Cement, Energy and Environment July-Sep 2002

- - t -- area. Further trials are underway to extend the life by usi ng either silicon carbide or dense castable in this area. Alkali bursting ofbrick lining - Si liceous fire clay bricks with an J\ 1,0 , content of less than 28% and - .. lower porosity wi th 12% AP were tried with great success. Painting the walls with zircon cement to close all the working joints also he lped to s top th e penetration of a lka li vapours. In the coming years, trials are be ing planned to use either silicon carbide bricks or dense low cement castable in these areas. Based on the last 18 yrs of operation and failure analysis, it was concl uded that most of the frequent brick failures at the lower transition and upper transit ion zones were att ributed to the mechanical stresses ge ne rated from the outl e t and middle tyre sections unfortunately located in these areas. The fo llowing case studies of investigated brick samples taken from these locations revea l th e st ro ng re lat ion of mechan ical stresses to the rate of failures. • lligh alumina brick fail ure • • Measurement and recording of foundation settlements. Ovality measurements of kiln sections near the lyres. • Measurement of kiln shel l deformations. • Inspection ofgirth gear pinion assembly and measurement of back lash and root clearance. • Measurement of kil n stresses and Hertz compression of kiln tyres and rollers. A II cement plants are forced to use their existing raw materials to prolong the existence of operation, and very few a lte rn atives are avai lable for plants such as Eastern Province Cement Co. which was the first in the region to reach this (run factor of 344 days) value during 200 I, and may be one of the few wo rldwide who has reached similar bench ma rks. This achievement is due to an effi cient operation crew coupled with the timely preventi ve ma intenance and co rrec tive measures impl emented year after year to keep this target active. Courtesy: IVorldCement, June 02, Pp.-3-1-39 Fax: +.f../(0) 1252 718992 • Fai lure of premium grade MA Email: mail@worldcement.com spine l bricks Web: \11\llll'.li'Orldcemeni.C0/11 • Failure of magnesi um chrome bricks Remedies undertaken Careful investigation and preventive measures were executed through a specia lised company, mostly from the OEM se rvice (namely the POLSCJ\ N), once every 2 yrs. The following meas urements were regu larly undertaken, documented properly as records and corrective measures were implemented: • I lot alignment of kil n axis by laser and adjustment ofrollers. • Measurement of roundness of supporting rollers and tyres and subsequent gri nd ing of surface if required. MODELING AND SIMULATION OF LIMRSTONE CALCINATION IN ROTARY KILNS PART 2: INDUSTRIAL ROTARY KILN M A. Martins, L.S. Oliveira, A. S. Franca, Department of Chemical Enginee ring, Univers ity Be lo Hori=onte, Belo Horizonte!Brazile Part I of this paper presented a one-dimens ional model fo r describ ing and s imu lat ing limestone calcination in rotary ki lns. The model was ~ ucce ss fu l ly validated on a pilot rotary kiln by comparing the simu lation results with experimental data from the li teratu re. Part 2 of the pape r incorporates a flame model in the model presented in Part I so that the processes in industrial rotary kilns can be simulated. The flame model, which has already been validated by ot her re sea rchers , is used success fu ll y in thi s wo rk for si mulati ng the effects of some ope rating variables on the performance characteristi cs of the industria l calcination process. Mathematical modeling Combustion mode/fo r natural gas Natural gas is often used as the prima ry energy sourc e fo r the limestone calcination in industrial rotary kilns. A double coaxial-type burner which introduces the natural gas into the ki ln, is normally used. T he mode l used in thi s wor k co nsiders that the combust io n reactions are stoichiometric and no residual fuel rema ins past the flame section. It is also assumed that the combustion reactions occur wi thout chemical d issoc iat ion or NO ' formation. Both the primary and secondary airflows are entrained into the fl ame and immed iate ly 111 ixed and burned with the nat ural gas. Implementation The mat hematical 1node l deve loped in Part I of this study, coup led wit h th e flame mode l presented here, was then used for simu lation of a typical rotary kiln . The bed depth was assumed to be constant along the rotary kiln. The indust rial kiln uses a double coaxial type burner to burn natural gas. The mode l for the limestone ca lcin ation in an industri a l kiln com pri ses ei ght ordi nary differentia l equat ion s (ODE ). correspondi ng to the mass and the m