Biogas Plant Components

Biogas plant components A Biogas plant is a complex installation Main components are to find in every plant Design depends on feedstock types and amount Components are defined by process steps Feedstock substrates Substrate Substrate conditioning Digesting technology Gas processing system Gas utilisation Digestate storage and -utilisation Delivery Storage Crushing Sorting Pasteurisation Wet digestion Dry digestion Discharge Desulphurisation Drying CO 2 -sequestration Heat CHP(electricty + heat) Feeding into gas grid Storage Application and Disposal Gas storage Fuel cells Fuel

Biogas plant components Digester Biogas storage Digestate storage Power Unit Energy Conditioning Digestate application Substrate storage Main components and general process flow

Process stages of agricultural biogas plants www.fitec.com Delivery and storage Conditioning and pre-treatment (optional) Separation, sorting, crushing, mashing, homogenisation Insertion transport, dosage 1. Process stage Biogas production Anaerobic digestion inside the digester Digestate Biogas 2. Process stage Digestate storage and/or post digestion Digestate conditioning Biogas Biogas conditioning and storage Drying, de-sulphurization Solid-lLiquid-sSeparation (optional) Liquid fertilize r Disposal,, Composting Disposal or composting wihtoutwithout ssolid /liquid separation Biogas utilisation Electricity and heat production 3. Process stage 4. Process stage

Feedstock delivery and storage Transport and supply plays an important role in the operation of a plant Should be stable and continous Control and record data (type, weight, quality)

Feedstock storage Compensate the seasonal fluctuations in supply Type depends on used feedstock (solid liquid) Bunker silo Storage tank

Bunker Silo Frequently used to store energy crops for biogas plants For dry material with a water content 55 70% Pressed to get out the air to avoid aerobic processes Fermentation process produces VFA (Volatile Fatty Acids) Usually covered with plastic foil or other materials Silage releases corrosive liquids with high nutrient content

Storage tanks Pumpable feedstock Concrete tanks, sometimes metal or plastic Co-substrate can be mixed, cut and crushed with stirrers Sedimentation should be considered Odour from the tanks can be reduced by cover or biofilter ventilation

Feedstock conditioning Sorting and separation Sanitation Crushing Mashing, homogenising

Feedstock sorting and separation Depends on the feedstock Agricultural feedstock is almost pure Stones and sand can be removed by sedimentation Household waste, catering and food waste are full of impurities. Removing is necessary to protect the process Several methods to separate www.fitec.com Grocery store waste Separation unit

Removal of contaminants, mass balance www.fitec.com Example food waste: Dry substance matter (DM): 20-30% Contamination up to 25% of DM dishes, cutlery, plastic bags bones, egg and seafood shells glass 90% 50% 50% The Material is pressed a second time, for example by a screw press, reducing the weight by 50% again. The efficiency and the mass of reject always depends on the quality of the waste.

Output of substrate and contaminants www.fitec.com 90 95 % 5 10 % Food waste afer treatment View into a container with contaminants

Feedstock sanitation Contamination risks for human, animal or the environment must be avoid Regulated by law (e.g. European Regulation EC 1774) The sanitation treatment is described with parameters Typical monitoring parameters are temperature, retention time, pressure and volume

Feedstock crushing Prepares the surface of the particles for decomposition Degradation is faster when particle size is smaller Extruder Crusher and separator

Feedstock mashing and homogenising www.fitec.com Obtain a higher water content to handle material with pumps Takes place in storage tanks or pre-digesters Liquids used: Liquid manure, digestate, process or fresh water Homogenisation for a constant and stabile gas production

Feeding system A continuous flow of feedstock is to aim (in practice several small batches) Feeding technique depends on dry substance matter of feedstock Stackable feedstock or pumpable feedstock

Transport and feeding of stackable feedstock Insertion into digester must be air-tight Pressing below surface layer Feed conveyors Feed pistons Wash-in shaft

Feeding of Stackable feedstock Stackable feedstock is transported from the storage (bunker silo) to the digester by loader or tractor Container system with scraper floor and conveyor screws

Pumps for transport of feedstock and digestate Two types: Centrifugal and displacement pumps A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure and flowrate of a fluid. Centrifugal pumps are often submerged. (not self-sucking) Cutting pumps for feedstock with long fibre are available A displacement pump causes a fluid to move by trapping a fixed amount of it then forcing (displacing) that trapped volume into the discharge pipe Self-sucking, pressure stable Flow depends on rotation speed (precise dosing)

Pumps for transport of feedstock and digestate For maintenance reasons, pumps are equipped with stop-valves, are easily accessible and ensure sufficient work room The function is often controlled by PLC or at least a timer In some biogas plants, the whole transport of digestate is realised by one or two pumps, located in a pumping station. Centrifugal pump Rotary piston pump Piston pump

Pipelines Material of the pipe depends on the transported material Must be corrosion proof PVC, PE, steel, stainless steel Long and angled pipelines lead to a loss of pressure

Valves www.fitec.com Corrosion proof Slide valves and butterfly valves are the most common types

Heating system - digester heating Constant process temperature is the aim www.fitec.com Temperature fluctuations have to be compensated

Digesters The digester is the core of the biogas plant Air proof container Different in size, material, shape. Two basic digestion systems Dry matter content Digestion system Digester type <15 % wet continous >15 % dry batch

Batch type digesters Operation: Feed Digestate Remove Feedstock: Biowaste, grass cutting, solid manure and energy crops No mixing or stirring while digestion Percolation liquid has to be circulated Garage Digester

Continous type digesters Operation: Feedstock is constantly fed in Produce biogas without interruption

Maintenance of Digesters Removal of Sediments and swimming layers Skimming unit Output Ø max. 13 m Floor scraper max. 10 m

Removal of sediments www.fitec.com The floor scraper wipes Sediments into an floor outlet from were the sediment is pumped into a classifier.

Removal of swimming layers www.fitec.com Gas proof separation : Floating material is skimmed from the surface and pumped to a sieve. Due to is construction the skimming unit is self regulating and gas proof.

Stirrer technologies www.fitec.com Methane bacteria is unable to move Nutrients have to be brought to them Passive stirring from thermal convection and bubbles Mechanical stirring (90% of the biogas plants) Pneumatic stirring Hydraulic stirring

Mechanical stirring Different speed with different geometries Paddle stirrers Axial stirrers Submersible axial stirrers

Biogas storage Compensate the fluctuation in biogas production Low pressure storage facilyties are most commen Gas tight membrane Gas bladder

Thank you for your attention.

Truck for the collection of food waste

Biogas plant for 4000 t/a of bio waste

Biogas plant for 8000 t/a of food- and biowaste