Bioenergy — a renewable carbon sink

Bioenergy Ð a renewable carbon sink

Ralph E.H. Sims*

Centre for Energy Research, Massey University, Palmerston North, New Zealand

Abstract

Bioenergy is a mature technology which, in its several facets using modern biomassconversion systems, provides a signi®cantly greater contribution towards the global primary

energy supply than do all the existing and planned wind and solar projects together. Wherespecialist long rotation energy crops are grown on land that was previously in pasture orannual crops, biomass also provides a carbon sink. However, the ``image'' of biomass is

generally much poorer than wind and solar in the public mind due to a lack ofunderstanding of the technology. Policy makers and the media also pay greater attention tousually more photogenic wind and solar technologies. This paper presents an outline of the

potential energy contribution from biomass with particular emphasis on examples ofcommercial projects in Australasia. 7 2000 Elsevier Science Ltd. All rights reserved.

1. Introduction

Biomass is a renewable energy source arising from a range of organic productssuch as forest residues, wastes or purpose grown crops that can be converted toheat, power or transport fuels (Fig. 1). Technically, biomass can be a totalsubstitute for fossil fuel products since it can also be used as feedstock to producevirtually any petrochemical or material currently sourced from oil, coal or gas [1].

Biomass already provides around 13% of the global energy demand but this islargely as domestic ®rewood used ine�ciently for cooking and heating indeveloping countries. In developed countries there is a growing trend towards

0960-1481/01/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.

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Renewable Energy 22 (2001) 31±37

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* Tel.: +64-6-3505288; fax: +64-6-3505640.

E-mail address: [email protected] (R.E.H. Sims).

employing modern and e�cient bioenergy conversion technologies using a rangeof biofuels which are becoming commercially competitive with fossil fuels. Asigni®cant contribution towards meeting national carbon emission reductionobligations may result.

In New Zealand, for example, biomass already provides over 30 PJ per year or6% of the primary energy supply [2]. This will double within the next decade andprovide around 10 times the energy contributed from all the existing or plannedwind, small hydro (<10 MW), and solar projects. This dominance of new andemerging renewables by biomass is also the case in Australia where signi®cantbiomass resources exist [3]. In Austria and Scandinavia, biomass contributes

Fig. 1. Biomass to bioenergy conversion routes to provide heat, power or transport fuels.

R.E.H. Sims / Renewable Energy 22 (2001) 31±3732

around 30% towards their total primary energy and in USA more electricity isgenerated from biomass annually than the total power demand of New Zealand.Furthermore, biofuels for transport are commercially available at service stationsin several countries including USA, Brazil, France, Germany and Austria. Atpresent, these biofuels tend to be heavily subsidised in order to compete withcheap oil products but research investment is increasing worldwide in order toreduce their production and processing costs. Examples include the bioethanolproduction programme being undertaken in Australia. Since a more detailedassessment of biofuels has been presented elsewhere [4], this paper outlines theexamples of bioenergy used for heat and power projects where these arecommercially competitive with fossil fuels without the need for subsidies. Futureopportunities to further develop bioenergy projects are also discussed.

2. Commercial projects

The forest product and sugar processing industries in Australia and NewZealand are already largely energy self-su�cient, using process residues to meettheir on site heat and power demands. Export of power o�-site is feasible in manyinstances where surplus fuel exists. For example, most Australian sugarcaneprocessing plants ``waste energy e�ciently'' simply to dispose of the bagasse by-product. In 1996, over 11 million wet tonnes of bagasse were produced with anenergy content of around 120 PJ. Annual volumes vary with the growing seasonand are produced only during the cane crushing period from mid June to midDecember. Currently, all of the 33 sugar factories are virtually self-su�cient inenergy with around 250 MWe of total capacity installed, generating over 500GWh/year and an abundance of medium grade heat suitable for sugar processing.However, if more modern and e�cient cogeneration plants were to be installed, asoccurred at the CSR Invicta sugar factory in 1998, the available bagasse couldthen supply over 1000 MWe capacity and generate nearly 4000 GWh/year, muchof which could be exported o�-site. Hence, there is opportunity to expand thecurrent power export capacity considerably using the existing biofuel resourcesand particularly if the additional bagasse burnt o� or left in the ®eld at harvestwas also collected and used for fuel. It is encouraging to note that the AustralianGreenhouse O�ce recently awarded the Rocky Point Green Energy Corporation aShowcase grant of $3 million to install a 30 MWe cogeneration plant at theirBrisbane sugar mill. The innovative concept of this project is to use locallysourced wood waste outside the 20-week crushing season to provide green powerto the Queensland grid all year round. No doubt other mills will follow suit wherewood resources exist nearby and eventually 10,000 GWh/year of electricitygeneration from biomass may become feasible.

