, which draws in large volumes of ambient air. The
secondary air is then directed via ductwork to the previously
described vents 86, 87 configured on opposing sides of the firebox
40. The secondary air assists in maximizing the combustion of the
fuel/air mixture while directing and regulating the flow of heated
flue gases 88 through the heat exchanger 50 during operation. By
controlling and regulating the heating of the heat exchanger 50 and
firebox 40 during operation, the oil-fired heat exchanger system
100 of the present invention can continuously heat large volumes of
treatment fluid safely.
[0076] In the embodiment of the present invention 100 depicted in
the Figures, the air supply system is comprised of matched sets of
primary and secondary blower systems disposed on opposing sides
(i.e., the front and rear) of the firebox 40 in a mirror-image
configuration. Each set includes a primary blower system 70 and a
secondary blower system 80, which are powered by a single motor
mechanism. For example, the first or front of blower system set is
powered by motor 36 while the second or rear blower system set is
powered by motor 37. The single motor mechanism 36, 37 are
preferably hydraulically powered. For example, in the depicted
embodiment, the motors 36, 37 are powered by hydraulic pumps 33,
34, respectively, which are driven by the accessory pump drive gear
box 32. As noted previously, in a preferred embodiment, the
hydraulic pumps 33, 34 comprise mechanically-driven hydraulic pumps
which are rated at 5000 psi, but typically operate at approximately
2500-3000 psi.
[0077] As shown in FIG. 5, which depicts in greater detail the
second or rear blower system of the present invention 100, each
primary air blower system 70 includes a high-pressure blower pump
74 having an intake which draws ambient air through an intake
filter 72 and intake conduit 73. In a preferred embodiment, each
high-pressure blower pump 74 is a positive displacement rotary
blower. Each high-pressure blower pump 74 is powered by its
respective motor mechanism 36, 37 through a rotary driveshaft 84.
The high-pressure blower pump 74 compresses the air and directs it
via primary air conduits 78a, 78b, 78c to the primary air inlet 62
of each oil-fired burner assembly 60. The primary air conduits 78a,
78b, 78c may further include a primary air silencer 76, which
muffles the noise generated by the suction of ambient air into the
primary air system 70. In one embodiment, the primary air conduits
78a, 78b, 78c also include a pressure relief "pop-off" valve, which
limits the primary air pressure to approximately 5 psi.
[0078] Each secondary air system 80 includes one or more secondary
air blowers 81, which are also powered by the respective motor
mechanism (e.g., 37) through a common rotary driveshaft 84. As
shown in the FIG. 6, in one embodiment the one or more secondary
air blowers 81 each comprise a conventional centrifugal or
squirrel-cage fan mechanism 82 contained in a protective housing
83. As depicted, the one or more fan mechanisms 82 are aligned in a
parallel configuration along and coupled to a common rotary
driveshaft 84 so that when the driveshaft 84 rotates, each fan
mechanism 82 also rotates within its housing 83. It is further
noted that the co-alignment of the rotary shaft 84 with the fan
mechanisms 82 of the secondary air system 80 and the high-pressure
blower pump 74 of the primary air blower system 70 enables both air
supply systems to be simultaneously powered by the same motor
37.
[0079] The protective housing 83 of each secondary air blower 81
includes an opening, which allows the fan mechanism 82 to draw
ambient air into its housing 83 where it is directed to the
ductwork of the secondary air system. The output of pressurized air
from the secondary air blowers 81 is combined in a first ductwork
85, which then divides into secondary ductwork 85a, 85b, which
supply pressurized secondary air to vents 86, 87 configured on
opposing sides of the firebox 40. In the depicted embodiment,
secondary air is pressurized to approximately 2.5-3 psi. As
previously noted, the vents 86, 87 are typically configured so that
their respective airflows F.sub.B, F.sub.C are generally directed
into the cavity/chamber or tunnel 65 formed in the heat exchanger
50. The secondary airflows F.sub.B, F.sub.C, which are projected
from their respective vents 86, 87, assist in regulating,
directing, and enhancing the convective flow of heated flue gases
88 through the heat exchanger 50 during operation.
