France – Biomass Furnace to Dry Bricks
Since December 2007, Imerys’ site in Gironde-sur-Dropt (France) uses a 4-megawatt hot air generator that is fired by biomass.
This Imerys Terre Cuite site (Building Materials Division), located near the Landes and Dordogne areas in a heavily forested zone, has used sawdust as fuel since the early 1990s. The first biomass-burning generator, a 2 MW unit, produced heat to dry firing dust. New furnaces supply heat to the plant’s brick dryers and allow for the screening of sawdust upon arrivals on site.
Sawdust is characterized by its moisture content (which can vary from 50 to 150%) and its particle size distribution. Imerys has to control for both factors before using the product in its manufacturing process. Sawdust is also highly flammable. Therefore, stocks are kept away from the plant, contained within ADEX* materials and very well ventilated.
Replacing natural gas with biomass has two economic benefits. First, it works on production costs as energy accounts for almost 30% of a brick’s cost price. In addition, the use of sawdust significantly reduces fossil CO2 emissions and saves on greenhouse gas quotas. Considering increases in sawdust prices, the division is looking into alternative renewable energy sources.
The Gironde site does not use sawdust just for fuel. It is also a raw material. Worked into clay before the extrusion phase, sawdust first helps to stabilize the mixture. It accounts for no less than one-quarter of a Monomur** brick. During the burning stage, the sawdust burns, causing porosities in the finished product. These microscopic vacuum bubbles enhance the brick’s insulating qualities. As a result, the walls function as natural air conditioning. This technical process is now implemented in all Imerys’ brickworks.
(1) ADEX (Advanced Explosive): walls guaranteed to withstand fire for 2 hours.
(2) Monomur: clay brick with a honeycomb structure. Its environmental performance is recognized by the HQE label. It protects the quality of indoor air, reduces the risk of condensation and forms a safe, lasting barrier against fire.