U.S. patent application number 10/121957 was filed with the patent office on 2002-12-12 for apparatus for cleaning a heater.
This patent application is currently assigned to ON STREAM TECHNOLOGIES INC.. Invention is credited to Sivacoe, Orlande.
Application Number | 20020185261 10/121957 |
Document ID | / |
Family ID | 27388406 |
Filed Date | 2002-12-12 |
United States Patent
Application |
20020185261 |
Kind Code |
A1 |
Sivacoe, Orlande |
December 12, 2002 |
Apparatus for cleaning a heater
Abstract
An apparatus for cleaning tubing in an operating heater, in
which the tubing has an inlet and an outlet. While the heater is in
operation, a pig is run through the tubing from the inlet to the
outlet and then returned to the inlet along return tubing, in
parallel connection to the heater tubing. A combined pig launcher
and receiver mounted parallel to the tubing, and controlled with
three-way full port valves, is used to launch pigs into the tubing
and remove them from the tubing. A boost pump is used to force pigs
back from outlet to inlet.
Inventors: |
Sivacoe, Orlande; (Red Deer,
CA) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE
SUITE 2800
SEATTLE
WA
98101-2347
US
|
Assignee: |
ON STREAM TECHNOLOGIES INC.
|
Family ID: |
27388406 |
Appl. No.: |
10/121957 |
Filed: |
April 11, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10121957 |
Apr 11, 2002 |
|
|
|
09240223 |
Jan 29, 1999 |
|
|
|
09240223 |
Jan 29, 1999 |
|
|
|
09160235 |
Sep 24, 1998 |
|
|
|
09240223 |
Jan 29, 1999 |
|
|
|
09160228 |
Sep 24, 1998 |
|
|
|
09160228 |
Sep 24, 1998 |
|
|
|
08961574 |
Oct 31, 1997 |
|
|
|
6170493 |
|
|
|
|
Current U.S.
Class: |
165/95 |
Current CPC
Class: |
F28D 2021/0059 20130101;
B08B 9/0553 20130101; F28G 1/12 20130101; F16L 55/46 20130101 |
Class at
Publication: |
165/95 |
International
Class: |
F28G 001/00 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. Apparatus for pigging an operating heater, the apparatus
comprising: heater tubing having inlet tubing and outlet tubing,
the heater tubing having a single path between the inlet tubing and
the outlet tubing; return tubing connected to the inlet tubing at a
first junction and to the outlet tubing at a second junction, the
return tubing and heater tubing together forming a circuit; pig
launching and receiving equipment connected for launching of pigs
into and removal of pigs from the circuit formed of heater tubing
and return tubing; a pig tripper on the circuit for detecting
passage of a pig; and an outlet valve on the circuit for
controlling flow into the receiving equipment in response to the
pig tripper.
2. The apparatus of claim 1 in which the pig launching and
receiving equipment comprises: a pig launcher mounted parallel to
one of the heater tubing and the return tubing; and a pig receiver
mounted parallel to one of the heater tubing and the return
tubing.
3. The apparatus of claim 2 in which a single combined pig launcher
and receiver functions as the pig launcher and the pig
receiver.
4. The apparatus of claim 1 further comprising: a boost pump
connected to the return tubing by a boost pump connection pipe.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of prior U.S. application
Ser. No. 09/240,223, filed Jan. 29, 1999, which is a continuation
of prior U.S. application Ser. No. 09/160,235, filed Sep. 24, 1998,
and of U.S. application Ser. No. 09/160,228, filed Sep. 24, 1998,
which is a continuation-in-part of U.S. application Ser. No.
08/961,574, filed Oct. 31, 1997, now U.S. Pat. No. 6,170,493,
issued Jan. 9, 2001, the disclosures of which are hereby
incorporated by reference, and the filing dates from which priority
is hereby claimed under 35 U.S.C. .sctn.120.
FIELD OF THE INVENTION
[0002] This invention relates to processes and apparatus used for
cleaning tubes, particularly tubes of a heater.
BACKGROUND OF THE INVENTION
[0003] Heaters are used in petrochemical installations to heat
fluids for a variety of purposes, typically to break apart larger
hydrocarbon molecules into smaller molecules. The heaters contain
tubes, up to and even more than a kilometer long in each of several
passes, that pass first through a convection section of a heater
and then through a radiant section. During use, the heater tubes
gradually become contaminated on their insides. This contamination,
typically coke, tends to degrade the efficiency of the heater over
time and can eventually cause the heater to stop working.
[0004] Various methods are known for decoking heaters. In one
method, the heater is shut down and steam cleaned with high
pressure steam. In another method, described for example in U.S.
Pat. No. 5,358,573 issued Oct. 25, 1994, by the same inventor, the
heater is shut down and pigs with appendages run through the heater
until it is clean. In another method, described in U.S. Pat. No.
5,186,815 issued Feb. 16, 1993, the heater tubes are treated while
the heater is in operation by injecting solid particles of very
small size into the heater tubes, recovering the solid particles at
the outlet and recirculating the solid particles back to the inlet
of the heater.
[0005] Use of pigs to clean heater tubes is very effective since
the pigs have a robust scraping action. Heater operators in South
America who have used the inventor's method described in U.S. Pat.
