Patent Application
20110016788
The field of the invention relates generally to integrated gasification combined-cycle (IGCC) power generation systems, and more specifically to methods and systems for heat recovery in IGCC systems.
At least some known IGCC systems include a gasification system that is integrated with at least one power producing turbine system. For example, known gasifiers convert a mixture of fuel, air or oxygen, steam, limestone, and/or other additives into an output of partially combusted gas, sometimes referred to as “syngas.” The hot combustion gases are supplied to the combustor of a gas turbine engine, which powers a generator that supplies electrical power to a power grid. Exhaust from at least some known gas turbine engines is supplied to a heat recovery steam generator that generates steam for driving a steam turbine. Power generated by the steam turbine also drives an electrical generator that provides electrical power to the power grid.
In some known IGCC plants, hydro-carbonaceous feeds that include coal, petroleum coke and high-ash residual oils, are reacted with high purity oxygen (typically 95% oxygen purity) to produce syngas in a temperature range of 2200° F. to 2700° F. Most of the heat in this syngas is recovered as the syngas is channeled from a radiant syngas cooler (RSC) to a convective syngas cooler (CSC). Known radiant syngas coolers, wherein the primary heat transfer mechanism is by radiation, cool the syngas to a range of about 1000° F. to about 1300° F. and generate high pressure steam thereform. Known convective syngas coolers, where the primary heat transfer mechanism is by convection, generate high-pressure and some medium-pressure steam. Some known IGCC plants include a cooled connection line that couples the two syngas coolers to one another for use in generating medium-pressure steam.
However, some known IGCC plants have experienced a tendency for fouling with particulate matter at some hot surfaces, particularly in the region of the entrance to the CSC. In such IGCC plants, the presence of hot surfaces results in the particulate within the fuel gas impacting and adhering to the hot surfaces along the interiors of the connection lines.
In one aspect, a tube and shell heat exchanger for a gasification system is provided. The heat exchanger includes a first shell-side inlet positioned proximate to a heat exchanger inlet. The first shell-side inlet is configured to receive a first portion of a scrubbed syngas flow therethrough. This first scrubbed syngas portion facilitates substantially preventing fouling at the heat exchanger inlet. The heat exchanger also includes a second shell-side inlet positioned proximate to a heat exchanger outlet. The second shell-side inlet is configured to receive a second portion of a scrubbed syngas flow therethrough.
In another aspect, a gasification system is provided. The system includes a gasifier configured to produce a flow of syngas, a syngas cooler configured to receive said flow of syngas from said gasifier and reduce a temperature associated with said flow of syngas; and a tube and shell heat exchanger. The heat exchanger includes a first shell-side inlet positioned proximate to a heat exchanger inlet. The first shell-side inlet is configured to receive a first portion of a scrubbed syngas flow therethrough. This first scrubbed syngas portion facilitates substantially preventing fouling at the heat exchanger inlet. The heat exchanger also includes a second shell-side inlet positioned proximate to a heat exchanger outlet. The second shell-side inlet is configured to receive a second portion of a scrubbed syngas flow therethrough.
In yet another aspect, a method for operating a gasification system is provided. The method includes scrubbing a first stream of raw syngas to facilitate removing impurities therefrom, producing a stream of scrubbed syngas from the scrubbed first stream, transferring heat from a second stream of raw syngas to the stream of scrubbed syngas to produce a cooled raw syngas stream and a heated scrubbed syngas stream. The method also includes channeling at least a portion of the stream of scrubbed syngas to facilitate substantially preventing fouling from the first stream of raw syngas.
Various refinements exist of the features noted in relation to the above-mentioned aspects of the present invention. Further features may also be incorporated in the above-mentioned aspects of the present invention as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present invention may be incorporated into any of the above-described aspects of the present invention, alone or in any combination.
Non-limiting and non-exhaustive embodiments are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.
The oxygen flow from air separation unit 54 is channeled to gasifier 56 for use in generating partially combusted gases, referred to herein as “syngas” for use by gas turbine engine 10 as fuel, as is described in more detail herein. In some embodiments, at least some of the nitrogen process gas flow, a by-product of air separation unit 54, is vented to the atmosphere. Moreover, in other embodiments, some of the nitrogen process gas flow is injected into a combustion zone (not shown) within gas turbine engine combustor 14 to facilitate controlling emissions generated within engine 10, and more specifically to facilitate reducing the combustion temperature and nitrous oxide emissions from engine 10. In the exemplary embodiment, IGCC system 50 also includes a compressor 60 for compressing the nitrogen process gas flow before it is injected into the combustion zone.
