REPORT ON

BIO GAS PLANT

FACULTY:-

PROF. NANDANI KULKARNI

PREPARED BY

ADITYA RAGHAW SINGH

6 TH SEM., B-ARCH (I.D.)

PRIYADARSHANI INSTITUTE OF ARCHITECTURE AND DESIGN STUDIES

Table of Contents

INTRODUCTION...................................................................................................................................... 3

WHAT IS BIO GAS.................................................................................................................................... 4

WHAT IS BIO GAS PLANT ........................................................................................................................ 4

ITS CONSTITUENTS ................................................................................................................................. 7

IT’S WORKING….. .................................................................................................................................... 8

ITS ADVANTAGES AND DISADVANTAGES................................................................................................10

THE ECONOMICS OF BIO GAS……………………………………………………………………………………………………………….12

CONTINUOUS FLOW STIRRED TANK DIGESTERS (bio gas plant in new direction)……….………………………..13

SAFTY PAGE…………………………………………………………………………………………………………………….……………………15

SUMMARY……………………………………………………………………………………………………………………………………………15

INTRODUCTION:-

Biogas is generated when bacteria degrade biological material in the absence of oxygen, in a process

known as anaerobic digestion. Since biogas is a mixture of methane (also known as marsh gas or natural gas, CH4) and carbon dioxide it is a renewable fuel produced from waste treatment. Anaerobic digestion is basically a simple process carried out in a number of steps that can use almost any organic material as a substrate - it occurs in digestive systems, marshes, rubbish dumps, septic tanks and the Arctic Tundra. Humans tend to make the process as complicated as possible by trying to improve on nature in complex machines but a simple approach is still possible, as I hope you see in this website.

Conventional anaerobic digestion has been a "liquid" process, where waste is mixed with water to facilitate digestion, but a "solid" process is also possible, as occurs in landfill sites.

As methane is very hard to compress I see its best use as for stationary fuel, rather than mobile fuel. It takes a lot of energy to compress the gas (this energy is usually just wasted), plus you have the hazard of high pressure. A variable volume storage (flexible bag or floating drum are the two main variants) is much easier and cheaper to arrange than high pressure cylinders, regulators and compressors.

I think biogas is best used directly for cooking/heating, Light or even absorption refrigeration rather than the complication and energy waste of trying to make electricity from biogas. You can also run pumps and equipment off a gas powered engine rather than using electricity.

There are many advantages of biogas over wood as a cooking fuel:-

Less labor than tree felling Trees can be retained Biogas is a quick, easily controlled fuel No smoke or smell (unless there is a leak - then you need to know

anyway!) so reduced eye/respiratory irritation Clean pots Sludge is a better fertilizer than manure or synthetic fertilizers (and

is cheaper then manufactured products) Reduced pathogen transmission compared to untreated waste

WHAT IS BIO GAS?

Biogas can provide a clean, easily controlled source of renewable energy from organic waste materials for a small labor input, replacing firewood or fossil fuels (which are becoming more expensive as supply falls behind demand). During the conversion process pathogen levels are reduced and plant nutrients made more readily available, so better crops can be grown while existing resources are conserved.

Since small scale units can be relatively simple to build and operate biogas should be used directly if possible (for cooking, heating, lighting and absorption refrigeration), since both electricity generation and compression of gas (for storage or use in vehicles) use large amounts of energy for a small output of useful energy. This concept is suited to "distributed" systems where waste is treated near the source, and sludge is also reused locally, to minimize transport and initial capital cost compared to a "centralized" system. As the distributed system will need a support network biogas contributes to the "triple bottom line"; benefiting the environment, reducing costs and contributing to the social structure.

WHAT IS BIO GAS PLANT?

A biogas plant is an anaerobic digester that produces biogas from animal wastes or energy crops. Energy crops are cheap crops grown for the purpose of biofuels, rather than food. Biofuels are liquid, gaseous, or solid fuel made from live or recently dead organic material known as biomass, as opposed to fossil fuels, which are composed of ancient biological materials. Biogas is a type of biofuels created via anaerobic, or oxygen-free, digestion of organic matter by bacteria. A biogas plant is composed of a digester and a gas holder.

The digester is an airtight container in which the waste is dumped and decomposed, and the gas holder is a tank that harnesses the gases emitted by the slurry. Bacteria within the digester tank breaks down the waste and, as it decomposes, gases such as carbon monoxide, methane, hydrogen, and nitrogen, are released. Through a pressurized system, the gas holder conducts the flow of these gases upward into a hole in its drum. The hole is specially designed to allow gases to pass freely into the holder while prohibiting any gases from escaping back

into the digester. In a controlled environment, the gases are later combusted, or reacted, with oxygen to create an energy source for such processes as heating and vehicle propulsion.

