Renewable energy

Renewable energies are one of the major trends of the decade. Although the replacement of conventional fossil and nuclear power plants by alternative energy sources cannot be ensured for decades to come, solar energy and geothermal energy, hydropower, wind power and bio-energy plants can make an increasing contribution to CO₂-neutral energy supply.

This trend has led to the European objective to achieve a 20% share of renewable energies by 2010. With this aim, different results are the goal, collectively the emphasis is on energy security that takes climate protection into account, is CO₂-neutral and economical, while at the same time reducing dependence on outside energy suppliers.

Biogas plants can make a significant contribution, since compared to solar, hydro and wind power; they do not depend on external conditions and ensure a continuous power supply, which combine electricity with the production of regionally usable heat energy, is to the benefit of the surrounding agricultural infrastructure, and also solve the waste problems of agricultural enterprises.

STULZ-PLANAQUA biogas plants are specifically tailored to the prevailing conditions. The efficiency of the systems is significantly influenced by the high industry standards and high plant availability. Many of the biogas plants built in recent years have been built without a view to long-term operation in terms of quality; due to the low availability and operational problems many operators of biogas plants have not achieved commercial operation. Through its superior quality, sophisticated detail solutions and optimal selection of material, STULZ-PLANAQUA biogas plants ensure long-term economic operation as only an experienced engineering company can guarantee.

Basic concept of biogas plants

In biogas plants, anaerobic microbial degradation of the substrate takes place in so-called fermenters. The substrate consists mostly of well-degradable biomass such as manure, silage (mainly corn silage) or bio-waste. So-called co-substrates such as industrial organic waste materials (e.g. flotates, fats, blood, glycerine, etc.) are increasingly mixed in as additives.

Various types of micro-organisms use the complex composite biomass (especially carbohydrates, fats and proteins) as nutrient and energy suppliers. Unlike in aerobic decomposition (respiration), the organisms can only unlock a small fraction of the energy contained during fermentation. It must therefore convert relatively large quantities in order to meet their energy. The main products of the decomposition is the so-called biogas with energy-rich methane (CH₄ approximately 55-65%) and carbon dioxide (CO₂ approximately 35-45%).

After gas treatment (drying and desulphurization), the biogas can be turned into electricity in CHPs for energy generation. With the latest gas engines, electrical efficiency can be reached around 40%.

The power generated is fed into the grid and are paid under the EEC. Since a large part of the energy of the biogas is converted into heat the combustion of biogas in gas engines, biogas plants should include integrated heat concepts.

Part of the heat needed to heat the fermenter/digester. Excess heat can be used as district heating for the heating of buildings, swimming pools, greenhouses, drying of wood chips or grain, drying of the fermentation waste, industrial uses, etc.

Due to the limited market for the heat produced, gas treatment processes that produce so-called green gas (biomethane) with natural gas quality from the biogas are increasingly used. In addition, the CO₂ is removed from the biogas by the relevant technologies (pressure swing adsorption, CO₂ washing, etc.) and a methane content of about 96-98% is set. This biomethane can be fed directly into existing natural gas networks and paid under the EEC.

Several quite different system concepts are currently applied in practice. Above all, the composition and texture of the substrate determine which concept is applied. However, legal requirements of the Renewable Energies Act (EEC), which determine the remuneration for the electricity fed, are relevant.