RU2268252C1 - Purge gas-based methanol production process - Google Patents

Abstract

FIELD: industrial organic synthesis.

SUBSTANCE: invention relates to improved process of producing methanol from purge gas produced in basic methanol or ammonia synthesis. Process comprises dispensing compressed carbon dioxide into basic synthesis purge gas, heating resultant gas mixture to starting synthesis temperature, passing thus heated gas through methanol synthesis catalyst, cooling reacted gas, recovering condensed crude methanol, and separating non-condensed gas stream into return stream and purge stream, the former being designed for mixing with basic synthesis purge gas stream and passed to one or two circulation jet compressors. Circulation is effected by energy provide either by (i) pressure of basic synthesis purge gas, which is supplied to jet compressor and further dispensed into compressed carbon dioxide stream, or by (ii) pressure of compressed carbon dioxide, which is dispensed into jet compressor and then introduced into basic synthesis purge gas stream, or by (iii) pressure of basic synthesis purge gas and pressure of indicated compressed carbon dioxide, both being supplied to one or two jet compressors. Ammonia or methanol production purge gas is successfully used for production of methanol without utilizing additional hydrogen-containing streams.

EFFECT: reduced methanol production cost.

4 cl, 5 dwg, 1 tbl, 4 ex

Description

The present invention relates to the field of chemical technology and can be used, in particular, in factories producing methanol and ammonia.

A known method for the production of methanol described in the application of the Russian Federation N 93054026, and involving the implementation of the methanol synthesis process, in which the purge gas of ammonia production is used as the source of hydrogen-containing gas. The formation of methanol proceeds according to the following reactions:

The purge gas consists of hydrogen and inert impurities: methane, nitrogen, argon and ammonia. At the same time, to ensure the synthesis of methanol into the purge gases for the synthesis of ammonia, carbon dioxide is dosed in such an amount that the maximum use of hydrogen in the purge gas. Moreover, the factorial value (f), representing the ratio f = (H ₂ -CO ₂ ) / (CO ₂ + CO), is 2.0-2.15. The main disadvantage of this method is the low efficiency, which is due to the fact that the circuit is flowing, and not circulating. There is also known a method for the production of methanol, described in US patent 5424335 and involving the implementation of the methanol synthesis process in two stages, one of which uses fresh synthesis gas, and the second stage carries out the synthesis of methanol from the purge gases of the first stage methanol synthesis according to the flow diagram. The disadvantages of this method include

1. The low content of carbon monoxide and carbon dioxide in the purge gas, which leads to a low production of methanol from these gases.

2. The flow diagram causes a small degree of response of the reactants of the initial synthesis gas and a large amount of catalyst.

The closest in technical essence to the claimed is the method described in US patent 4226795. A method comprising heating the purge gas to an initial synthesis temperature, passing gas through a methanol synthesis catalyst, cooling the reacted purge gas, isolating condensed methanol, withdrawing part of the non-condensed purge stream from the system gas and circulating the remainder of the non-condensed purge gas stream back to methanol synthesis on purge gases and characterized

using as a source of hydrogen-containing gas purge gas production of ammonia, methanol, etc .;

using additional hydrogen-containing gas with a lower pressure than the pressure of the purge gas, which is a purge gas of another production, by increasing the pressure of the second hydrogen-containing gas stream due to the energy of the purge gas in the jet compressor;

dosage of carbon oxides in the gas mixture to maintain the factorial in the range from 2: 1 to 12: 1.

A circulating compressor with a drive is used to circulate the non-condensed purge gas stream.

The disadvantages of this method should be attributed.

1. The need to use as an additional raw material purge gas of another production with a lower pressure than the main stream.

2. Additional energy costs for the drive of the circulation compressor.

An object of the invention is to more efficiently use purge gas for the production of ammonia or methanol to produce methanol without involving additional hydrogen-containing streams.

The task is achieved by

1) dosages of compressed carbon dioxide in the purge gas;

2) a process for the synthesis of methanol from a purge gas mixture of ammonia or methanol production with carbon dioxide in a circulation scheme;

3) using the purge gas pressure of the main synthesis of ammonia or methanol or the pressure of carbon dioxide compressed in the compressor to circulate with the help of a jet compressor in the methanol synthesis unit for purge gases.

