OPERATIONAL PERFORMANCE OF A CONVENTIONAL TWO-COMPARTMENT BALL MILL GRINDING CIRCUIT AT DIFFERENT CEMENT PRODUCTIONS

Madencilik, 2018, 57(2), 125-133 Mining, 2018, 57(2), 125-133 Orijinal Araştırma / Original Research OPERATIONAL PERFORMANCE OF A CONVENTIONAL TWO-COMPARTMENT BALL MILL GRINDING CIRCUIT AT DIFFERENT CEMENT PRODUCTIONS KONVANSİYONEL İKİ KAMARALI BİLYALI DEĞİRMEN ÖĞÜTME DEVRESİNİN FARKLI ÇİMENTO ÜRETİMLERİNDE İŞLETME PERFORMANSI Ömürden Gença,*, A.Hakan Benzerb,** a b Muğla Sıtkı Koçman University, Mining Engineering Department, Muğla, TURKEY Hacettepe University, Mining Engineering Department, Ankara, TURKEY Geliş Tarihi / Received : 27 Kasım / November 2017 Kabul Tarihi / Accepted : 19 Şubat / February 2018 ABSTRACT Keywords: Grinding, Ball mill, Air classifier, Cement, Energy. Anahtar Sözcükler: Öğütme, Bilyalı değirmen, Havalı sınıflandırıcı, Çimento, Enerji. The purpose of the study is to assess the grinding and classification performance of a conventional Polysius® two-compartment ball mill and a Sepol® dynamic air classifier closed circuit process at Portland CEMI/42.5R and Portland composite CEMII/32.5R cement production types. For this purpose, industrial scale sampling surveys were performed around the circuit. JKSimMet Steady State Mineral Processing Software was used to perform mass balance around the circuits. Size reduction performance of the ball mill was determined for the sampling cases. Classification performance of the dynamic air classifier was evaluated based on the efficiency curve approach. It was determined that, approximately 12% circuit capacity increase could be achieved in composite cement production when ball mill, ball mill filter and air classifier power consumptions were considered. This figure corresponded to overall energy savings of 7% in ball mill grinding. ÖZ Bu çalışmanın amacı, konvansiyonel Polysius® iki kamaralı bilyalı değirmen ve Sepol® dinamik havalı sınıflandırıcı kapalı devre işleminin Portland CEMI/42.5R ve Portland kompoze CEMII/32.5R çimento üretimlerinde öğütme ve sınıflandırma performanslarının değerlendirilmesidir. Bu amaçla, devre etrafında endüstriyel örnekleme çalışmaları yürütülmüştür. JKSimMet Cevher Hazırlama Yazılımı ile devre etrafında madde denkliği yapılmıştır. Bilyalı değirmenin boyut küçültme performansı örnekleme dönemleri için belirlenmiştir. Dinamik havalı sınıflandırıcının sınıflandırma performansı verimlilik eğrisi yaklaşımına göre değerlendirilmiştir. Bilyalı değirmen, bilyalı değirmen filtresi ve havalı sınıflandırıcı enerji tüketimleri düşünüldüğünde, kompoze çimento üretiminde devre kapasitesinde yaklaşık olarak %12’lik bir artış sağlanabilmektedir. Bu değer, bilyalı değirmen öğütmesinde %7’lik bir enerji tasarrufuna karşılık gelmektedir. * Sorumlu yazar: • https://orcid.org/0000-0003-3177-1425 ** • https://orcid.org/0000-0002-5614-5175 125 Ö. Genç, A.Hakan Benzer / Scientific Mining Journal, 2018, 57(2), 125-133 INTRODUCTION World’s cement production was recorded to be 4200000 million ton/year and Turkey has a share of 77000 ton/year. Turkey is ranking in the 4th row within the countries producing cement in the world (United States Geological Survey, 2016). The cement industry is energy intensive which consumes approximately 12-15% of total industrial energy use (Madlool et.al., 2011). Finish grinding of cement requires approximately 40% of the total electrical energy consumed in a cement plant (Norholm, 1995). In this respect, energy efficiency of finish grinding stage will save significant amount of energy. Thus, ways to improve cement grinding efficiency should be searched out. Useful insights could be obtained from industrial scale applications and production efficiencies for energy saving or more energy efficient production rates (Benzer, et.al., 2001; Genç et.al., 2006; 2008; Aydoğan and Benzer, 2011; Dundar et.al., 2011; Genç and Benzer, 2012; 2016). In this study, production performance and energy consumptions of industrial cement grinding circuit were analysed when CEMI/42.5R type Portland and CEMII/32.5R type Portland composite cements were produced in the circuits. It was demonstrated that, CEM II type Portland composite cement production provided overall energy savings of 7% with the applied circuit flow configuration. 1. MATERIALS AND METHODS 1.1. Materials CEMI/42.5R Portland cement was obtained by grinding Portland cement clinker and mineral additive material gypsum (CaSO4:2H2O). Portland cement clinker is a black nodular hydraulic material, made by burning in a rotary kiln (pyroprocessing), at least to sintering a precisely specified mixture of raw materials containing CaO, SiO2, Al2O3 and Fe2O3 at temperatures of about 1400oC (Hewlett ,2010). Portland composite cement (CEMII/32.5R) was obtained by grinding clinker, gypsum and natural puzzolanic material which is called trass. Pozzolana is a siliceous and aluminous material that contains volcanic material such as pumice or volcanic ash. Trass 126 effects several properties of cement mortar and cement clinker significantly such as strength, setting time, the amount of C3S (3CaO.SiO2) (alite mineral) and durability, depending on the their substitution ratio and fineness. In the investigated circuit, fly ash was added to air classifier feed stream directly due to its fineness in Portland composite cement (CEMII/32.5R) production case. Fly ash is a puzzolanic material and it is a by-product of burning pulverized coal in an electrical generating power station. It is collected from the exhaust gases by mechanical and electrostatic precipitators. It improves the longterm strength and reduces the permeability of the concrete (Thomas, 2007). 1.2. Plant-site Studies Figure 1 shows the circuit flowsheet with the sampling points for the (CEMI/42.5R) Portland cement production case. Polysius® twocompartment ball mill and a Polysius® Sepol® dynamic high efficiency air classifier were operated in closed circuit to obtain the required cement types. Figure 1. Simplified flowsheet of the industrial scale cement production circuit Sampling points correspond to the following streams in Figure 1: (1) Clinker feed (2) Gypsum feed (3) Total fresh feed (4) Mill overflow (5) Filter return (6) Air classifier (separator) feed (7) Air classifier reject (8) Air classifier fine (9) Trass (in composite cement production) (10) Fly ash (in composite cement production) Ö. Genç, A.Hakan Benzer / Bilimsel Madencilik Dergisi, 2018, 57(2), 125-133 Sampling surveys at the cement plant were performed to characterize particle size distributions around the circuits and inside the mills at the steady state conditions at Portland cement (CEMI/42.5R) and Portland composite cement (CEMII/32.5R) production types. Design specifications for the ball mill and air classifier are tabulated in Tables 1 and 2. An electrofilter at the discharge of the mill collects fine particles (100% -212µm in CEMI production and 100% -850µm in CEMII production) from the mill by air sweeping. The circuit was operated without grinding aid in survey-1. However, grinding aid was (...truncated)