Syngas Production, Clean-Up and Wastewater Management in a Demo-Scale Fixed-Bed Updraft Biomass Gasification Unit

Gabriele Calì,Simone Meloni,Paolo Deiana,Michele Mascia,Enrico Maggio,Alberto Pettinau,Claudia Bassano

doi:10.3390/en13102594

Abstract

This paper presents the experimental development at demonstration scale of an integrated gasification system fed with wood chips. The unit is based on a fixed-bed, updraft and air-blown gasifier—with a nominal capacity of 5 MWth—equipped with a wet scrubber for syngas clean-up and an integrated chemical and physical wastewater management system. Gasification performance, syngas composition and temperature profile are presented for the optimal operating conditions and with reference to two kinds of biomass used as primary fuels, i.e., stone pine and eucalyptus from local forests (combined heat and power generation from this kind of fuel represents a good opportunity to exploit distributed generation systems that can be part of a new energy paradigm in the framework of the circular economy). The gasification unit is characterised by a high efficiency (about 79–80%) and an operation stability during each test. Particular attention has been paid to the optimisation of an integrated double stage wastewater management system—which includes an oil skimmer and an activated carbon adsorption filter—designed to minimise both liquid residues and water make-up. The possibility to recycle part of the separated oil and used activated carbon to the gasifier has been also evaluated.

Highlights

The increasing attention towards climate change and greenhouse gas emissions makes the exploitation of renewable energy sources one of the key pathways for sustainable power generation.It is expected to involve a significant reduction of CO2 emissions in the power generation sector, according to the most recent assessment by the International Energy Agency [1]
The same target has been formally assumed by the European Union (EU) with the publication, in December 2018, of the revised “renewable energy directive” (2018/2001/EU), which aims at keeping the EU a global leader in renewable energy and to meet the commitments under the Paris Agreement [2,3]
The key index assumed as a measure of the global performance of the gasification process is the so-called cold gas efficiency, conventionally defined on the basis of the first law of thermodynamics as the ratio between the chemical energy of raw syngas and the chemical energy of primary fuel: ηCG =

Summary

Introduction

The increasing attention towards climate change and greenhouse gas emissions makes the exploitation of renewable energy sources one of the key pathways for sustainable power generation. It is expected to involve a significant reduction (some 8 Gt/yr by 2050, with a share of 32% among the other low carbon approaches) of CO2 emissions in the power generation sector, according to the most recent assessment by the International Energy Agency [1]. The diffusion of intermittent sources (i.e., wind and solar) makes grid regulation increasingly challenging since ever changing electrical loads must be balanced with ever changing, non-programmable generation [4]. Bioenergy can be considered a key option to mitigate greenhouse gas emissions, replace. Energies 2020, 13, 2594 fossil fuels, and—considering its programmable exploitation—ensure a more secure and sustainable energy system [5]. The use of waste biomass (e.g., agro-industrial, municipal and forestry residues) [6] is even more interesting since it allows production of almost CO2 -free energy as an alternative to landfill or inefficient biological processes

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Conclusion