The project is a new technology intended to produce methanol at a drastically reduced cost so that it can be used for power-generation purposes. The methanol is to be sold to power-generation companies that can use it without any substantial modification to their existing plants. According to the StarChem, this breakthrough technology can reduce methanol production costs by as much as $50/t.
STARCHEM METHANOL SYNTHESIS PROCESS
The cost savings of the process come from more than one source. The StarChem process employs, as a fundamental part of the plant, a GE gas turbine. This has two functions, acting as both a low-cost source of the power required to operate the process and a low-cost source of air for enrichment. The process is tied to GE turbines. The Starchem process also uses membranes, rather than cryogenics, to produce enriched air. This has the primary benefit of low cost, coupled with an operability advantage in that enriched air becomes available virtually instantaneously, in contrast to a cold box, where many hours are required. In the StarChem process, the synthesis gas passes through a cascade of reactors. The first reactors in the cascade see reactive gas, with only the final reactor having conditions comparable to a reactor in a synthesis loop. This makes the product of a higher quality. Managing composition and temperature profiles to user advantage minimises life cycle costs of the methanol synthesis system. Finally, a combination of isothermal and adiabatic reactors can be used to minimise costs.
The raw material for the methanol is natural gas. Based on reforming of natural gas, the process uses air, which is extracted from a gas turbine and enriched in membranes. Air is drawn into the suction of a gas turbine and a significant fraction of it is extracted from the gas turbine compressor through a booster compressor and into air enrichment membranes. The balance of the air is fed to the gas turbine combustor or is used for internal component cooling. The membranes, which work on the principle that oxygen diffuses faster across the membrane than nitrogen, produce enriched air. The major part of the nitrogen and some residual oxygen remains in the main gas stream as depleted air. Depleted air is heated against compressor discharge air and returns to the gas turbine as secondary air to the combustor, forming a significant part of the mass flow through the turbine. Enriched air is compressed, heated and fed to the catalytic partial oxidation section. Natural gas is heated, desulphurised, mixed with steam, heated further and fed to the catalytic partial oxidation reactor. Synthesis gas is cooled, recovering useful heat in various ways, and is then compressed to a suitable pressure for methanol synthesis. Methanol is synthesised in a cascade of reactors.
The crude methanol passes to a methanol distillation section, where it is stabilised and reduced to an economic water content for transport. Purge gas from the methanol synthesis cascade is treated to recover hydrogen for recycling with the tail gas passing to the gas turbine as fuel. This eliminates the need for the air separation unit normally required to supply oxygen for the process. An additional innovation is the use of a series of reactors, arranged in a cascade, in lieu of the conventional methanol synthesis loop.
FOSTER WHEELER PARTNERSHIP
The technology was developed by StarChem, which has since reached an exclusive licensing agreement with Foster Wheeler. StarChem, Inc. holds 20 patents on this technology and related applications. Foster Wheeler has the reputation and expertise to guarantee the product.
Methanol is an inherently safe fuel and can be handled conventionally at the user's site without the substantial capital investment in special purpose tankers or unloading facilities required by other fuel systems. Methanol is a clean burning fuel, containing no sulphur or nitrogenous materials. It produces power with very low emissions compared to those of a natural gas-fired, combined-cycle unit. Methanol can also be used as a feedstock for more sophisticated processes in the petrochemical industry. Methanol may also come to be used in fuel cell cars, although these are not commercially viable at present.