Patent Application
20160365591
The subject matter disclosed herein relates to a system for converting solid waste, such as municipal waste and conversion into electrical power using a polymer electrolyte membrane fuel cell.
Traditionally, municipal solid waste (MSW) was disposed of by dumping of the waste into the ocean, burning in incinerators or burying in landfills. Due to undesired environmental effects (e.g. release of methane into the atmosphere and contamination of ground water) of these practices, many jurisdictions have prohibited their expansion or implementation. In some parts of the world, gasification technologies have been used to eliminate municipal waste.
Gasification is a process that decomposes a solid material to generate a synthetic gas, sometimes colloquially referred to as syngas. This syngas typically includes carbon monoxide, hydrogen and carbon dioxide. The produced syngas may be burned to generate steam that drives large gas turbines (50 MW) to generate electricity. Several gasification technologies are used with municipal waste, including an up-draft gasifier, a down-draft gasifier, a fluidized bed reactor, an entrained flow gasifier and a plasma gasifier. All gasifiers utilize controlled amounts of oxygen to decompose the waste. One issue with current systems is that they use gas turbines to produce electrical power. Gas turbines typically require large amounts of waste and correspondingly large amounts of amounts of oxygen and have to be located close to areas where both the waste fuel and oxygen may be readily supplied in large volumes. Further, since steam is generated in the process, to maintain efficiencies the systems should be located in major industrial complexes where the steam can be used in process or district heating systems.
Polymer Electrolyte Membrane Fuel Cells (PEMFC) are electrochemical devices that use hydrogen as a fuel to generate electrical power. PEMFC systems are desirable because of their high conversion efficiency (˜60%) and ability to operate at relatively low temperatures (50-90 C). One challenge with PEMFC systems is the need for high purity hydrogen as a fuel. Due to the hydrogen purity requirements of the PEMFC, the hydrogen is typically acquired via steam reformation of natural gas or by water electrolysis. In the case of natural gas reformation, the gas stream is decomposed into hydrogen and carbon monoxide using a steam reformer having a catalytic heat exchanger. Subsequent processing is used to remove the carbon monoxide which will contaminate the catalyst used in PEMFC systems. A waste gas stream from the reformation process is burned to generate the thermal energy used in the catalytic heat exchanger. Unfortunately this arrangement does not transfer easily to the gasification of MSW as the solid material does not lend itself to integration with the catalytic heat exchanger. Further diluent compounds such as sulfur produced during gasification, will contaminate the heat exchanger catalyst.
Accordingly, while existing gasification to electrical power systems have been suitable for their intended purposes, the need for improvement remains; particularly in providing a system that can operate a PEMFC system using MSW as a an input fuel.
According to one aspect of the invention a system for a system for converting solid waste material to energy is provided. The system includes an input module having a low tar gasification generator configured to produce a first gas stream in response to an input stream of solid waste material, the first gas stream including hydrogen. A process module is fluidly coupled to receive the first gas stream. The process module includes a first heat exchanger operable to cool the first gas stream and at least one clean-up process module fluidly coupled to the first heat exchanger to receive the cooled first gas stream. The at least one clean-up process module is configured to remove at least one contaminant from the first gas stream and produce a second gas stream containing hydrogen and carbon monoxide. The process module further including a pressure swing absorption (PSA) device that receives the second gas stream and produces a retentate stream and a third gas stream comprised of substantially hydrogen. A polymer electrolyte membrane fuel cell is provided and configured to receive the third gas stream and generate electrical power based at least in part from the hydrogen in the third gas stream.
According to another aspect of the invention a method of producing electrical power from a solid waste stream. The method comprising the steps of: receiving the solid waste stream at a gasification generator; receiving an oxygen gas stream at the gasification generator; producing a first gas stream and residual materials using a gasifier; transferring the first gas stream to a first heat exchanger; decreasing the temperature of the first gas stream with the first heat exchanger; performing at least one clean-up process on the first gas stream to remove at least on contaminant; generating a second gas stream with the at least one clean-up process, the second gas stream including hydrogen and carbon monoxide; receiving the second gas stream at a pressure swing absorption (PSA) device; generating a retentate stream from the PSA device; generating a third gas stream from the PSA device; receiving the third gas stream with a polymer electrolyte membrane fuel cell (PEMFC) device; and generating electrical power with the PEMFC device based at least in part on receiving the third gas stream.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the disclosure, together with advantages and features, by way of example with reference to the drawings.
