Biogas Plant

SUBMITTED BY : MUAAZ ALI (BSME-01113094)

ASSIGNMENT ON BIOGAS PLANT

BIOGAS PLANT

WHAT IS BIOGAS ?• Biogas is a gas mixture which is generated when organic compounds are

fermented in the absence of air (anaerobic fermentation).

• This gas mixture is mainly made of carbon dioxide (CO2) and methane (CH4). Methane is a combustible gas, which means it can be burned.

• It can be used as a fuel for cooking and lighting.

C-O-O

PERCENTAGE OF COMPOSITION

• CH4 ( 45-80 )%

• CO2

• O2 ,H2S ,N2 ( < 5 )%

THREE MAIN WAYS OF BIOGAS PRODUCTION

• SEWAGE TREATMENT PROCESS

• AT WASTE DUMPS

• BY BIOGAS PLANT

WHAT IS BIOGAS PLANT• A plant to collect biological gas has five components:• The inlet, the fermentation chamber or digester , mixing and over flow

tanks, the gas storage bag or tank, and the outlet i.e the exit pipe through which the gas is removed.

• Simple biogas plant

INTRODUCTION

A biogas plant is an anaerobic digester of organic material for the purposes of treating waste and concurrently generating biogas fuel. The treated waste is a nutrient-rich, nitrogen-rich fertilizer while the biogas is mostly methane gas with inert gases including carbon dioxide and nitrogen. Biogas plants are a preferred alternative to burning dried animal dung as a fuel and can be used for the treatment of human waste. Other feedstock which can be used includes plant material, non-meat or grease food-wastes, and most types of animal dung. Over a million biogas plants

have been constructed in the developing world for treatment of organic wastes, alternative energy supply to direct burning in the home, and overall improvement of human health and the

environment. Many factors for selection of feedstock and site location must be researched before deciding to install a biogas plant

COMPONENTS OF PLANT

1. INLET TANK 2. DIGESTER WITH DOME 3. OUTLET CHAMBER

4. COMPOSIT PITS

DETERMINING PLANT SIZE

• Plant size is the sum of digester volume and gas storage .

• The biogas plant size is dependent on the average daily feed stock and expected hydraulic retention time of the material in the biogas system .

• For small size plant

• Generally, at least 24 kilograms of feedstock complimented with 24 to 50 liters of water per day with a hydraulic retention time of 3 to 5 days will require a 4-cubic meter plant .

What is HRT ???• The Hydraulic retention time (HRT) is a measure of the average length of time

that a soluble compound remains in a constructed bioreactor or DIGESTER.

:

GENERAL BIOGAS PLANT

RAW MATERIALS

CEMENT The cement to use in the plant construction must be of high quality Portland

cement from a brand with a known reputation. It must be fresh, without lumps and stored in a dry place.

SANDSand for construction purpose must be clean. Dirty sand has a very negative effect on the strength of the structure. If the sand contains 3% or more impurities by volume, it must be washed. the percent of mud should be less than 3% of the overall volume. Course and granular sand can be used for concrete work however fine sand is necessary for plastering work. PIPES

RAW MATERIALS

GRAVEL Gravel size should not be too big or too small. Individual gravel diameter should not

be greater than 25% of the thickness of concrete product where it is used. As the slabs and the top of the dome are not greater than 8 cm (3") thick, gravel should not be larger than 2 cm (0.75") in size.

WATER Water is mainly used for preparing the mortar for masonry, concrete and plastering

work. It is also used to soak bricks/stones before using them.

COBBLE STONES If cobble-sized stones, 7.5-30 cm (3-12”) in diameter are used for masonry work, they

must be clean, solid and of good quality.

Tools

• Welding equipments.• Shovels• Trowels• Metal saw and blades for cutting steel.

CONTRUCTION

FIRST THE CONSTRUCTION SITE IS SELECTED FOR BIOGAS PLANT TO BE CONSTRUCTED The following points should be kept in mind when deciding on a site for biogas

plant construction

• For proper function of the plant, the optimal temperature has to be maintained in the digester. Therefore, a sunny site should be selected to keep the digester near 35 degrees Celsius (95 degrees Fahrenheit).

• To make plant operation easier and to avoid wastage of raw feedstock the plant must be as close as possible to the feedstock supply (toilet, animal pen, compost pits, etc.) and water source. If a readily available supply of feedstock or water or both is not available then the biogas plant should not be installed.

• The plant should be at least 10 meters away from groundwater wells or surface water bodies to protect water from pollution.

