Boiler sands are used in power plants utilizing fluidized bed technology to form a firing grate. The purpose of boiler sands is to form a sand bed in the boiler, which allows the fuel fed into the boiler to burn on top of and within this layer of bed material.
Typical power plant boilers include circulating and bubbling fluidized bed boilers. The sand used in these power plant boilers is usually bed sand made of natural sand, or in other words natural sand that has been screened to the grain size suitable for use as bed sand.
When it comes in particular to the burning of biofuels, however, a problem emerges when the alkalis (sodium and potassium) in the biofuel ash react with silica in natural sand, causing the sand to sinter in the boiler environment. Consequently, the reaction between silica and the alkali compounds with a low melting point forms a liquid mixture, which causes the sand grains to stick together. Due to this, the flow of the bed material becomes weaker or stops completely, after which the bed material needs to be replaced.
Silica-Free Bed Materials
The issues caused by the alkali reaction can be significantly reduced by either replacing the bed material more frequently or by switching to a bed sand that contains less silica. There are several sands to choose from, but their commercial use is often limited by the materials’ limited availability and high prices.
Finn Recycling Oy processes recycled materials into bed material for fluidized bed boilers, which is resistant to alkali reactions and thus reduces the consumption of bed materials and the generation of waste sand.
Comprehensive Sand Treatment Service
Finn Recycling Oy offers power plants purification services of used bed sand using a mechanical method. The service includes collecting the used sand from the customer and then delivering new sand back to the customer.
The quality parameters of the sand are determined together with the customer:
- Electrical Conductivity
- Grain Distribution
- Loss on Ignition