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Horizontal high pressure feed water heater

key word:Heat exchange element


Product description

Horizontal high pressure feed water heater

 

1. Introduction

1.1. Application

High pressure heater with horizontal structure is mainly used for high parameter and large capacity units of large power station, and large bypass system is adopted for system layout, which is mainly used for 300 ~ 1000MW units; inverted vertical structure is mainly used for 330MW generating units.

The horizontal high-pressure feed water heater adopts two large and one small system configuration structure, and the heat exchange pipe adopts U-shaped tube form. The steam extraction of steam turbine is mainly used to heat the boiler feed water to make it reach the required feed water temperature, so as to improve the thermal efficiency of the power plant and save fuel.

1.2. Model meaning

JG**-##

JG -- Code of high pressure heater

**--------Heat exchange area (m2)

##-----------Extraction stages of steam turbine

1.3. Structural features (see Figure 21-1 and figure 21-2)

1.3.1. Water chamber structure of high pressure heater:

1.3.1.1. Hemispherical head is used in the water chamber (see Fig. 21-3), and the water inlet and outlet connecting pipes and elliptical manhole are set on the head. The manhole cover can be easily taken out by special tools. The sealing gasket material is stainless steel wire and flexible graphite.

1.3.1.2. The water chamber of high pressure heater is divided into two independent chambers, i.e. feed water inlet area and feed water outlet area. The feed water inlet area is to evenly distribute the feed water to the heat exchange pipe, and the feed water outlet area is to collect the heated water in the heat exchange pipe and send it out of the high-pressure heater. The split diaphragm in the water chamber adopts the independent cladding structure formed by pressing and then welding, which greatly reduces the thermal stress and avoids the phenomenon that the split diaphragm is directly connected with the water chamber head, which leads to the pull-down crack of the welded joint under the action of thermal stress.

1.3.1.3. In order to facilitate the maintenance of high-pressure heater, a special maintenance hole is set on the water chamber shell, and a safe and reliable concave convex sealing structure is adopted. The maintenance cover plate is connected by bolts and nuts, which is convenient for assembly and disassembly.

1.3.1.4. The special expansion joint (see Fig. 21-3) is used to connect the water chamber shell and the water supply outlet connecting pipe, which can expand freely, greatly reduce the influence of thermal stress and ensure the sealing of water chamber shell.

1.3.2. Piping structure of high pressure heater;

1.3.2.1. The piping system of high pressure heater is mainly composed of tube sheet, heat exchange tube, diaphragm, cladding and support plate. For horizontal U-tube high-pressure heater, the tube bundle is divided into three heat transfer zones, namely superheated steam cooling section, steam condensation section and drain cooling section. For the inverted vertical high pressure heater, when the superheat is large, the external steam cooler is often set.

1.3.2.2. The superheated steam cooling section is designed to make full use of the superheat degree of steam to heat the feed water in the pipe. In the structure, the overall pressed cladding and diaphragm form an independent sealing space. Steam channels are set at the inlet and outlet of superheated section to avoid direct impact of steam on heat exchange tube. The superheated steam cooling section is connected with the extraction inlet pipe with a special adjusting ring structure (see Fig. 21-4), which is convenient for assembly and can eliminate the thermal stress during operation.

1.3.2.3. The steam condensation section is the main heat exchange area of the high-pressure heater. In this section, the steam changes into saturated water and releases a lot of heat to heat the boiler feed water in the pipe. The condensed saturated water and the drain water from the heater accumulate at the bottom of the shell and flow to the drain cooling section. The clapboard of condensation section adopts rectangular plate, which increases the space of steam flow and makes the steam flow into the tube bundle centripetally. There is also a special continuous steam exhaust device in the center of the diaphragm, which can discharge non condensable gas continuously during operation, avoid corrosion of the tube bundle and ensure good thermal effect. For the condensation section of the inverted vertical high-pressure heater, a special steam and water diversion device is also provided.

1.3.2.4. In the drainage cooling section, the saturated water is turned into supercooled water to release heat to heat the boiler feed water. The integral pressed clad plate is used for independent sealing in this section, and the special drainage submerged tank structure is adopted at the inlet area of the drainage cooling section (see Fig. 21-5) to reduce the drainage flow rate and make the drainage water level more stable and reliable; There is enough diving depth in the drain submergence tank to ensure that the siphon of the high-pressure heater will not be damaged at low water level, so it has reliable water seal. The drainage outlet area adopts a unique drainage chamber structure to avoid erosion of the drain outlet, which has reliable sealing performance and can ensure smooth drainage.

