After seeing how the HES works, let's review the adjustments that can be madein order to influence the fineness of the product. These two parameters can be changed: The rotor speed, and The air flowIf the rotor speed is increased, the centrifugal force is increased too. Only veryfine particles will be carried inside the rotor by the air stream. The fineness of the finalproduct will be increased. If the air flow is increased, the aerodynamic drag force isincreased as well. The air stream will be able to carry larger particles through theseparation zone than before, and the fineness of the final product will decrease. The rotorspeed and the air flow impact the fineness in opposite ways, since the centrifugal anddrag forces act in the opposite directions as well.Although the above statements are true in general, from cement plant experienceit is known that the two parameters have some bias towards different aspects of thefineness characterization: namely, the Blaine surface area value and the percent materialretained on No. 325 sieve. If the deviation from the fineness target is not significant, but58the separator adjustment is still desired, it is advised to change the rotor speed inresponse to the Blaine value change, and the air flow in response to the value of No.325 sieve percent retained.This too can be explained by looking at the Generally, a cement clinker containing higher quantities of alite (C3S) and lowerquantities of belite (C2S) has a better grindability and lower specific weight. The"intermediate" phases (C3A and C4AF) are among the hardest, but their effect on overall74grindability is not clearly determined (also JuhaszConclusionsregarding the optimal cooling rates for different phases vary significantly depending onthe mineral composition of the clinker. Smaller crystals and a poorly defined structurewith no sharp edges are shown to enhance grindability of both alite and belite phases.Agglomeration during grinding impairs grindability and is more prominent in the belitephase than alite.Factors not related to the four dominant mineralogical phases also have an effecton the clinker grindability. Hills (1995) suggested that MgO (periclase) in excess of 2%may negatively affect grindability, whereas free lime (CaO) improves it (also Velez et al.,2001). Large clinker nodules and fine dust are more difficult to grind, but decreasedtemperature of the fresh feed (50-60C) reduces resistance to grinding.Even if the chemical composition of the raw mix is constant, the grindability ofclinker (i.e., its "softness") may fluctuate depending on its burning, cooling, and storingconditions. At the same time, the mill upgrades, including the ball charge and shell linersmaintenance, impact the robustness of the ball-clinker interaction and the lifting/sortingaction of the liners. The periodical maintenance procedures improve the mill's ability togrind and compensate for a heavy wear of the grinding media. Also, the ball mill maynot be run consistently from one work shift to another. The manner, in which the ballmill is operated, significantly influences its performance. For example, the material levelinside the mill may be too high and impair the optimal ball-clinker interaction, reducingthe grinding efficiency.Thereby, the grindability of the clinker mix should be distinguished from thegrinding ability of the ball mill. The former is due to the properties of the clinker mix,the latter is due to the installed hardware and the way it is operated. The common"denominator" of the two grindability aspects, however, is the consumed electricalenergy required to produce a desired level of cement fineness.4.2.2.3. Air Flow MeasurementsFor each separator fan speed, an actual air flow rate was calculated using themeasurements at the air sampling location A3, which represents the combined air flowpassing through the separator (see Figure 4.1). The basic formula for the air flow rate is:Q = 3600 v A, (4.1)where,Q Air flow rate at actual conditions, m3/h;v Gas velocity in the air duct, m/s;A Cross-sectional area of the air duct, m2.The cross-sectional area of the round air duct is defined by:4D2 A =p, (4.2)where,D Diameter of the round air duct, m.The air velocity, v, can be determined from the pressure measurements inside theair duct by means of a Pitot tube (e.g., S-tube). Bernoulli's principle suggests there arethree types of the pressures associated with the gas flow (Wang et al., 2004):t d s P = P + P , (4.3)where,Pt Total pressure, Pa;Pd Dynamic (velocity) pressure, Pa;Ps Static pressure, Pa.120Inserting the Pitot tube through the air sampling porthole provided readings ofthe total, Pt, and static, Ps, pressures inside the air duct (see Figure 4.3). A low dustcontent of the air flow is required for an accurate reading using the Pitot tube. Themeasurements should be taken at a straight section of the air duct and relatively far fromany possible flow disturbances caused by the cornering or branching of the duct.Figure 4.3. Duct Pressure Measurement Using Pitot S-Tube.The dynamic constituent in Bernoulli's formula, Pd, can be expressed through themeasured total and static pressures using Equation (4.3). The dynamic pressure is causedby