Microbial fuel cell for power and treat waste water

Penn State environmental engineers have shown that a microbial fuel cell (MFC) can generate electricity while simultaneously cleaning the wastewater that is flushed down the drain or toilet. Between 10 and 50 milli Watts of power per square meter of electrode surface can be produced, while removing up to 78 percent of organic matter as measured by biochemical oxygen demand (BOD). Thus MFCs represents a completely new approach to wastewater treatment in addition to power generation. The MFC technology can provide a new method to offset operating costs of wastewater treatment plant, making advanced wastewater treatment more affordable for both developing and industrialized nations as claimed by the researchers.

Other researchers have shown that MFCs can be used to produce electricity from water containing pure chemicals including glucose, acetate or lactate.

Principle

Microbial fuel cells work by the action of bacteria which can pass electrons to an anode, the negative electrode of a fuel cell. The electrons flow from the anode through a wire, producing a current, to a cathode, the positive electrode of a fuel cell, where they combine with hydrogen ions (protons) and oxygen to form water in accordance with the conventional fuel cell principles. The naturally occurring bacteria in wastewater drive power production via a reaction that allows them to transport electrons from the cell surface to the anode. In addition, a reaction (oxidation) that occurs in the interior of the bacterial cell lowers the biochemical oxygen demand thus cleaning the water. MFC used has an overall dimension of about six inches in length and 2.5 inches in diameter and contains eight anodes, composed of graphite. The cathode is a carbon/platinum catalyst/proton exchange membrane fused to a plastic support tube. The unit has about 36 square inches of surface area to which the bacteria can adhere and pass electrons.

See for photos at: http://live.psu.edu/still_life/2004_02_23_research/index.html and for animation : http://www.nsf.gov/od/lpa/newsroom/pr.cfm?ni

Carbonization of wood

Charcoal is produced by controlled combustion by supplying very limited available oxygen by which the volatile vapours and gases are driven off from biomass particularly wood.
Charcoal
Charcoal has a higher energy density than wood and is smokeless. Traditional charcoal kilns are used to make Charcoal by simply heaping mounds of wood covered with earth, or pits in the ground. But the process of carbonisation is very slow and inefficient in these kilns. Traditional earthen kilns have yields closer to 10% as there is less control. In general during the process of carbonization, considerable amount of carbon is emitted to the air and approximately 50% of the carbon in the biomass can be obtained in the form of charcoal. Carbon yield obtained using various types of kilns is less than 50 % on the average, which means that half of the total carbon contained in the raw material will be emitted to the air or stored in the form of half-carbonized matter which can easily get decomposed, but there is a need to increase the carbon yield. Field research has improved the efficiency of charcoal furnaces.Improved charcoal furnaces operating at about 600°C produce 25-35% of the dry wood as charcoal, and even the gases produced can be used for kiln drying. The charcoal produced is 75 - 85% carbon and is useful as a compact, controllable fuel. It can be burnt to provide heat on a large and small scale.
Composition of charcoal
Charcoal is composed of (1) moisture, (2) ash content, (3) volatile matter and (4)fixed carbon. These parameters are calculated as given below using standard methods.
Methods for calculation
(1) Moisture content: Moisture content of charcoal immediately after finishing carbonization in the kiln will be nil, but increases subsequently due to absorption from the air. Moisture content of charcoal is calculated as :
Moisture content (%) = (Weight of charcoal – Oven dried weight of charcoal)/Weight of charcoal x 100
(2) Ash content: It comes from few minerals contained in material (CaO, K2O,MgO, etc.)Ash content of charcoal is calculated as:
Ash content (%) = Weight of ash in charcoal/Oven dried weight of charcoal x 100
(3) Volatile matter: It contains all liquid and tarry matter not fully driven off in the process of carbonization. If the carbonization is prolonged and if the temperature is high , then the volatiles content of is low. Volatile matter content of charcoal is calculated as:
Volatile matter content (%) = Weight of volatile matter in charcoal/Oven dried weight of charcoal x 100
(4) Fixed carbon:Fixed carbon content of charcoal is calculated as:
Fixed carbon content (%) = 100 – Moisture content - Ash content – Volatile matter content.
Pure carbon in charcoal is difficult to be decomposed as it shows no chemical affinity to the oxygen of the air and it does not rot, neither in an aerobic nor in an anaerobic way. This component mainly contributes to carbon storage.
(5) Charcoal yield and carbon yield: Usually, efficiency of charcoal production is indicated by charcoal yield. Charcoal yield is calculated using formula as:
Charcoal yield (%) = Weight of charcoal (kg)/Oven dry weight of wood material (kg) x 100
It expresses the percentage of pure carbon derived from wood material which is preserved in the produced charcoal. This indicator, however, cannot explain the efficiency of carbon fixation potential.

Co-firing of biomass and wastes

Co-firing means firing materials along with coal or other fuels in the existing or modified boiler firing systems. Materials such as biomass and waste are solid fuels in their own right, but of low calorific value, of variable composition, and requiring special low-intensity combustion conditions. If mixed with coal, the average calorific value is increased, enabling it to be burned in conventional combustors and to have more average fuel properties. If coal is mixed with material such as a typical biomass, then the combustion process can be considered to be increasingly CO 2 neutral. If coal is mixed with refuse or other waste materials, its combustion provides a route to the disposal of unwanted materials with the advantageous production of energy.

Biomass co-firing

There have been extensive research to increase the use of biomass, and one of the easiest ways of introducing this technology is by co-firing with coal in existing coal installations. A similar approach can also be taken with the disposal of waste, especially domestic refuse. The combustion of biomass therefore also parallels that of coal in many respects. The first step involves devolatilization similar to that of coal.

Namely: Biomass volatiles + char

In this reaction volatiles have a composition controlled by the biomass composition, the heating rate, and the final temperature. A typical biomass will have cellulose linked via oxygen bands; hence the high oxygen content in biomass fuels. Many biomass materials contain mainly carbon and some hydrocarbons; consequently, the composition of the volatiles is dominated by the production of CO, some hydrocarbons, and a small amount of tar. The char itself has reactivity very similar to coal char and has enhanced catalytic reactivity at low temperatures due to the metallic content of Na and K. For the mixtures of biomass and coal, the initial components devolailize and their chars burn independently. The volatiles mix, however, and the calorific value of this mixture and resultant flame temperature is very much a function of the composition of the components; the combined flame temperature is fed back to the initial chemical steps and consequently there is a very significant synergistic interaction. The subsequent rates of burn out of the chars are determined by their individual reactivity (and combined temperature) and generally biomass chars burn out more rapidly than coal chars.

Waste co-firing

The types of wastes suitable for co-firing include biomass waste, municipal solid waste, and automotive tires. The comparison is variable but has a calorific value between 10-20 MJ/kg. When the waste is taken from a controlled source, e.g., waste paper, with a constant calorific value, then the process of co-firing is simplified. In the other extreme, relatively small amounts of certain toxic wastes can be co-fired with coal in cement manufacture. The cement contains the trace elements in a generally satisfactory way although great care has to be used to ensure that it meets the required environmental emission standards.

