Combined processes for utilizing synthesis gas with low CO2 emission and high energy output

Abstract

A process and system for producing liquid and gas fuels and other useful chemicals from carbon containing source materials comprises cool plasma gasification and/or pyrolysis of a source material to produce synthesis gas using the produced synthesis gas for the production of a hydrocarbon, methanol, ammonia, urea, and other products. The process and system are capable of sequestering carbon dioxide and reducing NOx and SOx.

Claims

1. A system for the production of a fuel from a carbon containing source material, said system comprising: a cool plasma gasifier configured for receiving a carbon-containing material and converting at least a portion of the source material into synthesis gas; a water gas shift reactor configured for receiving a feed of synthesis gas from the cool plasma gasifier and for converting at least a portion of CO in the synthesis gas into CO.sub.2; and a gas to fuel reactor configured for receiving synthesis gas from the water gas shift reactor and synthesizing a hydrocarbon and/or an alcohol from CO and H.sub.2 present in the synthesis gas wherein: said water gas shift reactor comprises a catalyst configured for catalyzing the conversion of CO into CO.sub.2 and said gas to fuel reactor comprises a catalyst configured for catalyzing the synthesis of the hydrocarbon and/or the alcohol, wherein the cool plasma gasifier is fluidically coupled to a combustor and is configured for receiving an exhaust from a combustion process.

2. The system according to claim 1, wherein the water gas shift reactor is fluidically coupled to a combustor and is configured for receiving an exhaust from a combustion process.

3. The system according to claim 1, wherein the catalyst in the water gas shift reactor and the catalyst in the gas to fuel reactor have the same composition.

4. The system according to claim 1, wherein the gas to fuel reactor and catalyst are configured for performing the net reaction nCO+2nH.sub.2.fwdarw.C.sub.nH.sub.(2n+2)+nH.sub.2O where n is an integer of from 1 to 30.

5. The system according to claim 1, wherein said gas to fuel reactor is configured to produce one or more C8 to C20 hydrocarbons.

6. The system according to claim 1, wherein the catalyst in the gas to fuel reactor comprises an alloy of Fe and Co or an alloy of Fe and Ru and a promoter selected from the group consisting of Pd, Pt, Cu, Rh, Ir, Ag, W, and combinations thereof.

7. The system according to claim 6, wherein Fe is present in the catalyst in an amount of from 20 to 80 weight percent and at least one of Co and Ru is present in the catalyst in an amount of from 20 to 80 weight percent and said promoter is present in the catalyst in an amount of from 0.01 to 10 weight percent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects, features and advantages of which embodiments of the invention are capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which

(2) FIG. 1 is schematic of a system and process for gasification of biomass using air as a gasification gas and

(3) FIG. 2 is schematic of a Gas to Fuel Process system and process for the production of diesel.

DETAILED DESCRIPTION OF THE INVENTION

(4) Specific embodiments of the invention are described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements.

(5) The following description focuses on an embodiment of the present invention applicable to a process and system for the synthesis of a hydrocarbon fuel and in particular to a process and system for the synthesis of diesel fuel, methane, and/or methanol. However, it will be appreciated that the invention is not limited to this application but may be applied to the synthesis of many other products including, for example jet fuel, gasoline, propane, butane, ammonia, urea, ethanol, and propanol.

(6) A first stage in one embodiment according to the invention comprises the production of synthesis gas from a carbon-containing material by gasification and/or pyrolysis. A process and system for the first stage of such an embodiment is shown in FIG. 1. This embodiment of the invention provides for energy recapture to provide usable energy as well as providing a gas that may be combusted or that contains large amounts of chemical energy.

(7) A feed of carbon-containing source material 101 is mixed with a feed of air, steam, and/or an oxygen-containing gas 102 in a mixer 103 and introduced into a gasifier 104. The gasifier 104 is configured to produce a feed comprising CO and H.sub.2 (syngas) 105. Examples of gasifiers that are suitable for commercial production of clean syngas according to the invention include cool plasma gasifiers and plasma gasifiers. The first stage of the process shown in FIG. 1 may comprise catalysts and other devices that produce syngas. Syngas contains H.sub.2 and CO and, depending on the source materials and reactions, may also contain on or more of CO.sub.2, H.sub.2O, N.sub.2, NOx, SOx, and CH.sub.4.

