New EU targets for carbon reduction mean that many countries are launching ambitious plans to increase energy production from biomass. Jørgen Hinge et al. scanned the European market for unexploited and 'alternative' biomass resources.

The use of biomass for energy production is widespread throughout the world and has been so for ages. In recent years, however, demand has increased significantly because biomass is used for new applications (large scale energy production, liquid biofuels etc). In order to meet new targets on CO2 reduction and to reduce dependency on fossil fuels, many countries are now launching ambitious plans to increase energy production from biomass.

The pressure on 'traditional' biomass resources is therefore increasing. There is also an intense parallel debate about whether large scale biomass is viable – especially biomass types which can be used for food or feed.

Therefore it is of great interest to identify and explore biomass resources which are not utilised at the moment, especially if they are not applicable for food or feed.

BIOMASS AVAILABILITY

Challenges to biomass availability gave rise to the EUBIONET 3 project (full title: EUBIONET III. Solutions for biomass fuel market barriers and raw material availability). The main objective of the project is to increase the use of biomass-based fuels in the EU by finding ways to overcome market barriers. The purpose is to promote international trade of biomass fuels to help demand and supply meet, while at the same time the availability of industrial raw material is to be secured at reasonable prices.

It is hoped that the EUBIONET III project, in the long run, will boost sustainable, transparent international biomass fuel trade, secure the most cost-efficient and value-adding use of biomass for energy and industry, boost investment in best practice technologies and new services in the biomass heat sector and enhance sustainable and fair international trade of biomass fuels. EUBIONET III has been focusing on the following topics:

  • Trade barriers;
  • Price mechanisms;
  • Legislative and technical frameworks;
  • New and unexploited biomass resources;
  • District heating and cooling with biomass;
  • Industrial applications.

Our aim was to identify and describe unexploited biomass resources and suggest methods for improving identified materials' fuel characteristics.

The project has 19 partners from 19 European countries. It began in September 2008 and will finish in August 2011. The project is supported by Intelligent Energy Europe. Energinet.dk has supported the Danish activities in the project

USE OF BIOMASS IN EUROPE

Especially in countries with few domestic biomass resources and high targets for renewable electricity, renewable heat and (eventually second generation) liquid biofuels may increasingly depend on imported solid biomass.

Germany (1080 PJ), Sweden (841 PJ), Spain (588 PJ), France (574 PJ), Italy (484 PJ) and Finland (428 PJ) are the richest EU countries in terms of biomass resources. Firewood is the most used biomass in Europe (30 percent of total), but this figure is not so accurate, because most firewood is not traded officially. Industrial by-products and residues represent the next biggest biomass types: use of solid by-products covers 20 percent of the total consumption, whilst the share of spent liquors (mainly black liquor) is 15 percent. Forest residues come next with 11 percent share of the total figure, and are followed by herbaceous and fruit biomass resources (7 percent) and refined wood fuels (5 percent). Use of pellets has increased in many countries and demand for them exceeds production.

The total annual figure for reported biomass resources (excluding biodegradable waste) in 24 EU countries and Norway is around 6557 PJ (157 Mtoe). According to EUBIONET III 48 percent of this annual biomass potential is currently used. 67 percent of this amount comes from woody biomass. The biggest potential to increase the use of biomass in energy production lies in forest residues and herbaceous and fruit biomass (almost half of the potential).

AGRO-INDUSTRIAL RESOURCES

A conservative estimate suggests that there is a potential of at least 300 PJ (7.2 Mtoe) in Europe from agro-industrial residues that are not currently used for energy purposes. The figure might be even 2.5 times higher.

During EUBIONET III we realised that it may be difficult to obtain information on amounts and quality of such products. The partners have contacted companies in their countries to acquire information, but many companies have been reluctant to provide official information, largely because amounts of agricultural waste product will often reveal much about production type and size – important competition parameters to many.

MOST IMPORTANT POTENTIALS

In Southern European countries such as Greece, Italy, Spain and Portugal, residues from olive production are by far the largest resource. Based on an overall olive harvest of just over 10 million tonnes, the EUBIONET partners estimated that the annual amount of residue would be more than 7 million tonnes, equivalent to a theoretical energy potential of more than 150 PJ. The energy utilisation of olive waste is growing rapidly at the moment. For example, in Spain the consumption of wood pellets is affected because olive pits are cheaper and only need conditioning, but not a manufacturing process.

The use of nut shells such as almond and hazel is growing as well. In southern Europe nut shells are already used to substitute for wood pellet fuel in small-scale stoves and boilers.

Another large resource is grain screenings, assessed at the European level at a theoretical potential equivalent to 40 PJ (1 Mtoe). Other biomass types could be residues from breweries, the tobacco industry and plant oil (besides olive oil) production, for example, sunflower shells and sheanut shells.

IMPROVING FUEL CHARACTERISTICS

Exploitation of agro-industrial residues and other alternative biomass products is not without challenges. The issue of biomass fuel quality has been raised by market actors in several countries. Often there may be a high water and/or ash content, or a chemical composition that causes problems during combustion.

There are different approaches to meeting these challenges, including:

  • Choosing a proper conversion technology;
  • Improving the physical characteristics of the biomass, i.e. reducing water content, pelletising etc;
  • Improving the chemical characteristics of the biomass, i.e. using additives to counteract the potentially negative influence of, for instance, the generation of chloride compounds during combustion.