BIOFUELS FOR TRANSPORT SECTOR

Hydrocarbon fuels - also called fossil fuels - have been the main source of energy for the transportation and other sectors for more than a century. However, their rapidly increasing consumption and consequent depletion of reserves clearly show that the end of the ‘Fossil fuel age’ is not very far off. Besides, these fuels are the chief contributors to urban air pollution and a major source of green house gases - considered to be the prime cause behind the global climate change.
Biofuels are renewable hence they can supplement hydrocarbon fuels, assist in their conservation, reduce GHGs as well as mitigate their adverse effects on the climate resulting from global warming. The term biofuels is usually intended to imply fuels sourced from biomass that are used for transportation purposes.
Biofuel include methane, producer gas, alcohols, esters and other chemicals made from cellulose biomass. Biofuels such as bio-ethanol and biodiesel have their own specific advantages.
Bio-ethanol, produced from substrates containing sugar, starches and cellulosic biomass, is an established oxygenate and transport fuel with many advantages:O It is an octane boosterO Being an oxygenate, it improves the combustion characteristics of gasolineO Reduces harmful emissions such as carbon monoxide, hydrocarbons and particulate matterO Readily blends with gasolineO Readily biodegradable, while a oxygenate such as MTBE is not
Biodiesel is produced mainly from vegetable oils and fats. Biodiesel, is commercially available in several countries from the esterification of vegetable oils including rape seed, soybean, sun flower and Jatropha oils as well as from tallow and waste cooking oils. O It can be used for greening waste landsO It is produced using a proven and low-capital-cost technology, hence can be readily implementedO It is biodegradable, non-toxic and free from sulfur.O It has properties that help reduce carbon monoxide, hydrocarbons, particulate matter and O It readily blends with diesel
Biofuels offer many benefits. They are beneficial for the environment because they add fewer emissions to the atmosphere than petroleum fuels on a per kilometer traveled basis, and they often utilize waste biomass resources that currently have no value and require disposal. Unlike petroleum, which is a non renewable natural resource, biofuels are renewable and inexhaustible sources of fuel, assuming the feedstock is produced in a sustainable fashion. Where energy crops are grown domestically, or other biomass sources are readily available for conversion, biofuels can reduce a country’s dependence on the vagaries of imported oil price fluctuations and uncertain supplies. The use of biofuels could therefore help to strengthen the energy security and boost a nation’s economy should crude oil prices reach and maintain levels above around $50/barrel.
All petroleum-derived fuels suitable for transport vehicles are compounds containing predominantly carbon and hydrogen atoms. Other constituent elements generally regarded as undesirable contaminants such as tetraethyl lead have been added in the past to modify fuel properties so as to reduce the tendency of the fuel to ‘knock’ during combustion in an internal combustion engine. Other chemical additives such as nitro methane have been added to specialty fuels to improve power output.
Liquid biofuels differ chemically from fossil fuels in that they contain oxygen in addition to the carbon and hydrogen atoms. As with fossil fuels, they may also contain other elements, notably nitrogen and once again this is generally regarded as an undesirable impurity.
For biofuels there is some discrepancy between their specifications and the measured octane or cetane number since the tests were originally developed for hydrocarbon fuels. A direct comparison between the octane and cetane numbers for fossil fuels and biofuels may therefore be misleading when compared in terms of engine performance. However, the measures can be used indicatively to show the suitability of the fuels for various applications.
Bioethanol and biodiesel are the two most common types of biofuel currently used around the world. This is due to good availability of suitable feed stocks, a relatively good understanding of conversion technologies and the opportunity for practical implementation by being able to blend the biofuels with petroleum-based gasoline or diesel.
The potential for biomass-derived products as lubricants is also gaining interest. Good varieties of oil seed rape have been bred for the good lubricity characteristics of the oils and have long been used in aircraft. They are also biodegradable, have low toxicity and therefore tend to be more environmentally acceptable than mineral oil, which can cause adverse effects on soils and plants when poorly disposed of.
With rising world prices of crude oil and petroleum products and increasing dependence on imports, developing countries is becoming more and more vulnerable in the matter of energy security. Biofuels will mitigate this vulnerability and other adverse effects of use of fossil fuels. In addition, harnessing of large areas of arable land resources for plantation of suitable energy crops will promote sustainable development and employment, mainly in rural areas.

BIOMASS AND WASTE CONVERSION TECHNOLOGIES

The once abundant conventional sources of energy like coal and oil are shrinking. Their escalating costs, coupled with problems of pollution, have necessitated a fresh look at alternatives. One such alternative is biomass. The term 'biomass' includes all plant life, trees, agricultural residues, bush, grass, algae and can be extended to livestock droppings which, of course, are derived from plants. Biomass may be obtained from forests in a planned or unplanned fashion or from agricultural lands. The entire organic content of biomass can be converted into usable forms of energy. The most obvious example is firewood, one of the most widely used fuels in the developing countries. Biomass potential Every year, plants convert about 200 billion tones of carbon into terrestrial and aquatic biomass through photosynthesis. The equivalent of the products of synthesis is 3000 billion giga joules. This is about 10 times the total energy being presently consumed in the world annually. One seventh of the world's total energy comes from biomass and this huge and potentially renewable resource is still left largely untapped. Potentially, organic residues can be utilized for a variety of purposes - fuel, fertilizer, feed, building materials, industrial chemicals and other products, medicinal and pharmaceutical formulations. keeping in view the importance of energy supply on decentralized basis for agro-industrial processing and agriculture, the primary residues need to be used as a source of energy and the secondary and tertiary leftovers for other purposes. Complete recycling will also help in reducing pollution resulting from biodegradation of organic materials. Therefore, the main objectives of residue management are two-fold: (i) use of residues as a source of energy and materials; and (ii) minimization of environmental pollution resulting from inefficient utilization. Biomass utilization for many major applications calls for its conversion into an adaptable fuel as a first step. The utilization of biomass as a source of energy involves thermo chemical or biochemical conversion. It can be used either by direct combustion in boilers, furnaces, cooking stoves, etc. or its utilization via gasification by thermo chemical or biochemical routes. For biomass to be able to substitute or supplement conventional fossil fuels, gasification is more appropriate. Biochemical conversion of biomass The products of biochemical conversion mainly include biogas from animal dung, sewage, and liquid fuel from fermentable sugars. Animal dung and agro-residues Anaerobic fermentation is a method of biochemical conversion of low lignin biomass in the presence of adequate moisture to produce methane rich gas called biogas. The calorific value of gas containing 60% of methane is 22 MJm-3. Cattle dung and large number of other agro-residues have been found suitable for anaerobic digestion in biogas plant. The biogas produced is a clean fuel for domestic cooking. Besides, it is used for illumination when burnt in silk mantle. It is also used as fuel for substantial replacement of diesel in engines for motive power and generating electricity. Biogas plants mitigate the drudgery of rural women, reducing the pressure on forest and recycling human waste by linking toilets with biogas plants, thereby improving sanitation in rural areas. Liquid waste (sewage) In recent years, increased urbanization in developing countries has given rise to a phenomenal increase in the quantity of sewage. Indiscriminate disposal of this wastewater results in pollution of ground water river systems, estuaries, lakes and land. The waste water can be used for the production of sewage gas which essentially consists of methane and CO2 with traces of hydrogen, nitrogen and hydrogen sulphide. It has relatively low calorific value which is more than that of gobar gas. It can successfully be used in diesel engine since its octane rating (110) is same as that of gobar gas. The presence of CO2 lowers the calorific value but increases the knock resistance about methane. It is estimated that the quantity of biogas generated per day by a sewage treatment plant is approximately 0.35 cft per capita of city's population. For example, it is calculated that a sewage treatment plant generating 5 million cft per day can yield energy equivalent to nearly 20 million litres of petrol per day. Collection, storage and utilization of sewage gas are economically justified only when the treatment works are large enough. The whole system has to be kept under pressure to avoid the formation of explosive mixture of gas and air. The gas becomes violently explosive in mixture of 1 vol. of gas to between 5-14 vols. of air, and at higher dilutions, gas burns freely. Also, the gas should be passed through scrubbers to remove unwanted constituents viz. CO2, H2S and water vapour. Fermentable sugars The use of biomass in alcohol manufacture is not a new discovery. In the 1930's and during the second world war, many countries converted waste agricultural products to alcohol for use in automobiles, as 10-15% blends with gasoline or as the entire fuel. Traditionally, alcohol for industrial use is manufactured from molasses. Grains, excess grapes or other fruits, potatoes, starchy roots like cassava, mahua flowers and palm juice may be used depending on their value in relation to human and animal foodstuffs. In countries like Sweden, Finland and Canada, which have flourishing pulp industries, the sulphite liquor, with its content of 2-3% of fermentable sugars constitutes a suitable raw material for the production of alcohol. In recent times, Brazil has been converting sugarcane, directly into alcohol and the produces from cane and cassava about 2-8 billion gallons of alcohol. The good deal of research work has been carried out in developing countries on the enzymatic production of ethanol from cellulose hydrolysate in batch and continuous systems employing free cells, recycled cells and also immobilized cells. A yeast strain which is tolerant to high concentrations of glucose and ethanol was also developed. The new technique of fixing yeast cells on an inert support and using it in continuous production of ethanol at various dilution rates has also been developed. It has been applied successfully to both biogas hydrolysis and cane molasses. Other studies include the use of thermo-tolerant yeasts and bacterial species. The cell recycle system has been run with 530 and 300 litre reactors and is ready to be scaled up; this technique has steady operational stability of nearby 400 hours, while the immobilized system has been run for more than 75 days without any loss of activity . The utilization of alternate fuels like ethanol, methanol and biogas as substitutes to petrol, diesel and kerosene for vehicular and stationary combustion engines has been in progress in the various Engines Laboratories in developing countries. After extensive trials, an' optimum ' blend has been perfected which gives improved engine performance (6-8% more power), lesser consumption (3-5%), lesser exhaust emission (10-30%, exhaust HC and CO), reduced carbon deposit and cooler engine operation as compared to that obtained with gasoline. Thermochemical conversion of biomass The products of thermo chemical conversion include combustible gas and a variety of chemicals besides energy from feed stocks by the action of heat. Fuel wood and crop residuesThe rural household sector accounts for nearly 75% of total energy consumption. About 90% of this energy is consumed for cooking activities alone. Fuel wood, crop residues and animal residues meet an overwhelming proportion of rural energy demand providing 85-90% of the household sector energy. Surplus biomass from industries The other important application of thermo-chemical combustion of biomass surplus is for power generation through optimum co-generation for surplus power from biomass produced in sugar mills, paper mills, rice mill, etc. and biomass combustion based power generation. Pyrolysis is essentially the burning of organic matter in the absence of air at temperature 400- 700° C. Although it is an endothermic process, yet it yields a number of hydrocarbon gases and liquids such as carbon monoxide, methane, butane, wood tar and a variety of other chemicals which have very high energy content. Gasification by contrast is carried out at much higher temperatures (1000-1100° C) by blowing a jet of air or oxygen into a fire zone at the bottom. Gasification yields combustible gas useful for running engines producing heat and even electricity. Urban waste Incineration became popular in the beginning but the huge volume of useless waste gas and fine ash along with the liberation of highly noxious and corrosive chloride, nitride and sulphurous gas made this system very costly due to the operation of pollution control standards. Physical sorting was another alternative which came into vogue. It divides the garbage into three fractions: the bulk which consists of vegetable wastes and inorganic matter like clay, earth, bones and the like are converted into compost for use in vegetables, fruit trees and other field crops. The second fraction consists of paper and plastics. These are shredded, dried and pressed into briquettes or pellets which have the same heating value as wood or a medium grade coal. This Refuse Derived Fuels (RDF) is finding a ready market in Europe for industrial and even domestic use. The third fraction consists of mainly scrap metals, used batteries, some heavy plastic products, stones and the like. These are separated by magnetic and metal separators. The energy content in the garbage, particularly in the RDF is only of marginal importance therefore, this practice has remained only on social grounds due to savings of land, reduction in the garbage transport cost and an almost complete absence of environmental pollution. Oil crisis during 1979 gave new impetus to technologies like pyrolysis and gasification of urban waste. Methanol production rather than power from fuel gases generated by pyrolysis or gasification can change the economics of the process radically. The energy that can be recovered from garbage may be of marginal relevance to the rich nations, but it is of central, even pivotal importance to the poor nations. According to an estimate if the garbage generated by a city of 3500 tones a day, is gasified or pyrolysed, it will, on the basis of its calorific value and the energy recovery efficiency, yield around 18,000 tones of methanol a year. Industrial and agro-industrial waste Many industries such as tannery, sago and other units discharge effluents which cause environmental pollution. Such of these effluents which are biodegradable can be converted to energy besides mitigating pollution. For example biogas can be extracted from effluents and the thermal needs of the factory and even power can be producing to meet the electrical requirement of the units. As detailed above there is now a renewed interest in biomass as a significant energy source for a wider range of reasons, such as concern over the Greenhouse effect, energy security and socio-economic benefits.

