US 3234580 A
Description (OCR text may contain errors)
Feb. 15, 1966 .1. w. KECK 3,234,580
TREATMENT OF HEAT EXCHANGER SURFACES Filed July 19. 1961 6 Sheets-Sheet l INVENTOR. 721/2277 M K 1.
zwz'Kst Feb. 15, 1966 J. w. KECK 3,234,580
TREATMENT OF HEAT EXCHANGER SURFACES Filed July 19, 1961 6 Sheets-Sheet 2' Feb. 15, 1966 J. w. KECK TREATMENT OF HEAT EXCHANGER SURFACES 6 Sheets-Sheet 3 Filed July 19. 1961 Feb. 15, 1966 J. w. KECK TREATMENT OF HEAT EXCHANGER SURFACES 6 Sheets-Sheet 4 Filed July 19, 1961 721/2477 QN/ wS ZX,
Feb. 15, 1966 1W. KECK 3,
TREATMENT OF HEAT EXGHANGER SURFACES Filed July 19. 1961 6 Sheets-Sheet 5 INVEN TOR. 754 127 M Aec'Z Feb. 15, 1966 Filed July l9, 19
J. w. KECK 3,234,580
TREATMENT OF HEAT EXCHANGER SURFACES 6 Sheets-Sheet 6 United States Patent 3,234,580 TREATMENT OF HEAT EXCHANGER SURFACES Julian W. Keck, 2520 San Domingo St., Coral Gables, Fla. Filed July 19, 1961, Ser. No. 125,194 2 Claims. (Cl. 15302) The present invention broadly relates to direct fired combustion apparatus and more particularly to an improved apparatus and system for treating the heat exchanger surfaces of boilers and the combustion chamber surfaces and gas passages of heat engines to inhibit corrosive attack of the metallic surfaces thereof and to concurrently retard the formation of slag deposits on the metallic surfaces and modify the structure of the slag deposits formed so as to facilitate their removal.
The system and apparatus comprising the present invention is applicable for treating the metallic surfaces which are directly exposed to the corrosive and deposit-forming constituents in the combustion gases of fuels such as, for example, the heat exchanger surfaces of high pressure steam boilers. By virtue of this system and the apparatus for applying the treating slurry, the corrosive constituents in the combustion gases are neutralized and the formation of hard adherent slag deposits is reduced by virtue of a reduction in the adhesive and cohesive properties of the slag deposits facilitating their physical removal from the metallic surfaces thereby substantially increasing the durability and operating efliciency of the combustion apparatus.
The increased capacity of modern steam generating plants employing higher temperatures and steam pressures has occasioned an increase in the severity of corrosive attack of the metallic heat exchanger surfaces subjected to the hot combustion gases accompanied by a substantial increase in the formation of heavy slag deposits on the steam generating walls, superheater tubes, reheater tubes, and economizer tubes as well as on the furnace floors. The severity of the corrosive attack and the slagging tendency are particularly aggravated when the heat exchanger surfaces are subjected to temperatures in excess of about 800 F. The use of higher grade fuels has in some instances alleviated this problem but the continuous use of such higher grade fuels in many instances is economically prohibitive and commercially impractical.
The slag deposits formed on the heat exchanger surfaces of power boilers by burning low grade fuels, in some instances cannot be efiectively removed with conventional fluid type cleaners, generally referred to as soot blowers, and, accordingly, in such instances it has heretofore been necessary to periodically shut down the boiler and physically remove the slag deposits from the heat exchanger surfaces with pneumatic powered chipping hammers, drills, chisels, and the like. This practice represents a substantial reduction in the eflicient utilization of the power boiler in addition to constituting a tedious, costly and time-consuming operation.
Various methods have heretofore been proposed for use including the inclusion of a variety of additives admixed with the fuel in order to attempt to reduce the quantity of deposits formed or, alternatively, to attempt to alter their structure so as to enable elfective removal of the slag formation by conventional soot blower equipment. The use of such additives in the fuel mixture, however, has resulted in tons of accumulation in the boiler of the additive compound employed, in sulfur compounds formed, and in the formation of slag boulders on the bottoms of the furnaces and in other low velocity portions of the gas passages of the boilers representing a significant reduction in the efficiency of the power boiler and concurrently requiring frequent boiler shutdowns in order to remove the slag accumulations. Accordingly, the use of such fuel ICC additives while being partially effective to retard corrosion and slag formation, concurrently introduces additional problems and disadvantages opposed to efficient and durable boiler operation which, in many instances, outweigh the advantages derived therefrom.
It is, accordingly, a primary object of the present invention to provide an improved apparatus and system for treating the heat exchanger and combustion chamber surfaces of power boilers which inhibit corrosion and minimize the formation of slag deposits thereon and modify the structure of the slag formed thereby facilitating its removal by conventional cleaning techniques.
Another object of the present invention is to provide an improved treating system for power boilers which can be readily incorporated in new as well as in existing structures and overcomes a heretofore unfilled need for retarding the corrosive attack and deposit formation on the heat exchanger and combustion chamber surfaces of directfired power boilers.
Still another object of the present invention is to provide an improved apparatus and treating system which substantially increase the operating efficiency, durability, ease of maintenance and cleaning, and the useful operating life of power boilers and of the components thereof.
A further object of the present invention is to provide a system and apparatus for intermittently or continuously spraying an aqueous slurry predominantly of magnesium oxide or hydroxide on the heat exchanger and combustion chamber surfaces of direct-fired power boilers which serves to neutralize the acidic corrosive constituents in the combustion gases retarding corrosive attack of the metallic surfaces and concurrently reacts with the slag deposits formed substantially reducing their adhesive properties toward the heat exchanger and combustion chamber surfaces and their internal cohesive strength whereby the slag deposits can be simply removed from the metallic surfaces by conventional cleaning equipment without requiring shut-down of operation.
