Title: Regenerative fume-incinerator with on-line burn-out and wash-down system
Abstract: A method and apparatus for on-line wash-down of a heat sink media bed in a regenerative heat exchanger of a regenerative fume incinerator is disclosed. When a heat sink media bed requires cleaning, the selected regenerative heat exchanger is cooled while the remaining regenerative heat exchangers are operated in their normal mode of operation. When the selected media bed reaches a temperature which is less than the thermal-shock temperature of the media material, a cleaning fluid is sprayed on the media surfaces through spray-pipes which are installed within the media bed. After the media surfaces are washed down, the selected regenerative heat-exchanger is reverted back to its normal mode of operation. The regenerative heat exchanger can also be automatically burnt-out of deposited gasifiable matter prior to the wash-down. Random or sequential burn-out and wash-down of the regenerative heat-exchangers can be performed. The apparatus can also be used to suppress fires within the media bed by spraying cold water on the media bed when a rapid rise in temperature is detected within the media bed.
Patent Number: 7,017,592 Issued on 03/28/2006 to Chiles, et al.
| Inventors:
|
Chiles; Joseph David (Rancho Cucamonga, CA);
Yerkes; Jeffrey J. (Santa Ana, CA);
Kirkland; John G. (Placentia, CA);
Cabarlo; Agustin (Chino Hills, CA);
Vij; Anu D. (Chino Hills, CA)
|
| Assignee:
|
Pro-Environmental Inc. (Rancho Cucamonga, CA)
|
| Appl. No.:
|
732600 |
| Filed:
|
December 9, 2003 |
| Current U.S. Class: |
134/22.1; 134/22.12; 134/22.15; 134/22.18; 134/24; 134/34; 134/36; 134/42; 422/175; 432/180; 432/181; 432/182 |
| Current Intern'l Class: |
B08B 9/00 (20060101) |
| Field of Search: |
422/175
432/180,181,182
134/221,221.2,221.5,221.8,24,34,36,42
|
References Cited [Referenced By]
U.S. Patent Documents
| 3023836 | Mar., 1962 | Kasbohm et al.
| |
| 4141754 | Feb., 1979 | Frauenfeld.
| |
| 4649987 | Mar., 1987 | Frauenfeld et al.
| |
| 5098286 | Mar., 1992 | York, deceased.
| |
| 5217373 | Jun., 1993 | Goodfellow.
| |
| 5229071 | Jul., 1993 | Meo, III.
| |
| 5259757 | Nov., 1993 | Plejdrup et al.
| |
| 5620668 | Apr., 1997 | Driscoll et al.
| |
| 5931663 | Aug., 1999 | Lewandowski et al.
| |
| 6235249 | May., 2001 | Fu et al.
| |
| 6423275 | Jul., 2002 | D'Souza.
| |
| 6579379 | Jun., 2003 | Noble.
| |
| 2004/0123880 | Jul., 2004 | Chiles et al.
| |
Primary Examiner: Carrillo; Sharidan
Attorney, Agent or Firm: D'Souza; Melanius
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This patent application claims priority from U.S. provisional patent application
No. 60/432,196 filed on Dec. 10, 2002.
Claims
We claim:
1. A method of washing the heat sink media in a selected regenerative heat exchanger
of a Regenerative Fume Incinerator while the remaining regenerative heat exchangers
of the Regenerative Fume Incinerator are on-line with the process, the selected
regenerative heat exchanger having an upper section and a lower section, and at
least one spray pipe installed in between the upper and lower sections, the spray
pipe connected to a source of cleaning fluid, the spray orifices on the spray pipe
being directed towards an upper surface of the lower section of the heat sink media
within the selected regenerative heat exchanger, the method comprising the following steps:
(a) cooling the lower section of the heat sink media of the selected regenerative
heat exchanger to a pre-set temperature less than 500 degrees Fahrenheit by passing
a process gas through the selected regenerative heat exchanger, while maintaining
the other regenerative heat-exchangers in their normal on-line operating modes
of operation;
(b) stopping the flow of the process gas through the selected regenerative heat
exchanger; and
(c) introducing the cleaning fluid into the spray-pipe of the selected regenerative
heat-exchanger to wash the upper surface of the lower section of the heat sink media.
2. The heat sink media washing method of claim 1, wherein the cleaning fluid
is water.
3. The heat sink media washing method of claim 1, wherein the cleaning fluid
is steam.
4. The heat sink media washing method of claim 1, wherein the cleaning fluid
is compressed air.
5. The heat sink media washing method of claim 1, wherein the pre-set temperature
is in the range of 200 to 250 degrees Fahrenheit.
6. The heat sink media washing method of claim 1, further including the step
of burning-out the heat sink media in the selected regenerative heat-exchanger
before execution of steps (a) to (c).
Description
BACKGROUND OF THE INVENTION
The present invention generally relates to an improved method and apparatus for
on-line cleaning of deposited matter from the surfaces of the heat-sink media in
Regenerative Fume Incinerators (RFIs). Specifically, it covers a system for washing
down the deposited matter from the heat transfer surfaces of the heat sink media
(HSM) within a Regenerative Heat Exchanger (RHX) of a regenerative fume incinerator.
Regenerative fume incinerators are widely used in industry to clean
polluted gas streams containing combustible pollutants before the gas stream is
exhausted to the atmosphere. As used herein, the term "Regenerative Fume Incinerator"
includes Regenerative Thermal Oxidizers (RTOs), Regenerative Catalytic Oxidizers
(RCO) and Thermal Catalytic Oxidizers (TCO).
