RU2475468C1 - Method of producing liquid synthetic hydrocarbons from hydrocarbon gases - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing liquid synthetic hydrocarbons from hydrocarbon gases, involving purification of starting material from sulphur compounds, steam-carbon dioxide catalytic conversion of the starting material purified from sulphur compounds at temperature of 950-1050°C to obtain synthesis gas by supplying high-grade heat to the catalytic reactor and feeding into said reactor carbon dioxide separated from exhaust flue gases, and water vapour which is generated in a steam boiler which is heated by hot synthesis gas, subsequent catalytic processing of the synthesis gas via a Fischer-Tropsch technique, separating a mixture of liquid hydrocarbons from products obtained from synthesis gas processing and subsequent separation of the mixture into fractions of commercial grade hydrocarbons. The method is characterised by that at the outlet of the steam boiler, synthesis gas is divided into two streams, one of which is fed for catalytic processing in a Fischer-Tropsch synthesis reactor and the second stream is fed into a hydrogen production unit in which steam conversion of carbon oxide, separation of water and absorption of carbon dioxide are successively carried out, after which the purified hydrogen is fed into a desulphurisation unit for hydrogenation of organic sulphur compounds contained in the starting material and carbon dioxide separated during regeneration of the absorbent is mixed with the stream of carbon dioxide separated from flue gases and then fed into the catalytic reactor for steam-carbon dioxide conversion of the starting material.

EFFECT: method is independent of external hydrogen sources needed to carry out desulphurisation.

3 cl, 2 dwg

Description

The invention relates to gas chemistry, and specifically to methods for the catalytic processing of gaseous hydrocarbon feedstocks into synthetic liquid hydrocarbons.

In connection with the depletion of oil reserves and an increase in the cost of its production, the problem of obtaining synthetic liquid hydrocarbons from alternative oil sources of hydrocarbon-containing raw materials, primarily hydrocarbon gases (natural gas, shale gas, associated petroleum gas, oil refining gases), is becoming increasingly urgent. In addition, the development of the utilization of associated petroleum gas for the production of liquid hydrocarbons, which are currently in large quantities flared, is of great importance not only in terms of the beneficial use of this potentially valuable product, but also for solving one of the main environmental problems - reduce carbon dioxide emissions.

All known technological processes for producing synthetic liquid hydrocarbon products, including fuel, from gaseous hydrocarbon feedstocks include, as the main stages, the catalytic conversion of gaseous feedstocks (steam, vapor-oxygen or carbon-dioxide) to produce synthesis gas (a mixture of CO and H ₂ with a small content СО ₂ , Н ₂ О, N ₂ , Ar, etc.) and the subsequent catalytic synthesis of liquid hydrocarbons from synthesis gas.

As a rule, hydrocarbon gases (natural, associated, shale, gaseous products of oil refining) contain more or less sulfur compounds as inorganic (hydrogen sulfide H ₂ S), and various organic compounds, including carbon disulfide CS ₂ , carbon sulfide COS, thiophene C ₄ H ₄ S, sulfides R ₂ S, disulfides R ₂ S ₂ , mercaptans (CH ₃ SN, C ₂ H ₅ SH, etc.).

The presence of sulfur compounds in the process gases entering the catalytic processing is unacceptable, because sulfur is a potent catalytic poison; in addition, the presence of sulfur causes intense corrosion of the equipment. Therefore, before carrying out the catalytic conversion of hydrocarbon gases to produce synthesis gas, desulfurization is an obligatory step, which is carried out in two stages.

In a first step, organic sulfur compounds are hydrogenated. The following reactions occur:

CS ₂ + 4H ₂ = 2H ₂ S + CH ₄

COS + H ₂ = H ₂ S + CO

C ₄ H ₄ S, + 4H ₂ = H ₂ S + C ₄ H ₁₀

С ₂ Н ₅ СН + Н ₂ = Н ₂ S + С ₂ Н ₆

etc.

Thus, sulfur from organic compounds is converted to hydrogen sulfide.

In the second stage, the resulting hydrogen sulfide is trapped at a temperature of 390-410 ° C with an absorbent, for example zinc oxide.

Consequently, hydrogen is needed to carry out effective desulfurization of hydrocarbon gases, in particular for hydrogenation of organic sulfur compounds.

