Regarding the excessive non-condensable gas in the butadiene recovery tower for cis-butadiene rubber
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In SBR, the recovery unit Tower 8 is in operation. There are 3 for recycling butadiene, and 2 for fresh butadiene. The other 3 are refined from solvent oil. My process is as follows: The recovered butadiene is separated from the solvent oil in a dehydration tower, and the material from the top of this tower is sent to another recovery tower where butadiene and solvent oil are further separated. The purity of butadiene exceeds 96%. Then it enters the butadiene dehydration tower and the butadiene dehydrogenation tower. A lot of my non-condensable gas has accumulated in the butadiene dehydration tower. This results in very poor heat exchange performance of the heat exchanger, with the recovery temperature of the chilled water remaining at around -8°. It is difficult to maintain the liquid level in the reflux tank. Where did these non-condensable gases come from? ? ? My solvent oil feed is in a atmospheric pressure tank equipped with a breather valve, and it seems that there are no problems with the nitrogen valves in my butadiene dehydration tower.
The butadiene dehydration tower should have a pipeline leading to the exhaust gas absorption tower; the owner can try reducing the flow of cold circulating water in the dehydration tower and increasing the amount of exhaust gas emitted, until all the non-condensable gases are removed, then check whether any non-condensable gases still accumulate. If it still exists, sample and analyze the exhaust gas pipeline of the dehydration tower to determine the composition of the exhaust gas. If nitrogen is present in the exhaust gas, it indicates that nitrogen has leaked into the recovery system; check the nitrogen pipelines related to the butadiene system (such as pressurization and pump purge lines) to locate the leak. Not only the butadiene dehydration tower, but also the previous towers need to be checked. There is almost no possibility that the recovery systems will be pressurized with air. Another possibility is that the operator filled it with nitrogen when the tower pressure was unstable. I guess if there’s no problem with the nitrogen filling line, and if blind flanges are not installed on the recycle pump, the TBC transfer pump, as well as at the bottom of the dehydration tower and on its recycle pump, then nitrogen leakage will occur.
The exhaust gas was analyzed, and it’s mainly nitrogen. There seem to be a lot of them; the nitrogen valve at the pump inlet is basically a dual-valve setup, with the backflow between the valves being enabled
This post was last edited by chenyong455 on 2012-8-1 22:42. Which towers contain non-condensable gas? Is it only the butadiene dehydration tower?
Now both the butadiene dehydration tower and the butadiene dehydrogenation tower have non-condensable gas. I also asked some people, and they said that the non-condensable gas issue is caused by my dehydration tower basically not discharging any non-condensable gas, or only very little of it. Shunbing asks: how much non-condensable gas needs to be vented from the dehydration tower? How should the top pressure, bottom temperature, and reflux be controlled?
It is possible that, in the absence of leaks, the failure to discharge exhaust gases over an extended period can lead to the accumulation of non-condensable gases inside the tower. If the exhaust gas absorption tower also does not discharge any gases, this creates a closed loop between the recovery system and V405, with trace amounts of nitrogen continuously accumulating within the system. One possible solution is to keep the small valves in the dehydration tower and the heavy gas removal tower open at all times to allow the non-condensable gases to be discharged; at the same time, reduce the amount of oil used in the exhaust gas absorption tower and increase the volume of exhaust gases sent to the flare. The exact amount to be discharged can be determined by analyzing the hydrocarbon content in the exhaust gases, and the increase in material consumption should be acceptable.
Dissolution is likely to occur under low temperature and high pressure, and the device involves no chemical reactions.
Describe the process, and everyone will help analyze the reasons for it
Was too much nitrogen added by the operator while the machine was parked? And was no flare used while it was in operation?
Either your butadiene isn’t pure enough, with a too high carbon content, which results in a low level in the reflux tank and high pressure at the top of the tower! How many condensers do you have at the top of your dehydration tower? You can start by using two condensers, gradually opening the return water valves all the way – there’s no need to rush! With a high carbon content, this is the only solution; otherwise, you’ll have to keep venting it through the flare