Dry air protection for the power industryCreating efficient conditions for increased productivity

p o w e r a p p l i c a t i o n s

Benefits of dry air protection

To optimise your mechanical equipment, you need to create the right environment. High humidity causes condensation, corrosion and rust, which in a power plant or wind turbine, causes problems with gas turbines power performance, pumps, switchgears and electronics operations. This could lead to start up failures after maintenance outages, with fines for non-delivery.

Munters equipment ensures that power plants and wind turbines are protected from corrosion and stay in perfect condition - all this for a fraction of the cost of a new plant or equipment.

Also fouling of power plant systems due to dust ingress, liquid or salt air can be reduced with Munters mist elimination techniques.

Munters technology has been successfully used in over 320,000 installations worldwide

Gas Turbine Evaporative Cooling results in more energy per cubic metre of natural gas.Munters high efficiency evaporative cooling media pre-coolers increase the combustion air density by reducing the combustion air temperature. Using Munters adiabatic cooling media power output is increased by at least 5%-6%, and up to 60% in very hot or dry climates.

LAY UP / STANDBY PERFECTLY PRESERVED READY FOR QUICK START UP

Prevent corrosion and condensationHumidity control for turbines, boilers, piping, reactors

WIND TURBINE CLIMATE CONTROL

Reliable prevention of moisture damage and particle ingress in wind turbines is very important to avoid short-circuiting and damage to electronics.

Prevent corrosion, mould and condensation of towers and nacellesIdeal for land and off shoreLow energy consumptionStop rain, hail, snow and particle ingress

COMPRESSOR STATIONS

Preserve standby gas compressor systemsReliable low cost operation and maintenance

Mist Elimination to increase filter life and improve outputWith cleaner air there will be less fouling of filters resulting in improved efficiency, which improves output and saves money.

Increased operating timeReduced pressure drop to improve gas flowLower maintenance

Create more efficient power productionAs a power station engineer, you will have a thorough knowledge of the equipment needed to successfully run your plant. But are you as familiar with the vapour in the atmosphere which can degrade your electrical equipment and affect your plant off-load?

Studies have shown that at a high relative humidity (RH) of 60-100%, rates of corrosion are 100-2000 times greater than at lower humidity value of, say, 30-50%. At high RH, electrical resistance is up to a million times worse in cables, wiring harness and insulation.

RH is a function of the temperature and moisture content of the air. The RH within a power station may be very different to that on the outside, and can vary within the building due to variations in operating temperatures and possible steam and water leaks. Knowing the alsolute humidity is important in determining whether materials, such as transformer oils, are at risk of degarding or becoming too wet for use.

Dehumidification by Munters removes the ambient moisture, eliminating corrosion and humidity-induced electrical and electronic faults. This ensures reliable operation with fewer failures, lower maintenance costs, maximisayion of plant availability and a key benefit in today's competitive market.

•Increase power output•High turbine efficiency•Low operating cost•Short payback

•Avoids humidity-induced faults•Lowers maintenance costs•Increases plant availability•Guaranteed to stop corrosion•Loss due to unavailability can be more than £100,000 a day

Power stations in operation

AlternatorsDuring operation, large machines are usually hydrogen cooled, working at four bars with pressure dew points varying between -6°c to -40°c. This can continue until the pressure boundary has to be disturbed, such as to allow inspection, repair or replacement of the rotor or stator (both of which can be preserved using the Munters method).

If the insulation is allowed to get wet it's electrical resistance is lowered. This has to be corrected before restarting. Traditional methods of drying-out include passing a current through the windings to heat them, or passing a dry gas like nitrogen or CO₂ through the casing. These methods can add up to four days in-line time at start-up following an overhaul.

Far better, is to circulate dry air through the casing, via convenient inspection points, or through an air-locked tent encasing the whole machine. This maintains the high insulation resistance of the windings, allowing immediate start-up and safeguarding earnings of, perhaps, £100,000 a day.

Dry air also avoids moisture which causes deterioration of the stator and winding supports and it protects the rotor end-caps which are vulnerable because they are made from non-magnetic austenitic steel. Experience has shown that corrosion has caused rotor end-caps to shear off, breaking through the casing and causing extensive damage. These items, costing millions of pounds, are kept dry and spares are stored in dry air sleeves.

Alternator excitersHigh RH conditions result in low insulation resistance and deterioration of the brush gear, incurring similar time penalties as the main generator.

