ENGINEERING: OCGTs get a Breather
Recent Western Cape Business News
DCD-Dorbyl Marine reports that the erection of seven additional air intake systems for Eskom’s two open cycle gas turbine (OCGT) power stations is on track to be completed by year end.
Five air intake systems are being installed at the state utility’s Ankerlig OCGT station in Atlantis, near Cape Town, and two at the Gourikwa OCGT station in Mossel Bay. Each station already has four 147 and three 148 MW generating units respectively.
Bill Flear, project manager: industrial at DCD-Dorbyl Marine, says that this contract was the second one received for the fabrication of the components for the air-intake systems and then the on-site erection. The first seven air in-take systems were manufactured and erected on site during 2007.
He says that the company, as main contractor, once again outsourced the entire fabrication portion of the project to sister company DCD-Dorbyl Venco. The main challenge on a project of this nature is the size of the components to be fabricated and Newcastle based DCD-Dorbyl Venco has the necessary physical space and capacity to undertake a task such as this.
The fabrication scope of work included the manufacture of the support structure and intake ducts, fitment of all acoustic materials, painting, corrosion protection as well as the fabrication of decking and walkways for the air intake systems.
Each air intake system comprises eleven separate elements including weather hoods, filter housing and silencers. Each structure is equivalent to a five storey building in height at 15 metres, and has a footprint of some 12 metres by 2.5 metres. A variety of materials was used in the manufacture including commercial sections, locally sourced mild steel plate, galvanised sheeting and stainless steel.
The filter house itself sits on a base of twelve square metres situated on top of the building structure. The filter house comprises eight side frame components with a roof structure. These eight components house pre-filter screens and walkways to facilitate access.
The nature of this project required absolute accuracy in fabrication and trial erection was carried out at DCD-Dorbyl Venco prior to the components being dispatched to Mossel Bay and Atlantis. The sheer physical size and relatively fragile nature of the various components necessitated the use of a special transportation framework as well as abnormal vehicles to transport the sections to site.
“To facilitate erection at both Mossel Bay and Atlantis, filter house sections are pre-assembled on site with final erection taking place after the base frame has been installed. A 120 ton mobile crane is being used to facilitate installation of both the filter house and the elbow,” Flear says.
The air intake systems and support structures were designed by Rheinhold & Mahla for Siemens, the main contractor on the complete project.
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