Benefits of Biogas Gas Plant for Homes

 

Introduction to Biogas Plant

• A biogas plant is used to generate wet natural gas for domestic cooking.
• This gas is ideally generated in oxygen-free conditions due to anaerobic digestion
• This is a conversion system where you can turn waste into sustainable energy and fertilizers, with positive effects on the environment.

 

What is biogas?

How much biogas is produced from cow dung?

• According to recent  studies, one kilogram (2.2 pounds) of cow manure can produce from 15 to 30 liters of biogas per day 
• Biogas yielding can be increased up to 40 liters per day.
•  A cow is assumed to produce around 10 kg of dung per day
• One kilogram of cow dung produces around 0.036 cubic meters of biogas.

 

What are the Benefits and Costs of a Biogas Plant?

• A biogas plant supplies energy and fertilizer. It improves hygiene and protects the environment
• A biogas plant can reduce the cost of LPG and electricity consumption
  housewife
• It is a modern energy source
• Improves life in the country with green energy
•  An abundant supply of energy
• By diverting people for cooking purposes, the cost of cooling can be brought down the cooking cost by 80%

Types of Biogas Plants

• Biogas plants are classified based on types of digestor design
• There are normally  three main types of simple biogas plants
  • Balloon dome plants
  • Fixed-dome Cement plants
  • Floating-drum plants.
• A balloon biogas plant consists of a plastic or rubber digester at the top to store gas
• The following are major types of Biogas Digesters
  • Balloon (flexible rubber) Plants
  • Fixed Dome Biogas Plants
  • Floating Drum Plants
  • Low-Cost Polyethylene Tube Digester
  • Horizontal Plant
  •  Earth-pit Plants
  • Ferro-cement Plants.

Fixed Floating Biogas  Plant

• A fixed-dome plant consists of a closed, dome-shaped digester with an immovable
• It is made of a top rigid gas tank and a displacement holding  which is called  a gas holder or compensation tank
• The biogas is stored in the top portion of the digester
• . When biogas (wet methane) gas production starts, the slurry is displaced into the side compensating tank

 

• The fixed dome has limited gas storage and more cost

 

 

  Floating Biogas Plant

• The construction of a floating biogas plant is similar to a fixed dome. The dome is replaced with flexible polyethylene bags
• This consists of an underground digester and a moving gas holder
• The floating can be cylindrical, hemispherical, or rectangular in shape 
• The top gas holder floats either directly on the fermentation slurry or in a water jacket of its own
• The biogas is collected in the gas drum, which can rise or fall as per gas pressure

 

 

Portable Biogas Plant

• These  units are designed for household and institutional purposes
• Portable biogas plants generate enough energy from the biodegradable wastes
• Benefit: hygienic environment and healthy surroundings for individual households as well as the general public.

• Portable biogas plant uses plastic tanks for digestor and slurry pipes

• The upper gas holder can be replaced by a plastic container

Ballon Type  Biogas Plant

• This biogas plant uses  a flexible rubber bag  (balloon) as heat-sealed plastic which  combines digester and top gas-holder
• The gas is stored in the upper part of the balloon
• The inlet and outlet are attached directly to the skin of the balloon.
• Gas pressure can be increased by placing weights on the balloon

• The ballon type biogas plants can be semiautomatic

Advantages of Floating dome biogas Plants

• Depending on the capacity and materials that come with the plant, the price can vary from Rs 10,000 to Rs 25 lakh (USD 12000)
• The area of the bottom  50×50 square feet of space; and if it’s a plug-in model, then a 20-square foot area.

Comparison of Fixed and Floating Dome Biogas Plant

Biogas Composition

• Biogas is a wet Natural gas
• Biogas is generated biologically from renewable biomass
• To reduce pollution from  fossil fuels, biogas consumption can achieve  greenhouse gas (GHG) emissions reductions to help for worldwide climate change mitigation strategies
• Biogas generated  is generally composed of:
  •   Methane – CH4  (55-65%)
  • Carbon dioxide -CO2 (35-45%
  • H2S (100-10000 PPM)
  • Water vapor  -H2S (saturated at biogas temperature)
  • Ammonia NH3, (traces)
• Like biogas, natural gas is composed primarily of methane
• Biogas is a wet natural gas  (WNG). Its purity  is  diluted due to carbon dioxide (CO2) and some corrosive gases
• Biogas generated from landfills has less Methane  (CH4) in proportion. This is because of the surrounding air (Nitrogen & oxygen) gets mixed into the biogas collection top.

 

How much energy Production by Biogas Plant?

• Each cubic meter (m3) of biogas contains the equivalent of 6 kWh of heat energy
•  The same volume of biogas converted to electrical power yields 2 kWh; the rest of the energy is dispersed as heat that can be reclaimed and applied to other uses.
• Biogas can provide energy
  • for 1 m³ of masonry: 1000 kWh or 180 m³ of biogas
  •  for 100 kg of steel: 800 kWh or 150 m³ of biogas,
  • for 1 kg of oil paint:  170 kWh or 28 m³ of biogas
• Construction and maintenance also consume energy:
  – for 1 km of transport by lorry, about 1.5 kWh or 1.05 m³ of biogas
  – for 1 km of transport by car, about 0.5 kWh or 0.35 m³ of biogas.
  A biogas plant must operate for one or two years before the energy put into it is recovered.

How much biomass is consumed to produce biogas?

• 30 kg of organic food waste such as sugar, starch, cellulose, protein, or fat)  yields 1 kg of biogas
• Normally Biogas plants transform only 10% of the mass they process into biogas
• The remaining 90% of the mass fed into the digester comes out as a fertilizer called digestate.
• It must have a long-term inexpensive outlet for this digestate otherwise the project will not succeed.

