8.3 dispersion modelling strategy

8/12/2019 8.3 Dispersion Modelling Strategy

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KCP-ENT-SHE-REP-0001Revision: 05

Project Title: Kingsnorth Carbon Capture & Storage Project Page 1 of 4

Document Title: Dispersion Modelling Strategy

Kingsnorth CCS Demonstrat ion ProjectThe information contained in this document (the Information) is pr ovided in good faith.E.ON UK plc, i ts subcontractors, subsidiaries, aff i l iates, employees, advisers, and the Department of Energy and Climate Change (DECC)make no representat ion or warranty as to the accuracy, rel iabil i ty or completeness of the Information and neither E.ON UK plc nor any of i tssubcontractors, subsidiaries, aff i l iates, employees, advisers or DECC shall have any l iabil i ty whatsoever for any direct or indirect losshowsoever arising from the use of the Information by any party.

Dispersion Modelling Strategy


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1. Introduction

Although dispersion modelling of gases and liquids emitted from vessels and pipelines as part of asafety risk assessment has been undertaken routinely by Industry for several decades, carbondioxide, CO2, presents a number of new challenges to dispersion models due to its particular thermo-dynamic properties.

This document describes the approach that will be taken by the ENT modelling team to ensure thatCO2dispersion modelling undertaken in support of the Kingsnorth CCS demo project is of a bestpractice standard, taking into account current understanding and research in what is a rapidlydeveloping area of research activity.

2. Selection of Dispersion Models

The project will make use of validated commercially available computer models where this is possible,taking into account the availability of such models. The following models will be used:

The PHAST dispersion model ( version 6.54 and the new revision 6.6 ) under licence from Det NorskeVeritas (DNV) will be used to make predictions of CO2concentrations at sensitive receptorsintercepted by the plume from a leaking CO2source, where this is an appropriate model to use.PHAST will be used to assess the extent of adverse CO2concentrations, for appropriate leakagescenarios from pipeline and other storage vessels under most circumstances but may not be suitablefor dispersion analysis in heavily built-up areas of plant or areas of varying topography.

Computational Fluid Dynamics (CFD) will be used to supplement the use of the PHAST model. It isexpected that this will primarily be when assessing CO2flows around buildings on the power plant siteas part of a safety risk assessment, and situations of potential CO2accumulation such as certaintopographical features. A commercial code,Ansys-CFX, will be used as the software platform and avirtual model of the plant layout will be built using information from the design layout team. Ansys area US company with a range of engineering software. Ansys-CFX is a general purpose CFD code,which includes models for particle transport, heat transfer and combustion. ENT has used this codeand its predecessors since 1994 and applied it to a wide variety of power plant problems from gasturbine blade heat transfer to coal combustion. Of particular relevance, ENT has done a number ofstudies of high pressure gas leaks in GT enclosures for safety case-making, and a similar approach,but with modifications for CO2, will be used in these studies.

CFD modelling will also be used to test various assumptions implicit in the PHAST dispersion model,in order to increase the confidence of the PHAST predictions. In particular, the sensitivity ofassumptions made regarding rate of sublimation of solid CO2formed in the initial jet of a CO2leak tothe subsequent dispersion will be examined.

Specified Level Of Toxicity (SLOT) and Significant Likelihood of Death (SLOD) distances will becalculated, as required and defined by the Health and Safety Executive (HSE).

3. Source Term Methodology

The thermodynamic properties of pure CO2are well known at all pressures and temperaturesconsidered likely during the CCS process. However, it is generally acknowledged that techniques for

predicting the rate of release of high pressure CO2from a pipeline or other containment vessel and itsphysical form after release are not so well established. As a consequence, the risks from subsequent


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dispersion of the CO2will be less easy to assess if based on overly conservative or poorly definedsource terms. An understanding of the sensitivity of model predictions to the physical approximationsused is also important in assessing the significance of model output.

At the time of writing, calculation of the source term for leaking CO2has not been standardised. Priorto the Kingsnorth CCS demo project, ENT had already made significant progress in developing asource term methodology taking into account the known physics and thermodynamics of CO2systems. This methodology will be used in the project. The methodology is developed from a reviewof research literature on the subject, and is compatible with published guidance such as that producedby the Energy Institute (EI) and Carbon Capture and Storage Association (CCSA) [1], or DNV, [2].