A still further object of the present invention is to provide a system for intermittently spraying an aqueous treating slurry into the combustion chambers of direct-fired combustion apparatus which does not significantly disturb the thermal equilibrium condition within the directfired apparatus and which concurrently reduces the discharge of solid materials from the exhaust flues.
Yet still another object of the present invention is to provide an automatic system which can be readily incorporated in the automatic phased sequence of the cleaning operations of power boilers wherein predetermined quantities of an aqueous treating slurry are injected continuously or at preselected intervals to retard corrosive attack and slag formation on the heat exchanger surfaces thereof.
Yet still another object of the present invention is to provide an improved soot blower cleaning apparatus which embodies therein a dual construction enabling alternate use of the same soot blower unit for discharging a pressurized cleaning fluid for removing slag formations from the heat exchanger surfaces of a power boiler and for alternatively discharging a treating slurry against the heat exchanger surfaces and which operation can be automatically and sequentially controlled in a predetermined time sequence.
Yet a still further object of the present invention is to provide for an automatic system for forming and maintaining an aqueous slurry of magnesium oxide and/0r calcium oxide or their equivalents and supplying controlled quantities of the slurry at preselected times and pressures to discharge outlets selectively located in a power boiler or heat engine which are adapted to discharge the slurry against the heat exchanger and combustion chamber surfaces inhibiting corrosive attack and reducing the formation of hard, water-insoluble slag deposits thereon.
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 side elevation view predominantly in section of a typical high capacity power boiler to which the present invention is applicable;
FIG. 2 is a side elevation view of a soot blower provided with means for injecting an aqueous treating slurry into a power boiler;
FIG. 3 is a side elevation view partly in section of a manually operable treating slurry spray nozzle positioned in the wall of a power boiler and connected to the treating slurry supply system shown in reduced scale;
FIG. 4 is a plan view partly in section of the lance tube construction employed in the soot blower illustrated in FIG. 2;
FIG. 5 is a fragmentary vertical sectional view of the forward portion of the lance tube and furnace wall shown in FIG. 4 and taken substantially along the line 55 thereof; FIG. 5A is a longitudinal sectional view of the feed tube of a soot blower provided with an alternative piping system for introducing the treating slurry, FIG. 5B is a transverse sectional view through the feed tube shown in FIG. 5A and taken along the line 5B-5B thereof;
FIG. 6 is a schematic view of a piping system for supplying a pressurized aqueous treating slurry to the slurry spray nozzles of a direct-fired power boiler;
FIG. 7 is a schematic piping diagram of an air panel control system which is coordinated with the slurry piping diagram shown in FIG. 6; and FIG. 8 is a schematic wiring diagram of the electrical control circuit providing for automatic phased sequential operation of the soot blowers for spraying the aqueous 'slurry into the combustion chamber of a direct-fired apparatus.
Referring now in detail to the drawings and as may be best seen in FIGURE 1, a typical high capacity steam boiler is illustrated of the general type to which the present invention is applicable. The power boiler shown in the drawing comprises a steam generating section generally indicated at 10 comprising a plurality of water wall tubes 12 extending along the walls of the boiler along which the hot rising combustion gases pass. The fuel for combustion is introduced through a series of burners 14 in onewall of the steam generating section. The walls of the steam generating section 10 are provided with a plurality of wall blowers generally indicated at 16 which are automatically operable in phased sequence in accordance with the central control system subsequently to be described to discharge a suitable pressurized cleaning medium such as air, steam or mixtures thereof, for example, against the heat absorption surfaces of the water wall tubes 12 to remove the accumulation of slag and other deposits therefrom.
A typical wall-type soot blower construction of the short travel retracting type is disclosed in US Patent No. 2,662,241, assigned to the present assignee, which can be satisfactorily employed by providing it with the embodiments subsequently to be described for discharging the treating slurry against the water wall heat absorption surfaces. The wall-type soot blowers conventionally comprise a short lance which is projected into the boiler chamber during operation and is retracted to a position beyond the furnace wall during intervals between blowing operations. The lance of the wall blower is provided with a plurality of discharge openings or nozzles in the forward end thereof through which the cleaning fluid and treating slurry can be discharged. The lance is conventionally rotated when in the projected position and during movement to and from that position whereby a substantially large wall area is subjected to the blowing medium and treating slurry dischaged therefrom.
The projecting and retracting movement of the lance and its rotation can be conveniently achieved by a suitable electric motor or fluid driven motor such as an air motor connected to the soot blower operating mechanism which is selectively operable in accordance with the phased sequence provided by the central control system.
The power boiler as shown in FIGURE 1 is also provided with a superheater section generally indicated at 18 including a series of pendant type superheater bundles 20 which extend downwardly from the upper end of the first pass of the boiler. A second series of superheater or reheater bundles 22 are disposed one above the other in the second pass of the boiler. In view of the fact that the superheater bundles 20 and superheater or reheater bundles 22 extend across the first and second passes of the boiler, a plurality of soot blowers 24 of the long travel retractable type are conventionally employed to provide a cleaning and deslagging of the deposits on the heat absorption surfaces thereof. A suitable long travel type soot blower 24 is illustrated in FIG. 2 and is described in detail in United States Patent No. 2,885,711, which is assigned to the same assignee as the present invention. The specific operation and construction of a typical long travel type soot blower 24 will subsequently be described in detail in connection with the injection of treating slurry into the power boiler.
Typical positions of a series of the long travel type soot blowers 24 in the superheater section 18 of the power boiler are indicated in FIGURE 1. Long travel type soot blowers 24 are also generally provided adjacent to the slag screen in the power boiler and for removing slag deposits from any economizer tube bundles in the second pass of the boiler.
