|An artist’s impression of Claus C power plant in the Netherlands, which will replace the Claus B steam unit with a high efficency combined-cycle plant that will increase power from 640 MW to 1300 MW|
Building new power plant is an expensive and time consuming business. Investment decisions are linked to economic growth, availability of finance, fuel costs, the regulatory regime and market incentives as well as likely future demand for energy.
If developers are to build new plant they need finance for the land and plant as well as resources to navigate the hurdles of regulation and planning permissions. In an economic climate of low growth, the option of upgrading existing plant rather that building a new facility may be more attractive. There are a range of options for renovating and improving existing plant, which can extend life expectancy, increase output and flexibility and help meet environmental and emissions regulations.
The drive to de-carbonise electricity supply means that European electricity companies are increasingly rewarded for being able to ramp up generation at short notice to provide cover for fluctuating capacity of renewable energy sources, notably wind power. Fossil fuel power plants perform best when operated at a relatively uniform pace. Gas turbines and coal fired boilers take between ten minutes and several hours to reach full power. Older plants have problems adapting to rapid changes in load, a situation that can to some extent be remedied by plant upgrade. Investing in efficiency improvements can also lead to reduced carbon dioxide emissions per kilowatt of energy produced.
Jonathan Robinson, senior consultant in the energy practice of consultancy Frost & Sullivan, told PEi: “Although new plant costs have fallen from the 2008 peak, the cost is still significant. Over the same period, project financing costs have increased as the cost of capital globally has risen. Banks are still lending, but at lower volumes than in the past. Many of the major utilities in Europe face significant financing challenges as they are under pressure to increase capacity in the system, but also need to reduce debt levels. This climate makes improving the efficiency of older assets very attractive. The costs are significantly lower and there is good upside potential. Even a modest increase in efficiency can deliver real returns.”
|Siemens estimates a comprehensive upgrade of a steam turbine system can “tease an extra 30 to 40 MW out of the plant”|
The European Union is relying on the market forces of emissions trading to bring about power plant modernisation. From 2013, the most efficient power plants will be used to set standards of emissions and will receive emission permits free of charge. Carbon dioxide emission certificates will be auctioned and power companies will have to pay for some of their CO2 emissions via emissions certificates. This will make old power plants increasingly unprofitable.
The 2001 EU Large Combustion Plant Directive decreed that all combustion plant built after 1987 must comply with emission limits for sulphur dioxide, nitrogen oxides and dust. For power stations that were operational before 1987, owners faced the choice of either installing emission abatement equipment or restricting operations from 2007 with a view to closing by the end of 2015. Thus a number of old oil and coal plant will retire within the next four years, while others have been subject to upgrade programmes.
Much of the coal fired generation capacity built before 1975 is in Europe, while the US accounts for over half of all plants that are more than 30 years old. Good maintenance regimes and control of coal quality and water treatment can help to keep existing coal plants running longer. However, as the new emissions regime comes into play, upgrading or refurbishment will increasingly make economic sense.
The average global efficiency of coal fired plants is 28 per cent compared with 45 per cent for the most efficient plants. Improving efficiency increases the energy that can be extracted from a single unit of coal. The World Coal Association says that improving the efficiency of the world’s oldest and most inefficient coal fired plants would reduce CO2 emissions from burning coal by almost a quarter, representing a 6 per cent reduction in global CO2 emissions. Options for upgrading coal fired power plants to extend life and improve performance include:
- Upgrading data analysis systems (typical lifetime 10–15 years) can improve operating flexibility, reduce maintenance costs, reduce emissions and extend plant life.
- Air heaters improve boiler efficiency by heating combustion air and cooling boiler exit flue gases. Improved air heater surface cleaning, air to gas path seal improvements, and other upgrades and refurbishments can improve efficiency.
- Efficient coal pulverisers give a plant the flexibility to use different types of coal. Improved and refurbished pulverisers often reduce unburned carbon. Automated systems can control coal and air distribution systems to improve performance, especially after installation of low-NOx burners.
- Boiler upgrades include upgrading the burners and improving the soot blowers to improve heat transfer and efficiency levels.
- Current turbine designs perform more efficiently than older designs. Steam turbines can be refurbished by repairing or replacing turbine blades and replacing or adjusting blade and shaft seals.
- The heat transfer coefficient in condenser tubes is reduced by a build up of scaling, which results in higher condenser pressures, reducing steam turbine output and efficiency. Cleaning or replacing the condenser tubes improves performance.
Factors affecting upgrade decisions and costs include the condition of the existing plant, the lifetime of the extension, the increase in power output and the environmental standards required from the refurbished plants. An International Energy Agency report published last year stated that project capital costs ranged from $0.25 million to over $1 million depending on the scope of the changes.
