Sastry Munukutla

Thermal boundary layer due to sudden heating of fluid

This paper proposes to solve computationally the heat-transfer problems (introduced by Munukutla and Venkataraman, 1988) related to a closed-cycle pulsed high-power laser flow loop. The continuity and the momentum equations as well as the unsteady energy equation are solved using the Keller-Box method. The solutions were compared with the steady-state solutions at large times, and the comparison was found to be excellent. Empirical formulas are proposed for calculating the time-dependent boundary-layer thickness and mass-heat transfer, that can be used by laser flow loop designers. 6 refs.

Modeling of the Performance of a Coal-Fired Power Plant in Real-Time

Efficient operation of a coal-fired power plant was not a serious consideration for the electric power industry until recently. The main reason for this was that until recently the power industry was regulated and as a consequence the customer base for a given generating station was almost predetermined. The fuel costs were passed on to the customer and there was no incentive for the power industry to improve operating efficiency which would have resulted in reduced fuel consumption. Deregulation of the electric power industry which is quickly spreading all over the world has brought about a big change in the thinking of the power industry. In a deregulated market the customer in principle can choose the power supplier. Obviously the customer would choose a supplier with the lowest cost of electricity. Thus there is an incentive for every power producer to generate power at the lowest cost which means improved efficiency. In most coal-fired units fuel cost accounts for nearly 60-70% of the total cost of generation which implies that there is an immediate need to reduce fuel cost by improving efficiency. As mentioned in the foregoing paragraph fuel costs account for nearly 60-70% of the total cost of generation. Therefore, if the fuel flow rate for a given unit were to be monitored accurately in real-time that would enable the power producer to declare a more realistic cost of electric power. It should be noted that before deregulation was contemplated, utilities used to measure fuel consumption on a semi-annual or annual basis. While some units are equipped with belt scales and gravimetric feeders for coal flow rate measurement, these devices need constant maintenance and calibration and are in general considered unreliable. Several developments have taken place in the last two decades due to which it is now possible to model the performance of a coal-fired unit in real-time. The key parameters that can be calculated by the model are: boiler efficiency, steam cycle heatrate, unit heatrate, and coal flow rate. In what follows, a brief review of the relevant literature will be given. This will be followed by a description of the model for performance monitoring. Finally some field results will be presented.

A novel approach to real-time performance monitoring of a coal-fired power plant

Real-time performance monitoring of a coal-fired unit is essential in a deregulated market. A real-time performance monitoring system requires real-time (online) coal analysis. Since online coal analyzers are not routinely available for use in power plants, a novel approach to the determination of online coal analysis from flue gas composition measurements is taken. Using this approach, real-time performance monitoring software have been developed for several units. The principle behind the method and some field results are presented in this paper.

Parametric Studies of Power Plant Performance Monitoring

Real-time performance monitoring of coal-fired power plants is becoming very important due to the impending deregulation of the electric power industry. Performance testing is made to be real-time by changing the traditional output loss method to include an estimation of coal composition based on the Continuous Emission Monitoring System (CEMS) data. This paper illustrates the robustness of the calculations by introducing a variance into each of the calculation inputs to access its effect on the final outputs of heatrate, boiler efficiency and coal flow. Though the original study was over five power plants this paper presents results for the two most diverse coals.Copyright

Scale Model Testing Towards Primary Air Optimization of a CFB Boiler

Primary air flow is supplied to the wind box of a 300 MW CFB boiler by means of three primary air ducts connected to a common plenum. A flow rate measurement is performed in each duct using an Annubar flow meter. Due to the tight configuration of the piping and the associated turbulence, the measured flows in the three ducts were not consistent, resulting in improper air flow distribution in the boiler. A primary air duct flow study was performed in an effort to improve measurement accuracy, which will lead to improved combustion efficiency and low load cycling by allowing precision air flow control in the furnace.The objective of this project was to employ a 1/10th scale model test to determine the best method to improve the flow upstream of each Annubar flow meter. Tests were conducted with room temperature air at several flow rates generated by a centrifugal fan. Reynolds number independence was achieved in the tests. Appropriate dimensionless Grashof and Prandtl number scaling was used to extrapolate the scale model tests to the high temperature conditions prevalent in the unit. Flow visualization and measurements using a five-hole directional velocity probe were performed. It was determined that mounting 50% open area screens in the primary air duct of the scale model had the effect of significantly reducing both yaw and pitch angles across the Annubar measurement plane. A complimentary benefit was that the velocity profiles in the flow direction were notably flattened by the addition of the screens. Furthermore the performance of the Annubar flow meters could be improved if the measurement plane was moved further upstream of the opposed blade flow control damper.Copyright

