Process discussion on heat exchanger piping

It is common sense that the cooling medium should flow in at low pressure and out at high pressure. Safety valves are installed to prevent overpressure in the cooling water pipeline in case the heat exchange tubes leak. To be honest, unless there is a relatively high pressure, having such safety valves or not makes little difference; however, regulations require their use.

Cooling water should enter from below and exit from above – that’s the basic principle. Why must it enter from above? Uncondensable gases and other substances can cause air blockages, leading to abnormal operation of the heat exchanger. If you insist on having water enter from above and exit from below, then at least the exhaust pipe should be connected at the highest point on the side of the heat exchanger where the cooling medium is present; it’s not worth the effort

The second floor is quite interesting; in this case, safety valves are installed to prevent pipeline overpressure – I’ve heard of that for the first time. The main purpose of installing a safety valve on the return water side is to protect the heat exchangers, especially those that are more fragile, such as graphite heat exchangers, charge heat exchangers, or metal heat exchangers with a relatively low design pressure. If the inlet water pressure is too high or if there is a blockage in the return water pipeline, it can cause the pressure inside the heat exchanger to rise above its design value, leading to cracks in the tubes or plates of the heat exchanger.

This post was last edited by DXJ122 on 2010-8-17 at 16:19. I have a general idea of how these safety valves came into being: it can be said that before the 1970s, the designs developed within GUO did not include safety valves； Later, foreign technologies from GUO were gradually introduced; foreigners generally use safety valves, so they were eventually accepted by us. The statement about 2# is correct. The designs from foreign engineering companies still need to be reviewed by HARZAP; when it comes to safety, there is no room for negotiation – it’s somewhat like a \"veto power\" system in our case.

Pushing forward with low output and poor cooling – it’s not worth it at all

I’ll take on one myself; I’m very grateful for all the analyses provided from different perspectives. My personal understanding is as follows for your reference: 1. Why is a safety valve installed at the cooling water outlet? Firstly, there is a prerequisite for this process setup: a safety valve is installed only when there are shut-off valves at both the inlet and outlet of the cooling water. However, cooling water systems usually have isolation valves for maintenance purposes, so safety valves are also commonly installed. Its function is as follows: when the shut-off valve is closed for maintenance of the heat exchanger, the pressure inside the heat exchanger’s tube bundle cannot be released. This is due to uneven temperatures within the tube bundle; in some areas, there is a risk of local overheating and vaporization. This vaporization occurs because heat cannot be dissipated, as well as as a result of a temporary increase in internal pressure. Therefore, the heat exchanger is weak at this point, so a safety valve is installed. 2. When the cooling water enters from below and exits from above, it certainly helps to reduce air resistance and ensure thorough heat exchange. But the problem is that in some projects, in order to achieve better heat transfer due to the properties of the process medium, the use of cooling water is neglected; as a result, in such projects, the cooling water enters from above and exits from below. A method that can be employed from a process perspective is to install a liquid seal at the cooling water outlet; from an economic standpoint, this ensures that the interior of the heat exchanger remains filled with fluid at all times. An less economical approach is to use a flow control valve downstream to ensure that the fluid level and flow rate in the heat exchanger meet the required conditions for effective heat transfer. These are some of my personal thoughts on reading, which I would like to share with everyone. I welcome any different opinions and suggestions!

I heard for the first time that a safety valve is needed; haha, that’s something new for me

OP, I’m not quite sure about this statement. Process media generally require cooling water to be cooled in order to undergo heat exchange; so if that’s not necessary, why carry out heat exchange at all?

This post was last edited by Xiao Mo on 2010-8-18 at 10:15. There’s still one thing I don’t understand: given that the heat exchanger design requires venting at the higher points and draining condensate at the lower points, how can there still be a problem with pressure not being able to be released?

In heat exchangers, the cooling medium enters from the bottom and exits from the top; from an energy perspective, this allows for better heat absorption and more efficient heat exchange, thereby saving energy consumption