Torrefaction of Biomass: An Overview

To improve the quality of biomass, especially for cofiring purposes, biomass waste can be processed with torrefaction (also known as mild pyrolysis). With the torrefaction process, it becomes easier to make powder (high grindability) so that the desired particle size for cofiring of biomass is easier to obtain. Another advantage of the torrefaction process is that the caloric value of biomass increases by about 20%. Torrified biomass is essentially hydropobic which means ease in storage including outdoor storage. This condition also makes it easier to handle and use, in addition to reduction in transportation costs.

torrefaction-of-biomass

What is Torrefaction

Torrefaction, which is currently being considered for effective biomass utilization, is also a form of pyrolysis. In this process (named for the French word for roasting), the biomass is heated to 230 to 300 °C without contact with oxygen. For comparison, pyrolysis of biomass is typically carried out in a relatively low temperature range of 300 to 650 °C compared to 800 to 1000 °C for gasification. Torrefaction is a relatively new process that heats the biomass in the absence of air to improve its usefulness as a fuel.

Torrefaction, a process different from carbonization, is a mild pyrolysis process carried out in a temperature range of 230 to 300 °C in the absence of oxygen. During this process the biomass dries and partially devolatilizes, decreasing its mass while largely preserving its energy content. The torrefaction process removes H2O and CO2 from the biomass. As a result, both the O/C and the H/C ratios of the biomass decrease.

steps-in-biomass-torrefaction

Advantages of Biomass Torrefaction

Torrefaction of biomass improves its energy density, reduces its oxygen-to-carbon (O/C) ratio, and reduces its hygroscopic nature. Torrefaction also increases the relative carbon content of the biomass. The properties of a torrefied biomass depends on torrefaction temperature, time, and on the type of biomass feed.

Torrefaction also modifies the structure of the biomass, making it more friable or brittle. This is caused by the depolymerization of hemicellulose. As a result, the process of size reduction becomes easier, lowering its energy consumption and the cost of handling. This makes it easier to cofire biomass in a pulverized coal-fired boiler or gasify it in an entrained-flow reactor.

Another special feature of torrefaction is that it reduces the hygroscopic property of biomass; therefore, when torrefied biomass is stored, it absorbs less moisture than that absorbed by fresh biomass. For example, while raw bagasse absorbed 186% moisture when immersed in water for two hours, it absorbed only 7.6% moisture under this condition after torrefying the bagasse for 60 minutes at 250 °C (Pimchua et al., 2009). The reduced hygroscopic (or enhanced hydrophobic) nature of torrefied biomass mitigates one of the major shortcomings for energy use of biomass.

In biomass, hemicellulose is like the cement in reinforced concrete, and cellulose is like the steel rods. The strands of microfibrils (cellulose) are supported by the hemicellulose. Decomposition of hemicellulose during torrefaction is like the melting away of the cement from the reinforced concrete. Thus, the size reduction of biomass consumes less energy after torrefaction. During torrefaction the weight loss of biomass comes primarily from the decomposition of its hemicellulose constituents. Hemicellulose decomposes mostly within the temperature range 150 to 280 °C, which is the temperature window of torrefaction.

torrified-biomass

As we can see from figure above, the hemicellulose component undergoes the greatest amount of degradation within the 200 to 300 °C temperature window. Thus, hemicellulose decomposition is the primary mechanism of torrefaction. At lower temperatures (< 160 °C), as biomass dries it releases H2O and CO2. Water and carbon dioxide, which make no contribution to the energy in the product gas, constitute a dominant portion of the weight loss during torrefaction.

Above 180 °C, the reaction becomes exothermic, releasing gas with small heating values. The initial stage (< 250 °C) involves hemicellulose depolymerization, leading to an altered and rearranged polysugar structures. At higher temperatures (250–300 °C) these form chars, CO, CO2, and H2O. The hygroscopic property of biomass is partly lost in torrefaction because of the destruction of OH groups through dehydration, which prevents the formation of hydrogen bonds.

