Industrial Scale Kiln Problems and Their Solution with Controlling Different Operating Parameters

Research Article

Austin Chem Eng. 2020; 7(1): 1073.

Industrial Scale Kiln Problems and Their Solution with Controlling Different Operating Parameters

Fazeel Ahmad*

Department of Chemical Engineering, University of Wah, Wah Engineering College, Pakistan

*Corresponding author: Fazeel Ahmad, Department of Chemical Engineering, University of Wah, Wah Engineering College, Pakistan

Received: April 19, 2020; Accepted: May 12, 2020; Published: May 19, 2020


The chemical composition homogeneity of kiln feed has an important relationship to fuel consumption, kiln operation, clinker formation and cement strength. Kiln operation can be made stable and smooth. The basis for this property is a well-burned clinker with consistent chemical composition and free lime. The main reason for the clinker free lime to change in situation with stable kiln operation is variation in the chemical composition of the kiln feed. This variation in chemical composition is related to raw mix control and the homogenization process. To ensure a constant quality of the product and maintain a stable and continuous operation of the kiln, the attention must be paid to storage and homogenization of raw materials and kiln feed. Due to variations in the kiln feed chemical compositions that affect its burn ability and the fuel consumption. The objective of this research paper is to provide solutions of the problems occurring in well burned clinker through stable kiln operation and efficient cooler heat transfer. The quality of cement is assessed typically from its compressive strength in concrete and mortland. The well-burned clinker and free lime with consistent composition is the basis for desired quality of the cement. To ensure product of constant quality ad kiln stable and continuous operation focus must be done on raw material hominization in the storage silos and kiln feed During the all reactions when all these parameters are altered then the chemistry of the reaction also changes and it effects on the Liter Weight (g/liter), Lime Saturation Factor, Degree of Calcination, Cement Blain, Silicate Module and Aluminum Moduli.

Keywords: Lime saturation factor; Free lime, Alumina ratio; Silicate ratio; Degree of calcination; Kiln speed; Residence time; Cement quality; Clinker burn ability Clinker; Limestone; Cement Quality; Portland cement


Ordinary Portland cement is the most commonly used cement around the world. It has been reported that cement manufacturing process consist of three steps [1] including raw mixture preparation, clinker production and cement formation. Requirement for the demand of cement in the developing countries is increasing rapidly but in the developed countries it has reduced. (Pacheco-Torgal et al., 2014). Studied has been done about origin of raw material prepared for the kiln which are usually quarried in the local rocks whose composition varies from location to location, and sometimes to meet the desired composition addition of limestone, clay and recycled material is done [2-3]. These are passed through crusher to reduce their sizes less than 80 mm. These all material are passed through raw mill where material bed is maintained and grinded into smaller parts and there is a classifier after grinding fine material is passed through this due to suction of system fan.

According to literature [4] the energy utilized by the cement manufacturing process is nearly about 110 KWh/ton and approximately 40% of this energy is consumed in the grinding process which totally depends upon clinker with desired free lime content and alite and belite content along with specified liter weight (g/liter) amount. Therefore, major concern is on the energy reduction in this process.

Con G. Manias et al., has reported about pyro processing stage of clinker formation according to which raw material coming from homogenize silos passed through rotary kiln in which many reactions take place. There is series of sequence endothermic and exothermic reaction taking place in the kiln. Suggestion further have been reported about kiln aerodynamics, it is extremely surprising to know how a small difference in kiln hood, cooler bull nose, cooler throat, tertiary air off takes, secondary air temperature and velocity, and air leakage can have a huge effect on the pattern of air flow in the rotary kiln burning environment.

Pre-calciner is used to decompose raw material into its components after passing and preheating into the cyclones after that updraft causes the raw material to enter in the last level of cyclone for the solid gas separation. Due to sufficient inclination and various kiln speed, raw material continuous enters into the cooler grates section [7]. Wang et al., suggested to pre calcine the raw material calciner time is reduced and temperature dropped to about 150ºC. Many researchers have reported about maintain temperature in the burning zone which totally depends upon fuel burning to assist in chemical reactions to take place.

Therefore, many experts in the cement technology presented a trend of pre calcination at about 1300ºC with the raw material in the fluidized form and suspended form in which the heating, sintering and decomposing can be complete at the same time because time and the temperature in the precalciner is very high [2,7]. Suggestion has been made to reduce lime saturation factor in the clinker leads energy reduction this helps to decrease and increase in the alite phase content and belite amount [3,5]. Free lime content are directly measured by the burning of clinker inside the rotary kiln. It also has crucial effect on the grinding of clinker into fine cement which determine the strength of cement.