COMMERCIALISATION OF BIOMASS GASIFIERS

Rapid Industrialization necessitated the supply of various energy sources to increase many folds. The obvious choice is fossil fuels and their excessive utilization brought ecological imbalance by polluting the environment. The ill effects due to excessive use of fossil fuels are being felt all over the world. It is time that the energy needs be met from Environmental friendly sources. One of the main sources is energy from Biomass. By gasification of Biomass, a convenient, cost effective and environmental friendly gaseous energy can be formed which meet the energy can needs have advanced societies, be it for engine running or industrial burning. The important fact is biomass is renewable as it can be grown. Biomass cultivation gives rural employment as it is an agriproduce. About 2000 hectors of waste land can provide enough Biomass to generate 3 MW of power besides supporting energy needs of village of 150 families. A 1000 kgs of Biomass can be processed to yield enough gas which is equivalent to 200 litres of oil or 380 Cubic Meters of Natural gas or 15 cylinders of LPG. In addition to solid woody Biomass, specific gasifiers work well with loose biomass like Rice Husk, Groundnut Husk etc. Gasification In this process, the Biomass is burnt under controlled conditions in a reactor Called Gasifier and the products of combustion are converted into a gaseous fuel called “Producer Gas". The Hot gas laden with tarry and dusty particles will be cooled and filtered in case of Engine application or directly burnt in a specially designed burner for heating purpose or hot air generation. In case of Engine application, either dual fuel diesel engines can be used to save more than 65% of diese1 oil or it can be fed to a specifically designed spark Ignition Engines running on 100% gas. In case of heating application, the flame Intensity can be Increased or decreased similar to gaseous fuel.

Salient Features of Biomass Gasifiers

1) High Conversion efficiency, 2) Clean environment compared to direct burning of Biomass, 3) Flame control is Convenient and easy, 4) Flame temperature up to 1000C can be achieved, 5) Positive environmental impact, 6) Saving of more than 65% Diesel Oil in case of Dual Fuel Diesel application, 7) Economic Hot Air Generation and 8) Negligible Carbon Dioxide emission.

Operational Economics

1) Capital Investment is low. Around 300 U.S.Dollars per KW in case of power mode and 100 US Dollars per KW in case of Heating Mode.

2) Very small project gestation period (it can be as low as three months).

3) Economical running when compared to fossil fuels.

4) Attractive pay back periods. In areas where biomass is available at nominal cost collection charges are to be incurred and in such cases the payback period will be less than 12 months.
The Gasifier technology has crossed the R & D Stage and Demo stage. Slowly awareness is coming in the users of fossil fuel based energy systems to go for Gasifier based systems. Still these prospective users are little bit hesitant to go for Gasifier based energy systems as not many such systems are in operation and very few proven manufacturers are available. Few prospective uses can be in Rice Mills, processing industries, Spinning Mills, Chemical Industries, Tribal School Hostels, Central Prisons and Sub Jails for Power Generation and for Thermal Applications.

