Power Engineering International

Welcome to the online version of our Power Engineering International (Pei) print publication. This is where to find archive magazine articles as well as our present edition. For any feedback on the content contact us here or discuss on PEi LinkedIn Group

Cooling flue gas to maximize power plant efficiency

The high efficiency rating of the new generating unit currently under construction at the Polish power station Belchatow, will, to a certain extent, be due to the implementation of innovative flue gas coolers equipped with heat exchange pressure hoses made from AlWaFlon®, a robust PTFE-based material.

Martin Brück, DuPont, Switzerland

The 12 existing generating units at Europe’s largest lignite fired power station in Belchatów, Poland, are to be supplemented by a new 858 MW rated unit (Figure 1). Following its scheduled completion in October 2010, the plant will be one of the country’s most efficient lignite fired power stations, with a rating of approximately 42 per cent, as well as one of the world’s most modern installations. As a consequence of this high rating, both fuel consumption and emissions will be reduced.

Figure 1: Construction as of the end of April 2009 of the new 858 MW unit at Belchatów in Poland
Click here to enlarge image

The prime contractor for the specification, construction and commissioning of the new power plant is Alstom, while the customer and future operator of the plant is the power company PGE Elektrownia Belchatow SA.

A significant contribution to the new power plant’s high efficiency rating are two innovative flue gas coolers. Each is equipped with five heat exchanger modules, incorporating approximately 500 000 metres of AlWaFlon pressure hose, they reduce the temperature of the flue gas by about 50 K. The out-coupled heat resulting from this process (two x 32 MW) contributes towards the feed water heating at the power plant, while the surplus steam is used for energy production, thereby significantly improving the overall energy balance of the plant.

Integrated pressure hose concept

Wallstein Ingenieurs-Gesellschaft of Recklinghausen, Germany, is the developer and supplier of the entire heat transfer system, including its associated systems engineering, housing and piping. It is also responsible for its on-site assembly, which was commenced at the beginning of 2009. When selecting the material for the heat exchanger pressure hoses, the company chose the AlWaFlon fluoropolymer system over the dominant corrosion-resistant nickel-based alloys. This was because although metals may allow better heat transfer they are unable – unlike polytetrafluoroethylene (PTFE) – to resist the levels of corrosion exposure associated with this application.

AlWaFlon is defined by the interaction of an almost entirely chemically inert fluoropolymer, designed for use in highly corrosive and reactive gases, and the use of complementary processing methods.

Its joint developers are Wallstein, DuPont of Switzerland, as manufacturer of the base material Teflon® PTFE, and Fluortubing of the Netherlands, as the producer of the assembly-ready pressure hoses for integration in the heat exchanger housing (Figure 2).

Figure 2: A fully assembled air gas cooler is 13 metres long and approximately 2 metres wide and high
Click here to enlarge image


Ideal for Demanding Applications

The AlWaFlon concept combines cost-efficient processing and application benefits, with exceptional property consistency over long production periods, from charge to charge and for the entire hose length.

Compared to many other fluoropolymer grades, the attributes of AlWaflon include higher upper service temperatures of a maximum of 260 °C and a significant increase in the Vicat softening temperature to between 130 °C and 140 °C, as well as high flexural fatigue strength and stress cracking resistance.

The overall result is long-term resistance in demanding conditions. Decisive for Wallstein was the ability of AlWaFlon pressure hoses to resist the extremely aggressive media that occur in the highly corrosive environments encountered during energy production, when the temperature of flue gases is cooled to below the acid dew point.

In such cases, contaminants such as sulphur dioxide (SO2), a high proportion of which is present in the flue gas emitted from the Belchatów lignite fired plant, sulphur trioxide (SO3), hydrogen fluoride (HF) and hydrochloric acid (HCl) all mix together with water to form corrosive mixed acids.

These condense on the colder surfaces of the heat exchanger pressure hoses and bond with dust contained within the gas to form solid coatings. Corrosion-resistant steels, even nickel-based alloys, can only resist such attacks for a limited time.

The heat exchangers deployed at Belchatów use pressure hoses with an outer diameter of 12 mm and a wall thickness of 1 mm. Further benefit is gained from the distinctive non-stick properties and self-cleaning effect of the fluoropolymer. In comparison to metal hoses, considerably fewer deposits are formed on the exterior and those that do form can be removed both quickly and thoroughly, and therefore in a cost-efficient manner. This helps extend maintenance intervals and increases the overall availability of the plant.

Long-term Reliability

The AlWaFlon pressure hoses, manufactured on the basis of the almost entirely chemically inert PTFE, provide long-term resistance to the combination of internal pressure, high temperatures and corrosive media. This has been confirmed by internal long-term hydrostatic strength tests according to DIN 16 887, carried out by a BASF Ludwigshafen testing laboratory in Germany, which compared the results from earlier tests with other polymers conducted under the same conditions.

The results of 10 000-hour tests, which, according to DIN ISO 9080, can be extrapolated to a time period of 50 years, are convincing. This can be seen Figure 3, which shows the long-term behaviour of AlWaFlon pressure hoses at different temperatures. While Figure 4 shows the higher performance of AlWaFlon when compared to other perfluoroalkoxy (PFA) and PTFE polymers used in power stations to date. Ongoing, long-term testing based on DuPont’s Teflon PTFE Fine Powder, conducted by the German TÜV Süd since the 1960s, confirms the accuracy and admissibility of the extrapolation in such cases.

