Industrial burners rely upon combustible fuel to produce energy, for example in the form of heat, as for radiant burners. Such fuel may be natural or liquefied petroleum gas, and light, medium and heavy liquid oil fuels. The combustible fuel must be combined with air in an appropriate ratio for maximum efficiency and safety of operation of the burner. In order to determine if such an appropriate ratio is present, devices are known in the art for measuring the concentration of one or more flue gases, which are gases emitted from the chimney as waste products after the fuel is burnt. Typical flue gases which are measured include, but are not limited to, carbon dioxide and carbon monoxide. However, since devices for measuring the concentration of carbon monoxide tend to be expensive, often only the concentration of carbon dioxide is measured.

Once the concentration of one or more flue gases has been measured, the flue gas efficiency can be calculated from equations which are known in the art. The efficiency of the burner can then be determined from the flue gas efficiency, and the fuel/air ratio adjusted if necessary. In particular, the fuel/air mixture must be adjusted such that the fuel is safely and efficiently consumed in order to avoid production of excess carbon monoxide as a combustion product.

In order to determine the efficiency of the burner and any necessary adjustments to the fuel/air ratio, various solutions have been proposed in the background art. For example, U. S.

Patent No. 4,913,647 to Bonne et al. discloses a method for adjusting the fuel/air ratio according to the ratio of two known chemical species in products of combustion in the flue gases, such as OH, C2, CO or CO2. These two chemical species can be measured according to their respective spectral emissions. However, these measurements require specialized equipment which may not be readily available.

U. S. Patent No. 5,599,179 to Lindner et al. discloses a method for regulating the air to fuel ratio by measuring the concentration of carbon dioxide, carbon monoxide and water.

However, this method relies upon the measurement of carbon monoxide, which requires

expensive specialized equipment as previously described.

U. S. Patent No. 5,222,887 to Zabielski et al. describes a method for controlling the fuel/air mixture by measuring optical burner flame emissions, rather than measuring combustion products in flue gases. These burner flame emissions are then fitted to a fourth-order polynomial, and the fuel/air mixture is determined from the mathematical inflection point. This method is both complicated and requires extra equipment, since it relies upon the measurement of optical burner flame emissions rather than the measurement of flue gases. The latter must be measured in any case to meet regulatory requirements against pollution, such that a method which employs data taken from the measurement of flue gases would clearly be more useful and would not require extra equipment.

Similarly, U. S. Patent No. 5,037,291 to Clark discloses a method for determining an optimum fuel/air ratio according to the intensity of radiation emitted by a radiant burner. Again, such a method does not incorporate the measurement of combustion products in flue gases which must be performed for regulatory requirements, and as such is less efficient.

There is thus a need for, and it would be useful to have, a method for determining whether the fuel/air mixture is appropriate and safe, which uses the concentration of at least one combustion product in the flue gases such as carbon dioxide, which does not require specialized equipment and which is simple yet robust.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, wherein: FIG. 1A is a schematic block diagram of an exemplary burner system according to the background art, while FIG. 1B is a background art graph of the concentration of several flue products as a percentage (y-axis) against the percentage of excess air; FIG. 2 is a flowchart of an exemplary method according to the present invention; and FIGS. 3A and 3B are exemplary graphic displays of the results obtained from the method of Figure 2.

SUMMARY OF THE INVENTION The present invention is of a method for determining whether a burner system is operating safely according to at least the measured concentration of carbon dioxide in the flue

gases and according to the temperature of the flue gases and the ambient temperature surrounding the burner. In addition, the method uses a standard curve of carbon dioxide concentrations plotted against the percentage of air in the burner system, either as a deficiency or as an excess of air. This curve has an inflection point. To the right of this inflection point, the burner system is operating safely and efficiently with excess air. To the left of this inflection point, the burner system is not operating safely and efficiently since the amount of air in the burner system is deficient. Thus, the method of the present invention must determine whether the concentration of carbon dioxide correctly lies on the left side or the right side of the graph, thereby determining whether the burner system is operating safely.

