Gasifier Throat Cooling

Abstract

A gasifier for converting a carbonaceous feedstock to produce syngas comprising a cone section and a throat section; wherein the throat section comprises a throat refractory material having an inside surface and a substantially cylindrical cooling element having an inner face and an outer face in a radial direction, and a top face and a bottom face in the vertical direction, wherein the inner, outer, top, and bottom faces define a cooling cavity; and wherein the cooling element is in thermal contact with the throat refractory material on the inner face, the top face, and the outer face.

Description

BACKGROUND

The partial combustion or gasification of solid carbonaceous fuels such as coal to produce gases having value as residential and industrial fuels, as starting materials for synthesis of chemicals and fuels, and as an energy source for generation of electricity has long been recognized and practiced on varying scales throughout the world. The high temperature and aggressive chemistry within the gasifier requires refractory material to protect the outer pressure vessel wall, particularly in the narrow throat at the exit of the reactor. This refractory material is degraded during operation and must be periodically removed and replaced.

SUMMARY

The present disclosure relates to a system for cooling the throat of a gasifier having a cooling cavity located therein using one or more substantially cylindrical cooling coils surrounded by refractory material on the inner face, the top face, and the outer face of the cooling cavity.

Aspect 1: A gasifier for converting a carbonaceous feedstock to produce syngas comprising a cone section and a throat section; wherein the throat section comprises a throat refractory material and a substantially cylindrical cooling element having an inner face and an outer face in a radial direction, and a top face and a bottom face in a vertical direction, wherein the inner, outer, top, and bottom faces define a cooling cavity; and wherein the cooling element is in thermal contact with the throat refractory material on the inner face, the top face, and the outer face.

Aspect 2: A gasifier according to Aspect 1, comprising a coolant inlet conduit in fluid flow communication with the cooling element and a coolant outlet conduit in fluid flow communication with the cooling element; wherein the coolant inlet conduit is in fluid flow communication with a coolant source external to the gasifier; and wherein the coolant outlet conduit is in fluid flow communication with a coolant sink external to the gasifier.

Aspect 3: A gasifier according to Aspect 2, wherein the coolant inlet conduit and the coolant outlet conduit comprise a section oriented in the radial direction perpendicular to the centerline of the gasifier.

Aspect 4: A gasifier according to any of Aspects 1 to 3, wherein the throat refractory material comprises refractory bricks.

Aspect 5: A gasifier according to any of Aspects 1 to 4, wherein the throat section has an inside surface and an inner radius defined as the distance from the centerline of the gasifier to the inside surface of the throat section; wherein the minimum value of the inner radius of the throat section is within 2% of the maximum value of the inner radius of the throat section.

Aspect 6: A gasifier according to any of Aspects 1 to 4, wherein the throat section has an inner radius that increases stepwise with increasing depth.

Aspect 7: A gasifier according to any of Aspects 1 to 6, further comprising a refractory support floor attached to the bottom face of the cooling element.

Aspect 8: A method of operating a gasifier comprising indirectly transferring heat from a refractory material having a refractory temperature to a coolant having a coolant temperature and a liquid stability limit; wherein the method comprises a dryout mode characterized by increasing the refractory temperature from ambient temperature to about 100° C. and a heating mode characterized by increasing the refractory temperature from about 100° C. to the liquid stability limit of the coolant; wherein during the dryout mode the coolant temperature is maintained between a dryout mode lower temperature limit and a dryout mode upper temperature limit; wherein during the heating mode the coolant temperature is maintained between a heating mode lower temperature limit and a heating mode upper temperature limit.

Aspect 9: A method according to Aspect 8, wherein the dryout mode lower temperature limit is less than or equal to 5° C. lower than the refractory temperature and wherein the dryout mode upper temperature limit is less than or equal to 5° C. greater than the refractory temperature.

Aspect 10: A method according to Aspect 8 or Aspect 9, wherein the heating mode lower temperature limit is less than or equal to 5° C. lower than the refractory temperature and wherein the heating mode upper temperature limit is less than or equal to 10° C. lower than the liquid stability limit of the coolant.

Aspect 11: A method according to any of Aspects 8 to 10, wherein the coolant has a coolant pressure; wherein the coolant pressure is kept constant at a value greater than the vapor pressure of the coolant at the liquid stability limit.

Aspect 12: A method according to any of Aspects 8 to 10, wherein the coolant has a coolant pressure; wherein the coolant pressure is maintained at a value greater than the vapor pressure of the coolant at the temperature of the coolant.

