biom4-x.txt
biom4-x.txt - - - - meth805\txt\pnt get pics?
3.9.10 Janata Model
The Janata model consists of a digester and a fixed biogas holder (known as Gas Storage Chamber) covered by a dome shaped enclosed roof structure. The entire plant is made of bricks and cement masonry and constructed underground. Unlike the KVIC model, the Janata model has no movable part. A brief description of the different major components of Janata model is described below:
The foundation: is well-compacted base of the digester, constructed of brick ballast and cement concrete. The upper portion of the foundation has a smooth plaster surface.
The digester: is a cylindrical tank resting on the foundation. The top surface of the foundation serves as the bottom of the digester. The digester (fermentation chamber) is constructed with bricks and cement mortar. The digester wall has two small rectangular openings at the middle, situated diametrically opposite, known as inlet and outlet gate, one for the inflow of fresh slurry and the other for the outflow of digested slurry. The digester of Janata BGP comprises the fermentation chamber (effective digester volume) and the gas storage chamber (GSC).
Gas Storage Chamber (GSC)
The Gas Storage Chamber (GSC) is also cylindrical in shape and is the integral part of the digester and located just above the fermentation chamber. The GSC is designed to store 33% (approx. 8 hours) of the daily gas production from the plant. The Gas Storage Chamber (GSC) is constructed with bricks and cement mortar. The gas pressure in Janata model varies from a minimum of 0 cm water column (when the plant is completely empty) to a maximum of up to 90 cm of water column when the plant is all full of biogas.
Fixed Dome Roof
The hemi-spherical shaped dome forms the cover (roof) of the digester and constructed with brick and cement concrete mixture, after which it is plastered with cement mortar. The dome is only an enclosed roof designed in such a way to avoid steel reinforcement. (Note: The gas collected in the dome of a Janata plant is not under pressure therefore can not be utilised. It is only the gas stored in the Gas Storage Chamber (GSC) portion of the digester and that is under pressure and can be said as utilisable biogas).
Inlet Chamber
The upper portion of the Inlet Chamber is in the shape of bell mouth and constructed using bricks and cements mortar. Its outer wall is kept inclined to the cylindrical wall of the digester so that the feed material can flow easily into the digester by gravity. The bottom opening of the Inlet Chamber is connected to the Inlet Gate and the upper portion is much wider and known as Inlet Displacement Chamber (IDC). The top opening of the inlet chamber is located close to the ground level to enable easy feeding of fresh slurry.
Outlet Chamber
It is a rectangular shaped chamber located just on the opposite side of the inlet chamber. The bottom opening of the Outlet Chamber is connected to the Outlet Gate and the upper portion is much wider and known as Outlet Displacement Chamber (ODC). The Outlet Chamber is constructed using bricks and cement mortar. The top opening of the Outlet Chamber is located close to the ground level to enable easy removal of the digested slurry through a discharge opening. The level of the discharge opening provided on the outer wall of the outlet chamber is kept at a somewhat lower level than the upper mouth of the inlet opening, as well as kept lower than the Crown of the Dome ceiling. This is to facilitate easy flow of the digested slurry out the plant in to the digested slurry pit and also to prevent reverse flow, either in the mixing tank through inlet chamber or to go inside the gas outlet pipe and choke it.
The Biogas Outlet Pipe: is fixed at the crown of the dome, which is made of a small length of GI Pipe fitted with socket and a Gate Valve.
3.9.10.1 The Deenbandhu Model: is a semi continuous-fed fixed dome Biogas plant. While designing the Deenbandhu model an attempt has was made to minimise the surface area of the BGP with a view to reduce the installation cost, without compromising on the efficiency. The design essentially consists of segments of two spheres of different diameters joined at their bases. The structure thus formed comprises of (i) the digester (fermentation chamber), (ii) the gas storage chamber, and (iii) the empty space just above the gas storage chamber. The higher compressive strength of the brick masonry and concrete makes it preferable to go in for a structure that could be always kept under compression. A spherical structure loaded from the convex side will be under compression and therefor, the internal load will not have any effect on the structure.
The digester of the Deenbandhu BGP is connected with the Inlet Pipe and the Outlet Tank. The upper part (above the normal slurry level) of the outlet tank is designed to accommodate the slurry to be displaced out of the digester (actually from the gas storage chamber) with the generation and accumulation of biogas and known as the Outlet Displacement Chamber (ODC). The Inlet Pipe of the Deenbandhu BGP replaces the Inlet Chamber of Janata Plant. Therefore to accommodate all the slurry displaced out from the Gas Storage Chamber (GSC), the volume of the Outlet Chamber of Deenbandhu model twice the volume of the Outlet Tank of the Janata BGP of the same capacity.
Being a fixed dome technology, the other components and their functions are same as in the case of Janata Model BGP and therefore are not elaborated here once again.
3.9.10.2 Shramik Bandhu Model:This new BRCM biogas plant model which is also a semi-continuous hydraulic digester plant was designed by the author and christened as SHRAMIK BANDHU (friend of the labour). Since then, three more models (rural household plants) in the family of SHRAMIK BANDHU Plants have also been developed. The second one, a semi-continuous hydraulic digester, works on the principle of semi-plug flow digester (suitable for use as a Night Soil based or Toilet attached plant). The third one uses simple low cost anaerobic bacterial filters, designed for possible application as a Low Cost and low Maintenance Wastewater Treatment System. The fourth one is a semi-batch fed hydraulic digester, ideally suitable for the regions where plenty of seasonal crop wastes and waste green biomass are available and population of domestic farm animals are less, for producing the desired quantity of biogas from it alone. For this reason the first model which is the simplest and cheapest in the family of Shramik Bandhu plants, is christened as SBP-I Model. The other three models, yet to be field evaluated, are, SBP-II, SBP-III and SBP-IV, respectively.
