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VN rotary air preheater

key word:Heat exchange element

Category:


Product description

VN rotary air preheater

 

1. Introduction

1.1. Purpose

It is mainly used for boiler in power plant.

1.2. Model meaning

29.5 (G) V(H) N(A,S,F) (T,Q,C) 1500

1500 --- total height of heat exchange elements (mm)

T. Q, C -------- the form of air preheater (without this item, it is divided into two semi-circle; T is tri-sector; Q is four quarter-sector; C is ring sleeve type)

N -------- sector plate and axial sealing plate are not adjustable

A -- the sector plate at the hot end is adjustable in two positions

S -- hot end sector plate is automatic tracking adjustable

F -- adjustable hot and cold end sensors

V is vertical arrangement of rotor shaft; h is horizontal arrangement of rotor shaft

G -- flue gas heat exchanger; without this item, it means air preheater

29.5 --- rotor flow area serial number

1.3. Structural features

1.3.1. The form of VN air preheater is shown in Figure 1-1.

1.3.1.1. Bi-sector type: as shown in Fig. 1-1 (a), air and flue gas flow through two separate sectors of air preheater respectively.

1.3.1.2. Tri-sector type: as shown in Figure 1-1 (b), an air preheater is divided into three sectors (primary fan area, secondary fan area and flue gas sector).

1.3.1.3. Quarter-sector type: as shown in Figure 1-1 (c), an air preheater is divided into four sectors (primary fan area, two secondary fan area and flue gas sector), and the primary fan area is arranged between the two secondary fan areas.

1.3.1.4. Ring sleeve type: as shown in Fig. 1-1 (d), there is a Bi-sector structure of primary air in the interior, and an annular sector for the secondary air to flow through outside. The two parts form an integral structure to work.

1.3.2. Structure of VN air preheater (see Figure 1-2). The central cylinder is supported by a thrust bearing at the bottom and a guide bearing at the top. The radial diaphragms are welded on the hub of the central cylinder to form a rotor compartment with a certain number of compartments for placing heat exchange elements.

The rotor is the core component of air preheater, which is equipped with heat exchange elements. The main radial diaphragms extending outward from the central cylinder divide the rotor into 24 compartments and 48 compartments. In addition, there used to be 36 compartments in China. The annular diaphragm between the primary and secondary radial diaphragms can strengthen the rotor structure and support the heat exchange element box. The total weight of the rotor and heat exchanger is supported by the spherical roller bearing at the bottom, while the spherical roller guide bearing at the top is used to bear the radial horizontal load.

The rotor shell is used to close the rotor, and the upper and lower ends are connected with transition smoke and air ducts. One side of the transition flue gas duct is connected with the rotor shell of the air preheater, and the other side is connected with the expansion joint of the user's flue gas and air duct. The height and size of the interface flange can be changed according to the layout requirements of the user's flue gas and air duct. The outer ring sealing strip is also arranged on the rotor shell, so as to control the direct air leakage from air to flue gas and the bypass quantity of flue gas and air.

The rotor shell is connected with the hinge end post of air preheater and welded as a whole to support on the bottom beam structure. The flue gas side and air side of the rotor shell are respectively supported on the foundation by the side pillars.

1.3.3. Heat exchange elements of air preheater. As the heat exchange element is the key part of air preheater, it is very important to ensure the reliability of heat transfer and resistance performance. At present, there are four kinds of common use (see Figure 1-3).

1.3.3.1. HS6 type. This is the simplest type of heat exchange element. Because of its low heat transfer performance and high rotor compartment, it is rarely used at present.

1.3.3.2. HS7 type. This wave pattern is especially suitable for coal types in China and can be used in hot end, middle temperature section and cold end.

1.3.3.3. HS8 type. This wave pattern is similar to HS7, and can be used in hot end, middle temperature section and cold end, and can also be used for enamel plated heat exchange elements.

1.3.3.4. HS9 type. A more open heat exchange element. The heat transfer efficiency is lower than that of hs7 and HS8, but the cleaning efficiency is higher.

