An evaluation of the production and combustion of fuel pellets from oilseed rape (Brassica napus L.) straw

Abstract

The project aims to investigate the production and utilization of OSR straw pellets for combustion purposes by considering: the storage of OSR straw and its compression into higher density products and the storage and combustion of OSR straw pellets.

Description

Fossil fuels represent the principal global source of energy accounting for approximately 80% of world energy consumption and 90% of UK energy demand in 2006.  Fossil fuels are an attractive energy source because they are associated with high energy densities and are easy to transport and handle compared with other energy sources such as biomass. However, fossil fuels are considered unsustainable because they are a finite resource and are detrimental to the global environment, being the principal source of UK carbon dioxide emissions, accounting for 586 million metric tons of carbon dioxide emissions in 2006.  There is a need to investigate the viability of other alternatives for energy generation.

The two main sources of biomass for energy generation are purpose-grown energy crops and waste materials. Energy crops, such as Miscanthus and Short Rotation Coppice, are cultivated mainly for energy purposes and are associated with the food vs fuels dilemma, which is concerned with whether land should be used for fuel rather than food production. The use of residues from agriculture, such as straw, for energy generation circumvents the food vs fuel dilemma and adds value to existing crops.

An example of an agricultural residue that could be used as a fuel for energy generation is oilseed rape (Brassica napus L.) straw . In the UK, the total area of OSR harvested increased between 2000 and 2008 from 332,000 ha to 598,000 ha, respectively, representing 12.6% of the total crop area (DEFRA, 2009). Currently there is not a significant market for oilseed rape straw in the UK, and a large proportion of it is chopped and incorporated into the soil through ploughing. Consequently development of a market for oilseed rape straw would add value to the gross margin of the crop at farm level.

But, straw exhibits a low bulk density which makes its transport more expensive than the transfer of natural gas or petroleum.  Reducing the cost of collection, transport and storage of biomass through densification is thus critical to developing a sustainable infrastructure capable of working with significant quantities of raw material.

The project main objectives are:

1. To determine the effect of on-farm storage of OSR straw and OSR straw pellets on the chemical and biological properties of the straw and pellets and the physical and combustion properties of the pellets.
2. To investigate the compression behaviour of OSR straw to higher density products and to develop a method to determine the applied pressure required to reach a particular density.
3. To assess the variation in physical, chemical and microbial properties when transforming OSR straw into pellets, and the associated advantages and disadvantages.  To determine how the OSR straw will affect the quality of the pellets (i.e. durability, hardness, particle density).
4. To assess the viability of using OSR straw pellets for combustion purposes and the associated environmental issues