ACCW Fin-Fan Units Apex Cleaned Without Scaffolding

Telescopic lance system improves ACCW performance

Scottish Power owns and operates a 715MW CCGT electrical power generating station in the UK where condenser cooling is provided by an impressive and extensive farm of 110 ACCW apex fin-fan units, probably one of the largest in the UK. The units are based on steel tubes with galvanised steel fins.

The Challenge

As with all ACCW fin-fan cooling systems, the units are prone to becoming blocked progressively over time with airborne dust contamination driven into them by the cooling fans.
This problem usually manifests itself as a reduced vacuum, due to lack of condensing, in the negative pressure side of the turbine as the cooling efficiency of the ACCW fails.
This in turn leads to reduced generator output.
In summertime, when ambient temperatures are much higher, there is a risk of generator output falling to uneconomic operating levels.
With such high output and consequent large cooling requirement, it is particularly important to maintain optimum efficiency in all stages of the generating process.

The Traditional Approach

Conventionally, the ACCW is cleaned by an automated in built, externally mounted system.
In addition to being relatively slow, there are areas of the units around the plenum internal finned surface periphery which it cannot reach at all, so it is difficult to restore commissioned air flow and therefore cooling performance.
Blocked or restricted air flow can create a stall situation; where blown air cannot escape the plenum through the finned surface and therefore returns in the direction of the fan only to be recycled back toward the fins gaining temperature through each cycle, the result being a severe underperformance of the unit due to lack of cooling.
Previous contractors employed by Scottish Power had not been able to clean the ACCW fin-fan cooling systems successfully.

The Solution

With the extensive experience of cleaning in-fan units of all sizes and configurations, Tube Tech assured Scottish Power that their ACCW’s could be cleaned to a higher standard and faster than had previously been thought possible.
The objective of the clean was to remove as much deposit as possible from the finned surfaces on both the internal and external of the plenums to improve air flow and therefore performance.
To ensure that output from the power station could be maintained during cleaning, the ACCW units would remain on-line, with individual fans isolated and re-instated chamber-by-chamber as the cleaning progressed.
To carry out the cleaning, Tube Tech used a custom-designed telescopic lance system. This enabled the team to work safely from the standard walkways inside the apexes of the fin-fan units – where the deposits accumulate the greatest while eliminating the need for costly scaffolding.

Tube Tech Comment

Scott Donson, Sales Manager: “Cleaning apex ACCWs at power stations is always very satisfying. Clients are often surprised at how much more quickly we can clean them in contrast to remote externally mounted systems and they are always delighted at how much the performance of the ACCWs and therefore the power stations improves after we’ve cleaned them. This site was no exception.”

Client Comment

“Tube Tech have worked well for us and we would welcome their return to site. They are a friendly bunch of lads and work well as a team. It was a pleasure to have them on site.”

Production Team Leader

“I can see daylight through the fin-fans for the first time in ages.”

Commercial Team Leader

“I was really impressed with the work Tube Tech did for us. Our management have since been talking about bringing Tube Tech back several times a year. Although charges appear high at face value compared to the previous company we have used, once the bottom line cost of the other company was added up, cost was almost identical to Tube Tech’s – the added benefit being that Tube Tech got the job done much faster than we expected and looked very professional.”