How Biogas is produced?

• Anaerobic Digestion  is an important process to generate biogas which is called a Biogas Digester
• In this process, bacteria help to biodegrade organic matter like solid animal manure, bio waste, and food waste
• This process is achieved in the absence of oxygen (o2)

What is  Anaerobic Digestion?

• Anaerobic digestion is a natural bacterial process by which a consortium of anaerobic bacteria biodegrading organic matter in an environment without oxygen
• These bacteria require a favorable environment to thrive
• There are several bacteria work together to convert waste material (digestible volatile solids) within the feedstock  converted into biogas
• But most feedstocks are mainly composed of water which can not help with biogas generation.
• You can make biogas out of the digestible fraction of the solids within the feedstock
• Lignocellulosic-like soft material (wood, organic waste) contains solid volatile materials which are burnable) but they are not digestible in an anaerobic digester
• The process of conversion of solids into biogas makes the substrate more liquid. This is due to  feeding solid materials into liquid digesters without clogging

Factors Affecting Anaerobic Digestion?

• The following are the key factors to efficient anaerobic digestion.
  • Proper temperature (> 25 C)
  • lack of oxygen (absence of oxygen)
  • Proper feeding of waste with a constant rate
  • Acidity
  • Feedstock mixing
• The anaerobic digestion process takes place in equipment called anaerobic digesters or, in short, digesters
• Digesters must be fed as constantly as possible regardless of feedstock fluctuations
• Biogas is composed mainly of methane (CH4) and carbon dioxide (CO2).

 

Biomethanation

• This is a process by which organic material is microbiologically converted under anaerobic conditions to biogas
•  Three are the main physiological groups of microorganisms :
  • Fermenting bacteria
  • Organic acid-oxidizing bacteria
  • Methanogenic archaea.

Role Feedstock to Enhance Biomethanisation

• The feedstock needs the biogas technology to be used, not the other way around
• For the effective  design  of a biogas plant, we need to fully understand its feedstock
• The composition of the feedstock must be  known to find out  the best suitable technologies for faster bioprocessing  material
• Proper understanding of feedstock composition allows us the predictions of digestate quality which will help identify outlets for the digestate
• The following feedstock properties are checked
  • pH
  • Alkalinity
  • Dry matter content or total solids (TS)
  • Volatile solids (VS)
  • Total Kedjhal Nitrogen (TKN)
  • Contaminants (plastics, glass, metals, etc.)

 

• The following  feedstocks are  commonly used in anaerobic digesters

Technology Used for Biogas Processing

• Anaerobic digestion processing technologies are divided into two major families:
  • Wet digestion
  • Dry digestion

Wet Digestion

• The process is considered wet digestion when the content of the digester is pumpable
• That means that the material inside the digester has a consistency of approximately 10% dry matter or less (90% water)
• There exist many configurations of wet digesters:
  •  Complete mix or Completely stirred tank reactor (CSTR)
  •   Plug-flow
  • Upflow Anaerobic Sludge Blanket (UASB)
  • Fixed film reactor
  • Floating films reactors
  • Sludge bed reactors
• These configurations have been designed to optimize the process for various feedstock conditions and market applications

 

Dry Digestion

• The process is considered dry digestion when the content of the digester is not pumpable
• The material inside the digester has a consistency of approximately 10% dry matter or more
• There exist many configurations of dry digesters:
  •   Continuous vertical
  •   Continuous horizontal
  •     Batch (Garages)
• These configurations have been designed to optimize the process for various feedstock conditions and market applications
• The mass balance of a typical dry digestion process

Which Digestion is better, wet or Dry? 

• As illustrated in the examples above, there is no silver bullet, and it is not true that dry digestion resolves all wastewater issues since composting plants have leachate treatment challenges of their own
• In the example above, using the wet digestion process resulted in 100 tonnes of SSO being converted into 45 tonnes of solid digestate and approximately 100 tonnes of wastewater (some recycled)
• The result of the dry digestion process is 80 tonnes of compost recycled to land and processed within a composting plant of equal size to the biogas plant
• Normally, it is possible to remove ammonia from the wastewater wet digestion is preferred, and if composting is possible dry digestion is used.

Use of Biomass for Thermal Energy

• Depending on H2S or siloxanes) biogas may be cleaned or not and fed into a boiler to make hot water or steam for industrial applications
• Boiler efficiency can be as high as 95%, so almost all the biogas energy gets converted into useful energy (hot water, steam, or hot air)
• However, natural gas equipment must be converted in order to burn biogas efficiently since biogas has less energy because it contains 40% CO2, which is not a fuel

Can we use Biomass as Natural Gas?

• Biogas can not be compressed directly like CNG and used for vehicles. This is because of its corrosive gases. Biogas needs to compromise the safety of the high-pressure cylinders
• Biogas will be used as LPG gas after removing its H2S, CO2, and H2O
• Biogas is converted to renewable natural gas (RNG) or biomethane which can fill up like CNG for gas vehicles

 

Biomass Storage 

• Biogas is typically stored at near atmospheric pressure
• Since biogas in its raw form is wet and corrosive, it cannot be stored in pressure vessels because it will cause corrosion leading to safety issues
• Pressure storage is possible only if the biogas has been upgraded to renewable natural gas pipeline specifications
• Storage at atmospheric pressure takes up a significant volume.

 

Conclusion

• Biogas plants provide a sustainable solution to waste management and energy generation
• By using organic waste to produce biogas, biogas plants reduce the environmental impact of waste disposal
• It provides  a source of clean energy, and promote sustainable development
• Investing in a biogas plant is an investment in a cleaner, greener future.