Known technical solutions, including patents relating to the production of liquid hydrocarbons from hydrocarbon gases, do not address issues related to methods for producing hydrogen for hydrocarbon gas desulfurization systems prior to catalytic conversion, or it provides for the supply of untreated exhaust gases emitted to the desulfurization unit of the feedstock in the synthesis of liquid hydrocarbons and containing hydrogen, or the preliminary evolution of hydrogen from crude flue gases House pressure swing adsorption, or the use of hydrogen from an external source. The disadvantages of these methods of providing hydrogen desulfurization are considered in the analysis of the prototype.

Below are a few analogues and a prototype of the invention, the consideration of which only drawbacks are associated with the problem solved by the invention - providing hydrogen desulphurisation of feedstock to produce synthetic liquid hydrocarbons from hydrocarbon feedstocks.

There is a method of producing motor fuels - dimethyl ether (DME) and / or gasoline from carbon-containing raw materials (patent RU 2143417, С7С 1/04, publ. 12/27/99, bull. No. 36), according to which, when producing synthesis gas supplied to converter carbon-containing raw materials add water and oxygen; then, to obtain liquid fuels, the resulting synthesis gas (CO + H ₂ + CO ₂ ) is subjected to catalytic processing at high pressure (up to 8 MPa) in two stages: in a stage 1 reactor at a temperature of 220-320 ° С (DME synthesis) and in the reactor of the 2nd stage at a temperature of 340-420 ° C (gasoline synthesis). In this case, the gas phase after the 1st stage reactor is divided into two streams - one is sent to the 2nd stage reactor for further processing, the second, to increase the DME yield, is returned to mix with synthesis gas in front of the 1st stage reactor, and the gas the phase after the 2nd stage reactor is returned to the inlet of the reactor to increase the gasoline yield. In another embodiment, the entire gas phase from the 1st stage reactor is sent to the 2nd stage reactor, after which the gas phase is returned to the synthesis gas stream in front of the 1st stage reactor. Thus, one or two gas recirculation circuits are provided. The water produced in these reactors is returned to the synthesis gas converter.

The disadvantage of this method is that it does not address issues related to the desulfurization of the feedstock, and, in particular, the source of hydrogen necessary for hydrogenation of the organic sulfur compounds contained therein has not been developed.

There is also known a method of producing liquid hydrocarbons by catalytic processing of hydrocarbon gases according to patent RU 2198156, С7С 1/04, publ. 02/10/03, bull. Number 4. According to this patent, the technological process includes a two-stage catalytic conversion of incoming gaseous hydrocarbon feeds sequentially in high and medium temperature converters with air and high temperature heat inlet and producing synthesis gas, which is further subjected to catalytic processing according to the Fischer-Tropsch method at a pressure of 3 MPa and a temperature of 520 K with the production of liquid hydrocarbons, the afterburning of part of the gaseous synthesis products with the release of carbon dioxide from the combustion products and low temperature conversion of mixed recycle gaseous synthesis products with carbon dioxide extracted from the combustion products. During the low-temperature conversion, the catalytic reduction of carbon dioxide mixed with hydrogen to carbon monoxide is carried out with the simultaneous formation of water. The resulting products are introduced into the composition of the synthesis gas supplied to the catalytic processing, or divided into two streams, one of which is directed to mixing with the feed to the conversion of raw materials, and the second is introduced into the composition of the synthesis gas supplied to the catalytic processing.

This method allows you to slightly increase the yield of liquid hydrocarbons, but its disadvantage is that issues related to the desulfurization of the feedstock are not considered, and, in particular, the source of hydrogen necessary for hydrogenation of the organic sulfur compounds contained in it is not developed.