Europe has over 500 operational steam turbine plants that are older than 25 years, although gas turbines tend to be newer than those used in coal fired plant. Upgrading steam turbines primarily involves replacing the rotor and the inner casing. Modern turbine blade technology and enlarged flow areas boost the efficiency and performance of the turbine. The use of new seals in high- and intermediate-pressure turbines reduces clearance losses, which increases efficiency. These measures can increase the service life of the turbine by 15 to 20 years.
Advances in 3D computer simulation have led to the development of turbine blades with very low flow resistance. Improvements to the blade path can further reduce losses improving efficiency so that more energy is transferred to the turbine blades.
Turbine manufacturer Siemens estimates costs of between €20 million ($27 million) and €60 million to comprehensively upgrade a steam turbine system for a medium-sized power plant which can “tease an extra 30 to 40 MW out of the plant”. The company cites an example where Energie Baden-Württemberg invested around €30 million on upgrading its cogeneration plant in Altbach, near Stuttgart, to keep the plant in operation for the next 30 years. Siemens renewed the plant’s control systems and upgraded its steam turbine, replacing the blades and seals while retaining the entire outer casing. This boosted output by 11 MW and led to a reduction in annual CO2 emissions of 50,000 tonnes over 4000 operating hours at full load per year.
Harald Thaler, industry director in Frost & Sullivan’s energy practice, said: “Greater operational flexibility is becoming an issue, and not only for new plants. Gas prices are currently fairly high and generator margins being squeezed, affecting the investment environment for new gas plant. As gas fired generation is less economical than coal in the current environment, coal plant operators are looking to become more flexible by upgrading their existing steam plant to achieve higher operational flexibility.”
Upgrading coal-fired plant: Belchatow, Poland
The 4450 MW PGE Elektrownia Belchatow is the largest fossil fuel power station in Europe. The plant consists of 12 x 370/380 MW lignite fired reheat units commissioned between 1982 and 1988 and generates a fifth of Poland’s electricity. Its owner, PGE (Polska Grupa Energetyczna), is undertaking a modernisation programme to increase output, ensure compliance with EU directives and to extend the working life of the units.
Flue gas desuphurisation systems have been installed on the ten units being modernised and the low-pressure turbines have been retrofitted. In April 2009 PGE awarded a €160 million contract to Alstom to retrofit unit 6. Most of the main equipment has been modernised, including boiler, steam turbine, feed heating system and generator. The scope of the contract covered the reconstruction of the boiler and its auxiliary equipment, replacement of high-pressure and intermediate-pressure part of the turbine, increasing power output of the generator and installation of new high-pressure heaters. The work will halve NOx emissions and reduce CO2 emissions by over 400,000 tonnes per year. The upgrade will improve availability and reliability and extend the unit’s lifetime by 20 years.
In November 2010 contracts worth approximately €140 million were awarded to retrofit the turbine island and air quality control equipment at units 7 to 12 of the plant. Alstom will engineer, supply and install the high-pressure and intermediate-pressure turbines, associated auxiliaries, the turbine controller, bypass systems, heater refurbishment, instrumentation and control and integration engineering, coupled with installation supervision. When completed, the retrofit will increase each of the six units’ power output by 20 MW, increasing output by 120 MW. The project will boost cycle efficiency by 2.4 per cent, reducing CO2 emissions by about 600,000 tonnes per year and thereby complying with EU emissions directive 2001/80/WE. The retrofit will also improve the six units’ availability and reliability as well as support the extension of the plant’s lifetime by 25 years. In March this year Alstom won a contract to retrofit six generators at units 7 to 12.
Upgrading Gas-Fired plant: Claus C, Netherlands
Essent’s Claus power plant in Maasbracht in southeast Holland originally consisted of two 640 MW gas fired steam-generating units, which came on stream in 1977 and 1978. Sixteen years later the units were converted to start/stop units. After another 20 years, with the steam units approaching the end of their normal operating life, the utility opted to re-power the existing power plant to create a new Claus C combined-cycle power plant.
In June 2008 Essent – which was now owned by RWE – awarded Alstom the contract to convert unit B of the Claus steam power plant into a high efficiency combined-cycle power plant. This would increase the power from 640 MW to more than 1300 MW and also raise the thermal efficiency of the unit from about 38 per cent to more than 58 per cent. Converting the unit into a combined-cycle power plant involved adding three GT26 gas turbine generator sets and heat recovery steam generators, and retrofitting the existing Unit B steam turbine. Much of the existing infrastructure was refurbished for further operation: a large section of the existing steam turbine building and electrical building, and the direct cooling facilities – such as the main cooling water pumps and the cooling tower – were reused, as was the condenser. Essent says that the refurbishment saved 15–20 per cent of the cost of installing a totally new combined-cycle power plant.
