Woodchips are a medium-sized solid material made by cutting, or chipping, larger pieces of wood. Woodchips may be used as a biomass solid fuel and are raw material for producing wood pulp. They may also be used as an organic mulch in gardening, landscaping, restoration ecology, bioreactors for denitrification and mushroom cultivation. According to the different chemical and mechanical properties of the masses, the wood logs are mostly peeled, and the bark chips and the wood chips are processed in different processes. The process of making wood chips is called woodchipping and is done with a woodchipper.
Biomass is an industry term for getting energy by burning wood, and other organic matter. Burning biomass releases carbon emissions, but has been classed as a renewable energy source in the EU and UN legal frameworks, because plant stocks can be replaced with new growth. It has become popular among coal power stations, which switch from coal to biomass in order to convert to renewable energy generation without wasting existing generating plant and infrastructure. Biomass most often refers to plants or plant-based materials that are not used for food or feed, and are specifically called lignocellulosic biomass. As an energy source, biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuel. Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into: thermal, chemical, and biochemical. Some chemical constituents of plant biomass include lignins, cellulose, and hemicellulose
Woodchips have been traditionally used as solid fuel for space heating or in energy plants to generate electric power from renewable energy. The main source of forest chips in Europe and in most of the countries have been logging residues. It is expected that the shares of stumps and roundwood will increase in the future. As of 2013 in the EU, the estimates for biomass potential for energy, available under current conditions including sustainable use of the forest as well as providing wood to the traditional forest sectors, are: 277 million m3, for above ground biomass and 585 million m3 for total biomass.
The newer fuel systems for heating use either woodchips or wood pellets. The advantage of woodchips is cost, the advantage of wood pellets is the controlled fuel value. The use of woodchips in automated heating systems, is based on a robust technology.
The size of the woodchips is particularly important when burning woodchip in small plants. Unfortunately there are not many standards to decide the fractions of woodchip. One standard is the GF60 which is commonly used in smaller plants, including small industries, villas, and apartment buildings. "GF60" is known as "Fine, dry, small chips". The requirements for GF60 are that the moisture is between 10–30% and the fractions of the woodchips are distributed as follows: 0–3.5mm: <8%, 3.5–30mm: <7%, 30–60 mm: 80–100%, 60–100 mm: <3%, 100–120 mm: <2%.
The energy content in one cubic metre is normally higher than in one cubic metre wood logs, but can vary greatly depending on moisture. The moisture is decided by the handling of the raw material. If the trees are taken down in the winter and left to dry for the summer (with tears in the bark and covered so rain can't reach to them), and is then chipped in the fall, the woodchips' moisture content will be approximately 20–25%. The energy content, then, is approximately 3.5–4.5kWh/kg (~150–250 kg/cubic metre).
Coal power plants have been converted to run on woodchips, which is fairly straightforward to do, since they both use an identical steam turbine heat engine, and the cost of woodchip fuel is comparable to coal.
Solid biomass is an attractive fuel for addressing the concerns of the energy crisis and climate change, since the fuel is affordable, widely available, close to carbon neutral and thus climate-neutral in terms of carbon dioxide (CO2), since in the ideal case only the carbon dioxide which was drawn in during the tree’s growth and stored in the wood is released into the atmosphere again.