F.L.Smidth’s R&D team successfully develops unit for accurate distribution of raw meal between several feed inlets.
Over the past few decades cement kiln preheaters have become increasingly complex because of the tighter emission limits and growing use of alternative fuels. Today, for example, the Low NOx ILC calciner is divided into three zones, one for NOx reduction, one for hightemperature combustion and one for final calcination. A ‘down-draft’ calciner can also include high-temperature combustion,
a particularly suitable solution for burning low-gas-content coals, and an additional option is FLSmidth’s newly developed HOTDISC that handles various types of waste.
Dividing the flow accurately
All this has created a need for accurate distribution of the preheated raw meal from the second lowermost preheater stage into at least three flows of material, in the future maybe four, because the ratio between the flows is used for precise temperature control in the respective zones and units. The solution applied so far has been either two conventional 2-way dividing gates placed in series below the second lowermost preheater stage or an upper division of the flow below the third lowermost preheater stage. These two
solutions require either considerable installation height or increased energy consumption.
From concept to prototype in 15 months
It was therefore an obvious task for the newly established R&D team at the Dania Research Centre to develop a new and more suitable raw meal divider. The short path from initial concept via a 3D ‘drawing board’ to manufacturing in the Centre’s own workshop and actual testing makes it easy to screen new ideas and examine their viability. The idea of the new dividing principle was born one December morning in 2002, and it took only four months from the rough model stage until a fullyfledged 5 t/h unit for cold raw meal was ready for testing. The tests showed that the unit divided the material accurately and with a high level of reproducibility.
Only two months later a unit with internal lining was fitted into Pilot 2 and tested successfully for 4 weeks, feeding 2 t/h of 700oC hot raw meal. Pilot 2’s operators reported that plant operation had become more stable and that the new divider worked with greater precision than the old type, and the unit is now an integrated part of the pilot installation.
Success on an industrial Scale
Encouraged by these results, it was decided in September 2003 to design an industrial-scale prototype and look for an interested customer. The answer to this search was close at hand. Aalborg Portland was looking for methods to reduce NOx emission from its Kiln 87. By substituting the new 3-way divider for the existing two-way unit between riser duct and calciner, it became possible to divide the calciner into a high-temperature combustion zone and a final calcination zone. A new flow of raw meal was to be introduced about halfway up the calciner.
In November 2003, the Dania team,working in close cooperation with F.L.Smidth’s Pyroprocessing Department, started the design work for the industrial scale 3-way divider. And in January 2004, the Research Centre’s own workshop began manufacturing the unit.During this hectic period of parallel design and manufacturing, two-way communication between the workshop and the R&D group was essential. The divider was to be ready by week 12 in mid March, ahead of the half-yearly kiln maintenance stoppage scheduled for week 13 and 14. The finished divider was ready for bench testing in week 11 and was heated up to some 700°C by an oil furnace. The test revealed two minor, yet significant faults in the rotor bearing design which were remedied in time.
More stable, more precise
At the time of writing, the 3-way divider has been in operation at Aalborg Portland for six months with only a few upsets. The rotor drive has stopped on few occasions due to a fault in one of the rotor shaft bearings, and also it appeared that the drives on the actuators for the dividing knives are too weak and suffer from backlash. This will be solved by changing to another, robust and maintenance friendlytype of bearing and drive system. The actuators for the dividing knives will be replaced by a completely new F.L.Smidth developed actuator design based on standard components. These two design changes will be implemented on the Aalborg Portland unit during the next kiln shutdown in November 2004.
The Kiln 87 operators report that production has become more stable, so once again it appears that dividing is significantly more precise than with the old concept.
Ongoing improvement
Meanwhile, it was not possible to achieve the desired level of high-temperature operation and resulting NOx reduction from Kiln 87, because the suspension of the raw meal entering the calciner at the new feeding point proved inadequate. The R&D department is working closely with Aalborg Portland to solve this problem. Possible solutions might be an improved spreader plate, a constriction of the calciner, changing the position of coal firing points, etc.
The inadequate suspension, however,is obviously not caused by the 3-way divider. With regard to dividing functionality it is definitely a success. The final version is expected to be released for sale by the end of 2004, incorporating all design changes and experience from the Aalborg Portland prototype - only two years after the idea was conceived. The divider may be included as a standard component in all new pyroprocessing projects where distribution into three or four raw meal flows is needed. This could be in Low NOx ILC systems or kiln systems including or prepared for a HOTDISC. The obvious advantages are minimum 2-3 metre reduced tower height or 20-30 kcal/kg clinker in addition to more stable operation and better temperature control, which is essential to achieve lower NOx emission. The new divider will also be an obvious choice in many upgrading projects for existing kiln systems.