Types of Heat Exchangers
Let's take a look at the different types of heat exchangers and their applications.
The different types of heat exchangers that are commonly used in the industry are as follows :
1.Plate and Frame Heat Exchangers
Plate and frame heat exchangers are the most economical heat exchangers of all the types available. However, the most economical choice comes with the most restrictions on the fluid to be introduced into the heat exchanger. The entering fluid must be exceptionally clean, operating at low pressure, and the fluid temperature ceiling is limited. Violation of any of the operating parameters can and will cause failures and ruin the heat exchanger. Plus, and of great importance, is the little or no variation in the process flow rate. Plate and frame heat exchangers produce extremely high heat transfer rates, which is the main reason for their being the most economical heat exchanger type.
They do not foul unless the process flow rate changes substantially, which can and will cause excessive fouling. The heat exchanger immediately ceases to perform and requires immediate dismantling and cleaning, which is expensive and is costly downtime. All these factors must be considered when selecting a plate and frame heat exchanger a choice to solve the plant's process problem. A small problem is that there is a limited choice of qualified plate and frame manufacturers in the industry. This may have a detrimental effect on available prices and deliveries.
2.SHELL & TUBE HEAT EXCHANGERS
The shell and tube heat exchanger is by far and away the most popular choice of heat exchanger utilized by processing plants. It solves most of their processing situations and is the 2nd most economical choice behind the Plate & Frame Heat Exchanger. An added benefit to the plants is the fact that there are dozens and dozens of bona fide shell & tube manufacturers in the world that assures the heat exchanger seeker the ability to secure multiple and probably the best choice of prices and deliveries that suit their project schedule.
The conventional metal shell and tube heat exchanger is the most durable. Most are very fragile and need tender loving care from the plant maintenance personnel, which hardly ever happens. The shell and tube heat exchangers are straightforward and almost always survive despite the plant field staff. For these reasons, it is the "go-to" heat exchanger for all processing plants.
- Fixed Tubesheet
- Floating Head
3.DOUBLE PIPE & HAIRPIN HEAT EXCHANGERS
Hairpin and double pipe heat exchangers are very similar to shell & tube heat exchangers but are constructed in "U" shaped construction. The size range does not match the shell & tube heat exchangers as the largest diameter shell available in the hairpin and double pipe heat exchangers are about 16". Their main function in the processing plants is to handle the heating and cooling of processes where a temperature occurs between the process streams.
When a temperature cross does occur, shell and tube heat exchangers have problems, as no longer can the heat exchanger have multiple tube side passes, which penalizes a shell and tube heat exchanger\'s performance. This is because the fluid\'s temperature cross dictates that fluids must flow in a counter-current flow direction, which once again penalizes shell and tube heat exchangers. However, hairpin and double pipe heat exchangers ALWAYS flow in a counter-current pattern. The only downside of hairpin and double pipe heat exchangers is that their comparatively smaller size can push them into multiple heat exchangers, which adds greatly to the initial expense and increases the field foundations and piping costs.
An added benefit is that in the double pipe version of the hairpin heat exchangers, the large size of the single tube allows the fluid to be much dirtier without plugging the heat exchanger. There are very few viable manufacturers of hairpin and double pipe heat exchangers, which severely limits available bidders, limiting price and delivery choices.
4. SPIRAL HEAT EXCHANGERS
Spiral heat exchangers are the "last resort" heat exchangers that are utilized when no other heat exchanger can perform the heating or cooling task, mainly due to the dirty, fouling, plugging nature of the process fluids. Therefore, they are the most expensive heat exchangers. While many different processing plants occasionally utilize spiral heat exchangers in their plants, the far and away number one user of spiral heat exchangers is the pulp and paper industry, where almost all the process streams are easily the dirtiest, most fouling-prone process streams in any plant. Spiral heat exchangers simply do not foul because of their unique construction and do not plug because of that same construction method. However, that construction method is extremely labor-intensive, which is the main factor in the expensive selling price. However, some processes are so prone to fouling and plugging that a spiral heat exchanger is the only solution to the heating and/or cooling processing dilemma and must be used regardless of the cost.
An added problem is that there are not many viable spiral heat exchanger manufacturers available, which severely limits choices, having a detrimental effect on pricing and delivery choices.
5. SPECIALTY HIGH CORROSION RESISTANT HEAT EXCHANGERS.
There are several types of specialty high-corrosion-resistant heat exchangers. All have their advantages over the others and have their disadvantages when compared to the others. They are Fluoropolymer Heat Exchangers, Graphite Heat Exchangers, and Glass Heat Exchangers.
Fluoropolymer heat exchangers are probably the most corrosion-resistant and foul-free heat exchangers but have many restrictions. Because of the poor heat transfer capabilities of fluoropolymer tubes, very small tubes must be used, requiring very clean fluid to be introduced into the heat exchanger. A major drawback to fluoropolymer heat exchangers is the maximum shell OD of 14", which creates the need for multiple shells at larger flow rates, adding greatly to the expense in terms of both initial cost and foundation and field piping cost.
Graphite heat exchangers, while probably less corrosion resistant than the fluoropolymer heat exchangers utilize much larger tubes and the shells have no restrictions on shell sizes. Therefore, the graphite heat exchanger can be made as large as required to meet the process demands. The major drawbacks to graphite heat exchangers are the way the tubes are connected to the tube sheet. While the graphite construction material may be corrosion-resistant to the harsh chemicals that flow through the heat exchanger, the tube joint connecting those tubes to the tube sheet is a weak point. Over time, those harsh chemicals will \"eat\" away at that joint, leading to leaks and needed repairs, which leads to expensive downtime. However, the major drawback to graphite heat exchangers, both shell and tube and block heat exchangers, is the catastrophic failures due to the thermal expansion of the graphite material. Any upset condition in the plant process stream causing a temperature spike can and will cause thermal expansion and immediate failure of all graphite heat exchangers. Many facilities will not allow them to use their facilities. Also, there are very few domestic manufacturers of graphite heat exchangers. Almost all are made in Europe, limiting choices and extending delivery times.
GLASS HEAT EXCHANGERS
Very few glass heat exchangers are even in existence nowadays. Their extremely fragile nature has forced the plants using these heat exchangers to remove them and replace them with other, more dependable synthetic heat exchangers made of materials like fluoropolymer, graphite, or exotic metals.