Regenerative thermal oxidizers, regenerative catalytic oxidizers, and
thermal catalytic oxidizers use different oxidation processes to destroy the pollutants
in the polluted gas stream. As defined herein, a regenerative thermal oxidizer
maintains a high operating temperature (between 1,200 to 2,000 degrees F.) in the
combustion chamber to facilitate the oxidation of the pollutants in the polluted
gas stream. Regenerative thermal oxidizers have been well described in the prior
art such as U.S. Pat. No. 5,098,286 to York, U.S. Pat. No. 5,259,757 to Plejdrup
et al. and others. Briefly, a regenerative thermal oxidizer generally comprises
a combustion chamber in fluid communication with a plurality of regenerative heat
exchangers. The polluted gas is first passed through a previously heated regenerative
heat exchanger and is preheated to a high temperature. The preheated polluted gas
is then passed into the combustion chamber where it is further heated to a temperature
high enough for generally complete oxidation of the combustible pollutants to a
cleansed gas containing harmless end-products such as water and carbon-dioxide.
The cleansed hot gas is then passed into a second regenerative heat exchanger which
was previously cooled by the passage of the cold polluted gas through it. The cleansed
hot gas releases its sensible heat to the relatively cooler heat sink media in
the second regenerative heat exchanger which gets heated for use in a subsequent
preheating cycle as described above. The cold polluted gas and cleansed hot gas
are alternately passed through the two regenerative heat exchangers to maintain
continuity of flow and heat transfer between the cold and hot gas streams.
As is well known and practiced in the art, more than two regenerative heat exchangers
can be used for increased capacity and to enhance the pollutant destruction capability
of the regenerative fume incinerator. An regenerative thermal oxidizer with more
than two regenerative heat exchangers, which uses a purge system to recycle entrapped
polluted gas, is described in the aforementioned patent to York.
A regenerative catalytic oxidizer is defined herein as a regenerative fume-incinerator
that is designed similar to a regenerative thermal oxidizer. However, it includes
a catalyst to facilitate the oxidation of the pollutants in the polluted gas stream
at a relatively lower temperature (about 400 to 800 degrees F.) to save energy.
A thermal catalytic oxidizer is defined herein as a regenerative fume-incinerator
which is a hybrid regenerative catalytic oxidizer and regenerative thermal oxidizer.
A thermal catalytic oxidizer is designed to operate initially at a relatively lower
oxidizing temperature (about 400 to 800 degrees F.) using a catalyst (as in a regenerative
catalytic oxidizer) and to operate at a high oxidizing temperature (about 1,200
to 2,000 degrees F. as in a regenerative thermal oxidizer) after the catalyst is
deactivated. This feature provides operating flexibility.
It is well known in the art that the relatively densely packed heat sink media
in the regenerative heat exchangers of regenerative fume incinerators is quite
susceptible to fouling due to the deposition of condensable and non condensable
aerosols in the polluted air streams. Since the fouling tends to vitiate the performance
of the regenerative fume incinerator, techniques have been developed to clean the
heat sink media in fouled regenerative heat exchangers. For example, Plejdrup et
al. describe a method of cleaning the condensed combustible matter from the heat
transfer surfaces of the heat sink media in a regenerative thermal oxidizer by
passing the hot oxidized gas through a fouled regenerative heat exchanger bed for
an extended period of time. However, while this "burn-out" (also referred to as
"bake-out") method is useful for removing combustible deposited matter, it is not
very useful in removing non-combustible deposited matter from the regenerative
heat exchanger.
U.S. Pat. No. 6,579,379 to Noble describes a method (the Noble method) and apparatus
to remove deposited matter from the surfaces of the heat sink media in a regenerative
heat exchanger. However, the Noble method suffers from various disadvantages, the
primary one of which is that it is mostly manual in nature. In the Noble method,
the regenerative fume incinerator has to be shutdown and cooled to ambient temperature
before the cleaning apparatus is manually assembled and operated within the regenerative
fume incinerator. The shut-down and cooling requirement results in an interruption
of production for a fairly long period of time. The Noble method also requires
additional time to manually assemble and disassemble the cleaning apparatus in
the regenerative fume incinerator. These time requirements result in lost revenue
and profits for the regenerative fume incinerator user. Further, the Noble method
is not effective against sticky combustible deposited matter which cannot be easily
dissolved by a water wash. Therefore, a burn-out operation is required to gasify
the sticky combustible deposited matter prior to the wash-down. Cooling the regenerative
heat exchanger bed from the higher burn-out temperature requires additional time
which further increases loss of production.
As a particular example, regenerative fume incinerators used in the wood industry
are subjected to fouling by fine wood particles as well as sticky condensable combustible
resin particles. This is a particularly difficult fouling situation which requires
that the regenerative heat exchanger be first subjected to a burn-out operation
to remove the combustible deposited matter and then washed out to remove the residual
non-combustible deposited matter such as inorganic salts which are present in wood
particles. The Noble method is not particularly well suited to this application
because, during the burn-out operation, the temperature of the heat sink media
in the regenerative heat exchanger is raised to a higher level than normal to effect
gasification of the combustible matter. Therefore, the regenerative fume incinerator
takes a much longer time to cool to ambient temperature as required in the Noble
method. Further, the Noble method requires operating personnel to open the regenerative
fume incinerator and enter into a potentially hazardous confined area, thereby
potentially jeopardizing the lives of the personnel. Yet further, the Noble method
requires that all beds be cleaned during a cleaning operation. The Noble method
does not disclose a way to selectively clean one or more of the regenerative heat
exchangers in a regenerative fume incinerator as needed due to adverse fouling
conditions associated with these regenerative heat exchangers.