The wall soot blowers 16 and the long travel soot blowers 24 are conventionally operated on a phased sequence as preselected in accordance with the central control system of the power boiler. The operating sequence of the blowers can be established on a straight time basis whereby each of the blowers are operated in a preselected sequence during a preselected time period. Generally, just a few soot blowers, and more usually, only one soot blower at a time is operated to avoid thermal shock to the heat absorption surfaces and to avoid a substantial interruption of the thermal equilibrium conditions in the boiler. Sequential selective operation of the soot blowers can also be automatically achieved by a control system operable in response to the specific slagging condition in a particular area of the power boiler.
As hereinbefore stated, the ability of the wall soot blowers 16 and the long-travel soot blowers 24 to effectively dislodge and remove slag deposits from the heat exchanging surfaces of the power boiler is dependent to a large extent on the specific type of deposits formed. Slag deposits having high adhesion characteristics toward the heat absorption surfaces and which have high cohesive strength make the cleaning of the heat exchanger surfaces by conventional soot blowers exceedingly diflicult and in some cases ineffective.
In accordance with the system comprising the present invention, the application of a spray of an aqueous treating slurry on the surfaces of the heat exchanging surfaces and on the slag deposits thereover results in inhibition of corrosion of the heat exchanger surfaces and simultaneously modifies the structure of the slag deposits reducing their adhesive and cohesive characteristics thereby facilitating dislodgment and removal thereof by the wall and long travel soot blowers. The introduction of the treating slurry into the boiler is achieved by incorporating slurry spray means directly in a soot blower such as the long travel soot blower 24 shown in FIG. 2, or alternatively, by a manually operable lance assembly 26 as shown in FIG. 3 which are positioned at various locations in the boiler wall wherein the spray emitted from the nozzles thereof impinges on and substantially completely coats all of the heat exchanging surfaces of the boiler which are subjected to corrosive attack and slag deposition from the hot combustion gases.
The specific composition of the aqueous treating slurry and the quantities employed can be varied dependent upon such related factors as the specific corrosion and slag-forming tendencies of the fuel used, the temperatures to which the combustion chamber surfaces are exposed, and whether the slurry is applied continuously or on an intermitted phased sequence. While slurries containing conventional commercial lime have been found to provide improved corrosion protection and a reduction in the formation of hard Water insoluble slag deposits, slurry compositions predominantly of magnesium oxide have been found particularly satisfactory and surprisingly superior to other chemical compositions heretofore known. Slag deposits treated with magnesium oxide wherein an alloying of the ash and magnesium is achieved have been found to be soft and porous and of a relatively high melting point facilitating their removal by conventional soot blower cleaning apparatus as opposed to slag deposits treated with slurries predominantly of calcium oxide which are less porous, harder, and of a lower melting point and consequently substantially more diflicult to remove. For this reason slurries which are predominantly of a magnesium oxide composition and preferably containing at least about 75% magnesium oxide and the balance calcium oxide provide for extremely satisfactory control of the slag formation and corrosion protection of the combustion chamber surfaces of power boilers and heat engines in accordance with the practice of the present invention.
It will be understood that the terms magnesium oxide and calcium oxide as employed herein and in the subjoined claims broadly encompass the oxides of magnesium and calcium as well as the hydrated forms thereof such as magnesium hydroxide and calcium hydroxide which can be used as such or are produced during the reaction of the oxides with water. In addition, calcium carbonate and calcium bicarbonate are also encompassed within the broad definition of calcium oxide which may be used as such or are produced as a result of the reaction of the oxide with water and carbon dioxide. Varying amounts of the conventional impurities present in commercial magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide, calcium bicarbonate, and calcium carbonate are also encompassed within the meaning of the terms magnesium oxide and calcium oxide. Accordingly, while either or combinations of the foregoing materials can be employed as the starting materials or are formed during subsequent reaction with water and carbon dioxide, the composition and concentration of the treating slurry are herein defined in terms of the weight equivalent of these materials based on magnesium oxide and calcium oxide.
The long travel soot blower 24, as may be best seen in FIGS. 2, 4 and 5, embodies therein means for spraying an aqueous slurry comprised predominantly of magnesium oxide in accordance with the preferred practice of the present invention providing a simple, effective, and economical method for treating the heat exchanging surfaces of the power boiler. The dual function soot blower 24 as will be subsequently described, is selectively and alternately employed for discharging the cleaning fluid from the nozzles thereof and at other times for discharging a fine spray of the treating slurry against the heat exchanging surfaces.
The long travel soot blower 24 to which reference is made to United States Patent No. 2,885,711 for a more detailed discussion thereof, comprises an overhead rail 28 having an I-shaped cross section and along the bottom of which a gear rack 30 is aflixed extending longitudinally for substantially the entire length thereof. A
carriage 32 is movably mounted on the rail 28 by a series of rollers 33 disposed in rolling contact on the upper surface of the lower web thereof. In the exemplary soot blower shown, the carriage 32 incorporates an air-driven motor 34 thereon for concurrently rotating a lance tube 36 and for moving the carriage 32 and lance tube 36 to and from a projected position and a retracted position as shown in FIG. 2. Movement of the carriage 32 along the rail 28 is achieved by a gear 37 disposed between the rollers 33 at the rear end of the carriage and which is drivingly connected to the air motor 34, and disposed in mesh with the gear rack 30.
The forward end of the lance tube 36 as shown in FIG. 2, is movably supported and guidably mounted in a guide bracket 38 while in the projected and retracted position and during its movement there'between. The lance tube 36 is telescopically and slidably fitted around a feed tube 39 which is stationarily affixed at its rearward end to a cam actuated poppet valve 40 as shown in FIG. 2. The rearward portion of the lance tube 36 is secured to a cylindrical sleeve 42 which is rotatably supported in the carriage 32 by a pair of spaced ball bearings 44 as is shown in FIG. 4. The sleeve 42 is provided with a sprocket 46 disposed in engagement with a driving member drivingly connected to the motor 34 for rotating the lance tube during its projecting and retracting travel. The rear portion of the lance tube 36 is slidably and rotatably sealed around the feed tube 39 by means of a series of packing rings 48 which are retained in appropriate position by a retainer ring 50 securely fastened to the sleeve 42.
