A. M. Al Taweel

Thermodynamic simulation and evaluation of a steam CHP plant using ASPEN Plus

A steam power plant thermodynamic model developed using the ASPEN Plus shell is presented. The model is validated using field data from two units, one with a capacity of 105 MWe and the other 150 MWe. The model is then modified and used to evaluate the thermodynamic feasibility of servicing a small (less than 20 MWt) thermal load in addition to generating electricity.

Modeling of heat recovery steam generator performance

The performance of the heat recovery steam generator (HRSG) strongly affects the overall performance of a combined-cycle power plant. An accurate simulation of the performance of the HRSG is therefore necessary to analyze the effects of various design and operating parameters on the performance of combined-cycle power plants. Unfortunately, there are many sources of uncertainty and operational variance which prevent the accurate prediction of the HRSG performance. Furthermore, the prediction of heat-exchanger performance is based on assumptions about flow patterns. Empirical correction for departures from these assumptions is not possible in cases where the benefits of new geometrical configurations are to be explored. A numerical method was developed to predict the performance of the HRSG in a fashion that accounts, as much as possible, for the design and operation constraints, while keeping computational complexity manageable. The method is intended for use in performance-simulation models of advanced power cycles, since its accuracy is acceptable without requiring large computational resources. The method was used to simulate the pressure, temperature, steam quality and heat-flux distributions in a commercially available HRSG (operating under full- and part-load conditions). The predicted results were found to compare well with measurements obtained on full-scale units.

Simulation of combined cycle power plants using the ASPEN PLUS shell

Abstract A computer simulation model in ASPEN PLUS shell has been developed to simulate the performance of IGCC and IGHAT cycle power plants. The model was used to study the effects of design and performance parameters on the efficiency and emissions from IGCC and IGHAT cycles. The simulation models are capable of performing mass, energy and exergy balances which may be used to trace system inefficiencies to their source component thereby providing insights into component interactions within the cycles and act as pointers to system optimization trade-offs.

Drag coefficient for axisymmetric flow around individual spheroidal particles

Abstract A correlation relating drag coefficients for spheroidal particles to Reynolds number and aspect ratio has been developed. Regression analysis was performed on available data; the resulting expression is capable of accurately predicting drag coefficients over a Reynolds number range of 1 to 200 with the aspect ratio varying from 0.2 to 5.

Dependence of separation properties on flocculation dynamics of kaolinite suspension

Abstract Solid–liquid separation is widely done by polymeric flocculation. But very little fundamental information is available for sheared suspension. In this work, online measuring of the particle number concentration, floc size and floc size distribution has been done in stirred suspension to understand the effects of addition of flocculant in stages, agitation speed and time, pH and solids loading in a kaolinite suspension on formation, growth, breakage and conformation of flocs and finally on separation properties, namely, turbidity of the suspernatant, capillary suction time (CST) and specific resistance to filtration (SRF). The exact amount of flocculant required for optimum results can be determined by stage addition of flocculant. The best separation properties are obtained from the flocs which can withstand shear for a long time. Higher agitation speed reduces the mean floc size and narrows the size distribution.

Beneficiation of Coal Fines by Aggregative Flotation

Abstract The effect of various operating parameters on the performance of the aggregative flotation process for beneficiating coal fines was investigated. The recovery of carbonaceous matter was found to be improved by high mixing intensity and by the utilization of preemulsified collector in the aggregate formation stage. The presence of salt in the flotation stage was found to enhance recovery of the aggregates and the use of a three-stage aggregative flotation technique was found to recover more than 95% of the carbonaceous matter while rejecting 94% of the liberated ash (67% of the total mineral matter). This was accomplished using 2 kg of kerosene per tonne of coal while, in contrast, conventional flotation techniques yielded a recovery of 47% at a collector dosage of 7.5 kg/t.

Estimation of bubble size in flotation columns

Abstract A non-iterative procedure for the estimation of bubble size in flotation columns is presented. In a bubble swarm, the bubble terminal rise velocity is estimated using an appropriate drift flux relation which depends on the frother type. For Dowfroth 250C, MIBC and Triton X-100, these drift flux relation were found to be those of Marrucci [1], Turner [2], and, Richardson and Zaki [3] respectively. By using dimensionless groups in the correlation procedure, dimensionally consistent correlations are presented. The analysis shows that in the presence of frothers, the drag coefficient of the air bubbles increases. This is attributed to surfactant adsorption at the gas-liquid interface.

Determination of the kinetic parameters of oat straw using thermogravimetric analysis

Abstract Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) techniques were used to study the thermochemical behaviour of three varieties of oat straw (Sentinel, Shaw, and Tibor). The thermal degradation of oat straw was studied in an oxidizing atmosphere (15% oxygen and 85% nitrogen) from ambient temperature to a temperature of 700°C using a heating rate of 20°C min−1. Two distinct reaction zones were observed on the TGA and DTA curves. The kinetic parameters (order of reaction, activation energy, and pre-exponential factor) were determined for each zone separately by applying thermo-analytical techniques to the reaction kinetics. Higher thermal degradation rates were observed in the first reaction zone due to rapid release of volatiles as compared to those in the second reaction zone. The activation energies were in the range of 83–102 and 58–75 kJ mol−1 for the first and the second reaction zones, respectively.

Influence of the surface characteristics of coal on its flotability

Abstract The flotability of coal was found to be strongly dependent on both its particle size and surface characteristics. A criterion for quantifying the average hydrophobicity of coal is proposed and a mechanistic interpretation of coal flotation data is presented. The flotation of small particles is mainly controlled by collision probabilities, whereas that of large particles was found to be strongly influenced by the strength of bubble/particle attachment forces.

Motion of hydrodynamic aggregates

Abstract The motion of hydrodynamic aggregates is analyzed with a particular emphasis on the effects size, shape and porosity have on the settling velocity. The model presented was found to agree quite well with the low Reynolds number data obtained with solid/liquid systems. It is also capable of presenting a phenomenological explanation that is consistent with many of the observations reported for gas/solid systems.