Principle, characteristics, advantages and disadvantages of fixed tube plate heat exchanger and solutions for leakage

There are many types of shell-and-tube Heat Exchangers. Under normal circumstances, shell-and-tube heat exchangers are divided into five types: fixed tube plate type, floating head type, U-shaped tube type, stuffing box type and kettle type reboiler.

Today I want to talk specifically about the fixed tube plate heat exchanger in the Shell-And-Tube Heat Exchanger.

What is a fixed tube plate heat exchanger?

The tube sheets at both ends of the fixed tube plate heat exchanger are connected and fixed by a welding method. The heat exchange tube can be a light pipe or a low fin tube. It is suitable for the case where the shell side medium is clean and not easy to scale and can be dissolved and cleaned. The temperature difference between the tube and the shell side is not large or the temperature difference is large but the shell side pressure is not high.

What is the working principle of it?

In the tube and shell side of the fixed tube sheet heat exchanger, fluids flowing at different temperatures are passed through the heat exchange to complete the heat exchange. When the temperature difference between the two fluids is large, in order to avoid high temperature difference stress, a compensation ring (expansion joint) is usually added at an appropriate position of the shell side. When the thermal expansion of the casing and the tube bundle are different, the compensation ring undergoes a slow elastic deformation to compensate for the thermal expansion caused by the temperature difference stress.

What are its structural characteristics?

The fixed tube sheet heat exchanger is mainly composed of a shell, a tube sheet, a tube bundle, and a top cover (also called a head). In the circular outer casing, the parallel tube bundle is installed, the two ends of the tube bundle are fixed on the tube plate by welding or expansion joint, the two tube sheets are directly welded with the outer tube, and the top cover bolt with the inlet or outlet tube is bolted to the outer shell. The flanges are connected at both ends.

It is characterized by simple structure, no shell side sealing connection, the same housing inner diameter tube is the most, the bypass is minimal in the flow of the baffle, the tube length can be divided into any tube number, because the two tube sheets are made of tubes Supporting each other, it is widely used in various shell-and-tube heat exchangers because its tube sheet is the thinnest and the lowest cost.

What are its advantages and disadvantages?

The characteristics of the fixed tube sheet heat exchanger are:

1. The bypass seepage is small;

2. The forgings are used less and the cost is low;

3. No internal leakage;

4. The heat transfer area is 20% to 30% larger than that of the Floating Head Heat Exchanger.

The disadvantages of fixed tubesheet heat exchangers are:

1. The temperature difference between the casing and the pipe wall is large. Generally, the temperature difference between the casing and the pipe wall is t ≤ 50 ° C. When t ≥ 50 ° C, an expansion joint must be provided on the casing;

2. It is easy to generate temperature difference stress, and the temperature difference stress between the tube plate and the tube head is easy to be damaged;

3, the shell can not be mechanically cleaned;

4. After the pipe is corroded and scrapped together with the casing, the life of the equipment is low.

Design of fixed tube sheet heat exchanger

The mechanical design of the fixed tubesheet heat exchanger is in addition to the most critical heat exchanger plates, there are two wall panels, which we call frame plates and pressure plates.

The frame plate is a non-movable wall plate on the outer side, the pressure plate is a wall plate on the other side of the heat exchange plate plate which can be adjusted by a tie rod bolt; a plurality of tie rod bolts are used to tighten the frame plate and the pressure plate; the upper and lower guide bars are connected to the frame Between the plate and the column, used to support and guide the pressure plate and the heat exchange plate; the frame plate and the column can be mounted with a foot for fixing the machine. In addition, a range of accessories such as flanges, filters, thermometers and pressure gauges can be installed.

What are the solutions for leakage?

In the production process, due to water erosion, cavitation and trace chemical media corrosion of the heat exchanger tube sheets, leakage often occurs in the welds of the tube sheets, resulting in mixing of water and chemical materials, and the production process temperature is difficult to control, resulting in the formation. Other products seriously affect product quality and reduce product grade.

After the weld pipe of the Condenser tube is leaked, it is usually repaired by the traditional repair welding method.

Internal pressure is easy to be generated inside the tube sheet, and it is difficult to eliminate, causing leakage of other heat exchangers, usually requiring pressure, inspection of equipment repair, repeated repair welding, experiments and other measures.

The heat exchanger is protected by the corrosion-resistant and anti-scouring polymer composite material, which not only effectively treats the weld seam and blisters in the heat exchanger, but also avoids the corrosion of the metal surface and the solder joint of the heat exchanger. And it can also handle the leakage that occurs during use.