Biomass Renewable Energy
Biomass is biological material derived from living, or recently living organisms and in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. It most often refers to plants or plant-based materials which are specifically called lignocellulosic biomass. As an energy source, biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuel.
Biomass is any organic matter that is renewable over time. More simply, biomass is stored energy. During photosynthesis, plants use light from the sun's energy (light energy) to convert carbon dioxide and water into simple sugars and oxygen.
Biomass, on the other hand, absorbs atmospheric carbon while it grows and returns it into the atmosphere when it is consumed, all in a relatively short amount of time. Because of this, biomass utilization creates a closed-loop carbon cycle. For example, you can grow a tree over the course of ten or twenty years, cut it down, burn it, release its carbon back into the atmosphere and immediately start growing another tree in its place. With certain fast-growing biomass crops such as switch grass, this process can occur even faster.
Based on their origin, biomass comes under four broad categories:
1. Woody biomass
2. Herbaceous biomass
3. Fruit biomass
4. Blend and mixtures.
Trees, bushes, and shrubs fall under woody biomass, but not the fruits or seeds that some of them bear. Herbaceous biomasses are those plants that die at the end of the growing season. These biomasses, however, include grains and cereals that grow on such plants. Fruits, though classified as a separate group, are part of woody plants. Additionally, we also have mixture or blends of biomass. Blends are intentional mixing of biomass, while mixtures are unintentional mixing of biomass.
Some of the physical properties of biomass affect its pyrolysis and gasification behavior. For example, permeability is an important factor in pyrolysis. High permeability allows pyrolysis gases to be trapped in the pores, increasing their residence time in the reaction zone.
Apparent density is based on the apparent or external volume of the biomass. This includes its pore volume (or that of its cell cavities). For a regularly shaped biomass, mechanical means such as micrometers can be used to measure different sides of a particle to obtain its apparent volume. An alternative is the use of volume displacement in water. The apparent density considers the internal pores of a biomass particle but not the interstitial volume between biomass particles packed together.
Gasification is a thermochemical conversion process, so the thermodynamic properties of a biomass heavily influence its gasification. This section describes three important thermodynamic properties: thermal conductivity, specific heat, and heat of formation of biomass.
Disadvantages of Biomass
Many consider Biomass to be the best alternative amongst other sources of energy but, it also have some disadvantages which makes people think twice before using biomass as a source of energy:
• Biomass Produces limited amounts of energy.
• In the case of biomass energy, the initial costs that need to be incurred are quite high. The biomass boiler is quite expensive for the masses to afford.
• Collection of Biomass is very time consuming.
• Although it is said that no harmful gases are released into the air, biomass does produce methane which depletes the ozone layer in the atmosphere.
• Biomass requires high Initial Cost.
• The clearance of large areas, including the forest areas for providing the material for biomass can have an adverse impact on the environment.
BIOMASS ENERGY IN INDIA
Biomass use is growing globally. Despite advancements in biomass energy technologies, most bioenergy consumption in India still remains confined to traditional uses. The modern technologies offer possibilities to convert biomass into synthetic gaseous or liquid fuels (like ethanol and methanol) and electricity. Lack of biomass energy market has been the primary barrier to the penetration of modern biomass technologies. Growing experience with modern biomass technologies in India suggests that technology push policies need to be substituted or augmented by market pull policies. A primary policy lacuna hampering the growth of modern biomass energy is the implicit environmental subsidy allowed to fossil fuels. Increasing realization among policy makers about positive externalities of biomass has now created conditions for biomass to make inroads into the energy market. Modern biomass has potential to penetrate in four segments –
i) Process heat applications in industries generating biomass waste, ii) cooking energy in domestic and commercial sectors (through charcoal and briquettes), iii) electricity generation and iv) transportation sector with liquid fuels.
Prospective Renewable Resource for Bio-Based Processes
Biomass is a renewable resource and refers to any material having recent biological origin, such as plant materials, agricultural crops, and even animal manure. Biomass available for energy on a sustainable basis includes herbaceous and woody energy crops, agricultural food and feed crops, agricultural crop wastes and residues, wood wastes and residues, aquatic plants, and other waste materials including some municipal wastes. Biomass is a very heterogeneous and chemically complex renewable resource.
Lignocellulose in the form of forestry, agricultural, and agro-industrial wastes is accumulated in large quantities every year. These materials are mainly composed of three groups of polymers, namely cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are sugar rich fractions of interest for use in fermentation processes, since microorganisms may use the sugars for growth and production of value added compounds such as ethanol, food additives, organic acids, enzymes, and others.
Cellulose, the major component of plant biomass (30-60% of total feedstock dry matter), is a homopolysaccharide composed of (P-glucopyranose units, linked by (P-(l—»4)-glycosidic bonds. The orientation of the linkages and additional hydrogen bonding make the polymer rigid and difficult to break. Cellulose has a strong physic-chemical interaction with hemicellulose and lignin. In natural celluloses, the chains are aligned in a way of forming complex organized fibrils, whether in crystalline or amorphous structures.