The family of SHRAMIK BANDHU biogas plants designs uses the fixed dome concepts as in the case of pervious two most popular Indian fixed dome plants, namely, Janata and Deenbandhu models. In other words, all the four Models of the family of SHRAMIK BANDHU Plant have both, (i) the Gas Storage Chamber (GSC) and (ii) the Dome shaped Roof. However, in this section, the description about Shramik Bandhu plants relates to SBP-I model only.
The SHRAMIK BANDHU Plant is made of Bamboo Reinforced Cement Mortar (BRCM), by pre-fabricated bamboo shells, using the correct size mould for a given capacity SBP-I model- Thus, completely replacing the bricks. These bamboo shells are made by weaving bamboo strips (weaving of which can be done in the village itself) for casting a BRCM structure. The BRCM structures on the one hand are used for giving the right shape to this plant, while on the other hand acts as the reinforcement to the cement mortar plaster as it is casted more or less like the ferro-cement structure. In order to protect the bamboo strips from microbial attack, they are pre-treated by immersing them in water mixed with prescribed ratio of Copper Sulphate (CuSO4) for a minimum of 24 hours before weaving of shell structure is done. As a further safety measure DPC powder in appropriate quantity is mixed while doing second layer (coat) of smooth plastering on the Main Unit of the Plant (MUP), Outlet Chamber (OC); as well as other BRCM components and sub- components, to make the entire structure of SBP-I moisture proof. The Shramik Bandhu plant made from BRCM would be much stronger because it has both higher tensile, as well as compressive strength, as compared to either First Class Bricks or Cement Concrete (CC) or Cement Mortar (CM), when used alone. The reason for this is that the bamboo shell structures used (for both reinforcement and shape of the plant) for the construction of Shramik Bandhu plant is made by weaving strips [only the outer harder surface (skin) and not the softer inner part of bamboo] from seasoned (properly cured) bamboo. Therefore, the entire structure (body) of the SBP-I model would be very strong, durable and have long useful working life. The two previous fixed dome models, namely Janata and Deenbandhu model have no reinforcement and are made of Bricks and Cement Mortar only, therefore, while they are very strong under compression but cannot withstand high tensile force. The hemi-spherical shell shaped (structure) of SHRAMIK BANDHU (SBP-I) model loaded from top on its convex side will be under compression. However, due to comprehensive strength provided by both cement mortar, as well as the reinforcement provided by the woven bamboo shell will ensure that the internal and external load will not have any residual effects on the structure. The bamboo reinforcement will provide added strength (both tensile and compressive) to make the entire structure of SHRAMIK BANDHU (SBP-I) model very sound, as compared to the previous two fixed dome Indian models (Janata & Deenbandhu), referred above.
The digester of SBP-I model is connected to the slurry mixing tank with inlet pipe made of 10 cm or 100 mm (4?) diameter Asbestos Cement Concrete (ACC) pipe, for feeding the slurry inside the plant.
The Outlet Displacement Chamber (ODC) is designed to accommodate the slurry to be displaced out of the digester with the generation & accumulation of biogas. The Outlet Displacement Chamber (ODC) of SBP-I model is also kept hemi-spherical in shape to reduce it?s surface area for a given volume (to save in building materials and time taken for construction)- The ODC is also made of BRCM, using a hemi-spherical shaped woven bamboo shell structure.
A Manhole opening of about 60 cm or 600 mm (2.0 Ft) diameter is provided on the crown of the hemi-spherical shaped ODC. The Manhole is big enough for one person to go inside and come out, at the same time small enough to be able to easily close it by a same size Manhole Cover, which is also made of BRCM.
COMPONENTS OF SHRAMIK BANDHU (SBP-I MODEL) BIOGAS PLANT (BGP)
The Shramik Bandhu (SBP-I) Model is made of two major components and several minor components and sub-components. They are categorized as, (a) Main Unit OF The Plant (MUP), (b) Outlet Chamber (OC) and (c) Other Minor Components. These major and minor components are further divided into sub-components, as given below:
Main Unit Of the plant (MUP)
The Main Unit of the Plant (MUP) is one of the major components of Shramik Bandhu (SBP-I) Model. The MUP has following six main ?Sub-Components?:
(i). Digester {or Fermentation Chamber (FC)}
(ii). Gas Storage Chamber (GSC)
(iii). Free Space Area (FSA), located just above the GSC
(iv). Dome (Roof of the Plant-entire area located just above the FSA); and
(v). The following three other sub-components:
[{(e)-(i) the Foundation of the MUP & (e)-(ii)} the Ring Beam for MUP (these two have also been considered here as the two sub-components of the MUP} and {the third is (e)-(iii) the Gas Outlet Pipe (GIP), for better explanation & understanding of the constructional aspects of SBP-I Plant].
Outlet Chamber
The Outlet Chamber (OC)) is the second major component of Shramik Bandhu (SBP-I) Model. The OC has the following four main ?Sub-Components?:
(i). Outlet Tank (OT)
(ii). Outlet Displacement Chamber (ODC)
(iii). Empty Space Area (ESA) above the ODC- though for all practical purpose the ODC includes the Empty Space Area (ESA) above it; however, from the designing point of view, the effective ODC of SBP-I model is considered up to the starting of discharge opening located on its outer wall
(iv). Discharge Opening (DO)
Minor Components of the SBP-I Plant
The Minor Components of the Shramik Bandhu (SBP-I) Model are as follows:
Inlet Pipe (IP), Outlet Gate (OG),Mixing Tank(MT)or Slurry Mixing Tank(SMT),
Short Inlet Channel(SIC),Gas Outlet Pipe(GOP),Grating (madeof Bamboo Sticks,
Manhole Cover (MHC) for ODC.
Being a fixed dome technology, the components and their functions are same as in the case of Janata and Deenbandhu Model BGP and therefore not elaborated here once again.
