Biogas plant for waste recycling

What is ZORG™ biogas plant?

ZORG™ biogas plant produces biogas and bio-fertilizer from biological wastes of agricultural and food industries as well as special energy crops by means of oxygen-free fermentation (anaerobic digestion).
Industrial biogas plant is a construction project which consist of equipment for 50-60%. Main part is closed reactors (or digesters, methane tanks, bioreactors) made of reinforced concrete or glass-fused-to-steel tanks. Most of substrates can be mixed with each other. The difference is only in substrate loading systems. For solid substrates this is screw loaders and for liquid substrates tanks with pumping stations. Facilites are of modular type with 8-24m in diameter and up to 9m in height. In case plant capacity increased the number of digestered increased accordingly.

ZORG™ biogas plant operational principle.

Liquid biological waste is pumped to biogas plant by sanitary pump or extraction pipeline. Sewage pumping station (SPS) is located in a separate service room. Solid biological waste (manure, dung) delivered by belt conveyor, and in case of manure or dung storage, delivery made by tractor. Liquid wastes initially come to primary tank. In primary tank waste homogenized and heated (sometimes cooled) for required temperature. As a rule such tank has 2-3 days storage capacity. Solid waste can be loaded to that tank as well for homogenization or get into digester through screw loader.

From homogenization tank and screw charger biomass (manure, dung or distillery waste) comes to digester (biological reactor, methane tank, fermenter). Biological reactor is gas-proof tank made of acid-resistant concrete. Reactor is heat-insulated. The heat-insulation is calculated depending on the biogas plant site climate conditions. For microorganisms' vital activity a constant and even temperature inside the digester is kept, usually it is mesophilic temperature mode (+30-41°С). In some cases termophilic mode of temperature is used (about 55°С). Biomass mixing inside the digester is made by several ways and depends on the type of raw material, its humidity and other features. Mixing can be done by inclined mixers, "paddle giant" type mixers or submersable mixers. Al mixer types are made of stainless steel. In some cases mixing device can be of hydraulic type instead of mechanical. Such mixers pump the biomass into the layers with bacterial clumps. Bioreactors are built with wooden or concrete dome and have service life of 25-30 years.

Digesters are heated by hot water with inlet temperature about 60°С and discharge temperature of about 40°С. Heating system is a network of pipes, which can be built-in to reactor wall or to be mounted to interior side of the digester wall. In case biogas plant equipped with co-generation unit, digester can be heated by generator cooling water. Generator cooling water has temperature of 90°С and before getting into digester heating system it is mixed with 40°С water so that heating system receives water with 60°С. The water is previously treated and returnable. In winter time biogas plant requires up to 70% of heat from generator cooling device and 10% in summer time. If biogas plant is purposed only for gas production hot water is taken from a special water boiler. Biogas plant self energy and heat consumption usually makes from 5% to 15% of overall produced.

The average hydraulic retention time of biomass in bioreactor (depending on the material type) is 20-40 days. During this time organic matter is metabolized (modified) by microorganisms presented in the biomass. Corn silage hydraulic retention time is about 70-160 days. The hydraulic retention time defines the size of the digester.

The fermentation process is made by anaerobic microorganisms, which are injected into the digester during the biogas plant start up. Any further microorganisms or additives injection is not required. Microorganisms injection is made by one of three ways: 1) microorganisms concentrate injection 2) fresh manure addition or 3) injection of biomass from operational biogas plant. As a rule 2nd and 3rd methods are used being cheapest ones. Microorganisms get into manure from animal bowels and are not harmful to human or animal. Moreover bioreactor is a hermetically sealed container. That is why bioreactors or fermenters can be placed near the farm or production facilities.

As end products we have: biogas and bio-fertilizer (solid and liquid).

Biogas is stored at a gasholder. Inside the gasholder pressure and biogas composition is evened. ZORG^TM gasholder is a 3 layer structure made of special PVC, PE and EPDM. Gas holder dome material is resistant to sunlight and internal bioreactor sediments and evaporations. Gasholder service lifetime is 15 years. Bioreactor hermetically sealed by the gasholder from the top side and covered by additional tilt cover. The space between the gasholder and tilt cover is pumped with an air in order to form pressure and heat insulation. Sometimes gasholder is a multichamber cover. Depending on the project solution such cover can be secured by belts on the top of the concrete dome or to be placed in a separate concrete tank. Gasholder volume capacity is 0.5 - 1 operational day.

From the gasholder biogas constantly comes to gas or diesel/gas co-generation unit. Here heat and electricity are being produced. 1m3 of biogas produces 2 kWh of electrical and 2 kWh of heat power. Big biogas plants are equipped with an emergency flare for instances of engines malfunction and the necessity to burn the excessive biogas. Biogas system can be equipped with ventilation, condensate extractor and desulphurization unit.

Process visualization at biogas plant (Velikiy Krupil, Ukraine) 

The whole system is operated by the automatic control unit. Control unit operates the work of pumping station, mixers, heating system, gas automatics and generator. For operational control only one person for 2 hours a day is required. This person affects the control with the help of computer. After two weeks of training any person without any special skills can operate the biogas plant.

Anaerobically digested biomass is finished and ready for use as fertilizer. Liquid bio-fertilizer is separated by separation unit and stored in a tank. In Germany this liquid (ammonia water) is used as a fertilizer due to high ammonia (NH4) content. Solid fertilizer is stored separately. From the storage tank liquid bio-fertilizer is pumped to transportation tanks for further distribution or sale. As an option biogas plant can be supplied with fertilizer packing line (bottles 0.3, 0.5, 1.0 l). In case liquid fertilizer is of no interest for biogas plant owner, such plant can be equipped with additional waste water treatment modules.

In case company doesn't need electricity but gas for vehicle filling, biogas plant supplied with gas treatment system and methane filling station. Gas treatment system is equipment that separates carbon dioxide from biogas and is based on absorption and stripper technology. Carbon dioxide content can be reduced from 40% up to 10% (even 1% is possible if required). This option is very interesting taking into consideration diesel fuel high prices.

For some types of biological waste above mentioned operation principle requires modification. For example it is not workable with single raw materials such as distillery slop and brewer's grain. In that instance two stage systems with additional hydrolysis reactor should be used. The peculiarity of the process is the support of acidity level in hydrolysis reactors. This technology patented by ZORG and is under protection that makes impossible it's usage by other companies.

Biogas plant self energy consumption is 10-15% in winter time and 3-7% in summer time. In order to operate even big biogas plant only one person for two hours a day required.

Biogas plant scope of equipment and facilities
1. Receiving tank with pumping station
2. Solid biomass loader
3. Reactor (bioreactor, methane tank, digester)
4. Mixing devices
5. Gasholder (gas storage)
6. Water mixing and heating system
7. Gas system
8. Pumping station
9. Separator
10. Control devices
11. Control equipment with visualization
12. Emergency flare system and security system

Biogas plant parts photoes

Solid waste loader	Pump station
Bioreactor inside	Separator
Gasholder	Biogas relief valve
Heat distribution system	Co-generator
Co-generator in container	Automatics
Process visualisation

 

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