VAPOR DESCALER WITH MULTIPLE NOZZLES ASSISTED BY SPRING
BACKGROUND OF THE INVENTION This invention relates generally to steam desuperheaters and more particularly to a de-superheater, for spraying water in a steam pipe, to maintain the steam at a predetermined temperature level. Many applications that use steam operate more efficiently using saturated or slightly superheated steam, while many steam generators, such as boilers, tend to produce steam that is sometimes overheated. This is particularly true when the steam demand of the application changes more rapidly than the output response of the steam generator. Under these conditions, optimum efficiency can be obtained by energizing the steam generator to produce superheated steam and then reducing the amount of overheating by injecting water into steam. A common type of water injection uses a spray head placed in the middle of the steam pipe and has a fixed spray head, adapted to produce a fine spray of water downstream in the circulating steam. The current volume of water injected into the steam is therefore varied by changing the pressure of the water supply, and the pressure must always be kept well above the steam in the line at the nozzle. Because the amount of overheating varies with the amount of steam production and the flow rate, among other variables, the only real regulation can be made by detecting the temperature of the steam at a point downstream, where the injected water has been evaporated and heated so that equilibrium conditions have been reached. This requires a spray nozzle that is optimized for a certain flow expense, and if the flow expense is varied outside of certain parameters, the resulting spray pattern may not give sufficient rapid heat transfer to allow an equilibrium condition to be detected and adequate steam conditions are achieved. However, these steam deheaters work well when dew requirements vary over only a narrow range. When a greater variation in spray volume is required, other types have been employed, including variable orifices and the use of a separate steam path to pre-mix with the water flow. Another structure has been the use of multiple nozzles with a movable or sliding plug member that discovers or chooses different nozzles to spray the water. Such a structure that has proven to be successful has been a multi-nozzle spray unit described in U.S. Pat. No. 4,442,047 property of the assignee of this application. This unit uses a spray tube that extends into the steam line and has a plurality of small nozzles on the downstream side at spaced apart distances from the end. The nozzles are connected to a borehole and a hollow plug moves to and from the end to discover different numbers of nozzles to vary the volume of water that is sprayed. The position of the plug is determined by a valve rod that moves linearly by a diaphragm actuator which in turn is controlled in response to signals from a temperature sensor located downstream in the steam line. The complexity of the drive system results in high original cost as well as high maintenance after installation. SUMMARY OF THE INVENTION The present invention provides a desiccant with a water spray nozzle, which combines the simplicity of control of a single-nozzle mechanical de-superheater with the wide range of modulation and variable capacity of multiple nozzle de-superheater. . A fixed nozzle desuperheater is based on variations in the pressure of the water line over the prevailing pressure in the steam line to in turn vary the volume and therefore the mass of the water. On the other hand, multiple nozzle injectors tend to use water at a controlled and fixed uniform inlet pressure and use a separate controller to move a plug to discover varying numbers of nozzles and vary the amount of water injected into the steam line as described in the aforementioned patent, US patent No. 4,442,047, which is incorporated herein by reference. The present invention provides a new deheater spray unit, which consists of a spray tube having a multiple number of nozzles placed in a helical assembly, on the axis of its bore and control is made of these nozzles when moving a plug or piston that has a hollow perforation. The plug is arranged to move in the main borehole of the spray tube to which the nozzles are connected and has a reduced diameter bore through which water enters the unit. The spray tube also contains a calibrated spring that adapts to bypass the plug to the disconnected position. The plug, due to the differential areas of the perforations, is under a differential hydraulic force that tends to move the plug to the fully open position, where all the nozzles operate, against the spring bypass force. In this way, the water pressure supplied through a control valve to the desuperheater unit operates to move the plug, so that initially changing the flow of the inlet water results in pressure buildup in the tube. spray that raises the cap and varies the number of nozzles that are discovered for spray purposes. Once the entire number of nozzles are open, further increase in water pressure will continue to increase the flow of water through the nozzles. According to the present invention, temperature measurements are taken at a point downstream in the steam line, a sufficient distance that the injected water is converted to steam, and an equilibrium condition predominates. These readings will determine the temperature of the steam at that point and this reading is then used by a controller unit, which compares the measured variable against the spray temperature or the required reference point and generates a signal to operate a control valve whose output to It is connected to the desuperheater unit. The control valve can be of any well-known type that can be used to vary the water pressure at the outlet, independent of the flow rate. In this way, with proper calibration, the control valve will supply water to the desuperheater at a pressure sufficient to move the plug to a position where the desired amount of water is sprayed into the steam line to reduce the amount of overheating to the desired level . BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic of a view of the steam line incorporating the desuperheater of the present invention; FIGURE 2 is an enlarged cross-sectional view of the spray unit shown in FIGURE 1; FIG. 3 is an elevation view of the nozzle head viewing in the upstream