Patent Application
20130072583
Disclosed are hydrocarbon compositions and a method of producing a hydrocarbon composition which can be used as such or as an intermediate for the production of various hydrocarbon products.
In a Fischer-Tropsch reactor (also hereinafter referred to as an FT reactor), hydrogen and carbon monoxide are reacted in the presence of a transition metal catalyst, such as cobalt or iron, to form a composition containing a broad range of linear alkanes. This hydrocarbon composition can be useful as an intermediate in the production of many products in the chemical and refining industry and business.
A number of carbonaceous sources can be used as raw-materials for producing a hydrogen and carbon monoxide containing gas (also known as a “syngas”) which can be fed into the FT process. Originally, coal was used as the primary raw-material, but lately also natural gas has been taken into use in commercial processes. Various processes can be used in which biological materials, such as plant oils, plant waxes and other plant products and plant parts or even oils and waxes of animal origin, are gasified and processed to produce a suitable feed. In a further alternative approach, for example, in the BTL process (biomass to liquid process), a biomass comprising whole plants can be used as a raw-material. The BTL process can allow for the utilization of forestry residues.
Gasification of biomass for producing a syngas can take place in the presence of oxygen. For fuel production by the FT process, an oxygen-containing gas, for example, oxygen gas, can be used for the gasification in order to attain reasonably high temperatures and to reduce the formation of nitrogenous by-product. An exemplary temperature in the gasification is about 750 to 1200° C. At these conditions, biomass, such as lignocellulosic materials, can produce a gas containing carbon monoxide, carbon dioxide, hydrogen and water gas. Further it can contain some hydrocarbons and impurities, such as sulphur, nitrogen compound and trace metals.
In case of gasification in the lower temperature range of about 750-950° C., the product of the gasification can contain some unreacted hydrocarbons. In order to convert all hydrocarbons to syngas components, the effluent of a gasifier can be fed into a reformer, either a thermal reformer or catalytic reformer, wherein the gas is subjected to further thermal reactions which give a syngas product mix containing less by-products.
The gaseous effluent of the reformer can be freed from carbon dioxide, water, sulphur and any other catalyst poisons before it is used as a syngas for a FT reaction. Furthermore, the hydrogen-to-carbon monoxide ratio can be increased. For example, whereas a gasifier produces a gas having a molar ratio of hydrogen to carbon monoxide of about 0.5 to 1.5, and reforming only marginally increases the ratio, it can be desirable in the Fischer-Tropsch reaction for the reactants to be present in a higher molar ratio of about 2:1. Therefore, it can be desirable to increase said ratio in the gas produced in a gasifier.
It can be possible to increase the ratio by subjecting the gas to a water gas shift (WGS) reaction, in which hydrogen is produced by the reacting carbon monoxide with water to produce carbon dioxide and hydrogen. However, this reaction can also increase the concentration of carbon dioxide by sacrificing some of the desired carbon monoxide. Before the FT reactor, it can be desirable to reduce the concentration of carbon dioxide to a level which is rather low, for example, below 3 mole-%. The amount of carbon dioxide removed from the syngas can therefore be significant, and it can correspond to about 50% of the total gasification capacity of the whole process. In other words, approximately half of the carbon content in the gas produced in the gasification of the biomass can be utilized for production of hydrocarbons by the FT process.
According to an exemplary aspect, a method of producing a hydrocarbon composition is provided, the method comprising: providing a biomass raw material; gasifying the raw material in the presence of oxygen to produce a gas containing carbon monoxide, carbon dioxide, hydrogen and hydrocarbons; separately increasing the hydrogen-to-carbon monoxide ratio of the gas to a value of about 2; feeding the gas to a Fischer-Tropsch reactor; converting in the Fischer-Tropsch reactor at least a part of the carbon monoxide and hydrogen contained in the gas into a hydrocarbon composition containing C4-C90 hydrocarbons; and recovering the hydrocarbon composition, wherein fresh hydrogen is introduced into the gas before the gas is fed into the Fischer-Tropsch reactor.
The disclosure will be examined more closely with the aid of a detailed description with reference to the attached drawings.
According to an exemplary aspect, at least a part of the problems related to the related art can be eliminated. Disclosed is a method of producing hydrocarbon compositions by gasification of biomass and Fischer-Tropsch processing of hydrogen and carbon monoxide.
