Solid Digestate—Physicochemical and Thermal Study

Krzysztof Dziedzic,Marta Arczewska,Michał Jurczyk,Marek Wróbel,Krzysztof Mudryk,Tadeusz Pająk,Marcin Jewiarz,Bogusława Łapczyńska-Kordon

doi:10.3390/en14217224

Krzysztof Dziedzic, Marta Arczewska + Show 6 more

Open Access

https://doi.org/10.3390/en14217224

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Abstract

Biogas production is an important component of sustainable energy management. In addition to energy-rich biogas, this process also generates solid waste in the form of digestate. The management of this stream has been problematic for many years. One promising method of utilizing this fraction seems to be incineration under controlled conditions. This paper presents an analysis of mixtures of different digestates to assess their suitability for incineration. Four digestates based on corn silage CS and apple pomace AP were used as test fuel. The ultimate and proximate analysis showed that this fuel deviates from the standards accepted for pure biomass, but was found in other fuels, especially those treated as waste. This materials can be a valuable source of energy, but combustion needs be undertaken in special units. Moisture content of investigated digestate-type ranges from 11.9–12.2% and ash content ranges from 8.2% to 11.6%. This could lead to ash sintering and slugging problems, which are problematic, especially because it is not designed for such types of fuel boilers. The study showed correlations between the elemental composition and the course of basic combustion processes. The ultimate analysis of all mixtures shows that the shares of major elements looks similar. These results are connected with the thermogravimetric analysis TGA, which shows similar thermal decomposition for all four mixtures. It is valuable information because, in this special case, when we have mixtures of corn silage and apple pomace originated digestates, the changes in the ratio CS:AP will not affect combustion significantly.

Highlights

The process of anaerobic digestion of organic waste produces a gas mixture called “biogas”, composed of approximately 50% methane (CH4 ) and 50% carbon dioxide (CO2 ).This process generates waste in the form of a digestate [1,2]
The highest ash content (11.6%) was found in the mixture containing 75% of maize silage and 25% of apple pomace (Table 3). Such a high ash content most likely resulted from the technology of obtaining maize biomass for biogas production
The achieved values were significantly lower than studies conducted by [14], where the specific density was 1.26 g cm−3

Summary

Introduction

The process of anaerobic digestion of organic waste produces a gas mixture called “biogas”, composed of approximately 50% methane (CH4 ) and 50% carbon dioxide (CO2 ). This process generates waste in the form of a digestate [1,2]. Due to the properties of the digestate, far, it has been used mainly for fertilizing purposes. This is often combined with the use of biocarbon produced from other agricultural products and residues [5,6]. Due to the construction of numerous biogas plants in Poland, in recent years—from 8 in 2008 to 93 in 2016

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