1.3.2.5. The tube sheet adopts deep bowl shaped forging, which can increase the water chamber space; the surface of tube sheet is overlaid with low carbon steel, which is convenient for welding with heat exchange tube.

1.3.2.6. The connection between heat exchange tube and tube sheet is the key point of high pressure heater quality control. The unique concave welding and full hydraulic expansion connection (see Fig. 21-6) are adopted to ensure the reliability of pipe end connection. At the same time, the inner wall of the heat exchange tube in the feed water inlet area is lined with stainless steel anti-wear sleeve, and the anti impact pressing plate with trumpet shaped hole is set above it, so as to effectively ensure that the pipe end welding joint is not eroded.

1.3.2.7. Continuous exhaust device is set in the center of condensation section. Since the steam carries air and other non condensable gases into the heater, it will form a gas layer around the condensate film on the outer wall of the heat exchange tube, which increases the heat transfer resistance at the steam side and reduces the heat exchange efficiency. Therefore, it is necessary to set up a continuous non condensable gas discharge device. Because the heat transfer in different areas of the whole condensation section is different, the amount of non condensable gas generated in different areas is also different. Therefore, a reasonable and perfect non condensable gas exhaust system is a powerful guarantee for high-pressure heater to have good heat transfer efficiency.

1.3.2.8. Enough supporting plates and diaphragms shall be installed inside the piping system with proper spacing to avoid bundle vibration under all operating conditions. The tube hole on the clapboard and tube plate is concentric with the tube bundle, and the tube hole is processed by reaming hole and chamfering on both sides, and the burr is removed to prevent the tube bundle from being scratched. The assembly of support plate and diaphragm allows free sliding.

1.3.3. Shell structure of high pressure heater:

1.3.3.1. The shell is mainly composed of cylinder body, standard elliptical head, support, nozzle seat, upper drainage inlet anti scour device, etc.

1.3.3.2. The upper level drain water enters the first stage high-pressure heater with high pressure and vaporizes rapidly after entering the first stage high-pressure heater with low pressure. The water droplets move with high-speed steam flow, and the steam and drainage two-phase fluid impact the tube bundle at the same time, which will cause serious erosion of the tube bundle in this area. The design of the protection device at the upper level drainage inlet should not only consider enough expansion space, but also have a large protection area, so as to avoid the upper level water directly impacting the heat exchange pipe. Therefore, it is very important to set up a double stainless steel protection device in the upper water inlet area to separate the steam and water, and completely eliminate the erosion problem at the upper water inlet (see Fig. 21-7).

1.3.3.3. There are two sliding supports with rollers on the shell, which can facilitate shell extraction and on-site installation; the fixed support is usually set on the tube plate, and the sliding support with roller in the middle should be removed before putting into operation, so as to avoid static instability caused by three supports. The skirt support is usually set on the shell side head for the upright type, and two ear seats are set on the tube plate for the inverted vertical type.

1.3.4. The shell of high-pressure feed water heater is of fully welded structure. For maintenance, the shell is marked with field cutting line.

1.3.5. The steam side of high-pressure feed water heater is equipped with pressure relief safety valve.

1.3.6 large bypass system is adopted for high-pressure feed water heater. One unit shares one water side pressure relief valve, which is set on the water supply pipeline.

1.3.7. The steam side and water side of the high-pressure feed water heater are provided with water outlets, which are used to relieve pressure and drain water during shutdown and maintenance.

1.3.8. The steam side and water side of the high-pressure feed water heater are equipped with steam outlets, which are used to exhaust steam during start-up and continuous operation.

1.3.9. The high-pressure feed water heater is equipped with low water level (alarm and close drain control valve), normal water level, high-level one water level (alarm), high-level two water level (alarm and open emergency drain control valve), high-pressure three-way water level (close feed water inlet and outlet three-way valves, close extraction inlet valve, and high-pressure heater disconnection).

1.3.10. The high-pressure heater is equipped with liquid level sampling and measuring interface to meet the requirements of high-pressure heater water level control and ensure the accuracy of field reading.

