New lining concept by using alumina bricks in place of basic refractories
In 21st century, due to big thrust upon infrastructure development; a huge demand of cement in worldwide, as result cement manufacturers are under tremendous pressure to increase production with quality at a competitive cost. It is quite obvious, longer life of the kiln with minimum downtime and low specific energy consumption help to cater the demand in time. However, to produce cost effective product; cement industries are focusing to use alternative fuels like pet coke, used tyre, oil sludge, municipal waste, etc.. These fuels are having higher content of SO2, NOx, and CO emissions, and dusty in nature which are affecting refractory life of cement rotary kiln causing thermo-chemico mechanical load on the refractory lining. Thus it is important to understand the real mechanism involved in cement rotary kiln (CRK) between refractory lining and kiln feeds at the elevated temperature.
To achieve desired life of refractories in CRK; it is therefore necessary to understand the characteristics, behavior and location/zone where refractory will be lined inside the kiln. TRL Krosaki has developed new generation cost effective energy saving alumino silicate refractory (TRL PS-1) which is replacing the higher cost basic quality bricks in transition zone of the CRK. This new developed brick has improved thermal shock resistance, better thin surface coating and better corrosion resistance. A new concept of lining pattern has been adopted by TRL Krosaki by using newly-developed alumino silicate brick for CRK application and accordingly improved quality bricks supplied and lined in CRK of a leading cement manufacturing industry in India. CRK is under operation and till date performance is satisfactory one. This paper presents the new concept of lining of CRK where basic bricks were replaced in phase wise manner with newly-developed alumino silicate bricks (TRL PS-1) in the transition zone.
Product design & experiment
TRLK has developed 70 per cent alumino silicate product by lowering impurities like Fe2O3, TiO2, alkalis, etc. along with addition of special kind of additives in the product can enhance the life of refractory lining of CRK. Table 1 shows the properties of developed product. The product is showing low apparent porosity, good volume stability, high refractoriness under excellent thermal shock resistance with water as well as in air.
To understand the corrosion behaviour of individual CRK input material with developed product; corrosion and penetration study has been carried out through static CUP-test method. Cement raw mix (CRM) and petcoke fines collected from site of one leading cement industry manufacturer in India and samples are analysed through chemical analysis as tabulated in Table 2. Fig. 1 (a) and (b) show the texture of CRM and petcoke fines respectively. Both CRM and petcoke fines have been mixed with ratio of 92:8 to get actual composition of CRK feed material [Fig. 1(c)] i.e. formulation is same as considered by cement manufacturer.
Fig. 2(a) shows the CUP specimens, which have been made from the developed product having cavity dimension of 50 mm diameter and 50 mm height. Fig. 2(b) show the cavities are being filled with individual as well as mix material i.e. cavity-(I)has been filled with desired quantity of petcoke fines only, similarly only CRM is filled in cavity-(II) and cavity-(III) is being filled with mixture (ratio; 92:8) of CRM + petcoke fines. Cut piece of high quality refractory brick has been used as lid cover of all CUPs, which is shown in Fig. 2(c). CUPs are fired in high temperature tunnel kiln at the temperature of 1450GùªC/4hrs. Fig. 3 (a-c) shows the physical appearance of fired CUPs followed by slicing to observe internal texture of respective cavities.
Results and discussions
Developed product designed with 92 per cent dense calcined Indian Bauxite and matrix part has been strengthened by incorporation of calcined alumina along with Kaolinite. Certain percentage of Phosphoric acid (PA) has been added in the product along with other binder system. Due to presence of PA and special kind of additives; developed product is showing low porosity as well as high strength and good high temperature properties.
Since developed product having low porosity and dense matrix; individual corrosion and penetration study is showing significant result against only petcoke fines, only CRM and with mix., as shown in Fig. 3 (a-c).In case of only petcoke; only infiltration phenomena has been observed in the cavity but due to presence of different type of oxides like Na2O, K2O, CaCO3, CaMg (CO3)2, and SiO2 in CRM; reaction followed by thin coating phenomena has been observed in the sample cavity due to reaction with Fe2O3, which is coming from the developed product i.e. alumino silicate system.
Similar type of coating behaviour is also observed in the cavity which contains mix (CRM + petcoke fines). In real operating condition of CRK; all the oxides are developing C-S-A-F system and a melt/liquid is being formed due to reaction between C-S-A-F and SO3 - which is entering into the system due to uses of petcoke. The melt which forms at temperature of 1280 degree Celsius and above is favorable for coating formation on refractory surface . Fig. 3(c) depicts similar type of coating at the bottom portion of CUP. But too much melt is undesirable because alumino silicate refractory system quickly destroyed by clinker melt due to induce of undesired excessive C3S phase . However from CUP test, there is no severe infiltration and corrosion phenomena have been observed where mix material has been tested, rather a thin layer of coating phenomena is observed in bottom of the cavity. Measurement and observation details of infiltration, corrosion and coating phenomena have been summarised in Table 3.
In general, both alumina refractory ranged from 40 to 70 per cent and basic quality bricks are used in different zone of CRK lining including monolithics. However, TRL Krosaki has attempted a new refractory lining concept for CRK by replacing basic quality bricks with high alumina fired bricks. After a year of phase wise study on corrosion phenomena and performance of the different quality of refractories used in CRK application; TRL Krosaki has adopted and executed a new lining concept by using newly developed alumina brick in place of basic quality brick as per the lining concept shown in Fig. 4. Developed product has been used completely in place of basic quality brick 3 m before discharge end.
Newly developed product exhibits special characteristics like balanced chemical properties, low porosity, good thermal shock resistance as well as high thermo-mechanical properties. As a result, excellent coating phenomena have been observed in CUP test. Keeping confidence upon characteristics of the newly developed alumino silicate product; TRL Krosaki has replaced the basic quality refractories completely by using this developed product for refractory lining of CRK. And developed product is performing satisfactorily at customer end for this said application.
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