00251034bfpt85210_cdfe00_11.pdf

ZUBAIR MISHRIF DGS FACILITY EXPANSION PROJECT FEED SERVICE ENGINEERING

FLARE/VENT THERMAL RADIATION AND GAS DISPERSION STUDY METHODOLOGY

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04/12/2017

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Date

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D. Costa

Description

Prepared

Company logo and business name

D.Rampoldi

D.Rampoldi

Checked

Approved

Company Document ID

00251034BFPT85210

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eni iraq b.v. Facility and Sub Facility Name ZUBAIR MISHRIF – New DGS and Water Injection Plant

Project name OPDS ZUBAIR OIL FIELD DEVELOPMENT

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FLARE/VENT THERMAL RADIATION AND GAS DISPERSION STUDY METHODOLOGY Software: Microsoft Word

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File Name: 00251034BFPT85210_CDFE00_11.doc

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REVISION LIST 00

Issue for Tender

HOLD RECORD

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TABLE OF CONTENTS 1.0 1.1

INTRODUCTION ................................................................................................................................................ 4 SCOPE OF WORK ................................................................................................................................................ 4

2.0

SCOPE OF THE DOCUMENT .......................................................................................................................... 5

3.0

ABBREVIATION LIST ....................................................................................................................................... 6

4.0

REFERENCE ........................................................................................................................................................ 7

4.1 4.2 5.0

PROJECT REFERENCE ......................................................................................................................................... 7 RULES, STANDARDS AND GENERAL REFERENCES.............................................................................................. 7 INPUT DATA........................................................................................................................................................ 8

5.1 GENERAL ........................................................................................................................................................... 8 5.2 BASIC DATA FOR FLARE DESIGN ......................................................................................................................... 8 5.3 ACCEPTABILITY CRITERIA .................................................................................................................................. 9 5.3.1 Heat radiation threshold values .................................................................................................................... 9 5.3.2 Toxic and/or flammable gas dispersion threshold values ........................................................................... 10 6.0 6.1 6.2 6.3

METHODOLOGY FOR FLARE SYSTEM VERIFICATION AND LAYOUT .......................................... 11 SCENARIO IDENTIFICATION .............................................................................................................................. 11 FIRE MODELLING.............................................................................................................................................. 11 FLAMMABLE AND TOXIC GAS DISPERSION MODELLING .................................................................................... 11

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1.0

INTRODUCTION

1.1

Scope of Work

00251034BFPT85210

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ENI has been awarded the Zubair project for the development of an oil field (ZUBAIR FIELD) in joint venture with, Korea Gas and Missan Oil COMPANY (as state partner), with Eni as operator. The Zubair project is a “brown field project”, with existing facilities and infrastructure. The field is currently in production. The Zubair Field Development Plan foresees the introduction of new facilities required for the ramp-up of the field and partial integration with the existing facilities. Zubair field is currently in production through 5 de-gassing stations (DGS) (one of them being Zubair Mishrif) plus Safwan flow station. In order to achieve the required overall revised ERP (Enhanced Re-development Plan) plateau of 700 kBOPD, in 2011-2013 a FEED and ITT Package (the “INITIAL FEED”) was issued to construct a new 5+1 DGS trains and Water Injection Plant in the Central Area of the Zubair field (Zubair Mishrif), while the existing facilities to be decommissioned. As the ITT relevant to INITIAL FEED was never awarded, the renewed strategy to achieve the plateau of 700 kBOPD is to construct additional 4 process oil trains (50 kBOPD each) and related facilities along with supporting utilities and Water Injection Plant, for which scope this ITT-3 is prepared. Moreover, with respect to the INITIAL FEED requirements, some facilities have been removed (such as Gas compression trains, additional spare equipment, etc…). As far as ITT-3 Project scope is concerned, reference shall be made to document “Scope of Work for EPC of Zubair Mishrif New DGS & Water Injection Plant” (doc. N° 00251034BGSC09304).

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2.0

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SCOPE OF THE DOCUMENT Flare system of new Zubair Mishrif DGS consists of three pressure levels: •

High Pressure (HP) Flare

•

Low Pressure (LP) Flare

•

Atmospheric Pressure (ATM) Flare

For each level, a dedicated Flare Package is already procured by COMPANY.Therefore, the scope of this document is to define the methodology to check the already purchased Flare packages and then define the Flare system positioning inside Plant area of Zubair Project. This methodology is in accordance with API standard 521 (Ref. [2]), and HSE Risk Management (Ref. [3]). The Flare system layout shall be defined on the basis of relieves from venting and emergency devices and in order to match the threshold values established for heat radiation and toxic and/or flammable dispersion.

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3.0

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ABBREVIATION LIST DGS ER BOPD RP ½ LFL

Degassing Station Enhanced Re-Development Barrels of Oil per Day Rehabilitation phase Half of Lower Flammability Limit

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4.0

REFERENCE

4.1

Project Reference

00251034BFPT85210

Reference [1]

4.2

00251034BFRB85001

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Title Loss prevention basis of design

&

environment

Rules, Standards and General References

Reference [2] [3] [4] [5]

ANSI/API standard 521, “Pressure-relieving and depressuring systems”, fifth edition, 2007. ENI E&P Division, “HSE Risk Management”, 2004. Softbis Consltants LTD, FLARESIM 4.0 DNV-Det Norske Veritas, “PHAST 7.1”

