US3257993A - Soot blower operation for vapor generator furnaces - Google Patents

Description

June 28, 1966 E. 1.. KOCHEY, JR

SOOT BLOWER OPERATION FOR VAPOR GENERATOR FURNACES Filed Sept. 28, 1964 63 Id a .i||+mm.) w 46W wma m a n2 MW 5 N 6 M fm mwww s lHT 0M 55 4 -iiiUii Z 5 wfwgfl lllfiii W 4 5 Z 5 497 i/ 1 ,1 J 31 2 5 s 3 r e 5 q mmw g 1 fl w /SIM J 0 B W o C fli l I I United States Patent 3,257,993 580T BLOWER OPERATION FOR VAPOR GENERATOR FURNACES 1 Edward L. Kochey, .lr., Colehrook, Conn, assignor to Combustion Engineering, inc, Windsor, Corns, a corporation of Delaware Filed Sept. 28, 1964, Ser. No. 399,558 9 Claims. (Cl. 122-392) This invention relates to soot blowers for a once-through circuit vapor generator furnace and in particular to a method and apparatus for selectively operating the soot blowers.

In a once-through circuit parallel tubes within the circuit must be constrained in some manner to maintain the over-all structure. This may be done by welding these tubes to bars which cross them transversely on the casing side, or as is now often done by welding adjacent tubes continuously throughout their length.

When an ash bearing fuel such as coal is burned within a steam cooled furnace, ash and slag form on the walls of the furnace in an erratic pattern. This uneven slagging condition results in uneven heat absorption which is refiected in an unbalance of the temperatures of the fluid passing through the furnace wall tubes. This temperature unbalance creates a condition where the hotter tubes want to expand relative to the cold tubes, setting up stresses in the over-all furnace wall structure in various locations. Repeated slagging and cleaning of the furnace walls will cause cycling of these stresses and may lead to fatique failures, even at relatively low stresses.

A circuit in such a situation may be controlled so that the outlet temperature is maintained constant regardless of the variations in heat absorption. This may be accomplished by measuring the outlet temperature and varying the relative flow through various groups of tubes in accordance with the heat absorption of these parallel groups of tubes to maintain the temperatures equal. In such a situation a group of tubes receiving high heat absorption will contain the same temperature fluid as the other tubes but it will be operating at a higher heat absorption rate. This higher heat absorption rate causes a higher metal temperature in these circuits creating the same type expansion problem as previously discussed although of lesser magnitude.

Normally in the operation of these units the over-all furnace dirtiness is sensed. This may be accomplished by measuring the gas temperature leaving the furnace, measuring the steam temperature leaving a convection heating surface of the unit, or measuring the position of a steam temperature controller. After this over-all dirtiness is sensed, the furnace wall soot blowers are operated in response to a predetermined amount of dirtiness. During this time the furnace may be operating with a heavily slagged condition in one portion of the furnace while the remainder of the furnace is relatively clean. Such heavy local accumulations of ash and slag lead to operating difliculties such as slagging of the burners, slagging up and plugging the superheaters, or damage to the lower furnace when these slag masses become too heavy and fall from the walls.

It is an object of my invention to provide a method and apparatus for the operation of furnace wall soot blowers in such a manner that excessive slag accumulations will not occur.

It is a further object to provide a method and apparatus for operating soot blowers in such a manner as to prevent excessive temperature differentials throughout a furnace wall circuit.

It is a further object to provide a method and apparatus for operating soot blowers in a once-through circuit of a vapor generator furnace in such a manner as to improve ice the distribution of temperatures in the elements of the circuit beyond that distribution which would exist in a completely clean furnace by selectively des lagging areas of the furnace wall.

Other and further objects of the invention will become appirent to those skilled in the art as the description procee s.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired, as hereinafter more particularly set forth in the following detailed p the stack (not shown).

description of an illustrative embodiment, said embodiment being shown by the accompanying drawing wherein the illustration depicts a side elevation of a oncethrough vapor generator with soot blowers located in the furnace walls and a schematic system illustrating the method and apparatus for operating the soot blowers.

In my invention a furnace wall circuit is divided into a plurality of groups of tubes, with particular soot blowers being associated with each group. The heat absorbed in each group is determined in some manner such as temperature or fluid flow measurements thereby indicating which of these groups have low heat absorption throughout their length. The average heat absorption of all the groups of tubes within the section is also obtained. The heat absorption of each particular group is then compared to the average. When the heat absorption of a particular group is a predetermined amount below the average, soot blowers associated with the particular group are activated cleaning the slag off the tubes of that particular group.

