Hoi Yeung

Guidelines for the use of ultrasonic non-invasive metering techniques

Abstract This paper provides a comprehensive set of Guidelines for the application of clamp-on transit time ultrasonic flowmeters to a wide range of industrial flows. These Guidelines have been drawn up in conjunction with users and manufacturers and sponsored by the United Kingdom’s Department of Trade and Industry. They represent the best practice to be used for the application of this technology to liquid metering. The Guidelines identify the range of possible non-invasive technologies which can be employed for the measurement of pipe flows and installation, pipework, fluid and operational effects on clamp-on transit time ultrasonic flowmeters, together with effects which may be specific to particular manufacturers. The paper concludes with the identification of further work which needs to be undertaken to strengthen the Guidelines.

Dynamic Modeling and Simulation of CO2 Chemical Absorption Process for Coal-Fired Power Plants

Post combustion capture via chemical absorption is viewed as the most mature CO2 capture technique. The effects of the addition of CO2 chemical absorption process on power plant performance have been studied using various steady-state models. However, there are several gaps in the understanding of the impact of post combustion capture on the operability of the power plant. These questions could be addressed by studying the dynamic behavior of such plants. In this study, dynamic models of the CO2 chemical absorption process were developed and validated. Dynamic analyses of the process reveal that absorber performance is sensitive to L/G ratio and that changes in reboiler duty significantly affect the regenerator performance.

Gas Void Fraction Measurement in Two-Phase Gas/Liquid Slug Flow Using Acoustic Emission Technology

The gas-liquid two-phase slug flow regime phenomenon is commonly encountered in the chemical engineering industry, particularly in oil and gas production transportation pipelines. Slug flow regime normally occurs for a range of pipe inclinations, and gas and liquid flowrates. A pipeline operating in the slug flow regime creates high fluctuations in gas and liquid flowrates at the outlet. Therefore, the monitoring of slugs and the measurement of their characteristics, such as the gas void fraction, are necessary to minimize the disruption of downstream process facilities. In this paper, a correlation between gas void fraction, absolute acoustic emission energy and slug velocities in a two-phase air/water flow regime was developed using an acoustic emission technique. It is demonstrated that the gas void fraction can be determined by measurement of acoustic emission.

Validation of a CFD Melting and Solidification Model for Phase Change in Vertical Cylinders

The complex nature of the phase change process makes the optimization of latent heat storage systems very difficult. A model that exists in Fluent CFD software for the modeling of melting and solidification can be employed for complex geometries. In this paper, comprehensive validation of this model for the modeling of melting in vertical cylinders was conducted, using well-documented experimental data and other numerical models from the literature. The model was able to predict the melt fraction with a maximum discrepancy of 7.5%. Comparison to other numerical models showed that the accuracy obtained is similar.

Production Potential of Severe Slugging Control Systems

Abstract The application of riser top valve choking in severe slugging control has shown that feedback control stabilises slug flow with a valve opening larger than manual choking, resulting in an increased oil production. However, the reason and ultimate potential for an active slug control system to increase oil production, as well as how to achieve this potential are still unclear. A systematic method based on the pressure bifurcation map of a riser system is proposed in this work to analyse the production and pressure loss relationship at the different operating points resulting from the various slug control strategies. It is shown that for a given unstable riser production system with known inlet and outlet boundary conditions, production loss or gain due to operation in stable or unstable operating conditions could be predicted by using a pressure dependent dimensionless variable known as production gain index (PGI). This gives a clear indication of the ultimate potential to increase oil production through feedback control. This analysis has been successfully applied to an industrial riser system modeled in the commercial multiphase flow simulator, OLGA. Production predicted by using the PGI agrees with actual simulated production. The analysis is based on the understanding that the closed-loop stable operating point must match the corresponding open loop unstable equilibrium point. This result is very significant in planning and implementing suitable control strategy for stabilizing unstable riser-pipeline production systems with the aim of achieving stability and ensuring increased productivity, especially for brown fields.

