Biogas vs dry food
DDGS (distiller' dried grains with solubles) competes on the market with grain and is often sold at a loss. This situation occurs every 3 years when the price for grain is low and the price for fuel is high.
Biogas plant gives own fuel to replace the natural gas or bunker oil. Processing of distillery stillage into biogas allows the distillery to eliminate 70-100% of its fuel consumption. Thus, it is possible to reduce the cost of alcohol and be independent from the market conditions. Biogas can be used directly in the same boilers in the mix with natural gas or alone.
Stilage can be treated in the anaerobic digester "as it is" with the dry matter 7-12% or evaporated to total solid 30%. Evaporation gives three advantages. (1) the volume of AD digesters is reduced 3 times. (2) the amount of effluent is reduced 3 times. (3) steam can be used back at the distillery. The disavantage is that the condensation or evaporation requires fuel for the evaporation. But stilage is still hot after the distilling and teh heat is not lost and steam is re-used
From our expeince the evaporation makes sense for big distilleries with the amount of stilage more than 300-350 tonnes a day. Because when the distillery is small, evaporation doesn't lead to the reduction of number of anaerobic digesters. There will be bigger or smaller but still 1 digester wherther stillage or the condensed stillage. If the distillery is big enough, evaporation gives an effect not only of the digester volume reducton but the digester number reduction.
The optimum total solid of the condensed stilage is 30%. This is because it results in the total solids 9-10% in the digester. And this is maximum with what mixers are able to work safe.
The best technology for stillage is vertical CSTR technology for 3 reasons. The vertical reactor has optimal mass and heat transfer and consumes less energy for own needs. Distilleries are often located in urban areas and are limited in space and the vertical reactor requires it less. One large vertical reactor costs less than several small CSTRs.
Zorg Biogas has experience at the ethanol distillery in Hincesti, Moldova, since 2013. The biogas plant was originally designed to work with grain stillage. But in fact, it works on grain one season and on the molasses the other.
The distillery in Hincesti changed burners in the existing boilers to work on the mix of natural gas and biogas but later completely refused from natural gas.
The CSTR biogas plant works well but it was built before we gained the experience with the vertical technology. The new biogas plants for distilleries we would make vertical CSTR like we do for sugar mills. For sugar mills we also started with CSTR but than switched to vCSTR.
When operating a biogas plant, it is necessary to take into account the insufficient content of micronutrients to support the bacterial growth. Therefore, the addition special chemical additives is required. But amount of these micronutrients is not that much though. 1 l additive per 300 tonnes of stillage average
Unlike grain stillage, molasses vinasse is not suitable for production of DDGS. Therefore, biogas plants for molasses distilleries are generally the only possible solution. The same is applied to the vinasse from sugar cane, vinasse from nopal, cactus, agave, beet juice, effluent from ethanol plants with straw as a substrate.
To calculate a quotation for a biogas plant, please fill out the questionnaire for distilleries.