Tag Archives: biofuels

Biofuels from Syngas

  By Salman Zafar | May 15, 2012 - 8:13 am | Biofuels, Biomass Energy
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An attractive approach to converting biomass into liquid or gaseous fuels is direct gasification, followed by conversion of the gas to final fuel. Ethanol can be produced this way, but other fuels can be produced more easily and potentially at lower cost, though none of the approaches is currently inexpensive.

The choice of which process to use is influenced by the fact that lignin cannot easily be converted into a gas through biochemical conversion. Lignin can, however, be gasified through a heat process. The lignin components of plants can range from near 0% to 35%. For those plants at the lower end of this range, the chemical conversion approach is better suited. For plants that have more lignin, the heat-dominated approach is more effective.

Once the gasification of biomass is complete, the resulting gases can be used in a variety of ways to produce liquid fuels discussed, in brief, below

Fischer-Tropsch (F-T) fuels

The Fischer-Tropsch process converts “syngas” (mainly carbon monoxide and hydrogen) into diesel fuel and naphtha (basic gasoline) by building polymer chains out of these basic building blocks. Typically a variety of co-products (various chemicals) are also produced.  Figure 2.1 shows the production of diesel fuel from bio-syngas by Fisher-Tropsch synthesis (FTS).

The Fisher-Tropsch process is an established technology and has been proven on a large scale but adoption has been limited by high capital and O&M costs. According to Choren Industries, a German based developer of the technology, it takes 5 tons of biomass to produce 1 ton of biodiesel, and 1 hectare generates 4 tons of biodiesel.

Methanol

Syngas can also be converted into methanol through dehydration or other techniques, and in fact methanol is an intermediate product of the F-T process (and is therefore cheaper to produce than F-T gasoline and diesel). Methanol is somewhat out of favour as a transportation fuel due to its relatively low energy content and high toxicity, but might be a preferred fuel if fuel cell vehicles are developed with on-board reforming of hydrogen.

Dimethyl ether

DME also can be produced from syngas, in a manner similar to methanol. It is a promising fuel for diesel engines, due to its good combustion and emissions properties. However, like LPG, it requires special fuel handling and storage equipment and some modifications of diesel engines, and is still at an experimental phase. If diesel vehicles were designed and produced to run on DME, they would become inherently very low pollutant emitting vehicles; with DME produced from biomass, they would also become very low GHG vehicles.

A Primer on Biofuels

  By Salman Zafar | May 11, 2012 - 7:55 am | Biofuels, Biomass Energy
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The term ‘Biofuel’ refers to liquid or gaseous fuels for the transport sector that are predominantly produced from biomass. A variety of fuels can be produced from biomass resources including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The biomass resource base for biofuel production is composed of a wide variety of forestry and agricultural resources, industrial processing residues, and municipal solid and urban wood residues.

The agricultural resources include grains used for biofuels production, animal manures and residues, and crop residues derived primarily from corn and small grains (e.g., wheat straw). A variety of regionally significant crops, such as cotton, sugarcane, rice, and fruit and nut orchards can also be a source of crop residues. The forest resources include residues produced during the harvesting of forest products, fuelwood extracted from forestlands, residues generated at primary forest product processing mills, and forest resources that could become available through initiatives to reduce fire hazards and improve forest health. Municipal and urban wood residues are widely available and include a variety of materials — yard and tree trimmings, land-clearing wood residues, wooden pallets, organic wastes, packaging materials, and construction and demolition debris.

Globally, biofuels are most commonly used to power vehicles, heat homes, and for cooking. Biofuel industries are expanding in Europe, Asia and the Americas. Biofuels are generally considered as offering many priorities, including sustainability, reduction of greenhouse gas emissions, regional development, social structure and agriculture, and security of supply.