Aspect 13: A method according to any of Aspects 8 to 12, further comprising a cooling mode characterized by decreasing the refractory temperature from the operating temperature of the gasifier to a value equal to ambient temperature; wherein during the cooling mode the coolant temperature is maintained between a cooling mode lower temperature limit and a cooling mode upper temperature limit.

Aspect 14: A method according to Aspect 13, wherein the cooling mode lower temperature limit is less than or equal to 5° C. lower than the refractory temperature and wherein the cooling mode upper temperature limit is less than or equal to the lesser of 10° C. lower than the liquid stability limit of the coolant and 5° C. greater than the refractory temperature.

Aspect 15: A method according to any of Aspects 8 to 14, wherein the coolant temperature is controlled by exchanging heat with a quench bath prior to indirectly transferring heat from the refractory material.

Aspect 16: A gasifier for converting a carbonaceous feedstock to produce syngas comprising a reactor section configured to react the carbonaceous feedstock with an oxidant to produce syngas, a quench section configured to contact the syngas with a quench bath, and a throat section configured to convey the syngas from the reactor section to the quench section wherein the throat section comprises a throat refractory material and a cooling element in thermal contact with the throat refractory material; wherein the quench section comprises a dip tube having an inlet in fluid flow communication with the throat section and an outlet in fluid flow communication with the quench bath; wherein the quench section further comprises a low liquid level located above the outlet of the dip tube; wherein the quench bath has a level at or above the low liquid level; wherein the quench section further comprises a quench heat exchanger in thermal contact with the quench bath; wherein the cooling element comprises an inlet in fluid flow communication with the outlet of the quench heat exchanger; and wherein at least a portion of the quench heat exchanger is located above the outlet of the dip tube and below the low liquid level.

Aspect 17: A gasifier according to Aspect 16, wherein at least a portion of the quench heat exchanger is configured to reduce level and flow instabilities in the quench bath.

Aspect 18: A gasifier according to Aspect 17, wherein the at least a portion of the quench heat exchanger configured to reduce level and flow instabilities in the quench bath forms a conical frustrum surface.

Aspect 19: A method of operating a gasifier comprising reacting a carbonaceous feedstock with an oxidant to produce a syngas stream; cooling a refractory material in thermal contact with the syngas stream by indirect heat exchange with a heat transfer fluid; contacting the syngas stream with a quench water stream to produce a quenched syngas stream; partially condensing the quenched syngas stream to produce a process condensate stream; wherein the heat transfer fluid comprises at least a portion of the process condensate stream.

Aspect 20: A method according to Aspect 19, wherein the quench water stream comprises at least a portion of the process condensate stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the appended figures wherein like numerals denote like elements. Further, reference numerals for analogous elements shared by figures may be indexed by multiples of one hundred. For example, an element 1xx in FIG. 1 that has been altered in FIG. 2 may be referred to as element 2xx.

FIG. 1 shows a cross section of a gasifier according to the prior art.

FIG. 2 shows a cross section of a gasifier with a cooling element behind the refractory in the throat.

FIG. 3 shows a cross section of a gasifier in which the cooling element is in fluid flow communication with a coolant source external to the gasifier and a coolant sink external to the gasifier.

FIG. 4 shows a control scheme for a closed loop cooling system.

FIG. 5A shows a control scheme for an open loop cooling system.

FIG. 5B shows a modification of FIG. 5A in which the pressure of the coolant is also controlled.

FIG. 6 shows a cross section of a gasifier comprising a reactor section and a quench section in which a quench heat exchanger is integrated into the quench section.

FIG. 7 shows a cross section of a modification of FIG. 6 in which at least a portion of the quench heat exchanger is integrated into a quench level stabilizer.

FIG. 8 shows a modification of FIG. 7 in which the quench heat exchanger and cooling element are integrated with a downstream process condensate system.

DETAILED DESCRIPTION

The ensuing detailed description provides preferred exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention, as set forth in the appended claims.

The articles “a” or “an” as used herein mean one or more when applied to any feature in embodiments of the present invention described in the specification and claims. The use of “a” and “an” does not limit the meaning to a single feature unless such a limit is specifically stated. The article “the” preceding singular or plural nouns or noun phrases denotes a particular specified feature or particular specified features and may have a singular or plural connotation depending upon the context in which it is used.

The phrase “at least a portion” means “a portion or all.” The “at least a portion of a stream” has the same composition, with the same concentration of each of the species, as the stream from which it is derived.

