RU2228901C2 - Synthesis gas production process - Google Patents

Abstract

FIELD: alternative fuels. SUBSTANCE: synthesis gas mainly containing hydrogen and carbon monoxide for producing alcohols, ammonia, and Fischer-Tropsch process products with specified H₂/CO ratio within 1.0 to 2.0 is obtained in two stage process comprising partial oxidation stage and catalytic conversion of residual methane with first-stage products. The first stage is accomplished by noncatalytic partial oxidation of natural gas with oxygen to give reaction products characterized by nonequilibrium content of H₂O and CH₄ and wherein O₂/CH₄ molar ratio is approximately 0.76-0.84, after which resulting reaction products are converted with adjusting additives of CO₂ and H₂O or H₂O and CH₄ to produce gas mixture, which undergoes catalytic conversion of residual methane with steam. EFFECT: reduced power consumption. 3 cl, 1 dwg

Description

The invention relates to the production of synthesis gas containing mainly H ₂ and CO for the production of alcohols or ammonia, Fischer-Tropsch processes and oxosynthesis.

The method in accordance with the invention preferably relates to the processing of natural gas into synthesis gas with a given molar ratio of H ₂ / CO in the range from 1.0 to 2.0.

Known methods for producing synthesis gas from natural gas, gas mixtures containing H ₂ and CO, based on various types of conversion: oxygen conversion or, as is customary in foreign technical literature, non-catalytic partial oxidation, autothermal reforming that takes place on a catalyst in a shaft reactor type and steam reforming carried out in a tube furnace with external heating of pipes (see. "Production of process gas for the synthesis of ammonia and methanol from hydrocarbon gases." Publishing house "Chemistry", Moscow, 1971, ed.A.G. Leibush).

Upon receipt of gas for methanol synthesis, autothermal reforming of natural gas with the addition of CO _{2 is} carried out by performing the following stages: saturation with Н ₂ О of the source natural gas, mixing it with СО ₂ and heating to 550-600 ° С in a heat exchanger with return converted gas and subsequent the conversion of the gas-vapor mixture of the initial composition at the following ratios: CO ₂ : H ₂ O: CH ₄ = 0.2: 0.9: 1.0 in a shaft catalytic reactor with oxygen at a ratio of O ₂ : CH ₄ = 0.6: 1, 0.

The reaction proceeds on a nickel-containing catalyst (6% NiO on an Al ₂ O ₃ support) at a temperature of 850-950 ° C. The resulting converted gas, after cooling in a waste heat boiler, a heat exchanger for heating the initial steam-gas mixture, and an aqueous scrubber, is further purified from CO ₂ using a monoethanolamine solution (MEA) (18-20 wt.% MEA) and then fed to the compression and synthesis of methanol.

The disadvantages of the above method include the following:

1. In the converted gas after autothermal conversion there is an increased content of CO ₂ (> 9 vol.%), Which requires further additional purification from CO ₂ .

2. The converted gas has a high hydrogen content and, consequently, an increased H ₂ / CO ratio (> 2.3), which leads to increased CO + H ₂ consumption per unit of output. In the synthesis of methanol requires a ratio, the so-called “functional” f = (H ₂ -CO ₂ ) / (CO + CO ₂ ) ≅2.05.

3. As a result of the methanol synthesis reaction, hydrogen is in excess and it enters the “purge”, which as a result leads to increased energy material costs.

Another method for producing synthesis gas with a low H ₂ / CO ratio for methanol synthesis is non-catalytic partial oxidation of natural or other hydrocarbon gas (Nitrogen Handbook, Khimiya Publishing House, Moscow, 1986). Natural gas reacts with oxygen at high temperature (1300-1500 ° C) in free volume. The resulting gas consists mainly of hydrogen and carbon monoxide.

In a first approximation, the process is described by the equation for methane:

and for methane homologues:

The possibility of carrying out the process in the absence of a catalyst is ensured by a high combustion temperature (1350-1400 ° C). To realize the autothermal process at the indicated temperature, the O ₂ : CH ₄ ratio is kept slightly higher than the stoichiometric one, as a result of which water products (H ₂ O) and carbon dioxide (CO ₂ ) appear in the reaction products, except for H ₂ and CO. The ratio of H ₂ and CO in the synthesis gas after non-catalytic partial oxidation of natural gas is about 1.7-1.8.