My invention therefore operates to maintain a uniform temperature distribution throughout a circuit. It may however actually improve the temperature distribution through the furnace walls when a maldistribution exists for other reasons. Independent of ash accumulation on the walls the distribution of combustion and gas flow pattern within the furnace may be such as to impose a particularly high heat absorption in certain sections of the furnace. According to my invention these sections which tend to receive too much heat will be permitted to slag up thereby decreasing the heat absorption in those sections and increasing the uniformity of heat absorption throughout the furnace. Maldistribution of temperatures within the section may also occur due to distribution of the fluid passing through the tubes. This may be caused by the characteristics of the supply piping which supplies the furnace wall tubes or by the particular configuration of the individual tubes themselves. Again, my invention will permit those tubes which tend to have low flows, and are therefore operating hot, to slag up so that the temperature balance within the furnace is improved.

Fuel and air are delivered through the burners 2 into the furnace 3 wherein the fuel is burned with the products of combustion passing through flue 4 discharging through Water is supplied at about 670 F. and 4100 psi. to the side wall inlet header 5 as well as the front and rear inlet headers 7. The furnace 3 has its walls lined with a plurality of vertical parallel tubes extending from the lower side wall header 5 to the upper side wall header 8, and also from the lower front and rear wall headers 7 to the upper front and rear wall headers 9. Thewater in passing through the furnace walls is heated to a temperature of about 800 F. and leaves at a pressure of about 4000 psi.

This fluid, which may now be considered steam, is conveyed through relief lines 10 to crossover pipe 12 through which it is conveyed to the finishing superheater section 13. This steam is then conveyed at a temperature of about 1000 F. through the steam pipe 14 to a steam turbine driving an electric generator (not shown).

Furnace wall soot blowers of the type illustrated in US.

Patent 2,662,241 are located in the furnace walls at three elevations, and are designated Row A, Row B and Row C. Each elevation contains soot blowers on all four walls of the furnace with the front and rear walls being similar to the side walls, one of which is shown in the illustration. This wall has four blowers at each elevation. These blowers are operative to clean the furnace wall in the general area of the corresponding blower. Accordingly, the furnace wall circuit in the side wall is divided into four sections by means of division plates in the upper header 8. Therefore one soot blower in each row corresponds to a particular group of tubes and when operated will claim a portion of these tubes.

Each group of tubes has a thermocouple and temperature transmitter 17 associated with it. This is preferably located in the relief line since the steam from the various tubes within the group are mixed and the temperature obtained is generally representative of each of the tubes within the group. Each of these temperature transmitters emits a control signal representative of the temperature measured through control line 18 sending this signal to an auctioneering controller 19. Such a controller is manufactured by and may be obtained from the Leeds & Northrup Company.

Steam temperature transmitter 20 by means of a thermocouple located in the crossover pipe 12 determines the temperature of the fluid which is leaving the furnace wall circuit. Since this is a mixture of all the fluid leaving all the groups of tubes it represents the. average temperature for all groups of tubes. A control signal representative of this temperature passes through control line 22 to controller 23.

Flow meter 27 is located in the steam line 14 and senses the outputof the steam generator. Controller 28 is associated with this flow meter and operates to emit a control signal to controller 23 through control line 29 which is representative of an allowable temperature difference which may be varied as a function of load.

This control system operates so that the temperature leaving each of the groups of tubes as sensed in accordance with temperature transmitters 17 and compared with the average temperature as sensed by means of temperature transmitter 20. When the temperature of any group of tubes is a predetermined amount below the average temperature, a soot blower associated with the particular group of tubes is to be operated. This temperature difference, which is desired, is not a fixed value throughout the load range but will vary depending on the output of the unit. This must be done in some designs since often it is found that the temperature unbalance in furnace wall circuit is inherently higher at lower loads than at higher loads. Conversely on other units wherein the furnace wall circuit operates as a portion of a recirculating system the temperature unbalance may be inherently less at lower loads than at higher loads. In accordance with the particular design characteristics of the units on which my invention is employed, controller 28 will operate as a function generator emitting the desired temperature difference limitation in accordance with the steam fiow sensed by flow meter 27.

This permissible temperature difference signal passing through control line 29 is combined with the actual average temperature signal passing through control line 22 so that controller 23 emits a signal through control line 30 which is representative of a minimum acceptable temperature. Each of the temperatures sensed by controller 17 representing fluid temperature leaving each group of tubes is compared in controller 19 to the minimum temperature signal passing through control line 30. When it is found that one of these temperatures decreases to the minimum acceptable value, a control signal is emitted through control line 32 to controller 33. This controller functions to operate a soot blower corresponding to the particular group of tubes which have indicated a low temperature. It will alternately select a soot blower from Rows A, B

and C for the particular circuit; so that if the last blower blown in that circuit were in Row A, Row B would now be selected with the next selection being Row C.