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5.0

INPUT DATA

5.1

General

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The primary function of a flare is to use combustion to convert flammable, toxic, or corrosive vapours to less hazardous compounds. It shall be designed considering the threshold values of radiant heat and toxic and/or flammable gas dispersion in order to allow also maintenance operations. The DGSs of Zubair Oil Field will be characterised only by the Emergency Flaring Mode: during this period the gas produced in the DGSs will sent to battery limit; the flares will be used only in case of emergency. The flare system is based on the Relief, Blowdown and Flaring Philosophy

5.2

Basic data for flare design

The basic data for flare design shall be in accordance with “Loss prevention & environment basis of design” (Ref. [1]). They are reported in Table 1. Value

Radiation Study

Dispersion Study

Ambient Temperature Air Humidity Wind Velocity/Pasquil Stability Class Ambient Temperature Air Humidity Wind Velocity/Pasquil Stability Class

34.6°C 36.2% 10 m/s / C 25°C 50% 2 m/s / F 6 m/s / D 10 m/s / C

Table 1: Basic data for Flare Radiation and Dispersion Studies.

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5.3 5.3.1

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Acceptability criteria Heat radiation threshold values

Heat radiation is the controlling factor in the spacing of the flares. Table 2 presents recommended design total radiation levels for personnel at grade or on adjacent areas.

Table 2: Recommended design thermal radiation for personnel. According to API 521(Ref. [2]), a solar-radiation-contribution adjustment to the values given in Table 2 shall be evaluated on a case-by-case basis. While an adjustment of 0.95 kW/m2 (solar radiation assumed in Iraq: see Ref.[1]) to a 6.31 kW/m2 level has a relatively small impact on flare cost, the same adjustment to a 1.58 kW/m2 level results in a significant increase in cost. Considering that the solar radiation spectrum is better accepted by the skin, it is suggested to consider the solar contribution only for the radiation greater than 1.58 kW/m2. In the following table the maximum permissible radiation levels are summarized:

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Heat radiation limits

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Note

8.51 kW/m2

The flare base is considered as the location where emergency action by personnel (with special protective Radiation Limit at apparel) is allowed. the flare base Therefore the heat radiation limit at the flare base shall be (9.46 - 0.95) 8.51 kW/m²

5.36 kW/m2

At the boundary of the sterile area the heat radiation shall be at the most 6.31 Radiation Limit at kW/m², including the effect of solar the Perimeter of radiation. Sterile Area Therefore the heat radiation limit at the boundary of the sterile area shall be (6.31 - 0.95) 5.36 kW/m² At maintenance points the heat radiation shall be at the most 4.73 kW/m², including the effect of solar radiation.

3.78 kW/m2

Therefore the Heat radiation limit at Radiation level at maintenance points shall be (4.73 - 0.95) maintenance point 3.78 kW/m² This value will be used to spacing the flares of a group, the access road and the position of the ignition panel.

1.58 kW/m2

At points where personnel could be present for long time the heat radiation shall be at the most 1.58 kW/m² Radiation Limit for excluding the effect of solar radiation. points where personnel could be This value will be used to spacing a present for long group of flares from the other group, to locate the fence of the flare area and to time define the position of the interlock manual valve used to switch the gas flow from one flare to its spare. Table 3: Maximum permissible heat radiation levels

5.3.2

Toxic and/or flammable gas dispersion threshold values

In Zubair Project there are not toxic substances, so the toxic gas dispersion will be not evaluated. The flammable gas dispersion threshold values, established as the concentration of flammable components at limit of process plant area, shall be less than ½ LFL (the half of Lower Flammability Limit).

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6.0

METHODOLOGY FOR FLARE SYSTEM VERIFICATION AND LAYOUT

6.1

Scenario identification

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Flare system design loads shall be identified analyzing all general emergency scenarios (such as general power failure, IA failure, fire, etc.), single emergency and all possible simultaneous flaring. The design relieving flowrate for heat radiation study shall be selected considering the one with the higher thermal heat content, in terms of mass flowrate and Lower Heating Value. Flare packages design verification and flare system layout determination. For each of the three Flares, the following steps shall be performed on the basis of the selected relieving design cases: • verification of riser diameter for maximum Mach number and allowable pressure drop (Flare packages are already procured) • Individuation of the best Flares layout that matches the heat radiation and dispersion thresholds requirements considering also potential simultaneous flaring, using Flaresim software. • In addition to the selected emergency relieving scenario Process data, Flaresim input data are: • Environmental parameter • Riser base plate elevation above ground • Riser Length and diameter • Tip Length and diameter The layout of the New Flares shall respect the threshold values and the criteria reported in section 5.3.1 in addition to the below: 6.2

Fire modelling

The heat radiation of the flare system shall respect the criteria reported in section 5.3.1. On the basis of the reached heat radiation values, the perimeter of the sterile area, maintenance area and the fence of the flare systems will be defined. The assessment of the thermal radiation levels originated by flares will be carried out using an extension of API model (Ref. [2]) implemented in software Flaresim (Ref. [4]).

6.3

Flammable and toxic gas dispersion modelling

In case of accidental flame out, the following features shall be investigated: • • •

the extension of flammable envelopes corresponding to ½ LFL concentrations. In particular it will be determined: the maximum downwind distances reached by flammable envelope curve corresponding to ½ LFL concentration; the minimum elevation from flare base reached by flammable envelope curve corresponding to ½ LFL concentration.

The flammable envelopes corresponding to ½ LFL concentrations shall not reach areas where personnel or ignition sources could be present. The dispersion calculations shall be performed using the software DNV Phast (Ref. [5]).

This document is property of eni Iraq B.V. It shall neither be shown to Third Parties not used for purposes other than those for which it has been sent.