| Standards for Oil Palm Fibre | |||||||||
In terms of hectare, the total area under oil palm cultivation is over 2.65 million hectares, producing over 8 million tonnes of oil annually. The oil consists of only 10% of the total biomes produced in the plantation. The remainder consists of huge amount of lignocellulosic materials such as oil palm fronds, trunks and empty fruit bunches. The projection figures of these residues are as follows:
* These figures depend on the life span of oil palm tree that is due for replanting after about 20-25 years old. Extracted from the paper entitled Fibre processing technology fractionation promss to produce fibrous strands from oil palm residues, by Mahmudin Saleh and Puad Elham Based on the above figures, Malaysia therefore has a great potential in turning its abundant supply of oil palm industry by-products into value-added products. Under the present scenario, Malaysia can no longer remain idle and complacent in its position as the top grower and supplier of palm oil. In view of the escalating challenge posed by the other oil producing countries, Malaysia has to change its objective of being a world producer of palm oil to amongst others a leader in converting biomass waste into value-added products. Malaysia has therefore to seriously resort in aggressive R&D to support its ambition. Before we embarked into identifying the parameters effecting the overall quality of the fibre, let us turn to look into the current utilisation of these fibres. Recent report shows that the mesocarp fibre and shell are used as boiler to produce steam and to generate power. Whereas, empty fruit bunches are mainly incinerated to produce bunch ash to be distributed back to the field as fertiliser. The conventional method of burning these residues often create environmental problems in that it generates severe air pollution and is prohibited by the Environment Protection Act. In abiding by the regulations, these residues are becoming expensive to dispose. Nevertheless, looking on the brighter side of things, extensive research has provided us with an alternative way of optimising the usage of oil palm residues fibrebased into value-added product. SIRIM Berhad in its effort to provide technical support through its standardisation activities has established a working group and put to task the preparation of a Malaysian Standard on the oil palm fibre. Through the concerted effort of the working group members comprising academicians, research institutions, manufacturers and related associations, the development of a Malaysian Standard was carried out. References were made against existing production technologies in Oil Palm Fibre the oil palm industry, research papers and literatures related to the subject matter and the following foreign references:
The empty fruit bunch fibre (EFB) was identified as the first of the series of standards on oil palm fibres because of logistic reasons. The EFB has the highest fibre yield and is the only material commercially utilised for fibre extraction but there are good potentials for the exploitation of the other two materials (oil palm fronds and trunks). The standard is unique in that it is an indigenous standard and is the first in the world that directly relates to the oil palm residues. Extensive study and research had been conducted both by FRIM and PORIM in collaboration with the manufacturers. After several meetings and discussions, the committee had identified critical parameters affecting the quality of the end product. The critical characteristics of oil palm fibre include the fibre length, moisture content, oil content and impurities. Details on the acceptable limits and methods of determination are given in the standard, MS 1408 :1997 (P) - Specification for oil palm empty fruit bunch fibre. For the purpose of commercialisation, the standard recommends ONE grade of empty fruit bunch fibre (EFB). In quantifying the percentage proportion of fibre length, the standard has established the following numerical values:
The method of determining the proportion by mass of the different EFB fibre length is described in Appendix B of the standard. The right mixture of fibre length is important for the aesthetic finished. Apart from dimensions of fibre length, the standard also defines specific terminology frequently encountered in the standard. In order to ascertain that samples are representative of the lot and that bales are randomly selected, the provision of a sampling procedure is being prescribed in the standard. Inherent characteristics such as high moisture content will have a detrimental effect on the oil palm residues. Degradation and infection will easily take place thus leading to deterioration in the properties of the fibres. To prevent this from happening, a maximum moisture content of 15% (on wet basis) was set. This value is comparable to the moisture content for all wood-based fibres. In addition, the standard has also identified impurities as a critical element in producing high quality fibres. Impurities by definition means the calyxes, spikes, aggregates or fibre strands, any dust or fine particles and parenchyma of EFB. Since it is practically impossible to have fibre free impurities, the maximum level of impurities allowed for in the standard is at 15% . Nevertheless with future improvement in the process technologies, this limit could be further reduced. The final EFB fibre characteristics that merits attention is the oil content of the fibre. The presence of a significant percentage of residual oil possess a major problem in that it will react with the moisture content hence giving rise to rancidity and ultimately fungal growth. The control limit for oil content shall not exceed 3%. Other inherent characteristics such as the salt content, odour, mass, etc. were taken into consideration during the process of formulating the standard. Since these parameters do not affect the overall quality of the EFB fibre significantly, it was therefore excluded from the general requirements of the standard. Standardisation only provides one of the means necessary to assist manufacturers in producing quality fibre for downstream uses. Manufacturers and the like should further spear-head investigations in improving existing technologies through aggressive R&D. Considering the abundance of residual fibres available for commercial exploitation, its market potential and business opportunities, and not withstanding the slow depletion of rubber-wood, is a challenge worth considering. SIRIM Berhad | |||||||||
Monday, January 8, 2007
Standards for Oil Palm Fibre
WILL BIOMASS GROW WITHIN THE GLOBAL ENERGY MARKET?
Biomass broadly describes renewable fuel resources which cover almost any biologically degradable fuel from farmyard manure through industrial liquid effluents and solid wastes, agro-industrial and forestry wastes, to part of the municipal waste fraction. Biomass use can stretch from large scale embedded power generation to small-scale wood stoves or even open cooking fires. Biomass has been humans' basic fuel since the beginning of time. Today biomass fuels are being revived after having been largely displaced by fossil fuels for energy generation.
At present, biomass contributes approximately 14% of the total global final energy demand – that is for cooking, heating, process and electricity. Various forecasters have anticipated that the use of fossil fuels could reach a plateau by 2020 and, by then, renewable energy will provide 5-10% of the world's electrical energy. In 50 years, it has been forecast that Renewables could increase their share to 30-60% of global energy needs and modern biomass will provide about 40% of this, that is to say 15-25% of the whole. Whatever the actual numbers, bearing in mind the rapid increase in energy demand over the next half century, the growth in demand for biomass deployment is huge.
In the UK alone, the Government's target of 10% of all electricity from Renewables by 2010 will require a contribution of 1000MW from biomass and a rate of plant installation 8 times faster than at present. In developing countries, where electricity demand growths of 10-12% are not uncommon, the rate of plant installation needs to be even greater.
Why invest in new biomass projects?