Biomass Exchange – Key to Success in Biomass Projects

Biomass exchange is emerging as a key factor in the progress of biomass energy sector. It is well-known that the supply chain management in any biomass project is a big management conundrum. The complexity deepens owing to the large number of stages which encompass the entire biomass value chain. It starts right from biomass resource harvesting and goes on to include biomass collection, processing, storage and eventually its transportation to the point of ultimate utilization.

biomass-exchange

Owing to the voluminous nature of the resource, its handling becomes a major issue since it requires bigger modes of biomass logistics, employment of a larger number of work-force and a better storage infrastructure, as compared to any other fuel or feedstock. Not only this their lower energy density characteristic, makes it inevitable for the resource to be first processed and then utilized for power generation to make for better economics.

All these problems call for a mechanism to strengthen the biomass value chain. This can be done by considering the following:

  • Assuring a readily available market for the resource providers or the producers
  • Assuring the project developers of a reliable chain and consistent feedstock availability
  • Awareness to the project developer of the resources in closest proximity to the plant site
  • Assurance to the project developer of the resource quality
  • Timely pick-up and drop of resource
  • Proper fuel preparation as per technology requirements
  • Removal of intermediaries involved in the process – to increase value for both, the producers as well as the buyers
  • No need for long term contracts (Not an obligation)
  • Competitive fuel prices
  • Assistance to producers in crop management

Biomass Exchange Model

The figure below gives a general understanding of how such a model could work, especially in the context of developing nations where the size of land holdings is usually small and the location of resources is scattered, making their procurement a highly uneconomic affair. This model is commonly known as Biomass Exchange

In such a model, the seed, fertilizer shops and other local village level commercial enterprises could be utilized as an outreach or marketing platform for such a service.  Once the producer approves off the initial price estimate, as provided by these agencies, he could send a sample of the feedstock to the pre-deputed warehouses for a quality check.

These warehouses need to be organized at different levels according to the village hierarchy and depending on the size, cultivated area and local logistic options available in that region. On assessing the feedstock sample’s quality, these centers would release a plausible quote to the farmer after approving which, he would be asked to supply the feedstock.

On the other hand, an entity in need of the feedstock would approach the biomass exchange, where it would be appraised of the feedstock available in the region near its utilization point and made aware of the quantity and quality of the feedstock. The entity would then quote a price according to its suitability which would be relayed to the primary producer.

An agreement from both the sides would entail the placement of order and the feedstock’s subsequent processing and transportation to the buyer’s gate. The pricing mechanisms could be numerous ranging from, fixed (according to quality), bid-based or even market-driven.

Roadblocks

The hurdles could be in the form of the initial resource assessment which could in itself be a tedious and time consuming exercise. Another roadblock could be in the form of engaging the resource producers with such a mechanism. Since these would usually involve rural landscapes, things could prove to be a little difficult in terms of implementation of initial capacity building measures and concept marketing.

Benefits

The benefits of  a biomass exchange are enumerated below:

  • Support to the ever increasing power needs of the country
  • Promotion of biomass energy technologies
  • Development of rural infrastructure
  • Increased opportunities for social and micro-entrepreneurship
  • Creation of direct and indirect job opportunities
  • Efficient utilization of biomass wastes
  • Potential of averting millions of tonnes of GHGs emissions

Conclusions

In India alone, there has been several cases where biomass power projects of the scale greater than 5 MW are on sale already, even with their power purchase agreements still in place. Such events necessitate the need to have a mechanism in place which would further seek the promotion of such technologies.

Biomass Exchange is an attractive solution to different problems afflicting biomass projects, at the same time providing the investors and entrepreneurs with a multi-million dollar opportunity. Although such a concept has been in existence in the developed world for a long time now, it has not witnessed many entrepreneurial ventures in developing nations where the need to strengthen the biomass supply chain becomes even more necessary.

