U.S. patent application number 10/719782 was filed with the patent office on 2006-05-11 for apparatus and process for power recovery.
Invention is credited to Leonard E. Bell, Keith A. Couch, Richard A. II Johnson.
Application Number | 20060096455 10/719782 |
Document ID | / |
Family ID | 36314998 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060096455 |
Kind Code |
A1 |
Couch; Keith A. ; et
al. |
May 11, 2006 |
APPARATUS AND PROCESS FOR POWER RECOVERY
Abstract
Disclosed is a third stage separator which includes two main
clean gas outlets. One main clean gas outlet communicates with a
power recovery unit such as an expander turbine while the second
main clean gas outlet communicates with a conduit that bypasses the
expander turbine. The present invention avoids use of the extra
equipment, engineering and installation labor required to prevent
the bypass conduit from placing a force load on the line to the
power recovery unit.
Inventors: |
Couch; Keith A.; (Arlington
Heights, IL) ; Bell; Leonard E.; (Streamwood, IL)
; Johnson; Richard A. II; (Algonquin, IL) |
Correspondence
Address: |
JOHN G TOLOMEI, PATENT DEPARTMENT;UOP LLC
25 EAST ALGONQUIN ROAD
P O BOX 5017
DES PLAINES
IL
60017-5017
US
|
Family ID: |
36314998 |
Appl. No.: |
10/719782 |
Filed: |
November 21, 2003 |
Current U.S.
Class: |
95/269 |
Current CPC
Class: |
B01D 45/14 20130101;
B01D 45/16 20130101 |
Class at
Publication: |
095/269 |
International
Class: |
B01D 45/12 20060101
B01D045/12 |
Claims
1. A system for separating particulate solids from a contaminated
gas stream, said system comprising: a separator vessel having a
main contaminated gas inlet, a solids outlet and a first main clean
gas outlet and a second main clean gas outlet; and a power recovery
unit having a unit inlet and a unit outlet, said unit inlet being
in downstream communication with said first main clean gas outlet
and said unit outlet being in downstream communication with said
second main clean gas outlet.
2. The system of claim 1 wherein said main contaminated gas inlet
is in communication with a catalyst regeneration vessel.
3. The system of claim 2 wherein said catalyst regeneration vessel
has two cyclones in series in communication with said main
contaminated gas inlet.
4. The system of claim 1 wherein a bypass conduit communicates said
second main clean gas outlet with said unit outlet and said bypass
conduit has an inner wall with a refractory lining.
5. The system of claim 1 wherein the solids outlet and the first
main clean gas outlet or the second main clean gas outlet extend
through the same nozzle of the separator vessel.
6. A system for separating particulate solids from a contaminated
gas stream, said system comprising: a vessel including: a main
contaminated gas inlet to said vessel; a plurality of cyclones,
each cyclone including a cyclone contaminated gas inlet in
communication with said main contaminated gas inlet, a cyclone
clean gas outlet and a cyclone solids outlet; a tube sheet within
said vessel surrounding at least some of said plurality of
cyclones; a main solids outlet extending from said vessel, said
main solids outlet being in communication with said cyclone solids
outlet; and a first main clean gas outlet and a second main clean
gas outlet defined by said vessel, said first main clean gas outlet
being in communication with an inlet to a power recovery device and
said second main clean gas outlet being out of communication with
said power recovery device.
7. The system of claim 6 including an additional tube sheet.
8. The system of claim 7 wherein said cyclones comprise a body
having a closed bottom end and a top end, the body defining said
cyclone contaminated gas inlet at said top end, the feed gas inlet
extending above the tube sheet, the cyclone body further defining a
sidewall with discharge openings located between the tube sheet and
the additional tube sheet for discharging particulate solids and a
minor amount of an underflow gas stream.
9. The system of claim 8 further including a swirl vane to induce
centripetal acceleration of the contaminated gas stream.
10. The system of claim 8 further including a cyclone gas outlet
tube defining a clean gas inlet end located within the cyclone body
for receiving a clean gas stream and further defining a cyclone
clean gas outlet extending through the closed bottom end of the
cyclone body and the additional tube sheet.