Steam raising equipment, steam and water sideA plant built and run to cause a minimum of corrosion whilst on-load, may not satisfactorily withstand high RH conditions during off-load periods. For instance, austenitic stainless steel, when contaminated with chlorides and , to a lesser extent, suplhates, can sustain intergranular attack. Only a dry environment will resolve the problem.

Power stations under maintenanceWhatever the method of power generation, most plants can benefit from dry air in various area, some of which may be neglected.

Phase Isolation Bus-BarsAn obvious example, where dry air saves maintenance costs and improves reliability, is in phase seperation (or isolation) bus-bars. Where dry air circulation is introduced into existing power stations, the cleaning intervals are extended from three, to 12 years.Expensive repairs and lack of availability due to ‘flash-over’ from moisture ingress are also avoided.

Stand-by PlantPlant on stand-by, such as pumps, fans and turbines, are sometimes in high humidity areas where driers can be used to advantage. For example, the motor insulation can degrade, even if heaters are fitted, so that the motor is not available when it is most needed.

Dry air can save the £60-70,000 cost of a 6000 BHP HP feed pump motor rewind and the associated in-house costs, such as that of uncoupling. A similar solution succeeds for emergency gas turbine generating sets kept on stand-by duty. Dry air promotes quick start-ups, with the bonus of eliminating stress corrosion cracking of rotor end rings due to off-load attack.

Switch Gear RoomsThe main switch gear rooms in power stations are in normally dry areas, but some which could be vital can become exposed to damp conditions. A failure in operation could result in the renewal of possibly obsolete equipment, or even worse, a failure of a complete turbine. Dehumidification units ensures performance and reliability.

Pre-stressing tendons in Nuclear reactor secondary containment and pressure vesselsPre-stresssed tendons play a vital part by contributing to the strength of the concrete pressure vessels of several nuclear power stations. They are fed into ducts which run over and round the cylindrical and hemispherical vessels. The strands are often coated or encased in protective grease, but pits can form due to the coating becoming contaminated by water. In extreme cases this can mean replacing the tendon at a major cost.

On other sites, dry air alone, protects. The consitions can then be controlled and monitored, and tendon inspections carried out easily with no grease to scrape off.

•Improves reliability•Extends cleaning intervals•Allows quicker start-ups from standby•Improves controllability of conditions

What Munters can save youThe boiler and superheaterThese have a protective magnetite internal coating but it does not last long under high humidity conditions. Dry air will inexpensively maintain a low RH, operator safe and trouble free protective environment, without hindering maintenance work on any of the steam and water side equipment. These items, emptied at as high a temperature as possible wilst admitting dry air, will remain dry and corrosion free. A vacuum pump, together with a heater or compressed air, helps to ensure that no water remains in pendant sections of superheaters or sagging tubes.

The reheaterVulnerable to inter-granular attack, due to boiler salts deposition from carry-over in the steam, (such as sulphate), this item can also fail due to the relative thinness of the tubes. The condenser vacuum plant is useful in drawing dry ait through the reheater tubes and consender itself. Or, if turbine cooling air is installed, this will result in a dry-out. Munters dry air is then most effective in maintaining corrosion free conditions.

Boiler and reheater lay-upA survey before boiler lay-up or maintenance dry-out, will show, if and where, extra drains should be fitted to achieve best results. Old methods are now being replaced by the Munters dry air method. Nitrogen can give safety problems if work has to be carried out on the plant and on its own does not prevent inter-granular attack and is expensive. Wet storage does not allow work on the equipment, requires constant recirculation, heating and monitoring to ensure the sufficient chemicals are in solution and that the system is full. Whatever the inhibitor used (the very effective Hydrazine is not encouraged in many countries for health reasons) it's concentration has to be reduced on re-starting, with a possible cost penalty imposed by the disposal authority.

Dry air storage has no such difficulties and at Pleinting, Germany £35,000 a year was saved by switching from wet to dry preservationMunters dry air also allows a very fast start up time. A study on a 107 MW unit at Gerstein, Germany, showed the boiler on on-line in just 1 hour and 40 minutes.

The penalty for not taking precautions is high. Pitting can occur in the boiler/economiser tubes and if complete failure occurs it can take a week to remedy and cost not less than £1.5 million. General rusting will certainly occur and contaminate the boiler feed water on raising power. Today's stringent controls over high-pressure and once-through boilers can mean two days of clean-up flushing during in-line time. The cost of water at £250 per 100,000 gallon is small compared with loss of availability at £200-300 per MW per day.

