Patent Application
20100266460
This invention relates generally to discharge from fluidized bed combustion or gasification systems. Specifically, the invention relates to the cooling and depressurization of coarse solid particles from high pressure and high temperature fluidized bed combustion or gasification systems.
Operating a pressurized reactor such as a fluidized bed coal gasifier or combustor involves discharging coarse solid particles under high pressure and temperatures to storage bins under atmospheric pressure and low temperature (i.e., below 350° F.). The most commonly used method in such systems is a combination of a lock vessel and a screw cooler system. The screw cooler receives solids under high pressure and temperature and cools the solids by contacting them with the screw and the inner surface of the container.
In this system, the lock vessel is a pressure swing vessel and has inlet and outlet valves. The lock vessel receives the cooled solids under pressure from the screw cooler through a normally open inlet valve. When the predetermined amount of solids enters the lock vessel, the inlet valve is closed. Then, the vessel is depressurized to almost atmospheric pressure. The bottom discharge valve is then opened to discharge the solids to an atmospheric vessel. The solids in the atmospheric vessel can be disposed to proper storage vessels.
There are disadvantages to this system. One inherent disadvantage of this system is the number of moving parts which need to cycle often and operate in a synchronous manner. A second disadvantage is the difficulty in sealing the two ends of the shaft of the screw when the shaft is rotating under high pressure. Additionally, there are a number of valves around the lock vessel, and the reliability of these valves can be less than desired because during each cycle, the valves must open and close in dusty environment. In normal operating conditions, the valves open and close millions of times under high pressure with a rapid flow of solid particles, thereby eroding the valves. Thus, conventional commercially available systems can have availabilities on average of less than 70%.
What is needed then is a system for cooling and continuously depressurizing the coarse solid particles without the inherent issues mentioned above.
The invention relates to a depressurization system in fluid communication with a high pressure, high temperature dense phase solids stream with entrained gas, such as, for example and without limitation, a coarser ash stream from a fluidized bed gasification system. In one aspect, the system comprises an apparatus for cooling the high pressure, high temperature dense phase solids stream with entrained gas and a pressure letdown device (i.e., a separator) for separating the cooled coarse solid particles from a portion of the entrained gas in order to reduce the stream pressure to a desired exit discharge pressure.
In one aspect, the pressure letdown device has a housing defining an interior separator cavity and having a housing wall and a filter within the interior separator cavity. In another aspect, the filter has an inner wall and a spaced outer wall, the outer wall being spaced therefrom the housing wall and defining an enclosed annulus between the filter and the housing wall. In this aspect, the inner wall defines a filter conduit in fluid communication with the high pressure, lower temperature solids stream with entrained gas. The filter is configured to allow at least a portion of the cooled coarse solid particles to pass therethrough the filter conduit and exit via a solids outlet positioned adjacent a distal end of the filter conduit, while at least a portion of the entrained gas is directed to the gas outlet, which results in a lower pressure outlet for the cooled coarse solid particles.
In one aspect, the depressurization system further comprises a moving packed bed of a solids stream entrained with gas in a horizontal or vertical column in which the gas is flowing faster than the solids to induce pressure reduction. Friction between the coarse particles and an inner wall of the column, and the speed of the gas in the column can substantially reduce the amount of gas to be separated from the solids in the pressure letdown device. In another aspect, the horizontal or vertical column can also be configured as a heat exchanger to provide at least a portion of the cooling to lower the temperature of the high pressure, high temperature dense phase solids stream with entrained gas.
In another aspect, no moving parts, such as for example and without limitation, a valve, are in the flow path of the solids stream, thereby improving the reliability of the depressurization system.
These and other features of the preferred embodiments of the invention will become more apparent in the detailed description in which reference is made to the appended drawings wherein:
The present invention can be understood more readily by reference to the following detailed description, examples, drawing, and claims, and their previous and following description. However, before the present devices, systems, and/or methods are disclosed and described, it is to be understood that this invention is not limited to the specific devices, systems, and/or methods disclosed unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.