 

2. Main technical parameters and product appearance

2.1. Main technical parameters (sorted by extraction pressure of steam turbine from high to low, see table 21-1 ~ table 21-5)

Table 21-1 main technical parameters of high pressure heater for 300MW subcritical unit

Item #1 High pressure heater #2 High pressure heater #3 High pressure heater
Feed water flowt/h 949.8 949.8 949.8
Feed water pressure [MPa(a)] appa. 20.52 appa. 20.52 appa. 20.52
Feed water inlet temperature(℃) 243 200.5 178
Enthalpy of feed water inletkJ/kg 1053.8 862.8 764.3
Feed water outlet temperature(℃) 275.7 243 200.5
Enthalpy of feed water outletkJ/kg 1209.8 1053.8 862.8
Extraction steam flowt/h 71.547 77.735 30.663
Extraction pressure [MPa(a)] 5.86 3.528 1.57
Extraction inlet temperature(℃) 387 320.24 437.26
Extraction inlet enthalpykJ/kg 3149 3031 3335.3
Upper drainage flowt/h 71.547 149.285
Drain inlet temperature () 248.6 206.1
Enthalpy at drain inlet (kJ/kg) 1078.9 880.1
Discharge drainage flowt/h 71.547 149.285 179.949
Drain outlet temperature () 248.6 206.1 183.6
Enthalpy of drain outletkJ/kg 1078.9 880.1 778.7
Design pressure of pipe sideMPa 27.5 27.5 27.5
Design temperature of tube side(℃) 315 280 240
Shell side design pressureMPa 7.5 4.7 2.2
Shell side design temperature (short section / long section)(℃/℃) 420/295 360/260 470/220
Upper end difference(℃) -1.7 0 0
Lower end difference(℃) 5.6 5.6 5.6
Allowable pressure drop on pipe sideMPa 0.1 0.1 0.1
Allowable pressure of each section on shell side MPa 0.035 0.035 0.035

 

Table 21-2 main technical parameters of high pressure heater for 600MW Subcritical unit

Item #1 High pressure heater #2 High pressure heater #3 High pressure heater
Feed water flowt/h 1934.12 1934.12 1934.12
Feed water pressure [MPa(a)] appa. 20.12 appa. 20.12 appa. 20.12
Feed water inlet temperature(℃) 247.7 208.1 177.2
Enthalpy of feed water inletkJ/kg 1076.1 896.41 760.95
Feed water outlet temperature(℃) 277.8 247.7 208.1
Enthalpy of feed water outletkJ/kg 1220.6 1076.1 896.41
Extraction steam flowt/h 136.71 151.985 85.66
Extraction pressure [MPa(a)] 6.058 3.828 1.838
Extraction inlet temperature(℃) 387.4 324.2 441.7
Extraction inlet enthalpykJ/kg 3146 3032.9 3341.3
Upper drainage flowt/h 136.71 288.695
Drain inlet temperature () 253.3 213.7
Enthalpy at drain inlet (kJ/kg) 1101.8 914.6
Discharge drainage flowt/h 136.71 288.695 371.62
Drain outlet temperature () 253.3 213.7 182.8
Enthalpy of drain outletkJ/kg 1101.8 914.6 775.3
Design pressure of pipe sideMPa 28 28 28
Design temperature of tube side(℃) 310 280 240
Shell side design pressureMPa 7.5 4.7 2.3
Shell side design temperature (short section / long section)(℃/℃) 430/290 365/260 485/220
Upper end difference(℃) -1.7 0 0
Lower end difference(℃) 5.6 5.6 5.6
Allowable pressure drop on pipe sideMPa 0.1 0.1 0.1
Allowable pressure of each section on shell side MPa 0.035 0.035 0.035

 

Table 21-3 main technical parameters of high pressure heater for 600 MW Supercritical Unit

