Biomass

Expanding the alternatives

While solar and wind energy can provide pollution free power some of the time, there is always the requirement to provide power at any time of the day or night independent of availability of solar or wind energy. This core or base line demand is at present met from coal, oil or gas fossil fuel sources, hydroelectric power or the nuclear sector. The concept of Biomass Energy is that is can be used to replace some of the use made of fossil fuel sources. It can be used as a fuel in specifically designed generating plant for Biomass systems or it can be mixed with conventional fuels such as coal to reduce dependence on fossil fuels.

Considerable research is at present on going to determine optimised methods of growing Biomass crops. The interfacing of agriculture to the energy supply infrastructure adds considerable complexity to such an initiative and to this extent the hurdles tend to be administrative, procedural, economic and political. The developing world as such uses biomass to provide some 12% of its energy requirements - compared with 3% in the developed world. Some contributions can be quite significant. In the USA for example, the use of biofuel-fired generating, mostly provided by wastes from saw mills provides around 9000 MW of capacity.

According to the UK's strategy following the 1994 UN Conference on Environment and Development at Rio De Janeiro the way forward is to provide an adequate supply of good quality food and other products in an efficient manner; to minimise consumption of non-renewable and other resources, including by recycling; to safeguard the quality of soil, water and air and to preserve and, where feasible, to enhance biodiversity and the appearance of the landscape, including the UK's archaeological heritage.

This directive has in particular focused attention on UK initiatives to add additional dimensions to forms of agriculture at present undertaken. While attention has been focused on the ability of the industrialised sectors to manufacture and export products, attention has been more recently focused on the resources within agriculture to contribute to the economy.

This involves, for example, using land taken out of food production, - the 'set aside' land - for the growing of non-food crops. At the same time there has also been identified the desirability of achieving this without cost to the environment and indeed with the emphasis on adopting techniques that will contribute to its benefit. These would include, for example, reduction of use of artificial fertilisers and change of work patterns to bring new opportunities for wildlife populations. This represents the beginning of a shift away from policies in open conflict with the environment.

Considerable work has already been undertaken in assessing the potential for steering agriculture towards Biomass farming in as much as at pilot scale level many projects have been demonstrated successfully and await expanding to more meaningful sized ventures.

Short rotation coppice
The ancient coppice system of woodland management is being used in what is called Short Rotation Coppice where selected high yielding clones of willow and poplar are planted at a density of around 10,000 per hectacre. After one year the young trees are cut back to ground level and then subsequent growth harvested after between two and four years later.

Existing UK plantations have yielded on average between 10 to 12 oven dry tonnes per hectacre. Yields as high as 15 tonnes have also been reported. There are indications, however, that yields as high as 20 tonnes may be possible with new species and improved land management. It is estimated that an SRC plantation would remain in production for at least 30 years on suitably fertile soils.

A range or markets of SRC is being studied. In rural communities, transport costs can add to the cost of conventional fuels so that locally produced SRC can be an attractive alternative. Standards applications include burning in conventional heating systems for domestic and limited scale industrial use. For power generation, generating plant in excess of 5 MW would provide higher efficiencies.

Studies are also being undertaken into gasification or pyrolysis where wood feedstock is converted to an intermediate gaseous or liquid fuel. In gasification the fuel is made to react with air to produce a mixture of carbon monoxide, carbon dioxide, methane and hydrogen. The resulting gas has a relatively low calorific value - approximately one seventh of that of natural gas. In pyrolysis the fuel is heated in the absence of air to produce gas, oil and char. The relative proportions of product depend on the temperature of operation. At the highest processing temperatures - termed flash pyrolysis - the proportion of liquid fuel produced is greatest with as much as 85% of biomass converted to liquid form.

The development of thermal gasification tends to be more advanced than that of pyrolysis. Gasification systems are becoming available for generating capacity between 100 kW to 30 MW. Pyrolysis processes present more technical problems but also hold out a range of advantages in expected performance. The production of a liquid product is certainly an advantage for storage and distribution compared with a gaseous product. Gasifiers are also very suitable for small scale production.