The following description of the invention is provided as an enabling teaching of the invention in its best, currently known embodiment. To this end, those skilled in the relevant art will recognize and appreciate that many changes can be made to the various aspects of the invention described herein, while still obtaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits of the present invention can be obtained by selecting some of the features of the present invention without utilizing other features. Accordingly, those who work in the art will recognize that many modifications and adaptations to the present invention are possible and can even be desirable in certain circumstances and are a part of the present invention. Thus, the following description is provided as illustrative of the principles of the present invention and not in limitation thereof.
As used throughout, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a valve” can include two or more such valves unless the context indicates otherwise.
Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.
As used herein, the terms “optional” or “optionally” mean that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.
As used herein, the term “high pressure” means a pressure at about 30 psig or above.
As used herein, the term “high temperature” means a temperature at about 500 degrees Fahrenheit or above.
The term “fine particles” means particles having a mean diameter less than or equal to 40 microns or below. The term “coarse particles” refers to particles having a mean diameter greater than 40 microns.
The invention relates to a depressurization system 10 that is in fluid communication with a high pressure, high temperature dense phase solids stream having gas entrained therein by coarser particles. The system is for use, for example, in processes that have particulate matter that needs to be cooled and depressurized prior to further processing or disposal of the particulate matter. In one exemplary embodiment, the system is intended for use in gasification processes, because, for example, the discharge of solids directly from an operating system to an atmospheric storage unit is not desired.
In one aspect, as illustrated in
In another aspect, a vessel outlet 160 is defined therein the vessel 100 that is in fluid communication with a lower portion 170 of the vessel. In another aspect, a screen 180 can be positioned in the vessel cavity 114, substantially enveloping the vessel outlet 160. The screen 180 can be configured, according to one aspect, to block larger extraneous materials from passing through the vessel outlet and potentially blocking the passageways downstream. In one aspect, the screen defines a plurality of screen openings 182, as shown in
In one aspect, the screen 180 can be shaped to deflect particles having a dimension larger than the predetermined dimension toward the lower portion of the vessel 100. As one can appreciate, the lower portion 170 of the vessel can have appropriate periodic fluidization to sink larger extraneous materials and can be equipped with a particle outlet 190 that is configured to enable an operator to selectively remove the larger particles therefrom the vessel cavity 114 when the system is not in operation. Additionally, in one aspect, a portion of the screen can be spaced therefrom the vessel outlet defining a screen cavity 184 in communication with the vessel outlet 160. In another aspect, a top face 186 of the screen, as illustrated in
The depressurization system 10 can also comprise a cooling apparatus 400, as shown in
In one aspect, the cooling apparatus 400 can be installed vertically or horizontally. In another aspect, the elongate cooling conduit 410 can be used as part of the depressurization system 10 to reduce the pressure of the solids stream entrained with gas and to minimize the amount of gas to be vented out through a gas outlet 290 on the pressure letdown device. In this aspect, the elongate cooling conduit can reduce the pressure of the solids stream entrained with gas when positioned vertically, horizontally, or in any other direction, and with or without thermal communication with a coolant source. In another aspect, a moving packed bed column can be formed in the cooling apparatus (for example, inside the inner pipe 412), wherein depressurization occurs as the gas is flowing faster than the solids due to the gas release from the pressure letdown device 200, described more fully below. In one aspect, the higher the pressure of the high pressure, high temperature dense phase solids stream having gas entrained therein, the longer the cooling conduit 410 needs to be for a longer moving packed bed column to increase the pressure drop. In one exemplary aspect, the cooling conduit can be 10 feet long for a 70 micron mean size gasifier ash particle stream at 275 psig pressure; however, as can be appreciated, the length of the conduit can also depend upon the particle size and/or characteristics.