There is therefore a need for a method and apparatus to burn-out and wash-down
a regenerative heat exchanger bed while the regenerative fume incinerator is on-line
with the process. The method has to be able to quickly and efficiently clean the
regenerative heat exchanger bed without shutting down the regenerative fume incinerator
and without cooling the regenerative fume incinerator to ambient temperature. The
method should be safe to practice and should not require the entry of personnel
into a hazardous confined area. Further, the method should be able to selectively
clean-out one or more of the regenerative heat exchangers of a regenerative fume
incinerator without shutting down the regenerative fume incinerator.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a regenerative fume incinerator for cleaning
a polluted gas containing organic and inorganic pollutants is disclosed. The regenerative
fume incinerator comprises a combustion chamber and a plurality of regenerative
heat exchangers. Each regenerative heat exchanger comprises a regenerative heat
exchanger compartment having a hot end and a cold end. The cold end of the regenerative
heat exchanger compartment is configured for fluid communication with a flow control
means (FCM) for the selective introduction of the polluted gas into the regenerative
heat exchanger compartment and for the selective removal of the cleansed gas from
the regenerative heat exchanger compartment. The flow control means is located
at the cold end of the regenerative heat exchanger and configured for fluid communication
with the cold end of the regenerative heat exchanger compartment. The regenerative
heat exchanger compartment further comprises a heat sink media bed located in between
the cold and hot ends of the regenerative heat exchanger compartment in the path
of flow of the polluted gas and the cleansed gas. A deposited matter removal means
for physically dislodging deposited matter from the surface of the heat sink media
is located within the regenerative heat exchanger compartment. The deposited matter
removal means comprises at least one spray-pipe containing a cleaning fluid, such
as water or steam or compressed air. The cleaning fluid is supplied to the spray
pipe at a pressure greater than the gas pressure within regenerative heat exchanger
compartment. The spray pipe is located within the heat sink media bed to direct
the cleaning fluid therein toward at least some of the surfaces of the heat sink
media to physically dislodge the deposited matter thereon.
In another aspect of the present invention, a method of washing the heat sink
media in a regenerative heat exchanger of a regenerative fume incinerator is disclosed.
The regenerative heat exchanger has at least one spray pipe installed within it.
The spray pipe is connected to a source of cleaning fluid such as water, steam
or compressed air. The spray orifices on the spray pipe are generally directed
towards the surface of the heat sink media within the regenerative heat exchanger.
The inventive method comprises the steps of cooling the heat sink media to a temperature
sufficient to prevent thermal shock to the heat sink media and introducing the
cleaning fluid into the spray pipe to wash the surface of the heat sink media while
the regenerative fume incinerator is on-line with the process.
In yet another aspect of the present invention, a regenerative fume incinerator
control system to perform on-line wash-down of the regenerative heat exchanger
media in a regenerative fume incinerator having a plurality of regenerative heat
exchangers is disclosed. Each regenerative heat exchanger is equipped with at least
one cleaning fluid spray pipe and a temperature measuring means. The regenerative
fume incinerator control system comprises an algorithm to perform the following
steps: (a) freeze a selected regenerative heat exchanger in a heat sink media cooling
mode of operation while maintaining the other regenerative heat exchangers in their
normal mode of operation; (b) read the measured temperature from the temperature
measuring means and continue to freeze the selected regenerative heat exchanger
in the heat sink media cooling mode of operation until the measured temperature
is less than a predetermined value; (c) close off all flow into the selected regenerative
heat exchanger to stop the flow of both the polluted and cleansed gases into and
out of the selected regenerative heat exchanger; (d) start the flow of the cleaning
fluid into the spray-pipe of the selected regenerative heat exchanger to dislodge
the deposited matter from the surface of the heat sink media within the selected
regenerative heat exchanger; (e) stop the flow of the cleaning fluid into the spray-pipe
of the selected regenerative heat exchanger after a predetermined period of time;
(f) operate the flow control means of the selected regenerative heat exchanger
in the bed heating mode while monitoring the temperature measured by the temperature
measuring means within the selected regenerative heat exchanger; and (g) revert
the selected regenerative heat exchanger back into the normal mode of operation
when the temperature measured within the heat sink media of the selected regenerative
heat exchanger by the temperature measuring means of the selected regenerative
heat exchanger reaches a predetermined level.
In yet another aspect of the present invention, a method of suppressing fires
within a regenerative heat exchanger of a regenerative fume incinerator is disclosed.
The regenerative heat exchanger contains regenerative heat sink media. The regenerative
heat exchanger further has at leas tone spray-pipe and at least one temperature
measuring means installed within it. The spray-pipe is connected to a source of
water. The spray orifices on the spray-pipe are directed towards the surface of
the heat sink media within the regenerative heat exchanger. The method comprises
the steps of (i) monitoring the temperature within the regenerative heat exchanger
indicated by the temperature measuring means; and (ii) introducing the water into
the spray pipe when the measured temperature reaches a pre-determined high level.
Other and further objects, advantages, and features of the present invention
will be understood by reference to the following specification in conjunction with
the annexed drawings, wherein like parts have been given like numbers.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a regenerative fume incinerator according
to the prior art.
FIG. 2 is a schematic representation of a regenerative fume incinerator according
to the present invention.
FIG. 3 is a general representation of the details of the spray-pipes of the
deposited matter removal means, which is located in the regenerative heat exchanger
of the regenerative fume incinerator of the present invention.
FIG. 4 is a representation of the control logic of the on-line burn-out control
system in the regenerative fume incinerator control system of the present invention.
FIG. 5 is a representation of the control logic of the on-line wash-down control
system in the regenerative fume incinerator control system of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
As defined herein, the term "inlet mode of operation" describes the mode of operation
of the regenerative heat exchanger wherein the gas is introduced in to the regenerative
heat exchanger from the cold end of the regenerative heat exchanger. The inlet
mode of operation occurs when (1) the cold polluted gas is introduced into the
regenerative heat exchanger through the inlet damper (a "normal inlet mode of operation")
or (2) a portion of the cooled cleansed gas is recycled back through a purge damper
into the cold end of the regenerative heat exchanger to displace the residual polluted
gas of the previous cycle into the combustion chamber (a "positive purge mode of operation").
