DESC:
FIELD
The present disclosure relates to the field of control systems for controlling operation of multistage burners.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Typically, a multistage burner includes a plurality of nozzles. The nozzles are fired by supplying air and oil to the nozzles. The nozzles are in fluid communication with oil block and air block respectively. The oil valves and the air dampers are controlled by mechanical pressure switches and mechanical actuators, which form a mechanical control system. In a multistage burner, the nozzles are fired in different stages typically shown in Table-1 below:
Mode No. Nozzle-1 Nozzle-2 Nozzle-3
1 ON OFF OFF
2 ON ON OFF
3 ON ON ON
TABLE-1
Based on mechanical pressure switch triggering, the multistage burner is switched between various stages. Table-2 below shows the status a typical configuration of multiple mechanical pressure switches for each stage:

Pressure Switch No. Mode-1 Mode-2 Mode-3
1 Open Open Close
2 Open Close Close
TABLE-2
When the pressure is above a set value, the contact of the pressure switch is opened and when the pressure is below the set value, the contact of the pressure switch is closed. Whenever pressure exceeds a set limit a boiler coupled to the burner is turned off.
However, the mechanical control system used for controlling the oil and air flow is subjected to hysteresis, which deteriorates the performance of the multistage burner. Also, when the pressure switch 2 is triggered, the oil valves and the air dampers are operated almost simultaneously to fire nozzle 1 and nozzle 2. This causes insufficient amount of air to be supplied for combustion to fire the nozzles of respective stages, which is not desired.
There is, therefore, felt a need of a control system that ensures right amount of air and fuel is supplied for firing the nozzles of the multistage burner and that alleviates the above mentioned drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to provide a digital control system for a multistage burner.
Another object of the present disclosure is to provide a system that maintains a desired boiler load.
Yet another object of the present disclosure is to provide a system that provides efficient Lead-Lag Control for air and fuel.
Still another object of the present disclosure is to provide a system that improves the performance of the burner.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages a digital control system for a multistage burner for maintaining desired boiler load. The system comprises a sensing module, at least three nozzles and a control unit. The sensing module is disposed in the boiler and is configured to sense pressure of the steam to generate a sensed pressure signal. The sensing module is further configured to generate a value of said sensed pressure signal. Each of the three nozzles is in fluid communication with air block and an oil block. The control unit includes a memory, a firing sequence controller and a lead/lag compensator. The memory is configured to store a pre-determined threshold value. The firing sequence controller is configured to cooperate with the memory and the sensing module to compare the pre-determined threshold value and the value to generate a comparison signal and is further configured to determine a mode of firing of nozzles based on the comparison. The lead/lag compensator is configured to cooperate with the firing sequence controller to either lead supply of air or lag the supply of air to fire a single nozzle or combination of nozzles based upon the determined mode to maintain desired boiler load based on the received comparison signal.
In an embodiment, the sensing module includes at least one sensor and a signal conditioning unit. The sensor is configured to sense pressure of the steam and is further configured to generate a sensed pressure signal. The signal conditioning unit is configured to cooperate with the sensor and is further configured to generate the value of the sensed pressure signal.
In an embodiment, the firing sequence controller and the lead/lag compensator are implemented using one or more processor(s).
In an embodiment, each of the three nozzles is of different capacity.
In an embodiment, the lead/lag compensator either leads supply of oil or lags supply of oil from the oil block to each of the nozzles.
In an embodiment, the air block has an actuator operably coupled to the lead/lag compensator. The lead/lag compensator is configured to control the actuator to either lead air supply or lag the air supply based on determined mode.
In an embodiment, the oil block has control valves operably coupled to the lead/lag compensator. The lead/lag compensator is configured to control the valve to either lead oil supply or lag the oil supply based on determined mode.
In an embodiment, the sensor is a pressure sensor selected from the group consisting of piezoresistive strain gauge, capacitive, electromagnetic, piezoelectric sensor, strain gauge, optical, potentiometric sensor and the like.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWING
A digital control system for a multistage burner of the present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a block diagram of the multistage burner with plurality of nozzles; and
Figure 2 illustrates a block diagram of a digital control system in communication with the multistage burner of Figure 1.
LIST OF REFERENCE NUMERALS USED IN DETAILED DESCRIPTION AND DRAWING
100 – Multistage Burner
102 – Oil Block
104 – Air Block
106 – Burner Combustion Head
108 – Pressurized Fuel Supply
110 – Air Supply
200 – System
202 – Sensing Module
202A – Sensor
202B – Signal Conditioning Unit
204 – Control Unit
204A – Memory
204B – Firing Sequence Controller
204C – Lead/Lag Compensator
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
When an element is referred to as being "mounted on," “engaged to,” "connected to," or "coupled to" another element, it may be directly on, engaged, connected or coupled to the other element. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Terms such as “inner,” “outer,” "beneath," "below," "lower," "above," "upper," and the like, may be used in the present disclosure to describe relationships between different elements as depicted from the figures.
The present disclosure envisages a multistage burner as shown in Figure 1, and a digital control system to control the multistage burner as shown in Figure 2.