However, one needs to be really careful while initiating such a model since it cannot be blindly copied from Western countries owing to entirely different land-ownership patterns, regional socio-political conditions and economic framework. With a strong backup and government support, such an idea could go a long way in strengthening the biomass supply chain, promotion of associated clean energy technologies and in making a significant dent in the present power scenario in the developing world.

Biomass as Renewable Energy Resource

Biomass is a key renewable energy resource that includes 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 biomass energy or bioenergy.

Biomass-Resources

A quick glance at popular biomass resources

What is Biomass

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 (cow manure, poultry litter etc)
  • 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 for biomass energy project 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 thermochemically 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 manure. 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 organic 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, known as landfill gas or LFG, 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.

Clean Cookstoves: An Urgent Necessity

Globally, three billion people in the developing nations are solely dependent on burning firewood, crop residues, animal manure etc for preparing their daily meals on open fires, mud or clay stoves or simply on three rocks strategically placed to balance a cooking vessel.  The temperature of these fires are lower and produce inefficient burning that results in black carbon and other short-lived but high impact pollutants.

These short-lived pollutants not only affect the persons in the immediate area but also contribute much harmful gases more potent than carbon dioxide and methane. For the people in the immediate area, their health is severely hampered as this indoor or domestic air pollution results in significantly higher risks of pneumonia and chronic bronchitis.

To remedy the indoor air pollution (IAP) and health-related issues as well as the environmental pollution in the developing world, clean cookstoves are the way to advance. But to empower rural users to embrace the advanced cookstoves, and achieve sustainable success requires a level of socio-cultural and economic awareness that is related directly to this marginalized group. The solution needs to be appropriate for the style of cooking of the group which means one stove model will not suit or meet the needs and requirements of all developing nation people groups.

Clean cookstoves can significantly reduce health problems caused by indoor air pollution in rural areas

Consideration for such issues as stove top and front loading stove cooking, single pot and double pot cooking, size of the typical cooking vessel and the style of cooking are all pieces of information needed to complete the picture.

Historically, natural draft systems were devised to aid the combustion or burning of the fuels, however, forced draft stoves tend to burn cleaner with better health and environmental benefits. Regardless of cookstove design, the components need to be either made locally or at least available locally so that the long term life of the stove is maintainable and so sustainable.

Now, if the cookstove unit can by powered by  simple solar or biomass system, this will change the whole nature of the life style and domestic duties of the chief cook and the young siblings who are typically charged with collecting the natural firewood to meet the cooking requirement.

Therefore the cookstoves need to be designed and adapted for the people group and their traditional cooking habits, and not in the reverse order. To assess the overall performance of the green cooking stoves requires simple but effective measures of the air quality.

The two elements that need to be measured are the black carbon emissions and the temperature of the cooking device.  This can be achieved by miniature aerosol samplers and temperature sensors. The data collected needs to be transmitted in real-time via mobile phones for verification of performance rates.  This is to provide verifiable data in a cost effective monitoring process.

Biomass Energy Potential in Philippines

The Philippines has abundant supplies of biomass energy resources in the form of agricultural crop residues, forest residues, animal wastes, agro-industrial wastes, municipal solid wastes and aquatic biomass. The most common agricultural wastes are rice hull, bagasse, cane trash, coconut shell/husk and coconut coir. The use of crop residues as biofuels is increasing in the Philippines as fossil fuel prices continue to rise. Rice hull is perhaps the most important, underdeveloped biomass resource that could be fully utilized in a sustainable manner.

At present, biomass technologies utilized in the country vary from the use of bagasse as boiler fuel for cogeneration, rice/coconut husks dryers for crop drying, biomass gasifiers for mechanical and electrical applications, fuelwood and agricultural wastes for oven, kiln, furnace and cook-stoves for cooking and heating purposes. Biomass technologies represent the largest installations in the Philippines in comparison with the other renewable energy, energy efficiency and greenhouse gas abatement technologies.