1.3.3.5. HS20 type. This kind of heat exchange element has the best heat transfer performance, and for a certain amount of heat transfer, the amount of elements required is the least. In addition, the pressure drop per unit of heat exchange is also lower than that of other heat exchange elements, so the pressure drop is the smallest.

1.3.4 sealing control. In the sealing area, because of the gap between the sealing baffle and the sealing strip, there will be air leakage to the flue gas due to the existence of pressure difference. The leakage control measures are as follows:

1.3.4.1. Reduce some possible ways of air leakage;

1.3.4.2. Cancel adjustable sealing baffle, sliding vane seal or expansion joint and other components;

1.3.4.3. Increase the number of sealing strips in key parts;

1.3.4.4. Reduce the air leakage path gap;

1.3.4.5. Improve the shape of sealing strip to improve its efficiency and service life;

1.3.4.6. Calculate the maximum deformation of the air preheater rotor in the hot state, and set the sector plate in the cold state, so as to minimize the gap between the deformation of the air preheater rotor and the sector plate, so as to reduce the air leakage.

Figure 1-4 shows the VN seal.

After the introduction of this advanced design, not only the air leakage rate is reduced, but also the air leakage does not change much in a long time, and the maintenance workload is greatly reduced.

The typical air leakage rate of VN air preheater is (which largely depends on the specific operating conditions)

A. Bi-sector air preheater: 5% ~ 7%.

B. Tri-sector air preheater: 6% ~ 8%.

C. Quarter-sector air preheater: 4% ~ 8%.

The above air leakage rate can be maintained within the boiler overhaul period (3 ~ 4 years), and there is no special maintenance requirements.

Fire alarm system. The fire alarm system is composed of a series of thermocouples, which are placed on the air outlet pipe. A thermocouple is arranged on each circle of heat exchange element. The local control panel can alarm the temperature rise of air outlet at each radius or the temperature gradient increases too fast. This signal is sent to the main control room of the boiler for taking corresponding measures. This alarm system is simple and reliable. There is no moving parts inside the air preheater. It is easy to maintain and maintain. It can be used as an effective protection equipment for air preheater.

1.3.6. Soot blowing system. The experience of the plant is to use a semi retractable sootblower with both steam and water flushing functions. Each air preheater is equipped with two sets of soot blowers, one set is located in the flue gas inlet pipe, and the other set is located in the flue gas outlet pipe. They are arranged separately at a certain angle, so that soot blowing can be carried out at the same time or separately to adapt to the operation of steel furnace.

1.4. Influence of SCR device on air preheater

In order to better control the emission of NOx in the atmosphere, adding SCR denitration device in power plants has become the first choice of many power plants. The synchronous construction or reservation of denitration device puts forward new requirements for the design of boiler and auxiliary equipment.

Ammonia is used as reducing agent in SCR denitrification process. Ammonia is injected into flue gas at a certain temperature. Under the action of specific catalyst, ammonia reacts with nitrogen oxides in flue gas to form nitrogen and water.

SCR denitration system has the following adverse effects on the operation and operation of air preheater

1.4.1. The conversion rate of SO3 in flue gas increases, that is, the amount of SO3 in flue gas increases and the acid dew point temperature of flue gas rises, which aggravates the acid corrosion and ash blocking of air preheater. As an indispensable catalyst for denitration unit, it can also catalyze the conversion of SO2 to SO3. The increase of SO3 concentration will increase the acid dew point temperature and aggravate the corrosion of air preheater

1.4.2. Ammonia escaping from SCR denitration system, SO3 and water vapor in flue gas generate ammonium bisulphate (ABS) condensate

NH3+SO3+H2O—>NH4HSO4

The ammonium bisulfate (ABS) condensate is moderately acidic and has great viscosity, which is easy to adhere to the surface of the heat exchange element of the air preheater and aggravate the corrosion and ash blocking of the heat exchange element again.