The forward end of the feed tube 39 as shown in FIGS. 4 and 5 is provided with a pressurized lantern seal 52 having a plurality of annular grooves 53 therearound which are disposed in communication with a supply tube 54 extending longitudinally through the feed tube 39 for supplying a pressurized fluid such as steam or air to the lantern seal 52. The supply tube 54 is maintained in substantially longitudinal axial alignment within the feed tube 39 by means of a series of radial vanes 56 secured to the periphery of supply tube 54 having the outer portions thereof disposed in sliding abutment against the inner wall of the feed tube 39. The pressurized fluid supplied through the supply tube 54 and discharged through the grooves 53 can alternately be derived from a separate fluid supply source, from the poppet valve 40, or from the main blowing medium supply header connected to the poppet valve 40. The lantern seal 52 is effective to prevent leakage of the treating slurry between the lance tube and feed tube as will hereafter become apparent.
The forward portion of the lance tube 36 as shown in FIGS. 4 and 5 is provided with a pair of diametrically disposed nozzle-s 58 therein through which the pressurized blowing medium is discharged during a cleaning operation or a combination of blowing medium and treating slurry during a treating operation. A plurality of drain holes 60 are provided around the periphery of the forward end of the lance tube to facilitate drainage of any entrapped condensate or slurry therefrom.
Operation of the soot blower 24 can be achieved remotely in accordance with the control system subsequently to be described whereby the air-driven motor 34 is energized causing the carriage 32 and lance tube 36 thereon to move toward the right as viewed in- FIGS.
-2 and 4 from a retracted position to a projected position and during which travel the lance tube is rotated. During the initial advancing movement of the carriage 32, one of a pair of actuator rods 63 mounted on each side thereof strikes a cam 62 pivotally mounted on the overhead rail 28 as shown in FIG. 2, which through suitable linkage operate-s the poppet valve 40 allowing high pressure blowing medium to enter the rearward end of the feed tube 39 and which is discharged through the nozzles 58 in the forward end of the lance tube 36. After the lance tube attains the fully projected position, the direction of rotation of the air-driven motor 34 is reversed and the lance tube and carriage move toward the retracted position. When the actuator rod 63 on the carriage 32 strikes the cam 62, the poppet valve 40 is again actuated and closed stopping the flow of pressurized blowing medium into the feed tube 39.
When the lance tube is in the fully retracted position, the forward end thereof is in a position substantially as shown in FIG. wherein the forward end portion thereof is retracted beyond the water wall tubes 12 and out of direct contact with the hot combustion gases in the furnace chamber. The forward end of the lance tube 36 is supported in a wall box 64 mounted on the exterior of a furnace wall 66 having a port 68 therethrough through which the lance tube passes during its projecting and retracting travel. The wall box 64 is provided with a resiliently mounted guide plate 76 having an aperture therethrough in which the lance tube is slida'bly supported. A removable plug 72 is provided in the side Wall of the wall box 64 to facilitate cleaning of the nozzlesv 58 and drain holes 60 when necessary or during periodic maintainence inspections.
The construction and operation of the wall blowers 16 is similar to that herein described in connection with the long travel type soot blowers 24. Since the wall blowers are intended to remove deposit formations from the surfaces of the water wall tubes 12 and inside surfaces of the furnace, the lance tube thereof is relatively short and when in the fully projected position is disposed just slightly beyond the outer surface of the water wall tubes whereby the pressurized blowing medium discharged through the nozzles in the end portions of the lance tubes impinges against the water wall tubes.
In accordance with the practice of the present invention, selected ones or all of the wall blowers 16 and long travel soot blowers 24 are embodied with treating slurry conduit means wherein the soot blowers are endowed wit-h a dual capacity of alternately supplying a pressurized blowing medium to the interior of the boiler and to inject controlled quantities of the aqueous treating slurry against the heat exchanger surfaces. A typical embodiment is illustrated in FIGS. 2 and 4 wherein a conduit supply system 74 is connected to the rearward end of the feed tube 39 and is disposed in communication with the interior thereof. The conduit supply system 74 as shown in FIG. 2 includes a check valve 76 and a flow control valve 78 which is mechanically opened and closed responsive to actuation by the other of the actuator rods 63 on the carriage 32 of a cam 80 mounted on the overhead rail 28 adjacent to the cam 62. The conduit supply system 74 is connected to a header pipe 82 which is connected to each of the conduit supply systems of each of the wall blowers and long travel soot blowers employed.
The cams 62 and 80 are longitudinally spaced from each other so that on the forward movement of the carriage 32, the blowing medium is first introduced into the feed tube followed thereafter by the introduction of the treating slurry. In one specific embodiment, the cam 80 is positioned 6 inches from the cam 62 so that during the projecting travel of the carriage 32 the poppet valve 40 is actuated 6 inches before the actuation of the cam 80. Similarly, during the retracting movement of the carriage 32, the treating slurry is turned off before the blowing medium is turned off to assure substantially complete purging of any residual treating slurry from the feed tube 39 and the lance tube 36. By virtue of the pressurized lantern seal 52, a closed seal is maintained between the inside of the lance tube and the forward end of the feed tube whereby the pressure differential created thereby prevents the treating slurry and blowing medium from reaching the packing rings 48 and leaking therebeyond.
Under normal operating conditions the pressure of the treating slurry in the header pipe 82 ranged from about 50 to p.s.i. and the blowing medium pressure during discharge of the treating slurry ranges from about 40 to 65 psi. The aqueous treating slurry is introduced into the feed tube at a pressure higher than that of the blowing medium and is immediately swept away thereby and discharged in the form of fine-sized droplets through the nozzles 58 at the forward end of the lance tube 36. Since it is generally desirable during a cleaning operation to employ pressures of the blowing medium above a range from 40 to about 65 .p.s.i., the control system which will later be described in detail, incorporates provisions therein for reducing the pressure of the blowing medium to the desired level during the discharge of the treating slurry.