The term “and/or” placed between a first entity and a second entity includes any of the meanings of (1) only the first entity, (2) only the second entity, or (3) the first entity and the second entity. The term “and/or” placed between the last two entities of a list of 3 or more entities means at least one of the entities in the list including any specific combination of entities in this list. For example, “A, B and/or C” has the same meaning as “A and/or B and/or C” and comprises the following combinations of A, B and C: (1) only A, (2) only B, (3) only C, (4) A and B but not C, (5) A and C but not B, (6) B and C but not A, and (7) A and B and C.

The adjective “any” means one, some, or all, indiscriminately of quantity.

“Downstream” and “upstream” refer to the intended flow direction of the process fluid transferred. If the intended flow direction of the process fluid is from the first device to the second device, the second device is downstream of the first device. In case of a recycle stream, downstream and upstream refer to the first pass of the process fluid.

The term “indirect heat exchange” refers to the process of transferring sensible heat and/or latent heat between two or more fluids without the fluids in question coming into physical contact with one another. The heat may be transferred through the wall of a heat exchanger or with the use of an intermediate heat transfer fluid. The term “hot stream” refers to any stream that exits the heat exchanger at a lower temperature than it entered. Conversely, a “cold stream” is one that exits the heat exchanger at a higher temperature than it entered.

FIG. 1 shows a cross section of a gasifier 100 according to the prior art. The vessel wall 102 holds the pressure of the gasifier and is protected by a layer of insulating wall refractory 104 and wall backup brick 106. One or more refractory support shelves 108 may extend inwardly from the vessel wall 102 toward the centerline of the gasifier to improve the structural integrity and/or simplify the installation of refractory material. A refractory support floor 110 extends from the vessel wall 102 to support the weight of the refractory, and one or more refractory support shelves 108 also may extend inwardly from a portion of refractory support floor 110. On the refractory support floor 110 may be found insulating floor refractory 112 which may comprise bricks and/or castable material. On the inside portion of the refractory support floor 110 may be found throat backup brick 114. The inside surface of the gasifier is formed by refractory brick 116 which forms a sidewall 118, a cone 120, and a throat 122. The throat 122 may be in a stepped configuration as shown in FIG. 1 in which the inner radius of the throat 122 increases stepwise with increasing depth in order to improve the flow of slag out of the gasifier, where the inner radius is defined as the distance from the centerline of the gasifier to the inside surface of the throat 122.

Refractory brick 116 in the cone 120 and throat 122 is susceptible to damage by slag, requiring frequent replacement which forces a costly shutdown and outage of the gasifier. Damage may be from any method such as erosion, corrosion, infiltration, and spalling. One method of increasing refractory lifetime is by introducing cooling elements such as heat exchanger tubes carrying a coolant such as water behind the refractory. FIG. 2 shows a cross section of a gasifier 200 with cooled refractory according to one embodiment of the present invention. A throat outer refractory 214 forms a cooling cavity 236 between the refractory 116 and the refractory support floor 110 in which a substantially cylindrical cooling element 230 is positioned. The cooling element 230 has an inner face nearest the centerline of the gasifier, an outer face nearest the vessel wall 102, and a top face and a bottom face in the vertical direction. In at least some embodiments cooling element 230 is attached to the refractory support floor 110. In at least some embodiments the throat outer refractory 214 may comprise a different refractory material than the insulating floor refractory 212. The cooling element 230 maintains thermal contact with the refractory brick 116 and throat outer refractory 214 through cooling cavity material 232 which may comprise one or more refractory materials such as refractory paper and/or castable refractory such as silicon carbide. The cooling cavity material 232 may be arranged to maintain thermal contact as the refractory expands and contracts with thermal cycling in the gasifier. In at least some embodiments, the throat 122 may have a stepped configuration as shown in FIG. 1. In at least some other embodiments, the throat 222 may be in a substantially cylindrical configuration as shown in FIG. 2. For some gasifiers, a substantially cylindrical configuration may allow better flow of slag through the throat than a stepped configuration. The variation between the widest and narrowest inner radius of the throat 222 may vary by less than 2%, or less than 1%, or less than 0.5% when the throat 222 is new. When the throat 222 is nearing replacement, the variation between the widest and narrowest inner radius of the throat 222 may vary by less than 50%, or less than 25%.

The insulating floor refractory 212 may comprise brick rather than a castable material or combinations of both to make installation and replacement easier.

