Cement, Energy and Environment July-Sep 2002

this techn ique even in very efficient plants, which are the following: • Reduct ion in spec ific rheat consumption ofapproximately I to 2% ofkCal/kg clinker. • Reduction in specific energy consumption of 3 to 10% of KWhiton cement. • In crease in comp ress ive strength values, to optimise the additions proportion ing. • Longer running factor of the kiln, with fewer shutdown times. • Increase of 35 to 50% in the li fe of refractory bricks. • Increase of app roxi mate ly 10% in kilns throughput. This tool wi ll be deployed in all the Ccmex plants worldwide to contribute in the microscopy impleme ntation effort and to become a standard wo rk ing technique. Courtesy: World Cement, June 02, Enquiry no. 7, Pp. 47-52. Fax: +./4(0) 1252 718992 Email: mail@worldcement.com Web: www. worldcement. com MINIMISING STOPPAGE TIME TVS Chidambaram and Zamil Al Markin, Eastern Province Cement Co. Saudi Arabia. Eastern Province Cement Co. one of the leading cement producers in the Kingdom ofSaudi Arabia, has two identica l ki ln lines with an annual production capacity of 2.3 million t of cl inker. Commercia l production from the lines started simultaneously during Q4 1984. Both kiln lines were supplied by Krupp Polysi us, Germany; each kil n with dimensions of 4.6 m dia x 70 m length, eq uipped with a 4-stage Depo l preheater, an inline Prepol calcincr, a grate cooler and a bypass system to vent out alka li salts up to 20%. The rated capacity of each kiln is 3500 tpd. and natural gas is used as fuel for the main burner, as well as for the calciner. It has become mandatory to run the bypass system at fu ll capaci ty du ring no rm a l operation of the kiln d~e to the presence of high leve ls of alkali su lphates and chlorides, as well as to meet the low a lkali content requi rements of customers. The in stall ed production capacity of cement in the ~ingdom is approximately 21.0 million t, whereas demand is on ly 15- 16 million t. Long term strategies were implemented, with the a im of curtai ling operating ·costs targeted towards stable operation ofthe kilns with maximum product ion efficiency, by minimising unplanned stoppages in order to increase the run factor of the kilns. In the Middle East, al most all cement plants operate with a bypass system due to the presence of high levels of volatile impurities in the raw material components. such as alkali sulphates and chl orides. Add itional unforeseen stoppages are encountered due to clogging and jamming problems in the kil n inlet region, as well as in the lower part of the preheater. A Ithough th ere cou ld be several contributing facto rs to the stoppages of the kilns, thi s article wi ll conce ntrate on two major causes, thei r impacts on refractory li fe and practica l guidelines to overcome/improve them. The two major causes are as follows : • Refractory fai lures du e to thermochemical erosion and infiltrat ion of vola tile components. • Refractory fa ilures due to mechanical stresses impaired by kiln components.· Thermochemical erosion - The problem was minimised by avoidi ng thermal overloads, proper adjustment of flame shape , minimi sing the variation in raw mea l chem istry and by the installation of premium grade spi nel bricks with sp ine l content in the range of 5-6% instead of l0- 12%. Failure due to alkali salt infiltration- The life of refractori es in thi s area was improved by mi nimising the variati on in the chemistry of raw meal, maintaining better ratio between the alkali sulphates and ch lorides, c losing brick joints tightl y with suitabl e grade mortars and by in sta lling premium grade spine l bricks with improved re sistance agains t chemical attacks. Dens(fication and structural failure- Since this area is part of the upper transition zone subject to on and off coating, alkali vapours tend to penetrate the pores of the bricks, or any other gaps avai lable between the brick joints o r ring join ts, leading to such failures. Selecting sp inel grade bri cks in stead of magnesium bricks, which are resistant to chemical attacks, as well as clos ing/fil ling a ll of the gaps between the rings with suitabl e mortar grade, helped to reduce such frequent failures. Corrosion on the kiln shell - At present, tight brick li ning is being followed by eliminating all possible gaps within the brick ri ngs by suitable grade mortar. However, trials are underway to coat the kiln shell area with hi gh tem perature silicon resin to protect it agai nst corrosion. Infiltration ofalkali salts into the castab/e mass - Since the raw material is rich in alkal i salts, possible alterations were made in the chemistry of the raw meal to balance the ratio between alkali sulphates and chlorides. The use of medium alumina castable with an Alp 3 content of less than 40% with 40-45% of zircon ium oxide (ZrO), as a replacement for alumina also improved the li fe of castable in this