US3163154A

US3163154A - Blower-type cleaning for heat exchanging apparatus

Info

Publication number: US3163154A
Application number: US305915A
Authority: US
Inventors: William F Cantieri; John R Thayer
Original assignee: Diamond Power Speciality
Current assignee: Babcock and Wilcox Co
Priority date: 1961-01-10
Filing date: 1963-08-14
Publication date: 1964-12-29
Anticipated expiration: 1981-12-29

Description

Dec. 29, 1964 w. F. CANTlERl ETAL 3,163,154

BLOWER-TYPE CLEANING FOR HEAT EXCHANGING APPARATUS Original Filed Jan. 10, 1961 4 Sheets-Sheet 1 1-5 {w {kg 1/ V I I 2,? id I y 4Q A \jifl /J j INVENTORJ.

D 9 w. F. CANTIERI ETAL 3,153,154

BLOWER-TYPE CLEANING FOR HEAT EXCHANGING APPARATUS Original Fil ed Jan. 10, 1961 4 Sheets-Sheet 2 g a E? 1414 161 7ressure lazyfrare! rfia. 5

Dec. 2

W. F. CANTIERI ETAL BLOWER-TYPE CLEANING FOR HEAT EXCHANGING APPARATUS Original Filed Jan. 10, 1961 4 Sheets-Sheet 4 United States Patent 2 Claims. (Cl. 122 sr2 The present invention relates to a continuous completely automatic system for selectively and sequentially controlling the operation of a plurality of fluid heater cleaners in heat exchanging apparatus. The present application is a division of prior co-pending U.S. patent application Serial No. 81,853, filed January 10, 1961.

In modern power boilers a continuing problem has been the effective control and regulation of the temperature of the final steam produced, particularly in view of such variables as boiler load, the type of fuel employed, and variations in temperature of the line gas entering the convection passes of the steam heating section as affected by the slagging conditions of the furnace. In view of the fact that the furnace walls or large capacity power boilers constitute a high percentage of the total heating surface and the heat absorption characteristics of the furnace walls have a major influence on the final steam temperature, selective controlled cleaning or deslagging of the furnace walls provides an extremely effective method of controlling the temperature of the final steam produced in the steam heating section in combination with conventional stem control devices. Conversely, haphazard cleaning of the furnace walls by manual operation of fluid heater cleaners, or soot blowers as they are usually referred to, or automatic haphazard operation as provided by systems heretofore proposed can and have resulted in drastic disruptions of the thermal equilibrium conditions of the power boiler resulting in large fluctuations in the final steam temperature. Although modern power boilers incorporate one or more steam temperature control mechanisms such as, for example, tilting burner mechanism, attemperation or desuperheater systems, and recycle flue gas damper controls, haphazard operation of the soot blowers as has been heretofore practiced has disrupted the iermal equilibrium conditions to the extent that the steam temperature controls have been unable to prevent the large fluctuations in final steam temperature. Such large fluctuations in the final steam temperature are undesirable particularly when the superheated or reheated steam is employed to drive a steam turbine for the gcneration of electricity, for example, preventing optimum design efiiciency of the turbine from being attained and producing fluctuations in the output power thereof.

In addition to avoiding large and abrupt deviations in the thermal equilibrium conditions of a power boiler by the operation of the soot blowers of equal importance is the necessity of preventing excessive slagging conditions from occurring along the furnace walls and convection passes which materially reduce the efiiciency of the boiler and can possibly result in permanent fouling necessitating a shut-down and physical cleaning of the fouled heat absorption surfaces. This necessitate that the automatic sequential operation of the soot blowers is closely correlated and balanced so as to maintain boiler cleanliness and thermal equilibrium so as to concurrently achieve optimum efiiciency and substantially constant final steam temperature.

Accordingly, it is a primary object of the present invention to overcome the problem heretofore present in the manual or automatic systems for operating soot blowers in heat exchanging apparatus by providing an improved fully automatic soot blower operating system which minimizes fluctuations in the. preselected final steam temperature, and concurrently prevents excessive slagging conditions along the heat absorption surfaces of the heat exchanging apparatus.

Another object of the present invention is to provide an improved operating sequence for a plurality of soot blowers in modern high capacity power boilers and automatic control means therefor whereby a plurality of. soot blowers in the generating section of the boiler and a plurality of soot blowers in the steam heating section of the boiler are selectively and sequentially operated responsive to the temperature of the final steam.

Still another object of the present invention is to provide an improved operating sequence for a plurality of soot blowers in a heat exchanging apparatus and which se quence embodies a predetermined delay-time period between the successive selected operation of the soot blowers enabling the stabilization of thermal equilibrium conditions after each soot blower operation and enabling response of the sensing means in order to properly select the next soot blower to be operated whereby fluctuations in the final steam temperature are minimized.

A further object of the present invention is to provide an improved fully automatic system for controlling the sequential operation of a plurality of soot blowers in large capacity power boilers and which system incorporates overriding control means herein assuring that each of the soot blowers are operated when excessive slagging conditions occur.

A still further object of the present invention is to provide a slag sensing device which on the accumulation of a predetermined thickness of slag on the heat absorption surfaces is effective to communicate this condition to the control system causing selective fully automatic operation of the soot blowers to remove the slag from the heat absorption surface.

Another object of the present invention is to provide an improved automatic control system for the operation of soot blowers in heat exchanging apparatus that relieves the operator for accomplishing other duties and which system is of simple design, durable operation, and of simple and economical installation.

