Modification of Design of Air Pre-Heater for Enhancing Efficiency of Boiler

Modification Of Design Of Air Pre-Heater For Enhancing Efficiency Of Boiler

1Bharat Dhakad, 2 G. R. Kesheorey, 3Abhishek Pandey 1M. Tech Scholar, 2 Head of Department, 3Assistant professor 1Mechanical Engineering, 1Vindhya Institute of Technology & Science, Indore, India

Abstract : In thermal power plants, Air Preheater is one of the most vital auxiliary of boiler. Air pre-heater is a heat transfer surface in which air temperature is raised by transferring heat from other media like flue gas. Hot air is necessary for drying coal in milling plants and also for rapid combustion in the furnace. So an air pre-heater is essential boiler accessory which serves this purpose. The performance of same will directly affect the efficiency of boiler. As a thumb rule, rise of 20 degree C in gas outlet temperature reduces boiler efficiency by 1.00%. This increases the fuel to be fired, air and gas quantity to be handled by fans. Hence performance of Air Preheater is very much essential for thermal power generating stations. This technical project covers the problems, major design deficiencies & improvements done/planned to overcome the same. In the present investigation, experimental data of air preheater has been collected from540 MW there are 4 x 135 MW thermal units at BALCO Raipur chhatisgarh.

IndexTerms - Thermal power plant, air preheater, efficiency of boiler, design deficiency.

1. 1 INTRODUCTION Bharat Aluminium Company Ltd. (BALCO) has CPP 540 MW there are 4 x 135 MW thermal units supplied by M/s Shandong electric power construction corporation (SEPCO) China on EPC basis. The air preheaters are supplied by M/s Harbin Boiler Company limited China & the basic design is of M/s. ABB. There are two APH, model no. 24 VIT 1833 for one unit & it is Trisector, Ljungstrom type with rotating elements & double sealing system. It’s a semi-modular design with 18 modules & 36 sectors. 1.2 Captive power Captive Power refers to generation from a unit set up by industry for its consumption, since industrial sector is one of the largest consumers of electricity in India. However, a number of industries are now increasingly relying on their own generation rather than on grid supply, primarily for the following reasons: . Non-availability of adequate grid supply. . Poor quality and reliability of grid supply. . High tariff as a result of heavy cross subsidisation. In Modern high capacity boilers, air pre heater is essential. Air preheater is an important auxiliary of boiler which is use for improve the efficiency of boiler. A boiler is an enclosed vessel that provides a means for combustion and transfers heat to water until it becomes steam. The steam under pressure is then usable for transferring the heat to a process. Many manufacturing processes require steam and hot water for heating. Steam is also use for generation of electricity. Steam is generated by heating water. The equipment where fire or hot gases heat the water in a confined space to generate steam is known as steam boiler. The flue gases flow through the tubes and water flow outside the tubes or flow gases flow outside the tubes wherein water is in the tubes. If the flue gases are flowing through the tubes the boiler is known as fire tube boiler and if water is flowing through the tubes than the boiler is called as water-tube boiler.

1.3Fire tube Boiler A fire-tube boiler is a type of boiler in which hot gases pass through many tubes running through a sealed container of water. The heat of the gases is transferred through the walls of the tubes to water by thermal conduction, heating the water and ultimately creating steam. The fire-tube boiler developed as the 3rd of the 4th major historical types of boilers: low-pressure tank, flued boilers with one or two large flues, fire-tube boilers with many small tubes, and high-pressure water-tube boilers. Fire tube boiler has an advantage over flued boilers with a single large flue is that the many small tubes offer a large heating surface area for the same overall boiler volume. This type of boiler was used on an around all steam locomotives. Fire tube boiler is the most basic types of boiler and the design is very old. It was popular in eighteenth century. It was used for steam locomotive engines. This steam is taken out from the steam outlet for required purpose. The water is send into the boiler through the feed water inlet. When the steam and water is stored is the same vessel, it is difficult to produce very high pressure steam. In general maximum capacity of this types of boiler is 17.5 kg/cm2 and with a capacity of nine Metric Ton of steam per hour. In a fire tube boiler, the main boiler vessel is under high pressure, so if this vessel is burst there will be a possibility of accident due to this explosion.