3.10 Conversion of biomass into electricity
Historically one of the earliest alternatives to fossil fuels is a wood fired boiler producing steam which powers an engine driving a generator. This, unfortunately is about the only advantage. But the steam power has all the disadvantages of an engine/generator and even several more. The wood must be chopped and carried, cured, split, and fed, just as for any wood stove. Ashes must be handled and hauled. The entire installation requires constant control while it is running. Due to compounds in some of the feedstocks, ?slagging and fouling? can occur. Slagging is accumulation of solid residues on parts of the combustion system. Fouling is simply the accumulation of liquid or semi-liquid residue. This is an important aspect of plant operation and operators need to understand how biomass differs from more commonly used fuels.
3.10.1 Gasification
Usually, electricity from biomass is produced via the condensing steam turbine, in which the biomass is burned in a boiler to produce steam? which is expanded through a turbine driving a generator. The technology is well-established, robust and can accept a wide variety of feedstocks. However, it has a relatively high unit-capital cost and low operating efficiency with little prospect of improving either significantly in the future. There is also the inherent danger in steam. Steam occupies about 1200 times the volume of water at atmospheric pressure (known as ?gage? pressure). Producing steam requires heating water to above boiling temperature under pressure. Water boils at 100° C at sea level. By pressurizing the boiler it is possible to raise the boiling temperature of water much higher. Elevating steam temperature has to be done to use the generated steam for any useful work otherwise the steam would condense in the supply lines or inside the cylinder of the steam engine itself.
Gasification is the newest method to generate electricity from biomass. Instead of simply burning the fuel, gasification captures about 65-70% of the energy in solid fuel by converting it first into combustible gases. This gas is then burned as natural gas is, to create electricity, fuel a vehicle, in industrial applications, or converted to synfuels-synthetic fuels. Since this is the latest technology, it is still under development.
A promising alternative is the gas turbine fuelled by gas produced from biomass by means of thermochemical decomposition in an atmosphere that has a restricted supply of air. Gas turbines have lower unit-capital costs, can be considerably more efficient and have good prospects for improvements of both parameters.
Biomass gasification systems generally have four principal components:
(a) Fuel preparation, handling and feed system;
(b) Gasification reactor vessel;
(c) Gas cleaning, cooling and mixing system;
(d) Energy conversion system (e.g., internal-combustion engine with generator or pump set, or gas burner coupled to a boiler and kiln).
When gas is used in an internal-combustion engine for electricity production (power gasifiers), it usually requires elaborate gas cleaning, cooling and mixing systems with strict quality and reactor design criteria making the technology quite complicated. Therefore, ?Power gasifiers world-wide have had a historical record of sensitivity to changes in fuel characteristics, technical hitches, manpower capabilities and environmental conditions?.
Gasifiers used simply for heat generation do not have such complex requirements and are, therefore, easier to design and operate, less costly and more energy- efficient.. All types of gasifiers require feedstocks with low moisture and volatile contents. Therefore, good quality charcoal is generally best, although it requires a separate production facility and gives a lower overall efficiency.
In the simplest, open-cycle gas turbine the hot exhaust of the turbine, is discharged directly to the atmosphere. Alternatively, it can be used to produce steam in a heat recovery steam generator. The steam can then be used for heating in a cogeneration system; for injecting back into the gas turbine, thus improving power output and generating efficiency known as a steam-injected gas turbine (STIG) cycle; or for expanding through a steam turbine to boost power output and efficiency - a gas turbine/steam turbine combined cycle (GTCC) (Williams & Larson, 1992). While natural gas is the preferred fuel, limited future supplies have stimulated the expenditure of millions of dollars in research and development efforts on the thermo-chemical gasification of coal as a gas-turbine feedstock. Much of the work on coal-gasifier/gas-turbine systems is directly relevant to biomass integrated gasifier/gas turbines (BlG/GTs). Biomass is easier to gasify than coal and has a very low sulphur content. Also, BIG/GT technologies for cogeneration or stand-alone power applications have the promise of being able to produce electricity at a lower cost in many instances than most alternatives, including large centralized, coal-fired, steam-electric power plants with flue gas desulphurization, nuclear power plants, and hydroelectric power plants.
Gasifiers using wood and charcoal (the only fuel adequately proved so far) are again becoming commercially available, and research is being carried out on ways of gasifying other biomass fuels (such as residues) in some parts of the world. Problems to overcome include the sensitivity of power gasifiers to changes in fuel characteristics, technical problems and environmental conditions. Capital costs can still sometimes be limiting, but can be reduced considerably if systems are manufactured locally or use local materials. For example, a ferrocement gasifier developed at the Asian institute of Technology in Bangkok had a capital cost reduced by a factor of ten. For developing countries, the sugarcane industries that produce sugar and fuel ethanol are promising targets for near-term applications of BIG/GT technologies.
Gasification has been the focus of attention in India because of its potential for large scale commercialization. Biomass gasification technology could meet a variety of energy needs, particularly in the agricultural and rural sectors. A detailed micro- and macroanalysis by Jain (1989) showed that the overall potential in terms of installed capacity could be as large as 10,000 to 20,000 MW by the year 2000, consisting of small-scale decentralized installations for irrigation pumping and village electrification, as well as captive industrial power generation and grid fed power from energy plantations. This results from a combination of favourable parameters in India which includes political commitment, prevailing power shortages and high costs, potential for specific applications such as irrigation pumping and rural electrification, and the existence of an infrastructure and technological base. Nonetheless, considerable efforts are still needed for large- scale commercialization.
3.10.2 CO-FIRING
Co-firing of biofuels (e.g. gasified wood) and coal seems to be the way how to reduce emissions from coal firing power plants in many countries. In 1999 a new co-firing system - biomass and coal - started its operation in Zeltweg (Austria). A 10 MW biomass gasification unit was installed in combination with an existing coal fired power station. The gasifier needs 16 m3 woody biomass (chips and bark) per hour. The calorific value of the gas ranges between 2,5 - 5 MJ/Nm3. The project named ?Biococomb? is an EU demonstration project. It was realised by the ?Verbund? company together with several other companies from Italy, Belgium, Germany and Austria and co- financed by the European Commission.
