Feed water heater
key word：Heat exchange element
Category:
Product description
Feed water heater
1. Introduction
1.1. Application
The feed water heater is one of the important auxiliary equipment in the regenerative system of power plant. It is a kind of heat exchange equipment which uses steam extraction of steam turbine to heat feed water and improve thermal efficiency. The high-pressure heater is located between the feed water pump and the boiler, and the heated feed water pressure is high (about 20MPa for subcritical unit, 30MPa for supercritical unit and 33Mpa for Ultra Supercritical Unit); the low-pressure heater is located between condensate pump and deaerator, and the heated condensate pressure is about 2MPa.
1.2. Model meaning
$$-**-##
$$--- name of feed water heater (JG for high pressure heater; JD for low pressure heater)
**------Heat exchange area (M2)
##----------Serial number of high pressure heater or low pressure heater
1.3. Structural features
1.3.1. Structural form. There are two types of feed water heaters: U-tube heater and header type high-pressure heater.
1.3.1.1. U-tube heaters are generally divided into vertical, inverted and horizontal (see Fig. 22-1 ~ Fig. 22-3).
1.3.1.2. The header type high-pressure heater is generally divided into vertical and horizontal type (see Figure 22-4 and figure 22-5).
1.3.2. Structure description. The characteristic of the feed water heater is that the heating working medium (extraction steam of steam turbine) and the working medium to be heated (boiler feed water) are not mixed with each other. The feed water is in the heat transfer tube, and the steam is outside the heat transfer tube. Heat is transferred through the surface of the tube wall (see figure 22-6). The steam gives off heat in the heater and condenses into drain, which is discharged from the drain port. The heating steam has a certain degree of superheat. In order to make the feed water temperature reach the expected value, the heating area should be as small as possible. Therefore, a superheated steam cooling section (DSZ) is set to make full use of the superheat of the extraction steam. The process of steam changing from vapor to saturated water and releasing latent heat of vaporization is completed in the condensation section (CZ), which provides most of the enthalpy rise of feed water in the tube.
1.3.3. Description of important parts:
1.3.3.1. U-tube heater. The U-tube heater is divided into water chamber, pipe system and shell in structure.
① Water chamber. The feed water heater has a water chamber welded on the tubesheet. The feed water inlet pipe, outlet pipe and manhole on the water chamber are welded on the head or cylinder. The water chamber consists of a process partition plate welded on its inner wall. The process partition cover plate and sealing gasket are fixed on the process partition plate with bolts.
The water chamber is divided into three types: hemispherical head (see figure 22-7), cylinder section with elliptical head (see figure 22-8) and full opening large forgings (see figure 22-9). The hemispherical head type water chamber is used for high-pressure heaters. Under the same pressure, the wall thickness of the hemispherical water chamber can be approximately reduced by one time, and the stress distribution is uniform. Because of its small internal operation space, it is generally recommended to be used for heaters larger than or equal to 300MW; the water chamber with cylinder section and elliptical head is generally used for low-pressure heaters and high-pressure heaters less than or equal to 300MW.
The full opening large forging water chamber is generally used for high pressure heater, steam cooler or drain cooler with less than 300MW and narrow internal operation space.
② Piping. The piping system consists of U-tube, tube sheet and support plate.
The pipe is supported by a support plate, which is fixed together by a distance pipe and a pull rod. A reinforcing plate is arranged at the lower part of the tube bundle to strengthen the tube bundle, so as to prevent the banana effect of the tube bundle; at the same time, a roller wheel is arranged under the base plate to facilitate loading and unloading. The superheated section of the heater can expand freely. Stainless steel anti scour baffle is set at the steam and drain inlet to protect the pipe.
There are many forms of piping arrangement.
The steam condensation area is the main heat transfer section. According to the different requirements of steam inlet parameters and system for feed water end difference and drain end difference, superheated steam cooling area or drainage cooling area is often configured.