According to an exemplary aspect, fresh hydrogen can be introduced into the gas produced by gasification of biomass before the gas is fed into the Fischer-Tropsch reactor. By using fresh (for example, externally produced) hydrogen for increasing the hydrogen to carbon monoxide ratio, the capacity of the process can be improved and the volumes of carbon dioxide exiting the process can be reduced.
Exemplary advantages can be obtained by employing exemplary aspects. For example, by using external hydrogen feed, the capacity (i.e., the production rate) of a biomass gasification process can be increased by at least about 40% (see, for example,
In addition to using external hydrogen to compensate for or replace hydrogen production by WGS, additional external hydrogen can be used to convert all or part of CO2 present in the synthesis gas to CO in a reverse WGS reactor. In an exemplary embodiment, CO2 is separated from synthesis gas and recycled to a reverse WGS reactor where CO2 is reacted with external hydrogen to produce CO and water. In an exemplary embodiment, the capacity of the process is increased at maximum by 160%. Both embodiments can naturally reduce investment costs by, for example, either eliminating any need for a separate Water Gas Shift reactor or greatly reducing the size of the equipment. The use of external hydrogen can enhance the chemical bounding of green carbon into the product instead of forming CO2 which is exhausted into atmosphere. This can decrease CO2 emissions of the whole process compared to a comparative FT process for the production of hydrocarbon from syngas obtained by gasification of biomass. The reduction of carbon dioxide emission can be, for example, on the order of 5 to 90%, for example, about 10 to 80% based on volume.
For example, at a fixed production rate of the FT reactor (“fixed capacity”), a reduction of gasifier capacity can be employed, for example, depending on the availability of biomass raw-material.
According to an exemplary embodiment, a method of producing hydrocarbon compositions by a Fischer-Tropsch reaction from a synthesis gas produced by gasification of biomass is provided. The hydrocarbon compositions can be suitable as raw-materials for various hydrocarbon compositions used in the chemical and petrochemical industry. They can be used, for example, as fuels or lubricants. An exemplary alternative is to use the hydrocarbons in the production of fuels for combustion engines or jet engines.
The hydrocarbon compositions can contain linear hydrocarbons having 4 to 90 carbon atoms. There can be some branched hydrocarbons in the product. For example, primarily the hydrocarbons are saturated (alkanes), although unsaturated compounds can be included in minor amount of less than 10 mol-%, for example, less than about 5 mol-%. Depending on the catalyst used, some oxygenated hydrocarbons can be formed as impurities in the FT reaction.
For example, in the first step of the process, an organic raw-material is gasified in the presence of oxygen to produce a gas containing carbon monoxide, carbon dioxide, hydrogen and hydrocarbons optionally together with inert components, and tarry compounds and some inorganic impurities, including metal particles. The organic raw-material or feedstock of the process can be a material composed of biological matter, for example, a matter of vegetable or animal origin. In the present context, the term “biomass” will be used for designating any such raw-material.
An exemplary feature of the feedstock materials of the present process is that they can contain carbon, for example, in excess of about 20%, for example, in excess of about 30%, for example, in excess of about 40% by dry matter. The biomass feedstock can be selected from annual or perennial plants and parts and residues thereof, such as wood, wood chips and particles (such as saw dust, etc.), forestry residues and thinnings; agricultural residues, such as straw, olive thinnings; energy crops, such as willow, energy hay, Miscanthus; and peat. It is also possible to use various waste materials, such as refuse derived fuel (RDF); wastes from sawmills, plywood, furniture and other mechanical forestry wastes; and waste slurries (including industrial and municipal wastes). Also microorganism residues and wastes can be available as biomass feedstock. In addition to said materials of vegetable origin, various animal products such as fats and waxes can be used.