At the same time, ammonium bisulfate will form serious blockage in a certain temperature section, which is just in the middle and low temperature section of air preheater. This will affect the resistance of the air preheater and put forward new requirements for the cleaning ability of the air preheater.

The reaction temperature of ammonium bisulfate (ABS) is higher, which is generally in the range of 150 ~ 200 ℃.

1.4.3. Compared with ordinary pulverized coal boiler, the pressure difference at the hot end of SCR denitration air preheater will increase by about 25%, and the air leakage rate of air preheater will increase by more than 10%.

As SCR device is added to the flue gas system of the boiler, the resistance of the flue gas system increases, so the strength and stiffness of the main structural parts of the air preheater must be strengthened in the design.

1.5. Design technical requirements of SCR denitration air preheater

According to the experience of the factory, after adding SCR denitration system to the boiler, the user should pay attention to the following points according to its impact on air preheater:

The conversion rate of SO2 to SO3 should be paid attention to when selecting catalyst. In general, the conversion rate should be controlled below 1%. If the conversion rate is too high, the corrosion of air preheater will be accelerated rapidly; if the reduction efficiency of catalyst is very high, less catalyst can be used, but the conversion rate of SO2 to SO3 will also be higher.

1.5.2. In order to control the NH3 emission, the concentration should be controlled at 1ppmv in general. If the NH3 emission increases, the ash plugging of ammonium bisulfate will be very serious.

1.5.3. The selection of materials for cold end heat exchange elements of SCR air preheater shall comprehensively consider sulfur content of coal, ash sulfur ratio, conversion rate of SO2 to SO3 in SCR, so as to prevent corrosion and ash blockage of heat exchange elements of SCR air preheater.

1.5.4. SCR air preheater shall be equipped with special cleaning device to eliminate abnormal ash blocking of air preheater. The fully retractable soot blower equipped with on-line high pressure water flushing device should be the best choice for SCR air preheater.

1.5.5. The sealing system of SCR air preheater shall be reliable and stable without complicated control device, so as to avoid the control device out of control after long-term operation, resulting in the increase of air leakage rate of air preheater, thus affecting the normal operation of boiler.

1.5.6. Air preheater manufacturers with mature experience shall be selected.

1.5.7. The supplier of air preheater shall provide the height of cold end heat exchange element to prevent ash blockage of air preheater with ammonium bisulfate (ABS), and provide the thermal analysis and calculation results of temperature field of heat exchange element of air preheater, so as to prove the suitability of this type selection.

1.6. Technical level

The function of air preheater is to use a lot of heat energy in waste flue gas to preheat the cold air entering the boiler, so as to improve the boiler efficiency and save coal.

At present, serious air leakage and low reliability of air preheater are common problems in power plants. In addition, the heat exchange elements of air preheater in many power plants have problems such as ash blockage, corrosion and high maintenance cost.

The main development process of air preheater includes adjustable seal, automatic tracking seal, double seal and the latest VN air preheater.

The main features of VN air preheater are as follows:

1.6.1. Compact structure.

1.6.2. The leakage rate is low and stable for a long time.

1.6.3. Imported central driving device is adopted.

The structure is simple.

1.6.5. Low operation cost.

1.6.6. The maintenance workload is small.

Low energy consumption.

1.6.8. The failure rate is low.

High reliability.

1.6.10. Design of air preheater for SCR device.

 

2. Main technical parameters

The main technical parameters of VN air preheater are shown in Fig. 1-5 and Table 1-1.

