U.S. patent application number 09/791614 was filed with the patent office on 2001-10-04 for fuel and waste fluid combustion system.
Invention is credited to Anderson, John Erling, Arnold, Glenn William, Bool, Lawrence E. III, Leger, Christopher Brian.
Application Number | 20010025591 09/791614 |
Document ID | / |
Family ID | 25154254 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010025591 |
Kind Code |
A1 |
Bool, Lawrence E. III ; et
al. |
October 4, 2001 |
Fuel and waste fluid combustion system
Abstract
A system for combusting difficult to combust fluid such as waste
fluid wherein fuel and gaseous oxidant combust in a hot combustion
gas chamber to form a hot combustion gas mixture which is
accelerated to a high speed and at a steady, i.e. non-pulsing, flow
is then used to atomize and then combust the fluid.
Inventors: |
Bool, Lawrence E. III;
(Hopewell Junction, NY) ; Anderson, John Erling;
(Somers, NY) ; Arnold, Glenn William;
(Poughkeepsie, NY) ; Leger, Christopher Brian;
(Houston, TX) |
Correspondence
Address: |
PRAXAIR, INC.
LAW DEPARTMENT - M1 557
39 OLD RIDGEBURY ROAD
DANBURY
CT
06810-5113
US
|
Family ID: |
25154254 |
Appl. No.: |
09/791614 |
Filed: |
February 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09791614 |
Feb 26, 2001 |
|
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09534523 |
Mar 24, 2000 |
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Current U.S.
Class: |
110/260 ;
110/262 |
Current CPC
Class: |
F23D 11/102 20130101;
F23G 2900/54402 20130101; F23G 2209/10 20130101; F23G 2900/50211
20130101 |
Class at
Publication: |
110/260 ;
110/262 |
International
Class: |
F23C 001/02 |
Claims
1. A method for combusting difficult to combust fluid comprising:
(A) contacting fuel with gaseous oxidant and combusting fuel with a
portion of the gaseous oxidant to produce a hot combustion gas
mixture containing gaseous oxidant; (B) passing the hot combustion
gas mixture through a nozzle to form a high speed combustion gas
mixture having a steady flow; (C) contacting the high speed steady
flow combustion gas mixture with a flow of difficult to combust
fluid and atomizing at least some of the flow of said fluid by the
contact with the high speed steady flow combustion gas mixture; and
(D) combusting the atomized fluid by reaction with the gaseous
oxidant of the high speed steady flow combustion gas mixture.
2. The method of claim 1 wherein the hot combustion gas mixture has
a temperature of at least 300.degree. F.
3. The method of claim 1 wherein the fluid which contacts the high
speed combustion gas mixture has a viscosity of at least 1
centipoise.
4. The method of claim 1 wherein the difficult to combust fluid is
waste fluid.
5. The method of claim 1 wherein the difficult to combust fluid
comprises conventional fuel.
6. The method of claim 1 wherein the difficult to combust fuel is
only partially combusted with the high temperature, high velocity
gaseous oxidant.
7. Apparatus for combusting difficult to combust fluid comprising:
(A) a hot combustion gas chamber, means for providing a non-pulsing
flow of fuel into the hot combustion gas chamber, and means for
providing a non-pulsing flow of gaseous oxidant into the hot
combustion gas chamber; (B) an atomization chamber and means for
providing difficult to combust fluid into the atomization chamber;
(C) a nozzle positioned for receiving a steady flow of fluid from
the hot combustion gas chamber and for ejecting a steady flow of
fluid into the atomization chamber; and (D) a combustion zone in
flow communication with the atomization chamber.
8. The apparatus of claim 7 wherein the nozzle is a converging
nozzle.
9. The apparatus of claim 7 wherein the means for providing fluid
into the atomization chamber is oriented substantially
perpendicular to the orientation of the nozzle.
10. The apparatus of claim 7 wherein at least one of the hot
combustion gas chamber and the atomization chamber is cylindrical.
Description
TECHNICAL FIELD
[0001] This invention relates generally to combustion of
combustible fluids and, more particularly, to the combustion of
waste fluid.
BACKGROUND ART
[0002] Numerous devices currently exist to combust fuels and waste
materials. The devices include combustion systems, such as boilers
and waste-to-energy facilities, which utilize the heat generated by
combustion for the generation of process heat, steam or power.
Other common combustion facilities include devices whose primary
purpose is waste destruction, such as rotary kilns, multiple hearth
incinerators, and fluidized bed incinerators. These devices are
used to combust a wide range of materials, and they are typically
able to handle low heating value waste materials, aqueous wastes,
or physically hard-to-handle waste materials such as sludges.
