Travail de fin d'études et stage[BR]- Travail de fin d'études : Validation of the natural circulation calculation in the high-pressure evaporator of a horizontal heat recovery steam generator subjected to high heat flux[BR]- Stage

Abstract

The aim of this thesis is to improve the circulation model of horizontal heat recovery steam generator evaporator with natural circulation used at John Cockerill. In this type of boiler, it is essential to have an accurate circulation model. Indeed, in natural circulation, the flow in the evaporator is only ensured by the boiler design because no pump allows the flow circulation.

In this report, a detailed description of the recovery boilers and the circulation model currently in use is presented with a focus on the pressure drop calculation. Different ways to improve the model are explored.

Firstly, the impact of radiation on pressure drop in evaporator tube is studied. It is concluded that it can increase or decrease the pressure drop depending on some conditions.

Then, a study of the flow pattern of two-phase flow in vertical tubes is done because the present John Cockerill's model takes only in charge the horizontal tubes.

Moreover, different pressure loss correlation models for two-phase flow in tubes are described and compared. The target is to choose one of them that could replace the correlation currently used at John Cockerill.

Finally, several pressure drop correlations in tees and bends are introduced and compared. It highlights some gaps between models for two-phase flow in bends. In tees, a more accurate pressure drop correlation than the one currently used is also analyzed.