11. The system of claim 6 wherein at least one of said first and
second main clean gas outlets are defined by said vessel below said
tube sheet.
12. The system of claim 6 wherein the solids outlet and the first
main clean gas outlet or the second main clean gas outlet are
disposed in the same nozzle of the separator vessel.
13. A system for separating particulate solids from a contaminated
gas stream, said system comprising: a vessel including a main
contaminated gas inlet to said vessel, a plurality of cyclones,
each cyclone including a cyclone contaminated gas inlet in
communication with said main contaminated gas inlet, a cyclone
clean gas outlet and a cyclone solids outlet, a tube sheet within
said vessel surrounding at least some of said plurality of
cyclones, a main solids outlet from said vessel, said main solids
outlet being in communication with said cyclone solids outlet, and
a first main clean gas outlet and a second main clean gas outlet
from said vessel; a power recovery device in communication with
said first main clean gas outlet; and a bypass conduit in
communication with said second main clean gas outlet that bypasses
said power recovery device.
14. The system of claim 13 wherein said bypass conduit in
communication with said second main clean gas outlet includes a
refractory lining on an inner wall thereof.
15. The system of claim 13 wherein an outlet conduit from said
power recovery device is in communication with said bypass
conduit.
16. The system of claim 13 wherein said main contaminated gas inlet
is in communication with a flue gas outlet of a catalyst
regeneration vessel.
17. The system of claim 13 wherein said catalyst regeneration
vessel has two cyclones in series in communication with said main
contaminated gas inlet.
18. A process for separating particulate solids from a contaminated
gas stream and recovering power from said contaminated gas stream
comprising: delivering said contaminated gas stream to a separator
vessel; separating particulate solids from said contaminated gas
stream in said separator vessel; withdrawing particulate solids
from said separator vessel; transporting a first clean gas stream
from a first main clean gas outlet of said separator vessel to a
power recovery unit; recovering mechanical power from said first
clean gas stream in said power recovery unit; withdrawing said
first clean gas stream from said power recovery unit; and
intermittently mixing a second clean gas stream from a second main
clean gas outlet of said separator vessel with said first clean gas
stream withdrawn from said power recovery unit.
19. The process of claim 18 wherein said contaminated gas stream is
obtained from a catalyst regeneration vessel.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a novel arrangement for
recovering power from a gas stream laden with solids. Specifically,
the present invention relates to a third stage separator (TSS)
vessel for removing catalyst fines from hot regenerator flue gas of
a fluid catalytic cracking (FCC) unit followed by a power recovery
unit.
BACKGROUND OF THE INVENTION
[0002] FCC technology, now more than 50 years old, has undergone
continuous improvement and remains the predominant source of
gasoline production in many refineries. This gasoline, as well as
lighter products, is formed as the result of cracking heavier (i.e.
higher molecular weight), less valuable hydrocarbon feed stocks
such as gas oil. Although FCC is a large and complex process
involving many factors, a general outline of the technology is
presented here in the context of its relation to the present
invention.
[0003] In its most general form, the FCC process comprises a
reactor that is closely coupled with a regenerator, followed by
downstream hydrocarbon product separation. Hydrocarbon feed
contacts catalyst in the reactor to crack the hydrocarbons down to
smaller molecular weight products. During this process, the
catalyst tends to accumulate coke thereon, which is burned off in
the regenerator.
[0004] The heat of combustion in the regenerator typically produces
flue gas at temperatures of 718.degree. to 760.degree. C.
(1325.degree. to 1400.degree. F.) and at a pressure range of 138 to
276 kPa (20 to 40 psig). Although the pressure is relatively low,
the extremely high temperature, high volume of flue gas from the
regenerator contains sufficient kinetic energy to warrant economic
recovery. To recover energy from a flue gas stream, flue gas may be
fed and directed into the blades of a power recovery expander
turbine. The kinetic energy of the flue gas is transferred through
the blades of the expander to a rotor coupled either to a
regenerator air blower, to produce combustion air for the
regenerator, and/or to a generator to produce electrical power.