Embodiments of the invention provide advantages in the high efficiency generation of electrical power from solid waste, such as municipal waste. Embodiments of the invention provide advantages in the generation of electrical power with high efficiency using low tar gasification systems that supply hydrogen enhanced syngas suitable for use with a polymer electrolyte membrane fuel cell (PEMFC). Still further embodiments of the invention provide advantages in producing a gas stream from municipal solid waste having lower levels of diluents.
Referring now to
The syngas 28 is transferred from the gasifier module 26 to a process module 32. As will be discussed in more detail herein, the process module 32 modifies the syngas stream 28 to provide an output fuel stream 34 having enhanced hydrogen content with a purity level suitable for use a PEMFC system. To accomplish this, the process module 32 provides several functions, including the quenching of the syngas to reduce or avoid the formation of undesirable compounds (e.g. dioxins and furans), the removal of particulates and solids from the gas stream, and the removal of impurities or diluents such as sulfur, nitrogen, chlorine, carbon monoxide, and carbon dioxide. The process module 32 further conditions the output fuel stream to have the desired pressure, temperature and humidity so that it is suitable for downstream use.
The process module 32 may include a number of inputs, such as but not limited to water, oxygen and solvents such as amine based solvents (e.g. Monoethanolamine). The oxygen input may be used to absorb thermal energy from the syngas 28. Thus, the oxygen stream 36 has an elevated temperature (200 C) when it is transferred to the gasifier module 26. Since the oxygen temperature is increased, the efficiency of the gasification is increased as well. In one embodiment, a steam loop may be used as a heat transfer medium between the syngas and oxygen. Still further advantages may be gained where the thermal energy from the steam loop is used to heat the solid waste stream 22 to reduce the moisture content and improve the quality of the solid waste as a fuel for the gasification process. As will be discussed in more detail herein, the steam loop 77 (
The process module 32 further conditions the output fuel stream 34 to have the desired temperature so that it is suitable for downstream use. In one embodiment, the syngas stream 28 exits the gasifier module at a temperature of 700-1000 C. The absorption of thermal energy from the syngas 28 by the oxygen gas stream allows the process module to condition the syngas stream for use with clean-up processes that operate at lower temperatures. In some embodiments, these clean-up processes operate at temperatures in the range of 50-450 C. However, as is discussed in more detail herein, in an exemplary embodiment, the downstream process is a power module 38 having a PEMFC. Since PEMFC systems operate at reduced temperatures, such as 50-90 C for example, the process module 32 may further condition the temperature of the output fuel stream 34 to the desired temperature.
It should be appreciated that the synergistic use and transfer of thermal energy and heat transfer mediums between the modules 26, 32 provides advantages in increasing the efficiency and improving the performance of the system 20.
Turning now to
In one embodiment, the plasma gasifier 42 includes an inverted frusto-conical shaped housing 44. A plurality of plasma torches 46 are arranged near the bottom end of the housing 44. The plasma torches 46 receive a high-voltage current that creates a high temperature arc at a temperature of about 5,000 C. It should be appreciated that while
A plasma arc gasifier breaks the solid waste into elements such as hydrogen and simple compounds such as carbon monoxide by heating the solid waste to very high temperatures with the plasma torches 46 in an oxygen deprived environment. The gasified elements and compounds flow up through the housing 44 to an output port 45 that fluidly couples the housing 44 to the process module 32. The syngas stream 28 exits the gasifier module 26 at a temperature of about 1000 C. The residual materials 30, typically inorganic materials such as metals and glasses melt due to the temperature of the plasma and flow out of the housing 44 and are recovered.
In one embodiment, the plasma torches 46 include a shroud 47 that receives the recycled syngas stream 37. The shroud allows the recycled syngas stream 37 to flow over or about the plasma torches 46 prior to entering the gasification chamber. Due to the relatively low temperature of the recycled syngas gas stream 37, heat is transferred from the plasma torches 46 to the recycled syngas stream 37 and overheating of the plasma torches is avoided. It should be appreciated that this also provides advantages in increasing the temperature of the recycled syngas stream 37 closer to the operating temperature of the process within the housing 44 which improves operation and efficiency of the gasification process. It should further be appreciated that using the recycled syngas stream 37 as a shroud cooling flow provides advantages over using air in that fewer or no nitrogen diluents will be formed during the gasification process.
