Anglesey pipeline projectT.D. Jones

Indexing terms: Materials handling, Oil technology

Abstract: The paper briefly describes a major project, recently completed by Shell UK Oil, comprising asingle-buoy mooring facility, with storage and pumping installations at Amlwch on the north coast ofAnglesey with a 127 km-long connecting pipeline to feed crude oil to its Stanlow refinery on Merseyside. Thepower installations are briefly described, together with other environmental aspects which influenced thedesign. These included the installation of pumps and motors ranging in size from 500 kW to 3280 kW, so thatthey did not exceed a permitted noise level of 29 dBA under full-load conditions; designing a lighting schemewhich would not draw undue attention at night to a large storage and pumping complex which by day is wellcamouflaged by the geography of the land; providing adequate earthing at installations built on rock andensuring the correct functioning of control equipment on a network subject to frequent lightning storms. Theways in which these and other problems were overcome are described.

1 Introduction

Nearly two-thirds of the UK consumption of petroleumproducts is used within a rectangle 150 km wide stretchingfrom Manchester to London. The Shell UK Refineries atStanlow (Merseyside) and Shell Haven (Thames) arestrategically placed at opposite ends of this rectangle.

The Stanlow Refinery, built 50 years ago on the banksof the Manchester Ship Canal, was served by the Tranmereoil terminal on Merseyside. Draught limitations and widthrestrictions in the Mersey channel make it impossible toaccommodate the very large crude-oil tankers which arenow in common use. A new site was sought for a dischargelocation, having water depths up to 37 m close to the shore,with protection from south-westerly gales, with easy accessinto the shipping lanes and preferably as near Stanlow aspossible. Such a site was found at Amlwch, on the northcoast of Anglesey. A Private Bill resulted in the AngleseyMarine Terminal Act receiving the royal assent in 1972.Planning permission for the land installations and for thepipeline construction was obtained and the work startedin 1973. The work was completed in early 1977 and thefirst crude-oil tanker was discharged into the system earlythat year.

2 The installation work

The project comprised four integrated installations:(a) Offshore facilities: twin submarine pipelines l-0m

diameter and 3 km long; submarine manifold; single-buoymooring (s.b.m) connected to the manifold by a flexipipesystem.

(b) Land installations: Shore booster pumping station atAmlwch connected by twin 1 -0 m pipelines 5 km long to amain tank farm at Rhosgoch.

(c) Main pipeline: 127km of 0-91 m diameter pipe fromRhosgoch to Stanlow, via a major sea crossing of the MenaiStraits and crossings of the Rivers Conwy, Clwyd and Dee.

(d) Amlwch harbour: deepening, and the provision ofnew outer and inner breakwaters, berthing facilities andservice buildings.

The pipeline route and the locations of the land instal-lations are shown in Fig. 1. Some of the problems to beovercome can be envisaged by reference to the cross-sectionof the pipeline route shown as Fig. 2. The hydraulics of the

Paper T407P, first received 30th March and in revised form22nd June 1979Mr. Jones is with Shell UK Oil, Stanlow Refinery, Ellesmere Port,Wirral, Cheshire

ELECTRIC POWER APPLICATIONS, AUGUST 1979, Vol. 2, No. 4

system are interesting, with the Rhosgoch tank farm beingat 3048 m (100 ft) above sea level, the highest point on theroute being at nearly 396 m (1300 ft) elevation, and withvarious intermediate elevations to Stanlow which is at sealevel. The importance of one centralised control point wasrecognised, and Rhosgoch was chosen.

The entire pipeline project is illustrated in a simplifiedform in Fig. 3. The facilities at Amlwch provide an off-loading rate of up to 20000m3/h, whilst Rhosgoch has astorage capacity of 700000 m3 and facilities to pump toStanlow at a rate of 5000 m3/h. (Note that 1 m3 of crudeoil weighs approximately 1 tonne).

From an electrical engineer's viewpoint most of thework is concentrated at the Rhosgoch and Amlwch sites.The paper hereafter concentrates on these sites and brieflydescribes the power installations and other aspects whichinfluenced the design.

3 Power system

Reference to Fig. 3 gives an indication of the power con-sumption required. Amlwch has an installed loading ofabout 6000 kW, mainly at high voltage. Rhosgoch has aninstalled loading of about 18 300kW at high voltage andanother 3750 kW at low voltage.

Discussions with the local supply authority (MANWEB)showed the need for establishing a grid substation in thearea to cater for these sizes of loads. A 132/33 kV gridintake substation has thus been constructed within theboundary of the Rhosgoch tank farm, and two 33 kVsupply points have been made available for Shell's use. Theconstruction of the new grid substation reinforced theNorth Anglesey grid system and thus enabled the Amlwchshore station to be fed from the existing Amlwch grid sub-station via a further two independent 33 kV feeders.