[0080] As shown in the embodiment depicted in FIG. 5, the first or
front vents 86 preferably comprise oblong circular vents positioned
below the nozzles 64 of the burner assemblies 60. The depicted
oblong circular vents 86 extend away from the firebox 40 wall and
project one secondary air stream F.sub.B up towards the fuel/air
mixture spray F.sub.A generated by the burner fuel nozzle 64. The
second or rear vent 87 is configured on the opposing wall of the
firebox 40. As noted previously, the configuration of the second
oblong circular vents 87 provides a layer of cooling air F.sub.C
between the main burner fire and the bottom of the firebox.
Moreover, the angular set of the secondary vents 86, 87 causes
their respective opposing secondary air flows F.sub.B, F.sub.C to
collide in the tunnel 65 formed in the heat exchanger 50, thereby
affecting the flow of heated exhaust or flue gases 88 up and
through the upper portion 53 of the heat exchanger 50 during
operation.
[0081] The integrated temperature controller mechanism 68 in
conjunction with forced-air supply system and refractive insulation
lining 48 in the firebox 40 enable the oil-fired heat exchanger
system 100 of the present invention to safely heat water
continuously. Operation time is limited only by fuel supply. For
example, the depicted embodiment of the present invention 100,
which is configured with six (6) burner assemblies 60, typically
consumes 150-165 gallons of fuel per hour. The burner fuel tank 20
on the unit holds about 2500 gallons and is therefore sized for
15-16.5 hours of continuous operation. The auxiliary powerplant 30
has its own fuel tank that holds approximately 150 gallons of fuel
that allow it to operate up to 18 hours depending on operating
conditions. In the field, operators may have additional fuel
delivered every 12 hours or so to allow the system 100 to continue
operations on large heating jobs.
Accessory Fuel Oil Heating System
[0082] With reference now to FIG. 9, a schematic depiction of an
embodiment of an Accessory Fuel Oil Heating System is shown. As
demonstrated in the depiction, the accessory fuel oil heating
system of the present invention may be an integral part of the frac
water heater system 100 of the present invention or comprise a
separate, stand-alone unit, which may be selectively attached to
any oil-fired frac water heating system. The accessory fuel oil
heating system of the present invention includes an accessory fuel
oil heat exchanger unit 110 having a manifold 112 for receiving and
distributing the fuel oil through a plurality of heat exchanger
tubes, and directing it to a heated fuel line 126, which supplies
the burners 60 with heated fuel oil for combustion. A return line
25a may also be installed to allow a percentage of the heated fuel
oil to return back to the fuel tank 20 to preheat the fuel oil in
the fuel tank 20. The unit 110 further includes an inlet 114 for
receiving heated treatment fluid from the frac water heater system
of the present invention. The unit 110 is typically configured
(either temporarily or permanently) along the outlet conduit 95
between the outlet 52 of the main heat exchanger 50 and the outlet
manifold 96. The unit 110 includes an inlet 114, which is fluidly
connected to outlet conduit 95, and an outlet 118 fluidly connected
to the outlet manifold 96. Thus, as the heated treatment fluid from
the frac water heater system passes through the accessory fuel oil
heat exchanger unit 110, it also passes over the plurality of heat
exchanger tubes in the accessory heat exchanger unit 110 prior to
being directed to the outlet 118 and on to the outlet manifold. As
the heated treatment fluid passes over the plurality of heat
exchanger tubes, heat energy is transferred from the treatment
fluid to the fuel oil raising its temperature significantly.
[0083] The accessory fuel oil heating system of the present
invention receives fuel oil from fuel oil inlet line 125 which is
fluidly connected to the fuel tank 20 via the standard
unpressurized fuel line 21, fuel pump 22 and pressurized fuel line
26. The unpressurized fuel line 21 may also include a shut-off
valve 21a to isolate the fuel tank 20 from the system during
transit and for maintenance. An isolation valve 121 is configured
between the oil inlet line 125 and the pressurized fuel line 26.
The isolation valve 121 may be closed to bypass the accessory fuel
oil heat exchanger unit 110 when weather conditions to do not
demand its use. In such instances, by-pass valve 123 is opened to
by-pass the accessory fuel oil heat exchanger unit 110 allowing the
pressurized fuel in pressurized fuel line 26 to flow directly to
the burners 60.