BIOGAS FROM CROP WASTES

Nearly all organic substrates have potential of significant energy generation via the process of anaerobic fermentation. There are several factors which must be taken into consideration to operate the digester based on alternate feed materials effectively. The factors which effects the biogas production in cattle dung holds good for this material also. So to make use of alternate material for biogas generation it is essential to control the environmental and operational factors. A wide variety of plant wastes as well as crop residues in the farm, terrestrial and aquatic species have been studied for their potential for biogas generation. The characteristics of the plant wastes and cattle dung are quite different therefore, anaerobic digestion of plant wastes need additional requirements for maintaining environmental and operational parameters. Some of basic requirements for crop wastes for biogas production are summarized as below.
 The C/N ratio of wastes varies widely from waste to waste. Maturity and type of species greatly effect the C/N ratio. It is also reported that fresh crop wastes has low C/N ratio, while after some time it increases. These is a necessity to bring C/N ratio to the optimum level of 30:1.
 Pre-processing of crop wastes is also essential in order to increase it's density and feed required quantity in the digestion chamber, this also accelerates the anaerobic reaction. This process includes chopping, cutting, mixing with other feed, steaming (if material is hard such as wood) for bringing the required C/N ratio and the concentration of solids to 7-9 % and reduce retention time.
 The density of crop wastes is less. Therefore, if it is used as such, it may form scum on the top of slurry in the digesters, thus, inhibiting methane production process.
 Pre-digested crop wastes have low hydraulic retention time, and it settles at the bottom, which require a perfect stirring mechanism, either mechanically or through gas recirculation. The system should be more reliable and effective for anaerobic digestion of the crop wastes.
The paddy straw, obtained as spoiled and waste material during collection, storage and use of paddy can be converted into biogas and valuable manure. It has been observed that wheat straw can yield biogas at a rate of 36 l/kg of dry matters, where as from the paddy straw the gas production is 260 l/kg of dry matter fed. Plant materials generate considerably higher biogas yield per kilogram of total solids than several animal wastes. Vegetable matter from young plants generates more gas than from old plants, and dry vegetable matter generates more gas than green vegetable matter. The studies carried out for anaerobic fermentation of crops and organic wastes at loading concentrations of 3-10 % TS.,biogas yield decreased with increasing loading concentrations. Above 5 % total solids, digestion of crops with high soluble carbohydrate content needs continual addition of alkali to maintain a pH of nearly 7. The composition of biogas varied with the material from 50 % methane from newsprint to 68 % from cattle manure. The balance was carbon dioxide in all cases with less than 0.001 % hydrogen sulphide. The potential of Gliricidia leaves is established as feed for biogas production and the use of digested effluent as a rich fertiliser which is superior to fresh glilricidia leaves. Mirabilis leaves produced nearly 400 l of gas/kg of dry matter which is double the amount produced by cattle dung. Methane content in biogas obtained from Mirabilis leaves was 69 % as against 62 % normally obtained from cattle dung.
The stalks of maize and sweet sorghum collected before and after the juice extraction, dried and finely powdered to pass a 40-60 mesh sieve, mixed with cow dung in the ratio of 1:1 on dry weight basis produced highest amount of biogas.This is obtained from a mixture of cow dung and fresh stalks of sweet sorghum followed by maize.
Rabbit droppings slurry at 9 % TS produced biogas at 0.24 m3/Kg as compared to 0.12 m3 gas/Kg of cow dung at the same concentration. In 6 m3 digester, 5 to 5.5 m3 of biogas was produced continuously after reaching steady state. The methane content of biogas from rabbit droppings was 68 to 70 % compared to 50 to 60 % from cow dung.

Use less energy to conserve it

(The following is an abridged form of an interesting article found in the web)
Most of our energy today comes from fossil fuels-coal, oil and natural gas. These fuels are the decayed remains of plants and animals that died millions of years ago. We are using these fuels, particularly oil, about a million times faster than they are forming; consequently, we will exhaust our supply of oil within a century or two unless we reduce the rate of use. Coal resources are plentiful, but burning coal pollutes the atmosphere and most scientists recommended reducing our use of coal or finding better, cleaner ways to use it. By conserving energy we give scientists, inventors and engineers more time to develop other ways of providing energy, ways that will not require fossil fuels.It is said that 80% of the world population living in the developing countries account for only 40% of global energy consumption and more than 2 billion people in these countries have no access to electricity. Also, worldwide, humanity encounters sever problems related to the global environment, energy use and depletion of natural resources.Today, the availability and the use of energy sources is one of the most decisive factors determining the quality of life in both urban and rural households. At house, energy is needed electrical appliance (geyser, water pumping etc.) while on farms, cultivation, irrigation, transport and post harvest processing are the most energy demanding activities. Industries live on energy only that too almost 100% on fossil fuel energy with nil or negligible portion coming from other sources. It is predicted (1996 base year) that would can expect to derive oil and gas energy only for 45 and 65 years respectively and later on look for nuclear, energy (not very well accepted by all community).In another aspect, when fossil fuels burn, they release carbon dioxide (CO2) gas into the atmosphere. As a result of the large and growing use of fossil fuels during the last century, the carbon dioxide level in the atmosphere has increased from 290 ppm (part per million), or 0.029 percent, to 350 ppm or 0.035 percent since carbon dioxide absorbs some of the radiant energy that passes from earth into space, scientists fear that its continued increase will cause the earth’s lower atmosphere to grow warmer. Carbon dioxide ‘traps’ energy much as do the windows in a green house consequently, this anticipated increase in atmosphere temperature due to the buildup of carbon dioxide and other gases, such as methane, is often referred to as the greenhouse effect. Reducing our use of fossil fuels decreases the rate at which CO2 is poured into the air. This, in turn, will reduce the greenhouse effect, an effect that could warm the earth, melt the polar ice caps, raise sea levels, flood coastal cities, and turn rich farmlands into deserts.Another way to reduce atmospheric CO2 is to plant trees in large numbers. Trees, like all green plants, absorb CO2 to carry on photosynthesis; however, to absorb the CO2 from one 500 MW (Mega Watt) coal – burning power plant would require 1000 square miles (2,590 sq km) of forest.In addition to above, it makes good financial sense to conserve energy because it will save money every family can cut its energy bills by reducing its heater, electrical, gasoline and other energy use. The more energy you transfer from fuels and power companies to do work in your home and car, the more your family spends. Conserving energy will reduce those costs.When most people speak of conserving energy, what they really mean is: use as little energy as possible to get jobs done. Burn only enough fuel oil to keep your well-insulated house reasonably warm in winter. Drive a car that uses as little gasoline as possible to get you from one place to another. Turn on electric lights and other appliances only when they are needed. Take short showers rather than baths and in general, use energy sources as little as possible.

Developments in Biomass energy

Developments over the last couple of decades, however, would seem to signal that the wheel is almost coming full circle with the increasing use of biomass being seen as imperative and in the larger interests of mankind. The driving forces behind such a move are briefly recounted and the recent technological developments particularly in the field of biomass conversion are evaluated.
There have been two major developments in the biomass field, the first of which is the rapidly growing emphasis on commercialization. This is evident not only in North America, where much of the pioneering work was carried out, but also in Europe where recent years have seen a surge of interest in biomass based renewable energy, encouraged by international concerns over global warming and regional concerns over agricultural policy. The second development is the rapid changes in funding patterns that have occurred in North America and Europe over the last few years. The Bio-energy Agreement involving 14 countries set up under the aegis of the International Energy Agency (IEA) is one such international effort in this direction.Rapid developments are taking place in most of the advanced countries. Many areas of the United States have to comply with ozone and carbon monoxide controls under the Clean Air Act Amendments of 1990(CAAA’90) and this called for concentrated efforts in thermochemical conversion of biomass which is well suited to the production of fuel matching with the CAAA’90 requirements.In Japan the Ministry of Agriculture, Forestry and Fisheries(MAFF) and Ministry of International Trade and Industry(MITI) are promoting thermochemical processing of biomass and organic wastes under the national projects named as “Star Dust 80” and “Aqua Renaissance ‘90”.The Biomass Research and Development Activities of the Commission of the European Communities (EC) has special reference to thermochemical conversion technologies named as ‘LEBEN’ (Less favoured area of Europe-Bio-energy programme). Similarly, Finland’s National Research Programme on fuel conversion named as “JALO” and Canadian programme concentrate on biomass-derived fuels.In India Ministry of Non-Conventional Energy Sources, presently MNRE concentrates on biomass based projects called “Green Power” with particular reference to co-generation in sugar mills.