the particle kinetics and defined as (Wang et al., 2004):2v2 Pd = ? , (4.4)where,? Density of the gas, kg/m3;v Gas velocity, m/s.From (4.4), the gas velocity measured using the S-type Pitot tube is given by:?d v K P= 2, (4.5)Pt Ps215Pitot S-Tube121where,K Calibration factor of the S-type Pitot tube (0.8-0.85).The velocity profile of the air flow is seldom uniform throughout the crosssectionof the duct. To achieve an accurate flow rate, the cross-section of the duct isdivided into a number of equal areas. The dynamic pressure, Pd, is then measured ineach area and the average velocity is calculated using the average dynamic pressure.Figure 4.4 illustrates a round air duct divided into 4 equal areas so that 8measurements of the dynamic pressure are taken along two orthogonal diameters in thecenter of each ring segment.Figure 4.4. Traverse Points for Pressure Measurements in a Round Duct.The density of air at ambient conditions, ?, can be calculated using the ideal gaslaw and the value of the air density at standard conditions.It is essential to explicitly state the standard reference conditions of temperatureand pressure, when dealing with the gas properties or volumetric gas flow rate (Wang etal., 2004). Here and later on, the standard (or normal) conditions are defined as: Temperature of 273.15 K (0C) Pressure of 101,325 Pa (1 atmosphere of absolute pressure at sea level)122Using the ideal gas law, the air density, ?, can be found as (McElroy, 2002):00PPTT gasgas? = ? N , (4.6)where,?N Normal air density at standard conditions, kg/Nm3;T0 Normal temperature of 273.15 K;P0 Normal pressure of 101,325 Pa;Tgas Actual temperature of gas, K;Pgas Actual pressure of gas, Pa.The normal density of air, ?N, can be defined using a molar mass approach:mairN VM ? = , (4.7)where,Mair Molar mass of the air, kg/k-mole;Vm Standard molar volume at normal conditions of 22.414 Nm3/k-mol.The molar mass of air, Mair, can be found as a weighted molar mass of the gasesconstituting the air (McElroy, 2002):=S iair i i M C M , (4.8)where,Ci Concentration of the individual gas i, fraction or percent;Mi Molar mass of an individual constituent gas i, kg/k-mole.Molar masses of the most common gases constituting the air are: MO2 = 32 kg/k-mole MCO2 = 44 kg/k-mole MN2 = 28 kg/k-mole123The value of the actual air temperature in Equation (4.6), Tgas, is obtained fromthe direct measurement of the temperature in the air duct. The actual pressure of air, Pgas,is determined from the following expression (McElroy, 2002):gas atm s P = P + P , (4.9)where,Patm Atmospheric pressure at the sampling site, Pa;Ps Static pressure defined in Equation (4.3), Pa.Atmospheric pressure, Patm, is a function of the sampling site elevation above thesea level and can be calculated using the barometric formula (McElroy, 2002):R Lg MrefrefatmairTT L hP P? ???? ??? - = 0 , (4.10)where,P0 Normal pressure at sea level of 101,325 Pa;Tref Reference temperature for this formula of 288.15 K (15C);L Standard temperature decrease rate of 0.0065 K/m;h Elevation of the site above the sea level, but below 11 km, m;R Universal gas constant of 8.3145103 Nm/(k-molK);g Gravitational constant of 9.80665 m/s2;Mair Molar mass of air defined in Equation (4.8), kg/k-mol.With all parameters defined, the air flow rate at actual conditions, Q, is foundusing Equation (4.1). However, to compare the air flows at different actual conditions,the air flow, Q, should be reduced to standard conditions using the ideal gas law:00PPTQ Q T gasgasN = , (4.11)where,QN Air flow at standard (normal) conditions, Nm3/h.To understand C3S drops, as you mentioned, please remember how C3S is formed and the kynetics of this reaction.C3S is the only clinker mineral that requires a liquid phase for its formation.Between 1250C and 1450C the only reaction that occurs in the BZ is the formation of C3S from C2S and freeC. First the C and the C2S dissolve in the liquid phase ( they do not melt, they dissolve). The the Ca+2 cations react directly with SiO2 to form C3S in solution. Upon cooling, the C3S cristalizes into one of the 6 polymorphs we call Alite.Since we are talking about a reaction in solution the liquid viscosity plays an important role in C3S formation. The more viscous the liquid, the lower the mobility of Ca2+ and less C3S is formed. The viscosity is controlled by the AM. The higher the AM, the higher the viscosity of the liquid. However, the higher the burning temperature, the lower the vicscosity and more Alite forms. MgO and sulfates reduce the clinker viscosity. Cl and F reduce it drastically. This is why Fluorite is a good mineralizer in the BZ.Besides temperature, time at temperature is another important variable. For instance, to dissolve a 25 micron Belite in the liquid at 1450C, it takes 12 minutes! If the Belite is coarser, it takes longer.You want more C3S?a) reduce the amount of raw mix retained in the 325 mesh sieve.b) keep the AM modulus in the lower sidec) increase the SO3 or alkali sulfatesd) increase the burning temperaturee) increase the clinker time in the burning zoneNow, do you need to stabilize the Alite you formed? Quench the clinker!All my comments assume you have the right LSF for the C3S you need.