3.10.3 COGENERATION
3.10.3.1 Biomass-Fired Gas Turbine
A current trend in industrialized countries is the use of increasing number of smaller and more flexible biomass based plants for cogeneration of heat and electricity. A newly developed biomass cogeneration plant in Knoxville, Tennessee, USA, is at the cutting edge of one of the promising technologies behind this development. The plant combines a wood furnace with a gas turbine. A hot, pressurized flue-gas filter cleans the exhaust gas from the furnace before it drives the power turbine. The plant can run on fresh cut sawdust (40% humidity), and produces 5.8 MW of electricity, while consuming 10 tons sawdust/hour, and delivering heat as hot exhaust gas at 370°C. This gives an electric efficiency of about 19% and overall efficiency of up to about 75%. The exhaust gas can be used in a steam turbine, increasing electric output to 9.6 MW, and electricity efficiency to over 30%. The plant in Knoxville has been operating since spring 1999.
An important feature for Salix is that it can be used for water purification - it is possible to grow Salix in purification systems and in the same time harvest the Salix for energy (10-20 tonnes of sludge can be used on each hectare every year). Other benefits of biomass for energy plantation includes forest fire control, improved erosion control, dust absorption, and used as replacement for fossil fuels: no sulphur emission and lower NOx emissions.
Employment
For Sweet Sorghum production cost 50% is manpower cost. Production of about 500 tonnes of dry biomass per year justifies the creation of one new job. Other new jobs could be created in related industries such as composting, pulp for paper, service organisation etc.
Hand Rule
Sweet Sorghum output for trials in different locations of Central and Southern Europe:
Annually 90 tonnes of fresh material = 25 tonnes of dry matter per hectare = 450 GJ or 11 tonnes of oil equivalent can be produced. 1/3 as ethanol from sugars and 2/3 of fuel from bagasse. This corresponds to the absorption of 30-45 tonnes of CO2 per hectare and per year.
Average yearly electricity consumption of a West European person can be met by growing poplar on 0.25 hectare.
3.11.5 Biogas
The largest potential for biogas is in manure from agriculture. Other potential raw-materials for biogas are:
* sludge from mechanical and biological waste-water treatment (sludge from chemical waste-water treatment has often low biogas potential)
* organic household waste
* organic, bio-degradable waste from industries, in particular slaughter-houses and food-processing industries
Care should be taken not to include waste with heavy metals or harmful chemical substances when the resulting sludge is to be used as fertilizer. These kinds of polluted sludge can be used in biogas plants, where the resulting sludge is treated as waste and e.g. incinerated.
Another biogas source is landfills with large amounts of organic waste, where the gas can be extracted directly from drillings in the landfill, so called landfill gas. Such drillings will reduce uncontrolled methane emission from landfills.
Energy Content
The biogas-production will normally be in the range of 0.3 - 0.45 m3 of biogas (60% methane) per kg of solid (total solid, TS) for a well functioning process with a typical retention time of 20-30 days at 32oC. The lower heating value of this gas is about 6.6 kWh/m3. Often is given the production per kg of volatile solid (VS), which for manure without straw, sand or others is about 80% of total solids (TS).
A biogas plant have a self-consumption of energy to keep the manure warm. This is typically 20% of the energy production for a well designed biogas plant. If the gas is used for co-generation, the available electricity will be 30-40% of the energy in the gas, the heat will be 40-50% and the remaining 20% will be self-consumption.
Resource Estimation
For manure, the available data is often the numbers of livestock. From this can be made an estimation of available manure. While the amount of manure produced from animals depends on amount and type of fodder, some average figures are made for most countries.
The following table shows the figures for Denmark : (kWh/yr)
Kind , dungtype, Ant(kg/day), Solids(kg/day,Biogas pr beastm3/day,nrg pr beast
Cow Slurry 51 5,4 1,6 3400
Cow Dry 32 5,6 1,6 3400
Sow Slurry 16,7 1,3 0,46 970
Sow Dry 9,9 2,9 0,46 970
Hen Dry 0,66 0,047 0,017 36
Yearly energy output is for biogas plant with 20% average self-consumption and 360 working days. When animals are not in stables around the year, the figure will be smaller. The figures are for milking cows and for sows with breeding pigs under 5 kg.
*biogas with 65% methane
To make an estimation of the yearly production, it should be evaluated how many days per year the animals are in stables. For large poultry farms and pig-farms it is often the whole year, while cows are in stables from a few months a year to the whole year.
To estimate amount of manure from calfs, pigs and chicken, the following estimates can be used:
* calfs 1-6 month: 25% of milking cows
* other cattle ( calfs > 6 months, cattle for meet, pregnant cows): 60% of milking cows
* small pigs, 5-15 kg: 28% of sows with pigs
* fattening pigs > 15 kg: 52% of sows with pigs
* fattening chicken: 75% of hens
Barriers
A number of barriers hold back a large scale development of biogas plants in CEEC:
* commercial technology for agriculture (the largest resource base) is not available and have to be developed from existing prototypes or imported.
* it is difficult to make biogas plants cost-effective with sale of energy as the only income. The most likely applications are when other effects of the sludge-treatment has a value. This can e.g. be better hygiene, easier handling, reduced smell, and treatment of industrial waste.
* little knowledge on biogas technology among planners and decision-makers.
The environmental effects of biogas plants are:
* production of energy that can replace fossil fuels, reducing CO2 emissions
* reduce smell and hygiene problems of sludge and manure
* treatment of certain kinds of organic waste that would otherwise pose an environmental problem
* reduce potential methane emissions from uncontrolled anaerobic degradation of the sludge.