Construction of a biogas plant may vary depending on the amount of gas needed, the amount of waste at hand, and whether the digester is designed for batch feeding or continuous feeding. Batch feeding systems use mostly solid wastes that are added to the tank in installments, and continuous feeding models feed mostly liquids to the digester. A biogas plant may be constructed either above or below ground, with advantages and disadvantages to both models. An above ground biogas plant is easier to maintain and benefits from solar heating, but takes more care in construction because it must be built to handle the internal pressure of the digester. A below ground biogas plant is cheaper to construct and easier to feed, but is more difficult to maintain.

To facilitate fast decomposition with optimal gas production, digesters are often kept between the temperatures of 29°C and 41°C (84.2°F-105.8°F). In an attempt to neutralize the slurry, more acidic carbon dioxide, which is a desired gas, will be created. The slurry within the tank must also be frequently stirred to prevent a hard crust from forming on top of the waste. A crust can trap the gases within the slurry and impede the machinery’s ability to harness the gases.

Biogas is increasingly preferred to fossil fuels, or fuels made from ancient organic matter like coal or oil. Carbon, in small amounts, is a vital component of a healthy atmosphere, but becomes problematic when too much is added into circulation. The carbon contained in fossil fuels has been buried for such a long time that is no longer part of the carbon cycle. When it is released through burning of fossil fuels, it raises the carbon concentration. Biogas, however, comes from live or recently dead organisms whose carbon content is still within the cycle, so burning these fuels does less to upset the carbon concentration in the atmosphere.

In addition to carbon output, biogas fuel is often preferred to fossil fuels because it is a low cost, renewable source of energy and it uses otherwise wasted materials. Biogas is also a valuable energy source for developing nations, as it can be produced in small-scale sites. Biogas fuel, however, also has its critics. Some argue that energy crops detract from food agriculture and will create a global food shortage. Biofuels may also cause deforestation, water pollution, soil erosion, and a negative economic impact on oil producing nation.

Biogas consists of about 2/3 methane (CH4), 1/3 carbon dioxide (CO2) a little hydrogen sulphide (H2S) and a little hydrogen (H2). It is created by the decomposition of manure and other forms of organic waste from industry or households in anaerobic (that is oxygen free) tanks where it is heated.

In the reactor a biological decomposition takes place where the bacteria are producing biogas. The biomass stays in the reactor for about 2-3 weeks.

Biogas can be used for production of heat and electricity.

Biogas is created naturally by the decomposition of organic matter; one example in the natural world is from moors where marsh gas is created.

It is possible to use about 65% of the energy available in biogas: 30% for electricity 35% for heat

This process has a loss of about 35%: 20% for the heating of the biomass 15% engine loss

In principle any kind of organic material can be transformed for biogas. But if the biogas plant is supposed to be profitable with the current energy prices there should be used; manure (slurry) from the agriculture, sludge from cleaning of waste water, plants and waste from the food industry. Manure is the main ingredient – waste is an additive that increases the production. Pure waste material produces too much gas and thereby foam which destroys the gas (it has to be separated first).

There are two kinds of different biogas plants in Denmark: common plants and farm plants.

Common plants receive manure from industry and households. In Denmark the first common plant was inaugurated in 1984 and today there are 20 common plants. The gas that these plants produce can be sold to local CHP units that generate electricity and heat. A farm plant uses only waste material from a single farm, but also uses manure as material.

In Denmark the first farm plants were builds after the energy crisis in the 1970ies, today there are about 60 plants running or under construction.

We have worked with biogas at the Folk center since 1984 and were among the pioneers at this field.

CONSTITUENTS:-

Methane (CH4)- 50 - 75%, Carbon dioxide (CO2)- 25-50%, Nitrogen (N2)-0-10%, Hydrogen (H2)-0-1%, Hydrogen Sulfide (H2S)-0-3%, Oxygen (O2)-0-0% in some cases, biogas contains siloxanes.

These siloxanes are formed from the anaerobic decomposition of materials commonly found in soaps and detergents.

During combustion of biogas containing siloxanes, silicon is released and can combine with free oxygen or various other elements in the combustion gas.

Deposits are formed containing mostly silica (SiO2) or silicates (SixOy) and can also contain calcium, sulfur, zinc, phosphorus.

Such white mineral deposits accumulate to a surface thickness of several millimeters and must be removed by chemical or mechanical means.

WORKING:-

The various forms of biomass are mixed with an equal quantity of water in the mixing tank. This forms the slurry.

The slurry is fed into the digester through the inlet chamber.

When the digester is partially filled with the slurry, the introduction of slurry is stopped and the plant is left unused for about two months.

During these two months, anaerobic bacteria present in the slurry decompose or ferments the biomass in the presence of water.

As a result of anaerobic fermentation, biogas is formed, which starts collecting in the dome of the digester.

As more and more biogas starts collecting, the pressure exerted by the biogas forces the spent slurry into the outlet chamber.

From the outlet chamber, the spent slurry overflows into the overflow tank.

