In the beginning of October, SCI in Sasolburg saw its recently acquired Stamolys phosphate analysers from Endress+Hauser commissioned to full operation. Since this was one of the first Stamolys phosphate analyser installations in South Africa, it was agreed between local instrumentation and control specialist Endress+Hauser and SASOL that the initial commissioning would be handled by an engineer from the factory in Germany, but because of the simple installation and on-the-job training provided, the next sites will be commissioned locally.
The supply of these products follows Endress+Hauser's acquisition of Staiger-Mohilo, a German company that has demonstrated superior capabilities in the wastewater analysis field. SASOL recognised an opportunity to automate their phosphate measurement on the wastewater plant as well as on the cooling tower circulation water. Three phosphate analysers were purchased for the analysis, and commissioned at the beginning of October under the supervision of a Staiger-Mohilo engineer, with SASOL reportedly being satisfied with their performance, which is within, or better than, specification.
The wastewater treatment facility at SCI receives wastewater for secondary clarification after the local council at Sasolburg has done primary clarification. The two analysers monitor the phosphate levels before and after flocculation and secondary clarification have been done. The first analyser monitoring the primary clarified water operates on the molybdate - vandate method - or phosphate yellow - as outlined in the ATV-M 269 protocol. This method of analysis is very economical, since only one request is used. The typical range is 0,5-25 mg/l PO4 - P. The signal output is used to control the dosing of coagulant for the secondary clarifiers. The second phosphate analyser monitors the effluent from these secondary clarifiers. This analyser operates in the low range of 0,5-2,5 mg/l PO4 - P according to the DIN 38405-D11-1 standard - or phosphate blue method.
The sample lines continuously supply sample to the analysers that draw a sample via a peristaltic pump on requirement. The sample preparation is done by in-line cartridge filters, which filter out any undissolved solid particles. The analysers were set up to sample every 30 minutes. The calibration of the analysers is automatically initiated every 48 hours with prepared standards. The reagents for the analysers are located in a specially cooled compartment that controls the temperature to 10°C, which ensures optimum life for the reagents. The phosphate blue reagents are colourless and require a cleaning cycle to ensure that the photometer lenses remain free of any reacted reagents. This automated cleaning cycle is initiated every 24 hours. The two analysers were commissioned simultaneously within a day. SASOL expressed satisfaction with the results stating that the analysers were well on par with the laboratory analysis.
The third analyser monitors the phosphate content of the recirculated cooling tower water to ensure adequate phosphate levels are maintained to guard against corrosion. The analyser also measures low range phosphate and therefore used the phosphate blue method. There is no sample preparation required, since the water is particle-free.
The engineer from Staigler-Mohilo also gave extensive training to the SCI personnel responsible for the operation and maintenance of the analysers. The operators were instructed in the various preventative maintenance tasks as well as the set-up parameters of the analysers.
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