ESB’s recently completed 435 megawatts natural gas-fired power plant at its Aghada site near Middleton in County Cork is the most efficient and cleanest large-scale thermal facility in Ireland and also one of the most technologically advanced in Europe.
The 435 megawatts Combined Cycle Gas Turbine (CCGT) power plant was built by global power engineering company Alstom for ESB at a cost of Eur360 million. The gas turbine used is Alstom’s latest GT26B 2.2 model.
It is the second GT26 gas turbine powered plant to be designed, engineered and built by Alstom in Ireland following the opening of the Synergen plant at Ringsend in Dublin in 2002. The new Aghada plant will generate sufficient power to provide electricity to around 450,000 homes.
The investment by ESB has expanded generating capacity at the Aghada power station site to 963 megawatts of electricity. ESB has also recently spent Eur75 million on upgrading the four existing units at the site, which have a combined capacity of 528 megawatts.
Aghada is now Ireland’s largest power station and ranks among the most efficient electricity generators in Europe. Eighty people are employed to operate the station.
The investment at Aghada is part of ESB’s programme to replace ageing and less efficient power stations with modern, high efficiency and environmentally-friendly plants.
The development phase for the CCGT project at Aghada started in 2003, construction commenced in 2007, and the new facility was officially opened in April 2010.
Features of the CCGT Plant
The CCGT comprises a gas turbine, a steam turbine and a generator. Hot flue gas exhaust from the gas turbine is passed through a Heat Recovery Steam Generator (HRSG), which incorporates a water piping system that uses this heat energy to convert water into steam. The steam is discharged from the HRSG via high pressure piping into the steam turbine, providing additional energy. “The gas turbine and the steam turbine operate in tandem to produce input into the generator, which produces the generated power supply,” explains Ken Larsen, project manager at Aghada for Alstom. “From the generator there are high voltage connections that transfer out to a transformer, which is in turn connected to the Irish power grid system.”
The CCGT and HRSG are supported by a number of systems and processes which provide water, cooling water, compressed air and chemical dosing. A cooling water pump house takes sea water from Cork Harbour, which is adjacent to the Aghada power station, for condensing the steam which is exhausted from the steam turbine. An electro-chlorination plant is used for dosing to stop marine growth within the sea water extraction system.
A demineralised water production plant sterilises mains water for use within the high pressure feed system for the HRSG. A high pressure pumping installation circulates water around the system for feed water and cooling purposes. Another plant supplies compressed air into a network which runs throughout the power station. Building services, including fire detection, fire prevention, security systems, heating, ventilation and air conditioning, are further aspects of the site.
The CCGT plant is fuelled by natural gas delivered through a new 12 kilometre gas pipeline from Midleton. Distillate oil is stored on site as a back-up fuel.
A novel feature of the new CCGT facility is the cooling water discharge system. Cooling water is discharged over 400 metres offshore in Cork Harbour. The construction of the outfall connecting the plant to the discharge point involved a major civil engineering project (see Panel). The pipeline was fabricated in one piece in Norway and ferried to the Aghada site.
Upgrade to Existing Plant
The existing electricity generating plant at Aghada comprised a 258 megawatt gas fired conventional steam generation unit (Unit 1) plus three 90 megawatt open cycle combustion turbines fired on gas with distillate oil as a back-up fuel. All four units have been modernised during the past four years under a Eur75 million investment programme.
A key aspect of this upgrade entailed the installation of a hi-tech control system to ensure that the existing Aghada generators operate with increased reliability and flexibility in the new All-Ireland Single Electricity Market. The control room at Aghada was also extensively renovated to ensure that management of the new CCGT plant could be seamlessly integrated with the existing system.
The enlarged Aghada power station, which will supply about 8% of the All-Ireland power demand in the Single Electricity Market, is now operated by this dedicated, centralised control system. “Every function to start, to monitor, to fault find, to shut down the plant the plant along with the individual systems and sub-systems are all channeled into one computerised processor, so that one individual can operate the power station automatically,” Ken Larsen points out.
“The new plant incorporates the very latest combined cycle gas turbine technology. It has a cycle efficiency of in excess of 58.5%, which would be the leading edge of what is achievable for any of this plant worldwide,” remarks Paul Smith, Station Manager, ESB Aghada. “Of all the conventional plant connected in Ireland, it is the most efficient and is likely to remain so for the foreseeable future.”