* easier handling of sludge, which can increase the fraction used as fertilizer and facilitate a more accurate use as fertilizer
-no end-
3.9.10 Janata Model
The Janata model consists of a digester and a fixed biogas holder (known as Gas Storage Chamber) covered by a dome shaped enclosed roof structure. The entire plant is made of bricks and cement masonry and constructed underground. Unlike the KVIC model, the Janata model has no movable part. A brief description of the different major components of Janata model is described below:
The foundation: is well-compacted base of the digester, constructed of brick ballast and cement concrete. The upper portion of the foundation has a smooth plaster surface.
The digester: is a cylindrical tank resting on the foundation. The top surface of the foundation serves as the bottom of the digester. The digester (fermentation chamber) is constructed with bricks and cement mortar. The digester wall has two small rectangular openings at the middle, situated diametrically opposite, known as inlet and outlet gate, one for the inflow of fresh slurry and the other for the outflow of digested slurry. The digester of Janata BGP comprises the fermentation chamber (effective digester volume) and the gas storage chamber (GSC).
Gas Storage Chamber (GSC)
The Gas Storage Chamber (GSC) is also cylindrical in shape and is the integral part of the digester and located just above the fermentation chamber. The GSC is designed to store 33% (approx. 8 hours) of the daily gas production from the plant. The Gas Storage Chamber (GSC) is constructed with bricks and cement mortar. The gas pressure in Janata model varies from a minimum of 0 cm water column (when the plant is completely empty) to a maximum of up to 90 cm of water column when the plant is all full of biogas.
Fixed Dome Roof
The hemi-spherical shaped dome forms the cover (roof) of the digester and constructed with brick and cement concrete mixture, after which it is plastered with cement mortar. The dome is only an enclosed roof designed in such a way to avoid steel reinforcement. (Note: The gas collected in the dome of a Janata plant is not under pressure therefore can not be utilised. It is only the gas stored in the Gas Storage Chamber (GSC) portion of the digester and that is under pressure and can be said as utilisable biogas).
Inlet Chamber
The upper portion of the Inlet Chamber is in the shape of bell mouth and constructed using bricks and cements mortar. Its outer wall is kept inclined to the cylindrical wall of the digester so that the feed material can flow easily into the digester by gravity. The bottom opening of the Inlet Chamber is connected to the Inlet Gate and the upper portion is much wider and known as Inlet Displacement Chamber (IDC). The top opening of the inlet chamber is located close to the ground level to enable easy feeding of fresh slurry.
Outlet Chamber
It is a rectangular shaped chamber located just on the opposite side of the inlet chamber. The bottom opening of the Outlet Chamber is connected to the Outlet Gate and the upper portion is much wider and known as Outlet Displacement Chamber (ODC). The Outlet Chamber is constructed using bricks and cement mortar. The top opening of the Outlet Chamber is located close to the ground level to enable easy removal of the digested slurry through a discharge opening. The level of the discharge opening provided on the outer wall of the outlet chamber is kept at a somewhat lower level than the upper mouth of the inlet opening, as well as kept lower than the Crown of the Dome ceiling. This is to facilitate easy flow of the digested slurry out the plant in to the digested slurry pit and also to prevent reverse flow, either in the mixing tank through inlet chamber or to go inside the gas outlet pipe and choke it.
The Biogas Outlet Pipe: is fixed at the crown of the dome, which is made of a small length of GI Pipe fitted with socket and a Gate Valve.
3.9.10.1 The Deenbandhu Model: is a semi continuous-fed fixed dome Biogas plant. While designing the Deenbandhu model an attempt has was made to minimise the surface area of the BGP with a view to reduce the installation cost, without compromising on the efficiency. The design essentially consists of segments of two spheres of different diameters joined at their bases. The structure thus formed comprises of (i) the digester (fermentation chamber), (ii) the gas storage chamber, and (iii) the empty space just above the gas storage chamber. The higher compressive strength of the brick masonry and concrete makes it preferable to go in for a structure that could be always kept under compression. A spherical structure loaded from the convex side will be under compression and therefor, the internal load will not have any effect on the structure.
The digester of the Deenbandhu BGP is connected with the Inlet Pipe and the Outlet Tank. The upper part (above the normal slurry level) of the outlet tank is designed to accommodate the slurry to be displaced out of the digester (actually from the gas storage chamber) with the generation and accumulation of biogas and known as the Outlet Displacement Chamber (ODC). The Inlet Pipe of the Deenbandhu BGP replaces the Inlet Chamber of Janata Plant. Therefore to accommodate all the slurry displaced out from the Gas Storage Chamber (GSC), the volume of the Outlet Chamber of Deenbandhu model twice the volume of the Outlet Tank of the Janata BGP of the same capacity.
Being a fixed dome technology, the other components and their functions are same as in the case of Janata Model BGP and therefore are not elaborated here once again.
3.9.10.2 Shramik Bandhu Model:This new BRCM biogas plant model which is also a semi-continuous hydraulic digester plant was designed by the author and christened as SHRAMIK BANDHU (friend of the labour). Since then, three more models (rural household plants) in the family of SHRAMIK BANDHU Plants have also been developed. The second one, a semi-continuous hydraulic digester, works on the principle of semi-plug flow digester (suitable for use as a Night Soil based or Toilet attached plant). The third one uses simple low cost anaerobic bacterial filters, designed for possible application as a Low Cost and low Maintenance Wastewater Treatment System. The fourth one is a semi-batch fed hydraulic digester, ideally suitable for the regions where plenty of seasonal crop wastes and waste green biomass are available and population of domestic farm animals are less, for producing the desired quantity of biogas from it alone. For this reason the first model which is the simplest and cheapest in the family of Shramik Bandhu plants, is christened as SBP-I Model. The other three models, yet to be field evaluated, are, SBP-II, SBP-III and SBP-IV, respectively.