However, this capability comes at a high cost; these devices are
mechanically complex, capital intensive, maintenance intensive, and
they are usually fuel intensive as well when burning wastes
containing little heating value. Liquid wastes, such as waste oils,
are frequently used as fuels in industrial furnaces if they have a
sufficiently high heating value. However, there are numerous liquid
waste streams that cannot be used for this purpose because
conventional burners will not produce a stable flame with them.
These wastes become much more expensive to dispose of as a result,
even though they contain considerable heat energy.
[0003] Aqueous wastes are by definition never used as fuels because
they contain so much water. Disposal costs can be very high,
especially if they must be incinerated. Currently they are simply
sprayed into a furnace, where other fuels are combusted to supply
the heat to evaporate the water. Sludges are particularly
problematic because of their poor physical handling
characteristics. They may have high or low heating values, but it
is usually difficult to get them to burn because of their
stickiness and tendency to clump up. For example, sludges from
wastewater treatment systems are burned almost exclusively in
multiple hearth furnaces or fluid bed incinerators, mainly because
these furnaces can handle the sticky material without plugging
up.
[0004] The current industry practice is to avoid the use of these
poor quality waste materials as fuels. Typically these wastes can
only be incinerated in specialized furnaces, such as rotary kilns,
multiple hearth incinerators, and fluidized bed incinerators which
are mechanically complex, capital intensive, maintenance intensive,
and usually fuel intensive when burning wastes containing little
heating value.
[0005] Rotary kiln incinerators tend to be mechanically complex and
expensive to operate and maintain. Multiple hearth incinerators are
designed specifically to handle sludges from wastewater treatment
processes. They rely on mechanical arms to break-up the sludge,
move it through the furnace, and expose it to flames. These
incinerators are even more mechanically complex than rotary kilns,
with associated high capital, operating and maintenance costs.
Depending on the moisture content of the sludge, these incinerators
may require large amounts of auxiliary fuel. Because of their
specialized design, these furnaces are poor at handling variations
in the waste materials, including variations in moisture content,
volatile organic content, and physical consistency of the sludge.
As an example, these furnaces have difficulty when fed grease-laden
scum in amounts greater than a few percent of the total sludge
feed. The scum, derived from wastewater skimming operations, causes
smoking, high organic emissions, local overheating, and generally
poor operability. At the other extreme, sludge that is much wetter
than normal can lead to a drastic reduction in waste throughput,
high fuel requirements, and difficulty in achieving complete
destruction of the organics.
[0006] Fluidized bed incinerators make use of an inert bed of
material that is fluidized with air from below. This design is
suitable for incinerating wet materials because the turbulence and
thermal inertia of the fluidized bed provides rapid drying of the
moisture-laden waste. However, the design is mechanically complex
and requires relatively large amounts of high pressure fluidizing
air. Precise control must be maintained to achieve efficient
incineration. The amount of fluidizing air must be carefully
balanced against the mass of the bed, with too much air leading to
attrition of particles and too little air causing loss of
fluidization and local cold spots in the bed. The bed temperature
must also be carefully balanced by control of the waste feed rate
and auxiliary fuel feed rate. If the temperature gets too low,
organic emissions become a problem, and if the temperature gets too
high, fused ash may cause the bed to agglomerate and fluidization
will be lost. Agglomeration of some types of sludge into large
masses can also be a problem.
[0007] One way to handle hard to burn wastes and fuels is through
the use of a pulse combustion system. When the chamber geometry and
operating conditions of a combustion chamber are such that the
acoustic, or pressure, waves generated during combustion are in
phase with the energy release, a stable high frequency oscillating
flow is formed. This oscillating flow can significantly increase
heat transfer and reaction kinetics in reacting systems. When a
pulsed combustor is coupled with an atomizing device, the pressure
waves serve to atomize the fluid while the hot combustion products
dry the droplets. Although capable of handling many types of
materials, these systems must be very carefully designed and
operated to maintain the correct phase relationship between the
acoustic waves and the energy release.
[0008] Although easier to deal with than many waste fluids, other
difficult to combust fluids such as heavy oil, coal-water slurries,
orimulsion, and entrained solid fuels as well as conventional fuels
can also benefit from the improved combustion system of this
invention.
[0009] Accordingly, it is an object of this invention to provide an
improved system for combusting waste fluid and other difficult to
combust fluids.