Table 1-1  (in mm)

Air preheter dimensions A B C D E F G H K K2 L M N P Q R Angle steel radius of rotor outer edge
22 2806 925 3235 560 1200 1650 80 80 760 500 300 1881 2244 3115 1480 1340 2885
22.5 2920 925 3350 560 1200 1650 80 80 760 500 300 1995 2336 3230 1480 1388 3000
23 3048 925 3480 560 1200 1650 80 80 760 500 300 2123 2439 3360 1480 1441 3130
23.5 3182 925 3615 560 1200 1650 80 80 760 500 300 2257 2546 3495 1480 1497 3265
24 3316 925 3750 560 1200 1650 80 80 760 500 300 2391 2653 3630 1480 1553 3400
24.5 3658 1250 4095 800 1200 1650 80 80 925 500 300 2408 2927 3975 1645 1696 3745
25 3812 1250 4250 800 1200 1650 80 80 925 500 300 2562 3049 4130 1645 1760 3900
25.5 3975 1250 4415 800 1200 1650 80 80 925 500 300 2725 3180 4295 1645 1829 4065
26 4149 1250 4590 800 1200 1650 80 80 925 500 300 2899 3319 4470 1645 1901 4240
26.5 4352 1250 4795 800 1200 1650 80 80 925 500 300 3102 3482 4675 1645 1986 4445
27 4546 1250 4990 800 1200 1650 80 80 925 500 300 3296 3636 4870 1645 2067 4640
27.5 4744 1250 5190 800 1200 1650 80 80 925 500 300 3494 3795 5070 1645 2150 4840
28 4987 1250 5435 800 1200 1650 80 80 925 500 300 3737 3989 5315 1645 2251 5085
28.5 5210 1600 5660 1100 1600 1750 110 80 1145 500 375 3610 4168 5540 1910 2344 5310
29 5448 1600 5900 1100 1600 1750 110 80 1145 500 375 3848 4358 5780 1910 2444 5550
29.5 5701 1600 6155 1100 1600 1750 110 80 1145 500 375 4101 4560 6035 1910 2549 5805
30 5993 1600 6450 1100 1600 1750 110 80 1145 500 375 4393 4794 6330 1910 2672 6100
30.5 6271 1600 6730 1100 1600 1750 110 80 1145 500 375 4671 5017 6610 1910 2788 6380
31 6563 1600 7025 1100 1600 1750 110 80 1145 500 375 4963 5250 6905 1910 2910 6675
31.5 6955 1850 7420 1300 1600 1750 110 80 1145 500 375 5105 5564 7300 1910 3073 7070
32 7277 1850 7745 1300 1600 1750 110 80 1145 500 375 5427 5822 7625 1910 3208 7395
32.5 7619 1850 8090 1300 1600 1750 110 80 1145 500 375 5769 6095 7970 1910 3351 7740
33 8040 1850 8515 1300 2000 1850 140 80 1145 500 500 6190 6432 8395 2005 3527 8165
33.5 8472 2000 8950 1450 2000 1850 140 80 1145 500 500 6472 6777 8830 2005 3707 8600
34 8898 2000 9380 1450 2000 1850 140 80 1145 500 500 6898 7118 9260 2005 3885 9030
34.5 9324 2000 9810 1450 2000 1850 140 80 1145 500 500 7324 7459 9690 2005 4063 9460
35 9800 2000 10290 1450 2000 1850 140 80 1145 500 500 7800 7840 10170 2005 4262 9940
35.5 10281 2000 10775 1450 2000 1850 140 80 1145 500 500 8281 8225 10655 2005 4463 10425
36 10806 2200 11305 1600 2400 1900 170 80 1320 500 500 8606 8645 11185 2150 4683 10955
36.5 11342 2200 11845 1600 2400 1900 170 80 1320 500 500 9142 9073 11725 2150 4906 11495
37 11922 2200 12430 1600 2400 1900 170 80 1320 500 500 9722 9537 12310 2150 5149 12080

 

The shape of VN air preheater is shown in Fig. 1-6.

 

 

3. Selection method

VN air preheater is selected by computer, which can meet the requirements of users. If users want VN air preheater, they should provide the following data:

3.1. Performance parameters

The following data, if available, shall be included in the user's inquiry:

3.1.1. Flue gas flow direction, whether the flow direction is vertical or horizontal.

3.1.2. The number of air preheaters and boilers for a boiler.

3.1.3. Location of air preheater, indoor or outdoor.

Altitude or atmospheric pressure.

