US3395657A - Automatic fire control for coal fired furnace - Google Patents

Description

J. A. SCHUSS 5 Sheets-Sheet l [NVE/V702 JAC/(A. SCI-[USS ATTORNEY AUTOMATIC FIRE CONTROL FOR COAL FIRED FURNACE Aug. 6, 1968 Filed Aug.

Aug. 6, 196s 1A. SCHUSS 3,395,657

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AUTOMATIC FIRE CONTROL FOR COAL FIRED FURNACE P E Q Y N lL u o N N N N Cp P fp A /J n a (e a N v N a N r y s Q N N '3 n d T T N 2 3 INVENTOR. 3 o n S n w JAcKAcHuss N N N N ATTOEN E Y United States Patent O "ice 3,395,657 AUTOMATIC FIRE CONTROL FOR COAL FIRED FURNACE Jack A. Schuss, Hartford, Conn., assignor to Combustion Engineering, Inc., Windsor, Conn., a corporation of Delaware Filed Aug. 1, 1966, Ser. No. 574,511 16 Claims. (Cl. 110-22) ABSTRACT OF THE DISCLOSURE A control system for operating the burners of a multiburner, coal-fired system to automatically place groups of burners in service in response to changing load requirements on the power plant. This system comprises a digital control effective to selectively place individual coal pulverizing mills together with their associated groups of burners in service when load demand on the power plant so requires. The system further includes means to monitor the operation availability of each mill and its associated burner group and to place in service only that mill and group of burners capable of increasing the total heat output of the burner system.

The present invention relates to automated fuel ring systems for vapor generators. More particularly, the invention concerns an electro-mechanical control system effective to automatically place the burners of a multiburner, coal-fired vapor generator burner system in service in response to increase in load demand requirements.

In recent years it has become accepted practice to operate the fuel ring equipment of thermal power stations from a centralized control where various instruments capable of indicating the state of unit operation, such as gauges, indicating lights and recorders, are assembled together with switches that are effective to control the operation of the fuel firing equipment. In such installations the boiler operator visually senses the condition or state of system operation and, when digressions from the desired state of operation occur, manually actuates the appropriate control switches for the purpose of controlling the firing system to offset these changes. The decision making in these installations remains with the operator and therefore is subject to human error. As the size and capacity of vapor generating stations increase, the number of sensing apparatus and the number of components that must be controlled are greatly multiplied thereby rendering it more diflicult for the operator to safely and efficiently control the operation of the power plant system. There is a growing demand, therefore, for unit automation to relieve the operators burden and to ensure plant safety and efficiency of operation. It is to this end that the present invention is directed.

The present invention is contemplated for use in power plants comprising vapor generators employing coal as the principal fuel. The fuel firing system of such units consists of a coal burner system that is operable over the normal load range of the vapor generators and an ancillary oil burner system that provides heat for warming up the unit prior to its being put on the line. The oil burner system is also operative to provide ignition energy for igniting each of the coal burners as they are placed in service. The coal pulverizing mills that supply coal to the burners are considered as being part of the fuel firing system inasmuch as burner operation is dependent upon and controlled by the operation of the pulverizing mills.

The control system of the present invention, together with conventional combustion controls, operates to provide the control and regulation of the fuel tiring system of large capacity vapor generators with a minimum of 3,395,657 Patented Aug'. 6, 1968 manual supervision. While the combustion controls are of an analog type and operative to regulate the operation of the fuel burners in service in response to varying load demand, the instant control system is an improved form of digital control that is effective to safely and effectively place burners in service when the load demand requirements of the unit so require.

According to the invention the coal burners and the oil burners that comprise the firing system are each arranged in groups with the grouping being such that each group of coal burners is capable of being ignited by an adjacent group of oil burners. The control system of the invention provides means responsive to the need for placing groups of coal burners into operation for placing an appropriate group of oil burners in service and thereafter, initiating the startup of the coal pulverizing mill which supplies coal to a group of burners that are ignited by the operating group of oil burners. Means are also provided to oversee the operational capability of the oil burners and mills and to initiate operation of a group of oil burners only when it is itself operational and the mill associated with the coal burners ignited by it is operational. Additional means are provided to automatically place an alternative group of oil and coal burners in service in the event the desired groups are incapable of being placed in service.

The various objects and advantages of the invention will be evident from the following description when read in light of the accompanying drawings in which:

FIGURE 1 is a schematic representation of a power plant employing the present invention;

FIGURE 2 is a schematic representation of a typical firing corner in the vapor generator of FIGURE 1;

FIGURE 3 is a schematic representation of a typical coal pulverizing mill contemplated for use in the present invention;

FIGURE 4 is a schematic representation of the fuel oil system utilized in carrying out the present invention;

FIGURE 5 is a circuit diagram, shown somewhat schematically, of the Pulse Initiation Circuit of the present -control system;

FIGURE 6 is a circuit diagram of the Oil Elevation Selection Circuit;

FIGURE 7 is a circuit diagram of the Mill Selector Circuit;

FIGURE 8 is a typical Mill Start Control Circuit;

FIGURE 9 is a typical Burner Counting Circuit contemplated for use in the present invention;

FIGURE 10 is a schematic representation of a Mill-in- Service Feedback Relay employed in the instant invention.

General arrangement Referring now to the drawings, FIGURE 1 illustrates a thermal power plant 10 that is operated in accordance with the present invention. It comprises a vapor generator 12 that is operatively connected to a steam turbine 14 which, in turn, drives an electric generator 16. Analog controls in the form of a Steam Output Control 18 and a Combustion Control 20 are employed to control plant output in response to changing load demand. These controls are of known construction and do not form part of the present invention.

As shown, the vapor generator 12 includes a furnace 22 lined with fluid conducting tubes 24 within which high temperature vapor is created and passed through line 26 to lthe turbine 14. In line 26 is located a vapor regulating valve 28 operated in response to the Steam Output Control .18 to regulate the supply of vapor to the turbine. Steam line 26 also contains a pressure sensing element 30 adapted to transmit a signal to the Combustion Control 20 which is effective to adjust liquid and fuel input to the vapor generator 12 in order to satisfy the demand requirements of the turbine.

The tiring system of the vapor generator includes burner assemblies 32 arranged to operate within the furnace 22. In the disclosed embodiment of the invention the burner assemblies 32 are disposed in each of the four corners of the furnace with the burners being adapted for tangential firing. Each assembly 32 consists of alternately vertically spaced pulverized coal burners 34, oil burners 36 and auxiliary air nozzles 38. The structural details of these burner assemblies are similar to those disclosed and described in U.S. Patent No. 2,697,422 issued Dec. 21, 1954, to Armacost and a description thereof is not deemed necessary herein for an understanding of the present invention. The burners are deployed in eleven elevations, indicated in FIGURES 1 and 2 as Elevations A through L. Each elevation comprises four burner nozzles, each disposed at one of the corners of the furnace 22. Elevations A, G and L comprise those nozzles 3S adapted to supply auxiliary combustion air to the furnace; Elevations B, D, F, H and K consist of coal burners 34 and Elevations C, E and I consist of oil burners 36 together with their associated pilot torches 40. As shown, each elevation of coal burners 34 is supplied with pulverized coal by mills 42 and their associated equipment through coal supply lines 44 having burner inlet vales 46 disposed therein for controlling the flow of coal to each of the burners. Each elevation of oil burners 36, on the other hand, is supplied with fuel oil through an oil supply line 48 that is connected to a main oil line 50.