The biomass can be gasified in a fluidized bed reactor or a circulating fluidized bed reactor (CFB) gasifier in the presence of oxygen at a temperature in the range of about 700 to 1200° C. For example, gasification can be carried out in medium-high temperature range of about 750 to 950° C. or 750 to 900° C. The circulating bed can be formed by a granular or particulate bed material, such as aluminosilicate (e.g., sand) or a similar inorganic material. CaO, which can be obtained by introducing Ca carbonate into the gasification reactor, can be used as a catalyst for the decomposition of tars in the gasification. The biomass can be in the form of particles, granules or chips or similar coarse or finely divided parts. According to an exemplary embodiment, the biomass can be used roughly as such as harvested. According to an exemplary embodiment, the biomass is milled or grinded to an average particle or granule size of less than about 50 mm, for example, less than about 40 mm, for example, about 25 to not more than 1 mm before gasification. The biomass can also be fed into the gasifier in the form of a liquid stream, for example, a liquid stream obtained by pyrolysis of biomass. Such pyrolysis products can include charcoal and tars.
In the case of solid biomass, it can be fed into the reactor with a moisture content of less than 30% by weight, for example, less than 25% by weight, for example about 5 to 20% by weight.
Gasification can be promoted by feeding steam, air or oxygen into the reactor, exemplary results being obtained with oxygen and oxygen in combination with steam.
Depending on the biomass and the temperature and on the concentration of oxygen, the “carbon conversion”, i.e., conversion of elemental carbon contained in the raw-material into light compounds, hydrocarbons and tar, can be higher than 70%, for example, higher than 75%, for example, in excess of 80% by weight of the carbon in the raw-material.
Based on the above, by gasification, a gas containing carbon monoxide, hydrogen and carbon dioxide as main components along with some water or steam can be produced. The gas can be recovered. It can be used in the Fischer-Tropsch process for producing hydrocarbons by reacting carbon monoxide with hydrogen in the presence of a catalyst for converting at least a significant part of the carbon monoxide and hydrogen contained in the gas into a hydrocarbon composition containing C4-C90 hydrocarbons.
According to an exemplary embodiment, the hydrocarbon composition thus obtained can be recovered and subjected to further processing for use, for example, as a fuel or lubricant for combustion engines, or even for jet engines. The fuel may be, for example, LPG (liquefied petroleum gas), gasoline, diesel or any jet fuel.
In case of waxes and similar hydrocarbons which are solid or semi-solid at ambient temperature, and also in case of any high-molecular weight hydrocarbons, for example, the FT hydrocarbon composition can be further processed by hydrogenation with hydrogen gas at an increased temperature in the presence of a catalyst in order to produce a hydrocarbon composition suitable as a diesel class hydrocarbon or as composition from which such a hydrocarbon can be produced. For example, hydrogenation with hydrogen gas can be performed at a temperature of about 220-270° C. in a fixed bed reactor. The catalyst can be a supported or unsupported metal catalyst, for example, nickel on carbon.
After the hydrogenation, for example, an isomerization step can be performed to produce paraffinic hydrocarbons and similar composition for use as fuels.
Hydrocarbon compositions suitable for fuel applications can have distillation cut points in the range of about 150 to 300° C., for example, 180 to 240° C. The carbon numbers of such compositions can be in the range of 10 to 25.
Lubricant compositions can be obtained from the FT product of the instant disclosure. For example, such compositions have carbon numbers in the range of 30 to 40.
In a gasification reactor, a product gas exhibiting a molar ratio of hydrogen to carbon monoxide of 0.5 to 1.5 can be produced. For example, gasification of a wood, annual plant or peat raw-material will upon gasification in the presence of oxygen gas yield a product gas in which the molar ratio of hydrogen to carbon monoxide is about 0.8 to 1.1. In practice, the molar ratio of hydrogen-to-carbon monoxide can be raised to about 2 before the FT reaction. For this reason, it can be desirable to employ a separate step in which the ratio is increased, said step being carried out at the latest immediately before the Fischer-Tropsch reaction.
In an exemplary embodiment, the molar ratio of hydrogen-to carbon monoxide is increased by introducing fresh hydrogen into the gas before the gas is fed into the Fischer-Tropsch reactor.
According to an exemplary embodiment, fresh hydrogen is introduced at a point immediately before the Fischer-Tropsch reactor in order to raise the hydrogen-to carbon monoxide ratio of the gas to about 2.
