Comparison of Amorphous Silica Deposition Rates Measured Using Packed Pipes and a Fluidised Bed at FP10, Wairakei

Abstract

At Wairakei Flash Plant 10 a quartz sand fluidized bed and pipes packed with zirconia beads were used to measure amorphoussilica scalingrates at temperatures between 70?C and 130?C.The residence times in the bed and pipes were shorter than the induction period required for silica polymerisation fiom solution. The rates measured in the fluidized bed were comparableto the rates measured in the packed pipes (12 to 20 mg except that scaling in the packed pipes at the highest temperature of 129 was unexpected. At this temperature the dissolved silica was calculated to be undersaturated with respect to amorphous silica. The precipitation of a less soluble scale enriched in aluminium may be the reason for this apparentlyanomalousresult.