TempLowHT Steam Desuperheater Model: 59/69/79

Transcription

1 NARVIK-YARWAY The TempLowHT utilizes the fundamental design concepts of the standard Templow, designed for temperatures up to 1150 F (621 C). The TempLowHT is designed to eliminate sliding trim parts in the hot zone, while providing the traditional integral probe style desuperheater with isolation (stop) and water proportioning (control) in response to a temperature feedback control signal. Features and benefits Easy installation Installation in straight, vertical or horizontal pipe. Minimal headroom is required for mounting Standard connections to ASME B16.5 Precision control of temperature Rapid evaporation of water is achieved to minimize the accumulation of water in the line. Control within 10ºF (6ºC) of saturation is possible. Water turndown capacity of 50:1 (typically) or higher is available. Low maintenance Forged body with, stainless steel internals eliminates corrosion and vibration issues. Inconel 718 nozzles minimize wear. Replaceable Stellite or 17% Cr seat for long life tight shut-off. Long trim life. Pressure drop is taken across the nozzles rather than the seating surfaces. Adaptable to changing needs Injection probe unscrews from body for easy capacity changes without changing stem/ disc or seat. Actual performance depends on the application and in many instances may exceed the design characteristics above. General application High pressure, high temperature steam attemperation Boiler Superheater Boiler Reheater Technical data Design ASME B class 1500/2500 Model 59 Steam connection : 3 Water connection : 1-1½ Model 69 Steam connection : 4 Water connection : 1½ - 2 Model 79 Steam connection : 5 Water connection : Pentair reserves the right to change the contents without notice NYWSB-0117-EN-1310

2 System comparison Conventional version (fixed nozzle system) consisting of: fixed size spray nozzle with external installed water control valve (see figure 1) without moving parts in the main steam line. Turndown is limited with this design. Figure 1 - Fixed nozzle Classic version (variable nozzle system) consisting of: variable size spray nozzle with integrated water control (see figure 2) with moving parts in the main steam line. Allow for most precise control and greatest turndown. Superior spray nozzle Narvik-Yarway has incorporated the latest technology in the spray nozzle design. The high quality surface finish minimizes frictional losses, thereby ensuring that the total water to steam p is available for atomization of the water (see figure 3). The nozzle consists of two components: A) the orifices and B) the nozzle body. Each nozzle is served by individual feed holes in the cylinder wall. Water enters the chamber behind the orifice plate through these openings. The relatively large volume of this chamber ensures that water is proportioned evenly through each orifice. The p across this orifice plate results in an increase in the fluid velocity. The water is subsequently rotated in the nozzle chamber before being emitted through the central hole. The combination of splitting the feed flow, increasing velocity and rotating effect, ensures that the water is injected into the system in a fine symmetrical hollow cone spray. The nozzles are assembled with the spray cylinder and sealed by a vacuum brazing process. This maintains the integrity of these components even under the most extreme conditions. Material compatibility of spray cylinder, piston and piston rings is well proven in hot/cold service conditions, as typically found in steam attemperators. This enables reliable operation over an extended period. Surfaces are finely machined to reduce frictional losses and internal contours are so designed as to optimize water swirl action, ensuring uniform and consistent droplet size. Minimum p allowable for TempLowHT Steam Desuperheater at inlet flange to steam pressure must be: Nozzles A through Dx : 15 psi / 1.0 bar Nozzles E through K : 30 psi / 2.0 bar Figure 2 - Variable nozzle Figure 3 Codes and standards The TempLowHT Steam Desuperheater is designed and manufactured to meet a wide variety of international codes and standards. Certified acceptance documents are available on request. If special codes or standards are required by your local authority, then we would be pleased to discuss them. Multiple nozzle configuration The TempLowHT Steam Desuperheater may be equipped with a variety of spray nozzle configurations with a wide range of C v (K v ) values. Standard configurations vary by model number and are with either 6, 8 or 10 equally sized spray nozzles but combinations are available. This feature enables the TempLowHT Steam Desuperheater to be customized to specific system requirements. Consult your local Pentair representative for details. Figure 4 - Desuperheater nameplate Pentair reserves the right to change the contents without notice page 2

