Disagreements regarding the answers to \"Methods for identifying leaking tubes in the external heat exchangers of catalytic cracking units\"
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This post was last edited by 3FCCtaofeng on 2015-8-31 at 11:04. The question for the Daily Question of August 30 was taken from the question bank for intermediate-level catalytic cracking technicians; it is a multiple-choice question asking what method is used to determine leaks in heat exchangers. The answer is C: Close the inlet valves of the heat extraction tubes one by one. (I added an extra character during editing, changing it to external heat exchanger.) But I don’t think this has much impact on the answer.) Some students chose answer A: shut down the inlet and outlet valves of the heat transfer tubes one by one. This answer also has a source. In the advanced catalytic cracking question bank: multiple-choice question. Among the following options, which one correctly analyzes the reasons for internal leakage in the tubes of the external heat exchanger? ( ) One of the options in the answer is: close the inlet and outlet valves and observe the pressure changes. Disagreements arose regarding the answer to this question. Everyone is welcome to discuss.
I think the heat pipes should be cut off in groups to observe the pressure changes. That is, both the inlet and outlet manual valves need to be closed.
In my opinion, the method for determining a leaking tube in a heat exchanger is ( ). The answer is C: It is appropriate to close the inlet valves of the heat extraction tubes one by one. I don’t think closing the inlet and outlet valves and observing the pressure changes is the correct approach. Because, what is meant by closing the inlet valves of the heat extraction tubes one by one here refers to the water inlet valves; once these valves are closed, there is only steam left inside the heat extraction tubes. In the event of a leak, there will be a significant pressure change due to the difference between steam and water. Of course, closing the inlet and outlet valves and observing the pressure changes will yield more obvious results, but this can cause the heat extraction tubes to overheat or experience high pressure, which may easily damage them; hence it is not a advisable approach.
Our plant suspected external leakage; at that time, we closed the inlet and outlet valves of the external heat exchanger for one set and waited for a while to see if there were any changes.
As for this answer, this is my opinion. The inlet pipelines of the external heat exchangers in catalytic units generally lead from the bottom of the steam drum. The outlet pipelines are usually connected to the steam-water separation layer in the middle of the drum. After closing the heat exchanger inlet valve, if the leaking tube bank is shut off, the drum liquid level should rise significantly. This is because what enters the heat exchanger through the inlet pipeline is the boiler water from the drum, while what flows back into the heat exchanger via the outlet pipeline is mainly steam from the upper part of the drum. (Similar to an emergency drain valve on a drum; its inlet is connected to the middle part of the drum, and once the liquid level reaches a safe level, it remains fully open, preventing the drum’s liquid level from dropping any further.) This allows for the identification of the leaking furnace tube. Close the outlet valve only after confirming the judgment is correct. During testing, the inlet and outlet valves are closed simultaneously; should the pressure gauge fail and provide false readings. If a furnace tube that is not leaking is cut out, the presence of heat sources inside the heat exchanger will cause the pressure in the furnace tube to rise sharply. It can even cause excessive back pressure on the valve, preventing it from opening. When the overpressure reaches a certain level, it can lead to unpredictable consequences. Our unit has experienced situations where the wrong heat exchanger tubes were selected, resulting in overpressure and the valves failing to open. A serious accident involving a pipeline burst.
Was the pressure relief valve opened after the single set of pipelines was cut off?
This post was last edited by Seven-Star Ladybug on 2015-8-31 at 16:58. It wasn’t left on for long – just 3-5 minutes before another set was used. I took a look at your opinion; it’s correct to close only the inlet valve.
If it is a minor leak, it is not possible to detect the leaking tube in this way. Practice has shown that it is necessary to identify each one by checking the pressure at the lowest possible load for external heat extraction.
Here, we operate it according to the C method; to ensure that the pressure gauge functions properly, we replace it, as this approach seems more intuitive!
If the inlet and outlet valves can be closed tightly, the pressure will rise rapidly