In gasification, up-draft or down-draft gasifiers can be used. The down-draft gasifier introduces the gas at a lower level which encourages hydrocarbon deposits to be removed during the gasification process. It is estimated that SRC can provide an annual production equivalent to 6 tonnes of oil per hectacre per year. In this form the fuel can deliver far higher conversion efficiencies. In a more distant future - will cars run on trees? In terms of present economics, the cost of production of SRC material is estimated at £14 - £24 per oven dried tonne.

Miscanthus
Miscanthus is a `woody' perennial - a type of elephant grass that is currently being investigated in the UK as a biomass product. It can grow to around 4 metres high in one year and is more readily grown in the warmer parts of the country.

While more difficulty is being encountered in establishing this crop, it can potentially provide yields as high as 20 tonnes of dry matter per hectacre per year. Also, in its harvested state it requires less drying - thus reducing post harvest costs. As a relatively recent newcomer to biomass development, its chief advantage is a more rapid cropping cycle compared to short rotation coppice. It may also be that alternative plants with even greater levels of productivity may be utilised in the future.

Straw
Each year the UK produces around 7 million tonnes of straw - corresponding to an energy content of 3.6 M tce (tonnes coal equivalent). The use of this byproduct as a fuel is relatively limited - with around 200,000 tonnes or some 3% of total being used as a farm based fuel.

With legislation now banning burning of straw in fields, it is anticipated that utilisation could increase four-fold by the year 2000. Efforts are being directed to developing technology in order to reduce the bulk of straw and render its transport more economical.

There is also considerable interest in the use of straw as a partial substitution for coal in industrial coal fired boilers.

Suitably processed material can in fact be used up to levels of 50% substitution. As a green bonus, the acid emissions at this level of substitution are reduced substantially. This in turn would be a factor minimising production of acid rain. There appears less interest in converting straw by gasification or pyrolysis since the combustion of straw is relatively well established and there are problems with its low bulk density and small particle size of the material.

By comparison, the Danes make much more use of straw than the UK. This is largely explained by the widespread use of community based heating schemes which initially used conventional fuels such as coal and oil but with the taxation of fossil fuels, have migrated to using straw instead.

A 30 MW straw burning plant has been operating for some time at Haslev. Another 70 MW plant co-fired by straw and coal has been built at Grena. The UK's first large scale straw fired generating station was completed in Cambridgeshire in 1997. On single farm installations, a typical Farm 2000 burner system will provide 200 kW and consume 300 large round bales per year.

Biodiesel oil
The largest single crop for industrial use is rapeseed oil - with a set aside value of 100,000 ha in 1994. A limited amount of rapeseed oil is processed in Europe for the production of biodiesel. In Austria, encouragement of development of biodiesel has led to a 5% uptake of this fuel in the 'diesel' market.

Rape seed oil can be processed to produce biodiesel. The process of its production can be described as: Rapeseed + methanol = diester (RME) + glycerol oil where RME = Rapeseed Oil Methyl Ester Studies are at present evaluating whether ethanol from Biomass production, can be used to replace the methanol in the conventional process. It is estimated that even if the entire set aside land area of the UK (1/6 th of arable land or 600,000 hectacres) was used to produce rapeseed for biodiesel, this would only produce some 6 % of the UK's current diesel consumption.

While Biodiesel is unlikely to supplant conventional diesel, there are however, certain uses notably on inland waterways where the use of Biodiesel would be beneficial to the environment. Specific geographical areas include the Norfolk Broads and the National Parks where in particular there is considerable pollution due to spillage of marine diesel.
Preliminary studies conducted by the Centre for Aquatic Plant Management, Sonning on Thames, have indicated that biodiesel produces less severe effect on the environment than marine diesel. Studies involved the effects on plankton, macrophytes and a range of aquatic animals.

The Transport Research Laboratory has carried out a trial of biodiesel in Reading where various factors were investigated with the fuel used in buses. While the biodiesel tended to produce less smoke, it at the same time appeared to produce more particulate material. A good sign indicates improved performance of biodiesel compared with fossil diesel.

Conventional litreature on biodiesel normally highlights the much lower levels of Sulphur Dioxide in biodiesel yet this study apparently does not make any reference to this pollutant. Other Biodiesel studies, however, have indicated reductions in particulate emissions. It would appear that more research requires to be undertaken to better investigate the environmental impact of biodiesel.

