CEE Jan-Mar 2012

with a thermal output of 10 MW to 300 MW and has been especially developed for the use of solid substitute fuels {Figure 6). Thus, with substitute fuels with an average grain size of dmax. <25 mm it has already been possible to achieve highest thermal substitution rates of 100%. During operation, the primary air nozzles are selectively adjustable radially and - independently - also tangentially so that any random swirl and divergence are possible and can be adjusted to the flow path of the substitute fuel particle. These flexible nozzles act as injectors and thus, allow for a specific reaction to fluctuating fuel properties, whereby e.g. a formation of rings and undesirable coating inside the kiln can be counteracted . An adapted particle size and intense mixing of fuel and combustion air ensures a quick and complete conversion and significantly shortens the reaction zone. This behaviour is especially important for slow-reacting, difficult or slowly ignitable secondary fuels or even anthracite coal. In order to be able to design the burner optimally, the multicomponent mixtures of the solid substitute fuels must first be fractioned in a sizing and chemically analysed. In the process, the fuel particles separate into particle fractions (Figure 7), in which the same properties result from equivalent solids of revolution , densities or grain shapes, i.e. the particles move on identical flow trajectories. Now, this method results in statements regarding the flow behaviour or the qual ity of processing , the former composition of the waste -single Figure 6. Front view of the POLFLAME VN clinkering zone burner Jl)<l,-----------r 0.4S ~ ! 200 ! ~ 15.0 ~ j 10() 50 • • • 0 0 ~J&-..-....-.. • 15 15 2 3 4 5 6 7 8 9 Claulfylng velocity of descent (m/sl 0.40 0.)5 0.30 02S 0.20 •Man d~1robutl()fl ( '4l 'SBS• 30 mm lhredded • M.II) dlstnbullon l%1 "SBS" JlO'l· trea!N (30 mm ~avy tractoon r;" removed. 10 mm P"'iets) E • Den\•ty IVm'J of the fractiOn "SSS" ~ post-trr1ted (30 mm. htavy fraction ~ .-moved, 10 mm pt'llel~ ~ •DenS•tY lt/m'J of the fractJon ··sss" 30 mm shredded C2l Density 0.145 tim' ' 0 Oens•ty 0.085 tim Figure 7. Flow fractioning of secondary fuels (SRF) by means of separation from identical particle fractions of high calorific value from the MBA. components become clearly perceptible - and the suitability of the respective particle fractions for the desired feed point at the rotary kiln. At relevant individual particle fractions, it is now also possible to determine the oxygen requirement or the ignition behaviour. Use of substitute fuels at the calciner In modern plants with calciners only 40 per cent of the thermal output is covered by the clinkering zone burner, while 60 per cent of the thermal power requirement is covered by one or more firing points at calciner. In the process, the necessary combustion air is fed via the tertiary air duct from the recuperation section of the clinker cooler to the firing points inside the calciner. With regard to reaction , the calciner requires only temperature of 850 to 900 °C to calcinate the limestone fraction. Inside the calciner, the 1000 - 1200 oc hot offgases of the rotary kiln and the 800 - 1000 °C tertiary air mix, whereby safe ignition and burning are also ensured by slow-reacting, large-sized substitute fuels. However, especially the burning of various and slow– reacting fuels takes significantly longer than the preheating and 43