Overview of Biomass Logistics

Biomass logistics include all the unit operations necessary to move biomass feedstocks from the land to the biomass energy plant and to ensure that the delivered feedstock meets the specifications of the conversion process. The packaged biomass can be transported directly from farm or from stacks next to the farm to the processing plant.

Biomass may be minimally processed (i.e. ground) before being shipped to the plant, as in case of biomass supply from the stacks. Generally the biomass is trucked directly from farm to biorefinery if no processing is involved.

Another option is to transfer the biomass to a central location where the material is accumulated and subsequently dispatched to the energy conversion facility. While in depot, the biomass could be pre-processed minimally (ground) or extensively (pelletized). The depot also provides an opportunity to interface with rail transport if that is an available option.

The choice of any of the options depends on the economics and cultural practices. For example in irrigated areas, there is always space on the farm (corner of the land) where quantities of biomass can be stacked. The key components to reduce costs in harvesting, collecting and transportation of biomass can be summarized as:

  • Reduce the number of passes through the field by amalgamating collection operations.
  • Increase the bulk density of biomass
  • Work with minimal moisture content.
  • Granulation/pelletization is the best option, though the existing technology is expensive.
  • Trucking seems to be the most common mode of biomass transportation option but rail and pipeline may become attractive once the capital costs for these transport modes are reduced.

The logistics of transporting, handling and storing the bulky and variable biomass material for delivery to the bioenergy processing plant is a key part of the supply chain that is often overlooked by project developers. Whether the biomass comes from forest residues on hill country, straw residues from cereal crops grown on arable land, or the non-edible components of small scale, subsistence farming systems, the relative cost of collection will be considerable. Careful development of a system to minimize machinery use, human effort and energy inputs can have a considerable impact on the cost of the biomass as delivered to the processing plant gate.

The logistics of supplying a biomass power plant with sufficient volumes of biomass from a number of sources at suitable quality specifications and possibly all year round, are complex. Agricultural residues can be stored on the farm until needed. Then they can be collected and delivered directly to the conversion plant on demand. Infact, this requires considerable logistics to ensure only a few days of supply are available on-site but that the risk of non-supply at any time is low.

Biomass Storage Methods

Sufficient storage for biomass is necessary to accommodate seasonality of production and ensure regular supply to the biomass utilization plant. The type of storage will depend on the properties of the biomass, especially moisture content. For high moisture biomass intended to be used wet, such as in fermentation and anaerobic digestion systems, wet storage systems can be used, with storage times closely controlled to avoid excessive degradation of feedstock. Storage systems typically used with dry agricultural residues should be protected against spontaneous combustion and excess decomposition, and the maximum storage moisture depends on the type of storage employed.

Moisture limits must be observed to avoid spontaneous combustion and the emission of regulated compounds. Cost of storage is important to the overall feasibility of the biomass enterprise. In some cases, the storage can be on the same site as the source of the feedstock. In others, necessary volumes can only be achieved by combining the feedstock from a number of relatively close sources. Typically, delivery within about 50 miles is economic, but longer range transport is sometimes acceptable, especially when disposal fees can be reduced.

Storage of biomass fuels is expensive and increases with capacity.

Agricultural residues such as wheat straw, rice husk, rice straw and corn stover are usually spread or windrowed behind the grain harvesters for later baling. Typically these residues are left in the field to air dry to moisture levels below about 14% preferred for bales in stacks or large piles of loose material. After collection, biomass may be stored in the open or protected from the elements by tarps or various structures. Pelletizing may be employed to increase bulk density and reduce storage and transport volume and cost.

Biomass Storage Options

  • Feedstock is hauled directly to the plant with no storage at the production site.
  • Feedstock is stored at the production site and then transported to the plant as needed.
  • Feedstock is stored at a collective storage facility and then transported to the plant from the intermediate storage location.

Biomass Storage Systems

The type of biomass storage system used at the production site, intermediate site, or plant can greatly affect the cost and the quality of the fuel. The most expensive storage systems, no doubt, are the most efficient in terms of maintaining the high fuel quality. Typical storage systems, ranked from highest cost to lowest cost, include:

  • Enclosed structure with crushed rock floor
  • Open structure with crushed rock floor
  • Reusable tarp on crushed rock
  • Outside unprotected on crushed rock
  • Outside unprotected on ground
  • Subterranean

The storage of biomass is often necessary due to its seasonal production versus the need to produce energy all year round. Therefore to provide a constant and regular supply of fuel for the plant requires either storage or multi-feedstocks to be used, both of which tend to add cost to the system.

Reducing the cost of handling and stable storage of biomass feedstocks are both critical to developing a sustainable infrastructure capable of supplying large quantities of biomass to biomass processing plants. Storage and handling of biomass fuels is expensive and increases with capacity. The most suitable type of fuel store for solid biomass fuel depends on space available and the physical characteristics of the fuel.