The single-line diagrams for the two sites are shown asFigs. 4a and 4b. At Rhosgoch the supply is metered at33 kV and the main 2-section h.v. switchboard is fed viatwo 20 MVA transformers at 6600 V.

At Amlwch, the main 2-section h.v. switchboard is fedvia two 7-5 MVA transformers at 6600 V. The supplymetering here is at 66kV; the two incomers on the boardbeing the property of MANWEB.

At present, in the UK, 11 kV is considered the mosteconomic voltage for power distribution. This voltage ismost suitable for motors rated above lOOOkW. For motorsbelow 1000 kW either 6600 or 3300 V have to be used.Establishing two separate h.v. voltages or using unit trans-formers was considered undesirable. A check with leading

113

0140-1327/79/040113 + 07 $01-50/0

s.b.m

0 5 10scale ta««d««l kilometres

Fig. 1 Pipeline route

20 3 0 / 40

Snowdonia range

Fig. 2 Cross-section through pipeline route

50 T~60 70

Mynydd Llaneilian

route . km —^

80 90 T ~ 1000

Clwydian range

110 120

tanker

s.b.m.Rhosgoch

storage and pumping

\ \ flexipipe\ \ system

»

" \ X submarine•— manifold

offshore pipelines

Amlwchshore station

f°10m diameter 3km long

boosterpumps

local1 0 m

1r-I

piplinesdiamete

•

ft

r 5

-ai

Stan lowrefinery

booster pumps

-

booster pumps2x262OkW

F ig. 3 Simplified diagram of the system

114

tankageAx 100,000m6x50,000m

mainline—' pumps

booster pumps2x1865 kWmainline pumpsAx 3280 kW

Rhosgoch -Stanlow pipeline0-91m diameter 127km

ELECTRIC POWER APPLICATIONS, AUGUST 1979, Vol. 2, No. 4

manufacturers of h.v. motors showed that 11 000 V motorswere about 40% more expensive than similar motors woundfor 6600 V. These increased costs are partly offset by thesavings achieved in cable-size reductions.

The larger motors on the Rhosgoch site vary from500 kW to 3280 kW. At Amlwch the variation is similar,from 315 kW to 2620 kW. For practical and economicreasons it was decided to adopt 6600 V as the standarddistribution at both sites.

The main power distribution throughout the Rhosgochsite is at 6600 V, with the local power distribution at415 V. The initial development of the site occupies some48-5 ha (120 acres) and this necessitated establishinga number of local substations around the site to transformfrom 6600 to 415 V for local usage. The layout of the siteand the relative positions of the substations favoured asimple radial distribution. The locations of the pump-houses, where the large h.v. motors are installed, were

to Wylfa/Caergeiliog(via 0/H line)

LlanddeusantAmlwch

132 kVto Wylfa/ Amlwch line(via underground cable)

45 MVA transformer132kV/33kV

33kV

— Cemaes Bay MANWEBAmlwch responsibility

* L9 ^ L 8 | L 7 j L 6 * L 5 | L 4 t L 3 * L 2 normally

®®@® ° P e nrL}fh}(T\ P211 P201 P205 P2O3

, , ,530 1865 3280 3280. A ){ A A A ) kW kW kW kW

20MVA transformers33 kV/6 6kV

R 1 6600 V

Shellresponsibility

R2 iR3 iR4 tR5 ; ;R6 ; ;R7 ; ;R8 ;;R9

P20A P206 P2O2 P221<T>1 Ch3280 32801865 520kW kW kW kW^A A A

substation 1415V

diesel/gen.set

^ 510 KVA

lOOOkVA T/Fs6600/415V

500 kVA T/F6600/415V

250kVA T/FA15/6600V

, 75 MVAAJtransformers

J 33 / 6-6kV

33 kV cables toAmlwch gridsubstation

MANWEBresponsibility

_ "Shell6600V responsibility

R2 ;;R3

fire pump boosterP115 P101315kW 262OkW

1000 kVA T/Fs . . .6600 /415 V Soj yy

<k) boosterP102

V 1 "0 2 6y 2620kWY side 1 V side 2 y

switchboard

diesel generator set105kVA415V

Fig. 4 Single line diagrams of the electrical systems

a Rhosgochb Amlwch

sufficiently close to the main intake substation to enablethese to be fed directly from the main h.v. switchboard..

