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Review: Step by Step Towards Alternative Fuels – part three

World Cement,

Continued from part two.

Day two

The second day of the seminar opened with a presentation on developments in calciner technology in relation to the use of alternative fuels from Michael Suppaner, A TEC. Mr Suppaner pointed out that unless you have a new kiln system, using alternative fuels would necessitate some modification. Residence time is particularly important for alternative fuels, as it needs to be more than twice as long as for traditional fossil fuels. Ordinarily, to add residence time it is necessary to extend the calciner length. However, A TEC has designed a post combustion chamber (PCC) that can be added to the top of the calciner instead of just extending it, and by so doing provides high material flow, decreased velocity, but increased turbulence, which means increased residence time. The investment cost is lower than for a calciner extension and it enables 100% TSR in the calciner. This presentation generated a lot of questions from delegates who were clearly very interested in the concept.

The Rocket Mill from A TEC was the subject of the next paper from A TEC, and was the focus of the plant visit to Wietersdorf, Austria, on the afternoon of 8th May. Hannes Uttinger described how A TEC’s research led it to decide that the key to improving alternative fuel utilisation was to improve the quality of the alternative fuels. The Rocket Mill is a power controlled mill with two grinding chambers, each containing four horizontally rotating chains. The impact of the chains crushes the material, which is pushed against the perforated screens on the sides of the chamber. A pilot version of this mill is in use at the Wietersdorf plant, where it is slightly scaled down with only one grinding chamber.

The visit to Wietersdorf also included a look at the FlexiFlame Eco Pro®, A TEC Greco’s new burner for 100% alternative fuels, which was the subject of a paper from Martin Willitsch. A TEC Greco used insights from CFD modelling to develop a burner that could burn 100% alternative fuels in the main burner by building in a ring channel wide enough to cope with high quality alternative fuels such as those produced in the Rocket Mill. This design makes the most of both the control gained from injecting the fuel through the burner, rather than beside or above it, but also makes sure it is getting the benefit of the high oxygen area. The plant has found an improvement in clinker quality since the burner was installed, having previously had problems with brown clinker. However, Mr Willitsch did take care to point out that the success of the burner is entirely dependent on the quality of the alternative fuels. This burner will work for fluff, but wouldn’t work with coarser, 3D materials such as tyre chips.

The Wietersdorf plant is home to many pioneering technologies – not least the Rocket Mill and new FlexiFlame Eco Pro®. The final presentation of the seminar was on the eXmercury system developed by A TEC, Scheuch and w&p Zement GmbH. The paper was presented by Friedrich Willitsch, A TEC, who noted that the cement industry is responsible for 9% of global mercury emissions and that mercury regulations are becoming increasingly strict worldwide. The eXmercury system, which is newly in operation at the Wietersdorf plant, basically works through a second, compact preheater, designed as an integrated part of the main process line. Therefore the first line is for the raw meal and the second for the mercury laden dust (e.g. filter dust). By preheating the dust, mercury is desorbed. Further, the cleaned dust is removed by a hotgas filter and reintroduced into the kiln. While the mercury-laden gas stream is cooled, reagents are added to absorb the mercury. The mercury bound on the activated carbon is then separated and deposited. This system only entered operation in April, but the results are promising. Mercury emissions at the stack have reduced from 45 µg/Nm3 to 2 – 3 µg/Nm3. No doubt this will be very interesting for the US market, as the system is highly effective and does not affect the specific heat consumption of the plant, while operating costs are low as the amount of activated carbon required is very low.

In all, the seminar provided an excellent introduction to alternative fuels utilisation, as well as an extended examination of the considerable achievements made in this field in the European cement industry. Delegates had much to discuss on the way to and from the plant tours and over dinner at a beautiful restaurant on the Thursday evening. Loesche and A TEC should be commended  for the excellent organisation of the event.

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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