3 Description For precise and economical control of steam temperature, the Narvik-Yarway probe-type TempLowHT desuperheater automatically introduces cooling water into steam flow in response to a pneumatic or electric control signal. The Narvik-Yarway desuperheater represents a major advance in the design of this type or equipment. It has an unusually high turndown ratio; -double that of units previously available. This permits its use in systems with wide fluctuations in steam flow rate. Water pressure up to 1450 psi (100 bar) above steam pressure is employed to generate thin-film, conical sprays which are injected into the steam flow through a series of vortex spray nozzles. The fine sprays evaporate rapidly in the steam. A separate water control valve is unnecessary because water flow control is a function of the desuperheater itself. How it works Desuperheating water, at a pressure of at least 15 psi (1 bar) above steam line pressure, enters the desuperheater through a the flanged water connection. The water flows down through the water jacket to the seating area above the disc, where tight water shut-off is achieved. When a reduction in steam temperature is required by the steam temperature control system, the actuator forces the stem/disc assembly of the desuperheater downward, progressively uncovering a series of multiple water inlet orifices which feed each vortex nozzle. As more desuperheating water is required, the disc moves further downward, bringing additional nozzles to surface. There are multiple stages of water control to each nozzle, plus the vortex nozzles, which create a rotating mist of water droplets for rapid evaporation and fast response to a change in temperature control signal. Maximum water pressure is assured at the nozzles because no upstream water control valve, reducing pressure, is utilized. This also eliminates flashing/ cavitation within the probe. Water flow is thus controlled at the point of the injection into the steam. Pentair reserves the right to change the contents without notice page 3

4 Design The TempLowHT desuperheater valve design is based on the more than twenty years of successful Templow service and extends the Templow operating temperature to 1150 F (621 C). High flow velocities and large thermal gradients are characteristic of all desuperheater valves with fixed nozzles. In addition, the TempLowHT valve relocates all moving and welded components to an air cooled upper portion of the valve that remains below creep temperatures. High temperature desuperheater valve operation can be divided into cyclic and non-cyclic service. TempLowHT Control shaft Templow Piston Uninsulated atmospheric conditions Steam flow conditions Piston Valves in non-cyclic service remain at a single opening position for most of their operating life and do not change the opening position excessively during either startup or shutdown. Valves in cyclic service often cycle multiple times during any one day, and during any power change may alter position tens or hundreds of times. Temporally irregular and indeterminant demand produces transient thermal strains which are difficult to predict. As a result, desuperheater valve components in cyclic, high temperature service may be susceptible to fatigue and creep damage at unknown rates and should be dealt with as a long-term, inspectable, and consumable item. The design of the TempLowHT places only the easily removable injection probe in this category. The probe has no moving parts or welds and all surfaces are machined to eliminate surface irregularities that may affect fatigue life or induce creep void formation. The highest stresses due to creep are on the outer surface and are readily accessible for replica inspection. The inspection interval can coincide with plant shutdowns and requires little more than unbolting a single flange or can be performed by boroscopic method. Actual plant cycles and operating conditions can be used to compute inspection intervals. Narvik-Yarway has optimized the injection probe design with the help of Finite Element Analysis in order to increase the lifetime during cyclic service operation. Pentair reserves the right to change the contents without notice page 4