Coal Supply System In FIGURE 3 is illustrated a schematic representation of a typical coal supply system contemplated for use in the invention for supplying pulverized coal` to the burners 34 of each of the coal burner elevations B, D, F, H and K. It comprises a coal pulverizing mill 42 which receives raw coal from a collection hopper (not shown) by means of a feeder 52 driven by a variable-speed motor S4. Lines 56 and 58, containing power-operated feeder inlet and outlet gate valves, `60 and 62 respectively, connect the feeder 52 between the hopper and the -mill 42. The rate at which coal is supplied to the burners 34 is controlled by the Combustion Control which operates to vary the speed of motor 54 and thereby regulate the amount of raw coal passed to the mill 42 and thence to the burners. As shown, a tachometer 64, or the like, may be employed for transmitting a coal flow measurement feedback signal to the Combustion Control 20. Hot air is supplied to the mill 42 through duct 66 having a power operated gate valve 68. This air serves both to dry the coal within the mill and to convey the pulverized coal fines to the burners 34. The latter function is effected by means of an exhaust fan 70 connected between the mill 42 and the line 44. A power-operated mill discharge valve 72 is connected in line 44 downstream of the exhaust fan 70 for initiating or terminating the admission of pulverized coal to the line. Mill air temperature is controlled by the admission of cold air through duct 74 with its power-operated gate valve 76 to the hot air duct 66 upstream of the mill. The total air flow to the mill is controlled by the Combustion Control 20 through damper 78 while the mill air temperature is controlled by the regulation of hot and cold air dampers 80 and 82 through a Mill Air Temperature Controller 84 which receives a feedback signal from an appropriately positioned mill air temperature measurement device 86.

Oil Supply System In FIGURE 4 there is shown a schematic representation of the fuel oil system employed in the preferred embodiment of the invention. It comprises a main oil 50 that is connected in common with all of the oil burners 36 in each oil burner elevation C, E and I. Positioned in the line 50 is a power-operated oil regulating valve 90 that is adapted to regulate the amount of fuel supplied to the burners 36 under the control of the Combustion Control 20. Actual oil ow through the line 50 is determined by a flow sensor 92 whose signal operates as a feedback to the Combustion Control. A bypass flow regulator 94 operates in parallel with the valve 90, lits purpose being to ensure the presence of a minimum amount of oil line pressure to the burners 36 regardless of the position of the valve when the oil system is in operation. This minimum oil pressure is determined to be that which is required to effect automation of the oil supplied to the burners in order that it can be readily ignited. In the instant example an oil pressure of approximately p.s.i. is considered to be adequate for this purpose.

The line 50 supplies oil to each elevation of oil burners, C, E and J, through take-off lines 48 which each have an associated power-operated admission valve 98. Likewise, each oil burner 36 is equipped with an associated admission valve 100 that is operative to terminate operation of each burner upon the occurrence of an unsafe condition as determined by an associated control device (not shown). Ignition of the burners 36 is effected by means of a pilot torch 40 associated with each burner. For the sake of brevity, only one such torch 40 is shown in FIG- URE 4. Each pilot torch 40, which is commonly gas-operated, has an associated fuel valve 102 and spark ignitor 104 that are actuated when it is desired to provide ignition energy for the oil burners 36.

In the herein disclosed arrangement the oil burner system of FIGURE 4 is operative to provide combustion energy to the furnace 22 during warm-up and also to provide ignition energy for the coal burners 34 during normal vapor generator operation. During the warm-up phase of unit operation the oil burner system is automatically controlled by an independent control sub-loop that is effective to place each oil burner elevation in service in a prescribed sequence such that vapor generator temperature is gradually increased up to its minimum operating temperature. The control sub-loop employed in a preferred embodiment of the invention is substantially the same as that embodied -in co-pending U.S. patent application Ser. No. 484,061 to the same inventor filed Aug. 31, 1965, now Patent No. 3,341,118, and a complete description thereof is therefore not required in this application. For the sake of describing the instant invention, it is only necessary to understand that when the vapor generator goes into operation upon completion of the warm-up procedure that terminates with the phase synchronization of the electric generator 16, all the oil burner elevations are considered to be in operation under thecontrol of the Combustion Control 20 and they remam in operation until such time as the generation of combustion energy generated in the furnace 22 is taken over by the coal burner system, the control of which is the subject of the present invention.

Control System Therefore, according to the present invention means are provided to safely and effectively place each elevation of coal 'burners B, D, Fl H and K in service automatically Without the need of manual supervision. This means comprises a fixed program digital control that is effective to place the coal pulverizing mills 42 associated with each coal lburner elevation in service in 4response to an increase in vapor generator load demand. The mills 42 are placed 1 n servlce according to a predetermined sequence, which, m the preferred embodiment, is according to the sequence D-B-F-H-K. The control means of the present invention is operative to scan the operational availability of each mill 42 and to place it in operation only when conditions permit its being placed in operation. In the event one or more of the mills in the sequence are incapable of safe operation or whose availability for service has been disrupted, as for example, for maintenance purposes, the control system is operative to seek out another -mill in the sequence that can be operated and place it in service in order to satisfy the indicated increase in load demand.

While in the herein described embodiment of the invention the fuel ring system is shown as containing five elevations of coal burners 34, three elevations of oil burners 36 and three elevations of air nozzles 38 with each elevation comprising elements disposed at each of the four corners of the furnace 22, it is to be understood that such arrangement has been employed for the purpose of illustration only and that a greater or less number of elevations can be employed according to the present teaching.

Fire Control Going now to the power plant control system, in FIG- URE 1 there is shown a Fire Control 106 which is adapted to control the operation of the mill 42 which in turn governs the operation of the coal burners 34. The Fire Control 106 yfunctions independently of the Combustion Control 20, the latter being an analog type of control and responsible for the regulation of operation of the mills and burners in response to condition changes in the system while the former is a fixed program digital controller whose control functions are superimposed upon those of the Combustion Control` More particularly, while the Combustion Control is effective to regulate the supply of working medium, namely fuel and water, to the vapor gener-ator in response to load changes, the Fire Control 106 is independently effective to alter the number of coal pulverizing mills 42 and thus the number of coal burners 34 that are placed in operation. It is the objective of the Fire Control 106 to place mills 42 and burners 44 in service and of the Combustion Control 20 to regulate the operation of those mills and burners once they are in service. In achieving this objective, the Fire Control 106 functions first to determine when the need for placing additional burners in service arises. After having determined that additional burners must be installed in service, the Fire Control 106 is operative to determine `which of the mills 42 are capable of being placed in service taking into account the availability of sufficient ignition energy from the associated oil elevations with which to ignite the coal supplied to the coal burners and the operability of the respective mills. Thereafter the control is operative to take appropriate steps to place the selected mill and coal burner elevation in service. This is accomplished according to a predetermined sequence of mill actuation. If, however, the selected mill and burner elevation cannot be safely operated, the Fire Cont-rol is effective to select the neXt mill in the sequence and to initiate its start-up, and so on, until the load demand has been satisfied.

Pulse Initiation Circuit The Fire Control 106 `comprises three principal control sub-loops, namely, the Pulse Initiation Circuit (FIG- URE 5), lche Oil Elevation Start Circuit (FIGURE 6) and the Mill Start Circuit (FIGURE 7). The Pulse Initiation Circuit as shown in FIGURE 5 consists of a seriesparallel circuit connected across the hot and ground lines of an electric source and is effective, upon completion of the circuit, to energize a pulse timer 108. As shown, the circuit comprises a start switch 110 that is manually operated to place the firing control in operation. The circuit also comprises parallelly connected lines 112 and 114, the line 112 being operative to govern unit operation prior to any mill being placed in service when one set of conditions is required to place a mill in operation and the line 114 being operative when one or more of the mills is operating and another set of conditions is applicable. Line 112 contains a series connection of switches 116, 118 and 120. Switch 116 is a normally open, manual or relay operated, switch associated with the turbo-generator installation and actuated to the closed position when the generator is synchronized and the unit therefore ready to be placed on the line. Switches 118 are normally closed, relay actuated switches associated with each of the mills 42 and therefore sufiixed in the drawing with letters B,

D, F, H and K indicating the mill with -which each is associated. In operation each of the switches 118` will remain closed until such time as its lassociated mill is placed in operation whereupon the appropriate switch is actuated to its open position by means of a feedback relay 272 (FIGURES 8 and 10) to thereafter render line 112 ineffective to pass an electric current to the pulse timer. Switch 120 is a normally open, relay operated switch associated with the oil flow sensor 92 in the main oil supply line 50. The arrangement is such that an operating relay (not shown) 'will be actuated to close the switch 120 at a predetermined oil flow setting, that setting corresponding to an oil flow to the burners 36 having a heating potential that corresponds to the heat potential of the coal supplied by one mill operating at its minimum output plus the heat potential of an associated oil tburner elevation that will be utilized to ignite the coal supplied by the mill. The purpose of this control element is to ensure the maintenance of a balance of heat within the furnace 22 when the source of combustion energy changes from oil to coal.

