Key words: orifice plate; stem; core package; orifice plate; flow rate
Plate valve hole of advanced technology, can successfully solve common control valve such as cavitation, high noise and vibration problems encountered by the door, there is also widely used in the power plant boiler I, Ⅱ grade by warm water, feed pump minimum flow valve, Boiler main water gate and other flow control. It can provide more accurate flow control, according to the different needs of users, can be designed into different flow characteristics, with a rigorous shutdown feature to ensure plant safety, stable operation, improve efficiency and extend maintenance cycle.
Orifice Series Regulating Valves are designed to meet different customer requirements and eliminate cavitation, noise, corrosion and vibration problems through media flow control, easy maintenance, and easy to replace spools.
Orifice series regulating valve spool has a long service life. Of course, the key to getting a good life is proper installation and proper maintenance in use.
1 Principle orifice plate series regulating valve anti-cavitation design is the use of multi-stage orifice core package buck principle, by forcing the medium flow through the many holes on the core plate orifice channel flow rate to be fully controlled, to achieve step by step Antihypertensive purposes. Regardless of pressure drop, the resistance of these orifices limits the rate of medium flow out of the cartridge. After multi-stage depressurization, the pressure of the medium is always maintained above the vapor pressure PV of the medium, thereby avoiding cavitation and eliminating the unsafe factors, as shown in FIG. 1.
Orifice cartridges consist of a large number of orifice plates machined to create a multitude of orifice channels, each passageway capable of passing through a dosing medium. When the medium flows through the hole, there is a great resistance and pressure drop.
According to the different parameters of various units in the power plant, through precise calculation, the number of different orifice plates and different small empty holes on the orifice plate and the different diameters of the orifice holes are selected so that the pressure drop of the medium flowing through the orifice plate core core reaches the power plant The needs of different occasions. And can make each level pressure drop is always maintained above the vaporization pressure, so as to achieve anti-cavitation requirements.
Orifice series valves use machining technology to manufacture orifice plates, and orifice plates are then welded together to form an integral core package (Figure 2).
Since the number of holes and the diameter of each hole plate are designed according to the parameters provided by the user, and the thickness of the hole plate can be designed very thin, the core package can be designed according to the special requirements of the user to provide accurate Flow control. According to the valve application and user requirements, the flow characteristics of the control valve can be designed into different forms, including linear, equal percentage, corrected percentage and other special curves.
Medium in the power plant are basically fluid medium (mainly water), so the orifice plate valve generally open-type structure. When using open-flow type, the medium first enters the valve body, passes through the valve seat, the valve core, passes through the core bag and the shroud, and finally flows out from the valve body (Figure 3). The flow of the valve is indicated by a label on the valve body.
2 structural features orifice plate series regulating valve consists of the following major components: body, including the orifice core package, including internal parts, shrouds, bonnet assembly, valve core, seat assembly. The actuator is bolted to the bonnet via the coupling bracket.
All parts of the orifice series valves have fast changing and long life characteristics. Seat does not use bolts or welding, easy removal. The sealing form of the valve cover, the type of internal components and the choice of sealing are in accordance with the application and working conditions. The seal between bonnet and valve body is made of metal wound mat made of multiple layers of stainless steel and graphite. Expanded graphite has good sealing performance. Stainless steel supports graphite and provides the elasticity needed for temperature changes.
2.1 spool assembly and spool seal design Balance spool: balanced spool to reduce the implementation of the actuator requirements, drilling a symmetrical hole in the spool. In the upper part of the valve is equipped with an open upward balance ring used to isolate the pressure between the outlet and the inlet. The symmetrical hole on the valve core balances the pressure in the valve core up and down, which greatly reduces the lifting force requirements. Thus reducing the torque of the actuator and reducing the size and weight of the actuator.
In medium and low temperature conditions, the balance ring made of filled PTFE. In high temperature conditions, the use of graphite materials.
2.2 Varistor characteristics orifice plate series valve in the small opening of the hate, due to the medium to flow through the core package, it can achieve high pressure drop, low flow requirements and will not produce cavitation. As the valve opening increases, the number of media through the orifice plate gradually reduced, the resistance is gradually reduced, if the valve opening exceeds the degree of core package, the media will flow completely through the shroud, the resistance can be Very small, so you can achieve high flow requirements, thereby reducing the energy consumption of the pump.
2.3 low noise characteristics The orifice plate series control valve consists of a plurality of orifice plates arranged according to a certain design rules staggered manner stacked together, the medium flows upward from the lower part of the orifice plate, as a result of a plurality of orifice plate points Section of the step-down to prevent the occurrence of cavitation, on the other hand, orifice itself is a perfect silencer, so the orifice plate regulating valve with low noise characteristics.
General orifice plate regulating valve has the following characteristics:
(1) low noise, anti-cavitation, can withstand high pressure;
(2) multi-layer step-by-step step-down plate pressure, limiting the flow rate of the medium, maintaining medium pressure is always above the vaporization pressure;
(3) variable resistance characteristics: the media axial flow, the valve opening increases, reduced throttling resistance;
(4) staggered orifice plate, no dead zone adjustment;
(5) balance valve core can reduce the driving torque of the actuator;
(6) spool, seat with a different angle, line contact seal, closing performance is good;
(7) sealing surface surfacing carbide, good punching resistance;
(8) the shroud to avoid media flushing of the valve body;
(9) flow characteristics: linear, such as percentage, user requirements.
3 purpose orifice plate series valve according to the different requirements of the user design different characteristics. It provides equal percentages, corrected percentages, and user-specific characteristics. Used in power plant main feed water regulating valve, bypass valve, recirculation valve, water regulating valve, continuous discharge valve and other high-pressure boiler flow adjustment occasions.