[0084] However, during operation of the accessory fuel oil heating
system of the present invention, the isolation valve 121 is opened
and the by-pass valve 123 is closed allowing fuel oil in
pressurized fuel line 26 to flow directly through the fuel oil
inlet line 125 and into the inlet manifold 112 of the accessory
fuel oil heat exchanger unit 110. As will be explained in greater
detail below, the fuel oil flows through the accessory fuel oil
heat exchanger unit 110, where it is heated, and exits the fuel
outlet 140 which is fluidly connected to the heated fuel discharge
line 126. By heating the fuel oil prior to combustion, the
accessory fuel oil heating system of the present invention greatly
improves the viscosity and flow rate of the fuel oil, thereby
allowing cheaper, less cold-tolerant grades of fuel oil to be used
in extreme cold climates with no degradation in the operation of
the system of the present invention.
[0085] The accessory fuel oil heating system of the present
invention may also include a fuel filter 23, which filters the fuel
oil prior to directing it to the burners 60 in much the same way as
the standard system of the invention. The fuel filter 23 is
configured downstream of the fuel relief line 25a, pressure relief
valve 24 and fuel return line 25. The pressure relief valve 25
maintains proper fuel pressure by relieving excess fuel oil back to
the fuel tank 20. Moreover, in the event the fuel filter 23 becomes
clogged, the pressure relief valve 24 permits excess fuel oil to
flow back to the fuel tank 20 via fuel return line 25a, 25.
[0086] The accessory fuel oil heating system of the present
invention may also include a solenoid operated safety valve 26a. In
the event of a malfunction, the safety valve 26a will lose power
from the control panel causing it to close and shutting off fuel
supply to the burners. The accessory fuel oil heating system of the
present invention utilizes the same fuel pressure control motor
valve 27 as previously disclosed. However, the system also includes
a pilot valve 27a configured around the fuel pressure control motor
valve 27. The pilot valve 27a permits an operator to allow a small
amount of fuel to bypass the fuel pressure control motor valve 27
and keep the burners lit when the fuel pressure control motor valve
27 is closed.
[0087] With reference now to FIGS. 10, 11A-B, and 12, an embodiment
of the accessory fuel oil heat exchanger unit 110 is depicted. The
accessory fuel oil heat exchanger unit 110 comprises a heat
exchanger manifold assembly 120 coaxially aligned with an outer
housing unit 116. The housing unit 116 includes a flange 117 at its
nominal end for coupling with a matching flange 115 formed on the
manifold assembly 120. In a preferred embodiment, the two flanges
115, 117 are fastened together with bolt fasteners. A flexible seal
configured between the two flanges 115, 117 is typically used to
ensure a water-tight seal.
[0088] The heat exchanger manifold assembly 120 includes a manifold
112 for receiving and distributing the fuel oil through a plurality
of heat exchanger tubes, and directing it to a fuel outlet 140 that
is fluidly connected to the heated fuel line 126. The assembly 120
further includes an inlet 114 for receiving heated treatment fluid
from the main heat exchanger 50 of the frac water heater system 100
of the present invention.
[0089] As best illustrated in FIGS. 13A and B, the manifold 112
includes a water inlet passageway 122 for receiving heated
treatment fluid. The passageway 122 is configured in the center of
the manifold 112 and is fluidly connected to the inlet conduit 114.
The manifold 112 further comprises two annular walls 136, 138,
which are coaxially aligned with the passageway 122. The annulus
between the inner 136 and outer 138 walls is divided into two
chambers by two divider walls 137. The two chambers 132, 142 are
enclosed by annular plates 124 fixably attached to the opposing
edges of walls 136, 137, 138. For example, in a preferred
embodiment the annular plates 124 are welded to the opposing edges
of walls 136, 137, 138.
[0090] The manifold 112 further includes an inlet 130 which fluidly
couples the fuel oil inlet line 125 to the first or inlet chamber
132. The inner wall 136 of the inlet chamber 132 includes openings,
which fluidly connect the inlet chamber 132 to a plurality of
inlets of heat exchange tubes. For example, in the depicted
embodiment the inner wall 136 includes four openings for receiving
inlets 152, 162, 172, 182 for four heat exchange tubes.
[0091] Correspondingly, the manifold 112 also includes an outlet
140 which fluidly couples the second or outlet chamber 142 to the
heated fuel discharge line 126. The inner wall 136 of the outlet
chamber 132 includes openings, which fluidly connect the outlet
chamber 142 to a plurality of outlets of heat exchange tubes. For
example, in the depicted embodiment the inner wall 136 includes
four openings for receiving outlets 154, 164, 174, 184 for four
heat exchange tubes.
[0092] Thus, the inlet chamber 132 is fluidly connected to the
outlet chamber 142 by means of a plurality of heat exchange tubes
connected to corresponding inlets and outlets.
