Dealing with emissions responsibly and efficiently is a fact of life for today’s production facilities. Authorities are ever-more demanding, enforcing tighter limits on specific substances and their allowable limits.
It is widely recognised that Germany, with its stringent regulations on gaseous hazardous pollutants, leads the way in emissions control. In January 2019, cement producers in Germany will be required to restrict NOx and NH3 emissions even more.
But several other countries are not far behind, according to Pietro Aresta, Global Product Manager for Catalytic Filtration Technologies at FLSmidth.
“While it’s important to look at the developments in Germany, we are also constantly monitoring developments in other countries focused on strict emissions limits.” - Pietro Aresta, Global Product Manager for Catalytic Filtration Technologies at FLSmidth.
One important development is that ammonia emissions will be included as part of the baseline limit. The limits will in fact apply to the ammonia concentration in the stack. Ammonia is emitted from the raw materials and alternative fuels in the preheater tower, so this will have dramatic consequences for many plants, where certain alternative fuels, or even the raw materials from the quarry, can give very high baseline level values. As a result of these developments, cement producers are under pressure to find new solutions to reduce emissions efficiently and cost-effectively.
“Unfortunately, it can’t be solved simply by optimising the selective non-catalytic reduction (SNCR) with high-efficiency techniques, since ammonia is released downstream at higher stages of the preheating tower,” says Pietro Aresta. Instead, catalytic filtration solutions are proving to be highly effective and increasingly important in the cement industry. Catalytic filtration can be implemented in different solutions on a cement plant to achieve NOx reduction targets. Depending on the efficiency of SNCR, the ammonia baseline and the plant configuration, catalytic filtration can achieve the most effective CAPEX and OPEX solution in different ways.
Reduced ammonia usage
A recent installation of a single-layer catalytic filter at a German cement plant has given extremely positive results. The mechanical filtration process (differential pressure and dust emissions) and the catalytic performance (NOx and ammonia removal rates) have been outstanding from day one. This solution combined with an existing SNCR has helped the plant achieve yearly savings of approximately 75,000 Euros from reduced ammonia usage.
Auxiliary systems can be used to enable a catalytic conversion process, if the current temperature level is not sufficient to allow a catalytic conversion process. But when the available heat in the system reaches the temperatures required by the catalytic reaction, modification only requires replacement of the bags and heat-balance adjustment. Such cases can be implemented very easily. For example, it took just three days to retrofit the fabric filter, with the biggest task being the bag and cage replacement.
A total retrofit to achieve a full deNOx solution reduces ammonia costs even more. It is estimated that savings in the range of 0.3 Euros per tonne of clinker can be achieved by using the ammonia released by the raw material and replacing SNCR with a more efficient catalytic NOx conversion method.
Effective all-in-one gaseous pollutants and dust removal
FLSmidth Airtech provides two catalytic filtration solutions that effectively meet cement producers’ toughest demands for air pollution control. They are the first solutions on the market to remove gaseous pollutants and dust in a single, compact installation. Both combine FLSmidth’s extensive process know-how and the newest ground-breaking technologies. The CataMax™ catalytic solution is based on ceramic filtration technology, while the CataFlex® catalytic filter bag applies unique, specially developed catalytic technologies to woven-glass bags.
Simple conversion of the kiln and raw mill fabric filter
Replacing ordinary bags with catalytic filter bags can be done without major plant layout modifications. It is an ideal solution when the SNCR system reduces NOx emissions to below or slightly above necessary limits. In such cases, the catalytic filter bags reduce ammonia emissions to below required limits, also removing approximately the same molar quantity of NOx.
A key difference with FLSmidth’s catalytic filtration solutions is that gases from the bypass do not pass through the preheater tower’s SNCR-active zones. They must be dealt with separately, if they contribute significantly to the combined NOx stack emission. In such cases, converting the bypass filter (electrostatic precipitator or fabric filter) into a catalytic fabric filter, together with the SNCR for the preheater/calciner gases, can be a very cost-effective solution.
High conversion rates
A catalytic fabric filter conversion of a bypass fabric filter with FLSmidth CataFlex® catalytic filter bags was commissioned at a German cement plant in October 2015. Tests have shown very good conversion rates with mechanical properties in line with the highest fabric filter quality standards. Satisfactory deNOx conversion rates were obtained at two different temperature levels (220°C and 240°C) with two-layer catalytic bags (plus one external, non-catalytic). Conversions above 80 percent were achieved easily, keeping ammonia slip below 10 mg/Nm3
dry (see figure 1).
Efficient multi-pollution control
Catalytic filtration is not only efficient in removing NOx and NH3, and the catalyst has proven its efficiency in converting a wide range of organic compounds into harmless species. As an example of this, a CataMax catalytic filter was commissioned recently in an American cement plant with the main purpose of removing high concentrations of organic hazardous air pollutants (OHAPs) according to local NESHAP rules.
A comparison of the total cost of ownership (over five years) of five different scenarios shows attractive savings (see figure 2). The cost levels of the three scenarios involving catalytic fabric filtration systems are significantly lower than common filtration solutions based on high and low-dust SCR.