3.1.5. Properties of the fuel being burned.

3.1.6. Mass flow at flue gas inlet of air preheater.

3.1.7. Ash content. If the ash content is very high, the ash analysis and specific heat capacity should be given.

3.1.8. Outlet mass flow of secondary air and / or primary air of air preheater.

3.1.9. Ambient humidity and temperature range and average value.

3.1.10. Flue gas inlet temperature.

3.1.11. Flue gas outlet temperature after air leakage correction and uncorrected and any requirements for minimum temperature.

3.1.12. Temperature of primary and secondary air at inlet.

3.1.13. Requirements for primary air mixed air temperature and air volume of coal mill.

3.1.14. Inlet air temperature regulation methods, such as secondary air hot air recirculation, adding heater before primary air or secondary air, etc.

3.1.15. Hot end pressure difference.

3.1.16. Maximum pressure loss on flue gas side and air side or pressure loss for combined flue gas and air of pressure boiler.

3.1.17. Any possible unstable factors, such as high flue gas inlet temperature or the need to reserve the position of heat exchange elements, etc.

3.1.18. Design mode of boiler, such as natural balance or forced circulation boiler.

3.1.19. The maximum allowable air leakage rate shall be expressed as the weight percentage of flue gas inlet or the change of O2 content on flue gas side. In this case, the oxygen content of flue gas shall be informed.

3.1.20. Performance guarantee requirements.

3.1.21. Hot end sector plate control.

3.2. Site conditions

If the following site conditions can be provided, it will be helpful for the selection:

3.2.1. The voltage, phase and frequency of the power supply provided.

3.2.2. The pressure and temperature of soot blowing medium provided, such as steam or air.

3.2.3. Pressure, temperature and composition of the water source provided.

3.2.4. Compressed air provided.

3.3. Supply requirements

3.3.1. Any special material requirements for structure, such as requirements for shell, transition flue gas and air duct, rotor, etc.

3.3.2. Any special material, thickness and life requirements of heat exchange elements.

3.3.3. Type of sootblower and whether local control is required, and whether there are supply requirements beyond the end of water pipe (flange plate). In this case, the material requirements of pipe and valve shall be specified.

3.3.4. Any additional requirements related to measuring instruments, such as pressure drop measuring instruments, bearing temperature measurement, etc. At the same time, the end points of the scope of supply should be specified, such as the junction box and wire of electrical appliances. The actual scope of supply generally includes rotor stop alarm device, bearing oil temperature thermocouple, etc.

3.3.5. Number and type of driving motor, such as AC, DC or compressed air.

3.3.6. Any other requirements, such as locking bolts, etc.

3.3.7. Special requirements for surface protection and paint packaging.

3.3.8. Special delivery place.

3.3.9. Any requirements on document language.

3.3.10. Whether there are requirements for field test.

 

4. Selection examples

4.1. Material of air preheater for typical coal fired boiler

The material of air preheater of typical coal-fired boiler is shown in table 1-2 for reference only.

Material of air preheater for typical coal fired boiler

Table 1-2

Item Material
heating element Hot layer and intermediate layer Medium carbon steel
Cold layer Low alloy high strength steel
Basket Medium carbon steel
Rotor BS 4360 Grade 43A or equal
Structural member Transition pipeline,up structure, rotor housing, bottom structure, end column,division plate, axial sealing plate, bottom support structure, bottom support beam BS 4360 Grade 43A or equal
Rotor driving shaft Forging to BS970 Grade 709 M40 or equal
Bottom bearing box BS 3100 Grade A1 forge steel or equal
Up bearing box BS 4360 Grade 43A or equal
Rotor sealing Low alloy high strength steel

4.2. Air preheater matching examples of typical 600MW and 1000MW units

4.2.1. The air preheater of 600MW unit is matched. The type selection parameters of VN air preheater are shown in table 1-3 (in mm) .

