Rotary Heater Technology Continuous Innovation in Regenerative Heat Exchangers Optimising Performance in the Power Generation Industry

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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 fl ue 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-fi red boilers and both bubbling rotate into the inlet air used to provide the oxygen to fi re and circulating fl uidised bed boilers and also emission control systems such as selective the fuel in the boiler furnace. This heats the air from catalytic denitrifi cation (DeNOx) and fl ue gas desulphurisation (FGD) processes. around 30 to 340oC, improving the effi ciency 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 benefi t is that hot air promotes and coal fi red power plant. For coal fi ring, 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, are designed around girder support consuming installation and outage cold end temperature control and the Custom designed and optimised to suit replacement of pin racks. use of the correct cleaning system external insulation. arrangement and client preference. maintains very high availability. The housing and ducts are Low maintenance Sealing system Conceptual and detailed design targets the Cleaning systems structurally independent of achievement of simplicity and minimal The sealing system has evolved to have static Unlike tubular or plate recuperative heat the rotor. Finite element maintenance. Fixed sealing surfaces and sealing surfaces set to achieve minimal gaps exchangers, fouling does not cause centre drive greatly reduce maintenance analysis has been used in with the moving seals at operating conditions deterioration in heat transfer in a rotary by removing actuators and pin racks. the generic design of the combined with labyrinth multiple seals. regenerative heat exchanger. Fouling 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. low design leakage between outages. with oil bath lubrication in all directions such that 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 and space restrictions, including: are kept to a minimum are available. viscosity oil have been used by Howden in during all modes this application for over ﬁ fty years. Water Semi retractable steam sootblowers of operation. Centre drive system with inverter cooling systems are employed at the hot end bearing. Fully retractable multi-ﬂ uid (air/steam speed control 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. 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 (wire frame for clarity) 12 years and has been shown to recover 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 TM designed to be used as an alternative avoided by on-line Enerjet cleaning. 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 with any type of air preheater from any of lost availability that arise due to excessive a number of different embodiments. By 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. 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. 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. 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. 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. Judicious selection of materials, together with advanced design features result in a heat exchanger with exceptional resistance to the cool moist acidic conditions of FGD plant, where fouling and corrosion are a constant challenge.

Specially formulated enamel with high acid resistance is used to protect the heat transfer elements. Areas where significant condensation is expected are coated with acid resistant flake glass vinyl ester linings. The concept of fixing sealing surfaces enables more of the surfaces to be properly protected by linings, whilst the double sealing enables active purge sealing to be applied to pressurise the space between radial plates with treated gas. This, coupled with scavenge gas to flush out entrained untreated gas, results in extremely low leakages, as low as 0.25%.

Features

as the drive system is completely removed Fully retractable multi fluid (compressed air or Tail End GGH Application from the extremely corrosive environment. steam and LP & HP water) cleaning devices In some power stations there is no space The additional leakage penetration of a have been developed for this application. available at the economizer outlet to fit peripheral drive is also eliminated. The lances are fully retracted from inside the the SCR catalyst. One option is then to SCR Gas Gas Heater when they are not operating install the SCR plant after the flue gas Low maintenance in a cleaning cycle, thereby protecting them cleaning equipment. Conceptual and detailed design targets from the corrosive environment and enabling The problem with this arrangement is that the achievement of simplicity, corrosion on-load maintenance of them. HP water the flue gas is at too low a temperature to protection and minimal maintenance. washing is carried out on load from the hot provide sufficient catalyst reactivity. Natural Fixed sealing surfaces and centre drive and cold ends. Fully retractable lances also gas has to be burned in the flue gas to raise greatly reduces maintenance by removing enable selective cleaning of the rotor to be the temperature. To reduce the quantity of actuators and eliminating pin racks from carried out, with the most severely fouled gas required a gas reheater can be installed the corrosive gases. rings being targeted. to recover the heat as the gas leaves the SCR reactor in order to preheat the gas Standard spherical roller bearings Seal air system GGH support method entering the reactor. with oil bath lubrication A sealing air fan is provided to pressurise Custom designed and optimised to suit In order to reduce NOx emissions on steel Standard proprietary rolling element bearings seals at gas heater penetrations with moving plant sinter strands, SCR systems are arrangement and client preference. If the Bag Filter with bath lubrication using extremely high parts – rotor shaft seals and cleaning devices. GGH is being mounted directly on top of required. Again higher gas temperatures are viscosity oil has been used by Howden in this the FGD Absorber, construction of the GGH necessary to raise the catalyst temperature application for over fifty years. No water High availability at ground level and a single lift can to within its band of maximum reactivity. cooling systems are necessary in FGD The major cause of reduced availability in reduce costs. In order to reduce the additional heat input GGH applications. Gas Gas Heaters is due to element fouling. from in-duct burners a large SCR GGH Careful element selection to suit the Centre drive system with inverter is required. Cleaning systems application and the use of the correct speed control Fouling increases pressure differentials and cleaning system maintains very The shaft mounted centre drive system is consequently booster fan power and leakage. high availability. even more advantageous in Gas Gas Heaters