a. The arrangement of steam condensation area: it is suitable for saturated or superheated steam extraction. There is generally no cladding inside except heat transfer tube and supporting baffle plate. The steam will gradually condense into water under the guidance of diaphragm and gather at the bottom of shell. Baffle plate is set at the steam inlet to prevent direct impact of steam on heat transfer tube bundle. A drain outlet is arranged at the bottom to discharge the drain. The heater must maintain a certain drain water level to prevent the steam from directly flowing to the next low-pressure equipment through the drain outlet. Therefore, water seal pipe or water level regulating valve installed on drainage pipe is adopted to control drainage quantity. In the process of steam condensation into hydrophobic, some non condensable gases (such as oxygen, ammonia, hydrogen, etc.) mixed in the steam will gather in the condensation area. With the accumulation of this gas, the heat transfer tube will be corroded and surrounded around the outer wall of the tube, which will affect the heat transfer effect. Therefore, it is necessary to improve the heat transfer effect of these exhaust ports on the inside of the shell and to eliminate some harmful gases. In addition, the arrangement in the exhaust also has the function of guiding the steam flow direction.
b. Two zone layout: according to different requirements, the built-in superheated steam cooling zone or drainage zone is set on the basis of pure steam condensation zone. Both the drainage cooling zone and the superheated steam cooling zone are enclosed by cladding, and guided by the guide diaphragm, so that the steam or drainage can flow through the heat transfer surface at a certain speed and direction
The layout of the two zones is condensation area plus superheated steam cooling area and condensation area plus drainage cooling area. The arrangement of condensation area plus drain cooling area is mainly used for low pressure heater (see figure 22-10)
In the horizontal heater, there is also a layout of full immersion drain cooling zone. In this form, the drain cooling zone is completely immersed in the condensate drain, that is, the water level is above the drain cooling section. In this way, the end plate and suction port of the drain cooling section can be omitted, and the drain cooling zone can work more stably and reliably. But this kind of drain cooling area can only be designed as part of the flow.
c. Three zone layout: the heater with three heat transfer sections of superheated steam cooling zone, condensation zone and drain cooling zone is called three section layout heater. It has the advantages of compact structure, reasonable layout, material saving and simple system.
The built-in drainage cooling area can be divided into full flow type and partial flow type according to different heater layout. The so-called full flow type is that all feed water passes through the drainage cooling section and then enters the condensation area. In other words, only part of the feed water passes through the drainage cooling area, while the other part directly enters the condensation area. That is to say, the drain cooling zone which contains all the heat transfer is called the full flow type; the one that only covers part of the heat transfer tube is called the partial flow type.
In a three zone vertical heater, the drain cooling zone is usually arranged very long. Since the drainage is at the bottom of the shell and the inlet area of the feed water is near the tubesheet, a fully sealed cladding is needed. The lower part is inserted into the water, and the upper part is closed connected with the tubesheet. An outlet liner sleeve is used to lead the drainage out of the shell. The water flows around under the guidance of the inner compartment of the cladding, which is called "siphon effect". Under different parameters, the area ratio of drain cooling zone to condensation zone is not a constant value. Sometimes the area of condensation section is large, but the area of drain cooling zone is only a small one. In this way, the drainage cooling zone can only be arranged as a partial flow type to ensure enough condensation section area, so the drainage cooling section will be made slender. At this time, in order to calculate the drainage pressure loss, the static pressure difference from the drain water level to the drain outlet should be added in addition to the resistance loss caused by the drainage flow in the cladding. If the pressure of the drain connection vessel is too high, that is, the pressure difference between the two vessels is too small, it will lead to drainage failure. Moreover, in the thermal calculation, the feed water flowing through the drain cooling area and not flowing through the drain cooling area must be calculated respectively, which makes it difficult to correctly estimate the heat transfer situation of each part in the heat transfer section and arrange the heat transfer tube hole area properly.
In the inverted vertical heater, the drain water is gathered in the lower part of the shell and above the tubesheet, which can protect the tubesheet from steam impact.
It is difficult to design three zone heaters, especially in high parameter and large capacity units (such as units above 300MW), because the required heat transfer tube is too long, which brings difficulties to the design. Therefore, it is necessary to adopt double row arrangement, or separate and independent layout, that is, external superheated steam cooler and drain cooler are used. It is suitable for the unit with higher operation reliability.
d. Heat transfer tube. In order to withstand high temperature and high pressure, high-pressure heater needs to select the pipe material with sufficient strength and processing. Carbon steel pipe is a kind of cheap and good performance material. The water quality of low-pressure heater is worse than that of high-pressure heater, and stainless steel pipe is usually used. Undoubtedly, stainless steel pipe is an ideal pipe material for both low-pressure heater and high-pressure heater, which has good high-temperature strength and excellent corrosion resistance. However, the price is high and the heat fraction is small. Compared with carbon steel pipe, the heat transfer surface is increased by 20% ~ 30%.