The family of SHRAMIK BANDHU biogas plants designs uses the fixed dome concepts as in the case of pervious two most popular Indian fixed dome plants, namely, Janata and Deenbandhu models. In other words, all the four Models of the family of SHRAMIK BANDHU Plant have both, (i) the Gas Storage Chamber (GSC) and (ii) the Dome shaped Roof. However, in this section, the description about Shramik Bandhu plants relates to SBP-I model only.
The SHRAMIK BANDHU Plant is made of Bamboo Reinforced Cement Mortar (BRCM), by pre-fabricated bamboo shells, using the correct size mould for a given capacity SBP-I model- Thus, completely replacing the bricks. These bamboo shells are made by weaving bamboo strips (weaving of which can be done in the village itself) for casting a BRCM structure. The BRCM structures on the one hand are used for giving the right shape to this plant, while on the other hand acts as the reinforcement to the cement mortar plaster as it is casted more or less like the ferro-cement structure. In order to protect the bamboo strips from microbial attack, they are pre-treated by immersing them in water mixed with prescribed ratio of Copper Sulphate (CuSO4) for a minimum of 24 hours before weaving of shell structure is done. As a further safety measure DPC powder in appropriate quantity is mixed while doing second layer (coat) of smooth plastering on the Main Unit of the Plant (MUP), Outlet Chamber (OC); as well as other BRCM components and sub- components, to make the entire structure of SBP-I moisture proof. The Shramik Bandhu plant made from BRCM would be much stronger because it has both higher tensile, as well as compressive strength, as compared to either First Class Bricks or Cement Concrete (CC) or Cement Mortar (CM), when used alone. The reason for this is that the bamboo shell structures used (for both reinforcement and shape of the plant) for the construction of Shramik Bandhu plant is made by weaving strips [only the outer harder surface (skin) and not the softer inner part of bamboo] from seasoned (properly cured) bamboo. Therefore, the entire structure (body) of the SBP-I model would be very strong, durable and have long useful working life. The two previous fixed dome models, namely Janata and Deenbandhu model have no reinforcement and are made of Bricks and Cement Mortar only, therefore, while they are very strong under compression but cannot withstand high tensile force. The hemi-spherical shell shaped (structure) of SHRAMIK BANDHU (SBP-I) model loaded from top on its convex side will be under compression. However, due to comprehensive strength provided by both cement mortar, as well as the reinforcement provided by the woven bamboo shell will ensure that the internal and external load will not have any residual effects on the structure. The bamboo reinforcement will provide added strength (both tensile and compressive) to make the entire structure of SHRAMIK BANDHU (SBP-I) model very sound, as compared to the previous two fixed dome Indian models (Janata & Deenbandhu), referred above.
The digester of SBP-I model is connected to the slurry mixing tank with inlet pipe made of 10 cm or 100 mm (4?) diameter Asbestos Cement Concrete (ACC) pipe, for feeding the slurry inside the plant.
The Outlet Displacement Chamber (ODC) is designed to accommodate the slurry to be displaced out of the digester with the generation & accumulation of biogas. The Outlet Displacement Chamber (ODC) of SBP-I model is also kept hemi-spherical in shape to reduce it?s surface area for a given volume (to save in building materials and time taken for construction)- The ODC is also made of BRCM, using a hemi-spherical shaped woven bamboo shell structure.
A Manhole opening of about 60 cm or 600 mm (2.0 Ft) diameter is provided on the crown of the hemi-spherical shaped ODC. The Manhole is big enough for one person to go inside and come out, at the same time small enough to be able to easily close it by a same size Manhole Cover, which is also made of BRCM.
COMPONENTS OF SHRAMIK BANDHU (SBP-I MODEL) BIOGAS PLANT (BGP)
The Shramik Bandhu (SBP-I) Model is made of two major components and several minor components and sub-components. They are categorized as, (a) Main Unit OF The Plant (MUP), (b) Outlet Chamber (OC) and (c) Other Minor Components. These major and minor components are further divided into sub-components, as given below:
Main Unit Of the plant (MUP)
The Main Unit of the Plant (MUP) is one of the major components of Shramik Bandhu (SBP-I) Model. The MUP has following six main ?Sub-Components?:
(i). Digester {or Fermentation Chamber (FC)}
(ii). Gas Storage Chamber (GSC)
(iii). Free Space Area (FSA), located just above the GSC
(iv). Dome (Roof of the Plant-entire area located just above the FSA); and
(v). The following three other sub-components:
[{(e)-(i) the Foundation of the MUP & (e)-(ii)} the Ring Beam for MUP (these two have also been considered here as the two sub-components of the MUP} and {the third is (e)-(iii) the Gas Outlet Pipe (GIP), for better explanation & understanding of the constructional aspects of SBP-I Plant].
Outlet Chamber
The Outlet Chamber (OC)) is the second major component of Shramik Bandhu (SBP-I) Model. The OC has the following four main ?Sub-Components?:
(i). Outlet Tank (OT)
(ii). Outlet Displacement Chamber (ODC)
(iii). Empty Space Area (ESA) above the ODC- though for all practical purpose the ODC includes the Empty Space Area (ESA) above it; however, from the designing point of view, the effective ODC of SBP-I model is considered up to the starting of discharge opening located on its outer wall
(iv). Discharge Opening (DO)
Minor Components of the SBP-I Plant
The Minor Components of the Shramik Bandhu (SBP-I) Model are as follows:
Inlet Pipe (IP), Outlet Gate (OG),Mixing Tank(MT)or Slurry Mixing Tank(SMT),
Short Inlet Channel(SIC),Gas Outlet Pipe(GOP),Grating (madeof Bamboo Sticks,
Manhole Cover (MHC) for ODC.
Being a fixed dome technology, the components and their functions are same as in the case of Janata and Deenbandhu Model BGP and therefore not elaborated here once again.
