Retrofits Brochure

UPGRADING AIR PREHEATERS TO THELATEST TECHNOLOGY STANDARDSBRINGS A WIDE RANGE OF BENEFITS.• It reduces the power demands of thedraught fan, and thus raises the saleablepower output.• If the operating conditions have changed,replacement elements can improveoverall performance significantly.• It helps to eliminate the temperature dilutioneffect of air leakage, and so helps reducecorrosion downstream of the air preheater.• By reducing leakage it makes more airavailable at the coal mills, ensuring anadequate supply of pulverised fuel to theburners – especially when the coal is wet –and compensating for shortfalls in output.• Reduced leakage also lessens the flowthrough the forced draught and induceddraught fans, and thus eliminates theoutput shortfall that would be causedby overloading the fans.• A routine cleaning of the elements withhighly efficient sootblowers will ensure a steady heat transfer and minimisepressure drop in the plant system.HOWDEN KNOW-HOWAIR PREHEATERS PLAY AN INTEGRALPART IN THE EFFICIENT OPERATION OFPOWER PLANTS. AS THE CONDITIONSIN THE PLANT CHANGE, FOR EXAMPLEBY CHANGES IN FUELS OR OPERATINGCYCLES, DEMANDS ON THE AIRPREHEATERS ALSO CHANGE. WHEN THIS HAPPENS, HOWDEN’SEXPERIENCED ENGINEERS AND SITE SPECIALISTS CAN PROVIDE A COMPLETE ADVISORY SERVICE.Upgrading or enhancing an air preheater isusually one of the most cost-effective ways ofimproving boiler performance. Dramatic resultscan be achieved by either increasing thermalperformance or reducing leakage. Beforeretrofitting FGD plant downstream of the boiler,it is always worth investigating air preheaterleakage, which can create unnecessarydemands elsewhere in the system. Improvingthe air preheater sealing system can actuallyreduce the size of the FGD plant, with obviouscost savings. In many cases, heat recovery can be increasedby installing higher performance elements, or increasing their overall depth, or both. RETROFITS AND ENHANCEMENTSARE COST EFFECTIVE WAYS OFIMPROVING BOILER PERFORMANCEwww.howden.comAIR PREHEATER RETROFIT AND ENHANCEMENTwww.howden.comSelecting from our broad range of profiles, we can supply direct replacements for all of the element types commonly used in airpreheaters, regardless of make. In many cases alternative profiles or arrangements canimprove performance significantly, particularly if the operating conditions have been changedsince the original elements were specified.Improving the use of space within the rotor can also make significant contributions tooverall boiler efficiency.In several designs of air preheater, leakage can significantly increase over time. Known as‘leakage drift’, this can impair boiler operation in several ways. It can increase the fan’s powerdemands, raise velocities and thus reduceeffectiveness in the precipitators, reduce theflow of hot air to the mills or greatly diminish the operational margins of the induced draughtfan. These problems can be vastly reduced, or even eliminated, by fitting the advancedHowden VN sealing system to the air preheater.Air preheaters on coal and oil fired plants aresubject to a degree of corrosion, caused when the dewpoint of either the water or the sulphuricacid is approached. Acid enhanced fouling isdependent on the sulphur content of the fuel and the amount of SO2 to SO3 conversion in theboiler and FGD plant. Corrosion can be minimisedby the use of a cold end layer of higher grade steel or an enamel coating. We have sophisticatedsoftware that can calculate the cold endtemperature for each case, enabling us todetermine the most economic choice of higher-cost material and the precise depth of it required.To maintain the optimum performance of airpreheaters it is vital to ensure that the elementsare routinely and effectively cleaned. Failure todo so will quickly lead to fouling, an increase inpressure drop and a reduction in heat transfer.We supply a wide range of highly efficientsootblowers, which combine steam or airblowing with high and low pressure waterwashing as appropriate.AIR PREHEATER RETROFIT AND ENHANCEMENTCORROSION CAN BE MINIMISEDBY THE USE OF A COLD ENDLAYER OF HIGHER GRADE STEELOR AN ENAMEL COATINGFor further information on Air PreheaterRetrofit and Enhancement please visitwww.howden.com or contact your localHowden company.