No. 5,358,573 have asked the inventor to provide cleaning of the
heater tubes by pigs while the heater is in operation. Since in
many heater tubes temperatures are far higher than conventional
polymer pigs will withstand, the inventor has identified a need for
a new pig for cleaning an operating heater, and a method for its
use. The inventor has thus come up with a novel solution to the
problem of providing a heater cleaning operation by using pigs
while a heater is in operation.
SUMMARY OF THE INVENTION
[0006] It is an object of this invention to provide a novel pig and
process for pigging tubes, as for example tubes of a heater, even
while it is operating.
[0007] In accordance with an aspect of the invention, there is
provided apparatus for pigging heater tubing in an operating
heater, the heater tubing having inlet tubing and outlet tubing.
Return tubing is connected to the inlet tubing at a first junction
and to the outlet tubing at a second junction. A boost pump is
connected to the outlet tubing by a boost pump connection pipe. Pig
launching and receiving equipment is connected for launching of
pigs into and removal of pigs from the heater tubing and return
tubing. An outlet valve is provided on the outlet tubing downstream
of the second junction. A first pig tripper is provided on the
outlet tubing downstream of the boost pump connection pipe. A
return valve is provided on the return tubing. A second pig tripper
is provided near the inlet tubing for detecting when the pig is
close to the inlet tubing.
[0008] In accordance with a further aspect of the invention, the
pig launching and receiving equipment comprises a pig launcher
mounted parallel to one of the heater tubing and the return tubing;
and a pig receiver mounted parallel to one of the heater tubing and
the return tubing.
[0009] In accordance with a further aspect of the invention, there
is provided a pig launcher and receiver comprising tubing in which
fluids may flow; and a pig launcher and receiver body, the pig
launcher and receiver body having an interior cavity for receiving
pigs, and a motive fluid inlet and a motive fluid outlet, and a
door for removal of pigs from and insertion of pigs into the pig
launcher and receiver body. A basket is provided in the pig
launcher and receiver body for holding pigs. An inlet pipe
controlled by an inlet valve, preferably a three way full port
valve, is connected to the tubing at a first Y junction and
connected to the motive fluid inlet. An outlet pipe controlled by
an outlet valve, preferably a three way full port valve, is
connected to the tubing at a second Y junction and connected to the
motive fluid outlet.
[0010] Preferably, the motive fluid outlet and the motive fluid
inlet are located at opposite ends of the interior cavity.
[0011] These and other aspects of the invention are described in
the detailed description of the invention and claimed in the claims
that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] There will now be described preferred embodiments of the
invention, with reference to the drawings, by way of illustration
only and not with the intention of limiting the scope of the
invention, in which like numerals denote like elements and in
which:
[0013] FIG. 1 is a schematic showing the manner of operation of
continuous cleaning of a heater while the heater is in
operation;
[0014] FIG. 2 is a section through a combined pig launcher and
receiver that for example may be used in the operation of the
invention;
[0015] FIG. 3 is a section through a pig that may be used during
the operation of the invention.
[0016] FIG. 4 is a perspective view of a knitted tubular mesh pig
according to the invention;
[0017] FIG. 4A is a detail of a first knit that could be used to
make the pig of FIG. 4 or FIG. 7;
[0018] FIG. 4B is a detail of a second knit used to make the pig of
FIG. 4;
[0019] FIG. 5A is a perspective view of an expander for use with
the tubular mesh pig of FIGS. 4 and 7;
[0020] FIG. 5B is a perspective view of the expander of FIG. 5A
inside the tubular mesh pig of FIG. 4;
[0021] FIG. 5C is a perspective view of a further embodiment of pig
made from a wire;
[0022] FIG. 6 is a section through a wire thread used to make the
mesh of the tubular mesh pigs of FIG. 4 and FIG. 7;
[0023] FIG. 7 is a perspective of a tubular mesh pig in which the
knit is at right angles to the knit of FIG. 4;
[0024] FIG. 8 is a perspective view of a woven tubular mesh
pig;
[0025] FIG. 9 is a schematic showing a first embodiment of an
apparatus for performing an embodiment of the method of the
invention;
[0026] FIG. 10 is a schematic showing a second embodiment of an
apparatus for performing an embodiment of the method of the
invention;
[0027] FIG. 11 is a schematic showing an electric injection
assembly for use with the apparatus of FIG. 10;
[0028] FIG. 12 is a schematic showing a third embodiment of an
apparatus for performing an embodiment of the method of the
invention, which uses a rotary pig injector;
[0029] FIG. 13 is a schematic showing a fourth embodiment of an
apparatus for performing an embodiment of the method of the
invention using a rotary pig injector; and
[0030] FIGS. 14A, 14B, 14C and 14D are respectively a first end
view, top view, second end view and front view of a rotary injector
for use with the apparatus of FIGS. 12 and 13.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0031] Referring to FIG. 1, a heater 10 may contain as much as 10
kilometers of tubing or pipe running through a convention section
and a radiant section from an inlet tube 12 to an outlet tube 14 in
several passes. Details of the heater are not shown since the pig
is intended for application to existing installations, the general
construction of which is well known. The pig is intended for
cleaning of the tubing in the heater while fluid being heated is
flowing through the heater from the inlet tube 12 to the outlet
tube 14. The cleaning may be effected by a single pass repeated
periodically as required. The time period between passes depends on
the rate of contaminant build up. It is preferred to begin the
process with the tubes clean, and thus before establishing
continuous pigging while the heater is in operation, it is
preferred to clean the tubes thoroughly with repeated passes of a
pig while the heater is not operating, since then a very robust
scraping action may be obtained with a polymer pig having metallic
scraping elements embedded in the polymer pig. Polymer pigs are
shown in U.S. Pat. No. 5,358,573, the content of which is herein
incorporated by reference. Care must be taken not to damage the
tubes while doing the scraping with polymer pigs.
