Renewable energy(Biogas)

BIOGAS

B.PRASHANTH

Biogas typically refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste. It is a renewable energy source and in many cases exerts a very small carbon footprint.

Biogas can be produced by Anaerobic digestion with Anaerobic ORGANISM, which digest material inside a closed system, or fermentation of biodegradable materials

Introduction

Biogas is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulfide (H2S), moisture and siloxanes. The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.

Biogas can be compressed, the same way natural gas is compressed to CNG, and used to power motor vehicles. In the UK, for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel. It qualifies for renewable energy subsidies in some parts of the world. Biogas can be cleaned and upgraded to natural gas standards, when it becomes bio methane.

WASTE FROM WHICH IT IS PRODUCED

Animal Dung

Chicken dung

Animal dung

Spoiled flour of wheat / corn

Stale, left over food

PLANT LAYOUT

PRODUCTION OF BIOGAS

Anaerobic digestion is a naturally occurring process through which organic matter such as manure, feed spills, meat processing wastes and crop residues are stabilized by microorganisms strictly in the absence of air.During this process, some organic compounds are converted to methane (CH4) and carbon dioxide (CO2) gases. This mixture of gases is known as biogas. The composition of biogas is 50 to 75 per cent CH4 and 25 to 45 per cent CO2. Like natural gas, biogas can also be used as a fuel in power generators, engines, boilers and burners. Following is the schematic diagram representing the anaerobic process:

Anerobic digestion

In practice, specially designed and insulated tanks are used to facilitate the anaerobic digestion process under a controlled atmosphere. These tanks are known as anaerobic digesters. The effluent coming out from the digester after the completion of the digestion process is known as digestate. Digestate has nutrient value and can be applied on land like manure. Digestate also has much less odour compared to stored manure.

Fixed dome type of biogas plant:

The fixed dome type is also popularly known as the “Deenbandhu Model”. The fixed dome type consists of a dome constructed of concrete, known at the digester tank. This dome is fixed and thus it is called fixed dome type of biogas plant. The feedstock along with water is mixed in the mixing tank to form the slurry and allowed to ferment. Once the pressure is enough within the dome, the gas can be taken out from outlet. The used slurry expands and overflows into the overflow tank.

The floating gasholder type is also popularly known as “Indian Khadi and Village Industries Commission (KVIC) Model”. The digester is constructed, which is divided into two parts. One part is an inlet, from where the slurry is fed to the tank, the other is the cylindrical dome of the tank, which is made out of stainless steel that floats on the slurry and collects the gas generated. Hence it is called floating gas-holder type of bio gas plant. The slurry is fermented and as gas produced by the bacterial fermentation, the pressure inside increases. The gas is collected from the outlet pipe and utilized.

Floating dome type biogas plant

EQUIPMENT FOR ELECTRICITY GENERATION

Conversion of bio gas to electricity

Theoretically, biogas can be converted directly into electricity by using a fuel cell. However, this process requires very clean gas and expensive fuel cells. Therefore, this option is still a matter for research and is not currently a practical option. The conversion of biogas to electric power by a generator set is much more practical. In contrast to natural gas, biogas is characterized by a high knock resistance and hence can be used in combustion motors with high compression rates.

In theory, biogas can be used as fuel in nearly all types of combustion engines, such as gas engines (Otto motor), diesel engines, gas turbines and Stirling motors etc.

Gas Motors with spark ignition (Otto system) can operate on biogas alone. In practice, a small amount of petrol (gasoline) is often used to start the engine. This technology is used for very small generator sets (~ 0.5-10 kW) as well as for large power plants. Especially in Germany, these engines have advantages as they do not need additional fossil fuels that would lead to lower feed-in tariffs according to the Renewable Energy Law (EEG).

Diesel Engines operate on biogas only in dual fuel mode. To facilitate the ignition of the biogas, a small amount of ignition gas is injected together with the biogas. Modern pilot injection gas engines (“Zündstrahlmotoren”) need about 2% additional ignition oil. Almost every diesel engine can be converted into a pilot injection gas engine. These motors running in dual fuel mode have the advantage that they can also use gas with low heating value. But in that case, they consume a considerable amount of diesel. Up to engine sizes of about 200kW the pilot injection engines seem to have advantages against gas motors due to slightly higher efficiency (3-4% higher) and lower investment costs.

Advantages of bio gas

1. Renewable Source of Energy: To begin with, biogas is considered to be arenewable source of energy. Since it often produced from materials that form sewage and waste products, the only time it will be depleted is when we stop producing any waste.2. Non-Polluting: It is also considered to be non-polluting in nature. The production of biogas does not require oxygen, which means that resources are conserved by not using any further fuel.3. Reduces Landfills: It also uses up waste material found in landfills, dump sites and even farms across the country, allowing for decreased soil andwater pollution.

4. Cheaper Technology: Applications for biogas are increasing as the technology to utilize it gets better. It can be used to produce electricity and for the purpose of heating as well. Compressed Natural Gas (CNG) is biogas that has been compressed and can be used as a fuel for vehicles. Production can be carried out through many small plants or one large plant.

5. Large number of Jobs: Either way, work opportunities are created for thousands of people in these plants. These jobs are a blessing in rural areas, which are the targeted grounds for the use of biogas. In fact, biogas can easily be decentralized, making it easier to access by those living in remote areas or facing frequent power outages.

6. Little Capital Investment: Biogas are easy to set up and require little capital investment on a small scale basis. In fact, many farms can become self sufficient by utilizing biogas plants and the waste material produced by their livestock each day. A single cow can provide enough waste material within a day to power a light bulb the entire day.7. Reduces Greenhouse Effect: It also reduces the greenhouse effect by utilizing the gases being produced in landfills as forms of energy. This is a major reason why the use of biogas has started catching on. It recycles most forms of biodegradable waste and works on simple forms of technology.

Disadvantages of biogas1. Little Technology Advancements: First of all, the current systems in place used to create biogas are not as efficient as they get. Little new technology has been introduced for streamlining the process and making it more cost effective. As a result, large scale industrial production of biogas is still not on the energy map. Although it could solve the energy issues being faced by countries all over the world, very few investors are willing to put in the startup capital. It is also not the best idea to construct one biogas plant per house, which means that a central system will have to be put into place.2. Contain Impurities: Biogas contains a number of impurities even after refining processes have been put into place. When compressed for use as fuel, these can become corrosive to the metal parts of engines.

3. Not Attractive on Large Scale: The process of using biogas on a large scale is not economically viable and it is very difficult to enhance the efficiency of biogas systems.4. Unstable: It is also somewhat unstable, making it prone to explosions if the methane comes in contact with oxygen and become flammable in nature.Even with all of the disadvantages present, countries have started to apply the uses of biogas in everyday life. Public transportation has been renewed and made efficient with the help of CNG. Remote locations that are off the electric grid receive a steady supply of power from these plants. The future use of biogas is bright, even with the problems it faces.