The biomass sector is largely underdeveloped and has a potential to grow rapidly in the future as demand for clean fuels increases. There are many different types of biomass and as many different reasons for companies to become involved in exploiting it for energy use. Agro-industrial residues such as bagasse from sugar cane mills, palm oil mill residues, rice husks, sawmill residues etc. have inherent waste disposal problems but can often be treated as negative cost fuels for co-generation or power projects. The mills themselves benefit as waste disposal is solved. Electricity and heat produced can be used to reduce internal costs. Often older, inefficient boilers will be taken out and replaced with better equipment thereby helping the energy conversion status of a plant.
Compared with all the other renewable energies, biomass will contribute major socio-economic benefits. Wind, mini-hydro, solar and geothermal produce socio-economic benefits in terms of introducing electrical energy to grid connected as well as off-grid populations, which may not otherwise have the opportunity of receiving it. However they bring no benefit in terms of the fuel source itself. Biomass fuel attracts significant employment in terms of cultivation, husbandry, harvesting, transport and fuel preparation and biomass power and co-generation plants will create more operational and maintenance jobs than any of the other Renewables per MW of installed capacity.
The success of a biomass plant is reliant on issues such as: What is the security and long term availability of the biomass fuel supply? Is there an alternative use for the fuel which may affect its long term cost? Is there a market for electricity and heat? Is it practical to build a plant? Is there a need and can we sell the electricity? Can it compete with fossil fuel generated electricity? Is there a prospect of funding the project and is it commercially viable?
Institutional constraints to biomass electrical generation
Biomass as an energy source has broad commercial, community and environmental benefits but before further investment takes place the biomass project has to be commercially viable.
In most countries, biomass and all other Renewables have to compete in an established energy market dominated by fossil fuel generation, which, until recently, has been run and supported by the public sector and in a large part of the world still is. Privatisation and de-regulation in the electricity sector is a pre-requisite to wholesale integration of biomass into the energy mix. Unless the biomass market can sell its product – electricity – there is no market and no point in even trying to develop biomass projects.
Even when the de-regulation process is under way there are ulterior motives for limiting incursions of alternative generation into the traditional fossil fuel generation mix. Governments, who want to sell their fossil fuel generation assets and gain full value for their taxpayers, want to ensure that those assets continue to have a long term market and don't become 'stranded', so they restrict access to new generators. For example, in the Philippines during President Estrada's term in office, the Department of Energy was only willing to consider allowing the National Power Company to buy a total of 15 MW of electricity from biomass so that the privatisation of NPC was not adversely affected by stranded generating capacity. And this was at a time when the same Department was advocating 'great' commitment to renewable energy and the potential from bagasse alone is 400-500 MW.
Many Governments also operate a subsidised energy market with subsidised fuel, which distorts the pricing structure of electricity, as does the 'written-down' value of capital plant. This means that, where there is current adequate generation capacity, the target price for selling biomass generated electricity is artificially low, often prohibitively low. For example, in 2001 the Malaysian Government is launching a renewable energy programme aiming to generate 5% of the country's electricity from renewable sources by 2005. The main contributor to this target will be biomass in the form of palm oil residues and it has been estimated that the current surplus waste could generate about 1100MW of electricity representing about 12% of the country's current average demand. However, the Government subsidises the fuel cost to existing generators by about 40% so the cost of generated electricity is artificially low at US 2.9c - 4.1c/kWh.
Typically electricity from palm oil residues will require about US 6.5c - 7.0c to be viable, so the Government either has to accept that there will be a different tariff for Renewables or that the only projects which are likely to be implemented are those in say East Malaysia where the competing generation is diesel. East Malaysia produces less than one third of the total palm oil output in Malaysia, so potential electricity generation from surplus waste could be very significantly less than current projections.
These limitations on access to the electricity market can last until there is urgent need for new generation capacity arising from increased demand and replacement of time-expired plant. Some markets may still be constrained for up to 10 years after de-regulation of the market, so deployment of biomass renewable energy will still be slow even up to the initial 5 or 10 year targets for Renewables which Governments are setting.
Without these constraints, biomass which is effectively a zero cost fuel, is already competitive with the fully burdened cost of new diesel. So deployment is commercially possible where countries are dependent on diesel generation, where there is substantial growth in demand for electricity and particularly in rural areas where substantial quantities of biomass are available.
PALM OIL MILL FRESH FRUIT BUNCHES ENTERING THE MILL
AIR POLLUTION EMITTED FROM BURNING PALM OIL MILLING WASTES
What are the physical constraints to selling electricity?
There are also physical constraints to selling electricity especially in isolated rural areas with poor infrastructure. Questions need to be answered such as: Is the plant to be captive or grid connected? Are the grids national or isolated? How far are the transmission lines? Is there enough long-term fuel supply and can the power be sold?
Sugar cane mills and palm oil mills are typically isolated and located far from urban areas without significant infrastructure connections. Traditionally, they have been energy self-sufficient because they have been unable to connect to transmission lines. Even with substantial and rapid expansion of grids, many mills will still be distant from transmission lines so interconnection will be prohibitively expensive. If you can't connect to the grid and cannot sell surplus energy, there will be no reason to improve energy conversion efficiencies and deployment will not be possible. Alternatively, in such conditions it will probably be uneconomic to transport the biomass to a location where connection is possible.
In many situations, often on islands, there is a concentration of one type of agro-industry. As examples, cultivation of sugar cane is concentrated in Hawaii, Cuba, Mauritius, Java and Negros (Philippines). If all the bagasse was converted efficiently to steam and electricity, in some cases the surplus electricity would exceed the demand of the local consumers particularly when existing generation capacity is taken into account.
There is often considerable competition between mills in both domestic and international markets which will tend to force those industries to consolidate. When this happens, the less commercially robust mills, often the smaller ones, may not survive in the long term. This effect will also restrict the deployment of modern biomass technology in concentrated biomass areas.
There is a potential of generating 400 - 500 MW of surplus electricity from the sugar industry in the Philippines. 55% of the sugar milling capacity, and therefore bagasse resource, is located on the island of Negros. However, the total demand on electricity on the island is only 100 – 150 MW and there is already committed generation capacity and an island interconnection grid which has embedded geothermal as part of its generation mix. For the time being, until overall demand on the island grows substantially, the likely penetration of bagasse generated electricity is probably only about 20% of its overall potential.
There is a tendency to want to make biomass projects as big as possible in order to maximise the benefits of scale. This leads to an aggressive approach to the collection and acquisition of biomass, sometimes putting undue stress on the biomass resource and its availability. The result is either failure to financially close and complete the project or sterilisation of biomass catchment areas such that other projects cannot also be completed, or both. This has an adverse effect on replicability of similar projects and on effective deployment.