Table 1-3

Selection parameters BMCR working conditions BRL working conditions
Inlet flue flow (kg/s) 629.5 601.02
Air flow at secondary air outlet (kg/s) 438.7 415.55
Air flow at primary air outlet (kg/s) 112.6 110.51
Inlet flue temperature () 380 374.4
Outlet flue temperature () 120 117.2
Primary air inlet temperature () 27.8 27.8
Primary air outlet temperature (after mixed, ) 274.4 269.2
Secondary air inlet temperature () 24.3 24.3
Pressure balance from primary air to hot layer at  flue side (kPa) 12.7 12.45
Pressure balance from secondary air to hot layer at  flue side (kPa) 5.478 5.229
Pressure drop at flue side (kPa) <1.121 ______
Pressure drop of primary air (kPa) <0.747 ______
Pressure drop of secondary air (kPa) <1.046 ______

According to the selection parameters in table 1-3, the following results can be obtained:

Each boiler is equipped with two sets of 31.5VNT2400 Tri-sector air preheater.

4.2.1.2. Heat exchange surface area of each air preheater (single side): 58119m2.

4.2.1.3. Net weight of each air preheater: 568t.

4.2.1.4. Rotation direction of rotor: flue gas → secondary air → primary air.

Speed of air preheater: 1r/min.

4.2.2.2 air preheater matching example of 1000MW unit. The type selection parameters of VN air preheater are shown in table 1-4 (in mm).

Selection parameters BMCR working conditions BRL working conditions
Inlet flue flow (kg/s) 1164 1128.7
Air flow at secondary air outlet (kg/s) 730.1 702.9
Air flow at primary air outlet (kg/s) 274.9 271.4
Inlet flue temperature () 424.4 417.8
Outlet flue temperature () 145.9 144.2
Primary air inlet temperature () 27.8 27.8
Primary air outlet temperature (after mixed, ) 360.4 355.3
Secondary air inlet temperature () 22.9 22.9
Pressure balance from primary air to hot layer at  flue side (kPa) 12.699 12.45
Pressure balance from secondary air to hot layer at  flue side (kPa) 5.478 5.229
Pressure drop at flue side (kPa) <1.121 ______
Pressure drop of primary air (kPa) <0.747 ______
Pressure drop of secondary air (kPa) <1.046 ______

According to the selection parameters in table 1-4, the following results can be obtained:

4.2.2.1. Each boiler is equipped with two sets of 34.5 VNT 2050 Tri-sector air preheaters.

4.2.2.2. Heat exchange surface area of each air preheater (single side): 93334m2.

4.2.2.3. Net weight of each air preheater: 886t.

4.2.2.4. Rotation direction of rotor: flue gas → secondary air → primary air

4.2.2.5. Speed of air preheater: 0.7r / min

 

5. Scope of supply and order requirements

5.1. Scope of supply (typical scope, which can be increased or decreased according to user's demand)

The scope of supply includes product design, procurement, manufacturing, factory testing, installation and commissioning drawings, operation and maintenance manuals.

5.1.1. Plant and equipment:

5.1.1.1. Rotor and heat exchange elements.

5.1.1.2. Rotor bearing.

5.1.1.3. Rotor seal.

5.1.1.4. Rotor housing.

5.1.1.5. Transition flue gas and air duct of air preheater body and its necessary fixing parts.

5.1.1.6. Main bearing bracket.

5.1.1.7. Top and bottom platforms.

5.1.1.8. Driving device. Including the main and auxiliary AC motors and their frequency converters.

5.1.1.9. Test windows and doors.

5.1.1.10. Access door.

5.1.1.11. Steam soot blowing and water washing device, including local control cabinet.

5.1.1.12. Fire nozzle header with nozzle cover flange.

5.1.1.13. Thermocouple fire detection system.

5.1.1.14. Rotor speed and fault alarm.

5.1.1.15. Rotor bearing oil temperature thermocouple.

5.1.1.16. Inject lubricating oil for the first time.

5.1.1.17. Name plate.

5.1.1.18. Standard surface protective paint.

5.1.1.19. Special tools.

5.1.2. Termination point:

5.1.2.1. For flue gas and air inlet / outlet transition pipe port method, drill holes according to customer requirements, excluding connecting bolts.

