Flue Gas Treatment

Flue Gas Treatment

Waste incineration and many other industrial processes generate flue gases. These often contain pollutants such as sulfur oxides (SO2 + SO3), hydrochloric acid (HCl), hydrofluoric acid (HF) as well as heavy metals, dioxins and furans. Lime, hydrated lime and limestone-based products are highly efficient reagents for capturing contaminants. When mixed with other components, they also remove so-called micro-pollutants.

Your activities have their own requirements in terms of pollutant capture; emission limits, hardware, etc. We provide customized solutions via different products:

  • Sorbacal® is a product portfolio for the removal of major acid pollutants (SOx, HCl and HF).
  • Sorbacal® Micro products are used for the elimination of micro pollutants (PCCD/DF, PAH, PCB and Hg).

Our flue gas treatment (FGT) solutions are ideal for processes that use different types of fuel; from lignite and hard coal to biomass and refuse-derived fuel (RDF).

Benefiting from a worldwide network of expertise backed by strong R&D resources, in-depth experience and specific on-site trial equipment, we provide:

  • high-quality products (lime, limestone, dolomite, minerals, etc.)
  • reliable and cost-effective solutions
  • full assistance and technical support for end users, as well as owners and FGT system builders.

Who uses lime products in the Flue Gas Treatment?

A wide range of industries are catered to, including:

  • minerals (cement, glass, ceramic, brick and tile, etc.)
  • non-ferrous (copper, aluminum, lead, etc.)
  • ferrous (sinter, electric arc furnace, coke oven, blast furnace, etc.)

Lhoist’s solutions offer particular benefits to:

Power plants

  • compatible with different fuel types
  • security of supply
  • wide variation of products that can be adapted to your needs
  • combination of proven technologies

Waste to energy industry

  • reduced FGT costs (lower stoichiometric ratio, less residues for disposal)
  • improved efficiency due to high pore volume and surface area
  • greater variation of waste input quality - due to Sorbacal®’s performance


  • increased fuel flexibility (low and high pollutant input)
  • compliance with regulations using Lhoists’ creative FGT combined solutions
  • reduced FGT costs due to higher efficiency.

 To discover how to use lime or limestone optimally for your specific application(s), click on the appropriate process.

Dry process

Dry processing of gaseous effluents involves injecting hydrated lime in the form of a dry powder to neutralize acid gases. The fly ash and salts resulting from the reaction are separated by an electrostatic precipitator or, preferably, by a fabric filter.

This process is considered to be ideally suited to low-capacity incinerators. It can easily be incorporated into existing installations and offers the following advantages:

  • low investment cost
  • simplicity of design and operation
  • extreme space-efficiency
  • easy to automate
  • low consumption of compressed air, electricity and water
  • flexible operation in terms of temperature and capacity.

In addition, the purification process by-product is a dry powder which is easy to handle. To minimize the quantity of secondary products yielded, Lhoist has developed highly reactive hydrated limes (Sorbacal® SP, Sorbacal® SPS, Sorbacal® H, etc.) that make dry processing a very competitive solution for a growing number of applications.

Semi-wet process

In spray-dry flue gas treatment, lime is added in the form of a lime slurry (or milk of lime) which is sprayed or atomized in a special reactor. The milk of lime or lime slurry serves a double function: to condition the flue gas by increasing humidity and to reduce the temperature. It also guarantees dispersion of calcium hydroxide in fine particles once the droplets are dry. The latent heat in the treated gas evaporates the water in the lime slurry and creates a liquid-gas reaction, leaving a dry powder.

Wet process

The wet process consists of cooling down the flue gas temperature to below the dew point. Condensed acid gases are washed using a liquor of either milk of lime/lime slurry or a suspension of calcium carbonate (milled limestone). This process is typically used in large installations because of the higher investment cost and the need to treat residual water.

Dry recycling process

This process is based on an intense recycling rate sometimes combined with an activation step to boost neutralization.

Ultra high temperature (dry)

Injected at the heart of the burning chamber (850°C to 1050°C), the dry powder shows better reactivity with SOx emissions.

Fluidized bed boiler (FBB)

The FBB is based on the principle of fuel combustion suspended in combustion air. Limestone of a specific particle size is mixed with the fuel to remove SO2 in situ.

Fixed bed

In the fixed bed reactor, flue gas passes through granular reagents. Their mission is to capture HF and SO3 (and some HCl) from a limited flue gas flow rate.

Special fractioned limestone particles (Sorbacal® C) and synthetic granulates (Sorbacal® G) with high porosity composed of limestone powder and hydrated lime offer high efficiency while requiring less supporting equipment.