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High and low pressure heaters

key word:Heat exchange element


Product description

High and low pressure heaters

 

1. Introduction

1.1. Purpose

The high and low pressure heater is one of the main auxiliary equipment in the regenerative system of power plant. It is a kind of heat exchange equipment which uses the extraction steam of steam turbine to heat the feed water to improve the heat efficiency of the unit. The feed water heater is arranged between the condensate pump and the boiler, among which the low-pressure heater is arranged between the condensate pump and the deaerator, and the high-pressure heater is arranged between the feed water pump and the boiler.

1.2. Model meaning

1.2.1. High pressure heater

JG-**-##-&&

JG code of high pressure heater

**-------Heating area of heater (M2)

##----------Design sequence

&&-------------Feed flow direction sequence

1.2.2. Low pressure heater

JD-**-##-&&

JD --- serial number of low pressure heater

**-------Heating area of heater (M2)

##----------Design sequence

&&-------------Feed flow direction sequence

Example: JG-1834-1-2 indicates that the heater area is 1834m2, the second stage high-pressure heater designed for the first time; JD-1700-1-4 indicates that the heater is the fourth stage low-pressure heater with heating area of 1700m2.

1.3. Structural features

1.3.1. Structural form:

1.3.1.1. Classification of heaters (see table 23-1 and figure 23-1 to figure 23-3).

Table 23-1 classification of heaters

Classification method Types Advantages Disadvantages
Acccording to the layout form Vertical In order Simple structure, large drainage volume and small floor area The accumulated water in the heat transfer tube can not be drained out, and the core pulling is not convenient
Invertsee fig. 23-2 Simple structure, reasonable layout and less land occupation The drainage volume is small and the water level is difficult to control
Horizaontalsee fig. 23-1 Simple structure, reasonable layout, convenient maintenance and large drainage volume It occupies a lot of land and is inconvenient to control water level
According to the structure Sealing form Flange bolt seal Small opening  [ see fig. 23-3a] Compact structure, small size When used in high pressure, the sealing effect is poor
Big  opening  [ see fig. 23-3b] Large maintenance space and convenient manufacturing High manufacturing cost, inconvenient disassembly and poor sealing effect
Pressure self sealing Small opening  [ see fig. 23-3c] Compact structure, sealing effect, easy disassembly and assembly It is convenient for personnel to get in and out
Big  opening  [ see fig. 23-3d] The maintenance space is large and the sealing effect is good Large volume, high cost, only suitable for vertical arrangement
Template seal [see 23-3e] The sealing effect is good and the structure is simple Inconvenient maintenance
Form of heat transfer tube Spiral tube The high-pressure water chamber and tube sheet are omitted, which can bear large temperature change rate Large volume, low thermal efficiency, high quality, many materials and easy leakage of welding joint
Serpentine tube
Straight tube The structure is simple and the assembly is convenient Free expansion of heat transfer tube should be considered
U tube Compact structure, reasonable arrangement and free expansion of heat transfer tube The tube to tubesheet connection requires strict control of temperature change rate

1.3.1.2. The sealing form of heater water chamber is shown in Fig. 23-3.

1.3.2. Structure description. The heat transfer tube of the heater flows through the feed water or condensate; outside the heat transfer tube is heating steam, which condenses into drain water and accumulates at the bottom of the shell, and then is discharged from the drain port. In order to make more effective use of the superheat of the extraction steam and make the drain of the shell have a certain degree of supercooling, the heat transfer surface is often divided into three parts: superheated steam cooling section, condensation section and drain cooling section. Condensation section is condensation heat transfer, superheated steam cooling section and drain cooling section are convective heat transfer. The heat transfer surface is sealed with cladding and equipped with appropriate guide baffle to make steam or drain flow through the heat transfer surface at a certain speed and direction.

1.3.3. Description of important parts:

1.3.3.1. Heat transfer tube. Whether the material and specification of the heat transfer tube of the feed water heater is appropriate or not will have an important impact on the life, reliability, safety and cost of the heater. See table 23-2 for the maximum service temperature of various heat transfer tubes

Table 23-2 maximum service temperature of various heat transfer tubes

Tube material Temperature () Tube material Temperature ()
Carbon steel 425 Copper nickel B10 315
Austenitic stainless steel 425 B30 (annealed) 370
Tin brass HSn70-1 230 B30 (stress relief) 425
Brass H68A with Arsenic 200

 

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 23-3 in any case.

