Operation of supercritical boiler - an overview

摘要

The present energy situation alerts a focused approach towards environmental preservation and cost-effectiveness. Increase in cycle efficiency by adapting supercritical technology is an important step in the reduction of fuel burnt and the greenhouse gas emission. The boiler that operates on critical pressure or above that is known as supercritical boiler. The supercritical boiler is spontaneously converting water into steam but in subcritical it has more circulation to convert the same. The layout of supercritical boiler includes water separator and boiler circulation pump with drumless which differs from subcritical unit. The operation of supercritical boiler has two modes of operation that is wet and dry mode and in subcritical is not the same. The water chemistry in supercritical unit is stringent and not as of subcritical which is controlled by blowdown process. The clean-up process carried out before boiler light up and pressurization is such as cold blow out, cold recirculation and hot clean up to maintain water chemistry. The control items and logic of controlling the parameters such as main steam temperature, reheat steam temperature, superheat rate, furnace fluid temperature, superheater outlet steam pressure, separator level, excess air, NO_x, sliding pressure control is mainly controlled by water fuel ratio which totally differs from subcritical boilers. The operational flexibility is better than subcritical boiler in prospect of temperature control and load variations. The supercritical boiler is more suitable for sliding pressure operation because of main steam temperature remains constant irrespective of load change. The supercritical boilers is tend to have higher efficiency because of less fuel input, less auxiliary power consumption, less emission and less water consumption.