Is it necessary to install a shut-off valve on the medium side of the heat exchanger?
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Are valves required for the flow from the vapor at the top of the tower to the top condenser, and from the condenser to the reflux tank? In the current design, there are no valves for the flow from the vapor at the top of the tower to the condenser, nor are there any valves for the flow from the condenser to the reflux tank; as a result, it is not possible to shut off this flow. Since the gas phase line at the top of the tower is relatively thick, it is not possible to determine an appropriate purging scheme; it is also difficult to maintain pressure. There are challenges associated with using flange misalignment along with rupture disks for purging. I hope everyone can advise me – why aren’t valves used? Is it to save on costs, or is there some other reason? Additionally, for the heat exchangers I’ve worked with in the past, the fluid side not only has inlet and outlet valves but also many have bypass valves. I would appreciate it if all of you could share your opinions. Thank you.
No valves are required from the top of the tower to the condenser, nor from the condenser to the reflux tank; valves are not needed for normal operation, and their use can instead pose a risk of blockage. For a tower without valves, condensers, or reflux tanks, one safety valve is sufficient. Adding valves is also to enable separate isolation during maintenance, but overpressure needs to be considered separately.
Whether valves are included in the heat exchanger design depends entirely on the process requirements; valves are added only if such requirements exist
Generally speaking, the fewer sealing points there are from the top of the tower to the air-cooling, cooling, and reflux tank systems, the better. In practice, connecting the tower, coolers, and reflux tanks without seals allows for the use of a single safety valve; in addition, valves and drain pipes can be used as well. Over time, however, proper maintenance may not be ensured, and leaks will require shutdown for repairs. Towers, coolers, and reflux tanks are relatively stable and generally do not experience equipment failures (except in cases of corrosion), so routine inspections are usually sufficient during major overhauls. If there is a strong requirement from the process or production side to add more sealing points, considerations such as pipe diameter changes can be taken into account, and requests can be made to the design team during the PFD and PID review stages – these requests are usually met
The gas-phase material coming out of the top of the tower usually has a relatively large pipe diameter; therefore, there is no need to install valves at the upper gas inlet to the condenser – doing so would be wasteful. A shut-off valve can be considered installing at the lower condensation outlet, leading directly to the reflux tank, to facilitate isolation from the reflux tank during maintenance and cleaning
A purging plan was prepared, but there is no feasible purging method for the vapor phase at the top of the tower. It’s not possible to pressurize the inside of the tower; moreover, performing purging by connecting the flange to the condenser and using a rupture disc presents difficulties as well, since that flange connection is extremely difficult to move. The idea of carrying out purging by offsetting the flange openings is just that – an idea alone, alas.