Line 114 contains a series connection of switch 122 and parallelly connected switches 124. Switch 122 is a normally open, relay actuated switch that is closed when the average loading of all the operating mills 42 is at least as great as of the total operating capacity of the mills. This switch is actuated by a relay (not shown) controlled by the Combustion Control 20 to operate when the average output of the number of mills in 0peration equals 80% of their combined capacity as determined by feedback signals obtained from the tachometer '70 associated with each mill feeder 58. Switches 124, appropriately sufiixed with an indication of the respective mill with which each is associated, are normally open, relay operated switches that are closed when their associated mill is placed in operation. Thus line 114 will govern the operation of the Fire `Control 106 after at least one coal mill 42 has been placed in operation.

The Pulse Initiation `Circuit also contains parallelly connected switches 126B, 126D, 126F, 126H and 126K connected in series with lines 112 and 114. The switches 126 are normally open switches operated by relays 218 (FIGURE 9) and associated with each of the respective mills 42 to be closed when the associated mill is available for service. By available for service is meant that all of the requirements for safe mill operation have been satisfied as indicated by the actuation of appropriate feedback relays to be discussed hereinafter. An additional requirement that must be met before a mill is considered to be available for service is that the mill is not already in service. This condition is also determined through the actuation of an appropriate feedback relay that will be hereinafter discussed.

The Pulse Initiation `Circuit further contains a series connection of parallelly connected switches 128C, 128B and 128] which are normally closed switches associated with each of the respective oil burner elevations and adapted to be actuated to an open position when the aS- sociated burner elevation is incapable of being placed in service. The switches 128 can be actuated to an open position manually, as when it is desired to perform maintenance on one of the respective burner elevations or automatically by means of a control relay. The system is arranged such that automatic actuation of the switches 128 will occur when the number of operable oil burners 36 in each of the elevations C, E and J is insufficient to ignite the coal burners 34 of an associated coal burner elevation.

For this purpose, burner counting circuits, such as that shown in FIGURE 9, are employed to prevent actuation of an entire oil burner elevation whenever more than one of the elevations four burners 36 are inoperative, it having been determined that if three of the four oil burners in each elevation are operable the elevation can provide a sufficient amount of ignition energy to ignite all of the coal burners 34 of an associated coal burner elevation. As shown, the counting circuit comprises a series-parallel connection of normally open switches 130 that are each associated with one of the four burners that comprise a given elevation. For the purpose of description, the numerals 130 are sutlixed with appropriate letters, a, b, c and d, to indicate the burner with which each is associated. The switches 130 in the preferred embodiment are in the form of limit switches actuated in response to movement of each burner valve 100 to be opened when the valve is open thereby indicating that the associated burner is operating. Thus when more than one valve G fails to open, an electric circuit will be completed through the appropriate switches 130 to actuate the relay 132, thereby opening its associated switch 128 in the Pulse Initiation Circuit of FIGURE 5. As shown, the relay 132 is also the operator of switches 156, 158, 182 and 184. The function of these switches is to provide feedback signals indicating the operability of the associated oil burner elevation to the Oil Elevation Selection Circuit (FIGURE 6) and the Mill Selection yCircuit (FIGURE 7) respectively. A more detailed explanation of the operation of these switches is contained hereinafter.

The pulse timer 108 which is operated by the Pulse Initiation Circuit may be in the form of a constant speed, synchronous motor that drives a cam element 134 adapted to intermittently actuate switch 136, which in turn intermittently energizes relay 138. The motor operates at the rate of one revolution per minute and the switch 136 is closed for a duration of two seconds in each revolution. Thus the relay 138 is pulsed at the rate of once every minute for two seconds duration when the pulse timer 108 is energized. Pulsation of the relay 138 operates to simultaneously close switches 140 and 142 which are the actuating elements of the Oil Elevation Selection Circuit (FIGURE 6) and Mill Selection `Circuit (FIGURE 7) respectively.

Oil Elevation Selection Circuit The `Oil Elevation Selection Circuit shown in FIG- URE 6 is operative to transfer the pulse generated by the pulse timer 10S to the operating members of one of the oil burner elevations to initiate operation of that elevation. The circuit contains the pulsing switch 140 operated by relay 138 connected to three parallelly con nected oil elevation operator relays 154C, 154B and 154]. The circuit arrangement is such that the pulsed closure of switch 140 will pulse only one of the relays 154 to place its associated oil elevation in service. In the disclosed embodiment of the invention it is desirable to have oil elevay tion C, which provides ignition energy to adjacent coal elevations B and D, placed in service lirst, followed by oil elevation E, serving coal elevations D and F, and then oil elevation J serving coal elevations H and K. By means of the circuit arrangement, closure of pulsing switch 140 will actuate relay 154C unless oil elevation C is incapable of being placed in service either because it has been locked out of service or the mills associated with coal elevations B and D are both not available for service. If relay 154C cannot receive the pulse then relay 154B stands next in the sequence to receive it to actuate the burners 36 of oil elevation E. Similarly, relay 154E will receive the energizing pulse as long as it is not itself locked out of service or its associated mills 42D and 42F are not available for service. If neither relay 154C nor 154E is actuated by the pulse then relay 154] will receive it to place one of its associated mills 42H or 42K in service. The circuit arrangement to perform this function, as shown in the ligure, is a relatively simple series-parallel arrangement of switches 156, 158, 160 and 162. For the sake of clarity like switches are assigned similar numerals but are sutxed with appropriate letters to indicate the elevation with which each is associated. Switches 156 are operated by the same burner counting circuit relay 132 and have the same sense as switches 128 in the Pulse Initiation Circuit of FIGURE 5 and are therefore closed when the associated oil elevation is not locked out of service. Switches 158, also operated by relays 132, have the opposite sense from switches 156 and are therefore closed when switches 156 are open and vice versa. Closure of switches 158 indicates that the associated oil elevation is locked out of service and therefore not capable of being placed in operation. Switches are normally open switches that are operated by Mill Available Relay 216 (FIGURES 8 and l0) and have the same sense as switches 118 in the Pulse Initiation Circuit of FIGURE 5. These switches are thus closed when the associated mill 42 is available for service and relay 216 energized. Switches 162, also operated by relay 216, have a sense opposite from that of switches 160 and are therefore closed when switches 160 are open and vice versa. Closure of switches 162 indicates that the associated mill is not available for service.

As shown, the Oil Elevation Selection Circuit comprises three parallelly connected sub-circuits 164, 166 and 168 each being effective to transmit the pulse generated by the momentary closure of switch 140 to one of the respective Oil lElevation Operator Relays 154C, 154B and 154]. Sub-circuit 164 contains a series connection of switch 156C with parallelly connected switches 160B and 160D. Therefore electric current will pass to relay 154C upon the pulsed closure of switch 140 if oil elevation C is not locked out of service and either mill 42B or 42D is available for service. Sub-circuit 168 contains a similar connection of switches 156B, 160D and 160F which permits relay 154B to accept the pulse as long as oil elevation E is not locked out of service and either of those mills, 42D or 42E, supplying the coal burner 34 ignited by the burners 36 of oil elevation E is `available for service. It also contains, however, a series-parallel arrangement of switches 158C, 162B and 162D that must deline a current path through the sub-circuit before relay 154B will be pulsed. Thus, relay 154E will accept the pulse generated by the closure of switch 140 only if oil elevation E is not locked out of service and either of the mills, 42E or 42F, are available for service but also contingent upon the fact that oil elevation C is not locked out of service as evidenced by closure of switch 158C or both mills 42B and 42D are not available for operation as evidenced by closure of switches 162B and 162D.

Sub-circuit 168 contains a similar connection of switches 156], 160H and 160K, the closure of the former plus one of the latter two thereby permitting relay 154] to be pulsed. This sub-circuit, however, also contains a seriesparallel arrangement of switches 158 associated with the other oil elevations C and E, together with switches 162 associated with mills 42B, 42D and 42E, which, as shown, will permit passage of the pulse to the relay 154] only if conditions exist that prevent both of the other relays 154C and 154B from being pulsed.