(8) Cool plasma gasification or pulsed plasma gasification effectively breaks down organic molecules into synthesis gas. Unlike gasifiers that rely solely on heat to provide molecular disassociation, temperature plays only a partial role in cool-plasma gasification. A plasma field is created in an oxygen-starved environment that generates a temperature of approximately 1,300 C. at the bottom end of the plasma arc spectrum. Biomass or organic waste is passed directly through the plasma field in such a way that both temperature and plasma dynamics combine to accomplish molecular disassociation. The plasma field is pulsed to create shock waves and molecular temperatures as high as 15,000 C. to 50,000 C., while the average temperature is maintained at 1300 C. The shock waves and high temperatures break down longer and complex molecular chains, resulting in the reduction of the raw feedstock into its elemental components. The relatively low average temperature allows an energy recovery of around 90%.

(9) Plasma gasification is used to break down waste materials that are infectious or in other ways pose an environmental hazard. High voltage, high current electricity is passed between two electrodes that are spaced apart, creating an electrical arc. Consequently, the process is more expensive and is associated with lower energy recovery (around 50%) than cool plasma gasification. Inert gas or gas with low oxygen content under pressure is passed through the arc into a sealed container of waste material. The temperature may be as high as 14,000 C. in the arc column, while the temperature a few feet from the torch can be as high as 2800 C.-5000 C. At these temperatures, most wastes are dissociated into elemental components in a gaseous form. The reactor operates at a slightly negative pressure, meaning that the feed system is complemented by a gas removal system, and also a solid removal system. In the case of plastic wastes, which tend to be high in hydrogen and carbon, gas from the plasma containment can be removed as syngas, and may be refined into various fuels at a later stage or used on site to provide power. Syngas is produced from organic materials with a conversion rate of greater than 99% using plasma gasification. Inorganic materials in the waste stream that are not broken down undergo a phase change (e.g. from solid to liquid) to form a slag. A portion of the syngas may be used to run an on-site turbine to power plasma torches and feed systems.

(10) Gasification of organic material according to the present invention is preferably performed with low levels of O.sub.2, i.e. O.sub.2 concentrations of the inlet gas in the range of 0.5%-15% O.sub.2 (v/v), but may also be performed by using exhaust gas, from a combustion process for example, with low levels of water and oxygen, by using water or steam, or by using pure oxygen at a level that will produce syngas. Any combination of the gases supra may be used. Gasification of the carbon-containing source material may be performed at a temperature in the range of 500 C.-5000 C., preferably within the range of 1000-5000 C., e.g. within the range of 500 C.-1000 C., 10001500 C., 1500 C.-2500 C., 2500 C.-3500 C., or 3500 C.-5000 C. The gasification pressure may range from 0.5 bar to 10 bar. The inclusion of, for example, exhaust gas containing CO.sub.2 and H.sub.2O in the feed increases the production of synthesis gas by the reaction C+CO.sub.2.fwdarw.2CO and C+H.sub.2O.fwdarw.CO+H.sub.2.

(11) The temperature of the syngas feed leaving the gasifier may be in the range of 100 C.-2000 C., depending on the conditions and starting materials selected. Examples of selected temperature ranges for the combustion products include 200 C.-1800 C., 300 C.-1500 C., 400 C.-1300 C., 500 C.-1250 C., 550 C.-1200 C., 600 C.-1100 C., 700 C.-1000 C. or any combination of these. If the temperature of the synthesis gas leaving the gasifier is high enough, a heat exchanger 106 may be used to generate electrical energy or supply heat for producing steam and to produce a cooled syngas feed 107. Water that may be present in cooled syngas feed 107 may be removed in separator 108 to separate condensed water 109 from syngas feed 110.

(12) Syngas feed 110, optionally preheated by optional heat exchanger 106, is mixed with steam 113 in mixer 112 to form a mixture of steam, H.sub.2, and CO 114, which enters a water gas shift reactor 115 where the steam and CO react to form CO.sub.2 and H.sub.2. This effectively alters the ratio of H.sub.2 to CO such that the ratio is raised, for example, to 2:1. The operation of the water gas shift reactor 115 may be controlled to produce a syngas feed having a desired H.sub.2:CO ratio which may range, for example, from 1:4 to 4:1. The final ratio may be selected based upon the fuel to be synthesized in the second stage of the process. The shift reaction may occur in a low temperature reactor or a high temperature reactor wherein CO reacts with steam over a suitable catalyst to produce CO.sub.2 and H.sub.2. Examples of suitable catalysts are iron oxide/chromium oxide and copper oxide/zinc oxide catalysts for low and high temperature reactors, respectively. The produced syngas, which now comprises H.sub.2 and CO in a desired ratio, e.g. 2:1, and CO.sub.2, provides a syngas feed 116 for a second stage of the process shown in FIG. 2. A heat exchanger 106 may be placed downstream of water gas shift reactor 115 to be used as the heat exchanger upstream of separator 108 and may also be used to maintain products of the reactor 115 at a desired temperature.

