Feasibility Study – Process Detail

1. Feasibility Study – Process Detail 6th May 2010

2. NG View • Enhance process information to provide greater clarity / transparency • Streamline process – provide templates • Provide enhanced indicative timescales & costs • Revised terms and conditions • Set timescales ? – costs and benefits

3. Contents • Why undertake any analysis? • UK’s gas supply and demand requirements • Commercial and operational drivers • Legislation • What is transient analysis? • Study Categories and associated timescales and costs • Uncomplicated • Intermediate • Complex • Project process • Transient analysis case study

4. Why undertake any analysis? In operating the NTS pipeline system National Grid NTS has to satisfy a wide range of the legal, regulatory, gas supply, commercial and operational requirements Large and rapid changes in operational parameters (offtake rate, ramp rate, pressure, etc.) due to supply variations, demand changes, compressor operations etc. may impact on the operation of the NTS pipeline systems and National Grid assets: Affect the efficient and effective operation of the pipeline system - lead to transient flow variations Trigger safety devices and cut off supply at the installation Cause damage to National Grid equipment at installations such as pressure regulators, filters and orifice plate meters Adversely affect other Users of the system (entry and exit points) in the vicinity

5. UK’s gas supply and demand requirements The NTS pipeline network is continually expanding to meet the UK’s gas supply and demand requirements Increasing number of supply and demand scenarios have to be considered and accommodated Flows through the pipeline network were historically North to South - now it has to be capable of flows East to West and West to East as well Increasing number of new entry points, storage sites and large exit connections (e.g. power stations)

6. Commercial and operational requirements Power station operation has changed over the years due to changes in the electricity commercial regime (i.e. the New Electricity Trading Arrangements (NETA) etc.) Many power stations were originally designed for “base load” operation but now operate in other modes (e.g. “2 shifting” etc.) Power station technology has developed over the years to be more efficient (increased flow requirement) and have greater flexibility As a result Customers are requesting changes to operating requirements to remain competitive

7. Legislation Health and Safety at Work etc. Act 1974 Applies to all persons involved with work activities, including employers, the self employed, employees, designers, manufacturers, suppliers etc. as well as the owner of premises Places general duties on such people to ensure, so far as is reasonably practicable, the health, safety and welfare of employees and the health and safety of other persons such as members of the public who may be affected by the work activity Pipeline Safety Regulations (PSR) 1996 Regulation 5 covers “Design of a pipeline” and National Grid are required to ensure that the design of a pipeline or any modification to it, takes into account the operating regime for the pipeline and the conditions of the fluid to be conveyed Pressure Systems (Safety) Regulations (PSSR) 2000 Imposes duties on designers, manufacturers etc. to ensure pressure systems are fit for purpose, so as to prevent “danger” (e.g. Regulation 4) Responsibility on National Grid to ensure Safe Operating Limits (SOLs) of our equipment and the Customer’s are not exceeded

8. Pressure Systems (Safety) Regulations 2000 The Approved Code Of Practice (ACOP) issued by the HSE (publication L122) provides further information on Regulation 4 which covers “Design and construction” Paragraph 58 states: “The designer, manufacturer, importer or supplier should consider and take due account of the following, where applicable: (c) all extreme operating conditions including start-up, shutdown andreasonably foreseeable fault or emergency conditions; (e) any foreseeable changes to the design conditions; (g) protection against system failure, using suitable measuring, control and protective devices as appropriate;” Paragraph 61 goes onto state: “Account should be taken of the most onerous combination of temperature, pressure and other relevant parameters to which the equipment may be subjected under reasonably foreseeable circumstances. These should include the conditions which will exist during start-up, shutdown and stand-by operation.”

9. What is transient analysis? The NTS pipeline network does not operate under “steady state” conditions Detailed analysis of the dynamic behaviour of the pipeline network and the facility needs to be undertaken to ensure the National Grid equipment and associated pipeline systems (providing the supply) can continue to operate safely The two main operational scenarios which could produce undesirable transient effects in the pipeline network are: During start-up (i.e. commissioning or normal start-up), when the load starts up against low pressure conditions in the pipeline/pipework system providing the supply During shutdown of the load in response to an emergency situation

10. Operating regimes: Start-up Start-up - when a large load (such as a power station) is brought into operation, the sudden flow demand can cause the supply pressure to reduce to an unacceptable level for a short period at the point of connection on the NTS/inlet to the installation supplying the load Equipment on National Grid installations needs to be considered to ensure they can respond at the required speed and to ensure they are not damaged

11. Operating regimes - start up (2) National Transmission System (NTS) Flow Load flow Supply to large load (e.g. power station) Operating scenario - gradual increase in load requirement Time Pressure Load pressure Time

12. Operating regime - start-up (3) National Transmission System (NTS) Flow Load flow Supply to large load (e.g. power station) Operating scenario - rapid increase in load requirement Time Pressure Load pressure Time

13. Operating regimes - Shutdown Shutdown - Under a fault condition the load could be required to shutdown quickly with rapid load shedding and this can occur in fractions of a second This event can pressurise the supply pipework/pipeline to an unacceptable level for a short period due to the “pressure wave” which propagates back through the supply pipework

14. Operating regimes - shutdown (2) National Transmission System (NTS) Flow Load flow Supply to large load (e.g. power station) Operating scenario - gradual reduction in load requirement (i.e. a slow transient issue where momentum effects are not dominant) Time Pressure Load pressure Time

15. Operating regimes - shutdown (3) National Transmission System (NTS) Flow Load flow Supply to large load (e.g. power station) Time Pressure Operating scenario - emergency shutdown event (i.e. typical example for a single supply pipe with flow curtailment following the shutdown) Load pressure Time Flow ‘Supply’ flow Time

16. Normal project process Feasibility Study Conceptual Design Detail Design Undertake work Initial analysis Preliminary analysis of work proposed Detailed analysis • Project/work proposed broken down into discrete elements • Analysis is undertaken at each stage • The further the project progresses through the project process, the more detailed the analysis required • Process systematic and structured but rigid

17. Project process adopted for analysis type work Feasibility Study Undertake work Design level analysis • Project process streamlined in order to reduce costs and timescales • Provides greater flexibility as the analysis is tailored to suit the Customer’s particular requirements • The level of detail required for the analysis is very much dependent on the application • Costs and timescales calculated accordingly

18. Study Categories – estimated timescales and costs

19. Basic transient analysis study - overall process

20. Basic transient analysis study process

21. Transient Analysis - Case study

22. Key considerations for Transient analysis • Interaction with NTS • Control system – heat exchangers • Control system – regulators • Common supply stream – where interaction between individual loads occurs • Individual stream modelling • Load profile/operating regime

23. Scenarios • NTS modelling – for start-up and shutdown • Ramp-up – for each load (individually and in combination) for each start-up profile • Shutdown – ESD events for each load (individually and in combination) for various NTS pressure conditions • For this case study over 60 scenarios were modelled

24. Any questions