Further, as defined herein, the term "outlet mode of operation" describes
the mode of operation of the regenerative heat exchanger wherein the gas is introduced
into the regenerative heat exchanger from the hot end of the regenerative heat
exchanger. The outlet mode of operation occurs when (1) the hot cleansed gas flows
from the hot end into the regenerative heat exchanger and then exits the cold end
of the regenerative heat exchanger through the outlet damper (a "normal outlet
mode of operation") or (2) a portion of the hot cleansed gas is drawn through the
regenerative heat exchanger to displace the residual polluted gas through the purge
damper in the cold end of the regenerative heat exchanger (a "negative purge mode
of operation".)
Further, as defined herein, the term "purge mode of operation" describes
the mode of operation of the regenerative heat exchanger wherein the residual polluted
gas from the previous normal mode of operation is removed from the cold end of
the regenerative heat exchanger. The residual polluted gas is removed either by
(1) displacing it with hot cleansed gas from the combustion chamber during a negative
purge mode of operation, as described above; or (2) displacing it with cooled cleansed
gas from the regenerative fume incinerator exhaust stack during a positive purge
mode of operation, as described above.
Further, as defined herein, a "heat sink media cooling mode of operation"occurs
when the regenerative heat exchanger is in a normal inlet mode of operation or
a positive purge mode of operation. In the heat sink media cooling mode of operation,
the cold polluted gas or the relatively cooler cleansed gas cools the previously
heated heat sink media.
Yet further, as defined herein, a "heat sink media heating mode of operation"
occurs when the regenerative heat exchanger is in a normal outlet mode of operation
or in a negative purge mode of operation. In the heat sink media heating mode of
operation, the hot cleansed gas heats the heat sink media which was previously
cooled. Yet further, as defined herein, a "normal without purge mode of operation"
occurs when the regenerative heat exchanger alternately executes at least a normal
inlet and a normal outlet mode of operation, each mode of operation being executed
for a predetermined period of time. In regenerative heat exchanger, which a re
equipped with purge systems, a "normal with purge mode of operation" occurs when
the regenerative heat exchanger alternately executes at least a normal inlet mode
of operation, a purge mode of operation, and a normal outlet mode of operation,
each mode of operation being executed for a pre-determined period of time. As defined
herein, a "normal mode of operation" includes either a normal without purge mode
of operation or a normal with purge mode of operation as defined above.
Yet further, as defined herein, a "burn-out mode of operation"occurs when the
regenerative heat exchanger is held in a heating mode of operation until the temperature
of the heat sink media in the regenerative heat exchanger reaches a pre-determined
high level, which is sufficient for the gasification of the deposited matter within
the heat sink media.
The present invention can best be described with reference to the prior art shown
in FIG. 1.
FIG. 1 shows a prior art regenerative thermal oxidizer with three regenerative
heat exchangers and with a burn-out mode of operation according to the prior art.
The design, construction, and operation of such regenerative thermal oxidizers
is well known in the art and is described in detail in the aforementioned US patents
to York and to Plejdrup et al. FIG. 2 shows a regenerative thermal oxidizer which
is modified to provide the regenerative thermal oxidizer of the present invention.
While a regenerative thermal oxidizer with three regenerative heat exchangers is
shown as an example in this description of the invention, the invention can also
be practiced with a regenerative thermal oxidizer having more than three regenerative
heat exchangers, as will be described later. Further, while an regenerative thermal
oxidizer is shown as an example in FIGS. 1 and 2, the invention can also be practiced
with other regenerative fume incinerators such as regenerative catalytic oxidizers
and thermal catalytic oxidizers.
Briefly, FIG. 1 shows a regenerative thermal oxidizer
100 comprising
a combustion chamber
105, a first regenerative heat exchanger
110,
a second regenerative heat exchanger
120, and a third regenerative heat
exchanger
130. Combustion chamber
105 is equipped with a means, such
as gas or fuel-oil burner system
101, to raise and maintain the temperature
of the polluted gas within combustion chamber
105 to a range between 1,200
to 2,000 degrees F. to oxidize the pollutants in the polluted gas processed by
regenerative thermal oxidizer
100. In FIG. 1, "P" denotes the cold polluted
gas, "P′" denotes the preheated polluted gas, "C" denotes the hot cleansed
gas, and "C′" denotes the cooled cleansed gas.
Regenerative heat exchanger
110 has a housing
110h
with a closed bottom
110b and a open upper end
110u
which is in fluid communication with combustion chamber
105. Regenerative
heat exchanger
110 further comprises a heat sink media support grid
113
on which is located a heat sink media bed
112.
Heat sink media bed
112 comprises a heat sink media
112m.
Heat sink media
112m could be random packing made of material such
as ceramic stoneware or porcelain or metal or any other material which has suitable
thermal properties for use in a regenerative thermal oxidizer. Standard commercially
available random packing include saddles, berl rings, raschig rings, intallox saddles,
or any other commercially available column packing. Random packing could also include
proprietary designs such as the Ty-Pak™ media that are available from US
suppliers such as Norton Process Industries, Koch Industries, American Ceramic
and Clay Co., and others. Alternatively, heat sink media
112m could
be structured media made of ceramic or porcelain or metal or any other material
which has suitable thermal properties. Structured heat sink media is commercially
available as extruded blocks from US suppliers such as Norton Process Industries
or as fabricated block sunder the trade-names Flexaramic™ from Koch Industries
and Multilayered Monolith Media (MLM™) from Lantec Products Inc.
Heat sink media support grid
113 is located near the cold end of regenerative
heat exchanger
110 so that a flow volume
114 is created under heat
sink media support grid
113 between bottom end
110b and heat
sink media support grid
113. As described below, a flow control means
110f
is connected to flow volume
114 to bring polluted gas P into regenerative
heat exchanger
110 or to remove the cooled cleansed gas C′ from regenerative
heat exchanger
110. A thermocouple or other temperature measuring means
115 which measures the temperature in volume
114 during normal and
burn-out conditions is located in volume
114.