(13) It is also possible to configure a gasification system that produces a synthesis gas comprising H.sub.2, CO, and CO.sub.2 having a desired H.sub.2:CO ratio by proper selection of, for example, the carbon-containing material for gasification, the concentration of oxygen present during gasification, the amount of water present in the carbon-containing material and/or during gasification, to effectively combine the water gas shift reaction into the gasification process. In such embodiments, the water gas shift reactor may be dispensed with and the synthesis gas produced by gasification may be used to provide a synthesis gas feed stream 116 for a second stage of the process shown in FIG. 2.

(14) A system for performing a second stage of a process according to the invention is shown in FIG. 2. A syngas feed 116 is compressed by a compressor 117 before being conveyed into a gas to fuel reactor 118 where the syngas is converted to a fuel-containing feed stream 119. The embodiment shown comprises a two stage compressor 117 comprising two compressors 117a, 117b with an optional heat exchanger 117c located between the two compressors to remove heat and cool the syngas to a temperature of. The compressor however, need not be a two-stage compressor, which is used for the purpose of describing this specific embodiment of the invention. The gas to fuel reactor 118 is shown comprising two rector vessels 118a and 118b but other embodiments may comprise more of fewer reactors (reactor vessels) arranged in series and/or in parallel and performing the same of different chemical reactions. In the case of exothermic reactions taking place in the gas to fuel reactor, an optional heat exchanger 120, which may be integrated in the reactor 118, may be used to cool the fuel-containing feed stream 119 and provide heat for electrical energy production and plasma gasifier operation and/or heat for steam production.

(15) The embodiment shown in FIG. 2 may be configured, for example, for the production of gasoline, kerosene, and/or diesel by exothermic reactions. While embodiments for the production of diesel and other specified fuels are described herein, the invention is not intended to be limited to the specific embodiments described. In the embodiment shown, the cooled fuel-containing feed 119 may contain, in addition to diesel, methane, ethane, CO.sub.2, and unreacted syngas. The cooled fuel-containing feed stream 119 is conveyed to and expanded in turbine 121, optionally cooled in heat exchanger 122, and separated into liquid and gaseous components 124, 128 in separator 123. The gaseous components 128, including methane, ethane, CO.sub.2, and syngas are mixed with an air feed 102 in mixer 129 and conveyed to a power generator 130 where they are combusted to provide, for example, electrical energy and combustion products 131. The liquid components 124 may be conveyed to a distillation apparatus 125 where diesel, water, and other liquid components are separated to produce diesel and water outlet streams 126, 127.

(16) The diesel synthesis reaction performed in the gas to fuel reactor 118 preferably uses a gas composition comprising a H.sub.2/CO ratio of about 2. The primary reaction for the formation of diesel from synthesis gas is:
nCO+2nH.sub.2.fwdarw.C.sub.nH.sub.(2n+2)+nH.sub.2O
where n has a value of 14-20. During CO hydrogenation, other products may be formed, such as higher alcohols and hydrocarbons. The selectivity of known catalysts for the reaction is over 80%. Diesel synthesis is performed at pressures above 25 bar at temperatures normally not exceeding 570K. The ratio of H.sub.2 may be controlled by the water gas shift reactor 115. Additionally or alternatively, the ratio of H.sub.2/CO may be adjusted by providing an additional hydrogen-rich feed from a source of hydrogen production.

(17) In some embodiments, the catalyst in the gas to fuel reactor 118 comprises Fe metal alloyed with Co metal and/or Ru metal coated on a support and comprising an amount of a promoter selected from the group of Pd, Pt, Cu, Rh, Ir, Ag, W, and combinations thereof. The weight percent of Fe, Co, and or Ru present in the catalyst is 20-80%. The weight percent of promoter in the catalyst may range from 0.01%-10% or preferably 0.01% to 1.0%. The use of such catalysts unexpectedly narrows the distribution of produced alkanes/paraffins in a temperature, pressure and residence time dependent manner. This allows a greater control of products formed from synthesis gas in the gas to fuel reactor with respect to existing processes, systems, and catalysts.

