CONTROLLING SEAL SYSTEMS IN ROTARY REGENERATIVE AIR PREHEATERS

Abstract: Control of the seal (13,25) of a rotary regenerative air preheater (12) is provided by a plurality of inductance sensors (S1-S8, S11-13) arranged around the path of travel of seal parts (13,25) borne by the rotating part (14,20) of the preheater (12). When these are sealing frames (13) borne on hoods (14) of a stationary matrix (11) type preheater (12) drive means such as magnetic actuators (5) are fed power signals through slip rings (4). When they are seal strips (25) on a rotat­ ing matrix (20) type, the drive means (D11-D14) are mounted on the sector plates (23,24) of the stationary body (21,22). A control circuit compares the signals received sequentially from the sensors (S1-S8, S11-S13) and drives appropriate one or ones of the drive means (5, D11-D14) to bring the sealing means (13,25) to a predetermined axial relationship, or to hold them there. The sensors(15) may be paired with comparison sensors (16) in the same environment whereby to reduce errors due to changes in temperature etc.

Description: We have disclosed in our United Kingdom Patent No.l559679 and Application 209l003 (8l.35292) how a sensor may be used to determine the proximity of sealing systems in rotary regenerative air pre-heaters and how to adjust the gap (or the extent of contact) in them using magnetic drive means controlled from those sensors. The sensors in those prior documents are mounted on moving hoods of a stationary matrix regenerator. This brings a difficulty with it. The signals are of low amplitude and they have to be transmitted through contacts such as a slip ring between the rotating hood and the stationary parts of the device. The regenerators work in very hostile environments and because of this and the low amplitude of the signals we have found that unless very special care is taken with the design of the slip rings the noise level in the signal is unacceptably high and may result in erratic functioning of the magnetic drive. In order to avoid having to provide special slip ring constructions and in order to give ourselves the possibility of mounting the sensors on a stationary part (which might either be the stationary matrix of a rotating hood regenerator or the stationary sector plates of a rotating matrix regenerator) we have evolved an entirely different construction and method of operation. In this, sensors are positioned on a non-­ rotating part around the path of relative movement of the two parts of the regenerator (hood and stationary matrix or sector plate and rotating matrix). As a seal borne on the moving part sweeps past each sensor in turn a control signal is derived from that sensor. This is dealt with by a control circuit (which can be stationary and outside the hostile environment in which the regenerator is placed) and is converted to a drive signal. This drive signal is communicated to a magnetic drive device which activates the sealing gap adjustment means at a time when the latter is in close proximity with the given sensor. If that part­ icular sensor perceives that the seal is at too great a gap it will give a signal to the drive such that it will be closed to a certain extent. The drive means is then held on that setting until the sealing means which it is controlling is in proximity with a next sensor. The signal from the next sensor is then fed to that drive means which if necessary adjusts itself and main­ tains the new setting until a subsequent sensor is passed, and so on. This construction allows it to be the power signal and not the control signal which is communicated through a slip ring to a moving part. This signal being at a high amplitude and current level is not susceptible to interference from noise and is comparatively easily conveyed through conventional slip ring constructions. To compensate for changes in conditions at at least some of the sensors, comparison means are associated with them to represent a preset gap in the form of "dummy" sensors adjacent the working ones. There may be sensors near the hub at the extreme periphery and at intermediate radial positions on the seal frame or on the sector plate, driving appropriately positioned magnetic drive means on the movable element. When the assembly and method is being used on rotatable matrix machines it would be desirable to use the particularly adapted sensors which have been disclosed in our EP-A-l33793, which discloses a sensor which consists of a U-shaped yoke on the parallel legs of which are mounted coils of unequal number of turns. The yoke is mounted behind a cover plate through which its ends are accessible and the cover plate is discontinuous between the ends of the yokes - most suitably there will be a comparatively narrow parallel side split in the cover plate. In the accompanying drawings: Figure l is a side part-sectional view of a rotating hood regenerative air preheater showing the position of sensors and drive assemblies; Figure 2 is a plan view of the regenerative air preheater of Figure l; Figure 3 is a block diagram of the circuitry involved; Figure 4 is a sectional plan view of a rotating matrix regenerative air preheater showing the position of the sensors; and Figure 5 is a sectional elevational view of the regenerative air preheater of Figure 4. As seen in Figures l to 3, a series of sensor assemblies Sl-S8 are mounted at regular intervals around the periphery of the upper face of the stationary body ll of a stationary matrix/rotating hood regenerative air preheater l2. Corresponding assemblies S′l-S′8 are similarly mounted round the lower face, but the following description will be given for only one of these series; the arrangement for the other is identical, mutatis mutandis. Alternatively, the sensor assemblies Sl-S8 may be located at another radial position or near the hub of the body ll. The number and position of the sensor assemblies Sl-S8 is dependent on the size of the air preheater and the speed of rotation. Each sensor detects inductively the proximity of the sealing frame l3 borne on the face of the rotating hood l4 adjacent to the end face of the matrix. Each assembly Sl-S8 includes a "live" sensor l5 and a "dummy" sensor l6, indicated (Fig. 2) by full and open circles respectively. Suitable sensors for use on a stationary matrix machine are to be seen in our GB-A-209l003, these sensing the proximity of comparatively massive sealing frames on the hoods. Wiring l7 from each of these sensors is taken to a control cabinet l8. In the control cabinet the input Xp from each of the sensor assemblies Sl-S8 successively is processed in circuit 2 and compared with a demand position signal Xd generated in circuit l. The signal Xi derived from the comparison in the comparator is fed to the power circuitry 3 and thence through conventional power slip rings 4 to magnetic drive devices 5 mounted on the rotating hoods, to lift the sealing frames or allow them to lower. Such magnetic drive devices are disclosed in our GB-A-l559679 as well as in GB-A-209l003. The signal Xi to the magnetic drive device 5 causes it to move in an appropriate direction to adjust the gap between the seal frame 3 and the sensor assemblies Sl-S8. This signal is maintained until a signal from a succeeding sensor out of the sensor assemblies Sl-S8 indicates, as the hood passes it, that the gap is now wrongly set when that signal will alter the signal Xi and cause an adjustment in the positioning of the sealing frame. It can be seen that all the sensing and compar­ itively low amplitude signal circuitry is stationary; the control box may be and preferably is quite remote from the regenerator so that its electronic elements are not subject to the hostile environment in which the regener­ ator works. However, control signals passing from that box to the magnetic drive devices being of comparatively high amplitude or power can readily pass through convent­ ional slip ring constructions to the drive devices borne on the rotating part. Furthermore, the sensor assemblies Sl-S8 are arranged in a bridge circuit so that they are unaffected by temperature variations. Figures 4 and 5 show a rotating matrix machine with stationary ducts and sector plates. The rotating matrix 20 extends into ducts 2l,22 for air and gas respectively. There are sealing strips 25 on the matrix. Sector plates 23,24 are located between the ducts 2l,22, one on each side of the matrix 20, each sector plate 2l,22 having two wings carrying sensors Sll to Sl4 and magnetic drive devices Dll to Dl4. The sensors used are preferably those disclosed in our EP-A-l33793. As can be seen from Figure 5, the sensor and drive arrangement on the sector plate 23 above the matrix 20 is the same as that on the sector plate 24 below the matrix 20. As shown in Figure 4 the drive devices Dll to Dl4 are arranged on a diametrical line. The number of drive devices is dependent on the size of the air pre-­ heater. Each drive device Dll-Dl4 has a corresponding sensor Sll-Sl4 which controls its operation, the sensor being placed in a position in advance of the corresponding drive device. For large air preheaters it may be necessary to provide sets of two or more drive devices, each set having drive devices spaced circumferentially on the sector plate. Each set would then have a single sensor. In the embodiment of Figures 4 and 5 the output of the sensor Sll-Sl4 is passed to a control cabinet (not shown) as in the embodiment of Figures l to 3. There is a similar strategy of control from one sensor governing the position set by the sector plate in relation to the sealing strips 25 until it becomes apparent from the signal received from the subsequent sensor that correction is needed, in which case corrective drive is applied. It is often found that the air preheaters flex relative to the hub so each wing of the sector plates 23 and 24 have a corresponding arrangement of sensors and drive devices. It is possible to provide a dummy sensor adjacent each sensor Sll-Sl4 for temperature compen­ sations, which is particularly important at the hot end of the rotating matrix air preheater. Alternatively, circuitry in the control cabinet may be used to achieve this. Aspects of the present disclosure relating to a stationary matrix machine are claimed in EP-A-­ l37670, from which the present application was divided.