In one aspect, the depressurization system 10 also comprises a pressure letdown device 200 (i.e., a separator), illustrated in
In one aspect, the filter 230 comprises a plurality of granular particles with a narrow size distribution to be used as a filter media. In another aspect, the inner wall of the filter comprises a first plurality of pores 242 having a first pore diameter that can be greater than a mean diameter of the coarse solid particles. This first plurality of pores enables the gas, as well as some fine solid particles, to flow therethrough the inner wall 240 of the filter initially to form a cake therein the filter. In another aspect, the outer wall 250 of the filter comprises a second plurality of pores 252 having a second pore diameter that is less than the mean diameter of the plurality of granular particles that are used as filter media in the filter 230. As such, the gas entrained within the dense phase solids stream entrained with gas can pass therethrough, however, any solid particles can be prevented from passing through the granular filter media. In this aspect, the inner wall and the outer wall of the filter define an enclosed filtration cavity 280 within which is disposed the filter media as a bed of granules. In still another aspect, the maximum penetration depth of ash into the granular bed can be predetermined based on the size distribution of the solids stream that is being depressurized. In one aspect, a top portion and a bottom portion of the filter 230 comprise solid plates to enclose the filtration cavity and prevent the escape of gas therethrough.
During operation, in one aspect, after exiting the cooling apparatus, the gas from the high pressure, lower temperature dense phase solids stream entrained with gas 30 flows through the first plurality of pores 242, through the bed of granules, through the second plurality of pores, and collects in the annulus 260 between the outer wall of the filter and the housing wall. In another aspect, some dust from the coarse solid particles also flows through the first plurality or pores and form a surface cake layer on the granular bed, which can prevent the coarse solid particles from penetrating deep into the granular bed. Thus, the bed rarely needs to be cleaned by a reverse flow of gas.
In one aspect of the pressure letdown device 200, the first pore diameter can be in the range from about 40 to about 150 microns. In another aspect, the second pore diameter can be in the range from about 40 to about 150 microns. The granules in the granular bed, in one aspect, have a mean diameter that can be greater than the first and second pore diameters.
Once the gas collected in the annulus 260 of the pressure letdown device reaches a predetermined pressure level, the gas egresses therethrough the gas outlet 290, thereby lowering the pressure in the pressure letdown device. The cooled coarse solid particles continue through the filter conduit 270 and exit the pressure letdown device via a solids outlet 310 positioned adjacent a distal end 300 of the filter conduit 270 at a lower pressure. In one aspect, the gas outlet can comprise a pressure regulating valve 294, although other methods of controlling the release of the gas from the pressure letdown device are contemplated. In one aspect, when the rate of solids discharged from the pressure letdown device is defined and constant, the gas outlet 290 comprises a gas outlet orifice with a diameter that can be varied depending on the particle properties and the total solids flow rate inside the filter conduit 270. In this aspect, the gas outlet 290 can be sized such that a velocity of gas in the outlet can be in the range of 30 to 100 feet per second. In another aspect, where the solids discharge rate and/or the process pressure varies, the pressure within the pressure letdown device can be controlled with the pressure regulating valve.
Additionally, in another aspect, the depressurization system 10 can comprise a collector device 320, as illustrated in
As mentioned herein above, the depressurization system, in one aspect, is part of a larger gasification or other commercial process system and is designed to depressurize and lower the temperature of the coarse solids particles from the high pressure, high temperature dense phase solids stream having gas entrained therein.
In an exemplary aspect, the coarse solid particles have a mean diameter from about 40 microns to about 1500 microns. In another aspect, the coarse solid particles have a mean diameter from about 40 microns to about 100 microns.
It is contemplated that the depressurization system can operate over a wide range of temperatures and pressures. In one aspect, high pressure, high temperature dense phase solids stream having gas entrained therein 20 can ingress the interior vessel cavity 114 at a pressure in the range from about 30 psig to about 1500 psig. In another aspect, the flow rate of the coarse solid particles into the vessel 100 can range up to 50,000 lbs/hr. After the high pressure, high temperature dense phase solids stream having gas entrained therein travels through the depressurization system 10, the coarse solid particles can egress the solids outlet 310 at a pressure in the range from about 0 psig to about 50 psig. In another aspect, the pressure of the coarse solids particles as they egress the solids outlet can vary, depending on the desired discharge rate and/or the conveying distance to a solids storage silo or disposal location. In another aspect, the high pressure, high temperature dense phase solids stream having gas entrained therein can ingress the vessel 100 at a temperature in the range from about 200 degrees Fahrenheit to about 2000 degrees Fahrenheit. After traveling through the depressurization system, according to one aspect, the coarse solid particles egress the solids outlet at substantially the same temperature as the gas released from the pressure letdown device. In one aspect, this temperature can be in the range of 200 degrees Fahrenheit to 850 degrees Fahrenheit. In another aspect, when the egress temperature at the solids outlet of the coarse solids is higher, the pressure letdown device can comprise an expansion joint 280 coupled to a lower portion of the inner wall 240 which is in contact with the high pressure, lower temperature dense phase solids stream entrained with gas 30.
