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Review: Step by Step Towards Alternative Fuels – part two

World Cement,

Continued from part one.

The paper drew on experiences at the Rohoznik plant in Slovakia, which delegates were able to visit in the afternoon. This plant was upgraded by FLSmidth to a 5-stage precalciner kiln and was the first to install a HOTDISC® Reactor, which the plant uses to burn SRF. The plant is achieving a TSR of 90% overall and 100% in the calciner. The quantity of SRF being burnt led to a lot of chlorine in the system – too much for a stable pyroprocess – and so a bypass was necessary, but the bypass dust extracted from the process was piling up. It couldn’t be recirculated in the system and had to be disposed of at high cost. A TEC and Holcim partnered initially to install the ReduChlor system in 2007 and in 2009 began working on the concept for the ReduDust system. The ReduDust mixes the bypass dust with water, filters it and then treats it to achieve a brine that can either be disposed of into the sea or crystallised to create salts. The process uses only simple chemicals that are easy to obtain. Two salt fractions are produced: potassium chloride (KCl), which is the majority, and a small amount of sodium cloride (NaCl). The ReduDust plant has been running for about 6 months now and achieves 4000 tpy of salt production. The water in the process is recycled; the filter cake is returned to the process, either to the cement mill or to the raw material. The salt produced complies with the quality that can be purchased in the market. An ORC waste heat recovery system from Turboden was also installed to supply the ReduDust plant with the required thermal power for crystallisation. Beside this, the WHR system produces up to 5 MW of electric power. Heat is collected from the preheater exhaust gas and the clinker cooler.

Delegates were fascinated to see the system on the afternoon of 7th May, when staff from the Holcim-owned plant showed us around. Our guide warned us not to taste the salt he showed us, as it is particularly salty! The small amount of sodium chloride produced is currently being stored while the plant decides on the best use for it. The mixing and filtration part of the system runs 12 hours a day, 7 days a week, and is remarkably efficient in its use and reuse of water and energy. This is the only such system in the world, but is surely a model for other plants looking to reduce the chlorine in their process in a useful way.

Also under discussion on that first day of the seminar was the calciner modification project at Buzzi Unicem’s Hranice plant in the Czech Republic, which included a new hot gas chamber. The goal of the project, which was presented by Harald Durstberger of A TEC Production & Services GmbH, was to maintain production capacity at 3000 tpd while increasing alternative fuels utilisation up to 100% in the calciner, with NOX emissions reduced below the legal limits and retention time increased to around 7 seconds. This project is an example of the benefit to A TEC of Loesche’s support, which enables the company to take on bigger projects. The project was undertaken with the Czech partner Aliacem and comprised a new calcining system consisting of a hot gas chamber, calciner and A TEC post-combustion chamber (PCC). A TEC supplied engineering, mechanical equipment, duct works, cyclones and the hot gas chamber, while Aliacem supplied the steel structure, refractory lining and conducted the erection of all components. One of the many unique features of the project was the installation of the separate hot gas combustion chamber. As the world’s first installation working without hot meal, it can also operate with very low quality solid alternative fuel. A jacket tube design also allows the utilisation of high quality fuel, so the system is highly flexible for alternative fuel combustion. Moreover, the combustion can be controlled perfectly to create the necessary atmosphere for NOX reduction in the calciner.

Matthias Mersmann then came back to the lectern to talk about the need for computational fluid dynamics modelling to identify how best to optimise your process. Modelling helps pinpoint the route cause of process problems, which are often exacerbated by the use of alternative fuels. The paper included examples of a successful optimisation project at a Cemex plant in Germany, which one of the delegates from Cemex Germany was able to contribute to from the audience.

The penultimate paper on the first day was from Georg Lechner at Scheuch, which detailed the DeCONOx, an exhaust gas treatment solution that uses energy from polluted exhaust gas to break down other pollutants. The DeCONOx process combines regenerative thermal oxidation (RTO) with a low-dust SCR (selective catalytic reduction) to reduce NOX and organic carbon compounds. This system, which has been installed in the Kirchdorfer plant in Austria, will be the topic of an article for a future issue of World Cement. Finally, Dr Hansjörg Diller of MVW Lechtenberg provided some insight into the global alternative fuel trends, looking particularly at the Arab world where traditional fuel subsidies are being reduced and greater efficiency is being targeted.

Article continues in part three. This article is taken from the June issue of World Cement. Subscribers can download the full issue by logging in here.

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