US 20050266363 A1
This invention relates to a flame detection method and apparatus. More specifically, this invention relates to a flame d on method and apparatus designed for simultaneously monitoring several flames of different types such as pilot flames and main flames of differing sizes and intensity. These detected flames can be in one combustion unit or in several combustion units such as industrial furnaces or ground flares. The underlying principle of the invention is to collect and transmit light from each of the flames by use of optical fibers and to insect the collected light by a video camera vision system at the other end of the optical fibers and to transmit the “live” images of the glows as well as the “on/off” status of the burners to the control room, through modern electronic communication techniques such as Ethernet and/or wireless radio units.
1. A method for monitoring the status of a combustion unit having at least one burner, comprising the steps of:
(a) Installing an optical fiber with tip its tip in or on the housing of the burner, collecting the light from the flame of the burner on the tip of the said optical fiber and transmitting said light to the tip of the other end of the said optical fiber.
(b) Acquiring a digital image of the glow at the end of the tip of the said optical fiber corresponding to the flame of the burner.
(c) Calculating a value for the relative intensity of the light in a frame defining an area of the image corresponding to the flame of the burner
(d) Comparing the relative intensity value against a tolerance range for the frame
(e) Generating an alarm state output if the relative intensity range is outside said tolerant range
2. The method of the
3. The method of
4. The method of
5. The method of
6. The method of
7. A method for monitoring the status of a combustion unit having at least one burner with a main burner flame and a pilot burner flame, comprising the steps of:
(a) Installing two optical fibers with their tips in or on the housing of the burner, one to collect the light from the said main flame and the other to collect the light from the said pilot flame and transmitting the said lights to the other ends of the fibers for the digital imaging of the two glows at the tips of the optical fibers.
(b) Acquiring a digital image of the two said glows corresponding to the main flame and the pilot flame.
(c) Calculating the values for the relative intensities of the frames defining the areas of the images corresponding to the two flames
(d) Comparing the relative intensity values against individual tolerance ranges for the two frames
(e) Generating an alarm state output if the relative light intensity value for each and any of the flames is outside its said tolerance range.
8. The method of
9. The method of
10. A method for monitoring the status of a combustion unit having a plurality of burners, comprising the steps of:
(a) Installing optical fibers in or on the housing of every burner so that the tips of the fibers inside the burners view the flames of the said burners and collecting the light from the flames of the burners and transmitting the light to the other end of the fibers
(b) Acquiring a digital image of the glows at the far end of the tips of the optical fibers.
(c) Calculating the values for the relative intensities of the frames defining the areas of the images corresponding to the flames of the burners
(d) Comparing the relative intensity values against a tolerance range for each frame
(e) Generating an alarm state output if the relative light intensity value is outside said tolerance range.
11. The method of
12. The method of
13. A method for providing additional safety by having more than one fiber in each optical fiber bundle while monitoring the status of flames in a combustion unit with one or more burners, comprising the steps of:
(a) Making special optical fiber cables with two optical fibers in parallel inside every bundle.
(b) Installing such said special cables in or on the housing of every burner.
(c) Setting the parameter in the vision system to recognize “two-distinct glows” inside the frame designated for each specific flame.
(d) Programming the vision software to display “flame on” or “pass” if the image has at least one “glow” and to display “flame off” or “fail” if both the glows are absent.
(e) Generating an alarm state output if the specific flame has no “glows”
14. A method for monitoring the status of several combustion units each having one or more burners, comprising the steps of:
(a) Installing optical fibers in every burner in all the said combustion units with their tips in or on the burners to view the flames of the said burners and collecting the lights from the flames on the tips of said optical fibers and transmitting the said lights to the tips at the other end of the fibers
(b) Acquiring digital images of the glows at the tips of the optical fibers corresponding to the flames of the burners
(c) Arranging the lights received in groups corresponding to each of the said combustion units from which they originated
(d) Calculating the values for the relative intensities of the frames in each said group defining the areas of the images corresponding to the flames of the burners
(e) Comparing the relative intensity values against a tolerance ranges for each of the frames.
