Q & A on heat exchanger technology

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How to classify the heat exchange equipment?

A: According to the “Petrochemical Corporation Equipment Classification Catalogue” can be divided into:

  • (1) Shell and tube heat exchanger
  • (2) Casing-type heat exchanger
  • (3) Water immersion heat exchanger
  • (4) Spray type heat exchanger
  • (5) Rotary (snake tube) type heat exchanger
  • (6) Plate heat exchanger
  • (7) Plate fin heat exchanger
  • (8) Tube and fin heat exchanger
  • (9) Waste heat boiler
  • (10) Other

How does the heat exchanger transfer heat?

A: In the most common inter-wall heat exchanger, the two main ways of heat transfer are conduction and convection. The thermal fluid first convection to the heat transfer to the side of the tube wall, and then to conduct the heat from one side of the wall to the other side, and finally the other side of the tube wall to convection to the heat transfer to the cold fluid, thus completing the heat transfer process of the heat exchanger.

What is the effect of media flow rate on heat transfer?

A: The greater the flow rate of the medium in the heat exchanger, the greater the heat transfer coefficient. Therefore, increase the media flow rate in the heat exchanger can greatly improve the heat transfer effect, but the negative impact of increasing the flow rate is to increase the pressure drop through the heat exchanger, increasing the energy consumption of the pump, so there must be a certain appropriate range.

What is the effect of the heat exchanger tube surface structure on the heat transfer effect?

A: The use of specially designed heat exchanger tube surface structure, such as finned tubes, nailhead tubes, threaded tubes, etc., on the one hand, increases the heat transfer area, on the other hand, the special surface of the turbulence greatly increases the degree of fluid turbulence outside the tube, both of which can improve the overall heat transfer effect of the heat exchanger, so these surface structures than the performance of the bare tube surface.

Heat exchanger tube surface descaling currently commonly used in those methods?

A: Heat exchanger tube surface descaling commonly used methods are.

  • Mechanical descaling: steel brazing manual scaling, pressure water scaling;
  • Chemical descaling.

What are the methods to prevent scale on the surface of heat exchanger tube?

A:

  • (1) Nickel phosphorus plating;
  • (2) Chemical coating, 847 coating.

What are the common methods to strengthen the heat transfer of heat exchange equipment?

A: The main methods of heat transfer equipment to strengthen heat transfer
First, the use of structures that increase the heat transfer surface, such as:

  • 1. Using finned tubes, nailhead tubes, threaded tubes, corrugated tubes, etc.
  • 2. Tube surface for mechanical processing: screw ring tube, spiral groove tube, threaded tube, etc.
  • 3. The use of small diameter tubes, can increase the number of tubes on the same tube plate area, increasing the heat transfer area.

Second, increase the flow rate of fluid in the heat exchanger, which can greatly improve its heat transfer coefficient, such as.

  • 1. Increase the number of spoilers, such as the insertion of a spiral band in the tube, set up outside the tube folding plate, false tube, etc.
  • 2. Increase the number of tube process or shell process.

In addition, the use of good thermal conductivity of materials to manufacture heat exchangers, heat exchanger anti-corrosion and anti-scaling measures, such as timely cleaning of scale are means to improve the heat transfer effect.

Tube heat exchanger maintenance, the number of blocked tubes have what requirements?

A: individual tube bundle corrosion perforation allows the use of processed cone for 3 ~ 5 ° metal plunger plugging. Generally in the same pipe, the number of plugged tubes does not exceed 10% of the total number of tubes, but according to the requirements of the process, can be increased.

Why must the gaskets on both sides of the pipe plate be made of the same material?

A: Because the flange fastening bolts on both sides of the pipe plate are the same bolts, and the specific pressure applied to the gaskets on both sides of the pipe plate is the same. If the gaskets on both sides are made of different materials, the gaskets on one side of the plate will not have enough pressure and cause sealing failure or the gaskets on the other side will have too much pressure and cause sealing failure, so the gaskets on both sides of the plate must be made of the same material.

Why does the cooling water heat exchanger produce scale?

A: Scale is formed by the crystallization of dissolved salts in the water, attached to the heat exchanger tube wall, which is characterized by dense and hard, firmly attached, difficult to remove. The presence of a large number of suspended particles in the water can become crystal species, other impurity ions, bacteria, rough metal surfaces, etc. have a strong catalytic effect on the crystallization process, greatly reducing the degree of supersaturation required for crystallization precipitation, so the cooling water heat exchanger is easy to produce scale.