(18) The same catalyst may be, but need not be, used in both the water gas shift reactor 115 and the gas to fuel reactor 118. It is also possible to perform the water gas shift reaction and the gas to fuel reaction simultaneously in a single reactor.

(19) In addition to diesel, synthesis gas may be converted to a wide range of hydrocarbons and/or alcohols in gas to fuel reactor 118 through one or more F-T process reactions:
Alkanes: nCO+(2n+1)H.sub.2.fwdarw.C.sub.nH.sub.2n+2n+H.sub.2O
Alkenes: nCO+2nH.sub.2.fwdarw.C.sub.2H.sub.2n+nH.sub.2O
Water-gas shift: CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2
Alcohols*: nCO+2nH.sub.2.fwdarw.H(CH.sub.2).sub.nOH+(n1)H.sub.2O
Bouoduard reaction*: 2CO.fwdarw.C+CO.sub.2 * side reactions

(20) One characteristic of F-T reactions is that they are highly exothermic. For example, the formation of 1 mol of CH.sub.2 is accompanied by a release of 165 kJ/mol of heat. Efficient removal of the heat of reaction is a consideration in the selection/design of suitable Fischer-Tropsch reactors. For example, fixed-bed and slurry reactors operate at relatively low temperatures, up to about 530 K and up to about 570 K, respectively, resulting in a selectivity towards heavy products (waxes), which may be cracked to produce lighter products. A low H.sub.2/CO ratio in the slurry reactor results in a relatively high selectivity towards liquid products. The riser reactor operates at higher temperatures, usually above 570 K, and produces gasoline as a major product as well as light products such as methane. Any of these reactors may be included alone or in combination in the gas to fuel reactor 118.

(21) The reaction performed in reactor 118 may also be a methanation reaction performed in the presence of Ni/NiO, Ru, Cu, Pt, Rh, Ag, Co, and/or W catalyst in the temperature range of 150 C. to 600 C. and pressures of from 1 bar to 50 bar. CO and CO.sub.2 react with H.sub.2 to form methane and water according to Methanation Reactions 2 and 3 in Table 1. The catalyst may also suppress the reverse shift reaction 4. The methane produced may be used as a fuel or as a raw material for the production of methane, diesel, ammonia, urea, nitric acid, ammonium nitrate, NPK, and PVC, for example. Reactors for these syntheses may be coupled to a fuel outlet 126 (FIG. 2) in an embodiment producing methane. The H.sub.2 and CO produced may also be used as raw materials for other uses and processes.

(22) The processes according to the present invention may be performed within a reactor for providing ways of controlling the physical and chemical parameters involved in the reaction equations shown in Table 1.

(23) TABLE-US-00001 TABLE 1 CO + H.sub.2O .fwdarw. CO.sub.2 + H.sub.2 Shift reaction 1 CO + 3H.sub.2 .fwdarw. CH.sub.4 + H.sub.2O Methanation reaction 2 CO.sub.2 + 4H.sub.2 .fwdarw. CH.sub.4 + 2H.sub.2O Methanation reaction 3 CO.sub.2 + H.sub.2 .fwdarw. CO + H.sub.2O Reverse shift reaction 4 C + H.sub.2O .fwdarw. H.sub.2 + CO Gasification reaction 5* C.sub.xH.sub.y + (x + y/4)O.sub.2 .fwdarw. xCO.sub.2 + (y/2)H.sub.2O Combustion reaction 6 nCO + 2nH.sub.2 .fwdarw. C.sub.nH.sub.(2n+2) + nH.sub.2O Diesel reaction 7 *C is any organic substance like, but not limited, to biomass or organic waste.

(24) Ratios of reactants in the gas to fuel rector(s) 118 may be controlled by providing addition streams of reagents and/or by way of one or more reactor vessels included in the gas to fuel reactor 118. For example, a reactor producing H.sub.2 and CO according to reaction 5 may provide H.sub.2 to a reaction vessel that is provided with additional H.sub.2, directly or indirectly, from a reaction vessel producing H.sub.2 in which reaction 1 takes place. Produced H.sub.2 may also be reacted with CO and CO.sub.2 in a single or in separate reaction vessels according to reaction 2 and 3 to produce methane. The reactions and reaction vessels in the gas to fuel reactor may be configured according to the product(s) to be synthesized using reactions 1-7 in Table 1 without relying on energy consuming processes for producing H.sub.2 such as water splitting.