The plant design was driven by the capacity of the existing steam turbine of 640 MW. The steam that could be generated from the thermal output of three GT26 turbines could drive a steam turbine of about 500 MW. That meant retrofitting the steam turbine to reduce the steam turbine load. The internals were completely retrofitted and new rotors, blades and vane carriers installed.
|Refurbishment of Waldeck 2 started in 2005 and increased its capacity from 440 MW to 480 MW|
The use of a trio of gas turbines will give flexibility as the plant can be operated with one, two, or all three. It will also mean high plant availability since the facility will not need to completely shut down when maintenance is scheduled. The Claus power plant will produce more than 100 per cent more power compared with the original steam power plant unit, and the increased efficiency will mean the total fuel consumption will only increase by 35 per cent. This will reduce the plant CO2 emissions by up to 40 per cent. The gas turbines at Claus C achieved first firing in July and have been synchronised since then.
The economic climate means that even upgrading may not be the answer. The 1875 MW Teesside Power Station in north east England is Europe’s largest combined-cycle gas turbine (CCGT) combined heat and power plant. It has a thermal efficiency level of 50 per cent and can produce up to 800 tonnes of process steam per hour for the neigbouring Wilton International chemical complex.
The power station opened in 1993 and after GDF Suez acquired the plant in 2008 ownership was transferred to International Power following its merger with GDF. In 2008, plans for a £500 million ($785 million) upgrade of the plant were approved. The plan was to replace existing gas and steam turbines with four new 300 MW gas turbines and two new 340 MW steam turbines, reducing the total number of gas turbines on site to maintain the overall power output. However, in March 2011 the owners announced that the plant was to be mothballed, capacity cut to 45 MW and the upgrade put on ice, due to cheaper foreign imports.
Upgrading pumped storage power plants
With the German nuclear phase-out, renewable energy has a vital role to play. E.ON operates the Waldeck pumped storage power plants in Northern Hesse, central Germany. Waldeck 1 has four horizontal units and a total installed capacity of 140 MW. It was commissioned in 1932 and forms part of the Edersee power plant complex, which includes Waldeck 2 cavern PSP (480 MW) commissioned in 1975, and the 20 MW Hemfurth storage power plant on the Edertal Dam.
E.ON has recently invested about €50 million in the modernisation and new build of Waldeck 1, and about €30 million upgrading Waldeck 2. Work on Waldeck 1 started in 2004 with a new shaft powerhouse constructed in parallel next to the existing machine hall. The existing upper basin and the penstocks of Waldeck 1 were refurbished and a new pump turbine as shaft powerhouse connecting to one of the penstocks was constructed. The planning, modernisation and construction took five years and the upgrading of Waldeck I was completed at the beginning of March 2009. Voith Hydro, a joint venture of Voith and Siemens, was appointed the main contractor for the construction.
The refurbishment of Waldeck 2 started in 2005. Modernising the facility would increase the original 1975 capacity from 440 MW to 480 MW. In 2006, one unit was rehabilitated by equipping it with a new turbine rotor allowing a rating of 240 MW, an efficiency increase of 10 per cent. Between 2009 and 2011, the second turbine was fully overhauled, increasing installed power to 480 MW.
E.ON is currently planning to raise the overall plant capacity of Edersee to 920 MW by installing a third underground pump turbine in the Waldeck 2+ project. The utility will begin building a new 300 MW pumped-storage plant with an underground turbine room alongside the existing Waldeck 2 facility next year. Construction is expected to take four years, with the new capacity entering service in 2016.
Nuclear power uprating: almaraz
Upgrades to nuclear facilities are thriving too. Spain plans to add 810 MW (11 per cent) to its nuclear capacity by upgrading its nine reactors. Recently work was completed to boost capacity at the Almaraz nuclear station by about 8 per cent at a cost reported to be about $50 million. Almaraz is operated by Nuclear Almaraz-Trillo (CNAT), a utility owned by Iberdrola, Endesa and Union Fenosa. The station consists of two PWRs which started operating in 1971 and 1983. In January the government approved newly completed 70 MW uprates for each reactor. The work did not impinge on the nuclear island, but revolved around the design and manufacture of improvements to the generators and high pressure turbines and associated plant.
Boosting the two reactors’ power from the initial plant capacity of 2686 MW to 2947 MW took four years to plan and implement. A small power augmentation ‘Miniaumento’ project to increase thermal power recovery by l.6 per cent took place in 2003, raising power from 2686 MWt to 2729 MWt. The recent work, completed earlier this year, added an additional 8 per cent.
The renovation programme included changing the control systems to a new digital Ovation platform system and the installation of new separators, super-heaters, transformers, alternators, exciter and isolated phase bars. The Spanish nuclear regulators have now approved the station to operate until 2020. This summer saw Areva sign a contract to modernise the reactor circulation system at the Leibstadt nuclear plant in Switzerland. The work, which will start next year and is due to be completed in 2015, will include replacing analogue technology with digital instrumentation and control systems, reworking pipes to reduce the number of welding seams installing medium voltage speed drives.
Uncertainty over economic growth and availability of finance mean utilities and developers are deferring major investment decisions. Where the option exists, upgrading existing plant can enhance plant lifetime, improve efficiency and give increased output for a fraction of the cost of building new plant. While the global economy remains in the doldrums, this option looks likely to be favoured.