See table 22-1 for the maximum service temperature of various heat transfer tubes
Table 22-1 maximum use decision of heat transfer tube
| Pipe | Carbon steel | Molybdenum steel | Stainless steel | Tin brass | Arsenic added brass | White copper B10 | White copper B30 | White copper B30 |
| HSn70-1 | H68A | (Annealing) | (Stress relief) | |||||
| Temperature (℃) | 425 | 500 | 425 | 230 | 200 | 315 | 370 | 425 |
The diameter of heat transfer tube is mainly in the range of ∮ 14 ~ ∮ 32. In general, small size tubes are used for straight and U-shaped tubes. The fluid inside and outside the tubes are in full contact with the tube wall, which is conducive to heat transfer, and the tube layout is flexible and the tube wall is thin. Once the tube is damaged, the tube needs to be blocked to avoid reducing the heat transfer surface too much; the spiral tube is mostly made of large-sized tubes, in order to obtain better stiffness and reduce the distribution of pipe joints on the header. For straight pipe and U-tube, the outer diameter of ∮ 6 is the most commonly used; for spiral pipe and serpentine tube, there are ∮ 25 ～∮ 32 and other specifications.
The wall thickness of heat transfer tube should be reasonably selected according to the design conditions and should not be lower than the value specified in table 22-2 in any case.
Table 22-2 minimum wall thickness of heat transfer tube
| Material | Copper and copper alloys | Nickel alloy | Stainless steel (U-tube) | Stainless steel (straight pipe) | Carbon steel |
| Minimum wall thickness (nominal wall thickness, mm) | 1 | 1 | 0.9 | 0.7 | 1.27 |
In general, heat transfer tubes should not be spliced, especially for high-pressure heaters. Due to the use of the fully enclosed shell, once the splice fracture occurs, it will bring difficulties to the maintenance. At the same time, when the inner diameter of the pipe at the joint is reduced, there will be a large loss of water supply resistance.
e. Tube sheet. The structural design of the tube sheet is the layout of the discharge tube hole after the flow rate, number of tubes and heat transfer area are basically determined (see figure 22-11)
In addition to the several layout forms shown in figure 22-11, it can also be arranged into six processes, eight processes, etc.
See Fig. 22-12 for the arrangement of tube holes in common tubesheets.
The direction indicated by the arrow in figure 22-12 is the flow direction of the fluid outside the pipe. The flow resistance of the form shown in figure 22-12 (b) is smaller than that in figure 22-12 (a), and the heat transfer effect is better than that in figure 22-12 (a). In addition, there are square and corner square arrangements.
f. Diaphragm. In terms of its function, the baffle plate on the heater pipe system can be divided into guide plate and support plate. The role of the guide plate is to make the fluid flow through the tube bundle at a certain speed and direction, while the support plate plays a role in reducing the winding of the heat transfer tube and improving the stiffness of the tube bundle. At the same time, the two kinds of diaphragms can play an anti vibration role.
g. Support plate. Generally used in the condensation section, there are two common forms: one is as shown in Fig. 22-13 (a), in which saturated steam enters into the tube bundle successively from the arcuate area on one side of the shell, so there is no need to open a window in the pipe layout area of the support plate; the other, as shown in Fig. 22-13 (b), is used to guide the saturated steam around the tube bundle by matching with the operating exhaust port on the shell It also has diversion function.
h. Deflector. The guide plate is usually used in the steam cooling section and drain cooling section of the superheater, and it is necessary to ensure that the medium outside the tube scours the tube bundle at a certain velocity and direction. Generally, the guide plates with notches can be arranged at a certain distance, as shown in Fig. 22-14
In the U part of U-shaped pipe, anti vibration isolation strip should be added to prevent vibration, as shown in Fig. 22-15.
In addition, the thickness of baffle and support should be limited. When the shell diameter is less than 457mm, the minimum thickness of the support plate and guide plate of the superheated steam cooling section and condensation section is 9.5mm; when the shell diameter is more than 457mm, the minimum thickness is 16mm. When the distance between the guide diaphragms is less than 457mm, the minimum thickness of the diaphragms in the drain cooling section of all heaters is 6.5mm; when the spacing of diaphragms is ≥ 457mm, the minimum thickness of corresponding diaphragms is 9.5mm
For the whole U-tube bundle, in addition to the fluid flow induced vibration, the continuous impact of some external forces, especially the impact force at the fluid inlet (such as steam inlet, upper drain inlet, drain inlet, etc.) will also stimulate vibration. In order to reduce the impact of fluid on the tube bundle, the anti shock baffle should be set at these places. The impact damper shall have sufficient coverage and shall not be less than the 45 ° diffusion range shown in figure 22-16. The support point of the anti impact baffle should not be set on the heat transfer tube metal, but should be fixed on the diaphragm, shell or other extended metal; the baffle should have sufficient thickness and should be made of corrosion-resistant stainless steel.