Closest to the invention is the prototype method for producing liquid hydrocarbons by catalytic processing of hydrocarbon gases according to patent RU 2247701 C2, M.cl. C7C 1/04, publ. 03/10/2005, bull. No. 7, the essence of which is as follows: the catalytic conversion of natural gas is carried out by interacting with water vapor and an oxygen-containing gas to produce synthesis gas in two stages. In a pre-reforming reactor at a temperature of 430-500 ° C, hydrocarbons contained in natural gas C ₂ and higher are converted to methane, CO and CO ₂ , after which the gas mixture is heated to a temperature of 550-650 ° C and together with oxygen or an oxygen-containing gas (air) ) are sent to an autothermal reforming reactor (ATR), where they are converted to synthesis gas under a pressure of 3-4 MPa. The temperature of the synthesis gas at the outlet of the ATR is maintained within the range of 950-1050 ° C. The resulting synthesis gas is cooled, and then sent to the Fischer-Tropsch synthesis reactor, where, at a pressure of 2-4 MPa and a temperature of 180-240 ° C, a crude synthesis product is obtained consisting of lower hydrocarbons, higher hydrocarbons, water and unconverted synthesis gas. This product is then separated into a stream of higher hydrocarbons, a stream of water and a stream of exhaust gases, containing mainly the remaining components. Further, at least a portion of the offgas with the addition of natural gas is subjected to steam reforming in a separate apparatus, after which they are introduced into the main synthesis gas stream in front of the Fischer-Tropsch synthesis reactor and / or into the gas stream entering the ATR reactor, and the other part the exhaust gases are fed into the desulphurization unit of the feedstock for hydrogenation with the hydrogen in them of the organic sulfur compounds contained in the feedstock.

The specified method of supplying hydrogen desulphurization is accepted in the invention as the main one (claims 6 and 7 of the formula). Alternative methods are also provided in the description of the invention:

- preliminary extraction of hydrogen from the specified exhaust gas during short cycle adsorption (CCA) with a pressure jump;

- hydrogen supply from an external source.

However, each of the proposed methods has significant disadvantages.

In addition to hydrogen, the raw exhaust gases contain various impurities and compounds, including organic compounds, the ingress of which into the desulfurization unit significantly slows down and reduces the efficiency of the above-mentioned process of converting organic sulfur compounds to hydrogen sulfide, which, in turn, reduces the degree of purification of sulfur from hydrocarbon gases entering the catalytic conversion.

To conduct exhaust gas purification using CCA, several parallel-connected adsorbers operating in a variable mode (adsorption-desorption) with pressure surges are required, which requires the inclusion of an additional compressor in the circuit, complicates and increases the cost of the installation, and also reduces its reliability.

When the hydrogen desulphurization system is powered by an external source, the autonomous operation of the installation is excluded.

The objective of the present invention is to provide an effective method for producing synthetic liquid hydrocarbons from hydrocarbon gases, independent of external hydrogen sources, which is necessary for desulfurization of the feedstock before feeding it to catalytic conversion, as well as providing an increase in the yield of marketable products per unit mass of hydrocarbon gas supplied to the plant .

To solve this problem, a method for producing synthetic liquid hydrocarbons from hydrocarbon gases is proposed, including purification of feedstock from sulfur compounds, steam-carbon dioxide catalytic conversion of feedstock purified from sulfur compounds at a temperature of 950-1050 ° C to produce synthesis gas by supplying high-temperature heat to the catalytic reactor and supplying carbon dioxide emitted from the flue gas, and water vapor, which is generated in a steam boiler heated by hot synthesis gas subsequent catalytic processing of synthesis gas according to the Fischer-Tropsch method, separation of products from the synthesis gas processing, a mixture of liquid hydrocarbons, and subsequent separation of the mixture into fractions of commercial types of hydrocarbons, which is characterized by the fact that at the exit of the steam boiler synthesis the gas is divided into two streams, one of which is sent for catalytic processing to a Fischer-Tropsch synthesis reactor, and the second stream is diverted to a hydrogen production unit, in which steam conversion is carried out sequentially carbon monoxide, water separation, carbon dioxide absorption and regeneration of the absorbent with the release of carbon dioxide, after which the purified hydrogen is fed to the desulfurization unit for hydrogenation of the organic sulfur compounds contained in the feedstock, and the carbon dioxide released during the regeneration of the absorbent is mixed with the carbon dioxide stream, emitted from flue gases and then fed into the catalytic reactor of carbon dioxide conversion of the feedstock.

Moreover, depending on the content of sulfur compounds in the feedstock, from 0.5 to 2% of the total volume of the produced synthesis gas is diverted to the hydrogen production unit.

In addition, the conversion of carbon monoxide is carried out mainly in a radial-spiral type reactor.