5.1.2.2. Connection points of bottom beam and side column of air preheater and steel frame of power plant boiler, excluding connecting bolts.

5.1.2.3. Upper and lower platforms of air preheater body structure.

5.1.2.4. Fire fighting water at smoke and air pipelines.

5.1.2.5. Upper and lower soot blower steam and water pipe flange.

5.1.2.6. Motor terminals.

5.1.2.7. Cooling water flange h of bearing housing at the top of rotor.

5.1.3. Those not within the scope of supply include:

5.1.3.1. Connect the pipe and insulation baffle.

5.1.3.2. Expansion connection of pipeline at connection flange of air preheater.

5.1.3.3. Pipes, valves and instruments outside the air preheater.

5.1.3.4. Connecting wires and cables of electrical equipment.

5.1.3.5. Motor starter.

5.1.3.6. Lubricating oil (except for primary filling).

5.1.3.7. Slide rail beam and crane.

5.1.3.8. Insulation layer, wrapping layer and anchoring.

5.1.3.9. Maintenance platform and ladder (except bottom and upper platform on the body).

5.1.3.10. Support steel frame.

5.1.3.11. Foundation and civil engineering.

5.1.3.12. Installation, commissioning and field test.

5.2. Technical specifications

5.2.1. Heat exchange elements. The heat exchange element is made of steel plate, leading to channel; the size of heat exchange component shall be designed to ensure the most effective heat transfer performance from flue gas to heat exchange element and from heat exchange element to air. The heat exchange elements are arranged in layers on the rotor. The element itself is placed in the element box for easy installation. The design of the element box enables the heat exchange elements to be interchanged from top to bottom.

5.2.2. Heat exchange elements of SCR air preheater. Low temperature corrosion and ash blockage are the main factors affecting the long-term, stable and efficient operation of air preheater and boiler, especially SCR air preheater. In order to prevent low-temperature corrosion, acid deposition and ash blockage of cold end heat exchange elements of air preheater during operation, the cold end heat exchange elements of SCR air preheater are imported enamel plated heat exchange elements, as shown in Fig. 1-7.

Among them, advanced technology and process are adopted in metal base material, enamel material, spraying process of enamel heat exchange sheet and pressing control of heat exchange element box. Its enamel surface quality, uniformity, bonding strength, wear resistance, acid corrosion resistance, dust blocking resistance, wear resistance, easy cleaning, mechanical and thermal shock resistance, and service life have obvious advantages 。

Aiming at the ash blocking phenomenon of ammonium bisulfate (ABS) in SCR air preheater, the height of cold end heat exchange element can be optimized according to the temperature field distribution of air preheater, so that the acid deposition at cold end and ash blocking area (belt) of ammonium bisulfate (ABS) are completely in the cold end heat exchange element, so as to prevent abnormal ash blockage of air preheater.

5.2.3. Rotor. The rotor consists of a central shaft and a radial partition plate with radial distribution. The clapboard is connected with an outer partition plate on the circumference to form a 24 compartment structure. Each sector is reinforced by Sector dividers at different radii, thus forming a wedge-shaped compartment with heat exchange elements.

5.2.4. Rotor housing. The rotor housing is made of mild steel. There are four small hinged side pillars between the end pillars to support the rotor shell. At the same time, the side pillars are also supported by the steel frame of air preheater. Six transition pipes are used to transfer flue gas, primary air and secondary air into and out of the rotor. They are connected with the end flange of boiler flue and air duct and supported on the rotor shell.

5.2.5. Supporting structure. The rotor is supported by the upper and lower bottom beams of the shell, and the upper and lower bottom beams are connected by the bottom pillars to form a box structure. Due to the differential expansion caused by temperature gradient on the rotor, the end post is hinged at the sill. In the rotor housing, the panel between the primary air and the secondary air serves as the third end post, which is supported by hinged side columns. The bottom beam across the steel frame structure is composed of two beams made of mild steel to support the full weight of the bottom bearing and rotor.