The essence of the invention in a method for producing methanol from a purge gas of the main synthesis of ammonia or methanol, which includes

- dosing into the purge gas of the main synthesis of compressed carbon dioxide,

- heating the resulting gas mixture to an initial synthesis temperature,

- passing the heated gas through a methanol synthesis catalyst,

- cooling the reacted gas, the release of condensed crude methanol,

- separation of the non-condensed gas stream into two: return and purge,

and consists in the following: the return non-condensed stream for mixing with the purge gas stream of the main synthesis is sent to one or two circulation jet compressors and the circulation is carried out

a) either due to the pressure energy of the main synthesis purge gas, which are supplied to the jet compressor, followed by the indicated dosing into the stream of compressed carbon dioxide,

b) either due to the pressure energy of the carbon dioxide compressed in the compressor, the indicated dosage of which is carried out in the jet compressor with the subsequent introduction of the main synthesis into the purge gas stream,

c) either due to the pressure energy of the purge gas of the main synthesis and the pressure energy of said carbon dioxide compressed in the compressor. Provided that the pressure of the indicated flows is equal, a mixture of these flows is supplied to one jet compressor, and provided that the pressure of the indicated flows is not equal, each stream is supplied to an individual jet compressor.

The multiplicity of circulation varies from 1.1 to 5.0, depending on the pressure of the process gases: purge gas of the main synthesis and carbon dioxide. Moreover, the higher the pressure of the process gases, the higher the multiplicity of circulation.

The implementation of the proposed method is illustrated by the accompanying simplified technological schemes (1, 2, 3, 4, 5) in accordance with preferred embodiments of the invention.

Option 1 (figure 1)

The purge gas of the main synthesis of ammonia or methanol (stream 1) under a pressure of 32-40 MPa is supplied to the jet compressor, item 9, the circulation gas of methanol synthesis on purge gases (stream 2) is also fed there. The pressure of the mixed gas at the outlet of the jet compressor (stream 3) reaches 8-9 MPa.

Next to stream 3, carbon dioxide is metered, compressed in the compressor pos. 10 to the same pressure of 8-9 MPa (stream 6). The resulting stream 4 is sent to the methanol synthesis department, item 11. Raw methanol (stream 8) and off-gas (stream 5) are removed from the methanol synthesis unit. Next, stream 7 is discharged from the effluent stream as purge gas in order to maintain a certain concentration of inert components in the synthesis cycle. The remaining stream 2 is returned to the jet circulation compressor.

Option 2 (figure 2)

Carbon dioxide (stream 6), compressed in a compressor, pos. 10, up to a pressure of 32-40 MPa is supplied to the jet compressor, item 9. A circulation gas of methanol synthesis on purge gases (stream 2) is also supplied to the jet compressor. In this case, the pressure of the mixed gas at the outlet of the jet compressor (stream 3) reaches 4.5–9.0 MPa. Further, stream 3 is mixed with the main synthesis purge gas (stream 1) under a pressure of 4.5–9.0 MPa. The resulting stream 4 is sent to the methanol synthesis department, item 11.

Raw methanol (stream 8) and off-gas (stream 5) are removed from the methanol synthesis unit. Next, stream 7 is discharged from the effluent stream as purge gas in order to maintain a certain concentration of inert components in the synthesis cycle. The remaining stream 2 is returned to the jet circulation compressor.

Option 3 (figure 3)

Carbon dioxide (stream 6), compressed in a compressor, pos. 10, to a pressure of 30-35 MPa, is mixed with a purge gas stream 1 of the production of ammonia or methanol under the same pressure and the gas mixture is supplied to the jet compressor, pos. 9. A circulation gas of methanol synthesis on purge gases (stream 2) is also supplied to the jet compressor.

In this case, the pressure of the mixed gas at the outlet of the jet compressor (stream 3) reaches 4.5–9.0 MPa. Next, stream 3 is sent to the methanol synthesis department, item 11.

Raw methanol (stream 8) and off-gas (stream 5) are removed from the methanol synthesis unit. Next, stream 7 is discharged from the effluent stream as purge gas in order to maintain a certain concentration of inert components in the synthesis cycle. The remaining stream 2 is returned to the jet circulation compressor.