Gasifier 56 converts a mixture of fuel, the oxygen supplied by air separation unit 54, and recycle solids, and/or liquid water and/or steam, and/or a slag additive into an output of syngas for use by gas turbine engine 10 as fuel. Although gasifier 56 may use any fuel, in some embodiments, gasifier 56 uses coal, petroleum coke, residual oil, oil emulsions, tar sands, and/or other similar fuels. In the exemplary embodiment, the syngas generated by gasifier 56 includes carbon dioxide. As such, in the exemplary embodiment, the syngas generated by gasifier 56 is cleaned in a clean-up device 62 before being channeled to gas turbine engine combustor 14 for combustion thereof. Carbon dioxide may be separated from the syngas during clean-up and, in the exemplary embodiment, the carbon dioxide is vented to the atmosphere. In the exemplary embodiment, a gasifier blowdown connection is coupled to a waste treatment system (not shown in
Power output from gas turbine engine 10 is used to drive a generator 64 that supplies electrical power to a power grid (not shown). Exhaust gases from gas turbine engine 10 are supplied to a heat recovery steam generator 66 that generates steam for use by steam turbine 58. Power generated by steam turbine 58 drives an electrical generator 68 that supplies electrical power to a power grid. In the exemplary embodiment, steam from heat recovery steam generator 66 is supplied to gasifier 56 for generating the syngas.
In the exemplary embodiment, IGCC system 50 includes a syngas condensate stripper 76 that receives condensate from a stream of syngas discharged from gasifier 56. The condensate typically includes a quantity of ammonia that is dissolved in the condensate. At least a portion of the dissolved ammonia is formed in gasifier 56 from a combination of nitrogen gas and hydrogen in gasifier 56. To remove the dissolved ammonia from the condensate the condensate is boiled. Stripped ammonia is discharged from stripper 76 and is channeled to a waste treatment system (not shown in
Upon exiting RSC 112, syngas is then channeled via a conduit 113 through a heat exchanger 114 where it is cooled and facilitates forming a raw syngas stream (not shown) at a temperature of about 350° F., but may range from about 350° F. to about 500° F. In the exemplary embodiment, heat exchanger 114 is a convective syngas cooler (CSC) used for transferring heat from the raw syngas exiting RSC 112 to a recycled scrubbed syngas stream, as described herein. More specifically, in the exemplary embodiment, heat exchanger 114 includes a tube and shell configuration, as described in more detail herein. The raw syngas stream is then channeled to a syngas scrubber 116 wherein any remaining particulate material (not shown) within the raw syngas stream is removed, forming a scrubbed syngas stream. More specifically, scrubbed syngas is formed when raw syngas from heat exchanger 114 has been contacted with a flow of water 118 in scrubber 116 to wet and remove any contained particulates. The scrubbing water is separated from the syngas, and the scrubbed syngas is channeled through a recycling conduit 120 into heat exchanger 114 to cool heat exchanger internal surfaces (not shown in
More specifically, and in the exemplary embodiment, heat exchanger 114 further facilitates heating the recycled, scrubbed syngas received from conduit 120 before the syngas is channeled combustor 14 of gas turbine engine 10 (shown in
Syngas exits heat exchanger 114 via conduit 122 and, in the exemplary embodiment, is channeled to a downstream cooling system 154 that recovers heat from the syngas and further increases the overall efficiency of the IGCC system 50. Syngas is channeled via conduit 150 to a first heat exchanger 156 having a tube and shell configuration. The syngas exits first heat exchanger 156 and is channeled via a conduit 158 to a sulfur removal system 160 that further cleans the syngas stream. Clean syngas exits sulfur removal system 160 and is channeled via a conduit 162 to the shell side of first heat exchanger 156 and is further heated therein by heat transferred from the syngas being channeled through the tube side of first heat exchanger 156. Clean syngas is then channeled from first heat exchanger 156 via conduit 164 to a combustion turbine 166 for use as a fuel source. In the exemplary embodiment, CO2 produced as a waste product within sulfur removal system 160 is via a conduit 168 to a shell side of a second heat exchanger 170, as described in more detail herein.
More specifically and in the exemplary embodiment, syngas exiting heat exchanger 114 is channeled via conduits 122 and 152 to second heat exchanger 170. More specifically, conduit 152 is coupled to a tube side 171 of second heat exchanger 170 and syngas is channeled therethrough. Waste CO2 is channeled through a shell side 173 of second heat exchanger 170 and heated therein, which further cools syngas being channeled through tube side 171. Waste CO2 exits shell side 173 of second heat exchanger 170 and is channel via conduit 108 to gasifier 102, as described in more detail herein. Syngas exiting tube side 171 of second heat exchanger 170 is channeled via a conduit 172 and mixes with syngas in conduit 158 at a junction 174.
In the exemplary embodiment, syngas exiting heat exchanger 114 is channeled via conduit 122 to a third heat exchanger 180. A temperature of syngas being channeled through a tube side 181 of third heat exchanger 180 produces a medium pressure steam 182 that may channeled via a conduit 184 to a steam turbine 186 for use in powering steam turbine 186. Syngas exiting tube side 181 of third heat exchanger 180 is channeled via a conduit 188 to join syngas being channeled within conduit 172 at a junction 190.
