1. Power Plant
The Power Plant is designed to have a nominal gross rating of 1,878 MW, consisting of 3 x 626 MW Units with a net available-for-sale power output slightly in excess of 1,653 MW. The actual gross power generated by each Unit at maximum output is 626 MW. The auxiliary power consumption during normal operation is 75 MW per Unit, resulting in a net power output of 551 MW per Unit. Of the net available-for-sale power output, 1,473 MW is contracted to EGAT, measured at the Thai-Lao border (the delivery point), and 175 MW to EDL, measured at the Hongsa Town Substation (the delivery point), while the remaining is lost in the transmission. The Power Plant operation will be controlled from a fully-equipped central control room. Each Unit will be highly automated to ensure strict compliance with operating limits, achievement of optimum performance, and to guarantee reliability and safety of the Power Plant. Additionally, the Power Plant will operate in compliance with the World Bank Environmental Guidelines 1998 (“WBEG98”). Each lignite-fired Unit produces electricity by burning lignite in a boiler to heat water to produce steam. The steam, at tremendous pressure, flows into a turbine, which spins a generator to produce electricity. The steam is then cooled and condensed back into water to be returned and reused again in the boiler.
2. Power Plant Design
The functional specification of the Power Plant has been prepared by the Employer’s Engineer, Pöyry Energy Limited. The specification of the design of the Power Plant reflects the performance required by the Employer with respect to the EGAT PPA as well as the limitations imposed by the EIA. Particular attention has been paid to delivering the Contracted Operating Characteristics specified by EGAT. The Power Plant has also been designed such that the environmental requirements of the Employer and the obligations stated within the EIA can be met in accordance with good industry practice for a facility of the Power Plant’s nature.
2.1 Boilers and Fuel Burners Designs
Each Unit consists of one boiler supplying steam to a turbine generator. Sub-critical boilers of a proven design were chosen to ensure good result when burning lignite as the main fuel. Each boiler has a single furnace in which all of the low NOx lignite burners are aligned to fire tangentially to a common circle within the furnace to produce a single fire-ball to ensure overall stability in the combustion. The design of the low NOx burners, together with staged introduction of the air for combustion, ensures that the production of NOx is minimised under all operating conditions.
To start up the boilers and to ignite the lignite burners, diesel oil burners are used for their ease of ignition and for their instantaneous heat generation capacity. Diesel oil burners will also be employed during adverse conditions to ensure combustion stability.
For normal operation, the lignite will be supplied to the burners after it has been pulverised by beater wheel mills so that the moisture content of the fuel will be dehydrated by the re-circulated flue gases from the top of the furnace. A Beater wheel mill is a particular type of mill designed to pulverise lignite having high moisture content. The drying capacity of these mills is much greater than that of mills designed to pulverise other types of coal and low moisture content lignite. Beater wheel mills pulverise the lignite by attrition and use high temperature flue gas drawn from the furnace exit of the boiler to dry the fuel and then transport the pulverised lignite to the burners. Some hot air from the air heater is mixed with the flue gas to act as primary air to support ignition of the mixture at the burner. This also provides a mean to control the mill temperature. An important safety feature is that the oxygen content of the drying and transport flue gas is low, ensuring that the mills operate under inert conditions.
The air required for combustion of the fuel is provided to the burners by large electric motor driven fans (2 x 50% fans) that first pass the air through regenerative pre-heaters to recover heat from the flue gases leaving the boiler. Steam air pre-heater are also provided to assist during start up and low load operation.
The boiler furnace will operate at slightly below atmospheric pressure. The flue gases will be drawn from the furnace to the FGD by 2 x 50% electric motor driven induced draft fans located downstream from the electrostatic fly ash collectors.