Description

Renewable Energy Group Assignment on Solid BiomassEnergy Supply

Group A

MSc Energy Supply Renewable Energy Group Assignment on Solid Biomass

2nd December 2008

Table of Contents

1Introduction

2Biomass Technologies

2Thermal systems

3Biological systems

3Anaerobic digestion

3Fermentation

3Bio fuels

4Maximising Biomasss contribution to the final energy consumption

41.Minimization of conversion losses

42.Final energy yields per hectare - as high as possible

43.Low production cost

5Global Biomass Availability

6Market development and international trade

8Main Uses Regarding World Scene

8Powering Transport

8Heat

8Electricity Production

9Advantages to Biomass

12Disadvantages of Biomass

Introduction

Energy supply is the subject of major universal concern. Volatility in the oil and gas markets, threats to a secure and stable supply and climate change have all pushed it up the international agenda. In its February 2007 report, the Intergovernmental Panel on Climate Change (IPCC) warned that global emissions must peak no later than 2015 and rapidly decrease after that in order to avoid dangerous climate change. Moving to an emissions pathway that will hold temperature increases and other impacts to a minimum will require a colossal effort. The technology is currently available to do this. The renewables industry is ready for take off and opinion polls show that the majority of people support this move. There are no real technical obstacles in the way of an Energy Revolution, and now with the required political support in place we can start rebuilding the energy sector. In this report we will concentrate on the future potential of Solid Biomass to the Global Renewable Energy Revolution.

Biomass is a broad term used to describe material of recent biological origin that can be used as a source of energy. This includes wood, crops, algae and other plants as well as agricultural and forest residues. Biomass can be used for a variety of end uses: heating, electricity generation or as fuel for transportation. The term bio energy is used for biomass energy systems that produce heat and/or electricity and bio fuels for liquid fuels used in transport.

Today, renewable energy sources account for 13% of the worlds primary energy demand, Figure 1 below. Biomass, which is mostly used in the heat sector, is the main renewable energy source. The share of renewable energies for electricity generation is 18%. The contribution of renewables to heat supply is around 24%, to a large extent accounted for by traditional uses such as collected firewood.

Figure 1: World Primary Energy Demand in Reference Scenario (Mtoe)

Biomass Technologies

A number of processes can be used to convert energy from biomass, Figure 2 below. These divide into thermal systems, which involve direct combustion of solids, liquids or a gas via pyrolysis or gasification, and biological systems, which involve decomposition of solid biomass to liquid or gaseous fuels by processes such as anaerobic digestion and fermentation.

Figure 2: Main conversion options for biomass to secondary energy carriers [WEA, 2000]Thermal systems

Direct combustion is the most common way of converting biomass to energy, for heat as well as electricity. Worldwide it accounts for over 90% of biomass generation. Technologies can be distinguished as fixed bed, fluidised bed or entrained flow combustion. In fixed bed combustion, such as a grate furnace, primary air passes through a fixed bed, in which drying, gasification and charcoal combustion takes place. The combustible gases produced are burned after the addition of secondary air, usually in a zone separated from the fuel bed. In fluidised bed combustion, the primary combustion air is injected from the bottom of the furnace with such high velocity that the material inside the furnace becomes a seething mass of particles and bubbles. Entrained flow combustion is suitable for fuels available as small particles, such as sawdust or fine shavings, which are pneumatically injected into the furnace.

Gasification Biomass fuels are increasingly being used with advanced conversion technologies, such as gasification systems, which offer superior efficiencies compared with conventional power generation. Gasification is a thermochemical process in which biomass is heated with little or no oxygen present to produce a low energy gas. The gas can then be used to fuel a gas turbine or combustion engine to generate electricity. Gasification can also decrease emission levels compared to power production with direct combustion and a steam cycle

Pyrolysis is a process whereby biomass is exposed to high temperatures in the absence of air, causing the biomass todecompose. The products of pyrolysis always include gas (biogas), liquid (bio-oil) and solid (char), with the relative proportions of each depending on the fuel characteristics, the method of pyrolysis and the reaction parameters, such as temperature and pressure. Lower temperatures produce more solid and liquid products and higher temperatures more biogas.

Biological systems

These processes are suitable for very wet biomass materials such as food or agricultural wastes, including farm animal slurry.