The methodology will be applicable across the range of conditions expected for CO2in pipelines orstorage vessels relevant to the Kingsnorth CCS demo project ( encompassing both gaseous, liquid

and dense phase conditions ). The methodology has been designed to be suitable for bothcommercial Gaussian-type dispersion models such as PHAST (where it is practical to do so) and theCFD-based models developed within ENT for the project.

A short description may be found in [3].

4. Internal Sources of Information

E.ON R&D Low Carbon Programme has supported internal research on CCS technologies for thepast 5 years. This initiative has enabled the accumulation of a significant amount of in-houseknowledge on CCS. Of relevance here is research assessing the fundamental properties of capturedCO2and their significance in relation to CO2handling and pipeline transportation and also the issuessurrounding accidental releases of CO

2. Information from relevant projects in the internal E.ON UK

programme will provide a source of supporting information and provide the basis for the methodologydescribed in section 3.

5. External Sources of Information

There is currently very little publicly accessible experimental data on CO2releases of the magnitudeand physical characteristics expected from a dense phase CO2pipeline or vessel failure. A number ofcollaborative projects are being planned, and one or two have recently commenced e.g.CO2PIPETRANS II. This means that validation of CO2dispersion models, particularly with regard toprediction of leakage rates and thermo-dynamic properties of plumes is not as well developed aswould ideally be the case.

Opportunities to attend external workshops on CO2modelling will be taken in order to ensure themodelling undertaken is up-to-date and using any new consensus over best practice.

In the likely event that E.ON becomes a consortium member of collaborative R&D projects whichundertake experiments to verify CO2dispersion models , such data or information as is availablewithin the time scale commensurate with the UK Government Competition, will be used to support themodelling techniques used.

E.ON is participating in the DNV Joint Industry Project (JIP) CO2PIPETRANS II. It is intended thatinformation which comes out of this project will be used to inform the dispersion modelling techniqueswhich will be employed in the pre-FEED (FEED 1A) or FEED studies, subject to this information beingavailable in time.

CO2PIPETRANS II builds on an earlier phase 1 of the JIP and also on previous DNV experience of


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similar CO2 experimental work. Objectives within the project of particular relevance here are listedbelow.CO2PIPETRANS II project will:

Undertake an experimental programme to enable depressurisation, release and dispersionmodel developers and modellers to develop test and validate their models across arepresentative range of CCS dense phase CO2 scenarios.

Collate and share the collected data and experience with the JIP participants so that they gainmaximum value from the activities undertaken.

Package and share sufficient data sets of the captured experimental data along withsupporting information to enable the modelling community to develop and validate theirmodels for use within CCS development projects,

Document the work undertaken and actively disseminate the knowledge gained bothinternally within the JIP and on a wider (external) basis

The project will also be looking at potential failure modes of pipelines; materials selection; andthermo-dynamic properties of CO2mixtures

Opportunities for early participation in this project will be identified. Of particular value areexperimental results from projects already undertaken by members of project which will be madeavailable to CO2PIPETRANS II.

6. Modelling Scenarios

Data relating to the operating conditions of the Kingsnorth capture plant, compressors andpipeline will be obtained from the relevant engineering teams. The site layout and pipeline routeinformation will be obtained from the design layout team and pipeline design contractorrespectively. The scenarios to be modelled will be based on the conclusions of HAZID studies

undertaken by the Kingsnorth CCS team using data from the afore-mentioned sources.

7. Communication with the Health and Safety Regulator

A dialogue with HSE experts on the methods and techniques to be employed in the application ofdispersion modelling and in the broader area of risk assessment will be maintained whereappropriate.

8. References

[1] Technical Guidance on Hazard Analysis for Onshore Carbon Capture Installations & OnshorePipelines

CCSA and Energy Institute 2010 Draft

[2] Mapping of potential HSE issues related to large-scale capture, transport and storage of CO2DNV Report no: 2008-1993

[3] Understanding the Consequences of CO2Leakage Downstream of theCapture PlantT A Hill, J E Fackrell, M R Dubal & S M StiffGHGT-10 2010 conference proceedings draftEnergy Procedia

8.3 dispersion modelling strategy

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