The fresh hydrogen can be derived from an external source of hydrogen. By the term “external source” is meant a source which is not an integral part of the other processing steps of the process. For example, hydrogen can be produced from the gasifier gas by a water gas shift reaction (WGS) in which some of the carbon monoxide is sacrificed for producing hydrogen by reducing water (steam) with carbon monoxide to liberate hydrogen from the water which oxidizing the carbon monoxide into carbon dioxide. This process step can increase the proportion of carbon dioxide which is withdrawn from the gas stream which eventually will be fed into the FT reactor. In an exemplary embodiment, at least a part of the hydrogen is obtained from a source other than a WGS reactor. As will be discussed more in detail below, in an exemplary embodiment, a WGS reactor can be totally eliminated, and in another exemplary embodiment, the desired hydrogen production capacity thereof can be greatly reduced.
For example, less than 20 mole-%, for example, less than 10 mole-%, for example, less than 5 mole-% of the carbon monoxide produced the biomass raw-material is used for producing hydrogen gas for use in the Fischer-Tropsch reactor.
For example, the external hydrogen fed (mol/h) in relation to the carbon dioxide from the gasifier (mol/h) can be as follows (
For example, an exemplary source of hydrogen is formed by natural gas, although other sources of light hydrocarbons, for example, methane, such as landfill gas, biogas, hydrogen produced by bioelectricity (i.e. electricity produced by use of renewable energy resources) and methane hydrate are also possible.
For example, any external hydrogen source which comprises hydrogen produced by electricity, for example, without emission of carbon dioxide and other greenhouse gases can be employed.
For example, during electrolytic production of hydrogen, considerable volumes of oxygen gas of high purity are obtained. This oxygen can be employed in the gasification of the biomass and in reformation of the gasification effluent.
Depending on the desired composition of the hydrogen feed gas, the source of methane and other light hydrocarbons can also be subjected to reformation optionally in combination with a shift reaction.
Natural gas can be a very clean source of methane. It can contain up to 98 vol-% methane or even more, the balance being formed by ethylene and C3 and C4 alkanes. As a feed for clean gas catalytic reformation (i.e., catalytic reformation substantially in the absence of catalyst poisons such as particles and sulphide and amine compounds), natural gas can be highly suitable.
An exemplary reactor set up can include at least one reformer and to at least one shift reactor, said reactor units being placed in the indicated order in a cascade.
In the reformer, reaction 1 can take place, and in the shift reactor, reaction 2 can take place:
CH4+H2OCO+3H2 (1)
CO+H2OCO2+H2 (2).
By the reforming and/or shift reactions, methane and other light hydrocarbons can therefore first be converted to hydrogen and carbon monoxide by reaction of methane with steam (reaction 1), and then more hydrogen can be produced from the carbon monoxide by reacting it with steam to yield carbon dioxide and hydrogen (reaction 2). Reformation can also be carried out in the presence of oxygen.
As will be evident, by merely subjecting the source of methane and other light hydrocarbons to reformation, a product mixture can be obtained having a hydrogen-to-carbon monoxide molar ratio of 3:1. This may be sufficient for raising the hydrogen-to-carbon monoxide ratio flow of the syngas produced by biomass gasification to a value in the range of 2. The product mixture of hydrogen and carbon monoxide can be useful also because, for example, the carbon monoxide is one of the components of the FT feed.
By subjecting the reformation effluent to a shift reaction, more hydrogen can be obtained along with carbon dioxide. Although the concentration of carbon dioxide in the FT feed can be restricted, a carbon dioxide can be used for producing carbon monoxide by a reversed shift reaction as disclosed herein. Therefore the effluent of a reaction cascade comprising a reforming unit and a shift unit can be fed into a reversed water gas shift reactor.
For example, the catalytic reformation for converting methane into hydrogen can be used for replacing a hydrogen unit, as explained in connection with the exemplary embodiment of
For example, a reformer can also be incorporated into the process either as a part of the reformation carried out for raw syngas or as a separate reformation of purified, i.e., clean syngas. The latter can be obtained by removing impurities, such as gaseous compounds selected from hydrosulphide (H2S), ammonia (NH3), hydrochloride (HCl), hydrogen cyanide (HCN) and particles all of which may act as catalyst poisons for the FT process.
In an exemplary embodiment, the external hydrogen is fed directly into a reformer or into a reversed water gas shift reactor or into both.