The measured concentration of carbon dioxide is compared to a predetermined constant, such that if the measured concentration of carbon dioxide is greater than the constant, it falls within a range which is near the inflection point of the standard curve of carbon dioxide concentrations. Within this range, any further adjustments would have a relatively small effect on the safety and efficiency of the burner system. However, optionally and preferably the concentration of carbon monoxide is measured in order to determine if any adjustments to the burner system are required.

If the measured concentration of carbon dioxide falls outside of the range, then air is injected into the burner system and the concentration of carbon dioxide is measured again. The difference between these two concentrations is determined, such that if the difference is less than a predetermined constant, the method ends. Otherwise, additional air is injected and the steps of the method are repeated. Thus, the method of the present invention has the advantage of being both simple and robust.

According to the present invention, there is provided a method for determining whether a burner system is operating safely, the burner system emitting flue gases, the method comprising the steps of: (a) measuring a first measured concentration of carbon dioxide in the flue gases; (b) injecting an amount of additional air into the burner system; (c) measuring a second measured concentration of carbon dioxide in the flue gases; and (d) comparing the first measured concentration of carbon dioxide and the second measured concentration of carbon dioxide to determine if the burner system is operating safely.

According to another embodiment of the present invention, there is provided a method for determining whether a burner system is operating safely, the burner system emitting flue gases, the method comprising the steps of: (a) measuring a measured concentration of carbon dioxide in the flue gases; (b) comparing the measured concentration of carbon dioxide to a predetermined

curve of concentration of carbon dioxide against amount of air in the burner system, the predetermined curve having an inflection point; (c) if the measured concentration of carbon dioxide lies on a portion of the predetermined curve right of the inflection point, determining that the burner system is operating safely; and (d) alternatively, if the measured concentration of carbon dioxide lies on a portion of the predetermined curve left of the inflection point, injecting additional air into the burner system.

Hereinafter, the term"computer"includes, but is not limited to, personal computers (PC) having an operating system such as DOS, Windows, OS/2 or Linux; Macintosh computers; computers having JAVATM-OS as the operating system; and graphical workstations such as the computers of Sun Microsystems and Silicon Graphies, and other computers having some version of the UNIX operating system such as AIX or SOLARISw of Sun MicrosystemsTM; or any other known and available operating system. Hereinafter, the term"WindowsTM"includes but is not limited to Windows95TM, Windows 3. XTM in which"x"is an integer such as"1", Windows NTTM, Windows98TM, Windows CEw and any upgraded versions of these operating systems by Microsoft Inc. (Seattle, Washington, USA).

Hereinafter, the terms"computer user"and"user"both refer to the person who operates the computer for performing the method of the present invention.

The method of the present invention can be implemented as a series of steps performed by a data processor, and as such can be implemented as hardware, software or firmware, or a combination thereof. As software, the method of the present invention can be implemented in any suitable programming language which is compatible with the hardware and operating system of the computer operating the software. Examples of such suitable programming languages include, but are not limited to, Visual Basic, C and C++.

DETAILED DESCRIPTION OF THE INVENTION The present invention is of a method for determining whether a burner system is operating safely according to at least the measured concentration of carbon dioxide in the flue gases and according to the temperature of the flue gases and the ambient temperature surrounding the burner. In addition, the method uses a standard curve of carbon dioxide concentrations plotted against the percentage of air in the burner system, either as a deficiency or as an excess of air. This curve has an inflection point. To the right of this inflection point, the burner system is operating safely and efficiently with excess air. To the left of this inflection point, the burner system is not operating safely and efficiently since the amount of air in the

burner system is deficient. Thus, the method of the present invention must determine if the operation of the system is such that the concentration of carbon dioxide falls on the left side or the right side of the graph.

The principles and operation of a method according to the present invention may be better understood with reference to the drawings and the accompanying description, it being understood that these drawings are given for illustrative purposes only and are not meant to be limiting.

Referring now to the drawings, Figure 1 A is a background art diagram of a typical burner system as known in the art, while Figure 1B is a background art graph of flue products concentration (y-axis) against percentage of excess air (x-axis).