First-generation biofuels are made from sugar, starch, vegetable oil, or animal fats using conventional technology. The basic feedstocks for the production of first-generation biofuels come from agriculture and food processing. The most common first-generation biofuels are:

  • Biodiesel: extraction with or without esterification of vegetable oils from seeds of plants like soybean, oil palm, oilseed rape and sunflower or residues including animal fats derived from rendering applied as fuel in diesel engines
  • Bioethanol: fermentation of simple sugars from sugar crops like sugarcane or from starch crops like maize and wheat applied as fuel in petrol engines
  • Bio-oil: thermo-chemical conversion of biomass. A process still in the development phase
  • Biogas: anaerobic fermentation or organic waste, animal manures, crop residues an energy crops applied as fuel in engines suitable for compressed natural gas.

First-generation biofuels can be used in low-percentage blends with conventional fuels in most vehicles and can be distributed through existing infrastructure. Some diesel vehicles can run on 100 % biodiesel, and ‘flex-fuel’ vehicles are already available in many countries around the world.

Second-generation biofuels are derived from non-food feedstock including lignocellulosic biomass like crop residues or wood. Two transformative technologies are under development.

  • Biochemical: modification of the bio-ethanol fermentation process including a pre-treatment procedure
  • Thermochemical: modification of the bio-oil process to produce syngas and methanol, Fisher-Tropsch diesel or dimethyl ether (DME).

Advanced conversion technologies are needed for a second generation of biofuels. The second generation technologies use a wider range of biomass resources – agriculture, forestry and waste materials. One of the most promising second-generation biofuel technologies – ligno-cellulosic processing (e. g. from forest materials) – is already well advanced. Pilot plants have been established in the EU, in Denmark, Spain and Sweden.

Third-generation biofuels may include production of bio-based hydrogen for use in fuel cell vehicles, e.g. Algae fuel, also called oilgae. Algae are low-input, high-yield feedstocks to produce biofuels.

Biomass Resources from Sugar Industry

  By Salman Zafar | May 9, 2012 - 7:03 am | Agricultural Residues, Biomass Energy
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Sugarcane is one of the most promising agricultural sources of biomass energy in the world. It is the most appropriate agricultural energy crop in most Cane producing countries due to its resistance to cyclonic winds, drought, pests and diseases, and its geographically widespread cultivation. Due to its high energy-to-volume ratio, it is considered one of nature’s most effective storage devices for solar energy and the most economically significant energy crop. The climatic and physiological factors that limit its cultivation to tropical and sub-tropical regions have resulted in its concentration in developing countries, and this, in turn, gives these countries a particular role in the world’s transition to sustainable use of natural resources.

 According to the International Sugar Organization (ISO), Sugarcane is a highly efficient converter of solar energy, and has the highest energy-to-volume ratio among energy crops. Indeed, it gives the highest annual yield of biomass of all species. Roughly, 1 ton of Sugarcane biomass-based on Bagasse, foliage and ethanol output – has an energy content equivalent to one barrel of crude oil.   Sugarcane produces mainly two types of biomass, Cane Trash and Bagasse. Cane Trash is the field residue remaining after harvesting the Cane stalk and Bagasse is the milling by-product which remains after extracting the Sugar from the stalk. The potential energy value of these residues has traditionally been ignored by policy-makers and masses in developing countries. However, with rising fossil fuel prices and dwindling firewood supplies, this material is increasingly viewed as a valuable Renewable Energy resource.

Sugar mills have been using Bagasse to generate steam and electricity for internal plant requirements while Cane Trash remains underutilized to a great extent. Cane Trash and Bagasse are produced during the harvesting and milling process of Sugar Cane which normally lasts 6 to 7 months.

Around the world, a portion of the Cane Trash is collected for sale to feed mills, while freshly cut green tops are sometimes collected for farm animals. In most cases, however, the residues are burned or left in the fields to decompose. Cane Trash, consisting of Sugarcane tops and leaves can potentially be converted into around 1kWh/kg, but is mostly burned in the field due to its bulkiness and its related high cost for collection/transportation.