“60% is the ‘holy grail’ of thermal efficiency for combined cycle power plants – no one has achieved that yet,” stresses Kevin O’Donoghue, Operations Manager at the station. “The gas turbine is Alstom’s tried and tested GT26 model. Alstom has upgraded the compressor and has made other improvements in terms of both the mass flow of air through the machine, which is directly proportional to the power output, while improving the efficiency of the engine. So in effect, Alstom has increased the net output of this gas turbine.”
The new CCGT meets all environmental standards, both national and international. It does not discharge any harmful liquids and any air emissions are well within European standards. NOx and CO2 emissions are low and CO2 emission per kW generated are reduced compared to existing electricity generating plants.
“The cooling water which is discharged into Cork Harbour is monitored 24/7 and is clean, if not cleaner going into the harbour following its extraction,” says Ken Larsen. With regard to noise levels, “the plant is one of the quietest of its kind and well within the statutory requirements for industrial plants,” he adds.
“Natural gas is a clean fuel and the carbon intensity is less than other fuels, such as coal, peat or heavy fuel oil. It is also very efficient. Sulphur emissions, of course, are zero and NOX emissions are also very low.” Paul Smith continues: “The new plant marks a big step in ESB’s strategic intent to achieve zero carbon by 2035 in that much of the plant that we have divested or closed was heavy fuel oil powered. We have replaced that plant with the most efficient gas-fired plant using a clean fuel.”
The new facility at Aghada is at the cutting edge of CCGT technology. “It is basically state-of-the-art and it is the most thermally efficient plant in Ireland and stands up alongside all the new CCGT projects that have been constructed by Alstom in the last couple of years in, for example, the UK, France, Spain, Italy, Brazil, Chine etc,” says Ken Larsen. “The prime moving equipment such as the gas turbine, the generator and the control system are absolutely state-of-the-art and give the best design, the best reliability, longevity, security of supply and, of course, efficiency.”
As the main contractor for the project, Alstom has retained a presence on site to support the client technically during a two year warranty period. ESB has also signed a long-term service agreement with Alstom to maintain and service the gas turbine, steam turbine and ancillary systems for 12 years.
The Eur435 million investment at the Aghada site – Eur75 million on upgrading existing plant and Eur360 million on the new CCGT facility – is a major part of ESB’s development strategy to adapt to the new trading environment following the introduction of the Single Electricity Market in November 2007 and to have the right type and mix of generating plant to be able to compete effectively in all three market sectors – base load, mid-merit and peaking demand.
With a current generating capacity of 963 megawatts, Aghada is now the largest capacity generating station in the Republic of Ireland. Indeed, Aghada accounts for about 25% of ESB’s total installed capacity throughout the whole of Ireland. Furthermore, it is the only power station in Ireland serving all three market segments.
“It gives us a foothold in each segment of the market from one location,” remarks Kevin O’Donoghue. “At Aghada we have a fleet of almost 1000 megawatts of plant which is flexible and can compete and win in the new market environment.”
Paul Smith elaborates: “The role of the three existing GE 90 megawatts open cycle gas turbines in the market is to address peaks in demand for electricity because they respond very quickly and can run up to full load within a matter of minutes. So if a generator was to trip, the Grid would instruct us to bring on one of these machines. They are also useful in terms of reserve and might sometimes be brought up to part load, for example 20 megawatts, to act as back-up for wind power, so if wind falls off they would be ramped up.”
The existing gas fired single fuel 270 megawatts generator (Unit 1) at Aghada was until recently operating at base load but is now supplying the mid-merit segment, having been superseded by newer and more efficient plant. The new 435 megawatts CCGT plant serves base load demand.
ESB is also focusing on the renewables sector, as reflected by the group’s ongoing heavy investment in wind energy along with its wave energy project at Carlingford to supplement the 500 megawatts of hydro energy already in its generating portfolio.
“It was part of a strategy agreed and approved by the Regulatory Authorities that has seen ESB close or divest a total of 1500 megawatts of existing plant so that we could build in return 435 megawatts of new plant,” says Paul Smith. “The investment at Aghada has allowed ESB to rebalance its power generation portfolio.”
According to Padraig McManus, chief executive of ESB, the very high efficiency rate of the Aghada power station means it will remain, not only the foremost generator in Ireland, but also among the best in Europe. “The challenge for all energy market participants is to deliver clean, safe and cost-effective electricity to our customers. The Aghada plant, built by one of the world’s leading engineering companies, does all of this. We now look forward to the opening of competition in all sectors of the electricity industry because value to the customer must lie at the heart of every strand of our business planning. ESB is ready to meet that challenge,” comments the ESB head.