In an exemplary embodiment, the present disclosure comprises a combination of low- to moderate-temperature gasification (750 to 950° C.) followed by catalytic reforming of the raw syngas produced by the gasification. Such an embodiment may comprise the following steps: gasification of the raw-material in the presence of oxygen to produce a gas containing carbon monoxide, carbon dioxide, hydrogen and hydrocarbons possibly together with inert components, conducting the gas obtained by gasification of the raw-material into a reformer, reforming the gas in the presence of oxygen in order to increase the molar ratio of hydrogen to carbon monoxide in a gaseous effluent of the reformer to a value in the range of 0.5 to 1.5, withdrawing the gaseous effluent from an outlet of the reformer, and further increasing the hydrogen-to-carbon monoxide ratio of the gaseous effluent to a value of about 2 by introducing fresh hydrogen therein.
In an exemplary embodiment, gasification is carried out at a first temperature and reforming at a second temperature, which is higher than the first temperature. For example, the high-temperature reforming can be carried out at a temperature in excess of 1000° C., for example, about 1050-1250° C., for example, without a catalyst. Autothermal reformation, on the other hand, is a catalytic process, not thermal, and can be carried out at temperatures of 900-1300° C., for example, at 1200° C.
In an exemplary embodiment, reforming is carried out in the presence of a catalyst, at excess temperatures of about 500-900° C. This is possible since the temperature of the reformation can be kept lower or equal to the temperature of the gasification when catalytic reformation is used.
An exemplary embodiment comprises high-temperature gasification. For example, an exemplary embodiment comprises the steps of:
gasification of the raw-material in the presence of oxygen at a temperature in excess of 1000° C. to produce a gas containing carbon monoxide, carbon dioxide, hydrogen and hydrocarbons optionally together with inert components; and
further increasing the hydrogen-to-carbon monoxide ratio of the gas effluent to a value of about 2 by introducing fresh hydrogen into the gas.
In any of the above exemplary embodiments, carbon dioxide can be withdrawn from the gas before it is fed into the Fischer-Tropsch reactor. The carbon dioxide concentration of the syngas fed into a FT reactor can be 1 to 10%, for example, no higher than about 3%, as mentioned above. In an exemplary embodiment, instead of purging the carbon dioxide into the ambient, the carbon dioxide can be recovered.
Carbon dioxide can be withdrawn from the gas at any point from or downstream any gas treatment process arranged before the Fischer-Tropsch reactor. The gas treatment process can include, for example, a hydrolysation reactor, washing unit, unit for removing water and hydrogen sulphide and purging beds for other impurities, such as HCl and carbonylic compounds. Carbon dioxide can be recovered even from a high-temperature outlet stream of the gasifier or any reformer by, for example, a metal membrane (a hydrogen cell).
The temperature of the gas subjected to carbon dioxide removal in the above units (except for hydrolysation reactors) can be less than 100° C., for example, about 20 to 80° C.
The pressure of the gas effluent of the gasifier and any optional reformer can be about 1 to 20 bar (absolute pressure), for example, about 3 to 10 bar, and it can be raised about 30 bar before the FT reactor. In certain cases under pressure, s.o. pressure below air pressure (absolute pressure less than 1 bar) can be used.
There are various exemplary means available for separating and washing away of carbon dioxide from gas streams containing carbon dioxide. Carbon dioxide can be separated from the gas, for example, by membrane, by pressure swing absorption (PSA) or by washing with a liquid, for example, methanol or amine, capable of absorbing carbon dioxide.
An exemplary advantage of using a methanol or amine washing unit for recovering carbon dioxide is that the carbon dioxide thus separated from the gas flow is pure and can obviate any need for further purification, for example, unless the sulphur content is too high. In this case, absorber bed reactors can be used to decrease the sulphur content, for example, from a level of 100-200 ppb of sulphur to a level of 10-20 ppb. The carbon dioxide can be recycled completely or partially to a reverse WGS reactor (to be discussed in more detail below), or a part of it can be emitted to the ambient.
Methanol or amine washing units can be expensive and they can be in an exemplary embodiment replaced by at least one membrane unit or by at least one pressure swing absorption unit for partial or total removal or recovery of carbon dioxide.