③ Shell. The shell is composed of interface, body and support
The steam inlet nozzle of the interface is arranged above the water level, and the design pressure is lower. The feed water heater is equipped with upper drainage inlet. Each heater is equipped with normal drain port and emergency drain port, and a water level control header is also equipped
Due to the phase change of the medium on the shell side of the feed water heater, the high temperature superheated steam is gradually cooled to saturated steam, then to saturated water, and finally to the subcooled drain water discharge shell. If the whole shell assembly is designed according to the inlet steam temperature, it is uneconomical to design the shell at the steam inlet area according to the inlet steam temperature.
The barrel can be divided into shell barrel and short section barrel, as shown in Fig. 22-17.
The shell body is made of low alloy steel, chromium molybdenum steel or thick low carbon steel with good high temperature performance; the shell body is made of low carbon steel.
Figure 22-17 (b) shows the insert block method, in which a piece of chrome molybdenum steel is inserted in the steam inlet area, while the shell and the rest of the short connection can be made of low carbon steel. The distance L between the weld seam and the center of the opening must be greater than or equal to the opening diameter D, or equal to the sum of the opening radius, the pipe seat thickness and the shell barrel thickness, whichever is the greater.
There are two types of supports: horizontal heater support and vertical heater support. The horizontal heater is equipped with three supports, one fixed support and two rolling bearings. The middle rolling bearing is not loaded during operation and is only for maintenance; the vertical heater is equipped with two supports, one fixed and the other sliding.
There are many connecting pipes of feed water heater, including feed water inlet and outlet, steam inlet and outlet, drain inlet and outlet, emergency drain and safety valve. In addition, there are some small nozzles, such as exhaust, drainage and water level measurement sampling port
a. Determination of nozzle diameter.
Steam inlet nozzle: the flow area a (mm2) and diameter di (mm) of steam inlet nozzle are respectively
Where qmi - steam flow rate, kg / h;
v-specific volume of steam, m3 / kg:
p-steam operating pressure, MPa;
n - number of steam connection pipes
In order to seal the steam, the heater with built-in superheated steam cooling section usually adopts the steam inlet stainless steel backing pipe, and the calculated diameter should be the inner diameter of the lining sleeve
The required flow cross-section shall be calculated for the diameter of water supply and drainage connection pipes. For the water supply and drainage outlet pipes, the flow area A (mm2) is
For the upper drain inlet connection pipe, the flow area A (mm2) is
among 
From this, the nozzle diameter dr (mm) is calculated
In the above formula, qmi - medium flow rate, kg/h, qm6 value for feed water inlet and outlet flow and qm5 value for drain outlet flow rate;
qmCD -- drainage inlet flow, kg / h;
v -- specific volume of medium at operating temperature, m3 / kg
ct -- medium flow rate, according to table 22-3.
G -- flow rate of steam water mixture, kg / (m2 · s)
ρ -- mixed density, kg / m3;
qmt -- liquid flow rate in the mixture, m3/h
qms -- steam flow rate in the mixture, m3/h
The diameter of emergency water connection pipe can be the same as that of normal drainage outlet pipe.
Table 22-3 medium flow rate of each interface
| Name of nozzle | State | Maximum velocity（m/s） |
| Subcooled drain outlet | Operating temperature | 1.2 |
| The water level of saturated drain outlet is controlled | Operating temperature | 1.2 |
| The water level of saturated drain outlet is not controlled | Operating temperature | 0.6 |
| Liquid inlet from flash tank | Operating temperature | 1.2 |
| Water supply inlet and outlet | Normal temperature | 3 |
| Upper drain inlet | Operating temperature | G |
Note: G ≤ 1220kg / (m2 · s)
b. Determine the position of steam inlet pipe and drain outlet pipe. The whole heating process of feed water in the heat transfer tube of the heater is unbalanced. If the heat transfer tube is divided into several areas according to the length direction, the temperature rise of feed water in each section will be different. If a dividing line can be found according to the size of heat transfer so that the total heat transfer on both sides of the dividing line is equal, then the dividing line and secant line are called the thermal center line. Obviously, the thermal center line must not be in the middle of the heat transfer tube, but at a certain position away from the geometric center of the heat transfer tube. When the heat transfer tube is
When U-tube is used, the deviation is more obvious. Figure 22-18 shows the feed water temperature rise curve of a U-tube heater and the location of geometric and thermal center lines of heat transfer tubes
For pure condensing and two zone heaters (condensation zone plus built-in drain cooling zone), the position of steam inlet nozzle should be set on the thermal center line, so that the steam can evenly distribute flow to both sides after entering the shell. The channel through which the flow is distributed is called the distribution chamber. The flow rate at the maximum steam flow rate in the distribution room shall not be greater than that at the steam connection pipe. In this way, when the steam pipe is located on the thermal center line, the required distribution chamber area is minimized, thus the shell diameter can be minimized.