Table 23-3 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

 

 

1.3.3.2. Tubesheet. See table 23-4 for the arrangement of tubesheet, hole arrangement and connection between tube and tubesheet

Table 23-4 arrangement, hole arrangement and connection of tubesheet

1.3.3.3. Diaphragms. The diaphragm in the steam side shell of the heater can be divided into guide plate and support plate. The role of the guide plate is to make the shell side fluid flow through the tube bundle at a certain speed and direction; the role of the support plate is to reduce the deflection of the heat transfer tube and improve the stiffness of the tube bundle. The two kinds of diaphragms can play an anti vibration role. In order to make the medium outside the tube sweep the tube bundle at a certain velocity and direction, the guide plate is usually provided with a gap. The gap and spacing of the guide plate should be selected appropriately to ensure the heat transfer effect and avoid excessive pressure drop and vibration.

1.3.3.4. Nozzle. The inner and outer diameter of the nozzle shall be calculated, and the inner diameter shall be selected to make the flow rate of medium in the pipe meet the requirements. For the inlet and outlet of water supply, the flow rate in the pipe shall not be greater than 3m/s; for the drain outlet, the flow rate shall not be greater than 1.2m/s.

1.3.3.5. Protection system. If the heater fails or the heat transfer tube leaks, the high-pressure water will enter the shell, causing the normal water level to fluctuate, and even the water will return to the steam turbine from the extraction port, thus causing the main engine to have an accident. Therefore, the protection system must be set up to prevent the accident.

1.3.3.6. Feed water bypass system. In the large bypass protection system (see Fig. 23-4), a hydraulic or electric three-way valve and an outlet gate valve are used to complete the bypass function of water supply. In addition, the drain control valve, emergency drain valve and safety valve form a complete protection system.

The difference between the small bypass protection system (see figure 23-5) and the large bypass protection system is that each high-pressure heater can be disconnected separately, and other heaters can continue to operate.

1.3.3.7. Safety valve. The safety valve should be correctly selected according to the following principles: there is no discharge requirement for the pressure relief valve on the pipe side. Once opened, the pressure will drop rapidly. Generally, the micro lift safety valve with nozzle diameter of DN20 is selected. The design temperature and pressure of shell side safety valve shall be equal to the design temperature (saturation temperature) and design pressure of shell side of heater body. The discharge of the shell side safety valve shall be 10% of the maximum overload water supply through the heater, and the diameter shall be determined based on this.

1.3.4. Description of important characteristics:

1.3.4.1. Temperature change rate. With the continuous increase of unit parameters, the volume of single piece of high-pressure heater is also increasing. Large forgings and thick plates are widely used, and the requirements of limiting thermal stress impact are more and more strict. In order to avoid excessive thermal stress impacting the heater body and causing unnecessary loss, the startup and shutdown of feed water heater should strictly comply with the provisions of temperature rise rate and temperature drop rate. The results show that the temperature rise rate and temperature drop rate should be controlled within 1.85 ℃ / min, and no more than 3.7 ℃ / min at most; with the increase of temperature change rate, the faults will increase obviously and the heater life will be shortened obviously. The feasible method to control the rate of temperature change is to monitor the change of feed water outlet temperature.

1.3.4.2. Thermal commissioning of water level. The geometric position of normal water level should be marked before the water heater is manufactured and delivered. However, due to the different positions of the upper and lower interfaces for water level sampling, different velocity will produce different static pressure under the Bernoulli effect. In this way, there will be a static pressure difference between the upper and lower sampling ports, so that the water level displayed by the instrument is higher than the real water level inside the vessel, which is especially obvious in the horizontal heater, and the water level difference sometimes reaches more than 50 mm. For the heater with built-in drain cooling section, the water level difference will make the inlet of the drain cooling section come out of the water surface, causing steam to enter into the drain cooling section, thus endangering the heater. Since it is difficult to accurately estimate the medium flow rate in the vessel in advance, the appropriate water level can only be determined by hot commissioning after the heater is put into operation.

1.3.4.3. Water quality requirements of feed water heater. The heat transfer tube wall of the heater is thin and easy to be damaged by corrosion. Therefore, some requirements for water quality shall be put forward: ① for carbon steel pipe heater, the pH value of inlet feed water shall not be less than 9.6, and the pH value of the whole system shall be kept between 9.3 and 9.6; ② the concentration of dissolved oxygen in the feed water shall not exceed 7 μg / L; ③ the iron ion concentration in the outlet feed water and drain water of the heater shall be less than 5 μg / L; ④ For heaters using copper and copper alloy tubes as heat transfer tubes, the contents of dissolved ammonia and dissolved sulfur should also be controlled to avoid stress corrosion and damage of dezincification and nickel removal; ⑤ for heaters using austenitic stainless steel as heat transfer tubes, the content of chloride ions should be controlled to avoid stress corrosion.

2. Main technical parameters and product appearance

2.1. Main technical parameters

2.1.1. Main performance index of heater. The main performance indexes of the heater include feed water end difference, drain end difference, tube side pressure drop and shell side pressure drop.