[0093] The heat exchange tubes comprise U-shaped tubes having a
single inlet and a single outlet. The U-shaped tubes have
substantially the same lateral width but are of varying length in
order to allow the plurality of heat exchange tubes to nest within
each while minimizing overall obstruction. For example, in the
embodiment depicted in FIGS. 10, 11A-B, and 12, the heat exchanger
manifold assembly 120 includes a first U-shaped heat exchange tube
150 having an inlet 152 fluidly coupled to the inlet chamber 132
and an outlet 154 fluidly coupled to the outlet chamber 142.
Likewise, the assembly 120 further includes a second U-shaped heat
exchange tube 160 having an inlet 162 fluidly coupled to the inlet
chamber 132 and an outlet 164 fluidly coupled to the outlet chamber
142. The length of the second heat exchange tube 160 is greater
than the length of the first heat exchange tube 150 which allows
the U-shaped turn 156 of the first heat exchange tube 150 to easily
nest between the second heat exchange tube 160 with minimal
obstruction. Similarly, the assembly 120 further includes a third
U-shaped heat exchange tube 170 having an inlet 172 fluidly coupled
to the inlet chamber 132 and an outlet 174 fluidly coupled to the
outlet chamber 142. The length of the third heat exchange tube 170
is greater than the length of the second heat exchange tube 160
which allows the U-shaped turn 166 of the second heat exchange tube
160 to easily nest between the third heat exchange tube 170 with
minimal obstruction. Finally, the assembly 120 also includes a
fourth U-shaped heat exchange tube 180 having an inlet 182 fluidly
coupled to the inlet chamber 132 and an outlet 184 fluidly coupled
to the outlet chamber 142. The length of the fourth heat exchange
tube 180 is greater than the length of the third heat exchange tube
170 which allows the U-shaped turn 176 of the third heat exchange
tube 170 to easily nest between the fourth heat exchange tube 180
with minimal obstruction.
[0094] The inlet chamber 132 and outlet chamber 142 may each
further comprise a pressure outlet for receiving a pressure gauge.
For example, the inlet chamber 132 may further include an outlet
134 for receiving a pressure gauge 135. Similarly, the outlet
chamber 142 may further include an outlet 144 for receiving a
pressure gauge 145. The pressure gauges may be simple sight gauges
as depicted or may comprise electronic gauges linked to a central
control panel.
[0095] As shown in the Figures, and in particular FIGS. 14A-B, the
heat exchanger manifold assembly 120 may also include one or more
support brackets 194 configured around the plurality of heat
exchange tubes. The support bracket 194 assists in maintaining the
spacing and alignment of the various heat exchange tubes, both in
relation to one another, and in relation to the outer housing unit
116. The support bracket 194 prevents the various heat exchange
tubes (e.g., 150, 160, 170, 180) from contacting the inner wall of
the outer housing unit 116. In a preferred embodiment, the support
bracket 194 comprises a plurality of rings 197 arranged in an
annular configuration and connected by linking bars 198 between
adjacent rings. The rings 197 have an inner diameter 196 which is
greater than the diameter of the various heat exchange tubes. The
maximum diameter 197 of the support bracket 194 is less than the
interior diameter of the outer housing unit 116.
[0096] The outer housing unit 116 of the accessory fuel oil heat
exchanger unit 110 includes an inlet of sufficient diameter to
receive the plurality of heat exchange tubes (e.g., 150, 160, 170,
180) extending from the heat exchanger manifold assembly 120. The
previously described one or more support brackets 194 assist in
preventing the various heat exchange tubes from contacting the
inner wall of the outer housing unit 116. The outer housing unit
116 also includes an outlet 118 at its distal end for discharging
the heated treatment fluid. The outlet 118 is fluidly connected to
the outlet manifold 96 of the overall system 100. For example, the
outlet 118 may include screw threads 119 for fluidly connecting to
the outlet manifold 96. It is important to note that the diameter
192 of the housing unit 116 at its nominal end is typically greater
than the diameter 190 of the housing unit 116 at its distal end. In
a preferred embodiment, the diameter 192 of the housing unit 116 at
its nominal end is almost twice the diameter 190 of the housing
unit 116 at its distal end (65/8 inches compared to 31/2 inches).