5 Definition S.G. K v = Q P Q S.G. P or C v = Q Q S.G. ΔP = m³/hr = kg/dm³ = bar S.G. P = GPM = specific gravity = psi Table 1 Size TempLowHT standard capacity range 6A C v = K v = E C v = K v = B C v = K v = F C v = K v = C C v = K v = G C v = K v = D C v = K v = H C v = K v = Dx C v = K v = K C v = K v = A C v = K v = E C v = K v = B C v = K v = F C v = K v = C C v = K v = G C v = K v = D C v = K v = H C v = K v = Dx C v = K v = K C v = K v = A C v = K v = E C v = K v = B C v = K v = F C v = K v = C C v = K v = G C v = K v = D C v = K v = H C v = K v = Dx C v = K v = K C v = K v = Note Flow capacity limitation is 110 GPM (25 m 3 /hr) in continuous service for model 59 and 69; 220 GPM (50 m 3 /hr) for model 79 hw Gw Figure 5 h1 Gst h2 Gst + Gw Sizing formula Every desuperheating station is a mixing point where there is a heat and mass balance. The universal formula is: Gw = Gst ( h1-h2 ) : ( h2-hw ) This formula enables calculation of the quantity of water required to lower the inlet steam temperature to the set - point temperature of the outlet steam. In which: Gw = Injection water mass Gst = Inlet steam mass h1 = Enthalpy of the inlet steam h2 = Enthalpy of the outlet steam hw = Enthalpy of the injection water Important system parameters Apart from the spray quality of the atomizer (primary atomization) there are other system parameters which influence the desuperheater stations performance. These are: Inlet steam velocity At high steam velocities, water droplets sizes are easily reduced. This factor contributes to the overall atomization quality (secondary atomization). The minimum acceptable steam velocity varies as a function of the nozzle size and pipe diameter. In case of doubt, consult Narvik-Yarway. Water to steam ratio This ratio is determined by dividing Gw by Gst. For system steam pressures below 225 psi (15.0 bar), this ratio should not exceed 10.0% for the normal operating conditions. System operating between 225 psi (15 bar) and 375 psi (25 bar) can have a ratio of up to 15%. For higher pressure duties, consult Narvik-Yarway. Distance to sensor The distance from the injection point to the temperature sensor should be 36 ft to 45 ft (12 to 15 meters). System operating at pressures above 375 psi (25 bar) can have significantly less run to the sensor, consult Narvik-Yarway. Required straight pipe run The distance from injection point to the first pipe bend is also a function of steam pressure, temperature and nozzle size. Experience has shown that in systems up to 375 psi (25 bar), 12 ft to 18 ft (4 to 6 meters), is an acceptable distance. Pentair reserves the right to change the contents without notice page 5

6 Figure 6 - Model Actuators Pneumatic diaphragm The Narvik-Yarway pneumatic actuators are specifically developed for sliding stem Desuperheaters for use on low-, mediumand high pressure steam applications. The actuator model for a stroke of 3,54 (90 mm) is suitable for operation under severe environmental conditions, e.g. at low or high temperatures or humidities. The actuator sets the valve in the closed position in the event of air failure. Other proprietary makes, and/ or failsafe requirements are available upon request. Valve positioners are available in pneumatic or electro-pneumatic operation, with various communicators depending upon customer preference. Additional options are, for example, feedback transmitters and limit switches. Figure 7 Figure 8 Electric actuators Because of the adapted trim construction, the TempLowHT Steam Desuperheater can be equipped with low-thrust electric actuators. (Consult Narvik-Yarway) Each actuator - valve assembly is functionally tested at the Narvik-Yarway factory. A functional test certificate is issued for all valves supplied. Figure 9 Control systems The injection water quantity is controlled as a function of the outlet steam temperature. The TempLowHT Steam Desuperheater actuation is compatible with conventional control systems operated from temperature transmitters, temperature indicating controllers and positioners. Fully pneumatic or fully electric systems are compatible and also combinations of the two. Exact requirements should be specified in the ordering/sizing data paragraph of this brochure. Pentair reserves the right to change the contents without notice page 6