Biomass energy plays a vital role in the nation’s energy supply. Nearly 30 percent of the energy for the 80 million people living in the Philippines comes from biomass, mainly used for household cooking by the rural poor. Biomass energy application accounts for around 15 percent of the primary energy use in the Philippines. The resources available in the Philippines can generate biomass projects with a potential capacity of more than 200 MW.

Almost 73 percent of this biomass use is traced to the cooking needs of the residential sector while industrial and commercial applications accounts for the rest. 92 percent of the biomass industrial use is traced to boiler fuel applications for power and steam generation followed by commercial applications like drying, ceramic processing and metal production. Commercial baking and cooking applications account for 1.3 percent of its use.

The EC-ASEAN COGEN Programme estimated that the volume of residues from rice, coconut, palm oil, sugar and wood industries is 16 million tons per year. Bagasse, coconut husks and shell can account for at least 12 percent of total national energy supply. The World Bank-Energy Sector Management Assistance Program estimated that residues from sugar, rice and coconut could produce 90 MW, 40 MW, and 20 MW, respectively.

The development of crop trash recovery systems, improvement of agro-forestry systems, introduction of latest energy conversion technologies and development of biomass supply chain can play a major role in biomass energy development in the Philippines. The Philippines is among the most vulnerable nations to climatic instability and experiences some of the largest crop losses due to unexpected climatic events. The country has strong self-interest in the advancement of clean energy technologies, and has the potential to become a role model for other developing nations on account of its broad portfolio of biomass energy resources and its potential to assist in rural development.

Biorefinery Prospects in India

India has a tremendous biomass potential which could easily be relied upon to fulfil most of our energy needs. An estimated 50 MMT (million metric tonnes) of liquid fuels are consumed annually in India, but with the actual biomass potential and its full utilization, India is capable of generating almost double that amount per annum. These biomass estimates only constitute the crop residues available in the country and essentially the second-generation fuels since the use of first-generation crop bases fuels in such food-starved nations is a criminal thought.

Biomass-India

Existing Technologies

Currently, there are various technologies available to process such crop residues and generate value products from them. However, essentially, they all revolve around two main kinds of processes, either biochemical or thermal.

The biochemical process involves application of aerobic/anaerobic digestion for the production of biogas; or fermentation, which results in the generation of ethanol. Both these products could be subsequently treated chemically and through trans-esterification process, leading to production of biodiesel.

Alternatively, the thermochemical processes involve either the combustion, gasification or pyrolysis techniques, which produces heat, energy-rich gas and liquid fuels respectively. These products can be used as such, or could be further processed to generate high quality biofuels or chemicals.

The Need

The estimated organized energy breakup for India is 40 percent each for domestic and transport sectors and 20 percent for the industrial sectors. The current share of crude oil and gases is nearly 90 percent for the primary and transport sectors and the remaining 10 percent for the generation of industrial chemicals.

The fluctuating prices of crude oil in the international market and the resulting concern over energy security, has lead developing nations to explore alternative and cheap sources of energy to meet the growing energy demand. One of the promising solution for agrarian economies is Biorefinery.

The Concept

Biorefinery is analogous to the traditional petroleum refineries employing fractional distillation process for obtaining different fractions or components from the same raw material, i.e. the crude oil. Biorefinery involve the integration of different biomass treatment and processing methods into one system, which results in the production of different components from the same biomass.  This makes the entire chain more viable economically and also reduces the waste generated.

Typical Model of a Biorefinery

The outcome ranges from high-volume, low-energy content liquid fuels, which could serve the transportation industry needs, to the low-volume but high-value chemicals, which could add to the feasibility of such a project.

Steam and heat generated in the process could be utilized for meeting process heat requirements. By-products like chemicals, fertilizers, pharmaceuticals, polymers etc are also obtained which provide additional revenue streams.

Benefits

Biorefineries can help in utilizing the optimum energy potential of organic wastes and may also resolve the problems of waste management and GHGs emissions. Wastes can be converted, through appropriate enzymatic/chemical treatment, into either gaseous or liquid fuels.

