RU2453525C1 - Method of producing methanol from natural gas and apparatus for realising said method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing methanol from natural gas, involving heating starting natural gas, obtaining superheated steam from prepared water and mixture thereof with the starting natural gas, single-step conversion of the vapour-gas mixture in a reforming furnace into converted gas, cooling the converted gas and single-step catalytic conversion of the converted gas into methanol in a synthesis reactor, wherein the heat of flue gases from the reforming furnace is used to heat the starting natural gas and the prepared water, superheating the steam and vapour-gas mixture, as well as heating the converted gas before inlet into the synthesis reactor. The invention also relates to apparatus for realising the described method.

EFFECT: use of the present invention increases efficiency of recycling energy from heat flux while simultaneously simplifying the conversion and synthesis processes.

11 cl, 1 tbl, 1 dwg

Description

The invention relates to an improved method for producing methanol by a two-stage process, in the first stage of which gas-vapor conversion of natural gas with steam is carried out, methanol synthesis is in the second stage, and an improved methanol production unit integrated into the complex gas treatment unit (UKPG).

A widely known method for the production of methanol, including the steam conversion of methane to synthesis gas (a mixture of CO and H ₂ ) with its subsequent catalytic conversion to methanol, and plants for its implementation [Karavaev MM, Leonov V.E. et al. Synthetic methanol technology. - M: Chemistry, 1984, pp. 72-125]. The main disadvantages of this process: high requirements for the purity of the source gas, high energy costs for producing synthesis gas and its purification, sophisticated equipment, a large number of intermediate stages of the process, unprofitability of small and medium-sized plants with a capacity of less than 1000 tons / day.

Closest to the proposed method and device is a plant for the production of methanol, integrated into the composition of technological objects of the gas field, and a method for producing methanol from natural gas (RU 2254322 C1, published June 20, 2005) implemented with its help. Hydrocarbon gas from the complex gas treatment unit (UKPG) at a pressure of 8.0 MPa and a temperature of 380-430 ° C enters the tube space of the tubular preliminary steam reforming reactor, the tubes of which are filled with the K-905 GIAP-16 nickel-containing catalyst. The gas resulting from the reforming proceeds to the next reforming stage, where the final synthesis gas is produced by adding oxygen. The process of formation of synthesis gas in a shaft reactor proceeds at a temperature of 600-950 ° C and a pressure of 8.0 MPa. The resulting synthesis gas with a temperature of 250-280 ° C enters a 2-stage isothermal methanol synthesis reactor with an external heat exchanger for cooling the reaction mixture. To carry out the methanol synthesis process, the reactor is filled with a copper-containing catalyst SNM-3C. The synthesis of methanol occurs at a temperature of 220-280 ° C and a pressure of 8.0 MPa. The cooled reaction mixture enters a separator to separate the crude methanol from the unreacted synthesis gas products. Raw methanol with a concentration of 78-84% is sent to the methanol storage park, and gases from the separator, mainly containing СН ₄ , Н ₂ and СО ₂ , are sent for use for own needs of the gas treatment plant (boiler room, power plant and other heaters) or mixed with gas treatment plant, and due to the small volumes of unreacted gas, the gas treatment plant does not affect the quality of the produced commercial gas.

The main difference between this method and traditional methods of producing methanol through synthesis gas (steam reforming, combined reforming, the Tandem process) is that by integrating the methanol production unit into the gas treatment plant, operating costs are reduced, while auxiliary production is used to the maximum extent possible, available as part of the gas treatment plant (flare, treatment facilities, sources of electrical energy, instrumentation and control air, operator room).

The disadvantages of this scheme are significant capital costs due to the need for compressor equipment to provide high pressure of natural gas (8.0 MPa) at the inlet of the reforming furnace, equipment for oxygen production and separation of the methanol synthesis unit into two reactors with an external refrigerator.

Given that the methanol production process is very energy-intensive, in the conditions of small-sized and largely autonomous methanol production, it is necessary to choose a technological process that would allow the plant to be profitable

- simplify the process from a technological point of view;

- The most efficient way to utilize the energy of heat flows;

- save on capital costs.

Previously known methanol production flowcharts did not satisfy this condition.

The technical result of the invention is to increase the efficiency of energy recovery of heat fluxes while simplifying the processes of conversion and synthesis.