Hemicelluloses are closely associated with cellulose in plant tissues and together with cellulose they are the most abundant carbonic material in plants. These macromolecules, contrarily to cellulose, present heteropolysaccharic nature and a considerable degree of ramification, consequently not presenting crystalline regions. Hemicellulose (20-40% of total feedstock dry matter) is a short, highly branched heterogeneous polymer consisting of pentose (xylose and arabinose), hexose (galactose, glucose, and mannose), and acid sugars. Mannose is the dominant hemicellulose sugar in softwoods, while xylose is dominant in hardwoods and agricultural residues.
Lignin is a natural macromolecule composed by p-propylphenolic units with methoxyl substituents on the aromatic ring and, between these units, exist principally ether-type bounds. Lignin is an aromatic polymer synthesized from phenylpropanoid precursors. Lignin is hydrophobic and highly resistant to chemical and biological degradation.
Recently, a great deal of research is being devoted to the area of sustainable processes. The need for such processes stems from the burgeoning human population and the accompanied required growth in availability of materials and energy. A significant part of the developments is dedicated to bio-based sustainable processes, which make use of renewable feedstocks, such as agro-industrial wastes and industrial byproducts, to decrease the use of nonrenewable fossil resources which are depleting very quickly. Owing to the higher efficiency in terms of energy and materials and the reduction of environmentally unfriendly wastes, the bio-based processes are clearly advantageous.
Biotransformation of Biomass
Biological transformation involves the utilization of living organisms or enzymes (biocatalysts) to catalyze the conversion of biomass into specialty and commodity chemicals. Generally, it is considered to be the most flexible mode for conversion of biomass into various industrial products. Compared to chemical transformations, where high temperatures and pressures are involved, operating conditions for biological transformations are relatively mild. Fermentation is the primogenital and the most fundamental and mature area of biotechnology for biological transformation.
Biotransformation of Biotechnological Process Wastes
The advancements in bioprocess technology led to commercialization of various biotechnological/fermentation processes for the production of various bioproducts, such as food and beverages, organic acids, antibodies, pharmaceutical products, and renewable fuels among others. These microorganism-mediated processes result in thousands of tons of waste biomass, such as of yeast, bacteria, fungi, and algae. These waste are rich in various kinds of bioactive compounds, such as biopolymers, proteins, lipids, and pigments, among others.
Edible mushrooms are produced and consumed on a large scale. The amount of waste remaining after removing the edible part mainly consists of stalks and mushrooms with irregular dimensions and shapes and accounts for 5-20 % of the total production volume. The huge amount of wastes of edible mushrooms, such as Agaricus bisporus, Lentinus edodes, Pleurotus species, and Volvariella volvacea, among others, can be potentially used for the extraction of the high-value-added product chitosan, which nowadays finds promising applications in various fields.
Biochemical from Biomass
Biomass conversion is the process of creating energy by burning materials of recent biological origin, such as wood waste. The conversion of biomass to energy (also called bioenergy) encompasses a wide range of different types and sources of biomass, conversion options, end-use applications and infrastructure requirements. Biomass can be derived from the cultivation of dedicated energy crops, such as short rotation coppice (SRC), perennial grasses, etc.; by harvesting forestry and other plant residues (forest thinnings, straw, etc.); and from biomass wastes such as sludge from organic industrial waste and organic domestic waste or the wastes themselves. In each case the biomass feedstock has to be harvested/ collected, transported and possibly stored, before being processed into a form suitable for the chosen energy conversion technology. Typically, biomass conversion is used to generate electricity for sale to a utility. Biomass conversion can also produce marketable products such as fly ash used in cement manufacturing.
Thermo Chemical Conversion
Three main processes are used for the thermo-chemical conversion of biomass. Thermo-chemical conversion uses heat as the process energy. It is usually divided into combustion, gasification, and pyrolysis technologies, all of which can treat solid biomass. Thermochemical conversion involves deconstructing biomass and upgrading the resulting intermediates into a range of fuels and other products. Research in thermochemical conversion focuses on the production of either gaseous intermediates or liquid bio-oil intermediates and their subsequent upgrading into fuels and other products.
Gasification is the conversion of biomass into a combustible gas mixture by the partial oxidation of biomass at high temperatures, typically in the range 800-900°C. It means heating of biomass with a sufficient amount of oxygen or air in a gasification reactor to produce synthetic gas (syngas), a mixture of carbon monoxide (CO) and hydrogen. After cleanup and conditioning, syngas can be burned in a gas turbine (GT), gas engine (GE), or integrated gasification combined cycle plant (IGCC) to produce power and heat. The low calorific value (CV) gas produced can be burnt directly or used as a fuel for gas engines and gas turbines. The production of syngas from biomass allows the production of methanol and hydrogen, each of which may have a future as fuels for transportation. Fuel cell technologies offer a great potential to convert purified syngas, hydrogen, or methanol into heat and power at very high efficiencies.
As biomass is a natural material, many highly efficient biochemical processes have developed in nature to break down the molecules of which biomass is composed, and many of these biochemical conversion processes can be harnessed.
