Flue gas desulphurisation plant: duct 12 refurbishment

Ratcliffe-on-Soar power station underwent partial refurbishment, completed to CDM regulations, by qualified TFL welders who were also trained to work in a range of challenging environments. The contract included the supply of materials, labour and equipment, plus arrangement of independent non-destructive testing of the welds, and was successfully completed within its 12-week schedule.

This power station took positive steps some years ago to reduce levels of sulphur in exhaust gas by building a flue gas desulphurisation (FGD) plant. Over time the corrosive nature of the exhaust gas has attacked the fabric of the FGD plant and certain area needed major repairs to secure a good life expectancy for the power station.

The on-site team

The duration of the project on-site was 12 weeks; TFL engineers attended site collectively for over 16,000 man hours. The project was completed successfully, on time and accident free.

TFL personnel had received training to ensure they could operate safely and with competence in challenging confined spaces, their safety and those of other contractors on-site being a primary concern. Supervisors and managers were NEBOSH qualified and all personnel possessed a Passport to Safety. Team members had also completed further training in confined space awareness, working at height, manual handling, abrasive wheels and fork lift truck driving.

Assessing the requirements

TFL Responsive Engineering Limited (TFL) was awarded the contract to supply materials, labour and equipment to rebuild and repair duct 12, a large carbon steel duct 6.5 meters high, 8 meters wide, and which contained central turning vanes that extended from floor to roof, which assist the smooth passage gas around a 90 degree bend.

In conjunction with our client, a detailed inspection of the duct took place and a decision was taken to completely overplate the inside, replace all turning vanes and supporting tubes, and to repair the duct to a standard suitable for flake glass lining. The extent of labour and time to be spent on this outage required that the works be completed under CDM regulations.

Given the tight time scale that existed for this work day and night shift working would be required to ensure completion by due date. Fifteen men, equipment and a site manager were supplied for this work. All welders were qualified to the current British standard.

OUTAGE WORKS AT RATCLIFFE ON SOAR POWER STATION

Completing the refurbishment

TFL supplied 38 tonnes of steel for the project in 6 metres by 2.5 metres by 6mm thick plates, each weighing around 700 kg. The only access into the duct was via a round, 600mm diameter door, which was removed to give safe and unrestricted access to personnel.

The existing turning vanes were cut out and scrapped, as new ones would be installed later. A slot was cut in the roof of the duct and a mobile crane lowered the new plates into position for fixing to the floor, roof and side walls – a difficult operation given the size of the plates. A new floor was installed, fully welded to the existing structure. All welds were ground flush and underwent a 100% magnetic particle inspection to ensure no defects existed.

Ratcliffe-on-Soar power station Image

Following acceptance of the floor by the Flake glass lining company, a series of scaffold towers were erected to give safe access to the side walls and roof. Using a series of winches and the crane, the large plates were hauled into position and were fully welded in place. The roof was fitted and welded in a similar manner.

The difficult and tricky task of installing the new turning vanes was then successfully completed and the vanes bracings were welded back in position. All the welds received a magnetic particle inspection by an independent company: all were deemed acceptable and the duct was declared gas tight. Many hours of grinding took place to ensure the profile of any welds laid was suitable for flake glass lining, which was verified by an independent company before TFL handed the duct over to the client.