Optimised and increased use of Refuse Derived Fuel as substitute for coal at Norcem Brevik cement plant

The use of alternative fuels, including waste derived fuels (WDF; such as refuse derived fuel, RDF), is very important for the competitiveness of Norcem Brevik and is an efficient and sustainable way to handle waste. The long-term goal of 75% thermal substitution rate (TSR) is hence important for Norcem, but simultaneously it is equally important to avoid non-compliance emissions of PCDD/PCDFs (dioxins) and no negative impacts on cement quality. As enhanced emissions had been experienced at the plant, Norcem Brevik together with Sintef applied for a BIA project with funding from NFR in 2014: ?Optimised and increased use of refuse derived fuel as a substitute for coal at Norcem Brevik cement plant?. The primary objective of the project was to be able to run the cement manufacturing process permanently with a waste derived fuel TSR of 75 % without causing non-compliance dioxin emissions, negative impacts on the process or product quality problems. The main tasks defined were: improved (or modified) precalciner (PC) enabling stable combustion of high amounts of RDF; improved specifications and quality of the RDF; improved recycling routines of filter dust; improved control of the process; understanding how dioxins are formed in the process and the role of waste combustion. During the project, many full-scale tests with different feeding rates have been carried out, and dioxin/furan and process measurements have been done, including 20 sampling campaigns with measurements in the stack and 9 campaigns with measurements at various positions inside the kiln system. Three full-scale tests with different RDF qualities were done by USN. The results showed that improving the RDF quality reduces the negative impacts on process conditions, product quality and emissions of TOC and CO. However, no direct correlation between RDF quality and dioxin emissions were observed. The computational fluid dynamics (CFD) analyses from Aixergee and USN shows that the geometry causes an uneven distribution of particles at the end of the precalciner, so that more particles are routed to cyclone 4.2 (about 67 %) than to cyclone 4.1 (about 33 %). Furthermore, large particle sizes may cause problems with CO generation if the particles drop through the orifice and end up in the kiln inlet, and the moisture content of the fuels affects the gas volume and temperature profile in the calciner. The analysis of dioxin formation indicates two main processes/contributions: i) dioxin may form as a result of the combustion process in the calciner and ii) dioxins circulate in the upper part of the pre-heating tower and filterdust system. It has not been possible to establish any direct correlation between feeding of waste derived fuels and the release of dioxins; both the production process and the formation mechanism are so complex that it is very difficult to demonstrate a clear correlation. Based on the results from the project, Norcem Brevik will continue working on improvement with the following actions: 1) Improving the WDF quality will be an ongoing task. The fuel suppliers will still be closely followed up, and the measures for improved quality control of WDF introduced in 2016/2017 will be continued/expanded. 2) O2 measurement equipment will be installed above cyclone 4.2 (in addition to the current equipment above cyclone 4.1), and will give improved possibilities for better O2 control in the calciner. 3) Dust removal will be installed at the bag-house filter on string no 1 during spring 2020. The dust will be deposited. 4) If dioxin emission compliance has not been reached after implementing the dust removal measure, dosing of activated carbon into the baghouse filter on string no 1 will be started.

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Norcem Brevik cement plant substitutes today approximately 50% of its coal with waste and refuse derived fuel, but wants to increase the substitution up to 75% by 2020. The waste feeding seems however to cause process- and product quality problems and occasionally to elevated emissions of dioxins. Norcem Brevik has together with SINTEF investigated the problems over the last three years and concluded that the only way forward is to conduct systematic long-term investigations as the problems are complex and interrelated. And many aspects of the process and its operation needs to be investigated in detail. Norcem has therefore applied the Norwegian Research Council for financial support to conduct a comprehensive project over a four year period. A future solution will probably be a combination of an upgrade or redesign the pre-calciner, improved waste specification and feeding routines, and possible new routines on recycling of the cement kiln dusts. Apart from solving problems at Norcem Brevik, the project will also contribute to increase the overall waste treatment capacity in Norway, contribute to save virgin raw materials and non-renewable fossil fuels, to reduce CO2 emissions and other air pollutants, and to make cement production more sustainable. The project will contribute to secure future operation at Norcem Brevik and will build competence at Norsk Gjenvinning in Larvik to produce high quality refuse derived fuels. SINTEF, which has been supporting Norcem Brevik since the nineteen eighties, has world class competence and experience with these kinds of problems and will be the main partner in the project. The project will also have support from HiT and Renor.