An alternate and preferred method of introducing the aqueous treating slurry into the dual function soot blower is illustrated in FIGS. 5A and 5B which represents a simplified and preferred construction in comparison to that hereinbefore described and shown in FIGS. 4 and 5. In the preferred embodiment as shown in FIGS. 5A and 5B, the aqueous treating slurry supplied from the conduit supply system 74 is introduced directly into a T-iitting 41 which is securely fastened to the wall of the feed tube 39 into which the conduit supply pipe 74 is threadably secured. The rearward end of the T-fittin-g 41 is provided with a plug 43 which is threadably engaged and removable therefrom to facilitate cleaning of any deposit accumulation that may occur in the T-fitting 41 and a discharge pipe 45 threada'bly connected thereto and extending longitudinally for a length greater than the length of the feed tube 39. The discharge pipe 45 is maintained in appropriate axial alignment within the feed tube 39 by a series of radial vanes 56' fastened to the exterior thereof and having the outer edges adapted to slidably contact the inner wall of the feed tube as shown in FIG. 5B.
This construction obviates the use of the supply tube 54 and lantern seal 52 assembly as shown in FIGS. 4 and 5 because the slurry discharged from the end of the discharge pipe 45 is positioned forwardly of the end of the feed tube and is swept forwardly by the pressurized blowing medium and out through the nozzles 58 in the forward end of the lance tube 36. In all other respects, the construction and operation of the soot blower as shown in FIGS. 5A and 5B are similar to that hereinbefore described in connection with the dual function soot blower shown in FIGS. 4 and 5.
An alternate satisfactory method of applying the aqueous treating slurry to the surfaces of the heat exchanger and to the deposits therein is by the manual lance assembly 26 as shown in FIG. 3 in lieu of the dual function soot blower construction hereinbefore described. The manual lance assembly is employed for spraying appropriate quantities of the treating slurry at periodic time intervals into the boiler. T-he lance assembly 26 comprises a lance tube 84 employing a nozzle 86 at the forward end thereof through which the slurry is ejected under an appropriate pressure in the form of spray of line-sized droplets preferably of a conical configuration. 'I he treating slurry can also be ejected in combination with a pressurized fluid such as air or steam for facilitating propulsion and fragmentation of the treating slurry into fine-sized droplets. The lance tube 84 as shown in FIG. 3, is positioned in the fully projected position wherein a collar 88 on the rearward portion thereof is disposed in abutting relationship against the end of a sleeve 90 in which the lance tube 84 is slidably mounted. The sleeve 90 is prowided with a series of threads around the forward portion thereof for threadably securing the sleeve in a mounting plate 92 removably secured to the outer casing 94 of the boiler wall and disposed over a port 96 therethrough.
A tubular nozzle casing 98 is fixedly secured to the inner surface of the mounting plate 92 and is disposed in axial alignment and threaded engagement with the inward projecting end portion of the sleeve 90. The nozzle casing 98 is adapted to slidably receive the nozzle 86 of the lance tube 84 when in the fully retracted position so as to shield the nozzle 86 thereof from the hot combustion gases when the manual lance assembly 26 is not in use. The forward end of the lance tube 84 adjacent to the nozzle 86 is provided with an annular ring 100 which is adapted to be s lidably disposed within the tubular nozzle casing 98 for guidably supporting the lance tube when in the fully retracted position. The lance tube 84 is maintained in the fully retracted position by suitable engaging means such as a thumb screw 102, having the shank portion thereof in threaded engagement in the sleeve 90 and adapted to abut the periphery of the lance tube 84 so as to prevent inadvertent outward axial sliding movement thereof.
The outer projecting end or left end of the lance tube 84 as viewed in FIG. 3 is connected to a flexible hose 104 which is connected to a treating slurry header pipe 106 and a purge line 108, as shown in reduced scale in FIG. 3, for supplying a pressurized fluid such as air or steam to the lance tube. A shutoff valve 110 is provided between the header pipe 106 and flexible hose 104 for controlling the flow of treating slurry to the manual lance assembly. Similarly, a shutoff valve 112 is provided in the purge line 108 for controlling the flow of the pressurized fluid to the lance tube 84. The purge line 108 is also provided with a check valve 114 to prevent a backup of the treating slurry into the purge line.
The operation and manipulation of the manual lance assembly 26 is achieved by first loosening the thumb screw 102 releasing the lance tube from the sleeve 90. The lance tube is then moved outwardly beyond the water wall tubes 12 and the valve 110 is opened wherein treating slurry is directed through the flexible hose 104 into the lance tube and is finally discharged through the nozzle 86 in the form of fine-sized droplets. At the completion of a predetermined spray application period, the lance tube is retracted and upon attaining a position wherein the nozzle 86 is again adjacent to the water wall tubes 12, the valve 110 is turned off stopping the flow of treating slurry. Thereafter, the valve 112 is opened directing the pressurized fluid from the purge line 108 into the lance tube whereby the interior of flexible hose and the lance tube 84 are purged of any residual treating slurry. The lance tube 84 is finally retracted to a point where the annular ring 100 is within the tubular nozzle casing 98 and the valve 112 is then turned off and the thumb screw 102 is secured so as to maintain the lance tube in the fully retracted position. The operation of the manual lance assembly can also be achieved by concurrently discharging a mixture of treating slurry and pressurized fluid through the nozzle 86.