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Fire tube boiler consists of a vertical cylindrical shell which have a fire box in the bottom, water space in the middle portion and steam space in the upper portion. The fire grate is placed at the below of the fire box and coal is fired in the fire box. An ash pit is located at the bottom portion of the grate to collect the ash of burnt coal, which is regularly removed. One or more cross tubes are riveted to the water space which are located in the fire box to increase the heating surface area and to improve the water circulation. A long chimney is connected at the top of the fire box to discharge the waste flue exhaust gases at some greater height. Manhole and hand holes are given for cleaning the interior of the boiler shell and cross tubes. The boiler consists of a pressure gauge, water level indicator, safety valve, steam stop valve and a manhole as mountings to provide safety and easy to working. Fire tube boilers are Cochran, Lancashire, and Locomotive.

1.4 Water tube Boiler A horizontal steam and water drum is the main part of the boiler. It is supported by a steel structure at some height and is independent of brickworks. The size of the boiler drum is small as compared to the fire-tube boiler of the same capacity. All safety and control devices are located on the boiler drum. A bundle of steel tubes in the boiler the front end of the boiler drum is connected to the uptake header by a short tube and the rear end is connected to the down header by a long tube. In between the headers, a number of small-diameter steel tubes are fitted at an angle of 5° to 15° with the horizontal to promote the water circulation. These steel tubes are arranged in the combustion chamber in a zigzag way so that more surface area of the tube is bring out to hot gases. Combustion chamber in the boiler is the space above the grate, below the front end of the drum where combustion of fuel takes place. This chamber enclosed by brickwork and is lined from inside by fire bricks. Doors are provided to give access for cleaning, inspection, and repairing. The combustion chamber is divided into the separate compartments above the furnace is the hottest and the last chamber is of lowest temperature. This makes the path of hot gases longer before leaving the boiler to the chimney. The super heater is placed between the drum and water tubes. Dampers are provided at the rear end of the chamber to regulate the fresh air supply for maintaining proper combustion of fuel. Safety and control devices in the boiler are called mountings, as basically these devices mount over boiler drum. These are the safety valve, pressure gauge, water-level indicator, feed check valve, steam-stop valve, and blow of cock, fusible plug, and manhole.

The water in water tube boiler pumped by a feed pump and it enters the drum through the feed check valve up to the prespecified level so that the headers and tubes are always flooded. When the combustion takes place above the grate, the products of hot gases come out and rush through each compartment of the combustion chamber. Hence, the rear part of the tubes has the lowest temperature and the front part of the tubes as highest temperature. When water is heated inside the tube. Due to continuous heat supply, some of the water gets vaporized into steam inside the tubes and a mixture of water and steam enters the boiler drum through the uptake header. The cold water from the boiler drum comes down through the uptake header and enters into the lower end of the water tubes for getting heated further. This circulation is called thermo siphon system. 2.1 AIR PREHEATERS: Air Preheater is heat recovery equipment. The prime purpose of the Air Preheater in a Boiler is to recover the heat from the flue gas, going out of the Boiler. 2.2 TYPES OF AIR PREHEATERS: There are two types of air preheaters for use in steam generators in thermal power stations: One is a tubular type built into the boiler flue gas ducting, and the other is a regenerative air preheater. These may be arranged so that gas flows horizontally or vertically across the axis of rotation.

2.2.1 Recuperative - 1. Plate Type, 2. Tubular type

2.2.2 Regenerative - Rotating Element – Ljungstrom - Rotating Hood - Rothomuhle - Gas Direction - Horizontal & Vertical - Sector Opening - Bisector, Trisector and Quadsector. Problems Faced In Air Preheater: 3.1 Erosion & Damage of APH baskets & other internals: During Unit # 2 opportunity shutdown it was observed that the baskets were severely eroded. On visual inspection it was decided to change the Hot end baskets. Later during statutory overhaul of Unit # 3 & 4, considering the extent of damage, it was decided to replace all the baskets of APH during Unit # 2 Statutory overhaul.