SUMMARY OF THE INVENTION
[0010] The above and other objects, which will become apparent to
those skilled in the art upon a reading of this disclosure, are
attained by the present invention, one aspect of which is:
[0011] A method for combusting difficult to combust fluid
comprising:
[0012] (A) contacting fuel with gaseous oxidant and combusting fuel
with a portion of the gaseous oxidant to produce a hot combustion
gas mixture containing gaseous oxidant;
[0013] (B) passing the hot combustion gas mixture through a nozzle
to form a high speed combustion gas mixture having a steady
flow;
[0014] (C) contacting the high speed steady flow combustion gas
mixture with a flow of difficult to combust fluid and atomizing at
least some of the flow of said fluid by the contact with the high
speed steady flow combustion gas mixture; and
[0015] (D) combusting the atomized fluid by reaction with the
gaseous oxidant of the high speed steady flow combustion gas
mixture.
[0016] Another aspect of the invention is:
[0017] Apparatus for combusting difficult to combust fluid
comprising:
[0018] (A) a hot combustion gas chamber, means for providing a
non-pulsing flow of fuel into the hot combustion gas chamber, and
means for providing a non-pulsing flow of gaseous oxidant into the
hot combustion gas chamber;
[0019] (B) an atomization chamber and means for providing difficult
to combust fluid into the atomization chamber;
[0020] (C) a nozzle positioned for receiving a steady flow of fluid
from the hot combustion gas chamber and for ejecting a steady flow
of fluid into the atomization chamber; and
[0021] (D) a combustion zone in flow communication with the
atomization chamber.
[0022] As used herein the term "atomizing" means to make in the
form of many droplets or particles.
[0023] As used herein the term "nozzle" means a device having an
input for receiving a fluid and an output for ejecting a fluid
whereby the fluid exits the device at a higher velocity than it has
when entering the device.
[0024] As used herein the term "waste fluid" means a fluid
typically containing organics, either as solids (sludges) or
liquids, residue or byproduct that by its nature is not reused and
must be disposed of.
[0025] As used herein the term "difficult to combust fluid" means
one or more of waste fluid, conventional fuels, heavy oil,
coal-water slurry, orimulsion and entrained combustible solids.
[0026] As used herein the term "steady flow" means non-oscillating
or non-pulsing flow, i.e. a flow of fluid wherein the bulk flow is
continuously moving without rapid cessation or reversal of
direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a simplified representation of one preferred
embodiment of the fluid combustion system of the invention.
[0028] FIG. 2 is a graphical representation of the flame
temperature achievable with the use of heated oxygen to combust low
heating value fluids.
DETAILED DESCRIPTION
[0029] The invention will be described in detail with reference to
the Drawings. Referring now to FIG. 1, fuel 1 is provided into fuel
tube 2 which is positioned for delivering the fuel into hot
combustion gas chamber 3 in a non-pulsing flow. The fuel may be any
suitable fluid fuel such as methane, propane, natural gas, fuel
oil, kerosene and the like.
[0030] Gaseous oxidant 4 is provided into gaseous oxidant tube 5
which is positioned for delivering the gaseous oxidant in a
non-pulsing flow into hot combustion gas chamber 3. The gaseous
oxidant may be air, oxygen-enriched air or commercial oxygen having
an oxygen concentration of at least 99.5 mole percent. None of the
fluids provided into the combustion chamber are provided using an
aerodynamic valve or a mechanical valve such as would be used in a
pulse combustion system to create the pulsating flow. In the
practice of this invention the flow of fluids into the combustion
chamber is externally controlled. Preferably the gaseous oxidant
has an oxygen concentration of at least 21 mole percent, most
preferably of at least 75 mole percent.
[0031] Within hot combustion gas chamber 3 the fuel and the gaseous
oxidant mix and react in a combustion reaction wherein some, but
not all, of the oxygen of the gaseous oxidant combusts with the
fuel. The reaction of the fuel with the gaseous oxidant within hot
combustion gas chamber 3 produces a hot combustion gas mixture
which comprises combustion reaction products, such as carbon
dioxide and water vapor, as well as remaining uncombusted gaseous
oxidant. Due to the combustion reaction within the confined volume
of hot combustion gas chamber 3, the temperature of the combustion
gas mixture within chamber 3 is at least 300.degree. F. and
generally within the range of from 1000 to 3000.degree. F.
[0032] The hot combustion gas mixture passes in a steady flow from
hot combustion gas chamber 3 into the input of nozzle 6. Nozzle 6
may be a pipe end, a converging nozzle, such as is illustrated in
FIG. 1, or it may be a converging/diverging nozzle. As the hot
combustion gas mixture passes through nozzle 6, it is accelerated
to a high speed. Nozzle 6 communicates with atomization chamber 7.