On the other hand, Bagasse has been traditionally used as a fuel in the Sugar mill itself, to produce steam for the process and electricity for its own use. In general, for every ton of Sugarcane processed in the mill, around 190 kg Bagasse is produced. Low pressure boilers and low efficiency steam turbines are commonly used in developing countries. It would be a good business proposition to upgrade the present cogeneration systems to highly efficient, high pressure systems with higher capacities to ensure utilization of surplus Bagasse.

Analysis of India’s Biodiesel Program

  By Salman Zafar | April 21, 2012 - 3:29 am | Biofuels, India
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The Government of India approved the National Policy on Biofuels in December 2009. The biofuel policy encouraged the use of renewable energy resources as alternate fuels to supplement transport fuels (petrol and diesel for vehicles) and proposed a target of 20 percent biofuel blending (both bio-diesel and bio-ethanol) by 2017. The government launched the National Bio-diesel Mission (NBM) identifying Jatropha curcas as the most suitable tree-borne oilseed for bio-diesel production. The Planning Commission of India had set an ambitious target covering 11.2 to 13.4 million hectares of land under Jatropha cultivation by the end of the 11th Five-Year Plan. The central government and several state governments are providing fiscal incentives for supporting plantations of Jatropha and other non-edible oilseeds. Several public institutions, state biofuel boards, state agricultural universities and cooperative sectors are also supporting the biofuel mission in different capacities.

The biodiesel industry in India is still in infancy despite the fact that demand for diesel is five times higher than that for petrol. The government’s ambitious plan of producing sufficient biodiesel by 2011-2012 to meet its mandate of 20 percent diesel blending is unrealized due to a lack of sufficient Jatropha seeds to produce biodiesel. Currently, Jatropha occupies only around 0.5 million hectares of low-quality wastelands across the country, of which 65-70 percent are new plantations of less than three years. Several corporations, petroleum companies and private companies have entered into a memorandum of understanding with state governments to establish and promote Jatropha plantations on government-owned wastelands or contract farming with small and medium farmers. However, only a few states have been able to actively promote Jatropha plantations despite government incentives.

The ambitious plan of producing sufficient biodiesel by 2011 – 2012 to meet 20 percent blending mandate is unrealistic. The unavailability of sufficient feedstock and lack of R&D to evolve high-yielding drought tolerant Jatropha seeds have been major stumbling blocks. In addition, smaller land holdings, ownership issues with government or community-owned wastelands, lackluster progress by state governments and negligible commercial production of biodiesel have hampered the efforts and investments made by both private and public sector companies.

The unavailability of sufficient feedstock and lack of R&D to evolve high-yielding drought tolerant Jatropha seeds have been major stumbling blocks. In addition, smaller land holdings, ownership issues with government or community-owned wastelands, lackluster progress by state governments and negligible commercial production of biodiesel have hampered the efforts and investments made by both private and public sector companies.

Another major obstacle in implementing the biodiesel programme has been the difficulty in initiating large-scale cultivation of Jatropha. The Jatropha production program was started without any planned varietal improvement program, and use of low-yielding cultivars made things difficult for smallholders. The higher gestation period of biodiesel crops (3–5 years for Jatropha and 6–8 years for Pongamia) results in a longer payback period and creates additional problems for farmers where state support is not readily available. The Jatropha seed distribution channels are currently underdeveloped as sufficient numbers of processing industries are not operating. There are no specific markets for Jatropha seed supply and hence the middlemen play a major role in taking the seeds to the processing centres and this inflates the marketing margin.