CONVERSION METHOD

Although pre-treatment of agrobiomass products may make their utilisation more feasible, it often adds considerable costs to the handling chain. Therefore, it is important to select the conversion technology (i.e combustion, fermentation, gasification etc) for which as little pre-treatment as possible is necessary. For biomass types with high moisture content like algae and animal manure/slurry, costs for drying the material to a degree where combustion or thermal gasification is applicable may be high, whereas the products can be fed directly into biogas digesters for immediate utilisation.

Also the 'costs' in terms of energy balance should be considered. For separated fractions from animal manure/slurry, there is a net energy surplus by combustion when the moisture content is lower than 85%, and with a moisture content of 70% there is a net surplus of 600 kWh/tonne.

Another way of optimising conversion of 'difficult' biomass types is to adjust the conversion technology - such as, for instance, co-combustion of difficult biomass types with other fuels.

PRE-TREATMENT OF BIOMASS

Choosing a proper conversion method may solve many problems in using agro-industrial and other biomass products with more challenging physical and chemical properties. However, in many cases it may not be possible to use the 'best conversion method', or there may be other reasons for using a certain conversion technology.

In these situations different physical and/or chemical pre-treatments of the biomass may be recommended, or even necessary. Pre-treatment can serve different purposes depending on the conversion technology.

OPTIMISING COMBUSTION CHARACTERISTICS

Biomass is often regarded as a 'difficult fuel' for combustion. This is especially so for biomass other than wood and wood products. A classic example is straw, which contains high concentrations of potassium and chlorine. When straw is combusted in large applications, condensation of potassium chloride on surfaces initiates ash deposition as well as high temperature corrosion. Furthermore, straw has a rather high ash content (4-5 percent) compared to wood pellets, making it a nuisance to remove ash from small boilers. And finally straw ash has a rather low melting point, often resulting in slag formation. Some agro-industrial waste products also have a high ash content, making them difficult to utilise, especially in small-scale applications.

To improve the combustion characteristics several pre-treatment methods can be applied. 'Washing' the biomass can remove a substantial part of the difficult substances in the biomass (i.e. potassium and chlorine in straw. Using additives including: a) combustion catalysts, in order to improve the combustion; b) coating inhibitors intended to prevent sulphur related coatings. and c) corrosion inhibitors, used to prevent chlorine and aerosol related corrosion and fouling can be useful for slag abatement and prevention of deposit formation. Pre-treatment can optimise energy production from biological and biochemical conversion methods.

For conversion methods using biological or biochemical processes, different pre-treatment methods may be applied in order to improve the processes and increase the energy yield. Enzymatic pre-treatment is typically used to speed up biological and biochemical processes such as degradation of low soluble chemical structures in the biomass. Thermo-chemical pre-treatment, a combination of heating and a chemical treatment (for instance with acid) can also 'open' chemical structures. A combination of pressure and temperature (steam explosion) also results in the opening of the biomass structure. Grinding or milling the biomass can improve its degradability, simply by increasing the surface of the biomass to expose it to microbial activity.

PRE-TREATMENT FOR OPTIMISING BIOMASS LOGISTICS

In order to optimise biomass logistics and supply, pre-treatment is often recommended. In this context, a simple handling operation like baling of straw is regarded as pre-treatment. Other examples of pre-treatment to optimise logistics rather than combustion/conversion characteristics include drying (improves storage stability); chipping (eases transport); pelletising/briquetting (eases transport and reduces transport costs); and torrefaction (improves storage stability and increases density, reducing transport costs).

HEATING AND COOLING WITH BIOMASS

Approximately half of the final energy demand of EU 27 is used for heating and in 2008 about 11.9 percent of this energy demand was covered by renewable energy sources. The most common biomass fuels for domestic heat production are wood logs, wood chips and wood pellets. Especially for modern low-energy houses, wood pellets in combination with grate furnace technology are used. Cooling with biomass is currently limited to centralised district solutions. The main market for district cooling is the service sector, followed by the food and mining industry.

The CO2 reduction potential of a biomass heating system depends on the type of fossil-fuelled heating system which was compared to. The highest reduction calculated in the case studies was more than 1020 kg CO2-equivalents per MWh, where an electric heater was changed by a log wood boiler. The average CO2-equivalents reduction for all described biomass fuels range from 330 kg/MWh to 410 kg/MWh. Depending on the type of fuels and boiler, the potential of emission reduction (CO2-equivalents) ranged from 90 percent up to 98 percent.

WASTE NOT, WANT NOT

Of the estimated biomass potential in Europe, only 48 percent is currently exploited – and there is much unexploited potential. If about 50 percent of European municipal waste (the typical biodegradable fraction) was added to this potential and used for energy, it could yield as much as 1540 PJ (37 Mtoe) of energy. The average net calorific value of this biodegradable waste in highly industrialised old EU Member States is on the order of 10 MJ/kg. If this biomass waste potential is added to the biomass potential found by the EUBIONET III project, the total biomass and estimated biodegradable fraction of waste potential would increase to a total of around 7347 PJ (175 Mtoe). This potential is entirely necessary in order to achieve targets for biomass use in 2020.

Jørgen Hinge is project manager at the Danish Technological Institute. Edita Vagonyte is European Affairs Manager for the European Biomass Association. Eija Alikangas is principal scientist at VTT Technical Research Centre of Finland. Leonardo Nibbi is an assistant researcher at the University of Florence.