[0032] To enable automatic operation of the system according to an
embodiment of the method of use of the pig, a return tube formed of
tubes 16 and 18 in parallel with the heater tubes is provided
between the outlet 14 and inlet 12, with a control valve 22 on tube
16 and return control valve 23 on tube 18. A boost pump 26 on a
boost pipe 28 is connected to supply boost fluid to the tube 16. A
bypass tube 32 which also forms part of the outlet tubing is also
connected in parallel to the boost pipe 28 between the tube 16 and
outlet 14. A valve 24 is provided on tube 14, and an outlet valve
25 is provided on tube 32 downstream of the junction between the
tube 16 and return tubing 18. Trippers 34, 36 and 38 are provided
on tubes 14, 16 and 18 respectively. The trippers 34, 36 and 38 are
conventional pig trippers that are activated when a pig passes
them. Tripper 38 should be located close to the junction of return
tubing 18 with the inlet tubing 12. Close or near in this context
means in position where it can be determined when the pig enters
the inlet tubing 12. This need not be at the junction if a timer is
used and it is known how long it takes for the pig to travel from
the tripper 34 to the junction of return tubing 18 and inlet tubing
12 Tripper 34 should be located close to and upstream of the pig
launcher 39.
[0033] A conventional pig receiver 39 is attached to the tube 14 in
parallel by tubes 40, 42 and controlled by valves 43, 44 and 45.
The parallel construction permits fluid to flow either through the
tube 14 or the pig receiver 39 depending on the positioning of the
valves 43, 44 or 45. Pig receiver 39 is used for removal of pigs
from the tube. A conventional pig launcher 49 is attached to the
tube 12 in parallel by tubes 50, 52 and controlled by valves 53, 54
and 55. The parallel construction permits fluid to flow either
through the tube 12 or the pig launcher 49 depending on the
positioning of the valves 53, 54 or 55. Pig launcher 49 is used for
launching of pigs into the tube. The pig launcher and receiver may
be connected to any tube that connects into the tubes 12, 14, 16 or
18, and is preferably on one of the tubes 12, 14, 16 or 18.
[0034] An alternative pig launcher and receiver design is shown in
FIG. 2. In this embodiment, there is provided a combined pig
launcher and receiver 80, that is mounted parallel to a set of
tubing 82 in which fluids may flow, which may for example be the
inlet or outlet tubing of a heater or the return tubing 18. The pig
launcher and receiver 80 is formed of a pig launcher and receiver
body 84, having an interior cavity 86 for receiving pigs.
Preferably on opposed sides of the interior cavity 86 there is
provided a motive fluid inlet 88 and a motive fluid outlet 90. A
door 92 is provided for removal of pigs from and insertion of pigs
into the pig launcher and receiver body 80. A basket 94 is
installed in the pig launcher and receiver body 80 for holding
pigs. Except as described here, the design of the pig launcher and
receiver follows conventional design. An inlet pipe 96 is connected
to the tubing 82 at a junction 97, which is preferably Y shaped but
may be T shaped, and connected to the motive fluid inlet 88. An
outlet pipe 98 is connected to the tubing 82 at a junction 99,
which is preferably Y shaped but may be T shaped, and connected to
the motive fluid outlet 90. A three way full port valve 100 is
provided on the inlet pipe at the junction 97. A three way full
port valve 102 is provided on the outlet pipe at the junction 99. A
tripper 104 is provided on the tubing 82 upstream of the pig
launcher and receiver 80.
[0035] This alternative pig launcher and receiver design works as
follows. The three way full port valves 100 and 102 may direct flow
and a pig carried by the flow into the pig launcher and receiver 80
or around the pig launcher and receiver 80 through tubing 82. When
the heater tubing is not being cleaned, or a pig is by-passing the
pig launcher and receiver 80 valves 100 and 102 are in left open
position (tubing 82 is open). When a pig is in the system and needs
to be stopped, three way valves 100 and 102 are placed into right
position. When the tripper 104 signals a pig has arrived at the pig
launcher and receiver 80, the valves 100 and 102 return to left
open position. One combined pig launcher and receiver is used for
each pass in a heater.
