The steam balance problem in coal-to-methanol production
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Gentlemen: In the comparison between Shell gasification and Texaco gasification technologies, how is steam balanced? Taking a methanol plant with an annual production capacity of 600,000 tons as an example, the steam generated by Shell boilers (at 5 MPa and 400°C) amounts to about 120 tons per hour. The main users of this steam are the shift reactor (about 30 tons per hour) and the methanol synthesis combined compressor (about 50 tons per hour); the remaining steam is basically sent to the medium-pressure steam network after being cooled and depressurized. And Texaco’s gasification technology does not produce steam; so what is the difference in terms of the extent to which thermal energy can be utilized compared to Shell’s technology? Ken would like to ask all the experts to provide a detailed explanation.
The 600kt/a Texaco gasifier generates much more steam than the Shell furnace’s by-product steam. The conversion unit associated with the gasification process is the main gas supply unit of the entire plant; there are 90 tons of saturated steam at 4.1 MPa, 340 tons at 1.1 MPa, and 160 tons at 0.46 MPa. 180 tons are produced as a by-product in the synthesis tower. The main users are ice machines with a capacity of 40 tons, and synthetic compressors with a capacity of 110 tons.
The amount of steam generated by the Texaco boiler is only about 5% of that produced by waste-heat boilers – a truly minimal amount. For methanol production projects, calculations must be done based on the individual units that require steam, such as those for synthetic compressors, turbine air compressors, and N2/CO2 compressors. As for whether high-pressure steam should be used for power generation, regarding the amount of steam generated as a by-product in the methanol production process, in methanol plants where steam consumption is relatively balanced (such as those operated by Shell), if the Texaco boiler type is adopted, it will be necessary to add more boilers to compensate for the 95% loss in steam volume resulting from the change in boiler type, given the same level of steam demand.