Total chlorine-hydrogen pipeline pressure difference control
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This post was last edited by sunjl1981 on 2013-1-6 at 22:47. It involves an electrolyzer from Beihua Machinery with a capacity of 200,000 tons; there are 10 electrolyzers in total. The diameter of the chlorine gas main pipe is 600 MM, while that of the hydrogen gas main pipe is 500 MM. The values for PCV216 are 300 and for PCV226 they are 200. The system is currently in the commissioning phase, with three electrolyzers operating at first, under a current level of 6000 A each. There is one chlorine compressor and one hydrogen compressor – the chlorine compressor is of German brand 3K, and the hydrogen compressor is from GKN. During the initial stages of operation, manual adjustment of PCV216 and PCV226 was used to maintain a stable pressure difference between chlorine and hydrogen. Once stability was achieved, automatic control was activated. In all three commissioning attempts, the pressure in the hydrogen gas main pipe became too high after 7–8 hours of stable operation, which caused the system to shut down due to excessive pressure differences; however, the chlorine pressure remained stable. Could anyone help analyze the reasons for this? # hcbbs
This post was last edited by pzhhuagong on 2009-11-14 at 14:58. In this case, it is most likely that there is liquid accumulation in the hydrogen pipeline; carefully check whether there is a possibility of liquid accumulation in the pipeline from the electrolyzer’s hydrogen outlet to the hydrogen compressor. Also, check where nitrogen is being added – was it added by someone without any reason?
Has it been observed whether the opening degree of the hydrogen valve increases as the pressure difference rises? Check if there is a problem with severe lag? Check with the DCS manufacturer to see if there is a problem with the DCS itself. To address this issue, the cascade control should first be disabled, so that the chlorine and hydrogen adjustments can be done independently; manually adjust 226. Check whether it is a false signal from the chlorine pressure that is causing the system to make incorrect judgments First, rule out issues with valve regulation, and then check the pressure changes behind valve 226. If the pressure behind the valve also increases as the pressure difference rises, it is necessary to examine the problems in the subsequent hydrogen treatment section. If you pay close attention to the details, there should be a result. Also, is there any manual intervention? Was it the sudden increase in pressure difference after 7.8 hours that triggered the interlock, or was it a gradual increase in pressure difference that caused the interlock? Is there any manual intervention available? Under conditions of increased pressure difference, can the 226 cascade be disabled and 226 adjusted manually independently to see what happens? The situation described by the original poster is well worth studying; I invite all forum members to discuss it. Please, the original poster, also provide more detailed information about the situation.
1. Hydrogen compressor failures, such as reduced suction capacity or clogged outlet. 2. Fluid accumulation in the pipeline. 3. Premature operation of PCV226, resulting in the injection of a large amount of nitrogen. 4. The drain pipe for the water seal at the hydrogen compressor inlet is too thin.
I agree with the analysis of the friend on the 3rd floor; one more thing to check is whether the valve position of valve 226 at the site matches what is displayed on the DCS. We have encountered this situation before as well: the chlorine pressure was stable and within the controlled range, while the hydrogen pressure was high and fluctuated significantly (over 150 mm of water column). After ruling out the possibility of water accumulation in the hydrogen pipeline, it was found that the difference between the actual valve position of the hydrogen control valve at the site and the value shown on the DCS was significant – the actual value was less than 20% while the DCS value was 100%. After having the instrumentation repaired, the hydrogen pressure returned to a stable level within the specified limits, and the problem disappeared.
We have also encountered the issue mentioned on floor 5; it mainly stems from a lack of proper coordination with the field team during DCS tuning – the opening degrees did not match. Once the DCS indicated 100%, it was no longer possible to open the valve any further. As a result, the valve on site was not opened to 100%, which explains why the hydrogen pressure was high It is also necessary to check whether there are any issues with the clips in the cabinet room.
In my opinion: (1) With the use of hydrogen/water seals for chlorine/hydrogen, the problems of liquid accumulation in the hydrogen and chlorine main pipes are eliminated. (2) It ensures proper operation of the 226/216 systems – there are fluctuations in the amount of fluid entering the tanks, as well as fluctuations in the liquid levels of the anode and cathode tanks and in the current level. There are also large fluctuations in the amount of acid added to the anode tank (in chlorine-related processes). The liquid level in the hydrogen water seal tank is too low, and there may be failures in the hydrogen compressors/turbines