If the heater needs to install more than two steam inlet nozzles, several thermal center lines shall be found out for the whole tube bundle according to the principle of equal heat transfer, and the steam inlet nozzles shall be respectively arranged on each thermal central line, as shown in Fig. 22-19. However, the distance between the two nozzles shall not be less than that shown in figure 22-19. However, the distance between the two nozzles shall not be less than the minimum dimension specified in figure 22-19. If not, the nozzles should be staggered so that they are not on the same longitudinal axis.
For the horizontal heater without built-in drainage cooling zone, the amount of condensate flowing from the tube bundle is different everywhere. Therefore, a flow center line should be found to make the drainage flow rate on both sides of the drain outlet connecting pipe installed on the central line equal and not greater than that in the drain outlet connection pipe. If the above requirements cannot be met, the drainage flow area at the lower part of the heater should be increased.
1.3.3.2. Header type high pressure heater. The header type high pressure heater is divided into feed water inlet and outlet header, serpentine pipe system and shell in structure.
The header type high pressure heater replaces the tubesheet of the traditional U-tube heater with the feed water inlet header and feed water outlet header, as shown in Fig. 22-20
The two headers are connected by serpentine tube bundles, as shown in Fig. 22-21
The serpentine heat exchange tube is butted with the header, as shown in Fig. 22-22.
The feed water entering the header in this way does not produce direct erosion on the serpentine heat exchange tube, which can effectively avoid the impact water damage. The shell, interface and other parts are similar to the U-tube heater.
This kind of high-pressure heater has larger steam inlet area, lower steam flow rate and smaller impact force. It can effectively protect the steam stagnant inner layer on the surface of heat exchange tube, so that the surface wall temperature of heat exchange pipe will not exceed the creep temperature of heat exchange pipe, so as to avoid serious tube explosion.
High pressure heaters with high reliability should be selected for high pressure heaters of supercritical generating units above 900 MW in large power stations.
2. Main technical parameters (see table 22-4 ~ table 22-9)
Table 22-4 technical parameters of 1000MW supercritical high pressure heater
| Heater number Design parameters |
HH1 | HH2 | HH3 |
| Heater type | Horizontal U-tube | Horizontal U-tube | Horizontal U-tube |
| Number of heaters (unit) | 2 | 2 | 2 |
| Heating area（m2） | 1647 | 2047 | 1406 |
| Shell side design pressure（MPa） | 10.39 | 5.87 | 2.76 |
| Shell side design temperature（℃/℃） | 460/315 | 380/276 | 525/232 |
| Design pressure of tube side（MPa） | 37 | 37 | 37 |
| Design temperature of tube side（℃） | 335 | 296 | 252 |
| Shell side test pressure（MPa） | 12.99 | 7.34 | 3.45 |
| Tube side test pressure（MPa） | 46.25 | 46.25 | 46.25 |
Table 22-5 technical parameters of 600MW high pressure heater
| Item | HH1 | HH2 | HH3 | |||
| Tube pass | Shell pass | Tube pass | Shell pass | Tube pass | Shell pass | |
| Design pressure（MPa） | 37 | 8.09 | 37 | 5.53 | 37 | 2.49 |
| Max. working pressure（MPa） | 30.34 | 7.45 | 30.34 | 4.906 | 30.34 | 2.36 |
