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Steam turbine bypass system (Valve system)

key word:Heat exchange element


Product description

Steam turbine bypass system (Valve system)

 

1. Introduction

1.1. Purpose

The steam turbine bypass system plays the role of regulation and protection in the start-up, shutdown and load rejection of the generator unit. It has the functions of shortening the start-up time, maintaining the low negative combustion of the boiler, bypassing the excessive steam of the steam turbine during load rejection, saving energy and protecting the reheater. The valve of bypass system is directly driven by intelligent electric (hydraulic / pneumatic) driving device, which is widely used in power station construction and transformation. According to the capacity of steam turbine units, the products can be divided into two series: 300 MW and 600 MW. Among them, more than 300 MW units can be divided into subcritical and supercritical, and each type can be divided into 15%, 30% and 40% according to the bypass capacity. It can also be customized according to the needs of units.

1.2. Model meaning

1.2.1. Design number.

PL-**/##@@-&&$$※※

PL --- code of steam turbine bypass

**------Unit capacity (MW)

##--------Bypass system capacity (% of boiler rated evaporation)

@@------------Design serial number (B for improved; C for supercritical)

&&---------------System code (g for high pressure bypass; D for low pressure bypass)

$$--- valve code (y for steam shift valve; t for spray control valve; J for spray stop valve; ST for three-stage desuperheating control valve)

※※-------No. of technical documents for drawing

1.2.2. Refer to JB / T 4018 "power station valve model compilation method" for model compilation

PL **/##@@-&&$$※※

PL ** / ####@ - & - $$-- same as 1.2.1.

※※-------Refer to JB / t4018

Example: PL600 / 40C-GWY963Y-P5725V represents the bypass of 40% capacity supercritical steam turbine of 600MW unit. The first design of high pressure bypass steam shift valve has electric drive, welding connection, shrouded structure, hard alloy seat sealing surface, 570 ℃ / 25MPa maximum design working temperature / pressure, and lattice molybdenum vanadium alloy steel valve body

1.3. Structural features

1.3.1. Structure description. The whole set of bypass system is composed of high pressure bypass and low pressure bypass in series. According to different working conditions, the bypass system is usually composed of 4 ~ 7 valves, including high-pressure bypass steam shift valve, high-pressure bypass spray water control valve, high-pressure bypass spray water isolation valve, low-pressure bypass steam shift valve, low-pressure bypass spray water control valve, low-pressure bypass spray water isolation valve, three-stage or warm water control valve.

1.3.2. Important characteristics:

1.3.2.1. All valve bodies are forged and welded, and the design life is the same as that of the unit.

1.3.2.2. The steam shift valve is designed with advanced pre opening valve or balanced structure, which can reduce the valve action torque or thrust

1.3.2.3. The high pressure by-pass valve adopts the structure of desuperheating water directly injected into the valve, and adopts cage valve disc. Steam and water are mixed in the valve disc to avoid the impact on the valve seat and valve body; the valve disc adopts surface hardening treatment to improve the performance of erosion resistance and high reliability.

1.3.2.4. The low pressure bypass valve adopts the structure of reducing pressure first and then reducing temperature; the temperature and pressure reduction are completed in one valve at the same time, and the system layout is simple. The desuperheating water of low-pressure bypass is condensed water source, which adopts the structure of decompression first and then desuperheating, that is, the spray point is placed at the tail of the valve, so as to obtain enough pressure difference for the desuperheating system and improve the performance of spray atomization of low-pressure bypass.

 

2. Main technical parameters and product appearance

See Table 2.1 for main technical parameters

Table 31-1 classification of main bypass valves

Unit type 300MW 300MW Supercritical 600 MW 600MW Supercritical
HP bypass steam valve LP bypass steam valve HP bypass steam valve LP bypass steam valve HP bypass steam valve LP bypass steam valve HP bypass steam valve LP bypass steam valve
Model 300/40 300/30C 600/30 600/35C
Flowt/h 410 480 385 455 608.4 356×2 746 435×2
Inlet pressureMPa 16.7 3.383 25.5 4.4 16.67 2.5 26.7 5.6
Inlet temperautre(℃) 538 538 571 569 538 322 576 576
Outlet pressureMPa 3.758 0.6 4.68 0.6 2.33 0.78 5.338 0.8
Outlet temperature(℃) 324 160 322.3 160 322 190 339 170
Opening and closing timeS 535

Note: special parameters are designed according to the working conditions of the unit.

2.2. Product appearance (30% capacity of 300 MW unit, see figure 31-1 ~ figure 31-9)

2.2.1. High pressure bypass steam shift valve.

2.2.2. Low pressure bypass steam shift valve.

2.2.3. High pressure bypass spray water control valve.

2.2.4. Low pressure bypass spray water control valve.

2.2.5. High pressure bypass spray isolation valve.

2.2.6. Low pressure bypass spray water control valve.

2.2.7. Three stage desuperheating water valve.

 

3. Selection method

For example, if the inlet pressure of the high pressure bypass system is 16.7Mpa and the flow rate is 307.5t/h, the corresponding model is PL300 / 30-GWY963Y-P5520V, and the design parameters can also be described directly, and then the model can be selected directly by the manufacturer.

The following requirements shall be provided when ordering:

3.1. Valve type (steam valve, water control valve or isolation valve)

3.2. Design parameters (inlet pressure and temperature, outlet pressure and temperature, inlet flow, etc.).

3.3. Valve form (angle, Z-shape, straight through).

3.4. Medium flow direction (flow closed, flow open).

3.5. Valve flow characteristics (linear, equal percentage, switch).

3.6. Valve driving mode (electric, hydraulic and pneumatic).

3.7. Specification and material of valve connecting pipe.

3.8. Valve connection form (flange, welding).

If there are no special requirements, the valve type, size and material will be selected according to the design requirements.

 

4. Scope of supply

According to the design requirements, select the specific valve, and select the electric actuator and hydraulic, pneumatic actuator.