Performance comparison between the use of wood and sugarcane bagasse pellets in a Stirling engine micro-CHP system

Abstract

The use of locally available agricultural residues is an interesting alternative for residential heat and power generation based on the Stirling engine technology. However, some biomass with high ash content (agricultural residues) may cause operational problems and impact on the performance of the Stirling engine and the overall CHP system. This work is focused on the evaluation of useful parameters of a CHP system based on a 20 kWth pellet burner, a 1 kWe Stirling engine and a 20 kWth residential boiler using wood and sugar cane bagasse pellets. Similar temperatures in the Stirling hot end were found when using both fuels under steady-state and transient conditions. CO emission levels when using bagasse were lower than for wood pellets but slightly higher levels of NOx and higher accumulated ash were found. A fouling factor of the Stirling heat exchanger was found to be around 1.1 m2 °C/kW after two cycles (6 h) and 3.2 m2 °C/kW after three cycles (9 h) of operation when using wood pellets. A linear relation between the Stirling power output and the accumulated ash was assessed which was used to predict a longer operation time using bagasse pellets. This shows that after three cycles of operation with bagasse pellets, without removing accumulated ash, the CHP efficiency is still kept over 83% and for wood pellets, the CHP efficiency was kept over 90%.