Project informations:
A biogas plant at a pig farm
Project site: Boluo, Huizhou, Guangdong Province of China;
Digester CSTR steel tank type,2*800 m3;
Biogas desulphurization: Dry type by Ferrix Oxide, GasCle series skid-mounted biogas pre-treatment System
Generator capacity: 2*120kW;
ALONG BIOGAS is responsible for design, equipment supply,installation and project acceptance under Turn-key solution;
Hunan Along New Energy Technologies Co., Ltd
can provide a entire solution from waste to energy, scope of equipment supply covers waste pre-treatment, anaerobic fermentation, biogas cleaning, Combined Heat&Power Unit(CHP), Bio-natural Gas making system, biogas flare/boiler and all auxiliary materials, in conjunction with services of process design, equipment selection, installation and operation & maintenance support.
ALONG BIOGAS is also professional in sewage treatment with non-production of biogas, with purpose of cleaning waste water for recycling of process water or being discharged environmental friendly.
General Process Description for each stage of a complete Biogas Project
1. Waste Material and Pre-treatment
Single or mixture of multiple substrates with high content of organic substance can be used for biogas production. Waste materials and by-products are accrued in conjunction with every single manufacturing operation, fromAnimal husbandrySlaughterhousesThe food-production industry and the food-processing industryAgriculture raw and residual waste, e.g. Strew,semi-rotten vegetable&fruitSupermarkets, e.g. spoiled food productsBreweries (malt spent grains)RestaurantsJuice productionThe ethanol industry (mash)The biofuel industry, e.g. glycerinePurification plants: Sewage sludgeThe animal feed industry
For feedstock in forms of solid or solid-liquid mixture, such as crop stalks, fruit and vegetable waste, food waste, etc., they should be shred to a fine dimension before fed into digester. Involving equipment such as shredders, crushers, beater, grinding system,dissolving devices etc. Kitchen garbage or community waste, due to its complex compositions, special manual or automatic sorting devices are needed.
Separation process occupies a large proportion in the stage of pre-treatment of waste materials, to remove large particles of inorganic suspended solids, debris and the like contained in the waste water. The equipment used are generally like screw-squeezed, spiral centrifugal, rotary mechanical grille, inclined sieving separator. Grease-water separator or horizontal spiral centrifuge to be used for grease separation if waste contains oil.
For waste materials with high consistence of fiber, long impurities and the like, cutting and grinding devices are required for further processing. For example poultry droppings, which contains soft feathers, it's difficult for primary solid-liquid separation to remove it, a special cutting&grinding system is wanted to solve such problem.
The feedstock should be cleaned, in order to ensure that it is harmless(from the point of view of hygiene) and it's free of pathogens, to avoid bad affection for microbiological process in digester.
2. Anaerobic Fermentation
In the heated and air-tight digester, the biomass ferments in conjunction with the production of methane, mixed with other by-product gas, it's so called biogas. The microbiological process in digester takes place in four stages, hydrolysis - acidification - acetic acid formation - methane formation.
According to the characteristics of TS total solids, SS suspended solids, COD, BOD etc in the waste water, we will choose the best suitable anaerobic fermentation process among the following types:
- CSTR Reactor (Continuous Stirring Tank Reactor). The feedstock to be fed into digester through bottom entrance. Digester is equipped with mechanical agitators, enables waste materials to be in full contact with micro-organisms. The biogas slurry is automatically discharged and the residue is periodically pumped out of digester. Biogas generated is collected in the gas holder at the top of the reactor or flows into the free-standing gas holder on the ground. Proper TS(total solid) content varies in the range 6% to 12%, HRT(hydraulic retention time) varies from 20 to 30 days depending on the actual TS% and reactor temperature.
- USR Reactor (Up-flow Solid Reactor). USR reactor is a simple structure, suitable for sewage with high content of suspended solids. 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 digestor. Proper TS(total solid) content varies in the range 3% to 5%, HRT(hydraulic retention time) is about 10~15 days.
- UASB Reactor (Up-flow Anaerobic Sludge Blanket). The feedstock enters digester through the water distributor at the bottom of the reactor. Above the water-distributor 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. Proper TS(total solid) content is about 1%, HRT(hydraulic retention time) is about 5 days.