Below the invention is illustrated by a specific example of its implementation and the accompanying drawings, in which:

figure 1 depicts a flow chart of the production of synthetic liquid hydrocarbons from natural gas;

figure 2 is a schematic flow diagram of a unit for producing hydrogen in figure 1.

The following elements are indicated on the diagrams:

1 - site desulfurization;

2 - burner;

3 - catalytic reactor for the conversion of hydrocarbon gas;

4 - compressor;

5 - steam boiler;

6 - synthesis gas cooler;

7 - Fischer-Tropsch synthesis reactor;

8 - block separation of liquid hydrocarbons;

9 - flue gas heat recovery unit;

10 - flue gas cooler;

11 - block separation of CO ₂ ;

12 - node water treatment;

13 - pump;

14 is a block for the production of hydrogen;

15 — carbon monoxide conversion reactor;

16 - capacitor;

17 - separator;

18 - carbon dioxide absorber;

19 - absorbent regenerator;

20 - absorbent recirculation pump;

21-46 - lines of supply and removal of working environments.

The proposed method for producing synthetic liquid hydrocarbons from hydrocarbon gases is implemented as follows.

The initial gaseous feedstock, hydrocarbon gas, is fed to the desulfurization unit 1, where it is purified from sulfur compounds and then separated into two streams, one of which is fed through line 21 to burner 2 of the catalytic reactor 3 as fuel, and the second stream through line 22 is directed to steam-carbon dioxide conversion to a catalytic reactor 3, and before entering the catalytic reactor 3, the hydrocarbon gas is mixed with the injection compressor 4 through line 23 of carbon dioxide released from the flue gases in the block 2 of the allocation of CO ₂ and water to the compressor 4 via line 24. To carry out the carbon dioxide conversion, steam is also supplied to the catalytic reactor 3 via line 25 from the steam boiler 5. The conversion is carried out at a pressure of 0.2-3.0 MPa and a temperature of 950-1050 ° C.

Since in most cases the pressure of the feedstock for processing (for example, natural gas) is within these limits, additional compression at the inlet to the catalytic reactor 3 is not required. If the pressure of the feedstock is below the specified limit (which occurs during the processing of associated petroleum gas, as well as gas from low-pressure low-debit wells), then the flow of hydrocarbon gas subject to steam-carbon dioxide conversion should be brought to line 24 in front of compressor 4 (shown by a dotted line).

The resulting synthesis gas through line 26 enters the steam boiler 5 as a heating medium to generate steam, which is necessary for the steam-carbon dioxide conversion of hydrocarbon gas, where it is partially cooled, after which it is removed from the steam boiler 5 through line 27 and is divided into two streams. The main part of the synthesis gas obtained through line 28 enters a cooler 6, in which it is additionally cooled by an external coolant (for example, water or air) to a temperature of 20-40 ° C and is separated from moisture, after which it is fed through line 29 to the Fischer synthesis reactor 7 -Tropsha, where at a temperature of 180-220 ° C, a liquid hydrocarbon synthesis reaction takes place, resulting in a mixture of liquid hydrocarbons, water and exhaust gases. The mixture of liquid hydrocarbons through line 30 is sent to block 8 for the separation of liquid hydrocarbons, where it is divided into commercial types of liquid hydrocarbons (LUH), for example various types of synthetic fuels, as well as liquid hydrocarbons C ₂₁₊ . Exhaust gases are removed from the Fischer-Tropsch synthesis reactor 7 to line 31, from where they can be fed to burner 2 as fuel and / or to catalytic reactor 3 to produce synthesis gas.

Hydrocarbon gas, which is fed through line 21 to burner 2, is burned in it at a temperature not exceeding 1150 ° C. The air required for combustion is preheated in the flue gas heat recovery unit 9, after which it is fed to burner 2 via line 32.

Flue gases (FG) are removed from the catalytic reactor 3 and fed through line 33 to the flue gas heat recovery unit 9, where they are partially cooled, and then sent to a cooler 10, in which they are additionally cooled by an external coolant (for example, water or air) and separated from moisture. Cooled flue gases are fed through line 34 to the CO ₂ separation unit 11, after which they are discharged via line 35 to the atmosphere, and carbon dioxide is sent via line 24 to the inlet of compressor 4 for subsequent supply to the catalytic reactor 3.