Other objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a diagrammatic side elevation view partly in section of a typical high capacity power boiler to which the present invention is particularly applicable;

FIG. 2 is a schematic view of the control system adapted to provide selective and sequential operation of the soot blowers in the generating section and in the superheater or reheater section of the boiler shown in FIGURE 1;

FIG. 3 is a schematic view illustrating the operating angularity of a burner tilt mechanism;

PEG. 4 is a transverse vertical sectional View through a boiler tube provided with slag sensing device which is electrically connected to a differential amplifying means shown schematically;

PEG. 5 is a wiring diagram of the control circuit regulating the operation of the long-travel soot blowers in the steam heating section; and

PEG. 6 is a wiring diagram illustrating the control circuit regulating the operation of the wall blowers in the generating section of the boiler.

Referring now to the drawings and particularly FiG- water wall tubes extending along the walls of the boiler along which the rising heated flue gases pass. The walls of the steam generating section 1b are provided with a plurality of wall blowers generally indicated at 12, which are automatically operable in accordance with the control system subsequently to be described, to discharge a suitable cleaning medium such as air, steam, or mixtures thereof, for example, against the heat absorption surfaces of the steam generating section to remove the accumulation of slag and the like therefrom. A typical soot blower construction suitable for this purpose is disclosed in US. Patent No. 2,662,241 which is of the shorttravel retracting type whereby the discharge nozzle thereof is projected into the boiler during operation and 1s retracted to a position beyond the furnace wall during the intervals between blowing operations. The proecting and retracting movement of the soot blower nozzle can be conveniently achieved by a suitable electric motor drivingly connected to the soot blower operating mechanism providing for remotely controlled operation.

The typical power boiler 8 shown in FIGURE 1 is also provided with a superheater section generally indicated at 14 including a pendant type superheater bundle 16 extending downwardly from the upper end of the first pass and a series of superheater bundles 18 disposed one above each other in the second pass of the boiler. Inasmuch as the tubes of the superheater bundles l6 and 18 extend across the first and second passes of the boiler, soot blowers of the long-travel retractable type are usually employed to provide cleaning and deslagging of the heat absorption surfaces thereof. A suitable soot blower of the foregoing type is described in US. Patent No. 2,885,711 and incorporates a lance having a nozzle at one end thereof which is projected into the boiler durmg operation and is thereafter retracted to a position beyond the surface of the boiler wall during intervals of nonuse. The lance tubes are generally adapted to rotate during their projecting and retracting travel whereby the cleaning medium discharged from the nozzle is directed against the heat absorption surfaces of the tube bundles causing the effective removal of soot and slag accumulations thereon. A suitable driving means such as an electric motor is employed enabling remote controlled operation thereof. The long-travel soot blowers 2t and the short-travel wall blowers 12 are generally arranged in a series of rows at a prescribed spacing so as to achieve a slight overlapping between the cleaning patterns of adjacent blowers thereby assuring proper deslagging of all of the heat absorption surfaces. The soot blowers are generally operated one at a time to avoid overloadmg the capacity of the blowing system.

In addition to the Wall blowers 12 and long-travel blowers 20 for cleaning the furnace water wall tubes and superheater tube bundles, respectively, additional soot blowers usually of the long-travel type are also provided for deslagging a slag screen generally indicated at 22 and any reheater bundles in power boilers provided with a reheat section. The operation of the soot blowers adjacent to the slag screen 22 can be conveniently tied in with the operating sequence of the wall blowers 12. In power boilers provided with an economizer section generally indicated by the economizer tube bundle 24 one or more additional soot blowers can be provided to deslag the economizer tube bundle and which can be operated independently of the remaining soot blowers and preferably on a straight time cycle. In addition an air heater section generally indicated at 26 can be provided with a plurality of soot blowers which are also independently operable on a straight time cycle to re move soot and other extraneous material from the heat exchange surfaces thereof.

The automatic soot blower operating sequence control system as specifically shown and described herein functions to control the sequential operation of the wall blowers disposed along the furnace wall water tubes of the steam generating section as one group which also can include soot blowers along the slag screen 22 if present, and a second group comprised of the long-travel soot blowers 2G disposed adjacent to the

superheater bundles

16 and 18 of the superheater section 14 in response to the temperature of the superheated steam produced. It is also contemplated within the scope of the present invention that the automatic control system herein described is equally applicable to power boilers provided exclusively with reheater tube bundles wherein the opera tion of the soot blowers is established by the temperature of the reheated steam and to boilers having a combined superheater section and reheater section.

The automatic control of the operation of the soot blowers is predicated on the heat absorption characteristics of the steam generating section It and the steam heating section or superb-eater section 14 as specifically shown in the drawings. As slag and soot accumulate on the surfaces of the walls in the steam generating section the absorption of heat in this section decreases with a corresponding rise in the temperature of the flue gases passing through the superheater bundles l6 and 18. In addition, the slag on the surfaces of the steam generating section increases the reflection of radiant heat against the pendant type superheater bundles 16 causing a further increase in the temperature of the superheated steam produced. Conversely, the accumulation of soot and slag on the surfaces of the tubes of the superheater bundles id and 18 decreases their heat absorption and increases reflection of radiant heat directed thereagainst tending to reduce the temperature of the superheated steam. Accordingly, by controlling the slagging conditions in the steam generating section 1% and the superheater section 14, a dynamic equilibrium can be established with respect to the heat absorption characteristics of the heat transfer surfaces therein whereby the resultant temperature of the superheated steam can be maintained within a relatively small range. Since in modern power boilers the furnace walls of the steam generating section constitute a high percentage of the total heat transfer surface, the slagging condition of the furnace Wall has a greater effect on the superheated steam temperature than does the slagging condition of the superheater tube bundles. For this reason, the operation of the wall blowers in the steam generating section It} constitutes the primary control of the superheated steam temperature while the operation of the long-travel blowers of the superheater tube bundles constitutes a secondary control.

