Design and evaluation of a catalytic off-gas solution for a European Portland Cement plant
With more than 200 plants and 160 million tons of cement produced in 2014, the Portland cement industry in Europe continues to represent a significant portion of the global cement market. In fact, 4 of the top 10 global cement producers are based in Europe with more than 500-million-tonnes of collective, annual capacity.
Europe has maintained a strong manufacturing base in this area due to the economics of cement distribution and its technology leadership in the field. Furthermore, because up to 35% of the cost of cement is attributable to transportation costs, it is advantageous to have localized production and distribution.
Although European manufacturers are bound by EU-wide legislation, country-specific and region-specific administration and regulations can vary. Emissions limits for toxic pollutants in the case of cement production differ and, in some cases, are significantly more stringent than the overall EU limits. Furthermore, cement producers in particular regions or states within a country may be subject to additional local pressure to operate with the optimal available technologies, such as sites in the vicinity of outdoor recreation areas or local populations.
In Germany, for example, the Federal Ministry for Environment, Nature Conservation and Nuclear Safety has been a driver for emissions reduction in Europe through the enactment of the “Federal Pollution Control Act". Recently this legislation was revised with respect to the combustion of waste materials to include Portland cement plants. Being designated as “co-incinerators” of waste materials, these plants are subject to the emissions restrictions created for combustion plants, including restrictions for the emission of carbon monoxide.
In most cases, these regulations are applied with specific exceptions for the operation of cement plants given unavoidable emissions due to the carbon-bearing nature of the raw materials. However, this revised regulation presents a difficult problem for German cement manufacturers. There are few, if any, demonstrated technologies to deal with these emissions, and the technologies that are commercially available, such as thermal oxidation, are often not practical due to energy costs. One cement producer affected by the aforementioned legislation identified the high risk of inaction and engaged in a pilot testing program to identify a combined catalytic solution for the abatement of VOCs, carbon monoxide, nitrogen oxides and particulate matter. The problem of identifying such technology was not trivial; until now no conclusively demonstrated catalytic oxidation technologies have been demonstrated to withstand the process conditions.
In order to test the combined catalytic solution under realistic conditions, a mobile set-up was designed to utilize a slip stream and perform the tests using actual cement off-gas. The test unit was installed in the cement plant for the duration of the screening and continued operation over one year to include long-term testing. Subsequently, the testing was continued at another facility in the region to evaluate the effect of different effluent gases on the catalyst system. The flexible design of the unit allowed for variation of process conditions to test a combination of: dust-removal, selective catalytic removal (SCR) of NOx, as well as catalytic oxidation of the volatile carbon species and carbon monoxide (see figure).
The testing unit was then used to screen a combination of different SCR and oxidation catalysts – from monolith-type vanadium-tungsten-titanium (VWT) catalysts to combination ceramic filter cartridges – for their lifetime performance in NOx reduction and CO/VOC oxidation. These cartridges were loaded with an active SCR component based on iron zeolite. The oxidation unit was comprised of monolith-type catalysts chosen from a range of commercially available products, as well as, a new generation of air purification catalysts based on a platinum-loaded zeolite coating.