Option 4 (figure 5)

Carbon dioxide (stream 6), compressed in a compressor, pos. 10, to a pressure of 30-35 MPa, enters the jet compressor, pos. 12. In the jet compressor, pos. 12, a portion of the methanol synthesis gas circulating gas on purge gases is also supplied (stream 2a). From a jet compressor, pos. 12, stream 3 emerges. The purge gases from ammonia or methanol production (stream 1) under a pressure different from the pressure of carbon dioxide are fed to the jet compressor, pos. 13. The remainder of the circulating methanol synthesis gas in the purge gases is fed there (stream 26). From a jet compressor, pos. 13, stream 4 emerges. Streams 3 and 4 mix and form stream 9, which is sent to the methanol synthesis department, pos. 11. The pressure of the gas streams at the outlet of the jet compressors should be the same, due to the corresponding division of stream 2 into streams 2a and 2b. Raw methanol (stream 8) and off-gas (stream 5) are removed from the methanol synthesis unit. Next, stream 7 is discharged from the effluent stream as purge gas in order to maintain a certain concentration of inert components in the synthesis cycle. The remaining stream 2 is divided into two streams 2a and 2b, which are returned to the jet compressors, pos.12 and 13.

The results obtained during engineering calculations of the above process options are shown below in table 1. The invention is illustrated by the following examples.

Example 1 (illustrates the circulation with the electric drive) (figure 4)

The purge gas (stream 1) of the main methanol production has the following composition: СО - 9.97%, СН ₄ - 8.95%, Н ₂ - 68.71%, CO ₂ - 0.58%, Ar - 2.6% N ₂ - 9.19%, consumption 5140 nm ³ / hour and pressure 5.0 MPa. The purge gas is mixed with carbon dioxide compressed to 5.0 MPa (stream 6) in an amount of 770 nm ³ / h. A mixture of gases (stream 3) enters the inlet of the circulation compressor, item 9, previously mixed with the circulation gas (stream 2). Compressed circulating gas (stream 4) enters the synthesis compartment, item 11. The electric circulation pump provides a multiplicity of circulation of 4.5. Raw methanol (stream 8) in the amount of 1.043 t / h and residual gas (stream 5) are removed from the methanol synthesis unit. Then purge gas (stream 7) is separated from the residual gas, the remaining gas (stream 2) is returned to the inlet of the circulation compressor. The energy consumption for compressing carbon dioxide and circulating is 336 kWh per tonne of raw methanol.

Example 2 (FIG. 1)

Purge gas (stream 1) of the main methanol production having the following composition: СО - 9.97%, СН ₄ - 8.95%, Н ₂ - 68.71%, CO ₂ - 0.58%, Ar - 2.6%, N ₂ - 9.19%, consumption 5140 nm ³ / hour and a pressure of 40.0 MPa, it is supplied to the jet compressor, item 9, the circulation gas of methanol synthesis on purge gases (stream 2) is also fed there in an amount of 14991 nm ³ / hour, which corresponds to a circulation ratio of 2.54. The pressure of the mixed gas at the outlet of the jet compressor (stream 3) reaches 9.0 MPa. Then, carbon dioxide (stream 6) is dosed to stream 3 in an amount of 770 nm ³ / h and compressed to a pressure of 9.0 MPa. The resulting stream 4 is sent to the methanol synthesis department, item 11, where methanol is formed. Raw methanol (stream 8) is removed from the methanol synthesis unit (stream 8) in an amount of 1.578 t / h, and the electric energy consumption for compressing carbon dioxide is 101 kWh per ton of raw methanol.

Example 3 (figure 2)

Carbon dioxide in the amount of 770 nm ³ / hour (stream 6) is compressed in the compressor, item 10, up to 35.0 MPa is fed to the jet compressor, item 9, the circulation gas of methanol synthesis on purge gases (stream 2) in the amount of 23130 is also fed there nm ³ / hour, which corresponds to a multiplicity of circulation of 4.5. The pressure of the mixed gas at the outlet of the jet compressor (stream 3) reaches 5.0 MPa. Purge gas (stream 1) of the main methanol production, having the following composition: СО - 9.97%, СН ₄ - 8.95%, Н ₂ - 68.71%, CO ₂ - 0.58%, Ar - 2.6%, N ₂ - 9.19%, consumption 5140 nm ³ / h and a pressure of 5.0 MPa, is fed into the gas mixture after the jet compressor, item 9. The resulting stream 4 is sent to the methanol synthesis department, item 11, where methanol is formed. Raw methanol (stream 8) is removed from the methanol synthesis unit (stream 8) in an amount of 1.043 t / h, and the electric energy consumption for compressing carbon dioxide is 290 kWh per ton of raw methanol.