The technical result is achieved by the fact that the method of producing methanol from natural gas includes heating the source of natural gas, obtaining superheated steam from the prepared water and mixing it with the source of natural gas, one-step conversion of the gas-vapor mixture in the reforming furnace into converted gas, cooling of the converted gas and one-stage catalytic conversion converted gas to methanol in the synthesis reactor, and the heat of the flue gases of the reforming furnace is used to heat the source of natural gas and under otovlennoy water, steam superheating and vapor mixture, and heating the reformed gas before entering the synthesis reactor.

In addition, the heat of converted gases is used to heat unprepared water, to produce steam from prepared water.

In addition, methanol is isolated from a part of the reaction gases leaving the synthesis reactor in a distillation column, and the other part is mixed with the converted gas as a circulation gas before entering the synthesis reactor.

In addition, the heat of the reaction gases leaving the synthesis reactor is used to heat the mixture of converted and circulating gases.

In addition, the heat of the converted gas is also used to heat the water-methanol solution in the cube of the distillation column.

In addition, the temperature in the synthesis reactor is controlled by withdrawing part of the cold mixture of converted and circulating gases and supplying it directly to the reaction zone.

The technical result is also achieved by the fact that the installation for producing methanol from natural gas contains successively installed and interconnected by a system of pipelines heat exchangers for heating natural gas and gas mixture, a reforming furnace to produce converted gas; a synthesis reactor for the catalytic production of methanol from the converted gas and a separator, as well as a heat exchanger for heating the converted gas, a heat exchanger for heating the prepared water, a waste heat boiler for receiving steam and a heat exchanger for superheating the steam, the outlet of the flue gas reforming furnace to use their heat is connected with annular space of heat exchangers for heating natural gas, prepared water, for overheating water vapor and heating the gas mixture, as well as with a heat exchanger for heating a converted gas.

In addition, the outlet of the converted gas reforming furnace is connected to the feed line of the converted gas to the synthesis reactor, successively passing through the recovery boiler, the annulus of the heat exchanger for heating unprepared water and the heat exchanger, with the outlet of the synthesis reactor connected to the tube space.

In addition, the heat exchanger at the outlet of the synthesis reactor through the separators is connected in one line with the inlet of the distillation column for methanol separation and in another line with the feed line of the converted gas to the synthesis reactor.

In addition, the distillation column cube is connected to the annular space of the heat exchanger, through which the converted gas supply line passes to the synthesis reactor after the heat exchanger to heat unprepared water.

In addition, a portion of the converted gas supply line to the synthesis reactor in front of the heat exchanger connected to the outlet of the synthesis reactor is connected to the synthesis reactor in the reaction zone.

The most optimal for methanol production at gas fields in the Far North in permafrost zones was the use of the steam conversion process.

The supply of natural gas to the methanol production unit is envisaged from the boundary of inter-workshop communications from the network of the existing complex gas treatment unit (UKPG) with a pressure of at least 2.2 MPa.

The invention is illustrated in the circuit shown in figure 1.

Positions in the diagram mean the following.

1 - reforming furnace;

2 - synthesis reactor;

3 - distillation column;

4-13 - shell-and-tube heat exchangers-recuperators;

14 and 15 - air cooling devices;

16 - waste heat boiler;

17-21 - separators;

22 - methanol collection capacity;

23 - antifreeze capacity;

24 - compressor unit (24/1 and 24/2 - compressors);

25-27 - pumps;

28 - smoke exhaust;

29 - block water treatment;

30 - deaerator.

A plant for producing methanol from natural gas contains successively installed and interconnected by a pipeline system heat exchangers 6 and 4 for heating natural gas and a gas mixture, a reforming furnace 1 for producing converted gas; a synthesis reactor 2 for catalytically producing methanol from the converted gas and separators 20 and 21. A heat exchanger 8 for heating the converted gas is connected to the converted gas supply line to the synthesis reactor 2. The tube space of the heat exchanger 7 for heating the prepared water through the separator 17 is connected to a recovery boiler 16 for receiving steam, which, in turn, is connected through the same separator 17 to the heat exchanger 5 for superheating the steam, which is mixed with heated natural gas and enters the pipe the space of the heat exchanger 4. The outlet of the flue gas reforming furnace 1 for using their heat is connected to the annular space of the heat exchangers 6, 7, 5 and 4 for heating natural gas, prepared water, for overheating the water pa and heating the steam-gas mixture and a heat exchanger 8 for heating the reformed gas.

