FAQ – Frequently Asked Questions
Can a Dry Digestion Process be a continuous process?
Yes, A Dry Digestion Process can be continuous process if the challenges of mixing and stability of the process are taken into account in the design of the plant. Eneferm Oy has made innovative solutions to keep the mixing ratio high and the overall process stable.
Currently, dry digestion is commonly carried out in batch processes. The implementation and operation of these processes are significantly different compared to a continuous process. In batch process, biogas output and composition are dependent on the state of the reactor, thus the output is not constant. The batch reactors are closed vessels, called as garage reactors. Organic waste is transferred in to the reactor by heavy machines. After the reactor is closed and sealed, the fermentation process starts. During the process, liquid digestate is circulated and sprayed on top of the solid digestate. After the retention time has been reached, the reactor will be opened, ventilated and emptied. The digestate can be clamped for composting. Challenges of the batch processes are mixing the digestate, and controlling the process temperature. Additionally, as mentioned before, the biogas output, and composition varies. Treatment of the organic waste and fermented digestate requires big space. With these big differences, a batch process should not be compared directly with continuous biogas process of Eneferm Oy.
Biogas output and composition with continuous dry digestation are steady. Digestate is treated continuously, which requires less space, and the teatment is easier. In continuous processes, mixing and efficient control of process temperature are the biggest benefits compared to batch processes. With innovative solutions, process of Eneferm Oy has a highly accurate process temperature control, efficient mixing, and low need of process energy.
When is it necessary to use thermal sanitation, and what are the benefits of it?
Due to regulations, digestate sanitation is mandatory, if the digestate will be used as a fertilizer or as a soil improvement agent. Sanitation kills pathogens, thus prevents spreading animal and plant diseases.
When a biogas plant meets the requirements of feed-in tariff in EU?
Feed-in tariffs and other support schemes are set to promote renewable energy production in 23 EU countries. Support schemes are meant to reduce market risks related to investments.
Each EU country has made decisions nationally regarding which support schemes are in use, and what are the requirements. The support schemes in use are feed-in tariffs, green certificates, tax support schemes, and investment support schemes. For example, in Finland, feed-in tariffs and investment support schemes are in use. Additionally taxation on fossil fuels has an effect on the markets.
There are minimum unit requirements for feed-in tariffs in Finland. The minimum unit size for a biogas plant is 100 kVA. The feed-in tariff guarantees a certain goal price for produced electric energy. The difference between market price and tariff goal price is paid every 3 months for 12 years for verivied electric energy production. The tariff goal price currently for a biogas plant is 83.50€/MWh. There is also a raised production support fee for biogas plants where the heat energy is utilized simultaneously. A CHP plant will get additional 50€/MWh, if ti produces heat and electric energy simultaneously, and the operating efficiency is higher than 50%. If all the previous requirements are met, the tariff goal price is 133,50€/MWh.
Can both, investment support and feed-in tariff, be applied for a biogas plant in EU?
Only one of the support schemes can be approved. It is important to assess which scheme is best option for the plant. For a biogas plants options are investment support, and feed-in tariff. The latter has requirements regarding to the plant unit size. The feed-in tariff provides a solid tariff price for maximum 12 years. The support fee is the difference between market pricess and tariff price.
Does a biogas plant convert biowaste to non-harmful form? Handling fee for harmful biowaste is 50-80€/ton.
With approved thermal sanitation unit, a biogas plant converts biowaste to non-harmful form. The digested and sanitized biowaste can be used as fertilizer. This turns the cost to income. Please, check your local regulations for digestate usage.
Which organic waste fractions are suitable for a dry digestion biogas plant?
The suitable fractions are most of secondary material flows from agriculture, such as spoiled silage, grain straws, turnip rape straws, green canary grass, spoil grain batches. Other suitable fractions are dry manure (bovine animals, chicken, fur animal), separated liquid manure (pig, bovine animals), and organic waste from vegetable farms, potato peel, potato sludge, and sludges from fodder cooking departments.
Do plastics harm a biogas plant?
Separation of plastics has been considered as the most challenging problems of utilization of organic wastes from food industry, shops, and agriculture, especially in wet digestion plants and batch dry digestion plants. Currently, there are reliable methods to separate plastics from biowastes. Well crushed and treated plastic fractions do not affect the fermentation process itself. They may cause problems in pumps and pipelines in wet digestion plants. Plastic fraction can also cause problems for utilization of the digestate.
Does a biogas plant reduce greenhouse gas emissions?
Agriculture produces 17% of all greenhouse gas emissions in Finland according to MTT Agrifood Research Finland. The greenhouse gas emissions of agriculture are generated mainly from side material flows and from organic waste. There are two ways how biogas plants affect on greenhouse gas emissions: biogas can be substitute for fossil fuel consumption, and organic wastes and side material flows of agriculture can be utilized in the biogas production. If organic waste decomposes in anaerobic conditions in nature, it generates greenhouse gas emissions, which has direct effect on the atmosphere.
Can energy produced from biogas reduce need of imported energy?
Biogas is produced locally from secondary material flows of agriculture and food industry, and from other organic wastes. Biogas based energy can especially replace imported fossil fuels such as natural gas, oil and coal. This improves self-sufficiency and security on energy. CHP plants can produce energy directly to the grid. This is one way to increase distributed energy production, which improves the maintenance support performance too.
Can the digestate be used as a fertilizer, and are there conditions for this?
The digestate can be used as a fertilizer if it is sanitized according to local official requirements. There are some restrictions for purification plant digestate if it contains heavy metals. In this case it is not allowed to use as a fertilizer.
Farm size biogas plants are common in Sweden and in Germany. Why they are not common in Finland?
Traditional centralized biogas plants get their profit from waste treatment fees. Investment cost of farm size biogas plants with most common plant types have been unprofitable. Payback times for the investment have been simply too long, which did not change, even with agriculture investment support scheme or feed-in tariffs. Support schemes were not enough to start investments.
New technologies entering to the markets are enabling profitable business also with farm size biogas plants. Investment costs related to plant expected yield are now on economically profitable level. Payback times have got significantly shorter. Eneferm Oy is working determinately with these novel technologies with innovative solutions. Our leading idea is to bring to the markets a biogas concecpt which is profitable for our clients.DRY DIGESTION THERMOPHILIC FAQS