The improved heat transfer to the cooling element 230 via the refractory brick 116, the throat outer refractory 214, and the refractory support floor 110 reduces temperatures in the refractory brick 116, improving overall lifetime. In at least some embodiments the bottom of the cooling element 230 may be attached to the refractory support floor 110 to maintain its position relative to the refractory support floor 110 and to conduct heat to the cooling element 230. Surprisingly, the improved lifetime may be achieved without active cooling in the cone 120. In at least some embodiments, there are no cooling elements in or behind the cone 120.

The refractory support floor 110 may comprise a refractory support shelf 234 to support the refractory brick 116 in the throat 222. The refractory support shelf may form a continuous ring or be segmented in multiple tabs to reduce the risk of cracks forming due to hoop stress caused by differential thermal expansion.

The cooling element 230 may comprise tubing for carrying a coolant such as water. The tubing may form one or more layers in the radial direction (horizontal direction in FIG. 2). The tubing in the cooling element 230 may be oriented circumferentially within the cooling cavity 236 to form a cylindrical path or may be oriented in a serpentine path within the cooling cavity 236. In at least some embodiments, the serpentine path may comprise straight segments in the vertical direction while changing direction 180 degrees circumferentially to produce a serpentine path with vertical switchbacks. In at least some other embodiments, the serpentine path may comprise curved segments in the circumferential direction while changing direction 180 degrees vertically to produce a serpentine path with horizontal switch backs. The cooling element 230 may comprise multiple sections that can be installed individually and then be welded together with expansion joints in series and/or in parallel.

FIG. 3 shows a cross section of a gasifier 300 in which the cooling element 230 is in fluid flow communication with a coolant source 340 external to the gasifier and a coolant sink 342 external to the gasifier. In at least some embodiments the coolant source 340 is in fluid flow communication with the coolant sink 342 with heat rejection to the environment incorporated into the coolant loop. The cooling element 230 may comprise a coolant inlet conduit 344 and a coolant outlet conduit 346, both of which may travel through the throat outer refractory 214, the insulating floor refractory 212, and/or the refractory support floor 110 on the way through the vessel wall 102. The pressure and flow rate of the coolant may be controlled by one or more devices located upstream or downstream of the cooling element 230. For example, the coolant inlet conduit 344 may comprise a pressure regulating device 352 such as a valve or orifice in order to allow operation of the coolant within the cooling element 230 at a pressure that is the same, above or below that of the gasifier. Similarly, the coolant outlet conduit 346 may comprise a flow regulating device 350 such as a valve in order to allow operation of the coolant within the cooling element 230 to be at a desired flow rate. The cooling element 230 may comprise a single loop wherein the coolant flows in series from the coolant source 340 to the coolant sink 342, or the cooling element 230 may comprise multiple loops that connect to the coolant source and coolant sink via a manifold wherein the coolant flows in parallel. The coolant may comprise any suitable heat transfer fluid such as water.

The temperature of the gasifier is normally maintained at high temperatures even when it is not producing syngas. However, periodically the gasifier temperature may be cycled up and down between high temperature and ambient temperature to conserve fuel or for maintenance purposes. Under typical conditions, the heating curve and cooling curve as a function of time are steep as the operator wishes to maximize the amount of time the gasifier is at the normal operating temperature, constrained mainly by the thermal expansion and contraction of the refractory. However, when starting up the gasifier after replacing refractory material such as the insulating floor refractory 212 or the throat outer refractory 214, a slower heating curve allows moisture in the refractory to be driven out slowly in a dryout mode. Rapid vaporization of liquid water within the refractory can damage the material due to the large volumetric expansion of the resulting steam. In order to maintain the heating curve at a safe rate, during the dryout mode of operation the coolant may be kept between a dryout mode coolant lower temperature limit and a dryout mode coolant upper temperature limit for an extended period of time. In at least some embodiments the dryout mode the coolant lower temperature limit is defined relative to the refractory temperature, for example less than or equal to 5° C. below the refractory temperature. In at least some embodiments the dryout mode coolant upper temperature limit is defined relative to the refractory temperature, for example less than or equal to 5° C. above the refractory temperature. One advantage to maintaining the coolant temperature near the refractory temperature during dryout is to better control the rates of moisture removal from within the refractory during dryout. Another advantage is to minimize the strain from thermal expansion of dissimilar materials in the refractory and coolant conduits.

During the dryout mode of operation the coolant may be operated at a pressure sufficient to ensure the coolant is maintained in the liquid phase. One means to control the pressure is to maintain the pressure at a constant level greater than the saturation pressure of the coolant at the maximum coolant temperature during all modes of gasifier operation. Another means to control the pressure is to gradually increase the pressure of the coolant as the temperature of the coolant increases, while always maintaining the pressure of the coolant above the saturation pressure of the coolant at the current coolant temperature. During the dryout mode of operation the coolant may comprise cooling water, process condensate, and/or boiler feed water.