Performance Monitoring of Coal-Fired Units in Real-Time

Power plant performance monitoring can be accomplished in real-time using the data already available on the plant computer in the control room. Because of this, plant operators can be provided with quantitative real-time feedback on the impact of any operational change on plant efficiency and economics. With funding from several major U.S. Utilities and the Electric Power Research Institute (EPRI) the Center for Energy Systems Research (CESR) at Tennessee Technological University (TTU) has developed a Real-Time Performance Monitoring System for evaluating plant operations continuously. The calculations are based on the output/loss method. Coal analysis in real-time is obtained by using information on flue gas composition. This is a unique technology developed at CESR. The steady-state thermodynamic model includes on the fire-side the FD and ID fans, the air preheater, the coal pulverizers and the boiler. It includes flow rate, pressure and temperature of the feedwater, main steam, cold reheat steam and the hot reheat steam on the steam-side of the calculations. The model performs calculations and displays results every minute (or whatever averaging time is chosen) by reading relevant data from the plant computer. One of the primary advantages of this method is that it can be customized to a given unit with given instrumentation. The Real-Time Performance Model has been successfully installed in 10 coal fired units in the U.S.A., four 200 MW units in New Zealand, one 200 MW unit in India and one 900 MW unit in China. In this paper the output/loss method will be introduced. The thermodynamic model with which calculations are performed will be described in detail. Field results from several units around the world will be presented. Examples of strategies for performance enhancement based on real-time performance monitoring will be discussed.Copyright

CFD Studies on Burner Secondary Air Flow

In many fossil power plants operating today, there is insufficient means to assure the proper balancing of the secondary airflows between the individual burners of wall-fired units in addition there is a problem of dust deposition on the floor. This mismatch leads to decreased boiler efficiency and increased emissions. In this study, a Computational Fluid Dynamics (CFD) modeling of a fossil power plant wind box scale model is performed using the commercial software CFX5.6. The model solves the three dimensional Reynolds averaged Navier-Stokes equations with the K-epsilon turbulence model. The CFD results are validated by the experimental data taken from a 1/8th scale model of a wall fired fossil unit. Simulations under various flow conditions are obtained to identify the optimum design in terms of the equalization of the secondary airflow through the burners.Copyright

Numerical and Experimental Study of Pressure Drop Reduction in a Power Plant Stack

As governmental regulations on the emission of the power industry became more restrictive, many power plants operating today experience severe problems. The fans that handle the flow through the stack, that were originally designed to handle a certain maximum flow rate, are now required to handle even higher flow rates due to the introduction of emission control devices. In this study, computational fluid dynamics (CFD) and experimental studies have been carried out on the scale model of a stack to identify means for pressure drop reduction. The CFD model was constructed using the commercial software CFX-5.6. The model solves the Reynolds averaged Navier-Stokes equation with Shear-Stress turbulence model (SST) and the CFD results are validated by data taken from the scale model. Baffles of different orientation have been installed in the stack under different flow conditions. Both numerical and experimental results confirm that adding baffles can reduce the pressure drop in a stack significantly. Thus, with minimum effort, power plants can keep running the stacks at a higher flow rate.Copyright

CFD Applications for Coal/Air Balancing in Power Plants

A new method for balancing coal / air flow to individual burners connected to a mill in a pulverized coal fired unit was proposed. A generalized calculation procedure based on this method was developed for sizing the orifices needed for balancing the coal / air flow. Efficient use of commercially available computational fluid dynamics (CFD) software was suggested for the calculation of the pressure drop in pipes with unclear specifications of geometries. The current industry practice is to balance the clean air flow and accept the resulting imbalance in the coal / air flow. By this new method the clean-air flow would be unbalanced in a tailored manner so that balanced coal / air flow would result. In order to implement this new method the power plants would still have to conduct clean air tests only.Copyright

An exact solution for batch sedimentation

Abstract An exact closed form solution to general equations of one dimensional particle/fluid two phase flow is obtained which describes an idealized version of batch sedimentation. This solution is then used to evaluate the accuracy of the commonly used quasistatic approximation.