7 Actuator stem forces The stem forces for the TempLowHT Steam Desuperheater is determined by the following formula: Model 59 and 69 P water x = Newton (P water in bar) (P water x =...lbf (P water in psi) Model 79 P water x =...Newton (P water in bar) P water x =...lbf (P water in psi) The maximum stem force must be limited to 3370 lbf (15 kn) for model 59 and 69. For model 79 this figure is lbf (50 kn). Special care should be taken when electric actuators are used. By their moment of inertia these actuators can generate stem forces exceeding the specified nominal stem force during short intervals. Narvik-Yarway supplies special spring loaded couplings for such applications. Actuator sizing formula Units: D seat in cm d stem in cm D bal in cm P water in bar F1 = π / 4 (D seat 2 - d stem 2 ) x P water F2 = π / 4 (D bal 2 - d stem 2 ) x P water F3 = P water x F friction (+ or -) Figure 10 D bal F actuator F1 D d F3 F2 P water Ordering/Sizing data Steam desuperheaters are selected specifically against application data. For optimal sizing, the following comprehensive data should always be supplied. Steam data Water data Inlet pressure psi (bar) Water pressure psi (bar) Inlet temperature F [ C] Water temperature F ( C) Outlet temperature (setpoint) F [ C] Steam flow max lbs/hr (t/hr) Steam flow normal lbs/hr (t/hr) Steam flow min lbs/hr (t/hr) General Pipe size inch (mm) Pipe schedule Required spray position (1) (2) (3) (4) It is essential not to over-specify required turndown ratio i.e.: steam flow max. steam flow min. Spray water must be injected in the direction of the steam flow. To facilitate installation of the water supply line, 4 different spray positions are available in relation to the steam flow direction. Specification of this spray orientation is required with the ordering data. Narvik-Yarway always recommends a strainer with a mesh size of approx. 100 µ (400 µ upon request) in the water supply line to protect the TempLowHT Steam Desuperheater from mechanical particles and clogging. Figure 11 - Spray position Standard Pentair reserves the right to change the contents without notice page 7

8 Dimensions The primary dimensional variable is the length ( X ) of the pipe that supports the steam flange through which desuperheater is inserted in the steam line. This dimension varies so the injection probe is always centered with respect to steam pipeline O.D.( Y ). Formula: X = Z - Y 2 Dimensions - inch (mm) Item A (++) 32 1 /3 (820) B 16 1 /2 (420) C /32 (574) 18 2 /3 (474) 19 2 /3 (500) D 16 3 /4 (426) 13 3 /4 (350) E 9 7 /16 (240) /16 (300) Z *** Figure 12 B Notes ++ Add 12 (305 mm) if side-mounted handwheel is included. * X may vary. ** Can vary from this standard depending on actuator selection. *** To be specified. A E C D Z X Y Pentair reserves the right to change the contents without notice page 8

9 Parts list Item Quantity Name Material Figure 13 (shown model 69) 1 1 Body A182 F91 / F Seat Stellite 6/17% Cr 3 1 Control cylinder assembly AISI Seal SS/Graphite 5 1 Gasket SS/Graphite 6 1 Stem AISI 431 nitrited 7 1 Injection probe A182 F91 / F Pin, spray cylinder AISI Packing, set Graphite 10 1 Gland, packing AISI Bushing, spacer AISI 431 nitrited 12 1 Bushing, gland AISI 431 nitrited 13 4 Stud, packing gland A193 B Nut, packing gland A194 4H 15 8 Stud, injection probe A193 B Nut, injection probe A194 4H 17 Nozzle Inconel Name plate AISI Seal ring Inconel 20 1 Yoke nut C-Steel 21 1 Coupling C-Steel 22 1 Water flange A182 F91 / F Yoke C-Steel 24 3 Piston ring AISI 431 nitrited 25 1 Actuator 26 1 Positioner 27 1 Air filter regulator Notes Recommended spare part. See certified drawing. Materials and data of units supplied, may deviate from this brochure. Please consult order documents in case of doubt Trademark Stellite is a registered trademark of Deloro Stellite Pentair reserves the right to change the contents without notice page 9