Energy Evaluation of the Cement Manufacturing Process Using Natural Gas-hydrate Technology in Consideration of CO₂ Separation

Abstract

Recently Japanese government's energy policy calls for an expanded use of natural gas in order to reduce the emission of greenhouse gases. Especially, natural gas hydrates, which are solid materials that resemble ice, are expected to become one of new type natural gas resources, and several applications such as natural gas storage and cold thermal energy storage have been applied in various industrial applications. Typical, cement industry consumes a huge amount of heat and energy, and much of carbon dioxide (CO₂) emission occurs not only from fossil fuel combustion but also from the calcinations of limestone, which is the main material. Therefore the authors have put forward a scheme which makes possible the CO₂ separation and energy saving by using hydrate technology for cement manufacturing process, and then evaluated the validity of the scheme by calculating the energy balance. Consequently, by cooling the introductory air of a cement grinding process by hydrate cold energy, the grinding efficiency has improved about 1% and 0.4kWh/t-cl reduction of the power consumption was achieved. By cold-water use to condenser of a tower waste heat boiler, the power generation output increased from 21.9kWht/t-cl with 22.5 kWt/t-cl, and boiler efficiency has been improved by 1.6%. By proposing CO₂ separating by the hybrid system with using the chemistry absorbing method together, the energy 234kWh/t-cl and 53% of a simple hydrate system. CO₂ was reduced from 782kg/t-cl to 492kg/t-cl. In addition, the proposed system was validated based on these trial calculation results.