A schematic piping diagram of the treating slurry supply system is shown in FIG. 6 for supplying two power boilers with the aqueous treating slurry in the appropriate quantities and at a preselected pressure. The remote actuated solenoid valves in the piping system shown in FIG. 6 are operated in response to the automatic air panel control as shown in FIG. 7 and in accordance with the automatic electrical control circuit shown in FIG. 8. The treating slurry supply system shown in FIG. 6 comprises a tank 116 provided with an agitator 118 in which an aqueous slurry is prepared prior to actuation of the treating system. Water is introduced into the tank 116 through a water supply pipe 120 having a manual shutoff valve 122 which is employed to fill the tank to the appropriate level after which the appropriate quantity of the magnesium oxide and/or calcium oxide are added.
The slurry is prepared by adding the magnesium oxide and calcium oxide or equivalent hydrated or carbonate form thereof as hereinbefore set forth in the form of a finely particulated powder to a quantity of water in the amount generally ranging from about pound up to about 1 pound on a weight equivalent basis of magnesium and calcium oxide of the dry powder mixture per gallon of water. Concentrations of about pound of powder per gallon of water are generally satisfactory for treatment of relatively clean heat exchanger surfaces whereas higher concentrations such as about /2 to about pound powder per gallon of water or greater are preferred for treating heat exchanger surfaces subjected to a high corrosion attack and slagging tendency. The particle size of the powder can broadly range from about 50 mesh down to a size range of 300 mesh or smaller. Generally, powders having a particle size wherein thereof passes through a 200 mesh screen facilitates forming and maintaining a substantially homogeneous suspension of the particles in water and provides for excellent distribution thereof on the heat exchanging surfaces of power boilers. Powders wherein of the particles thereof pass through a 300 mesh screen are preferred for pre paring slurries employed for treating the combustion chamber surfaces and operating components of heat engines such as gas turbines, for example, to minimize physical erosion of the turbine blades thereof. It should also be pointed out that the use of slurries comprising predominantly magnesium oxide or magnesium hydroxide, provide the further advantage of possessing relatively low deposit forming characteristics, thereby minimizing fouling of the piping system employed for supplying the slurry to the soot blowers, in contrast to slurries predominantly of calcium oxide which have a tendency to react with carbon dioxide forming dense hard deposits in the piping system in a comparatively short interval of use, necessitating periodic maintenance and cleaning.
The appropriate quantity of slurry applied to the heat exchanger surfaces is a function of the temperature of the surfaces, and the composition of the fuels fired as hereinbefore set forth. The optimum correlation is best achieved by trial during actual operation. Generally, the application of a uniform coating of the treating slurry in an amount ranging from about .05 pound up to about .1 pound based on the weight equivalent of dry magnesium and/or calcium oxide powder per barrel (42 US. gallons) of fuel oil fired provides efficient protection of the heating surfaces of a power boiler. As a typical example, the use of residual fuel oil having a sulfur content of 3% or less, and/ or a vanadium content of 500 parts per million (p.p.m.) or less in a power boiler having commercially clean heat exchanger surfaces which are subjected to temperature of approximately 1000 F. or higher can be effectively controlled by a daily application of a treating slurry comprised of pound dry powder per gallon of water consisting of 90% magnesium oxide and 10% calcium oxide at a ratio of about .06 pound of dry powder per barrel of fuel oil fired. For those combustion chamber surfaces which are exposed to temperatures below 1000 F. adequate control and protection of slag formation and corrosion can be achieved by one weekly application.
The slurry tank 116 is provided with an outlet pipe 124 having a manual shutoff valve 126 therein and a remotely actuable solenoid valve SOL-2 operable in response to the sequence of the central control system. The outlet pipe 124 is connected to the inlet side of a pump 128 which is of a design capacity in excess of that required to supply the operating soot blowers or manual lance assemblies such as, for example, 10 gallons per minute, so as to assure continuous circulation of the treating slurry through the supply system. A check valve 130 and a strainer 132 are preferably provided in the outlet pipe 124 at a point before the inlet portion of the pump 128. The
ing an pump 128 shown in the drawing, is preferably provided with a conduit line 134 for supplying pressurize-d water to the gland seal of the pump.
The treating slurry is discharged from the pump 128 through a discharge tube 136 at the desired pressure as indicated by a pressure gauge 138. The discharge pipe 136 is connected to a T-fitting 140 wherein the pressurized slurry is selectively transmitted to the header pipe 142a of boiler No. 1, or to the header pipe 14% of boiler No. 2 in accordance with the position of solenoid valves SOL4-1, SOL4-2, as controlled by the central control system. The header system 1421) for boiler No. 2 corresponds to the header system 142a shown in FIG. 6 for supplying treating slurry to the soot blowers in boiler No. 1. The header pipes 142a, 1421) are connected to the conduit supply systems 74 similar to that shown in FIG. 2 at each station where a soot blower is located.
The treating slurry is circulated through the header pipes 142a and 14217 and is returned to the supply tank 116 through return lines 144a, 144b, respectively, which are preferably provided with sight flow indicators 146a, 146b, respectively. The return lines 144a, 144b, are provided, respectively, with valves 148a, 14811 which are sized so as to maintain proper pressure of the treating slurry in the header lines.
In order to purge the treating slurry supply system at the completion of a treating cycle, a water supply line 150 is provided including solenoid purge valve SOL-3, which is automatically actuable to allow water to enter the inlet side of the pump 128 after solenoid valve SOL-2 has been closed stopping the flow of treating slurry into the pump. Accordingly, pressurized water is circulated through the header system 142a, 142b, removing substantially all traces of the treating slurry thereform so as to avoid accumulation of deposits and fouling of the piping system. The circulating pressurized water is drained from the system through solenoid valve SOLSal, in header pipe 142a, and solenoid valve SOL-2 in header pipe 14%. For most installations, a water purging of the slurry supply system for a period of about 3 minutes provides adequate cleansing of the lines.