 Biodiesel distribution channels are virtually non-existent as most of the biofuel produced is used either by the producing companies for self-use or by certain transport companies on a trial basis. Further, the cost of biodiesel depends substantially on the cost of seeds and the economy of scale at which the processing plant is operating. The lack of assured supplies of feedstock supply has hampered efforts by the private sector to set up biodiesel plants in India. As of now, only two firms, Naturol Bioenergy Limited and Southern Online Biotechnologies, have embarked on commercial-scale biodiesel projects, both in the southern state of Andhra Pradesh. In the absence of seed collection and oil extraction infrastructure, it becomes difficult to persuade entrepreneurs to install trans-esterification plants.

A Glance at Biomass Resources

  By Salman Zafar | March 5, 2012 - 9:41 am | Agricultural Residues, biogas, Biomass Energy, Energy-from-Waste, Waste-to-energy
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Biomass is the material derived from plants that use sunlight to grow which include plant and animal material such as wood from forests, material left over from agricultural and forestry processes, and organic industrial, human and animal wastes. The energy contained in biomass originally came from the sun. Through photosynthesis carbon dioxide in the air is transformed into other carbon containing molecules (e.g. sugars, starches and cellulose) in plants. The chemical energy that is stored in plants and animals (animals eat plants or other animals) or in their waste is called bio-energy. Biomass comes from a variety of sources which include:

  • Wood from natural forests and woodlands
  • Forestry plantations
  • Forestry residues
  • Agricultural residues such as straw, stover, cane trash and green agricultural wastes
  • Agro-industrial wastes, such as sugarcane bagasse and rice husk
  • Animal wastes
  • Industrial wastes, such as black liquor from paper manufacturing
  • Sewage
  • Municipal solid wastes (MSW)
  • Food processing wastes

Biomass energy projects provide major business opportunities, environmental benefits, and rural development.  Feedstocks can be obtained from a wide array of sources without jeopardizing the food and feed supply, forests, and biodiversity in the world.

Agricultural Residues

Crop residues encompasses all agricultural wastes such as bagasse, straw, stem, stalk, leaves, husk, shell, peel, pulp, stubble, etc. Large quantities of crop residues are produced annually worldwide, and are vastly underutilised. Rice produces both straw and rice husks at the processing plant which can be conveniently and easily converted into energy. Significant quantities of biomass remain in the fields in the form of cob when maize is harvested which can be converted into energy. Sugar cane harvesting leads to harvest residues in the fields while processing produces fibrous bagasse, both of which are good sources of energy. Harvesting and processing of coconuts produces quantities of shell and fibre that can be utilized.

Current farming practice is usually to plough these residues back into the soil, or they are burnt, left to decompose, or grazed by cattle. These residues could be processed into liquid fuels or thermochemical processed to produce electricity and heat. Agricultural residues are characterized by seasonal availability and have characteristics that differ from other solid fuels such as wood, charcoal, char briquette. The main differences are the high content of volatile matter and lower density and burning time.

Animal Waste

There are a wide range of animal wastes that can be used as sources of biomass energy. The most common sources are animal and poultry manures. In the past this waste was recovered and sold as a fertilizer or simply spread onto agricultural land, but the introduction of tighter environmental controls on odour and water pollution means that some form of waste management is now required, which provides further incentives for waste-to-energy conversion.

The most attractive method of converting these waste materials to useful form is anaerobic digestion which gives biogas that can be used as a fuel for internal combustion engines, to generate electricity from small gas turbines, burnt directly for cooking, or for space and water heating.

Forestry Residues

Forestry residues are generated by operations such as thinning of plantations, clearing for logging roads, extracting stem-wood for pulp and timber, and natural attrition. Harvesting may occur as thinning in young stands, or cutting in older stands for timber or pulp that also yields tops and branches usable for biomass energy. Harvesting operations usually remove only 25 to 50 percent of the volume, leaving the residues available as biomass for energy.

Stands damaged by insects, disease or fire are additional sources of biomass. Forest residues normally have low density and fuel values that keep transport costs high, and so it is economical to reduce the biomass density in the forest itself.