The dryout mode of operation comes to an end when the temperature of the refractory reaches a final dryout refractory temperature and is held there for a prescribed period of time also referred to as a holding time. In at least some embodiments the final dryout refractory temperature may be about 100° C. (the boiling point of water at ambient pressure) and the holding time may range from 12 to 24 hours. At this point the cooling system enters a heating mode in which the refractory temperature is increased from the dryout refractory temperature to the light off temperature of the gasifier. In at least some embodiments the light off temperature of the gasifier ranges from 950 to 1400° C.

During the heating mode the coolant temperature may be kept between a heating mode coolant lower temperature limit and a heating mode coolant upper temperature limit. As in the case of the dryout mode, the heating mode coolant lower temperature limit may be defined relative to the refractory temperature, for example less than or equal to 5° C. below the refractory temperature, and/or the heating mode coolant upper temperature limit may be defined relative to the refractory temperature, for example less than or equal to 5° C. above the refractory temperature.

As the temperature of the refractory approaches the liquid stability limit of the coolant, cooling system transitions from the heating mode to a normal operating mode. While the cooling system is in the normal operating mode, the gasifier may be in any number of modes including swapping from preheat burner to feed injector, starting up, producing syngas, entering shutdown, entering standby, performing heat maintenance, or swapping from feed injector to preheat burner. During the normal operating mode the coolant temperature may be kept between a normal operating mode coolant lower temperature limit and a normal operating mode coolant upper temperature limit. The normal operating mode coolant upper temperature limit may be defined as less than or equal to 5° C. below the liquid stability limit, or less than or equal to 10° C. below the liquid stability limit. The liquid stability limit of the coolant is defined as the temperature at which the coolant starts to boil or thermally decompose. When syngas is being produced, the normal operating mode coolant lower temperature limit may be defined as less than or equal to 5° C. above the dew point of the syngas, or less than or equal to 10° C. above the dew point of the syngas, or less than or equal to 25° C. above the dew point of the syngas, to prevent condensation.

When the gasifier must be cooled to ambient or near ambient temperatures, strain from thermal contraction may be minimized by maintaining the coolant temperature between a cooling mode lower temperature limit and a cooling mode upper temperature limit, similar to the heating mode. In at least some embodiments the cooling mode lower temperature limit may be defined relative to the refractory temperature, for example less than or equal to 5° C. below the refractory temperature, or less than or equal to 10° C. below the refractory temperature, or less than or equal to 25° C. below the refractory temperature, and the cooling mode coolant upper temperature limit may be defined relative to the refractory temperature, for example less than or equal to 5° C. above the refractory temperature, or less than or equal to 10° C. above the refractory temperature, or less than or equal to 25° C. above the refractory temperature, provided that it doesn't exceed the normal operating mode coolant upper temperature limit.

Typically liquid coolants are maintained at a constant temperature with varying flow rate to vary the cooling duty provided. Operating a gasifier with coolant temperatures tracking the refractory temperatures requires a redesign of the coolant control loop to allow changing the coolant temperature while either changing the flow rate of the coolant or keeping the flow rate of the coolant constant. This is possible in both open loop and closed loop cooling systems.

FIG. 4 shows a control scheme for a closed loop cooling system 400. In this example, makeup coolant 402, such as boiler feed water, is fed to a vessel 410 where it is pressurized with nitrogen 404. The flow rate of makeup coolant 402 is controlled by a level controller LC1 in the vessel 410 and the pressure of nitrogen in the vessel 410 is controlled by a pressure controller PC1 that sends an electrical signal to a valve on the nitrogen supply and/or a valve to vent 406. The vessel 410 may be equipped with a drain (not shown) to remove excess water if needed. A pump 420 delivers coolant from vessel 410 to line 422 where a temperature controller TC1 may control the temperature by feeding an electrical signal back to heater 430 in the vessel 410, such as during the drying and heating modes or when the coolant temperature in vessel 410 or line 422 is less than desired. However, most of the time, the coolant in line 422 will be hotter than desired due to heat removed from the refractory, such as refractory 116, through the cooling element 230. Thus, line 422 delivers the coolant to a cooler 440, for example an airfan cooler, to reject heat picked up by the coolant during operation of the cooling system. For example, when the gasifier is producing syngas under steady-state conditions, the cooler 440 may be used to reject heat picked up by the boiler feed water as it passes through the gasifier. The cooling duty required in the cooler 440 will increase when the gasifier is cooling down. The coolant is delivered to line 442, where a temperature controller TC2 may control the temperature by feeding an electrical signal back to cooler 440, for example via a speed controller SC1 on the airfan cooler. The coolant is delivered via line 442 to the cooling element 230 and exits the cooling element 230 via line 446. In at least some embodiments, the flow rate of the coolant through cooling element 230 will be fixed. In other embodiments the flow rate of the coolant through the cooling element 230 may be variable. For example, a temperature controller TC3 and flow controller FC1 may control the temperature and flow rate of the coolant in line 446 by TC3 sending an electrical signal to flow controller FC2 that manipulates a control valve 450 before returning the coolant water to the vessel 410, or by temperature controller TC3 directly manipulating control valve 450. In other embodiments, the flow rate and temperature of the coolant water in line 446 may be controlled by adjusting a speed of pump 420 and/or by adjusting the opening of a valve, such as valve 452.

