Co-firing of natural gas and Biomass gas in biomass integrated gasification/combined cycle systems

This work aims to evaluate the co-firing of gas derived from biomass and natural gas in combined cycles. It is suggested that co-firing can solve some of the initial technological problems associated with the gas turbines of BIG-GT (Biomass Integrated Gasification/Gas Turbine) plants. De-rating is the simplest strategy that allows continuous gas turbine operation with low calorific value fuels, but it also reduces cycle power and efficiency. The proposed biomass gas is derived from sugar-cane residues and has a lower heating value of around to 6 MJ/Nm3. Modeling results show that if the natural gas content is higher than 35–50% (energy basis) no de-rating will be necessary. At these proportions, the efficiency of electricity generation is not substantially reduced vis-à-vis the reference case. Another important outcome of the modeling is that the peak in power that occurs for natural gas contents slightly higher than 50% in energy basis. Another advantage of co-firing is that it will entail only small hardware modifications to the gas turbines. A comparison is made between the co-firing strategy and the improvements likely to arise from retrofitting gas turbines for LCV fuels.