The use of reverse osmosis as a 35,600m 3/day concentrator in the waste water management scheme at 4640 MW Bayswater/Liddell Power Station complex - Australia

Abstract

Water is an essential resource for power generation. It is used for steam generation, transportation, cooling, washdown, domestic services and in miscellaneous process water systems. The water distribution system and storages extend throughout a power station and interface with virtually all of the plant. The quality of water required for.each application varies from demineralised water with a conductivity of less than 10μS/m, used as boiler make-up, to brackish or saltwater used for ash transportation or cooling. The quality of water used for each application must be carefully controlled to ensure safety of personnel and prevent damage to equipment by scaling or corrosion while minimising water treatment cost. In recent years it has also become necessary to design power station water management systems to minimise water consumption as well as satisfy more stringent environmental requirements. This has resulted in a significant increase in water treatment requirements including water recycle and reuse via water recovery system. The Electricity Commission of New South Wales' (ECNSW) coal fired Bayswater/Liddell Power Station complex, which has a combined generating capacity of 4640 MW, includes one of the world's largest power station water treatment and water management systems. The water systems associated with both Bayswater and the adjacent Liddell Power Station will achieve “Zero Discharge” of all aqueous streams from the combined power station sites. To achieve “Zero Discharge” without deterioration of the water quality of the associated water storages, approximately 24,000 tonnes per year (66 tpd) of dissolved salts must be removed from the power stations water systems. The water treatment plant included in the water management scheme for Bayswater will have the capacity to remove 36,000 tpa (100 tpd) of dissolved salts from the power stations water systems. The capacity to remove additional salts will enable the Commission to improve the quality of water in the Liddell Power Station cooling dam (Lake Liddell) which has deteriorated since the commissioning of Liddell Power Station in 1971. The water treatment technologies that form part of the Bayswater/Liddell water management scheme include 160,000 m 3/day of lime softening, a 149,000 m 3/day carboxylic cation exchange resin alkalinity reduction system, a 35,600 m 3/day reverse osmosis (R.O.) facility incorporating extensive pretreatment, and a 6,600 m 3/day brine concentrator system (vapour compression evaporators operating with seed recycle). This paper presents an overview of the conceptual design of the Bayswater/Liddell Power Station water management system with focus on the detailed design and initial operation of the R.O. osmosis plants which have been installed as part of the cooling water sidestream treatment plant. The R.O. plants are installed to concentrate cooling tower blowdown at high recovery to minimise subsequent treatment of the R.O. reject using brine concentrators. The R.O. system is the world's largest installation of its type treating cooling tower blowdown with a designed salinity of 2500 mg/l operating at a design recovery rate of 82.5%. The paper will also discuss the impact of potential scalents (such as CaSO 4, BaSO 4, and CaF 2) on the operation of the R.O. concentrator at the high recovery rates. Results of pilot plant efforts to determine upper limits of concentration using R.O. will be presented along with recommendations of the role of R.O. in similar projects.