Anaerobic digestion

Anaerobic digestion means the breakdown of organic waste by bacteria in an oxygen-free environment. This produces a biogas typically made up of 65% methane and 35% carbon dioxide. Purified biogas can then be used both for heating and electricity generation.Fermentation

Fermentation is the process by which growing plants with a high sugar and starch content are broken down with the help of micro-organisms to produce ethanol and methanol. The end product is a combustible fuel that can be used in vehicles.

Biomass power station capacities typically range up to 15 MW, but larger plants are possible of up to 400 MW capacities, with part of the fuel input potentially being fossil fuel, for example pulverised coal. The worlds largest biomass fuelled power plant is located at Pietarsaari in Finland. Built in 2001, this is an industrial CHP plant producing steam (100 MWth) and electricity (240 MWe) for the local forest industry and district heat for the nearby town. The boiler is a circulating fluidised bed boiler designed to generate steam from bark, sawdust, wood residues, commercial bio fuel and peat. A 2005 study commissioned by Greenpeace Netherlands concluded that it was technically possible to build and operate a 1,000 MWe biomass fired power plant using fluidised bed combustion technology and fed with wood residue pellets42.

Bio fuels

Converting crops into ethanol and bio diesel made from rapeseed methyl ester (RME) currently takes place mainly in Brazil, the USA and Europe. Processes for obtaining synthetic fuels from biogenic synthesis gases will also play a larger role in the future. Theoretically bio fuels can be produced from any biological carbon source, although the most common are photosynthetic plants. Various plants and plant-derived materials are used for bio fuel production. Globally bio fuels are most commonly used to power vehicles, but can also be used for other purposes. The production and use of bio fuels must result in a net reduction in carbon emissions compared to the use of traditional fossil fuels to have a positive effect in climate change mitigation. Sustainable bio fuels can reduce the dependency on petroleum and thereby enhance energy security.

Maximising Biomasss contribution to the final energy consumption

In order to maxamise Biomasss contribution to the final energy consumption there are a number of principles to be considered:

1. Minimization of conversion lossesDepending on what is the final energy product -heat, electricity or biofuels, the efficiency varies between 90% (heat in modern installations) and 25% (electricity production alone in old installations). Therefore, the basic principle is to use the biomass resources as efficiently as possible.

2. Final energy yields per hectare - as high as possibleThe final energy output per hectare varies between 1,0 toe per hectare to 6,0 toe per hectare depending on the plant cultivated and the conversion technology chosen. Therefore, the principle is to prioritize those energy crops and conversion chains that maximize the output of final energy per hectare.

3. Low production cost

The price of final energy (heat, electricity, biofuels) varies depending on what primary fuels (wood chips, pellets, wheat, corn, etc) was used to produce it. Therefore, the principle is to give priority to the most competitive options (calculated without support).

Considering all these principles, it is obvious that in the future the heat followed by liquid fuels should be prioritized. The production of electricity alone is the least favourable option due to the high cost and low efficiency. However, cogeneration (heat and electricity) is possible. Biomass production should be sustainable, maintaining the fertility of the land, biodiversity and taking social aspects into account.

In the context of fuels, biomass is taken to mean any recently grown solid organic matter suitable for burning. This includes wood, grass, and straw.

The advantages of biomass over fossil fuels are that:

Biomass, being a carbon-based (i.e. organic) material, produces carbon dioxide when burnt. However the carbon was extracted from the atmosphere by the growing plant. It is recycled back into the atmosphere on a very short timescale so that there is no net increase in atmospheric carbon dioxide. The energy so produced is renewable and sustainable provided that the source plant is replaced.

There is likely to be some energy consumed in its production and delivery that originates from fossil fuels so that there is a net carbon dioxide emission in practice. This is usually relatively small. Biomass can also be thought of as a short-term solar energy store. The solar energy drives the photosynthesis process whereby the atmospheric carbon dioxide is absorbed and converted into plant tissue.

Global Biomass Availability

There are a number of factors which influence the availability of biomass for energy purposes. The worldwide biomass system is complex and therefore availability is difficult to quantify, particularly when biomass is in direct competition with land for food, fodder, materials and energy. The availability of biomass for energy is also influenced by population growth, population diet, availability of water, agricultural density and nature. Given all these factors a scenario based approach is the most useful way to look at future availability. Projections of the volume of additional biomass that could be made available for energy purposes varies significantly with different assumptions about the rates of technology development and the levels of international trade in food along with different assumptions on population growth and diet.