3.10 Conversion of biomass into electricity
Historically one of the earliest alternatives to fossil fuels is a wood fired boiler producing steam which powers an engine driving a generator. This, unfortunately is about the only advantage. But the steam power has all the disadvantages of an engine/generator and even several more. The wood must be chopped and carried, cured, split, and fed, just as for any wood stove. Ashes must be handled and hauled. The entire installation requires constant control while it is running. Due to compounds in some of the feedstocks, ?slagging and fouling? can occur. Slagging is accumulation of solid residues on parts of the combustion system. Fouling is simply the accumulation of liquid or semi-liquid residue. This is an important aspect of plant operation and operators need to understand how biomass differs from more commonly used fuels.
3.10.1 Gasification
Usually, electricity from biomass is produced via the condensing steam turbine, in which the biomass is burned in a boiler to produce steam? which is expanded through a turbine driving a generator. The technology is well-established, robust and can accept a wide variety of feedstocks. However, it has a relatively high unit-capital cost and low operating efficiency with little prospect of improving either significantly in the future. There is also the inherent danger in steam. Steam occupies about 1200 times the volume of water at atmospheric pressure (known as ?gage? pressure). Producing steam requires heating water to above boiling temperature under pressure. Water boils at 100° C at sea level. By pressurizing the boiler it is possible to raise the boiling temperature of water much higher. Elevating steam temperature has to be done to use the generated steam for any useful work otherwise the steam would condense in the supply lines or inside the cylinder of the steam engine itself.
Gasification is the newest method to generate electricity from biomass. Instead of simply burning the fuel, gasification captures about 65-70% of the energy in solid fuel by converting it first into combustible gases. This gas is then burned as natural gas is, to create electricity, fuel a vehicle, in industrial applications, or converted to synfuels-synthetic fuels. Since this is the latest technology, it is still under development.
A promising alternative is the gas turbine fuelled by gas produced from biomass by means of thermochemical decomposition in an atmosphere that has a restricted supply of air. Gas turbines have lower unit-capital costs, can be considerably more efficient and have good prospects for improvements of both parameters.
Biomass gasification systems generally have four principal components:
(a) Fuel preparation, handling and feed system;
(b) Gasification reactor vessel;
(c) Gas cleaning, cooling and mixing system;
(d) Energy conversion system (e.g., internal-combustion engine with generator or pump set, or gas burner coupled to a boiler and kiln).
When gas is used in an internal-combustion engine for electricity production (power gasifiers), it usually requires elaborate gas cleaning, cooling and mixing systems with strict quality and reactor design criteria making the technology quite complicated. Therefore, ?Power gasifiers world-wide have had a historical record of sensitivity to changes in fuel characteristics, technical hitches, manpower capabilities and environmental conditions?.
Gasifiers used simply for heat generation do not have such complex requirements and are, therefore, easier to design and operate, less costly and more energy- efficient.. All types of gasifiers require feedstocks with low moisture and volatile contents. Therefore, good quality charcoal is generally best, although it requires a separate production facility and gives a lower overall efficiency.
In the simplest, open-cycle gas turbine the hot exhaust of the turbine, is discharged directly to the atmosphere. Alternatively, it can be used to produce steam in a heat recovery steam generator. The steam can then be used for heating in a cogeneration system; for injecting back into the gas turbine, thus improving power output and generating efficiency known as a steam-injected gas turbine (STIG) cycle; or for expanding through a steam turbine to boost power output and efficiency - a gas turbine/steam turbine combined cycle (GTCC) (Williams & Larson, 1992). While natural gas is the preferred fuel, limited future supplies have stimulated the expenditure of millions of dollars in research and development efforts on the thermo-chemical gasification of coal as a gas-turbine feedstock. Much of the work on coal-gasifier/gas-turbine systems is directly relevant to biomass integrated gasifier/gas turbines (BlG/GTs). Biomass is easier to gasify than coal and has a very low sulphur content. Also, BIG/GT technologies for cogeneration or stand-alone power applications have the promise of being able to produce electricity at a lower cost in many instances than most alternatives, including large centralized, coal-fired, steam-electric power plants with flue gas desulphurization, nuclear power plants, and hydroelectric power plants.
Gasifiers using wood and charcoal (the only fuel adequately proved so far) are again becoming commercially available, and research is being carried out on ways of gasifying other biomass fuels (such as residues) in some parts of the world. Problems to overcome include the sensitivity of power gasifiers to changes in fuel characteristics, technical problems and environmental conditions. Capital costs can still sometimes be limiting, but can be reduced considerably if systems are manufactured locally or use local materials. For example, a ferrocement gasifier developed at the Asian institute of Technology in Bangkok had a capital cost reduced by a factor of ten. For developing countries, the sugarcane industries that produce sugar and fuel ethanol are promising targets for near-term applications of BIG/GT technologies.
Gasification has been the focus of attention in India because of its potential for large scale commercialization. Biomass gasification technology could meet a variety of energy needs, particularly in the agricultural and rural sectors. A detailed micro- and macroanalysis by Jain (1989) showed that the overall potential in terms of installed capacity could be as large as 10,000 to 20,000 MW by the year 2000, consisting of small-scale decentralized installations for irrigation pumping and village electrification, as well as captive industrial power generation and grid fed power from energy plantations. This results from a combination of favourable parameters in India which includes political commitment, prevailing power shortages and high costs, potential for specific applications such as irrigation pumping and rural electrification, and the existence of an infrastructure and technological base. Nonetheless, considerable efforts are still needed for large- scale commercialization.
3.10.2 CO-FIRING
Co-firing of biofuels (e.g. gasified wood) and coal seems to be the way how to reduce emissions from coal firing power plants in many countries. In 1999 a new co-firing system - biomass and coal - started its operation in Zeltweg (Austria). A 10 MW biomass gasification unit was installed in combination with an existing coal fired power station. The gasifier needs 16 m3 woody biomass (chips and bark) per hour. The calorific value of the gas ranges between 2,5 - 5 MJ/Nm3. The project named ?Biococomb? is an EU demonstration project. It was realised by the ?Verbund? company together with several other companies from Italy, Belgium, Germany and Austria and co- financed by the European Commission.
