Cement Energy and Environment

Energy Efficiency and Conservation PROCESS OPTIMISATION SAVINGS* Victor }. Turnell, Penta Engineering Corpn., USA 1 n the present day scenario of falling cement prices in a highly competitive market against spiralling cust uf inputs, very few cost effective alternatives are left at the disposal of manufactures. Good house-keeping is one area where any company can consistently bring down operational costs with higher productivity. Mr.Turnell provides some valuable tips for effective cost saving in this article -Ed. Introduction This aJt icle presents methods for achieving optimisation in cement manufacturing processes and includes several examples, includingoptimisation clinker cooler operation, heal transfer and combustion conditions; reducing air infiltration and adding substitute fuels. Pyroprocessing Systems Clinker Coo ler Clinker coo lers have two major fun ction s in a pyroprocess ing system : to suppl y hot combustion air to the kiln and to lower the clinker temperature for material handli ng after the kiln system. An ideal clinker cooler discharges clinker at a temperature close to ambient with all the heat recovered from the ch nker used to rai se combustio n air temperature, or for other purposes, such as drying coal or raw materials. Clinker cooler efficiency is measured by the percentage of useful heat recovered from clinker. With grate coolers, kiln operators have significant control over combustion air temperature and hence, clinker cooler efficiency. Combustion air temperature from grate coolers is controlled by clinker bed depth and air flow rate. Typically, as bed ~ Vl 0) Vl "" ~ u 0) -o "0 <::: :'l Vl 0) Vl :'l ~ u .5 depth increases, so does combustion air temperature. Maximumbed depth is limited by one of the following : undergrate fan capacities, the grate drive, or overheating in the kiln firing hood area. * Courtesy: World Cement, March 1999 6 5 4 3 2 I 0 - I -2 -3 -4 In contrast with planetary coolers, kiln operators do not have much control over the efficiency of the cooler. However, the operator can ensure all observation ports and doors are closed to minimise the infiltration of cooler ambient air. The effects of increasing secondary air temperature on clinker production, specific fuel consumption and clinker cooler efficiency for a preheater kiln equipped with a grate cooler are shown in Fig.! . In this example, the ki ln exit gas flow rate was held at a constant level and the fuel firing rate, clinker production and clinker cooler efficiency were allowed to vary. I_ Clin~er coioler eili::c~ - Clinker production ~ - _- Specilic ~uel~~nsurn~tio~ 0 20 40 60 80 100 increase in secondary air temperature (°C) Fig.] Effects ofincreasing secondary air temperature Kiln operators at a number of plants visited maintain shallower clinker bed depths than could be achievable with the existing undergrate fan s. By increasing and optimising clinker bed depth,kiln operators can increase 9