direction; and FIGURE 4 is a cross-sectional view of the nozzle head taken on line 4-4 of FIGURE 3. DETAILED DESCRIPTION OF THE PREFERRED MODALITY Now with reference to the drawings in greater detail and FIGURE 1, FIG. shows a schematic structure for using the desheater unit according to the present invention. In a portion of a steam line 10, a mounting fitting 11 is provided in the side wall and a spray unit 13 is mounted in the fitting as previously described. The spray unit 13 is supplied with water under pressure through a water line 14 from the control valve 16, connected in turn to a convenient high pressure water supply 17. The control valve 16 operates to control the flow of water in the water line 14, in response to a temperature sensor 19 mounted on the steam line 10 a distance spaced downstream of the spray unit 13. This temperature detector sends a measured variable to a temperature controller 12, which evaluates this against a desired reference point, and sends a corrective signal to the control valve 16. The distance to the detection element is chosen to be sufficient to allow the steam to reach to equilibrium after the water has been injected to give a real reading of the steam temperature. In this way, the control valve 16, by varying the water flow, produces a varying water pressure in the line 14 that is greater than the pressure in the steam line 10. A convenient controller for this purpose is a pneumatic controller Series 40 produced by Ametek PMT Division, in Feasterville, PA. Turning now to FIGURE 2, which shows the spray unit in greater detail, the mounting flange 11 fits over an opening 21 in the wall of the steam line 10 and includes a welding seat 22, welded directly to the line of steam on the opening 21. At the upper end, the welding seat 22 is welded to a welded flange 23 having a standard pipe flange 24 at the outer or upper end. It will be understood that the entire mounting flange structure 11 is substantially permanently connected to the steam line and will remain in place while the remainder of the spray unit 13 can be removed and replaced as desired. The welded flange 23 has a large bore 26 extending into the steam line 10, and connected to the flange 24 is a mounting flange 28 connected to the flange 24 with gaskets 29 and suitable bolts 31 for flange assembly of the flange 24. standard pipe. The spray unit 13 is mounted on the flange 24 and has a body 32 that includes a spray head or inner portion 38 and a support tube or outer portion 33 that extends through a closely dimensioned opening 34, which is formed in the mounting flange 28. The support tube 33 is fastened to the flange by a convenient weld 36 on the outer side to prevent any possible leakage around the support tube from the steam line 10. The support tube 33, when it is fastened in place to the mounting flange 28, extends inwardly adjacent the welded seat 22, where it is connected to the spray head 38. The spray head 38 is a generally cup-shaped member, having a wall bottom 39 with a flat end surface 40. On the bottom wall 39 is a main bore 41 which terminates at a shoulder 42, where it meets a slightly enlarged counter bore 43. At its upper end, the bore is cut away from the bottom wall 39. 43 opens in a threaded bore 46 which is screwed into the bottom end 47 of the support tube 33. A sleeve 48 is placed within the bore hole 43, to butt against the shoulder 42 and the end of the support tube 47 without movement. In this way, when the spray head is mounted on the support tube, the threaded bore 46 is threaded onto the end 47 until it abuts the sleeve 47, after which it is preferable to weld the spray head directly to the tube. support to avoid any possible loosening of this joint. A piston or cap 50 is slidably mounted within the spray head 38 and has a head 51 having a seal ring or piston 52, which makes a sliding seal fit within the main bore 41. The end face of the piston 53 normally it butts against the bottom wall 39 when the spray head is in the "OFF" position as explained in more detail below. The piston 50 has a reduced diameter rod 54 that extends upwardly within the bore 49 of the sleeve 48, where it carries a seal ring 55 to make sealing contact with the bore 49, and the rod 54 terminates at an end face. annular 56. Similarly, an annular face 58 is formed in which the rod 54 joins the head 51, and the piston 49 has a bore 59 extending through the end-to-ex row. A coil spring 61 is positioned within the bore 62 and the support tube 33 and abuts its lower end at the rod end face 56. The spring 61 is generally made quite long to give a relatively low ratio and relatively high preload and extends upwards to buttly confine against the lower end of the tubular spacer 63 located at the upper end of the bore 62. The spacer 63 in turn buttresses against a washer member 65 attached to the upper end of the support tube 33 by suitable screws 66. A pipe flange 68 is welded together at the upper end of the support tube 33 for connection to the water line 14 in the usual manner. The lower end of the spray head adjacent to the main bore 41 has a thickened spray wall 71, which is also circular in shape, but formed in a radius that moves to the downstream side from the axis of the support tube 33, to provide the largest diameter that can be inserted through the perforation 26. The spray wall 71 contains the spray nozzles which, as illustrated in FIGURES 3 and 4 can by way of example be only 6 in number, spaced apart one over the other in a stepped pattern. Each of the openings in the spray nozzles comprises a bore 73 that extends partially through the spray wall 71 from the outside where it connects with a rectangular opening 74 connected to the main bore 41. A spray nozzle insert convenient 76 is screwed into the branch hole 73 and fits in place, and the nozzle insert 76 is configured such that it provides a fine atomization spray in the downstream direction. The dew wall 71 also has a small purge hole 78, which extends from the outside into the shoulder 42 to allow fluid trapped around the piston rod 54 to escape to the exterior and prevent blocking of the piston movement. The spray head is normally in the "OFF" position with the piston head 51 abutting the bottom wall of the spray head 39, and the operation is controlled by the water pressure from the line water 14. Helical spring 61 has a calibrated ratio and predetermined