Efficient operation of a gas turbine on methanol using chemical recuperation

Environmental and political concerns, together with new legislations, are pushing for a fuel shift in the power industry and more generally for many thermal applications. Adding to the coming decrease of oil and natural availability (or price increase), it opens avenues for new fuels. Among those, alcohols are strong candidates. In fact, short alcohols are easily produced and stored and require only moderate modifications of existing combustion systems. For example, operating an existing gas turbine (GT) on methanol requires moderate modifications (mainly in the combustion system). However, methanol can be used more efficiently. Unlike methane or other hydrocarbons that decompose at high temperature (1000K), methanol undergoes an endothermic decomposition at low temperatures (400K to 600K) to give CO and H2. It therefore opens avenue for coupling the GT with a chemical recuperation system. In other words, the methanol will be cracked using the waste heat of the flue gases with a gain in fuel heating value hence the original fuel is thermally upgraded. The present study will investigate the upgraded fuel combustion properties. The laminar flame speed of the upgraded fuel/air mixtures will be presented and compared to methane and methanol under conditions relevant to GT combustion. Several upgraded fuel compositions will be considered depending on the water content in the feed methanol. Further, we consider a recuperated micro GT (Turbec T100) based cycle fueled with methanol. The numerical study focuses on different thermodynamic cycles. Firstly, a reference case is considered assuming a direct fueled GT. Further, cycles including the cracker are studied keeping the power constant. The fuel efficiency gain due to the cracker will be investigated as function of the water content in the feed methanol. Finally, a case including CO2-removal will be presented and it will be shown that the cracker enables an efficient carbon capture and sequestration scheme