Introduction tube heat exchanger
Read the number：(2700) Time：2014/3/9 18:16:17
Introduction tube heat exchanger
And tube heat exchanger is the most widely used chemicals and a heat exchanger on alcohol production currently. It mainly consists of shell, tube sheets, tubes, head, baffles and other components. Required material, respectively, ordinary carbon steel, copper, or stainless steel. When performing heat exchange of a fluid into the connecting pipe at the head of the tube flows out from the outlet tube and the other end of the head, which tube termed; other - species fluid into the housing by the receiver from the Another case took place on the outflow, which is called the shell and tube heat exchanger.
Types of tubular heat exchanger
Fixed tube plate heat exchanger
Such heat exchanger structure is relatively simple, compact, cost is cheap, but not mechanical tube cleaning. Such heat exchanger tubes connected to the tube sheet, tube plates are welded at both ends of the housing and is connected at its upper cover, the cover and the housing is equipped with fluid and export over. Usually means a series of perpendicular to the tube bundle bezel. Meanwhile tubes and tube plate and shell connections are rigid, while the inner tube is a tube of fluid two different temperatures. Therefore, when the temperature difference between the wall and the shell wall is large, due to the different thermal expansion between the two, resulting in a lot of thermal stress, as well as the tube or pipe twist loose from the tube plate, or even destroy the heat exchanger.
In order to overcome thermal stress must have temperature difference compensation device, usually when the temperature difference between the wall and the shell wall above 50 ℃, for safety reasons, the temperature difference between the heat exchanger due compensation device. However, compensation means (expansion section) can be used in the housing wall and the wall is less than 60 ~ 70 ℃ temperature difference between the shell and the fluid pressure is not high. General pressure exceeds 0.6Mpa shell ring due compensation is too thick, difficult retractable, compensating the loss of the role of the temperature difference, it should consider other structures.
Floating head heat exchanger
The plate heat exchanger is connected to a tube flange and the housing, the other tube plate is not connected to the housing, so that the heating or cooling pipe can expand and contract freely, but in a tube plate connected to a cover piece, called " floating head ", so this is called the floating head heat exchanger. Its advantages are: the tube bundle can be pulled out for cleaning; constant expansion of the housing tubes, and hence is when both the temperature difference between the heat exchanger medium, the amount is not due to different thermal expansion of the tube bundle and the housing thermal stress generated . The disadvantage of complicated structure and high cost.
Packing function exchanger
This type of heat exchanger tubes at one end is free to expand, simple structure than the floating head, the cost is lower than the floating head. But there are leaks in the shell of the media may, the shell should not be treated volatile, flammable, explosive and toxic media.
U-tube heat exchanger
U-tube type heat exchanger, each of the tubes are bent into a U shape, with both ends fixed to a tube plate, each tube can be free to stretch, so as to solve the thermal compensation. At least for the two-way tube, tube bundle cleaning can be withdrawn, the tube is free to expand. The disadvantage is difficult to clean inner surface of pipes, pipe replacement difficult, less pipe tube plate arrangement. Advantage of simple structure, light weight, suitable for high temperature and pressure conditions.
And tube heat exchanger baffles
To improve the flow rate of fluid in the shell, and often a certain number of tubes mounted mutually perpendicular baffles within the housing. Baffles not only prevents fluid short circuit, increasing fluid flow rate, but also the path many times as required to force fluid through the tube bundle cross-flow, so that greatly increased the degree of turbulence. Commonly used baffles are round-shaped and disc-shaped missing two, the former is more commonly used.
Column multi-tube heat exchanger shell heat exchangers
Heat exchanger tube must be considered from the thermal expansion of the structure to take various compensation methods to eliminate or reduce the thermal stress according to the measures taken to compensate the temperature difference.
Heat exchanger tube leak resolved
Heat exchanger leak is the most common use of equipment management problems, leakage is mainly caused by corrosion, a small part is due to the heat exchanger itself, selection and manufacturing process defects, tubular heat exchanger The basic form of corrosion control in two ways: electrochemical corrosion and chemical corrosion. And tube heat exchangers in the production, tube plate and tube welding generally use manual arc welding, weld shape varying degrees of defects such as dents, holes, slag, weld stress distribution is not uniform. When using the tube plate portion generally in contact with industrial cooling water, and industrial cooling water impurities, salts, gases, microbes will constitute the tube plate and weld corrosion. This is what we often say electrochemical corrosion. Studies have shown that either fresh water or industrial water, there will be various ions and dissolved oxygen, and wherein the change in oxygen concentration of chloride ions, the etching shape of the metal plays an important role. Moreover, the complexity of the structure also affect the corrosion of metal form. Thus, the tube plate and tube weld corrosion to pitting and crevice corrosion based. From the outside, the management board will have a lot of corrosion products and surface sediments accumulate, the distribution of pits of varying sizes. In seawater medium, will produce galvanic corrosion. Chemical corrosion is corrosive medium, heat exchanger tube sheet exposure of various chemical mediators, would be corrosive chemical media. In addition, between the heat exchanger tubes and tube sheets also have some bi-metallic corrosion. Some tube sheet erosion is also a long-term corrosion medium. Especially the fixed tube sheet heat exchanger, as well as thermal stress, the joint of the tube plate and tubes can easily leak, resulting in heat exchanger failure.
In summary, the main factors affecting the corrosion of the heat exchanger tube sheet are:
(1) the composition and concentration of the media: the impact of varying concentrations, such as hydrochloric acid, the greater the concentration of corrosion generally more serious. Corrosion of carbon steel and stainless steel at a concentration of about 50% sulfuric acid is the most serious, and when the concentration increases to more than 60%, but a sharp decline in the corrosion;
(2) Impurity: harmful impurities include chloride ions, sulfur ions, cyanide ion, ammonium ion, and in some cases these impurities can cause severe corrosion
(3) Temperature: Corrosion is a chemical reaction, the temperature of each upgrade 10 ℃, the corrosion rate increased by about 1 to 3 times, but there are exceptions;
(4) ph value: smaller general ph value, the greater the corrosion of metals;
(5) Flow rate: In most cases the greater the velocity, the greater corrosion.