6 7 Seismic loading ﬁnite element analysis Heater Design, Development and Analysis

Continual research, development and analysis of both new and aftermarket heaters to optimise product performance and reliability.

FEA rotor buckling

Heater Development

Howden Group, which was founded in 1854, R&D is carried out by several international is the world’s largest and longest established development teams working together in the fan manufacturer and was the first company location most appropriate to suit the work. to form a joint venture with Fredrik Ljungström To better quantify and eliminate the damage in 1923 to commercialise the rotary heat caused by excessive sootblowing, we have exchanger. This combination of performance recently carried out extensive testing of critical fan and heat exchangers provides element fatigue using a purpose designed Howden’s customers with unrivalled steam sootblower test rig sited within a power experience in air and gas handling station. applications. 3D design modelling of heaters is also Although a very mature product, research carried out throughout the Group. In house and development is still constantly ongoing engineering analysis including Finite Element to refine and improve rotary heaters to suit Analysis and Computational Fluid Dynamics changing customer requirements, fuel types, capabilities are also applied by highly qualified emissions legislation and efficiency and experienced professional engineers. improvements. This continual improvement Element fatigue testing rig Computational fluid dynamics of purge & scavenge system FEA mounting bell stress Top bearing, mounting bell of the product is reflected in our core value and shaft “innovation defines our future”.

8 99 Element design and technology

We have a wide range of proﬁ les available, enabling us to offer the right balance of thermodynamic performance, pressure drop and ease of cleaning for any situation.

As the choice of element profi le is obviously and international standards. We can supply elements in a critical to the availability and effi ciency variety of materials, including: Additionally through life, aftermarket of the entire plant, we are continually support and Howden expertise is Carbon steel developing improved profi les for particular available to recommend alternative operating conditions. Low alloy corrosion resistant steel (LACR) profi les or arrangements that can All designs have been fully tested in our improve the performance of the Decarburised steel enamelled laboratories to establish the basis of our regenerative heat exchanger, particularly Carbon steel enamelled thermal and pressure drop predictions, if the operating conditions have been and this performance has been verifi ed changed since the original elements LACR enamelled at site in accordance with major national were specifi ed.

Air preheater baskets for loading into standard shipping Element fouling solutions Our latest HCP ElementTM, Elements can be supplied in a variety containers. Elements are required to cope with several the fi rst dual profi le element, combines a cold end profi le of baskets, which have been developed Corrosion types of fouling; hot end popcorn ash, cold to maximise the rotor area and to end acid enhanced fouling and sticky with an intermediate profi le Corrosion can be minimised by the use reduce the amount of gas bypassing ammonium bisulphate (ABS) fouling on the one sheet of a cold end layer of low alloy corrosion the elements. after an SCR. resistant steel or enamel coating. Using The use of aerodynamically “closed” The baskets are strongly constructed to in-house software we optimise the extent profi le elements as embodied in our range ensure that the elements remain tightly of the cold end elements to suit of HC ElementTM increases the effectiveness packed to avoid damage during the operational duties. of the sootblowers for cleaning the elements operation of the air heater. Unconventional Gas Firing throughout the depth of the heater. Moreover, In many cases replacement element Where pulverised fuel fi red boilers are our latest HCP ElementTM, the fi rst baskets can be supplied with signifi cant being converted to fi re unconventional commercially available dual profi le element, design and operational improvement gas, Howden have very high performance provides the combination of a low-fouling, compared to those originally installed, elements to maximise effi ciency in this physically closed profi le at the cold end, with a resulting in improved ease of installation clean, non fouling application. higher performance aerodynamically closed and longer life. profi le at the hot end, thereby eliminating the inter tier space. This further increases Each basket is protected for shipment cleanability, allowing successful operation at by being plastic wrapped and palletised lower gas outlet temperatures and with increased effi ciency.