[0036] In the normal operating condition, the inlet 12 is at a
lower temperature and higher pressure than the outlet 14, and with
no pigs in the system, valves 22 and 25 are open, and valves 23 and
24 closed, permitting flow through tubes 14, 16 and 32 which
together form an outlet tube. When it is desired to operate the
system with a pig, a pig is injected into line 14 through pig
launcher 49. To do this, valves 53 and 54 on tubes 52 and 50
respectively are closed, with valve 55 on tube 12 open. A pig may
then be placed in the launcher 49. Valves 53 and 54 are opened, and
then valve 55 on tube 12 is closed, forcing the pig into tube 12
and into the heater 10. The pig exits the heater through tube 14,
and since valve 24 is closed, the pig passes into line 16 and trips
tripper 36 which is located on the tubing 16 downstream of the
junction of the boost pump connection pipe 28 with the tubing 16.
When the pig trips tripper 36, valves 23 and 24 are opened, valves
22 and 25 are closed and boost pump 26 is started. The boost pump
26 provides the required pressure to force the pig to return to the
inlet 12 past tripper 38. For an exemplary inlet pressure of 150
psi, and outlet pressure of 110 psi, the boost pump pressure is 200
psi.
[0037] When tripper 38 is tripped, boost pump 26 is shut off,
valves 22 and 25 are opened and valves 23 and 24 are closed, thus
completing the cycle automatically. While pigs are being shunted
around the system automatically, the valve 45 is kept open and
valve 44 closed. When it is desired to remove pigs from the system,
for example for inspection of the pigs, upon tripping of tripper 34
by a pig, valve 45 is closed, and valves 43 and 44 opened,
permitting the pig to enter the pig launcher. Valve 45 may then be
opened and valves 43 and 44 closed, and the pig may be removed from
the launcher.
[0038] Each of the pig launcher 49 and pig receiver 39 contains a
basket 62 and pressure gauge 60. The basket permits fluid flow
through the receiver, while the pig may be caught before or in the
basket. The pressure gauges 60 inform an operator that the pressure
is low enough for the door of the launcher and receiver to be
opened. A drain valve 64 is provided in each of the launcher and
receiver to permit draining of fluids. The inside diameter of the
launcher and receiver should be two sizes larger than the clean
inside diameter of the tube being treated. For example, a launcher
and receiver inside diameter of 5 or 6 inches would be used for
treatment of a 4 inch tube. The launcher and receiver should be
made of metal having similar metallurgical properties to the metal
of the heater tubes being treated. A door(not shown) is provided on
the launcher or receiver in conventional fashion.
[0039] The preferred manner of operation of the pig, is to run the
pig at a predetermined cycle or time interval. This time interval
is established by the operating parameters of the furnace, the
process fluid, and by experimentally determined fouling rate
onset.
[0040] The purpose of the on-stream cleaning method is to inhibit
the onset and subsequent formation of coke. This will lengthen the
operating period or run-length of a given furnace and maintain
furnace operation at the designed peak efficiency.
[0041] Starting with a clean and polished pipe, the coke onset
period has been determined by laboratory experiments to be from
minutes to as long as 18 hours. This period of onset is the most
crucial time period during which the cleaning or wiping action of
the on-line pig has to be performed. At this point in the operating
cycle, it is not practicable to measure any temperature changes
that would reflect fouling with conventional sensing elements,
since the temperature changes would be measured in millidegrees.
The time interval of running the on-line pig is best established by
the operating conditions and analyzing coke build up in the tubing
under the operating conditions. Under laboratory conditions, the
coke onset and the amount is actually determine by weight. This is
then converted into a time period characterizing the differing
thicknesses of coke build-up.
[0042] Once coke buildup has occurred and temperature changes can
be observed, the underlying coke layer is likely to be too hard to
be removed with an on-line pig. Only the most recent formation on
top of the already formed coke layer is expected to be able to be
wiped away. Wiping away a new, thin and soft layer of coke before
it builds up is believed to retard the progression of coke
formation and extend the run time period. Thus, it is preferred to
run the pig repeatedly through the tubing before the contaminant as
hardened, or solidified. Initially, coke in a hydrocarbon stream is
in a creamy state, but solidifies and hardens in the time frame
mentioned above.
[0043] It is the extension of the run time together with the energy
savings by virtue of improved efficiency, that on-line cleaning is
expected to have its most significant accomplishment. Eventually,
it is expected that build up of coke will necessitate removal by
conventional pigging.
[0044] Thus, it should be clarified that it is not prudent to rely
solely on conventional monitoring methods, but rather indirect
means should be used to establish cleaning run intervals.
Conventional monitoring methods may also be used to augment the
pigging control process.
[0045] Thus, automatic cleaning of the heater tube may be effected
whenever there is a degradation of efficiency of the heater.
Efficiency of the heater may be monitored by monitoring the
temperature at the outlet 14 of the heater 10 with a conventional
temperature sensor. For a given heat input to the heater 10, the
fluid in the tube will be heated a lesser amount when there is a
greater amount of contamination in the tube. The contamination in
effect acts as an insulator for the fluid in the tube. Hence, when
the temperature at the outlet 14 of the heater 10 indicates a
degradation of efficiency of the heater 10 below a given set point,
a pig may be run through the tube in the manner described to clean
the tube while the heater is operating.
[0046] The on line cleaning of the heater may also be controlled by
other process parameters such as pressure, change in temperature or
pressure from inlet to outlet or volumetric flow rate. Conventional
devices may be used for monitoring these parameters.