Item #1 High pressure heater #2 High pressure heater #3 High pressure heater
Feed water flowt/h 1807.902 1807.902 1807.902
Feed water pressure [MPa(a)] appa. 29.7 appa. 29.7 appa. 29.7
Feed water inlet temperature(℃) 256.7 218.4 189.4
Enthalpy of feed water inletkJ/kg 1119.1 945.8 818.7
Feed water outlet temperature(℃) 280.5 256.7 218.4
Enthalpy of feed water outletkJ/kg 1232.4 1119.1 945.8
Extraction steam flowt/h 106.336 144.853 76.108
Extraction pressure [MPa(a)] 6.31 4.45 2.25
Extraction inlet temperature(℃) 363.7 317 475.9
Extraction inlet enthalpykJ/kg 3072.1 2991.5 3410.6
Upper drainage flowt/h 106.336 251.189
Drain inlet temperature () 262.3 224.1
Enthalpy at drain inlet (kJ/kg) 1146.3 962.5
Discharge drainage flowt/h 106.336 251.189 327.297
Drain outlet temperature () 262.3 224.1 195
Enthalpy of drain outletkJ/kg 1146.3 962.5 830.1
Design pressure of pipe sideMPa 34 34 34
Design temperature of tube side(℃) 315 295 255
Shell side design pressureMPa 7.9 5.6 2.8
Shell side design temperature (short section / long section)(℃/℃) 410/295 360/275 510/235
Upper end difference(℃) -1.7 0 0
Lower end difference(℃) 5.6 5.6 5.6
Allowable pressure drop on pipe sideMPa 0.1 0.1 0.1
Allowable pressure of each section on shell side MPa 0.035 0.035 0.035

 

Table 21-4 main technical parameters of high pressure heater for 600 MW Ultra Supercritical Unit

Item #1 High pressure heater #2 High pressure heater #3 High pressure heater
Feed water flowt/h 1709.232 1709.232 1709.232
Feed water pressure [MPa(a)] appa. 30.29 appa. 30.29 appa. 30.29
Feed water inlet temperature(℃) 259.7 213.5 185.6
Enthalpy of feed water inletkJ/kg 1133.1 924.7 802.9
Feed water outlet temperature(℃) 289.2 259.7 213.5
Enthalpy of feed water outletkJ/kg 1274.4 1133.1 924.7
Extraction steam flowt/h 120.453 155.356 66.034
Extraction pressure [MPa(a)] 7.17 4.67 2.05
Extraction inlet temperature(℃) 405.2 345.2 484.7
Extraction inlet enthalpykJ/kg 3165.6 3061.3 3433.1
Upper drainage flowt/h 120.453 275.809
Drain inlet temperature () 265.3 219.1
Enthalpy at drain inlet (kJ/kg) 1161.2 939.6
Discharge drainage flowt/h 120.453 275.809 341.843
Drain outlet temperature () 265.3 219.1 191.2
Enthalpy of drain outletkJ/kg 1161.2 939.6 812.8
Design pressure of pipe sideMPa 36 36 36
Design temperature of tube side(℃) 325 300 250
Shell side design pressureMPa 9 5.8 2.6
Shell side design temperature (short section / long section)(℃/℃) 435/305 380/280 520/230
Upper end difference(℃) -1.7 0 0
Lower end difference(℃) 5.6 5.6 5.6
Allowable pressure drop on pipe sideMPa 0.1 0.1 0.1
Allowable pressure of each section on shell side MPa 0.035 0.035 0.035

 

Table 21-5 main technical parameters of high pressure heater for 1000 MW Ultra Supercritical Unit

Item #1 High pressure heater #2 High pressure heater #3 High pressure heater
Feed water flowt/h 2944.66 2944.66 2944.66
Feed water pressure [MPa(a)] appa. 34 appa. 34 appa. 34
Feed water inlet temperature(℃) 261.2 220.8 190.2
Enthalpy of feed water inletkJ/kg 1139.9 955.7 821.1
Feed water outlet temperature(℃) 300.7 261.2 220.8
Enthalpy of feed water outletkJ/kg 1333.4 1139.9 955.7
Extraction steam flowt/h 279.321 233.291 123.275
Extraction pressure [MPa(a)] 8.73 4.931 2.429
Extraction inlet temperature(℃) 429.9 348.3 500.8
Extraction inlet enthalpykJ/kg 3208.2 3066.5 3465.1
Upper drainage flowt/h 279.321 512.612
Drain inlet temperature () 266.8 226.4
Enthalpy at drain inlet (kJ/kg) 1168 974
Discharge drainage flowt/h 279.321 512.612 635.887
Drain outlet temperature () 266.8 226.4 195.8
Enthalpy of drain outletkJ/kg 1168 974 833.8
Design pressure of pipe sideMPa 37 37 37
Design temperature of tube side(℃) 335 300 255
Shell side design pressureMPa 10.4 5.9 2.9
Shell side design temperature (short section / long section)(℃/℃) 460/315 375/280 530/235
Upper end difference(℃) -1.7 0 0
Lower end difference(℃) 5.6 5.6 5.6
Allowable pressure drop on pipe sideMPa 0.1 0.1 0.1
Allowable pressure of each section on shell side MPa 0.035 0.035 0.035