In one embodiment, the gasifier module 26 may include a heat transfer element 48 that transfers a portion of the thermal energy “q” from the heat transfer medium to the waste stream 22 prior to the waste stream 22 entering the plasma gasifier 42. The heat transfer element 48 may be coupled to receive the heat transfer medium from one or more points within the system 20. It should be appreciated that solid waste, such as municipal waste, may have a high moisture content and it may be desirable to lower this moisture content prior to gasification to improve efficiency. Thus the thermal energy q may be used to dry the solid waste stream 22. In one embodiment, the transfer of thermal energy may be selectively applied to the waste stream 22, such as in response to changing conditions in the solid waste for example.
It has further been found that plasma gasifiers provide advantages over other gasifier technologies since they generate very little tar (mixture of hydrocarbons and free carbon) due to the high temperatures used in operation.
Referring now to
The oxygen gas stream 52 absorbs thermal energy from the syngas stream 28 as it passes through the heat exchanger 50 to form an oxygen gas stream 36. In one embodiment, the heated oxygen stream 36 has a temperature of 200 C at a pressure of 10 atm (about 147 psi or 1 megapascal). It should be appreciated that heating the oxygen to the boiling phase change point allows for an increase in pressure without the use of a compressor. Providing the oxygen stream 36 with an elevated pressure level provides advantages in increasing the pressure level of the syngas stream 28. As will be discussed in more detail below, a pressurized syngas stream 28 provides further advantages in allowing certain cleaning processes to operate without the use of, or with a reduced amount of, secondary compression. It should be appreciated that mechanical compression of the syngas would be a parasitic load on the system 20 that would reduce the overall efficiency. In the exemplary embodiment, the system is configured to provide the oxygen gas stream 52 at a pressure sufficient to provide a syngas stream 28 at the output of the gasification module 26 at a pressure greater than about 140 psi (0.95 megapascal).
The cooled syngas stream 28 flows from the heat exchanger 50 to a first clean-up process module 54. In one embodiment, the first clean-up process module 54 is a scrubber that receives a solvent (typically water) input 56 and precipitates particulates, such as metals (including heavy metals) and dissolves chemicals, such as halides and alkali, from the syngas stream 28. The first clean-up process module 54 may further remove chlorine from the syngas stream 28. The precipitate stream 58 is captured and removed from the system 20.
In one embodiment, once the particulates and some diluent compounds are removed, the syngas stream 28 flows to an optional compressor 60 that elevates the pressure of the syngas for further processing. In a system with pressurization achieved by boiling of the liquid oxygen supply, the compressor only needs to drive a recirculation flow through the process and power generation modules. The compressor 60 increases the pressure of the syngas stream 28 to 147 psi (1 megapascals). The compressor 60 may include intercoolers that cause water within the syngas stream to condense from the gas. This condensate is captured and removed from the system via a condensate trap 62. It should be appreciated that since the syngas stream 28 enters the process module 32 at an elevated pressure due to the pressurization performed (and the energy used) by the compressor 60 is considerably less than a system where the syngas stream 28 starts at a lower or ambient pressure. It should be appreciated that for a system without a pressurized gas supply, about 22% of the gross electric output would be required to drive a compressor to elevate the syngas pressure from about 14.7 psi to 147 psi (0.101 megapascals to 1 megapascals).
In one embodiment, a retentate gas stream 64 is injected into the syngas stream 28 before compression. As will be discussed in more detail below, this retentate gas stream 64 may be received from a pressure swing absorber (PSA). In other words, the retentate gas stream 64 consists of CO, CO2 and water that was exhausted from the PSA during regeneration. It should be appreciated that advantages are gained by flowing the retentate gas stream 64 prior to compression as the compressor 60 will remove water product from the retentate gas stream and the absorber 66 will remove the CO2 to reduce accumulation of these and other diluents. Further, the energy from the remaining CO may be recovered by a water gas shift (WGS) process.
Once the syngas stream 28 has been compressed, the stream enters a second clean-up process module 66. In one embodiment, the second clean-up process module 66 is an amine based absorber that uses an input solvent 68 such as monoethanolamine (MEA) that absorbs and removes diluents such as carbon dioxide and sulfur (typically as H2S) from the gas stream. These diluents are captured and removed via a diluent stream 70.