Mill Selection Circuit The Mill Selection Circuit illustrated in FIGURE 7 functions to select one of the mills 42 to be placed in operation when conditions require the addition of another coal burner elevation in service. The circuit comprises four parallelly connected sub-circuits 170, 172, 174 and 176 which are each effective to transmit the pulse generated by the momentary closure of switch 142 to one of the respective mill operator relays B, 180D, 180F, 18m-I and 180K. The arrangement is such that the pulsed closure of switch 142 by the pulse timer relay 138 will be transmitted to only one of the relays 180 to place its associated mill 42 and coal burner elevation in service. In the disclosed embodiment of the invention the desired sequence of coal burner elevation start-up is in the following order: D-B- F-H-K. Thus the circuit arrangement shown in FIGURE 7 is such that relay 180D is adapted to be pulsed first, and, if the associated coal burner elevation D is incapable of being safely placed in service, either because there is insuiiicient ignition energy available from the adjacent oil burners 36 or the mill 42D is not available lfor service, the pulse will be next adapted for reception by relay 180B, and so on through the sequence. The Mill Selection Circuit is a series-parallel arrangement of switches 182, 184, 186 and 188. Again for the sake of description, like switches are assigned similar numerals suxed with appropriate letters to indicate the elevation with which each is associated. Switches 182 are normally open switches operated by burner counting circuit relays 132 (FIGURE 9) and are closed when the relay 132 is de-energized thereby indicating at least three of the four burners in the associated oil burner elevation are in service and that sufficient ignition energy will be available to ignite the coal issuing from the burners 34 when the respective mills are placed in service. Switches 184 also are operated by relays 132, but have a sense opposite from that of switches 182, thus the former will be closed when the latter is open and vice versa. Therefore closure of switch 184 indicates that the associated oil elevation cannot provide suicient ignition energy to ignite the adjacent coal burners. Switches 186 are normally open switches operated by relays 216 (FIGURES 8 and 10) and have the same sense as switches 118 and 160 referred to above. Closure of switches 186 therefore indicates that the associated mill 42 is available for service. Switches 188, also operated by relays 216, but having a sense opposite from that of switches 186, are therefore closed when the associated mill 42 is not available for service.

As shown in FIGURE 7, each of the sub-circuits, 170 through 176, are effective to transmit the pulse generated by closure of switch 142 to one of the mill operator relays 180. Sub-circuit 170, associated with relay 180D, contains a series connection of switch 186D with parallelly connected switches 182C and 182E. Thus current will pass through the circuit to relay 180D upon the pulsed closure of switch 142 if at least one of the two oil burner elevations, C or E, adjacent coal burner elevation D is in service and mill 42D is available for service. Subcircuit 172, associated with relay 180B, contains a series connection of switches 182C, 186B and 188D. Thus, the associated relay, 180B, will be energized when oil elevation C is proven to be in service by closure of switch 182C and mill 42D is not available for service but mill 42B is so available as indicated by closure of switches 188D and 186B, respectively. Sub-circuit 174 contains switches 182L, 186F and 188D which are connected in series with parallelly connected switches 184C and 188B. Relay 180F will therefore be energized upon closure of switch 142 if oil elevation C is not in service or, if in service, neither mills 42B or 42D are available for service, provided oil elevation E is proven to be able to supply suicient ignition energy to ignite the coal supplied to the burners 34 of one of the associated coal elevations and provided also that mill 42F is available for service. Subcircuit 176 is arranged to operate both mill operator relays 180H and 180K. The series-parallel arrangement of the various switches 182, 184, 186 and 188 is such that relay 180H will be energized if its associated mill 42H is -available for service and associated oil elevation J is delivering suicient ignition energy by any one of the four routes defined by the arrangement. First, current will pass to the relay through the line dened by switches 184C and 184B if oil elevations C and E are both out of service; secondly, through the line defined by switches 188B, 188D and 184B if elevation C is in service but neither mills 42B or 42E are available for service and oil elevation E is out of service; thirdly, through the line defined by switches 188B, 188D and 188F if either or both oil elevations C and E are in service but none of the mills 42B, 42D nor 42F are available for service; and fourthly, through the line defined by switches 184C, 188D and 188F if oil elevation E is in service but mills 42D and 42F are not available for service and oil elevation C is not in service. This sub-circuit, 176, also contains parallelly connected switches 186K and 188H that connect with mill operator relay K. Thus relay 180K will receive the energized pulse by one of the four routes described above if, in addition, its associated mill 42K is available for service but mill 42H is not.

Mill Starr Control Circuit FIGURE 8 is a schematic representation of a Mill Start Control Circuit as employed in the present invention. The circuit shown typifies the control arrangement provided for placing one of the pulverizing mills 42 in operation. In the described embodiment of the invention ve such circuits are employed but, in order to avoid duplication only one is described here. The -Mill Start Control Circuit comprises a plurality of parallelly connected sub-circuits 190 through .202, each of which controls various aspects of the start-up program of the associated mill 42. Sub-circuit 190 contains parallelly connected switches operated by the feedback signals from t'he several components associated with sensing apparatus of each mill. The sensing means are adapted to register each of the several mill permissives that must be satised prior to the mill being permitted to be placed in sevice. For the sake of brevity only ve such switches are shown in sub-circuit 190, these Ibeing switch 204 that Ireceives a feedback signal from the cold air gate'76 indicating that it is open; switch 206 that receives a feedback signal from the mill discharge valve 72 indicating that it is open; switches 208 and 210 that indicate that the feeder inlet and outlet gate valves 60 and 62, respectively, are open; and switch 282 which is actuated by relay 280 to indicate that the mill is not locked out. With the exception of switch 282 these feedback signals can be conveniently obtained from limit switches on the respective valves that are closed when the valve is in its open position. In actual practice, several other similarly connected switches indicating other permissive conditions are included in the sub-circuit Iand must be closed before lthe mill can be considered as being ready for service. Such permissive conditions include: the mill temperature is normal; adequate lubricating oil and cooling water are available; seal air Iand tramp iron valves are open; etc. When all of the permissive conditions are satisfied the circuit is completed through sub-circuit 190 to Mill Ready Relay 212, thereby effecting actuation of the relay to close switch 214 in sub-circuit 192. Actuation of Mill Ready Relay 212 indicates that all permissives required for safe operation of the associated mill 42 are satisfied. If any one of the conditions is not satistied, the appropriate s-witch will remain open thus prevention relay 212 from being actuated.

Sub-circuit 192 contains Mill Available Relay 216 connected in series with switches 214 and 218. Switch 214, as mentioned above, is associated with the Mill Ready Relay 212 and is closed upon energization of that relay. Switch 218 is a normally closed switch that is associated with relay 272 (FIGURE 10) in sub-circuit 202, to be opened when the associated mill is placed in service. Thus, completion of sub-circuit 192 will energize relay 216 when the permissive conditions of the associated mill are all satisfied and provided that the mill is not already in service. As shown in FIGURE 11, the Mill Available Relay 216 operates several other switches which 'have been referred to hereinabove. These switches include switch 126 in the Pulse Initiation Circuit of FIGURE 5, switches 160 and 162 in the Oil Elevation Selection Circuit and switches 186 `and 188 in the Mill Selection Circuit.