The outlet of the converted gas reforming furnace 1 is connected to the feed line of the converted gas to the synthesis reactor 2 sequentially passing through the recovery boiler 16, the annulus of the heat exchanger 9 for heating unprepared (undeaerated) water and the heat exchanger 11, with the outlet of the synthesis reactor 2 connected to the tube space .

The heat exchanger 11 at the outlet of the synthesis reactor 2 through the separators 20 and 21 is connected in one line with the inlet of the distillation column 3 for methanol separation and in another line with the converted gas supply line to the synthesis reactor 2 (circulating gas).

The cube of the distillation column 3 is connected to the annular space of the heat exchanger 12, through the pipe space of which passes the feed line of the converted gas to the synthesis reactor 2 after the heat exchanger 9 for heating unprepared water.

A section of the converted gas supply line to the synthesis reactor 2 in front of the heat exchanger 11 connected to the outlet of the synthesis reactor 2 is connected to the synthesis reactor 2 in the reaction zone at several levels.

A method of producing methanol from natural gas is as follows.

Part of the natural gas supplied to the methanol production unit (UPM) (Fig. 1), intended for the conversion process, enters the heat exchanger 6 — the natural gas heater of the heat-using equipment unit (BTA) of the convection zone of the reforming furnace 1, where it is heated to a temperature of 350-450 ° C. Natural gas is then mixed with superheated water vapor. Overheating of saturated water vapor is carried out in heat exchanger 5 - BTA superheater. The technological scheme provides for automatic regulation of the ratio of natural gas and steam consumption for methane conversion, ensuring the required ratio of steam: gas = 2.7 ÷ 3.2: 1.

The resulting vapor-gas mixture with a temperature of 350-450 ° C is fed for heating to a heat exchanger 4 BTA. The vapor-gas mixture heated by flue gas heat to 500-580 ° C enters the reaction tubes of the reforming furnace 1, where the reaction of natural gas to water conversion takes place on a nickel catalyst at a temperature of 780-850 ° C and a pressure of 2.0-2.5 MPa steam to form a converted gas containing residual methane 4-5 vol.%, hydrogen 45-50 vol.%, carbon monoxide 9-10 vol.%, and water vapor 30-35 vol.%.

The output temperature of the converted gas is 780-850 ° C, as well as the temperature of the flue gases at the exit from the radiant zone of the furnace 1 of about 950 ° C is automatically controlled by the supply of fuel gas to the hearth burners of the tube furnace 1.

Part of the natural gas supplied to the unit is used as fuel gas. Before feeding into the furnace 1, fuel gas is distributed into streams for supply to the "pilot" and main burners.

Flue gases with a temperature of up to 200 ° C smoke exhaust 28 are emitted into the atmosphere to a height of not less than 30 m, ensuring the dispersion of harmful emissions to the maximum permissible values.

The technological scheme also provides for the use of converted gas heat leaving the reaction zone of the reforming furnace 1 in the gas cooler — heat recovery boiler 16. Due to the cooling of the gas from 780-850 ° C to 300-380 ° C, saturated steam is generated with a pressure of 2.0-2.5 MPa, which is fed from the drum separator 17 to the heat exchanger 5 - a BTA superheater.

The feed water, brought to the appropriate quality in the primary water treatment unit of the gas treatment unit, after the preparation unit 29, the heat exchanger 9 and the deaerator 30, is fed to the heat exchanger 7 from the discharge of the feed pumps 25, where it is heated to the saturation temperature due to the heat of the flue gases with partial formation of wet steam. Next, the feed water is supplied to the drum separator 17.

The technological scheme provides for the sequential recovery of the converted gas heat in the heat exchanger 9, a non-deaerated water heater, where non-deaerated (softened) water is heated by cooling the converted gas.

Then the heat of the converted gas is used in the heat exchanger 12 - the boiler of the distillation column 3, where due to the cooling of the gas the heat necessary for the rectification of raw methanol is transferred. After the boiler, the converted gas passes through the separator 18. The released condensate with a temperature of 141.5 ° C is used in the steam generation system of the installation.

