C A S E S T U D Y

EMSWORTH GASHOLDER DECOMISSIONING PROJECT

CLIENT: SGN

MAIN CONTRACTOR: DSM DEMOLITION

PERIOD: JUNE 2015 – APRIL 2016

HOLDER PROFILE:

CONSTRUCTED: 1933

ABOVE GROUND GASHOLDER

THREE LIFT SPIRAL GUIDED HOLDER

DIAMETER: 45.6M

HEIGHT: 10.1M

Prior to commencement of demolition, we undertook the following enabling works:

• Water Treatment of 16,902m3 of Contaminated Gasholder Seal Water

• Weekly Water Sampling

• Contaminated Gasholder Sludge Minimization

• Contaminated Gasholder Sludge Disposal

Restricted space on the site required careful planning and cooperation with the main Contractor. Accordingly all programme targets were achieved.

Emsworth gasholder contained a total Volume of 16,902 m3 of contaminated seal water that required treatment prior to foul sewer discharge. Following consultation with the local water authority, permission was granted to discharge the treated water at a rate of 1.31 l/s for 24 hours a day, seven days a week. This required a bespoke system designed for the continual treatment of water over the lengthy 145 days of discharge. Our system was designed to treat a range of contaminants including methane, hydrocarbons and suspended solids. The bespoke system included a smart digital flow meter system, enabling us to have full remote access of the system - allowing us to view the precise flow rate at any given time. To ensure compliance with discharge consent, a weekly water sampling/specialist laboratory analysis regime was undertaken.

Upon completion of our dewatering operations we worked closely with the demolition contractor who prepared access to the gasholder so we could progress onto our desludging operations. Due to the nature of the sludge and the limited ventilation in the gasholder, careful and meticulous confined space risk assessments were completed. The results highlighted the need to minimise the number of personnel in the confined space, so the team consisted solely of 3 men inside the tank and 1 outside acting as “Top Person”. Initially scaffold access platforms were installed to provide a safe access and emergency escape. Prior to man entry, atmospheric tests were conducted to ensure the confined space was a safe working environment. The operation was then undertaken utilising an innovative electric conveyor system thereby significantly reducing the manual handling required. Throughout the operation the confined space atmosphere was continually monitored to eliminate any risk. These works were also completed well within the Demolition Contractors’ programmed dates.

Our primary aim was to deliver waste minimization. We achieved a sludge reduction rate of around 60% providing significant financial savings to both the client and ourselves. We also achieved a significant environmental benefit by reducing the transportation requirements to our chosen licensed disposal facility.