Introduction to the types and functions of heat exchangers in pharmaceutical water systems

In the water system, the main function of the heat exchanger is to maintain a certain temperature in the water system and perform periodic disinfection or sterilization. There are three main types of heat exchangers commonly used in the pharmaceutical industry, namely plate heat exchangers, double-tube plate-shell-and-tube heat exchangers, and tube-in-tube heat exchangers.

①Plate heat exchangers are mostly used in the pretreatment stage before purification, to raise the temperature of raw water, and to pasteurize the pretreatment system and activated carbon filter on a regular basis. This kind of heat exchanger has the advantages of low investment cost, easy disassembly and easy increase of heat exchange area, but its drainability is not as good as that of double tube plate Shell And Tube Heat Exchanger, and there is a greater risk of microbial growth, so it is not recommended Use plate heat exchangers without self-cleaning function in storage and distribution systems.

②The double-tube shell-and-tube heat exchanger is generally installed on the return water pipe network at the end of the distribution system, and is used to cool down the injection water point. The working principle is that two or more fluids at different temperatures pass through the shell side and the tube side of the double tube plate shell-and-tube heat exchanger, and transfer heat from the higher temperature fluid to the lower temperature fluid, so that the fluid temperature reaches the process level. Specified indicators, so as to meet the requirements of process conditions. This heat exchanger has a shell-and-tube structure. Two fluids exchange heat inside, one fluid flows inside the tube (tube side), and the other flows outside the tube (shell side), which can effectively prevent cross-infection of the system. Its structure The advantages of easy cleaning and self-draining are well matched with the characteristics of the pharmaceutical water storage and distribution system, making the double-tube plate shell-and-tube heat exchanger the mainstream method of heat exchangers in the current pharmaceutical industry.

There are two commonly used ways to connect the inner Tube Sheet and the outer tube sheet of the double-tube-sheet shell-and-tube heat exchanger: first, the combination of welding and expansion joints is adopted. At present, most domestic enterprises adopt this method, that is, the expansion joint of the inner tube and the welding of the outer tube, but there are obvious shortcomings in the welding of the outer tube plate, which shows that the weld seam and its vicinity are prone to corrosion, such as the weld seam is prone to corrosion, Stress corrosion cracking due to uneven heating near the weld, high temperature welding leads to intergranular corrosion of stainless steel due to heating, etc. Once the heat Exchanger Tube Sheet and heat exchange tube welds leak, it will seriously affect the safety of production. Second, both the inner tube sheet and the outer tube sheet adopt the expansion joint method, and the tube array and the tube sheet are connected and fixed by the tube expander, which belongs to the physical processing method. This method requires relatively high machining accuracy, and can effectively prevent chemical crystallization corrosion caused by heat exchanger welding. It is currently a relatively advanced heat exchanger processing technology in the world.

③Tube-in-tube heat exchangers are mostly used at the cooling point of water for injection cooling. Although the heat exchange area is limited, it has the advantages of less investment and convenient installation, which brings convenience to the modular design of the open cooling point of water for injection.