The Amlwch site, although occupying some 121 ha (30acres), is electrically very compact. The h.v. motors are feddirectly from the h.v. switchboard and all other supplies onthe site are fed from the main l.v. switchboard.

The fault level calculations on the Rhosgoch system,making allowances for induction motor load contributions,show an initial fault level of 185 MVA at 6-6 kV. If thefuture planned development was undertaken this faultlevel would rise to 201 MVA.

The calculations for the Amlwch system show an initialfault level of 137 MVA at 6-6 kV. Future developments atAmlwch can be achieved in a number of ways, resulting inthe maximum expected fault level of 244 MVA at 6-6 kV.For these reasons a short-circuit level of 250 MVA wasspecified for the h.v. switchgear at both sites.

4 Emergency supply systems

To cater for a complete power failure of the MANWEBsupply systems, an automatic mains-failure diesel-generatingset is provided at each site.

At Rhosgoch, the diesel generator is rated at 510kVA415 V. For practical reasons, owing to the large area of thesite, it was not economic to establish a completely separateemergency supply system. Consequently, the output from

ELECTRIC POWER APPLICA TIONS, A UGUST19 79, Vol. 2, No. 4 115

the set is divided into two, and each half fed into the mainh.v. switchboard via 250 kVA 415/6600 V transformers.The distribution of emergency power throughout the site isthus through the normal distribution system.

At Amlwch the diesel generator set is rated at 105 kVA415 V, and, as the electrical system is so compact, the set isarranged to feed directly into the 415 V system.

At both sites a comprehensive system of interlocking isprovided to prevent parallel operation with the MANWEBsystems.

The reason or the need for the diesel generating sets isnot immediately obvious. From the ratings it is clear thatthe sets cannot permit any pumping to occur.

At an early stage in the project development the supplyauthority was asked to provide any information availableregarding the security of their network. The grid system onAnglesey is almost entirely overhead lines, and the area issubject to frequent lightning storms.

During 1972 the supply authority had monitored thevoltage levels at a number of locations and at differentvoltages in their network. Voltage dips of up to 70% hadbeen recorded, the majority being below 20%. The durationof the dips varied from a few cycles up to 30 cycles.

The design of the control system was well advanced.Most of the control and alarm functions were of thefleeting type, necessitating large numbers of relays and logicunits. To ensure a safe and efficient operation it wasnecessary to install no-break supply equipments to over-ride the voltage dips, to prevent relay and status mal-functions. The alarm and indication facilities on both sitesare supplied at 24 V d.c; the control systems being at 48 Vd.c. At Rhosgoch, some 20kVA total of no-break batteryequipment is installed, with a 15min emergency rating. AtAmlwch a total of 8kVA is installed, but with a 30minemergency rating.

The automatic mains-failure diesel-generator sets areprovided and are rated to:

(i) maintain building services supplies(ii) maintain some site lighting(hi) enable isolation valves on pipelines and tanks to be

moved to safe positions until normal activities can beresumed.

(iv) supply power to the no-break equipments, thusmaintaining the integrity of the alarm, control and indi-cation facilities.

5 Noise control

The project was subject to a number of planning criteria.The most important of these with respect to the engineeringfunction was noise.

The Rhosgoch tank farm is located in a particularlyquiet area of Anglesey, where, hitherto, there had been nosources of industrial noise. At Amlwch there was less of aproblem since there was already some industry present. Abackground noise level survey had been conducted on thesites well before work on the construction began.

Noise levels in a community will vary with time, and it issometimes necessary to resort to a statistical quantification.That used for Rhosgoch and Amlwch was the L90 noiselevel (i.e. the level of noise which is exceeded for 90% ofthe time). This L90 level was used as the background noiselevel for which the design criteria was derived.

Six reference points, three at Rhosgoch and three atAmlwch, were agreed and the background noise was estab-lished and agreed for these reference points. Agreement was

then reached with the local planning authority with respectto the noise levels due to the plant alone. The resultantnoise level at the reference points was thus established. Theactual levels agreed with the planning authority were verylow, mainly because the existing background levels were solow. The most critical value was for the reference pointnearest to the Rhosgoch site (this point being about 800 mfrom the site). Here, the background noise level had beenagreed at 26 dBA; the noise level due to the plant had alsobeen agreed at 26 dBA, making a resultant of 29 dBA.

How did these noise restrictions affect the project? Theanswer is very much, as shown by the designs of the pump-houses on the site.

Originally, the design concept was for all the main-lineand booster pump units to operate in the open-air con-ditions. But pumps and motors of this size are major noiseproducers and their installation in the open air would notbe permitted. Eventually the acoustic cab was evolved,taking noise, security, and routine and breakdown main-tenance as influencing factors. The design is shown diagram-matically in Fig. 5 and in reality in Fig. 6.