Key challenges for biochemical conversion include the considerable cost and difficulty involved in breaking down the tough, complex structures of the cell walls in cellulosic biomass.
Fermentation is used commercially on a large scale in various countries to produce ethanol from sugar crops and starch crops (e.g. maize, wheat). The biomass is ground down and the starch converted by enzymes to sugars, with yeast then converting the sugars to ethanol. Purification of ethanol by distillation is an energy-intensive step. The solid residue from the fermentation process can be used as cattle-feed and in the case of sugar cane, the bagasse can be used as a fuel for boilers or for subsequent gasification.
Ethanol Fermentation of Saccharine Materials
Saccharine materials used for ethanol production at a large scale are juice and molasses of sugar cane and sugar beet. Molasses is a byproduct which is concentrated mother liquid after sugar crystallization. Sugar concentration of molasses is around 50% and contains glucose, fructose and sucrose as main sugar components. These saccharine materials are good substrate for ethanol fermentation by yeast and Zymomonas. A lot of cane juice is used for ethanol production in Brazil and India.
Products of Acetone-Butanol Fermentation
Acetone-butanol fermentation was industrialized for supply of raw materials of smokeless powder and fighter planes. Presently, acetone and butanol are synthesized in petroleum industry. Biofuels, renewable gasoline or diesel additives are now paid much attention throughout the world. Butanol can be added to both gasoline and diesel fuels and has more affinity for gasoline than ethanol. Therefore, butanol will be promising biofuel.
Anaerobic fermentation is a reaction in which anaerobic microorganisms oxidatively decompose organic materials to get energy under anaerobic conditions. We call fermentative reactions in which hydrogen is the final product as hydrogen fermentation. In hydrogen fermentation, some organic materials and alcohols are produced with hydrogen.
Lactic Acid Fermentation
Lactic acid has alcohol (OH) and carboxylic (COOH) sites inside the molecule. Since it includes chiral carbon, it has two chiral isomers, D-lactic acid and L-lactic acid. Recently, demand of poly-lactate, a biomass plastic, is increasing, and demand of lactic acid is also increasing as a raw material of poly-lactate. Then the lactic acid with almost 100% of the optical purity is strongly requested. Generally, lactic acid is produced by chemical syntheses or by microbial fermentations.
Biomass Resources for Lactic Acid Fermentation
Glucose is a major substrate for lactic acid fermentation, which is usually obtained by hydrolysis of starch. Starch is now obtained from crops. However, we sometimes worry about competition between energy or materials and food, as claimed in the ethanol production from biomass resources. Thus soft cellulosic biomass like rice husk which has been currently not used is expected for biomass resources.
Biomass Based Chemicals
Chemicals from Biomass as Feedstock
The world has a wide variety of biofeedstocks that can be used for the production of chemicals. Biomass includes plant materials such as trees, grasses, agricultural crops, and animal manure. Cellulose, hemicellulose, and lignin are components of woody biomass, grasses, stalks, stover, etc. Starch and cellulose are both polymeric forms of hexose, a six-carbon sugar. Hemicellulose is a polymer of pentose. Lignin is composed of phenolic polymers, and oils are triglycerides. Starch is primarily found in corn, sweet sorghum, and other crops.
There are primarily two different platforms of conversion technologies for converting biomass feedstock to chemicals, the biochemical and the thermo-chemical. The biochemical platform focuses on the conversion of carbohydrates (starch, cellulose, and hemicellulose) to sugars using bio-catalysts like enzymes and microorganisms and chemical catalysts. These sugars are then suitable for fermentation into a wide array of chemicals. Apart from this, chemical catalysis used in transesterification reaction can produce fatty acid methyl and ethyl esters and glycerol.
Biomass Conversion Chemicals
Biomass can be converted to chemicals. The Biomass Research and Development Act of 2000 had set up a Biomass R&D Technical Advisory Committee, which has fixed a goal of supplying the United States with 25% of its chemicals from biomass by the year 2030. Bulk chemicals can be defined as those costing $1.00-$4.00 per kg and produced worldwide in volumes of more than 1 million MT/year. The production cost of these chemicals can be reduced by 30% when petrochemical processes are replaced by bio-based processes. Some of these chemicals are:
Methane from natural gas is an important industrial raw material for the production of acetylene, synthesis gas, methanol, carbon black, etc. Natural gas is a nonrenewable source, and ways to produce methane from biomass are needed.
Methanol is a liquid transportation fuel that can be produced from fossil or renewable domestic resources. Methanol is the simplest form of all alcohols -CH3OH -also known as "wood alcohol." Methanol produced from biomass are promising carbon neutral fuel. Methanol can be produced from any carbon-based source. These would include: natural gas, coal, municipal wastes, landfill gas, wood wastes and seaweed. It is well suited for use in Fuel Cell Vehicles (FCVs) which are expected to reach high efficiencies, about a factor 2-3 better than current Internal Combustion Engine Vehicles (ICEVs). In addition Methanol is quiet and clean, emitting none of the air pollutants SOx, NOx, VOS or dust. When methanol is derived from sustainably grown biomass, the overall energy chain can be greenhouse gas neutral.