As shown in FIG. 1, regenerative heat exchangers
120 and
130 are
constructed similar to regenerative heat exchanger
110. For example, regenerative
heat exchanger
120 also has a housing
120h, a heat sink media
support grid
123, a heat sink media bed
122 comprised of heat sink
media
122m, and volume
124 between bottom end
120b
and heat sink media support grid
123. The open hot ends
110u,
120u, and
130u of regenerative heat exchangers
110,
120, and
130 respectively are connected to combustion chamber
105
so that preheated polluted gas P′ can flow into combustion chamber
105
from regenerative heat exchangers
110,
120, and
130. Similarly,
hot cleansed gas C can flow from combustion chamber
105 into regenerative
heat exchangers
110,
120, and
130 through open ends
110u,
120u, and
130u respectively. Thermocouples or other
temperature measuring means
125 and
135 are also located under heat
sink media support grids
123 and
133 of regenerative heat exchangers
120 and
130 respectively.
Temperature measuring means
115,
125 and
135 provide
temperature level signal s to Burnout Control System (BCS)
150, which may
be separate from or may be a part of the overall regenerative thermal oxidizer
control system
150r. For example, the regenerative thermal oxidizer
control system may be a Programmable Logic Controller (PLC) and BCS
150
may be computer code or a sub-program or a sub-routine within the regenerative
thermal oxidizer main control program which is loaded in the PLC. As described
in previous referenced patent to Plejdrup et al., the computer code would execute
an algorithm to burn-out the regenerative heat exchanger bed to remove condensed
organic matter deposited therein.
A flow control means (FCM)
110f is connected to regenerative heat
exchanger
110 as stated above. Flow control means
110f comprises
a cross shaped duct
110x, an inlet damper
116, an outlet damper
117, and a purge damper
118. Duct section
110x communicates
at its first open end to flow volume
114 and at its other three open ends
to inlet damper
116, outlet damper
117, and purge damper
118
respectively. As shown in FIG. 1, inlet damper
116 and outlet damper
117
are of the block-and-bleed butterfly type of design while purge damper
118
is a single-bladed butterfly damper Block-and-bleed butterfly dampers are described
in the sales literature of US damper manufacturers such as Effox Inc, Bachmann
Dampers Inc., and others. The use of block-and-bleed dampers is mandated within
the USA by the Factory Mutual Insurance Co. for isolating an regenerative fume
incinerator from the process when the regenerative heat exchanger bed is being
burnt-out of its deposited matter.
As described in the previously referred patent to Plejdrup et al., during the
burn-out mode of operation, the average temperature of the heat sink media in the
regenerative heat exchanger is raised to a temperature which is high enough (generally
in the range of 400 to 800 degrees F.) to gasify the organic matter that may have
been deposited on the surfaces of the heat sink media during the normal operation
of the regenerative thermal oxidizer. As used herein, the term "gasify" means to
volatilize the low-boiling combustible matter or to fully or partially oxidized
(pyrolize) the combustible matter or otherwise convert the organic matter to a
gaseous form by either chemical reaction or phase change means. The gaseous matter
is then swept away by the hot gas to provide relatively cleaner heat transfer surfaces
in the heat sink media. Alternately, non-gasifiable matter, such as inorganic salts,
is left behind. As described in the Noble method, this non gasifiable deposited
matter is then washed down with a cleaning fluid.
As shown in FIG. 1, block-and-bleed damper
116 comprises two major damper
blades
116a with an intermediate space between them. When the major
damper blades
116a are in a closed position, the closed intermediate
space between them is evacuated by means of an open single-bladed bleed damper
116b. The bleed damper
116b prevents the leakage of
polluted gas P on the first side of the first blade into cooled cleansed gas C′
on the second side of the second blade to increase the overall pollution cleaning
performance of regenerative thermal oxidizer
100. Outlet damper
117
is constructed similar to inlet damper
116 with double-blades
117a
and a single-bladed bleed damper
117b. As commonly practiced
in the art, the inlet, outlet, purge dampers, and bleed dampers are operated by
commonly available pneumatic or hydraulic or electric actuators. A representative
example wherein actuator
137r of damper
137 is controlled
by regenerative thermal oxidizer control system
150r is shown in
FIG. 1. This example applies to all dampers of regenerative thermal oxidizer
100.
As shown in FIG. 1, similar flow control means
120f and
130f
are connected to bottom ends
120b and
130b of regenerative
heat exchangers
120 and
130 respectively to bring polluted gas P
to and to remove cooled cleansed gas C′ from regenerative heat exchangers
120 and
130.
As generally described in the previously referenced patent to Plejdrup et al.,
polluted gas P from the process is conveyed to regenerative heat exchangers
110,
120, and
130 through inlet duct
152. A branch duct
142a
connects inlet duct
152 to damper
116 through a removable spool-piece
of duct
141. The use of the removable spool-piece is also mandated by the
Factory Mutual Insurance Co. Removable spool-piece
141 isolates regenerative
thermal oxidizer
100 from the process when the condensed organic material
in the heat sink media of the regenerative heat exchanger beds is being gasified
during the burn-out mode of operation of regenerative thermal oxidizer
100.
Similar branch ducts
142b and
142c are provided in
parallel to branch duct
142a. Branch ducts
142b and
142c connect inlet duct
152 to damper
126 of flow control
means
120 of and damper
136 of flow control means
130f
through spool-pieces
241 and
341 (shown removed in FIG. 1) respectively.
Similarly, outlet dampers
117,
127, and
137 are connected
to outlet duct
154 through mutually parallel branches
144a,
144b, and
144c respectively. Outlet duct
154
is connected to induced draft fan
158 which evacuates cooled cleansed gas
C′ to atmosphere or to a downstream process.