The spent slurry is manually removed from the overflow tank and used as manure for plants.

The gas valve connected to a system of pipelines is opened when a supply of biogas is required.

To obtain a continuous supply of biogas, a functioning plant can be fed continuously with the prepared slurry.

Table: gross energy production of different types of manure and waste in biogas plants:-

  Biogas production per ton biomass [m3/ton]

Equal to liter of fuel oil

Slurry from pigs 22 14

Slurry from cows 22 14

Manure from  poultry 50-100 33-65

Intestine waste from slaughter houses

40-60 26-39

Fat containing waste from slaughter houses

>100 >65

Fish oil waste 100-1000 65-650

Advantages of biogas:-

- Biogas is a renewable energy form. Biogas is CO2 equivalent reducing. Biomass naturally decomposes releasing methane and other gasses into the atmosphere, by gathering this material, extracting and burning the gas, the green house gas emission are significantly reduced. By utilizing biogas as an energy source we can reduce our dependency on fossil based carbon such as coal, oil and natural gas.

The smell from the slurry is reduced when the slurry is degassed.

Reduced risk of pollution when this material is applied to the fields (compared with raw manure), Since it is partially decomposed the nutrients are readily available (80%) to plants and bacteria.

Biogases plants reduce the risk of disseminate seeds of weed.

Renewable Source of Energy : To begin with, biogas is considered to be a renewable 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.

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.

Reduces Landfills : It also uses up waste material found in landfills, dump sites and even farms across the country, allowing for decreased soil and water pollution.

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.

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.

Little Capital Investment: Biogas is 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.

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 biogas:-

Biogas can cause obnoxious smells

Degasification increases the risk of evaporation of ammonia

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.

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.

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.

Unstable : It is also somewhat unstable, making it prone to explosions if the methane comes in contact with oxygen and become flammable in nature.

The economics of biogas:-

The economics of biogas plants have been improved significantly since the electricity generated can obtain a fixed price of 74,5 area per kWh until the year 2012. There is also the possibility of trading with CO2 quotas since the methane emissions are reduced.

Private biogas plantThe economy of each household has its own biogas plants is a good idea, but unfortunately not realistic:

A pig gives approx. 5kg manure a day and a man gives roughly the same. 1 cubic meter (equivalent to 1000kg) gives between 6-25m ³ of gas, each containing about 5-6kWh.

So at best, 4 people will give 20kg manure (1 / 50 of a cubic meter). This will provide between 0.3 to 1.25 cubic meters of gas which will provide between 1.5 - 7kWh.

Heat in a normal house in 150 square meters is around 15,000kWh = 40kWh/dg.

Continuous Flow Stirred Tank Digesters:-

SAFETY PAGE:-FIRE/EXPLOSION

Methane, which is makes up from 0% to 80% of biogas, forms explosive mixtures in air, the lower explosive limit being 5% methane and the upper limit 15% methane. Biogas mixtures containing more than 50 % methane are combustible, while lower percentages may support, or fuel, combustion. With this in mind no naked flames should be used in the vicinity of a digester and electrical equipment must be of suitable quality, normally "explosion proof". Other sources of sparks are any iron or steel tools or other items, power tools (particularly commentators and brushes), normal electrical switches, mobile phones and static electricity.

If conducting a flammability test take a small sample well away from the main digester, or incorporate a flame trap in the supply line, which must be of suitable length (minimum 20 m). View sketches of Flame trap.

As biogas displaces air it reduces the oxygen level, restricting respiration, so any digester area needs to be well ventilated to minimize the risks of fire/explosion and asphyxiation.

DISEASE

As Anaerobic Digestion relies on a mixed population of bacteria of largely unknown origin, but often including animal wastes, to carry out the waste treatment process care should be taken to avoid contact with the digester contents and to wash thoroughly after working around the digester (and particularly before eating or drinking). This also helps to minimize the spread odors which may accompany the digestion process. The digestion process does reduce the number of pathogenic (disease causing) bacteria, particularly at higher operating temperatures, but the biological nature of the process need to be kept in mind.

ASPHYXIATION

Biogas consists mainly of CH4 and CO2, with low levels of H2S and other gases. Each of these components has its own problems, as well as displacing oxygen.

CH4 - lighter than air (will collect in roof spaces etc), explosive (see above). CO2 - heavier than air (will collect in sumps etc), slightly elevated levels affect respiration rate,

higher levels displace oxygen as well. 

H2S - (rotten egg gas) destroys olfactory (smelling) tissues and lungs, becomes odorless as the level increases to dangerous and fatal. More details an actual case and detection equipment are available.

Adequate ventilation, suitable precautions and adequate protective equipment will minimize the dangers associated with biogas, making it a good servant rather than a bad master.

SUMMARY

Like water, electricity, automobiles and most of life biogas is not completely safe, but by being aware of the dangers involved you are well on the way to a safe and happy digestion experience.