Claims: 1. A rotary regenerative air preheater having means for sealing between relatively rotatable parts (ll,l4; 20,23) of the preheater, and a plurality of drive means (5,Dll-Dl4) for driving the sealing means (l3; 23,25) in a predetermined axial relationship, and control means comprising a plurality of electrical sensors (Sl-8, Sll-l3) placed sequentially in the path of relative rotation of the sealing means, and a control circuit, each sensor being linked through the circuit to at least one associated said drive means (5, Dll-l4), the circuit including means for comparing the sensed axial relationship at each sensor with a predetermined axial relationship and driving the associated drive means to bring the sealing means to the predetermined axial relationship, whereby the sealing means is sequentially checked and adjusted as necessary on a plurality of occasions during each relative rotation, at least some of said sensors (l6) having comparison sensors (l5) adjacent to them and representing a preset gap. 2. A rotary regenerative air preheater according to claim l wherein the sensors (l5) circuit means comprise respective bridges two legs of which are a said sensor and comparison sensor. 3. A rotary regenerative air preheater according to claim l or claim 2 wherein the predetermined axial relationship is a gap of between l and 2 mm. 4. A rotary regenerative air preheater according to any one of the preceding claims wherein the control means includes a control box (l8) which is mounted stationary and remote from the preheater. 5. A rotary regenerative air preheater according to any one of the preceding claims wherein the preheater is of the rotating matrix type, the rotating seal means being strips (25) on the end faces of the matrix (20) and the sensors (Sll-l3) and drive means (Dll-l4) being borne on sector plates (23) of a stationary body of the preheater. 6. A rotary regenerative air preheater according to any one of claims l - 4 wherein the preheater is of the stationary matrix type, the rotating seal means being frames (l3) on rotating hoods (l4), the sensors (Sl-8) being stationary and the drive means (5) being borne on the hoods, electrical power supply means to the drive means including slip rings (4) about the axis of rotation of the hoods.

Inventors: GIBSON, STANLEY, TINDALL, COLIN
Applicants: DAVIDSON & COMPANY LIMITED
Application year: 1984
Main classification: F28D19
IPC codes: F16J15, G01B7, F28D19, F28D17, F23L15