The ratio of H ₂ / CO can be varied either by an additional supply of H ₂ O or by an additional supply of CO ₂ .

The final state of the process of non-catalytic partial oxidation of natural gas corresponds to the equilibrium of the reaction of water gas:

which is set to a temperature of ~ 1200 ° C. At lower temperatures, due to kinetic inhibition, the gas composition will differ from the equilibrium one.

Regardless of the composition of the starting natural gas, only methane remains in the reaction products in a small amount.

In the process of incomplete oxidation of a hydrocarbon, it is possible to release free carbon (soot) by the reaction:

The release of free carbon increases with the conversion of higher hydrocarbons. To limit the process of soot recovery, water vapor is added to the starting reagents.

Thus, the composition of the produced gas, the ratio of H ₂ / CO, the temperature and the border of soot emission are set in accordance with the initial parameters.

The incomplete oxidation reaction of natural gas is accompanied by an increase in volume; therefore, the use of pressure should prevent oxidation.

With increasing temperature (more than 1200 ° C), pressure does not limit the quantitative oxidation of methane, since the temperature factor compensates for the negative effect of pressure and is decisive.

However, non-catalytic partial oxidation has a number of significant disadvantages:

1. Increased oxygen consumption for the source methane (or natural gas) leads to increased costs compared with autothermal reforming. Equipment for the production of oxygen is expensive and accounts for up to 70% of the cost of production of methanol (Me). In addition, oxygen production is energy intensive.

2. In the process, a small amount of soot (carbon) is released, which requires an additional purification step, complicates the work in subsequent technological stages.

All this leads to large energy costs per unit of output.

The closest in technical essence to the claimed invention is a method developed by the British company ICI (UK patent 2139644 from November 14, 1984 and US patent 4618451 from October 21, 1986).

Synthesis gas is produced in a two-stage process. In the first stage, natural gas reacts with oxygen or an oxygen-containing gas. A sufficient amount of oxygen is taken to avoid soot formation.

The hot gas stream obtained in the first stage, containing H ₂ and CO, has a temperature of the order of 1093-1260 ° C. An additional amount of hydrocarbons and water vapor or CO _{2 are} introduced into this gas.

In the second stage, the resulting gas mixture is sent to the autothermal steam reforming catalyst, where the adiabatic process of steam conversion proceeds to produce synthesis gas.

The final temperature of the obtained gas is 750-950 ° C. The process pressure is from 0.5 to 5 MPa. The result is a synthesis gas with f = (H ₂ -CO ₂ ) / (CO + CO ₂ ) ≅1.5-2.2, where H ₂ , CO, CO ₂ is the number of moles of these gases in the gas stream, which makes it possible to use this gas in the production of Me.

This method of production of synthesis gas also has several disadvantages:

1. The resulting low temperature in the first stage leads to an increased methane content in the final synthesis gas; unreacted methane in the next stages in the Me production cycle will accumulate, which will lead to increased purges of the synthesis gas and, as a result, to increased consumption of O ₂ and the initial hydrocarbon per unit of the obtained product.

2. The proposed steam supply in the second stage directly in front of the catalyst will not lead to intensive mixing with the hot converted gas, since there is no mixing zone and, as a result, there will be an uneven temperature distribution over the cross section of the shaft converter.

3. Based on the calculations of thermodynamics, in accordance with the method described in the aforementioned patent of ICI, it is impossible to obtain a gas with a molar ratio of H ₂ / CO equal to 1: 1, because the thermal potential in the first stage of conversion will not be enough for the conversion of CO ₂ by reaction:

The objective of the present invention is to develop a method for producing synthesis gas of a given composition of the main components of H ₂ and CO in the range of H ₂ / CO ratios from 1: 1 to 2: 1 and reducing energy costs.

This problem is solved by the method of producing synthesis gas of a given composition of the main components of H ₂ and CO in the range of changes in the ratio from 1: 1 to 2: 1 for the production of methanol, dimethyl ether or for Fischer-Tropsch syntheses, which includes two stages: stage A) partial oxidation and stage B) the conversion of residual methane with the products of stage A on the catalyst, while stage A) partial oxidation is carried out in two stages: a) non-catalytic partial oxidation of natural gas with oxygen to obtain unequal reaction products the abundant content of Н ₂ О and СН ₄ at a molar ratio of oxygen and methane of approximately 0.76-0.84, b) the conversion of reaction products of step (a) with corrective additives CO ₂ and Н ₂ О or Н ₂ О and CH ₄ to obtain a gas mixture that undergoes the conversion of residual methane with water vapor on the catalyst.