Under typical boiler operating conditions when the final steam temperature rises to a predetermined level indicating low heat absorption in the steam generating section a suitable sensing device actuable in response to the temperature of the final steam is operative to cause successive and sequential operation of the wall blowers 12 in the steam generating section thereby progressively increasing the heat absorption characteristics thereof with a corresponding reduction in the temperature of the flue gases entering the convection passes and a reduction in the temperature of the final steam. After a period of sequential operation of the wall blowers, the heat absorption in the steam generating section is increased to the point where the temperature of the flue gases is reduced to a level where the temperature of the final steam decreases to a preset limit wherein the sensing means are operative to discontinue operation of the wall blowers and initiate operation of the long-travel blowers 29 in the superheater section increasing the heat absorption characteristics thereof with a corresponding rise in the final steam temperature. The operation of each of the wall blowers 12 or the long-travel blowers 20 produces an incremental increase in the heat absorption characteristics of the furnace walls or superheater bundles, respectively. Since the incremental increase in heat absorption is not immediately reflected in the temperature of the superheated steam,

suitable delay timers are incorporated in the control circuits of the wall blowers and the long-travel blowers providing for a period of inactivity between the operation of successive blowers to enable stabilization and re-establishment of thermal equilibrium conditions within the boiler thereby enabling the elfect of the operation or" each soot blower to be reflected in the temperature of the superheated steam. Accordingly, in the preferred practice of the present invention a delay-time period between the operation of successive wall blowers usually ranging from about seconds to about 3 minutes enables reestablishment of thermal equilibrium conditions while a delay-time period ranging from about 5 to about minutes is usually employed between the successive operation of the longtravel blowers in the superheater section. The necessity and duration of the delay-time period are, of course, dependent on the specific design characteristics of a boiler in winch the system is employed and can be varied to achieve optimum operation. In some power boilers, all or certain groups of blowers can be operated in rapid succession without any appreciable delay-time period between successive blowers. In the usual and preferred practice, however, delay-time periods are provided in the system of the general magnitude set forth above. By virtue of the delay-time period between successive soot blower operation and selective correlated operation of the wall blowers and long-travel blowers, large disruptions in the thermal balance of the boiler are avoided enabling accurate control of the final steam temperature. In manual systems and automatic soot blower systems heretofore proposed it has been common practice to operate all of the soot blowers in each section in rapid succession causing an abrupt change in the thermal balance of the boiler and a corresponding large fluctuation in the temperature of the final steam which frequently is as high as 30 F. An experimental installation of the automatic control system comprising the present invention in a modern large capacity boiler has provided extremely close control of the final steam temperature with deviations thereof restricted to a range of usually from about 5 F. to 8 F. Moreover, the automatic control system has provided a conservation of the soot blower blowing medium, a minimum of labor for regulation and observation, and less corrective action by the steam temperature control mechanisms.

The alternate selective operation of the wall blowers 12 in the steam generating section iii and long-travel blowers 2d in the superheatcr section i4 is controlled by conventional steam temperature controls which are arranged in accordance with the arrangement illustrated in FIGURE 1 and the schematic diagram shown in FIG. 2. As shown in FIGURES 1 and 2, a suitable temperature sensing device =23 such as the thermocouple, resistance thermometer, or bulb'like pyrometer, for example, is associated with the superheater or reheater steam outlet 29, as the ease may be, which is electrically connected to a suitable controller 39 of the type well known in the ant which converts the intelligence communicated thereto to an actuating energy such as a variable air loading pressure which is directly fed to a suitable steam temperature compensating mechanism such as an attemperator 31 in the steam outline and a variable flue gas recirculation damper mechanism 32 as shown in FIGURE 1 or a tilting lburner mechanism 33 as shown in FIGURE 2. The actuating air loading pressure can also be directly fed to a pressure operable selector switch TS which in response to the pressure applied is operable to alternately select and energize the wall blower operating sequence in the steam generating section or the longstrave-l blower operation in the superheater section.

The temperature compensating mechanism may comprise any one of a variety of control devices intended to compensate for changes in the final steam temperature such as, for example, a conventional burner tilt mechanism, variable dam er control for re ulatin the recir- O cuiation of spent flue gases to the-first pass of the boiler steam temperature.

' soot blower control system in combination with a director the amount of excess combustion air, or attemperation of the final steam by either a surface or direct contact type attemperatorr The foregoing compensating devices may be employed singly or in combination to prevent aggravated disruptions in the thermal equilibrium of the power boiler. In a tilting type burner mecham'sm 33 as shown schematically in FIG. 3, the air loading pressure derived from the controller 30 is effective to actuate suitable reversible motor means 34 connected to a burner 36 causing the burner to tilt upwardly or downwardly in response to the temperature of the final steam. Genenally, burner tilts ranging up to about 30 above and below "a horizontal position are usually satisfactory vto effect a substantial change in the radiant heat directed against the water wall tubes in the steam generating section affecting the heat absorption thereof with a resultant effect on the temperature of the final steam. It will be apparent that by tilting the burner upwardly the radiant heat transmitted to the superheater section is increased and the heat absorption in the steam generating section is reduced resulting in a rise in the temperature of the final steam. Conversely, by tilting the burner downwardly an increase in the absorption of heat bythe steam generating section is achieved with a concurrent reduction in the radiant heat to the superheater section producing a decrease in the temperature of the final steam. 'It is also contemplated within the practice of the present invention that the actuation of the selector switch TS as shown schematically in FIG. 3 can be achieved by or in response to suitable switch means incorporated in the tilting burner mechanism in accordance with the angularity of tilt of the burner relative to the horizontal position. In the tilting burner mechanism schematically shown in FIG. 3, it is preferred to incorporate an angular overlap indicated at X of about 20 for example, to provide a :suliicient tilt variation in the burner to spread the slag spray therefrom over a wider area of the furnace. Accordingly, as :the burner moves down wardly from a position disposed above the horizontal in response to an increasing temperature :of the final steam, actuation of the selector switch TS is not achieved until the burner as completes the are indicated by the arrow Y. Similarly as the burner moves upwardly due to a decreased temperature in the final steam temperature, the selector switch TS is not actuated until the burner has completed the angularity indicated by'the arrow Z.