Floating head heat exchanger has those main components?

A: The main components are: tube bundle, folded plate, anti-flush plate, tie rod, fixed distance tube, shell, tube box, tube plate, inlet flange, outlet flange, floating tube plate, floating head flange, floating head cover, floating head hook ring, floating head gasket, outer head cover flange, outer head cover side flange, outer head cover, outer head cover gasket, air release port, liquid discharge port, tube box flange, tube box side flange, tube box gasket, tube box side gasket, fixed saddle, movable Saddle.

What are the main components of a fixed tube plate heat exchanger?

A: The main components are: tube bundle, folded plate, tie rod, fixed distance tube, shell, tube box (top cover), tube plate, inlet flange, outlet flange, tube box flange, tube box gasket, fixed saddle, movable saddle, ear support, expansion joint.

What are the main components of U-tube heat exchanger?

A: The main components are: U-tube bundle, folding plate, anti-flush plate (inner guide tube), tie rod, fixed distance tube, shell, tube box, tube plate, inlet flange, outlet flange, tube box flange, tube box side flange, tube box gasket, tube box side gasket, fixed saddle, movable saddle.

What are the main components of the casing type heat exchanger?

A: The main components of the casing type heat exchanger are: inner tube, outer tube, back elbow.

What are the main components of the water immersion heat exchanger?

A: The main components of the water immersion heat exchanger are: inlet tube, outlet tube, collection tube, snake tube, cooling water tank.

What are the main components of the spray heat exchanger?

A: The main components of the spray heat exchanger are: tube bundle, fan, water nozzle, drainage pipe, feed pump.

What are the characteristics of fixed tube and plate heat exchanger, U-tube heat exchanger and floating head heat exchanger?

A: Fixed tube plate heat exchanger is characterized by compact structure, simple, low cost, the same shell diameter within the number of tubes, single tube replacement and maintenance is convenient, easy to clean the tube, but more difficult to clean outside the tube, the tube and shell temperature difference stress. Shell process and between the tubes, but the tube elbow is not easy to clean, the number of tubes on the tube plate, the tube spacing is large, the center of the tube bundle has a gap, the fluid outside the tube is easy to go short circuit. Floating head heat exchanger is characterized by free movement of the tube bundle, no temperature stress problem, the tube bundle can be freely withdrawn, easy to clean outside the tube and tube bundle, but the floating head structure is complex, high cost, floating head sealing requirements are more stringent, the operation of the floating head is easy to leak and not easy to check found.

Fixed tube plate heat exchanger for which places?

A: Fixed tube and plate heat exchanger is suitable for shell process media clean, not easy to scale, the media temperature difference is relatively small occasions.

U-tube heat exchanger for which places?

A: U-tube heat exchanger is suitable for the shell and tube wall temperature difference is large, the tube to go clean media of high temperature and high pressure occasions.

Floating head heat exchanger for which places?

A: The floating head heat exchanger is suitable for the tube and shell temperature difference is large, the medium is not clean, the need for frequent cleaning occasions.

Tube heat exchanger arrangement with a triangular arrangement and a square to 45 ° angle arrangement, why?

A: Triangular arrangement and square to 45 ° angle arrangement have their advantages and disadvantages. The advantage of triangular arrangement is compact, high heat transfer efficiency, in the same tube plate area on the largest number of tubes, about 15% more than the square arrangement, but not easy to clean the outer surface of the tube; and square to 45 ° angle arrangement to clean the outer surface of the tube is more convenient, but the number of tubes than the triangular arrangement is much less.

Tube heat exchanger in the commonly used tube materials are?

A: Commonly used materials of the tube are: 10 #, 20 #, 12CrMo, 15CrMo, 0Cr13, 1Cr13, 1Cr5Mo, 0Cr18Ni9Ti, 1Cr18Ni9Ti, titanium tube, 410, 321, etc.

In the column tube heat exchanger, why are the tube diameters of φ32, φ25, φ19 and φ16 selected respectively?

