Combined-cycle gas-fired power station returns to full 860MW output
Global power generation firm, InterGen, was experiencing a steady decline in output from its 860MW combined-cycle, gas-fired, power station in the UK. The problem was traced to reduced efficiency of the plant’s air cooled condenser (ACC), whose fin-fan units had progressively become clogged with pollen and other dust from surrounding agricultural land.
The built-in cleaning system could not clean the ACC fast enough, so Tube Tech was called in. Following a week of intensive night working by Tube Tech, the ACC was completely cleaned and the power station was restored from a 500MW low to its design output. The 860MW plant is a combined-cycle facility, using a combination of two GE gas turbines and a Hitachi steam turbine.
The facility’s extremely efficient, low-noise, environmentally sound air-cooled condenser technology allows it to use 90% less water than typical water-cooled plants. The plant also achieves very high levels of efficiency by directing the exhaust heat from the combustion turbines to heat recovery steam generators (or boilers) that then produce additional power from a steam turbine.
The steam condenses rapidly as it is passed through a massive air cooled condenser (ACC) to create a vacuum that increases pressure and efficiency in the turbine. The ACC is comprised of 35 fin-fan units arranged in seven ‘streets’, with five plenums per street. The plant’s efficiency means that it is among the cleanest fossil-fuel power plants in the United Kingdom
During 2006, the plant management became aware that on hot days it was difficult to maintain the necessary vacuum. On investigation, extensive accumulations were discovered on the cooling fins of the ACC. The power station is located in an area of quite intensive agriculture, which gives rise to high levels of airborne pollen in the spring and, to a lesser extent, dust at harvest time. These airborne particles had been steadily clogging up the cooling fins of the condenser, resulting in a significant loss of efficiency – the power station’s output had fallen to around 60% of its design rating* – around 500MW.
Although the ACC is inspected regularly and cleaned where necessary, it tends to clog up again fairly quickly. There is a built-in semi-automatic cleaning system, which has to be manoeuvred into place manually for each fan unit. This was tried first for four days and was proving successful, but it was taking too long, with significant loss of production each day. The manufacturer of the built-in cleaning system was unable to help in the time available, but fortunately a member of staff at the plant had had dealings withTube Tech before and passed the contact details to the appropriate manager.
The client takes up the story: “Tube Tech responded very well to our enquiries – from initial contact to coming on site and beginning work was only a week, which was very helpful. The job done was excellent; I have no complaints at all. Tube Tech happily accommodated working night shifts for us, which enabled us to shut down some fin-fan units to improve the working environment for them. It also helped us maintain output during peak demand. We didn’t really need to get involved at all – the Tube Tech team just did their stuff and we hardly knew they were here – apart from the obvious results.” The client says that the improvement in performance was almost immediate: “It took a week to clean the whole ACC, by which time it was back to design performance.”
For the clean, Tube Tech used a special telescopic lance system, which enabled the team to work from walkways inside the apexes of the fin-fan units – where the deposits were worst – eliminating the need for costly scaffolding.
Speaking about how the job went, the client comments: “The Tube Tech operatives were clean and tidy, with good adherence to health and safety requirements. We carried out a visual inspection ourselves once the cleaning was completed and we also brought in an independent consultant, who agreed that the cleaning had been carried out to the correct standard. We had already fitted monitoring equipment to each fan unit, to enable us to measure actual performance against design performance, from which we could see that the units were performing at or close to design spec. We are currently discussing another clean of the ACC with Tube Tech, to ensure it is as clean as possible before this year’s warm weather.”
The client concluded: “I was pleased with the service from Tube Tech and am happy to continue that relationship. I tend to measure these things by how much involvement is required from us. The whole plant is run by just thirty two of us, so resources for monitoring contractors are limited. I am satisfied that the Tube Tech teams worked safely and productively with the minimum of supervision, which is a big plus.”