In a similar manner in the case of a variable damper control compensating mechanism for controlling the temperature of the flue gases by regulating the rate of recircuiation of the flue gases to the firl St pass :of the furnace, the angularity of the dampers between a fully closed and fully open position can be utilized to actuate suitable limit switches associated therewith or the selector switch TS directly whereby selective operation of the wall blowers or longatravel blowers is accomplished. The actuation of the selector switch TS can also be accomplished by a flow switch incorponated in the iatternperator water line of surface or direct contact [type attemperator which is presettable to be tripped when the water flow rate attains a preselected rate. A suitable overlapping area similar to that utilized in the case of the tilting burner mechanism as shown in FIGURE 3 can also be employed in the case .of the variable recirculating flue gas damper and the flow switch in the attempenator water system.

Although the foregoing compensating mechanisms are effective to regulate the temperature of the final steam, they are nevertheless susceptible to causing substantially large fluctuations in the final steam temperature. The automatic sequential soot blower operating sequence comprising the present invention operating in conjunction with the compensating devices of the type liereinbefore described is effective to substantially reduce these temperature fluctuation providing for a substantially uniform final Moreover, the automatic sequential contact type attemperator reduces the amount of water sprayed into the superheated or reheated steam to reduce and control the temperature thereof. This constitutes another advantage because large quantities of water are undesirable since any unevaporated droplets in the final steam introduce a serious errosion problem of the steam turbine blades.

The operating sequence of the soot blowers as provided by the automatic control system comprising the present invention will now be described in connection with the control wiring diagrams shown in FIGURES and 6. The wiring diagram of FIGURE 5 illustrates the control circuit regulating the operation of the long-travel blowers in the superheater section and is interlocked with the wiring diagram of FIGURE 6 which comprises the control circuit regulating the selective sequential operation of the wall blowers 12 in the steam generating section of the boiler. The wiring diagrams of FIGURES 5 and 6 are electrically connected together at junctions I1J1, J2J2, J3J3, I i--14, and l5l5, respectively. The exemplary circuitry as shown in FIGURES 5 and 6 incorporates stepping switches for selecting specific sub groups of soot blowers within the long travel soot blower group and the wall blower group and a second stepping switch for sequentially selecting an individual soot blower for operation within the selected sub group. A suitable time delay relay is further incorporated to provide for a preselected time delay period between the operation of successive soot blowers within each sub group. A minimum cycle timer is provided to prevent the operation of the soot blowers too frequently. Interlocking circuitry is provided between the wiring circuits of FIGURES 5 and 6 to prevent energization of a soot blower such as a wall blower, for example, before a long travel soot blower has completed its operation and vice versa. Since the wiring diagram of the control circuit shown in FIGURE 5 for controlling the selective and sequential operation of the long-travel blowers is essentially identical to the wiring diagram of FIGURE 6, the numbers and letters employed in FIGURE 5 to designate components of the control circuit have also been employed for similar components in FIGURE 6 with a prime affixed thereto. The system is energized by closing main disconnect switch 38 whereby electrical power received through main transmission conductors L1, L2, and L3, is transmitted to the open starter contacts of each of the soot blower motors 40,

' 40 of the long-travel blowers such as the blower 29a and wall blowers such as the blower 12a, respectively, as shown diagrammatically in FIGURES 5 and 6. In addition the closing of the main disconnect switch 38 energizes I the control circuits through a control power transformer 42 initiating the selected automatic sequential operation of the soot blowers.

In order to facilitate a review of the circuit diagrams shown in FIGURES 5 and 6, the individual components have been labeled in accordance with the following letter code:

(ZR-control relay CRRreverse control relay CRFforward control relay TDtime delay relay TMtimer motor TCtimer clutch LSR-reverse limit switch LSFforward limit switch TSR-transfer stepping switch (for selecting a particular group of soot blowers for operation) SRstepping switch (for selecting individual sequential operation of soot blowers within a group) S-socket SW-manual group selector switch IC-interrupting contact ONC-off normal contact TLC-time closed contact Q as:

Under a boiler operating condition wherein the temperature of the final steam is in the lower portion of a preselected operating range, the selector switch TS has closed its contact TS1 in the control circuit of the longtravel soot blowers as shown in FIGURE. 5. Under these conditions, one or a combination of the supplementary steam temperature compensating mechanisms, if the boiler is so equipped, have also assumed an operating condition so as to promote an increase in the temperature of the final steam. For the purposes of illustrations each control circuit is designed to operate two groups of soot blowers comprising two soot blowers in each group. For example, in the long-travel soot blower circuit shown in FIGURE 5, the control circuits of the two soot blowers comprising group I are respectively connected to the terminals I31 and D2 and the two soot blowers comprising group 2 are individually connected to the terminals indicated at D3 and D4, respectively. It will, of course, be appreciated that the particular automatic control system herein shown and described is adapted to operate a large number of soot blowers in both the steam generating section and superheater section such as, for example, in numbers as hi h as about 643 which may be arranged in four individual groups comprising 15 soot blowers in each group.