The thermochemical production of methanol from biomass involves the production of a synthesis gas rich in hydrogen and carbon monoxide which is then catalytically converted into methanol. Production of the synthesis gas is accomplished by thermal gasification.
USES AND APPLICATIONS OF METHANOL
Waste Water Treatment
When wastewater is collected in a treatment facility, it generally contains high levels of ammonia. Through a bacterial degradation process, this ammonia is converted into nitrate. In a subsequent process called denitrification, the nitrate is removed through a combination of chemical treatment and bacterial degradation.
Methanol fuel cell systems convert chemical energy directly into electricity with greater efficiency than combustion-based power systems, thereby reducing associated greenhouse gas and urban smog forming emissions.
Safety in Automotive Fuels
Pure methanol has been used in open wheel auto racing since the mid- 1960s. Unlike petroleum fires, methanol fires can be extinguished with plain water. A methanol-based fire burns invisibly, unlike gasoline, which burns with a visible flame.
Ethanol is a widely used biofuel. In addition to being renewable, ethanol has a major advantage in that it can be easily blended with gasoline. In some cases ethanol is first converted to its ether form, obtained in reaction with refinery isobutene. When small amounts of ethanol are added to gasoline, there are many advantages, in particular the reduction of carbon monoxide and other toxic pollution from exhaust gases of vehicles. Because ethanol is made from crops that absorb carbon dioxide and give off oxygen, it helps reduce greenhouse gas emissions.
Properties of Ethanol
Ethanol is a volatile, colorless liquid that has a slight odor. It burns with a smokeless blue flame that is not always visible in normal light. Ethanol is a versatile solvent, miscible with water and with many organic solvents, including gacetic acid, acetone, benzene, carbon tetrachloride, chloroform, diethyl ether, ethylene glycol, glycerol, nitromethane, pyridine, and toluene. It is also miscible with light aliphatic hydrocarbons, such as pentane and hexane, and with aliphatic chlorides such as trichloroethane and tetrachloroethylene.
Ethylene is a colorless flammable gas with a faint "sweet and musky" odor when pure. This hydrocarbon has four hydrogen atoms bound to a pair of carbon atoms that are connected by a double bond. All six atoms that comprise ethylene are coplanar all of the ethylene produced being used as a feedstock in the manufacture of plastics and chemicals.
Production of Glycerol
Glycerol may also be produced by various routes from propylene. Theepichlorohydrin process is the most important; it involves the chlorination of propylene to give allyl chloride, which is oxidized with hypochlorite to dichlorohydrins, which reacts with a strong base to give epichlorohydrin. Epichlorohydrin is then hydrolyzed to give glycerol. Chlorine-free processes from propylene include the synthesis of glycerol from acrolein and propylene oxide.
Lactic acid is a commonly occurring organic acid, which is valuable due to its wide use in food and food-related industries, and its potential for the production of biodegradable and biocompatible polylactate polymers. Lactic acid can be produced from biomass using various fungal species of the Rhizopus genus, which have advantages compared to the bacteria, including their amylolytic characteristics, low nutrient requirements, and valuable fermentation fungal biomass byproduct.
Propylene glycol is industrially produced from the reaction of propylene oxide and water. Capacities of propylene glycol plants range from 15,000 to 250,000 ton/year. It is mainly used (around 40%) for the manufacture of polyester resins that are used in surface coatings and glass-fiber-reinforced resins. A growing market for propylene glycol is in the manufacture of nonionic detergents (around 7%) used in petroleum, sugar, and paper refining and also in the preparation of toiletries, antibiotics, etc. Around 5% of propylene glycol manufactured is used in antifreeze.
1,3-Propanediol is a derivative that can be used as a diol component in the plastic polytrimethyleneterephthalate (PTT), a new polymer comparable to nylon. Two methods to produce 1,3-propanediol exist, one from glycerol by bacterial treatment and another from glucose by mixed culture of genetically engineered microorganisms.
Acetone is the organic compound with the formula (CH3)2CO. It is a colorless, volatile, flammable liquid, and is the simplest ketone. Acetone is miscible with water and serves as an important solvent in its own right, typically for cleaning purposes in the laboratory.
Biobutanol, which is also sometimes called biogasoline, is an alcohol that is produced from biomass feedstocks. Butanol is a 4-carbon alcohol that is currently used as an industrial solvent in many wood finishing products. Biobutanol can be utilized in internal combustion engines as both a gasoline additive and or a fuel blend with gasoline.
Butanol Fermentation Process
Biobutanol is made via fermentation of biomasses from substrates ranging from corn grain, corn stovers and other feedstocks. Microbes, specifically of the Clostridium acetobutylicum, are introduced to the sugars produced from the biomass. These sugars are broken down into various alcohols, which include ethanol and butanol. Unfortunately, a rise in alcohol concentration causes the butanol to be toxic to the microorganisms, killing them off after a period of time.
