In the cement industry, many plants are looking for ways to reduce gaseous emissions to comply with new environmental regulations. Norcem AS, part of HeidelbergCement, wanted to reduce their gaseous emission of sulfur dioxide (SO2) by 400 tons per year.
Defining the project
The Brevik plant explored various methods to reduce their SO2 emissions. The plant uses two different raw mixes to make three types of clinker. One of the raw mixes produces a negligible SO2 emission, while the other raw mix produce SO2 emission of up to 400 mg/Nm³ dry. Therefore the plant required a technology that only needs to be used when operated with the raw mix producing high SO2. After reviewing potential technologies the plant decided to install FLSmidth’s gas suspension absorber technology. Norcem AS was already familiar with this technology as they in 1991 purchased a FLS-GSA® semi-dry scrubber for installation at the Kjøpsvik plant.
As there are two separate gas streams from the kiln system, it had to be decided if two separate semi-dry systems was required. With one gas stream passing through the raw mill system, which is a natural SO2 scrubber, it was decided to only install a semi-dry scrubber system in the gas stream not passing through the raw mill.
The scope of the project includes the complete semi-dry scrubber system (see figure 1: reactor1, cyclones2, recirculation box3, lime/water mixing tank4, lime slurry spray nozzle system5, pumps and compressors6, water tank7). An existing 60 ton silo8 was reused for burnt lime storage. A new booster fan was installed to handle the extra pressure drop across the system. Based on the process design criteria the reactor dimensions are 3.65m in diameter by 14.2m tall and the two cyclones are 4.0m in diameter.
Due to the very limited space available for the GSA installation, it was a challenge to fit in the new equipment. Even with a GSA footprint at only 50 m², the space available was fully utilized. The GSA was erected while the cement plant was in operation. Only 17 days was required for system shutdown.
The semi-dry scrubber system installed at the Brevik plant has exceeded its designed performance, achieving 97.3% reduction of SO2 emissions and 95.2% reduction of HCl emissions. It has proven that it can achieve reductions in SO2 and HCl emissions that are similar to what can be achieved in a more expensive wet scrubber system.
Emissions testing has shown that semi-dry scrubber system also gives the plant the capability to reduce mercury (Hg) emissions by 90%.
To achieve this Mercury reduction on a long-term basis, the plant would only need to start shuttling dust from the semi-dry scrubber system to the finish mill.