Solving the problem of including volumetric flow rate in the material calculation
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In our production process, styrene from the storage tank is fed into the reaction vessel, and this flow is controlled by a volume flow meter. The ongoing issue is that changes in ambient temperature affect the density of styrene, leading to inaccuracies in the quality of the material. I would like to know how experts address this problem – is the density determined based on extensive empirical data regarding the relationship between temperature and density? Is there any other better and simpler way? Thank you!
I guess many people don’t know about this thing; I don’t even know what bodily fluids are. But it’s probably the gas that is greatly affected by temperature. I’m not sure if it’s a smart meter, or if it’s connected to a DCS; in either case, it should be possible to perform temperature and pressure compensation. Ask the manufacturer or experts if there is a compensation formula. It’s not possible to do as you say: \"Densities are determined based on a large amount of empirical data regarding the relationship between temperature and density,\" and it’s not necessary to make changes every time the temperature changes! For materials whose density is highly affected by temperature, I think it’s better to use a mass flow meter·
Given such high precision requirements, a mass flow meter should be used; if the diameter is large and volumetric flow rate is measured, temperature and pressure compensation can be applied to address this issue
Reply to 2# zzyslhj: It is in liquid state at room temperature. Since the amount of material fed in is usually large, even small changes in density can result in significant differences. We currently perform calibrations on a quarterly basis, by filling the container and then weighing it; this process is quite troublesome and, in my opinion, prone to errors. Not long ago we changed one of the density parameters, and as a result the differences between input and output increased, which was quite problematic. If a mass flow meter were used, this problem wouldn’t exist. As for a volume flow meter combined with a density meter, that might also be expensive.
If you refuse to use a mass flow meter, then add temperature and pressure compensation for flow measurement; temperature and pressure changes have a significant impact on the density of styrene. Adding temperature and pressure compensation is usually sufficient, so it’s not really necessary to use a densitometer.
Reply to 5# autochem: Hello, it seems we haven’t used this compensation method. I’m not sure how temperature compensation works; could you recommend some materials or information on the topic? Thank you!
The simplest way for temperature and pressure compensation is to add temperature and pressure measurements, and then calculate the density based on the known temperature-pressure curve for styrene (a compensation formula can be created within the DCS); it’s not clear whether such a curve exists or not.
For applications involving material feeding where high measurement accuracy is required, it is recommended to use a Coriolis mass flow meter. http://www.shakic.com/cp/product9.htm
If the reaction conditions specified by the poster are based on volume, then it is necessary to make temperature and pressure corrections for each material. There are many methods for this; some rely on experience, while others use actual measured values to be processed by DCS modules. It is recommended to make improvements by using a mass-based ratio for ingredient mixing (in my experience, in some polymerization processes such as those involving styrene, it is already standard practice to use a mass-based ratio for mixing, and mass flow meters should be used for measurement). For bulk chemical products or raw materials, both purchasing and selling involve large quantities. Materials from different sources are stored in separate tanks, which allows for corrections of deviations caused by temperature and pressure based on the testing data of the raw materials. Batch control in the polymerization process is a set of strict control procedures; it is advisable to use reliable measurement methods, otherwise it can have a significant impact on the production process and product quality.
Add temperature compensation. Volume flowmeters generally come with temperature/pressure compensation options, provided that you supply the compensation curves.