A: The size of the tube diameter will directly affect the performance of the heat exchanger. Pipe diameter is small, the heat transfer coefficient is large, the effective heat transfer area in the same volume is also large. This can make the structure compact, but also save material. But the tube diameter is too small will also bring adverse effects, for the same flow rate of fluid, the smaller the tube diameter, the greater the resistance to flow, its pressure loss also increases, in addition to too thin tube is also easy to be clogged with dirt, making it difficult to clear, so the heat exchanger tube diameter is generally 16 mm to 32 mm.

Why is the heat exchanger support bolt holes have a round, but also a long round?

A: The bolt hole on the fixed support is round, in order to be able to fix the shell tightly on the foundation. The bolt holes on the movable support are long and round, in order to make the shell free to expand and contract when subjected to temperature changes, so as to avoid generating large stresses to protect the equipment.

What are the commonly used heat exchanger gaskets?

A: Commonly used heat exchanger gaskets are oil-resistant asbestos pad, iron clad pad, wave tooth pad, metal pad.

Floating head heat exchanger small floating head bolt selection to pay attention to what issues?

  • (1) Length
  • (2) Wet H2S stress corrosion
  • (3) Temperature

Tube heat exchanger in the folded plate (folded rod) what role?

A: The heat exchanger folding plate (folding rod) can play a role in changing the flow direction of the fluid in the shell process, improve the flow rate of the fluid in the shell process, increase the degree of turbulence of the medium, improve the heat transfer efficiency and support the role of the tube bundle.

Why is there a single-tube heat exchanger, two-tube, four-tube, six-tube, eight-tube process?

A: When the total number of tubes in the heat exchanger is the same, increasing the number of tubes can make the flow rate in each course of the tube becomes larger, so you can increase the heat transfer coefficient and reduce the required heat transfer area. But also increases the pressure drop, and make the fluid can not be all the way to counter-current heat transfer, and the heat exchanger structure more complex. Therefore, the number of tubes generally used is not less than 2, not more than 8, the specific should be based on the actual process requirements to choose.

Tube heat exchanger leakage caused by what causes?

A: Heat exchanger leakage may have the following causes.

  • Heat exchanger tube corrosion perforation, or fracture.
  • Tube mouth corrosion thinning caused by leakage.
  • heat exchanger tube and tube plate expansion at the loose.
  • Heat exchanger tube and tube plate weld cracks, porosity or corrosion perforation.
  • Loose or broken small floating head bolts.
  • Damage to the small floating head gasket.
  • Small floating head or floating tube plate seal damage.

Why do you need to test the water pressure after the heat exchanger overhaul?

A: The purpose of the water pressure test after heat exchanger overhaul is to check whether the heat exchanger has the ability to safely withstand the design pressure (i.e., pressure strength), tightness, the quality of the interface or joint, the quality of the welding and sealing structure of the tightness. In addition, you can also observe the residual deformation of the parent weld of the vessel and pipe after pressure, and timely detection of material problems.

Tube heat exchanger installation location why some are standing, some are lying (horizontal)?

A: Some of the tubular heat exchanger is vertical and some are horizontal, mainly from the following aspects:

  • ① Production process requirements: such as some heavy boilers need a certain level of medium height, if the use of horizontal heat exchanger, that is, can not reach the level of the requirements, so you must choose a vertical heat exchanger;
  • ② Large-scale: if a process unit heat transfer area of several thousand square meters, if you choose the length of the heat pipe 6 meters of horizontal heat exchanger, you may need several heat exchangers, covering a large area, is not conducive to the effective arrangement of the device space, if you choose the heat exchanger tube length of 12 meters of the vertical heat exchanger, 1 can solve the problem;
  • ③ Reduce pressure drop: some production processes require to minimize the pressure drop in the media delivery process, the choice of vertical heat exchanger and the tower side by side arrangement, so that it shortens the connection line with the tower to reduce pressure drop.

Why some places choose casing type heat exchanger, water immersion heat exchanger, while other places choose the tube heat exchanger?

A: The current refinery, chemical production equipment selected for heat transfer equipment, most of the tube heat exchanger, but in some production facilities, still retain a small number of casing-type heat exchanger, water immersion heat exchanger. Although the tube heat exchanger compact structure, high heat transfer efficiency, but due to the heat exchanger tube is small, if used for the media containing solid particles, it is easy to cause blockage. Therefore, in the place of media containing solid particles, the general choice of casing-type heat exchanger or water immersion heat exchanger.

Source: Network Arrangement – China Tube Sheet Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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