Levulinic acid (LA) was first synthesized from fructose with hydrochloric acid by the Dutch scientist G.J. Mulder in 1840. It is also known as 4-oxopentanoic acid or y-ketovaleric acid. The first commercial-scale production of LA in an autoclave was started in the United States by A.E. Stanley Decatur, Illinois. LA has been used in food, fragrance, and specialty chemicals.
Itaconic acid is a five-carbon dicarboxylic acid, also known as methyl succinic acid, and has the potential to be a key building block for deriving both commodity and specialty chemicals. The basic chemistry of itaconic acid is similar to that of the petrochemicals derived maleic acid/ anhydride. The_ chemistry of itaconic acid to the derivatives is shown in Figure 14. Itaconic acid is currently produced via fungal fermentation and is used primarily as a specialty monomer.
Xylitol is a chemical used as a diabetic sweetener. Xylitol is naturally found in low concentrations in the fibers of many fruits and vegetables, and can be extracted from various berries, oats, and mushrooms, as well as fibrous material such as corn husks and sugar cane bagasse, and birch.
Xylitol is produced by hydrogenation of xylose, which converts the sugar (an aldehyde) into a primary alcohol. It can also be extracted from natural sources, and is often harvested by tapping birch trees to produce birch sap. Another method of producing xylitol is through microbial processes, including fermentative and biocatalytic processes in bacteria, fungi, and yeast cells, that take advantage of the xylose-intermediate fermentations to produce high yield of xylitol.
Sorbitol, also known as glucitol, is a sugar alcohol, which the human body metabolizes slowly. It can be obtained by reduction of glucose, changing the aldehyde group to a hydroxyl group. Most sorbitol is made from corn syrup, but it is also found in apples, pears, peaches, and prunes. It is synthesized by sorbitol-6-phosphate dehydrogenase, and converted to fructose by succinate dehydrogenase and sorbitol dehydrogenase. Sorbitol is produced by the Hydrogenation of glucose.
Biofuel Production from Biomass Crops
A discussion focusing on biomass production sustainability is difficult because the definition itself of sustainability is still being debated. Its dynamic character has been acknowledged: "Sustainability is a moving target" wrote Hoag and Skold and later the Project Group 'Sustainable production of biomass' confirmed: "Sustainability is a continuous process of improvement and adjustment".
Pretreatment of Lignocellulosic Biomass to Biofuel
Most advanced biofuels production technologies are focused towards converting lignocellulosic biomass into transportation fuels. Lignocellulosic biomass, or lignocellulose, consists of plant biomass that is comprised of cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are natural polymers of carbohydrates and are thereby potential sources of sugars for fermentation. Lignin however is not fermentable under anaerobic conditions.
The inhibitors that are present in lignocellulose are liberated relatively easy during the pretreatment step. For instance, under relatively mild conditions, acetylated hemicellulose is hydrolyzed and beside monosaccharides, the organic acid acetic acid is liberated. Inhibitors that are produced under too extreme pretreatment conditions generally consist of degradation compounds of sugars.
BIOETHANOL FROM SUGAR BEET
Sugar beet has been commercially grown as a source of table sugar (sucrose) since beginning of the 19th century, initially in Europe. It was introduced as a European replacement for sugar cane which is grown in tropical climate.' Today sugar beet is an important crop mainly in the industrialized countries of the northern hemisphere - also in Asia and North America - where the climate is temperate. It is usually planted in the spring and harvested in the autumn but in warmer climates it is a winter crop, planted in the autumn and harvested in the spring. Farmers can choose between numerous sugar beet varieties suitable for a range of climatic conditions, soil types and local risks including pest and disease. The farming methods are very well developed and all field operations are mechanized.
BIOLOGICAL HYDROGEN FROM SWEET SORGHUM
The hydrogen production is discussed. Sweet sorghum (Sorghum bicolor) has a great potential as energy crop and becomes even more interesting when its production can be oriented towards the sustainable production of clean fuels, such as hydrogen. It belongs to the C4 family, it has a high photosynthetic efficiency, and is a heat- and drought-tolerant crop. One of the most important inherent characteristics of sweet sorghum is its high yields of 20-30 ton dry weight per ha. Currently about 10% of sweet sorghum production in the USA is used for ethanol production. In the EU there is currently no large commercial production of biofuels from sweet sorghum.
Biomass gasification is the conversion of solid fuels like wood and agricultural residues into a combustible gas mixture. Gasification is the controlled partial oxidation of a carbonaceous material, and it is achieved by supplying less oxygen than the stoichiometric requirement for complete combustion. A central process between combustion (thermal degradation with excess oxygen) and pyrolysis, it proceeds at temperatures ranging between 600 and 1500°C. Depending upon the process type and operating conditions, low- or medium-value producer gas is created.
In addition, it includes the ability to house a wide variety of gaseous, liquid, and solid feedstocks. Conventional fuels such as coal and oil, as well as low- or negative-value materials and wastes such as petroleum coke, heavy refinery residuals, secondary oil-bearing refinery materials, municipal sewage sludge, and chlorinated hydrocarbon byproducts have all been used successfully in gasification operations. Biomass and crop residues also have been gasified successfully. Gasification of these materials has many potential benefits over conventional options such as combustion or disposal by incineration.
