1 Rotary Heater Technology Continuous innovation in regenerative heat exchangers Optimising performance in the power generation industry worldwide Howden has been supplying Rotary air preheaters to the power industry since 1923. Howden Rotary Heat Exchangers are optimised for performance and reliability, they are custom designed to suit the arrangement, application, fuel and system design. They provide a very compact and cost effective solution for heat recovery in power plant, contributing up to 15%. of the boiler heat transfer process for only around 2% of boiler unit investment. Heat Transfer Process The Heater absorbs waste heat from the flue gas as it leaves the economiser at typical temperatures around (370oC) and transfers this energy to the rotating steel Howden has gained an extensive knowledge not only of our products but also their various heat transfer element plates. The hot elements then applications which include pulverised coal, oil or biomass-fired boilers and both bubbling rotate into the inlet air used to provide the oxygen to fire and circulating fluidised bed boilers and also emission control systems such as selective the fuel in the boiler furnace.
2 This heats the air from catalytic denitrification (DeNOx) and flue gas desulphurisation (FGD) processes. around 30 to 340oC, improving the efficiency of the boiler plant as energy is transferred back to the furnace, thus Bi-sector air preheaters are supplied for combustion air preheating on heavy fuel oil, gas saving fuel. A further benefit is that hot air promotes and coal fired power plant. For coal firing, separate mill air preheaters and composite stable combustion conditions. In the case of a mill Heater tri-sector and quad-sector preheaters have been supplied to suit the boiler arrangement. the heated Primary Air is used to dry and transport the fuel to the furnace. b 1. Air Preheaters Rotary regenerative air preheaters have a much reduced size and cost relative to recuperative tubular or plate heat exchangers. Features The Howden air preheaters Centre column or bottom air preheater and doesn't require the time element selection to suit the application, girder support consuming installation and outage cold end temperature control and the are designed around replacement of pin racks.
3 Use of the correct cleaning system Custom designed and optimised to suit external insulation. arrangement and client preference. maintains very high availability. The housing and ducts are Low maintenance Conceptual and detailed design targets the Cleaning systems structurally independent of Sealing system achievement of simplicity and minimal The sealing system has evolved to have static Unlike tubular or plate recuperative heat the rotor. Finite element sealing surfaces set to achieve minimal gaps maintenance. Fixed sealing surfaces and exchangers, fouling does not cause analysis has been used in with the moving seals at operating conditions centre drive greatly reduce maintenance deterioration in heat transfer in a Rotary by removing actuators and pin racks. regenerative heat exchanger. Fouling the generic design of the combined with labyrinth multiple seals. increases pressure differentials and rotor which is free to expand The Howden VN sealing concept maintains Standard spherical roller bearings consequently fan power and leakage.
4 Low design leakage between outages. in all directions such that with oil bath lubrication Several proven cleaning systems are thermally induced stresses Where the application requires Hot End Standard proprietary rolling element bearings available to suit the degree of fouling actuated sector plates, advanced systems with bath lubrication using extremely high are kept to a minimum are available. viscosity oil have been used by Howden in and space restrictions, including: during all modes this application for over fifty years. Water Semi retractable steam sootblowers cooling systems are employed at the hot end of operation. Centre drive system with inverter Fully retractable multi-fluid (air/steam speed control bearing. and LP & HP water) sootblowers The shaft mounted centre drive employs a high ratio gearbox with the option of multiple High availability Semi retractable HP water washing electric motors and an air motor.
5 The drive The major cause of reduced availability in air system is completely removed from inside the preheaters is due to element fouling. Careful 2 3. Air Preheater Technology and experience EnerjetTM cleaning system The Howden EnerjetTM cleaning system is burden on the fans. Stopping production for used during everyday operation. This system Sector plates a method of on-line high pressure water cleaning is costly. In extreme cases the build has successfully operated in a growing washing of air preheaters designed to provide up of contaminants can lead to unplanned number of air preheaters for more than Rotor effective and efficient cleaning of severely outages, with even more serious financial 12 years and has been shown to recover (wire frame for clarity). fouled heat exchanger elements while the air consequences. All of these unwanted and from excessive fouling while producing no preheater is in normal use. It is has been expensive situations and risks can now be detectable damage to the rotor structure or designed to be used as an alternative avoided by on-line EnerjetTM cleaning.