The remaining portion of the low temperature scrubbed syngas stream is then channeled via second flow conduit 224 to a shell side entrance on the tube-side outlet end 230 of heat exchanger 200. In the exemplary embodiment, about 90% of the scrubbed syngas flow is channeled to shell side entrance 230 of heat exchanger 200. Alternatively, about 75% to about 95% of the scrubbed syngas may be channeled to shell side entrance 230, dependent upon the amount of syngas channeled via first flow conduit 222 to the shell-side inlet on the hot gas end 226 as regulated by restriction orifice 228. In the exemplary embodiment, the syngas stream within second flow conduit 224 is channeled counter to the flow of hot syngas within the tube-side system 212. Such a flow maximizes the counter-current flow effect, resulting in a lower raw syngas outlet temperature, i.e. the scrubbed syngas exit temperature may be substantially higher than the hot syngas exit temperature. The hot scrubbed syngas exit nozzle positioned downstream at a location 233 where the flow pattern inside the tubes has become streamlined.
During operation, an interior surface 234 of an inlet area of heat exchanger 200 is particularly prone to fouling as particulate within the raw syngas stream impacts and adheres to interior surface 234 due to a turbulent flow pattern of the hot syngas flowing into heat exchanger 200. The insertion of a flow of relatively cooler scrubbed syngas, i.e., through heat exchanger hot gas end 226, cools the heat exchanger inlet tube surfaces substantially prevents the accumulation of particulate within heat exchanger inlet tube walls, and facilitates streamlining the syngas flow pattern immediately downstream from inlet area 236 so that particles no longer impinge against the tube wall surface.
The remaining portion of the low temperature scrubbed syngas stream is then channeled via second flow conduit 324 to a shell-side, cold-end entrance 330 of heat exchanger 300. Control valve 329 that is positioned along first flow conduit 324 regulates the flow of scrubbed syngas therethrough. In the exemplary embodiment, about 90% of the scrubbed syngas flow is channeled to shell side cold end entrance 330 of heat exchanger 300. Alternatively, about 75% to about 95% of the scrubbed syngas may be channeled along conduit 324 to shell-side entrance 330, dependent upon the amount of syngas channeled via first flow conduit 322 to hot gas end 326. In the exemplary embodiment, the syngas stream within second flow conduit 324 is channeled counter to the flow of hot syngas along path 316 within tube side system 312.
In the illustrated alternative embodiment, syngas that is channeled to hot gas end 326 traverses a plurality of baffles 340 within isolated entrance section 302 and exits heat exchanger 300 at an outlet 344. The syngas is then channeled via a conduit 346 to second flow conduit 324, wherein the flow within conduit 346 remixes with the syngas flow within second flow conduit 324 at a junction 348. Syngas channeled along path 316 exits heat exchanger at an outlet and is channel downstream therefrom via conduit 122. This arrangement allows the total scrubbed syngas stream to be in counter-current flow, increasing the possible temperature exchange.
During operation, depending on the amount of heating of the first portion of scrubbed syngas, it may be beneficial to feed this stream into a separate nozzle in the counter-current portion of the shell side of the exchanger. Optimally, the temperature on the shell side matches the temperature of the first portion after it has been preheated.
Described herein is a heat exchanger that may be utilized in IGCC plants that provides a highly efficient and reliable means facilitating lowering tube wall temperatures in the proximity of the heat exchanger inlet by recycling a quantity of scrubbed, cooled syngas. In each embodiment, the heat exchanger system diverts a small portion of the cooler, scrubbed syngas from the syngas cooler back to the heat exchanger inlet. Since the flow pattern in the hot syngas is turbulent and the interior surface of the inlet tube is prone to fouling, this action facilitates the prevention of particulate impingement of the heat exchanger inlet tube wall. Further, in each embodiment, the reheated clean syngas produced following this recycling leads to a direct reduction in the syngas rate required by the gas turbine. As a result, an increase in the overall efficiency of the IGCC plant is realized. Moreover, the heating of carbon dioxide prior to recycling to the gasifier increases the amount of carbon dioxide that can be recycled, thereby substantially reducing adverse cooling of the reactor effluent. This higher carbon dioxide recycle maximizes the beneficial effects on carbon conversion and cold gas efficiency. Accordingly, the beneficial effects on carbon conversion and cold syngas efficiency are maximized.
Although the foregoing description contains many specifics, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some of the presently preferred embodiments. Similarly, other embodiments of the invention may be devised which do not depart from the spirit or scope of the present invention. Features from different embodiments may be employed in combination. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions and modifications to the invention as disclosed herein which fall within the meaning and scope of the claims are to be embraced thereby.
Although the apparatus and methods described herein are described in the context of IGCC plant heat exchangers, it is understood that the apparatus and methods are not limited to such systems. Likewise, the system components illustrated are not limited to the specific embodiments described herein, but rather, system components can be utilized independently and separately from other components described herein.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