The converted gas after the separator 18 is sent to the refrigerator-condenser 10, where antifreeze is used as an intermediate coolant. Due to the cooling of the gas, condensation of residual moisture occurs, which is separated in the separator 19. The released condensate is also sent to the vaporization system of the installation, and the dried converted gas is fed to the inlet of the compressor unit 24.

A mixture of converted and circulating gas, compressed to 5.0 MPa, from the discharge of the compressor unit 24 enters the heat exchanger 8 BTA, then to the heat exchanger-recuperator 11, where it is heated by the reaction products of methanol synthesis. Next, the mixture of converted and circulating gas enters the methanol synthesis reactor 2.

On the shelves of reactor 2 is a low-temperature copper-containing catalyst, the use of which determines the parameters of the synthesis process: relatively low temperatures 200 ÷ 280 ° C and low pressure of about 4.5-5.5 MPa. In order to achieve a more complete degree of methanol conversion, the synthesis gas is circulated with a constant supply of purge gases from the separator 20 for utilization on a gas treatment flare in order to maintain a predetermined level of inertia. The circulation gas after the separator 20 is directed to mix with fresh converted gas.

Temperature control in the catalysis zone of synthesis reactor 2 is carried out automatically by supplying a cold mixture of converted and circulating gas through bypass lines. The flow of cold gas is taken from the discharge of the compressor unit 24.

Heat recovery of the reaction gas leaving the synthesis reactor 2 is provided for heating the converted and circulating gas mixture in the heat exchanger-recuperator 11. Next, the cooled reaction gas is supplied to the condensation of methanol in air coolers 14, and then to the separator 20, designed to separate methanol- condensate from a gas-liquid mixture.

The methanol-condensate released in the separator 20 is fed into the tank, the separator 21, from where, after depressurization, it is sent for rectification.

The process of distillation of methanol-condensate is carried out in a packed distillation column 3.

The bottoms liquid taken from the bottom of the column 3 passes through a heat exchanger 12 - a boiler, where it boils due to the heat of the converted gas and is sent to the distillation column 3.

The temperature in the bottoms of the column 3 is regulated by passing the converted gas past the boiler. The bottoms product of column 3 (saline effluents) is sent to the treatment plant of the gas treatment plant.

The distillate of column 3 is condensed in a heat exchanger 13 and sent to a methanol collector 22, where it is under a nitrogen “pad” with a pressure of 50 mm Hg. From collection 22, production methanol is pumped by pump 26 to the methanol storage facility of UKPG.

The material balance of the installation is presented in the table.

In the conditions of a small-tonnage installation, this is the most economical method, which made it possible to exclude the supply of oxygen to the conversion of natural gas. This moment is important, because Failure to use oxygen significantly increases process safety. In addition, an oxygen evolution unit was excluded from the technological scheme, which significantly reduced capital costs.

As noted above, the efficiency of utilization of heat fluxes is of great importance for increasing the profitability of a methanol production plant. The best option in the conditions of autonomy of the installation is a scheme that allows not only to completely utilize the energy of heat fluxes, but also to do without additional sources of thermal energy, limiting itself to the heat released by the reaction apparatus. At the installation under consideration, the following scheme of heat flux utilization was proposed.

The heat of the flue gases generated during the combustion of fuel in the furnace 1 is used in heat exchangers of the heat-using unit of the convection zone of the reforming furnace 1:

- 4 for heating the vapor-gas mixture entering the conversion into reaction tubes;

- 5 for overheating of saturated water vapor coming from the drum-separator 17;

- 6 for heating natural gas mixed with superheated steam;

- 7 for heating feed water;

- 8 for heating the converted gas in front of the methanol synthesis reactor 2.

The heat of the converted gas generated in the reforming furnace 1 is used mainly in the system for producing water vapor in heat exchangers:

- 16 to obtain saturated water vapor;

- 9 for heating non-deaerated (softened) water;

- 12 for heating the water-methanol mixture in the process of rectification of crude methanol.

The heat of the reaction gases of the methanol synthesis reactor 2 is used to heat the mixture of converted and circulating gas in the heat exchanger 11, sent to the synthesis reactor 2.