Boiler feed and condensate systemsThese systems are often quite short, but there are still worthwhile economies to be made by using dehumidification to prevent corrosion during shutdown, thereby reducing maintenance. On restarting, the reduced level of flushing needed, brings further savings. Longer systems, typically in nulcear stations with once-through boilers, have a much greater propensity for corrosionm so that the payback on dehumidification (as the plant comes off-line for overhaul) far outweighs its cost. Even if feed-line flushing on restart can be carried out, so that it is not an in-line activity, there is still the cost of water at £20 per 100,000 gallons to be consdiered.

Steam raising equipment - flue gas sideWhatever fuel is burnt in the boiler, there will be some wastage on the outside of the tubes, particularly at lower temperatures. Sulphur-containing fuel causes acid depositis, especially in the boiler outlet ducts, economiser and air heater. Thin plates of rotary air heaters are obviously vulnerable. They cost around £1,200 each, for some 20 sections in a 200 MW unit, to replace, and can only be fitted during a major overhaul. For a shutdown of any duration, parts should ideally be washed and dried using Munters driers. Although purely drying the affected areas, without washing, can reduce corrosion. Otherwise, remaining acid will continue to attack.

Electrostatic dust precipitatorsDown to the nature of their rolem these units are dusty on shutdown. Moisture ingress at this time can be absorbed by the dust, to clog the rapping mechanisms and cause corrosion of the precipitator wires and unit casing. Dry air eliminates all these risks.

De-Nox equipmentTo reduce the oxides of nitrogen in boiler flue gases, combustion arrangements are often modified to produce more advantageous temperatures. Otherwise, catalytic De-Nox equipment is fitted into the flue gas chain of ductwork. The catalyst must not be exposed to an RH greater than 50%, or the performance will suffer, leading to a need for it’s premature replacement at a cost of £25 million for a 500 MW unit. Even a two year reduction of it’s life might cost £5 million. A Munters drier, which comes on-line as the main plant is taken off, eliminates any risk.

De-sulphurisation plantEquipment fitted into flue gas ductwork to remove oxides of sulphur can be wet or dry. The wet type incorporates a rotary plate reheater similar to the combustion air heater. Being in an acid environment, such as the air heater, it must be kept dry on shut down. Otherwise, corrosion could lead to premature replacement of the plates costing up to £240,000.

ChimneysThe acidity of flue gases and their inherent low temperature on exit from the flutes, means that acid condensation occurs very soon after shutdown. This is not desirable in concrete stacks and even less so in steel ones. Smaller units have dampers fitted to the top to prevent rain from aggravating the condition and to promote a dry, non-corrosive environment by dry air admission. For chimneys without dampers, the same desirable conditions can be created by temporarily installing tarpaulings, or adding inflated rubber seals to the top before fitting the drier.

Condenser water boxes and other tanksEquipment which needs to be coated or recoated must be dried and sometimes heated prior to the surface preparation. For some tanks - square ones in particular- heat alone is not enough, as the corners are difficult to warm to the correct temperature. New flue gas desulphurisation plants need to be coated on site which materials which, to be successful, must be applied under stringently controoled RH and temperature conditions. Coating failures result in coal holding up, causing anxious moment during operation and even shut down, until the chutes are freed to allow coal to flow to the mills and boiler. For condenser water boxes, Munters equip-ment can dry a complete 500MW set in a week, compared with blower heat which can easily take two to three weeks. This need not all be in-line time, but the savings still amount to some £100,000.

Saving money with dry air

Happy customers around the GlobeElectricité de France have conducted studies on a 970 MW turbine suffering from corrosion at the Fassenheim/Alsace Station. Dehumidification was employed to remove 60kg of water per hour on day one. Within 24 hours the turbines, seperator, superheater, pipes and vertical walls of the condenser were dried. Heating does not provide a good solution, because moisture that is initially absorbed condenses out again when the air comes into contact with colder machine parts, renewing the danger of corrosion. To avoid this, the whole turbine would have to be heated at considerable expense.

Comparisons have been made between hot air drying and dehumidification. VEW Power Station studies showed hot air conservation to be 5 times more expensive. In Zugweg a factor of 7 was determined and in other measured instances power consumption can be 10 times greater. Considerable savings can therefore be made.