(f) Generating an alarm state output if the relative light intensity value is outside said tolerance range.
15. The method of
16. The method of
17. Apparatus for monitoring the status of one or more combustion units having a plurality of burners, comprising:
Optical fibers with tips designed for easy installation in or on a burner housing at the light-receiving end and into a dark chamber box at the light-displaying end
A dark chamber box: All the light displaying ends of the said optical fibers will be installed on one end plate of this enclosure impervious to external light.
A machine vision camera will be installed at the other end of the said box for acquiring a digital image of the plurality of glows from the flames corresponding to the burners.
Special vision software on a computer: The special software enables analyzing the specific flame monitoring application and programming it into the camera system. The program is thus customized for each application as per its needs.
The said programmed software is capable of
(1) Calculating an array of light intensity values relative to a baseline light intensity value for a plurality of frames, each frame defining a sub-area of the digital image corresponding to the flame for one of the burners,
(2) Comparing the relative intensity values against a tolerance range for each frame, and
(3) Generating an alarm state output for each relative light intensity value that is outside the range
The data communication module: This module is capable of receiving and transmitting through the Ethernet the video images, the data of the on/off status of all the flames, other statistical data such as history of the monitored data, and the time of flame failure.
An Ethernet cable to physically connect the above referred communication module at the camera end to the below referred gateway module at the control room end.
A communications gateway module that can receive and send video images and data from several camera vision systems.
One or more video monitors in the control room to display the live images of the light glows from the flames of the burners, the on/off status on all the burners, and other statistical and-historical data on the performance status of the burners.
An alarm system activated by the alarm state output.
18. The apparatus of
High speed Ethernet wireless radio transmitters and receivers are used instead of hard wire ethernet cable connection for communication between the camera and the control room.
U.S. Pat. No. 6,278,374 B1
USPTO's Number for the provisional application of this patent: 6052 0535
Provisional Application filing date: Nov. 17, 2003
Heaters, boilers, furnaces, flares, ovens, incinerators, driers, heated baths and other combustion equipment have single or multiple burners. The term furnace will be used in all of the text below to cover all the combustion units mentioned above. Some large heat capacity burners, both gas and oil fired, modulated and fixed capacity, are fitted with smaller heat capacity pilot burners. In many cases both Pilot and the Main flames are continuously monitored for the safety of the furnace.
Well-known flame detection methods are Ultra Violet scanners, thermocouples and flame rods. The currently available flame detection technologies have several disadvantages. These are listed here.
Ultra Violet (UV) Scanners
These provide flame control signals, depending on the intensity of illumination detected, which varies directly with the electrical current generated. They fail frequently if the flame intensity or composition of the fuel fluctuates and/or dust settles on the viewing glass of the scanner. Also the generated current is very small in magnitude, in the order of micro-amps. UV scanners are effective only with certain fuels whose combustion results in a flame with a lot of UV component in it. This is a big limitation. Oil fired burners, which make a good percentage of burners in the world, cannot use them. In addition, the sensitivity of the UV scanners reduces with shelf life and the operating life. Frequent replacements are necessary.
The UV scanning technique also presents great difficulty when desired to monitor pilot flames. Due to the small size of the pilots and their inaccessible locations, great difficulties are encountered in finding a suitable location for the scanner.
Flame rods work on the ionization principle. The sensing end of the flame rod is actually placed within the body of the flame. But continued exposure to flame and high temperatures leads to thermal degradation leading to extremely short lifespan, typically a few months. Replacement and even maintenance are difficult since the sensor locations and the insulated mounting arrangements are difficult to access. Also the furnace has to be shut down for inspection and repair. Such shutdowns result in high operating costs for the facility.
Thermocouples fail after sometime due to their close proximity to the flame and pose similar difficulties as Flame Rods to access and higher costs.