The diameter of the inlet 114 is substantially similar, preferably
the same, as the diameter 190 of the outlet 118. This difference in
diameters of the outer housing unit 116 is critical to ensuring a
smooth flow of the heated treatment fluid through the accessory
fuel oil heat exchanger unit 110 while preventing the inducement of
back pressure on the main heat exchanger 50.
Method of Operation
[0097] The system 100 of the present invention includes novel
methods for heating large volumes of treatment fluid in a
continuously flowing fashion so that on-site heating operations can
be performed "on-the-fly", i.e., without the use of preheated
stockpiles of treatment fluid. For example, the embodiment of the
system 100 of the present invention depicted in the Figures, is
capable of heating sufficient quantities of continuously flowing
water to conduct "on-the-fly" hydraulic fracturing operations at
remote well sites. The system 100 of the present invention also
includes novel methods for controlling the heating of the treatment
fluid as it passes through the system 100. The system 100 of the
present invention further includes novel methods for controlling
the temperature change and volume flow of treatment fluid as it
passes through the system 100.
[0098] With reference again to the Figures and in particular FIGS.
7 and 8, the method of the present invention is depicted. A
treatment fluid, such as water, is drawn from an ambient fluid
source into the system 100. The treatment fluid is then pumped
through a single pass of a tubular coil heat exchanger 50 contained
within firebox 40 where it is heated. As the treatment fluid
proceeds through the heat exchanger 50 it increases in temperature
until it reaches the outlet 52 of the heat exchanger 50 where it is
directed via tubular conduits or hose to the well head for
injection into the formation.
[0099] The main fluid pump 94 is used to control the flow rate of
the treatment fluid through the system 100. For example, a supply
hose (not shown) extending to the fluid source is connected to the
intake manifold 90 so as to put the system 100 in fluid
communication with the fluid source. The main fluid pump 94 draws
the treatment fluid via conduits 93a, 93b from the fluid source and
supplies it to the inlet 51 of the heat exchanger 50. The main
fluid pump 94 has sufficient power to both draw the treatment fluid
from the fluid source and pump the treatment fluid through the heat
exchanger 50 and on to the well head for injection into the
formation.
[0100] For example, in one embodiment, the main fluid pump 94 is
capable of supplying treatment fluid to the heat exchanger 50 at a
pressure of about 150 psi. In a preferred embodiment, the main
fluid pump 94 is also capable of drawing and pumping a maximum of
252 gpm of treatment fluid through the system 100. The requisite
volumetric flow rate of treatment fluid is typically dictated by
the particular operational requirements desired at the well head.
By adjusting the speed of the main fluid pump 94, the volumetric
flow rate of treatment fluid is controlled. The main fluid pump 94
is driven by a hydraulic motor 38 powered via supply line 35a by a
hydraulic pump 35 attached to the accessory pump drive gear box 32.
Consequently, the speed of the main fluid pump 94 is controlled by
the operator using a control lever 12 to increase or decrease the
amount of pressurized hydraulic fluid supplied to hydraulic motor
38. In a preferred embodiment, control lever 12 comprises an
electronic joystick actuator, which regulates the displacement of
the hydraulic pump to change the speed of its respective hydraulic
motor. The hydraulic pressure depends on the loads placed on the
hydraulic motors.
[0101] As the treatment fluid is pumped through the heat exchanger
50 contained within the firebox 40, the fluid is heated by the
transfer of thermal energy generated by the combustion of a
liquid-fuel/air mixture in the firebox 40. As previously detailed,
pressurized primary air and liquid fuel are combined in the
multiple burner assemblies 60, which each project an atomized fuel
spay F.sub.A into the firebox 40 where it is combusted. The burner
assemblies 60 are configured near the bottom of the firebox 40 and
oriented so as to initially generate a substantially horizontal
combustion flow 69 within the firebox 40. Pressurized secondary air
assists in directing and controlling the thermal energy generated
by the substantially horizontal combustion flow 69 to exhaust in a
convective flow up and through the upper portion 53 of the heat
exchanger 50.
