Sodium and Chloride Removal from Lake Phillipson Low Rank Coal by Aqueous Leaching
Flinders Power, formerly NRG Hinders, is considering the possible use of low rank coal from Lake Phillipson, South Australia (SA) in its power stations at Port Augusta, SA. Typically, this coal contains about 35% moisture and 10% ash. Unfortunately, it also contains high levels of sodium (1% Na) and chloride (0.95% Cl) with a Na2O level in ash of 18.9%. Such levels cause serious problems during coal combustion, making the use of as-mined coal impractical for power generation.This paper describes the development of an aqueous leaching technique to remove 90% of the sodium and chloride and to yield a product with a Na2O level in ash of less than 3%.Small-scale agitation leaching tests with good quality tap water at ambient temperatures showed that the coal needed to be crushed to minus 5.6 mm to obtain maximum removal of water-soluble sodium and chloride in 30 min. Leaching kinetics, but not the ultimate removal of salt, were enhanced by the use of higher temperatures (up to 150℃), but this was deemed uneconomic. Varying the pulp density between 20% and 50% had little effect on extractions and there was no benefit in multiple stage water washing. The best results by water leaching were 69%～74% extraction for sodium and 95%～97% for chloride, meaning that the sodium removal was well below the target level.From SEM examinations of the leached product it was concluded that the remaining sodium was organically bound to the carbon atoms in the coal.Further tests using aqueous solutions containing cation exchange additives such as calcium chloride (CaC12) or ammonium chloride (NH4Cl) or sulphuric acid (H2SO4) showed that significantly enhanced sodium extractions were possible and target specifications were met. Two options, namely a single-stage and a two-stage leach, were then investigated.In a single-stage leach with additive, minus 5.6 mm coal was leached at 33%～50% solids for 30 min at ambient temperature and then filtered and washed with fresh water. This gave a sodium removal level of about 81% and a Na2O level in ash of about 5%. These levels do not quite meet target specifications. In a two-stage leach, the coal was first leached with water alone without an additive as in the single stage leach, and the washed residue re-leached under similar conditions for about 5 min with an additive (CaC12), and then filtered and washed. This gave a cumulative sodium removal of 96% and a Na2O level in ash of 1.4%～2.4%. These levels are well within target specifications.
Low rank coal Desalination Aqueous leaching
W.J. Bruckard J.T. Woodcock R. Williams
CSIRO Minerals, Australia Flinders Power, Australia
国际会议
XXIV International Mineral Processing Congress(第24届国际矿物加工大会)
北京
英文
1908-1917
2008-09-24（万方平台首次上网日期，不代表论文的发表时间）