All the abovementioned flame sensors have the common disadvantage of requiring multiple sensors for multiple burners, since these sensors are capable of monitoring only one flame at a time.
Video Camera Technology
In order to overcome the abovementioned disadvantages, the author of this invention patented (see U.S. Pat. No. 6,278,374 B1) a technology that uses a video camera in combination with vision software to monitor the status of a multiple flames within one furnace unit. Also with that technology multiple burners can be monitored simultaneously and on a continuous basis. The camera is set up directly on the furnace to view the flames through a view glass mounted on the furnace.
However that technology has the following disadvantages:
One disadvantage of this method is the unavailability in practice of such view glasses in desirable locations. A large number of existing furnaces do not have sight ports where the camera can be mounted to view the flames. Often existing or planned sight ports are not ideally located to view all the burners. That makes the method difficult to apply especially since installation of a new sight port can be done only when the furnace is shut down. Often a suitable maintenance shut down is typically scheduled in intervals of several years. This difficulty results in continued reliance on less reliable UV detection methods for flame monitoring and control, raising safety concerns.
Even when such maintenance shut down is scheduled, mounting of the camera in a suitable location requires extensive advance planning and significant additional costs in the necessary extension of the shut down period (leading to charges for lost production), as well as in the costs of the modification itself. The modification involves, at a minimum, steel work, refractory patch up work and scaffolding inside the furnace etc. Also since the cameras have to be located on top of the furnace in some cases, ladders and platforms to access the sight port have to be provided. They add to the cost in addition to a lot of engineering and planning.
The camera has to be installed on the heater, and safety considerations in facilities such as petroleum refineries, chemical plants etc dictate that the camera and its accessories have to be in explosion proof housing. This also increases the system cost considerably.
Proposed Optical Fiber Technology
In contrast, the present invention allows the optical fiber ends to be installed in or on the burner housings by drilling and tapping the burner casing plate while the heater is in operation rather than be dependent upon or wait for the installation of a view port for mounting the camera.
Additionally, in many cases, the field of the camera does not permit the entire range of burners to be viewed comprehensively and allows viewing only a few burners well. This necessitates installing multiple cameras on multiple sight ports on the same furnace. This will increase the cost and make the controls more complicated. The proposed invention solves that problem; one camera can view all the optical fiber glows from all the burners simultaneously.
Another disadvantage of the before mentioned patent is that in many furnaces, such as industrial boilers, code regulations require both the pilot flame and the main flame of all burners to be monitored directly. A camera directly viewing the flames may find it difficult to distinguish the presence of small pilot behind larger main flame envelopes. The present invention can view the glows from the pilot and the main flame individually and simultaneously.
The principal advantage and a major breakthrough in the monitoring technology due to the present invention of using fiber optics is the extension of one camera's capability to monitor several burners in several combustion units simultaneously. This totally eliminates the use of dedicated camera for each and every combustion unit separately as required by the author's previous patent.
There exists, therefore, a need for a flame detection method and apparatus that can utilize a single apparatus to concurrently monitor and detect failure in one or more burners in one or more combustion units.
The present invention relates to a new technology in the furnace flame detection, both in principle and in the choice of detection equipments. Optical fibers are used to collect the light from several flames from the burners at the furnace end and transmit the light through a desired distance to a video camera box, which is protected from external light sources and located in a safe area and convenient place. Thus the operator at the control center can conveniently and continuously view the “live” images of the glows and the status data on the burners.
The uniqueness of this invention lies in the fact
The technology to monitor flames using optical fibers and the video camera using commercially available software will be described here briefly. The light energy received from the flames and transmitted to the far end tips of the fibers is viewed as “glows” (the glows will look like “full moons”) by the video camera. The image of the glow from each of the flames is framed inside an envelope termed as a region of interest on the monitor screen. The vision software in the solid-state processor of the camera system determines the presence or absence of the flame using a few parameters. The first parameter looks for an object inside the frame. This is a case of “presence or absence” determination; “the presence of glow” confirms the presence of flame. The second parameter is based on “the intensity of the glow”. If the glow is bright, the flame is strong. If it is dim, the flame is weak. The software can distinguish hundreds of gradations within the range between very dim and very bright.