The actuation of the solenoid valves in the treating slurry supply system shown in FIG. 6 is controlled in accordance with the control circuit shown in FIG. 8, which is electrically connected to conductors L1 and L2 in conjunction with a typical air sequential panel steam blowing system as shown in FIG. 7. The air control system shown in FIG. 7 incorporates an air panel 152 of the general type disclosed in United States Patent No. 2,565,689 and assigned to the same assignee as the present invention. The air control panel 152 employs air as the actuating fluid and is provided with a selector switch 154 for selecting an Off position, boiler No. 1 treating position, or boiler No. 2 treating position. A second selector switch 156 is provided for alternately selecting manual or automatic operation of the soot blowers in the boiler. The air control panel 152 as described in the aforementioned US. patent to which reference is made for a more detailed description of its operating details, incorporates a vertically movable slide member 158 havactuator thereon which is biased toward the upper position as viewed in FIG. 7 and during its ascending movement is adapted to selectively actuate trip valves 160 disposed adjacent to its path of travel. The trip valves 160 are selectively positionable by the operator to an operative and inoperative position depending on which soot blowers are to be operated. Each of the trip valves are effective to cause one of the soot blorwers to undergo its operating cycle at the completion of which the slide member 158 ascends until the next trip valve 160 disposed in the operable position is tripped thereby.
Pressurized control air is supplied through the supply line 162 connected to a suitable air pressure source and thereafter passes through a diaphragm valve 164 and is transmitted by control pipe 166 to a slurry pressure con- 12 troller 168 and a blowing medium pressure controller 170, WhICh are operative on the opening of solenoid valve SOL11 to regulate the diaphgram reducing valve 172 in a steam header 174 supply blowing medium to the soot blowers. As hereinbefore set forth, a reduction in the pressure of the blowing medium is necessary during ejection of the treating slurry into the boiler in view of the fact that the blowing medium during conventional cleaning operations is at a pressure substantially in excess of from 40 to psi.
The air control panel 152 is also provided with timing means including a timing receiver 176 and a pressure switch 178 which is preferred when steam is employed as the blowing medium in order to provide a delay time to enable warm-up of the steam header and removal of any condensate from the steam supply system before steam is supplied to the soot blowers. A pressure switch PS-l is connected to the air control panel and is operable on actuation of the slide member 158 to actuate the slurry supply system and electrical control system as will hereinafter be described.
The electrical control circuit shown schematically in FIG. 8 comprises an interlocked circuit for controlling alternate slurry treatment of the heat exchanger surfaces of boiler No. 1 and boiler No. 2. The electrical control system and air control system are coordinated to provide automatic sequential operation of the soot blowers in a preselected sequence and automatically provides for sequential automatic treatment of the heat exchanger surfaces with a controlled quantity of treating slurry. It will be understood by those skilled in the art that the automatic sequential control of the application of treating slurry from the slurry supply system shown in FIG. 6 can also be satisfactorily achieved by employing an electrical control panel in lieu of the air panel herein shown and wherein the blowing medium can alternately comprise air of steam, or mixtures thereof, and wherein the reciprocating travel of the soot blowers can be powered by air, steam, or electrical motor means.
A typical operating sequence in accordance with the slurry supply systems and air and electrical control systems schematically shown in FIGS. 6 to 8 will now be described for a multiple boiler installation as illustrated. The energization of the slurry treating system is preferably done after the soot blowers have completed their cleaning cycle whereby the treating slurry impinges on the substantially clean heat exchanger surfaces coating the metal thereof to inhibit corrosive attack by the hot combustion gases. The slurry tank 116 is first filled with an appropriate quantity of water to which the desired quantity of the powdered magnesium oxide and lime is added and the agitator 118 is energized forming a substantially homogeneous slurry. The selector switch 154 on the air control panel 152 is then turned to the desired position, such as boiler No. 1, for example, and the slide 158 on the air panel is pulled down to the start position. The pressure switch PS-l is energized closing its contact PSI-1 (FIG. 8). With the selector switch 154 in the boiler No. 1 position contacts SW-l and SW-3 are closed and contacts SW2 and SW-4 are opened. The closing of pressure switch contacts PS11 energizes the coil SOL-2c of solenoid valve SOL-2 and the coil of the time delay relay TD. On energization of the coil SOL-2c the solenoid valve SOL-2 opens whereby the treating slurry is permitted to flow from the tank 116 into the inlet side of the pump 128. The time delay relay TD on energization opens its instantaneous contact TD-2 (Inst) and closes its timed open contact TD-l (T.O.) whereby the coil SOLl-lc of the solenoid valve SOLl-d is energized and the regular valve 172 (FIG. 7) is operated to reduce the pressure of the blowing medium in the steam header line 174 which is connected to the poppet valve 40 of each of the soot blowers in the boilers.
At the same time the closing of contacts TD-l (T.O.)
.13 energizes the control relay CR1 through normally closed contact CR22 and contact SW3 which in turn closes its normally open contacts CR1-1, CR1-3, and CR1-4 and opens its normally closed contact CR1-2. The opening of contacts CR12 locks out the control system of the circuits shown in FIG. 8 applicable to controlling the operation of the slurry treatment system in boiler No. 2. The closing of contacts CR1-3 energizes the pump motor 180 of the pump 128 which commences circulating the treating slurry through the treating slurry header pipe 142a of boiler No. 1. The solenoid valve SOL41 is opened and the solenoid valve SOL4-2 in the header line 1421) leading to boiler No. 2 is closed. The solenoid valve SOL4-1 is opened and the solenoid valve SOL4-2 in the header line 142b leading to boiler No. 2 is closed.