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Fig1: Erosion & Damage of APH baskets & other internals. The drawings of baskets were not available. So during statutory overhaul of Unit # 3, baskets from one sector were removed & drawing was developed by reverse Engineering. Various Air preheater suppliers were consulted & finally order was placed to one supplier. The problem of high pressure drop & lesser heat pickup was discussed with supplier. It was decided to change the profile of basket heating elements for better performance. Detailed data was provided to the manufacturer for calculating the predicted performance of new APH baskets. On the basis of provided data, supplier has suggested following two different set of heating element profiles. 3.2 Observations of Unit # 2 APH: Unit # 2 was stopped for statutory overhaul. APH manhole doors were opened & the observations were as follows: 1. All the baskets were severely damaged due to erosion & secondary damages during boiler outages. In some of the sectors, there was no heating element remaining in the basket of cold end & hot end. 2. The radial, Rotor post, Static seals & bypass seals were severely damaged due to erosion & secondary damages. 3. Severe erosion of bracing, water washing, fire fighting pipes & casings were found. 4. Soot blower pipe & nozzles was eroded. 5. Cold end diaphragm plate of APH 2B at inbore was found completely damaged. Also there was no rotor post seal remaining in that area.

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Fig 2: Erosion of Radial seals 3.3 Rectifications carried out in Unit # 2 APH: 1. Baskets removal doors at SA & Flue gas side were opened. All eroded cold end, hot intermediate and hot end baskets were removed. 2. Gratings were repaired and grating to diaphram plate welding was done. 3. New cold end, hot intermediate and hot end baskets were loaded. 4. Outer basket locking was done. 5. Hot end sector plate static seal were repaired at eroded area by patch-up work. 6. The support bearing housing cover was opened and bearing was cleaned and inspected found ok. More ash was found in APH 2B inside the bearing housing. 7. The guide bearing housing cover was opened. The bearing was inspected, after that the bearing was cleaned and it was observed that the gap found between the bearing inner race and adopter sleeve is 0.2 to 0.3 mm. To avoid bearing failure, locktite was provided between adopter sleeve & bearing inner race. 8. New oil was filled upto the dipstick level at both guide bearing and support bearing. 9. Leveling of the rotor was done. 10. Eroded bracing pipe and connecting plates were repaired at gas sides. 11. Rotor seal angle run-out reading was taken. 12. Hot end and cold end sector plate leveling was done. 13. In APH 2A new hot end rotor post seal were fitted, 2-3 mm away from the sector plate highpoint. 14. APH 2B new cold end rotor post seal was fitted, 2-3 mm away from the CE sector plate highpoint. 15. New cold end radial seal were fitted. Seal clearance IB 0-0.1 mm and OB 7-8mm. 16. New hot end radial seal were fitted. It was observed that the hot end sector plates were severely eroded and level variation is more than 5mm. 17. New axial seal were fitted. (Reading enclosed). It was observed in APH 2B axial seal plate one adjuster rod (HE) found in jammed condition. Due to this the axial seal plate (hot end) unable to adjust to the required seal clearance.(Ref seal clearance reading) 18. Eroded hot end and cold end bypass seal were replaced with new one. 19. Main drive gear box oil was replaced. 20. Oil sealing tube gland packing rope was replaced. 21. Guide bearing air seal Assy was removed, cleaned and refitted. 22. It is recommended that the modified air seal Assy has to be fitted for better sealing at guide bearing area. 23. It was observed that the hot end inboard tracking rod locknuts are not properly tighten to the turn-buckles and locknuts found in jammed conditions in APH 2B. 24. Soot blowing nozzle and eroded pipe were replaced. Soot blowing gear box oil was replaced. 25. APH trial run was taken. No abnormality was noticed. Finally baskets were water washed before starting CAVT. Twice soot blowing was done prior to boiler light-up for cleaning the corrosion resistive oil film of new baskets. It is important to run the fans immediately after water washing of APH. 3.4 Various Profiles of heating elements: Change of Profile for cold end Baskets: In old air pre-heaters, the cold end baskets are provided with 1.2 mm thick elements of NF6 profile. Operating conditions for Indian, this can be changed to 0.8 mm DU profile. This will increase the heat transfer area of air preheater, thereby reducing the flue gas as outlet temperature. It is calculated that by changing the profile as suggested, the as outlet temperature will decrease by 40C, that means 0.2% improvement in efficiency. This change has already been incorporated in the current design. Still some of the air pre-heaters are operating with cold end NF6 profile. This can be changed. New Profiles: for improving the thermal performance of air preheater A highly efficient element profiles are available. Case Study-I is presented to show the performance changes with the introduction of new profiles. With the introduction of new profile, the outlet temperature of gas can be achieved to 135.60C.

