FLEX-CRASH

Mechanical disintegration of lignocellulosic substrates by means of a ball mill for substrate treatment and flexibilization of the biogas production

Topic

The use of lignocellulosic residues such as horse manure, landscape maintenance material or straw from agriculture represent a new utilization path for biogas production. Since these substrates usually have high dry matter and lignin contents, special pre-treatment is required for utilization in the biogas plant. Without this pre-treatment, the fermentation substrates are not completely and slowly degraded. This is accompanied by low methane yields and a resulting uneconomical operation. Furthermore, process-related problems, such as increased floating layers and a higher stirring effort in the fermenter, arise without a pretreatment. Mechanical pretreatment by means of a ball mill can accelerate the kinetics of the degradation and gas formation process and increase the resulting methane yield of unused residues. Additionally, the process reliability and economic efficiency are enhanced. Therefore, it contributes to a flexible and sustainable electricity production.

Goals

The aim of the project is to further develop the ball mill and to optimize its design and process technology so that lignocellulosic substrates can be optimally processed for flexible biogas production. As a result, operational as well as economic advantages can be expected. This would make the use of by-products and residues from agriculture in biogas plants attractive and thus replace a part of the energy crops cultivated for biogas production. Furthermore, it would mean an improvement in the CO2 footprint of the entire process chain and contribute to the sustainability of biogas plants.

Project tasks of the State Institute

In 2022, the ball mill could be put into operation. In preliminary test operation, the system was tested with different substrates under various operating settings. Furthermore, more safety elements were constructed and implemented at the housing and the sampling spots of the substrate pre-treatment plant. In the last quarter of the year, the ball mill was switched from test operation to continuous operation and is now feeding fermenter 1 of the research biogas plant with pre-treated substrate.

A pre-treatment trial with an increased share of solid manure is planned for the coming year at the biogas plant over a period of 6 months. Digester 1 will be fed with pre-treated substrate through the ball mill, whereas digester 2 will be fed with the same amount of substrate and the same substrate composition in form of untreated material. The aim of the experiment is to determine the influence of the substrate treatment with the ball mill on the gas yield and the viscosity of the digesters.