Referring to Figure 1, the multistage burner (herein after referred to as “multistage burner 100”) comprises oil block 102, an air block 104, a burner combustion head 106. The burner combustion head 106 includes a plurality of nozzles (N1, N2…, Nn). Each of the plurality of nozzles (N1, N2…, Nn) is in fluid communication with the oil block 102 and the air block 104. The multistage burner 100 of the present disclosure has at least 3 nozzles in the burner combustion head 106.
The oil block 102 include a plurality of oil valves configured to allow pressurized oil supply 108 into each of the plurality of nozzles (N1, N2…, Nn). The air block 104 includes at least one actuator configured to allow the air into the combustion head for each of the plurality of nozzles (N1, N2…, Nn). The oil under pressure and the compressed air gets mix and chemical reaction takes place between the pressurized oil and compressed air to ignite a flame downstream of each of the nozzles (N1, N2…, Nn).
To switch between various nozzle firing modes and to control the air supply and the oil supply to each nozzle, the digital control system (herein after referred to as “system 200”) is coupled with the multistage burner 100.
Referring to Figure 2, the digital control system 200 comprises a sensing module 202, at least three nozzles (N1, N2, N3) and a control unit 204.
In an embodiment, the sensing module 202 includes a sensor 202A and a signal conditioning unit 202B. The sensing module 202 is disposed near the boiler (not shown in the figures). The sensor 202A is configured to sense the steam pressure and is further configured to generate a sensed pressure signal. The signal conditioning unit 202B is configured to cooperate with the sensor 202A to generate a value of the received sensed pressure signal.
The control unit 204 is configured to cooperate with the sensing module 202. The control unit 204 includes a memory 204A, a firing sequence controller 204B and a lead/lag compensator 204C.
The memory 204A is configured to store a predetermined threshold value and set of pre-determined firing modes for nozzles.
The firing sequence controller 204B is configured to cooperate with the memory 204A and the sensing module 202 to compare the value with the predetermined threshold value to generate a comparison result. The firing sequence controller 204B is further configured to determine which mode nozzles to be fired to maintain a desired boiler load. The firing sequence controller 204B starts and stops the multistage burner 100. As the firing sequence controller 204B generates the comparison signal, it executes a set of predefined steps to start and stop the multistage burner 100. Initially, the actuators and the oil valves are closed to prevent supply of air and oil to each of the nozzles. Further, the temperature of the oil and the pressure inside the boiler is checked. After checking for desired temperature and pressure, the actuator is activated to pre-purge any unburned gases inside a furnace. The pre-purging prevents from an explosion hazard.
The set of predefined steps executed by the firing sequence controller 204B while starting the burner 100 are as follows:
• Closing actuator;
• Checking oil temperature and boiler pressure;
• Activating the actuator;
• Pre-purging the furnace;
• Activating the actuator for supplying air suitable for mode 1 firing;
• Injecting oil/fuel for ignition; and
• Detecting flame.
After completion of the mode 1 firing, a set of predefined steps are executed by the firing sequence controller 204B to shut down the multistage burner 100. The actuator is activated to supply air to post purge i.e. to exhaust any flue gases remaining inside the furnace. After post purging the firing sequence controller 204B closes the actuator, thereby shutting down the multistage burner 100. The set of predefined steps executed by the firing sequence controller 204B while shutting down the multistage burner 100 are as follows:
• Opening the actuator;
• Post-purging the furnace; and
• Closing the actuator.
In an embodiment, the number of firing modes of the multistage burner 100 is defined by the formula:
2N-1,
Where, N – number of nozzles in the burner; and wherein each of the nozzles is having a different capacity.
For e.g. a multistage burner of the present disclosure is having at least 3 nozzles, the burner can be operated at 23-1 = 7 modes.
In conventional multistage burner, while switching from Mode-1 to Mode-2, both the oil valves and the air dampers are operated simultaneously to fire two nozzles. This causes insufficient amount of air available for firing the nozzles. To avoid this problem, the lead-lag compensator 204B is used, wherein the actuator is first activated to ensure there is sufficient air for combustion and then the oil valve is opened to fire the nozzles. This is a lead operation, where the air supply is leading the oil supply. Similarly, when the sequence is reversed i.e. switching from Mode-2 to Mode-1, the oil valve is triggered first and the air supply is gradually decreased, because of which the amount of air required for burning operation is optimized and the flame downstream of the nozzles is put off. This is a lag operation, where the air supply is lagging the oil supply. The lead-lag compensator 204C function ensures that a right amount of air and oil is supplied for firing the multistage burner 100 while switching between various modes of operation.
If the value of the sensed pressure signal is less than the predetermined threshold value, then the firing sequence controller 204B will select a mode of nozzle firing and accordingly will command the lead/lag compensator 204C to supply more air in advance, as the burner 100 will have to move from low energy levels to high energy levels. This will ensure that right combination of nozzles is fired to achieve desired boiler load.
Similarly, if the value of sensed pressure is greater than the predetermined threshold value, then the firing sequence controller 204B will select mode of nozzle that will supply less heat to the boiler and will accordingly command the lead/lag compensator 204C to gradually decrease the supply of air so that the nozzles will shut down and only selected nozzles will supply the required amount of heat.