Sub-circuit 194 contains the motor drive of the mill operator timer 220 connected in series with switches 222, 224 and 226. Switch 222 is a normally open switch `operated by the associated Mill Available Relay 216, switch 224 is a normally open switch operated by relay 132 (FIGURE 9) in the associated Burner Counting Circuit which is closed when there is suicient ignition energy available to ignite the coal burners 34, and switch l l 226 is a normally open switch operated by the associated Mill Operator Relay 180 of the Mill Selection Circuit. Completion of sub-circuit 194 will effect re-set and start of the timer 220 which is set to have a timing duration of at least 12() seconds. During this period each of the various steps attendant to mill start-up are etected in response to the sequenced actuation of each of the timer contacts 228, 239, 232 and 234 which may be operated by timer cams or the like. Thus, closure of timer contact 228 in sub-circuit 196 will energize parallelly connected solenoids 244er, 244]), 244e and 244d to open the coal burner inlet gate valves 46 that control admission of coal to the burners 34 in the associated coal Eburner elevation. Sub-circuit 198 contains relay 257 connected in series with timer contacts I230` and switches 248, 250 and 252. Timer contact 230 is set to close approximately l seconds after the closure of contact 228 in sub-circuit 196. Switches 248 are normally open limit switches that are closed when each of the associated gate valves 46 is opened. Switches 250 and 252 are associated with the Mill Ready Relay 212 and Burner Counting Circuit Relay 232, respectively. The presence of these two switches in sub-circuit 198 ensures an immediate cessation of the mill start-up procedure upon the occurrence of any conditions that would remove the associated mill from its ready status as indicated by a de-actuation of relay 212 or upon the loss of ignition energy as indicated by deactuation of relay 132. Completion of sub-circuit 198 elects energization of relay 246 to simultaneously actuate the mill motor 254 and hot air gate solenoid 256 by the closure of switches 258 and 260, respectively. Energization of relay 246 also effects closure of switch 262 in subcircuit 208 which arms the Feeder Motor 264. The Feeder Motor 264 will be started upon actuation of relay 262 upon the expiration of approximately l seconds after the mill motor 245 is energized when timer contact 240 is closed, completing sub-circuit 200. Again, actuation of Feeder Motor 264 is contingent upon the Mill Ready Relay 212 and burner counting circuit relay 132, both remaining energized to close switches 268 and 270. Subcircuit `202 contains relay 272, indicated as the Mill-in- Service Relay, which is armed -by the actuation lof the relay 266 and energized by closure of timer contact 234 which occurs approximately 60 seconds after the closure of timer contact 232. Energization of relay 272 opens the normally closed switch 218 in sub-circuit 192, thereby de-energizing the Mill Available Relay 216 t0 open switches 162, 188 and 217 and close switches 126, 160` and 186.

Energization of the Mill-in-Service Relay 272 also opens contacts 276 in sub-circuit 203. Sub-circuit 203 contains relay 280 which is serially connected with switch 276 and timer contact 278. The relay 280` is indicated as the Mill Lockout Relay and is adapted to actuate switch 282 in sub-circuit 190 to the open position whenever the Milln-Service Relay 272 fails to be energized. Timer contact 278 is set to close approximately ve seconds after the closure of contact 234. Thus, if the mill startup procedure fails to be completed for any reason, the relay 272 will not be energized but instead relay 280 will be energized to open switch 282 in sub-circuit` 190 and thereby de-energize Mill Ready Relay 212 and `thence Mill Available Relay 216.

Control System Operation The operation of the control system as applied to the herein described vapor generator fuel burner system will now be described. For the purpose of description, it will be assumed first that vapor generator start-up is initiated from a cold condition and that all of the pulverizing mills 42 are in operational condition and therefore available for service. The vapor generator, being placed in service from a cold condition, must first undergo warm-up, or a gradual application of heat, in order that the various pressure parts of the unit are not subjected to undue thermal Cil stresses. Warm-up is accomplished by supplying water to the tubes 12 and fuel oil to one of the oil burner elevations C, E or J. Heat is gradually increased within the furnace 22 by increasing the flow of oil through the regulator valve in the main oil line 50. As warm-up temperature requirements increase, additional elevations of oil burners are placed in service by means of an independent sub-loop that does not form part of this invention.

When the warm-up phase has been completed the power plant is then capable of being placed on line in the power system. This is accomplished when the output voltage of the electric generator 16 is placed in phase with that of the power system. Upon this occurrence the power plant is considered to be operating under normal conditions and it is at this point that the Fire Control 186 of the present invention becomes operative to control the placement of the several coal burner elevations B, D, F, H and K in service.

Referring now to the various circuits that comprise the Fire Control 106 under the conditions specified, namely that all of the oil elevations C, E and J are in operation and none of the pulverizing mills 42 have as yet been placed in service but are capable of being placed in service, the status of the electrical switches in the various portions of the control circuit will be as follows. The actuation switch 110 in the Pulse Actuation Circuit will be in the on position and the Fire Control 106 thereby operative. In the Mill Start Sub-Loop (FIGURE 8) associated with each mill 42 all of the switches in the subcircuit 19t) will be closed and the Mill Ready Relay 212 energized since all of the permissives for safe mill operation are satisfied. Also, since the associated mill 42 is not in service, the Mill-in-Service Relay 272 is de'energized and its associated switch 218 in sub-circuit 192 therefore closed. Moreover, with the respective Mill-in-Service Relays 272 de-energized, switches 118B through K in line 112 of the Pulse Initiation Circuit will be closed and switches 124B through K in line 114 of that circuit will be open. With the Mill Ready Relay 212 energized and the Milln-Service Relay 272 de-energized, switches 214 and 218 in sub-circuit 192 of the Mill Start Sub-Loop will be closed and the circuit complete to the Mill Available Relay 216 to close switch 217 in sub-circuit 194. In addition, energization of the respective Mill Available Relay 216 effects closure of switches 126B through K in the Pulse Initiation Circuit, closure of switches B through K and opening of switches 162B through K in the Oil Elevation Circuit (FIGURE 6) and closure of switches 186B through K and opening of switches 188B through K in the Mill Selection Circuit (FIGURE 7). Since all of the oil elevations C, E and J are in operation, the burner counting circuit relays 132 are de-energized and thus switches 128C, 128E and 128] in the Pulse Initiation Circuit are all closed; switches 156C, 156B and 156] are closed and switches 158C, 158E and 158] are open in the Oil Elevation Selection Circuit (FIGURE 6); and switches 182C, 182B and 182] are closed and switches 184C, 184B and 184] open in the Mill Selection Circuit (FIGURE 7).

Referring again to the Pulse Initiation Circuit (FIG- URE 5), when the output valve of the electric generator 16 is brought in phase with that of the power system, switch 116 in line 112 is closed. If, at this point, load demand on the unit is suiciently low and capable of being carried by the operation of the oil burners 36 in oil elevations C, E and J, the load will be so carried under the control of the Combustion Control 20 and the Fire Control 106 will remain ineiective. As the -load demand increases, however, the oil ow through line 50 will be increased by operation of the oil ow regulator 90 under the control of the Combustion Control 20 until such time as the heating value of the oil being passed to the burners corresponds to that of the sum of the heatingJ values of the coal to be supplied by one pulverizing mill 47 operating at minimum output plus that of its supporting oil whereupon switch 120 operated by ow sensor 92 will close and a circuit will be established through line 112 to the operating motor of the pulse timer 108. Upon energization, the pulse timer 108 is immediately re-set to its start position followed by commencement of its timing function comprising the intermittent closure of switch 136 for two seconds duration every 60 seconds, thereby effecting the pulsed closure of switches 140 and 142 in the Oil Elevation Selection Circuit and the Mill Selection Circuit. The operation of the pulse timer 108 is such that it will continue to emit periodic pulses until such time as the condition that effected energization of the timer has been removed. That is, barring loss of availability of all of the pulverizing mills 42 or of the oil burner elevations, the timer 108 will continue to pulse the switches 140 and 142 until, with no mill already in service, a mill is placed in service whereupon the circuit through line 112 in the Pulse Initiation Circuit would be open, or, with at least one mill already in service, the average mill loading of all of the mills in service falls below 80% of their rate of capacity as determined by the Combustion Control 20, whereupon the circuit through line 114 will be opened.

With reference to FIGURE 6, the pulsed closure of switch 140 by the pulse timer 108 is transmitted to oil elevation operator relay 154C through sub-circuit 164 since, under the conditions specified above, this is the only circuit that will be completed by the closure of switches 156 and 160 and the opening of switches 158 and 162. Actuation of relay 154C would normal-ly be effective to initiate operation of oil elevation C but, in view of the fact that the oil elevation is already operating, as a result of having remained in operation after the warm-up phase of unit operation was completed, pulsation of relay 154C will have no effect. Instead, the pulsed closure of switch 142, which occurs simultaneously with switch 140, will be effective to transmit the pulse through sub-circuit 170 to mill operator relay 180D. Since all switches 182 and 186 in the Mill Selection Circuit are closed at this time and switches 184 and 188 are open, sub-circuit 170 is the only sub-circuit effective to pass current and therefore relay 180D is the only mill operator relay that can be energized. Actuation of mill operator relay 180D pulses the Mill Start Pulse Switch 226 in sub-circuit 194 of the Mill Start Control (FIGURE 8) associated with mill 42D which supplies coal to the coal burners 34 in elevation D. Closure of switch 226 completes the circuit through subcircuit 194, switches 217 and 224 having been closed beforehand by the energization of Mill Available Relay 216 and de-energization of oil burner counting circuit relay 132 thereby actuating mill operator timer 220 which remains energized after its actuating pulse terminates to effect the sequence closure of its associated contacts 228 through 234.