[0047] The tubes, valves and launchers should all be made of
similar metal to the metal in the heater tubes. The pig should be
made of similar metal. The pig must be able to bend sufficiently to
move around the bends in the tubes.
[0048] Any pig used in the operation of the invention should be
dimensioned to fit within the tube with its cleaning elements able
to compress against contaminants in the tube and effect a scraping
action. The pig itself is constructed to bias the cleaning elements
against the contaminants.
[0049] An exemplary hollow metallic pig is shown in FIG. 3. An
exterior partly cylindrical and partly conical shell 70 is made of
spring metal of the same material that the tubes in the heater are
made from, or such other material that will withstand the high
temperature corrosive conditions within the heater tubes. Bristles
or metallic wires 72 acting as cleaning elements are formed into
U-shapes and pass through openings in the cylindrical portion of
the shell 70 in conventional fashion for forming a brush with
bristles. The metallic wires 72 extend circumferentially around the
cylindrical portion of the conical shell 70. Other methods of
securing the wires 72 may be used. An interior cylindrical and
conical shell 74 of similar but slightly smaller cross-section than
the conical shell 70 is pressed into the conical shell 70 to assist
in securing the metallic wires 72 in the conical shell 70. An
annular lip 76 holds the interior shell 74 inside the exterior
shell 70. The metallic wires 72 and the shell 74 should be made of
the same material as the shell 70 or a material having equivalent
characteristics.
[0050] A preferred pig designed in accordance with the invention is
shown in FIGS. 4-8. Referring to FIGS. 4-8, there is shown a pig
for cleaning tubes which is in the form of a tubular mesh 110 made
of flexible abrasive material. The tubular mesh 110 forms a body
having a circular cross-section in a plane perpendicular to the
axis of the tubular mesh. A suitable flexible abrasive material is
304 or 316 stainless steel wire, cold rolled to a square,
rectangular, flat, or other polygonal cross-section as shown by
wire 111 shown in FIG. 6. The wire 111 may be plated, coated or
bi-metallic, and may be annealed or heat treated. A square
cross-section is preferred, but the wire may be in the form of a
ribbon. In the case of a soft scale, a rounded wire could be used,
a line running along the outermost longitudinal surface of the wire
thus forming a scraping edge, but it is preferred that the scraping
edge be angular. Other materials may be used for the wire besides
metal if they are sufficiently hard, flexible and robust for the
scraping action. For high temperature applications, a heat
resistant metal such as Inconel.TM. 600 or other nickel alloy may
be used. However, other materials including other metals and
ceramics may be used, depending on the intended application. The
selection of an appropriate metallurgy for cleaning a tube is well
within the skill of a person in the art. For example, it is well
known that the hardness of the abrasive material should not exceed
the hardness of the tube or other fittings such as valves in the
tube system. In addition, the material should not corrode easily
within the tube operating environment. The square edges 113 of the
wire 111 form scraping edges on the outer periphery of the tubular
mesh 110. These scraping edges 113 extend longitudinally
(lengthwise) along the wire 111. The scraping edges preferably lie
in planes perpendicular to an axis of the body, and at least lie at
an angle sufficient to effect a scraping action. In the case of a
cylindrical body, the axis is the central axis of the cylinder. In
the case of a spherical body, any diameter is an axis. For high
temperature applications, and particularly for operation at
temperatures over 500.degree. F., based on currently available
polymers, the pig should be made entirely of metal or a similar
material such as flexible ceramic, and have no polymeric material
associated with it. The tubular mesh or metallic wire should
preferably be unconstrained by other material, such as that of a
solid pig, to permit it the flexibility to adapt to different sizes
of pipes.
[0051] The tubular mesh may be a knit (FIGS. 4, 4A, 4B, 5B and 7)
or a weave (FIG. 8) or may be knotted, not shown. In the case of
the knit, the loops 112 (FIG. 4A) may be oriented parallel to the
longitudinal axis of the tube (FIG. 4) or may, preferably, form a
tubular mesh 114 with loops 112 oriented at any appropriate angle,
for example perpendicular, to the longitudinal axis of the tube
(FIG. 7). Double knitted loops 116 are shown in FIG. 4B. The knit
shown in FIGS. 4A and 4B when used in the orientation of tubular
mesh 118 shown in FIG. 7 is capable of radial expansion from full
compression to twice the diameter. As an example, a tubular mesh 8
inches in diameter in the fully expanded condition will fit within
a tube having inner diameter of 4 inches when fully compressed. A
slight overcompression to less than half the original diameter is
also possible by overlap of some of the loops of the knit. In the
fully compressed position, there is little, if any, bypass of
motive fluid. As the tube expands downstream, the mesh will expand
up to 8 inches in diameter. In general any knit may be used, though
it is preferred that the tubular mesh have an axial view profile
that is as close to circular as is practicable. That is, it is
preferred that the knit not be ribbed, but present a smooth outer
circumference when viewed along the axis of the tubular mesh. This
ensures complete circumferential cleaning of a pipe.
