Like all chemicals plants the Octel site was dependant on a number of basic services. These are described below.
Fresh water is supplied to site via a single water main that enters the site near the gate house. A local authority water meter is located outside the gate house. A bypass around the meter may be opened if water supply is restricted because of the meter. The water board must then be informed for them to rectify the fault.
The single main supplies a water tower, with two inter connected chambers and a direct site main. The direct site main is used mainly for domestic services. The water tower is used to supply most of the process water requirements. A level gauge in the SPM office indicates the level in the water tower. A low-level alarm is also located in the BOT control room. The alarm activates once the tower level drops below 90%. The minimum level on the gauge in the SPM office corresponds to a drop in depth of around 5 foot in the tower. A drop in height of 1 foot is approximately equivalent to 20 m3 of water. The water tower also supplies the water for the MPBF automatic fire / foam system.
In the advent of a water supply failure to the site the local water board should be contacted immediately. Any prolonged loss of supply will lead to a progressive shut down in process activities. The major fresh water users are the SAP for steam raising and BOT for fresh water make up of PAL. If these plants have to be shut down they have a knock on effect on other plants which will soon lead to a total site shut down.
At least one auxiliary boiler will need to be kept working to ensure that the sulphur in the stock tanks does not solidify. One auxiliary boiler on its own, with the rest of the site shut down, will use around 1 foot/hr from the water tower level.
Fresh water is fed to the sulphuric acid plant demineralisation water plant. Here the incoming fresh “raw water” is treated with a cation and anion resin before being decarbonated and degassed. The demineralisation water is then dosed with water treatment chemicals before being used as boiler feed water. In the event of a failure of the demineralised water system “Raw water” can be fed to the boilers for up to 24 hours with additional water treatment chemicals being added. Advice on additional treatments for prolonged use of raw water to the boiler should be sought from the Process laboratory.
Normal site usage is around 12 MVA. Electricity is supplied from the National Grid to transformers on the former Shell Site.
At the Shell site there are two transformers that reduce voltage to 11KV and this is distributed via an 11 KV switchroom alongside the Manweb substation. The transformers and 11KV switch board and the rest of the electrical system are controlled by Great Lakes. However we have a maintenance contract with Manweb for assistance if required for the distribution equipment at any of the substations on site.
There are three 11KV underground cables which feed power from the ex-shell site to no3 pipetrack and from here along cable hangers to the incoming substation by BOT1 pump house. At the substation 6 transformers reduce the voltage to 3.3 KV for two distribution boars which feed the large drives for BOT1 and BOT2. Part of BOT1 3.3 KV system is fed from a separate board in No3 switch room to the east of BOT lab.
There is a 11KV ring feeder which supplies No1 and 2 substations. No1 is located next to the incoming substation and no2 is located opposite the day Services garage.
There are three transformers at each of these substations which reduce the voltage from 11KV to 415V for all small drives, lighting and small power distribution.
The ring feeder is literally a cable which goes along the cable track from the incoming substation to No1 and then No2 sub station and back to the incoming substation to form a ring feeder. Protection is designed so that 415 V supplies should be maintained at all times unless all power is lost to the site.
The three 11KV cross site feeder cables from the ex shell site to the incoming substation are monitored. It is possible to run both BOTs with one of the cables out of action provided extra care is taken during the starting of fan motors.It is also possible to run both BOTs with only one 33KV cable or transformer provided the load is limited to 10 MVA and start ups are very carefully controlled.
An alarm panel in the BOT lab monitors the 33KV transformers and 3 cross site feeders and each substation has a red warning lamp outside which when illuminated warms that the protection batteries at that substation need attention.
There are Standing Instructions for Electrical Safety for the site which list all the Authorised personnel and their level of switching authority. These personnel should be contacted appropriately in the event of difficulties with the electrical supplies on site.
The site will on occasions suffer from electrical supply failures. These may be minor with only a few drives being lost or can result in the major BOT drives tripping.
The site supply system has a selector switch which can be used to determine which BOT will trip first in case of a reduction in supply. The BOT with the off work sea water services pump must always be selected to trip first. The selector switch is located in the incoming sub station close to No1 pump house and must be changed by the SPM, with an operator in attendance, if the on work sea water services pumps are changed over.
The first priority in a total loss of supply must be to re-establish Sea water services. This must be done either by starting one of the Sea Water Services pumps. The second priority must be to re-start the site compressed air supply system.
The sea water services are required for cooling duties around the plant and also as back up scrubbing medium. Two of the most important duties are as the cooling medium for the acid plant plate heat exchanger and as scrubbing water to the SOTs.
The loss of sea water flow to the acid plant plate exchangers will mean that the SAP plant will have to be shut down if it has not already tripped.
The SOT bromine vent scrubber can be supplied with back up fresh water from the in coming main to act as a scrubbing medium until sea water flow is re-established. The SOT cannot be operated normally without sea water being available.
Once the sea water flow has been re-established at the BOT, the dilute acid flow from the Dilute acid tank (DAT) can be re-established. This will prevent the tank over flowing. The SAP plant should then be restarted, to provide the BOTs with SO2 gas and then chlorine flow re-established to the BOT. This will also allow chlorine tanker discharging to restart. The SOT will probably require steaming out before it can be re-started followed by the DBE reactor, bromine driers, HBr DBM and NaBr plants as required.
All losses in electricity supply must be notified to the electricity supply company. In addition an incident report and “Loss of electricity supply” report must be produced.
To help to minimise the cost of electricity the company has a load reduction agreement with the electricity supply company. From around November to March we agree to minimise our electricity usage for short periods on demand. The supply company informs the SPM of the load reduction requirement before 09:00. The SPM must confirm the notification by return Fax.
