Discussion on acid charging and metering methods in acid storage tanks
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With the advancement of technologies in the sulfuric acid industry, the number of plants capable of producing millions of tons of acid per year is increasing day by day. The resulting issue is the storage and transportation of sulfuric acid. Storage problems are relatively easy to address, as the design of acid storage facilities is already well-developed; however, loading the acid into these facilities is a complex and crucial process. Taking an annual acid production capacity of 1.5 million tons as an example, the average daily amount of acid loaded is 4,500 tons, which corresponds to 75 train tank cars. If a capacity factor of 1.2 is taken into account, then the acid loading facility needs to have a capacity equivalent to that of 90 tank cars per day. With such a large loading volume, to improve loading efficiency, the only options are to increase the loading speed and level of automation; at the same time, it is also necessary to enhance the accuracy and safety of acid measurement. In the past, the process for loading acid usually involved transferring it from acid tanks to underground tanks (by gravity), then to high-level metering tanks (also by gravity), and finally to tank trucks. This method was feasible for small-scale shipments ； However, for acid plants with the aforementioned production capacity, using this method requires the construction of a large number of metering tanks, as well as a large workforce; most importantly, the speed at which acid can be filled is relatively slow. Let’s discuss how to improve the automation level of acid handling, so as to enhance production efficiency while ensuring safety and reliability. The method I have been considering is to change the purpose of the measuring tank to that of a high-level tank, and to install electromagnetic flow meters, flow switch valves, and manual valves on the pipeline leading to the acid loading crane. Measurement is carried out each time acid is loaded; once the desired measurement value is reached, the valves close automatically, while a signal indicating completion is sent. The operator then closes the manual valve to adjust the crane. To ensure a continuous acid filling rate, the underground tank pump can be kept running, which keeps the acid level in the upper tank at a high level; any excess acid then returns to the underground tank through the overflow pipe. This can reduce the workload on the operators and increase the acid filling speed. The issue here is the accuracy and reliability of electromagnetic flowmeters. I consulted an instrumentation expert from a smelting plant, who said that this method is not feasible; they rely on manual operation for adding acid. Indeed, human labor is the most reliable method, but is it really necessary to have humans monitor such a basic measurement process? Can’t automated instruments handle it? Hehe, the so-called acid dosing is just a rough measurement to prevent acid leakage incidents; for commercial purposes, weighing is done using rail scales. Please discuss based on the situation in your respective factories and share your opinions :)
Railway scales are generally quite accurate, but they are only suitable for heavier weights. The metering tank is the most reliable.
The original poster’s post is great. To achieve automation, many objective conditions are required. Based on personal experience and opinions: 1. From the perspective of flow measurement instruments, rail scales are the most reliable and accurate; followed by electromagnetic flowmeters, with mass flowmeters being the least accurate. From the perspective of level measurement, it is the most reliable among all types of measuring instruments. Any measuring instrument can break down. But the bad possibilities are different. The advantage of rail scales is that they can provide accurate measurements for weights of 60 tons or more, even in the presence of weight fluctuations, provided that the scales are of high quality – meaning that the sensors are of good quality and that the scales have proper lightning protection measures, etc. If so, give it priority. But it is generally not possible to have redundant configurations. 2. For electromagnetic flowmeters, choose well-known brands that are joint ventures or of higher quality. From personal experience, all electromagnetic flowmeters can last at least 6 years; some models (not specific brands) require calibration with sulfuric acid initially (most electromagnetic flowmeters give accurate readings for water, but overestimate the volume for sulfuric acid). The accuracy of electromagnets can change over time during use, but not to an extreme extent. Moreover, it is the easiest to construct and the cheapest, so it can be configured redundantly. The continuous variation or the extent of variation in acid flow rate affects the accuracy of acid dosing (what is it called now for uncertainty?) Personally, I think uncertainty is a good thing, but its unpredictability is too great; it’s like mysticism! I still prefer accuracy). 3. Mass flow meter. Its feature is that as long as the flow meter is in good condition, it can provide stable and accurate readings over long periods of time. Constant changes in acid flow rate, or changes of only minor magnitude, have a slight impact on the accuracy of acid dosing. The disadvantages are high price and short lifespan (such as 3 years or even less). During bad times, the flow volume can change by tens of millions of tons. Haha. 4. Using a level gauge in the measuring tank is the most reliable among all measuring instruments; the measuring level gauge can be a radar + pressure transducer combination. 5. If automatic acid addition is indeed to be achieved, the main factor is that the automatic addition of sulfuric acid is not as widely used and distributed as petroleum-based products; there have been fewer researchers working on this area, and petroleum-based products are easy to measure, which makes automation possible. It is also possible to achieve sulfuric acid. In my opinion, there are several points to consider when automating the use of sulfuric acid: 1. The device in question must have high and frequent flow rates of materials in and out. 2. Leaders must pay attention, especially the top executive. 3. The plan needs to be considered objectively and thoroughly; for example, it must feature dual or triple redundancy designs, along with historical trends that can be tracked. For example, load cell + electromagnetic, electromagnetic + level, electromagnetic + mass, electromagnetic + electromagnetic + level; an alarm should be triggered when deviations exceed the specified limits, and all measurements provide both instantaneous values and cumulative trends. Automatic control solutions require research; don’t expect to achieve perfection right away. The accompanying components need to be of good quality, and the control valves must be carefully selected (none of the domestic valves I’ve used worked well, but they became stable after some minor modifications). The success of automatic loading and unloading depends on systematic design, careful consideration, and appropriate investment; otherwise, repeated failures can lead to the wrong conclusion that an automatic solution is not feasible.
3# zxg.wylton believes that a control system based on electromagnetism and level detection is superior to other methods. This raises the need to select an appropriate level gauge. Since this gauge needs to be placed on the tank truck and must move along with the acid loading mechanism during each loading and unloading process, and due to the effects of acid handling, common ultrasonic or radar level gauges are not suitable; float-type gauges, on the other hand, are too cumbersome
In some places, all radars or ultrasonic devices are unreliable; it depends on where they are used. Everything I see with floats is unreliable; after making adjustments myself, it works more or less, but the precision isn’t high. It is estimated that for your case, electromagnetic + electromagnetic or electromagnetic + mass would be a good choice.
What we use is an automatic acid loading system: the acid flows from large tanks to a metering tank, from where it is pumped into a high-level tank for acid storage; from there, it flows into tank trucks. It usually takes 6 to 7 hours to fill about ten such trucks
To increase the acid filling speed, automated metering methods must be used. With current technology, it should be possible to select appropriate measuring instruments.
Agreed. It is recommended that companies with large logistics operations take the lead in doing this.