Selection among the various groups within the longtravel soot blowers in the superheater section or within the wall blowers in the steam generating section is achieved by a conventional 26 position transfer stepping switch of the type employed in telephone switching apparatus and the like incorporating a bridge rectifier and condenser and generally indicated at TSR, TSR. The sequential stepping movement of the transfer stepping switch from one contact to the next contact is achieved by a solenoid actuated mechanism which is energized after all the blowers in one group have been operated. Sequential selection of the soot blowers within any one group is achieved by a similar 26 position transfer stepping switch which is generally designated at SR1, SR1. It is usually convenient but not necessarily restrictive to combine the soot blowers in one general area of the power boiler within the same group. Frequently the soot blowers are positioned in a series of vertically spaced horizontal rows comprising a plurality of soot blowers in each row. Each horizontal row or tier of soot blowers can be conveniently incorporated within one group which on selection by the transfer stepping switch TSR, TSR are caused to successively operate in accordance with the preselected sequence as provided by stepping switch SR1, SR1. In some instances it may be desirable to operate the groups of soot blowers sequentially commencing with the lowermost row and moving upwardly therefrom to the next row and so on until all of the groups have been operated. Alternatively, it may be desired to scramble the operating sequence of the individual groups whereby the groups are operated in random sequence jumping from one level of the power boiler to another depending on the specific scrambling sequence desired.

To enable scrambling between the groups of soot blowers as shown in FIG. 5, plugs P1 though P4 are provided which can be alternately connected in sockets S-IA, S-lB, 84A and S-2B to achieve the desired group sequence. In the specific arrangement shown in FIG. 5, the connection of the plugs P1 to P4 .to the sockets S-1A, S1B, S-ZA and S-2B, effects successive energization of the plugs P1 through P4 as established by the transfer stepping switch TSR which will cause alternate operation of the

groups

1 and 2. It will be appreciated that where a large number of groups are provided a large number of variations in the group sequence is feasible merely by interchanging the connections betwen the plugs and the corresponding sockets.

In the specific control circuit shown two sets of sockets are provided for each group of soot blowers which causes each soot blower in each group to operate twice during each sequencing cycle of the control system. However, each group circuit is provided with a group selector providing still funther flexibility and versatility in the operating sequence of the soot blowers and can be positioned in either one of three positions The group selector switch in the circuit of group 1 is provided with contacts SWl-A, SWl-B, SWl-C and SWl-D, and the group selector switch in the circuit of group 2 is provided with contacts SWA, SW-B, SW-C, and SW-D. When in an Oil position the group selector switch in the group it circuit for example, closes contacts SWl-A, SWl-C whereby the group circuit is bypassed and the transfer stepping switch TSR is quickly step transferred to the next group whereby the soot blowers in group 1 are not operated during the operating cycle of the control system. In the number 1 position of the group 1 selector switch, contacts SW1B and SWi-C are closed whereby the soot blowers in group 1 me operated once per cycle on energization of socket S1A and are bypassed on energization of socket S-lB. When the group selector switch is in the number 2 position contacts SW1B and SWl-D are closed whereby the soot blowers of group 1 are operated twice during each operating cycle of the control system.

With the selector switch contact TS1 closed, the transfer Stepping switch TSR in the number 2 position, for example, and with the stepping switch SR1 in its number one position, for example, the long-travel soot blower such as the soot blower 20a schematically shown in FlGURE 5, which is connected to the terminal D-l is energized md concurrently time delay relay TDI and control relay CR1 are energized and timer motor TMZ is running. At the same time time delay relay TD3, control relay CR2, transfer stepping switch TSR and stepping switch SRl are deenergized. Energization of the blower motor 40 of the long-travel soot blower Zila as shown diagrammatically in FIGURE is achieved through contacts lCSRll, lCTSR-l, CR1l, CR2l, TS?l, TDl-Z', TSR-ZC, plug P1, socket SllA, group selector switch contact SWl-B, SR11A, applying power to the terminal D-i which is electrically connected by conductor 41 to terminal A-Z in the control circuit of the soot blower a energizes the forward starter coil of the forward control relay CRF through the manual reverse switch contact 44 and normally closed contacts LSF-l and CRR-1. Energization of forward control relay CRF causes it to close its holding contact CRF1 and contact CRF2, lighting forward indicator light 56a and opens its normally closed contact CRF-S to prevent energization of reverse control relay CRR, and closes motor contacts car-4 energizing the blower motor 4% whereby the lance tube 46 thereof commences its projecting travel through a port 48 in the furnace wall 59. As the lance 46 moves forward, rear limit switch LSRa is released and closes its normally open contact LSR-la and opens its normally closed contact LSR2a in the series circuit (GG) including the remaining normally closed contacts such as LES-2b, etc. which in turn deenergizes time delay relay TDl which opens its contact TDl-l (T.C.) controlling relay CR1 and deenergizes control relay CR1. The series circuit (G-G) incorporates the normally closed contact of the rear limit switch of each soot blower in a series such that the series circuit is opened each time a soot blower advances from its fully retracted position toward the projected position. Deenergization of control relay CR1 causes its normally closed contacts CRl-Z to close thereby energizing control relay CR2 In addition, deenergization of control relay CR1 causes its normally open contact CR1-1 to open removing electrical energy from the terminal D1 and the conductor 41 connected to terminal A-Z of the blower circuit. However, the holding contact CRF-l which has been closed on the energization of forward control relay CRF closes the circnit between the A-Z terminal of the soot blower circuit and the A-l terminal of conductor 51 through a parallel iii holding circuit maintaining the forward control relay CRF energized.

