611 / 2019-01-20 15:39:42

Influence of operation parameters on hydrothermal carbonization characteristics of Agroforestry biomass

Hydrothermal carbonization Biomass pretreatment Solid biofuel Fuel upgrading

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As a carbon-neutral fuel, biomass is the only alternative to renewable organic petroleum on the earth, accounting for about 10% of global energy consumption, which has a very promising utilization prospect. However, biomass raw materials have problems such as high water content, low conversion rate and difficulties in collection, grinding and storage, etc. Hydrothermal carbonization is a method of thermochemical treatment of biomass in hydrothermal medium or hot compressed water, which can treat biomass with high moisture directly and reduce the ash content of solid product (biochar) at the same time. It is a promising pretreatment technology for biomass application. Biomass species and hydrothermal operation parameters have significant impacts on the physicochemical properties of biochar, such as calorific value, mass density and ash content in the process of hydrothermal carbonization. Therefore, it is of great significance to explore the hydrothermal carbonization characteristics of raw biomass materials.

In this study, corn straw and poplar sawdust were selected as biomass materials. The hydrothermal carbonization was carried out in a hydrothermal benchtop autoclave reactor of 500 mL in volume from Beijing Century Senlong Experimental apparatus Co Ltd. The effects of initial pressure, reaction temperature, holding time and biomass species on biomass hydrothermal carbonization were analyzed. The physicochemical properties of raw biomass and solid product (biochar) (such as proximate analysis, ultimate analysis, heating value, morphology, etc.) were characterized by different methods. The obtained results indicate that the mass yield and energy yield of biochar decrease with the increasing of reaction temperature or holding time, however, the fuel performance of biochar involving fixed carbon content, the heating value, has a remarkably improvement. The solid product yield fraction decreases and the hydrothermal reaction rate increases significantly with the increasing of reaction initial pressure. The ash content is decreased significantly compared with raw biomass. In addition, under the same conditions, the biochar of poplar wood have better fuel properties than corn straw.

The reaction temperature and holding time have a significant effect on the solid yield, energy yield and fuel performance of biochar. On the other hand, it appears that poplar sawdust is more reactive and produces less solid products than corn straw, in the same hydrothermal carbonization conditions.