 

2.2. Product appearance (in order of extraction pressure of steam turbine from high to low, see table 21-6 ~ table 21-10)

Table 21-6 main structural dimensions of high pressure heater for 300MW subcritical unit

Item #1 high pressure heater #2 high pressure heater #3 high pressure heater
Heat exchange aream2 1100 1100 780
Overall dimension (length × width × height)mm×mm×mm 11112×1900×2480 11672×1875×2455 9200×1860×2440
Shell extraction length (mm) 8060 8820 6250
Net weight of equipment (kg) 48000 41000 31000
Running weight (kg) 55000 49000 36500
Full water weight (kg) 61750 56800 41800

 

Table 21-7 main structural dimensions of high pressure heater for 600MW Subcritical unit

Item #1 high pressure heater #2 high pressure heater #3 high pressure heater
Heat exchange aream2 2200 2100 16000
Overall dimension (length × width × height)mm×mm×mm 11820×2446×3330 11890×2412×3330 9865×2400×3330
Shell extraction length (mm) 8730 8550 5625
Net weight of equipment (kg) 93000 78500 60000
Running weight (kg) 106300 92200 70900
Full water weight (kg) 119800 106260 82200

 

Table 21-8 main structural dimensions of high pressure heater for 600 MW Supercritical Unit

Item #1 high pressure heater #2 high pressure heater #3 high pressure heater
Heat exchange aream2 2400 2100 1500
Overall dimension (length × width × height)mm×mm×mm 12170×2590×3330 11570×2555×3330 9275×2550×3330
Shell extraction length (mm) 9085 7995 5750
Net weight of equipment (kg) 113500 95000 72000
Running weight (kg) 128700 107000 83100
Full water weight (kg) 144800 123000 94400

 

Table 21-9 main structural dimensions of high pressure heater for 600 MW Ultra Supercritical Unit

Item #1 high pressure heater #2 high pressure heater #3 high pressure heater
Heat exchange aream2 1970 2000 1500
Overall dimension (length × width × height)mm×mm×mm 10980×2550×3350 11600×2515×3350 9600×2505×3350
Shell extraction length (mm) 7690 7880 5710
Net weight of equipment (kg) 106000 94000 71500
Running weight (kg) 119000 107300 82300
Full water weight (kg) 131700 121400 93500

 

Table 21-10 main structural dimensions of high pressure heater for 1000MW Ultra Supercritical Unit

Item #1 high pressure heater #2 high pressure heater #3 high pressure heater
System layout Double series, large bypass
Quantity of high pressure heater of single unit (set) 2 2 2
Heat exchange aream2 1650 1730 1280
Overall dimension (length × width × height) mm×mm×mm 10453×2425×3285 11309×2385×3285 9287×2390×3285
Shell extraction length (mm) 6945 6951 5529
Net weight of equipment (kg) 97000 82000 64000
Running weight (kg) 107500 93400 73300
Full water weight (kg) 117860 105250 82550

 

3. Selection method

According to the main technical parameters table, heat balance diagram of steam turbine under various working conditions, special requirements for design conditions and design parameters, special requirements for structure and performance assessment indexes, the area of high-pressure heater is preliminarily selected after calculation, and then the form of high-pressure heater is finally selected according to the provisions and technical requirements in the technical agreement.

The technical agreement of high-pressure heater shall be signed before supply, including main technical parameters of high-pressure heater, natural conditions (environmental temperature, altitude, earthquake and wind load, etc.), specific requirements for equipment body, specific types, specifications, quantities and relevant requirements of valves and accessories, and specific types, specifications, quantities and relevant requirements of instrument control elements.

 

4. Scope of supply

4.1. High pressure heater body, including support and anchor bolt.

4.2. Safety valves on the tube and shell side.

4.3. Local magnetic flap water level gauge.

4.4. Pressure gauge.

4.5. Bimetallic thermometer.

4.6. Balance container.

4.7 primary valve of instrument (refers to the primary valve connecting water level gauge, balance vessel and pressure gauge).

4.8. Primary valves for water and gas discharge at pipe and shell side.

4.9. Shell side continuous exhaust valve and orifice.

4.10. Shell side nitrogen filling interface and primary valve.

4.11. Hook nail and self-locking pressing plate for thermal insulation.

4.12. Manhole gasket (spare part).

4.13. Special tools for dismantling manhole.