Achieving sustainable production with low environmental impact is one of the main objectives of the cement industry today. In this respect, the industry has a long track record in lowering its emissions, also taking into account the technical and economic viability of appropriate emission abatement measures. National and European requirements, as well as the progress in abatement technologies, provide the framework in which new technologies for emission control are being introduced.
Environmental regulations for industrial production facilities go hand in hand with the installation of efficient emission abatement technologies, especially legislation on air pollution control. Emission limit values for several industrial activities, including cement kilns co-processing alternative fuels, have been set in the European Industrial Emissions Directive (IED). The so-called BAT conclusions under the IED, which were published in March 2013, contain a list of Best Available Techniques (BATs) via which an environmentally compatible cement production and furthermore the associated emission levels (BAT-AELs) can be attained. The BAT documents are reviewed and updated regularly so that technical progress and further developments in abatement technologies can be taken into account.
Although the IED and the BAT conclusions have established a framework for NOx reduction in the cement industry, there is an enduring discussion about the appropriateness of the potential reduction measures. According to the BAT reference document for the cement industry, secondary abatement measures like SNCR and SCR (Selective Catalytic Reduction) are efficient NOx abatement technologies for achieving low emission levels. The SNCR process is cost-effective but entails the risk of additional NH3 emissions (NH3 slip) due to an overstoichiometric injection of ammonia solution. This can be of importance because individual countries have set an emission limit value for ammonia. In particular, this is based on the National Emissions Ceiling Directive (NEC Directive), the ammonia limits of which have been exceeded in some countries.
The performance of the SNCR process has been improved more and more during the past years to comply with all environmental requirements. The application of the so-called ‘high-efficiency SNCR’ process (he-SNCR) seems to be a promising approach for minimising the proportion of unreacted ammonia, which would lead to lower NH3 emissions and a lower consumption of reducing agents.
The catalytic SCR process, which is state-of-the-art in the power sector, was not investigated in the cement sector until a few years ago. This technology was therefore classified as BAT subject to appropriate catalyst and process developments. In the meantime, experiences from several full-scale SCR projects in Italy, Austria and Germany (Figure 1) have been gained. These projects included different SCR variants, such as high-dust, semi-dust and tail-end solutions. As a result, certain authorities are of the opinion that SCR is now an available technology to meet challenging NOx and NH3 abatement targets. It should be pointed out, however, that SCR technology is very costly and due to the additional pressure drop the electrical energy demand of the plant increases by about 5 kWh/t of clinker.
RTO facility in a cement works.
This is part 1 of a 2-part article that was originally published in Newsletter 2/2015 of the European Cement Research Academy and is reproduced by kind permission of ECRA.
Read the article online at: https://www.worldcement.com/europe-cis/12082015/current-developments-in-emission-abatement-technologies-part-1-312/