Oil Palm Wastes Co-firing in an Opposed Firing 500 MW Utility Boiler: A Numerical Analysis

Abstract

Malaysia is rich in palm oil plantations, where oil palm wastes (OPWs) are one of the readily accessible biomass resources. OPWs has the potential to be used as a fuel for electricity generation. Hence, the evaluation of OPWs co-firing for one of Malaysia's 500 MW utility boilers was executed numerically. Three types of OPWs were tested including empty fruit bunches (EFB), palm kernel shell (PKS), and palm mesocarp fibres (PMF). The predicted furnace exit gas temperature (FEGT) from the numerical model was validated against the actual FEGT from the power plant where the current boiler is situated, revealing a difference of less than 10%. The nose area temperature was predicted to exceed the cap of 1200°C in OPWs co-firing cases due to higher volatile matter (VM) in OPWs than the baseline of pure coal case, leading to higher levels of volatile release. When co-firing with OPWs, the predicted unburned carbon (UBC) at the boiler's outlet is lower because OPWs-coal blends contain less fixed carbon (FC) than the pure coal blend. UBC levels were anticipated to be lower than the loss of ignition (LOI) limit in all cases, highlighting its positive impact on carbon reduction. Slightly lowered mill performance was observed as a result of the calculated OPWs fuel flow surpassing the normal operation in the power plant to make up for the low gross calorific value (GCV) of OPWs while meeting the required load from the boiler. OPWs co-firing was predicted to emit lower carbon monoxide (CO) and carbon dioxide (CO2) than baseline coal due to lower FC. Nonetheless, higher thermal nitrogen oxides (NOx) were predicted due to the higher flame temperature created by OPWs co-firing. Even so, it is recommended that the ash mineral composition be included in future numerical studies since the ash minerals may have an effect on the emitted NOx.