The operation of the mill operator timer 220 proceeds with rst, the closure of contact 228 in sub-circuit 196 ten seconds after the timer is initially energized, thereby actuating solenoids 244 to open each of the inlet gate valves 46 associated with the burners 34 in elevation D. When valves 46 reach their open position, limit switches 248 associated with each of the respective burners in subcircuit 198 are closed. Switches 250` and 252 in sub-circuit 198 will be closed as long as the Mill Ready Relay 212 associated with mill 42D remains energized and the burner counting circuit relays 132 associated with oil burner elevations C or E remain de-energized. The presence of these switches in sub-circuit 198 and comparable switches 268 and 270 in sub-circuit 200 serve to terminate the mill start-up procedure in fthe event of the loss of one or more of the permissive conditions for safe mill operation after the mill operator timer 220 has been energized. Timer contact l230 closes ten seconds after the closure of contact 228 and, if all of the burner inlet gates have opened, the circuit is complete to the Mill Motor Actuator Relay 257, the energization of which simultaneously actuates Mill Motor Start Switch 258 and the Hot Air Gate Solenoid Switch 260 t-o start the motor 56 and energize Hot Air Gate Solenoid 256 to open the Hot Air Gate Valve 68 associated with mill 42D. Energization of relay 257 also closes the Feeder Motor Arm Switch 262, in subcircuit 200. This sub-circuit is completed 30 seconds after the actuation of re-lay 257 by the closure of Timer Contact 232, it having been determined that 30 seconds is sufficient time within which to pass an adequate supply of air to the mill for etlicient operation thereof. Completion of sub-circuit 200 effects energization of the Feeder Motor Start Relay 266 which closes Motor Start Switch 267, thereby actuating the Feeder Motor 54 to supply raw coal to the pulverizing mill 42D. Relay 266 also serves to actuate switch 274 in sub-circuit 202 to the closed position to arm the Mill-in-Service Relay 272 which is energized 60 seconds after the actuation of the Feeder Motor 54 upon closure of Timer Contact 234. Energization of relay 272 actuate-s switch 218 in sub-circuit 192. of the Mill Start Control Circuit to the open position, thereby de-energizing the Mill Available Relay 216 to open switch 217 in sub-circuit 194, switch 126D in the Pulse Initiation Circuit (FIGURE 5), switches 160D in the Oil Elevation Selection Circuit (FIGURE 6) and switch 186D in the Mill Selection Circuit (FIGURE 7) while closing switch 162D in the Oil Elevation Selection Circuit and switch .188D in the Mill Selection Circuit. Ene-rgization of relay 272 also serves to open switch 118D in line 112 of the Pulse Initiation Circuit and to close switch 124D in line 114, thereby de-energizing the pulse timer 108 and transferring all subsequent control of the mills from line 112 of that circuit to line 114.

If, for any of a number of reasons, mill 42D is unable to be placed in service, the Mill-in-Service- Relay 272 would remain de-energized and iive seconds later upon closure of Timer Contact 27'8, Mill Lockout Relay 280 would be energized to open switch 282, thereby de-energizing Mill Ready Relay 212 and Mill Available Relay 2.16. De# energization of the Mill Available Relay 216 would effect -opening of switches 126D in the Pulse Initiation Circuit, D in the Oil Elevation Selection Circuit and 186D in the Mill Selection Circuit and closure of switches 162D in the Oil Elevation Selection Circuit and 188D in the Mill Selection Circuit. Failure of the Mill-in-Service Relay 272 associated with mill 42D to energize would maintain the pu'lse time-r 108 in an energized condition since the switches in line 112 of :the Pulse Initiation Circuit would remain closed. Therefo-re, the Pulse Selection Circuit would be pulsed again by another closure of switch 142.. Since switch 186D in the Mill Selection Circuit is now opened and switches 188D closed the pulse would be transmitted to mill selection re-lay B which would initiate start-up of mill 42B that supplies pulverized coal to the burners of coal elevation B by means of the Mill Start-up Control Circuit (FIGURE 8) associated with mill 42B in the same manner as previously described for start-up of mill 42D.

Similarly, if mill 42B failed to 'be placed in service', its Mill Lockout Relay 280 would be energized 115 seconds after the initiation of the second pulse :t-o effect opening of switches 126B in the Pulse Initiation Circuit, 186B in the `Oil Elevation Selection Circuit and 186D in the Mill Selection Circuit while closing switches 162B in the Oil Elevation Selection Circuit and 188B in the Mill Selection Circuit. Since no mill has yet been placed in service, the pulse timer 108 would remain energized and still another pulse would be generated to close switch 142. Closure of switch 142 would now generate a pulse that would be transmitted to the mill selection relay 180F and thereafter to mill selection relays 180H and 180K in seque-nce in the event the previous mill in the sequence failed to be placed in service.

Assuming mill 42D was successfully placed in operation, pulverized coal is supplied to the burners 34 in coal elevation D :through the associated coal supply line 44. In the furnace the coal is ignited by means of the ignition energy provided by the lburners 36 in oil elevations C and E thus placing the first coal elevation in service. It should be noted that ignition of the coal issuing from an elevation of coal burners 34 can be accomplished from the combustion energy provided by a single elevation of oil burners. Due to the physical arrangement of the burner assembly 32, coal elevation D is located intermediate oil elevations C and E and there-fore can obtain ignition energy from one or both groups of oil burners.

When mill 42D is placed in service, switch 118D in line 112 of the Pulse Initiation Circuit is actuated .to the open position lby Mill-in-Service Relay 272, thereby breaking the circuit and de-energizing the pulse timer 108. At the same time switch 124D in line 114 is closed to transfer operati-on of the pulse timer 108 from line 112 to the circuitry of line 114. After the mill and its associated elevation of coal burners has once been placed in service operation proceeds under control of the Combustion Control which regulates the supply of coal to the mill .and thence to :the burners in response to load de-mand on the unit. The Combustion Control 20 is also effective at this point to first, actuate the main oil supply valves 96 in the three oil burner elevations to the closed position, thereby lterminating the ow of oil through these valves. Oil continues to fiow, however, through each of the bypass fiow regulations 94 such that oil, at minimum pressure, continues to fiow to the oil burners 36. This oil flow is sufiicient to maintain 4a arne at the burners and to provide sufficient ignition energy to an adjacent group of coal burners to sustain their ignition. Following this, the Combustion Control 20 operates to close the lbypass valve 94 associated with all but the oil burner elevation associated with the burners 34 of oil elevation D, namely oil elevation C. The termination of oil fiow tothe 'burners 36 in this man- .ner is accomplished by means of a control sub-loop of Combustion Control 20 which is not considered germane to the present invention and therefore is not described herein.

At this point, the regulation of the operation of the mill 42D is under the control of Combustion Control 20. As load demand on the unit rises, the speed of motor 54 driving the feeder 52 associated with mill 42D is increased to deliver coal at an increased rate to the mill. When the load on the mill reaches 80% of its rated capacity as measured by the tachometer 64, switch 122 in line 114 of the Pulse Initiation Circuit is closed to energize the pulse timer relay 108, thereby re-setting it and thereafter initiating its timer operation to energize relay 138 and simultaneously pulse switchesr 140 and 142 that operate the Oil Elevation Selection Circuit and Mill Selection Circuit, respectively, at the rate of one pulse every 6() seconds.

