HiPGaS 1: Experimental characterisation of fluid parameters in real systems

Objectives

To perform experiments on phase equilibria and phase properties for hydrocarbon systems and aqueous phases containing gas-treating chemicals such as glycol and amines, and to get the new experimental knowledge systemised into appropriate thermodynamic models. Experiments will be performed at relevant operating conditions for high-pressure gas processing equipment.

Background and scope of work

All process design and equipment design in gas processes is normally based on steady state simulations, where heat and mass balances are established and phase properties are generated. The process streams contain hydrocarbon mixtures in supercritical or sub critical state. Representative process streams may also contain significant amounts of water and gas treating chemicals such as glycol, methanol and amines, in addition to traces of other oil or gas treating chemicals that might have been added for specific purposes during the exploitation.

The three-phase performance of existing calculation models is not satisfactory for the different relevant mixtures. None of the published models are for instance capable of predicting hydrocarbon, glycol, and water liquid/liquid equilibria. New experimental data for thermodynamic equilibrium in relevant systems are needed. The solubility of different classes of hydrocarbons, and different molecule sizes, in different water/chemical solutions varies significantly. The presence of water and chemicals in the system will therefore result in gas/liquid (HC)/liquid (aqueous) equilibrium distributions and compositions that are specific for each hydrocarbon system. The added chemicals will also influence on phase properties, which forms an essential basis for the equipment design. A tentative plan for the doctoral study could be:

1. Strategy for extended hydrocarbon characterisation that accounts for water/chemical-hydrocarbon mutual solubility. Corresponding thermodynamic modelling.
2. Measurement of equilibrium compositions in representative three-phase systems of hydrocarbon and aqueous phase containing different gas treating chemicals. Corresponding phase equilibrium modelling.
3. Measurement of apparent density (average density for liquid with entrapped distributed gas).
4. Measurement and modelling of interfacial tensions.
5. Measurement and modelling of viscosity.

Most of the experimental work involved can be accomplished using standard high-pressure equilibrium cells. Special attention has been devoted to the sampling and analysis of the equilibrium liquid phases.

Supervisors:

Bjørn Kvamme (UiB) in collaboration with Hallvard F. Svendsen (NTNU) and Arne Olav Fredheim (Statoil).

Affiliation:

University of Bergen, Department of Physics

Author: Hallvard F. Svendsen

HiPGaS 2: Experimental characterization of wire mesh demister operated at high pressure

Objectives

To develop experimental equipment, and to investigate fundamental mechanisms for droplet deposition and droplet re-entrainment on liquid films and on surfaces. The equipment will be designed in such a way that experiments can be performed at relevant operating conditions for gas processing equipment, e.g. for high pressures.

Background and scope of work

Entrainment of liquid into gas streams is one of the main problems experienced during operation of gas-separation equipment. By this is meant both droplet entrainment and liquid entrainment by foam. Most of the available experiments have been performed on air-water system or other model-fluid systems. In order to understand the entrainment-deposition and coalescence mechanisms for liquid droplets in real equipment, experiments have to be performed with realistic fluid parameters, such as gas-condensate-water composition, pressure and temperature. The experiments will be performed on a micro scale level.

The entrainment-deposition phenomena will be observed by use of visualisation techniques (for instance by high-speed video camera) and quantitatively measured by use of different techniques like filtering or iso-kinetic sampling. Measurements of droplet size distribution and droplet velocity are also planned.

The measurements will be performed in a high-pressure gas loop, with an optical section where liquid is introduced directly or through the gas flow itself. Additional fluid characterisation measurements, such as interfacial tension, will also be performed in order to link measured entrainment and visual observations to measured fluid parameters.

The deposition and re-entraiment rate will be measured as function of different parameters, such as fluid properties, flow velocities, geometrical properties and surface characteristics. Mixtures with two liquid phases (aqueous and hydrocarbon) and additional foam phases will be introduced.