Stage a) of stage A) is carried out at a supply of 100% of the total required oxygen consumption, 75-100% of the total consumption of the source of natural gas to obtain an oxygen: methane molar ratio of approximately 0.76-0.84, while staying in the zone burning t equal to 0.005-0.01 s in the range of working pressure of 2.0-10 MPa, while the molar concentration of Н ₂ О in the produced gas is from 18 to 30%, and СН ₄ is from 1 to 8%, stage b ) stage A) is carried out while supplying the remainder of the natural gas from 25 to 0%, corrective additives with a residence time t = 0.003-1 s.

The first stage is carried out in the mode of non-catalytic partial oxidation (autothermal) with a temperature of 1800-1400 ° С with obtaining in the synthesis gas a nonequilibrium content of Н ₂ О and СН ₄ and a molar ratio of Н ₂ / СО≅1,4-1,8.

The second stage is carried out on a nozzle, which may have several layers; the first layer along the gas is inert, having a developed surface for gassing of soot and the subsequent layers are catalytic for the pre-conversion of the remaining methane.

The advantages of the proposed method are as follows:

1. At the first stage of the first stage, the conversion process is carried out as thermodynamically nonequilibrium with a residence time of 0.005-0.01 s, while the converted gas retains an increased content of water vapor in the reaction products (H ₂ O) up to 18-20 vol.% At pressure up to 2.0 MPa or 25-30% at pressures up to 10.0 MPa and unreacted methane 1-3% and 7-8%, respectively, with pressure, the minimum amount of soot formed (up to 50 mg / nm ³ converted gas).

2. The amount of oxygen supplied to the first stage of the first stage corresponds to a molar ratio α = 0.5 [O ₂ ] / [CH ₄ ] in the range of 0.38-0.42 depending on the desired molar ratio of H ₂ : CO in the final product - converted gas, as well as the content of unreacted methane.

3. In the second stage of the first stage, the correction part of СО ₂ and Н ₂ O or Н ₂ О and СН ₄ (15-25% of the total consumption) is supplied, and due to the high content of Н ₂ О vapor in the gas, soot formation does not occur.

The residence time is 0.3-3 s, at the exit from the second stage, an equilibrium temperature is established, which is 1100-1500 ° C.

Thanks to the decisions made, an economical technological method is implemented.

The method can be carried out according to the following scheme shown in the drawing, where:

1 - mixing burner (SG);

2 - conversion chamber for the implementation of the process of non-catalytic partial oxidation;

3 - a chamber for mixing CO ₂ and H ₂ O or H ₂ O and CH ₄ with products of primary non-catalytic partial oxidation;

4 - correction camera;

5 - shaft reactor;

6 - filter from special materials;

7 - catalyst;

8 - filter;

9 - support grid.

The proposed process is carried out as follows: natural gas after compression from 2 to 15 MPa and heated to 520 ° C is supplied to the burner (p. 1), where oxygen is also supplied, compressed to a pressure of 2 to 15 MPa and heated to 150-250 ° FROM. The oxygen concentration is 95-99 vol.%. Temperature, pressure and flow rates are automatically controlled.

Oxygen and natural gas are separately fed into the conversion chamber (item 2), where the methane conversion reaction takes place at a temperature of from 1200 to 1900 ° C.

The residence time of the converted gas, temperature and pressure are calculated in such a way as to obtain a gas of a given composition after the shaft reactor (Clause 5).

The gas composition after the conversion chamber is nonequilibrium, i.e. thermodynamic equilibrium of the reaction is not achieved

and the gas has the following composition, vol.%: CH ₄ - 1-8; CO ₂ - 1.5-4; H ₂ O - 15-20; H ₂ - 40-50; СО - 25-35.

Up to 50 mg / nm ^{3 of} unreacted carbon (soot) is present in the gas.

