Data processing: measuring – calibrating – or testing – Measurement system – Performance or efficiency evaluation
Reexamination Certificate
1999-03-22
2003-02-18
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Performance or efficiency evaluation
C702S022000, C700S274000
Reexamination Certificate
active
06522994
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a fossil-fired power or steam generation thermal system, and, more particularly, to a method for determining its fuel chemistry, fuel heating value, fuel flow, and thermal performance from its basic operating parameters.
The importance of accurately determining thermal efficiency is critical to any thermal system. If practical day-to-day improvements in efficiency are to be made, and/or problems in thermally degraded equipment are to be found and corrected, then accuracy in determining thermal efficiency is a necessity. The tracking of the efficiency of any thermal system lies fundamentally in measuring the useful output, and the total in-flow of fuel. The useful output from a fossil fueled system includes the generation of electrical and/or mechanical power and/or the production of a heated working fluid such as steam.
The measuring of the useful output of thermal systems is highly developed and involves the direct measurement of electrical output and/or mechanical drives and/or thermal energy flow. Measuring electrical and mechanical power is well established. Measuring thermal energy flow involves direct measurement of the inlet and outlet pressure, temperature and/or quality of a fluid being heated by the combustion gases, as well as measurement of its mass flow rate (m). From this information enthalpies (h) may be determined, and thus the total energy flow, m(h
outlet
−h
inlet
), delivered from the combustion gases, when also considering incidental losses, may be determined.
The measurement of the energy flow of the input fuel requires knowledge of the heating value of the fuel and its mass flow rate. For thermal systems using gaseous fuels, the fuel's composition may be well characterized, thus its heating value may be determined based on known heats of combustion associated with individual components.
However, there are numerous situations where a fossil-fueled system's fuel energy flow is not well characterized. For example, even a gas-fired system, having no on-site fuel gas analyzer, may receive fuel from multiple sources whose composite heating value variation is ±5 percent or greater. The measurement of fuel flow may often present a problem of measurement accuracy, especially at lower loads where flow measurement devices are not calibrated. In either case the determination of fuel energy flow is critical for proper thermal understanding of any fossil-fired system, either for direct confirmation of computed results and/or for improving system thermal efficiency.
The importance of accurately determining pollutant concentrations and their flow rates is also critical to the practical operation of any fossil-fired system due to environmental constraints imposed through regulation, the potential of regulatory induced fines, and concern by the owner of the facility for environmental protection.
Given these considerations, it is equally important to have analytical evidence of the errors made in the determination of fuel flow and the errors in fuel heating value, and thus the resultant errors in the determined thermal efficiency of the system. Further, any error in effluent flow, which is proportional to any error made in fuel flow, is significant when monitoring and reporting to regulatory agencies the effluents from any source of fossil combustion. The method of this invention provides a technique for specifying and correcting possible errors based on the consistency of the primary measurements of effluent O
2
, CO
2
, indicated Air/Fuel ratio, assumed or measured effluent H
2
O, possible air pre-heater leakage and the concentration of O
2
in combustion air.
The measurement of fuel flow has traditionally been accomplished via measurement of its mechanical effects on a device. Such effects include the pressure drop across nozzles or orifice plates, unique fluid densities, integrated weighing of a fuel handling conveyor belt (commonly used for bulk fuels such as coal), speed of sound, nuclear resonance, change in bulk storage levels, etc. Present industrial techniques for measuring gas or oil fuel flow result in typical errors of 1 percent to 10 percent relative to true values, depending on the care taken in designing, manufacturing, installing and calibrating the flow metering equipment and in its data reduction. Under ideal circumstances, tighter accuracies (i.e., smaller errors) are possible for gas and oil fuels, reaching at best 0.25 percent, but this is considered very unusual, always requiring extraordinary expense.
For bulk fuel such as coal, bio-mass, slurry fuels, wood, agricultural byproducts such as shells from nuts, trash and refuse, the typical accuracies of flow metering range upwardly from 5 percent and higher. Historically, bulk flow measurements have such poor accuracy that they are used only as a relative indicator of fuel flow. For fossil-fired systems any fuel flow error greater than approximately 1 percent, and certainly greater than 2 percent, is sufficiently high to preclude trending of the monitored fuel flow rate for reasons of thermal efficiency or for detecting degraded equipment. Improvement of efficiencies in a thermal system is classically concerned with a number of small incremental improvements, typically each in the range of 0.2 percent to 0.6 percent. A dozen or more of these, taken together, may result in 3 percent to 6 percent improvement. For example, an average 4.5 percent improvement has been physically demonstrated at over two dozen conventional power plants, see F. D. Lang, “Methodology for Testing and Evaluating Power Plants Using Computer Simulators”, 1990 Performance Software User's Group Meeting, May 1-4, 1990, St. Louis, sponsored by EI International, now Scientech Inc. of Idaho Falls, Id. Prior approaches which attempt to address the accurate determination of fuel flow are discussed below.
Another critical consideration in determining thermal efficiency is the variation in the fuel's heating value due to variations in fuel chemistry. Chemical variations appear through the mix of fuel water, fuel mineral matter (called fuel ash), and the relationships of the elements comprising the basic hydrocarbon molecular chain and any free inorganic elements: nitrogen, oxygen, carbon, hydrogen and sulfur; but principally carbon, hydrogen and oxygen. If an accurate and direct flow measurement of bulk fuels is not practical, the only alternative is the determination of fuel energy flow, which is the product of flow rate and heating value of the fuel, based in part on the measured energy flow to the working fluid. If errors exist in the heating value, either an assumed, measured, or calculated value, errors will then result in the fuel flow. Prior approaches which attempt to address the determination of fuel energy flow are discussed below. Further, over the past 140 years of producing safe high pressure steam for society, mostly from coal, there has been no invention or process even suggesting an ability to determine a coal's fuel ash content in real time based on thermodynamics.
The approach of this invention is a much improved “Input/Loss Method”. Prior input/loss methods have been known to the inventor, and to T. Buna as early as 1955.
One prior approach related to the present invention was developed by T. Buna in 1955 for the analysis of multiple fuels fed to a power plant. His approach was to characterize a fuel's effluent CO
2
, given differing effluent O
2
values, by assuming fuel chemistry of the individual fuels. With this data for multiple fuels and knowledge of the Useful Energy Flow Delivered, he advocated determining each fuel's flow rate. He presents an “output-loss” and an “input-loss” approaches to determining boiler efficiency. The present invention is related only in that a course reversed from Buna's method is accomplished. This invention computes fuel chemistry based on effluent measurements, it assumes that all secondary fuels, unlike Buna, are known having defined chemistries, heating values and As-Fired flows.
Barbee Manuel L.
Exergetic Systems LLC
Hoenig Gary
Hoff Marc S.
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