Another part of the synthesis gas in the amount of 0.5-2% of the total amount of the synthesis gas obtained is taken after the steam boiler 5 from line 27 and sent through line 36 to the hydrogen production unit 14 (see FIG. 2), where synthesis gas exposed in a catalytic reactor 15 steam reforming of carbon monoxide. The resulting vapor-gas mixture is supplied through line 37 to a condenser 16, cooled by a coolant from an external source, then through line 38 to a separator 17, where it is separated from water, after which the dried gas flows through line 39 to an absorber 18, in which carbon dioxide is trapped, and purified hydrogen is sent via line 40 to desulfurization unit 1 for hydrogenation of organic sulfur compounds contained in the feedstock - hydrocarbon gas.

From the absorber 18, the carbon dioxide-saturated absorbent passes through line 41 to the regenerator 19, in which it is freed from carbon dioxide, after which it is fed back to the absorber 18 by the pump 20, and the carbon dioxide released through line 43 is introduced in front of the compressor 4 into line 24 and mixed with the main carbon dioxide stream coming from the CO ₂ separation unit 11.

Water generated during the Fischer-Tropsch synthesis reaction, as well as condensate from coolers 6 and 10, respectively, of synthesis gas and flue gases, as well as from a separator 17, is supplied to the water treatment unit 12, after which it is sent by pump 13 via line 44 as feed water to the steam boiler 5. The initial filling and replenishment of the water system is carried out by water from an external source via line 45. A portion of the water vapor generated in the steam boiler 5 is sent through line 46 to the steam power plant to receive electricity, n sary for driving compressors, pumps, fans, and other mains equipment, thereby providing independent operation from an external power source.

In the presented scheme, the catalytic reactors 3 and 15, the Fischer-Tropsch synthesis reactor 7, the steam boiler 5, coolers 6 and 10, the condenser 16, the flue gas heat recovery unit 9, and other heat and mass transfer apparatuses of the installation are mainly made in radial-spiral type.

The proposed method has the following significant advantages compared with known technical solutions.

1. Provided using the proposed method, the hydrogenation of sulfur compounds contained in the initial hydrocarbon feedstock, with hydrogen obtained from a small part of the intermediate product - synthesis gas directly in the technological process for the production of liquid hydrocarbons, eliminates the need for using hydrogen from an external source for this purpose and allows to solve one of the tasks of ensuring the autonomy of a liquid hydrocarbon production plant.

2. The involvement of carbon dioxide formed during the production of hydrogen in the process of steam-carbon dioxide conversion of the feedstock allows one to almost completely eliminate the emission of this greenhouse gas into the atmosphere and increase the amount of synthesis gas produced, and, accordingly, the yield of the final product per unit of feedstock.

Claims (3)

1. A method of producing synthetic liquid hydrocarbons from hydrocarbon gases, including purification of the feedstock from sulfur compounds, carbon-dioxide catalytic conversion of the feedstock purified from sulfur compounds at a temperature of 950-1050 ° C. to produce synthesis gas by supplying high-temperature heat to the catalytic reactor and feeding carbon dioxide emitted from the exhaust flue gas, and water vapor, which is generated in a steam boiler heated by hot synthesis gas, the subsequent catalytic processing of synthesis gas according to the Fischer-Tropsch method, separation of products from the synthesis gas processing, a mixture of liquid hydrocarbons and subsequent separation of the mixture into fractions of commercial types of hydrocarbons, characterized in that at the outlet of the steam boiler, the synthesis gas is divided into two a stream, one of which is sent for catalytic processing to a Fischer-Tropsch synthesis reactor, and the second stream is diverted to a hydrogen production unit in which steam conversion of carbon monoxide, water separation and absorption are carried out successively carbon dioxide, after which the purified hydrogen is fed to the desulfurization unit to hydrogenate the organic sulfur compounds contained in the feedstock, and the carbon dioxide released during the regeneration of the absorbent is mixed with the carbon dioxide stream released from the flue gases and then fed to the catalytic steam-carbon dioxide conversion reactor of the initial raw materials. 2. The method according to claim 1, characterized in that, depending on the content of sulfur compounds in the feedstock, 0.5 to 2% of the total volume of the produced synthesis gas is diverted to the hydrogen production unit. 3. The method according to claim 1, characterized in that the conversion of carbon monoxide is carried out mainly in a radial-spiral type reactor.

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