Figure 3: Behaviour of AlWaFlon pressure hoses at different temperatures during long-term hydrostatic strength tests
Click here to enlarge image


Figure 4: Comparison of AlWaFlon pressure hoses and equivalent products in internal long-term hydrostatic strength tests
Click here to enlarge image

On the basis of their high, long-term resistance to internal pressure and tensile strength, AlWaFlon pressure hoses can be used at lower wall thicknesses than pressure hoses made, for example, from the equally corrosion resistant fluoropolymer PFA, whilst providing the same levels of safety and being exposed to the same mechanical stress. Accordingly, larger amounts of heat energy can be out-coupled at the same length, or alternatively the number/length of pressure hoses used can be reduced to achieve the same level of heat exchange performance.

Basis for Continued Success

Wallstein has conducted pioneering work in the area of heat exchanger production and has developed a system that combines high cost efficiency with long maintenance intervals, while also making a significant contribution to energy saving.

In addition, DuPont, in cooperation with the TÜV Süd, has attained certification of AlWaFlon for use as a pressure hose at high temperatures. Such a range of benefits has been a convincing argument for additional suppliers of heat exchangers for power stations. Indeed, Wallstein has managed to win further large European projects where AlWaFlon pressure hoses will again be used. These include the power station sites Siekierki in Poland and Ledvice in the Czech Republic.

The author would like to thank Peter Dittmann of Wallstein Ingenieurs-Gesellschaft, Germany and Alex Soeterbroek of Fluortubing, the Netherlands for their invaluable contribution to the article.

More Powe Engineerimg International Issue Articles

Follow Power Engineering International on Twitter

Editor's Picks

GE unveils transformational Digital Power Plant

GE yesterday unveiled a digital initiative that it claims will revolutionise the power industry and save plant operators b...
Anne Carpenter of IEA Clean Coal Centre

Report highlights need for enlightened approach to water and power generation

The International Energy Agency’s Clean Coal Centre has produced its latest insights into what is referred to as the ‘wate...

UK gives £2bn backing to Hinkley Point nuclear project

The UK government has reaffirmed its commitment to Hinkley Point C new nuclear power station by unveiling a £2bn ($3.1bn) ...

Policy tinkering sees financial lure of UK renewables sector plummet

The UK’s attractiveness for renewables investment has plummeted in the last few months thanks to “policy-making in a vacuu...

US leapfrogs China to top renewables investment table

The US has leapfrogged China to the top slot in a highly-regarded annual analysis of the best countries in the world for r...

Latest Articles

Editorial Guides

Lubrication Challenges for the Biogas Industry in 2015

The biogas industry is growing in importance as the world continues to look for alternative, clean energy sources. However...

Maximising Power Plant Efficiency

The need for power plants to operate at maximum efficiency and flexibility while cutting emissions is greater than ever be...

How to cut your OPEX

How to cut your OPEX In a constantly evolving electricity market, factors such as over capacity and low coal costs can pu...

Buyers Guide Companies

Rolls Royce Energy Systems

We supply gas turbines, compressors and diesel power units to customers ...

Lenox Instrument Co

Lenox Instrument Co is a manufacturer of highly reliable fixed and porta...

ATG Electronics

For more than a decade, ATG Electronics has established itself as a lead...

SWAN Analytical Instruments AG

Is one of the leading manufacturers of online analytical instruments.

Bran & Luebbe, An SPX Brand

Bran & Luebbe, an SPX brand, has been a worldwide leader in metering, an...

Buyers Guide Products


Compact voltage regulator, integrates all ...

Excitation System

Our excitation systems are recognized worl...

DMT340 Series Dewpoint and Temperature Transmitters for Very Dry Conditions

The Vaisala DRYCAP® Dewpoint and Temperatu...

MHT410 Moisture, Hydrogen and Temperature Transmitter

The Vaisala Moisture, Hydrogen and Tempera...

Control Servo Motor SMR

A Voith control servo motor is a linear el...

Power Engineering International


The Effect of Moisture Sensor Location on Reliable Transformer Oil Monitoring

Power transformers are among the most valuable and important assets in electrical power networks and moisture is one of the key factors impacting the operational performance of transformer oil.&nbs...

Engineering & Design for Lean Construction

AVEVA introduces the benefits of Engineering and Design for Lean Construction by challenging the concept of ‘right first time design' and presenting a ‘Lean’ approach. A Lean approach to project ex...

Bridging the Power Gap in Africa: Testing options to manage constrained short to medium term system operations

Around the world, existing power systems face increasingly constrained operations in the short to medium term with available ageing generation capacity.  In this paper, PLEXOS® has been used t...

AVEVA’s Digital Asset Approach - Defining a new era of collaboration in capital projects and asset operations

There is constant, intensive change in the capital projects and asset life cycle management. New challenges and opportunities are continually appearing thanks to dramatic developments in technology...

Latest Digital Edition

Look Inside >
Current Issue

Article Archives for Power Engineering International Magazine