At a time where there is particular concern over the link between particulate contamination and the rising incidence of asthma, a more thorough review is perhaps necessary. Studies are also being undertaken of the use of vegetable oils for offshore drilling.

Conventional oil drilling technology makes extensive use of mineral oils in water suspension to lubricate the drill bit. Surplus fluid invariably contaminates the marine environment. There is a specific interest in use of rapeseed oil in formulation of drilling fluids to reduce toxicity to marine communities, eliminate taint in fish and enhance recovery of sea bed following periods of exploration.

Bioethanol
The USA and Brazil have established bioethanol industries where ethanol is produced from agricultural feedstocks by fermentation. The cost of bioethanol is approximately three times that of chemical methods.

Ethanol can be used as a single fuel or it can be added to petrol as a fuel oxygenate to improve its calorific value. In addition, ethanol can be processed to form ethyl tertiary butyl ether (ETBE) which is a preferred oxygenate agent for petrol. In Brazil, all non-diesel vehicles run on either gasohol which is 22% ethanol and 78 % petrol or neat hydrated ethanol which consists of 95% ethanol and 5 % water.

In the USA, ethanol is produced from corn or maize which is initially broken down by enzymes to produce sugars from starch which can in turn be fermented. There is considerable interest, however, in developing processes which would allow low grade sources containing cellulose such as crop residues to be processed to produce ethanol. While methanol can also be used as a fuel, its prime sources tend to be from fossil fuel sources such as methane. There is considerable interest, however, in developing gasification systems which use high concentration of oxygen for the production of methanol.

Vegetable Oils
Biodiesel can be burnt in existing diesel engines. While vegetable oils such as rapeseed can be burnt directly as a fuel, this requires modification of existing engines. A limited number of agricultural vehicles have been converted in Germany to run on raw vegetable oil for a trial period. While this has been demonstrated as a success in terms of reduced emissions, and the fuel is considerably cheaper to 'produce' than biodiesel, it is none the less more expensive than fossil diesel as available on farms with duty free fuel.

Pyrolysis Oils
Although at an early stage in development, the pyrolysis process where dry biomass such as wood or miscanthus is processed by heat with limiting oxygen may offer the most effective means of producing the biofuels of the future. In addition to providing fuels, this process could also provide useful chemical industry feedstocks.

Algae
One of the more futuristic biomass candidates is algae. Algae tend to make the news by reports of its infestation into nutrient rich waterways. If algae could be reared and fed on, for example, sewage effluent, the processed dried biomass would produce a high yield of oil based substances.

Taxation on Biofuels
As ever, the financial framework within biomass production has a critical effect on its development. The levels of taxation of Member States in the EC on biofuels will have a significant effect on the speed of developments.

While the environmental arguments against the spiralling use of road transport are self evident, there would appear to more than a little sense in lessening the impact of such an expansion on the environment by taking steps to encourage the use of biofuels in the future.

Growing raw materials
The recent changes in environmental perception and the addition of new crops indicate that in some ways aspects of agriculture are being re-integrated into industrialised society. Progress is being made in identifying products used as raw materials that can be provided as renewable commodities rather than ones processed, for example, using nonrenewable products.

There is considerable interest in development of plant oils as a substitute for some ranges of products derived from mineral oils. The UK each year uses around 750,000 tonnes of lubricating oils and greases so this is a large potential market to investigate. Generally short molecular length chains tend to be used in production of soaps and detergents with longer molecular chains being used for lubricants and more specialist applications.

Developments in plant breeding (and also genetic engineering!) may on the one hand improve existing crop efficiencies and also introduce wholly new creations targeted to produce specific agro products.
The increase in land production in set aside is in turn a reflection of the significantly increased efficiencies of food production within the European Community.

Wastes
While there is a certain focus of attention on the role of agriculture to grow energy crops, there is all the time a vast supply of wastes from a modern industrialised society with a high level of 'development' within agriculture. Among so-called 'dry' wastes can be considered domestic refuse, industrial and agricultural wastes including straw and forest residues. The so called wet wastes can be included such as sewage, animal wastes and industrial effluents.

The production of wastes continues relentlessly and in such a way that the activity is in place almost uniformly across the country. At a time when there is increasing anxiety from environmental considerations about the disposal of wide ranges of wastes, including slurry from agricultural sources, the processing of such wastes for use as fuel may offer two main advantages - provision of energy and reduction of pollution.

