BioCrack: Greater stability and energy efficiency in the biogas plant
Case Study - Biogas plant project of WHG Anlagenbau GmbH & Co. KG
Residual gas potential in the open final storage
Reducing residual gas potential and re-circulated quantities with BioCrack
The customer and the Problem
The biogas plant of ACD Bioenergy in Upper Franconia was planned and erected by WHG Anlagenbau in 2005. In the course of time, the 765 kWel plant was extended. In 2008 it finally consisted of two digesters with a capacity of 1,000m³ each, two secondary fermenters with a capacity of 1,730m³ and 2,260m³, and an open final storage with a usable volume of 3,180m³.
A mixture of silage maize, whole plant silage as well as pig and cattle manure was added to the biogas plant each day. The relatively short retention time of approx. 72 days in the digester and post digester led to high tank loads and floating crusts. Regular sample analyses showed that there was a high residual gas potential in the open final storage. The residual gas potential was intended to be used to optimize the biogas plant as a whole. The operators decided to try BioCrack before investing 30,000 to 40,000 euros into covering the open final storage.
WHG Anlagenbau installed 3 BioCrack modules and one BioCut in a standard container and connected the latter to the central pump station. For four weeks, each day part of the organic suspension in the digesters was treated in a bypass. The overflow substrate, which is conveyed from the digesters to post digester, was also led through the BioCrack modules.
There were positive effects very soon: floating crust formation clearly decreased. At the same time the current consumption of the digester mixers dropped by approx. 10% to 14.8 A, and the mixing times in the post digester and the final storage could be reduced by 30%. The required amount of re-circulated matter also dropped by 50%. The gas yield increased by 12%, biogas plant operation was smoother. A subsequent 6-week fermentation test produced a residual gas yield of 150 liters of biogas per kg of dry matter, i.e. a reduction of 14%.
In the words of Herr Derks: "The test results were so positive that we immediately took over the pre-installed system. The residual gas potential of our biogas plant is so low today, we don't need the expensive final storage covering."