TIPPING SUGAR CANE
STORED BAGASSE
Funding the biomass projects
Funding the biomass projects has to take into account issues such as the financial and political stability of the countries, security of payments and confidence in the technologies.
The financial and political instability of many developing countries, particularly those which have high biomass potential, is a major impediment to financing commercial projects. In fact a large number of countries are simply off the radar screen for financing institutions, whether they are multi-lateral, bi-lateral or private sector. Unless the G8 and other industrialised countries can come up with a formula which provides financial security for biomass and other renewable projects, no headway at all will be made by the private sector in these countries.
Using biomass technologies to produce electricity is a relatively new concept for financiers of biomass projects. There is a common misconception, particularly in the finance sectors, that biomass technologies are not yet commercially proven. Biomass technologies have been around since the start of the industrial revolution. Every sugar mill and every palm oil mill around the world have had their own biomass boilers fuelled by their own biomass waste from the beginning. Many, particularly those remotely located, also have their own steam turbo-generators and are completely energy self-sufficient and have been reliably operating for more than 100 years. Traditional biomass combustion systems are as proven as can be. Gasification technologies have also been successfully proven, driven by fossil fuel shortages in the two World Wars and wood charcoal is produced by pyrolysis.
So why the finance sector's misconceptions? In the UK, the Government has, through financial constraints and a determination to 'lead' the market, only supported the development of 'new' advanced wood conversion systems such as gasification and pyrolysis. It has not supported the re-introduction of wood biomass power using proven combustion technologies. Furthermore, modern biomass has been asked to compete in an electricity market dominated by large scale, coal, oil, gas and nuclear generators, all of which have received a century or more's worth of public subsidy. Until conventional combustion biomass technologies are allowed to find their place in the market, with the equivalent support fossil fuels have received, then they will be deemed to be 'unproven' by the financiers in the industrialised countries.
In the industrialised countries, wood fuel, whether it comes from forestry residues or is grown as an energy crop, is more expensive than coal when prepared and delivered to the power plant. It is no surprise therefore that wood generated electricity is going to be more expensive than fossil fuelled electricity, especially when wood power plants are small compared with conventional gas, coal or nuclear plants and the benefits of scale are not available. Biomass generated electricity will have a hard time being deployed in the market in industrialised countries until there is full acceptance of the different cost basis from fossil fuels or substantial carbon taxes or equivalent start to penalise the use of fossil fuels.
Conclusion
For biomass to grow within the world energy market, it has to overcome barriers such as competition from fossil fired generation, subsidised energy markets, policy restrictions caused by public sector/government biases, physical constraints and lack of confidence within the financial sector. All the above factors restrict the commercial deployment of biomass to a greater or lesser extent and the effects are different in every country. There is no hard and fast rule which applies everywhere.
However, biomass projects will continue to grow as the benefits of co-generation and the value of a negative cost fuel, which can compete with the fully burdened cost of diesel are recognised. Biomass conversion technologies are also becoming more and more efficient therefore maximising conversion efficiencies. These technologies can be located in remote areas or fitted into urban centres, providing essential electricity for local communities or electricity to add to existing capacity.
Internationally, there is a commitment to generate the increasing demand for electricity from clean, renewable fuels. This support will create a rapid increase in biomass projects coming onto the energy market. Biomass will give the world energy market positive socio- economic and environmental attributes which it has not had before.
Bronzeoak develops and supports renewable energy projects. Its background in development, engineering, project and construction management has focused on energy and environmental work, particularly the production of electricity and heat from biomass and waste fuels.
In association with local partners, Bronzeoak is actively developing and arranging finance for biomass to energy projects overseas. Technologies employed include conventional and fluidised bed combustion, pyrolysis, gasification and anaerobic digestion.
ENERGY RECOVERY FROM PALM OIL WASTES
ABSTRACT
In 1998 ninety million tonnes of oil palm fruit production was recorded, 43-45% of this will be mill residues in the form of empty fruit bunches (EFB), shell and fibre. Additional wastes generated include palm fronds and stems. These wastes are currently underutilised. Maximising energy recovery from the wastes is desirable for both economic and environmental reasons. Most crude palm oil mills harness the energy from the shell and fibre in their own low pressure boilers and the EFB's are usually burnt causing air pollution or returned to the plantation. A 60T/FFB/hour mill based within a 10,000 hectare plantation, can generate enough energy to be self sustaining and supply surplus electricity to the grid if it utilises all of its wastes. Boiler technology, gasification, pyrolysis and anaerobic digestion are alternate conversion technologies available to maximise energy recovery. The Clean Development Mechanism will promote the reduction of emissions and sustainable development by encouraging energy projects for the long term, utilising local skills and creating employment.
INTRODUCTION
This paper discusses how energy recovery can be maximised from palm oil wastes. We will look at the current palm oil production climate, in order to establish the amount of palm oil residues generated and where. The residues will be identified and their current usage and disposal assessed along with alternative uses. This then leads on to how energy recovery from the residues can play an essential role in the economics of the mills and how surplus electricity can be fed to the grid. We will discuss the appropriate technologies available. Finally, the implications of the Kyoto Protocol and carbon trading will be addressed.
BIOENERGY IN THE WORLD CONTEXT
Biomass has a significant role to play in solving the worlds energy needs. Biomass combustion is carbon neutral. The carbon dioxide released in combustion is recycled by trees and crops which may provide fuel for the future. By utilising biomass as a fuel instead of a non renewable fossil fuel, the net carbon dioxide released into the atmosphere is deemed to be reduced. Biomass is capable of replacing fossil fuels in order to provide electrical power and generate heat in those areas where it is abundantly available. Commercial, community and environmental benefits also ensue. However, before the biomass projects can be implemented, the commercial viability of projects has to be proven. The cost effectiveness and availability of the resource must be weighted as evenly as the green issues. A project needs to be viable in the long term in order to maintain an economic return and for the project to achieve its environmental, social and technological objectives.
In order for biomass to be widely accepted, overall cost factors have to be fully analysed. Comparing the use of biomass to other established fossil fuels has to be taken into account, together with the investment and infrastructure already in place. Incorporating bioenergy into a holistic framework which assesses the total cost including the environment shows that biomass can be a competitive energy source (Shell, 1999).
THE ENVIRONMENT AND THE FUTURE
It is difficult to estimate the potential contribution of biomass to world energy supplies because it depends on assumptions concerning price, socio-political influences and technical developments. The Riges model (Renewable Intensive Global Energy Scenario) suggested that by 2050 around half the worlds primary energy consumption could be met by biomass. According to the report, promoting energy efficiency and renewables aggressively could reduce global carbon dioxide emission levels to 75% of 1985 levels by 2050. Other assumptions suggest that biomass would expand to produce 18% of electricity requirements during the period 2025-2050. Biomass plantations are envisaged as the main sources of material for modern biomass conversion technologies with degraded and surplus land providing the areas needed. However, existing plantations such as those of oil palm will contribute significantly to this figure, especially in the early years, since the resource is already available.