The pre-treatment processes involved in biorefining generate products like paper-pulp, HFCS, solvents, acetate, resins, laminates, adhesives, flavour chemicals, activated carbon, fuel enhancers, undigested sugars etc. which generally remain untapped in the traditional processes. The suitability of this process is further enhanced from the fact that it can utilize a variety of biomass resources, whether plant-derived or animal-derived.

Applicability

The concept of biorefinery is still in early stages at most places in the world. Problems like raw material availability, feasibility in product supply chain, scalability of the model are hampering its development at commercial-scales. The National Renewable Energy Laboratory (NREL) of USA is leading the front in biorefinery research with path-breaking discoveries and inventions.

Although the technology is still in nascent stages, but it holds the key to the optimum utilization of wastes and natural resources that humans have always tried to achieve. The onus now lies on governments and corporate to incentivize or finance the research and development in this field.

Biomass Conveyors: An Overview

A well designed biomass conveyor system should take into account the variability of the material and provide the consistent and reliable flow that is crucial to power generation. Depending upon the type of boiler and conversion system, the fuel is either transported directly to the powerhouse via a belt conveyor, or first processed in a chipper/grinder to produce a finer texture.

For example, municipal solid waste is deposited into pits where cranes mix the refuse and remove any large, non-combustible items. Sometimes, it is further processed to remove ferrous materials, glass, and other non-combustible materials.

Biomass_Conveyor

For large pellet-fired biomass system, rail dump method is very common where railway tracks are constructed to transport biomass. Station is specified for train and fuel receiving bins are typically located below the track and rail cars dump into bins, either directly or through a rotary dumper. Fuel received is then transferred by belt conveyors to the biomass storage bins.

For small particle size, pneumatic conveying system offer greater flexibility in routing than traditional belt conveyors. Equipment specific to pneumatic systems include positive displacement blowers and rotary feeders that function as air locks.

In a typical biomass thermal power plant, the initial process in the power generation is biomass fuel handling. A railway siding line is taken into the power station and the biomass is delivered in the storage yard. It is then unloaded from the point of delivery by means of wagon tippler. It is rack and pinion type. The biomass is taken from the unloading site to dead storage by belt conveyors. The belt deliver the biomass to warehouse.

The transfer points inside the warehouse are used to transfer biomass to the next belt. The belt elevates the biomass to breaker house. It consists of a rotary machine, which rotates the biomass and separates the light inorganic materials (viz. plastic or other incombustible particles) from it through the action of gravity and transfer it to reject bin house through belt. The belt further elevates the biomass until it reaches the crusher through belt.

In the crusher a high-speed 3-phase induction motor is used to crush the biomass according to the requirement, for gasification size range is usually upto 15-20mm, while for biomass-fired boiler, size of 50mm is acceptable. Biomass rises from crusher house and reaches the dead storage.

Cost-effective production of biomass energy is very much dependent on efficient handling of available biomass sources, as well as the efficiency of each process. An important, but often overlooked, area is the efficient receiving of different types and different capacities of biomass as it enters the plant and then conveying this material to the production equipment.  In many cases, the space available for biomass handling is limited.

Receiving equipment can be installed in a pit or at the ground level. The size and volume of the receiving pocket can be suited to vehicle volumes or turn-around times. The receiving pit can be used as small buffer biomass storage or as an emergency or mixing pocket.

Belt conveyors are an economical and reliable choice for transferring biomass over long distances at high capacities with lower noise levels. Designs range from simple, open configurations to totally closed and washable conveyor galleries. Well engineered conveyors have the maximum safe distance between support legs to minimize the cost of civil construction as well as reducing the number of obstructions on the ground.

Chain conveyors are a reliable choice for transporting unscreened or dusty biomass, or when the available space is limited. Screw conveyors are a very economical alternative for transporting biomass over short distances.