Wood Wastes

Wood processing industries primarily include sawmilling, plywood, wood panel, furniture, building component, flooring, particle board, moulding, jointing and craft industries. Wood wastes generally are concentrated at the processing factories, e.g. plywood mills and sawmills. The amount of waste generated from wood processing industries varies from one type industry to another depending on the form of raw material and finished product.

Generally, the waste from wood industries such as saw millings and plywood, veneer and others are sawdust, off-cuts, trims and shavings. Sawdust arise from cutting, sizing, re-sawing, edging, while trims and shaving are the consequence of trimming and smoothing of wood. In general, processing of 1,000 kg of wood in the furniture industries will lead to waste generation of almost half (45 %), i.e. 450 kg of wood. Similarly, when processing 1,000 kg of wood in sawmill, the waste will amount to more than half (52 %), i.e. 520 kg wood.

Industrial Wastes

The food industry produces a large number of residues and by-products that can be used as biomass energy sources. These waste materials are generated from all sectors of the food industry with everything from meat production to confectionery producing waste that can be utilised as an energy source.

Solid wastes include peelings and scraps from fruit and vegetables, food that does not meet quality control standards, pulp and fibre from sugar and starch extraction, filter sludges and coffee grounds. These wastes are usually disposed of in landfill dumps.

Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruit and vegetables, pre-cooking meats, poultry and fish, cleaning and processing operations as well as wine making.

These waste waters contain sugars, starches and other dissolved and solid organic matter. The potential exists for these industrial wastes to be anaerobically digested to produce biogas, or fermented to produce ethanol, and several commercial examples of waste-to-energy conversion already exist.

Pulp and paper industry is considered to be one of the highly polluting industries and consumes large amount of energy and water in various unit operations. The wastewater discharged by this industry is highly heterogeneous as it contains compounds from wood or other raw materials, processed chemicals as well as compound formed during processing.  Black liquor can be judiciously utilized for production of biogas using anaerobic UASB technology.

Municipal Solid Wastes and Sewage

Millions of tonnes of household waste are collected each year with the vast majority disposed of in open fields. The biomass resource in MSW comprises the putrescibles, paper and plastic and averages 80% of the total MSW collected. Municipal solid waste can be converted into energy by direct combustion, or by natural anaerobic digestion in the engineered landfill. At the landfill sites the gas produced by the natural decomposition of MSW (approximately 50% methane and 50% carbon dioxide) is collected from the stored material and scrubbed and cleaned before feeding into internal combustion engines or gas turbines to generate heat and power. The organic fraction of MSW can be anaerobically stabilized in a high-rate digester to obtain biogas for electricity or steam generation.

Sewage is a source of biomass energy that is very similar to the other animal wastes. Energy can be extracted from sewage using anaerobic digestion to produce biogas. The sewage sludge that remains can be incinerated or undergo pyrolysis to produce more biogas.

Agricultural Biomass in Philippines

  By Salman Zafar | February 28, 2012 - 7:46 pm | Agricultural Residues, Biomass Energy, Southeast Asia
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The Philippines is mainly an agricultural country with a land area of 30 million hectares, 47 percent of which is agricultural. The total area devoted to agricultural crops is 13 million hectares distributed among food grains, food crops and non-food crops. Among the crops grown, rice, coconut and sugarcane are major contributors to biomass energy resources. The most common agricultural residues are rice husk, rice straw, coconut husk, coconut shell and bagasse. The country has good potential for biomass power plants as one-third of the country’s agricultural land produces rice, and consequently large volumes of rice straw and hulls are generated.

Rice is the staple food in the Philippines. The Filipinos are among the world’s biggest rice consumers. The average Filipino consumes about 100 kilograms per year of rice.  Though rice is produced throughout the country, the Central Luzon and Cagayan Valley are the major rice growing regions. With more than 1.2 million hectares of rain-fed rice-producing areas, the country produced around 16 million tons of rice in 2007. The estimated production of rice hull in the Philippines is more than 2 million tons per annum which is equivalent to approximately 5 million BOE (barrels of oil equivalent) in terms of energy. Rice straw is another important biomass resource with potential availability exceeding 5 million tons per year across the country.