As populations expand and develop, industrialising economies will require additional energy sources, much of which will be provided by renewable sources. Within twenty five years renewable energy will provide between 5-10% of the worlds energy sources and maybe 50% by the middle of the century (Shell, 1999).
By 2020 electricity use is expected to increase by 97% on the 1995 figure, with demand more than tripling in developing countries. In developed countries an increase of 42% is predicted as new uses are found for electric power. Global energy in that year will be about three times that consumed in 1970. By the year 2020 fossil fuels will have reached a plateau and renewable energy will become significant. Renewable energy will grow to compete with traditional fuels. The energy supply will become more diversified.
PALM OIL PRODUCTION AND RESIDUES
The growth of the oil palm industry is rapid with over 8.8 million hectares under production in 1998. Oil palm fruit production has risen at a huge rate from 11 million tonnes in 1990 to 94 million tonnes in 1998, FAO 1999. By next year yields will be over 100 million tonnes, FAS online 1990, 43-45% of this will become mill residue in the form of Empty fruit bunches (EFB), shell and fibre.
The following chart illustrates the actual and forecast production of residues from the palm oil milling process.
Oil palm residues will continue to accumulate. Residues will not only accumulate from the mills but from the extensive replanting programmes ongoing in plantations. Substantial additional biomass in the form of oil palm fronds and stems will also be generated. Recovering additional energy from palm wastes offers extra financial and environmental benefits without interfering with primary production of oils for the market.
Normally a palm oil mill can achieve a recovery of approximately 93% of the available palm oil from the fresh fruit bunches (FFB's). In general the FFB contains approximately:
Crude palm oil | 21 - 23% |
Palm kernel | 6 - 7% |
Fibre | 14 - 15% |
Shell | 6 - 7% |
EFB | 23% |
The energy which can be generated from these wastes depends on the moisture content. Empty fruit bunches are wet and have a lower calorific value.
Residue | Moisture content | Calorific value |
EFB | 65% | 4.4 MJ/kg |
Fibre | 40% | 9.6 MJ/kg |
Shells | 25% | 13.4 MJ/kg |
Fronds | 3.0 MJ/kg | |
Palm wood | 7.4 MJ/kg |
PRINCIPLES OF WASTE MANAGEMENT
The Fundamental principles of waste management are to 'Minimise, Recycle, Recover (energy) and finally Disposal'. These principals apply as much to agro-industrial wastes such as palm oil residues as they do to municipal waste. We can simply no longer afford to dispose of, or dump the residues when there is an economically useful alternative.
Whilst our aim here is to address the potential for recovery of energy in the palm oil industry we must first consider the current uses and disposal of mill residues.
CURRENT USES AND DISPOSAL OF MILL RESIDUES
- Fibre and shell
Typically crude palm oil mills use fibre and shell as a boiler fuel to produce process steam for sterilisation, etc and also possibly for electricity generation as an alternative to diesel generation. The power house may also have to supply electricity for other parts of the mill complex. These residues make oil palm mills self sustainable in energy. The fibre and shell alone can supply more than enough energy to meet the mill's requirements using low pressure relatively inefficient boilers.
- Empty Fruit Bunches
The empty fruit bunches have traditionally been burnt in simple incinerators, as a means of disposal and the ash recycled onto the plantation as fertiliser. This process causes air pollution and has now been banned in some countries, for example Malaysia. Under this route of disposal no energy is recovered. Alternatively EFB can be composted and returned to the plantation, or returned directly as mulch.
Using the EFB's as a mulch or compost can reduce the applied fertiliser cost and is a step towards environmental conservation by reducing dependence on fossil fuel required for the manufacture of inorganic fertiliser. However, inorganic fertilisers are still necessary for growth. Oil palm makes heavy demands on the nutrient supplies of the soils, especially K and N. Therefore it is essential that nutrients are returned to the soil.
Empty fruit bunches are a good sources of organic matter and plant nutrients. It has been calculated that EFB mulching at 27 tonnes per hectare is equivalent to the current fertiliser practice involving inorganic fertilisers. It is claimed that using the EFB as mulch has several advantages for the nutritional sustainability of the plantation. Mulch benefits crop production because it releases nutrients slowly to the soil via microorganisms therefore effectively recycling the plant nutrients. It improves the soil structure due to better aeration, increases the water holding capacity and increases the soil pH. It is claimed that this also increases the FFB yield over and above the increase due solely to the fertiliser value.
However, since FFB return only just over 20% EFB from an average production of 25tonnes/FFB/Ha only about 5 tonnes of EFB can be returned to the field as nutrients. So only 1/5 to 1/6 of the plantation can be maintained without inorganic fertilisers (Loong et al, 1987). Some plantation owners claim that the benefits of EFB as fertiliser and as a soil conditioning agent are significant, whilst other mill owners welcome alternate methods of disposal. This is due to the inconvenience of handling and transporting, as well as the costs and problems concerning disposal of the wastes onto the plantation.
On the optimistic side, the value of returning the EFB to the plantation can be quantified as follows:
- Typically a hectare yields about 25T FFB, which results in 5.5T EFB.
- At 35-50T/ha/y spreading rate, only 11-16% plantation can be treated
- 1T/ FFB/ha/yr is gained due to soil conditioning effect above the pure fertiliser benefit
- Total benefit of spreading EFB is $ 60/ha (value of fertiliser saved/ha)
plus $120/ha/yr (Value of increase yield of FFB)
$180/ha/yr - Estimated benefit in tonnes EFB $ 3.6 to $5.1/T EFB
- Allowing for transport and spreading costs
the net benefit value is: $ 2.1 to $3.3/ T EFB
This can also be considered to be the cost of EFB if it is alternatively used as a fuel.
The following conclusions can be drawn. The net value of EFB as a fertiliser and soil improver, allowing for transporting the EFB back to the plantation varies depending on the soil type/conditions. For a mature plantation in Indonesia, for example, the net value of the EFB can be expected to range form zero to as high as $6.9/T/EFB with perhaps a typical value of $2-3/T/EFB. Many owners find the transporting and handling of the wastes a nuisance and often the wastes are not properly spread around the plantations. For many the process of transporting the wastes into plantations over 10,000 hectares is not feasible time wise or economically. The other conclusion is that EFB's can only cover an average one fifth of the plantation and there is still a need to have inorganic fertilisers bought in to supplement the rest of the plantation, in any case.