[0052] For a 4 inch diameter tubular mesh, a wire of 0.013 inches
cross-section is suitable. For an 8 inch diameter tubular mesh, a
wire of 0.025 inches cross-section is suitable. The diameter of the
tubular mesh is chosen to suit the intended application. If the
tubular mesh is to be used in tubes of variable sizes, then a
tubular mesh whose range of expansion will cover all tube sizes, or
as many as possible, should be chosen.
[0053] Although the tubular mesh of FIGS. 4A-4B and 7 is
self-expanding under pressure, it is preferred to provide an
expander 120 (shown in FIG. 5A) biased against the tubular mesh 110
for urging the tubular mesh radially outward (as shown in FIG. 5B).
The expander 120 may be used to control the force applied to the
inside wall of the pipe to control the cleaning action. In
addition, the bias force applied by the expander 120 regulates the
speed at which the device travels in the tube. The expander 120 in
FIG. 5A is in the form of a helical wire spring. The wire size may
be varied to vary the tension in the spring. Other shapes of
expander may be used. A simple helix is not required, and a wire
expander could have various contortions of wire. The expander 120
may be symmetrical, tapered at both ends, or be tapered at only one
end. In addition, the expander 120 may have control surfaces or
apertures that allow more or less fluid to bypass the expander 120
and thus control the speed of the expander. The expander 120 may
itself be considered a body with circular cross-section
perpendicular to its axis and may itself be used to form a pig,
without using the tubular mesh. In this case, the expander 120 is
preferably made of the same wire as described above for the tubular
mesh, with scraping edges extending along the wire, hence around
the outer periphery of the expander.
[0054] The expander of FIGS. 5A and 5B has the disadvantage that
since its expansion requires its loops to move circumferentially
any friction between the expander loops and the tubing or the mesh
will tend to prevent the expander from expanding. Thus, it is
preferred to make the expander, as shown in FIG. 5C, made of
lengthwise wire 121. For use as a pig in itself, this expander has
less efficient coverage since the scraping edges that carry out the
scraping function are then effectively only the end pieces, which
tend to become worn, and thus are not preferred. An alternative is
to have the wire 121 be wavy along the length between the end
pieces, so as to provide more scraping action.
[0055] The body of the pig may also be spherical and could in one
embodiment consist of a ball of wire or wires compressed together
with random portions of the wire forming the outer periphery of the
ball.
[0056] In operation, the tubular mesh 110 or 118 should be tapered
at one end 122 (shown in FIG. 5B) with the mesh bound together at
the apex of the taper to close the end of the tubular mesh. For a
knit, this can be done with a wire loop, or the loops may be welded
together or otherwise secured or tied together. The expander should
be capable of expanding the diameter of the tubular mesh 100% and
at least 50% of its initial diameter.
[0057] The tubular mesh shown in FIGS. 4, SB or 7 may also be made
from a weave 124 shown in FIG. 8. In this instance, the weave
should be at 45.degree. to the longitudinal axis of the tubular
mesh, and the edges of the mesh should be welded together to
prevent unravelling. In this example, the tubular mesh compresses
axially when it expands radially, and vice versa. The tubular mesh
10 or 18 should be at least 20% longer than the biggest ID of
tubing to be cleaned to prevent cross-ways motion of the tubular
mesh through the tube.
[0058] The pipe pig of the present invention is propelled through a
heater either using conventional methods or using the new method of
operational fluid (liquid, gas or a mixture of liquid and gas)
passing through the heater while the heater is operating. The pipe
pig can be circulated through the tubes of the heater as often as
is required to clean the heater. When commencing a continuous
operation, it is preferred to get the tube very clean first, and
then continuously cleaning a small amount of and preventing build
up of thick deposits. While the tubing is very hot, as it is during
operation, the coke tends to be soft and to be removed easily.
[0059] While the system may be manually operated, it is preferred
to operate the system automatically. For this purpose, a control
system may be connected to the trippers, valves, boost pump and pig
launcher and receiver for controlling their operation in accordance
with the operating principles outlined herein. Other than as
described, the tubing, trippers, valves, and boost pump mentioned
herein are all conventional.
[0060] It should be appreciated that FIG. 1 is not to scale. In
practice, both inlet 12 and outlet 14 may pass out of the heater in
close proximity to each other, and thus the return tubing 18 may be
a very short length.
[0061] FIG. 9 shows an apparatus that may be used to pig an
operating heater with one of the pigs described herein. A tube or
pipe 130 in the furnace section of an operating heater is supplied
fluid from an in-flow manifold 132 in conventional manner and
discharges fluid in conventional manner through outflow manifold
134. A pig return line 136 is connected in parallel to the tube 130
between the inlet and outlet of the tube 130 at junctions 138 and
139. Valves V1 and V4 at the junctions 139 and 138 respectively
isolate the pig return line 136 from the tube 130. A pig catcher
140 and pig access port 142 are provided on the pig return line 136
between V1 and V4. Drive fluid for driving the pig along the pig
return line 136 is provided through line 144 and valve V2. Motive
power is provided by pump 146 on line 144. The pump 146 accesses
fluid from a reservoir 148, which may for example obtain fluid from
line 150 which connects at pitot tap 152 to the tube 130. Flow
along lines 150 and 144 is controlled by valves V5 and V2. A fluid
return line 154 is provided between pig access port 142 and valve
V2. A fluid drain 156 with flow controlled by valve V6 is provided
on line 154. A catcher bleed line 158 with valve V3 connects the
pig catcher to the tube 130 outflow line. Pig signalling devices
160, 162 and 164 are located at the junction 138, junction 139 and
pig catcher 140 respectively. A pressure sensor 166 is located near
the injector pump, and a pressure sensor 168 is located on the
reservoir 148.
