Optimization of process parameters in oxygen enriched combustion of biocoal and soma lignite blends by response surface methodology

Abstract

Co-combustion of coal and biomass in power plants has the potential to reduce emissions compared to burning coal alone. However, the use of biomass with coal in power plants has its own limitations. For this reason, biomass and coal are not often used together in power plants. Torrefaction is a method that can be used to eliminate / reduce all these negative effects. Torrefied biomass (biocoal) prepared under 300 °C and 30 min has similar properties to selected Turkish lignite. Existing power plants will improve CO2 capture by using oxygen enriched combustion: a promising retrofitting option. In this study Response Surface Methodology (RSM) by using Central Composite Designs (CCD) were performed to obtain the optimal conditions for the oxygen enriched combustion (OEC) of a biocoal / Soma Lignite blends. It was found that the proportion of biocoal in the blend was the most effective parameter for the all responses. Besides, the interactions of the two factors (the oxygen concentration and the proportion of biocoal in the blend) for all responses were successfully described by the Central Composite Design (CCD) model. Also, the process of oxygen enriched combustion optimization results showed that optimum values of oxygen concentration and the proportion of biocoal in the blend to minimize the CO, NOx and the bed temperature values, and to maximize the CO2 and combustion efficiency values were selected as 22.8 % by vol. and 37.2 % by wt., respectively. On the other hand, CO2 concentration in the flue gas increased when 50 % biocoal is added to lignite mixture which increases energy efficiency. Since the concentration of CO2 in the flue gases increased, the CO2 in the flue gases can be separated and captured by using CCS technology that is considered as the most energy and cost efficient technology.