FIG. 5A shows a control scheme for an open loop cooling system 500A to supply at least one of a hotter coolant 502, such as boiler feed water and a colder coolant 504, such as cooling water via line 512 to the cooling element 230. In at least some embodiments, such as the beginning of dryout mode, the coolant may be limited to cooling water. Just as in the closed loop example from FIG. 4, the temperature of the coolant in line 512 may be increased or decreased as required by the current mode of operation. In FIG. 5A the temperature may be controlled by changing the relative flow rates of the hotter coolant 502 and the colder coolant 504. In at least some embodiments the temperature of the coolant may be decreased using a cooler as in FIG. 4. The coolant temperature may be increased by heating the coolant by indirect heat exchange in heat exchanger 510 against a heat transfer fluid 506 such as steam. When the coolant is heated by steam, heated coolant leaves via line 512 and condensate 514 leaves the hot side of the heat exchanger 510. A temperature controller TC3 on line 512 may control the temperature of the coolant by sending an electrical signal back to the control valve 520 regulating the flow of the heat transfer fluid 506. The coolant is delivered to the cooling element 230 via line 512 and exits via line 546. A temperature controller TC4 on line 546 and/or flow controller FC4 on line 512 may be used to control the temperature and flow rate of the coolant by sending an electrical signal to manipulate a control valve 550 before returning the coolant to the condensate system 552 and/or a drain 554. For example, the drain 554 may be the preferred destination for the coolant when plant cooling water is the source of coolant, such as during at least a portion of the dryout mode. In at least some embodiments the flow controller FC4 may be placed on line 546 rather than line 512. In at least some embodiments the temperature controller TC4 may control the temperature and flow rate of the coolant in line 546 directly. In at least some embodiments, the flow rates of hotter coolant 502 and colder coolant 504 may be controlled using valves located upstream of exchanger 510. In at least some embodiments, the cooling system in FIG. 5A could eliminate the steam heating section comprising heat exchanger 510, valve 520, TC3 and condensate line 514.

FIG. 5B shows a modification of the control scheme in FIG. 5A in which the pressure of the hotter coolant 502 is controlled by a pressure controller PC4 on line 512 feeding an electrical signal back to a control valve 560.

For both open and closed loop cooling systems, multiple coolants may be used. In at least one embodiment, when the gasifier is operating process condensate is used as a coolant, switching to an alternate coolant such as boiler feed water when process condensate is not available. A person of skill in the art will appreciate that the flow rate of process condensate produced by the gasifier may in some cases exceed the flow rate of coolant required. When that occurs at least a portion of the process condensate may be bypassed around the open or closed cooling loop.

FIG. 6 shows a cross-section of a gasifier comprising a reactor section 600 and a quench section 650. The syngas and slag exit the gasifier throat 222 and contact a quench stream comprising water delivered by a quench ring 651 at the base of the gasifier throat 222. The syngas, slag and quench stream travels down a dip tube 653 and contacts a quench bath comprising water. The level of the quench bath is maintained above a low liquid level 655. The syngas and slag travel down through the quench bath past the outlet of the dip tube 653, where syngas separates from the slag and rises up through the annulus formed between the dip tube 653 and a draft tube 657. The syngas then exits via a quenched syngas exit port 659. Quench water may exit the quench section 650 via a water blowdown outlet 661. Slag may exit the quench section 650 via a slag outlet 663.