After the conversion chamber, the gas is mixed with CO ₂ and CH ₄ if you want to get the final synthesis gas with a ratio of H ₂ / CO≅1: 1, or with H ₂ O and CH ₄ if you want to get the final synthesis gas with a ratio H ₂ / CO≅2: 1.

After the mixing chamber (Clause 3), the gas enters the correction chamber (Clause 4), in which a homogeneous reaction (5) occurs at a temperature of 1200-1100 ° С.

Further conversion of residual CH ₄ occurs in a shaft converter (Clause 5). Soot is filtered at the entrance to the shaft reactor by a filter (item 6) and completely converted by water vapor.

The invention will be further explained in more detail with specific examples, which are given as an illustration of the invention and in no way limit the scope of the claims claimed in the claims.

Example 1. Obtaining synthesis gas with a molar ratio of H ₂ : CO equal to 2: 1

Natural gas in an amount of 1000 nm ³ / h at a pressure of 3 MPa and a temperature of 450 ° C and oxygen in an amount of 730 nm ³ / h at a pressure of 3 MPa at a temperature of 150 ° C are fed to the burner (item 1) and then to the conversion chamber ( item 2).

In the conversion chamber, a high-temperature conversion reaction takes place at a temperature of 1860 ° C to produce a converted gas containing (per wet gas), vol.%: CH ₄ - 2.39; CO ₂ 2.03; H ₂ O, 16.43; H ₂ - 48.64; СО - 30.51.

An additional 166 nm ³ / h of CH ₄ and 373 nm ³ / h of H ₂ O are additionally fed into the obtained gas into the mixing chamber. The mixture of converted and additional gas enters the correction chamber (p. 4) and then into the shaft reactor (p. 5).

At the outlet of the shaft reactor, the gas has the following composition, vol.%: CH ₄ - 0.65; CO ₂ - 2.78; H ₂ O - 15.33; H ₂ - 54.16; СО - 27.08 in the amount of 3821 nm ³ / h.

The resulting gas with a temperature of 1240 ° C is then sent for cooling with heat recovery and the release of process condensate and then for further processing.

Example 2. Obtaining a converted gas with a molar ratio of H ₂ : CO equal to 1: 1

In the first stage, the conversion is carried out as described in example 1.

192.0 nm ³ / h of Н ₂ O and 754 nm ³ / h of СО _{2 are} additionally fed into the obtained gas into the mixing chamber (Clause 3).

The mixture of converted and additional gas enters the correction chamber (p. 4) and then into the shaft reactor (p. 5).

At the outlet of the shaft reactor, the gas has the following composition, vol.%: CH ₄ - 1.94; СО ₂ - 9.86; H ₂ O, 21.10; H ₂ - 34.00; СО - 33.10 in the amount of 4276 nm ³ / h.

Claims (3)

1. A method of producing synthesis gas of a given composition of the main components of H ₂ and CO in the range of the ratio from 1: 1 to 2: 1 for the production of methanol, dimethyl ether or for Fischer-Tropsch syntheses, which includes two stages: stage A) partial oxidation and stage B) conversion of residual methane with the products of stage A) on the catalyst, characterized in that stage A) of partial oxidation is carried out in two stages: a) non-catalytic partial oxidation of natural gas with oxygen to obtain a nonequilibrium content in the reaction products H ₂ O and CH ₄ at a molar ratio of oxygen and methane approximately equal to 0.76-0.84, b) the conversion of the reaction products of step (a) with corrective additives CO ₂ and H ₂ O or H ₂ O and CH ₄ s obtaining a gas mixture that undergoes the conversion of residual methane with water vapor on the catalyst. 2. The method according to claim 1, characterized in that stage a) of stage A) is carried out when 100% of the total required oxygen flow rate is supplied, 75-100% of the total flow rate of the source natural gas to obtain an oxygen: methane molar ratio of approximately 0 , 76-0.84, and with a residence time in the combustion zone t = 0.005-0.01 s. in the range of working pressure of 2.0-10 MPa, while in the resulting gas the molar concentration of H ₂ O is 18 - 30%, and CH ₄ 1 - 8%. 3. The method according to claim 2, characterized in that stage b) of stage A) is carried out while supplying the remaining part of natural gas from 25 to 0%, corrective additives with a residence time t = 0.003-1 s.