As shown in Figure 1A, a typical background art burner system 10 features a burner 12 for consuming the combustible fuel in a fuel/air mixture. Burner 12 is connected to a furnace 14, which may also be a boiler, for harnessing the energy produced by burner 12. The flue gases and other combustion products are emitted through a chimney 16. Thus, burner system 10 produces both energy and waste (combustion) products as part of regular operation.

As shown, several measuring devices are also featured in burner system 10 in order to ensure the safe operation of burner system 10. These measuring devices include a flue gas parameter measurer 18. Flue gas parameter measurer 18 preferably measures at least the temperature of the flue gases and the concentration of carbon dioxide. Preferably, a computer (not shown) is in communication within flue gas parameter measurer 18 for collecting this information. Optionally, the computer is in constant direct communication, or else intermittent direct communication, with flue gas parameter measurer 18, such that the data is automatically sent to the computer, for example through a data logger. Alternatively, the data could be obtained from flue gas parameter measurer 18 and then entered manually into the computer.

An ambient temperature measuring device 20 is preferably also present for measuring the ambient temperature, in order to perform various calculations which are known in the art for determining the concentration of carbon monoxide and other combustion products with concentrations which are not directly measured. Thus, the combination of flue gas parameter measurer 18 and ambient temperature measuring device 20 enable the concentrations of flue gases to be determined, for example in order to fulfill regulatory requirements concerning pollution levels and for safe operation of burner system 10.

The concentration of each flue gas, carbon dioxide, oxygen and/or carbon monoxide, is measured in order to determine whether the fuel/air mixture should be adjusted. If the fuel/air

ratio is not appropriate, excess amounts of carbon monoxide may be produced, thereby causing burner system 10 to operate in an unsafe manner. Figure 1B shows a graph of combustion efficiency for a background art burner system such as that shown in Figure 1A, in which the flue gas concentration (y-axis) is plotted against the percentage of excess air (x-axis).

As shown in Figure 1B, a clear demarcation is made on the graph between flue product concentrations obtained when the percentage of excess air is negative, as opposed to these concentrations obtained when the percentage of excess air is positive. If the percentage of excess air is negative, not only is the performance of the burner compromised, but safety is also endangered, since carbon monoxide levels may increase from fuel which is not consumed. Thus, in order to maintain safe operation of the burner, the fuel/gas ratio must be maintained such that the percentage of excess air is positive.

As shown, simply performing a single measurement of the concentration of carbon dioxide is not sufficient, since the graph of the concentration of carbon dioxide has an inflection point 22. Before inflection point 22, the slope of the graph is rising; after inflection point 22, the slope of the graph is falling. As a result, a first point 24 can have the same carbon dioxide concentration as a second point 26, yet second point 26 falls on the"safe"portion of the graph (with extremely low concentrations of carbon monoxide), while first point 24 falls on the "unsafe"portion of the graph (with relatively high concentrations of carbon monoxide). The portion of the graph is actually determined by the percentage of excess air (or lack of air), which is calculated according to the concentration of carbon dioxide, relative to inflection point 22.

Therefore, first point 24 can be stated to lie on the left side of inflection point 22, while second point 26 falls on the right side of inflection point 22, such that the"side"of inflection point 22 is important for determining safety of the system. Thus, the same apparent carbon dioxide concentration may be obtained from completely different fuel/air ratios, with correspondingly different amounts of carbon monoxide.

As shown in Figure 1B, the difference between safe, efficient operation of the burner system, and unsafe, inefficient operation, can be determined according to the side of inflection point 22 at which the concentration of measured carbon dioxide lies, since this side determines the relative amount of air in the burner system. Previous methods in the art have ignored values lying the left of inflection point 22, and have instead determined the efficiency of the burner system for conditions of excess air only.

In order to determine whether the burner system is operating safely and efficiently, simply measuring multiple points for calculating the slope of the line or curve formed by these

points may be misleading. Furthermore, creating a new curve from multiple measurements is both difficult and requires sophisticated software and measuring equipment, particularly given the error of measurement. Therefore, the method of the present invention, as shown in Figure 2, is operative with only one measurement of the concentration of carbon dioxide (if carbon monoxide is also measured), although of course multiple measurements of carbon dioxide and/or measurements of the concentrations of both carbon monoxide and carbon dioxide are preferable.