A quench heat exchanger 671 may be placed in fluid flow communication with the coolant inlet conduit 344 and in thermal contact with the quench bath. Allowing indirect heat exchange between the quench bath and the coolant in the quench heat exchanger provides several advantages. In the normal mode of operation the coolant in the cooling element 230 must be maintained in a narrow range of temperatures: below an upper limit typically set by either a coolant saturation temperature, a coolant thermal destruction limit, and/or the materials of construction and above a lower limit typically set by the syngas dew point. The quench bath provides thermal inertia to better control the coolant temperature in the cooling element 230, particularly to keep the coolant from falling below the lower limit when the gasifier is operating. To further control the coolant temperature, at least a portion of the coolant exiting the quench heat exchanger 671 may be divided and sent to an external heat exchanger (not shown) via an external heat exchanger conduit 673. The external heat exchanger may heat or cool the coolant as needed, with the coolant returning via an external heat exchanger return 675 in fluid flow communication with the coolant inlet conduit 344.

In at least some embodiments, the quench heat exchanger 671 is placed such that at least a portion of the heat exchange area is located above the outlet of the dip tube 653 and below the low liquid level 655. This ensures that the quench bath will be able to provide thermal inertia to the coolant during gasifier operation, while also minimizing the thermal contact between the quench heat exchanger 671 and the quench bath during gasifier downtime when the liquid level in the quench bath is much cooler and typically maintained at a level below the bottom of the dip tube 653.

FIG. 7 shows a cross section of a modification of FIG. 6 in which at least a portion of the quench heat exchanger 771 is integrated into a quench level stabilizer 780. The quench level stabilizer reduces the potential for level and flow instabilities in the quench bath, that might otherwise result in incomplete quenching of the syngas and excessive carryover of quench bath water downstream. In at least some embodiments the quench level stabilizer 780 forms a conical frustrum surface. The at least a portion of the quench heat exchanger 771 may be attached to a solid surface of the quench level stabilizer 780, and/or the at least a portion of the quench heat exchanger 771 may be welded to form a solid surface of the quench level stabilizer 780. The quench level stabilizer 780 may be connected to the wall of the quench section 650 by one or more support brackets 781. The quench level stabilizer may be positioned above, at, or below the low liquid level 655. In at least some embodiments the quench level stabilizer may be positioned above the low liquid level 655.

FIG. 8 shows a modification of FIG. 7 in which the quench heat exchanger 771 and the cooling element 230 are integrated with a process condensate system 800 downstream of the gasifier. At least a portion of a process condensate stream 802 formed by condensing water out of a downstream syngas stream is divided to form a process condensate coolant fraction 804 which enters the quench heat exchanger 771. A heated process condensate stream 806 exits the quench heat exchanger 771 and enters the cooling element 230, exiting as a hot process condensate stream 808 which is combined with a quenched syngas stream 812 exiting the gasifier. The quenched syngas stream 812 is further contacted with a nozzle scrubber water stream 814 in nozzle scrubber 820 before entering a syngas scrubber 830. In the syngas scrubber 830 the quenched syngas stream 812 is contacted with an aqueous stream comprising at least a portion of the process condensate 802 and/or a grey water stream 832 to produce a scrubbed syngas stream 834 with a reduced concentration of entrained solid particles. An aqueous stream 841 with an increased concentration of solid particles exits the syngas scrubber 830, is pumped in a quench pump 840, and enters the quench ring 651 as a quench water stream 842. At least a portion of the quench water stream 842 may be divided to form the nozzle scrubber water stream 814. At least a portion of the process condensate coolant fraction 804 may be bypassed around the quench heat exchanger 671 to form process condensate bypass 852 which may be combined with the quenched syngas stream 812. At least a portion of the heated process condensate stream 806 may be bypassed around the cooling element 230 to form heated process condensate bypass stream 854, which may be combined with the quenched syngas stream 812. In at least some embodiments, the quench cooler 771 may be omitted and the process condensate 804 may be supplied to the cooling element 230.

While the principles of the invention have been described above in connection with preferred embodiments, it is to be clearly understood that this description is made only by way of example and not as a limitation of the scope of the invention.

Claims

1. A gasifier for converting a carbonaceous feedstock to produce syngas comprising a cone section and a throat section;

wherein the throat section comprises a throat refractory material and a substantially cylindrical cooling element having an inner face and an outer face in a radial direction, and a top face and a bottom face in a vertical direction, wherein the inner, outer, top, and bottom faces define a cooling cavity; and

wherein the cooling element is in thermal contact with the throat refractory material on the inner face, the top face, and the outer face.