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4.1 Major modifications carried out are as follows: 1. Cooling water line was modified. 2. Deflector plate provided at guide bearing. 3. Correction of seismic stop location. 4. Provision given for manometer at PA side for measuring exact pressure drop. 5. Provision given for O2 probe at the outlet of APH.

Fig 3: New Baskets Table 1: Comparison of parameters after APH rectification: Predic S. ted Before Overhaul After Overhaul Data Unit Design PG Test No. Perfor Date: 03.09.18 Date: 30.09.18 mance 1 Unit Load MW 135 135 132.8 137.6 Fuel 2 T/hr 105.1 93.2 37.7+42.8+B? 97.4 Consumption No. of mills in 3 No. 3 A, B & C A, B & C A, B & C service APH A APH B APH A APH B APH A APH B Flue Gas Inlet 4 °C 360 325.6 338 330 313.6 302.3 312.9 294.7 Temp. Flue Gas Outlet 5 °C 146.1 140 143.4 150.1 144.8 147.4 Temp. PA inlet 6 °C 38 32.9 32.9 40 51.7 52.8 55.6 54.1 temperature PA outlet 7 °C 310 268.1 283.8 290 239.4 223.7 285 279.5 temperature SA inlet 8 °C 38 24.7 24.3 40 43 43.1 43.3 43.5 temperature SA outlet 9 °C 327 284.9 298.2 280 273.1 262.3 293.4 291.8 temperature PA pressure 10 mm WC 945.59 899.12 897.65 882.67 before APH PA pressure after 11 mm WC 700 7695 635.22 623.78 632.14 634.23 APH SA pressure 12 mm WC 141.5 133.97 165.21 163.43 before APH SA pressure after 13 mm WC 66.39 65.31 65.09 63.23 APH 14 DP Across PA mm WC 180 310.37 275.34 265.51 248.44 15 PA flow at outlet T/hr 234.5 186.97 207.4 16 SA flow at outlet T/hr 263.9 223.5 322.32 233.99 251.3 227.7 17 PA fan current Amp 52.3 56 52.41 50 52.1 49.7 Additional PA 18 Amp 26.4 17.6 fan C 19 FD fan current Amp 23.9 23.4 23.4 23.6 13.6 13.3 20 ID fan current Amp 71.4 102.1 84.1 51.7 65.5