[0062] The apparatus of FIG. 9 works as follows. A pig is placed in
pig access port 142 with V1-V6 all initially closed. VS is opened,
the pump 146 is started and then valve V2 is opened to place
pressure on the pig. V4 is then opened until the pig trips pig
signalling device 160. After the pig passes the junction 138, V4 is
closed, and then V2 and VS are closed. V6 may be then opened and
closed to drain the pig launcher 142. The pig circulates through
the tubes 130 until it reaches junction 139 where its momentum
carries it towards V1. V1 is opened (either based upon timing after
V4 closes, or opened when V4 closes or by sensing the location of
the pig in the tubes 130 as it nears V1) and the pig is pushed by
pressure from fluid in the tubes 130 into the pig catcher 140. V3
is also opened to allow return of fluid into the out flow manifold
134. The pig catcher 140 is shown as a restriction in the line, but
the catching function may be carried out by throttling V3 to place
back pressure on the pig in the catcher 140. Once the pig is in the
catcher, which may be sensed by passage of the pig past sensor 162
or by another sensor, V1 and V3 are closed. The cycle may then be
repeated as desired. Pump 146 is preferably a variable pressure
pump, since it is preferably to maintain the pressure in line 136
slightly higher than the pressure in the line 130 at the junction
138. Sensor 166 may be used to sense the pressure supplied by the
pump 146, and the pressure varied accordingly. In addition, it is
desirable to avoid any back flow in line 144 that could damage the
pump.
[0063] Referring to FIG. 10, a tube or pipe 170 in the furnace
section of an operating heater is supplied fluid from an in-flow
manifold 172 in conventional manner and discharges fluid in
conventional manner through outflow manifold 174. A pig return line
176 is connected in parallel to the tube 170 between the inlet and
outlet of the tube 170 at junctions 178 and 179. Valves V11 and V12
at the junctions 179 and 178 respectively isolate the pig return
line 176 from the tube 170. A pig catcher 180 and pig access port
182 are provided on the pig return line 176 between V11 and V12. A
drive mechanism for driving the pig into the pig return line 176 is
provided by a hydraulic injector 186 coupled to a hydraulic fluid
injection system 188 through line 190. The hydraulic injector 186
has a ram 192 which is extendible into the pig arrester 180 by
action of hydraulic fluid in the injector 186. A fluid return line
194 with V14 is provided between pig access port 182 and a drain
reservoir 195. Sensor 196 detects when reservoir 195 is full and
requires emptying through outlet 197. A catcher bleed line 198 with
valve V13 connects the pig catcher to the tube 170 outflow line.
Pig signalling devices 200, 202 and 204 are located at the junction
178, junction 179 and pig catcher 180 respectively.
[0064] The apparatus of FIG. 10 works as follows. A pig is placed
in pig access port 182 with V11-V13 all initially closed. V12 is
opened, the hydraulic actuator 186 is activated to drive a pig into
the line 170. After the pig passes sensor 200, V12 is closed and
V11 and V13 are opened.
[0065] The pig circulates through the tubes 170 until it reaches
junction 179 where its momentum carries it towards V11. V1 is open
and the fluid exiting the catcher 182 through bleed line 198
carries the pig into the catcher 180. The pig catcher 180 is shown
as a restriction in the line, but the catching function may be
carried out by throttling V13 to place back pressure on the pig in
the catcher 180. Once the pig is in the catcher, which may be
sensed by passage of the pig past sensor 204 or by another sensor,
V11 and V13 are closed. V14 is opened to drain fluid from the pig
catcher 180 and pig access port 182. The cycle may then be repeated
as desired. A variation of the pig return drive mechanism shown in
FIG. 10 is shown in FIG. 11, wherein an electric ram 208 is used
with a lead screw 210 replacing ram 192, and a motor 212 with motor
controller 214 replacing the hydraulic drive 188 of FIG. 10.
[0066] Referring to FIG. 12, a tube or pipe 220 in the furnace
section of an operating heater is supplied fluid from an in-flow
manifold 222 in conventional manner and discharges fluid in
conventional manner through outflow manifold 224. Various other
furnace sections 223 may also be treated in like manner. Pig return
line 226 is connected in parallel to the tube 220 between the inlet
and outlet of the tube 220 at junctions 228 and 229. A rotary pig
injector 230 is provided on the pig return line 226 between V21 and
V25. Valves V21 and V25 at junction 229 and on the other side of
the rotary pig injector 230 respectively isolate the rotary pig
injector 230 from the tube 220. A drive mechanism for driving the
pig into the pig return line 226 is provided by a line 232
connected to the inflow line at junction 234 and to the rotary pig
injector 230 V23 at junction 234 controls fluid flow into the line
232. V24 controls fluid flow on the inflow line between junction
234 and 228. V25 on line 226 at the rotary injector 230 also
controls flow of fluid in line 226. Sensors 238, 239, 240 and 242
are provided respectively at junction 228, junction 229, rotary
injection 230 and on line 232 near the rotary injector 230. A drain
line 244 is provided on the rotary injector 230, which drain line
244 discharges through reservoir 246 and pump 248. A catcher bleed
line 249 with valve V26 connects the pig catcher to the tube 220
outflow line.