In one aspect, wherein the solids flow rate varies, the rate of egress of solid particles from the solids outlet can be controlled by adjusting the pressure at the gas outlet 290 with the pressure regulating valve 294, as previously discussed. The size of the solids discharge line at the solids outlet can also have an impact on the rate of egress of the coarse solid particles. In another aspect, it is also contemplated that there can be a plurality of solids outlets. In yet another aspect, a conveying gas can be introduced adjacent the solids outlet to assist in the egress of the coarse solid particles. Additionally, the solids outlet 310 can also comprise a large solids filter and/or a collection system to prevent oversized solids or extraneous materials from being discharged from the solids outlet possibly plugging the line.
Should a larger drop in pressure be necessary, it is contemplated that a plurality of pressure letdown devices can be cascaded together in series, each having an outlet capable of removing gas. In one aspect, for example, in a process with an operating pressure of 650 psig and a solids removal rate of 50,000 lbs/hr, there can be 4 pressure letdown devices in series, each about 5 feet long.
In a large pilot facility installation where the depressurization system 10 has been tested, the solids flow rate is in the range 0 to 10,000 lbs/hr and the particle diameter is in the range 1 to 6000 microns with mean particle size ranging from 70 to 700 microns. The solids inlet temperature at the vessel inlet 110 is in the range 1600 degrees Fahrenheit to 1800 degrees Fahrenheit and the solids inlet pressure is in the range 200 psig to 275 psig. The solids discharge pressure has been varied from 5 psig to 40 psig in order to vary the solids discharge rate from 0 lbs/hr to 1000 lbs/hr, as desired. The solids discharge temperature ranges from 100 degrees Fahrenheit to 350 degrees Fahrenheit.
The depressurization system 10 can be used to process coarse solid particles from industrial applications. The system has been tested with process pressures varying up to 500 psig input into the vessel 100 for over 5,000 hours. High temperature coarse ash from the facility's gasifier operating up to 275 psig is withdrawn to a buffer volume. Potential clinkers and any other large pieces of extraneous material are separated from the coarse ash through a screening process. The coarse ash then flows as a moving packed bed through a horizontal column of a cooling apparatus 400 for initial depressurization. This horizontal column also acts as a double pipe heat exchanger. After initial depressurization and cooling in the horizontal column, the ash flows through a pressure letdown device 200 for further depressurization. The depressurized coarse ash is further cooled in the collector device 320 and discharged to an ash silo through a conveying line 329. The system has been fully integrated with the gasification process and the solids level in the gasifier has been maintained within a narrow range by varying the discharge rates of coarse solids through the depressurization system 10. The depressurization system has been successfully operated with coarse materials derived from lignite, subbituminous coal and bituminous coal.
In one aspect, multiple trains of depressurization system can be coupled together. In another aspect, each train can have coarse ash handling capacity of 36,000 lbs/hr, ranging up to 50,000 lbs/hr. In this aspect, the depressurization system can be operated at pressures up to 650 psig and inlet temperature up to 1850 degrees Fahrenheit. The coarse ash can be cooled in a solids cooler and then depressurized through a horizontal column and multiple stages of a pressure letdown device before being discharged to an atmospheric ash silo for storage and disposal.
Although several embodiments of the invention have been disclosed in the foregoing specification, it is understood by those skilled in the art that many modifications and other embodiments of the invention will come to mind to which the invention pertains, having the benefit of the teaching presented in the foregoing description and associated drawings. It is thus understood that the invention is not limited to the specific embodiments disclosed hereinabove, and that many modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although specific terms are employed herein, as well as in the claims which follow, they are used only in a generic and descriptive sense, and not for the purposes of limiting the described invention, nor the claims which follow.
This invention was made with some government support under Cooperative Agreement Number DE-FC21-90MC25140 awarded by the United States Department of Energy. The United States government has certain rights in the invention.