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As indicated from the above comparison sheet following are the improvements after replacement of APH baskets: 1. Increase in PA outlet temperature by around 40 – 45oC. 2. Increase in SA outlet temperature by around 20oC. 3. Reduction in fan loading due to proper seal setting. 4.2 Profits Gained After Overhauling in APH A) Cost saving per hour: 1. Fuel saving = 233.9- 227.7 = 6.2 T/Hr 2. Assuming cost of coal = Rs 2000 per MT 3. Cost saving per hour = 2000 X 6.2 = Rs 12,400 4. Cost of fuel saving per year =12400X24X365 =Rs10,86,24,000 B) Cost benefit due to fan loading: 1. Total fan loading before overhauling = 177.91 amps 2. Total fan loading after overhauling = 117.4 amps 3. Total saving in current = 60.51 amps 4. Power saved = 1.73X3.3X60.51X 0.86 = 178.25KWhr = 0.178MWhr 5. Energy saved per year = 178.2X24X365=15,61,032 6. Power cost = Rs 2.60 per unit 7. Saving per year = 1561032 X 2.60 = Rs 4058683 C) Total savings per year = 108624000 + 4058683 = Rs 10,86,24,000

4.3 PARFORMANCE OF AIR PREHEATER APH Thermal efficiency;  Gas side efficiency of air preheater - ηgas.  Air side efficiency of air preheater-ηair.  X – Ratio. If, Tig -inlet temperature of flue gas. Tog -outlet temperature of flue gas. Tia -inlet temperature of air. Toa -outlet temperature of air. Tog (nl) -outlet temperature of flue gas at no leakage. Cpa – mean specific heat between Tig & Tog. Cpg - mean specific heat between Tog & Tog(nl).

Gas side efficiency of air preheater, inlet temperature of flue gas − outlet temperature of flue gas at no leakage ηgas = inlet temperature of flue gas − inlet temperature of air 푇ig − 푇og (nl) ηgas = 푇ig − 푇ia

Corrected gas temperature for no seal leakage, 퐶pa(푇og − 푇ia) Tog (nl) = AL × + Tog 100 ×퐶pg Air side efficiency of air preheater, outlet temperature of air − inlet temperature of air ηair = inlet temperature of flue gas − inlet temperature of air 푇oa−푇ia ηair = 푇ig−푇ia

Gas side efficiency of air preheater X–Ratio = Air side efficiency of air preheater η푔푎푠 X–Ratio = η푎푖푟

% of weight of air leakage through seal (AL) = 푂2out − 푂2in AL= × 100 ×(0.9 for coal) 21− 푂2out

C pa = 0.95 for coal Cpg

4.4 Calculations of Ljungstrom air pre-heater:

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The method determines air pre-heater as per this procedure is the volumetric method this is an approximation of air heaters leakage with an accuracy of±1%. % of weight of air leakage through seal (AL), 푂2out − 푂2in AL= × 100 ×(0.9 for coal) 21− 푂2out

O2in - % of O2 in gas at inlet of air preheater: 3.3 O2out - % of O2 in gas outlet of air preheater: 5.2 5.2 − 3.3 AL= × 100 ×0.9 21− 5.2 AL= 10.82% Collected data before overhaul, Tig -inlet temperature of flue gas = 313.6 Tog -outlet temperature of flue gas = 143.4 Tia -inlet temperature of primary air = 51.7 Toa -outlet temperature of primary air = 239.4 Tia -inlet temperature of secondary air = 43 Toa -outlet temperature of secondary air = 273.1 Tog (nl) -outlet temperature of flue gas at no leakage. o Cpa – mean specific heat between Tig & Tog: 1.023 KJ / kg k o Cpg - mean specific heat between Tog & Tog(nl): 1.109 KJ / kg k

Corrected gas temperature for no seal leakage, 퐶pa(푇og − 푇ia) Tog (nl) = AL × + Tog 100 ×퐶pg 1.023(143.4 − 51.7) Tog (nl) = 10.82 × + 143.4 100 ×1.109 o Tog (nl) = 152.55 C

4.4.1 Gas side efficiency of air preheater before overhaul, 푇ig − 푇og (nl) ηgas = 푇ig − 푇ia 313.6 −152.55 ηgas = 313.6 − 51.7 ηgas = 0.614 ηgas = 61.4%

4.4.2 primary air side efficiency of air preheater before overhaul, 푇oa−푇ia ηair = 푇ig−푇ia 239.4−51.7 ηair = 313.6−51.7 ηair = 0.7166 ηair = 71.66%