The “presence of glow” and the “intensity of glow” are two independent parameters in the flame analysis and decision making process. Commercially available softwares have many other parameters available to analyze the flame. The inspection results as well as the live video images of the glows are transmitted to the remotely located control room through modern communication methods such as hard wired Ethernet cables and/or wireless radios. The video camera views only the light brought to it by the optical fibers from the burner flames. This feature brings with it a lot of advantages and opens up a lot of application possibilities in the industry; these will be elaborated in the text below.
The light-receiving end of the optical fiber is located at an ideal place in or on the burner housing to view the flame; the tip of the fiber is usually inside a cool air stream. Dust will not collect on the sensing head since there is a constant flow of air across it. The fiber could be made of glass or silicon quartz material, which can withstand high temperatures normally encountered in the furnace. Stainless steel tube sheathing protects the fiber on the sides. Such optical fiber cables are commercially available.
The flame detection system has several self-checking features.
An Ethernet cable transmits the video signals of the glows as well as the on/off data to a wireless radio transmitter near the camera. A wireless radio receiver at the control room end far away from the furnace receives such video signals and the on/off data and transmits them to the video monitor screen and to the computers (programmed logic controllers, commonly termed PLC, or the Distributive Control System, commonly termed DCS). The PLC and the DCS take further control action on the burners and/or the furnace. The vision software system, the PLC and the DCS have the capability to communicate with each other through the digital I/O inputs and outputs of the system. Alternatively, the video signals and the inspection data can be transmitted using hard cable connection, instead of the “wireless radio”, to the monitor through a communication link module.
Digital data communication devices and wireless high-speed radio transmitters and receivers are commercially available.
One has the option to select the appropriate vision software, the communication devices, the wireless radios etc from a large number of suppliers.
This invention has several major advantages over the presently commercially available technologies.
A preferred embodiment of the present invention provides a method for monitoring the status of a combustion unit having at least one burner. An optical fiber (OF in short) is installed in or on the housing of the burner to receive the light from the flame. The flame could belong to the main burner or the pilot burner. OF transmits the light through the long length of a sheathed cable to its other open end. This far end is inserted into a dark box so that the camera can focus on the glow at its tip. The glow at the tip of the OF will look like a full moon. A digital image of this is acquired by the video camera. The vision software can use any of the various parameters available to determine the presence or absence of the flame based on the glow and its intensity. It can define total absence of a glow as flame failure or a very weak glow (based on the intensity parameter) as a flame failure. An alarm state output is generated to inform the furnace operator of the flame failure. The monitor in the control room will show the video image of the glows as well as the inspection results.
Another preferred embodiment of the present invention provides a method for monitoring the status of a main flame and a pilot flame in a combustion unit having at least one burner. Two optical fibers are located in the burner, one to sense the light from the main flame and the other to sense the light from the smaller pilot flame. The two far ends of the OF cables are inserted into the dark chamber. A digital image of the two “full moons” is acquired by the video camera. The decision making process to declare a flame failure is the same as described in the first embodiment above.
Yet another preferred embodiment of the present invention provides a method for monitoring the status of flames in a combustion unit having several burners. Optical fibers are run from all the burners, (from both the main flame and the pilot flame of each burner if so required), to the dark chamber. A digital image of all the “full moons” is acquired by the video camera. The decision making process to declare a flame failure is the same as described in the first embodiment above.
Yet another preferred embodiment of the present invention provides a method for monitoring the status of flames of a plurality of burners from several independently operated combustion units. Optical fibers are run from all the burners of the different said combustion units, (from both the main flame and the pilot flame of each burner if so required), to the dark chamber. A digital image of all the “full moons” is acquired by the video camera. The decision making process to declare a flame failure is the same as described in the first embodiment above. The monitor screen can have split sections to show the furnaces as separate entities on the screen; monitoring results on flames belonging to each furnace can thus be seen separately. Such split screen vision technology is readily available.