6 Detrimental effects on the downstream gas system when normal sootblowing practices cleaning equipment. prove inadequate to keep the heat transfer The EnerjetTM system uses carefully designed While the EnerjetTM system can be used elements clean. By eliminating the problems nozzle jets and carrier lances that come in a number of different embodiments. By with any type of air preheater from any of lost availability that arise due to excessive fouling, the EnerjetTM system can repay its adjusting and testing the volumes and manufacturer, and works well with most kinds initial investment in well under a year, pressures used, we have eliminated all of of element profile, it is at its most effective depending on the speed of the fouling. the problems traditionally associated with when used in conjunction with Howden 's water-based cleaning systems, and moved enamelled HC ElementsTM or HCP. Fouling and plugging lead to an increase in the Technology on to include moving lance ElementsTM.
7 Each of these designs offer pressure drop, which places an additional systems that allow EnerjetTM cleaning to be radically improved flow and cleanability. Circumferential seal leakage Axial seal leakage After HP washing After normal sootblowing Radial Hub region seal leakage leakage Features Fire detection and fire Leakage sealing systems fighting systems Over the many years of our ongoing Heater leaf design that had been proven to be an Equally, in this pursuit of ever lower leakage Air preheaters can be susceptible to fires applications experience, Howden have improvement over the previous channel levels while listening to the Voice of the when operated under adverse conditions. investigated and developed a large number design. Since then, many hundreds of air Customer (VOC), we have continued to work Such problems are generally caused by of different leakage sealing system designs heaters throughout the world have had the and develop our approach towards actuated periods firing heavy fuel oil with poor to both minimise leakage level and eliminate system retrofitted.
8 In the last few years, well sealing systems that are designed to minimise combustion when soot and oil residue can the leakage drift' that inevitably occurs in over 500 new air preheaters and FGD gas the seal gaps at all times and loads. In doing be deposited on the Heater elements. actuated systems with time. reheaters have been supplied with VN sealing. so, we have redesigned our moving sector The risk of fire is further increased in coal plates, seals, actuators and gap sensors to fired units during subsequent transient In that respect, the sealing arrangement for A further benefit is that annual maintenance optimise their performance while maintaining operating conditions, when the coal mills which Howden is most renowned is our hours are reduced by more than 50% over excellent long term operation and minimised are brought on line. advanced VN sealing system which keeps the more traditional designs. leakage drift.
9 Leakage consistently low for extended Howden 's experienced engineers have While VN sealing was originally conceived, periods. The original VN sealing system was Indeed, whenever the need occurs (as it had developed fire detection systems, which developed and demonstrated with double developed as a result of Howden 's experience done on GGH applications), we have taken use fast-response fire detection probes sealing many years ago, and continues to which showed that moving sector plates are further steps towards a Zero Leakage Heater and an associated fire detection panel to be successful today, the further development consistently the prime cause of increasing by designing and implementing dynamic continuously monitor the rotor for a higher of VN sealing systems has never stopped. leakage due to wear on the rotor seals and sealing variants, where small supplementary temperature hot spots and also a high rate Indeed, Howden have continued to develop deterioration of seals between the adjustable low leakage fans are used to modify the of change of temperature.
10 The fire fighting VN sealing to achieve progressively lower sector plates and the casing. pressure pattern between the seals to further system is manually activated once the leakage levels by integrating designs with reduce (or even eliminate or reverse) the operator has confirmed that there is a fire The solution developed over thirty years ago triple, quadruple and even sextuple seals direction of direct leakage from the high and that it is spreading. was to use fixed sector sealing plates and to over the sealing plates at any time thereby pressure air side of the Heater to the much compensate for the increased gaps between maximizing the benefits of no-contact lower pressure gas side of the Heater . rotor and sector plate by doubling the number labyrinth sealing. of seals on the rotor. In addition the sealing strips on the rotor were changed to a single 4 5. Gas Gas heaters The Howden VN design concept is ideally suited to the FGD Gas Gas Heater application.