Adjustment of acetylene to hydrogen chloride ratio in VCM plant mixer
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The mixer is equipped with a system for adjusting the ratio of dry acetylene to dry hydrogen chloride gas; it is necessary to maintain a volume ratio of acetylene to hydrogen chloride between 1:1.01 and 1:1.03, with a deviation of 1% to 3%. During the design process, I observed that both pipelines for these two gases share the following two characteristics: 1. The inlet pressure is low, at only 50–60 kpag in each case. 2. To control the flow rate, the pipe diameters are fairly large: 16 inches for hydrogen chloride and 18 inches for acetylene. If standard orifice plates are used, the calculated differential pressure is too low, the permanent pressure loss is too high, and the range ratio that allows for sufficient accuracy is too low. Moreover, the theoretical accuracy of orifice plates is only 1.5 grade. After consulting manufacturers and taking the operating conditions into account, it’s already quite fortunate if an accuracy of 10% FS can be achieved across the entire range in practice. I was wondering if anyone among you knows of manufacturers who have actually used this control system in practice? What kind of solution is being used?
The ratio should be: acetylene:HCl = 1:(1.05~1.10); in practical operation, considering that the purity of HCl is between 93.5% and 95.5%, this ratio may reach around 1:1.20. We use orifice plate flow meters, which essentially serve as a reference. The load is greatly influenced by the gas generation rate of the acetylene generator and the catalytic activity of the converter; ultimately, it is determined by the excess amounts of acetylene and hydrogen chloride after conversion.
It mainly depends on the excess amounts of acetylene and hydrogen chloride after the transformations in stage 1 and stage 2
The control system has been put into use, but it serves only as a rough reference – precise control is not possible. On-site control is primarily based on the amounts of acetylene and hydrogen chloride produced after conversion
Is there so much excess hydrogen chloride? What should the moisture content be in ppm? Won’t it exacerbate equipment corrosion?
The excess amount of hydrogen chloride is determined mainly in consideration of its purity; the purity is only 94%-96%, and some additional hydrogen chloride is consumed during mixing and dehydration. Moreover, the flow meter has significant errors. As everyone has said, this is just for reference – the conversion rate should be the key factor to consider. A surplus of about 5% hydrogen chloride in the system is appropriate.