The load reduction period is normally for some time between 16:00 and 18:00 the same day. During this period it is normal for one BOT to be taken off work and for the second BOT to be run with only two pump operation. However specific instructions will be issued in advance of each load management period.The company normally agrees to a maximum of around 24 load reductions over the period. It is the electricity supply company’s responsibility to try and predict when the national peak load demand will be required and to arrange load reduction to try and hit these periods. If the site electricity usage exceeds our agreed limit during the period, we suffer a financial penalty.
Sea water is supplied from one of two sea water services pumps. A stand by bore hole pump in No1 pump hose can be used to draw sea water from the BOT1 tunnel shaft if for some reason none of the 6 BOT sea water pumps can be run.The discharge pressure from the sea water services pump should be around 100 psi. The water is fed to the BOT rotary screens where it is used to remove material screened from the ponds. It is also used as the cooling medium in the acid plant plate heat exchangers , as make up water to control the strength of acid in the dilute acid tank and to assist in the operation of the SOTs.
Loss of sea water supply is normally caused by a power supply fault. It is important to get a sea water services pump back on as soon as possible. Failing that the bore hole pump should be run to maintain some sea water to other plants.
If the sea water system has been depressurised , either planned or by pump failure, great care must be taken to avoid water hammer during pump start up. It is advisable to allow trapped air to be expelled from the site pipework system by opening up some fire hydrates before any pumps are started.
In addition each individual plant operator must take care to ensure that his plant’s sea water isolation valve is closed while the main pumps are started up. Each operator must then slowly open up to his plant ensuring that trapped air is allowed to leave the system at a convenient point.
The changing over of sea water services pumps is an operation that needs care to ensure that supply is neither totally lost nor too high a pressure is generated in the mains while both pumps are on work.
The basic layout of the sea water services supply system and the problems that can be encountered during pump start up or change over must be familiar to the SPM.A cross connection is made from the sea water service main to the site fire main. If for some reason the sea water services system is to be de-pressurised the fire main must be isolated from the sea water main and then charged from the fresh water system using hoses.
The SPM should be familiar with the basic lay out of the fire main the location of the main fire hydrant points and on site fire equipment boxes. He should also be familiar with the range of equipment stored in the fire station and site fire engines. Each shift has a number of trained fire men who are trained in the use of this equipment.
The MPBF plant has it’s own foam and water fire protection system which is initiated either manually or automatically by heat detection in some parts of the plant. A manually initiated foam system is also situated in the liquid ethylene plant. The manual initiation points of both the MPBF and LEP must be familiar to the SPM.
Some plant areas are fitted with a fire detection system and alarm. The alarm panel is located in the SOT control room. If the fire alarm is activated the SPM should investigate with trained fireman in attendance.
Compressed air is supplied from the acid plant electrically driven compressors. Usually two of the three is sufficient for all the site compressed air requirements. In the event of a power failure the compressors must be re-started as soon as possible. The main users of compressed air are the acid and SO2 plants where it is used to oxidise the sulphur to SO2 for the BOT and H2SO4 converter processes.The compressed air is also used to supply instrument air to the many pneumatically driven instruments around the site.
In the event of compressed air supply failure the standby diesel compressor should be used to maintain supply. This is unable to supply sufficient air for all the site needs and it is likely that the SO2 plant will have to be taken off. The instrument air pressure will also have to monitored and plants may have to be taken off if it drops too low.
The compressed air is dried via electric de-humidifiers as detailed in the relevant operating manual.
Padding air is supplied from three compressors in the chlorine house. The compressed air is dried via electrically regenerated de-humidifiers to a dew point of around -70 0C. A back up calcium chloride drier system is also continually used. Padding air is used to aid in the discharge of chlorine tankers , to load bromine tankers and to supply chlorine to the SOTs and BOTs. Any supply failure will quickly lead to a shut down of all of these operation.
Mask air is produced from a compressor situated on the west shore. A bulk cylinder is located to the North of the SOT building which supplies a site supply main. The supply main has a number of take off points into which our site Breathing apparatus can be plugged. The system is used mainly for planned maintenance work with small BA cylinders being used for emergency response.
Steam is produced as a by product of the sulphur burners at around 280 psi. This is reduced to around 150 psi for transport around the acid plant building. At 150 psi it is used to drive the turbines which supply the air to enable combustion of sulphur in the burners.
Two medium density fuel oil auxiliary boilers supply 150 psi steam when the sulphur plants are shut down and to top up the site main as required when the sulphur burners are on line. Steam from the oil burners are used to turn the turbines when the sulphur burning plants are started up. Once the sulphur burners are operational their exhaust steam is let down to 150psi to turn the turbines. A 150psi main also runs to the Multi Product Bromination facility (MPBF)
The exhaust steam from the turbines is vented to the 40 psi main. The pressure in the main is maintained by letting down steam from the 150 psi main as required. The 40 psi steam main is used to supply steam services to process plants around the rest of the site.
Loss of steam supply is usually caused by one of the sulphur burners tripping out or being taken off line. The auxiliary boilers would normally trip in to maintain the 150 psi pressure which in turn maintains the 40 psi site steam main. During periods of high site steam usage or low generation capacity priority must be given to process plants. This may mean that steam to heating services and amenity buildings may have to be isolated. In extreme situations plants may have to be shut down to conserve steam. It is absolutely imperative that a 40 psi supply of steam is maintained to the sulphur storage tanks. This is also true if the supply of clean fresh water for steam raising services is restricted.