Question to the experts: Potential risks of operating a distillation tower beyond its designed capacity
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Through technical upgrades while retaining the fixed distillation tower (packed tower) structure, the production capacity has been increased to more than three times the original design capacity (nearly four times now). No flooding has been detected at present; the system is operating normally, and the component test results are also satisfactory. Since the actual operating results differ significantly from the theoretical values of the original design, there is concern that operating in this manner for an extended period might pose certain unforeseen potential risks. It is desired to know the actual production capacity of this distillation tower, but due to historical reasons, the original designers have left their former companies and cannot be contacted. Therefore, I would like to ask the experts here: for a distillation column that operates beyond its designed capabilities, are there any other potential risks besides flooding (such as damage to the packing, etc.)? PS: The packing is made of 304 stainless steel. I hope the experts will not hesitate to offer their guidance and answers; I am extremely grateful!
This post was last edited by CHANGBAISHI on 2018-10-11 09:27. According to standard procedures, the relevant regulatory authority should issue a technical modification assessment report and an implementation plan, as well as documents equivalent to the equipment usage instructions and related operational data provided by the manufacturer. Without such relevant data, carrying out mere imitation-style technical upgrades is an irresponsible approach to such upgrades. Even if a certain goal is achieved, it cannot be considered a safe and usable device. All of this is based on design data that complies with relevant standards.
The design load for towers is generally between 60-110%; in some cases, 120% has been considered as well, but loads exceeding 150% are very rare. The possibility of loads exceeding 300%, as mentioned by the poster, is certainly not realistic in practice. The main reasons for this are as follows: 1. The heat source at the bottom of the tower – since the heat source used in the original designs is usually a reboiler, it is the heat exchange area and the intensity of the heat source that determine its efficiency, and it’s not possible to achieve a dramatic increase in efficiency in such cases； 2. The gas-liquid separation in trays is subject to limitations regarding the processing load; in fact, laboratory towers are usually designed for very high loads in order to test different loading conditions. An excessive processing load will certainly lead to a decrease in product quality as well as issues such as tower flooding ； 3. For each inlet and outlet pipeline, the flow rate within the pipeline is restricted by a certain speed limit, which in turn limits the flow volume. Overloading the pipelines as designed may lead to issues such as excessive flow rates and overly small pipe diameters ； 4. The discharge capacity of the safety valve needs to be modified; otherwise, an accident could lead to delayed discharge ； 5. It is very difficult to upgrade and increase the processing capacity for systems other than the towers
Has the composition of the raw materials changed, has the operating pressure changed, and has the reflux ratio changed? Confirm these first before discussing the tower’s capacity or load. If all other conditions remain unchanged, the processing capacity of the tower increases by 4 times; it can only be said that this tower is a bit too large (it’s not ruled out that the diameter of the tower is originally small, resulting in a relatively large margin).
It’s just an internal technical upgrade by the company; without data support from third parties, it’s impossible for them to provide endorsement.
1: The heat source system and the heat exchanger have been upgraded, and their capacity is sufficient. 2: The component accuracy remains unchanged, and no tower flooding or flooding phenomenon was observed. 3: There’s no need to worry about the dimensions of the inlet and outlet pipes; the pipes originally installed have more than enough capacity. 4: The relief capacity of the safety valve is also sufficient. 5: Same as point 1. I want to know right now, under the current circumstances, are there any other potential risks besides tower flooding?
The raw material composition remained unchanged; only the tower pressure was increased by 1.2 kilograms (the current operating pressure is far below the system’s design pressure). While the processing capacity was increased, it was also found that the component precision stayed within the specified limits. As for the gas-liquid reflux ratio, there is no data available on this aspect due to constraints. It is generally assumed that there is a certain margin of safety, but in practice the actual results turn out to be much higher than expected.
Was the equipment designed by a design institute or by the manufacturer? Perhaps the designers exaggerated things to some extent for insurance purposes, and also to make more money
It seems that a large margin was built into the design from the start
A large design margin is definitely included. If both the pressure and temperature of the tower meet the process requirements and the product quality remains unchanged, it can operate beyond its designed capacity.
In my opinion, there is considerable design margin. However, when the production capacity is increased to 300%, qualitative analysis suggests that the gas and liquid flow rates inside the tower will definitely increase significantly. But if the pressure drop within the tower does not change markedly, then there is no need to worry about issues such as flooding. What concerns me more are the problems related to the fixation of the components inside the tower – for example, issues that may arise at the connections of the liquid distributors, or whether the packing might shift due to these changes in flow rates. It is important to pay attention to these potential problems. And should any issues occur with the components inside the tower, the person in charge should be aware of the impact they will have on the tower.