Because of the pressure drop of 138 to 207 kPa (20 to 30 psi)
across the expander turbine, the flue gas discharges with a
temperature drop of approximately 125.degree. to 167.degree. C.
(225 to 300.degree. F.). The flue gas may be run to a steam
generator for further recovery.
[0005] The power recovery train may include an expander turbine, a
generator, an air blower, a gear reducer, and a let-down steam
turbine. The expander turbine may be coupled to a main air blower
shaft to power the air blower of a regenerator of the FCC unit. The
expander turbine is a single stage machine. The gas to the expander
turbine is accelerated over a parabolic nose cone. The pressure
energy is converted to kinetic energy as the flue gas passes
through the blades of the turbine. The blades of the expander
turbine rotate at very high velocities necessitating measures to
protect the blades from physical damage.
[0006] A major distinguishing feature of an FCC process is the
continuous fluidization and circulation of large amounts of
catalyst having an average particle diameter of about 50 to 100
microns, equivalent in size and appearance to very fine sand. For
every ton of cracked product made, approximately 5 tons of catalyst
are needed, hence the considerable circulation requirements.
Coupled with this need for a large inventory and recycle of
catalyst with small particle diameters is the ongoing challenge to
prevent this catalyst from exiting the reactor/regenerator system
into effluent streams.
[0007] Catalyst particles can cause erosion of expander turbine
blades resulting in loss of power recovery efficiency. Moreover,
even though catalyst fines; i.e., particles less than 10 .mu.m in
dimension, do not erode expander turbine blades as significantly,
they still accumulate on the blades and casing. Blade accumulation
can cause blade tip erosion and casing accumulation can increase
the likelihood of the tip of the blade rubbing against the casing
of the expander turbine which can result in high expander shaft
vibration.
[0008] Overall, the use of cyclone separators internal to both the
reactor and regenerator has provided over 99% separation efficiency
of solid catalyst. Typically, the regenerator includes first and
second (or primary and secondary) stage separators for the purpose
of preventing catalyst contamination of the regenerator flue gas,
which is essentially the resulting combustion product of catalyst
coke in air. While normally sized catalyst particles are
effectively removed in the internal regenerator cyclones, fines
material (generally catalyst fragments smaller than about 50
microns resulting from attrition and erosion in the harsh, abrasive
reactor/regenerator environment) is substantially more difficult to
separate. As a result, the FCC flue gas will usually contain a
particulate concentration in the range of about 200 to 1000
mg/Nm.sup.3. This solids level can present difficulties related to
the applicable legal emissions standards and are still high enough
to risk damage to the power recovery expander turbine.
[0009] A further reduction in FCC flue gas fines loading is
therefore often warranted, and may be obtained from a third stage
separator (TSS). The term "third" in TSS typically presumes a first
stage cyclone and a second stage cyclone are used for gas-solid
separation upstream of the inlet to the TSS. These cyclones are
typically located in the catalyst regeneration vessel. More or less
separator devices may be used upstream of the TSS. Hence, the term
TSS does not require that no more nor less than two separator
devices are upstream of the TSS vessel, herein. The TSS induces
centripetal acceleration to a particle-laden gas, stream to force
the higher-density solids to the outer edges of a spinning vortex.
To be efficient, a cyclone separator for an FCC flue gas effluent
will normally contain many, perhaps 100, small individual
cylindrical cyclone bodies installed within a single vessel acting
as a manifold. At least one tube sheet affixing the upper and/or
lower ends of the cyclones act to distribute contaminated gas to
the cyclone inlets and also to divide the region within the vessel
into sections for collecting the separated gas and solid
phases.
[0010] Proper design of the gas delivery equipment is essential to
protecting the power recovery system, particularly the blades of
the expander. Cold wall piping. comprises a refractory lining on
the inside of a metal pipe to insulate the pipe from the hot gas
carried therein to minimize thermal expansion. Cold wall piping is
not typically specified between the TSS vessel and the expander
turbine inlet due to concerns of spalling refractory lining
entering the expander turbine and damaging the blades. Hot wall
piping, which may be made of stainless steel, without refractory
lining thermally expands over five times as much as cold wall
piping. The large thermal expansion associated with hot wall piping
systems results in significantly higher piping loads that must be
accommodated in the design of the piping components and equipment.