- EGSB Reactor (Expanded Granular Sludge Blanket). EGSB is the third generation of anaerobic reactors developed on the basis of UASB. Unlike UASB, EGSB has a dedicated sewage recovery device. The expanded Blanket of granular sludge improves contacting between organic matter and microorganisms in the fluid, enhances the mass transfer effect and improves the biochemical reaction rate of the reactor, thereby greatly improving the efficiency of the reactor treatment. EGSB reactor is always in cylindrical column shape with a high height/diameter ratio, generally up to 3~5,can be up to 15 to 20 meters high. EGSB has high loading ability, the organic loading rate(OLR) is 2~3 times higher than UASB, up to 6 ~ 18mgCOD / m³.d.
- IC Reactor (Internal Circulation). IC is an internal loop type of anaerobic reactor, similar to the series of two UASB tanks, and like EGSB, with a big height/diameter ratio. The biggest difference in operation between IC and UASB is the performance of bearing shock load, IC can automatically dilute the input materials through the internal circulation, effectively ensuring the stability of input fluid concentration in the first reaction chamber. The second advantage is that it only requires a short residence time, suitable for considerable biodegradable sewage with high SS content. IC has a significant advantage over UASB,due to the high flow rate of IC, SS does not accumulate in the reactor, and sludge can maintain high activity.
The material for the above reactors can be enamel steel tank, made of titanium-alloy enamel steel plate, with double-sided enamel coating, beautiful appearance, easy to clean, easy maintenance with good wear resistance, corrosion resistance, impact resistance,insulation performance, anti-static; No special anti-corrosion treatment required, lifetime designed for 30 years at least.
In addition, the above reactors can be also LIPP tanks under unique construction method. During construction, the steel coils with a certain width are taken into the molding machine by uncoiler, to be processed into the required geometry, and then to be bended and seamed through bending machine, to form a round of spiral protruded ridge with 30mm-40mm width at outer side of tank, playing the role of strengthening the tank.
3. Biogas Storage Process
For tank type of digester, structure of integrated all-in-one with biomass fermentation and biogas storage combined together is always welcome by customers, in order to reduce investment. The biogas storage is in the form of double-membrane gas holder mounted on top of tank. It consists of inner/outer membrane,support,air blower,anchoring device and other auxiliaries.
It can also be free-standing type on the ground when tank is very high, to avoid affection of speedy wind for safety. Top of tank has to be covered by steel plates too, what's more, additional civil works for gas holder is caused. In this regard, it will increase the investment significantly.
Another simple design is gas bag that made of reinforced single PVC membrane, anchored in specif area on the ground.
No special biogas storage devices required when digester is HDPE enclosed anaerobic lagoon or floating soft digester that made of PVC membrane;
4. Biogas Cleaning
Biogas pre-treatment process is mainly to remove hydrogen sulfide, moisture and solid impurities in the raw biogas, reduce corrosion and wear for subsequent equipment. Biogas pressure to be increased for transportation and regulated to meet the requirements of inlet pressure of follow-up equipment, involving equipment such as roots blower with explosion-proof motor under anti-corrosion treatment.
Moisture and solid impurities can be removed through physical means while the most difficult is the removal of hydrogen sulfide. Traditional methods are chemical dry type(iron oxide) and chemical wet type(sodium carbonate) or a combination of both, or the latest biological desulphurization technology(oxygen-absorbing microbial absorption solution).
Our patented ALBS series integrated biogas pre-treatment system, provides all-in-one solution to perform the above functions,it mainly includes the following:
- Desulphurization tanks;
- Water&particles removal tanks;
- Roots blowers, 2 units(one for operation,the other for standby);
- Constant-pressure feed system(Variable frequency drive,LCD display etc);
- Instruments,like pressure gauge,flow meter etc;
- Base steel frameworks.
A on-line biogas analyzer is strongly advised, to measure the main components (methane,hydrogen sulfide,carbon dioxide,oxygen etc) in the purified biogas.
- Biogas Utilization
5.1 Bio-natural Gas.
If biogas is used to produce CNG(Compressed Natural Gas) for vehicle or gas grid networks, except the above biogas pre-treatment, decarburization process is required for further treatment. Now we could provide containerized type biogas upgrading system in conjunction with the four kinds of mature technologies, including MS(Membrane Separating), PSA(Pressure Swing Absorption), MEA/MEDA(Mono Etobaccool Amine/ Methyldiethanolamine) and DWW(Pressurized Water Washing).