A scenario which includes high population growth, a meat intensive diet, little improvement in agricultural intensity and high demand for biomass for competing uses or as a carbon sink will add very little to the overall biomass potential. By contrast, in the most optimistic scenario for bioenergy, where population growth is low, diet becomes lessmeat-intensive, agricultural intensity increases significantly and there is less competition for resources, then bioenergy could increase very significantly, providing over 1000 EJ/year. Other factors which need to be considered when generating different scenarios:

1. Will water availability be the same as today, or will it be limited?

2. Biomass utilisation should be done in a balanced and integrated way, looking at systems which optimise the production of food and fodder as well as fuel.

3. There may be potential to develop aquatic biomass (algae) as a new resource in the oceans.

4. Priority must be given to the supply of food, if the price of bioenergy created competition between food and energy supply it would possibly affect food supply.

Globally, suitable abandoned cropland and pastureland amounts to approximately 1.5 million square miles. Realistically, energy crops raised on this land could be expected to yield about 27 exajoules of energy each year. This is a huge amount of energy, an exajoule is a billion billion joules which is equivalent to 172 million barrels of oil. But this biomass yield could satisfy only about 5% of global primary energy consumption by humans, which in 2005 was 483 exajoules.

Figure 3 below gives an overview of the global potential of biomass for energy (EJ per year) to 2050, it pulls together data extracted from 3 research papers covering a number of categories and the main preconditions and assumptions to determine these potentials

Figure 3: Overview of the global potential of biomass for energy to 2050

Market development and international trade

Biofuel and biomass trade flows are modest compared to total bioenergy production but are growing rapidly. Trade takes place between neighbouring regions or countries, but increasingly trading is occurring over long distances.

The possibilities for exporting biomass-derived commodities to the worlds energy markets can provide a stable and reliable demand for rural regions in many developing countries, thus creating an important incentive and market access that is much needed. For many rural communities in developing countries such a situation would offer good opportunities for social-economic development. Sustainable biomass production may also contribute to the sustainable management of natural resources.

Importing countries on the other hand may be able to fulfil cost-effectively their GHG emission reduction targets and diversify their fuel mix.

Given that several regions of the world have inherent advantages for producing biomass and biofuels in terms of land availability and production costs, they may gradually develop into net exporters of biomass and biofuels.

International transport of biomass is feasible from both the energy and the cost points of view. The import of densified or pre-treated lignocellulosic biomass from various world regions may be preferred, especially for second generation biofuels, where lignocellulosic biomass is the feedstock and large-scale capital intensive conversion capacity is required to achieve sound economics. This is a situation comparable to that of current oil refineries in major ports which use oil supplies from around the globe.

Very important is the development of a sustainable, international biomass market and trade. Proper standardisation and certification procedures are to be developed and implemented to secure sustainable biomass production, preferably on the global level. Currently, this is a priority for various governments, market players, and international bodies. In particular, competition between production of food, preservation of forests and nature and use of land for biomass production should be avoided. As argued, this is possible by using lignocellulosic biomass resources that can come from residues and wastes, which are grown on non-arable (e.g., degraded) lands, and in particular by increased productivity in agricultural and livestock production.

Demonstration of such combined development where sustainable biomass production is developed in conjunction with more efficient agricultural management is a challenge. However, this is how bioenergy could contribute not only to renewable energy supplies and reducing GHG emissions, but also to rural development.

Main Uses Regarding World Scene

It is important to identify the main uses of biomass with regard to the world energy solution.

Powering Transport

There is potential for biomass derived Biofuels to replace our dependence on fossil fuels with regard to transport. This is a main area to consider because of our dependence on transport. Below we can see that though Biofuels do not contain the same amount of energy as there equivalent fossil fuel there is a potential to use these fuels for our transport needs.

Diesel calorific value: 43 MJ/kg, Biodiesel calorific value: 37 MJ/kg

Standard petrol calorific value: 40 MJ/kg, Ethanol calorific value: 27 MJ/kg

However there is still the consideration with regard to land use as, for example, Biodiesel yield is 1.4 t/ha and Bioethanol yield is 2 t/ha. As mentioned above the amount of unused agricultural land is approximately 1.5 million square miles (388.5 million hectares), this could produce a significant amount of biodiesel and bioethanol.