Invariably, this leads to added cost for support and installation.
Additionally, the rotor of the turbo expander turbine may not be
allowed to exceed a maximum velocity or the blades could detach
from the rotor.
[0011] TSS vessels typically only have one main clean gas outlet in
communication with the multiple main clean gas outlets of
respective cyclones in the TSS vessel as shown in U.S. Pat. No.
5,690,709 and U.S. Pat. No. 5,779,746. GB 2 077 631A shows two
clean gas outlets in the top hemispherical head of the TSS vessel.
This reference discloses that the clean gas outlets may be
connected to a power recovery turbine.
SUMMARY OF THE INVENTION
[0012] The power recovery unit, which is usually an expander
turbine, for recovering energy from a hot, pressurized gas stream
provides extra power to other equipment when needed such as an air
blower shaft or an electrical generator, or both. If the power
recovery unit produces more energy than is required by the other
equipment, the machine may act as a generator and feed power into
the refinery power grid. Feeding power into the refinery power grid
acts as a braking mechanism and provides some over-speed
protection. Given an electrical breaker disconnect from the power
grid, a fast acting over-speed valve and bypass conduit or line
around the power recovery unit may be required to rapidly divert
flue gas around the expander turbine to limit the rotational
velocity of the expander turbine. Additionally, diverting a portion
of the flue gas around the expander turbine through the bypass
conduit may be necessary to control the pressure in the upstream
catalyst regenerator. However, as the bypass valve opens, the flow
of hot flue gas would cause the hot wall piping to rapidly heat up
and thermally expand. The resultant pipe expansion would impose a
great deal of force loading and rotational moment on the expander
turbine inlet line. The loading and moment on the expander turbine
inlet must be relatively small to ensure that the housing of the
expander turbine does not deform which could promote the blades to
brush with the inner surface of the casing. Additional equipment,
engineering design and construction installation labor, would be
required to ensure that expansion of the bypass conduit does not
translate to a load on the expander turbine inlet line that is in
excess of the nozzle loading limits.
[0013] The present invention is a system for separating particulate
solids from a contaminated gas stream and recovering energy from
the contaminated gas stream, typically a hot flue gas stream from a
catalyst regeneration vessel. A TSS vessel has a main inlet for
receiving gas laden with solids. A plurality of cyclones in the TSS
vessel separates the solids from the gas. A solids outlet from the
TSS vessel dispenses solids from the TSS vessel and two main clean
gas outlets remove clean gas from the TSS vessel. A TSS vessel may
have a tube sheet that separates the inlet to the TSS vessel from
the outlet from the TSS vessel. In an embodiment, the two main
clean gas outlets extend from the TSS vessel below the tube sheet.
A first main clean gas outlet from the TSS vessel delivers clean
gas to a power recovery unit. A second main clean gas outlet from
the TSS vessel is transported through a bypass conduit that
bypasses the power recovery unit and mixes with the effluent clean
gas from the power recovery unit.
[0014] If the actual flowing volume of the clean gas in the main
clean gas conduit exceeds a level at which the power recovery unit
is rated, a valve in the bypass clean gas conduit is opened to a
proportional degree, so a portion of the clean gas being directed
to the power recovery unit can be re-directed to bypass the power
recovery unit, and maintain proper pressure control of the FCC
regenerator and avoid mechanical damage to the power recovery
expander. The bypass clean gas conduit is anchored on the TSS
vessel instead of on the main clean gas conduit to the power
recovery unit, so sudden exposure of the bypass clean gas conduit
to hot gases and its concomitant rapid thermal expansion will not
suddenly impose a load or moment on the power recovery unit beyond
allowance. Hence, equipment, engineering, and installation labor
necessary for neutralizing such effects are not necessary.
Moreover, because the bypass clean gas conduit does not join with a
conduit to the power recovery unit, the bypass clean gas conduit
may be lined with insulating refractory to minimize thermal
expansion thereof without fear that spalling refractory will damage
the power recovery unit.