It is estimated, moreover, that an energy content of 21 million tonnes of coal equivalent (M tce) are discarded in the UK each year through disposal of wastes!
Some key problems, however, in the processing of such wastes lies in the relatively low energy density of the product and the production of wastes at some distance from the energy market.

Landfill gas
Anaerobic digestion is a process in which natural bacterial decomposition takes place in the absence of oxygen. Such a process can be used, for example, to break down sewage, animal wastes and plant residues in large tanks called digestors.

The gaseous products of such a process is a methane rich biogas. Such a gas is also released in landfill sites that have been filled with domestic waste. In the UK, several installations have been constructed to tap into this gas byproduct to either provide combustible gas for industrial processes such as kilns, boilers or furnaces or also for generating of electricity.

The gas produced - landfill gas - typically contains equal proportions of methane and carbon dioxide. While this can be compressed to produce a liquid byproduct or cleaned for supply to the gas utility network, these operations are both complex and expensive.
From initial observations of London Brick's Stewartby Site, it was realised that commercial quantities of landfill gas can be produced from landfill sites. An array of simple wells is drilled into the landfill volume and the gas collected by a pumping system as indicated on figure 5. The collection of the gas has also a positive environmental effect of minimising odour and also reducing migration of gas from the landfill sites.

The present annual production of gas from such landfill sites is of the order of 300,000 tce. There are many such landfill sites in the UK - as many as 5000. Some landfill schemes have been established on completed landfill schemes where landscaping conceals the vast amount of municipal waste that has been infilled.

The production of landfill gas from such systems has largely been achieved in an empirical way.. It is estimated, however, that only around a third of the available gas is in fact extracted. Various options are being investigated for management of land fill sites in order to increase gas collection efficiency. It is estimated that the UK potential for such landfill gas schemes could with improved management range between 1 to 3 M tce per year.

The methane released by landfill sites is a potent green house gas. Thus its collection and burning does represent a positive effect for reduction of global warming. The UK now has around 50 landfill schemes currently active and generating around 80 MW of power. A further 177 projects with a potential capacity of 358 MW are also being considered.

Municipal waste
This poses a challenge to recycling schemes to sort relevant useful material or for processes to concentrate fuel fraction. Processing systems have already been developed to supply what is termed Refuse Derived Fuel (RDF). In the UK, the landfill of refuse is a preferred option - primarily due to its lower cost. Elsewhere in Europe, the direct incineration of domestic waste is widely adopted.

The UK has developed demonstration systems for the processing of domestic waste to produce a fuel acceptable to many applications. So called coarse RDF, where a modest degree of processing is undertaken, can find use in a limited range of applications - such as cement kiln heating and chain grate water tube boilers. With further processing of the pellets, however, in which the fuel fraction of the rubbish is mechanically separated and concentrated in the processed product, it is possible to produce an RDF pellet with around 60% of the calorific value of typical British coal. A number of RDF production installations are already in production although the technical problems in using such RDF fuel have been greater than anticipated.

While domestic waste is much the same between Lands End and John 0' Groats, industrial waste can be considerably more diverse, with each byproduct requiring its own potential controls on processing and compaction.

Developments in this sector tend to focus on optimising the function of combustion systems such as the cyclone combustion unit with integral ash remover being developed at University College, Cardiff. There are reservations, however, on the widespread use of incineration plants in relation to the production of dioxins. These highly toxic chemicals tend to be released when products containing chlorine are incinerated. High temperatures, around 1000 C are required to be sustained to reduce emission levels to 'safe' levels.

Pig slurry
One of the largest anaerobic digestors in the UK is at Piddlehinton in Dorset. A 750 cubic metre digester is capable of handling 22,000 gallons of slurry a day. The slurry is processed for between 7 to 10 days at a temperature of 37 to 40 C to maintain stable conditions for bacterial growth. The rate of production of biogas can power generators at around 90 kW. While the system does operate at a commercial profit under a NFFO (Non Fossil Fuel Obligation) scheme agreed in 1990, of more significant benefit is the reduction in odour and biological oxygen demand (BOD) arising from the process of anaerobic digestion. This term has fallen by around 60% with indications that further reductions can be achieved.

