Lazarus & Associates Ltd
Rowecord Engineering Ltd
Rowecord Engineering Ltd
Corus Uk Ltd
The new Energy Recovery Plant will allow the harnessing of the off-gas, rich in carbon monoxide, generated by the ‘Basic Oxygen Steelmaking’ (BOS) process as a source of energy for on-site power plants. To facilitate this new process, a large gas holder along with 3km of associated pipe work and two 70m high stacks, was needed.
Central to the scheme was the new 75,000m3 gas holder which has been constructed roughly equidistant between the power plants and the BOS plant. Approximately 2,700 tonnes of steelwork went into this large structure which is 63m high to the apex of its rooftop vent, 54m in diameter and erected from steel plates.
To avoid excessive working at height, and to minimise the use of scaffolding, the entire gas holder was built from the roof down – one ring of steel at a time using hydraulic jacks to lift the whole structure up to allow the next ring to be welded to the one previously installed.
Early works on site involved ground preparation and piling, prior to concrete slab and steel floor plate being installed. This then allowed the main steel erection programme to begin, with the uppermost ring of plate steel installed first. Each steel plate is 2.4m high x 11.3m long and one circumference – with welded connections – took seven days to complete.
Next the roof framework was erected consisting of a series of 600mm deep rafters which fan out to the perimeter from a central point that was temporarily supported on a trestle. The roof structure also includes steel bracing while all connections for this part of the structure were bolted. Once the roof was clad the structure was raised by a series of hydraulic jacks placed around circumference. The jacking process took approximately five hours and raised the entire steel ring 2.4m, which allowed another complete circumference of steel plates to be installed – this was repeated until the gas holder reached its full height.
As each successive circumference of steel plates was inserted the structure’s weight increased and so the number of jacks had to be increased from 24 at the start to 120 units at end. Likewise, the steel plates’ thickness also increased – due to extra loadings – from 10mm for the upper rings to 16mm thick plates at the bottom.
The final steel ring included a 6m wide access opening, which served the dual purpose of allowing the cherry pickers, used inside the structure’s footprint, an exit route and allowed the gas holder’s internal steelwork to be inserted. Internal steelwork was brought to site ‘piece small’ and once inserted was bolted together. This steelwork included the 18m high piston which when assembled weighed 480 tonnes. As gas enters the holder the piston, which rests on a lattice framework at ground level, rises to 1.5m from the roof when full. As the piston rises an attached rubber membrane, fixed to both the piston and the wall of the holder, unfolds and acts as a seal preventing gas leaks.
This is a project with environmental, cost and energy efficiency credentials.
In a tough industrial environment, this large scheme shows how steelwork contributes to enormous environmental benefits.
Waste gases (previously flared to atmosphere) are now treated and transported via nearly 5 kms of large pipeline on complex steel support structures, to a large welded steel gas-holder for re-use. The challenges of working in an operational steelworks were huge. The project saves energy and Corus reduces atmospheric emissions
Structural steelwork on a large scale is key to the astonishing pay-back time of less than 3 years! This is outstanding.