Biomass Power- prospects and problems

The end of fossil fuel based economy is in sight and the Biomass based economy has begun. Biomass based systems are the only energy generating systems which have the combined benefits of renewability, decentralization and availability on demand without need for separate storage. In some case, they may mean waste recycling or captive power generation as well. In other cases, it is necessary to take note of existing site specific uses of biomass to avoid competition with manure/fodder needs.Agriculture yields enormus wastes every year, capable of partly supplementing coal. Biomass in the form of agro residue and industrial waste is available in all geographical locations of developing countries. Power plants set up in rural areas using biomass will help in the development of rural areas. Biomass based power plants will increase the commercial value of agro-residues and this will induce the farmers not only for biomass collection but also for effective utilization of the barren and uncultivable land for energy plantations.Biomass, as a fuel, has been in use for centuries all over the world. But, over the last five decades, with the conventional sources of energy playing a dominant role, biomass more or less became a fuel of the poor in the developing countries. However, of late, biomass, as a valuable renewable energy source, is attracting the attention of energy planners in both the developed as well as developing countries. Biomass fuels have several advantages as well as problems. The advantages of using biomass as compared to fossil fuels and nuclear power are numerous. More importantly, we do not have to worry about its availability as they are produced locally almost everywhere. They are generally available in sufficient quantities and have less economic value at present. Some of the benefits include CO2 neutrality, improved SOx and NOx, good water and soil quality, biodiversity, landscape, job creation, rural rehabilitation, etc.As concern for environmental protection and climate change increases, the importance of biomass as a viable fuel source for power generation is attracting greater attention. In these days of economic sustainability, technologies for biomass usage for power generation purely on commercial basis are being developed around the world.These biomass fuel could also pose problems. Their availability at the field and mill site requires elaborate coordination and management. They also cause transport problems due to their low bulk density. In spite of these problems, the prevailing economic conditions in many developing countries provide good opportunity to look into these issues seriously and solve these problems so that wide spread use of biomass fuel takes place.

A successful plant system details for a poultry litter based gas plant

High rate anaerobic digestion technology

When compared to cattle dung poultry litter has a high nitrogen anf phosphorous and hence offers an immence potential for biomethanation in aneorobic digesters with energy recovery in the form of gas besides organic manure. For the gas production conventional digesters are used for biomethanation of organic wastes including cattle dung. For this purpose many types of digesters have been developed. The high rate reactor is one of them. The knowledge base of high rate anaerobic digesters is rather limited in most of the developing countries except for few sewage treatment plants, where commercial in-house or open sale utilization of biogas was practiced. The American Society of Civil Engineers classify the digesters as low rate, high rate, anaerobic contact and phase separation
variations. A low rate digester operates with a very low volatile solids (VS) loading rate of 0.6 to 1.6 kg / m3 / day, a feed solids concentration of about 2- 5%, and high hydraulic residence time of 30 to 60 days. Being open intermittent feed, unless environmental conditions are controlled, these systems are unstable. High Rate Digestion operates at higher feed solids concentration, in general has supplemental heating for either the mesophilic (30 - 38° C) or thermophilic (50- 60° C) ranges and uniform feeding rates. As it is operated at high solids concentration, it would result in reduced tank volumes. The anaerobic contact process involves thickening of digested sludge and recycling to the inlet with a similarity to
contact stabilization in activated sludge. This is mainly meant for high strength soluble wastes only as it has hydrolysis and acid methane formation phase separated. Though a sound process theoretically, this has practical difficulties in keeping the phase separation in the two separate tanks and often requires process readjustments. In general, a vast majority of successful digesters are of the high rate mesophilic type, but the problems arises from either equipment plugging. Line problem incidental to each type accounted for almost 65- 85% of the problems encountered with such systems. Current technologies of digestion The information made available from various digester manufacturers reveals that various technology providers claim differing energy recovery potentials for the same feed and operating temperatures. Theoretically, given a unit weight of feed, and all other conditions remaining unchanged, the conversion to energy and new cells is a fixed percentage and cannot be influenced unduly by any single factor. However, the one variable, which may have some
influence, is mixing, which would either result in a complex mix or stratified regime or subsequently result in higher or lower gas yields.

Underground masonry structure type poultry litter waste biomethanation plant

A typical poultry litter waste biomethanation plant of high rate reactor system which can successfully produce gas is described below.

i) Reactor: A drum type. partially underground masonry structure can be constructed having approximately 5.5 m diameter and 10 m depth. The bottom of the digester is truncated to 1 m dia. The drum diameter is nearly 7 m and height 1.5 m with the dome rise of 0.5 m. Recirculation arrangement can be made to draw the slurry from top layer as well as middle layer and distribute from the bottom. The reactor can also be installed with immobilization arrangements for microbes. The floating drum can be allowed to travel with in a limited height by suitable locking arrangements. The drum can have a water seal at its bottom and fitted with a gas pipe of 75 mm diameter at the top.

ii) Water remover: A cylindrical drum fitted with overflow arrangement can be used as water remover from the moisture laden gas. This can be fitted at the immediate outlet of the gas line. An overflowing arrangement can be made to continuously drain out water during operation. A removable lid can be provided for easy cleaning and refitting.
iii) Water shower: The water can be arranged to be sprayed to remove hydrogen sulphide and CO2 to some extent if present in the gas using a cylindrical drum with counter current flow of gas and water shower.

iv) Activated carbon bed: To remove carbon dioxide from the biogas produced from the gas plant so as to make it rich in methane for operating the engine, an arrangement fitted with activated carbon bed to three fourth of its height in a cylindrical container made of iron can be made.

v) Filter bed for moisture filtering and gas storage: In order to remove gas-laden moisture these two to three beds can be provided as the last components of gas cleaning chain before admitting the gas to compressor. A single or two-stage compressor can be fitted in the line to suck and compress the gas for admitting to a cylindrical storage drum. The outlet of the compressor may be fitted with a non-return valve. The storage cylinder should be capable of withstanding at least 100-psi pressure, also fitted with a non-return valve. The gas stored in the cylinder can used as fuel for running the generator sets to produce electric power.

Operation of the plant: If the poultry shed is a layered type arrangement the poultry litter is not mixed with other bed materials. The feedstock is collected by a tractor and transported to the biomethanation site. The feedstock is unloaded into a shredder where it can be reduced in size and conveyed in to a tank where water is mixed with the shredded feedstock in the appropriate ratio and delivered to the reactor. The gas produced from the reactor is stored in a cylindrical container and used to operate generator sets. Part of the power produced is used to run the shredder, compressor, recirculation pump and other accessories.

Bags with solar charger

The above is a solar powered backpack with trolley case capable of charging any personal devices. This solar power backpack with trolley case charger can be used to charge mobile phones, digital cameras and MP3/MP4 players. It comes with enough charging adapters to power up just about any major mobile phone on the market as well. Its onboard battery pack can be charged by solar power and/or by connecting to an AC outlet power supply.

The above bag is integrated with solar powered panels to charge phones on the road. The portable charger is able to charge gadgets like notebook as well.

Solar powered glow brick

The above is a solar powered glow brick capable of glowing at night. This gadget can be charged from the sun. At night, the stored energy is released, causing the solar light bulb to glow green. The glow Brick makes a cool home accessory or can be used as a comforting night light for children.

The above is a solar powered mini clip fan capable of blowing air. This gadget can be charged from the sun. This mini clip fan is an innovative device which helps to stay cool during the hot summer days. This light weight fan can be cliped on to the hat and gets power from the sun’s rays. This is a cool home accessory.

Solar powered plant pot and mower

The above is a solar powered plant pot. This works in the same way as any other solar powered lamp works. The only difference is that this pot can hold a nice plant and delight our eyes with flashing colour. This pot comes in either white or the one wich flashes in several different colors and look nice at night.

The above is a solar powered lawn mower capable of cutting lawn grass and it can be programed to come on and automatically mow the lawn whenever needed. This hybrid gadget can also be charged from the mains as well as the sun.It also has embedded sensors to safely navigate around garden obstacles to give the lawn a perfect cut.

Solar PV toy car

A mini solr photo voltaic (PV) panel powered car is shown above. It is claimed as the smallest solar car ever developed. As you know it can move under sun light or when bright light rays fall on it, very similar to the power source for solar calculators. This is really a miniaturisation attempt against the fast development of solar PV powered cars running on streets.

Solar powered toothbrush-Toothbrush that doesn't need toothpaste

A team of researchers led by Dr. Kunio Komiyama, a dentistry professor emeritus at the University of Saskatchewan in Saskatoon, Saskatchewan, Canada, has invented a toothbrush that makes a solar-powered chemical reaction in a person's mouth to clean their teeth.

With their latest invention, researchers can eliminate the need to use toothpaste. Currently Komiyama and his colleague Dr. Gerry Uswak are searching for volunteers to test their new toothbrush, dubbed the Soladey-J3X.

Manufactured by a Japan-based company the Shiken, the latest invention is to be tested by 120 youngsters.