10 11 Enamelled Elements

Enamel coating produces an element with the combination of The quality and life of the enamel coating depends on a number of critical factors including: both corrosion protection and good cleanliness when used in the rigorous environments experienced in the low temperature, cold Base material end layers of air heaters, and the even more aggressive regimes Enamel constituents associated with FGD gas heaters and air heaters located after Enamel thickness SCR DeNOx installations. Enamelling technique

Dry Electrostatic Enamelling Process

Enamel coatings are applied to decarburised a quality controlled environment at a High resistance to mechanical Mild steel / low alloy corrosion resistant steel enamelled enamelling steels (DC04ED), mild steel and temperature of around 850˚C creating a and thermal shock In the past, it was not possible to manufacture high quality enamelled cold end elements LACR. Prior to their acceptance the coils are mechanical and chemically bonded vitreous Excellent bonding to metal substrate for heaters using standard mild steel or Low Alloy Corrosion Resistant Steel (LACR). After sampled and checked for their suitability for enamel coating. As a result we produce a carrying out extensive research, we have now developed the breakthrough technology that enamelling. The base steel coil is rolled to high quality product suited to withstand Homogeneity in the internal enamel allows us to meet customer demands for these elements. the correct element profile geometry and severe operational conditions. structure minimises porosity plate size in our fully automated rolling lines Standard mild steel and LACR are more widely available Finally the heating enamelled elements Much improved coating thickness tolerance before being passed to our integrated are packed using the SurePack Elements® (allowing for thinner coatings and higher The new materials enable effective washing or sootblowing enamelling lines. system. element basket compression pressures) Greater strength and corrosion resistance increases element life In order to ensure the maximum element Uniformity of enamel thickness, absence durability, Howden uses the latest dry powder Superior quality enamel Reduced fouling and plugging increases intervals between downtime or outages of excessive enamel accumulation (greater process for enamelling heating elements. Howden’s enamelling process ensures a edge coverage produces increased The elements are designed specifically for cold end applications in air preheaters The frit is electrostatically charged in superior quality compared to other systems corrosion resistance) Reduced pressure drop over the heater due to fouling reduces demands on FD and ID fans robotically controlled spray guns, within a of enamelling. The benefits of Howden’s dry Surface finish (the smooth, vitreous surface special cabin where the negatively charged enamel coating include: When used in conjunction with new HCP Element™ and the Howden Enerjet™ cleaning reduces the adhesion of solids) frit “powder-fog” is attracted to the positively system, the benefits of the new enamelling techniques for mild or LACR steel are even more Greater resistance to acid attack charged element plates. Production process is non-toxic and dramatic. By taking a systematic view of the science of the contamination and cleaning cycle, Erosion resistance environmentally safe we have evolved an integrated system that delivers far more than the sum of its parts. The next step is to fuse the enamel in

SurePack Elements®

As heat transfer elements are regularly subjected to high energy excitation forces from the sootblowers used to clean them, it is essential that these elements are sufﬁciently tightly packed in their containers to minimise the element vibration and consequent fatigue damage.

Full sector baskets Whenever enamelled elements are used, of pressure across the whole plate area ® it is equally important that the element packs Whenever required, SurePack Elements The installation of dedicated, are not over-compressed as this can cause can be assembled and welded to create computer-monitored control panels localised damage to the enamel coating that full sector baskets as adopted for speed that both prevent either under or over can lead to subsequent pack loosening of installation in many horizontal shaft compression and provide an automatic during heater operation. As part of our air preheaters. This much improved packing record for each element basket commitment to the ongoing development manufacturing technique for full-sector of our element manufacturing methods, As a result of the application of these baskets matches the thermal performance Howden have re-engineered the element latest processes, we can ensure the obtained by more traditional manufacturing packing presses and packing procedures. customer will receive consistent, processes, but with extended element life This involved: high-quality element baskets that will be as a result of the improved packing process. best suited to withstand the rigours of The result is consistent superior quality A major upgrade of the hydraulic circuitry, through-life operation. Such attention to packing, giving reduction in element controls and load distribution system to detail inevitably results both in improved vibration as a result of steam sootblowing, produce a even and controlled distribution ﬁrst quality and extended element life. and reduction of element movement in horizontal heaters.

12 13 Heater Global Manufacturing

We enforce the same rigorous Howden and International quality standards worldwide.

Howden factory in Weihai, China.