EFB are a resource which has huge potential to be used for power generation, currently not being utilised.
- Palm Oil Mill Effulent (POME)
POME is generated mainly from the sterilisation and clarification processes. It is made up of @ 95-96% water, 0.6%-0.7% oil and 4-5% total solid including 2-4% suspended solids which are mainly debris from palm mesocarp.
Most palm oil mills and refineries have their own treatment systems for POME, which due to its high organic content is easily amenable to biodegradation. The treatment system usually consists of anaerobic/aerobic ponds. However, because of silting and short circuiting many do not reach discharge standards to water courses. This situation can be significantly improved by introducing enclosed anaerobic digestion systems which reduce the BOD/COD of the effluent and capture methane, one of the more potent greenhouse gases. The energy in the methane can then be recovered, either as a supplementary boiler fuel, or in a biogas engine generator. When the BOD level is reduced to below 5000 ppm, the digested material can be applied to land as a fertiliser. This can also create savings on fertiliser costs within a plantation (Ngan, 1995).
Other uses of POME include use as an animal feed equivalent to rice bran.
- Stems and fronds
One hectare supports approximately 130-143 trees. A hectare can also produce 10 tonnes of palm fronds. Estimates from 1993-1994 suggested that 44,000 hectares had to be replanted in Malaysia which involved felling approximately 6 million palms. This leaves a lot of waste wood and fronds. These wastes are currently often left on the ground as mulch, composted or burnt. There is an obvious benefit for soil fertility and structure, if properly managed. The wastes can also be harnessed for significant energy recovery.
ALTERNATIVE USES OF WASTES
- Pulp and paper from oil palm fibres
The fibre from EFB resembles the short fibred hardwoods like Eucalyptus. The high number of fibres/unit weight indicates the paper from EFB would have good printing properties and a good formation within paper making. Studies show that EFB could produce thin, high quality printing paper, speciality papers for example for cigarette and photographic papers and security papers.
- Preformed furniture from trunks and fronds
Oil palm fronds and trunks have been chipped and waxed with resin to produce pre formed desk tops and chair seats for schools. The furniture is characterised for resistance against knocks, scratches, ink, termites and fungus (Hassan et al, 1997)!
- Planting medium/substitute for rock wool
Oil palm wastes can be reduced in size and processed into blocks of planting medium. The medium can be used to grow a wide range of vegetables. The product is biodegradable, has good water retention and fertiliser qualities. It is readily available and produced from renewable resources (Kamarudin, 1995).
- Charcoal briquettes
Proprietary proposals have been made to chip and dry EFB and then pyrolyse it to produce charcoal, which in turn can be briquetted for use as a fuel.
MAXIMISING ENERGY RECOVERY
Palm oil mill residues are currently underutilised. Maximising energy recovery from the wastes is desirable for both economic and environmental reasons.
As mentioned before, most crude palm oil mills harness the energy from the shell and fibre in their own low pressure steam boilers. The introduction of advanced cogeneration (combined heat and power) can play a major role in combatting climate change, as well as introducing significant economic benefits. Cogeneration cuts energy/fuel costs, uses fuels at high conversion efficiencies which results in an overall reduction of emissions of carbon dioxide and other pollutants. However, it is only worth doing if one can sell the additional surplus energy (electricity) to a customer at an economic rate. Nowadays the ability to sell electricity into the local grid provides an opportunity to turn waste into a valuable commodity.
- Potential electricity generated from waste – world wide!
Forty countries are involved in palm oil production with a world cultivation in 1998 of nearly 9 million hectares. The worldwide production capacity is 94 million tonnes of oil palm fruit.
A approximate estimate of the potential electricity which could be generated is:
94,000,000 T x 132 kWh = 12.4 TWh
Self consumption in palm oil mills is:
94,000,000 T x 12 kWh = 1.1 TWh
Potential surplus electricity that could be used outside the mills is 11.3 TWh annually. At current per capita consumption this could provide electricity for 12 million people in countries with utilisation similar to Thailand.
CASE STUDY – A WORKING MODEL – SUPPLYING ELECTRICITY TO THE GRID (INDONESIA)
It has been estimated in a particular case study that a 60T/FFB/hour mill, located within a 10,000 hectare plantation, can generate enough energy to be self sustaining and to supply surplus electricity to the grid if it utilises all of its wastes. The mill has a gross electrical output of 7843 kW and when the mill is not operating a maximum net output of 7216kW. There is a high process steam demand which causes the electrical output to fall to 4128kW. After deducting the energy utilised by the mill the net quantities available to sell to the grid are 7096kW when the mill is not operating and 3428 kW whilst in operation.
Factory profile (10,000 hectare plantation) 7.8 MW plant | ||
Installed capacity | 60 T FFB/hour | |
Actual production target | 250,636T/FFB/Year | |
Daily Quantity | 964 T/FFB | |
Effective working days | 260 | |
Effective working hours | 16 | |
Products: | 54,137T/year CPO (21.60T/100TFFB) | |
Residues generated | ||
EFB | 60,162T | 24.0 |
Fibre | 30,578 | 12.2 |
Shell | 16,792 | 6.7 |
Liquid waste | 72,528 | 28.9 |
Unrecovered oil/kernel etc | 16,439 | 6.6 |
Type | Medium pressure boiler system | |
Process steam requirement | 425-500kg/T of FFB | |
Electricity produced: | ||
Mill shut down | ||
Elec.output (gross) (kW) | 7,843 | |
Elec.output (net) (kW) | 7,216 | |
Elec. to grid (kW) | 7,096 | |
Mill operating | ||
Elec. Output (gross) (kW) | 4,755 | |
Elec. Output (net) (kW) | 4,128 (after steam demand) | |
Elec. to grid (kW) | 3,428 | |
Elec. To host | 3,502,008 (kWh/year) | |
Elec. To grid | 41,841,505 (kWh/year) | |
Total Elec. | 45,343,513 (kWh/year) | |
- Additional sources of biomass and effect on case study
The palm fronds have the potential energy quantity of approximately equal to that of fibre or about 2.5MW in electrical base load equivalent. However, they are not always available since they are usually left in the plantation as mulch.
The usage of dead palm trunks could increase the electrical output by about 3.3MW. The additional cost of collecting and preparing the palm trunks has to be allowed for.
Energy can also be recovered from the anaerobic digestion of the POME although this is less significant at 260 kW. However, the biogas may help combustion stability and reduce the need for any oil firing when the fuel moisture content is high.