Yet another embodiment of this invention provides for a complete system to monitor the status of several flames, main and/or pilot. The optical fibers installed in or on the burners bring the light to the dark chamber. The camera vision system inspects the images. The results of the inspection are communicated through a physically routed Ethernet cable, if necessary over a few hundred feet to another communication module in the control room. This latter module sends the video images and the results to the monitor. It can also send the data to the PLC and/or the DCS for them to take further logical actions.
Yet another preferred embodiment of the invention provides an apparatus for monitoring the status of a combustion unit or combustion units having a plurality of burners. The apparatus consists of optical fiber cables, a collection box for the far end of the tips of the cables, a digital camera system that has an embedded vision software, a communication module with Ethernet technology, wireless high speed Ethernet radio transmitter and receiver, a video monitor in the control room and digital I/O input output boards, PLC and/or DCS. The optical fibers bring the light of the flames to the dark chamber. The camera views the images. The embedded vision software determines the intensity values and compares them against the tolerance ranges. The inspection results and the video images are sent through the communication module to the radio transmitter. The radio receiver at the other end sends the live video images and the on/off data to a module, which is a communication gateway. This module sends the data to the monitor screen, to the PLC and or the DCS. The monitor screen displays the live images of the “full moons” indicating which of the burners are on and which are off.
Other features and advantages, of the present invention will be made clear to those skilled in the art by the following detailed description of the preferred embodiments constructed in accordance with the teachings of the present invention.
Closely related figures in the drawings have the same number but different alphabetic suffixes.
FIGS. 1 to 12
The camera vision system for monitoring the status of the flames in furnaces using optical fibers is illustrated in the FIGS. 1 to 12.
The purpose of the figures is to illustrate the invention. The actual number of elements (example: number of burners, number of optical fiber cables etc) will vary from case to case in industrial applications. The furnace illustrated in the example has 4 burners. The furnace 1 has four burners.
Several different applications of flame monitoring are described.
Main Flame Monitoring:
Optical fiber ends 6 installed in or on the steel housings of the burners receive light from the main flames 2 and transmit it through the optical cables 8. The glow emitting ends of the optical fibers 9 are installed on one end of a dark enclosure 10.
The radio receiver 14, the communication module 15, the video monitor 16, the PLC (Programmable Logic Controller) 21 and/or the DCS (Distributive Control System) 22 are in the control room at a location far away from the furnace 1.
Information received by 14 is sent to the module 15. It sends the data to a video monitor 16 in the control room. The operator can see the “live” images of the “light glows” 17 and the “on/off” data 18 and 19 on the screen. 18 lists the burners. 19 shows the inspection results.
Pilot Flame Monitoring
The technology is the same as in the case of main flame monitoring except that the light receiving optical heads are placed in or on the steel housing of the pilots. There are industrial burner applications in which only the pilot flames are monitored. This invention is applicable in such cases.
Monitoring of the Main Flame and the Pilot Flame of the Same Burner
The inspection method of this invention is applied to both the main flame and the pilot flame of each burner. So the video camera will be looking at 4 optical heads for the 4 main flames (in this example illustration) and 4 optical heads for the 4 pilot flames. This is shown in
Complete System with Hard Wired Ethernet Cable 23 Between Camera End and Control Room End.
This figure shows a complete system wherein the optical fibers bring the light of the burners as glows to be inspected by the camera. The communication between the module 12 at the camera end and the module 15 at the control room end is through a hard wired Ethernet cable 23. All other details are similar to the description for the other figures listed above.
Complete System with Radio Transmitter and Receiver
This figure shows a complete system wherein the communication between the camera end and the control room end are through high speed Ethernet wireless radios. The radios replace the hard wire 23.