With the passing of Biofuels Act of 2006, the sugar industry in the Philippines which is the major source of ethanol and domestic sugar will become a major thriving industry. Around 380,000 hectares of land is devoted to sugarcane cultivation. It is estimated that 1.17 million tonnes of sugarcane trash is recoverable as a biomass resource in the Philippines. In addition, 6.4 million tonnes of surplus bagasse is available from sugar mills. There are 29 operating sugar mills in the country with an average capacity of 6,900 tonnes of cane per day. Majority is located in Negros Island which provides about 46% of the country’s annual sugar production.

The Philippines has the largest number of coconut trees in the world as it produces most of the world market for coconut oil and copra meal. The major coconut wastes include coconut shell, coconut husks and coconut coir dust. Coconut shell is the most widely utilized but the reported utilization rate is very low.  Approximately 500 million coconut trees in the Philippines produce tremendous amounts of biomass as husk (4.1 million tonnes), shell (1.8 million tonnes), and frond (4.5 million tonnes annually).

Maize is a major crop in the Philippines that generates large amounts of agricultural residues. It is estimated that 4 million tonnes of grain maize and 0.96 million tonnes of maize cobs produced yearly in the Philippines. Maize cob burning is the main energy application of the crop, and is widely practiced by small farmers to supplement fuelwood for cooking.

Ethanol Production via Biochemical Route

  By Salman Zafar | November 27, 2011 - 5:10 pm | Bioethanol, Biofuels, Biomass Energy
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Ethanol from lignocellulosic biomass is produced mainly via biochemical routes. The three major steps involved are pretreatment, enzymatic hydrolysis, and fermentation as shown in Figure. Biomass is pretreated to improve the accessibility of enzymes. After pretreatment, biomass undergoes enzymatic hydrolysis for conversion of polysaccharides into monomer sugars, such as glucose and xylose. Subsequently, sugars are fermented to ethanol by the use of different microorganisms.

Pretreated biomass can directly be converted to ethanol by using the process called simultaneous saccharification and cofermentation (SSCF). Pretreatment is a critical step which enhances the enzymatic hydrolysis of biomass. Basically, it alters the physical and chemical properties of biomass and improves the enzyme access and effectiveness which may also lead to a change in crystallinity and degree of polymerization of cellulose. The internal surface area and pore volume of pretreated biomass are increased which facilitates substantial improvement in accessibility of enzymes. The process also helps in enhancing the rate and yield of monomeric sugars during enzymatic hydrolysis steps.

Pretreatment methods can be broadly classified into four groups – physical, chemical, physio-chemical and biological. Physical pretreatment processes employ the mechanical comminution or irradiation processes to change only the physical characteristics of biomass. The physio-chemical process utilizes steam or steam and gases, like SO2 and CO2. The chemical processes employs acids (H2SO4, HCl, organic acids etc) or alkalis (NaOH, Na2CO3, Ca(OH)2, NH3 etc). The acid treatment typically shows the selectivity towards hydrolyzing the hemicelluloses components, whereas alkalis have better selectivity for the lignin. The fractionation of biomass components after such processes help in improving the enzymes accessibility which is also important to the efficient utilization of enzymes.

The pretreated biomass is subjected to enzymatic hydrolysis using cellulase enzymes to convert the cellulose to fermentable sugars. Cellulase refers to a class of enzymes produced chiefly by fungi and bacteria which catalyzes the hydrolysis of cellulose by attacking the glycosidic linkages. Cellulase is mixture of mainly three different functional protein groups: exo-glucanase (Exo-G), endo-glucanase(Endo-G) and β-glucosidase (β-G). The functional proteins work synergistically in hydrolyzing the cellulose into the glucose. These sugars are further fermented using microorganism and are converted to ethanol. The microorganisms are selected based on their efficiency for ethanol productivity and higher product and inhibitors tolerance. Yeast Saccharomyces cerevisiae is used commercially to produce the ethanol from starch and sucrose.