There are various exemplary PSA masses which are selective for CO2, hydrogen and water. For example, molecular sieves for absorption of CO2 can include, for example, aluminosilicates and alkaline earth metals. For adsorbing water, various alumina compounds can be used (see, for example, U.S. Pat. No. 5,604,047). The feed gas of the PSA unit can contain hydrogen, carbon dioxide and carbon monoxide. A temperature and a pressure on the levels indicated above (for example, temperature of about 40° C. and pressure higher than 10 bar and up to about 30 bar) can be suitable for the PSA absorbers.
In an exemplary embodiment, carbon dioxide can be separated with a selective membrane from the gaseous effluent of the previous unit. Selective membranes of polymeric type based on polyamines and polyimide are commercially available for selective carbon dioxide separation from synthesis gas.
For a membrane unit, the temperature and pressure can be on the same level as indicated above for the PSA unit.
The recovered carbon dioxide can be used for forming carbon monoxide. According to an exemplary embodiment, at least a part of the carbon dioxide is used for forming carbon monoxide by a reversed water gas shift reaction by use of external hydrogen.
The reversed water gas shift reaction can be carried out at a temperature, for example, in the range of about 500 to 1000° C. For example, the reversed water gas shift reaction can be carried out at a temperature of about 700 to 900° C. The pressure range can be about 1 to 10 bar, a pressure range of about 4 to 8 bar being exemplary. Such conditions can favor the reaction of carbon dioxide and hydrogen to yield carbon monoxide and water. The reactions can be endothermic which means that the temperature of an adiabatic reactor can drop with about 130° C. during operation. Suitable catalysts are optionally supported iron and nickel metal catalysts.
In an exemplary embodiment, external hydrogen can be fed into the gas both in order to increase the hydrogen-to-carbon monoxide ratio of the gas and for forming carbon monoxide by the reversed water gas shift reaction.
The molar ratio between the hydrogen fed into the gas related to carbon dioxide from gasifier and that used for forming carbon monoxide and satisfying the desired hydrogen to carbon monoxide ratio of 2, respectively, can be in the range 0.5:1 to 6:1, for example, 0.9:1 to 4:1.
In an exemplary embodiment, a method is provided comprising the steps of:
feeding the carbon dioxide together with fresh hydrogen into the gaseous effluent of a reformer or a high-temperature gasifier in order to produce a modified gaseous flow; and
feeding the modified gaseous effluent into a reaction zone for a reversed water gas shift reaction.
Before the FT reactor there can still be at least some guard beds for removing metals and hydrogen sulphide.
In an exemplary embodiment, a concept can be employed of substantially not using any of the carbon monoxide produced by gasification of the biomass raw-material for producing hydrogen gas for use in the Fischer-Tropsch reactor. Instead, for example, a corresponding volume of external, fresh hydrogen gas can be introduced into the process. The recovered carbon dioxide can be used for forming carbon monoxide. According to an exemplary embodiment, at least a part of the carbon dioxide is used for forming carbon monoxide by a reversed water gas shift reaction by use of external hydrogen.
Therefore, the capacity of the process can be greatly increased. In an exemplary embodiment, the capacity of the process can be increased at maximum by 160% (see the right-hand side of the graph in
The molar ratio of the fresh hydrogen fed into the gaseous effluent to the carbon monoxide produced by gasification of the biomass raw-material can amount to 2 to 3, for example, 2,4.
Next, the disclosure will be elucidated with the aid of the attached drawings. The following reference numerals are used:
Turning first to
Reference numeral 2 signifies a reformer which can be a catalytic reformer which can be operated at temperature up to about 1000° C. As explained above, the reformer can be, for example, a catalytic reactor with solid catalyst beds and provided with feed for oxygen or other gases for enhancing the reformation reactions.
The task of the reformer is, for example, to free gas fed into the reformer from tarry compounds and to convert hydrocarbons to synthesis gas components. The feed for gas from a gasifier into a reformer 2 is indicated with an arrow pointing at reformer 2.
The gasifier can be of any suitable type, for example, a circulating bed reactor wherein biomass is combusted at increased temperature in the presence of oxygen.
There can be a line 6 for release of gases from the Fischer-Tropsch reactor unit 8.