The results will form an important basis for design of de-misting internals in gas separators.

Supervisors:

Hallvard F. Svendsen (NTNU) in collaboration with Kai Hjarbo (SINTEF) and Rune Engeskaug (SINTEF).

Affiliation:

NTNU, Department of Chemical Engineering

Author: Hallvard F. Svendsen

HiPGaS 3: Experimental Characterisation of Multiphase Separation in High-Pressure Vertical Gas-Scrubbers

Objectives

To characterise the multiphase flow in a vertical three-stage gas scrubber, and to develop a fundamental understanding of how the flow pattern and hence the separator performance, is affected by different relevant parameters like e.g. pressure, fluid properties and geometry.

Background and scope of work

Within the supply industry, there seems to be quite good knowledge on the separation performance for different separator units within a gas scrubber. However, the efficiency-predictions seem to be based on lab-tests done separately for each demisting unit, under near ideal flow conditions and low pressure. For instance, a spray nozzle is often used to create a uniform gas-liquid distribution for the inlet of the actual demisting unit being tested. The understanding of what is affecting the separator performance, when the different units are combined in a gas scrubber, seems to be unclear and undescribed. CFD-models exist, but they don’t seem to reflect the situation in gas scrubbers that are in daily operation. This project will therefore focus on the relevant aspects of separator performance for a composite and complete scrubber, and not just the different demisting units. It is vital to understand all uncharted conditions in order to both develop CFD-models and design rules for gas scrubbers. Several parameters will be manipulated to investigate the effect on the multiphase flow and hence the scrubber performance. These parameters can include:

Pressure effects. In both lab-scale and large-scale applications, the pressure will be varied in order to identify effects on flow pattern and separation efficiency. These effects could for example be density changes or surging.

Geometry effects. By varying the mutual distance between the separator units and also the size of the units, the resulting change in flow pattern will affect the separator efficiency.

Scaling effects. Results achieved from lab-scale testing would be tested on large-scale equipment in order to verify the results or to identify possible deviations as a result of large-scale geometry. Wall effects like for instance liquid film deposition, is expected to have a larger impact on the flow pattern in a small diameter separator than in a large diameter separator.

Effects from varying fluid properties. Fluid properties like density, viscosity and interfacial tension, would influence the separation efficiency. This project would focus on 2-phase hydrocarbon mixtures, with and option to extend the tests to include a third phase containing i.e. a water-glycol mixture.

Effect from varying gas-liquid ratios and rates.

Supervisors:

Alex Hoffmann (UiB) in collaboration with Lars Henrik Gjertsen (Statoil)

Affiliation:

University of Bergen, Department of Physics

Author: Hallvard F. Svendsen

HiPGaS 4: Modelling of dispersed systems, coalescence and break-up of droplets and liquid films

Objectives

To develop models for the physical processes of droplet/droplet and droplet/liquid surface coalescence and for droplet and liquid film break-up. These models will form the basis for a population balance model to be implemented into the fluid dynamic models described in HiPGaS 5.

Background and scope of work

The physical mechanisms that, apart from the flow in separation equipment, determine the efficiency of any separator, are the mechanisms that affect the droplet size distribution and the ease at which droplets adhere to and coalesce with already existing liquid surfaces. This PhD concentrates on describing the mechanisms involved in the coalescence of two droplets colliding with each other or a droplet colliding with a liquid surface. The film drainage and final rupture will be described. This is also highly relevant for foam formation and foam destabilisation. In high-pressure separation equipment the flows experience both pressure and temperature variations. This leads to non-equilibrium situations and the effect of mass transfer, in the form of component transfer or condensation/evaporation, will be included. Also the effect of added chemicals and solids will be analysed. In addition, models for droplet break-up and re-entrainment caused by flow shear and turbulence will also be developed. Together these models will be developed into a population balance model of such a nature that it can directly be included into CFD codes. The suggested PhD builds on two previous PhD's that have come a long way in solving this problem and parts of the earlier work has already been incorporated into an existing commercial code, CFX. However, improvements are needed before a complete coalescence/break-up model with good predictive power is established.