It is worth mentioning that the Soladey-J3X uses a solar panel installed at its base to send electrons to the top of the toothbrush via a lead wire. The electrons then come into reaction with acid in the mouth, thus leading to a chemical reaction that not only breaks down plaque but also kills bacteria.

Top Solar Powered Gadgets for everyday use

1. Solar Powered Tent:- The solar powered tent has its own solar panel and integrated interior LEDs. The solar panels independently charges batteries and 4-6 hours of direct light are enough to produce 2-4 hours tent light. There mainly two version of the tents. One having the capacity of 4-person and another having the capacity of 6 person.

2. Sunflower Solar Power Station:-It is a new and powerful home and office equipment. It has a solar powered music system. In this device electricity is generated with the help of solar energy through three built in standard sockets. The top solar panel receives solar energy during day time and the rechargeable solar batteries keep the appliances working throughout the night.

3. Voltaic Solar Backpack:- Voltaic Solar Backpack is very useful during business trips and campings. This solar backpack has several pockets and wire channels to keep and charge the electronic devices like cell phones, PDA's and handheld GPS, mp3. It has a Li Ion battery charger that stores excess power from sunny days for charging when the durable, water and scratch-proof solar panels don’t get enough of sun rays. It has three solar panels which operates independently to generate 4 watts of power. It has a set of 11 standard adaptors to charge other devices and a car lighter adapter.

4. Solar Attic Fan:- It is a compact, simple and environment friendly fan that is powered completely by solar energy. It is constructed of .080 (14 gauge) aluminum. It has a hardware made up of stainless steel and a animal protection screen made up of stainless steel. It is also coated with powder to withstand any environment. This solar attic fan reduces the temperature of attic, save stress on the cooling system, conserves power, and saves your money.

5. Solar Panel Sun Glasses:- These sunglasses has the ability to trap the solar energy and than convert it into electric energy. So that it can charge the small hand held devices through the power jack at the back of the frame. This Gadget is very useful. It protects from sun tanning, also helps to listen iPod. Just Zap these glasses on and start charging your iPod.

6. Voltaic Generator Solar Laptop Charger:- Voltaic Generator Solar Laptop Charger is a more efficient version of freeloader solar charger. It is the first of its kind. It has enough power to charge a laptop. This gadget has high-efficiency cells and also includes a battery pack that is custom designed to store and convert the electricity generated more efficiently. It is also useful in charging cell phones and other hand held electronics.

7. Solar Under Ground Pest Deterrent:-It is an environment friendly pest deterrent powered by an integrated solar panel that helps to bring out underground pests like moles, voles, and gophers without any complicated set up or external power. On putting the waterproof anodized aluminum spike on the ground, it emits sonic vibrations every 30 seconds that irritate burrowing pests and compel them to split up.

8. Solar Hanging Lights and Lanterns:- As the name reflects Solar Hanging Lights and lanterns runs with the help of solar energy. These Solar Hanging Lights are made of the highest quality materials and utilize the latest LED Lighting technology for maximum brightness, and extra long run times. These lights creates a wonderful Victorian Lantern effects as well as provides additional functionality for ground placement, table placement or it can simply remove from the solar lantern from the hook and can be hang any where.

9. Freeloader Solar Charger:- If you want to take your gadgets during trips. Than you must require the Solar Powered Portable charger. This Freeloader solar charger is an advanced portable charging system that can power any hand held mobile device anywhere. Once charged, Freeloaders internal battery can power an iPod for 18 hours, a mobile phone for 44 hours, PSP for 2.5 hours and a PDA for 22 hours.

10. Solar Power purse:- Jo Hynek,a doctoral student has designed the "Power Purse" . It puts function over form. It is a fashion-friendly gadget, which is covered with solar panels. It is designed to charge all the mobile accessories such as cell phones, mp3 players, etc.

Solar PV powered cordless fan

Solar energy is really taking over every aspect of our lives and if you are willing to spend that extra initial amount, then it really can go a long way in making sure that you never run out of power. Solar gadgets are only growing in number, but they are surely going down in price in the last few years. If technology for cheaper synthesis of solar cells and fabrication of solar panels indeed takes off, then we could soon be living a very bright and clean life.

The fan has a set of accessories that include LED lamp, quartz clock, mobile phone charger and battery charger. The powerful 12V 4.5Ah sealed lead acid battery can be charged by the solar panel during the day or can be charged via an AC/DC adaptor. Typically, on a full charge the unit will give you up to six to eight hours of fan use on full speed and twelve to sixteen hours at low speed and five to seven hours of light.

Energy from the Wind - Wind Turbines

Renewable Energy: Wind Power

GAS CONDITIONING FOR POWER GENERATION USING GASIFIER

Need for gas cleaning
Biomass gasification is a process of converting biomass to a combustible gas in a reactor, known as gasifier, under controlled conditions. During gasification, biomass is subjected to partial pyrolysis under sub-stoichiometric conditions. A typical gasifier plant consists of a reactor, which receives air and solid fuel and converts them into gas, followed by a cooling and washing train where the impurities are removed. The clean combustible gas at a nearly ambient temperature is a must for running diesel-generator sets in dual fuel mode or gas engine generator sets suitable for running on producer gas alone. In thermal applications, the cooling and cleaning of the raw gas is limited to the requirements of the thermal process.
The gasification system development has also included extensive research and development on product gas cleanup. Raw gases contain particulates, tars, ammonia, and other impurities that interfere with equipments and downstream processes and components or create emission problems. For low-technology thermal applications where the product gas is simply burned to provide heat, such as a cement kiln, the gas clean-up requirements may be minimal. However, high technology systems such as fuel cells and gas turbines or systems using synthesis gases require clean fuel gases. Extensive clean up may also be required to meet the environmental regulations even in relatively undemanding applications. There are examples of failure due to non-adherence of critical fuel quality requirements with end-use.
In 1993, the International Energy Agency (IEA), Bioenergy Gasification Activity repared a document summarizing the status of gas clean-up systems. This document identified primary gas contaminants, discussed unit operations that could potentially remove such contaminants, and discussed gas-cleaning strategies in relation to the end-use of the product gas. Since then, progress has been made in developing a better understanding of the chemistry and mechanisms of hot gas cleanup and conditioning as evinced by recent gasification systems which have incorporated technologies to improve gas cleanup.
Gas ontaminants
Gasification processes, particularly updraft gasification produces a dirty gas that has a relatively low level of purity and includes toxic chemicals and other contaminants besides carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen and water vapor. Pollutants such as tars, dust, and ash are also present, in relatively high concentrations, in these crude gases. Following a gasification process the crude gas must normally be cleaned of tar, filtered, purified and cooled before it is used in many energy-producing applications.
Cleanup systems
Gas cleanup systems may contain several components individually or in combination viz., cyclones, scrubbers, or filters; each of which removes one or more contaminants. Systems producing gas must deal with the cleanup of five primary contaminants including:
· Particulates
· Alkali compounds
· tars
· nitrogen-containing components
· Sulphur
Various gas-conditioning systems employed are:
Barrier Filters – Rigid, packed bed filters, bag filters, sieve-plate scrubbers, wet scrubbers, cyclone filters, electrostatic precipitators, sand bed filters, water wash towers and catalytic thermal tar destruction beds.
The application of particulate removal technologies to biomass gasification systems in general has matured over the past decade. Cyclones are routinely being used for bulk particulate removal, and technologies including bag filters and wet scrubbers are being used in large-scale systems. While this progress is incremental in nature, it is required for wide- spread deployment of gasification technologies. Based on the available data except for the catalytic tar crackers, none of the gas cleaning systems can meet a targeted cleaning objective exceeding 90 %.