When used in water supply regulating valve and water reducing valve, it has the features of high pressure drop and small flow at small opening to prevent the cavitation. Under the conditions requiring large flow and low pressure drop, the medium is directly guided The flow hood passes without passing through the orifice wadding. When used in recirculation valve occasions, because the valve before and after the pressure is very high, so the medium must flow from the orifice core package, in order to achieve the purpose of high pressure drop. Flow characteristics of the curve shown in Figure 4. 4 TL967Y (K) - 25/50 orifice plate recirculation valve overall design and calculation 4.1 Specific requirements Used in power plant 125MW units and below the boiler feed pump recirculation system, can withstand greater pressure.
4.2 Technical parameters Nominal pressure: 25Mpa;
Nominal passage: 50mm;
Import pressure: -18Mpa;
Export pressure: 0.61Mpa;
Working temperature: ≤240 ℃;
Flow coefficient: 1020 (British)
Working medium: boiler feed water;
Characteristic curve: linear or other;
Implementing agencies: electric or pneumatic;
Valve opening and closing the whole trip: 56mm;
Inlet and outlet Connection type: Flange connection or counter seam welding.
4.3 The overall structure of the valve design 4.3.1 Design of the valve structure (1) the valve flow channel using right-angle (down into the), shown in Figure 5.
(2) The inlet and outlet diameter of the valve body is 50mm.
(3) Body 25 steel.
4.3.2 Body wall thickness calculation According to thick wall container formula as shown in formula (1) below.
(Valve Design Manual P359 Equation 4-4)
S = (KO-1) + C (1)
Where C-additional margin;
KO - valve body and the inner diameter ratio, according to equation (2) calculation.
KO = (2)
Body 25 steel, look-up table calculated:
KO = 1.3 into the formula (1) were:
S = 24.5mm Take the body wall thickness S = 30mm
4.3.3 bonnet design reference to the calculation formula of flat bonnet (valve design manual P391 formula 4-59) as formula (3) Institute.
δP = DC (3)
By calculating:
δP≈53.7 mm
Take the cover thickness δP = 60mm
4.3.4 Design of bonnet bolts Diameter Φ130mm, number of bolts n = 8 Material Selection 35CrMo High-strength alloy steel on each bolt Pn by the valve design manual P379 formula 4-32 as shown in equation (4) .
Pn = (4)
Where df-pressure area;
m-gasket coefficient;
A-channel cross-sectional area Pn ≈ 82260N
Bolt material 35CrMo steel, the [σ] = 220Mpa, by the formula (4) ≤ Bolt diameter d ≥ 22mm, the choice of M242 bolts 8, the layout shown in Figure 6.
4.3.5 Design and calculation of stem diameter (1) stem diameter D assumption D = 18mm;
(2) ring seal with expanded graphite ring Φ34Φ188;
The friction coefficient μs = 0.15, ds = 34mm.
First seek the maximum required output of electric actuator F = F1 + F2
F1 for μd unbalanced force + μp stem part of the friction;
F2 is completely close the actuator pressure on the seat.
μd = π · ds · L · p · μs = 21971N
μp = 16001N
F1 = μd + μp = 37972N
F2 = π · dg · bm · p = 3847N
∴ F = 41819N
Body material selection 1Cr17Ni2
σb = 1080 Mpa
ηb = 4.25
fc = 1080 / 4.25 = 254.1 Mpa
d ≤ = 14.5cm so the stem diameter of 18mm design is reasonable.
4.3.6 Adjustment section and decompression section orifice design and calculation orifice total of 12, namely 12 layers; 16 layers for the flow adjustment section, 712 layers for decompression section.
(1) the establishment of flow formula.
Flow formula as shown in formula (5) below.
Q = μ · F · ν = μ · F · (5)
μ = 0.60.8 (taking 0.8); γ value of 180 ℃ water ≈0.9 (now assuming normal temperature water ≈1)
Calculated as Q = 0.04032 · F · (6)
(2) recirculation flow.
According to 125MW unit recirculation flow is generally 120t / h, first seek decompression section total area F value, such as type (7).
Q again = 0.04032 ΣF × (7)
ΔP = 17.4 Mpa
Calculate ΣF should be 224mm2
Decompression section according to the calculated total area of the decompression section drawing sheet drawings (Figure 7).
Check the decompression section total area F value as (8).
(8)
ΣF = 269.2mm2 to meet the requirements (3) Sectional flow calculation Q1-12 = 0.04032ΣF1 × = 24.7t / h
Q2-12 = 0.04032ΣF2 × = 42.9t / h
Q3-12 = 0.04032ΣF3 × = 71t / h
Q4-12 = 0.04032ΣF4 × = 94.3t / h
Q5-12 = 0.04032ΣF5 × = 116t / h
Q6-12 = 0.04032ΣF6 × = 131.7t / h
Q7-12 = 0.04032ΣF7 × = 144.3t / h
4.3.7 Calculation of Flow Coefficient Cv The Cv is as shown in Eq. (9).
Cv = 1.17 × Q and then × ≈13 (9)
4.3.8 Electric Actuator Operation Torque Calculation The operation torque is calculated as shown in equation (10).
Operating torque = ΣF Stem coefficient (10)
Tr3212 (P6) LH stem coefficient look-up table (DZ series valve design manual P16) the following values.
Valve stem coefficient = 0.00308;
That is, the operating torque = 128.8 N · m.
References [1] Yang Yuanquan. Valve Design Manual [D]. Machinery Industry Press, 1992.
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