All the pumphouses on the sites are designated zone 1areas as defined by the Institute of Petroleum Model Codeof Practice, Part 1,1965. Fully certified flameproof motorsof the ratings required are not available and would havenecessitated special development costs. Recourse to BSCode of Practice CP 1003: Part 2: 1966, 'Methods ofmeeting the explosion hazard other than by the use offlameproof or intrinsically-safe electrical equipment' hastherefore been made in the design.

The motors have all been designed as pipe-ventilatedenclosures, with separately mounted centrifugal fans

filteriroor

inlet

chimneyheight tosuit zonalclassification

inlet attenuator

removable roof

air due tine

oilcooler

centrifugalfan unit

electricmotor

I V

dense concretewalls cladding

^externally, 25mmthick adsorbentmaterial sprayedinternally

outlet attenuator

louvred outlet

ground level

boosterpumpunit

Fig. 5 Diagrammatic representation of pumphouse showingacoustic-cab concept

116 ELECTRIC POWER APPLICATIONS, AUGUST 1979, Vol. 2, No. 4

supplying air for cooling through an enclosed ductworksystem.

The air used is ducted from safe areas and is filtered andsilenced before entering the motor system. Flameproofpattern air flow switches are fitted in the duct work systemto isolate and trip in the event of mechanical failure of thefan system.

As an added precaution, the motors were specified asnonsparking type N in accordance with BS 5000: Part 16:1970. The designs were all approved and certified by thetest authority BASEEFA.

The roofs of the acoustic cabs are all designed such thata section can be removed for maintenance purposes on thepump units. This led to a possibility that the motors couldbe subject to long periods of weather exposure. The motorsare all weatherproof construction to meet this eventualityand suitably rated flameproof heaters have been fitted toprevent condensation whilst the motors are switched off.

To minimise the noise levels all the h.v. motors havebeen designed with no shaft-mounted cooling fans. Theinsulation on the windings is to class F type, but the tem-perature rise is limited to 80°C above a 40°C ambient, i.e.the limits laid down for. class B materials. Under normalcircumstances the motors can never be run without theseparately mounted fan units and suitable interlocking hasbeen provided in the control system to ensure this.

The motors are all started direct on line, the startingswitch being the oil circuit breaker units on the h.v. switch-board. A power-factor correction capacitor, suitably rated,is switched on individually with each motor to improve itspower factor to about 0-93 or 0-94.

To provide flexibility in the pumping operation sequencethe motors have been designed to withstand three startswithin a period of 15min from cold with a subsequent45min minimum period before any further starts. Toensure this, a counting and timing device has been fitted oneach motor circuit switch with a limit of 3 starts in any one60min period. An attempt at an extra start is prohibitedand indicated in the control room as a 'start limiter'.

To comply with the supply authority restriction of300 A instantaneous increase on the 33 kV system, thestarting currents on all h.v. motors were restricted to amaximum of 1500 A on the 6600 V system. These restric-tions were easily met during the witness testing of themotors.

At the tender stage, a capitalisation of losses excercisewas conducted, and the most efficient h.v. motors quotedwere purchased. The guarantee values quoted (from 96%to 97% on full load) were proven during the witness testsconducted.

The doors in the cabs have been designed as acousticdoors. The walls are of dense concrete blocks, insulated andclad externally for visual appearance. Internally the wallsare sprayed with a 25 mm thick layer of sound absorbingmaterial.

A final noise test to prove the acoustic design conceptwas conducted in mid 1978. The tests were witnessed bythe local planning authority, and were based on normalrunning conditions. The tests proved that the acousticdesign criteria had been successful and that the limitingvalues at the agreed reference points had been met withsufficient in hand for any future expansion.

6 Lighting

Lighting was another aspect that the planning authority was

ELECTRIC POWER APPLICATIONS, AUGUST 1979, Vol. 2, No. 4

Fig. 6 General view of completed pumphouse

particularly keen on and one which was subject to a formalplanning agreement.

Normally, for installations such as those at Rhosgochand Amlwch, the most effective and economic way forlighting would be to use conventional or high-mast flood-lighting towers supplemented by road-lighting columnsalong the main access roadways. As far as the planners wereconcerned this was unacceptable, especially for Rhosgoch.Having chosen a site which by daylight is well hidden bythe geography of the land, they did not want a 'beacon' liton the site to draw attention to it by night. We thereforehad to resort to much more subtle means of lighting.

