The pyrolysis and gasification of digestate from agricultural biogas plant / Piroliza i gazyfikacja pofermentu z biogazowni rolniczych

Abstract

Anaerobic digestion residue represents a nutrient rich resource which, if applied back on land, can reduce the use of mineral fertilizers and improve soil fertility. However, dewatering and further thermal processing of digestate may be recommended in certain situations. Limited applicability of digestate as fertilizer may appear, especially in winter, during the vegetation period or in areas where advanced eutrophication of arable land and water bodies is developing. The use of digestate may be also governed by different laws depending on whether it is treated as fertilizer, sewage sludge or waste. The aim of this paper is to present the effects of thermal treatment of solid fraction of digestate by drying followed by pyrolysis and gasifi cation. Pyrolysis was carried out at the temperature of about 500°C. During this process the composition of fl ammable gases was checked and their calorifi c value was assessed. Then, a comparative analysis of energy parameters of the digestate and the carbonizate was performed. Gasifi cation of digestate was carried out at the temperature of about 850°C with use of CO 2 as the gasifi cation agent. Gasifi cation produced gas with higher calorifi c value than pyrolysis, but carbonizate from pyrolysis had good properties to be used as a solid fuel.

Air gasification of digestate and its co-gasification with residual biomass in a pilot scale rotary kiln

“…3b). Very probably, the air that gets at the head of the kiln, favoured the fast and exothermic combustion reactions (8)(9)(10)(11). The temperature drop between the head and tail of the kiln was of (11)…”

“…Its water content is about 90 wt%, so that moving it at any distance using trucks is expensive. Therefore, planning how to manage the digestate waste is a crucial task when a biogas plant is to be realized, especially when spreading in agricultural land is not possible [8]. In anaerobic digestion the major limitation is usually the feedstock incomplete conversion.…”

“…Wiśniewski et al gasified digestate at 850 °C with use of CO 2 as gasifying agent in a batch reactor electrically heated. Gasification test run for 1500 s, along this time syngas composition was measured, and the corresponding gas heating value was found to be 3.7 MJ/Nm 3 dry [8]. Nanna et al gasified digestate in a continuous bench scale rotary kiln by CO 2 , steam and mix of them at 800 °C.…”

Integration of Hydrothermal Carbonisation with Anaerobic Digestion; Opportunities for Valorisation of Digestate

“…As a result, there is a growing need to explore alternative digestate markets and land recycling, with emphasis on digestate enhancement technologies capable of adding value to the whole digestion process. Transforming digestate into carbonaceous solid and liquid fractions using technologies such as pyrolysis [3][4][5][6][7][8][9][10] and hydrothermal carbonisation (HTC) [11][12][13] are now under investigation. The main barriers for industrial uptake of pyrolysis include the requirement for feedstocks to have low moisture content (10% or less) to reduce negative effects of stability, viscosity, pH, and corrosiveness of the pyrolysis liquids [14]; unfavourable energy balances (i.e., high OPEX due to energy consumption for initial feedstock preparation and drying, including high operating temperatures in addition to heat loss and maintenance) [15,16]; controlling the emissions from pyrolysis processes [17]; issues of treatment, upgradability and utilisation of pyrolysis liquids [18,19].…”

Small-Scale Energy Use of Agricultural Biogas Plant Wastes by Gasification

“…A digestate from a pilot biogas plant located at the Experimental Station in Bałdy, Poland (N54° 36′ 1.8073″, E20° 36′8.5295″) was used in this research. The following technological parameters of the fermenter were used [11]:…”