The method of the present invention is able to distinguish between safe and unsafe operation of the burner system according to the side of inflection point 10 at which the measured concentration of carbon dioxide lies.

More preferably, the method of the present invention distinguishes between different degrees of unsafe operation according to a plurality of different levels of the relationship between air and carbon dioxide, with regard to the excess air level (from positive to negative). As an example, 5 four different levels of this relationship may be determined, ranging from significant excess air, down to up to 10% of lack of air in the air to fuel ratio, which is dangerous. Most preferably, different recommendations for action are automatically performed by software according to the method of the present invention, which may range from adjusting the burner for conditions of no excess air, which is inefficient but not dangerous, to ceasing operation of the burner for the dangerous condition of negative excess air.

In step 1 of Figure 2, the concentration of carbon dioxide is measured. Preferably, the temperature of the flue gases and the ambient temperature are also measured. In step 2, the measured concentration of carbon dioxide is compared to a predetermined concentration of carbon dioxide. Preferably, the predetermined concentration of carbon dioxide is equal to the difference of the maximum possible concentration of carbon dioxide and a constant. More preferably, the constant is fairly small, such as 1.5. Therefore, the range defined between the predetermined concentration of carbon dioxide and the maximum possible concentration of carbon dioxide is preferably relatively narrow and is centered at the inflection point of the graph of concentrations of carbon dioxide, such that the slope can change from positive to negative with relative small adjustments in the measured concentration of carbon dioxide. Thus, if the measured concentration of carbon dioxide is greater than the predetermined concentration of carbon dioxide, then measuring carbon dioxide alone may not produce optimal results, since effort could be wasted in an attempt to adjust the carbon dioxide concentration within such a narrow range.

As shown in step 3a (1) of the left branch of the flowchart, preferably if the measured

carbon dioxide concentration falls within this narrow range, such that this measured concentration is greater than the predetermined concentration, the concentration of carbon monoxide is measured. Measuring the concentration of carbon monoxide provides another method for determining the safety and efficiency of the burner system. If the concentration of carbon monoxide is less than a predetermined safe level, then in step 4a (1), the method ends.

Alternatively, in step 4a (2), the method proceeds to step 3b, described in greater detail below.

Preferably, the predetermined safe level of carbon monoxide is about 500 ppm, more preferably about 250 ppm, although another value for this level may be substituted according to the requirements of the environment and regulatory structure within which the burner system operates.

Optionally and preferably, if the concentration of carbon monoxide is measured, then the second concentration of carbon dioxide is not needed to locate the correct side of the inflection point of the graph for the points for determining whether the system is operating safely, such that steps 4 (b) and following of the method are not necessarily performed. These steps could be performed to improve efficiency if needed.

Alternatively, if the concentration of carbon monoxide is not measured, then in step 3a (2), a preprogrammed default action is performed, which could be for example to stop the method without executing further steps.

Turning now to the right branch of the flowchart, if the measured concentration of carbon dioxide is less than the predetermined concentration of carbon dioxide, then in step 3 (b), additional air is injected into the burner system, since there is a lack of air. Preferably, about five percent additional air is injected into the burner system. In step 4 (b), the concentration of carbon dioxide is measured again, as well as the ambient temperature and the temperature of the flue gases.

In step 5, the first measured concentration of carbon dioxide (from step 1) is compared to the second measured concentration of carbon dioxide (from step 4 (b)). Preferably, the difference between the first measured concentration of carbon dioxide and the second measured concentration of carbon dioxide is determined. If this difference is less than a constant, then there is excess air and the burner system is operating safely. The method then ends in step 6 (a).

Alternatively, if this difference is greater than the constant, then the burner system is not operating safely, and the method is repeated from step 3 (b), as shown in step 6 (b). More preferably, the constant is a relatively small number, such as about 0.5. This comparison is performed in order to allow for a certain amount of system error, such as measurement error for

example, without requiring repeated adjustments in an attempt to compensate for such a small deviation from the safe value for operation of the burner system.

