Hunan Along New Energy Technologies Co., Ltd.
provides a complete set of process design and relevant equipment supply from fresh livestock manure to biogas energy based on principles of rational and reliable technology application, maximum economic efficiency, maximum environmental and social benefits.
Description of technological process
1. Pre-treatment of feedstock
Pre-treatment process is mainly to adjust the feedstock concentration and remove large inorganic suspended solids. Pigs, cattle and sheep manure contain a small amount of fiber and inorganic solid matter, and chicken manure contains gravel and feathers, etc., which must be removed in the pre-treatment process to reduce the loading of follow-up processing and avoid wear for the relevant equipment.
There is always a existing fecal collection basin in livestock farm. The mixture of manure and washing water is pumped into grille canal. Mechanical grilles would be installed in front of canal, to be used for removing large size of suspended solids and a variety of debris(Alternative solution is to use a spiral extrusion separator,to remove more solids in the waste water, while the separated solids can be used for bio-fertilizer making if it's the main purpose).
The waste water gets out of grille canal and is pumped into hydrolysis regulation basin, where a vertical mixer is installed for TS(Total Solids) content regulated to be 6~12%. With mechanical stirring, VSS could be totally resolved in the water. A certain degree of hydrolysis would occur in this basin. The sediment like sand at the V-shaped bottom of basin needs to be taken out regularly by spiral desander.
Necessary measurements of temperature, pH, C/N elements of waste water in the basin should be done preliminarily. If possible,a certain amount of straw could be added,because livestock manure is rich in nitrogen element while straw is poor,so their mixtures can reach the most proper C/N balance which prefers around 25 : 1.
What's more,make sure that no harmful substance exists in the waste water which may affect the normal metabolism of anaerobic bacteria.
In case of pre-heating of feedstock, the hydrolysis regulation basin would be designed as reinforced concreted structure underground with cover. Inclined agitator to be installed for stirring. Extruded plastic sheet to be installed inside for heat keeping. Spiral plate heat exchanger to be installed inside the feed pipeline.Hot water could be from biogas boiler.
Cutting & grinding pump if installed in front of charging pumps before digester, to be used for cutting the remaining long soft feather, fibers, impurities and the like, to avoid clogging and wear for the subsequent equipment.
2. Process of Anaerobic Digestion(AD)
As the mixture of livestock manure and washing water is a kind of organic waste water with high TS content at 6~12%, therefore CSTR(Continuous Stirring Tank Reactor) type of digester is strongly recommended.
The mixture to be fed into digester through bottom entrance. Digester is equipped with stirring system, enables mixture to be in full contact with micro-organisms,to speed up the process of hydrolysis,acidification,acetic acid formation and methane formation. The biogas slurry is automatically discharged and the residue is periodically pumped out of digester. Biogas generated is collected in the gas holder on the top of the reactor or flows into the free-standing gas bag on the ground. HRT(Hydraulic Retention Time) varies from 15 to 30 days depending on the actual TS% and reactor temperature.
If project budget is sufficient, we would advise customer to adopt two-stages anaerobic fermentation process which is CSTR + UASB, to improve waste utilization and increase biogas production,meanwhile waste water could be cleaned further, total COD removal rate could reach 95%.
The waste water from CSTR enters UASB digester through the water distributor at the bottom of the reactor. At the bottom of the reactor there is a high concentration, highly active sludge blanket, where most of the organic matter is dissolved and fermented to methane and carbon dioxide. Due to the stirring of water flows and bubbles that full of biogas, there is a floating sludge layer above the sludge blanket. Gas,Liquid and sludge particle Solids are separated automatically through a special three-phases mechanical separator. Biogas flows into the gas storage chamber, sludge particles automatically fall to the sludge blanket, slurry gets out of reactor at clarification chamber.
In case of TS% at 3~5% of waste water from CSTR with high content of suspended solids, USR(Up-flow Solids Reactor) type of digester is also good. Waste is pumped into digester from bottom of reactor, and contact with activated sludge during up-flowing, so that the biomass to be quickly fermented. Unprocessed biomass solid particles and microorganisms remains inside reactor by natural sedimentation, and the bio-liquid overflows from the upper part of the digester.
If project budget is tight and customer can't afford high investment by adopting process of CSTR enamel steel tank, we will advise client to use our HDPE membrane enclosed anaerobic lagoon as digester. This kind of digester is a regular trapezoidal lagoon; Lagoon surface and bottom are rectangular (Surface is large, bottom is small); The trapezoidal slope is designed at generally 30 degrees to 45 Degrees according to actual volume of lagoon.It is a complete enclosure sealed by HDPE geo-membrane.
3. Utilization of Digestate
Digestate means residue and slurry after fermentation, be rich in N.P.K, humic acid, organic matter and trace elements. Therefore the solid substance of digestate can be used as soil additive or compost, and the resultant liquid nutrient concentrate replaces the mineral fertilizers. And the separated water is processed so that it can be directly routed in the surrounding water body or can be used as processing water.
The fermented liquid could also be partially returned to fecal collection basin, with the purpose of saving feed water sources.
4. Utilization of Biogas
Generally speaking, the utilization of biogas could be following purposes as below:
For cooking. For small project with daily biogas production less than 100 cubic meters, biogas after cleaned could be used for cooking in the farm, or distributed to nearby households through pipeline.
For combined heat and power. The biogas can be used for power generation. Generator with heat recovery system could provide hot water for digester heating or farm workers' bathing,warming,etc.
For bio-natural gas. For big project with sufficient biogas production, the biogas can be used for making bio-natural gas through our desulphurization and decarburization system. Through pressure devices and feed system,bio-natural gas could be fed to vehicle or into national gas network.
For boiler or lamps. Biogas after cleaned could be fed for boiler for warming in the farm or biogas lamps for lighting of farm or animal breeding e.g. The hatch of poultry.
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