Heat

The heating of homes, businesses and the use of heat in industry is the most efficient use of biomass energy with the use of;

Boilers

District heating

CHP

CCHP incorporates cooling potential

In typical conventional power generation, much of the total energy input is wasted. CHP, where the heat produced in electricity generation is used, can reach efficiencies in excess of 85% However, for buildings such as offices, the small heating and hot water demand does not normally show CHP to be cost effective. Where air conditioning is in use, the duty and operating hours of the CHP can be extended by using the rejected heat to fire absorption chillers. This is referred to as tri-generation or combined cooling, heating and power (CCHP).

Unfortunately, the coefficient of performance of absorption chillers is very low compared to modern vapour compression machines so that in new-build installations, gas-fired tri-generation will result in only small or no reductions in CO2 emissions. However, a CHP or tri-generation fired on biomass could result in significant savings.

Electricity Production

The production of electricity from traditional means is the least efficient use of biomass due to the inefficiency of the thermal process which has a maximum efficiency of 60% when using a combined cycle gas turbine and excluding other losses due to transmission and inefficient conversion at power at the usage point especially when using electricity in heating processes.

However, there is the possibility of using biomass to provide base load power to offset intermittence of other sources of renewable energy such as such as wind and wave energy as well as hydro power in dry years.

Advantages to Biomass

Globally significant environmental benefits may result from using wood for energy rather than fossil fuels. The greatest benefit is derived from substituting biomass energy for coal. The degree of benefit depends greatly on the efficiency with which the wood is converted to electricity. If the efficiency of conversion of wood to electricity is similar to coal conversion to electricity then the benefits are several.

There are many environmental, economic and social benefits associated with the development of biomass as an energy source:

Health benefits can result with decreases with respiratory diseases and deaths. Airborne pollutants such as toxic heavy metals, ozone-forming chemicals, and releases of sulphur that contribute to acid rain will be reduced.

Sustainable biomass is carbon neutral and could produce annual net reduction in CO2 emissions (there is no net increase in CO2, the main greenhouse gas, in the atmosphere) and can save millions of tonnes of CO2 emissions per annum.

Fig 11. Average CO2 emissions for fossil fuels and biomass

Biomass can offer an alternative for the disposal of waste (commercial, non-commercial and agricultural waste); reducing waste delivered to lad fills. Beneficial environmental impacts from the use of biomass include improving sewage treatment prior to discharging effluent and sludges to waterways or oceans; avoiding methane emissions from landfills and reducing odours from direct application of animal wastes to land by first processing in a biogas plant.

Secure energy supply - as an indigenous and self-sufficient source of energy, there is no risk of cut off in supply. This is a complex subject revolving around future oil supplies, technical power system outages, sabotage and terrorism, geopolitics, weather patterns etc. Bioenergy (and other renewable energy) projects can assist in reducing the risks of these various energy supply constraints which can have serious political consequences. However they also carry their own risks of insecurity, variability and unreliability. To enhance the security of power generation systems, bioenergy power and cogeneration plants built reasonably close to the demand load will reduce transmission losses and can at times strengthen the local electricity distribution grid by providing additional and alternative resources. Security of supply can also be improved by greater diversification of the portfolio mix.

Environmental gains

Biomass is sustainable and does not deplete future resources.

Energy forestry crops have a much greater diversity of wildlife and flora than arable or pasture land and careful design of energy crops will enhance local landscapes and provide recreational facilities.

Protection of water quality

Reduction of floods during wet seasons and maintenance of water supplies during dry seasons

Erosion prevention

Improvement of local microclimate through evaporative cooling and humidification

Wind breaks and shelters that reduce erosion and conserve water, particularly in dry regions

Reduction of fire danger

Reduction in use of fertilizer and agricultural chemicals

Improvement of soil properties

Protection of wildlife and other components of biodiversity The ash and waste products from burning will, in most cases, be sufficiently benign to return to the soil. There will be a considerable reduction in net carbon dioxide emissions that contribute to the greenhouse effect. For example, one dry tonne of wood will displace 15 GJ of coal. The 15 GJ of coal will have the equivalent of 0.37 tonnes of carbon assuming the wood is converted at an efficiency of 25%.