The lance tube 46 continues its forward travel until it attains its fully projected position. On reaching the fully projected position, the lance tube actuates forward limit switch LSF which opens its contact LSF-l deenergizing the forward control relay CRF. Deenergization of forward control relay CRF causes its motor starting contact CRF4 to open deenergizing the blower motor 415 and simultaneously opens its contacts CRF-l and CRF-Z which extinguishes the forward indicator light Eda and deenergizes the terminal A-2 in the blower circuit. Simultaneously, the normally closed contact CRF-3 is closed energizing the reverse control relay CRR. Energization of a reverse control relay CRR causes it to open normally closed contact CRR-l to prevent energization of the forward control relay CRP and closes reverse indicator light 52a, contact (ERR-2 and reversing motor contacts CRR-S causing a reversal in the direction of rotation of the blower motor 40 whereby the lance tube 46 commences its retracting movement. After the initial retracting movement of the lance tube, the forward limit switch LSF is released permitting normally closed contact LSF-l to close and the lance tube continues its retracting movement until reverse limit switch LSRa is tripped when the fully retracted position is attained. The tripping of limit switch LSRa causes the opening of normally open contact LSR-la deenergizing reverse control relay CRR which opens its contacts CRR-Z and CRR-3 extinguishing the reverse indicator light 52a and deenergizing the blower motor 4!), respectively, and simultaneously closes normally closed contact CRR-l. In addition, the tripping of reverse limit switch LSRa causes its normally closed contact LSR-Za to close in the series circuit (GG) which energizes time delay relay TDl which commences to time a predetermined time period. It is the function of the time delay relay TDl to provide a predetermined delay time period between the successive operation of the blowers to enable stabilization and reestablishment of thermal equilibrium conditions within the power boiler as hereinbefore set forth. As hereinbefore set forth, the delay time period can be varied for any one specific boiler installation from a duration of substantially zero to an appreciable time delay, such as several minutes, for example, to achieve optimum operation. v

At the completion of the predetermined time delay period, time closed contacts TDl-ll are closed thereby energizing control relay CR1 which opens its normally closed contacts CRIl-Z. Simultaneously, control relay CR1 closes its contacts CRl-S and CRl-l wherein the coil of stepping switch SR1 is energized through contacts CR1-3 and CRZ-Zl and ONC-SRl-Z contacts. Energization of stepping switch SR1 causes its interrupting contact IC-SRl-l to open whereby control relay CR2 is deenergized. Deenergization of control relay CR2 causes its contact CR2-3 to open thereby deenergizing the solenoid coil of the stepping switch SR1 causing step transfer thereof to the number two position and in which position it again closes its interrupter contact IC-SRl-l and closes number 2 position contact SRl-ZA energizing the terminal D-Z connected to the second one of the blowers in group 1 through a conductor similar to conductor 4-1 connected to the A-Z terminal (not shown) of the second soot blower control circuit. Accordingly, the long travel blower such as a soot blower 20]; (not shown) connected to terminal D-Z will commence its projecting travel in accordance with the cycle hereinabove described in connection with the first long travel blower.

After the second long-travel blower has completed its operation and has attained the fully retracted position stepping switch SR1 is step. transferred to its third position whereby contact SRl-3A is closed and power is applied to the coil of stepping switch SR1 through contacts SRl-3A and off normal contact ONCSRl-2. Thereafter the rapid opening and closing of interrupter contact ICSR11 will cause the stepping switch SR1 to fast step transfer through spare contacts SR1-4A to SR1- 24A which are connected in parallel to each other as indicated in dotted lines to its 25th position on attainment of which will cause its contact SR12K to close energizing the coil of the trarisfer stepping switch TSR. Energization of the TSR coil causes its normally open interrupting contact IOTSR2 to close energizing the coil of stepping switch SR1 through contact ONCSR12. Energization of SR1 in turn causes its contact ICSRl2 to open deenergizing the coil of TSR which in turn opens its interrupting contact IC-TSR-Z deenergizing the coil of stepping switch SR1. Accordingly, the transfer stepping switch TSR step transfers to its third position and the stepping switch SR1 step transfers to its 26th or Off position. In the third position, transfer stepping switch TSR closes its contact TSR-3C and contact IQTSR1 thereby energizing plug P2. Accordingly, power is now applied to the coil of the stepping switch SR1 through interrupter contacts IC-SRl-l, interrupter contact IC-TSR-l, CRl-l, (11224., TS-l, TD1-2', TSR-3C, plug P2, socket S2A, group selector switch contact SW-B, and contact Sill-25. Energization of the coil of stepping switch SR1 causes its interrupter contact lO-SRl-l to open causing the stepping switch SR1 to transfer to its number one position. Accordingly, the terminal D-3 connected to the first blower of group 2 will be energized on closing of contact lCSRlll and SRl-lB which will undergo its projecting and retracting travel in accordance with the cycle hereinbefore described. Thereafter the long-travel soot blower connected to terminal Dl will be caused to operate in the same manner after which the stepping switch SR1 will fast transfer to its 25th position wherein the transfer stepping switch TSR will be caused to step transfer to its number four position causing its contact TSR-4C to close thereby energizing plug P3. The soot blowers of group 1 having their socket SlB connected to plug P3 will undergo sequential operation followed thereafter by subsequent energization of plug P4 to which the group 2 blowers are connected causing their sequential operation.

t the completion of the second cycle of the group 2 soot blowers, the transfer stepping switch TSR transfers from its fifth position to its sixth position and will be caused to fast transfer through its interrupting contact IC-TSR1 and spare contacts TSR-6D through TSR-24D which are connected in parallel to each other until it reaches its 25th position. At this point the transfer step ping switch TSR is prevented from fast transferring to its 26th or Otf position unless the minimum cycle timer, comprising timer clutch TC-Z which may be of the electromagnetic or solenoid actuated types well known in the art, contact T2, and timer motor TMZ, has completed the timing of a predetermined time period thereby preventing the initiation of another complete cycle so as to assure that the system is not operated too frequently. If the minimum cycle timer has completed its timing period or upon expiration of that timing period its contact TMZ- 1 is closed whereby the transfer stepping switch TSR transfers to its 26th position through contacts TSR-25D and TMZ-l.