[0102] The tubular coil heat exchanger 50 is designed to maximize
the heat transfer of the thermal energy within the confines of the
firebox 40. The heat exchanger 50 is, therefore, comprised of a
tubular coil which is configured in a two interconnected portions,
which are oriented along two distinct axes so as to maximize
exposure to the heat generated by the oil-fired burner assemblies
60. The ambient or cool treatment fluid enters the heat exchanger
50 through the inlet 51 configured at or near the top of the heat
exchanger coil 50. As the fluid flows through the upper portion 53
of the heat exchanger 50 thermal energy is transferred by the
convective flow of the hot flue gases 88 over and between the
stacked horizontal rows of interconnected adjacent tubes faked down
in a series of reversing loops oriented about a vertical axis. As
the fluid continues through the lower portion 56 of the heat
exchanger 50 it flows through a helical coil oriented about a
horizontal axis, thermal energy is transferred by the both the
convective flow of the hot flue gases 88 and the radiant heat
emanating from the substantially horizontal combustion flow 69
within the cavity/chamber or tunnel 65.
[0103] The convective flow of flue gases 88 through heat exchanger
50 is substantially enhanced by the secondary air system, which
continually supplies large volumes of pressurized air to
strategically configured vents 86, 87 on opposing sides of the
firebox 40. The secondary air flow is essentially a forced air
system which uses air as its heat transfer medium to extract
thermal energy from the substantially horizontal combustion flow
69. The vents 86, 87 are positioned near the bottom of the
closed-bottom firebox 40 and configured so that their respective
airflows F.sub.B, F.sub.C are generally directed into the
cavity/chamber or tunnel 65 formed in the heat exchanger 50.
[0104] The treatment fluid continues to absorb thermal energy as it
flows through the lower portion 56 of the heat exchanger 50 until
it reaches the outlet 52 of the heat exchanger 50 where it is
directed via tubular 95 and supply hose (not shown) to the well
head for injection into the formation.
[0105] As the heated treatment fluid exits the outlet 52 of the
heat exchanger 50 its temperature is monitored. The temperature of
the treatment fluid exiting the heat exchanger outlet 52 is a
function of three variables: the volumetric flow rate of the
treatment fluid through the heat exchanger 50; the flow rate of the
pressurized secondary air; and the heat generated by the multiple
burner assemblies 60 configured in the heat exchanger 50. The flow
rate of the secondary air is typically held constant during all
operations while the volumetric flow rate of the treatment fluid is
typically constant for a given operation. Thus, the temperature of
the treatment fluid exiting the heat exchanger outlet 52 is
controlled by regulating the volume of fuel supplied to the
multiple burner assemblies 60.
[0106] In one embodiment, the operator monitors the temperature of
the heated treatment fluid as it exits the outlet 52 of the heat
exchanger 50. The operator then adjusts the temperature controller
mechanism 68 sending a control signal to the fuel pressure control
motor valve 27 to increase or decrease the volume of fuel supplied
to the multiple burner assemblies 60 via pressurized metered fuel
lines 28. The control signal may comprise an electrical, wireless,
pneumatic, or hydraulic signal. For example, in the depicted
embodiment, the adjustable temperature controller mechanism 68
comprises a simple manual rotary valve, which controls the
pneumatic pressure supplied to the fuel pressure control motor
valve 27.
[0107] In another embodiment, the temperature controller mechanism
68 is an automated thermostat mechanism that continually monitors
the temperature of the treatment fluid exiting the heat exchanger
outlet 52. An operator inputs a desired temperature reading (i.e.,
set point temperature). The temperature controller mechanism 68
compares the actual temperature of the treatment fluid exiting the
heat exchanger outlet 52 with the set point temperature and
automatically adjusts the control signal supplied to the fuel
pressure control motor valve 27. For example, if the temperature of
the treatment fluid exiting the heat exchanger outlet 52 is less
than the set point temperature, the temperature controller
mechanism 68 adjusts the control signal supplied to the fuel
pressure control motor valve 27 to increase the volume of fuel
supplied to the multiple burner assemblies 60 via pressurized
metered fuel lines 28 in order to maintain a set point temperature.
Conversely, if the temperature of the treatment fluid exiting the
heat exchanger outlet 52 is higher than the set point temperature,
the temperature controller mechanism 68 adjusts the control signal
supplied to the fuel pressure control motor valve 27 to decrease
the volume of fuel supplied to the multiple burner assemblies 60
via pressurized metered fuel lines 28 in order to maintain a set
point temperature.