Techno-Economic Analysis of a Natural Gas Combined Cycle Power Plant with CO2 Capture

Abstract Power generation via natural gas is projected to increase over the next decade. CO2 capture would be required to mitigate the associated emissions. Integrating a capture plant to power plants can be explored via process simulation. Hence, high fidelity models of a natural gas combined cycle power plant and a post-combustion capture plant were built – a 440MW power plant model that is tuned and validated with data from GE’s GateCycle®, and a rate-based capture plant model that is scaled up from a previously validated model. Along with a suitably sized compression train, the plants are integrated for 90% CO2 capture. Net power output is observed to fall by 14%, but cooling water demand increases by 33%. A 40% exhaust gas recirculation (EGR) results in a marginal recovery in output, but also raises cooling water demand further. A redesign of the steam cycle to account for integration would potentially improve performance. Economic analysis is performed via a bottom-up approach. The integrated plant overnight cost is determined to be 45% higher than cost of the power plant without capture, but is only 43% higher with EGR. The cost of electricity also increases by 41% for the integrated plant, but by only 38% with EGR. Lastly, the cost of CO2 avoided is estimated to be €69 per ton of CO2, but reduces to €63 with EGR.

Approach flow direction effects on the cross-flow induced vibrations of a square array of tubes

Abstract Water tunnel experiments were conducted on a square array of tubes with a pitch ratio of 1·5. The array could be rotated about an axis perpendicular to the direction of flow so that the effects of incident flow direction on cross-flow tube response could be studied. Constant Strouhal number vorticity response was observed over a range of orientations with some Strouhal number dependence on orientation angle. While incident flow direction was found to have some effect on the fluid-elastic stability threshold, no dramatic changes, such as occurred for triangular arrays, were found. Experiments were also conducted to determine the stability behaviour of a single flexible tube in otherwise rigid arrays.

Mathematical Modeling and Optimal Operation of Industrial Tubular Reactor for Naphtha Cracking

Abstract The tubular reactor in a naphtha cracking furnace is modelled rigorously in this paper. The mathematical model can be used to predict product yields, coking buildup inside the tube wall, run length (i.e. the time between two consecutive decoking operations), residence time and pressure drop. A powerful modelling, simulation and optimisation tool gPROMS was chosen to implement the proposed work. This model provides detailed understanding of the naphtha cracking process. Steady-state optimisation was then applied to the operation of this industrial tubular reactor. The operating profit is maximised when the process gas temperature profile along the reactor and the inlet steam to naphtha ratio vary within certain ranges. The effects of coking on heat transfer, on reduction of manufacturing time and the decoking cost have been considered in the optimisation. Process simulation and optimisation based on this detailed model will give process engineers in the ethylene industry some insights on ethylene furnace design and operation.

The Stability of Fluid Production From a Flexible Riser

The prediction of slug formation and slug size has a direct impact on the design of topsides separation facilities and flow assurance to the process. The characteristics and stability of liquid production from an S-shaped riser have been studied over a range of pressures, focusing on the implications for flow management. Severe slugging in an S-shaped riser gives a period of no liquid production, followed by a period of steady production and finally a large production spike, many times larger than the steady production. In contrast with classical severe slugging in a vertical or catenary riser the transient spike is broken into two parts as a direct consequence of the bend in the line. Little attention has been paid to transition-type flows (between stable and unstable flow) previously. Data collected to date has shown transition flows have production peaks that are larger than those of classical severe slugging.

CFD Modeling of the Charging and Discharging of a Shell-and-Tube Latent Heat Storage System for High-Temperature Applications

In this study, a validated CFD model was employed for the simulation of the charging and discharging processes in a long shell-and-tube latent heat storage system suitable for high-temperature applications, such as solar thermal power generation. A shell-and-tube enclosure, having a height of 0.92 m and shell inner radius of 0.0325 m, was simulated. The results indicated that the effect of natural convection cannot be neglected during charging. The heat transfer rate during discharging, which is primarily dictated by conduction, is lower than that during the charging process and thus the design of such systems must be based on the discharging process. Models that neglect the effect of convection during discharging can predict the amount of heat discharged with a maximum discrepancy of 6%