In a similar manner, purge dampers
118,
128, and
138 are
connected to purge recycle duct
156 through mutually parallel branches
145a,
145b, and
145c respectively. Purge recycle duct
156
is connected to inlet duct
152 through an interconnecting branch duct
155
which, as described in the previously referenced US patent to York, recycles residual
polluted gas P from volumes
114,
124 and
134 under heat sink
media beds
112,
122, and
132 when the selected bed is in a
negative purge mode of operation. The negative purge mode of operation of regenerative
thermal oxidizers is described in detail in the previously referenced patent to
York. A purge recycle fan
157 is located in purge recycle duct
156
to assist in evacuating the purged gas. Dampers
155a and
159a
are located in ducts
155 and
159 respectively to control the
amount of purged air that is recycled to the inlet duct
152 and to the combustion
chamber
105 respectively.
During the normal mode of operation of regenerative thermal oxidizer
100,
the inlet, outlet and purge dampers are opened and closed as generally described
in the previously referenced patent to York. When a burnout is required to clean
the bed of deposited gasifiable matter, the regenerative thermal oxidizer is operated
according to the procedure generally described in the previously referenced patent
to Plejdrup et al. For example, in regenerative thermal oxidizer
100, regenerative
heat exchanger
130 is shown to be in the burn-out mode of operation. Thus,
double blades
136a of inlet damper
136 are closed, bleed damper
136b is opened and spool piece
341 is manually removed to
isolate the hot zone in space
134 under heat sink media support grid
133
from polluted gas P. If there are no environmental concerns for exhausting a smoky
plume to the atmosphere, then purge damper
138 is closed and outlet damper
137 is opened to exhaust the smoky gasified products of the burn-out to
the atmosphere through blower
158. Gasification of the deposited gasifiable
matter in heat sink media bed
132 is effected by allowing hot cleansed gas
C to flow from combustion chamber
105 into and through heat sink media bed
132 for an extended period of time. The continuous flow of cleansed hot
gas C through heat sink media bed
132 raises the temperature of heat sink
media
132m. This increase in temperature causes gasification of the
gasifiable matter which was deposited on heat sink media
132m. The
burn-out mode of operation is continued for a period of time as required to adequately
gasify the deposited gasifiable matter from the surfaces of heat sink media
132m.
In the meanwhile, regenerative heat exchangers
110 and
120 are operated
in a normal without purge mode of operation.
Alternately, if a smokeless burnout is required, outlet damper
137
is also closed and purge damper
138 is opened and cleansed hot gas C is
allowed to pass through heat sink media bed
132 of regenerative heat exchanger
130 for an extended period of time. The smoky gasified products of the burn-out
are recycled back to inlet duct
152 for purification in combustion chamber
105 through open damper
155a in duct
155. Alternatively,
as shown in FIG. 1, the smoky gasified products of the burnout are recycled directly
back to combustion chamber
105 through open damper
159a in
duct
159. This burn-out mode of operation is described in detail in Plejdrup
et al.
When the cooled cleansed gas temperature in volume
134 reaches a preset
temperature, generally in the range of 400 to 1,000 degrees F., the burn-out mode
of operation for regenerative heat exchanger
130 is concluded. Outlet damper
137 and purge damper
138 are closed. Spool-piece
341 is reattached
between branch
142c and inlet damper
136. Inlet damper
136
is then re-opened. Cold polluted gas P is again passed into regenerative heat exchanger
130 through duct
142c. The open position of inlet damper
136
is maintained for a period of time as required to cool heat sink media
132m
in regenerative heat exchanger
130 to a pre-determined temperature.
This concludes the burn-out mode of operation for regenerative heat exchanger
130.
The burn-out mode of operation described above for regenerative heat exchanger
130 can be conducted, randomly or in sequence, for each of the remaining
regenerative heat exchangers
110 and
120. While the burn-out mode
of operation, described above, is generally effective in cleaning the heat sink
media of deposited matter which can be gasified by high temperature, it is not
very effective in cleaning the heat sink media of deposited non-gasifiable matter.
Furthermore, particulate matter that may be deposited within the heat sink media
may consist of organic and inorganic matter. Yet furthermore, combustible particulate
matter such as wood sawdust, may gasify leaving behind an ash which consists mainly
of non-gasifiable inorganic matter. For example, it is well know that wood contains
alkalis such as sodium. During the burn-out process, the alkalis get converted
to alkali salts which remain on the surface of the heat sink media after the burn-out
and affect the thermal performance and pressure drop characteristic of the regenerative
thermal oxidizer heat sink media bed. The alkali salts can also attack the ceramic
material of the heat sink media and vitiate its performance enough to require periodic
replacement, thereby increasing the operating cost of the regenerative thermal oxidizer.
The present invention described herein and shown in FIG. 2 overcomes these disadvantages.
It allows for the automatic or manually selected on-line gasification of the deposited
gasifiable matter as well as the on-line washing out of the remaining non-gasifiable
matter in the heat sink media. Further, it economically simplifies the system by
eliminating the need for the insurance company mandated block-and-bleed dampers
and the duct spool-pieces to isolate the hot zones in the regenerative heat exchangers
from the process during the burn-out mode of operation. Yet further, it simplifies
the burn-out operation because manual removal of the spool-pieces is not required
during the burn-out process of the present invention. Therefore, shutdown of the
regenerative thermal oxidizer is not required and loss of production does not occur.
As a further advantage, it provides automatic fire-suppression in the event that
the combustible deposited matter within the regenerative heat exchanger bed auto-ignites
during normal operation or burn-out operation of the regenerative fume incinerator.