(25) The system and process may comprise more than one gasifier 104, for example arranged in parallel, using different carbon source materials and or different oxygen concentrations to produce streams of syngas comprising different CO:H.sub.2 ratios. The different streams of syngas may be blended in a controlled manner before being fed into, for example, gas to fuel reactor(s) 118.

(26) Reacting CO and/or CO.sub.2 with H.sub.2 to produce methane may be performed in a single reactor with a catalyst. The heat developed may be used for gasification, steam production, and/or generating electricity. The shape of the catalyst is not critical and may inter alia comprise coated monoliths, nano materials, and/or other types and forms of carriers. The carriers may be selected from e.g. TiO.sub.2, Al.sub.2O.sub.3, cordierite, and Gd-doped CeO. The catalytic material may also be present in any form as a pure catalyst material. The form and composition of the reactor and the catalyst depends on the source of CO and/or CO.sub.2. If the source is an impure exhaust gas with large amounts of dust (e.g. from the combustion of coal) a monolithic catalyst carrier may be used, whereas a catalyst in the form of pellets may be used with a pure exhaust gas (e.g. from a natural gas turbine). All types of exhaust gases from all types of combustions of organic material may be used as a source material for the second stage gas to fuel reactor 118 (FIG. 2) to produce methane. Examples of usable catalysts include Ni/NiO, Ru, Cu, Pt, Rh, Ag, Co, and W and/or oxides of the described elements catalysts and combinations thereof.

(27) In some embodiments of the invention it is possible to produce nitrogen containing compounds such as ammonia and urea using known chemical syntheses. For example, H.sub.2 may be separated from CO and/or CO.sub.2 produced by gasifier 104 and reacted with oxygen depleted air or nitrogen in an exhaust gas:
N.sub.2+3H.sub.2.fwdarw.2NH.sub.3

(28) The present invention is also useful for the sequestration of CO.sub.2 produced by the burning of fossil fuels. During gasification in gasifier 104 (FIG. 1) CO.sub.2 may react with carbon in the carbon-containing source material to form CO, which is ultimately used in the gas to fuel reactor 118 to produce diesel fuel, for example. CO.sub.2 produced by fossil fuel combustion may alternatively or additionally enter the process/system in stream 102 (FIG. 1) with or without addition of air and/or oxygen and/or steam. For example, in one embodiment of the invention, a fossil fuel is combusted with air in a burner or combustor and electricity is produced from the combustion process in a conventional manner. The exhaust, containing H.sub.2O and CO.sub.2, is cooled to condense and remove H.sub.2O. An ordinary concentration of CO.sub.2 in the combustion gas is about 1-20% by volume. CO.sub.2 from the exhaust is used as a feed in addition to feed 116 into reactor 118 for methane production according to reaction 3 or reactions 2 and 3 in Table 1. The methane produced is recirculated while the hydrogen and CO produced by the gasification is used for producing methanol.

(29) The combustion/gasification of organic waste, biomass, biological waste, and fossil fuels often produces nitrogen-containing gases such as NOx, which may treated by selective non-catalytic reduction, selective catalytic reduction, and other NOx-reducing apparatus known to the skilled artisan. NOx and SOx may also be present in a gasification or pyrolysis exhaust gas. An advantage of the present process is that these pollutants can be reduced to elemental nitrogen and sulfur in the gas to fuel reactor(s) 118 and thereby reduce air pollution compared to existing processes. Reduction of NOx and SOx may be achieved by one or more of the following reactions with synthesis gas:
NO.sub.2+2H.sub.2.fwdarw.N.sub.2+2H.sub.2O
NO.sub.2+CO.fwdarw.N.sub.2+2CO.sub.2
NO+H.sub.2.fwdarw.N.sub.2+H.sub.2O
NO+CO.fwdarw.N.sub.2+CO.sub.2

(30) Sulfur present in an exhaust stream from the combustion of high sulfur coal, sulfur containing biomass, or sulfur containing municipal waste may be reduced by reaction with carbon in a gasifier 104 or additional gasifier according to the reaction
SO.sub.2+2C.fwdarw.S+2CO
with the resulting CO optionally being fed into stream 116 for use in the gas to fuel reactor 118.