Installation and Maintenance of Heat Exchangers

Before installing the heat exchanger, please make sure the equipment has a reliable infrastructure, and will never influence the pipelines beneath. The base of the device has two most common types, one is saddle shaped brick-built type, which allows the machine to be placed directly onto it without any measure of fastening, and the other one is concrete base, which allows the machine to be fixed onto it with saddle supports.

Before installing the heat exchanger, we should check the quality of infrastructure including the height, flatness, position, shape, dimensions, pre-opened hole, foundation bolt position, screw, etc.

After we make sure the base is eligible, we can adjust the levelness of the machine by means of iron shim and screw jack. Flatten the base so than the iron shim can contact the base well. In this way, the weight of equipment can be conducted to the base evenly. The iron shims can be classified into the flat type, wedge type, front opening type, and therein the wedge type should be used in pairs. The screw jack also should be used with the iron shims without risk of heat swelling.

When the installation is done, we should level the machine with gradienter. In this way, we can finish the pipelining without inner stress. After the leveling is done, we can weld the wedge iron shim with the basic support. If we need to stack up more than two heat exchangers, we should level and fix the lower one at first, and then install the upper one or ones. Afterwards, we should check the quality of pipes by picking out some of them, and placing them onto the special support. The thing we ought to pay enough attention to is protecting the sealing property and baffles of the equipment.

Due to the linear structure of heat exchanger, some space should be reserved at both ends for ease of maintenance. E.g. the floating head type features the two lids inside and outside. It should have big enough space at the side of floating head, so that the pipes can be draught out easily. The lid outside the machine should also have enough space around, so than the assembly and disassembly can be fairly convenient.

The heat exchanger will be unstable working under the conditions exceeding the rated parameters marked on the name plate. The regular inspection on the temperature and hydraulic pressure of the media in pipe is advisable. The shell and tube heat exchanger fulfills the heat transfer by means of phase changes, including cooling, condensing, heating, evaporation. It contact the corrosive liquid in large scale so there are extra requirements about the anti corrosion capability of the machine. When the heat exchanger works with the water or steam, most of the solutes will get its solubility enhanced, but the calcium sulfate will not, and the water scaling deposit will become a problem after a long term of use. Therefore, the regular cleaning of the machine is supposed to be a very important thing.

The heat exchanger has a big family. We can see many of them used in the fields, like chemical industry, petroleum exploration, atomic energy. As we known, the residential heat supply system, condensing engine on steam turbine, oil colder on aerospace plane are all the family members of heat exchanger. The most important job of the heat exchanger is to maintain the temperature of liquid medium at the required level.

The heat exchanger can be regarded either as an independent system or as a part of the large scale industrial system, such like the ammonia synthesis system.

For the reason of lagging technique and science, the traditional heat exchangers only have a very simple structure with small heat conductive area, but big size and heavy weight. However, the science never stops, we now have the shell and tube type heat transfer equipment with large thermal conductive area, and high energy conductivity efficiency.

In 1920s, the plate type heat exchange appeared on market, and distinguished itself in food process industry. It adopts the plate instead of tube, so its structure is compact, and heat transfer capability is superior. At the beginning of 1930s, the first spiral plate heat exchanger appeared in a workshop in Sweden. Afterwards, the British technician worked out the first plate-fin heat exchanger with the copper and other alloy materials, which is widely used in the engine of aircraft. To the end of 1930s, the Swedish people made the first plate shell heat exchanger used in the pulp mill. Meanwhile, for purpose of using corrosive liquid as the medium, people started to value the strong anti-corrosion capability of new material.

In about 1960s, the rapid development of modern space technology and the high end science make the urgent need in the compact type heat exchanger, plus punching, brazing and sealing techniques. To converse, the promotion and improvement of heat exchanger push the advanced science and technology to move forward. Further, at the beginning of the 1960s, for the purpose of stable heat exchange and energy saving efficiency within the environment of high temperature and pressure, the typical shell-tube type heat exchanger also got the great chance to develop. In the middle of 1970s, the scientists around the world worked on the new heat pipe type exchanger and succeeded.

The heat exchangers can be classified into the contact, heat accumulation and dividing wall types, according to the work principles.

The contact type works by means of mixing the two fluid media directly. Because the two media is wanted to be available for detachment, so one of them should be gas and the other should be liquid, like steam-water. E.g. the water cooling tower, a heat exchange facility widely used in the Chemical industrial factory and electricity power generation station. The hot water rains from the top, and the cold air ascends from downside. After the contact, hot water is cooled down and the cold air is warmed up, and finally, they detach from each other for the differential of density.

The heat accumulation type heat exchanger features the heat accumulator, a medium stuff, which can absorb, store and discharge the thermal energy, such like the coke oven. The equipment is designed for recycling the waster industrial thermal energy, and widely used in the air separation device.

The dividing wall type heat exchanger works by separating the hot and cold fluid media from each other, and then transferring the thermal energy via the wall. It is also known as the surface heater. It can be classified into the tube type and plate type, regarding the middle surface. The tube type refers to the coil, sleeve and shell-tube. The plate type covers the spiral, plate-fin and umbrella plate types.

Generally, the flow orientation of the two fluid media inside the heat exchanger usually is converse. At the inlet, the temperature varies greatly between the two liquid media, but will soon become approaching at the outlet. The countercurrent makes the constant thermal energy distribution, and the heat transfer efficiency. In another word, the countercurrent can finish the heat transfer process better, faster and more cost saving than the fair current.

When either of the cold and hot fluids got its phase changed, like boiling or condensing, the temperature of liquid will not change. The reason is the steam or solid will release or absorb the latent heat. In this situation, the current orientation does not matter too much.

During the thermal energy transmission, the problem is how to lower the thermal resistance for the increase of thermal exchange coefficient. The thermal resistance generated mainly by the fluid layer, scaling deposit upon the heat transfer surface.

A good way to enhance the heat transfer efficiency is to intense the flow rate and interference of fluid, as well as thin the wall of metal pipe. However, the interference will consume more thermal energy, thus the designer of heat exchanger should consider sufficiently about both the balance between the two factors.

Generally speaking, the heat exchanger is mostly made of the metal materials, among which the carbon steel and low alloy steel are used to make the low-medium pressure container, the stainless steel is applied in the anti-corrosion environment, the austenite stainless steel is applied in the high temperature and pressure environment, the copper, aluminum and many other alloys are used to make the low temperature heat exchanger and the nickel alloy can be used in the high temperature environment. The nonmetallic materials, like graphite and fluoroplastics, are used to make the related accessories or the heat exchange itself.

FAQ
1. The temperature at outlet is not constant
Check out the equipment to see if there was air left inside the pipe, if the heat exchange plates were assembled well, if somewhere within the pipe is jammed. Take some measures to tackle the issues

2. The two fluid media contact with each other somewhere unexpectedly.
Stop the machine at once, especially in the situation that one of the media is combustive or explosive. Then check the machine to find out the leakage point upon the heat exchange plate. Control the inner temperature and pressure of the machine below the rated values.

3. The clamp bolts of heat transfer plates are loosened.
When the equipment is working, it is forbidden to fasten the clamp bolts, because the inner pressure is amazingly high and will cause the damage on the plate.
Attention to the interval of plates, when fasten the clamp bolts in case of damaging the plates.

Maintenance
The trundles on of the equipment should be oiled regularly.
The heat exchanger is available for non-stop running, if no bug occurred. Only when the fluid resistance drop exceeded the permissible value and the back washing does not work, or the leakage of media lost control must we stop the machine and conduct the maintenance.

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