Moving Bed (Fixed Bed)
Moving- bed gasifiers were the first type of gasifier used. They originated in the early 1800s. At that time biomass was the primary source of energy. In a moving-bed gasifier, a bed of solid fuel moves slowly downwards. A characteristic of this type of gasifier is the formation of four zones (drying, pyrolysis, oxidation, and reduction), many manufacturers of biomass gasifiers produced moving- bed gasifiers for transport applications.
This type of gasifier consists of a fixed bed of carbon-rich fuel which the oxidising medium flows through downwards. The gas produced is at a high temperature and the thermal efficiency is also relatively high. The downdraft gasifier features a co-current flow of gases and solids through a descending packed bed which is supported across a constriction known as a throat where most of the gasification reactions occur.
This gasifier is similar to the down-draft type except that air, oxygen or steam flow through the bed upwards. The downward moving biomass is first dried by the upflowing hot product gas. After drying, the solid fuel is pyrolysed giving char which continues to move down to be gasified, and pyrolysis vapours which are carried upward by the upflowing hot product gas. The volume percentage of methane in the producer gas is significant, which facilitates methanation for Synthetic Natural Gas (SNG) production.
Fluidized Bed Gasifier
Fluid bed gasifiers are a more recent development that take advantage of the excellent mixing characteristics and high reaction rates of this method of gas-solid contacting. Fluidised bed reactors are the only gasifiers with isothermal bed operation. In the fluidized bed gasifier, the feed is introduced at the bottom, which is fluidized using air, nitrogen and/or steam and the product gas then moves upward.
Bubbling Fluidized Bed
In case of the bubbling fluidized bed gasifier, the flow rate of the fluidizing agent is comparable to the minimum fluidizing velocity. In bubbling fluidized beds, granular material is fed into a vessel through which an upward flow of gas passes at a flow rate where the pressure drop across the particles is sufficient to support their weight (incipient fluidization).
Circulating Fluidized Bed Gasifier
The fluidising velocity in the circulating fluid bed is high enough to entrain large amounts of solids with the product gas. Circulating fluidized beds have higher flow rates of the fluidizing agents which move most of the solid and ungasified particles to an attached cyclone separator, from which the solids are re-circulated to the gasifier bed.
Char Gasification Reactions
The gasification step involves chemical reactions among the hydrocarbons in fuel, steam, carbon dioxide, oxygen, and hydrogen in the reactor, as well as chemical reactions among the evolved gases. Of these, char gasification is the most important. The biomass char produced through pyrolysis of biomass is not necessarily pure carbon. It contains a certain amount of hydrocarbon comprising hydrogen and oxygen.
Reuse of Bio-Genie Iron Oxides and Woody Biomass Fly Ash in Cement Based Materials and Agricultural Areas
Phosphorus (P) is an essential element in plant nutrients, because many biochemical processes such as photosynthesis, respiration, and energy transfer depend on inorganic P or its organic derivatives. However, P is difficult for plants to obtain from the rhizosphere and P deficiency is one of the major limitations on crop production. This is because soluble P in soil, the primary P source for plants, is extremely low concentration and significant portions of P in the soil are various organic complexes and unavailable. On a worldwide scale, land covering 5.7 billion hectares is estimated to be deficient in P for optimal crop production. Since the soluble P in the soil is easily taken up by plants and microorganisms, continuous application of P fertilizer is necessary for crop production.
A new method for the recovery of P from natural water bodies using Fe-oxidizing bacteria and woody biomass as a carrier has been proposed. A woody carrier is immersed in water in which Fe-oxidizing bacteria are abundant and then removed several weeks later. In this chapter, this method was tested in an agricultural area, dominated by rice paddy fields, located in the eastern part of Shimane Prefecture, Japan. As the woody carrier, sawdust from the Japanese cedar and Japanese cypress were used. Since the accumulation of biogenic Fe oxides was observed throughout the year at several locations, the water quality at these points was monitored.
Materials and Methods
The WBFA used in this study came from the electrostatic precipitators of an Italian chipped-wood burning plant. The sample of WBFA "as received" contained less than 1% (w/w) moisture and about 30% (w/w) of particles with sizes above 150 /am. This fly ash was first sieved with a 150-|um sieve, and the retained portion was ground to fineness below 150 um and then mixed with the remaining ash portion.
Preparation of Hardened Cement Paste Specimens
A sample of WBFA was dry-mixed with Portland cement with an ash-to-cement ratio of 30:70 by mass, and the resulting blended cement (binder) was used for environmental compatibility studies.
Characterization of WBFA
As shown in Table 1 the WBFA was characterized by a significant presence of heavy metals of particular environmental concern, such as cadmium, chromium, copper, lead, and zinc. Zinc was the predominant heavy metal whereas cadmium was the heavy metal with the lowest concentration (9 mg/kg).