The present invention is best understood by the following description, which
highlights the major differences between the prior art regenerative thermal oxidizer
100 shown in FIG. 1 and the regenerative thermal oxidizer
100a
of the present invention as shown in FIG. 2. For simplicity, the same reference
figures are used in both figures to denote features which are common to both the
prior art regenerative thermal oxidizer
100 and regenerative thermal oxidizer
100a.
Heat Sink Media Bed Construction:
Heat sink media beds
112,
122, and
132 of regenerative
heat exchangers
110a,
120a, and
130a respectively
in regenerative thermal oxidizer
100a of the present invention are
modified as shown in FIG. 2
Using regenerative heat exchanger
110a as an example, heat sink
media bed
112 of regenerative heat exchanger
110a in FIG.
2 is shown divided into two sections. Upper heat sink media bed section
112a
is supported by an upper heat sink media support grid
113a and
lower heat sink media bed section
112b is supported by the lower
heat sink media support grid
113b. Upper heat sink media support
grid
113a can be independently supported from housing
110h
of regenerative heat exchanger
110a. Alternatively, upper heat
sink media support grid
113a can rest on and be supported by the
upper surface of lower bed section
112b. The relative heights of
heat sink media bed sections
112a and
112b is determined
by the temperature profile in the overall bed. Generally, the height of lower heat
sink media bed section
112b can be about one-eight to three-quarter
of the total height of bed
112 in FIG. 1.
Similarly, heat sink media bed
122 is divided into bed sections
122a and
122b, which are supported on heat sink media
support grids
123a and
123b respectively. Also, heat
sink media bed
132 is divided into sections
132a and
132b,
which are supported on heat sink media support grids
133a and
133b respectively.
Upper heat sink media bed section
112a and lower heat sink media
bed section
112b are located such that a free volume
114a
is created between the upper end of lower heat sink media bed section
112b
and heat sink media support grid
113a which supports upper heat
sink media bed section
112a. Similar free volumes
124a
and
134a are created in regenerative heat exchangers
120a
and
130a respectively.
Addition of Cleaning Fluid Spray System:
Cleaning-fluid spray systems are provided in each of modified regenerative
heat exchangers
110a,
120a, and
130a respectively
in regenerative thermal oxidizer
100a of the present invention. Cleaning-fluid
"F" can be any suitable fluid such as water, steam, or compressed air.
As an example, the following detailed description is given for spray system
160
in regenerative heat exchanger
110a as shown in FIG. 2. Spray system
160 comprises a plurality of distribution pipes
166 which are located
within free volume
114a. As shown in FIG. 3, spray orifices such
as spray nozzles
167 are provided on each distribution pipe
166.
Alternately, the spray orifices could be spray holes which are drilled at suitable
locations on each distribution pipe. As yet another alternative, commercially available
atomizers could also be used to distribute cleaning-fluid F from the spray-pipe.
Nozzles
167 are aimed at the lower heat sink media bed section
112b.
The number of pipes
166 and nozzles
167 is selected to generally
provide complete coverage of the horizontal cross-section of heat sink media bed
lower section
112b so that cleaning-fluid F sweeps away substantially
all of the deposited matter which coats the heat transfer surfaces in heat sink
media bed lower section
112b.
Each distribution pipe
166 is connected to a header pipe
165 which
extends through housing
110h of regenerative heat exchanger
110a.
The external end of header pipe
165 is connected to the outlet side of a
flow control valve
164, which controls the flow of cleaning-fluid F to header
pipe
165. A cleaning-fluid supply pipe
162 is connected to the inlet
side of flow control valve
164 to provide cleaning-fluid F for cleaning
the bed lower section
112b. An actuator
164a is connected
to valve
164 to provide the motive force for opening or closing valve
164.
Actuator
164a can be an electric or pneumatic or hydraulic actuator
as described previously herein. These actuators are commercially available from
US suppliers such as Parker-Hannifin, Honeywell, Barber-Colman, Foxboro-Jordan
and others.
A Wash-down/Burn-out Control System (WBCS)
150a, which will be
described
below, controls actuator
164a Wash-down/Burn-out Control System
150a
is similar to BCS
150 in FIG. 1 but has the added functionality of being
able to control the operation of actuator
164a as required to wash-down
heat sink media bed lower section
112b. A thermocouple or other suitable
temperature measuring means
115a is also located in free space
114a.
Temperature measuring means
115a is connected to Wash-down/Burn-out
Control System
150a and measures the gas temperature within free
space
114a to initiate or end the wash-out mode of operation in accordance
with a control algorithm within Wash-down/Burn-out Control System
150a.
It is not necessary that free space
114a be an open volume in between
upper bed section
112a and lower bed sections
112b.
For example, the two bed sections could be separated by the location of the spray
pipes
166 only. In such a configuration, the free space
114a would
be the volume around spray-pipes
166 around which the gas temperature is
measured by temperature measuring means
115a.
The cleaning-fluid spray system
160 is also capable of being operated
as a fire suppression system by using water as the spray-fluid. This feature is
initiated during the normal or burn-out modes of operation if the temperature measured
by thermocouple
115 in zone
114 reaches a pre-determined high value,
generally above 600 degrees F. When this temperature is reached or exceeded, an
alarm can sound and water can be sprayed on the lower bed section
112b
to extinguish the fire and prevent further damage to regenerative thermal oxidizer
100a.
Similar cleaning-fluid spray systems
170 and
180 are also located
within regenerative heat exchangers
120a and
130a.
The construction and operation of spray systems
170 and
180 is similar
to that described above for spray system
160.