The hot combustion gas mixture passes out from the output of nozzle
6 at a steady flow into atomization chamber 7 as a high speed hot
combustion gas mixture having a steady flow and a velocity of at
least 300 feet per second (fps) greater than the unheated inlet
gaseous oxidant, and generally having a velocity within the range
of from 1000 to 3000 fps.
[0033] Difficult to combust fluid such as waste fluid 8 is provided
into fluid tube 9 which is positioned for delivering the waste
fluid into the atomization chamber 7. In the embodiment of the
invention illustrated in the Figure, the flow of waste fluid is
provided into atomization chamber 7 in a direction of about 90
degrees to the flow of the high speed hot combustion gas mixture
through atomization chamber 7. It is understood, however, that the
contact of the fluid flow with the stream of high speed hot
combustion gas mixture within chamber 7 could be at any effective
angle including about 0 degrees, i.e. substantially aligned flow of
the waste fluid stream and the high speed hot combustion gas
mixture stream within atomization chamber 7.
[0034] The invention differs from conventional systems which use
pulses or oscillation to atomize difficult to combust fluid by
using steady flow turbulent gas at a high temperature and at a high
velocity to achieve the atomization. An oscillating or pulsating
flow system uses pressure waves to break the fluid into droplets.
These pressure pulses create intense noise at a frequency, 1000 to
6000 Hz, where human hearing is most sensitive. In contrast, the
invention creates a lower intensity of steady (no dominant
frequency), turbulent jet noise, which is less objectionable even
at a given sound intensity. The pressure pulses also create
vibrational stresses in the burner and any equipment attached to
it, leading to problems such as fatigue failure of materials and
stress corrosion cracking. Transfer of these vibrational stresses
to downstream components or refractory lining will significantly
reduce the useful life of these components. The invention avoids
all these issues because there are no pressure pulses or
vibrations. In addition, the oscillating flow reverses direction
for part of each pulse, which could draw the atomized fluid
droplets or particles back into the resonator tubes or the pulse
combustor chamber, potentially causing buildups, corrosion or
erosion in these parts. If the droplets ignite in this area, it
could cause local overheating of the burner. The invention has
one-directional steady flow, which prevents fuel particles or
droplets from going upstream through the nozzle and into the oxygen
combustion chamber. Finally, the composition and temperature of the
atomizing fluid from the pulsed combustor is unsteady, potentially
leading to higher emissions of hydrocarbons, Nox, CO, or soot.
[0035] Pulsed flow systems are also more inherently complex than
the present invention. The pulse combustor is a specially tuned
device requiring considerable expertise to design and fabricate and
must typically operate within a narrow range of flows and
conditions. The special tuning requirement of the device will
necessitate frequent maintenance to operate at optimum conditions.
The invention has no moving parts and needs no tuning or
maintenance other than the occasional cleaning. Further, if
aerodynamic air inlet valves are used, these require considerable
design effort and will be suited to a relatively narrow range of
flow rates. If mechanical air inlet valves are used, this is a
moving part subject to failure and requiring maintenance. The
narrow operating range of the device limits turndown, and limits
flexibility to change gas characteristics, such as temperature and
composition, without significant changes in hardware and flows. In
contrast, the present invention is a very simple design with no
moving parts and externally controlled fuel and oxidant flows, and
only requires occasional cleaning for optimal operation. Further,
this invention uses a simple turbulent diffusion burner to maintain
combustion, which is stable over a wide range of flows and
conditions.
[0036] In the preferred practice of this invention at least one of,
and preferably both, of the hot combustion gas chamber 3 and the
atomization chamber 7 are substantially cylindrical, i.e. have
substantially the same diameter along their length. The cylindrical
shape aids in the attainment of the important steady flow of the
invention.
[0037] Among the many fluids which can be used in the practice of
this invention one can name sludges, such as sewage sludge, low
heating value liquids, aqueous wastes, high viscous fluids with
medium heating values such as skimmings, and slurries of suspended
solids.
[0038] Although the invention may be used to combust fluid having
any heating value and flowable viscosity, the invention will have
particular utility for the combustion of fluid having relatively
low heating value, such as below 10,000 BTU/lb, typically between
1000 and 6000 BTU/lb, and/or relatively high viscosity, such as 20
centipoise or more although it may be used to process fluids having
lower viscosities such as 1 centipoise.