In the Oil 4Elevation Selection Circuit (FIGURE 6) closure of switch 140 will transmit current to relay 154C since switches 160B and 156C are closed, mill 42 bein-g available for service and Oil Elevation Circuit not being locked out of service. But, since oil elevation C is already in operation energization of relay 154C will have no effect. In the Mill Selection Circuit (FIGURE 7), however, closure of switch 142 will complete sub-circuit 172 to energize relay 180B since switch 132C is closed because the Oil Elevation Circuit is delivering sufiicient ignition energy with which to ignite its associated coal burners, and switch 188D is closed because mill 42D is now in service and therefore no longer available to be placed in service. Switch 188D was closed when relay 217 associated with mill 42D was de-energized and switch 186B is closed because relay 217 associated with mill 42B is energized due to the fact that its mill operator relay 180B is energized and switch 218, indicating the mill is not in service, is closed. Energization of mill start relay 180B pulses switch 226 in sub-circuit 194 of the Mill Selection Circuit (FIGURE 8) associated with mill 42B to energize timer 220 and thereby initiate the start-up sequence for mill 42B. The start-up sequence of this mill thereafter proceeds in the same manner as earlier described with regard to the start-up of mill 42D. Upon completion of the start-up sequence, Mill-in-Service Relay 172 is energized opening switch 218 in sub-circuit 192 to de-energize Mill Available lRelay 216, as well as opening switch 118B in line 112 of the Pulse Initiation Circuit and closing switch 124B in line 114. When the Mill Available Relay 216 is de-energized, switch 126B in the Pulse Initiation Circuit, switch 160B in the Oil Elevation Selection Circuit and switch 186B in the Mill Selection Circuit are closed and switches 162B in the Oil Elevation Selection Circuit and 188B in the Mill Selection Circuit opened, thereby arming the selection circuits for the next pulse generated by the pulse timer 10S.

When the burners 34 of coal elevation B are placed in service, switch 122 in line 112 of the Pulse Initiation Circuit is opened since there are now two mills in service and their average load will be less than the required to close the switch. The opening of switch 122 opens the circuit through line 114, thereby de-energizing the pulse timer 108.

In the event that mill 42B is unable to be placed in service, either because its permissive conditions are not satisfied or because component malfunction occurred after the sub-circuit sequence was initiated, the Mill Available Relay 216 `will be de-energized to close switches 160B and 186B and also switches 162B and 188B in the respective selection circuits. if the former occurs the failure of one or more of the switches 204 through 21) in sub-circuit 190 to close would prevent the Mill Ready Relay 212 from being energized. If the latter occurs Mill Lockout Relay 280 will be energized to open switch 282 in sub-circuit 190 and de-energize the Mill Ready Relay 212. Such occurrence would necessitate placing Ianother elevation of oil burners 36 in service before another elevation of coal burners 34 could be placed in operation due to the fact that oil elevation C is capable of providing ignition energy only for the burners 34 of coal elevations B and D. Therefore, before coal elevation F can become operational the burners 36 in oil elevation E must be placed in service in order to provide ignition energy for the elevation F coal burners.

Placing oil elevation E in service is accomplished by the pulse closure of switch 140, which pulse is transmited to oil elevation start relay 154B to effect start-up of the pilot torches 40 associated with that elevation and admit lfuel to the oil burners thereof. This is accomplished by the fact that with oil elevation C operati-ng. mill 42D in service and mill v42B not capable of being placed in service, sub-circuit 166 in the Oil Elevation Selection Circuit is now rendered effective to transmit the pulse from switch to the relay 154E through switches 162B, 162D, 160]? and 156B all of which are now closed. Switches 162B and 162D lare closed because their associated Mill Available Relays 216 are de-energized. Switch F is closed because its associated rel-ay 21-6 is energized and switch 156B` is closed because its associated burner counting circuit relay 132 is de-energized indicating that oil elevation F is not locked out of service. Thus, energization of Pulse Timer Relay 138 by the timer 108 will pulse switch 140 to the closed position, which pulse will then be transmitted to relay 154B to initiate start-up of the burners 36 of oil elevation E. Start-up of the oil elevation is effected by first 'actuating the Elevation Inlet Gate Valve 98 and the pilot torch fuel valves 102 to their open positions and thereafter ener- -gize the spark ignitors 104 to ignite the torches which, in turn, ignite the oil issuing from the burners 36. When the oil elevation is placed in service switches 182B are then closed and s-witches 184B are opened in the Mill Selection Circuit. The length of time required to place an oil elevation in service is approximately 50 seconds. Therefore, when the next pulse is generated by the pulse timer 108, 60 seconds after the previous pulse, sub-circuit 174 will then be effective to transmit the pulse from 17 the switch 142 through switches 188B, 188D, 182B and 186F to mill start relay 180B. When relay 180F is energized to actuate the Mill Start Control associated with mill 42F start-up of the mill will thereafter proceed in the same manner as previously described with regard to the start-up of mill 42D.

When the mills 42B and 42D and the coal burners 34 supplied by them in elevations B and D are in operation and a further increase in load demand requires that another elevation of coal burners 34 be placed in service, mill 42F will be placed in service in the same manner as described above with the first pulse generated by the pulse timer 1118 being transmitted to the oil elevation start relay 154B and the next pulse then transmitted to the mill start relay 1801:. Sub-circuit 164 can no longer transmit the pulse since mills 42B and 42D are in operation and switches 160B and 160D are therefore open. Similarly, sub-circuit 168 cannot transmit the pulse since oil elevation E is not locked out of service and mill 42F is available for service and switches 158B and 162F are therefore open. Thus, upon the pulsed closure of switch 140, current can only pass through switches 162B, 162D, 160F and 15615 to relay 154E thus initiating the start-up of the burners 36 of oil elevation E. When the pulse timer 108 generates the next pulse it is transmitted from switch 142 in the Mill Selection Circuit through sub-circuit 174 c011- taining switches 188B, 188D, 182B and 186F which are all closed to energize the relay 180F in the same manner as was described above and start-up of mill 42F will then proceed accordingly.

With coal elevations B, D and F in operation the need for an additional elevation of coal burners to be placed in service due to a further increase in load demand will be satised by start-up of the burners 36 of oil elevation J followed by the placement of mills 42H and 42K in service. According to the desired sequence mill 42H will be placed in service rst but if, however, that mill is unable to be placed in service, mill 42K will then be rendered effective to be placed in operation. This occurs as follows. The pulse generated by the pulse timer 108 upon closure of switch 122 in the Pulse Initiation Circuit will be transmitted upon closure of switch 140 through subcircuit 168 to oil elevation start relay 154]. The pulse will be passed through switches 162B, 162F, 162D, 160H, 160K and 156] all of which are closed due to the fact that mills 42B, 42D and 42F are now in service and therefore are not available to handle the additional load s that their respective relays 216 are de-energized and the switches 162 associated with these relays are therefore closed. Since mills 42H and `42K are each available for service their associated relays 216 will be energized so that switches 16() associated with these relays are closed. Since oil elevation J has not been locked out of service, its associated burner counting circuit relay 132 will be de-energized such that switch 156] will be closed. After the burners 36 of oil elevation J are placed in service, the next pulse generated by the pulse timer 8 will be transmitted through switches 188B, 188D, 188F, 182] and 186H of sub-circuit 17 6 and the Mill Selection Circuit to the mill start relay 180H which is effective to initiate start-up of mill 42H.

Current will not pass to relay 130K if mill 42H is available for service since switch 188H would then be open. lf, however, mill 42H were not available for service, switch 186H would be open, thereby preventing energization of relay ISDH and switch 188H, being operated by the same relay but having the opposite sense of switch 186H would be closed thereby effecting energization of relay 189K to initiate start-up of mill 42K.

After mill 42H has been placed in service switch 186H is caused to be opened by the actuation of relay 272 in sub-circuit 202 which, in turn, opens switch 218 in subcircuit 192 to de-energize the relay 216. The opening of switch 186H effects closure of switch 188H thereby arming relay 180K to enable it to receive the next pulse generated by the pulse timer 108. Thus, upon a further increase in load demand requiring the placement of yet another elevation of coal burners in service, energization of the pulse timer 108 will effect the generation of a pulse that will be received by relay K to initiate start-up of mill 42K and the placement of coal burners 34 of elevation K in service.

There has thus been described an electro-mechanical control system for automatically controlling the start-up of burners of a coal-tired, multi-burner vapor generator that is characterized by simplicity of design and efficiency and flexibility of operation. By means of the present invention the plurality of coal pulverizing mills that govern the operation of the coal burners in the fuel burning system of a large capacity vapor generator can be manipulated to place only that elevation of coal burners in service that is capable of being operated safely. The system also provides means for ensuring that the increase in load demand is satisfied in the event that the selected burner elevation cannot be placed in service by automatically selecting another elevation and placing it in service. The invention, when employed in conjunction with analog controls for regulating the performance of the burners after they are once placed in operation, is operable to achieve total automation of the burner systems of large capacity vapor generators.