Of the $10 million made available for Showcase grants, a further $2 million wasawarded to another biomass project to enable EDL to design and install a solidwaste-to-energy conversion facility. This will reuse and recycle resources prior togasifying the residual organic components and generating heat and power from

R.E.H. Sims / Renewable Energy 22 (2001) 31±37 33

the gas. Such waste-to-energy processes are sensible conversion routes since thewaste disposal costs are also avoided and environmental impacts can beminimised. Many other commercial waste-to-energy projects exist includingland®ll gas, biogas from organic wastes, and use of wood process residues toprovide heat, power and transport fuels. For example, in New Zealand, a 39MWe cogeneration plant using bark and other wood wastes was recentlycommissioned at Carter Holt Harvey's pulp and paper plant at Kinleith.Previously around 200,000 t of residues were dumped in land®lls at high economicand environmental costs to the company. Combusting the material to recover theenergy through the steam cycle for use mainly on site made commercial sense.Some excess power is exported to the grid.

3. Future opportunities

The proportion of primary energy supplied from biomass is likely to continueto increase in the foreseeable future in spite of new and improved wind and PVtechnologies being continually developed. The most modern biomass conversionplants also incorporate improved designs and performance e�ciencies, particularlywhen designed for cogeneration of heat and power. New concepts such asintegrated combined cycle gasi®cation plants giving clean gas, improvedconversion e�ciencies, and resulting low air emissions are rapidly becomingcommercially viable. Plant capacities currently range from 50 MWe down to 50kWe. The latter are perhaps better suited to rural communities particularly indeveloping countries where abundant and sustainable supplies of biomass exist(such as old coconut trees, rice husks, copra, etc.) and labour is relatively cheapand readily available [5].

In many developed countries, biomass fuel sources such as arisings from theharvesting of plantation forests, wood process residues, and speci®cally grownenergy crops are all available in relatively large volumes. The use of such fuels canbe fully sustainable and environmentally acceptable assuming the overallproduction system is designed and managed correctly. The main problemsassociated with utilising biomass are:

. competition with food and ®bre production for land use;

. the removal of additional nutrients from the soil thereby depleting reserves; and

. the transport of large volumes of low energy density biomass fuels to theconversion plant [6].

. The key to overcoming these problems and to ensuring the use of such biofuelsremains an economic and environmentally acceptable option in competitionwith cheap coal, oil and gas, as well as with other renewables, is to obtainadditional bene®ts from their use. Such bene®ts include:* improving the fertility of unproductive saline soils (of which there are 4

million ha in Western Australia alone) by growing a proportion of the areain short rotation energy plantations to lower the water table and hence


reduce the overall salinity problem for cereal production;* providing easier re-planting of a commercial forest after stemwood harvest

by clearing the residual trash traditionally left to decompose;* avoiding the disposal costs for waste organic products by utilising them on

site;* treating e�uents from municipal sewage works, food and ®bre processing

industries and farms by irrigating them on to energy crops rather than on tofood crops or discharging into waterways; and

* sequestering carbon thereby gaining tradeable credits when used to displacefossil fuels.