[0067] The rotary pig injector 230 is shown in FIGS. 14A-14D. The
pig injector 230 has a rotating barrel 252 with a chamber 250 in
the rotating barrel. Flanges 254 and 256 retain the rotating barrel
252. Ports 258 and 260 in the flanges 254 and 256 respectively
connect between the tube 220 and the bleed line 249. Ports 262 and
264 in the flanges 254 and 256 respectively connect between the
tube 226 and 232. A single port 266 in flange 256 permits access to
the chamber 250 from the outside for emplacement and recovery of
pigs into and out of the chamber 250. The chamber 250 may rotate
from being between ports 258 and 260 (RETRIEVE position), to
connecting with port 266 (ACCESS position) and to being between
ports 262 and 264 (LAUNCH position). Any suitable means, such as a
chain drive (not shown) may be used to rotate the barrel 252.
[0068] The apparatus of FIG. 12 works as follows. A pig is placed
in chamber 250 of rotary injector 230 through port 266 with all
valves except V24 initially closed. V23 and V25 are opened to fill
lines 226 and 232 with fluid. The chamber 250 is rotated to the
LAUNCH position and the pig enters line 226. V24 is then closed and
the pig is driven through line 226 into the tubes 220 and past
sensor 238. When the pig trips sensor 238, V24 is opened, and V23
and V25 are closed. Chamber 250 and lines 232 and 226 are then
drained through line 244. Chamber 250 is rotated to the RETRIEVE
position. The pig is driven by operating fluid through the tube 220
to junction 229 where it trips sensor 239 and V21 and V26 open to
allow the pig to enter chamber 250. V21 and V26 are then closed,
and the bleed line 249 and chamber 250 may be drained through line
244. The pig may then be returned to the LAUNCH position to
continue the cleaning cycle as required, or returned to the ACCESS
position for retrieval. The rotary injector 230 is not preferred
due to the difficulty of sealing the chamber 250 in the LAUNCH and
RETRIEVE positions.
[0069] A further embodiment of pig return system is shown in FIG.
13. Referring to FIG. 13, a tube or pipe 270 in the furnace section
of an operating heater is supplied fluid from an in-flow manifold
272 in conventional manner and discharges fluid in conventional
manner through outflow manifold 274. Various other furnace sections
273 may also be treated in like manner. A pig return line 276 is
connected in parallel to the tube 270 between the inlet and outlet
of the tube 270 at junctions 278 and 279. A rotary pig injector 230
(same as the one shown in FIG. 12) is provided on the pig return
line 276 between V31 and V32. Valves V31 and V32 at junction 278
and junction 279 respectively isolate the rotary pig injector 230
from the tube 270. A drive mechanism for driving the pig into the
pig return line 276 is provided by a line 282 connected to the
inflow line at junction 284 and to the rotary pig injector 230. V33
at junction 284 controls fluid flow into the line 282. V34 controls
fluid flow on the inflow line between junction 284 and 278. Sensors
288 and 289 are provided respectively at junction 278 and junction
279. A drain line 294 controlled by valve V36 is provided on the
rotary injector 230, which drain line 294 discharges through
reservoir 296 and pump 298. A catcher bleed line 299 with valve V25
connects the pig catcher to the tube 270 outflow line. Sensor 300
is supplied on the rotary pig injector to detect when the pig exits
the rotary injector.
[0070] The apparatus of FIG. 13 works as follows. A pig is placed
in chamber 250 of rotary injector 230 through port 266 with all
valves except V34 initially closed. V33 and V31 are opened to fill
line 282 with fluid. The chamber 250 is rotated to the LAUNCH
position and the pig enters line 275. V34 is then closed and the
pig is driven through line 275 into the tubes 270 and past sensor
288. When the pig trips sensor 288, V34 is opened, and V31 and V33
are closed. Chamber 250 and lines 282 and 276 are then drained
through line 294. Chamber 250 is rotated to the RETRIEVE position.
The pig is driven by operating fluid through the tube 270 to
junction 279 where it trips sensor 289 and V32 and V35 open to
allow the pig to enter chamber 250. V32 and V35 are then closed,
and the bleed line 298 and chamber 250 may be drained through line
294 The pig may then be returned to the LAUNCH position to continue
the cleaning cycle as required, or returned to the ACCESS position
for retrieval.
[0071] The method of the invention may also be used to clean tubing
used in other chemical processes, such as heat exchangers, while
the tubing is being used to convey fluids.
[0072] A person skilled in the art could make immaterial
modifications to the invention described in this patent document
without departing from the essence of the invention that is
intended to be covered by the scope of the claims that follow.
* * * * *