The subsequent compressor is to be installed for increasing pressure to a certain degree(e.g. 20Mpa), to be fed into tank lorry through gas dispenser.
5.2 Combined Heat and Power(CHP).
Purified biogas is combusted in the internal combustion engine of Combined Heat&Power Plant(CHP); Electricity for which compensation can be obtained is generated, for local use or connected with power grid networks. The heat from engine jacket water and exhaust can be used for digester heating, or return to respective company for warming,bathing etc. The CHP can be regulated in terms of its utilization. Consequently,it can correspond to various remuneration regulations and be complemented through other heating concepts.
We could provide quality CHP with high electrical efficiency,low oil consumption and long overhaul time.Our ACG and ADG series CHPs are associated with world-famous engine technologies, such as USA Cummins and German Deutz. Single unit capacity from 20kW to 400kW, to be configured automatic air-fuel ratio system, automatic oil feed system, exhaust purification mechanism and Grid connection cabinet,etc. according to customers' actual requirements.
5.3 Biogas Boiler.
Purified biogas can be used for producing hot-water or steam through boiler,which is equipped with high efficient burner. Hot water and steam generated are always used for material drying.This kind of utilization is very popular with food-processing factories,feed mill plants etc. Biogas production is not depending on climatic factors,and it can be stored and converted into energy at any time,it can meet base-load and peak-load requirements.
Each country and region for the pressure vessel has a corresponding quality and safety standards,Special attention should be paid to boiler design and quality control,make it be subject to the quality standard as local relevant authority requires.
6. Digestate Treatment
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.
Fermentation residue from bottom of digester is generally with water content 15~20%, after sediment treatment,through a dedicated solid-liquid separation equipment, after dried under sunshine and bag packed,the precipitations can be made for solid organic fertilizer. This is a relatively primitive approach, suitable for customers with little budget on small biogas plant.
For the project with big digestate output, considering the return on investment, the solid organic fertilizer can be processed into granular fertilizer. The general process includes solid-liquid separation, batching system, mixing system, granulation, hot air oven drying and cooling , Dust removal, screening systems and packing machine.
The slurry flows out of digester at upper position,together with the filtration liquid from residue,it can be used for nearby plant irrigation or horticultural purpose after further processing.If waste material is solid like livestock manure etc,slurry could be partially returned to pre-mixer with raw waste,in order to reduce water consumption,but have to keep carbon/nitrogen balance of feestock,which is best at 25 : 1.
7. Further Treatment of Slurry
In order to prevent pollution on the environment, in the countries and regions with strict laws of environmental protection,the fermented slurry still has to be cleaned further. ALONG could offer solutions to solve this problem by air flotation, A/O(Anaerobic-Oxic) or A2/O(Anaerobic-Anoxic-Oxic) technologies. Their common function is to remove organic matters in slurry.After treatment,the purified water can be discharged environmental friendly.
What's more,we can provide membrane separating technologies for treating slurry further.The water after purified can be used for process water for local usage in customers' plant,such as food-processing industry.
The whole biogas project and sewage treatment process design principles:
1. Advanced technology, reliability, and adaptability.
1.1 According to the actual situation of the plant, choose the most advanced technology program.
1.2 According to the actual situation of the local, choose a successful case of the project to ensure that the project can be long-term stable operation.
1.3 According to the owners of economic conditions and operational skills level, select the most appropriate program, easy to actual operation and maintenance.
2. The principle of maximizing economic efficiency
2.1 to ensure the advanced nature of technology on the basis of optimizing the process and the various unit design, reduce one-time investment to ensure the best cost-effective and the shortest payback period.
2.2 follow the concept of circular economy, the entire field of energy flow analysis and design, to minimize energy consumption, to ensure that biogas projects for enterprises to bring the overall maximum benefits.
3. The principle of maximizing environmental and social benefits
3.1 to the product (biogas, biogas residue, biogas slurry) to make full use of, and focus on design and landscaping, so that the overall area of the station area and the harmonization of the community.
3.2 The design and implementation of the process to comply with national and local laws and regulations and industrial policies to ensure that the project in line with local environmental, economic and social development planning, after the completion of the project can improve public heating, catering and other energy, and play an exemplary role in driving the local economy And social development.
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