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Wilton Olefins 6 Unit to increase output via 'Project Lift-Off'

25 Jun '08

7 min read

The Olefins Cracker complex at Wilton is an extremely complicated and highly technological facility. Completed in 1979 at a then astronomical cost of £200 million, it has literally millions of components and parts and is spread across a site of over 223 acres.

It operates 24 hours a day, 365 days a year and has a planned major overhaul like the one coming up in May around every 5-6 years.

It can use different feedstocks ranging from a light fraction of crude oil called naphtha to natural gas liquids such as Propane and Butane. The gases we use on the Cracker are from the same family of gases used on your gas cooker at home and in camping gas canisters.

The Cracker itself is rather like a giant pressure cooker, heating up its feedstocks to very high temperatures (up to 850C) and thereby breaking up the big molecules (or 'Cracking' them) into valuable and useable other products such as ethylene and propylene.

After heating up the feedstocks to such high temperatures, the gases are then chilled to very low temperatures (up to -170C) to enable the various molecules being produced to be separated.

WHY DO WE NEED TO FLARE AND WHY IS IT NOISY?:
Flaring is avoided wherever possible because, apart from the noise and nuisance it can cause, it is very expensive, basically burning off valuable products.

Flaring is an essential part of the Cracker's safety system. If there is an unplanned breakdown or process upset which leads to product quality issues, automatic instruments can stop the flow of gas through the plant and divert it to the flare stacks to be flared off safely. This process can also be done manually by the Control Room operators.

As mentioned previously, because the Cracker complex is similar to a giant pressure cooker. When pressure builds up in a pressure cooker, a valve can be operated on top of the cooker to release some of its steam to atmosphere. Similarly, on a Cracker plant, there are similar valves which can be release the gases to the flare stacks.

The gases being flared off come from the same family of gases used in domestic cookers and central heating systems.

When flaring takes place on the Cracker, steam has to be injected into the flames at the flare stack tips to make the flame burn cleanly. Without the steam, the flame would be very smoky. It is the act of injecting the steam at high rates that causes most of the noise.

We only flare as a last resort and it is the safest and most effective way of dealing with an unplanned plant upset.

For the major overhaul which is held every five to six years, we know almost precisely when this is going to happen, which is why we are able to inform our neighbours through publications such as this to give a high degree of advance notice about the flaring.

Before we can carry out the necessary safety inspections and major maintenance work as part of the overhaul, we have to empty the Cracker complex of all of its contents of hydrocarbon materials, so the engineers and contractors can get on with their work safely and without hindrance.

We would like to apologise in advance for the flaring associated with the forthcoming major overhaul and we would like to reassure the public that we will do everything we possibly can to keep any inconvenience to a minimum as much as possible.

Work on the overhaul itself will take around 50 days in total, and when all the work on the overhaul has been completed around the end of June, we will bring the complex back on line and this again will involve some fairly significant flaring as we recondition the plant back to normal operation.

Again, we will do this with as quickly as we can and with the minimum of nuisance, but this process can last up to 24 hours or more.

During the overhaul, we will employ around 1,500 contractors, as well as our own staff, which will provide much needed work and economic wealth generation for the Teesside area and beyond.

As stated earlier, the Cracker is regarded as the heart of the chemica

Saudi Basic Industries Corporation (SABIC).

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