FactorWood

WoodCoal

Coal

Energy density (GJ/Dry tonne)19.829.3

Heat rates (kJ/kWh)7,200-18,00010,900

Feedstock carbon (kg C/GJ)5070

% Carbon25.324.1

Input carbon (kg C/GJ)1.340.53

Total carbon (kg C/GJ)26.6224.65

1 dry tonne of wood displaces 370 kg of coal carbon (19.8GJ/tonne*10.9/14.4 MJ/kWh)*24.65 kg C/tonne)

Note: Feedstock carbon is the carbon embodied in the biomass or the carbon sequestered by plant growth. Input carbon is the carbon embodied in the factor inputs (e.g., diesel fuel) used to grow, harvest, and transport the biomass

Table 12. Example carbon offsets from short-rotation energy used for power production and displacing coal.

Source: Biomass Fuel from Woody Crops for Electric Power Generation

ORNL-6871, September 21st, 1995. There is little doubt that biomass can provide useful employment both for agricultural workers, possibly in the off-season when some harvesting or processing of energy crops can be carried out, and also for both skilled and unskilled workers at the bioenergy processing plant. Biomass developments provide a valuable source of employment. The main employment categories created are: Fuel supply - cultivation of energy crops, recovery and transportation of wood wastes, forest residues, agricultural wastes etc.

Engineering consultants - feasibility studies, design and engineering/construction management

Environmental services - environmental impact assessments

Construction - roads, buildings, electrical infrastructure etc.

Legal/Financing - planning, contractual and financing

Manufacturing - while there are some manufacturing companies in Ireland e.g. pellet equipment, there is significant potential for establishment of manufacturers of the various components of biofuel systems.

Maintenance, servicing and administration

Source: SEI Factsheet - What is Biomass?

Disadvantages of Biomass

Lack of experience and familiarity with biomass technologies amongst key players such as policy makers, local authorities, investors and resource owners inhibits development of biomass systems. Misconceptions can hinder development of biomass as a renewable energy source. Consultation and demonstration of successful or best practice examples of biomass facilities will help to build confidence.

The attitude of the electricity, heat and fuel supply industries to biomass technologies is poor. These industries prefer to avoid risk, use familiar energy technologies and maintain the status quo. The lack certainty of long term fuel supplies and availability can be a significant barrier to achieving increased deployment if bioenergy developments.

Initial capital costs of solid biofuel systems and the interest associated with these costs are much higher than for liquid or gas fuelled systems. This can act as a significant barrier to development of energy production from biomass. Biomass is not piped directly into buildings on demand and transportation of fuels is a major consideration.

Uncertainty as to the availability of biomass resources e.g. farmers doubt the stability of the biofuel market, resulting in a reluctance to change over to the production of energy crops. The biomass energy market is much less mature than either the fossil fuel markets.

There is a need for an integrated biomass policy to incorporate the agricultural, environmental, rural and transport sectors. Energy crops should be given the same stability as conventional forestry and food crops and not used as part of set-aside to counter surpluses in food production.

The low prices of fossil fuels make biomass fuels appear non-competitive. If biomass technologies were to receive the same level of subsidies as fossil fuels this would increase their cost competitiveness considerably.

Taxes on renewable energy systems. Value Added Taxes on renewable energy systems and their components reduce the competitiveness of biomass technologies in relation to fossil fuel technologies. In countries such as the Netherlands and domestic consumers of green energy pay a lower VAT rate, which enables renewable energy technologies to compete well with fossil fuel technologies. The introduction of tax incentives such as this, as well as the exemption of biomass-derived fuels from energy taxes in Ireland, will attract investors. For biofuels, reducing excise taxes, especially if the overall benefits can be shown to offset the loss in government revenue, may be applied to the use of fuels with a biofuel component as is already the case for biodiesel in Germany and bioethanol in France. Lack of subsidies for research, development and demonstration. Certain biomass technologies e.g. anaerobic digestion are well established and therefore require support for demonstration, while others are at an earlier stage of development e.g. growth of Miscanthus as an energy crop and require support for research.

Lack of information, education and training, which is fundamental to overcoming all of the above barriers. Sustainable development along with comprehensive technical expertise and education will help elevate misconstrued general opinions. People are generally afraid of change and stick to what they know best.

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