η푔푎푠 X–Ratio = η푎푖푟 61.4 X–Ratio = 71.66 X–Ratio = 0.8568

Outlet temperature of gas without leakage, Tog = Tig – X(Toa - Tia ) Tog = 313.6 – 0.856(239.4 – 51.7) o Tog = 153 C 푇oa−푇ia ηair = 푇ig−푇ia 239.4−153 ηair = 313.6−51.7 ηair = 0.3298 ηair = 32.98% 4.4.3 Secondary air side efficiency of air preheater before overhaul, 푇oa−푇ia ηair = 푇ig−푇ia 273.1−43 ηair = 313.6−43 ηair = 0.8503 ηair = 85.03%

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η푔푎푠 X–Ratio = η푎푖푟 61.4 X–Ratio = 85.03 X–Ratio = 0.722

Outlet temperature of gas without leakage, Tog = Tig – X(Toa - Tia ) Tog = 313.6 – 0.722(273.1 – 43) o Tog = 173.4 C 푇oa−푇ia ηair = 푇ig−푇ia 273.1−173.4 ηair = 313.6−43 ηair = 0.3684 ηair = 36.84% Collected data after overhaul, Tig -inlet temperature of flue gas = 312.9 Tog -outlet temperature of flue gas = 144.8 Tia -inlet temperature of primary air = 55.6 Toa -outlet temperature of primary air = 285 Tia -inlet temperature of secondary air = 43.3 Toa -outlet temperature of secondary air = 293.4 Tog (nl) -outlet temperature of flue gas at no leakage. o Cpa – mean specific heat between Tig & Tog: 1.023 KJ / kg k o Cpg - mean specific heat between Tog & Tog(nl): 1.109 KJ / kg k

Corrected gas temperature for no seal leakage, 퐶pa(푇og − 푇ia) Tog (nl) = AL × + Tog 100 ×퐶pg

1.023(144.8 − 55.6) Tog (nl) = 10.82 × + 144.8 100 ×1.109 o Tog (nl) = 153.5 C

4.4.4 Gas side efficiency of air preheater before overhaul, 푇ig − 푇og (nl) ηgas = 푇ig − 푇ia 312.9 −153.5 ηgas = 312.9 − 55.6 ηgas = 0.619 ηgas = 61.9%

4.4.5 primary air side efficiency of air preheater after overhaul, 푇oa−푇ia ηair = 푇ig−푇ia 285−55.6 ηair = 312.9−55.6 ηair = 0.8915 ηair = 89.15%

η푔푎푠 X–Ratio = η푎푖푟 61.9 X–Ratio = 89.15 X–Ratio = 0.694

Outlet temperature of gas without leakage, Tog = Tig – X(Toa - Tia ) Tog = 312.9 – 0.694(285 – 55.6) o Tog = 153.6 C 푇oa−푇ia ηair = 푇ig−푇ia 285−153.6 ηair = 312.9−55.6 ηair = 0.5106 ηair = 51.06% 4.4.6 Secondary air side efficiency of air preheater after overhaul,

푇oa−푇ia ηair = 푇ig−푇ia

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293.4−43.3 ηair = 312.9−43.3 ηair = 0.9276 ηair = 92.76%

η푔푎푠 X–Ratio = η푎푖푟 61.9 X–Ratio = 92.76 X–Ratio = 0.667

Outlet temperature of gas without leakage, Tog = Tig – X(Toa - Tia ) Tog = 312.9 – 0.667(293.4 – 43.3) o Tog = 145.8 C 푇oa−푇ia ηair = 푇ig−푇ia 293.4−145.8 ηair = 312.9−43.3 ηair = 0.5474 ηair = 54.74% Table2: Comparison of Air Preheater before and After Overhaul RESULT VALUE S Before overhaul After overhaul Gas side efficiency 61.4 61.9 X-Ratio for PA 0.856 0.694 X-Ratio for SA 0.722 0.667 primary air side efficiency 32.98 51.06 secondary air side efficiency 36.84 54.74