As far as the use of washed WBFA in cement-based materials is concerned, it is likely that a washing treatment of fly ash with a liquid-to-solid ratio above 10 L/kg could reduce the chloride content below the 0.1% limit. In that case, the wastewater resulting from the washing of fly ash could contain chloride and sulfate concentrations below the limits established for wastewater disposal. However, this wastewater should be treated for pH correction and, probably, for heavy metal removal. In this regard, the pH of WBFA, defined as the pH of the aqueous suspension of fly ash with an L/ S ratio of 10 L/kg, was 12.9. This high pH, which is compatible with the use of WBFA in cement-based materials, was attributable to the release of alkalies and calcium oxide from fly ash.
Leaching Behavior of Blended Cement Pastes
Table 4 gives the results of the monolith leaching test on cubic specimens of cement pastes (water-to-binder weight ratio 0.50) made with blended cement [70% (w/w) Portland cement and 30% (w/w) WBFA]. In this table, the concentrations of selected heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) in each of eight leachates are reported as the average values of three replicate leaching tests.
For copper, lead, and zinc, the leaching rates dramatically reduced after the first leachant renewal (the first two renewals for Zn), thus revealing the existence of two different mechanisms governing the leaching process of such heavy metals. At early leaching times (first two renewals), the controlling mechanism appeared to be the release of heavy metal from the outer surface of the monolith specimen by dissolution into the leaching solution or by wash-off, or both. At longer leaching times, the release was probably controlled by diffusion, and the heavy metal ions had to migrate within the pore liquid of the cementitious matrix of the test specimen prior to reaching the liquid bulk. As a result, this leaching phase was characterized by a much lower rate as compared with the initial leaching phase. In the case of cadmium, chromium, and nickel leaching, no dissolution/wash-off phenomenon was detected during the early release phase.
Biofuel Briquettes from Biomass
Biomass briquettes are a biofuel substitute to coal and charcoal. Briquettes are mostly used in the developing world, where cooking fuels are not as easily available. There has been a move to the use of briquettes in the developed world, where they are used to heat industrial boilers in order to produce electricity from steam. The briquettes are cofired with coal in order to create the heat supplied to the boiler.
Briquetting is a way to convert loose biomass residues, such as sawdust, straw or rice husk, into high density solid blocks that can be used as a fuel. Biomass briquettes (including pellets, which are very small briquettes) replace fossil fuels or wood for cooking and industrial processes. They are cleaner and easier to handle, and cut greenhouse gas emissions.
Owing to the high pressure briquetting (1-3 t/cnf), the coal particles and the fibrous biomass material in the bio-briquette strongly intertwine and adhere to each other. As a result, they do not separate from each other during combustion, and the low ignition temperature biomass simultaneously combusts with the coal. The combined combustion gives favorable ignition and fuel properties, emits little dust and soot, and generates sandy combustion ash, leaving no clinker. In particular, the bio-briquettes produced with low grade coal containing large amounts of ash and having low calorific value combust cleanly, thus the bio-briquette technology is an effective technology to produce clean fuel for household heaters and small industrial boilers.
Properties of Biomass Briquettes
Biomass briquettes is an ideal and best ready substitute to coal, fire wood, lignite etc. and easily replaces these conventional fuels for heating, steam generation etc. The solid biomass offers numerous advantages other than consistent quality and economical prices.
Pre-processing of Biomass Residues
Before briquetting, biomass material often needs to be broken down in size by processing. Depending on the residue, in a rural setting this might involve chopping, crushing and hammering the material by hand or using hammer mills, hand cranked devices or a pestle and mortar. This process can potentially consume a large amount of energy, and therefore the most suitable method for the individual situation needs careful consideration.
Bio-briquette Manufacturing Process
In the process of bio-briquette production, The raw materials, coal and biomass, are pulverized to a size of approximately 3 mm or smaller, and then dried. The dried mixture is further blended with a desulfurizing agent, Ca(OH)2. The mixture is formed by compression molding in a high-pressure briquetting machine. Powder coal may be utilized without being pulverized. A small amount of binder may be added to some coal ranks. The production process does not involve high temperatures, and is centered on a dry, high-pressure briquetting machine. The process has a simple flow, which is safe and which does not require skilled operating technique.
The briquetting plant can be operated in two ways. In the first case while pre-processing the raw material, the temperature of the feed material is not considered. In fact, the temperature is not at all critical for the production of briquettes. But if we take into consideration the power consumption, the wear behavior of the screw and the temperature of the die, then the temperature of the raw material at the time of feeding to the screw extruder plays a significant role.
Biomass Based Activated Carbon
As a result of environmental requirements in many countries and new areas of application the demand on activated carbon is still growing. Due to the unavailability of the main basic materials like hard coal, wood or coconut shells in many countries other biomass matters were tested for their appropriateness of activated carbon production.
Biomass Pyrolysis and Char Activation
The experiments on pyrolysis and activation of waste biomass matters were run in lab-scale facilities. The advantage of these small-scale equipments is that the experiments could be run very quickly without long heat-up times and with one operating person. Only small amounts of biomass were needed and the operation conditions could be changed quite easily. Not many efforts had to be made in gas cleaning procedure due to the low exhaust gas flow. The screening test to figure out the optimal char residence time in the activation facility was a one or two day work with an output of 6 - 10 data points. The description of the lab-scale experiments is given in detail for both, pyrolysis and activation activities.