This in turn reduces the impact of the intensive agriculture on the local environment. Perhaps the Berrybank Farm in Victoria, Australia was the inspiration for the gas production system graphically displayed in the movie Mad Max Il. Raising 24,000 pigs a year and producing 200,000 litres of slurry per year, slurry is digested in a two stage process. Methane produced as a byproduct is used to generate 160 kW of electricity with a small amount being exported to the local electricity grid.

The main environmental benefit of the system, however, is the safer processing of the large amount of organic material thus produced. What will always remain a mystery in Mad Max II is what the pigs were fed on!

Chicken litter
In a curious twist to the tale of biomass energy, the mere fact that chicken litter is proving to be a major biomass fuel is an indication of the chicken loving habits of the UK. The Eye Power station in Suffolk, operational since June 1992, burns 130,000 tonnes of chicken litter per year - enough to generate 12.7 MW of capacity to the grid.

A further 82 MW of capacity which plan to use chicken litter have been subsequently awarded via NFFO (Non-Fossil Fuel Obligation) -3 and the Scottish Renewable Obligation for chicken litter schemes. As such, this must still represent a relatively small component of the available resource from this specific biomass fuel.

Combined Heat and Power (CHP)
Combined heat and power can provide much better utilisation of energy from biomass and other sources. A state of the art combined heat and power system at Mabjervaerket in Denmark. The first stage uses biomass fuel to produce steam which in turn is superheated using natural gas prior to entry to the turbine system.

Around 28 MW of electrical power is exported and 67 MW of heat provided to the local district heating system. As fuel, the system is designed to burn 135,000 tonnes of municipal waste, 50,000 tonnes of straw and 17,000 tonnes of wood chips. This sensible extraction of energy can be contrasted with the large quantities of heat blown off into the UK sunset by giant concrete cooling towers at its numerous power stations. Such vast quantities of heat could never be used by the local 'neighbourhood'. Are any Power Utility companies diversifying into such schemes?

Summary
The initial reflection after the energy crisis of 1974 was based on the risk to world economies from restricted supplies of fossil fuels. With upward revisions on the levels of recoverable oil and gas in the world, the anxiety in the energy equation has been replaced by uncertainty in the context of global warming.

As the developing world struggles for rapid industrialisation and in so doing risks further massive releases of carbon dioxide, the developed world has if not a duty then an obligation to provide a future 'soft landing' for these economies in terms of developing responsible systems of energy production. In many ways the largely agricultural based economies of the developing world represent a good platform from which to establish biomass derived sources of energy.

Points of Contact

The Centre for Alternative Energy, Machynlleth, Powys, SY20 9AZ,
Tel 01654 702400 Fax 01654 702782

National Network for Alternative Technology and Technology Assessment, c/o Faculty of Technology, The Open University, Walton Hall, Milton Keynes, Bucks.
Tel 01908 653272 Fax 01908 653744

TSU, Harwell, Oxfordshire, OX1 1 ORA. Tel 01235 432450
Fax 01235 433066

Power Plants: Biofuels made simple, Brian Horne, CAT Publications, New Futures number 16

Renewable Energy General Literature List: Agriculture, ETSU.

Crops for Industry and Energy: Information Pack, MAFF Alternative Crops Unit.
MAFF Alternative Crops Room, Room 401,
10 Whitehall Place, London, SW1A 2HH. Tel 0171 270 8323 Fax 0171 270 8607

Internet Sites

http://solstice.crest.org
The Center for Renewable Energy and Sustainable Technology (Major Source)

The Bioenergy Mailing List at Solstice is: <http://www.teleport.com/-tmiles/biolist.htm>

http://greenpeace.org Greenpeace

http://www.oneworld.org/ One World Online

http://erg. ucd. ie. opethermie. html EU Thermie Programme

http://www.demon.co.uk/ici
ICI's Environmental Performance information

http://www.iisd.c/linkages/consume/
Sustainable Production and Consumption dialogue

http://asd.nrel.gov/projects/rredc/data/biomass>
National Renewable Energy Laboratory Biomass Resource

http://web.ngdc.noaa.gov/dmps/ols-app-bio.html> DMSP Biomass Burning (US Government Agency)