The time delay means comprising the timing receiver 176 and pressure switch 178 (FIG. 7) connected to the air panel control system delays operation of the soot blowers by maintaining the slide member 158 in the down position for a period of time suflicient to allow the steam header to warm up and to enable the treating slurry header 142a to fill up with treating slurry at the desired pressure. After the expiration of the time delay period the slide member 158 commences its ascending movement and the sequential operation of the soot blower commences in accordance with the cycle hereinbefore described in connection with the dual function soot blower shown in FIG. 2. In order to assure that the treating slurry is at the appropriate pressure in the header line 142a, a safety pressure switch SPS-l is preferably provided at the highest portion of the slurry header which is interlocked by its contact SPS-l (FIG. 8) to energize the coil SOL6-1c of panel brake solenoid valve SOL6-1 to halt the movement of the air panel slide member 158 and stop further operation of the soot blowers until the treating slurry pressure again attains a pressure within a preselected range. At such time that a low pressure condition exits, a low pressure indicator light 182 is illuminated to visually signal the operator at the control panel of the low pressure condition in the treating slurry header.
After each of the soot blowers have completed their respective slurry spraying cycles, and the slide member 158 on the air panel 152 reaches the upper position, the control air to the air panel is shut off and the pressure switch PS1 opens its contact PS1-1 deenergizing the coil SOL-2c of solenoid valve SOL-2 which closes preventing further flow of treating slurry from the tank 116 to the inlet of the pump 28. At the same time the opening of contact PS1-1 deenergizes the coil of time delay relay TD which closes its instantaneous contact TD-Z (Inst), thereby energizing the coil SOL-3c of purge solenoid valve SOL3 whereby water is allowed to flow into the inlet side of the pump 128 which circulates through and purges the treating slurry header 142a. The coil SOLS-lc is also energized opening drain solenoid valve SOL-1 whereby the purge water is discharged from the system to an open drain. The time delay contact TD-l (T.O.) remains closed for a preselected time period to provide the requisite period for achieving substantially complete purging of the treating slurry header. At the expiration of the time delay period the time open contact TD-1 (T.O.) opens deenergizing the entire electrical control system wherein the remaining open solenoid valves are closed and the entire system is shut off.
Control relays CR1 and CR2 in the electrical circuit shown in FIG. 8 serve to interlock the control system of boiler No. 1 and boiler No. 2 to prevent both boilers from operating on the slurry treatment cycle at the same time. In addition, the control systems by virtue of the time open delay cont-act TD-1 (T.O.) causes the water purging sequence to commence at any time that the boiler selector switch 154 is turned to the Off position before all of the soot blowers have completed the treating slurry operating sequence. This embodiment assures that the slurry system will be purged and prevents fouling thereof.
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 an apparatus for treating and cleaning heat exchanger surfaces of direct-fired power boilers to inhibit corrosive attack and the formation of dense adherent slag deposits theeron, the combination comprising a plurality of soot blowers positioned on the exterior of the boiler at spaced intervals, each of said soot blowers comprising a frame, a lance tube including discharge nozzles at the forward end thereof for discharging a blowing medium against the heat exchanger surfaces, said lance tube rotatably and longitudinally movable on said frame to and from a retracted position out of the path of the hot combustion gases and a projected position disposed in the interior of the boiler, and power means for rotating and for moving said lance tube to and from said positions, first conduit means connected to said lance tube of each of said soot blowers for supplying a pressurized blowing fluid thereto, second conduit means connected to said lance tube of each of said soot blowers for supplying an aqueous treating slurry thereto, supply means including a supply tank and third conduit means connected to each of said second conduit means, pumping means for recirculating said treating slurry through said third conduit means in an amount in excess of that discharged through said lance tubes and returning said excess to said supply tank, means for purging said second conduit means with water at the completion of a sequentially phased operating cycle of said soot blowers, actuating means on each of said soot blowers operable in response to movement of said lance tube thereof from said retracted position toward said projected position to introduce said blowing fluid a predeterrnined interval before said treating slurry is introduced and for stopping the flow of said blowing fluid a predetermined interval after said treating slurry is stopped responsive to movement of said lance tube from said projected position toward said retracted position, and control means for automatically actuating said power means of selected ones of said soot blowers in accordance with a preselected sequentially phased operating cycle.
2. In an apparatus for treating and cleaning the heat exchanger surfaces of direct-fired power boilers to inhibit corrosive attack and the formation of dense adherent slag deposits thereon, the combination comprising a frame positioned on the exterior of the boiler, a feed tube mounted on said frame, a lance tube disposed in overlying movable telescoping relationship about said feed tube and rotatably and longitudinally movable relative thereto to and from a retracted position and a projected position, power means for rotating and for telescopically moving said lance tube to and from said positions, said lance tube provided with at least one nozzle in the forward end thereof for alternately discharging a blowing fluid during a cleaning cycle and a combined blowing fluid and treating slurry therefrom during a treatment cycle against the heat exchanger surfaces, first conduit means connected to the rearward end portion of said feed tube for supplying said blowing fluid thereto, second conduit means connected to the rearward end portion of said feed tube and extending forwardly and axially through the interior of said feed tube to a point beyond the forward end thereof and adjacent to said nozzle in said lance tube when in said retracted position for supplying said treating slurry thereto, means operable during a treatment cycle in response to movement of said lance tube from said retracted position toward said projected position to introduce said blowing fluid a predetermined time interval before said treating slurry is introduced and for stopping the flow of said blowing fluid a predetermined time interval after the flow of said treating slurry is stopped responsive to movement of said lance tube fromsaid projected position toward said retracted position, valve means selectively operable for introducing said treating slurry to said second conduit means during treatment cycles, and valve means in said first conduit means for reducing the pressure of said blowing fluid during a treatment cycle to a pressure below that used during a cleaning cycle.
References Cited by the Examiner UNITED STATES PATENTS Hibner et al. 1-5-318 Harlow.
16 Howse -12237 X Walters 1l0--l Hardgrove 15317 X De Mart 15-317 Cantieri ,153 17 Welch 110-1 FOREIGN PATENTS Great Britain.
OTHER REFERENCES Combustion (January 1961), article by Cantieri and Cappelli on page 48.
ROBERT W. MICHELL, Primary Examiner.
CHARLES A. WILLMUTH, WALTER A, SCHEEL,