Biomass conveyors are an integral feature of all biomass conversion routes

Nowadays, automated conveyor systems are getting traction around the world. Fully automated fuel handling systems employ a biomass storage bin that can hold upto 50 tons (or more) of biomass. The bin is filled by a self-unloading truck with negligible or no onsite staff assistance. From the biomass storage bunker, the fuel is fed automatically to the boiler by augers and conveyors. The fully automated system is a good match for biomass plants where maintenance staff has a large work load and cannot spend much time working with the biomass conversion plant.

Pellet-based hopper systems offer low costs for both installation and operation. In a modern biomass pellet boiler system, fuel is stored in a relatively low-cost grain silo and automatically fed, with no operator intervention, to the boiler or boilers with auger systems similar to those used for conveying feed grain on farms.

The fuel-handling system uses electric motors and is run by automated controls that provide the right amount of fuel to the combustion chamber based on facility demand. Such conveyor systems require minimal maintenance, around 20-30 minutes daily, for ash removal and maintenance of motors and augers, estimated to be about 20-30 minutes per day.

Bioenergy Resources in MENA Countries

The Middle East and North Africa (MENA) region offers almost 45 percent of the world’s total energy potential from all renewable sources that can generate more than three times the world’s total power demand. Apart from solar and wind, MENA also has abundant bioenergy energy resources which have remained unexplored to a great extent.

biomass_resources

Around the MENA region, pollution of the air and water from municipal, industrial and agricultural operations continues to grow.  The technological advancements in the biomass energy and waste-to-energy industry, coupled with the tremendous regional potential, promises to usher in a new era of energy as well as environmental security for the region.

The major biomass producing countries in MENA are Saudi Arabia, Egypt, Yemen, Iraq, Syria and Jordan. Traditionally, biomass energy has been widely used in rural areas for domestic purposes in the MENA region, especially in Egypt, Yemen and Jordan. Since most of the region is arid or semi-arid, the major bioenergy resources are municipal solid wastes, agricultural residues and organic industrial wastes.

Municipal solid wastes represent the best source of biomass in Middle East countries. Bahrain, Saudi Arabia, UAE, Qatar and Kuwait rank in the top-ten worldwide in terms of per capita solid waste generation. The gross urban waste generation quantity from Middle East countries is estimated at more than 150 million tons annually.

Food waste is the third-largest component of generated waste by weight which mostly ends up rotting in landfill and releasing greenhouse gases into the atmosphere. The mushrooming of hotels, restaurants, fast-food joints and cafeterias in the region has resulted in the generation of huge quantities of food wastes.

In Middle East countries, huge quantity of sewage sludge is produced on daily basis which presents a serious problem due to its high treatment costs and risk to environment and human health. On an average, the rate of wastewater generation is 80-200 litres per person each day and sewage output is rising by 25 percent every year. According to estimates from the Drainage and Irrigation Department of Dubai Municipality, sewage generation in the Dubai increased from 50,000 m3 per day in 1981 to 400,000 m3 per day in 2006.

The food processing industry in MENA produces a large number of organic residues and by-products that can be used as biomass energy sources. In recent decades, the fast-growing food and beverage processing industry has remarkably increased in importance in major countries of the region. Since the early 1990s, the increased agricultural output stimulated an increase in fruit and vegetable canning as well as juice, beverage, and oil processing in countries like Egypt, Syria, Lebanon and Saudi Arabia.

The MENA countries have strong animal population. The livestock sector, in particular sheep, goats and camels, plays an important role in the national economy of respective countries. Many millions of live ruminants are imported each year from around the world. In addition, the region has witnessed very rapid growth in the poultry sector. The biogas potential of animal manure can be harnessed both at small- and community-scale.

Agricultural Wastes in the Philippines

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 wastes in the Philippines 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 19 million tons of rice in 2019.

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.

rice-biomass-philippines

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.

Overview of Biomass Energy Technologies

A wide range of bioenergy technologies are available for realizing the energy potential of biomass wastes, ranging from very simple systems for disposing of dry waste to more complex technologies capable of dealing with large amounts of industrial waste. Conversion routes for biomass wastes are generally thermo-chemical or bio-chemical, but may also include chemical and physical.