The above information suggests that a typical 10,000 hectare plantation could result in a power plant with a output of between 5MW and 11 MW (at a better boiler heat rate) produced entirely from its own biomass waste. These figures also take into account the steam requirements. If wastes are also utilised from other mills the power output is much higher.
ALTERNATIVE CONVERSION TECHNOLOGIES
In order for the plant to run more efficiently various options within the plant can be considered.
- Boiler technology
A traditionally designed palm oil mill burns all its fibre and about 50% of its shell in order to produce the electrical and process steam needs of the plant while the mill operates. The boilers are normally low pressure, typically 20 bar and feed back pressure steam turbines. A 60 T/hr FFB mill requires approximately 700kWe and 21,000kWth (30 te/hr process steam at 3.5kg/cms and 270°C*). This represents a very low cycle efficiency for the production of electricity approximately 3.5% but a very high overall cogeneration efficiency which exceeds 90%.
By raising the boiler pressure and introducing condensing steam turbines with extraction to provide process steam, the use of palm oil residues can be optimised in more energy efficient systems. Using a boiler pressure of 45 bar, medium pressure, with a condensing steam turbine and the same process steam as before, results in a cycle efficiency for electrical production of about 13%. In addition, the boiler can be designed to burn all of the wastes not just the fibre and shell. At 13% efficiency, the fibre from one tonne of FFB will produce about 41kWhe, shell will produce about 47kWhe and EFB will produce about 46kWhe. The total waste from 1T of FFB will, therefore, produce about 132kWe. This compares to only about 12kWe per 1T of FFB for the waste from the traditionally designed plant. For example a 60 T/h FFB mill could produce 8040 kWe. With mill use remaining at 700kWe, the surplus available for export would be 7340 kWe.
A high pressure boiler system, 65 bar, 450°C, costs about 35% more than a 45 bar system for both capital and O&M costs. The increase in efficiency going from 47bar/370°C to 65 bar/ 485°C will be about 25%. Alternatively, the MW output should increase from 7.34 MWe (net) to about 10.78 MWe (net). Table1 summarises the above.
Table 1 Boiler summary
Low pressure | Medium pressure | High pressure | |
Pressure/ boiler outlet conditions | 20bar/270°C* | 45 bar/370°C | 65 bar/485°C |
Capital cost | Base cost | 35% more | |
Cycle efficiency:process | 17% | 25% | |
Mwe (net) | 7.3MWe | 10.78Mwe |
- Boiler combustion and EFB
Utilising EFB's in the boiler can create combustion problems due to the moisture content of the fuel (60-65%), its fibrous nature and the amount of soluble alkalis contained within it. A solution to the problem of machine wear is the use of a shredder to reduce materials and moisture content. The moisture content needs to be reduced to 40% or less before it can be used in a boiler. A special screw press can be used for this.
Solutions concerning the combustion of palm oil wastes include:
The fluidised bed approach. This approach however, is not useful when the soluble alkalis are as high as they are in palm oil since the temperatures in the bed exceed the eutectic temperature, indicating that slagging in the bed will result. It is also more expensive than a stocker approach.
Combustion should be staged in order to minimise the production of nitrogen oxides and to promote better burnout of the carbon in a fuel. This approach has been refined to handle high moisture wastes, such as EFB, where temperatures in the lower furnace remain low.
- Large scale gasification
This process involves heating solid or semi solid carbonaceous material with steam and limited amounts of air. Some of the material burns to maintain the temperature and the rest reacts chemically with the residual oxygen present and with the steam to produce fuel rich gases. The gas produced from biomass has a calorific value of about 14% of natural gas. The resulting gases can be burned in conventional boilers after suitable clean up but are most efficiently used in gas turbines as part of an integrated gasification combined cycle (IGCC) process. The use of gas turbines with steam turbines in a combined cycle generation for electricity generation, coupled with biomass gasification offers theoretical efficiency gains over the use of conventional steam boilers and turbines.
However, gasification has not yet been commercialised successfully and has never been used for palm oil wastes. The technology requires a consistent fuel with a low (10-15%) moisture content and is unlikely to be economically competitive with combustion technologies below a capacity of about 30MW.
- Pyrolysis
Pyrolysis involves heating biomass or other organic material in the absence of oxygen so that volatile materials are driven off leaving a solid residue or char behind. These volatiles are then condensed as hydro-carbon rich liquids or bio-oils which can be used as a fuel for diesel engines or gas turbines. The residual char can be burnt as it is or sold as charcoal. Pyroloysis has not been used for the disposal of palm oil wastes. However, there are potentially major advantages in locations where it is not possible to sell electricity economically or at all. Bio-oil and charcoal can be transported elsewhere where they can be economically used. Conversion of biomass can be de-coupled from energy recovery.
- Anaerobic digestion
Anaerobic digestion, whilst treating effulent, produces a valuable product, in captured methane rich biogas.
In a 60 T/FFB per hour palm oil mill operating for 20 hours per day, approximately 20,000 cubic metres of biogas can be obtained per day. The gas has a calorific value of 53,000kcal per cubic metre. The gas contains about 65% methane, 35% carbon dioxide and less than 2000mg/L of hydrogen sulphide, (Ma 1999).
CLEAN DEVELOPMENT MECHANISM AND CARBON EMISSIONS TRADING
The Kyoto Protocol was adopted in December 1997 in response to the Earth summit held at Rio de Janeiro in 1992. It reflects the objectives of the UNFCC (United Nations Framework Convention on Climate Change) to stabilise the concentration of green house gases in the atmosphere. Developed countries (Annex 1) are responsible for 80% of the worlds emissions of green house gases. The Kyoto Protocol caused the Annex 1 countries to reduce their emissions by 2008-2012 to levels 5% lower than those emitted in 1990. In order for parties to achieve this, a number of flexible mechanisms were employed including 'emissions trading and the Clean Development Mechanism (CDM). Each Annex 1 country has been assigned a given amount which will be equal to the greenhouse gas emission limit for that party. The tradeable units are one tonne of carbon dioxide equivalent. At the moment a price of $20/metric tonne is being considered for forward sales, with the possibility that this will rise to over $100 when the mechanism is fully operational. The Annex 1 countries will be able to buy or sell permits. The mechanisms reduce the overall price of meeting the Kyoto targets by allowing countries with high reduction costs to acquire "emission credits" from countries where reductions are cheaper or free.
The purpose of CDM is to assist developing countries to achieve sustainable development by encouraging energy projects which are long term, utilise local information and technologies and create employment. It will also assist the Annex 1 countries in achieving compliance with their quantified emission limitation and reduction commitments by paying money to finance climate friendly projects in non Annex 1 countries. The CDM will benefit developing countries which are rapidly industrialising by reducing emissions and creating cleaner industrial environments. It will keep a focus on the environmental consequences of industrial activity. At the same time external investment in developing countries will also be encouraged.