2.1.1.1.1. The feed water end difference is the difference between the saturation temperature at the heater inlet extraction pressure and the feed water outlet temperature.

2.1.1.2. The drain end difference is the difference between the drain temperature leaving the heater shell and the feed water inlet temperature on the tube side.

2.1.1.3. The tube side pressure drop is the friction loss of the medium flowing through the heat transfer tube (including the pressure loss in the inlet and outlet chambers).

2.1.1.4. Shell side pressure drop is the pressure loss of medium flowing through the shell side of heater (excluding static pressure loss).

2.1.2. Main technical indexes (see table 23-5 and table 23-6).

Table 23-5 main technical indexes of high pressure feed water heater

Model Type Heating area Design pressure Working pressure Design temperature Working temperature Weight Remark
m2 (Tube side / Shell side)
(Mpa)
(Tube side / Shell side)
(Mpa)
(Tube side / Shell side)
()
(Tube side / Shell side)
()
t
JG-1025-3-3 Horizontal hemispherical water chamber
 
1025 28.05/7.25 22.59/6.16 295/420 278/388 39.48 Suit 300MW unit
JG-1110-3-2 1110 28.05/4.81 22.59/3.73 265/360 225/320 38.55
JG-885-3-1 885 28.05/2.07 22.59/1.70 215/470 195/440 29.1
JG-2063-1-3 2063 27.5/7.47 19.87/5.972 290/420 276.9/383.6 90.01 Suit 600MW subcritical units
JG-2231-1-2 2231 27.5/4.73 19.87/3.784 265/360 247.1/325 85
JG-1745-1-1 1745 27.5/2.07 19.87/1.655 215/460 203/429.1 63.2
JG-2520-1-3 2520 35/8.11 29/6.31 325/410 256.7/278.8 107.189 Suit 600MW Supercritical unit
JG-2460-1-2 2460 35/5.55 29.7/4.663 300/350 218.4/302.5 101.55
JG-1745-1-1 1745 35/2.8 29.7/2.249 258/510 190.4/469.1 72.177
JG-2050-1-3 2050 38.5/9.72 31.3/8.2 325/450 298.4/425.6 108 Suit 600MW Ultra Supercritical Unit
JG-2250-1-2 2250 38.5/6.37 31.3/5.128 300/390 265.5/359.3 109.7
JG-1650-1-1 1650 38.5/2.96 31.3/2.503 250/520 224/493.9 80.9
JG-1660-1-3 1660 38/9.63 33.71/8.372 310/441 299.9/418 86.86 Suit 1000MW Ultra supercritical unit (double row)
JG-1796-1-2 1796 38/7.44 33/6.042 295/405 276/367 90.88
JG-1308-1-1 1308 38/2.77 33.71/2.405 230/488 221.9/463.7 62.02
JG-3400-1-3 3400 39/9.39 36/7.919 310/444 294.3/401.1 171 Suit 1000MW Ultra supercritical unit (single row)
JG-3500-1-2 3500 39/7.14 32.402/6.045 290/400 276.1/362.8 186.72
JG-2600-1-1 2600 39/2.71 32.2/2.298 230/495 219.5/464.6 137.73

 

Table 23-6 main technical indexes of low pressure feed water heating

Model Type Heating area Design pressure Working pressure Design temperature Working temperature Weight Remark
m2 (Tube side / Shell side)
(Mpa)
(Tube side / Shell side)
(Mpa)
(Tube side / Shell side)
()
(Tube side / Shell side)
()
t
JD-530-7-4 Horizontal  U tube
 
530 3.92/0.686 2.45/0.554 164/332 153/155 13.05 Suit 300MW unit
JD-530-2-2 530 3.92/0.48 2.45/0.143 138/266 107.1/109.8 12.06
JD-1112-1-4 1112 3.62/0.396 2.5/0.3167 170/250 132.6/222.8 20.16 Suit 600MW subcritical units
JD-985-1-3 985 3.62/0.167 2/0.1334 120/170 105.1/137.5 25.28
JD-735-4-2 735 3.92/0.345 2.8/0.0574 150/150 82/86.1 36.59
JD-872-4-1 872 3.92/0.345 2.8/0.0219 150/150 59.3/63.2 36.59
JD-1550-1-2 1550 4/0.795 2.5/0.61 160/340 157.7/304.9 28.7 Suit 600MW Supercritical unit
JD-1280-1-1 1280 4.5/0.345 2.5/0.199 120/240 118.1/182.8 25.9
JD-1190-1-4 1190 4.5/0.75 1.6/0.598 170/330 138/275.1 23.63 Suit 600MW Ultra Supercritical Unit
JD-1170-1-3 1170 4.5/0.3 1.612/0.22 150/230 97.9/170.9 24.08
SL-200-2-1
(Drain cooler)
200 0.1/4.5 0.1/1.6 120/120 120/120 12
JD-1800-1-4 1800 4.5/0.85 1.392/0.635 173/330 158.3/283.1 31.38 Suit 1000MW Ultra supercritical unit 
JD-1700-1-3 1700 4.5/0.35 1.386/0.238 140/250 123/183.6 34.5
SL-368-2-1
(Drain cooler)
368 0.1/4.4 0.1/4.4 120/120 120/120 11.5
JD-1590-2-2 1590 4.5/0.1 1.486/0.0637 120/120 84.7/87.5 33.12
JD-1900-2-1 1900 4.5/0.1 1.543/0.0237 120/120 61/63.8 36.43

