New study compared biomass storage techniques of willow chips in piles during 12 months. Mositure, ashes and calorific value changes are reported.

The high cost of biomass harvest and considerable loss of dry weight during the storage of wood chips remains a considerable issue. The biomass quality (thermophysical properties) depends on the species and the time of biomass harvest, but also on another two main factors: technology of biomass harvest and the method of its further storage.

Biomass for bioenergy and/or bioproducts can be sourced from forests, agricultural crops, various residue streams, and dedicated woody or herbaceous bioenergy crops. Despite this wide spectrum of promising feedstocks, no single biomass source can meet the projected demand, or is clearly superior to alternatives in all aspects of cost, quality, and acceptance.

In this research, authors explored five methods of chips storage for a period of 12 months:

1. Vapour-permeable and waterproof roof foil with a weight of 110 g m2 . The membrane is used as cover to protect against dampening and leaking of roofs. The material is easily available and relatively cheap.

2. Toptex 130 membrane with a weight of 130 g m2 . This membrane is a gas-permeable fleece composed of 100% endless polypropylene filaments. Its properties and forms of supply are adjusted to the requirements of each individual application in the field of agriculture (e.g. beetroot, potato, straw, wood chips covering).

3. Toptex 200 membrane with a weight of 200 g m2 , with extended stability and higher strength than Toptex 130.

4. Wooden shed with a roof.

5. No cover, in an open space, on concrete slabs, as a control.

A video from Idaho National Laboratory found similar trends and results in storage research:



Willow chips during were affected by many factors: climatic conditions, temperature, pile size, aeration of the piles and the method of their storage. The authors of this study found that the use of cover made of permeable materials improves the biomass quality: its moisture content decreased more than twice, its heating value increased more than twice and the energy content in piles increased by 10%.

Authors condluded:

The loss of dry weight of wood in the stored piles during one year was small and ranged from 4% to 5%. The storage of willow chips under cover in an open space could be a cheaper alternative compared to roofed warehouses. Moreover, it has been found that long-term storage of willow chips in small uncovered piles in the climatic conditions of Poland results in a considerable increase in their moisture content, with a consequent decrease in energy content in biomass and its large loss, associated with the microbiological decomposition of wood.

To read the full study you need to click here.