STEPS FOR CONSTRUCTION

• After selection of the plant size and site location, the site layout is marked on the ground surface with wooden stakes, rocks, chalk or other materials. After the site layout is marked, “the engineer should review the selected location again to ensure the best site has been chosen and will not interfere with other activities normally performed at the planned biogas plant. “

1. EXCAVATION It is the first step of construction. The excavation work should only be started after deciding the location of manhole and outlet tank.

STEPS FOR CONSTRUCTION

2.Construction of Digester Main Chamber i. The digester foundation is placed using cobbles and gravel as mixture

then filled with concrete. The foundation should be 15 cm thick and allowed.

ii. At the center of the pit, a straight rod or pipe (the 0.5“ * GI gas pipe) must be placed in an exact vertical position.

iii. After the Foundation has cured for at least two days, the round wall is constructed

* GI:- galvanized steel pipe i.e. zinc coated to protect from corrosion

VIEW OF MANHOLE IN DIESTER

STEPS FOR CONTRUCTION

3.DOME CONSTUCTION When the round wall of the digester is complete, the dome is then constructed. The dome is

constructed using a mould or cast technique. This can be accomplished by constructing a timber frame for proper arch design .After the dome has cured for approximately one week, the timbers and earth of the mould can be removed through the manhole.

4. OUTLET CHAMBER CONSTRUCTION The Outlet Chamber excavation and manhole is completed concurrently with the digester vessel and

the manhole shares a common foundation with the digester vessel5. CONSTRUCTION OF INLET TANK The Inlet Tank is constructed to mix feedstock and water. This can be constructed with or without a

mixing device. The top of the structure should not be more than one meter above ground level and both inside and outside of the tank must be covered with a smooth layer of plaster The finished bottom of the Inlet Tank must be at least 5 cm above the Outlet Chamber overflow level.

6.LAYOUT OF PIPELINE The gas pipe conveying the gas from the plant to point of user is vulnerable to damages by people,

domestic animals and rodents. Therefore, only light quality galvanized iron pipe should be used which must be, where possible, buried 30 cm (1 foot) below ground level.

BREIF DESCRIPTION OF PROCEDURE

• The required quantity of feedstock and water is mixed in the inlet tank and the slurry is discharged to the digester vessel for digestion. The gas produced through methanogenesis in the digester is collected in the dome. The digested slurry flows to the outlet tank through the manhole. The slurry then flows through the overflow opening in the outlet tank to the compost pit. The gas is supplied from the dome to the point of application through a pipeline.

HOW IT WORKS ?

• HERE IS A SMALL DEMONSTRATION .

A SHORT CLIP FOR BETTER UNDERSTANDING

Just click on black screen to start the clip !

IMPORTANCE

The anaerobic production of biogas does not produce any offensive smell hence it is environmentally friendly, reduces green house effect, greatly increases the fertilizer value of manure and protects water source.

The Chinese has long identified the importance of biogas towards meeting the energy needs in rural areas.

Transformation of organic wastes into high quality fertilizer IN THE NEWS

ISLAMABAD - Pakistan Council of Renewable Energy Technologies (PCRET) will install 368 Biogas plants in different rural areas by the June 2012 under the project “Development and Promotion of Biogas Technology for meeting domestic fuel needs of rural areas and production of Biocfertilizer”. This project was launched in 2008 through which 2500 family size Biogas plants are to be installed in the country, out of these 2132 plants have been installed and the remaining will be installed by end of financial year 2011-12

ANALYSIS• What questions would be asked by a person who wants to build a

domestic plant that could fulfill his needs of cooking?i) How large biogas plant does I need?ii) How much money would it cost?

How large biogas plant does I need• To cook food for six people we required farm yard manure of six buffaloes or

ten cows. In Pakistan an average family has 6 people . Lets assume how large biogas plant would be needed for six people.

• It is said that a buffalo or cow produces at least 20 kg of dung per day which is dependant on the amount and quality of feed given to the animal.(if 40 kg fodder is given to the cow).

• On the other hand the plant can also be connected with a toilet as a human being also produces a waste of about a kg per day.

• Now, upon some research I found that different dung produces different amount of gas per kg of it.

Lets calculate my personal need• First lets have a look on the following conversion table for methane i.e (natural gas

and biogas) 1 cubic meter = 35.315 cubic feet 1000 cubic feet = 1 MMBTU 1 cubic meter = 3.5315 x 10^-2 MMBTU

MY LAST GAS BILL SHOWS THAT MY FAMILY HAS CONSUMED ABOUT 2.662 MMBTUOF GAS NOW LET’S CONVERT IT INTO CUBIC METERS. 1/1000 MMBTU = 1 CUBIC FEET 35.315/1000 MMBTU = 35.315 CUBIC FEET 3.5315 X 10^-2 MMBTU = 1 CUBIC METER 1 MMBTU = 1 / 3.5315 X 10^-2 CUBIC METER 2.662 MMBTU = 2.662 / 3.5315 X 10^-2 CUBIC METER SO. 2.662 MMBTU = 75.37 CUBIC METERSWHERE AS THE PER DAY CONSUMPTION IS = 75.37 / 30 = 2.51

THERE ARE 6 MEMBERS IN MY FAMILY SO , PER PERSON CONSUMES ABOUT = 2.51 / 6 = 0.41 NOW HOW LARGE PLANT DO I NEED ??????