The operating circuit for each of the soot blowers will include a blocking timer 35 which will operate to prevent the particular soot blower from operating within one hour of the time it was previously operated. This will prevent continuous operation of a series of soot blowers when a low temperature is sensed leaving the particular circuit which is due to some cause other than heavy slagging in the area. In such a situation repeated operation of the soot blower on a wall that is already clean would be useless and would consume expensive blowing media as well as creating possibilties of unnecessary tube erosion.

After the selected soot blower is operated in response to controller '33 no further action will be taken directly in response to the initial determination of low temperature. However since controller 19 is still operating and comparing temperatures, it may sense that even after the operation of this selected blower the temperature leaving the particular group of tubes is low. In this case the system will proceed as previously described with controller 33 selecting a soot blower in the next row.

Thus the soot blowers will be operated in such a manner as to keep the walls of the furnace generally clean 'by blowing those areas which become excessively dirty as soon as they become dirty.

The described soot blower system operates to balance the heat absorption within the furnace, but there is no provision to regulate the over-all dirtiness of the furnace. Therefore the gas temperature leaving the furnace is sensed by gas temperature controller 37 which emits a control signal through control line 38 to controller 39. Flow meter 27 again senses the steam flow of the unit with controller 40 emitting a control signal through control line 42 which is representative of the maximum desired gas temperature for the particular load sensed. This control signal is compared to the actual gas temperature control signal in controller 39. When the actual gas temperature exceeds the maximum allowable a controlling signal is emitted through control line 43 to controller 44 which in turn operates all the furnace wall blowers, thus effecting a general cleaning of the furnace walls. This controller may, of course, respond to other means for sensing the over-all dirtiness of the furnace such as desuperheating spray quantity, amount of gas recirculation or tilting burner position.

This controller 44 may function in several fashions. It may operate all the soot blowers with no preferential selection being made. Alternately, as shown in the illustration, the control signal may be emitted from controller 44 through control line 45 which passes to controller 28. Controller 28 is that controller which establishes the allowable temperature difference as a function of the load of the steam generator. The control signal passing through control line 45 operates on this controller to reduce the allowable temperature difference. In accordance with the previously described scheme, the control signal emitted through control line 29 would function to operate soot blowers associated with groups of tubes where the temperature difference between that group and the average was more than the amount indicated as allowable by the control signal passing through control line 29. Therefore by reducing this allowable temperature difference, furnace wall soot blowers will operate with a selection being made such that those soot blowers associated with tubes having the lowest temperature will be operated.

When the gas temperature sensed by temperature transmitter 37 is reduced to an acceptable value for the particular load, there will be no need for additional operation of soot blowers and the signal emitted by controller 44 through control line 45 reducing the allowable temperature difference will be stopped. Controller 28 will therefore function to perform its function of establishing the preprogrammed allowable temperature difference.

While I have illustrated and described a preferred embodiment of my invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

What I claim is:

l. A vapor generator furnace; tubular surface lining the walls of said furnace; a plurality of groups of tubes connected in parallel comprising at least a section of said furnace walls; means for passing fluid to be heated through said groups of tubes; at least one soot blower associated with each group of tubes; means for determining the average temperature of the fluid leaving said furnace section; means for determining the temperature of fluid leaving each group of tubes; means for comparing the temperature of the fluid leaving each group of tubes with the temperature of the fluid leaving said section; means for establishing a predetermined allowable temperature difference between the fluid leaving each group of tubes and the fluid leaving the section; means responsive to said comparing means for operating a soot blower associated with a group of tubes when the difference between the temperature of the fluid leaving the corresponding group and the average temperature leaving said section exceeds said predetermined allowable temperature difference.

2. An apparatus as in claim 1 including: means for determining the overall dirtiness of the furnace walls; means for operating the soot blowers in response to a first predetermined over-all dirtiness comprising means for reducing the predetermined allowable temperature difference.

3. An apparatus as in claim 2 including: means for stopping operation of the soot blowers in response to a second over-all furnace dirtiness comprising means for increasing the predetermined allowable temperature difference to its original value.

4. In a vapor generator furnace having a plurality of groups of tubes lining the walls of said furnace, the method of operation comprising: burning an ash bearing fuel within said furnace; passing fluid to be heated through said groups of tubes in heat exchange relationship with said burning fuel; sensing the temperature of the fluid leaving each group of tubes; sensing the average temperature of the fluid leaving all groups of tubes; comparing the temperature leaving each group of tubes with that leaving all groups of tubes; and operating a soot blower corresponding to a particular group of tubes when the temperature leaving that group of tubes exceeds a predetermined amount below the temperature leaving all groups of tubes.