Thermal Technologies

The three principal methods of thermo-chemical conversion corresponding to each of these energy carriers are combustion in excess air, gasification in reduced air, and pyrolysis in the absence of air. Direct combustion is the best established and most commonly used technology for converting wastes to heat.

During combustion, biomass is burnt in excess air to produce heat. The first stage of combustion involves the evolution of combustible vapours from wastes, which burn as flames. Steam is expanded through a conventional turbo-alternator to produce electricity. The residual material, in the form of charcoal, is burnt in a forced air supply to give more heat.

Co-firing or co-combustion of biomass wastes with coal and other fossil fuels can provide a short-term, low-risk, low-cost option for producing renewable energy while simultaneously reducing the use of fossil fuels. Co-firing involves utilizing existing power generating plants that are fired with fossil fuel (generally coal), and displacing a small proportion of the fossil fuel with renewable biomass fuels.

Co-firing has the major advantage of avoiding the construction of new, dedicated, waste-to-energy power plant. An existing power station is modified to accept the waste resource and utilize it to produce a minor proportion of its electricity.

Gasification systems operate by heating biomass wastes in an environment where the solid waste breaks down to form a flammable gas. The gasification of biomass takes place in a restricted supply of air or oxygen at temperatures up to 1200–1300°C. The gas produced—synthesis gas, or syngas—can be cleaned, filtered, and then burned in a gas turbine in simple or combined-cycle mode, comparable to LFG or biogas produced from an anaerobic digester.

The final fuel gas consists principally of carbon monoxide, hydrogen and methane with small amounts of higher hydrocarbons. This fuel gas may be burnt to generate heat; alternatively it may be processed and then used as fuel for gas-fired engines or gas turbines to drive generators. In smaller systems, the syngas can be fired in reciprocating engines, micro-turbines, Stirling engines, or fuel cells.

Pyrolysis is thermal decomposition occurring in the absence of oxygen. During the pyrolysis process, biomass waste is heated either in the absence of air (i.e. indirectly), or by the partial combustion of some of the waste in a restricted air or oxygen supply. This results in the thermal decomposition of the waste to form a combination of a solid char, gas, and liquid bio-oil, which can be used as a liquid fuel or upgraded and further processed to value-added products.

Biochemical Technologies

Biochemical processes, like anaerobic digestion, can also produce clean energy in the form of biogas which can be converted to power and heat using a gas engine. Anaerobic digestion is a series of chemical reactions during which organic material is decomposed through the metabolic pathways of naturally occurring microorganisms in an oxygen depleted environment. In addition, wastes can also yield liquid fuels, such as cellulosic ethanol and biodiesel, which can be used to replace petroleum-based fuels.

Anaerobic digestion is the natural biological process which stabilizes organic waste in the absence of air and transforms it into biogas and biofertilizer. Almost any organic material can be processed with anaerobic digestion. This includes biodegradable waste materials such as municipal solid waste, animal manure, poultry litter, food wastes, sewage and industrial wastes.

An anaerobic digestion plant produces two outputs, biogas and digestate, both can be further processed or utilized to produce secondary outputs. Biogas can be used for producing electricity and heat, as a natural gas substitute and also a transportation fuel. Digestate can be further processed to produce liquor and a fibrous material. The fiber, which can be processed into compost, is a bulky material with low levels of nutrients and can be used as a soil conditioner or a low level fertilizer.

A variety of fuels can be produced from biomass wastes including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The 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 largest potential feedstock for ethanol is lignocellulosic biomass wastes, which includes materials such as agricultural residues (corn stover, crop straws and bagasse), herbaceous crops (alfalfa, switchgrass), short rotation woody crops, forestry residues, waste paper and other wastes (municipal and industrial).

The three major steps involved in cellulosic ethanol production are pretreatment, enzymatic hydrolysis, and fermentation. 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. Bioethanol production from these feedstocks could be an attractive alternative for disposal of these residues. Importantly, lignocellulosic feedstocks do not interfere with food security.