Cement Energy and Environment

I Analyzing Preheater Fan Deposition Coatings Chemica-Mineralogically for Addressing Vibration Problems Mohan Medhe, Narendra Kumar, Sanjeev Srivastava, Subrato Chowdhury and Sanjay Agrawal UltraTech Cement Ltd., Mumbai, /ndia-400093 J1bstract: Due to ever increasing demands of kiln tl1roughput and thermal efficiencies in cement naking, induced draft fans are put to maximum L se for meeting increasing gas volume and static ~~ressure requirements during pyre-processing. However, it tends to increase frequency of problem related to material build up on the fan impellers I ~ading to problems like increased mechanical \'ibrations, frequent trippings and reduced E!qu ipment availability for continuous production. Present case study illustrates one such instance of problem at cement manufacturing unit in Northern India resulting in considerable losses in productivity. For analyzing the problem, a detailed chemical and mineralogical characteri zation is carried out for kiln feed, fan deposition material ;md fan outlet dust samples using various .malytical techniques to analyze and elucidate the nost probable mechanism leading to the said .jeposition. Results indicated that the deposition Jroblem is related to combination of segregative jeposition of fine clay and iron add itive particles 3scaping from dust cycle set up in the top preheater cyclones and formation of anhydrite over a period of time. Introduction: Large Induced Draft fans, being working horses in cement manufacturing, play an important role in maintaining increasing productivity standards. With ever increasing demands with respect to kiln through put and thermal efficiencies, induced draft fans are being used to the maximum for meeting increasing volume and static pressure requirements apart from operating at considerably higher process gas temperatures as compared to designed duties. In other words, existing fan rotors are being forced to cope up with very high tip speeds and considerably higher temperature environments in fulfilling the requirements. Probably, as a consequence of these demanding situations, the problem of material build up on the fan impellers is known to be aggravating markedly. In many of the situations frequency of the problem tends to affect the system productivity adversely raising serious concerns. In one of the group units in Northern India, the said material buildup problem on the preheater fan was observed to create severe hindrances in the availability of the kiln for continuous clinker production. Therefore, before identification of a possible solution of downtime associated with the frequency of fan cleaning cycle, a need was felt to understand the causes of the deposition by characterizing them chemically and mineralogically. In general there are several research papers available elaborating impact of fine particles on smooth surfaces at moderate velocities with consequent adhesion characteristics [1-3] . But these works mainly deals with idealized cond itions in lab scale experimentation at relatively moderate conditions of velocity and temperatures unlike actual preheater fan conditions in typical cement manufacturing. The information related to the impact of actual extreme operating conditions on the adhesion & deposition characteristics of fine particles is relatively scarcely reported in the literature available in the public domain, partly due to proprietary reasons and case specific nature of the problem. However, there are few notable attempts to address the issue by fan manufacturers themselves [4, 5]. In one of the group units in Northern India having clinkering capacity of around 4800 tonnes per day, the fan deposition problem was quite frequent. The unit is having six stage preheater system. The problem consisted of deposition of hot & fine particulate raw material escaping from preheater top cyclones on the moving parts of the fan resulting in extremely hard, layered, brick-like build-up. Typical photographs and microphotographs of the build up material collected during cleaning cycle of the fan are shown in Figure 1.