[0015] Accordingly, an object of the present invention is to
provide a TSS vessel with a first main clean gas outlet that feeds
a power recovery unit and a second main clean gas outlet that feeds
a bypass conduit that bypasses the power recovery unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic view of the system of the present
invention.
[0017] FIG. 2 is a schematic view of a TSS vessel of the present
invention.
[0018] FIG. 3 is a schematic view of an alternative embodiment of a
TSS vessel of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention applies to the purification of a broad
range of solid-contaminated gas streams, and especially those
containing dust particles in the 1 to 20 .mu.m range. A number of
commercial gas purification operations meet this description,
including the treatment of effluent streams of solid catalyst
fluidized bed processes, coal fired heaters, and power plants.
Several well-known refinery operations rely on fluidized bed
technology, such as a preferred embodiment of the process for
converting methanol to light olefins, as described in U.S. Pat. No.
6,137,022, using a solid catalyst composition. Another area of
particular interest lies in the purification of FCC effluent
streams that contain entrained catalyst particles resulting from
attrition, erosion, and/or abrasion under process conditions within
the reactor.
[0020] As mentioned, fluid catalytic cracking (FCC) is a well-known
oil refinery operation relied upon in most cases for gasoline
production. Process variables typically include a cracking reaction
temperature of 400.degree. to 600.degree. C. and a catalyst
regeneration temperature of 500.degree. to 900.degree. C. Both the
cracking and regeneration occur at an absolute pressure below 5
atmospheres. FIG. 1 shows a typical FCC process unit of the prior
art, where a heavy hydrocarbon feed or raw oil in a line 12 is
contacted with a newly regenerated catalyst entering from a
regenerated catalyst standpipe 14. This contacting may occur in a
narrow reactor conduit 16, known as a reactor riser, extending
upwardly to the bottom of a reactor vessel 10. The contacting of
feed and catalyst is fluidized by gas from a fluidizing line 8.
Heat from the catalyst vaporizes the oil, and the oil is thereafter
cracked in the presence of the catalyst as both are transferred up
the reactor conduit 16 into the reactor vessel 10 itself, operating
at a pressure somewhat lower than that of the reactor conduit 16.
The cracked light hydrocarbon products are thereafter separated
from the catalyst using a first stage internal reactor cyclone 18
and a second stage internal reactor cyclone (not shown) and exit
the reactor vessel 10 through a line 22 to subsequent fractionation
operations. More or less cyclones may be used in the reactor vessel
10. At this point, some inevitable side reactions occurring in the
reactor conduit 16 have left detrimental coke deposits on the
catalyst that lower catalyst activity. The catalyst is therefore
referred to as being spent (or at least partially spent) and
requires regeneration for further use. Spent catalyst, after
separation from the hydrocarbon product, falls into a stripping
section 24 where steam is injected through a nozzle 26 to purge any
residual hydrocarbon vapor. After the stripping operation, the
spent catalyst is fed to a catalyst regeneration vessel 30 through
a spent catalyst standpipe 32.
[0021] FIG. 1 depicts a regeneration vessel 30 known as a
combustor. However, other types of regeneration vessels are
suitable. In the catalyst regeneration vessel 30, a stream of air
is introduced through an air distributor 28 to contact the spent
catalyst, burn coke deposited thereon, and provide regenerated
catalyst. The catalyst regeneration process adds a substantial
amount of heat to the catalyst, providing energy to offset the
endothermic cracking reactions occurring in the reactor conduit 16.
Some fresh catalyst is added in a line 36 to the base of the
catalyst regeneration vessel 30 to replenish catalyst exiting the
reactor vessel 10 as fines material or entrained particles.
Catalyst and air flow upward together along a combustor riser 38
located within the catalyst regeneration vessel 30 and, after
regeneration (i.e. coke burn), are initially separated by discharge
through a disengager 40, also within the catalyst regeneration
vessel 30. Finer separation of the regenerated catalyst and flue
gas exiting the disengager 40 is achieved using a first stage
separator cyclone 44 and a second stage separator cyclone 46 within
the catalyst regeneration vessel 30. More or less separator
cyclones may be used in the regeneration vessel 30. Flue gas enters
the first stage separator cyclone 44 through an inlet 44a. Catalyst
separated from flue gas dispenses through a dipleg 44b while flue
gas relatively lighter in catalyst travels through a conduit 46a
into the second stage separator cyclone 46. Additional catalyst
separated from the flue gas in the second stage separator cyclone
46 is dispensed into the catalyst regeneration vessel 30 through a
dipleg 46b while flue gas relatively even lighter in solids exits
the second stage separator cyclone 46 through an outlet tube 46c.