4.5 Comparison of Efficiency of Air Preheater before and After Overhaul

62 61.9 61.8 61.6 61.4 61.4 61.2 61 Before overhaul After overhaul EFFICIENCY%

Fig 4: Comparison of gas side Efficiency of Air Preheater before and After Overhaul

60 51.06 50 40 32.98 30 20 10 EFFICIENCY% 0 Before overhaul After overhaul

Fig 5: Comparison of primary air side Efficiency of Air Preheater before and After Overhaul

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60 54.74

50 40 36.84

20 EFFICIENCY % 10

0 Before overhaul After overhaul

Fig 6: Comparison of secondary air side Efficiency of Air Preheater before and After Overhaul

5.1 Proposals for Major Modifications: 5.1.1 Other Modifications planned: 1. Exploring the provision of replacing the oscillating type soot blower with retractable type for better cleaning of APH baskets. 2. Static seal design to be modified for better sealing. 3. The door has to be fitted at axial seal plate for inspecting the axial seal plate, repairing of axial seal plate static seal and measuring the axial seal clearance. 4. To protect the baskets heating elements from the scrap falling from boiler, a cover sheets has to be provided on the APH sectors during the overhauling work. 5.2 Proposal 1: Reducing the size of PA centre Section Currently the width of the primary centre section sector plate is designed to cover the double sealing. The width of the primary centre section can be reduced to cover the single sealing. This will increase both primary air opening and secondary air opening. Refer Fig. below. This modification includes the change of hot end and cold end primary centre sections, sector plates, static seals, expansion bellows, duct modifications, etc. Table 3: Expected benefits # Proposal 1 Increase in PA temperature by 5oC. Expected Decrease in flue gas outlet temperature by 4oC. benefits Decrease in Pressure drop across AP is 15 mmWC

GAS G

AS 55° 55° PA PA SA SA

Fig. 7(a) Existing Double Sealing Fig. 7(b) Proposed Single Sealing with reduced PA centre section size

5.3 Proposal 2: Increase in PA angle opening from 55º to 80º. In the existing air preheaters the primary angle opening available is 55°. This angle can be increased from 55° to 80°. This will increase the PA flow area and will decrease the secondary flow area. The heat gain will be more in Primary air and pressure drop will be less. Correspondingly secondary air outlet temperature will be less and the pressure drop will be more.

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This modification includes the change of hot end and cold end primary centre sections, sector plates, static seals, expansion bellows, duct modifications, etc. Table 4: Expected benefits # Proposal 2

Increase in PA temperature by 15oC. Expected Decrease in flue gas outlet temperature by 7 oC. benefits Decrease in Pressure drop across AP is 60 mmWC

GAS GAS

55° 80° P PA A SA SA

Fig. 8(a): Existing Primary Air Opening - 55° Fig. 8(b): Primary Air Opening - 80°

6.1 Conclusions The modifications and proposals as discussed above should give importance so as to increase primary air outlet temperature, decrease secondary air outlet temperature, decrease in Pressure drop across Air Preheater. Modifications planned and proposals given as discussed above if implemented will increase the boiler efficiency nearly by 1 percent. The performance of air preheater increase by using above modification. Load on the fans are reduce due to this power consumption and cost is reduce. The main advantage of this proposal is that, the heat transfer rate in the boiler will be increased. Results are found in above calculation is that decrease air leakage area, increase air and gas side efficiency and X-ratio indicates that the maximum heat recovery in the Air preheater.

References,

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7. Shomita banerjee, prof. pooja tiwari 2017, study on optimization of primary air inlet opening which minimize the pressure drop across the air preheater and study of effects of variation in rpm of rotor on aph performance. ijsrd - international journal for scientific research & development 2321-0613. 8. Dilip s. patel, mitesh d. patel, shreysh a. thakkar 2016, to optimize the design of the basket profile in ljungstrom air preheater. international research journal of engineering and technology (irjet),601-606.

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