Biomass gasifier

Biomass gasification is a process of converting biomass to a combustible gas in a reactor vessel, known as gasifier under controlled conditions. The combustible gas, known as producer gas has a composition of approx. 19 % CO, 10 % CO2, 50% N2, 18% H2 and 3 % CH4. This gas has a calorific value of 4.5 - 5.0 MJ/cubic metre. It has to be cooled and cleaned before using in internal combustion engines for power generation purposes.
Biomass fuel
A wide range of woody biomass in the form of wood or agro residue can be used in the gasifier. In general any biomass that has a density of more than 250 kgs per cubic meter can be used for gasification. Biomass from trees of Eucalyptus, Casuarina, Acacia, Albizzias, Cassia siamea and many other species and agricultural residues such as coconut shell, husk, fronds, corn cobs, corn stalks, mulberry stalks, briquettes of biomass or saw dust, coffee husk, groundnut husk, rice husk etc. can be used as fuel in fuel specific gasifiers.
Conversion efficiency
High Conversion efficiency from solid Biomass to gaseous fuel of upto 85% in hot gas mode, 75% in cold gas mode and 65% with rice husk is possible. Each Kg of biomass can producer 2.5 to 3.0 cubic meters of gas having a average calorific value of 4.5 - 5.0 MJ/cubic metre. During power generation through gen set upto 85% diesel saving is possible in duel fuel mode.

Alkaline fuel cell stack design

Alkaline fuel cell stack design involves working out the details of optimum configuration of the individual module, array or pack to develop the required output. The basic concept in the design being the assembly of pair of electrodes, provision of hydrogen and oxygen gases to the appropriate electrodes and supply of electrolyte into the individual cell assemblies. Cascading the electrode pairs is possible in many different ways. The basic configuration can be either mono or bipolar with either internal or external manifolding. Also electrolyle supply by matrixing or stagnant boundary or by circulation are the various possibilities. The technique to be adopted in the stack boundary or by circulation are the various possibilities. The technique to be adopted in the stack fabrication mainly depends on the limitation in materials to be used.
Stack design concepts
Various possibilities of stack disign are possible, The options for air electrode of hydrophilic and hydrophobic nature with electrolyte circulation by pump / fan or by natural respiration are possible.
Internal manifolding where electrolyte and gas manifolds arranged internally or external manifolding is possible..
The choice of internal or external manifolding have their inherent problems. The external type has all plumbing works done externally which are amenable for easy maintenance, while the choice of polarity and coupling depends on the capacity. In the internal type cell reliability of fluid transfer depends on seals and O rings and the maintenance requires dismantling of cell assembly.
Stack designs
The stack design adopted by various investigators are described below:
Filter press type: Hydrogen - oxygen fuel cell have circular frame and electrodes. The frame consists of rooms for KOH, H2 and O2. There are six passages two each for entry and exit of electrolyte, hydrogen and oxygen and the frame was clamped by six bolt holes. The electrolyte and gas diffuse radially inwards and leave radially out. This design akins to Grove's design concept.
Monocell construction: The monocell of the actual design contains seven structural components. The central matrix of 20.4 x 20.4 x 0.025cm is connected by means of film gluing with an epoxy frame layer, with the later supported with Teflon mesh screen. Adjacent nickel collectors of the electrodes consist of galvanised screens which are soldered and filled with tin at two opposite edges and sealed in the frame zone after having been charged with catalyst.
Bipolar alkaline fuel cell battery: This consists of bipolar cells, separator packages, electrolyte frame and end plate assembly. The electrodes are rectangular size and framed with suitable slots for gas and electrolyte entry.

Partial oxidation of biogas to hydrogen

The conversion of gaseous hydrocarbons to hydrogen can be achieved in many ways. Partial oxidation with air is one of the options. In this process methane in the biogas with oxygen in air to form hydrogen in a bed of catalyst.
Principle
This commercial process route is basically the result of sequential combustion reactions in which the gas is burnt with deficit oxygen (nearly 30 % of stoichiometric requirement). Depending on the feed -stock the product gas may require purification of sulphur compounds and CO2 - removal. The advantage of dispensing with an external heat source favours the partial oxidation step, since the oxidation of CO supplies the necessary heat.
Process flow
The biogas containing 55-60 % methane , 40 % CO2 and traces of H2 S is first dehydrated and then purified from H2 S. The gas is then sent to the partial oxidizers to form hydrogen. Depending on the composition of the outlet gas from the oxidizer methanation of residual carbon oxides can be incorporated. Finally a Co2 scrubber may be added depending on the type of fuel cell to be used in the power plant.
Process
The process occuring in the partial oxidizer is
CH4 + 0.5 O2 = Co + 2H2
The process requires oxygen, which may be separated and supplied from air and is favoured by moderately high pressure. It is understood that due to residence time limitations, the process approaches equilibrium leaving some residual methane and carbon in the product gas. Hence CO2 needs to be scrubbed and recycled in the plant (Balthasar).
Need for pure oxygen
If air is used instead of oxygen the separation of hydrogen from nitrogen is difficult. Hence oxygen at a purity of at lease 95 % and has to be used in large scale systems. Pressure of notrogen could be accepted in small scale fuel cell applications. After all the cathode gas (air) contains 80% nitrogen. The process has thus to be modified for operation on air in this particuler study.
Factors controlling the process
As the partial oxidation proceeds through a flame reaction, it is necessary to moderate the flame temperature, preferably by means of steam. The raw gas composition is controlled by the oxygen to methane ratio and by the steam addition. In order to reduce the oxygen consumption for the oxidation step the biogas and steam has to be preheated and have to be metered precisely to the reactor.
The operating conditions vary with the non-catalytic reactors.
Pressure: 60 to 90 bar. Reaction temperature: 1200 to 1370 C.
Under catalytic partial oxidation a commercial process, topsoe SBA has specified the following conditions.
Pressure: up to 30 bar or more. Temperature: 90c.
Catalyst: Ni
Feed-stock gas and super heated steam are mixed and preheated to 60c and mixed with oxygen
Reactor
The reactor may be a refractory lined stainless steel vessel with one or more burners. In order to initiate the reaction part of the gas has to be burnt inside the reactor. Johnson Matthey Ltd. report in their patent a reactor made of SS tube with entry for gas at the middle of the reactor and exit for product gas from the end. As gas entry is made near the middle of catalyst bed, they have observed a higher temperature of 450 c at the tip and a uniform temperature of 280 c surrounding the hot zone. This is claimed to be superior to at once through reactor. The reactor may then have multiple (4 or 5 entries from the sides).
A theoretical model developed by Opris et. al describes the temperature and product distribution profiles along the length of the reactor. This fits well with the commercial data. The reactor requires a minimum length for complete partial oxiation of methane leading to a continuous supply of hydrogen at a fixed concentration.
Catalysts
The catalyst used by Johnson Matthey let. in their Hot Spot TM reactor contained 0.01 to 5 wt % platinum and from 1 to 15 wt % chromium oxide supported on a refractory solid such as silica. The support may be monolith honeycomb or particles with a maximum size of 1.5 mm.
Catalyst deactivation
The successful economic and technical utilization of the process depends on the avoidance of free carbon deposition which decreases the catalyst surface area resulting in lower reaction rates. It is suggested that carbon deposition shall be avoided by operational techniques rather than by inhibition.
Product gas
The hot product gas is expected to have the following composition on a dry basis.
Hydrogen and CO, 93 % by volume
Carbon dioxide, 5 % by volume
Nitrogen and argon, 1.5 % by volume
Methane, 0.6 % by Volume
The reactor effluent needs rapid cooling to freeze the gaseous equilibria established at the high temperature reactor by a direct water quench or by heat exchange. The product gas then has to be washed free of carbon-sulphur compounds, carbon dioxide and inert gases.