The effluent from the reformer 2 can contain a product mixture of carbon dioxide, carbon monoxide, water and hydrogen as main components. Depending on the biomass combusted, there can also be some sulphuric gases and nitrogen compounds as well as hydrocarbons. The effluent of the reformer 2 is, in the embodiment of the figure, fed into a reversed water gas shift reactor 3. Further, the feed of the shift reactor includes a stream of hydrogen gas from the hydrogen unit 1 along with some recycled gases separated from the gas mixture conducted to the Fischer-Tropsch reactor 8. Although the two or three gas flows can be separately fed into the reversed shift reactor 3 as indicated in
In the reversed shift reactor 3, carbon dioxide and hydrogen, primarily external, fresh hydrogen from hydrogen unit 1, can be used for producing carbon dioxide by a reversed water gas shift reaction (reaction 3):
CO2+H2CO+H2O (3).
The reaction is an equilibrium reaction and by increasing the temperature and proportion of hydrogen and the proportion of recycled carbon dioxide, the production of carbon monoxide can be increased.
The reaction can be carried out at about 700 to 900° C. For example, the reaction can be performed by using a nickel catalyst or another catalyst which is capable of withstanding the reaction conditions prevailing in this “dirty reversed shift” reaction. This expression refers to the fact that the gas fed into the reversed shift reactor can contain considerably high amounts of hydrogen sulphide and other sulphuric compounds (in concentrations from about 10 to several hundred ppms). For example, steam can be introduced into the reactor to mitigate the risk of catalyst deactivation. The pressure of the reaction can be 1 to 15 bar, for example, about 5 to 10 bar. The space velocity, GHSV can be in the range of about 3,000 to 5,000 1/h, although a broader range of about 1,000 to 10,000 is also possible.
The gaseous effluent of the reversed shift reactor can be withdrawn and conducted through a series of washing units 4 and units for specific removal of carbon dioxide 5. The washing unit 4 of the drawing can be, for example, an amine washer wherein the gas is conducted with an organic amine to bind gaseous impurities, for example, sulphuric compounds and other catalyst poisons. The washing unit 4 is optional.
The unit for selective carbon dioxide removal 5 can be a methanol washing unit or a membrane unit or a PSA unit, as explained above.
The carbon dioxide can be circulated via recycle line. A part thereof can be emitted to the ambient, for example, after a further purification step in unit 9.
After unit 5 there can be an optional washer unit 7, for example, an amine washer, as shown in the drawing. Finally, the syngas is fed into a Fischer-Tropsch reactor 8 wherein hydrocarbons are synthesized by reacting carbon monoxide and hydrogen. The conditions in reactor can be, for example: a pressure of about 30 bar and a temperature of about 200 to 250° C. There can be a catalyst comprising an iron or cobalt catalyst. The reactor type can be a slurry-type reactor or a fixed bed reactor, wherein the strongly exothermic FT reaction can be controlled by the use of efficient cooling means.
Finally, a FT product (of the above explained kind) comprising a hot, viscous liquid stream of hydrocarbons can be recovered. Light volatile gases can be separately removed and recycled, as explained above.
In the reformer 10, methane can be partially oxidized by an exothermic reaction. The temperature of the reaction can be about 800 to 950° C. and the pressure about 5 to 100 bar (abs). A metal catalyst, such as a transition or nobel metal catalyst can be used.
The shift reaction 11 can be carried out at a temperature in the range of, for example, about 150 to 400° C. and at a pressure of about 1.5 to 10 bar (abs.). For example, the shift reaction can be carried out in two stages, comprising a first, high temperature shift reaction at about 350° C. and a second, low temperature shift reaction at a temperature of about 180 to 220° C. Suitable catalysts can include various metal oxide catalysts, such as transition metal oxides and mixtures thereof on supports, including iron oxide, chromium oxide and zinc oxide.
As shown in
In an exemplary embodiment,
It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20105503 | May 2010 | FI | national |
This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/FI2011/050430, which was filed as an International Application on May 10, 2011 designating the U.S., and which claims priority to Finnish Application No. 20105503 filed in Finland on May 10, 2010. The entire contents of these applications are hereby incorporated by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/FI2011/050430 | May 2011 | US |
| Child | 13675720 | US |