On attaining its 26th position the off normal contact ONC-TSR-3 of the transfer stepping switch TSR is closed energizing time delay relay TDS which opens its time closed (T.C.) contact TD31 having a two second delay enabling the resetting of minimum cycle timer. In addition, after a delay period, time closed contact TDS-Z closes whereby the coil of the transfer stepping switch TSR is energized through contacts TSR-26D and TD3-2. Energization of the coil of the transfer stepping switch causes its interrupter contacts ICTSR1 to open deener gizing the TSR coil and causing the transfer stepping switch to step transfer to its number one position. The

entire operating sequence as hereinbefore described is thereafter repeated.

The operation of the wall blower circuit is essentially identical to that hereinabove described in connection with the control circuit for the long-travel soot blowers. The wall blower circuit similarly incorporates a minimum cycle dwell timer comprising a timer clutch TCZ' and timer motor TMZ' and an adjustable limit switch contact T2 which opens deenergizing the timer motor T M2 on the expiration of the preset time period.

In typical well designed and properly controlled power boilers, the completion of the cycle of the operation of the wall blowers and the cycle of operation of the longtravel blowers generally falls after the time period provided by the minimum cycle timer. Accordngly, the wall blowers and the long-travel blowers are operated essentially all of the time in the sequence provided by the control circuit and in accordance with the selectivity of the selector switch TS in response to the temperature of the final steam. The system as disclosed is essentially a continuous one wherein either one of the Wall blowers is operating or one of the long travel blowers is operating. Brief periods of inactivity are of course provided by virtue of the delay timers operative to space the successive operation of the soot blowers to provide for stabilization and equalization of the thermal equilibrium conditions in the boiler. inasmuch as the selector swtich TS is operative to open and close its contacts TS-l, TSll at any point in the operating cycle of the wall blowers or the long travel blowers. the control circuits shown in FIGS. 5 and 6 are mutually interlocked by time delay contacts TDl2' and TDl2, respectively, to prevent operation of a blower in one boiler section while a blower is still operating in the other boiler section. For example, the deenergization of time delay relay TDll in the control circuit for the long-travel blowers by the opening of a reverse limit switch contact LSR2a in the seri s circuit (GG) causes the opening of its instantaneous contact TD12 disposed in series adjacent to the selector switch contact TS-l' of the wall blower circuit as shown in FIG. 6 preventing energization of a wall blower should the selector switch contact TS-l' close after the long-travel blower has initiated operations. When the long-travel soot blower has completed its operating cycle the reverse limit switch contact is closed in the series circuit (GG) reenergizing the time delay relay TDl which closes its contact TDl-Z enabling initiation of operation of the appropriate wall blower in accord ance with the sequence provided by the control circuit of FIG. 6. Similarly, the moment the wall blower initiates operation wherein its reverse limit switch contact opens in the series (G-G') circuit, time delay relay TDl opens its instantaneous contact TDl-Z. in the control circuit of FIG. 5 preventing initiation of the operation of a long-travel blower as selected by the closing of selector switch contact TS1 until the completion of the operating cycle wall blower.

By virtue of the group selection and individual blower selection provided by transfer stepping switches TSR, TSR and selector switches SR1 and SR1, deenergiza tion and energization of the control circuits of FIGS. 5 and 6 causing interruption and resumption of their respective operating cycles assures that the next soot blower in the cycle is operated in each control circuit on re sumption of operation in accordance with the sequence at the time the control circuit was interrupted. By this arrangement the soot blowers in the steam generating section and in the steam heating section undergo a prescribed operating sequence in accordance with the predetermined cycle which is alternately interrupted and resumed by the selector switch actuable in response to the temperature of the final steam.

While the specific control system shown and described herein embodies the alternate operation of the wall blowers in the steam generating section and the long travel, blowers in the steam heating section such as the superheater section or reheater section, it will be appreciated by those skilled in the art that a basic form of the control system is one which is effective to control the o eration of only the wall blowers in the steam generating section. In such event, the selector switch would be operative to energize the control circuit as shown in PEG. 6 at such times as the final steam temperature increased to a preslected level and to deenergize the control circuit by moving to an Off position when the steam temperature decreased to a preselected level. The operation of the soot blowers in the steam heating section and other sections of the boiler under such circumstances, could be controlled on a straight time cycle sequence or by a slag sensing device subsequently to be described and operative independently of the automatic selective control sequence of the wall blowers, or during those periods when the wall blowers were not operat mg.

it is also contemplated within the scope of the present invention that a suitable slag sensing device of the type schematically shown in FIG. 4 can be employed and is particularly applicable to operation of the long-travel blowers in the super-heater section of the power boiler. However, the slag sensing device can be incorporated at any heat exchange surface to provide automatic controlled operation depending upon the accumulation of a predetermined layer of the slag and the like. The slag sensing device can be employed to override the temperature sensing selector switch TS calling for selective automatic sequential operation of the long-travel blowers whenever a predetermined slagging condition exists in the superheater section. In the event of such a slagging condition, the slag sensing device operates causing operation of the long-travel blowers either to the completion of their cycle or until the slagging condition is alleviated. It is also contemplated that several slag sensing devices can be incorporated at various locations each of which is adapted to operate a selected group of sootblowers.