All these materials are transported into silo where homogeneous blending of material happens by roots blower of any type which are providing air perpetually into the silo (Pacheco-Torgal et al., 2014). Counter flow process happens in the rotary kilnin which endothermic and exothermic series of complex reactions takes place at different temperature starting from 800ºC to 1500ºC. Researcher have reported that for raw meal water evaporation to burning this highest temperature is required either in the cyclone pre heater section and in the kiln. Highest temperature is achieved in the burning zone of the kiln.

There is series of different individual reactions which takes place during the synthesis of clinker and its phases. Energy comes from the different sources which are the basic requirement in the kiln heating for decomposition of the many reactions. There are various kinds of fuels which can be used in the kiln consist of biomass, petroleum coke and mineral coal (Madlool et al., 2011). Due to global warming threat is posed which has created awareness in the public for the anthropogenic carbon emission and their great effect on the climate change in the global warming. The forthcoming level of CO2 emission in the atmosphere has reached 380 ppm (Sabine et al., 2004).

Including CO2 during the synthesis of clinker in the kiln many reactions also ejects NOx and SOx and other minor amount of toxin which covers range for local to global environmental impact.This toxic waste may damage to the nearby area through different disease including lungs and breathing problems. (Phair, 2006). There is eject point from where all these pollutants goes into the atmosphere. The most suitable tool for judging clinker synthesis and its supply chain impact on the environment is life cycle assessment (Boesch and Hellweg, 2009). Now a days, it is a big challenge to minimize CO2 emissions in the atmosphere by reducing component of clinker in the cement.

Due to some reasons mashing of clinker does not get complete and these small portion content goes inside the cement which reduces the strength of cement. When this cement is used in the building these particles get involved in the surrounding and evolves CO2. Many grinding aids which assist for complete clinker grinding such as fly ash and glycol, ash, slag and volcanic ashes which minimizes clinker content in final product of cement (Huntzinger and Eatmon, 2009). At the last Unit of clinker reforming there is also particulate matter which is in small size emissions in the atmosphere. There is also a huge challenge to reduce these losses into the atmosphere.

The main objective of this paper is to reduce the incomplete combustions during the reactions in the kiln so that toxic waste should be in very small amount in the all exhaust point of the clinker as well as cement synthesis process. Coal to air and fuel to air ratio place crucial role in the reactions which take place in the rotary kiln. By the alteration of these combustion product may vary from original products. These two important parameters are responsible for the temperature which is required during the different phases of the clinker in the kiln within different zones like calcination, burning and cooling zone.

There should be a fixed ratio of air and coal so that complete reactions should take place in the kiln and desired quality clinker should be produced. It has been studied that cement plant are large source of CO2 emissions in which its denseness goes high in the exhaust gases about 14-13 percent and in comparison, to cola fired plant which produces 12-13 percent. But there is a big issue of CO2 separation from the exhaust. Many technologies are available and have been studied to separate CO2 from flue gases. In this paper a complete review of amine scrubbing has been presented [2-3].Lime saturation factor and liter weight also plays important role in the cement grinding. When these parameters are in control manner then toxins emission are in control manners and can produce less environmental effects on the surrounding area. With the variation in the coal to air ratio both above parameter can be controlled which in terns will produce desired quality clinker.

Experimental Materials and Procedure

Sample preparation

Usually, the raw material sample is taken out from crusher outlet and after grinding mill but clinker sample is taken out from the last cyclone C5 as well as pre-calciner and cooler outlet. Liter weight (g/liter) test is done in the industrial scale laboratory. X- ray analysis is done to check all the compositions of the development of clinker formation studies on the basis of free lime contents mainly but other factors including liter weight, degree of calcination and alite and belite formation as well. Studies procedure is the most commonly used in all over the world. Initially, from the decomposition of calcium carbonate Cao is formed, which gradually consumed in the clinker phases. When amount of lime tends to be zero, complete clinker phases phenomenon take place.

Sample testing

Clinker formation and burning process in rotary kiln

Clinker formation : Well blended raw material enters into cyclones for efficient mass and heat transfer process through counter current contact with air. Pre-calcination and calcination process taking place into the pre-calciner as well as inside the kiln. For many years cement was synthesized by practical experience used by educated people experience which was gathering from the process plant physically checking samples of clinker and raw mill for kiln at different sections including cyclone 5 and cooler outlet There are many reactions taking place inside the kiln. Portland cement clinker includes higher values than 95% of CaO, SiO2 and Fe2O3. Figure 1 represent the clinker. It has been reported that transformation results initially with clinker phases [4].