[0108] The temperature of the treatment fluid is also typically
monitored at the inlet 51 of the heat exchanger 50. The temperature
spread between the inlet 51 and outlet 52 of the heat exchanger 50,
when combined with the volumetric flow rate of treatment fluid, is
indicative of the heating capacity of the system. Field testing has
determined that the depicted embodiment of the oil-fired heat
exchanger system 100 of the present invention is capable of heating
ambient water from 70.degree. F. to 210.degree. F. at a maximum
volumetric flow rate of 252 gpm. Moreover, field reports further
indicate that the system 100 is capable of heating water from
40.degree. F. to 210.degree. F. in ambient atmospheric temperatures
below 25.degree. F. at a slightly reduced volumetric flow rate
(e.g., 200-250 gpm).
Method of Operation of Accessory Fuel Oil Heating System
[0109] When not needed, the accessory fuel oil heating system of
the present invention may be isolated from the frac water heating
system 100 of the present invention. For example, as shown in FIG.
9 the isolation valve 121 is closed in such instances and the
by-pass valve 123 is opened allowing fuel oil in the pressurized
fuel line 26 to by-pass the accessory fuel oil heat exchanger unit
110 and proceed directly to burners in accordance with the standard
operating procedure discussed previously. In such cases, the heated
treatment fluid still proceeds through the outlet conduit 95 and
the accessory fuel oil heat exchanger unit 110, but no heat
transfer to the fuel oil occurs in the accessory fuel oil heat
exchanger unit 110.
[0110] When the weather conditions warrant utilization of the
accessory fuel oil heating system of the present invention the
isolation valve 121 is opened and the by-pass valve 123 is closed
allowing fuel oil in pressurized fuel line 26 to flow directly
through the fuel oil inlet line 125 and into the inlet manifold 112
of the accessory fuel oil heat exchanger unit 110. The inlet
manifold 112 receives the fuel oil via inlet 130, which directs the
fuel oil into the inlet chamber 132 where it is distributed to the
inlets (e.g., 152, 162, 172, 182) of the plurality of heat exchange
tubes (e.g., 150, 160, 170, 180). Heated treatment fluid from the
frac water heater system 100 is directed through the accessory fuel
oil heat exchanger unit 110 where it passes over the plurality of
heat exchanger tubes prior to being directed to the outlet 118 and
on to the outlet manifold 96. As the heated treatment fluid passes
over the plurality of heat exchanger tubes, heat energy is
transferred from the treatment fluid to the fuel oil raising its
temperature significantly.
[0111] Each of the plurality of heat exchanger tubes (e.g., 150,
160, 170, 180) direct the fuel oil to its respective outlet (e.g.,
154, 164, 174, 184) where it is discharged into the outlet chamber
142. The outlet chamber 142 directs the heated oil to the heated
fuel discharge line 126 via the fuel outlet 140. The heated fuel
oil then proceeds via heated fuel line 126 to the burners 60 in
substantially the same manner as previously described in the method
of operation of the system 100 of the present invention.
[0112] In the event that the accessory fuel oil heat exchanger unit
110 produces more heated oil than required at the moment by the
burners, the system of the present invention will direct the excess
fuel oil back to the fuel tank 20 via fuel return line 25a, 25 when
the pressure in fuel line 126 triggers the pressure relief valve
24.
[0113] By heating the fuel oil prior to combustion, the accessory
fuel oil heating system of the present invention greatly improves
the viscosity and flow rate of the fuel oil, thereby allowing
cheaper, less cold-tolerant grades of fuel oil to be used in
extreme cold climates with no degradation in the operation of the
system of the present invention. While the heat energy extracted
from the treatment fluid has a negligible effect on the overall
temperature of the treatment fluid, it significantly affects the
temperature of the fuel oil discharged by the system. Although
diesel fuel is typically utilized as the preferred form of fuel oil
in the present invention, it is understood that the accessory fuel
oil heating system of the present invention is applicable to a wide
variety of fuel oils and significantly improves the combustion and
flow characteristics of many fuel oils, which would otherwise be
impractical to use.
[0114] It will now be evident to those skilled in the art that
there has been described herein an improved heat exchanger system
for heating large, continuously flowing volumes of treatment fluids
at remote locations. Although the invention hereof has been
described by way of a preferred embodiment, it will be evident that
other adaptations and modifications can be employed without
departing from the spirit and scope thereof. For example, instead
of the treatment fluid being water, it could be a petroleum based
liquid such as oil for hot oil well treatments. The terms and
expressions employed herein have been used as terms of description
and not of limitation; and thus, there is no intent of excluding
equivalents, but on the contrary it is intended to cover any and
all equivalents that may be employed without departing from the
spirit and scope of the invention.
* * * * *