The slag sensing device as shown in FIG. 4 is installed along the surface of a superheater tube 52, the periphery of which is coated with a relatively thin layer of slag 54- as shown in solid lines. A pair of temperature sensing elements such as thermocouples 56a, 56b, for example, are disposed with the ends thereof in radially spaced relationship relative to the boiler tube 52. The end portion of the thermocouple 56a is affixed to the peripheral surface of the superheater tube 52 such as by soldering or brazing while the end portion of the thermocouple 56b normally projects into and is exposed to the hot flue gases passing through the superheater tube bundle. The distance separating the end portions of the thermocouples 56a, 55b, is adjustable and establishes the thickness of the layer of slag on the superheater tube 52 which will cause the temperature sensing device to be actuated causing the overriding sequential operation of the long-travel blowers in the superheater section. Tne thermocouples 56a, 56b are suitably mounted on a suitable strap and hanger assembly 58 providing for adjustable radial movement of the thermocouple 56b relative to the periphery of the superheater tube 52 and maintaining the thermocouples in appropriate adjusted relationship. The current or voltage generated at the end junctions of the thermocouples 56a, 56b, is fed into a suitable differential amplifying means 60 of any one of a number of types well known in the art which on the happening of preselected conditions as subsequently described, is effective to actuate a switch DA as shown in FIGS. 2 and 4 to cause the energization of control relay CR3 in the control circuits of the long-travel soot blowers.

The use or installation of the slag sensing device in the control circuit of the long-travel soot blowers is illustrat d in FIGURE 5. The slag sensing device of a type illustrated in FIGURE 4 provides an overriding action to the automatic control circuit in the event a preselected accumulation of slag has occurred on the heat exchanger surfaces. The differential amplifying. means 60 (FIG. 4) is operable in response to the sensing of a preselected accumulation of slag on the surfaces of the heat exchanger tubes to operate a switch DA as indicated in FIGURES 2 and 4 to effect a closing of a contact indicated at DA1 inFIGURE 5 which is positioned in series with the coil of control relay CR3. Accordingly, in response to the closingof contact DA-ll, control relay CR3 is energized which in turn closes its contact CR32 positioned in parallel around the selector switch contact T84 and time delay relay contact TDl-Z to keep the system operating. Simultaneously, the energization of control relay. CR3 causes its normally closed contacts CR3-l and CR3-3 to open which are disposed and interlocked in the control circuit of the wall blowers as shown in FIGURE 6 preventing the operation of the wall blowers in spite of the closing of contact T34 in the wall blower circuit until the long-travel blowers have completed their operating cycle.

In accordance with this arrangement, the long-travel blowers complete the remaining portion of their cycle after which the transfer stepping switch TSR is fast transferred to its 26th position whereupon oif normal contact ONC-TSR3 closes energizing time delay relay TD3 which opens its contact TD3-1 deenergizing control relay CR3 causing an opening of its contact CR3-2 and a closing of its normally closed contacts CR3-ll and CR3-3. If, during the operation of the long-travel blowers as controlled by the slag sensing device, the slag deposit is removed thereby restoring the slag sensing device to its normal position, the differential amplifying means causes, contact DA-fl to open deenergizing control relay CR3 whereupon the system resumes its normal preselected operating sequence.

In operation, the thermocouple 56a registers the temperature substantially equal to the temperature of the superheated steam passing through the tube which may range, for example, in the order of about 1000 to about 1500 P. On the other hand, the thermocouple 561) will register the temperature of the flue gases adjacent to the superheater tube 52 which can range for example, from about 1700 F. to about 2200 F. Accordingly, as long as the layer of slag 54 around the superheater tube 52 does not encompass the thermocouple 5611 a differential temperature reading between the thermocouples 56a and 5612 will be transmitted to the differential amplifying means 6!). When the layer of slag 54 builds up to a thickness as shown in phantom in FIG. 4 and exaggerated for the purposes of illustration, wherein the end portion of the thermocouple 56b becomes coated with and insulated from the surrounding flue gases, the temperature reading of the thermocouple 5612 will rapidly approach that of the thermocouple of 56a. .When the dilferentialtemperature readings of the two thermocouples 56a, 56b approach each other to within a preselected differential, the differential amplifying means 6%} is 0perated and is effective to override the automatic selective sequential operation of the soot blower system causing the wall blowers 29 to be operated regardless of the position of the temperature selector switch TS.

The slag sensing device can also be satisfactorily employed in the independent control systems such as, for example, in the economizer section which normally uses a straight time cycle for operating the soot blowers. In addition, the slag sensing device can be employed on the slag screen 22 of the power boiler to operate a series of long-travel blowers independently of the control system hereinbefore described in connection with the steam generating section and superheater section.

While it will be apparent that the preferred embodiments herein illustrated are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. In a heat exchanging apparatus having a soot blower 3a.; for cleaning the heat absorption surface thereof and incorporating a control system providing for remote actuation thereof, the combination including a slag sensing device comprising a diflerential temperature indicating means for sensing the temperature at the heat absorption surface and at a point spaced outwardly therefrom, and difierential temperature amplifying means connected to said difierential temperature indicating means for energizing the control means causing operation of the soot blower when the temperature differential decreases to a predetermined level as occasioned by the accumulation of slag and the like on the heat absorption surface.

5% temperature thereof, a second temperature sensing means spaced outwardly from said first temperature sensing means and exposed to the heated flue gases passing the heat absorption surface, and differential temperature amplifying means connected to said first and said secondtemperature sensing means for measuring the difierential temperatures indicated thereby, said differential temperature amplifying means operative to energize the control circuit causing operation of the soot blower When the differential temperature decreases to a predetermined level as occasioned by the accumulation of slag and the like on the heat absorption surface.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. IN A HEAT EXCHANGING APPARATUS HAVING A SOOT BLOWER FOR CLEANING THE HEAT ABSORPTION SURFACE THEREOF AND INCORPORATING A CONTROL SYSTEM PROVIDING FOR REMOTE ACTUATION THEREOF, THE COMBINATION INCLUDING A SLAG SENSING DEVICE COMPRISING A DIFFERENTIAL TEMPERATURE INDICATING MEANS FOR SENSING THE TEMPERATURE AT THE HEAT ABSORPTION SURFACE AND AT A POINT SPACED OUTWARDLY THEREFROM, AND DIFFERENTIAL TEMPERATURE AMPLIFYING CONNECTED TO