This post will focus on yet another highly common piece of equipment that can be found in most manufacturing facilities around the world, whether you notice it, or not. That piece of equipment is the ever-efficient and highly necessary heat exchanger. This piece of equipment’s main task is to transfer heat from one medium to another. However it does serve other functions, for example in some chemical facilities liquids are heated up during the production process in order to create a necessary gas. Since this gas is a key ingredient, companies will make sure it is passed through a heat exchanger, so that any excess gas is captured, and reverted back to a liquid, ultimately ensuring that none of their product goes to waste.
When starting your search for a heat exchanger, you will first want to consider the following:
- High/ Low pressure limit
- Sq. Ft. of surface area
- Thermal Performance
- Temperature ranges
- Product Mix (liquid/liquid, particulates or high-solids liquid)
- Pressure Drops across the exchanger
- Fluid flow capacity
- Cleanability, cost of maintenance and repair
- Materials required for construction
- Ability and ease of future expansion
Types of Heat Exchangers used in Industrial applications:
There are several types of heat exchangers on the market today; however the following two are most used in industrial applications:
Shell and Tube Heat Exchanger:
A shell and tube heat exchanger is the most common type of heat exchanger used in chemical processing facilities. This type of heat exchanger consists of a series of interior tubing, encased in a shell constructed of mild steel or stainless steel. If the shell is in contact with a corrosive material than an alloy such as hastelloy is used. The tubes, or tube bundle, is generally constructed of stainless steel or some other alloy, and contains the fluid that is to be either heated or cooled. Within the heat exchanger’s shell, but on the exterior of the tube bundle, flows a liquid that will pass over the tube bundle’s exterior surface to either heat the tube bundle, or absorb the heat being emitted from the bundle. This type of heat exchanger is capable of maintaining pressures more than 30 bar and temperatures higher than 260 degrees Celsius.
When considering a used shell and tube heat exchanger you will want to know as much about its design as possible. The following is a brief overview of all the design elements of a shell and tube heat exchanger:
- Tube Length
Tube length is important to take note of, since generally speaking, the longer a heat exchanger is, then the smaller the shell diameter is, which translates to an overall less expensive heat exchanger. However be careful, and always keep in mind that the thinner a tube is, the more difficult it is to efficiently clean.
- Tube Layout
There are four different tube layouts used in heat exchangers: square, rotated square, triangular, and rotated triangular. The square layouts are generally used when the application will cause the heat exchanger to be cleaned frequently. The square pattern allows for an easier cleaning experience. The triangular layouts are used to provide a greater heat transfer.
- Baffle Design
A baffle is an artificial obstruction used for checking or deflecting the flow of either a liquid or gas. With regard to heat exchangers they are used to direct the shell’s fluid over the tube bundle. It
is important to note the spatial distance between the baffles, because it plays a major role in the conversion of pressure drop and heat transfer. It is suggested that the baffles are spaced no closer than 20% of the shell’s interior diameter, to achieve optimal thermo economic conditions. Continue Reading →