Rice Husk as a Substitute Fuel in Cement Kiln Plant

L. M. Farag, H. A. El-Hamid
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Abstract

A simple mathematical model of heat balance was applied to a cement kiln plant with a precalciner to estimate the effect of using rice husk as a substitute fuel for natural gas on specific heat consumption. Effects of the husk ash on the characteristics of the raw mix and clinker of ordinary Portland cement were also evaluated. Referring to Egyptian kiln plants data, it was found that the weight of rice husk required to supply fuel heat in the precalciner represented about 11-13% of the raw mix weight and about 90% of the total fuel weight (natural gas + husk). Specific heat consumption increased by about 3.7%, and the amount of combustion flue gases increased by about 20% when natural gas was completely substituted by rice husk. The use of rice husk as a substitute fuel in a cement kiln plant was accompanied by a marked decrease of lime saturation factor of the raw mix, a drastic decrease of tricalcium silicate and an increase of dicalcium silicate in the clinker. This data can provide the basis for the formation of a new type of cement such as high belite cement. The raw mix design was adjusted using pyrite as a correcting factor to keep the characteristics of the raw mix and the clinker similar to the factory data. KeywordsAlternative Fuel; Rice Husk; Natural Gas; Raw Mix Design; Clinker Mineral Composition; Raw Mix Parameters; Specific Heat Consumption Nomenclature ms1 = mass of the inlet raw mix to the preheater (kg) hs1 = specific enthalpy of the inlet raw mix to the preheater (kJ/kg) mf = mass of the fuel (kg) hf = low calorific value of the fuel (kJ/kg) hu = specific enthalpy of the fuel (kJ/kg) mA3 = mass of tertiary air from the cooler to the calciner (kg) hA3 = specific enthalpy of tertiary air from the cooler to the calciner (kJ/kg) mA5 = mass of secondary air from the precooling zone in the kiln (kg) hA5 = specific enthalpy of secondary air from the precooling zone (kJ/kg) mA6 = mass of secondary air from the cooler to the kiln (kg) hA6 = specific enthalpy of secondary air from the cooler to the kiln (kJ/kg) mG1 = mass of outlet flue gas from the preheater (kg) hG1 = specific enthalpy of outlet flue gas from the preheater (kJ/kg) ms6 = mass of clinker leaving the firing zone to the cooler (kg) hs6 = specific enthalpy of clinker leaving the firing zone (kJ/kg)  HR.c, HR.K = heat of reactions in the calciner and the kiln, respectively (kJ) Qw.p.c, Qw.k, Qw.c. = wall heat losses from the preheatercalciner, kiln, and cooler, respectively (kJ) Vaf = theoretical amount of fuel combustion air (Nm /kg fuel) Vgf = theoretical amount of fuel combustion gases (Nm /kg fuel)  = excess air factor for fuel combustion MCO2 = mass of evolved CO2 from calcination Cpg, Cpa = specific heat of flue gases and air, respectively (kJ/Nm 3 C) Tg, Ta = temperature of flue gas and combustion air, respectively ( C) h.f.o. = heavy fuel oil cli. = clinker LSF = lime saturation factor SIM = silica modulus AM = alumina modulus C3S = tricalcium silicate C2S = dicalcium silicate International Journal of Energy Engineering Apr. 2015, Vol. 5 Iss. 2, PP. 16-27 17 DOI: 10.5963/IJEE0502001 C3A = tricalcium aluminate C4AF = tetracalcium aluminate ferrite Borders of the heat balance zones, as shown in Fig. 2: [1] [2] = preheating zone [2] [3] = precalciner zone [3] [4] = bottom stage cyclone [4] [5] = heating zone of the rotary kiln [5] [6] = precooling zone [6] [7] = cooler
稻壳在水泥窑厂替代燃料的研究
采用简单的热平衡数学模型,对带预分解炉的水泥窑厂进行了热平衡数学模型计算,估算了稻壳替代天然气对水泥窑厂比热耗的影响。还评价了壳灰对普通硅酸盐水泥生料和熟料性能的影响。参考埃及窑厂的数据,发现在预分解炉中提供燃料热量所需的稻壳重量约占原料混合物重量的11-13%,约占燃料总重量(天然气+稻壳)的90%。当稻壳完全替代天然气时,比热消耗增加约3.7%,燃烧烟道量增加约20%。在某水泥窑厂使用稻壳作为替代燃料,生料的石灰饱和系数明显降低,熟料中硅酸三钙含量急剧下降,硅酸二钙含量增加。该数据可为高白石水泥等新型水泥的形成提供依据。以黄铁矿为校正因子对原拌料设计进行了调整,使原拌料和熟料的特性与出厂数据相近。KeywordsAlternative燃料;稻壳;天然气;原拌料设计;熟料矿物组成;原始混合参数;比焓的二次空气预冷区(焦每千克)mA6 =质量的二次空气冷却器的窑(公斤)hA6 =比焓的二次空气冷却器的窑(焦每千克)mG1 =从预热器出口烟气的质量(公斤)hG1 =比焓的出口烟气预热器(焦每千克)ms6 =熟料冷却器离开发射区域的质量(公斤)hs6 =比焓的熟料离开发射区(焦每千克)HR.c,人力资源。K =煅烧炉和窑内反应热(kJ) Qw.p.c, Qw。k, Qw.c。=墙热损失preheatercalciner窑和冷却器,分别(kJ) Vaf =理论燃料燃烧空气量(Nm /公斤燃料)Vgf =理论量的燃料燃烧气体燃料(Nm /公斤)=过量空气系数对燃料燃烧MCO2 =质量发展CO2煅烧Cpg, Cpa =烟气和空气的比热,分别(kJ /纳米3 C) Tg, Ta =烟气温度和燃烧空气,分别(C) h.f.o。=重油cli。=熟料LSF =石灰饱和系数SIM =二氧化硅模量AM =氧化铝模量C3S =硅酸三钙C2S =硅酸二钙国际能源工程杂志2015年4月第5卷第2期,PP. 16-27 17 DOI: 10.5963/IJEE0502001 C3A =铝酸三钙C4AF =铝酸四钙铁氧体热平衡区边界如图2所示:[1][2] =预热区[2][3]=预分解区[3][4]=底级旋风[4][5]=回转窑加热区[5][6]=预冷区[6][7]=冷却器
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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