Cement, Energy and Environment

SUPERCRITICAL TECHNOLOGY Did you know that in supercritical technology critical pressure is what enables the boilers to run on less fuel Issues concerning feedstock to run power generation turbines have come centre stage in the past few decades as the entire world is facing a grim situation marked by a steep rise in the prices of oil and possibility of these rising further, given the unabated demand. This has led to the return of coal as a fuel that is available more easily and at lower cost. The flip side of this, however, is that coal is a highly polluting fuel and many nations of the world have agreed to lower emission of carbon dioxide (C0 2) which is identified as among the green house gases that are damaging the environment and leading to climate change problems such as global warming and ozone layer depletion. Technology developers have therefore been engaged in an effort to devise solutions that will burn coal more efficiently and ensure that the electricity generation is economical and benign to the world's environment. Supercritical (SC) technology which basically deals with the temperature and pressure to which water is subjected while generating steam. Supercritical steam generators are frequently used for the production of electric power. They operate at "supercritical pressure" in contrast to a "sub-critical boiler." A supercritical steam generator operates at such a high pressure (over 3,200 psi/22.06 MPa or 220.6 bar) that actual boiling ceases to occur, and the boiler has no water steam separation. There is no generation of steam bubbles within the water, because the pressure is above the "critical pressure" at which steam bubbles can form. It passes below the critical point as it does work in the high pressure turbine and enters the generator's condenser. This is more efficient, resulting in lesser fuel use. Conventional steam power plants operate at a steam pressures in the range of 170 bar. These are sub-critical power plants. The new generation power plants operate at pressures higher than the critical pressure. These are supercritical power plants. The operating pressures are in the range of 230 to 265 bar. Supercritical power plants operate at temperatures resulting in higher efficiencies - up to 46 percent for supercritical plants - and lower emissions than traditional (sub-critical) coal fired plants. The "efficiency" of the thermodynamic process of a coal-fired power describes how much of the energy that is fed into the cycle is converted into electrical energy. The greater the output of electrical energy for a given amount of energy input, the higher the efficiency. A supercritical power plants uses a boiler/turbine system that operates at 1075 degrees F; sub-critical plants operate at 850 degrees F.A. supercritical plant is much more efficient than a sub-critical plant, producing more power from the less coal and with lower emissions. Benefits of advanced supercritical power plants: • Reduced fuel costs due to improved plant efficiency. • Significant reduction in C02 emissions. • Excellent availability, comparable with that of an existing sub-critical plant. • Plant costs comparable with sub-critical technology and less than other clean coal technologies. • Much reduced NOx. SOx and particulate emissions. • Compatible with biomass co-firing. "Supercritical" is a thermodynamic expression describing the state of a substance where there is no clear distinction between the liquid and the gaseous phase (i.e. they are a homogenous fluid). Water reaches this state at a pressure above 22.1 MPa. The efficiency of the thermodynamic process of a coal-fired power describes how much of the energy that is fed into the cycle is converted into electrical energy. The greater 26