After exiting the second clean-up process module 66, the processed syngas stream enters a PSA 67. A PSA is a device used to separate gas components from a mixed gas stream under pressure using an absorbent material. Typically, a PSA will be comprised of a plurality of vessels or “beds” containing a medium that is selected to absorb one or more of the gas components and removing these gas components from the gas stream. The PSA will have multiple vessels, with only some vessels being active for absorbing the gas components at any given time. When the absorbent material in the vessel has reached it absorptive capacity, the PSA switches the gas flow to an unused vessel. A slip stream of the gas is taken from the exit of the vessel currently being used and a small amount of the purified gas is diverted to flow back through the previously used vessel to regenerate the medium. During the regeneration process, the pressure in the vessel being regenerated is lowered allowing the medium to release the previously absorbed gas component and form a retentate gas stream 69.
In the exemplary embodiment, the processed syngas stream from the second clean-up process module 66 is processed by the PSA 67 to pass H2. As a result, a retentate gas stream 69 is formed from the regeneration of the PSA 67 medium. This retentate gas stream 69 includes CO, CO2 and water. The retentate gas stream 69 passes through a heat exchanger 71 to increase the temperature of the retentate gas stream to a temperature (e.g. 250-300 C) desirable for operation of a water gas shift process. Upon exiting the heat exchanger 71, a first portion of the retentate gas stream 69 is diverted to form the recycled syngas stream 37 while the remaining or second portion of the retentate gas stream flows to the water-gas-shift (WGS) module 76.
In a WGS reaction the syngas is exposed to a catalyst, such as iron oxide-chromium oxide or a copper-based catalyst for example. The water-gas shift module 76 reduces the carbon monoxide content of the syngas stream to less than or equal to 10 percent by converting it with water vapor to additional hydrogen and carbon dioxide. In one embodiment, the WGS module 76 includes multiple-stages that operate in the 150-450 C temperature range. Each of these stages may be exothermic and additional heat exchangers may be used to remove thermal energy between each stage. It should be appreciated that different catalysts may be used in different stages of the WGS module 76. Steam 77 may be injected into the syngas stream 28 to provide water vapor to enhance the water gas shift reactions occurring within the WGS module 76. In one embodiment, the steam 77 may be generated by flowing a stream of water 79 through the heat exchanger 50. The output gas stream 74 from the WGS module 76 flows through heat exchanger 71 to increase the temperature of retentate stream 69 and is then injected back into the syngas stream prior to the compressor 60.
The output fuel stream 34 exits from PSA 67 as nearly pure H2 having had the CO and other gas components substantially removed. With the CO gas component substantially removed, the output fuel stream 34 has sufficient purity to operate a PEMFC. In one embodiment, the purity of the H2 at the exit of the PSA 67 is 99.999%. The output fuel stream 34 is then transferred to the power module 38 (
Turning now to
Referring now to
The hydrogen gas electrochemically reacts at the anode electrode to produce protons and electrons, wherein the electrons flow from the anode through an electrically connected external load, and the protons migrate through the polymer membrane to the cathode. At the cathode, the protons and electrons react with oxygen to form water, which additionally includes any feed water that is dragged or carried through the membrane to the cathode. The electrical potential across the anode and the cathode can be exploited to provide power 24 to an external load.
More specifically, the output gas stream 34 enters the power module 38 and is received by the PEMFC system 78. To produce electrical power 24, the PEMFC system 78 receives an oxidant, such as air for example, as an input 80. The air passes through the cathode side of the cells in the PEMFC system 78 and cooperates with the hydrogen in output gas stream 34 to produce electrical power 24. The exhaust stream 84 (air and water) then exits the system.
It should be appreciated that embodiments of the invention provide advantages in allowing the gasification of solid waste to produce electrical power using a PEMFC system. Further embodiments provide for recycling a portion of the processed syngas to the gasifier. This recycled syngas stream may be used to cool plasma torches in the gasifier in place of air and reduce the introduction of nitrogen diluents into the generated syngas stream. Still further embodiments provide advantages in reducing the CO content of the syngas stream to produce a purified hydrogen fuel that is suitable for use with a PEMFC system.
The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, “about” can include a range of ±5%, or 2% of a given value.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
While the disclosure is provided in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments of the disclosure have been described, it is to be understood that the exemplary embodiment(s) may include only some of the described exemplary aspects. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14739285 | Jun 2015 | US |
| Child | 14830846 | US |