| Design temperature（℃/℃） | 317 | 406/297 | 292 | 348/272 | 246 | 492/226 |
| Corrosion allowance（mm） | 1 | 1 | 1 | 1 | 1 | 1 |
| Welded joint coefficient | 1 | 1 | 1 | 1 | 1 | 1 |
| Hydrostatic test pressure（MPa） | 46.25 | 10.5 | 46.25 | 7 | 46.25 | 3.11 |
| Heat exchange area（m2） | 1880 | 2032 | 1425 | |||
| Opening pressure of safety valve（MPa） | 37 | 8.09 | 37 | 5.53 | 37 | 2.49 |
| Container type | ⅢME | ⅢME | ⅢME | |||
| Form | Horizontal | Horizontal | Horizontal | |||
Table 22-6 technical parameters of 300MW high pressure heater
| Item | HH1 | HH2 | HH3 | |||
| Tube pass | Shell pass | Tube pass | Shell pass | Tube pass | Shell pass | |
| Design pressure（MPa） | 27.5 | 7.3 | 27.5 | 4.7 | 27.5 | 2.16 |
| Design temperature（℃/℃） | 290 | 420/290 | 265 | 360/265 | 220 | 455/220 |
| Corrosion allowance（mm） | 1 | 1 | 1 | 1 | 1 | 1 |
| Welded joint coefficient | 1 | 1 | 1 | 1 | 1 | 1 |
| Hydrostatic test pressure（MPa） | 41.25 | 11.01 | 41.25 | 7.05 | 41.25 | 3.24 |
| Heat exchange area（m2） | 1025 | 1110 | 885 | |||
| Opening pressure of safety valve（MPa） | 25.4 | 7.3 | 25.4 | 4.7 | 25.4 | 2.16 |
| Container type | ⅢME | ⅢME | ⅢME | |||
| Form | Horizontal or inverted | Horizontal or inverted | Horizontal or inverted | |||
Table 22-7 technical parameters of 1000MW supercritical low pressure heater
| Item | 5# Low pressure heater（LH5） | 6# Low pressure heater（LH6） | 7#+8# composed low pressure heater | ||
| （LH7+LH8） | |||||
| Heater code | LH-5 | LH-6 | LH-7 | LH-8 | |
| Form | Horizontal U-tube | Horizontal U-tube | Horizontal U-tube | ||
| Total heat transfer area（m2） | 1108 | 8638 | 715 | 816 | |
| Flow pass quantity (tube pass/shell pass) | 2 | 2 | 2 | 2 | |
| Design pressure（MPa） | Tube side | 4 | 4 | 4 | 4 |
| Shell side | 0.5+vacuum | 0.35+vacuum | 0.35+vacuum | 0.35+vacuum | |
| Design temperature（℃） | Tube side | 160 | 150 | 150 | 150 |
| Shell side | 260 | 150 | 150 | 150 | |
| Design flow（t/h） | Tube side | 1400 | 1400 | 700 | 700 |
| Shell side | 95 | 48 | 44 | 41 | |
Table 22-8 technical parameters of 600MW low pressure heater
| Heater number Design parameters |
LH-5 | LH-6 |
| Heater type | Horizontal U-tube | Horizontal U-tube |
| Number of heaters (unit) | 1 | 1 |
| Heating area（m2） | 1749 | 1991 |
| Shell side design pressure（MPa） | 0.68 | 0.35 |
| Shell side design temperature（℃/℃） | 335/170 | 265/148 |
| Design pressure of tube side（MPa） | 4 | 4 |
| Design temperature of tube side（℃） | 170 | 148 |
| Shell side test pressure（MPa） | 1.02 | 0.53 |
| Tube side test pressure（MPa） | 6 | 6 |
Table 22-9 technical parameters of 300MW low pressure heater
| Heater number Design parameters |
LH-5 | LH-6 | LH-7 | LH-8 |
| Heater type | Horizontal U-tube | Horizontal U-tube | Horizontal U-tube | |
| Number of heaters (unit) | 1 | 1 | 1 | 1 |
| Heating area（m2） | 605 | 549 | 768 | 798 |
| Shell side design pressure（MPa） | 0.52/-0.1 | 0.52/-0.1 | 0.35/-0.1 | 0.35/-0.1 |
| Design temperature of shell side（℃） | 160 | 160 | 150 | 150 |
| Design pressure of tube side（MPa） | 4 | 4 | 4 | 4 |
| Design temperature of tube side（℃） | 160 | 160 | 150 | 150 |
3.Selection method
The technical parameters of feed water heater vary greatly due to the different turbine parameters and the requirements of the owner's Design Institute. The typical technical parameters used for type selection are shown in table 22-4 to table 22-9
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