An important point in terms of energy and resource conservation is that all unreacted water during reforming is released in separators 18, 19 and returned to the vaporization system, thereby minimizing industrial effluents.

A significant reduction in capital costs was made possible by integrating the methanol production unit directly into the complex gas treatment unit at the gas field. This not only significantly reduced capital costs, but also reduced the cost of methanol.

A distinctive feature of integrated technology compared to traditional technology is the exclusion of a number of technological units from the technological scheme:

- there is no need for a block for the preparation of raw materials, because the commercial gas prepared at the gas treatment facility at the fields of the Far North of the Russian Federation does not contain sulfur compounds that poison the catalysts for the conversion of the vapor-gas mixture and the synthesis of methanol;

- excludes the block purification of crude methanol from impurities, because its concentration of 85-95% allows you to use the resulting methanol as an inhibitor of hydrate formation;

- no primary water treatment unit is required, as such a unit, as a rule, is part of the GPP.

Technical and economic assessments show that through the integration of a small-capacity methanol plant into the gas treatment facility, an almost threefold reduction in capital costs is achieved, which largely makes the construction of methanol production in gas production areas profitable.

Currently, two such plants have been built with a capacity of 12,500 and 40,000 tons per year. Both are located at the Yurkharovskoye oil and gas condensate field, a subsidiary of OAO NOVATEK.

The material balance of a methanol production unit with a capacity of 12,500 tons of methanol per year.

Claims (11)

1. A method of producing methanol from natural gas, including heating the source of natural gas, obtaining superheated steam from the prepared water and mixing it with the source of natural gas, a one-stage conversion of a gas-vapor mixture in a reforming furnace into a converted gas, cooling the converted gas and a one-stage catalytic conversion of the converted gas into methanol in the synthesis reactor, and the heat of the flue gases of the reforming furnace is used to heat the source of natural gas and prepared water, overheating water vapor steam and gas mixture, as well as heating the converted gas before entering the synthesis reactor. 2. The method according to claim 1, characterized in that the heat of the converted gases is used to heat unprepared water to produce steam from the prepared water. 3. The method according to claim 1, characterized in that methanol in the distillation column is isolated from a part of the reaction gases leaving the synthesis reactor, and the other part is mixed with the converted gas as a circulating gas before entering the synthesis reactor. 4. The method according to claim 3, characterized in that the heat of the reaction gases leaving the synthesis reactor is used to heat the mixture of converted and circulating gases. 5. The method according to claim 3, characterized in that the heat of the converted gas is also used to heat the water-methanol solution in the cube of the distillation column. 6. The method according to claim 4, characterized in that the temperature in the synthesis reactor is controlled by removing part of the cold mixture of converted and circulating gases and feeding it directly to the reaction zone. 7. Installation for producing methanol from natural gas, containing heat exchangers for heating natural gas and a gas-vapor mixture sequentially installed and connected by a system of pipelines, a reforming furnace to produce converted gas; a synthesis reactor for the catalytic production of methanol from the converted gas and a separator, as well as a heat exchanger for heating the converted gas, a heat exchanger for heating the prepared water, a waste heat boiler for receiving steam and a heat exchanger for superheating the steam, the outlet of the flue gas reforming furnace to use their heat is connected with annular space of heat exchangers for heating natural gas, prepared water, for overheating water vapor and heating the gas mixture, as well as with a heat exchanger for heating a converted gas. 8. Installation according to claim 7, characterized in that the outlet of the converted gas reforming furnace is connected to the feed line of the converted gas to the synthesis reactor successively passing through the recovery boiler, the annular space of the heat exchanger for heating unprepared water and the heat exchanger, with the pipe space of which synthesis reactor output. 9. The apparatus of claim 8, characterized in that the heat exchanger at the outlet of the synthesis reactor through the separators is connected in one line with the inlet of the distillation column for methanol separation and in another line with the converted gas supply line to the synthesis reactor. 10. The installation according to claim 9, characterized in that the distillation column cube is connected to the annular space of the heat exchanger, through which the converted gas supply line to the synthesis reactor passes through the tube space after the heat exchanger for heating unprepared water. 11. Installation according to claim 9, characterized in that the portion of the converted gas supply line to the synthesis reactor before the heat exchanger connected to the outlet of the synthesis reactor is connected to the synthesis reactor in the reaction zone.