Article pubs.acs.org/IECR
CaC2 Production from Pulverized Coke and CaO at Low TemperaturesInfluence of Minerals in Coal-Derived Coke Guodong Li, Qingya Liu, and Zhenyu Liu* State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China ABSTRACT: Compared to the traditional electric arc process for the production of CaC2 from coke and CaO, the autothermal process requires less energy. However, the coke used for in situ heat generation results in more minerals in the reactor, because of the presence of minerals (or ash) in coke. This paper studies the influence of minerals (Fe2O3, MgO, SiO2, and Al2O3) commonly found in coal-derived coke on the formation of CaC2. The effect of CaF2, which is an additive used in some of the electric arc processes, on CaC2 production is also evaluated. The results show that Fe2O3 and MgO have little influence on CaC2 formation. SiO2 and Al2O3 do not react with coke at temperatures lower than 1460 °C, but they do react with CaO to form Ca3SiO5 and Ca2Al2O5, respectively, or calcium aluminosilicates in the presence of the both. All these Ca-containing compounds are able to react with C to form CaC2 but at rates lower than that of CaO and consume more C (to form CO). CaF2 has little influence on CaC2 formation in terms of mass change and CO formation, but promotes decomposition of CaC2 into Ca and C. The use of coke with low SiO2 and low Al2O3 is important for CaC2 production for lower coke consumption.
1. INTRODUCTION Calcium carbide (CaC2) can be produced by reacting coke (C) with calcium oxide (CaO) via Reaction 1: 3C + CaO → CaC2 + CO
minerals (generally more than 10 wt % as ash). The minerals mainly SiO2, Al2O3, Fe2O3 and MgO, in addition to CaOmay influence the formation of eutectics and react with CaO, and, consequently, alter the mass transfer and CaC2 production rates. The mineral effect has been a crucial issue in many coal conversion technologies, such as in coal gasification and coal combustion, especially when ash is rejected in the molten state or in eutectic form. In these technologies, CaO was added frequently to reduce the melting point of the eutectics. Clearly, the minerals may also play an important role in the autothermal production of CaC2 since the oxygen combustion of coke would certainly result in increased coke consumption and increased ash content in the reactor, ∼3 times more than that in the electric arc process. However, the mineral effect on the production of CaC2 has not been studied in detail in the past and little information is available in the literature. The information available today is limited to the beneficial effect of CaF2 for the reduction of melting point of the product eutectics8−10 and the negative energy effect due to increased heating load for the melting of the ash and consumption of carbon. In this paper, the influence of major minerals in a coalderived coke and CaF2 on the formation of CaC2 was studied to support development of the autothermal CaC2 production process that is operable at temperatures lower than the current electric arc process.
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The technology practiced today can be traced back to one century ago and is characterized by electric arc heating and a moving-bed furnace.1−3 Because of the use of large size feeds (5−30 mm), the production of CaC2 is limited by mass transfer and is energy-intensive. It was reported recently that CaC2 can be produced using pulverized feed (