Modern manufacturing Technology A reputation for quality and service Heater Rotor Bay in the At custom built production facilities located We are accredited to ISO 9001, ISO 14001 Weihai Factory worldwide, Howden has invested heavily in and OHSAS 18001 and are regularly audited the latest modern manufacturing technology by major customers and internationally and our production facilities are staffed by recognised assessment organisations. experienced engineers and fully qualiﬁ ed Howden have manufactured rotary heat operators. This enables us to address the exchangers for over 90 years. During this needs of each major market and to respond long period we have built a reputation for quickly and effectively to customers’ quality, service and innovation. In addition to demands. our own equipment supply, over the past decade, Howden has won more than 2000 Our latest state of the art facility at Weihai in international contracts to supply replacement China has new ofﬁ ces and factory covering elements for air preheaters and FGD gas Howden have invested heavily in the latest 154,792m2, on the 203,884m2 Howden reheaters produced by other original modern manufacturing technology Industrial Park. equipment manufacturers.

14 15 Installation, maintenance, refurbishment and enhancement

With products whose operating life can be anything up to 40 years and beyond, we believe in building lasting relationships with our customers. It’s our duty to offer only the very highest standards of service, from initial installation of plant and equipment through routine maintenance to subsequent refurbishment and enhancements.

Routine maintenance and spare parts Efficiently meeting our customer requirements We have the experience and expertise to plan and carry out routine maintenance, allowing Howden has thousands of air and gas requirements with the security of proven our customers to focus on their core activities. heaters installed in more than 70 countries performance. Wherever our customers Using the very latest computer based around the world. are located, a Howden office is close at maintenance management systems we are hand. With engineering and sales offices With a wide range of heater solutions able to schedule work load so as to minimise throughout the world, we understand we can efficiently meet our customer disruption. We have the capability to carry out and satisfy local market needs. inspections and servicing, designed to keep expensive equipment trouble free. From maintenance records, we can recommend critical interventions or suggest upgrades that will improve performance or economy.

We have extensive experience of routine maintenance of Howden products. This includes fans, rotary heat exchangers and other plant on power station sites, in addition to process plants using our mechanical, electrical control and instrumentation skills.

We regard the supply of parts as a core activity, and we treat it with the same attention that we bring to new installations. Enquiries and orders are handled by experienced staff, to ensure that the correct components are supplied in a timely manner. Where appropriate, we will advise on new technologies or developments that might raise the performance, longevity or economy of installed plant.

Our site service activities

Refurbishment to original specification and upgrade of any regenerative rotary heat exchangers to latest technology Plant enhancement Performance upgrades With the growing demand for enhanced of improving boiler performance. Dramatic demands on rotary regenerative heaters that performance and life extension of plant, results can be achieved by either increasing greatly benefit from specific adaptations to Turnkey supply of design, material, site management, site installation Howden has the engineering expertise thermal performance or reducing leakage. help them cope with the more arduous fouling Site surveys, inspection and plant evaluation and experience to provide cost effective Before retrofitting FGD and/or plant environment. site solutions. downstream of the boiler, it is always worth Preventive maintenance and maintenance advice investigating air preheater leakage, which can In many cases, heat recovery can be increased Medium and long-term planned outage management and support Our research and development coupled with create unnecessary demands elsewhere in by installing higher performance elements, for unplanned outages long standing links with specialist suppliers, the system. Improving the air preheater or increasing their overall depth, or both. enables us to improve the performance of our Performance and function tests and the relevant problem solution/implementation sealing system can significantly reduce the Leakage reduction can make significant savings own products as well as that of equipment size and cost of the FGD plant, with obvious in fan power consumption. Each retrofit project is Custom-made replacement spares, upgrade spares for any air and gas movement supplied by other manufacturers. cost savings. based on a thorough analysis of the prevailing equipment as well as air preheaters Upgrading or enhancing an air preheater is The use of Selective Catalytic Reduction situation as well as a concise determination of usually one of the most cost-effective ways (SCR) equipment also makes special the target performance.

16 17 www.howden.com

At the heart of your operations

Howden people live to improve our products and services and for over 160 years our world has revolved around our customers. This dedication means our air and gas handling equipment adds maximum value to your operations. We have innovation in our hearts and every day we focus on providing you with the best solutions for your vital operations.

Howden UK Old Govan Rd Renfrew PA4 8XJ United Kingdom

Tel: +44 141 885 7300 Email: [email protected]