5.2.6. Sealing between flue gas and air. The seal is made of steel plate and generally includes the following parts:

5.2.6.1. The sealing strips are installed on the radial partition plates at the cold and hot ends of the rotor, which can be adjusted and form a seal between the flue gas, primary air and secondary air with the surface of the sealing plate of the fixed sector.

5.2.6.2. There is a circumferential seal on the outer circumference of each end of the rotor, which forms a seal with the sealing strip attached to the shell

5.2.6.3. There is a circumferential sealing strip on the inner circumference of each end of the rotor, which is attached to the rotor and can be adjusted to form a seal with the inner sector sealing plate.

5.2.6.4. There is an axial sealing strip at the outer edge of the rotor to form a seal with the arc-shaped axial baffle. At any time, the axial plate has at least two sealing strips to achieve the labyrinth sealing effect, and the hub seal on the rotor shaft forms a peripheral seal with the partition baffle plate.

5. It is provided by an AC motor and driven by a bearing box type reducer directly installed on the rotor drive shaft. The drive can be limited by a flexible coupling in the top support structure. In addition, a manual rocker arm can be installed on the extension shaft of a drive motor for maintenance.

5.2.8. Rotor bearing. The rotor is supported by self-aligning spherical roller bearings in the bearing housing of the bottom girder. The other end of the shaft is mounted on a guide bearing, which should be self-aligning spherical roller, in a bearing housing mounted in the top steel frame structure, just below the drive gear. Both the support bearing and the guide bearing are lubricated by oil bath. The guide bearing box is equipped with matching water-cooled flange, and no external pump oil lubrication system is required.

5.2.9. Rotor stop alarm. The alarm system can give an alarm when the rotor is stopped to avoid overheating damage; when the power is off, the system can also give an alarm to ensure the safety of operation.

5.2.10. Soot blower. The soot blower is designed as an electrically driven semi telescopic spray gun. When the driving motor is powered on, the spray gun extends into the air preheater: when it reaches the internal position, the spray gun automatically retracts to the original position. During the retraction process of the spray gun, the position of the spray gun is designed so that all heat exchange surfaces can be covered by steam, and the expansion distance of each time is consistent with the range of the nozzle. Each soot blower is equipped with a suitable interface with the air preheater shell, with sealing arrangement, extended spray gun, stainless steel steam inlet pipe, support frame, flange matched with valve, motor and limit switch, etc. In case of power failure, the soot blower can operate automatically, and the operating mechanism is all outside the air preheater for maintenance. The soot blower is also equipped with a rod for water washing.

5.2.11. Soot blowing and cleaning device of SCR denitration air preheater. In addition to normal steam soot blowing, SCR denitration air preheater is also equipped with a special fully retractable soot blowing cleaning device, with on-line high-pressure water flushing system, so the soot blowing cleaning capacity has been greatly improved. The soot blowing cleaning mode is as follows:

5.2.11.1. Online air / steam soot blowing.

5.2.11.2. On line high pressure water flushing.

5.2.11.3. Offline low pressure water flushing.

5.2.12. Fire fighting system. Fire water valves are installed on the upper pipes of primary air, secondary air and flue gas, and external flange ports are provided outside each nozzle to connect fire water pipes.

5.2.13. Access hole on rotor. In order to maintain the rotor sealing strip, an inlet hole is provided on the flue gas and air transition pipe.

5.2.14. Fire alarm system. The system can set temperature alarm and temperature gradient change alarm. The system consists of a series of thermocouples. According to the number of chambers of the heat exchange elements, they are placed on the outlet pipe of the air preheater, and these thermocouples are connected with the control panel. If the temperature exceeds the preset value or the temperature changes abnormally, the control board will alarm and indicate which circle of heat exchange element alarms. After receiving the alarm signal, the operator should go to the scene, judge whether the fire occurs according to the situation provided by the on-site control panel, and take corresponding measures.