This paper presents an on-line method which detects steam generator tube leaks and the heat exchanger in which the leak occurs. This method (the Tube Failure Model) has been demonstrated by direct testing experience. It is based on the Input/Loss Method, a patented method (1994–2004) which computes fuel chemistry, heating value and fuel flow by integrating effluent measurements (CEMS data) with thermodynamics. This paper explains the technology supporting the detection of tube failures, the method of identifying the location of the failure, and cites direct experience of detecting tube failures at two power plants. Most importantly, this paper presents the results of direct testing at the Boardman Coal Plant in which high energy steam/water lines were routed from the drain headers of all major heat exchangers into the combustion space. When allowed flow, these lines were used to emulate tube leaks from any of the major heat exchangers. Their flow rates and locations were then compared to Tube Failure Model predications. This testing is considered significant as for the first time Δheat rate effects of tube failures will be directly determined; and, further, this testing will provide the Tube Failure Model its on-line proof-of-process.

This paper compares two methods for calculating boiler efficiency using test data obtained from the Boardman Coal Plant. The two test methods are ASME PTC 4’s Energy Balance Method as evaluated by Sargent & Lundy LLC, Chicago, IL, and the Input/Loss Method as evaluated by its owner, Exergetic System Inc., San Rafael, CA. The differences in methods are fundamental: varying in basic definitions of boiler efficiency and calculation methodology.

Portland General Electric’s (PGE) Boardman plant is a nominal 600 megawatt (MW) coal fired unit that burns sub-bituminous Powder River Basin (PRB) coal from Wyoming. This paper will cover the experience and results of PGE’s Boardman plant operating on 100% torrefied wood (TW) pellets at 255 MW consuming almost 5000 tons of pellets. Results were positive and include suitable handing after inclement weathering for months. Pulverizers were able to handle the TW pellets with adjustments, resulting in near 100% combustion efficiency. Particulates were controlled with an electrostatic precipitator (ESP). Topics investigated include torrefied wood production, fuel handling and storage on the front end of the test. Fuel handling, pulverization, combustion, emissions, and ESP performance were monitored during the test and are reported here. Several one mill tests were conducted prior to the 100% test to evaluate and improve mill performance. This test showed that a pulverized coal (PC) boiler can operate on 100% TW fuel with minimal operational changes.

This paper examines the effects of particle size on the calorific value of hydrocarbons, shedding light on the thermodynamics of pulverizing coal in a commercial power plant. Both laboratory testing results and energy balances around an actual pulverizer are presented. Although tacitly known to any power plant engineer, efficient combustion is seen in two parts: preparation of the material’s surface/mass ratio, and then its combustion with the proper air/fuel mix and associated mechanics. This work attempts to put a thermodynamic face on the first part. A theory is presented which demonstrates that a hydrocarbon’s surface/mass ratio affects its potential to release its full chemical energy. This theory has been generally supported in this work by laboratory testing of pure substances; however this testing was not conclusive and should be repeated. If an optimum surface/mass is not achieved, unburned combustibles will result — and this regardless of subsequent air/fuel mixtures and/or burner sophistications. This work is suggests that a unique optimum surface/mass ratio exists for each hydrocarbon substance (and coal Rank); that once its full potential is reached, a higher ratio provides no further benefit. Since surface tension describes a material’s free energy, an aspect of surface tension, termed hydrogen bonding free energy, was shown to relate to the A¨calorific value penalty associated with non-optimum surface/mass ratio. A correlation was developed relating surface/mass ratio to observed an A¨calorific value penalty and hydrogen bonding free energy. This correlation’s form may be applied to coal if supported with additional research. The impetus for this work was the ASME Performance Test Code 4’s allowance of pulverizer shaft power to influence boiler efficiency’s “credit” term, thus affecting efficiency. It was demonstrated that surface/ mass affects calorific value and thus efficiency. However, there is no observable difference between grinding a hydrocarbon to a given surface/mass ratio, versus manufactured spheres. Although laboratory preparation of coal samples should emulate pulverizer action, this work suggests that a renewed and careful review of laboratory procedures is required. Recommendations are provided for critique and debate.

This paper examines the sensitivities of ambient conditions on the most basic understanding of fossil-fired power plants: boiler efficiency and associated computed fuel flow. Conditions studied were ambient oxygen in the combustion air, and the air’s water content. This research was conducted at the 610 MWe Boardman Coal Plant operated by Portland General Electric. Burning Powder River Basin coal, it has been tested numerous times by the authors including several 4 to 6 month long projects used to throughly understand the system. This experience, coupled with many other such projects, has suggested that ambient oxygen and humidity — normally taken as constants or simply ignored in common analyses — may have significant influence on boiler efficiency. There are, of course, any number of inputs which might affect a computed efficiency, and associated computed fuel flow. This work separates data making up efficiency into water-side data and system stoichiometric data. We argue that fundamental understanding of fossil-fired systems begins with system stoichiometrics, and, for this work, ambient oxygen and humidity. Demonstrated is that depletion of ambient oxygen can cause a very high error in boiler efficiency (>1% Δη) if unrecognized. In addition, given intrinsic complexity of combustion air systems, uncertainty in the amount of water in combustion air can well contribute to error. Further, this work demonstrates a technique whereby plant fuel flow can be verified based on ambient conditions. This paper demonstrates the very real advantage of using high accuracy ambient instrumentation — for oxygen and relative humidity — whose measurements may not have dramatic affects when used at a well run plant such as Boardman, but whose use at plants not well monitored will easily justify their employment. Taking such ambient measurements a step further, this paper demonstrates a method whereby ambient humidity can be used to verify a coal-fired plant’s fuel flow.