Developing renewable energy projects, using palm oil residues for example, in countries that are rapidly becoming industrialised affords a challenge. The countries are seeking to grow economically whilst being confronted with the environmental lessons learned in the process of economic growth by the industrialised countries. Within developing countries much of the infrastructure that would support an industrialised economy is not yet in place. This allows greater scope for alternative energy sources and patterns of end use consumption as this new capital stock is put into place. Of course rapidly industrialising economies are not going to adopt patterns of energy production and consumption if they are perceived as policies which are more costly and likely to undermine impending growth objectives. However, in certain locations, palm oil residues are already competitive with existing fossil fuels, so the combined objectives of economic growth and reduced environmental impact can be achieved.
MAXIMISING ENERGY FROM BIOMASS
Biomass is the fourth largest energy resource after coal, oil and natural gas. It has been used as a fuel for millennia and in many parts of the world, especially in rural areas in developing countries, it still is. Today biomass fuels are being revived having been displaced by fossil fuels for energy generation. It is now being reconsidered as a fuel for advanced forms of electricity generation.
This change around from fossil fuels to sources of renewable energy has been gathering momentum since the 1970's when oil prices were raised and oil availability was questioned. Additionally rapid global industrialisation and a growing hydro-carbon dependent society has raised legitimate concerns on the intensive use of finite fossil fuels and their degrading effect on the environment. Over the past 100 years the average temperature of the earth's atmosphere has risen by 0.5° C. It is predicted that by 2100 there will be a rise of between 1°C and 3.5° C. This rise is being attributed to the 'enhanced green house effect', caused by heightened carbon dioxide, methane, halogenated compounds and nitrous oxides released into the atmosphere, EC 2000.
Currently the world energy system is based largely on fossil fuels. They provide 80% of the worlds commercially available energy. Without considerable policy changes this figure will rise to 90% by 2020. Energy demand will increase in relation to the rapid economic growth in Latin America, Africa and the Asia-Pacific region. The World Bank has estimated that over the next four decades developing countries will require five million megawatts of new electrical generating capacity to meet the anticipated needs. Currently the world's total installed capacity is three million megawatts, IEA, 1999.
Renewable energy sources will capture a huge portion of the demand for power. It is also important that renewable energy technologies are transferred to the developing world to contribute to global climate change commitments.
Renewable energy means electricity generated from solar, wind, biomass, geothermal and hydropower resources. The drive for the use of renewable sources of energy to replace fossil fuels was expressed most vociferously in 1992 at the Earth Summit in Rio de Janeiro. In response, the Kyoto Protocol was adopted in 1997 and reflects the objectives of the UNFCC (United Nations Framework Convention on Climate Change) to stabilise the concentration of green house gases in the atmosphere. The Kyoto Protocol is calling for all industrialised (annex 1) countries to reduce their emissions by 2008-2012 to levels 5% lower than those emitted in 1990 in an attempt to challenge climate change.
This paper summarises the commercially proven technologies used to maximise the energy arising from agricultural residues. The technologies reviewed are direct combustion and steam technologies and biochemical processes (anaerobic digestion). Three case studies will be examined which include: anaerobic digestion of pig slurry in China; combustion and steam cycle technologies involved in converting palm oil mill residues to energy in Indonesia and the energy conversion technology used to turn rice husks to energy, whilst producing a practical by product. The projects will avoid 30,000, 600,000 and 216,000 tonnes of carbon emissions over the next thirty years respectively. The projects described are being developed with support from the UK government's Climate Change Challenge Fund.
Biomass to Energy–Project criteria for energy conversion
The physical and chemical properties of differing biomass materials determines that gauging the most suitable technology for fuel processing and conversion to heat and electricity is critical in order to optimise conversion efficiency. Biomass is also carbon neutral, the carbon released on combustion is assimilated by the biomass source by photosynthesis when it is growing. The prime, practical concerns which need to be taken into account when developing biomass projects are listed below.
- The security and long term availability of biomass fuel supply including variations in types of fuel, seasonality and availability coverage.
- Technical issues of plant design to address moisture content, bulk density, particle size and distribution, ash content, chemical properties such as alkali content for example.
- Practical location considerations and local technological capability.
- The ability to find a contracted long term user of electricity or steam generated from biomass resources.
- The ability to make use of value added by-products of the process.
- The project economics and ability to secure equity and debt financing for the project.
- The environmental and socio-economic benefits derived from carrying out the project, Stowell 1998.
Case study – Oil palm residues to energy in Indonesia
Indonesia is the second biggest palm oil producing country in the world, after Malaysia, representing 18% of the world-wide production. The Indonesian palm oil industry continues to expand rapidly using large mills which produce hundreds of tons of waste on a year round basis. Considerable opportunity exists in Indonesia and other countries to produce significant quantities of electricity from the residual biomass while mitigating environmental impacts both locally and globally, Walden, 1997.
The case study is based on utilising palm oil residues generated from the palm oil production process. The fresh fruit bunches (FFB) or the oil palm fruit produce Crude palm oil (CPO) and Kernel palm oil (KPO). The residues in terms of percentage by weight of the incoming FFB's are:
- Empty fruit bunches (EFB) 24%
- Fibre (from fruit after oil extraction) 12%
- Shells (from fruit) 7%
- Liquid waste 29%
- Unrecovered oil 2-5%
Residues will not only accumulate from the mills but from the extensive replanting programmes ongoing in plantations including palm fronds and stems.
Two hundred and twenty thousand tonnes per year of residues are collected from six mills. The residues are additional to the wastes that the six mills use for their own steam and power use. The basic concept of the project is to collect the wastes from the mills, transport the wastes to a central site for preparation, burn the waste in a specially designed but generally conventional, water tube boiler to generate electricity by a steam turbine generator. Steam will be extracted from the steam turbine for use by the mill as process steam. A substation will be constructed here to transmit the surplus electricity generated from the residues. Maximum generating capacity is estimated to be 10.5 MWe.
The principle fuel will be the EFB's with smaller quantities of shell and fibre. All fuels will be procured under long term supply contracts. Since the quantity of waste varies with the season, the blended waste fuel will also vary. In the high growth season, it is anticipated that up to 100% EFB will be burned. In the low growth season, the EFB quantity will be supplemented by shell and fibre which has been stored during the high growth season.