Natural gas as a source of hydrogen

A common misconception about natural gas is that it is running out quickly. In fact, there is a vast amount of natural gas estimated to still be in the ground. According to latest estimate of Energy Information Administration (EIA) of proved natural gas reserves, the total available future supply can be available for more than about 100 years of supply at current rates of consumption in the case of US alone. Natural Gas is one of the principle sources of energy for many of our day-to-day needs and activities.
Chemical composition of natural Gas
Component Range (mole %)
Methane 87 - 96
Ethane 1.5 - 5.1
Propane 0.1 - 1.5
iso – Butane 0.01 - 0.3
normal – Butane 0.01 - 0.3
iso – Pentane trace - 0.14
normal – Pentane trace - 0.04
Hexanes plus trace - 0.06
Nitrogen 0.7 - 5.6
Carbon Dioxide 0.1 - 1
Oxygen 0.01 - 0.1
Hydrogen trace - 0.02
Specific Gravity 0.57 - 0.62
Gross Heating Value (MJ/m3), dry basis: 36.0 - 40.2
Hydrogen can be generated from natural gas with approximately 80% efficiency and the steam reforming of methane or natural gas usually produces bulk hydrogen. The primary methods in which natural gas is converted to hydrogen are:
(1) reaction with either steam (steam reforming),
(2) oxygen (partial oxidation), or
(3) both in sequence (auto thermal reforming).
Steam-Methane Reforming
Steam reforming is a process in which high-temperature steam (700°C–1000°C) is used to produce hydrogen from natural gas. In steam reforming, methane reacts with steam under high pressure in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Heat is supplied for the reaction to proceed. In the second stage carbon monoxide and steam are reacted using a catalyst to produce carbon dioxide and more hydrogen. Carbon dioxide and other impurities are removed from the gas stream, leaving essentially pure hydrogen using pressure-swing adsorption.
Partial Oxidation
In Partial oxidation process methane in natural gas reacts with oxygen in air to form hydrogen in a bed of catalyst. This commercial process route is basically the result of sequential combustion reactions in which the gas is burnt with deficit oxygen (nearly 30 % of stoichiometric requirement). Depending on the feed -stock the product gas may require purification of sulphur compounds and CO2 - removal. The advantage of dispensing with an external heat source favours the partial oxidation step, since the oxidation of CO supplies the necessary heat. Partial oxidation is an exothermic process—it gives off heat. The process is, typically, much faster than steam reforming and requires a smaller reactor vessel. As can be seen from the chemical reactions of partial oxidation (below), this process initially produces less hydrogen per unit of the input fuel than is obtained by steam reforming of the same fuel.
Auto thermal reforming (ATR)
Auto thermal reforming (ATR) uses oxygen and carbon dioxide or steam in a reaction with methane. Auto thermal reactor concepts for the heat integrated coupling of endothermic and exothermic reactions are required for an efficient on-site production of hydrogen from natural gas for use in fuel cells. The reaction takes place in a single chamber where the methane is partially oxidized. The reaction is exothermic due to the oxidation. When the ATR uses carbon dioxide the H2: CO ratio produced is 1:1; when the ATR uses steam the H2: CO ratio produced is 2.5:1 The advantage of ATR is that the H2: CO can be varied, this is particularly useful for producing certain second-generation biofuels.

Hydrogen Production Technologies

Various technologies that can be used to produce hydrogen, they are:
(1) reforming of natural gas to hydrogen,
(2) conversion of coal to hydrogen,
(3) use of nuclear energy to produce hydrogen,
(4) electrolysis,
(5) use of wind energy to produce hydrogen,
(6) production of hydrogen from biomass, and
(7) production of hydrogen from solar energy.
Methods of hydrogen generation
Compared with other fossil fuels, natural gas is a cost-effective feed for making hydrogen, in part because it is widely available, is easy to handle, and has a high hydrogen-to-carbon ratio, which minimizes the formation of by-product carbon dioxide (CO2). The primary methods in which natural gas is converted to hydrogen are:
(1) reaction with either steam (steam reforming),
(2) oxygen (partial oxidation), or
(3) both in sequence (autothermal reforming).
Reaction of carbon monoxide with steam (water-gas shift) over a catalyst produces additional hydrogen and carbon dioxide, and after purification, high-purity hydrogen is recovered.
Since natural gas is a mixture containing carbon monoxide, carbon dioxide and unconverted methane bulk hydrogen is usually produced by the steam reforming of methane or natural gas. At high temperatures (700–1100 °C), steam (H2O) reacts with methane (CH4) to yield syngas.
CH4 + H2O → CO + 3 H2 + 191.7 kJ/mol
In a second stage, further hydrogen is generated through the lower-temperature water gas shift reaction, performed at about 130 °C:
CO + H2O → CO2 + H2 - 40.4 kJ/mol
Essentially, the oxygen (O) atom is stripped from the additional water (steam) to oxidize CO to CO2. This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane.
In most cases, carbon dioxide is vented to the atmosphere today, but there are options for capturing it in centralized plants for subsequent sequestration. For distributed generation, the cost of sequestration appears prohibitive.
Integrated steam reforming / co-generation- It is possible to combine steam reforming and co-generation of steam and power into a single plant. This can deliver benefits for an oil refinery because it is more efficient than separate hydrogen, steam and power plants.
In spite of the above facts, natural gas can not be considered as a long-range fuel for centralized plants for the hydrogen economy. Whether it will be possible to utilize partial oxidation or autothermal reforming for the distributed generation of hydrogen appears to depend on developing new ways of recovering oxygen from air or separating product hydrogen from nitrogen. This is needed because conventional, cryogenic separation of air becomes increasingly expensive as unit size is scaled down. Membrane separations, in contrast, appear amenable to this application and may provide the means for producing small, efficient hydrogen units. A mass-produced hydrogen appliance suitable for distributed generation in fueling stations is to be developed.

Briquetting of powdery biomass

The process of briquetting consists of applying pressure to a mass of particles, with or without a binder and converting it into a compact mass. The end product may be in a solid geometrical form or in the form of hollow cylinders which may be a solution to the large volume, low-density products having high transportation/handling cost problems associated with biomass. Cow dung cakes, fuel balls made with coal dust, half burnt cinder as well as hand compressed special fuel lumps are some of the prime examples. High-density briquettes are also made by power driven machines to make wood like solid briquettes from powders/dust of various materials.The vital requirement of briquette formation form wood biomass is the destruction of the elasticity of the wood, which could be done either by high pressure or by previous heat treatment or by a combination of both. There are two processes of briquetting, namely, direct compaction and indirect compaction after pyrolysing or carbonization of the residue.

Direct compaction

In this ease, the briquettes may be prepared with or without binding agents.

a) Without binding agents: This process involves two steps: Pretreatment of biomass through application of high pressure in the range of 120 - 200 MPa at which condition the biomass gets heated to a temperature of about 182°C and the lignin begins to flow and acts as binder. Compaction or densification of material: The powdered biomass is densified through briquetting machines available in the capacity range of 100 - 300 kg/h or more operating by electric power. The cost of such briquetting units depends upon the capacity.

b) With binding agents: In this process, the briquetting machines operate at lower pressure range of 50 - 100 MPa and are powered by electricity. This process requires additional binders like molasses, lingo-sulphonate, sodium silicate, dung slurry etc. Such machines are available in the capacity range of 100 to 400 t / h.

Indirect compaction

Pyrolysis is the process or destructive distillation of organic materials heated at slow rate to about 270°C in the absence of oxygen. During process of pyrolysis, solid char, liquid tar and combustible gases are produced besides organic liquids. The nature and quantum of these products depend on various factors such as composition of biomass, and residence time in kiln and temperature. During the pyrolysis, the fibre content of the biomass is broken which latter facilitates in briquetting of charcoal. The obtained charcoal is briquetted through extrusion process.

Arecanut husk - biomass

To the Indians, Malayans, or the Indonesians, betel-nut chewing is as familiar as chewing gum to the Americans. In India the use of arecanut and its cultivation constitute a distinct agricultural practice scarcely less important than that of other economic crops. Arecanut husk is mainly used for manufacturing of thick boards, fluffy cushions, non-woven fabrics, thermal insulation and wrapping paper. Areca husk is used as a substrate for mushroom cultivation. Arecanut husk fibre is generally longer than woolenised jute,. Although value added products can be created with the areca husk, these practices do not seem to be really popular, because still piles of areca husk remains after processing in the developing countries. On a weight basis, the husk is 60 to 80% of the whole fruit. The husk fiber itself is mainly constituted of cellulose. A sun-dried areca husk has a mass loss of 28-33% when compared to a green husk. The major constituents of arecanut are pectin at 1.5-3.6%, protopectine at 1.5-2.1%, hemi cellulose at 35-65.8%, lignin at 13-26%, furfuraldehyde at 18.8% and ash at 4.4% and moisture content varying from 91% when very tender to 74 % when ripe.