Example 4 (figure 3)

Purge gas (stream 1) of the main methanol production, having the following composition: СО - 9.97%, СН ₄ - 8.95%, Н ₂ - 68.71%, CO ₂ - 0.58%, Ar - 2.6%, N ₂ - 9.19%, consumption 5140 nm ³ / h and a pressure of 40.0 MPa is mixed with compressed to the same pressure carbon dioxide (stream 6) in an amount of 770 nm ³ / h. The gas mixture is supplied to the jet compressor, item 9, the circulation gas of methanol synthesis on the purge gases (stream 2) in the amount of 26558 nm ³ / hour, which corresponds to a circulation rate of 4.5, is also fed there. The pressure of the mixed gas at the outlet of the jet compressor (stream 3) reaches 9.0 MPa. Stream 3 is sent to the methanol synthesis department, pos. 11, where methanol is formed. Raw methanol (stream 8) is removed from the methanol synthesis unit (stream 8) in an amount of 1.859 t / h, and the electric energy consumption for compressing carbon dioxide is 183 kWh per ton of raw methanol.

As can be seen from examples 1, 2, 3, 4,

the use of circulation organized by the energy of compressed process streams in the methanol synthesis section on purge gases allows to reduce the specific energy consumption per ton of crude methanol in the range from 15 to 70%,

when using the energy of carbon dioxide compressed to 40.0 MPa and the purge gas energy of ammonia or methanol production for gas circulation in the synthesis section, the extraction of raw methanol increases by 18%,

at low pressure of the main synthesis, it is advisable to organize the circulation of synthesis on purge gases due to the energy of carbon dioxide compressed in the compressor.

Table 1 Name Purge gas synthesis Pressure: purge. gases / carbon dioxide, MPa Airflow gas synthesis nm ³ / h Consumption of CO ₂ nm ³ / h Synthesis pressure, MPa Circulation rate Electric energy consumption kW · h / t raw methanol Production. raw methanol t / h Example 1, taking into account the prototype Electric Compressor Circulation 5.0 / 5.0 5140 770 5.0 4.5 336.0 1.043 Example 2
Option 1 Purge Gas Circulation 40 / 9.0 5140 770 9.0 2.54 101.0 1.578 Example 3
Option 2 Circulation due to the energy of carbon dioxide compressed in the compressor 5.0 / 35.0 5140 770 5.0 4.5 290.0 1.043 Example 4
Option 3 Circulation due to purge gas and carbon dioxide energy 40/40 5140 770 9.0 4.5 183.0 1.859

Claims (4)

1. A method of producing methanol from a purge gas of the main synthesis of methanol or ammonia, comprising dosing compressed carbon dioxide into the purge gas of the main synthesis, heating the resulting gas mixture to an initial synthesis temperature, passing heated gas through a methanol synthesis catalyst, cooling the reacted gas, and condensed methanol raw and separation of the non-condensed gas stream into two: return and purge, characterized in that the return stream for mixing with the stream pr The main synthesis blow gas is sent to one or two circulation jet compressors and the circulation is carried out: a) either due to the pressure energy of the main synthesis purge gas, which is supplied to the jet compressor, followed by the indicated dosage into the stream of compressed carbon dioxide, b) either due to the pressure energy of compressed carbon dioxide, the dosing of which is carried out in a jet compressor with the subsequent introduction of the main synthesis into the purge gas stream, c) either due to the pressure energy of the purge gas of the main synthesis and pressure energy of the specified compressed carbon dioxide, which are supplied to one or two jet compressors. 2. The method according to p. 1c, characterized in that, provided that the purge gas pressure of the main production is equal to the pressure of carbon dioxide, the mixture of these streams is fed into one jet compressor. 3. The method according to p. 1c, characterized in that, provided that the purge gas pressure of the main production and the carbon dioxide pressure are not equal, each stream is supplied to an individual jet compressor. 4. The method according to claim 1, characterized in that the circulation ratio is in the range from 1.1 to 5.0, depending on the pressure of the gases — purge gas of the main synthesis and carbon dioxide: the higher the gas pressure, the higher the circulation ratio.

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