| Sulphuric acid |
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The need for inline analysis of H2SO4 in conversion processes of sulphurdioxide gas into sulphuric acid has increased in recent years, due to safety regulations and the need for reducing the costs of laboratory analyses. The Rhosonics Model 8500 concentration analyzer, which uses the velocity of ultrasound as the measured parameter, enables an easy, reliable and maintenance-free analysis. Sulphuric acid is mainly produced in concentrations of 93% to 99%. In order to obtain polynomial values for the calibration, samples of 70 to 100 % have been tested in the temperature range of 20ºC to 60ºC and at ambient pressure. (For tests in the oleum region, above 100% acid, refer to the Oleum Application Note). The average intrinsic error of analysis of the Rhosonics Model 8500 concentration analyzer can be determined based on the accuracy of sound velocity and temperature measurement. Due to the high accuracy of both parameters, the error is below ±0,05% acid for concentrations above 80% and below ±0.01% for concentrations above 90%. The intrinsic error of any instrument used to measure concentration is inversely proportional to the slope of the measured variable vs. concentration. The density curve flattens out above 95%, and the conductivity curve flattens below 94%. Consequently, the errors of analysis of densitometers and conductivity sensors are large in these respective regions and it is in these regions that the ultrasonic concentration analyzer offers greatest benefit. The sound velocity curve has a continuous, steep slope throughout the most common range of concentrations, resulting in the remarkable accuracy’s. The Rhosonics Model 8500 analyzer is also more accurate than refractometers. In addition, its insensitivity to fouling of the sensor part makes it virtually maintenance-free.Cost savings As an illustration of cost-savings due to accurate analysis, consider a plant which installs a Rhosonics sensor in a pipe-line, thereby improving analysis by 0,5%. On a daily basis a plant producing 200 tons per day at $50 per ton would save $60/day. With this amount of savings, the payback time of the analyzer is less than a year. Consequently, annual savings are as much as $ 20,000 per year. Conclusions The Rhosonics Model 8500 Concentration Analyzer is the most accurate instrument in the 90%-100% sulfuric acid range. It is the only instrument that can be used over the entire range of commercial concentrations with remarkable accuracy. In addition, it has no moving parts and its accuracy is not degraded by fouling as are densitometers and conductivity sensors. In addition, the UltraSmart system makes the analysis highly reliable, all together resulting in higher profitability in any plant where the concentration of H2SO4 must be carefully measured and/or controlled. The sensor is made of AISI-316L, Hastelloy C-276 or C-2000.
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