Escherichia coli strain has also been developed recently for ethanol production by the first successful application of metabolic engineering. E. coli can consume variety of sugars and does not require the complex growth media but has very narrow operable range of pH. E. coli has higher optimal temperature than other known strains of bacteria.

The major cost components in bioethanol production from lignocellulosic biomass are the pretreatment and the enzymatic hydrolysis steps. In fact, these two process are someway interrelated too where an efficient pretreatment strategy can save substantial enzyme consumption. Pretreatment step can also affect the cost of other operations such as size reduction prior to pretreatment. Therefore, optimization of these two important steps, which collectively contributes about 70% of the total processing cost, are the major challenges in the commercialization of bioethanol from 2nd generation feedstock.

Enzyme cost is the prime concern in full scale commercialization. The trend in enzyme cost is encouraging because of enormous research focus in this area and the cost is expected to go downward in future, which will make bioethanol an attractive option considering the benefits derived its lower greenhouse gas emissions and the empowerment of rural economy.

Production of Cellulosic Ethanol

  By Salman Zafar | September 10, 2011 - 7:51 am | Agricultural Residues, Bioethanol, Biofuels, Biomass Energy, Energy-from-Waste, Thermochemical Conversion, Waste-to-energy
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The production of biofuels from lignocellulosic feedstocks can be achieved through two very different processing routes. They are:

  • Biochemical – in which enzymes and other micro-organisms are used to convert cellulose and hemicellulose components of the feedstocks to sugars prior to their fermentation to produce ethanol;
  • Thermo-chemical – where pyrolysis/gasification technologies produce a synthesis gas (CO + H2) from which a wide range of long carbon chain biofuels, such as synthetic diesel or aviation fuel, can be reformed.

Lignocellulosic biomass consists mainly of lignin and the polysaccharides cellulose and hemicellulose. Compared with the production of ethanol from first-generation feedstocks, the use of lignocellulosic biomass is more complicated because the polysaccharides are more stable and the pentose sugars are not readily fermentable by Saccharomyces cerevisiae. In order to convert lignocellulosic biomass to biofuels the polysaccharides must first be hydrolysed, or broken down, into simple sugars using either acid or enzymes. Several biotechnology-based approaches are being used to overcome such problems, including the development of strains of Saccharomyces cerevisiae that can ferment pentose sugars, the use of alternative yeast species that naturally ferment pentose sugars, and the engineering of enzymes that are able to break down cellulose and hemicellulose into simple sugars.

Lignocellulosic processing pilot plants have been established in the EU, in Denmark, Spain and Sweden. The world’s largest demonstration facility of lignocellulose ethanol (from wheat, barley straw and corn stover), with a capacity of 2.5 Ml, was first established by Iogen Corporation in Ottawa, Canada. Many other processing facilities are now in operation or planning throughout the world.

Ethanol from lignocellulosic biomass is produced mainly via biochemical routes. The three major steps involved are pretreatment, enzymatic hydrolysis, and fermentation as shown in Figure. Biomass is pretreated to improve the accessibility of enzymes. After pretreatment, biomass undergoes enzymatic hydrolysis for conversion of polysaccharides into monomer sugars, such as glucose and xylose. Subsequently, sugars are fermented to ethanol by the use of different microorganisms.

Pretreated biomass can directly be converted to ethanol by using the process called simultaneous saccharification and cofermentation (SSCF).  Pretreatment is a critical step which enhances the enzymatic hydrolysis of biomass. Basically, it alters the physical and chemical properties of biomass and improves the enzyme access and effectiveness which may also lead to a change in crystallinity and degree of polymerization of cellulose. The internal surface area and pore volume of pretreated biomass are increased which facilitates substantial improvement in accessibility of enzymes. The process also helps in enhancing the rate and yield of monomeric sugars during enzymatic hydrolysis steps.