Simplification of Inlet and Outlet Dampers:
Because of the added protection provided by the fire suppression operating
mode (as described above) of spray system
160, insurance companies do not
mandate the use of block-and-bleed dampers on regenerative heat exchanger beds
110a,
120a, and
130a for regenerative
thermal oxidizer
100a of the present invention. Thus dampers
116′
and
117′ in flow control means
110f′ on regenerative
heat exchanger
110a of the present invention can be simple single-bladed
dampers. Similarly, dampers
126′ and
127′ in flow control
means
120f′ on bed
120a and dampers
136′
and
137′ in flow control means
130f′ on bed
130a can also be single-bladed dampers. The use of single-bladed
dampers greatly reduces the cost and complexity of regenerative thermal oxidizer
100a of the present invention compared to prior art regenerative
thermal oxidizer
100.
Elimination of Spool-Pieces on Inlet Duct Branches:
As described above, cleaning-fluid spray systems
160,
170 and
180
on regenerative heat exchangers
110a,
120a, and
130a
respectively are also capable of being operated as fire-suppression systems.
Therefore, insurance companies do not require spool-pieces to be installed in inlet
duct branches
142a,
142b, and
142c of
regenerative heat exchangers
110a,
120a, and
130a
respectively in regenerative thermal oxidizer
100a of the present
invention to isolate it from the process during the burn-out operation. Thus spool-pieces
141,
241, and
241 which were required for prior art regenerative
thermal oxidizer
100 shown in FIG. 1 are not required for regenerative thermal
oxidizer
100a of the present invention shown in FIG. 2.
Drains on Regenerative Thermal Oxidizer Bed Floors:
If cleaning fluid F is a liquid or steam, a drain
168 is provided on the
floor of regenerative heat exchanger
110a to remove liquid cleaning-fluid
or condensate from the steam, which is sprayed by the cleaning-fluid spray system
160 into regenerative heat exchanger
110a. Drain
168
is not required if compressed air or some other non-condensing gas is used as the
cleaning-fluid. Drain
168 also removes water that may be used to suppress
fires in regenerative heat exchanger
110a as described above. A one-way
check valve
169 is provided in drain
168 to prevent outside air from
entering regenerative heat exchanger
110a during normal operation
of the regenerative heat exchanger
110a. Instead of a one way check
valve, a suitable barometric leg or a P-trap could also be used to achieve the
same result.
Similar drains
268 and
368 with check valves
269 and
369 are provided on regenerative heat exchangers
120a and
130a respectively in regenerative thermal oxidizer
100a.
The foregoing paragraphs described the physical changes in regenerative thermal
oxidizer
100a of the present invention relative to prior art regenerative
thermal oxidizer
100. The following paragraphs describe the burn-out and
wash-down modes of operation of regenerative thermal oxidizer
100a of
the present invention:
On-Line Burn-Out:
With reference to FIG. 2, on-line burn-out is provided on regenerative thermal
oxidizer system
100a such that the heat sink media beds in individual
regenerative heat exchangers
110a,
120a, or
130a
are burned out randomly (a "random burn-out"). Alternatively, the initiation
of the burn-out cycle can automatically burn-out the heat sink media in all of
the regenerative heat exchangers
110a,
120a, and
130a
in sequence (a "sequential burn-out "). The control logic for the burn-out
mode of operation is shown in attached FIG. 4 and is as follows:
- 1) The burn-out cycle is initiated from the Man-Machine Interface (MMI)
of the regenerative thermal oxidizer Control System 150r to instruct
Wash-down/Burn-out Control System 150a to burn-out the heat sink
media bed in one of regenerative heat exchangers 110a, 120a,
or 130a. As an example, it is assumed herein that regenerative heat
exchanger 110a is selected for burn-out.
- 2) On completion of the normal mode of operation for regenerative heat
exchanger 110a as described previously with respect to regenerative
thermal oxidizer 100 in FIG. 1, regenerative heat exchanger 110a
is frozen in a heat sink media heating mode of operation.
- 3) The overall regenerative thermal oxidizer cycle then automatically
converts from a normal with purge mode of operation to a normal without purge mode
of operation as described previously with respect to regenerative thermal oxidizer
100 in FIG. 1. In this example, regenerative heat exchangers 120a
and 130a operate in a normal without purge mode of operation
while regenerative heat exchanger 110a is frozen in a heat sink media
heating mode of operation. Thus regenerative heat exchangers 120a and
130a alternately operate in a normal inlet and a normal outlet mode
of operation.
- 4) Regenerative heat exchanger 110a remains locked in
the heat sink media heating mode of operation until the pre-set burnout temperature
is reached as indicated by thermocouple 115 located in volume 114
of regenerative heat exchanger 110a. The pre-set burn-out temperature
is generally in the range of 400 to 1,000 degrees F. but is normally set at 600
degrees F. for adequate burn-out in most regenerative thermal oxidizers.
- 5) Once the pre-set burn-out temperature is reached, heat sink media
112m in lower bed section 112b of regenerative heat
exchanger 110a is substantially cleansed. Wash-down/Burn-out Control
System 150a now operates newly cleansed regenerative heat exchanger
110a in a heat sink media cooling mode of operation for cool-down
of heat sink media bed sections 112a and 112b to normal
operating average temperatures.
- 6) Cool-down of regenerative heat exchanger 110a is considered
complete when temperature measuring means 115a in free space 114a
reaches the average equivalent temperature measured by temperature measuring
means 125a and 135a in regenerative heat exchangers
120a and 130a.
- 7) If the sequential burn-out mode of operation was selected, Wash-down/Burn-out
Control System 150a automatically initiates the burn-out of the next
regenerative heat exchanger, for example regenerative heat exchanger 120a
followed by regenerative heat exchanger 130a. Thus the lower
heat sink media bed sections 122b and 132b in regenerative
heat exchangers 120a and 130a respectively are sequentially cleansed.
- 8) On completion of the random or sequential burn-out of any or all
of regenerative heat exchangers 110a, 120a, and 130a,
Wash-down/Burn-out Control System 150a operates regenerative thermal
oxidizer 100a in a normal with purge mode of operation.
In a random burn-out
