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Due to the liberalization of the energy markets and the globalization of coal procurement, fuel management became of substantial importance to power plant operators, which are faced with new challenges when operating with coal types different from the originally designed ones for the specific boiler Environmental regulations, combustion behavior, possible malfunctions and low operation, and maintenance cost became of essential importance. Fouling is one of the major challenges when new coals are being used. For that purpose we initiated a comprehensive study of fouling on the water-wall tubes in a 575 MW tangential-fired pulverized-coal utility boiler We developed a methodology to evaluate fouling propensity of coals and specifically tested two bituminous South African coals: Billiton-Prime and Anglo-Kromdraai. The methodology is based on the adherence of ash particles on the water walls. Adherence of the ash particle depends on the particle properties, temperature, and velocity vector at the boundary layer of the water walls. In turn, the flow and temperature fields were determined by computational fluid dynamics (CFD) simulations. For CFD simulations we also needed the combustion kinetic parameters, emissivity, and thermal resistance, and they were all determined experimentally by a 50 kW test facility. Using this methodology we mapped off the locations where fouling is mostly to occur It was found that our results fitted with the experience from the data obtained for these two coals in the Israel Electric Corporation utility boilers. The methodology developed was shown to be able to provide the fouling propensity of a certain coal, and yielded good prediction of the fouling behavior in utility boilers. Therefore, the methodology can assist in the optimization of the soot-blowing regime (location and frequency). [DOI: 10.1115/1.4001297] Keywords: fouling, fuel combustion, heat transfer, power systems

In this paper, different rates of steam flow (swing rates) are used to demonstrate the transient changes in both the drum-boiler steam pressure and the wall temperature levels in addition to stresses in the walls of steam risers. A MATLAB code was written to integrate the nonlinear dynamic governing equations for solving the water volume, the drum pressure, and the steam quality at the exit of the riser tubes. The same code is also used for calculating the steam riser inner and outer wall temperatures based on the inner wall heat transfer coefficient. The temporal riser pipe pressure and the inner and outer pipe wall temperatures have been incorporated into an ANSYS model for calculating the effective combined thermal and pressure-caused stresses numerically. The combined effective stress fluctuation for the highest swing rate (40%) is found to be too low to induce any damage in the riser tube. The controlled pressure level has been compared with an actual pressure reading from an existing drum boiler under operating conditions for the purpose of validating the control parameters employed in the study. An optimization method for reducing the steam pressure overshoot level in the boiler is also proposed. [DOI: 10.1115/1.4001653] Keywords: boiler dynamics, boiler control, drum boiler, riser tube, effective stresses

Loop-seal is a critical component of a circulating fluidized bed (CFB) boiler, and yet very little information on its working or design is available in published literature. Among the limited available information, none is on twin-exit loop-seal though it is one of the most commonly used loop-seal in large commercial CFB boilers. To circulate larger amounts of solids, a twin-exit loop-seal provides larger solids flow sections. It receives solids from one standpipe but delivers it through two recycle chambers and two delivery pipes. The present research was conducted in a twin-exit loop-seal of a 3.2 M[W.sub.th] CFB boiler operating in a thermal power plant for cofiring purpose. Data obtained in this industrial unit were supplemented with those collected in a single-exit bench-scale loop-seal in the authors' laboratory from the single-exit loop-seal in a 65 t/h CFB boiler and a scale model of a 30 MW CFB boiler. The effect of recycle chamber's aeration on the solids circulation rate was studied for several particle sizes. Results suggest that the total solids circulation rate does not increase proportionately with the increase in loop-seal discharge area provided by the twin-exit loop-seals. The linear horizontal velocities of solids and the minimum aeration in the recycle chambers are comparable to those measured in a single-exit loop-seal. The implication of these new findings on the design procedure of loop-seals is discussed. [DOI: 10.1115/1.4000174] Keywords: circulating fluidized bed boiler, loop-seal, standpipe, fluidization, twin-exit

Strong acoustic resonance with acoustic pressures reaching up to 165 dB developed in the boiler bank of a package boiler at full load. At first, the resonance developed at a lower frequency in the downstream portion of the tube bank and was suppressed by an acoustic baffle covering the downstream section of the flow channel. After about one year of operation, a second resonant condition developed. Tests confirmed that, again, a strong resonant condition developed at a higher frequency in the unbaffled upstream portion of the flow channel. Computer analysis confirmed that the initial resonance occurred at the first acoustic mode of the flow channel while the follow-up resonance occurred at the second mode of the flow channel expressed as a first-mode resonance in a different (upstream) location. An extension of the acoustic baffle covering the entire depth of the tube bank eliminated the vibration. This paper gives a description of the problem and summarizes the theoretical and experimental results substantiating the findings. [DOI: 10.1115/1.2767369]

Boiler piping of fossil-fuel combustion power generation plants are exposed to high-temperature and high-pressure environments, and failure of high-energy piping due to creep damage has been a concern. Therefore, a precise creep damage assessment method is needed. This paper proposes a nondestructive method for creep damage detection of piping in fossil-fuel combustion power generation plants by ultrasonic testing. Ultrasonic signals are transformed to signals in a frequency domain by Fourier transform, and a specific frequency band is chosen. To determine the creep damage, the spectrum intensities are calculated. Calculated intensities have a good correlation to life consumption of the weld joints, and this method is able to predict the remaining life of high-temperature piping, which has been already installed. [DOI: 10.1115/1.2767364] Keywords: nondestructive testing, frequency analysis, creep damage, maintenance, fossil-fuel combustion power generation plants, boiler piping, frequency spectral intensity, life consumption, ultrasonic testing