Biogas is a form of energy produced by anaerobic digestion (the decomposition of biodegradable matter constituents in an oxygen-free environment). It is a mixture of gases, mainly carbon dioxide and methane. Approximate composition of biogas:
– Methane (CH4) 55 to 65%
– Carbon dioxide (CO2) 30 to 35%
– Water vapor 1 to 5%
– Hydrogen sulfide (H2S) 0 to 3%
– Hydrogen (H2) 0 to 1%
The decomposition of waste material during anaerobic digestion is caused by bacterial action rather than high temperatures. It takes place in almost any biological environment, but is favored by warm, humid, low-oxygen conditions.
Anaerobic digestion also occurs in two main situations created by human activities:
– Wastewater (human waste) or animal manure.
– Landfill gas produced by household garbage buried in landfills.
In nature, there are also many raw materials (organic materials) from which biogas can be extracted: human and animal manure, leaves, twigs, grasses, garbage, agricultural and industrial waste with organic content greater than 2%.
The biogas produced can be used for cooking, heating, lighting (using gas lamps), generating electricity, operating the farm and other energy needs. The effluent produced from the process can be used as fertilizer for crops.
Biogas blowing systems
Landfill biogas is transported from the landfill well field to the blower facility through the main gas collection main. The LFG normally passes through a liquid removal vessel for removal of gas and liquid particles, before being sent to the blower. Block valves and bypass valves can be actively used in some landfills if there is a desire to conduct gas around the liquid disposal vessel. This is generally not recommended because condensate removal helps protect instrumentation and processing equipment.
The blower installation and associated control equipment may be housed within a building or exposed to the outside elements. It should have a central location with room for expansion and power supply. It must also have the capacity to handle 100 percent of the estimated peak biogas production, plus additional size for biogas migration control. Butterfly valves are often installed in the inlet and outlet piping for each blower used to allow continuous operation of the fan during scheduled maintenance and shutdowns.
The purpose of the LFG blower (also known as compressor) is to create a vacuum for gas extraction from gathering wells and trenches under pressure, pull the LFG into the blower, and push the LFG into the flare or other treatment equipment. This process is known as active LFG control, which contrasts with passive LFG control. Passive systems, where LFG is generally allowed to be vented into the atmosphere with little or no treatment, are often not recommended for modern landfill operations. The main mechanical component of the blower system is the gas compressor or blower itself. Other associated equipment may include:
- Valves (automatic lock, control)
- Flow measurement and recording
- Instruments to measure pressure, temperature, etc.
- Condensate treatment and handling equipment
- Electric equipment
Selection of the appropriate blower is determined by factors such as the quantity and end use of the LFG, the vacuum required to extract the gas, the pressure required for processing, etc. The main types of blowers used for GRS applications include single and multi-stage centrifugal blowers: IE Vacuum/constant pressure, variable gas volume machines, which incorporate a butterfly valve at the inlet of the unit.
Biogas and the environment.
There is a significant amount of unused organic elements (animal waste) in rural areas. Organic compounds can produce large quantities of methane gas and current technology can be used and adapted to local conditions.
Biodigester design and production expectations must be tailored to the available rosources, climatic conditions, and construction materials. To minimize the capital cost of equipment, it is important to ensure that the digester is properly designed.
Anaerobic digestion also occurs in ponds, marshes, and manure pits where rotting organic materials are abundant. Bubbles are often seen rising to the surface and, after the combustion of the bubbles (filled with methane), a violet-blue, smokeless and odorless flame is observed. Methane is about 23 times more potent of a greenhouse gas than carbon dioxide (CO2).
Feeding potential for biodigesters
The raw materials that can be considered suitable substances for the production of biogas through the bioconversion process in a digester are:
1. Harvest residue – Cane trash, weeds, corn and stubble, straw, spoiled forage, etc. Studies have shown that the content of water-soluble substances such as sugars, animoacids, proteins and mineral components decreases with the age of the plant and is low enough to limit the speed of the digestion process. Therefore, the decomposition of crop residues takes longer than composts due to their fiber content and larger particle sizes.
2. Manure: livestock waste (dung, urine, leaf litter), sheep and goat excrement, household waste (blood, meat), fishing industry waste, leather, etc. of the agricultural community represent an important source of raw material for biogas production. Manure is a source of carbon and nitrogen necessary for the successful operation of the fermentation process. The amount and composition of animal waste depends on the type of animal. Pultry, for example, produces more volatile solids, nitrogen and phosphorus, per unit of weight. In addition, the composition of manure largely depends on the animal’s feed ration. Animals fed only grass show much lower nitrogen content in manure and urine.
3. Human waste: Human faces and urine are raw materials that can be used for biogas production.
4. By products and waste from industries based on agriculture and aquatic growth: oil cakes, bagasse, rice bran, seeds, water from fruit and vegetable processing, filter sludge from sugar factories, seaweed, seaweed , etc., can also be sued. feeding plate for biodigesters.
Requirements for a successful system
- Keep the digester away from naked flames and electrical equipment than may spark.
- Buildings should be well ventilated.
- Explosion proof motors, wiring and lights should be used.
- Perform periodic system checks for gas leaks.
- Follow Bunsen burner safety rules when testing the gas with a flame.
- Use gas detection and alarm devices in enclosures.
- Do not divert the effluent from the unit directly into lakes or streams.
Safety concerns related to biogas generation include health hazards and risks of fire or explosion. Biogas is flammable and can be explosive when mixed with air.
- Acceptance by potential users.
- Ability to use the gas when produced.
- Sufficient demand for gas.
- Availability of sufficient raw materials to meet the production requirements.
- Adequate maintenance and operational control.