Munters equipment and expertise have been harnessed for the first two plants of this kind to be built in the UK. Munters also have extensive experience of maintaing the correct, low humidity conditions for the successful ‘non-stick’ coating of coal bunkers and hoppers, should the RH of ambient air, used for fume extraction, become too high.

TurbinesSteam TurbinesAll turbine blades are highly stresses during operation and are designed for maximum efficiency. Off-load attack in the form of general corrosion or pitting is possible in damp conditions and even austenitic steel is susceptible, in the presense of aggressive ions, particularly Chloride. General corrosion decreases efficiency on restart and pitting at blade roots can cause fracture wuth catastriphic results. Dry air supplied into the turbine casing and exhausted via the condenser, eliminates these risks and also preserves the condenser, which in turn shortens the restart clean up of the condensate system. This can save at least £100,000 per day for a 500MW unit.

Gas Turbine unitsDry air storage of off-load turbine/compressor units is recommended to prevent potentially dangerous embrittling contamination of the highly stressed alloy steel blades and to minimise corrosion of the lower allloy components. Corrosion of the turbine shaft itself can cause some imbalance and corrosded blades heat unevenly, which then produces unacceptable vibration especially during normal quick start of gas turbines. The proven remedy is to close the air inlet valve (damper) and admit dry air, which is allowed to exhaust through the hot gas system.

Wylfa Power StationAt Wylfa Nuclear Power Station, air quality control assistance was required when shutting down Reactor 2 for the duration of bulk defuelling. Munters provided a full turnkey dehumidification system to ensure the air was dry and at the optimum level in line with the brief set and providing consistent protection against the harmful effects of condensation, corrosion and electrical damage. “It was nice to see standard Munters products working well in such an intense industry and serving the purpose of the project” (The physics department, Wylfa.)

Having used the hire equipment for some time workers at the Wylfa site were growing tired of the heavy duty nature of the equipment, the space it used up (40sqm by 40sqm) and of course the amount of money it was costing them in both fuel and hire costs (in excess of £230,000 per reactor per year). Therefore, when Munters air quality control systems were chosen to replace the hired equipment, they had to ensure that the issues that were identified were no more. The Munters solution provides the necessary conditions in the reactor with a greatly reduced airflow and power consumption.

The nuclear industry can be a challenging environment to get a project done for the reason of security regulation and bulk legislation meaning that the design, plant modification and implementation stages can take considerable time and resources. As Magnox became familiar with the technology available in our marketplace, numerous changes were made throughout the duration of this project which Munters and Doosan took in their stride. Workers at the power station commented on how good the Munters people on the ground were at recognising it is not an easy industry to adapt to and work in. It was also mentioned that the relationship between Munters and Doosan was strong as they established clear demarcations so that the work was carried out efficiently. This was Munters first full turnkey installation at a nuclear power station.

James Hiller, Commercial Specialist at Wylfa commented that, “Munters acted professionally and in accordance with the contract. They delivered what was promised, on budget and on time. I have no hesitation incorporating Munters in future tenders at a similar scale.”

Since December 2013, Wylfa Nuclear Power station have reported various positive changes from their Munters products such as;

• Projected savings of approx. £1,000,000 from lower purchase of equipment and running costs• Reduction in electricity usage• Producing required air quality at lower capacities• Space reduction• Fixed-installation solution• Greatly reduced emissions • Completed within budget and time scales• Two companies working together in unison with a shared common goal • Improved supplier relationship• Energy efficient• Combined expertise & application knowledge• Flexible manpower with negligible compensation events• Joint understanding of clients requirements and objectives• Combined environmental responsibility & appreciation

Nuclear ReactorsReactor vessel ventilationThe rules for allowing RH and absolute moisture values in CO₂ cooled/graphite moderated reactors, are set by the operators and governed by the fuel and graphite properties. When off-load for inspection (even by remote viewing equipment) or maintenance work, the CO₂ is replaced by air. This must be dry enough to keep the RH at the austenitic steel fuel cladding lower than 10%; prevent excessive moisture absorption by the graphite and prevent corrosion of nuts and bolts and, in particular, control rod mechanism. The latter are sited in cooler regions of stand pipes attached to the upper part of the reactor vessel. RH is higher here than in the main air stream and unexpected corrosion can occur. This can lead to an excessively high drop test time and require a replacement mechanism during an on-lone period.

