Cooling system - towers, air-cooled condenser or direct cooling

How does Cooling system - towers, air-cooled condenser or direct cooling work, step by step?

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   Step 1: Establish what water the site can actually have

   The starting point is the resource. The team establishes what water is available, how reliably, at what quality and on what terms, and what the environmental regulator will permit to be taken and returned. Where a large water body is available and abstraction is acceptable, direct cooling is possible. Where only a modest make-up supply exists, wet towers become the answer. Where water is scarce or abstraction will not be permitted, air cooling follows almost automatically. This assessment sits alongside the consent application and drives it.

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   Step 2: Weigh efficiency, footprint, cost and visual impact together

   The designer, the plant supplier and the operator compare the options on a common basis. Direct cooling generally gives the best plant efficiency, wet towers sit between, and air cooling costs efficiency but removes the water constraint. Against that sit capital cost, land take, height, noise, plume and the long-term operating burden. Public and planning reaction to a tall structure or a visible plume is assessed honestly at this stage, because it is a common cause of late redesign and it cannot be engineered away afterwards.

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   Step 3: Fix the interface with the steam turbine and the condenser

   The cooling system and the steam turbine exhaust are one system, not two. The plant supplier sets what the turbine can exhaust into and the cooling design has to deliver it across the full range of ambient conditions the site experiences. That interface fixes the condenser type and size, the duct or pipe routing and the space needed immediately around the machine. It is agreed and frozen early, because a change to the cooling system after the turbine hall layout is set is one of the most expensive changes available on a power project.

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   Step 4: Build wet cooling towers where that is the option

   Wet towers are substantial civils. The basin is a large water-retaining structure, the tower above it is either a tall shell or a bank of cells with fans, and the internal fill, distribution and drift eliminators are supplier scope installed within it. Circulating water pumps, large diameter pipework and the connection to the condenser follow. A make-up and blowdown regime is provided and connected to the water treatment plant, and the whole arrangement is designed with the operator around cleaning, inspection and long-term maintenance access.

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   Step 5: Build an air-cooled condenser where water is not available

   An air-cooled condenser is a very large elevated steel structure carrying tube bundles and fans, connected to the turbine by exhaust duct of exceptional size. The civils are extensive, the steel is tall and the equipment is lifted to full height, so cranage and working at height dominate the programme. Wind loading on a tall open structure governs its design, and wind at the site governs its performance. The duct from the turbine is a major fabrication that has to absorb movement and be supported without loading the machine.

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   Step 6: Build direct cooling intake and outfall works where a water body allows

   Direct cooling brings the project into marine or river construction. Intake and outfall structures, screening and cleaning plant, and very large diameter buried or submerged pipework all have to be built, commonly within seasonal windows set by the environmental regulator to protect fish and other wildlife. This work is specialist, weather dependent and consent driven, and it usually starts long before the main plant civils because its windows are fixed and cannot be moved.

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   Step 7: Complete the circulating system, screens and chemical control

   Whatever the arrangement, the circulating side has to be completed as a system: pumps, valves, large diameter pipework, screens or strainers, and the instrumentation and control that runs it. Biological growth and fouling control are part of the operator's environmental permit and the equipment for them is installed under the specification and connected to the monitoring the permit requires. The circulating system is often the first large system on the plant to be filled and run, which makes it an early test of the site's system turnover discipline.

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   Step 8: Fill, run and prove the system before it is needed

   The cooling system is filled, flushed, cleaned and run cold well ahead of the steam plant, because the steam turbine cannot be commissioned without it. Pumps, fans and drives are proved individually and then as a system, controls are checked and performance is measured against the design. Any shortfall found here affects the whole plant output, so it is resolved before hot commissioning starts. The system is turned over to the commissioning team formally and comes under the operator's permit system from that point.