[0039] The impact of using heated oxygen to combust low heating
value fluids is shown in FIG. 2. For the data presented in FIG. 2,
ambient temperature oxygen is assumed to be heated by combustion
with natural gas, similar to the embodiment previously discussed,
to some temperature. This heated oxygen is then used to combust a
fluid having a heating value of 5000 Btu/lb, 3000 Btu/lb, or 1500
Btu/lb. In this example it is assumed that excess oxygen is
supplied such that the flue gas contains approximately 1% oxygen by
volume, wet. As can be seen from FIG. 2, increasing the oxygen
temperature serves to increase the flame temperature as well as
enhancing atomization of the waste. Thus, even with an aqueous
waste containing as little as 1500 Btu/lb heating value, it is
possible to reach temperatures of 1500.degree. F. Higher
temperatures are available if the oxygen is heated beyond
3000.degree. F.
[0040] Within atomization chamber 7 the contact of the flow of
waste fluid with the flow of steady flow high speed hot turbulent
combustion gas mixture causes at least some and preferably most or
substantially all of the waste fluid flow to atomize. The high
speed hot combustion gas mixture contacting the flow of waste fluid
improves the atomization effect. The use of hot gas improves the
atomization process in several ways. The following nozzle equation
can be used to illustrate some of these improvements. 1 U = 2 g c
RT o M ( - 1 ) ( 1 - P P 0 ) 1 - 1
[0041] Where:
[0042] R=gas constant
[0043] To=Gas temperature
[0044] P=outlet pressure
[0045] P.sub.0=supply pressure
[0046] M=molecular weight of gas
[0047] .gamma.=ratio of specific heats Cp/Cv
[0048] gc=gravitational constant
[0049] U=gas velocity
[0050] By raising the temperature of the gas, the same velocity is
achieved using a lower supply pressure. Alternatively, with the
supply pressure kept constant, a much higher gas velocity through
the nozzle can be achieved.
[0051] This increase in velocity increases the force deliverable
from the high speed hot combustion gas stream to the fluid flow,
thus causing more fluid to atomize and also causing the atomization
to form droplets of smaller mean diameter for any given set of
conditions. The high temperature of the gas also serves to transfer
heat to the fluid from the high speed hot combustion gas stream.
This heat transfer enhances drying and/or ignition of combustibles
of the fluid. It is thus seen that the method of this invention
effectively provides both increased mechanical energy and increased
thermal energy to the fluid and this combined increase in energy
synergistically translates into improved atomization and ignition
of the fluid.
[0052] The atomized fluid along with the high speed hot combustion
gas mixture passes from atomization chamber 7 into combustion zone
18 wherein the atomized waste fluid combusts with the gaseous
oxidant of the high speed hot combustion gas mixture. In the
embodiment of the invention illustrated in FIG. 1, combustion zone
18 is shown as being a separate enclosure in flow communication
with atomization chamber 7. It is understood however, that the
atomization chamber and the combustion zone downstream of the
atomization chamber could be a single contiguous enclosure.
[0053] The high degree of atomization of the waste fluid enhances
the efficiency of the combustion reaction within the combustion
zone. Moreover, the high velocity of the high speed steady flow hot
combustion gas mixture that promotes atomization of the waste fluid
also facilitates intimate and homogeneous mixing of the waste fluid
with the gaseous oxidant within the combustion zone further
improving the combustion. Still further, the high speed of the hot
combustion gas mixture promotes recirculation of material that has
already reacted within the combustion zone, this recirculated
material being hotter than the incoming material to the combustion
zone, thus serving to stabilize the flame and further sustain the
combustion reaction.
[0054] The combustion zone may be any suitable device, such as a
furnace, incinerator or burner, wherein the waste fluid may be
combusted. If desired heat transfer fluid, e.g. water, may be
brought into heat exchange relation with the combustion reaction so
as to absorb and subsequently gainfully employ heat generated by
the combustion reaction taking place in combustion zone 18. The
combustion reaction or products may be brought into direct contact
with other heat consuming processes to use the combustion heat such
as for melting, heating, raising steam or causing a reaction to
take place. The resulting gases from the combustion of the atomized
waste fluid are withdrawn from combustion zone 18 as shown by
arrows 10.
[0055] If the difficult to combust fluid contains sufficient
heating value, it may be particularly desirable to only partially
combust the fluid with the high speed, high temperature oxidant
stream. This partial combustion is accomplished by feeding more
combustible material than is needed for stoichiometric combustion
with the gaseous oxidant. Subsequently the partially combusted
gases are supplied with additional oxidant, typically in the form
of air. This partial combustion can be used to control the peak
flame temperatures in the combustion reactor. This partial
oxidation can also improve the economics of this process by
reducing the amount of purchased oxidant for combustion in exchange
for air.
[0056] Although the invention has been described in detail with
reference to a certain preferred embodiment, those skilled in the
art will recognize that there are other embodiments of the
invention within the spirit and the scope of the claims.
* * * * *