It was established with the operating staff the areas thatwould be regularly visited at night and also the areas whereclosed-circuit television coverage would be advantageous.These areas were lit with conventional fluorescent fittings(of the EXe type) locally mounted, but, for maintenanceconsiderations, at a maximum mounting height of 2 m.These areas in total represented about 5 to 10% of the siteonly. The remainder of the site was agreed to be leftnormally dark, but with lighting provided capable of beingswitched remotely.

In conjunction with a lighting manufacturer a speciallighting column with a mounting height of 1 m wasdesigned as shown in Fig. 7. The columns have been in-stalled all along the roadways throughout the site. Thefittings include an MBT lamp, this being a blended mercury-tungsten lamp requiring no external control gear. The lampprovides an instanteous start on switch on, with about 50%of its light output available in the first minute, increasing tofull output over the next minute or so. As these fittings areremotely switched from the control room, this is con-sidered ideal as the full output will have been achieved bythe time the operator reaches the roadway. Similar fittingshave been provided inside and around the tank compounds(locally switched at access points) and around the entireperimeter fence. These fittings have been provided withtungsten lamps to provide instanteous lighting.

7 Earthing

Anglesey is a rocky island. All attempts to drive earth rodsat Rhosgoch and Amlwch met with solid resistance atdepths ranging from 150 mm to 450 mm. Soil resistivitytests were conducted, showing atrociously high values.

117

Fig. 7 Typical lighting column

Earthing at an oil installation is important for electrical,static and lightning protection purposes. Owing to the highprospective earth fault currents on the grid substation,earthing was particularly important at Rhosgoch.

A proposal to set up large numbers of suitably con-nected artificial earths was considered, with the possibilityof using the sea as an earth at Amlwch. A subcontractorwas on the site at this early stage drilling holes in the rockprior to blasting. We established that the drill could make ahole 50 mm diameter and up to 15 m deep in rock at areasonable cost. A number of such holes were drilledthroughout the sites and some experiments were con-ducted. Bare copper cable and galvanised and ordinaryconduit were tried as earth rods and the intervening spacefilled with a paste of carbon dust and water. These provedvery successful, and by monitoring for a few weeks it wasfound that the values improved with time. Per hole theearth resistance values ranged from a few ohms to about100 SI.

The rock strata on both sites was heavily faulted and thedrilled holes, in passing through the fault lines, picked upmoisture, where any was present.

The supply authority, MANWEB, showed an interest inour earthing experiments and later conducted some of theirown, improving the earthing values by the use of a pro-prietary filler in place of our carbon dust paste. This pro-prietary material is often used in back filling cable trenchesto maximise cable ratings, and is extremely hygroscopic,attracting any moisture to itself.

This method of earthing was used on the main instal-lations at both Amlwch and Rhosgoch with good results.The final as-built network of earthing at Rhosgoch wastested and found to have an ohmic value of less than 0-1 £1.

8 Control systems

Supervisory and control information for the entireAnglesey system, including the pipeline and the receivingend at Stanlow, is presented within the Rhosgoch controlcentre.

A graphic panel provides a complete schematic of theentire hydrocarbon handling linework, from the tanker atthe s.b.m. through to the receipt of crude oil at the Stanlowtank farm. This panel provides not only the status but alsothe control of all major functions necessary for theoperation. Some functions are directly operated from thisgraphic panel, whereas others are preselected on the graphicpanel but do not operate until further controls are operatedon the master controller's desk, which is centrally locatedin the control room.

The controller's desk contains all essential operatingcontrol information and emergency shutdown buttons forthe system, together with data-logging, communication,surveillance and gauging equipment.

An auxiliary console in the control room is provided foressential information and controls for functions notdirectly connected with crude-oil handling and transfer, forinstance fire alarms.

Fig. 8 General aerial view of Rhosgoch tank farm

Fig. 9 General view of the control room showing the graphic paneland the controller's desk

118 ELECTRIC POWER APPLICATIONS, AUGUST 1979, Vol. 2, No. 4

The heart of the control system is a telemetry system, and Fig. 9 shows a general view of the control room withwith a master station at Rhosgoch. All other locations are the graphic panel and controllers desk clearly visible,treated as outstations and are connected, either directly bylandlines or via a microwave link, operating through anumber of relay stations. The microwave system, in g Acknowl d tsaddition to the telemetry, also carries a direct speech linkto Stanlow, a teletype link to Stanlow and a v.h.f. radio The author wishes to thank Shell UK Oil for permission tocontrol and marine channel link. publish this paper and for permission to reproduce the

An aerial view of the Rhosgoch site is shown in Fig. 8, photographs and diagrams shown.

ELECTRIC POWER APPLICATIONS, AUGUST 1979, Vol. 2, No. 4 119