preload for vapor pressure within line 10. In this way, the valve is not allowed to open until the pressure in water line 14 is of a value predetermined on the pressure end of the line 10 to ensure positive water flow through the spray nozzle inserts 76. When the pressure in the water line 14 exceeds this predetermined value, the pressure, due to the differential between the areas on the face of the head end of the piston 53 tends to move the piston in the upward direction and the pressure against the end face of the rod 56 opposite to that movement, the net force is exerts on the coil spring 61, and after the preload has been exceeded, the piston begins to move upwards, such that the end face 53 begins to discover the lowermost of the rectangular openings 74. As the piston begins to move upwardly as determined by the ratio of the spring 61, the openings 74 are positioned in such a way that as one is fully discovered, the next one begins to be discovered, so that the current area of the openings is increased in one way substantially linear, since the vertical height of the openings 34 is substantially equal to the differential spacing between the various derived holes 73. As the piston moves toward above, all the water trapped around the rod 54 within the main bore 41 is allowed to drain through the purge retention 78, to avoid any interlocking action that would prevent piston movement. When the piston reaches the upper part of its path where the annular face 58 buttresses the lower end of the sleeve 48, all the rectangular openings 74 will have been discovered, but although the area can not be increased further, increasing the pressure will still cause that an increased amount of water is discharged into the steam due to the increased pressure differential across the nozzles. The operation of the spray unit is therefore completely controlled, by the pressure level of the water supplied through the water line 14 from the control valve 16, as determined by signals that are sent from the controller. The controller 12 detects the temperature within the vapor line 10 in the detector 19 which is located far enough downstream that all injected water will completely evaporate, and it is often convenient to use multiple detectors at that point to obtain an accurate reading . Considering that the steam at this point is saturated, there is no reason to add water, and the controller 12 will direct the control valve 16 to be closed in such a way that no water enters the supply line 14. The piston 50 will then be in the position illustrated in FIGURE 2, and the space in the main bore 41 around the piston rod 54 will be at the pressure within the steam line, since the vapor pressure can be moved backwards through the nozzles of the piston. dew 76 and the bleed hole 78 within the space, and the piston will be maintained by that pressure and the force of the spring 61 in the fully closed position. As pressure builds up across the supply line 14, considering that there is demand for water due to excess heat in the steam, as determined by the controller 12, this pressure acts on the rod end face 56 in one direction downstream and as it passes through the bore 59 and the piston 50, it also acts in an upward direction on the end face of the piston 53. Due to this construction, the area of the piston end face 53 is equal to the sum of the areas of the rod end face 56 and the annular face 58, such that there is no upward force in the piston 50 until the pressure line 14 begins to exceed the pressure in the vapor line 10. Since the net area of the end face 43 which is effective for forcing the piston in an upward direction, is exactly equal to the annular area 58, an upward force results each time the pressure of the supply line 14 exceeds that in l to steam line 10, and this is only opposed by the preload of the spring 61. Considering by way of example, that the spring 61 has a preload of 27.24 kg (sixty pounds) when the piston 50 is in the lowermost position, and the force of 90.8 kg (two hundred pounds) when in the uppermost position, and that the area differential when the end face of the piston 53 which is equal to the annular area 58 has an area of 6.45 cm2 (one square inch) ), the pressure in the water line 14 must rise to a pressure of 27.24 kg (sixty pounds) above the pressure in the steam line 10 before the piston 50 can start moving upward. If the pressure line 14, as regulated by the controller 12 and the control valve 16, starts to increase more in response to an increasing amount of superheat in the steam line 10, the piston 50 will begin to move upwards to discover the lowermost rectangular opening 74, and water will exit through the adjacent nozzle insert 76 and atomize to form a mixture with the steam downstream, away from the spray unit 13. The control valve will allow an increased flow, and thus both water pressure in line 14, and if the pressure in line 14 rises to 14.06 kg / cm2 (two hundred PSI), at this point, piston 50 will be in the uppermost position, and annular face 58 will engage the end bottom of the sleeve 48 to prevent further movement. Any increase in pressure from the line 14 will allow more dew, only due to the increased force of the water through all the openings 74 and the nozzle inserts 76, which are now in the fully open position. Therefore, it will be seen that full control is obtained through a single control valve 16 and controller 12 adapted to regulate the flow rate, and therefore the water pressure in line 14. In addition, it will be seen that this The structure provides uniform and continuous variation over a much wider range, as compared to single-nozzle spray units, and the extension of this range can be varied depending on the number and size of the nozzle and aperture inserts. The preload amount in the spring 61 is determined by the minimum desired pressure through the spray nozzle 61 to obtain adequate water evaporation. The higher pressure level again given, for example as 14.06 kg / cm2 (two hundred PSI), is determined by other system parameters, such as sensitivity and spray performance, at these higher pressures. Although the preferred embodiment of the invention has been shown in the drawings and illustrated in the detailed description, it is recognized that other modifications and rearrangements may be resorted to without departing from the scope of the invention as defined in the claims.