2.5 Cooling Water Systems
The main cooling water systems will be of the closed type, and will take advantage of natural convection that occurs when heat is dissipated from a falling spray of warm water to a rising
column of ambient air. Warm water from the Power Plant will be sprayed into the cooling tower uniformly over specially designed plastic components in the form of packs of corrugated panels
1.25 m deep installed in the tower to increase contact between the cooling air and warm water.
Re-cooled water will then be collected in a pond at the base of each cooling tower and will be drawn to the main condenser of each Unit via a concrete pipe buried below ground by 2 x 50% circulating water pumps. Isolated sections of the system can be inspected and maintained by using the installed valves. The auxiliary cooling systems will also take water from the inlet of the condensers through the tubular auxiliary heat exchanger before the cooling water is returned to the cooling towers. To ensure that the performance of the cooling water system is not compromised, the following measures will be instigated:
The operation of the condenser is optimised by periodically injecting abrasive coated sponge balls to clean the condenser tubes; sodium hypochlorite will be mixed into the cooling water to prevent the growth of organic materials in the system; and some cooling water will be purged periodically, and fresh treated water added to avoid scaling and fouling problems from the build-up concentration of impurities overtime due to natural water evaporation.
2.6 Water Treatment Plant
Raw water from the east lake will be used in the Power Plant’s operation. The raw water will be pumped to a pre-treatment plant where any resulting sludge will be dried and disposed to the west dump site. Most significant water loss from the system will be due to natural evaporation in the cooling towers.
The high purity water that shall be required in the boilers will come from further treatment of the pre-treated water in a conventional demineralisation plant. Chemicals required in the ion exchange units will be stored in one-month supply size tanks in impermeable bunds. In normal circumstances, staff will not come into direct contact with any of the chemicals as the chemicals will be discharged into the treatment tanks directly from the road tankers.
2.7 Wastewater Treatment Plant
No wastewater will be discharged from the Power Plant. It will all be used within the ash handling system. In addition, the standard of treatment of wastewater has been increased such that all treated wastewater will comply with the Thai Royal Irrigation Department Standard B.E 2532-1989, the Thai Industrial Effluent Standard B.E. 2539-1996 and the World Bank effluent limitations.
2.8 Ash Disposal
The production of ash and gypsum when 3 Units are operating at full load and burning average quality lignite is expected to be about 13,400tonnes/day. Gypsum produced by the FGD plant has been included because this will be disposed of with the ash.
Ash produced in the combustion process is dealt with in 2 ways according to the weight of the particles. Heavy particles that fall to the bottom of the furnace, or bottom ash, will be collected in twin hoppers that will then be removed via slow moving drag chain conveyors immersed in water. It will then be passed through crushers and be flushed by water to the bottom ash disposal system where it will be dewatered before storage and loading onto disposal conveyors and to be transported to the west dump area.
The light particles, or fly ash, will pass through the boiler in the stream of hot flue gases. Fly ash will be removed from the flue gases stream by ESPs, where it will be collected in a series of hoppers. The fly ash will then be transferred from the ESP hoppers to the fly ash silos by a dense phase pneumatic transport system. Most of the fly ash will be transported from the silos via the disposal conveyors to the west dump after being conditioned with water. Facilities will also be included to enable the fly ash to be separated for use in products or as engineering fill.