Pretreatment methods can be broadly classified into four groups – physical, chemical, physio-chemical and biological. Physical pretreatment processes employ the mechanical comminution or irradiation processes to change only the physical characteristics of biomass. The physio-chemical process utilizes steam or steam and gases, like SO2 and CO2. The chemical processes employs acids (H2SO4, HCl, organic acids etc) or alkalis (NaOH, Na2CO3, Ca(OH)2, NH3 etc). The acid treatment typically shows the selectivity towards hydrolyzing the hemicelluloses components, whereas alkalis have better selectivity for the lignin. The fractionation of biomass components after such processes help in improving the enzymes accessibility which is also important to the efficient utilization of enzymes.

Presently, a ton of dry biomass typically yields 60-70 gallons of bioethanol. The major cost components in bioethanol production from lignocellulosic biomass are the pretreatment and the enzymatic hydrolysis steps. In fact, these two process are someway interrelated too where an efficient pretreatment strategy can save substantial enzyme consumption. Pretreatment step can also affect the cost of other operations such as size reduction prior to pretreatment. Therefore, optimization of these two important steps, which collectively contributes about 70% of the total processing cost, are the major challenges in the commercialization of bioethanol from 2nd generation feedstock.

Major Issues in Biomass Energy Projects

  By Salman Zafar | March 27, 2011 - 11:00 pm | Agricultural Residues, Biochar, Biofuels, biogas, Biomass Energy, Waste-to-energy
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The issues enumerated below are not geography-specific and are usually a matter of concern for most of the biomass energy projects:

  1. Large Project Costs: In India, a 1 MW gasification plant usually costs about USD 1-1.5 million. A combustion-based 1 MW plant would need a little more expenditure, to the tune of USD 1-2 million. An anaerobic digestion-based plant of the same capacity, on the other hand, could range anywhere upwards USD 3 million. Such high capital costs prove to be a big hurdle for any entrepreneur or clean-tech enthusiast to come forward and invest into these technologies.
  2. Low Conversion Efficiencies: In general, efficiencies of combustion-based systems are in the range of 20-25% and gasification-based systems are considered even poorer, with their efficiencies being in the range of a measly10-15%. The biomass resources themselves are low in energy density, and such poor system efficiencies could add a double blow to the entire project.
  3. Dearth of Mature Technologies: Poor efficiencies call for a larger quantum of resources needed to generate a unit amount of energy. Owing to this reason, investors and project developers find it hard to go for such plants on a larger scale. Moreover, the availability of only a few reliable technology and operation & maintenance service providers makes these technologies further undesirable. Gasification technology is still limited to scales lesser than 1 MW in most parts of the world. Combustion-based systems have although gone upwards of 1 MW, a lot many are now facing hurdles because of factors like unreliable resource chain, grid availability, and many others.
  4. Lack of Funding Options: Financing agencies usually give a tough time to biomass project developers as compared to what it takes to invest in other renewable energy technologies.
  5. Non-Transparent Trade Markets: Usually, the biomass energy resources are obtained through forests, farms, industries, animal farms etc. There is no standard pricing mechanism for such resources and these usually vary from vendor to vendor, even with the same resource in consideration.
  6. High Risks / Low Pay-Backs: Biomass energy projects are not much sought-after owing to high project risks which could entail from failed crops, natural disasters, local disturbances, etc.
  7. Resource Price Escalation: Unrealistic fuel price escalation too is a major cause of worry for the plant owners. Usually, an escalation of 3-5% is considered while carrying out the project’s financial modelling. However, it has been observed that in some cases, the rise has been as staggering as 15-20% per annum, forcing the plants to shut down.

Contributed by Setu Goyal, TERI University (New Delhi) who can be reached at setu.goyal@gmail.com)