Analysing terminal facilities for biomass operations


Dr Mi-Rong Wu, consultant, TBA, Delft, The Netherlands




The use of solid biomass (e.g. wood pellets) has been boosted by the recent development in bioenergy and EU directives. For instance, some power stations are in the process of a con-version to co-firing with sustainable biomass. The worldwide growing demand promotes the international biomass trade because the supply potential is unevenly spread out and shipping is and will continue to be the main method for transporting solid biomass.i Bulk terminals around the world have been dealing with solid biomass for some time on a small scale. However, with the expectation of the use of bioenergy growing (see Figure 1) and consequently the international solid biomass trade market. It is necessary to address comprehensive analyses of the terminal facilities for solid biomass operations.ii,iii

Several ports already have appropriate handling facilities but the storage and inland transpor-tation will require additional investment. Various aspects should be taken into account to provide a thorough picture of solid biomass operations: the significant material types for large-scale handling; the physical/flow properties of solid biomass; a comparison between handling of solid biomass and other common bulk material; and the effects caused by the stochastic parameters (e.g. vessel arrival patterns) to the storage capacity and storage time of solid biomass operations. These aspects are further discussed in the following sections.

Material type and properties

There are various kinds of solid biomass, but not every type is suitable for being transported over long distances and handled in dry bulk terminals. Selection criteria such as potential availability, the application preference/possibility by major users and logistical concerns were used to estimate which materials will be commonly handled. Based on these criteria, the types of solid biomass to be expected by dry bulk terminals are: wood pellets, wood chips and torrefied pellets.

It is essential to understand the material properties of these selected solid biomass types, in order to know how to handle and store them properly. Selection and design of handling and storage equipment for solid biomass types strongly depends on their physical material proper-ties/flow properties. Furthermore, the flow properties may also affect the operational process.

Although some handling properties of wood pellets and wood chips have been obtained by various studies, a completely range of their flow properties was not very clear. As a newly developed material, there is no information available yet for the flow behaviour of torrefied pellets. Various experiments such as density testing, largescale linear annular shear testing, and linear wall friction tests were performed recently to determine the handling characteristics of wood pellets, wood chips and torrefied pellets.v (see Figures 2, 3 & 4) For a better understanding regarding equipment it is important to make further interpretations: to compare these solid biomass properties with other bulk materials that have been handled and studied frequently, such as coal. Table 1 shows an overview of the flow properties of some solid bio mass types and coal.

Comparison between biomass and coal

The following points can be made on the similarities and differences between the selected solid biomass and coal (see Table 1):
• Wood pellets have better flowability among the selected solid biomass materials and coal. The flow behaviour of torrefied pellets is more resembling to the flow behaviour of coal. Wood chips have the poorest flow ability among these materials.
• Values of bulk density and lower heating value (LHV) together show that up to eight times more volume of solid biomass is required for the same energy input.
• Similar to coal, solid biomass properties vary in a wide range. Equipment designed for the handling solid biomass should take this fact into account.

In terms of handling and storage equipment, the following conclusions can be made for solid biomass:
• Sensitive towards material degradation. Therefore the storage time should be shorter than for coal.
• Equipment designed for coal can be used for solid biomass. However, the number or capacity of equipment has to increase (three to four times more due to bulk density) for same tonnage performance requirement.
• Enclosed or covered equipment is required (e.g. flat storage, covered belt conveyors).
• Handling methods should be adjusted to cope with biomass material properties for un-wanted effects (e.g. against self-heating).

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