3.10.3 COGENERATION
3.10.3.1 Biomass-Fired Gas Turbine
A current trend in industrialized countries is the use of increasing number of smaller and more flexible biomass based plants for cogeneration of heat and electricity. A newly developed biomass cogeneration plant in Knoxville, Tennessee, USA, is at the cutting edge of one of the promising technologies behind this development. The plant combines a wood furnace with a gas turbine. A hot, pressurized flue-gas filter cleans the exhaust gas from the furnace before it drives the power turbine. The plant can run on fresh cut sawdust (40% humidity), and produces 5.8 MW of electricity, while consuming 10 tons sawdust/hour, and delivering heat as hot exhaust gas at 370°C. This gives an electric efficiency of about 19% and overall efficiency of up to about 75%. The exhaust gas can be used in a steam turbine, increasing electric output to 9.6 MW, and electricity efficiency to over 30%. The plant in Knoxville has been operating since spring 1999.
An important feature for Salix is that it can be used for water purification - it is possible to grow Salix in purification systems and in the same time harvest the Salix for energy (10-20 tonnes of sludge can be used on each hectare every year). Other benefits of biomass for energy plantation includes forest fire control, improved erosion control, dust absorption, and used as replacement for fossil fuels: no sulphur emission and lower NOx emissions.
Employment
For Sweet Sorghum production cost 50% is manpower cost. Production of about 500 tonnes of dry biomass per year justifies the creation of one new job. Other new jobs could be created in related industries such as composting, pulp for paper, service organisation etc.
Hand Rule
Sweet Sorghum output for trials in different locations of Central and Southern Europe:
Annually 90 tonnes of fresh material = 25 tonnes of dry matter per hectare = 450 GJ or 11 tonnes of oil equivalent can be produced. 1/3 as ethanol from sugars and 2/3 of fuel from bagasse. This corresponds to the absorption of 30-45 tonnes of CO2 per hectare and per year.
Average yearly electricity consumption of a West European person can be met by growing poplar on 0.25 hectare.
3.11.5 Biogas
The largest potential for biogas is in manure from agriculture. Other potential raw-materials for biogas are:
* sludge from mechanical and biological waste-water treatment (sludge from chemical waste-water treatment has often low biogas potential)
* organic household waste
* organic, bio-degradable waste from industries, in particular slaughter-houses and food-processing industries
Care should be taken not to include waste with heavy metals or harmful chemical substances when the resulting sludge is to be used as fertilizer. These kinds of polluted sludge can be used in biogas plants, where the resulting sludge is treated as waste and e.g. incinerated.
Another biogas source is landfills with large amounts of organic waste, where the gas can be extracted directly from drillings in the landfill, so called landfill gas. Such drillings will reduce uncontrolled methane emission from landfills.
Energy Content
The biogas-production will normally be in the range of 0.3 - 0.45 m3 of biogas (60% methane) per kg of solid (total solid, TS) for a well functioning process with a typical retention time of 20-30 days at 32oC. The lower heating value of this gas is about 6.6 kWh/m3. Often is given the production per kg of volatile solid (VS), which for manure without straw, sand or others is about 80% of total solids (TS).
A biogas plant have a self-consumption of energy to keep the manure warm. This is typically 20% of the energy production for a well designed biogas plant. If the gas is used for co-generation, the available electricity will be 30-40% of the energy in the gas, the heat will be 40-50% and the remaining 20% will be self-consumption.
Resource Estimation
For manure, the available data is often the numbers of livestock. From this can be made an estimation of available manure. While the amount of manure produced from animals depends on amount and type of fodder, some average figures are made for most countries.
The following table shows the figures for Denmark : (kWh/yr)
Kind , dungtype, Ant(kg/day), Solids(kg/day,Biogas pr beastm3/day,nrg pr beast
Cow Slurry 51 5,4 1,6 3400
Cow Dry 32 5,6 1,6 3400
Sow Slurry 16,7 1,3 0,46 970
Sow Dry 9,9 2,9 0,46 970
Hen Dry 0,66 0,047 0,017 36
Yearly energy output is for biogas plant with 20% average self-consumption and 360 working days. When animals are not in stables around the year, the figure will be smaller. The figures are for milking cows and for sows with breeding pigs under 5 kg.
*biogas with 65% methane
To make an estimation of the yearly production, it should be evaluated how many days per year the animals are in stables. For large poultry farms and pig-farms it is often the whole year, while cows are in stables from a few months a year to the whole year.
To estimate amount of manure from calfs, pigs and chicken, the following estimates can be used:
* calfs 1-6 month: 25% of milking cows
* other cattle ( calfs > 6 months, cattle for meet, pregnant cows): 60% of milking cows
* small pigs, 5-15 kg: 28% of sows with pigs
* fattening pigs > 15 kg: 52% of sows with pigs
* fattening chicken: 75% of hens
Barriers
A number of barriers hold back a large scale development of biogas plants in CEEC:
* commercial technology for agriculture (the largest resource base) is not available and have to be developed from existing prototypes or imported.
* it is difficult to make biogas plants cost-effective with sale of energy as the only income. The most likely applications are when other effects of the sludge-treatment has a value. This can e.g. be better hygiene, easier handling, reduced smell, and treatment of industrial waste.
* little knowledge on biogas technology among planners and decision-makers.
The environmental effects of biogas plants are:
* production of energy that can replace fossil fuels, reducing CO2 emissions
* reduce smell and hygiene problems of sludge and manure
* treatment of certain kinds of organic waste that would otherwise pose an environmental problem
* reduce potential methane emissions from uncontrolled anaerobic degradation of the sludge.
* easier handling of sludge, which can increase the fraction used as fertilizer and facilitate a more accurate use as fertilizer
-no end-
posted by Arise! at 5:05 PM
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