Regenerated catalyst is recycled back to the reactor vessel 10
through the regenerated catalyst standpipe 14. As a result of the
coke burning, the flue gas vapors exiting at the top of the
catalyst regeneration vessel 30 in a nozzle 42 contain CO, CO.sub.2
and H.sub.2O, along with smaller amounts of other species. While
the first stage separator cyclone 44 and the second stage separator
cyclone 46 can remove the vast majority of the regenerated catalyst
from the flue gas in the nozzle 42, fine catalyst particles,
resulting mostly from attrition, invariably contaminate this
effluent stream. The fines-contaminated flue gas therefore
typically contains about 200 to 1000 mg/Nm.sup.3 of particulates,
most of which are less than 50 microns in diameter. In view of this
contamination level, and considering both environmental regulations
as well as the option to recover power from the flue gas, the
incentive to further purify the relatively contaminated flue gas
using a TSS vessel is significant. A conduit 48 delivers the
contaminated flue gas to a TSS vessel 50.
[0022] The TSS vessel 50, containing numerous individual cyclones
51, that may be used in the present invention is shown in FIG. 2.
Although only four cyclones 51 are shown in FIG. 2, at least 10 and
as many as 200 cyclones 51 are anticipated for variously sized
units. The cyclones 51 and the TSS vessel 50 need not include all
the details disclosed herein to utilize the present invention. The
TSS vessel 50 is normally lined with a refractory material 52 to
reduce erosion of the metal surfaces by the entrained catalyst
particles. The fines-contaminated flue gas from the catalyst
regeneration vessel 30 enters the top of the TSS vessel 50 at a
main contaminated gas inlet 54 through a nozzle 53. The main
contaminated gas inlet 54 is above an upper tube sheet 56 that
retains top ends 58 of each cylindrical cyclone body 62. In an
embodiment, the upper tube sheet 56 at least in part defines an
inlet chamber 57, limits communication between the inlet chamber 57
and the rest of the TSS vessel 50 and/or extends the entire
cross-section of the TSS vessel 50; A cover 56a of an optional
manway provides access through the upper tube sheet 56 and assists
in the aforementioned functions. An optional diffuser 55 may spread
out the flow of contaminated flue gas into the TSS vessel 50. The
contaminated gas stream is then distributed among cyclone
contaminated gas inlets 60 and encounters one or more swirl vanes
64 proximate the inlets 60 to induce centripetal acceleration of
the particle-contaminated gas. The swirl vanes 64 are structures
within the cylindrical cyclone body 62 that have the characteristic
of restricting the passageway through which incoming gas can flow,
thereby accelerating the flowing gas stream. The swirl vanes 64
also change the direction of the contaminated gas stream to provide
a helical or spiral formation of gas flow through the length of the
cylindrical cyclone body 62. This spinning motion imparted to the
gas sends the higher-density solid phase toward the wall of the
cylindrical cyclone body 62. The cyclones 51, in an embodiment,
include a closed bottom end 66 of the cylindrical cyclone body 62.