Traditionally the EFB's have been burnt in simple incinerators, as a means of disposal and the ash recycled into the plantation as fertiliser. Slow burning incineration gives rise to incomplete combustion resulting in excessive emissions of particulate matter and partially oxidised derivatives, some of which are toxic. Chemically bound nitrogen and sulphur present in the biomass are oxidised to nitrogen and sulphur oxides. Pollution also arises from open burning of the wastes. Incineration is progressively being phased out and has already been banned in Malaysia.
At the centralised plant, a well designed combustion and air pollution control system will be installed to limit emissions to internationally acceptable standards. By standing down diesel elsewhere, 10.5 MW of biomass fuelled generation will avoid approximately 16,800 tonnes/year of carbon emissions. An additional 3,500 tonnes/year of carbon emissions from open bonfires will also be saved. Over the thirty year life of a project there will be a total saving of approximately 600,000 tonnes of carbon.
Direct Combustion and Steam Cycles
A traditionally designed palm oil mill burns all its fibre and about 50% of its shell in order to produce the electrical and process steam needs of the plant while the mill operates. The boilers are normally low pressure, typically 20 bar (or lower) and supply back pressure steam turbines. A 60 T/hr FFB mill requires approximately 700kWe and 21,000kWth (30 T/hr process steam at 3.5kg/cm and 270°C). This represents a very low cycle efficiency for the production of electricity (approximately 3.5%) but a high overall co-generation efficiency exceeding 90%.
By raising the boiler pressure and introducing condensing steam turbines with extraction to provide process steam, the use of palm oil residues can be optimised in more energy efficient systems. Using a 45 bar medium pressure boiler, with a condensing steam turbine and the same process steam as before, the cycle efficiency for electrical production rises to about 13%. In addition, the boiler can be designed to burn all of the wastes not just the fibre and shell. At 13% efficiency, the fibre from one tonne of FFB will produce about 41kWh, shell about 47kWh and EFB about 46kWh. The total waste from 1 tonne of FFB will, therefore, produce about 134kWe. This compares to only about 12kWe per tonne of FFB for the waste from the traditionally designed plant. For example a 60 T/h FFB mill could produce 8040 kWe. With mill use remaining at 700kWe, the surplus available for export would be 7340 kWe.
A high pressure boiler system, 65 bar, 450°C, costs about 35% more than a 45 bar system for both capital and O&M costs. The increase in efficiency going from 47bar/370°C to 65 bar/ 485°C will be about 25%. Alternatively, the MW output should increase from 7.34 MWe (net) to about 10.78 MWe (net).
Boiler combustion and EFB
Utilising EFB's in the boiler can create combustion problems due to the moisture content of the fuel (60-65%), its fibrous nature and the amount of soluble alkalis contained within it. Machine wear is minimised by using a shredder to reduce material size and moisture content. The moisture content needs to be reduced to 50% or less before it can be fed to the boiler without use of supplemental fuel. This can be achieved by suitable preparation using a shredder and screw press.
Solutions concerning the combustion of palm oil wastes include:
-
The fluidised bed approach. This approach however, is not useful when the soluble alkalis are as high as they are in palm oil waste, since the temperatures in the bed will exceed the eutectic temperature, indicating that slagging in the bed will result. It is also more expensive than a stoker approach.
- Combustion should be staged in order to minimise the production of nitrogen oxides and to promote better burnout of the carbon in a fuel. This approach has been refined to handle high moisture wastes, such as EFB, where temperatures in the lower furnace remain low to promote drying before combustion occurs.
Case Study – Maximising energy from rice husks by producing electricity and a practical by product
In Indonesia over 11 million hectares are under rice cultivation producing approximately 50 million tonnes of rice in 1997. This resulted in over 14 million tonnes of residual rice husk being produced. The majority of this is disposed of by open burning
This case study is based on a plant which will require 31,000 tonnes/year of rice husk to produce 3 MW. Approximately 20% of harvested rice remains as husk after milling which means that the plant will consume the husk from about 155,000 tonnes of rice paddy. The plant will therefore be located in a catchment rice producing area of 8-14,000 hectares. As with the palm oil wastes, utilising the wastes to fuel a power plant with the correct combustion system will result in rice husks being converted to electricity efficiently. The environmental benefits include providing a disposal route for a large quantity of waste and avoiding uncontrolled burning. In addition, if the combustion process is properly designed, the high silica ash can be used as a valuable by-product for the steel industry or for the manufacture of light weight, high strength blocks for building. Value is being maximised from the biomass by producing additional by products.
The project will lead directly to reductions in greenhouse gas emissions because diesel generation will be replaced with carbon neutral biomass. Assuming that the 3 MW plant results in the backing off of fossil fired power plants burning oil, the avoided carbon emissions accumulated at a rate of about 0.3kg/kWh would result in credits of 7,200 tonnes/year of carbon emissions. Over the thirty year life of the plant, 216,000 tonnes of carbon can be avoided.
The husks are combusted in boilers and electricity generated by steam. Due to the rice husks having different physical and chemical properties to the oil palm residues, the boiler/combustion process is different. Rice husks are a relatively low density, low moisture but high ash fuel with a good calorific value. In addition the ash has a high silica content. Due to its low density there is a possibility for unburned husk to be carried out of the boiler with associated loss of efficiency and increased loss on ignition (LOI) of the ash. The high silica content of the ash can result in accelerated wear in the convection and final stages of the boiler. Provided the boiler is designed to produce an ash with high amorphous silica and low granula silica, the ash is a valuable additive for production of concrete blocks and for other purposes.
Conclusion
Developing renewable energy projects, in countries which are rapidly becoming industrialised affords a challenge. These countries are seeking to grow economically whilst being confronted with the environmental issues encountered in the process of economic growth by the industrialised countries. Within developing countries much of the infrastructure that would support an industrialised economy is not yet in place. This allows greater scope for alternative energy sources and patterns of end use consumption as new capital stock is put into place. Of course, rapidly industrialising economies are not going to adopt patterns of energy production and consumption if they are perceived as policies more costly and likely to undermine impending growth objectives. However, in certain locations, agricultural residues such as palm oil residues are already competitive with existing fossil fuels, so the combined objectives of economic growth and reduced environmental impact can be achieved.
Maximising energy from biomass with specific projects requires a practical view to be taken. These include the security of long term fuel supply; awareness of the technical issues of plant design to address the wide variety of physical and chemical properties of biomass; a suitable location and knowledge of local technological capacity; a long term user of electricity or generated steam; the ability to maximise the use of value added by products and sound project economics. The case studies described are designed to be highly replicable whilst maximising the energy produced from biomass. This will lead to creating not only a clean environment but will contribute to providing employment, improving local and national economies, creating awareness of the environment and help with the challenge to prevent further adverse climate change.
