What is Circulating Dry Scrubber (CDS) process?

CDS technology was first developed for SO2 removal in coal-fired power plants. Today it is also used in flue gas treatment for industrial furnaces and boilers that use biomass, industrial or municipal waste as fuels. The CDS process is able to remove both acidic gas components and micropollutants. It is based on the recirculation of filter residue which consists of sorbent reaction products and fly ash from the filter. CDS units operate exclusively with calcium-based sorbents.

CDS technology, which is less capital intensive than wet processes and based on a multi-pollutant approach, is gaining momentum. Lhoist, equipment designers and suppliers are further developing this technology to improve acid gas treatment performance and decrease sorbent consumption. 


The CDS process consists of a reactor followed by a particulate filter. A large part of the solids from the filter are recycled into the reactor, where the fresh sorbent is added. In most cases water is injected into the reactor or onto the solids. Addition of water plays a critical role for temperature control and to improve removal performance. Some installations use quicklime (CaO) that is hydrated prior to entering the CDS process. 

Recirculation of the residue decreases sorbent consumption, especially when combined with water addition to the residue. It can also enable systems to achieve high acid gas removal levels: more than 99% for SO2, SO3, HF and HCl.

Lhoist product range dedicated to CDS

CDS performance is primarily driven by the recirculation rate and the moisture content of the recirculating residue. Sorbacal® CDS can handle more than double the moisture content of standard hydrates which also improves flowability. This significantly enhances the efficiency and performance of CDS systems. If needed, micropollutants can also be removed, by adding PAC, lignite coke or Sorbacal® Micro. 

  • Sorbacal® SPS
  • Sorbacal® SP
  • Sorbacal® H
  • Sorbacal® CDS
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Circulating Dry Scrubber