2. The gasifier of claim 1, comprising a coolant inlet conduit in fluid flow communication with the cooling element and a coolant outlet conduit in fluid flow communication with the cooling element;

wherein the coolant inlet conduit is in fluid flow communication with a coolant source external to the gasifier; and

wherein the coolant outlet conduit is in fluid flow communication with a coolant sink external to the gasifier.

3. The gasifier of claim 2, wherein the coolant inlet conduit and the coolant outlet conduit comprise a section oriented in the radial direction perpendicular to the centerline of the gasifier.

4. The gasifier of claim 1, wherein the throat refractory material comprises refractory bricks.

5. The gasifier of claim 1, wherein the throat section has an inside surface and an inner radius defined as the distance from the centerline of the gasifier to the inside surface of the throat section;

wherein the minimum value of the inner radius of the throat section is within 2% of the maximum value of the inner radius of the throat section.

6. The gasifier of claim 1, wherein the throat section has an inner radius that increases stepwise with increasing depth.

7. The gasifier of claim 1, further comprising a refractory support floor attached to the bottom face of the cooling element.

8. A method of operating a gasifier comprising:

indirectly transferring heat from a refractory material having a refractory temperature to a coolant having a coolant temperature and a liquid stability limit;

wherein the method comprises a dryout mode characterized by increasing the refractory temperature from ambient temperature to about 100° C. and a heating mode characterized by increasing the refractory temperature from about 100° C. to the liquid stability limit of the coolant;

wherein during the dryout mode the coolant temperature is maintained between a dryout mode lower temperature limit and a dryout mode upper temperature limit;

wherein during the heating mode the coolant temperature is maintained between a heating mode lower temperature limit and a heating mode upper temperature limit.

9. The method of claim 8, wherein the dryout mode lower temperature limit is less than or equal to 5° C. lower than the refractory temperature and wherein the dryout mode upper temperature limit is less than or equal to 5° C. greater than the refractory temperature.

10. The method of claim 8, wherein the heating mode lower temperature limit is less than or equal to 5° C. lower than the refractory temperature and wherein the heating mode upper temperature limit is less than or equal to 10° C. lower than the liquid stability limit of the coolant.

11. The method of claim 8, wherein the coolant has a coolant pressure; wherein the coolant pressure is kept constant at a value greater than the vapor pressure of the coolant at the liquid stability limit.

12. The method of claim 8, wherein the coolant has a coolant pressure; wherein the coolant pressure is maintained at a value greater than the vapor pressure of the coolant at the temperature of the coolant.

13. The method of claim 8, further comprising a cooling mode characterized by decreasing the refractory temperature from the operating temperature of the gasifier to a value equal to ambient temperature;

wherein during the cooling mode the coolant temperature is maintained between a cooling mode lower temperature limit and a cooling mode upper temperature limit.

14. The method of claim 13, wherein the cooling mode lower temperature limit is less than or equal to 5° C. lower than the refractory temperature and wherein the cooling mode upper temperature limit is less than or equal to the lesser of 10° C. lower than the liquid stability limit of the coolant and 5° C. greater than the refractory temperature.

15. The method of claim 8, wherein the coolant temperature is controlled by exchanging heat with a quench bath prior to indirectly transferring heat from the refractory material.

15. The method of claim 8, wherein the coolant temperature is controlled by heating with at least one of resistive heating, steam, and a heated heat transfer fluid prior to indirectly transferring heat from the refractory material.

16. A gasifier for converting a carbonaceous feedstock to produce syngas comprising a reactor section configured to react the carbonaceous feedstock with an oxidant to produce syngas, a quench section configured to contact the syngas with a quench bath, and a throat section configured to convey the syngas from the reactor section to the quench section:

wherein the throat section comprises a throat refractory material and a cooling element in thermal contact with the throat refractory material;

wherein the quench section comprises a dip tube having an inlet in fluid flow communication with the throat section and an outlet in fluid flow communication with the quench bath;

wherein the quench section further comprises a low liquid level located above the outlet of the dip tube;

wherein the quench bath has a level at or above the low liquid level;

wherein the quench section further comprises a quench heat exchanger in thermal contact with the quench bath;

wherein the cooling element comprises an inlet in fluid flow communication with the outlet of the quench heat exchanger; and

wherein at least a portion of the quench heat exchanger is located above the outlet of the dip tube and below the low liquid level.

17. The gasifier of claim 16 wherein at least a portion of the quench heat exchanger is configured to reduce level and flow instabilities in the quench bath.

18. The gasifier of claim 17, wherein the at least a portion of the quench heat exchanger configured to reduce level and flow instabilities in the quench bath forms a conical frustrum surface.