5. A vapor generator furnace; tubular surface lining the walls of said furnace; a plurality of parallel groups of tubes comprising at least a section of said furnace walls; means for passing fluid to be heated through said groups of tubes; at least one soot blower associated with each group of tubes; means for determining the average heat absorption of all the groups of tubes in said furnace section; means for determining the heat absorption of each group of tubes; means for comparing the heat absorption of each group of tubes with the average heat absorption of all the groups of tubes in said section;

means for establishing a predetermined allowable heat absorption difference between each group of tubes and average of all groups of tubes; means responsive to said comparing means for operating a soot blower associated with a group of tubes when the difference between the heat absorption of the corresponding group and the average heat absorption of the groups within said section exceeds said predetermined allowable heat absorption difference.

6. An apparatus as in claim 5 including: means for determining the over-all dirtiness of the furnace walls; means for operating the soot blowers in response to a first predetermined over-all dirtiness comprising means for reducing the predetermined allowable heat absorption difference.

7. An apparatus as in claim 6 including: means for stopping operation of the soot blowers in response to a second over-all furnace dirtiness comprising means for increasing the predetermined allowable heat absorption difference to its original value.

8. In a vapor generator furnace having a plurality of groups of tubes lining the walls of said furnace, the method of operation comprising: burning an ash bearing fuel within said furnace; passing fluid to be heated through said groups of tubes in heat exchange relationship with said burning fuel; sensing the heat absorbed by the fluid passing through each group of tubes; sensing the average heat absorbed by the fluid passing through all groups of tubes; comparing the heat absorbed by the fluid passing through each group of tubes with the average heat absorbed by the fluid passing through all groups of tubes; and operating a soot blower corresponding to a particular group of tubes when the heat absorbed by the fluid passing through that group of tubes exceeds a predetermined amount below the aver-age heat absorbed by the fluid passing through all groups of tubes.

9. A supercritical once-through vapor generator furnace comprising: vertical parallel tubes lining the walls of the furnace divided into parallel groups of tubes; means for passing supercritical fluid through said tubes; a soot blower associated with each group of tubes; means for determining the average temperature of the fluid lea'ving said tubes; means for determining the temperature of the fluid leaving each group of tubes; means for comparing the temperature of the fluid leaving each group of tubes with the average temperature of the fluid leaving said tubes; means for establishing a predetermined allowable difference between the temperature of the fluid leaving each group of tubes and the average temperature of the fluid leaving said tubes; means responsive to said comparing means for operating a soot blower associated with a corresponding group of tubes when the difference between the temperature of the fluid leaving the corresponding group of tubes and the average temperature of the fluid leaving said tubes exceeds said predetermined allowable difference.

References Cited by the Examiner UNITED STATES PATENTS 2,110,533 3/1938 SHOW et al. l22392 2,811,954 11/1957 Hibner et al. 122---392 3,137,278 6/1964 Cantieri et al. 122392 FREDERICK L. MATTESON, lR., Primary Examiner.

CHARLES J. MYHRE, Assistant Examiner.

Claims (1)

1. A VAPOR GENERATOR FURNACE; TUBULAR SURFACE LINING THE WALLS OF SAID FURNACE; A PLURALITY OF GROUPS OF TUBES CONNECTED IN PARALLEL COMPRISING AT LEAST A SECTION OF SAID FURNACE WALLS; MEANS FOR PASSING FLUID TO BE HEATED THROUGH SAID GROUPS OF TUBES; AT LEAST ONE SOOT BLOWER ASSOCIATED WITH GROUP OF TUBES; MEANS FOR DETERMINING THE AVERAGE TEMPERATURE OF THE FLUID LEAVING SAID FURNACE SECTION; MEANS FOR DETERMINING THE TEMPERATURE OF FLUID LEAVING EACH GROUP OF TUBES; MEANS FOR COMPARING THE THE TEMPERATURE OF THE FLUID LEAVING EACH GROUP OF TUBES WITH THE TEMPERATURE OF THE FLUID LEAVING SAID SECTION; MEANS FOR ESTABLISHING A PREDETERMINED ALLOWABLE TEMPERATURE DIFFERENCE BETWEEN THE FLUID LEAVING EACH GROUP OF TUBES AND THE FLUID LEAVING THE SECTIONS; MEANS RESPONSIVE TO SAID COMPARING MEANS FOR OPERATING A SOOT BLOWER ASSOCIATED WITH A GROUP OF TUBES WHEN THE DIFFERENCE BE-

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