Considerable recent debate has been undertaken internationally by the IPCCand other environmental organisations concerning utilising forests as carbonsinks (Fig. 2). Assuming sinks are ultimately accepted by the internationalsignatories to the Kyoto Protocol, growing more plantation forests can onlyprovide a short term solution to reducing the ever increasing atmosphericcarbon levels until eventually all the available land is covered by trees. So theconcept only makes sense as a long term solution if the accumulated carbonstored in the biomass can be utilised for energy purposes; either forcogeneration of heat and power or for the production of transport fuels ormaterials. Then the carbon is recycled within the overall biomass productionand bioenergy utilisation system and the ``renewable carbon sink'' can lastforever [5].

Calculations of land availability have shown that su�cient suitable land existsto supply all food and ®bre needs of the growing world population together withenough energy to meet a signi®cant proportion of the global demand. There ismuch yet to learn about growing the biomass, transporting it and operating highlye�cient conversion plants. It is exciting to note that the company ShellInternational Renewables has recently been established as a ®fth division of theRoyal Shell Group in their long term strategy to become an energy companyrather than an oil company. Growing short rotation forests to supply woodybiomass for gasi®cation features highly in their core business plan for the future[7]. With the high level of investment made available for this initiative, rapidadvance in the current knowledge relating to the biomass production, harvesting,processing and utilisation chain can be expected.

To become fully successful, a ¯edgling biomass industry in a country needs anactive support organisation to promote its bene®ts, to seek ways to overcome anybarriers to new project implementation, and generally to enhance its public image.The British Biogen model has been extremely successful in this regard [1] and themore modest New Zealand Bioenergy Association and the Australian BiomassTask Force are gradually following suit. In addition, liaison with other new andemerging renewable energy industry organisations to lobby more e�ectively onareas of common interest (such as introducing methods for including theexternalities when costing the use of fossil fuels and their environmental impacts)is another essential role.


Fig.2.Carbonstoragein

biomass

andsoil¯uctuateswithlanduse

over

timewhen

indigenousforest

isclearedforpasture

andlaterreplantedin

plantation

orshort

rotationenergyforests.


4. Conclusions

Modern biomass conversion plants are technically mature and in many caseseconomically viable, though there is still room for reducing costs and increasingperformance. Once the role of bioenergy as a means of recycling carbon throughthe atmosphere by displacing fossil fuels is better recognised by the public andpolicy makers, biomass will make an even greater contribution to the world'sprimary energy supply than at present. The industry must continue to work atimproving the image of commercial modern bioenergy systems by continuing tostrive for improved standards, sustainability and low emissions and to promotethe additional bene®ts resulting from its use.

References

[1] Billins P. Power from the land. In: Proc. 36th Annual Conference of the Australian and New

Zealand Solar Energy Society, Christchurch. 1998. p. 3±6.

[2] EECA. New and emerging renewable energy opportunities in New Zealand. Centre for Advanced

Engineering and Energy E�ciency and Conservation Authority, Wellington, 1996; 266.

[3] ERDC. Biomass in the energy cycle study. Energy Research and Development Corporation,

Canberra. Report ERDC 234 1994; 272.

[4] Sims REH. Energy sources from agriculture. In: Proc. International Conference on Sustainable

Agriculture for Food, Energy and Industry. Braunschweig, Germany: James and James, 1997. p.

748±52.

[5] Hall DO. The role of bioenergy in developing countries. In: Proc. 10th European Conference on

Biomass for Energy and Industry. Wurzburg, Germany: CARMEN, 1998. p. 52±5.

[6] Sims REH, Culshaw D. Fuel mix supply reliability for biomass-®red heat and power plants. In:

Proc. 10th European Conference on Biomass for Energy and Industry. Wurzburg, Germany:

CARMEN, 1998. p. 188±91.

[7] van der Veer J. Dawson J. Shell International Renewables Ð bringing together the group's

activities in solar power biomass and forestry. Media release, London, 6 October 1997.


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Bioenergy — a renewable carbon sink