Cement, Energy and Environment

CHINA NOW WORLD'S BIGGEST ENERGY USER China overtook the US last year to become the world's biggest energy user, the International Energy Agency said. Beijing's new status is expected to make it even more influential in global markets, in determining prices and how it is used. China clinched the top slot more quickly than had been expected because the US has, over the past decade, far outpaced China in using energy more efficiently. On a per capita basis, the US still uses far more energy than China and remains less efficient than Europe. Courtesy: TERI (The Energy and Resources Institute) Newswire, 16-31 July 2010, P20. Energy Conservation RECOVERING HEAT FOR ENERGY Dr. Thomas Biirki and Thomas Bornert, ABB Switzerland and Ltd, Local Business Unit Minerals, Heat Recovery, examine how energy efficiency can be boosted by converting low temperature waste heat to electricity. The reduction of waste heat losses can be classified into two categories: i) waste heat recovery and ii) waste heat conversion. Waste heat recovery Waste heat recovery means to reuse waste heat as heat in the production process ("keep the heat in the process") and thus reduce the supply of heat by burning (fossil) fuels. Modern cement plants can be thought of as huge heat exchangers. After firing the kiln (and eventually the precalciner), the heat in the stack gas and in ''Increasing energy efficiency is one of the most important current entrepreneurial imperatives - for ecological and economic reasons." the waste air from the clinker cooler is used, more or less, to a large extent within the plant, for example: • Secondary air preheating • Tertiary air preheating • Preheater tower with 3 - 6 stages to preheat the raw mix. • Coal drying • Drying of alternative fuels • Use of clinker cooler waste heat to feed district heating systems. Waste heat recovery, as the most important measure towards low heat losses, has the highest priority. It is the most efficient ,1 kWh= 1 kWh" way to increase energy efficiency of the heat recovery is high: 1kWH of waste heat reused in the plant ends in ± 1kWh of useful heat. Waste heat conversion Waste heat conversion means allowing the waste heat to leave the process, but converting it (partially) into electricity before it is discharged (at lower temperature level) to the environment. Therefore, after the efficiency of a cement plant has been driven to the economic optimum, the remaining waste heat is converted into electricity. It must be kept in mind that with any conversion technology the thermal efficiency of the conversion (rJth) comes into the game. Therefore 1kWh of used waste heat only produces r]kWh of useful energy-but now it is electrical energy. One thing of obvious: the more efficient the cement plant, the lower the waste heat temperatures, specifically the temperature of the waste gas after the preheater tower. Temperature after the preheater tower in efficient cement plants can be considerably below 300'C. Therefore waste heat conversion technology has to be configured to match this situation. - Power plan!_j Fig. 1: Comparison of waste heat recovery and waste heat conversion. Left waste heat recovery in a cyclone. Right waste heat conversion in a power plant. 28 _ _. i