Experimental Analysis of Brewers’ Spent Grains Steam Gasification in an Allothermal Batch Reactor

Sérgio Ferreira,Paulo Brito,Carlos Castro,Luís Calado,Cândida Vilarinho,Eliseu Monteiro

doi:10.3390/en12050912

Sérgio Ferreira, Paulo Brito + Show 4 more

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https://doi.org/10.3390/en12050912

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Abstract

In this work, brewers’ spent grains (BSG) were evaluated and studied in order to obtain a combustible gas by means of allothermal steam gasification. BSG were preprocessed in a rotary dryer and a pelletizer prior to gasification in an indirectly heated batch reactor. BSG characterization was conducted by means of proximate, ultimate, and thermogravimetric analysis, allowing us to conclude that BSG have characteristics comparable to those of regular lignocellulosic biomasses. Gasification tests were performed in an allothermal bench-scale batch reactor in order to determine the effect of temperature and steam-to-biomass ratio (S/B) in the produced gas. The produced gas was mainly composed of 22.8–30.2% H2, 15.1–22.3% CO, and 7.2–11.1% CH4, contributing to a heating value of 8.11–9.0 MJ/Nm3 with the higher values found for a low S/B ratio and for high temperatures. The performance of the process was assessed by evaluating the cold gas and carbon conversion efficiencies. These indicators were found to be in the ranges 47.0%–52.1% and 57.0%–62.7%, respectively. The main conclusion of this work is that the produced gas obtained from BSG steam gasification has sufficient quality to open other options to beer producers to use their own brewing wastes to satisfy their energy needs, allowing them to progress toward the circular economy concept.

Highlights

Faster industry is required by contemporary consumers, which can lead to high power consumption and the production of large amounts of wastes [1]
The results showed that the brewers’ spent grains (BSG) displayed good potential for bio-oil production owing to their high volatile matter content and high heating value
BSG characterization through proximate, ultimate, and thermogravimetric analysis and a van Krevelen diagram allowed us to conclude that BSG have characteristics comparable to those of regular lignocellulosic biomasses

Summary

Introduction

Faster industry is required by contemporary consumers, which can lead to high power consumption and the production of large amounts of wastes [1]. One way in which industries become more efficient is by using their own by-products and wastes to produce their own energy. With this approach, a company can move closer to the circular economy concept [2]. 1% of the gross domestic product—a relevant weight in the country’s economy. This sector in Portugal produces about 160 thousand tonnes of waste per year, most notably brewers’ spent grains (BSG), which represent about 85% of these wastes [3,4]. About 135,000 tonnes of BSG are produced per year in Portugal as a by-product of the beer production process

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