In an embodiment, slots in the cylindrical cyclone body 62 allow
solid particles that have been thrown near the wall of the
cylindrical cyclone body 62 to fall into a solids chamber 68
between the upper tube sheet 56 and a lower tube sheet 74. The
upper tube sheet 56 and the lower tube sheet 74 limit communication
between the solids chamber 68 and the rest of the TSS vessel 50. In
an embodiment, the upper tube sheet 56 and the lower tube sheet 74
define at least in part the solids chamber 68. The lower tube sheet
74 may extend the entire cross-section of the interior of the TSS
vessel 50. However, a solids outlet tube 76 allows solids to pass
from the solids chamber 68. In an embodiment, the solids outlet
tube 76 extends from the TSS vessel 50 through an outlet 84 defined
by a nozzle 83. In an embodiment, the upper tube sheet 56 and/or
the lower tube sheet 74 define an inverted cone to facilitate the
exit of solids from the downward vertex of the conical lower tube
sheet 74 at an inlet 75 to the solids outlet tube 76. Clean gas,
flowing along the centerline of the cylindrical cyclone body 62,
passes through an inlet 70 of a cyclone gas outlet tube 72. The
clean gas is then discharged via the cyclone gas outlet tube 72
below the lower tube sheet 74 into a clean gas chamber 78. In an
embodiment, the lower tube sheet 74 at least in part defines the
clean gas chamber 78 and limits communication between the clean gas
chamber 78 and the rest of the TSS vessel 50 and particularly the
solids chamber 68. The combined clean gas stream, representing the
bulk of the flue gas fed to the TSS vessel 50, then exits through
one of a first main clean gas outlet 80 and a second main clean gas
outlet 82 (shown in phantom in FIG. 2) near the bottom of the TSS
vessel 50. Both main clean gas outlets 80, 82 may be defined by a
first clean gas outlet nozzle 81 and a second clean gas outlet
nozzle 83, respectively. The first and second main clean gas
outlets 80, 82 communicate only with the clean gas chamber 78. In
an embodiment, the first and second main clean gas outlets 80, 82
are below the upper and lower tube sheets 56, 74 and particularly
below the lower tube sheet 74. The first and second main clean gas
outlet nozzles 81, 83 may extend from a vertical wall 86 of the TSS
vessel 50. Manways 88 to the TSS vessel 50 are covered during
operation and allow access during maintenance and construction.
Separated particles and a minor amount (typically less than 10 wt-%
of the contaminated flue gas) of underflow gas are removed through
a separate solids outlet 84 at the bottom of the TSS vessel 50. A
trash screen or grating (not shown) may be installed in the main
clean gas outlets 80, 82 to block passage of spalling
refractors.
[0023] Turning back to FIG. 1, the clean gas exiting the first main
clean gas outlet 80 travels in a power recovery inlet line 90 or
conduit through a control valve 92 to a power recovery unit 94
through a power recovery inlet 93. Clean gas outlets 80, 82 are
shown schematically different in FIG. 1 than in FIG. 2 for purposes
of illustration. The power recovery inlet line 90 is devoid of
refractory lining. In an embodiment, the power recovery unit 94 is
an expander turbine. A typical expander turbine has an outer casing
96 and a plurality of blades 98 fastened to a rotor (not shown). As
the hot flue gas enters the power recovery unit 94 and accelerates
over a parabolic nose cone 100, the high velocity pressurized flue
gas propels the blades 98 to turn at high velocity, turning a shaft
102. The shaft 102 may be linked to a generator 104 through a gear
box 106. The flue gas exits the power recovery unit 94 through a
power recovery outlet 99. Although not shown, the shaft 102 may
alternatively or additionally be connected to the main air blower
that pumps air into the catalyst regeneration vessel 30 or other
equipment on site. Power generated by the power recovery unit 94 in
excess of that required to power the main air blower or other
equipment is translated into electricity that feeds the power grid
for the facility for which the TSS is a component or may be fed to
another power grid. Although the power required to operate the main
air blower or other equipment and to generate electricity in the
generator 104 serves to resist excessive rotational speed of the
blades 98, other precautions must be taken to ensure proper
pressure control of the catalyst regeneration vessel 30 and ensure
that the expander blades 98 do not exceed a maximum speed which
would cause damage to the power recovery unit 94. Therefore, the
second main clean gas outlet 82 feeds a bypass conduit 110 or line.
