Updraft gasifier and ORC system for high ash content biomass: A modelling and simulation study

Abstract

Ash content, and the problematic related to it are currently the most important drawbacks of biomass combustion. The present work carries out the modelling and simulation of an innovative CHP system composed of an updraft gasifier, an external combustion chamber and Organic Rankine Cycle (ORC) generator for the energetic valorization of olive leaves: a free and abundant by-product of the olive oil industry. The CHP system can produce 93.8kW of net electrical power and approximately 412kW of available thermal power for the heating necessities of a medium-sized olive oil mill. The CHP efficiency achieved is 58.41% and the net electrical efficiency 10.82% together with a biomass consumption of 240kg/h. Based on the simulation results, the producer gas reaches a suitable lower heating value (4.60MJ/kg) and a gasification efficiency of 88.10%. At the gasifier operating conditions, the producer gas presents the following mole composition: 12.8% H2, 19.2% CO, 2.6% CH4, 8.3% CO2, 11.8% H2O, 42.1% N2, 1.7% Tar and the rest Ar, O2, H2S, dust and particulates. The results from ORC simulations show a very good efficiency (18.7%) at 25bar of working pressure and 300°C of turbine inlet temperature. Toluene has been selected as suitable organic fluid for high temperature heat sources (>900°C). In this paper, an innovative energy recovery system for high ash content biomass has been theoretically developed, representing a good opportunity to promote distributed generation systems.