Water absorbed by the graphite will be released when the reactor is warmed on power raising. An excessive quanitity may prove too much for the in-built driers to handle, demanding a slower rate of power raising or expensive purging with CO₂. There is a need to provide a controlled environment for fuel when the reactor is shutdown and air-filled. Failure to maintain control can adversely affect the proportion of the fuel cladding. This could lead to downtime lasting at least three days and a revenue loss of £360,000 in the case of a 600 MW station.

The munters soluton provides air of the right quality at high volume and low pressure. It is simple to operate and more economical than other options which are costlier to run.Although described for AGR access whilst nuclear fuel is still loaded, the method is applicable to any situation where a controlled low humidity environment is required, such as decommissioning or work within containment vessels.

Reactor decommissioningDry air is also essential throughout reactor decommissioning, during and after the fuel removal stage. Corrosion is probably the greatest enemy and can ha,per further dismantling work. The additional cost for designing remotely controlled equipment to voercome the problem is substantial.

Dry air technology

Hydro-electric power stationsOften equipment installed in hydo-electric power stations is positioned below ground level. In many such cases, water cannot be prevented from seeping into the plant rooms, nor can wet external air be totally excluded. These two factors combine to create an aggressive atmosphere giving rise to corrosion and electrical faults.

Conventional heating and ventilation, together with the best possible floor and wall sealing, may adequately solve the problem in the larger areas, such as the turbine hall. It is not always a practical solution for smaller rooms. Desiccant dehumidifiers installed in such places producte a dry, warm, abient condition which is suitable for preserving both the operational and off-load plant in good running order at a much lower cost than other methods.

Consequently, desiccant dehumidification has been employed in numerous power stations, particularly in colder regions where refrigeration type dehumidifiers are much less effective. Dehumidifers are used preferably in turbine auxiliary plant annexes, as well as more distant rooms, to preserve the integrity of remotely controlled valves, particularly in pumped storage schemes. In addition, actuators of valves, positioned above ground level and used for controlling the reservoir water level, are normally kept operational with dry air rather than expensive heating.

In bulb turbines, condensationforms when moist air from the exterior comes into contact with the inside of the cold hull. This causes corrosion and reduces insulation in the alternator, but is avoided with Munters dehumidification.

The dehumidifier is based on Munters unique wheel;

•Process air passes through the drying wheel and leaves the dehumidifier as dry air

•Heated reactivation air collects the moisture absotbed by the drying wheel and lesves the dehumidifier as wet air

Cost estimates are based on loss of generating revenue calculated at £200 per MW day. Unless specified, an average 500 MW unit has been used.

Munters a global leader in energy-efficient air treatment solutions for comfort, process and environmental protection. Our air treatment systems are designed to control all your ventilation needs, contributing to quick installation, high indoor comfort and low life cycle costs.

Munters has over 30 years experience of air treatment solutions and air treatment production in our global factories and provided customers with a greater availability of our highly successful NA, Drycool and Oasis™ technology. Today with offices in 30 countries, 3,000 employees and more than 300,000 systems installed, we guarantee you a first class partnership and access to our international network of fast acting and competent engineers.

Quality Air with Low Energy Consumption.

Munters air treatment solutions are designed to supply indoor-air-quality, space humidity and conditioned air solutions with a lower energy consumption. Munters air handling systems control the quality of the air supplied and optimize the best possible performance over the lifetime of the system. The systems are designed, tested and produced at our Belgium factory to applicable standards including ISO 9001, ISO 14001, CEN and are certified by EUROVENT.

Munters air treatment systems incorporate optional heat recovery systems to reduce your operating costs, whilst meeting the differing demands between applications. Our heat recovery wheels are based on the original design by Carl Munters and our green air treatment thinking means we use dehumidification and evaporative cooling to obtain the right comfort environment to exacting performance demands.

An international name, where the customer comes first.Munters, part of Nordic Capital, has offices in 30 countries and over 3,000 employees in many branches around

the world. We are global leaders in energy efficient air treatment for comfort, process and environmental protection. Munters shares ideas within its international network, giving the Group an outstanding reputation as a reliable, fast-

acting and customer-orientated expert in air conditioning. Munters philosophy of customer satisfaction is central to our decision-making. When developing and manufacturing our systems, we see happy customers as

our number one target. And this is what our employees strive to ensure every day.

For more information on Munters, please visit www.munters.com

Your closest office

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