Rotary Kiln Reactor for Char Activation
The advantage of the lab-scale pyrolysis and activation facilities is the easy way of handling and the short heat-up times. Many experiments can be made in a short time interval. Unfortunately the possibility of treating larger amounts of biomass is not given. Likewise these facilities do not serve for an up-scale to an industrial production process neither for biomass pyrolysis nor for char activation. For this a new concept of an activated carbon production process had to be worked out.
For the pyrolysis step an already existing screw driven rotary kiln reactor was used to transfer the lab-scale experiments into a continuous production process. Unfortunately the pyrolysis temperature was limited to 500°C within this reactor. Tests were run with wheat straw pellets, olive stones, coconut press residues, rape seeds and spent grain. The chars were activated in the lab-scale facility. No influence of the chars from lab-scale experiments and rotary kiln pyrolysis was found after the activation step.
Basic Operational Parameters of BAC Process
To design a BAC system, it is necessary to comprehend the characteristics of water quality, water amount and some certain index of water treatment. First of all, the experiments on the adsorption performance and biodegradability of the waste water are indispensable. Then, according to the result of static adsorption isotherms experiment on the raw water, the appropriate kind of the activated carbon can be chosen, and on the basis of dynamic adsorption isotherms experiment, the basic parameters can be determined. Ultimately, according to the process scale and condition of the field, BAC adsorption devices and its structure as well as supplementary equipment can be determined.
Improvement of Biochemical Properties of Organics by Ozonation
During the process of ozonation, complex chemical reactions occurred between ozone and organics. Pre-ozonation can change the biodegradability of organics in water, so generally BDOC is used as an index to analyze the water after ozonation.
Improvement of Ozonation on Biodegradability of Organic Matters
Relevant researches indicate that ozonation can change the molecule weight distribution, structures and the biodegradability of the organics in water. To thoroughly understand the role organics degradation and ozonation played in the whole process, degradation of the organics without dosage of ozone shall be taken for comparison.
In the current time, the importance of alternative energy source has become even more necessary not only due to the continuous depletion of limited fossil fuel stock but also for the safe and better environment, with an inevitable depletion of the world's energy supply, there has been an increasing worldwide interest in alternative sources of energy. Over millions of years the solar energy was accumulated in form of fossil fuels such as coal, petroleum, natural gas. The other carriers of energy which arose from their processing, such as petrol from petroleum, coke andgas from coal, are being adjusted to civilisation demands. The world is presently confronted with the twin crises of fossil fuel depletion and environmental degradation.
Biofuels are liquid or gaseous fuels used in transport which are produced from biomass - biodegradable fractions of products, wastes and remains from agricultural production, forestry as well as biodegradable fractions of municipal and industrial wastes. These alternative energy resources are highly environment-friendly but need to be evaluated on case-to-case basis for their advantages, disadvantages and specific applications. Some of these fuels can be used directly, while some others need to be formulated to bring the relevant properties closer to conventional fuels. Environmental concerns have increased significantly in the world over the past decade. Excessive use of fossil fuels has led to global environmental degradation effects such as greenhouse effect, acid rain, ozone depletion and climate change.
IMPACTS OF WOODY BIOMASS HARVEST
Ecological impacts on soils, wildlife, fire regimes, and water quality of using biomass for bioenergy depends on existing forest conditions and the timing, methods, and amount of biomass removed over a specific period. Although options being considered in Cook County and Ely demand relatively small volumes of biomass, they could alter forestry practices in procurement areas. Positive benefits of biomass harvest for local forests and communities are numerous.
ENVIRONMENTAL IMPACTS OF BIOFUELS
Although biofuel production remains small in the context of total energy demand, it is significant in relation to current levels of agricultural production. The potential environmental and social implications of its continued growth must be recognized. For example, reduced greenhouse gas emissions are among the explicit goals of some policy measures to support biofuel production.
Unintended negative impacts on land, water and biodiversity count among the side-effects of agricultural production in general, but they are of particular concern with respect to biofuels. The extent of such impacts depends on how biofuel feedstocks are produced and processed, the scale of production and, in particular, how they influence land-use change, intensification and international trade.
Biodiesel - whether pure or blended- results in lower emissions of most pollutants relative to diesel, including significantly lower emission of particulates, sulphur, hydrocarbons, CO, toxins. Emissions vary with engine design, condition of vehicles and quality of fuel. In biodiesel- diesel blends, potential reductions of most pollutants increase almost linearly as the share of biodiesel increases, with the exception of NOx emission.
Overall animal based biodiesel did better in the study than plant based biodiesel with regard to reducing emission of NOx, CO and particulates. On average, the EPA determined that B20 (made with soybeans) increase NOx emission the least, followed by rapeseed biodiesel and that soybean based biodiesel; the same relationship held true for CO reduction, as well. Reductions in particulate emissions were also greatest for animal based biodiesel.