It will be understood that various changes in the details, materials, and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. A fuel burning system having primary burner means, secondary burner means adapted to provide ignition energy for said primary burner means, coal pulverizing mill means connected with said primary burner means for supplying fuel thereto, signal responsive actuator means operatively associated with said mill means and said secondary burner means respectively for placing each in operation, and control means operating said actuator means for automatically placing said primary burner means in service in response to the need for operation thereof, said control means comprising:

(a) first circuit means operatively connected to said secondary burner actuator means and adapted to energize said actuator means upon receipt of -a pulsed signal;

(b) second circuit means operatively connected to mill actuator means and adapted to energize said actuator means upon receipt of a pulsed signal;

(c) said second circuit means including means preventing the energization of said mill actuator means until after said secondary burner means are established in operation;

(d) means responsive to the need for operation of said primary burner means and adapted to emit a signal in response thereto;

(e) means operated by said need responsive signal for generating a periodically pulsed signal;

(f) and 'means for simultaneously transmitting said pulsed signal to said rst and second circuit means for actuating said secondary lburner means and thereafter, said mill means.

2. Apparatus as recited in claim 1 including:

(a) load demand indicator means adapted to emit a a signal at a predetermined value of load demand;

(b) means for transmitting said load demand signal to said pulsed signal generating means for operating the same.

3. Apparatus as recited in claim 1 including:

(a) a plurality of primary burners arranged in groups;

(b) a coal pulverizing mill operatively associated with each group of primary burners;

(c) means responsive to the need for operation of said lprimary burners comprising circuit means for operating said pulsed signal generating means including:

(i) tirst and second lines each responsive to different need conditions of said system and each being adapted to transmit :a signal to energize said pulsed signal generator upon the occurrence of the respective need conditions;

(ii) and means for rendering said first line operative when none of said primary burner groups are in operation and for rendering said second line operative when at least one of said primary burner groups Iare in operation.

4. Apparatus as recited in claim 3 including:

(a) load demand indicator means adapted to emit a signal at a predetermined value of load demand; (b) means for transmitting said load demand signal `to said pulsed signal generating means through said second line.

5. Apparatus as recited in claim 1 including:

(a) a plurality of primary burners arranged in groups;

(b) a plurality of secondary burners arranged in groups and each adapted to provide ignition energy for an associated group of primary burners;

(c) a coal pulverizing mill associated with each primary burner group for supplying 4fuel thereto; (d) independently operated actuator means associated with each of said pulverizing mills and secondary burner groups;

(e) said first and second circuit vmeans comprising:

(i) means operative to transmit said pulsed signal to the actuator of a single secondary burner group according to a preselected sequence;

(ii) and means for transmitting .a subsequent pulsed signal to the actuator of a pulverizing mill operating a group of primary burners associated with said single secondary burner group.

6. Apparatus as recited in claim 5 including:

(a) means preventing the energization of each of said -actuators of said pulverizing mill and said secondary burner groups upon failure of the same to satisfy predetermined permissive conditions;

(b) means for transmitting a pulsed signal to the actuator of another secondary burner group upon failure of the selected actuator to be energized;

(c) and means for transmitting a subsequent pulsed signal to the actuator of a pulverizing mill operating a group of primary burners associated with said other secondary burner group.

7. Apparatus as recited in claim 6 including:

(a) means for transmitting a pulsed signal to the lactuators of all of said secondary burner groups in sequence;

(b) means for terminating the transmission of -a pulsed signal to said secondary burner group actuators upon the energization of one of said actuators;

(c) and means for transmitting a subsequent pulsed signal to the actuator of a pulverizing mill operating a group of primary burners associated with said actuated secondary burner group.

8. Apparatus as recited in claim 5 wherein said first circuit means comprises:

(a) a plurality of subcircuts, each adapted to energize an actuator associated with one of said secondary burner groups;

(b) each of said subcircuts including:

(i) means responsive to the operability of the associated secondary burner group for transmitting said pulsed signal to said yactuator only when said associated secondary burner group is operable;

(ii) and means responsive to the availability of the pulverizing mills operating the primary burner associated with said secondary burner group for transmitting said pulsed signal to said actuator only when said associated pulverizing mill is available for service.

9. Apparatus as recited in claim 8 wherein each of said subcircuts includes means for transmitting said pulsed signal to the actuator of the associated secondary burner group only when the actuator for opening the previous secondary burner group in said sequence fails to receive said pulsed signal.

10. Apparatus as recited in claim 8 wherein said second circuit means comprises.

(a) a plurality of subcircuts each adapted to engage an actuator associated with one of said pulverizing mills;

(b) each of said subcircuts including:

(i) means responsive to the operation of a secondary burner group associated with the primary burner group operated by said pulverizing mill for transmitting the pulsed signal to the mill actuator only when said associated secondary burner group is in operation;

(ii) and means responsive to the availability of the associated pulverizing mill for transmitting said pulsed signal to the actuator of said associated mill only when said mill is available for service.

11. Apparatus as recited in claim 10 including:

(a) a pair of primary burner groups capable of being ignited by each of said secondary burner groups;

(b) means for transmitting said pulsed signal to the actuator of the pulverizing mills operating one of said primary burner groups when the associated secondary burner group is operating;

`(c) and means for transmitting said pulsed signal to the actuator of the pulverizing mill operating the other of said primary burner groups when said one actuator fails to be energized.

12. Apparatus as recited in claim 5 including:

(a) electrically operated actuators;

(b) first sensing means for sensing the operability of each of said secondary burner groups;

(c) second sensing means for sensing the avaliability for service of each of said pulverizing mills;

(d) third sensing means for sensing the state of operation of said secondary burner groups;

(e) first circuit means including a plurality of parallelly-connected subcircuts each operating one of said secondary burner group actuators and each containing means to pass an electric current to said actuator when said tirst sensing means indicates the associated secondary burner group is operable and said second sensing means indicates the associated pulverizing mill is available for service;

(f) second circuit means including a plurality of parallelly-connected subcircuts each operating one of said pulverizing mill actuators and each containing means to pass an electric current to said actuator when said second sensing means indicates the associated pulverizing mill is available for service and said third sensing means indicates the associated secondary burner group is operating;

(g) pulse generating means for simultaneously transmitting a periodic electric pulse to said rst and second circuit means;

(h) and means responsive to the needs for operation of an additional primary burner group for energizing said pulse generating means.

13. Apparatus as recited in claim 12 including load demand sensing means operatively connected to said pulse generating means to energize the same at a predetermined value of said load demand.

14. Apparatus as recited in claim 12 wherein the subcircuits comprising said iirst circuit means each include,

in series:

(a) an electrically actuable relay for operating said secondary burner group actuator;

(b) first switch means responsive to said rst sensing means to be closed when the associated secondary burner group is operable;

(c) second switch means responsive to said second sensing means to be closed when the associated pulverizing mill is available for service.

15. Apparatus as recited in claim 14 wherein means are provided for operating said secondary burner group actuators according to a preselected sequence, said means comprising switch means having an opposite sense from said first and second switch means in the earlier subcircuits connected in successive subcircuits in series with the first and second switch means in said successive subcircuits whereby an electric current can pass through only one of said subcircuits at a time.

16. Apparatus as recited in claim 12 wherein the subcircuits comprising said second circuit means each include, in series:

(a) an electrically actuable relay for operating said pulverizing mill actuator;

burner group is established in operation.

References Cited UNITED STATES PATENTS 15 2,073,346 3/1937 Kuernpel l10L-103X `CHARLES I. MYHRE Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION August 6, 1968 Patent No. 3,395,657

Jack A. Schuss It is certified that error` appears in the above identified patent and that said-Letters Patent are hereby corrected as shown below:

Column l, line 2l, "operation" should read operational Column 3, line 24, "vales" should read valves line 70, after "oil" insert line Column 9, line 47, after "182", cancel "L" and insert E -4 l Column l0, line 38, "the" should read. this line 5l, "prevention" should Column l5, line 26, "regulations" should read regulators Column 20, line 7, "opening" should read operating line ll, should read line l2, "engage" should read energize Signed and sealed this 7th day of April 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

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