Largest circulating fluidised bed boiler begins production

21st February 2013

Lagisza power plant in Poland offers cost effective energy while reducing emissions.

When the Lagisza power plant began commercial operations in late June 2009, it marked a new era in the evolution of circulating fluidised bed (CFB) technology.

At the heart of the 460 megawatt electric (MWe) Lagisza power plant is the world's largest CFB boiler, which is also the world's first once-through unit (OTU) supercritical CFB boiler. Large enough to produce electricity at utility scale, the Lagisza plant has met or exceeded all emissions and performance expectations since coming online.

The design of the Foster Wheeler supercritical once-through CFB boiler is affordable, efficient, and enhances environmental performance. High efficiency leads to lower fuel requirements, and lower levels of ash and emissions, including carbon dioxide (CO2). In addition, CFB technology has excellent fuel flexibility and offers the option of co-firing of biofuels with different grades of coals, which can further reduce CO2 emissions.

The plant also features many other advanced design features that further improve reliability, operational flexibility and overall power generation efficiency and economics. These features include compact solid separators, Intrex super heaters, and low-temperature flue-gas heat recovery that recycles the low temperature heat back into the steam cycle, recovering valuable heat that would otherwise be lost.

The adoption of the Kyoto Protocol for reducing greenhouse gas (GHG) emissions has increased the urgency of reducing CO2 emissions in fossil fuel power plants. Since coal will remain an important source of energy, the focus has been on improving the efficiency and environmental performance of new or repowered older coal-fired power plants.

To achieve this goal, Foster Wheeler has been developing its CFB boiler technology over the past three decades. CFB technology is a clean coal platform with a low temperature combustion process that cleanly and efficiently burns both traditional fuels and carbon-neutral fuels.

Unlike conventional steam generators that burn the fuel in a massive high-temperature flame, CFB technology does not have burners or a flame within its furnace. CFB uses fluidisation technology to mix and circulate fuel particles with limestone as they burn in a low temperature combustion process. The limestone captures the sulphur oxides as they are formed, while the low burning temperature minimises the formation of nitrogen oxides.

The fuel and limestone particles are recycled over and over back to the process, which results in high efficiency for burning the fuel, capturing pollutants, and for transferring the fuel's heat energy into high-quality steam to produce power.

CFB technology offers a number of advantages for refurbishment of older power plants like Lagisza, including improved plant efficiency, multi-fuel capability, and emission control without the use of secondary systems. CFB plant sizes up to 340MWe are in commercial operation, and the start-up of the 460MWe Lagisza CFB plant with supercritical steam parameters marks an important milestone.

The Lagisza plant, owned by Polish utility company Poeudniowy Koncern Energetyczny SA (PKE), replaced old power blocks of the existing 1960s-era Lagisza Power Plant. The CFB boiler was built adjacent to the old boilers and many existing plant systems were renovated for use with the new CFB unit. The plant uses Polish bituminous coal as a primary fuel source, provided from ten local coal mines, and has been designed to co-fire up to 30 per cent coal slurry.

Since all emission requirements can be met without the need for wet desulphurisation and selective catalytic reduction (SCR) systems, total plant investment cost was lower for a CFB boiler, compared to the traditional pulverised coal (PC) alternative also investigated for the Lagisza plant. In addition, plant efficiency has increased from about 35 per cent to nearly 44 per cent. Compared to the original plant, nitrogen oxide (NOx) at the new CFB plant is reduced by 71 per cent and CO2 by 28 per cent.

Foster Wheeler provided the turnkey boiler island, including engineering and design, boiler civil work and foundations, boiler and fuel feeding parts and equipment, environmental controls and flue gas heat recovery system. Foster Wheeler was also responsible for plant construction, start-up, and commissioning.

The Polish plant is the first CFB power plant in the world to integrate CFB technology with vertical-tube, once-through unit (OTU) supercritical steam technology, which provides the best combination of features for efficient, cost effective, and environmentally responsible power production. The Benson low mass-flux vertical tubing technology, licensed from Siemens AG, Germany, offers some clear advantages for CFB technology, including a lower pressure drop over the furnace tubing, resulting in less power needed for feed water pumps, and more power sent to the grid.

The Lagisza design also features integration of the compact separators for circulating solids within the furnace. Instead of hot cyclones with heavy refractory linings, the unit uses steam-cooled compact separators. Advantages of this design include reduced maintenance costs, shorter start-up time, and a smaller boiler foot-print, which is especially important because the new boiler has to fit into an existing site.

The unit design was further enhanced with INTREX (integrated heat exchanger), which extracts heat from the hot circulating material that is returned from the separator, or solids that are taken directly from the lower part of the furnace. Continuous flow of dense solids enables high heat-rate coefficients within a small physical space and prevents formation of deposits on tube surfaces. No mechanical devices are needed to control the heat duty to the INTREX, which is accomplished by air fluidisation of the hot solids.

Overall, initial operating experiences of the world's first CFB using supercritical steam parameters have been excellent. Boiler operation has been stable and easily adjustable while heat fluxes to furnace walls on coal firing have been low and uniform - as was expected. Experience with the Lagisza plant provides a good knowledge base for Foster Wheeler to propose CFB technology with supercritical steam parameters for plants as large as 800MWe in the near future.

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Justin Wehrenberg is with Foster Wheeler Global Power Group, Clinton, New Jersey, USA.


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