Optionally and preferably, in step 7, if the system is not operating safely, then the level of danger inherent in the operation of the burner is preferably calculated. An even or slightly negative percentage of excess air to fuel more preferably results in an adjustment to the burner operation, while a more significantly negative percentage of excess air, such ten percent for example, more preferably results in the operation of the burner ceasing.

In addition, preferably the loss of efficiency is calculated from the measured concentrations of carbon dioxide, the temperature of the flue gases and the ambient temperature.

The amount of the loss varies according to the differential between the temperature of the flue gases and the ambient temperature, as well as according to the measured concentration of carbon dioxide. More preferably, the calculated loss of efficiency is used to determine the relative amount of air present in the burner system, as well as to determine how much additional air should be injected, if any.

Optionally and preferably, the amount of loss of energy with regard to the cost is also calculated, as the loss of efficiency in terms of lost energy multiplied by the cost per unit of energy. In addition, once the burner has been properly adjusted, if necessary, and there has been a corresponding gain in efficiency of operation, now the saving in the cost of energy is preferably calculated.

Also optionally and preferably, the weight of the released carbon dioxide is also calculated, preferably in addition to the calculation of the percentage of carbon dioxide released to the atmosphere. The weight of the released carbon dioxide is preferably calculated as follows.

The velocity of the gases is then determined. In addition, the flue area and the volumetric gas flow are determined according to the diameter of the flue. Also, the percentage of carbon dioxide is determined. Next, the weight, or mass flow, of the released carbon dioxide is determined from these factors.

Results obtained by performing the method of Figure 2 are shown in Figures 3A and 3B.

In Figure 3A, multiple measurements of carbon dioxide have been obtained and are plotted on the curve with vertical hatch marks. The concentration of oxygen and other combustion products are optionally calculated from the concentration of carbon dioxide and are then plotted on the graph. The calculated concentration of oxygen is plotted on the curve with boxes. The loss of efficiency is calculated and plotted as"loss"curves, each loss curve corresponding to a different temperature differential between the temperature of the flue gases and the ambient temperature.

The presentation of these points as separate points, plotted against an ideal graph of the curves for the concentrations of carbon dioxide, oxygen and so forth, clearly shows how even relatively noisy data can be used to determine whether a burner system is operating safely.

In Figure 3B, a schematic graph is shown with a single measurement of the carbon dioxide concentration and a single measurement of the carbon monoxide concentration shown.

The combination of the single measurement of the concentration of carbon dioxide and carbon monoxide enables the method of the present invention to determine whether the burner system is operating safely, according to the side of the graph relative to the inflection point on which the carbon dioxide concentration falls. The schematic nature of the graph of Figure 3B emphasizes the location of the air concentration as inside the zone or outside the zone.

In addition, the software of the present invention is able to present these results in table format or according to burner system efficiency or lack thereof. Optionally and preferably, the software of the present invention is able to graphically display the measured values of carbon dioxide, and optionally the measured values of carbon monoxide, relative to the standard curves of concentrations for these gases. These standard curves preferably display the curves of the measured concentrations of gases such as carbon dioxide relative to the calculated excess air.

Such a display is able to visually indicate the relative efficiency of the burner system, and whether such a system is operating safely. Optionally, the software of the present invention is able to recommend whether to inject more air or otherwise to adjust the operation of the burner system, for example by ceasing the operation of the burner system if the percentage of excess air becomes too dangerous for burner operation, as previously described. Thus, the present invention is preferably able to both graphically demonstrate whether the burner system is operating safely and to recommend injecting more air or to maintain the amount of air according to these circumstances.

Optionally and preferably, a report is also generated in one or more of a variety of report media, including but not limited to, e-mail (electronic mail) messages, reports which are printed on paper and automatic facsimile transmission. These reports are more preferably sent automatically to the relevant authority or authorities with regard to air quality and/or worker safety, for example.

The software of the present invention may also optionally provide a calculator for calculating conversions between different types of energy and technical units, which may be useful for the operation of the burner system.

It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the spirit and the scope of the present invention.