The firing sequence controller 204B triggers right combination of the nozzles to maintain desired boiler load as shown in the Truth Table-1:
Sr. No. Mode No. Nozzle-N1 Nozzle-N2 Nozzle-N3
1 Mode 1 Active Inactive Inactive
2 Mode 2 Inactive Active Inactive
3 Mode 3 Inactive Inactive Active
4 Mode 4 Active Active Inactive
5 Mode 5 Active Inactive Active
6 Mode 6 Inactive Active Active
7 Mode 7 Active Active Active
Truth Table-1
As seen from above Truth Table-1, in first three modes only a single nozzle is fired while the remaining nozzles are kept inactive i.e. for mode 1 first nozzle is fired keeping second and third nozzles inactive, in mode 2 second nozzle is fired keeping first and third nozzles inactive. In mode 3 only the third nozzle is fired while keeping first and second nozzle inactive. In mode 4, first and second nozzle is fired in combination and the third nozzle is kept inactive. In mode 5, first and third nozzle is fired in combination and the second nozzle is kept inactive, and at mode 6, the second and third nozzle is fired in combination and the first nozzle is kept inactive. Finally in seventh mode all the nozzles are fired simultaneously.
In an embodiment, the firing sequence of the nozzles is determined by the firing sequence controller 204B depending upon the required boiler load.
Similarly, the multistage burner 100 can be operated in fifteen different modes i.e. a single nozzle is fired or two or more nozzles are fired in combination as per requirement, as shown in below Truth Table-2:
Sr. No. Mode No. Nozzle-N1 Nozzle-N2 Nozzle-N3 Nozzle-N4
1 Mode 1 Active Inactive Inactive Inactive
2 Mode 2 Inactive Active Inactive Inactive
3 Mode 3 Inactive Inactive Active Inactive
4 Mode 4 Inactive Inactive Inactive Active
5 Mode 5 Active Active Inactive Inactive
6 Mode 6 Active Inactive Active Inactive
7 Mode 7 Active Inactive Inactive Active
8 Mode 8 Inactive Active Active Inactive
9 Mode 9 Inactive Active Inactive Active
10 Mode 10 Inactive Inactive Active Active
11 Mode 11 Active Active Active Inactive
12 Mode 12 Active Active Inactive Active
13 Mode 13 Active Inactive Active Active
14 Mode 14 Inactive Active Active Active
15 Mode 15 Active Active Active Active
Truth Table-2
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a digital control system for a multistage burner that:
• efficiently controls boiler pressure;
• provides efficient lead-lag Control for air and fuel;
• improves efficiency of the boiler; and
• provides an improved modulation control.
The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. these and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

,CLAIMS:WE CLAIM:
1. A digital control system (200) for a multistage burner (100) for maintaining desired boiler load, said system (200) comprising:
a. a sensing module (202) disposed in said boiler and configured to sense pressure of said steam to generate a sensed pressure signal and further configured to generate a value of said sensed pressure signal;
b. at least three nozzles (N1, N2, N3), each of said nozzles in fluid communication with an air block (104) and an oil block (102); and
c. a control unit (204) comprises:
i. a memory (204A) configured to store a pre-determined threshold value;
ii. a firing sequence controller (204B) configured to cooperate with said memory (204A) and said sensing module (202) to compare said pre-determined threshold value and said value to generate a comparison signal and further configured to determine a mode of firing of nozzles based on said comparison; and
iii. a lead/lag compensator (204C) configured to cooperate with said firing sequence controller (204B) to either lead supply of air or lag the supply of air to fire a single nozzle or combination of nozzles based upon said determined mode to maintain desired boiler load based on said received comparison signal,
wherein said firing sequence controller (204B) and said lead/lag compensator (204C) are implemented using one or more processor(s).
2. The system (200) as claimed in claim 1, wherein said sensing module (202) includes:
a. at least one sensor (202A) configured to sense pressure of said steam and further configured to generate said sensed pressure signal; and
b. a signal conditioning unit (202B) configured to cooperate with said sensor (202A) and further configured to generate said value of said sensed pressure signal.
3. The system (200) as claimed in claim 1, wherein each of said three nozzles (N1, N2, N3) is of different capacity.
4. The system (200) as claimed in claim 1, wherein said lead/lag compensator (204C) either leads supply of oil or lags supply of oil from said oil block (102) to each of said nozzles.
5. The system (200) as claimed in claim 1, wherein said air block (104) has an actuator operably coupled to said lead/lag compensator (204C), said lead/lag compensator (204C) is configured to control said actuator to either lead air supply or lag said air supply based on determined mode.
6. The system (200) as claimed in claims 1, wherein said oil block (102) has control valves operably coupled to said lead/lag compensator (204C), said lead/lag compensator (204C) is configured to control said valve to either lead oil supply or lag said oil supply based on determined mode.

7. The system (200) as claimed in claim 2, wherein said sensor (202A) is a pressure sensor selected from the group consisting of piezoresistive strain gauge, capacitive, electromagnetic, piezoelectric sensor, strain gauge, optical, potentiometric sensor and the like.