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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

Crushing

Sorting

Pasteurisation

Discharge

Desulphurisation

Drying

CO2-sequestration

Gas storage

Heat

CHP(electricty + heat)

Feeding into gas grid

Fuel cells

Fuel

Wet digestion

Dry digestion

Feedstock substrates

Substrate Substrate

conditioningDigesting

technology

Gas processing

system

Delivery

Storage

Gas utilisation Digestate storage

and -utilisation

Storage

Application and

Disposal




• Main components and general process flow

Substrate storage

Conditioning

Digestate storage

Digestate application

Digester

Energy

Biogas storage Power

Unit

Biogas plant components




Process stages of agricultural biogas plants

Delivery and storage

Conditioning and pre-treatment (optional)

Separation, sorting, crushing, mashing,

homogenisation

Insertion

transport, dosage

Biogas production

Anaerobic digestion inside the digester

DigestateBiogas

1. Process stage

2. Process stage

Digestate storage and/or post

digestion

Digestate conditioning

Biogas

Disposal or

composting

wihtoutwithout

sSolid /liquid

separation

Solid-lLiquid-sSeparation

(optional)

Liquid

fertilize

r

Disposal,,

Composting

4. Process stage3. Process stage

Biogas conditioning and storage

Drying, de-sulphurization

Biogas utilisation

Electricity and heat production




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

Grocery store waste Separation unit




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.

50% 50%

Removal of contaminants, mass balance

90%

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




Output of substrate and contaminants

View into a container with contaminantsFood waste afer treatment

90 – 95 % 5 – 10 %




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

• 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 Wash-in shaftFeed pistons




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.

Rotary piston pumpPiston pump

Centrifugal 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

• Corrosion proof

• Slide valves and butterfly valves are the most common types




Heating system - digester heating

• Constant process temperature is the aim

• 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

batchcontinousDigester type

drywetDigestion system

>15 %<15 %Dry matter content




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

Skimming unit

Ø max. 13 m

max. 10 m

Output

Floor scraper

• Removal of Sediments and swimming layers




The floor scraper wipes

Sediments into an floor outlet

from were the sediment is

pumped into a classifier.

Removal of sediments




Removal of swimming layers

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.

Gas proof separation :




Stirrer technologies

• 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.




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biogas plant components - eihp plant components ... homogenisation insertion transport, ... •...

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