What is a Biofuel?
Biofuel is a renewable fuel energy source produced from living things, or the "waste that living things produce". These include:
- Wood, wood chips and straw
- Pellets or liquids made from wood
- Biogas (methane) made from animal excrement
- Ethanol, diesel or other liquid fuels made by processing plant material
In other words, biofuels are produced from biomass - the gaining of energy from burning wood and other organic matter. Burning biomass releases carbon emissions, but it is classified as a renewable energy source.
What is the difference between biofuel and fossil fuel?
Biofuel, is essentially different from fossil fuels in that, biofuel is a renewable energy source. It is a product of biomass. Biofuel is unlimited, inexpensive and recycles carbon dioxide while fossil fuel is limited, expensive and introduces carbon dioxide to the atmosphere.
Biofuel has been gaining acceptance as a better alternative to fossil fuels as it cuts down on carbon dioxide emissions.
Sappi on Biofuels
Biofuels are an important renewable fuel source at Sappi.
In South Africa 42,8% of the energy we use is derived from biofuels: mainly from black liquor and some bark. Black liquor, created during pulp production, is a biofuel and a primary renewable fuel source in our integrated pulp and paper mills. At a mill level, the amount of biofuel that is used depends on the type of mill and the pulping process.
Fast Fact: Globally, black liquor is the fifth most important fuel in the world, after coal, oil, natural gas and gasoline. Being derived from wood, a renewable resource, it is the world's most prominent biofuel-derived energy source.
What is black liquor?
Black liquor is a renewable energy fuel source. It is created during Kraft recovery wood pulp production.
Pulpwood chips are digested (cooked under pressure in white cooking liquor) into pulp by removing lignin, hemicellulose and other extractives from the wood to free the cellulose fibres. The resulting spent liquor, weak black liquor, is a diluted aqueous solution of extractives, and the inorganic chemicals used to make up white cooking liquor.
Black liquor contains more than half of the energy contained in digested wood. As a renewable biomass-derived fuel, black liquor replaces fossil fuels with a corresponding reduction in greenhouse gas emissions.
Black liquor is an effective technology that:
- Recycles pulping chemicals
- Efficiently generates steam and electrical power
- Effectively disposes of extractives
How does black liquor generate energy?
The recovery process starts by concentrating weak black liquor in concentrators and evaporators. The resulting thick black liquor is then burned in a recovery boiler to produce steam and energy, which is used in the mill.
The role of black liquor in the pulping process
The inorganic chemicals originally used to make up the white cooking liquor, are recovered as a smelt from the recovery boiler. The smelt is dissolved in water to form raw green liquor, which is then causticised with unslaked lime (calcium oxide), yielding white cooking liquor again. The precipitated lime mud (calcium carbonate) resulting from the caustising reaction is washed and heated to a high temperature in a lime kiln to be regenerated as calcium oxide and reused to causticise raw green liquor again.