The bypass conduit 110 passes through a control valve 112 and joins
a power recovery outlet conduit 114 or line passing from the power
recovery outlet 99. A combined flue gas outlet line 116 carries the
gas in the lines 110, 114 to the atmosphere or to further
processing. The clean gas effluent from the TSS vessel 50 captures
nearly 100% of particles having a dimension of greater than 10
microns and has an overall concentration of solids that meets the
most stringent environmental protection regulations in the United
States and internationally. A pressure indicator controller (PIC)
120 is linked to the control valves 92 on the power recovery inlet
line 90 and the control valve 112 on the bypass conduit 110. The
PIC 120 will signal the control valve 92 first to control the
pressure in the catalyst regeneration vessel 30 while the control
valve 112 in the bypass conduit 1110 will be closed. However, if
the control valve 92 is fully open to reduce the pressure in the
catalyst regeneration vessel 30, the control valve 112 in the
bypass conduit 110 can be opened in an appropriate amount from the
signal from the PIC 120 to ensure that the kinetic energy in the
power recovery inlet line 90 will not cause the power recovery unit
94 to exceed its allowance rating.
[0024] The solids retrieved from the TSS vessel 50 in the solids
outlet 84 can be optionally taken by a line 122 to a fourth stage
separator (not shown) to further remove underflow gas from catalyst
and collect the catalyst in a spent catalyst hopper and/or the
underflow gas may be delivered to other types of additional
processing.
[0025] The configuration of the present invention permits the
bypass conduit 1 10 to be a refractory lined, cold wall line
connected directly at an inlet end to the second main clean gas
outlet 82 on the TSS vessel 50. The piping design from the fixed
foundation TSS vessel 50 to the inlet 93 of the power recovery unit
94 becomes a very elegant design. The transient loads applied to
the inlet to the power recovery unit 94 associated with
intermittently bypassing hot flue gas to the bypass conduit 110 are
eliminated. The bypass conduit 110 becomes a much shorter, cold
wall design, lowering the overall capital cost. The first main
clean gas outlet 80 is in upstream fluid communication with the
power recovery inlet 93 to the power recovery unit 94 through the
power recovery inlet line 90 and the control valve 92. The second
main clean gas out 82 is not in downstream communication with the
power recovery unit 94 but in upstream fluid communication with the
power recovery outlet conduit 114. The power recovery inlet 93 is
in downstream fluid communication with the first main clean gas
outlet 80 via the power recovery inlet line 90 and the control
valve 92, and the power recovery outlet 99 is in downstream fluid
communication with the second main clean gas outlet 82 via the
bypass conduit 110, the control valve 112 and the power recovery
outlet conduit 114. In other words, the power recovery inlet 93
receives at least a portion of the clean gas effluent from the
first main clean gas outlet 80, but none of the clean gas effluent
from the second main clean gas outlet 82. Moreover, the flue gas
outlet line 116 receives clean gas effluent from the second main
clean gas outlet 82 and clean gas effluent from the first main
clean gas outlet 80 via power recovery outlet 99. The bypass
conduit 1 10 and the power recovery outlet conduit 114 join
together to deliver the two effluents to the flue gas outlet line
116.
[0026] FIG. 3 shows a TSS vessel 50' as shown in FIG. 2 but with a
different main clean gas outlet and solids outlet configuration.
All the reference numerals in FIG. 3 will be the same as in FIG. 2
unless the element designated by the reference numeral in FIG. 3 is
configured differently than in FIG. 2. FIG. 3 shows a second main
clean gas outlet 82' that extends from the bottom of the TSS vessel
50' instead of the second main clean gas outlet 82 shown in phantom
in FIG. 2 in the vertical wall 86 of the TSS vessel 50. A solids
outlet tube 76' extending from the lower tube sheet 74 extends
through the second main clean gas outlet 82' defined by a nozzle
83' and then diverges from a power recovery inlet line 90'. This
configuration provides flexibility for incorporating the TSS vessel
50' into a particular flow scheme. The second main clean gas outlet
82' at the bottom of the TSS vessel 50' may be in upstream fluid
communication either with the bypass conduit 1 10 or the power
recovery inlet line 90'. Additionally, the configuration in FIG. 3
may be used when only one main clean gas outlet 82' extends from
the TSS vessel 50' which may omit the first main clean gas outlet
80 shown in FIG. 3.
[0027] Although it is not shown in the drawings, it is also
contemplated that both main clean gas outlets may extend through or
be contained in the same nozzle of the TSS vessel.
* * * * *