 

2.2. Product appearance

2.2.1. High pressure feed water heater (see figure 23-6 and table 23-7).

Table 23-7 product dimensions of high pressure feed water heater

Model L W H Remark
JG-1025-3-3 9580 2012 2300 Suit 300MW unit
JG-1110-3-2 11360 1964 2300
JG-885-3-1 9950 1936 2300
JG-2063-1-3 10770 2625 3007 Suit 600MW subcritical units
JG-2231-1-2 12098 2595 3007
JG-1745-1-1 10970 2570 3007
JG-2520-1-3 11571 2575 3107 Suit 600MW Supercritical unit
JG-2460-1-2 12850 2575 3107
JG-1745-1-1 9710 2540 3017
JG-2050-1-3 9750 2715 3107 Suit 600MW Ultra Supercritical Unit
JG-2250-1-2 11500 2665 3107
JG-1650-1-1 10000 2615 3107
JG-1660-1-3 9308 2645 2983 Suit 1000MW Ultra supercritical unit (double row)
JG-1796-1-2 11028 2615 2983
JG-1308-1-1 9753 2550 2983
JG-3400-1-3 10395 3200 3781 Suit 1000MW Ultra supercritical unit (single row)
JG-3500-1-2 12300 3300 3781
JG-2600-1-1 10963 3405 3781

 

2.2.2. Low pressure feed water heater (see figure 23-7 and table 23-8).

Table 23-8 product dimensions of low pressure feed water heater

Model L W H Remark
JD-530-7-4 10950 1723 2109 Suit 300MW unit
JD-530-2-2 10342 1723 2109
JD-1112-1-4 12580 2261 2660 Suit 600MW subcritical units
JD-985-1-3 12540 2261 2660
JD-735-4-2 15940 2200 2015
JD-872-4-1 15940 2200 2015
JD-1550-1-2 12280 2261 2660 Suit 600MW Supercritical unit
JD-1280-1-1 10745 2261 2660
JD-1190-1-4 12399 2131 2530 Suit 600MW Ultra Supercritical Unit
JD-1170-1-3 13099 1962 3421
SL-200-2-1
(Drain cooler)
7000 1428 1930
JD-1800-1-4 12540 2361 2730 Suit 1000MW Ultra supercritical unit
JD-1700-1-3 14514 2262 3810
SL-368-2-1
(Drain cooler)
9002 1930 1345
JD-1590-2-2 18660 2638 2187
JD-1900-2-1 18660 2638 2187

 

3. Selection method

The technical data provided by the equipment purchaser are as follows.

3.1. Environmental conditions for equipment operation

3.1.1. Operation conditions of steam turbine (heat balance diagram of each working condition of steam turbine).

3.1.2. Feed water quality entering the heater.

3.1.3. Type of water supply pump.

3.1.4. Environmental conditions.

3.2. Design conditions

3.2.1. Type of heater.

3.2.2. The turbine governing valve is fully open.

3.2.3. Rated condition of steam turbine.

3.3. Technical requirements

3.3.1. Equipment performance requirements.

3.3.2. Equipment manufacturing requirements.

3.3.3. Material requirements.

3.3.4. Welding requirements.

3.3.5. Instrument control requirements.

3.3.6 cleaning requirements.

3.3.7. Equipment marking requirements.

3.4. Quality assurance and test requirements

3.4.1. Standards adopted.

3.4.2. Equipment performance guarantee.

3.4.3. Equipment inspection and test.

3.4.4. Equipment packaging and transportation requirements.

 

4. Scope of supply

4.1. Heater body, including support and interface pipe socket in each system.

4.2. Matching valves and accessories.

4.3. Instrument control elements.

4.4. Special tools.

4.5. Spare parts.

4.6. Provide the owner's completion data for equipment acceptance, safety review, installation, commissioning and maintenance.

Items 4.2.  to 4.5 can be manufactured, purchased and configured by the supplier or purchased or configured by the owner.