The modelling work will be verified using data from HiPGaS 3 and the basic understanding of the coalescence and break-up processes is linked to HiPGaS 2.

Supervisors:

Hugo Jakobsen (NTNU) in collaboration with Hallvard F. Svendsen (NTNU) and Pavel Havelka

Affiliation:

NTNU, Department of Chemical Engineering

Author: Hallvard F. Svendsen

HiPGaS 5: Fluid dynamic modelling of high-pressure gas/liquid separation, droplet deposition and re-entrainment

Objectives:

Develop flow models for the various types of separation equipment, vane packs, demisters and cyclone separators, and to include in them models for droplet deposition and re-entrainment . The fluid dynamic model will be coupled with closure models on macro scales for coalescence, break-up and droplet phase mixing mechanisms. These closures will be based on the physical understanding of the mechanisms involved on micro- and meso scales, as analysed in HiPGaS 2 and 4.

The numerical model will be validated with experimental data on liquid volume fraction, droplet size distributions and droplet velocities at various local positions in the separator as well as by in- and outlet data. The model predictions will also be compared with estimates of internals efficiencies at different operating conditions.

Background and scope of work:

Fluid dynamic modelling of high pressure gas/liquid separation design can significantly help to reduce the experimental efforts required to develop design rules for and to optimise industrial separator equipment. However, any fluid dynamic model must be properly validated in order to produce reasonable predictions of the equipment operation and internals effectiveness.

Models of very different complexity can be applied describing the physical phenomena involved. In an early stage of the PhD study the candidate will thus analyse the physical problem to enable an optimal choice of model framework being a trade off between computational requirements and modelling accuracy. It is sometimes convenient to apply models of very different complexity to describe different parts of the separator equipment. For the description of droplet deposition and re-entrainment on equipment walls and internals, detailed models are needed including interfacial transport phenomena, whereas for macro scale calculations it may be possible to reduce the model resolution considerably.

To be able to take into account effects of non-ideal thermodynamics, the extended flow models will also be coupled with rigorous thermodynamic modules.

The work will end up in a numerical description of droplet size distributions and thermodynamics implemented into a fluid flow solver, enabling predictive simulations of the separator equipment.

Supervisor:

Stein Tore Johansen (NTNU) in collaboration with Hugo A. Jakobsen (NTNU)

Affiliation:

NTNU, Department of Applied Mechanics, Thermodynamics and Fluid Dynamics

Author: Hallvard F. Svendsen

Post doc. programme

The work will be directly associated with the PhD programme and particularly with HiPGaS 2 and possibly HiPGaS 3. It will thus focus on the experimental investigation of droplet coalescence and breakup, and droplet deposition and re-entrainment. The post doc. will be instrumental in the choice, design and erection of the small-scale high-pressure laboratory. It is therefore of importance that applicants for this position have both good theoretical and experimental background in the field.

Another early task of the post doc. will be to establish a working database on existing design criteria and operational procedures for gas scrubbers, used by the industry and found in the open literature. Into this database will also be entered information on the performance of gas scrubbers. The information gathered is to be critically evaluated and commented with the aim of extracting as much information as possible for improved understanding and for verification of developed models and procedures.

Affiliation:

NTNU, Department of Chemical Engineering

Author: Hallvard F. Svendsen

Contact Address for HiPGaS

All enquiries regarding the HiPGaS program should be directed to:

Prof. Hallvard F. Svendsen
Department of Chemical Engineering, NTNU
NO-7491 Trondheim
NORWAY
Telephone: +47-73594100
Fax: +47-73594080
e-mail: Hallvard.Svendsen@chemeng.ntnu.no

Responsible: Elisabeth Thorbjørnsen