Developing Mixed Fuel and Multifuel Usage

by T Järvinen of VTT Energy, Finland


Finnish companies and VTT Energy started a handling technology programme for mixed fuels and multifuels at the beginning of 1996. The goal of the programme is to improve the level of handling technology in multifuel applications, enhance the availability of installed power plant capacity, and develop new systems for use in Finland and for export.


Wood fuel and fuel heating system at UPM-Kymmene Ltd, Kaipola, Finland


The growing use of multifuel boilers, particularly of the fluidised bed type, together with the introduction of new types of fuel and fuel combinations, call for increasingly sophisticated fuel handling systems. The basic problem is that current combustion and boiler technology requires closely controlled fuel feeding and data on the properties of the fuel stream used, particularly the

heat content.This has become increasingly difficult as the range of fuels used has broadened and as the properties of many of the new fuel options vary from batch to batch. As a result, existing plants are faced with new sets of problems and difficulties in running their operations.

In the case of new plants, the problem is often one of insufficient data on dimensioning needs and a lack of experience with the relevant operating parameters. Engineering and implementation are complicated further when different fuels are mixed. Additional problems are faced by manufacturers supplying power plant and fuel handling systems for export to countries where the range of fuels on offer can be very different from what the supplier is familiar with.

Fuel handling systems represent a sizeable proportion of power plant investment, typically
4-9%, but sometimes more. The maintenance costs of fuel handling and feed systems compared to investment costs are in excess of 5% a year. However, the impact of these systems on the availability of a multifuel-fired plant is significant.


The three-year programme includes all of Finland's major companies involved in producing, using, and manufacturing equipment for solid fuels, as well as various forest
products companies and systems suppliers. The programme will review all the activities and technologies used in fuel production and transport until it reaches the boiler door. The multifuel streams to be studied include all wood and peat-based fuels and other biomass materials, such as bark; recycled and waste-derived fuels; paper and plastic that cannot normally be reused; waste sludge produced by the forest products industry; and coal and lignite.


As part of work to evaluate equipment failure, cost levels, and availability, the programme will look at the multifuel handling systems used in tens of industrial and municipal power and heat plants around Finland and some in Sweden.

In collaboration with a group of equipment manufacturers, VTT Energy has designed advanced test equipment for fuel crushing and unloading applications that manufacturers can use in developing new end-applications. A system based on artificial vision technology has also been tested for recognising multifuel composition and regulating feed levels.

The programme has drawn up a quality classification system for wood fuels, and proposed an equivalent system for recycled fuels. A databank on the critical properties of various solid fuels has been created for use by equipment manufacturers in designing new and improved systems. Other work has concentrated on testing corrosion and erosion questions in fuel handling equipment manufactured from conventional and new materials when handling new types of fuel.

Another sub-project within the programme is devoted to expanding and developing the use of automatic or mechanical sampling for wood and peat, and possibly also recycled fuels based on waste materials. Safety is also a subject of attention, and tests have been carried out to establish dust explosion and self-ignition behaviour and thereby improve fuel handling safety.

For more information contact the CADDET Finnish National Team in Helsinki.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

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