Methanol Production Units
One of priority lines of Technex activity is project management and supply of Methanol Production Units of low and medium output from 10 000 to 100 000 tons annually.
Our units are primarily focused on associated gas processing.
Technex propose to their clients a time proved and traditional method for methanol production by means of syngas from associated gas.
Associated gas related Methanol Production Unit includes:
- gas sweetening;
- steam reforming;
- crude methanol synthesis;
- methanol rectification.
In case of necessity Methanol Production Unit can be equipped with water purification systems and thermal and electrical power generation systems, as well as water treatment systems and sewage treatment systems.
Methanol Production Unit can also produce hydrogen of any treatment level, for example, for catalytic hydrogenation in oil processing units.
Therefore the methanol production unit can become a part of oil and associated gas processing units at extraction sites.
Process description
Feeding Gas Fine Desulphurization
To meet the requirement of reforming catalyst to the sulfur content, fine desulfurization is required for the feed gas. After this process, the total sulfur content shall be limited to less than 0.1ppm.
The fine desulfurization is completed by hydrogenation conversion of organic sulfur, and absorption of generated hydrogen sulphide H2S by zinc absorbent ZnO.
Hydrogenation is driven with Co-Mo catalyst at a temperature 250-400 С, for hydrogen sulphide adsorption zinc oxide ZnO is applied.
Reforming/Conversion
The conversion of feed gas is completed in a primary steam conversion
furnace composed of radiation section and convection section.
Radiant section:
Top-fired furnace of square box structure is applied. Conversion pipes are arranged into upright rows in the square
box of the radiation section. Top-fired burners are provided between the rows of conversion pipes.
The heat generated from the burning of fuel gas is transferred by radiation for steam conversion the hydrocarbons in the reaction pipes. The preheated mixture of feed gas and steam enters the primary steam conversion furnace and undergoes the steam reforming in the presence of catalyst.
The main reactions are described as follows:
2CnH2n+2+nH2O==nCH4+nCO+(n+2)H2
CnH2n+2+nH2O==nCO+0(3n+1)H2
CH4+H2O==CO+3H2
CO+H2O==H2+CO2
Convection section:
The convection section is provided for waste heat recovery. The flue gas from the lower side of the radiation section enters the convection section, where it flows horizontally. Heat exchangers are arranged in the following sequence: gas mixture preheater, power steam superheater, feed gas preheater, flue gas WHB and furnace supply air preheater. After the final temperature is dropped to about 133ЃЋ, the flue gas is vented by induced draft fan through chimney.
In the convection section of the conversion furnace, most of the heat is transferred through convective heat transfer.
Compression of syngas
After the converted gas is cooled and separated from moisture, the fresh methanol syngas is produced. Fresh methanol syngas and circulating methanol syngas feature common gas flow, and centrifugal compressor is suitable for compression.
The centrifugal compressors are designed in a combined manner based on the process requirements that allows to send the converted gas and circulating gas with the same pressure after mixing.
In the first stages, the fresh methanol syngas is pressurized separately up to the circulating methanol syngas pressure and directly enters the compression cylinder of the circulating gas. Then the mixture is pressurized up to the synthesis pressure and sent to methanol synthesis system without cooling.
The syngas compressor is driven by a condensing steam turbine. In the unit operation the superheated steam of 3.82MPaG, 450⁰C is generated and used as the turbine power steam. For exhaust-steam condensing the cooler with a water cooling system is used. The steam condensate will be sent back to the water treatment plant.
Methanol synthesis
To produce methanol, syngas is catalyzed and at the same time following opposing exothermic reactions take place:
CO+2H2 = CH3OH+90.73kJ/mol
CO2+3H2 = H3OH+H2O+48.02kJ/mol
The above are exothermic reversible reactions.
The key techniques influencing methanol synthesis efficiency are the structure of synthesis reactor and the activity of the catalyst.
To reduce the consumption of cooling water, the methanol syngas is cooled and the methanol is condensed with pure air and water.
Methanol rectification.
Methanol rectification can be applied with two-column, three-column or even four-column rectification process.
Two-column rectification process means that gas and low-boiling impurities dissolved in crude methanol are distilled out in a pre-rectifier, and qualified product methanol is distilled out in a main rectifier.
Three-column rectification process means that main rectifier is divided into two columns, one operating under pressurized conditions and the other at atmospheric pressure. Vapor-phase latent heat of condensation at top of the first column is used as the heat source of the reboiler at bottom of the atmospheric column. So the atmospheric column requires no external heat sources.
Two-column process requires less investment but consumes more energy. Therefore, when steam is used as the heat source of rectification, three-column process saves about 0.4-0.6 t of low-pressure steam per each ton of methanol.
The low-grade waste heat in converted gas is used as the heat source of methanol rectification. This not only requires no external supply of low-pressure steam, but also reduces consumption of cooling water of the plant.
Waste water resulted from methanol rectification is sent to a stripper (together with process condensate). Purified condensate is used as wake-up water.
Air fans are used for the methanol condensation.
Storage tanks of product methanol
The tanks for product methanol storage are flat-bottom tanks with atmospheric pressure and outer insulation against heating by solar radiation.