HOW LARGE PLANT DO I NEED ?• Before building a plant some animals are needed how many of them do in need.• As a buffalo produces at least 20 kg of dung so (NO OF ANIMALS) X ( AMOUNT OF DUNG) X ( PER KG PRODUCTION OF GAS) = GAS PRODUCTION NO OF ANIMALS = (2.51) / (20 kg)( 0.040) no of animals needed = 3.1 = 3 buffaloes needed to fulfill my gas requirement

MAKE SLURRY WE KNOW WATER IS ADDED TO DUNG THE RATIO OF WATER PER DAY =1: 1 20 Kg + 20 liters = 25–30 kg (slurry) total input / day = 25 kg (slurry) now, THE MINIMUM CAPACITY NEEDED FOR MY HOUSE IS 2.5 CUBIC METERS TOTAL INPUT FOR SIX WEEKS = 25 X 42 =1050 Kg = 10.52 CUBIC METERSTHUS ,THE MAXIMIUM CAPACITY NEEDED WOULD BE 10.52 CUBIC METERS

For a family of 8 with a few animals (say 8-10 cows), at least 10m³ digester is a commonly used size in India, with 2 m³ gas storage. ( LINK http://www.small-farm-permaculture-and-sustainable-living.com/methane_generator.html)

EXAMPLE Calculationso A SAMPLE EXAMPLE OF A FARMER !o First we should get to know how many buffaloes the person has ???o Lets assume that the person is having 2 buffaloes and 3 CHICKENS . o An average cow or a buffalo produces 20kg of manure and lets assume that the feed of his cattle is good so 1 kg of fresh manure can produce up to 0.04 cubic meter of a gas from the table.

2 x 20 kg/animal x 0.04 = 1.6 cubic meters gaso Each person produces an average of about 1 kg of waste per day so,

6 x 1 kg/person x .028 = 0.168 cubic meters gaso Almost every farmer with cattle also has some poultry (chickens) , 1 kg of chicken’s dung produces an average of 0.065 to 0.116 cubic meters of a gas. Lets assume the person has 3 chickens. So,

3 x 0.2kg/ chicken x .0116 = 0.069 cubic meters gas so, Total = 0.069+0.168+4 = 1.837 cubic meters

The size of plant !

• Total input per day ! The ratio of water per day is 1:1 so,

2 cattle = 20 kg dung + 20 liters water 6 people = 6 kg dung + 6 liters watersAnd lets add 2 kg of dung and water for the chickens !

Total input / day = 30+2 = 32 kg input for six weeks = 32 x 42 = 1344 kg • in volume = 1 cubic meter = 1000 kg so , 1344 kg= 1.3 cubic meter Thus this is the maximum capacity of fermentation/digester well needed by

that farmer.

Production of gas Production of gas depends upon the amount and nature of the fermentation

slurry, digester, temperature and retention time. The produced gas is collected in the gas holder , cap or drum above the dome.

To minimize the size and to keep the price as low as possible, the drum is not built to accommodate a full day's gas production. The drum is made to hold between 60 and 70 percent of the volume of the total daily gas production.

The pressure of natural gas being supplied by the government is usually 2psi but the pressure of biogas produced is generally low thus the drum constructed on top floats upon slurry and continuously creates pressure

on the gas being collected. Pressure of 600 mm of water column is usually created inside the digester .

600 Water Column [millimeter] = 0.853 400 600 06 pound/square inch That means round about pressure of 1 psi is obtained in the stoves

Cost

• Maximum cost including the price of materials and labour would not exceed 50,000 !

COMMENTS

Biogas plants are a cheap source of energy,PAKISTAN as a developing country should get equipped with this technology

especially in the rural areas to reduce their problem of load shedding as it could fulfill their requirements up to the mark.

REFERENCES

• http://desertification.wordpress.com/2010/09/10/the-importance-of-biogas-towards-meeting-the-energy-needs-in-rural-areas-google-ezine-articles/

• http://www.biogasenergy.rs/how_it_works.html• http://www.greenpowerindia.org/biogas_benefits.htm• journeytoforever.org• ohioline.osu.edu/b804/804_3.html