Cement Energy Environment

67 Analysis by scanning electron microscopy of the sample from waste incineration (Picture 9) shows that the slag has infiltrated the matrix and slowly eroded the refractory lining by washing out grains of aggregates These relatively simple experimental set-ups and analysis clearly illustrate how the gaseous and liquid phases from thermal treatment of alternative fuels concurrently affects refractory materials, and may cause deleterious effects in a cement kiln. Alkalis react with the alumina-silicates of the refractory and may even infiltrate aggregates causing structural changes, whereas the liquid phases infiltrate the matrix and corrodes the lining by washing out grains and forming build up. An optimal refractory lining in the critical areas at a cement plant must be strong and dense and with a low open porosity to minimize the infiltration of both gaseous and liquid phases. Very low open porosity of As an optimal alternative to preheating on site, the best castable performance can be achieved by using precast and preheated elements that are made ready-to- use. At HASLE Refractories A/S we manufacture lining systems under controlled condition in our production facility. Castable mixing, casting and preheating are optimized to give the elements a very low porosity and dense surface, which in combination with raw material properties ensures protection from corrosion. HASLE Precast Modular Lining Analysis of Post Mortem Sample Picture 9: The coating (light part) on a post-mortem castable sample (dark part). The melted slag has infiltrated the castable and small fractions of the castable can be seen in the coating (arrows) Volatile potassium infiltrates and migrates into the refractory lining, whereas sulfur was not found inside the casted pieces in this case (Table 3). The reaction zone between the castable and the ash was heavily enriched by potassium and the zone appeared porous that are subsequently embedded in the coating and adds to the build-up. refractory materials can be achieved by optimization of the particle size distribution. HASLE Precast is characterised by very low values of open porosity; 10-11% at 1000-1500°C as these precast elements are made under very strict supervision for water addition, mixing, casting and most important preheating in very controlled atmosphere to ensure a low apparent porosity and high strength of the precast elements. Preheating reduces the number of micro cracks that inevitably are formed by thermal shock during fast heat-up which increases the risk of chemical attack from both gaseous and liquid phases of alkalis, sulfur and chloride. Some of the cement plants in India had serious problems with coatings in the kiln inlet area, feed pipe caused by alkali and sulfates from the use of alternative fuels; in this case rubber combined with pet-coke and coal. Heavy build-up and clogging in the preheater cyclone feed pipes and riser ducts lead to reduced production capacity and unstable calciner operation. HASLE precast Modular Lining was selected to solve the problems. and fragile. Under the reaction zone patches of SiO 2 rich glassy phases were found with high potassium content which indicates that alkalis to some extent have been encapsulated. Potassium was also found in more dense alumina-rich grains near the surface.