A combined air preheater

Abstract

The invention discloses a combined air preheater, wherein a hot flue gas inlet duct is connected with a cold flue gas outlet duct via a flue gas side rotary air preheater, a medium-temperature flue gas outlet duct, a medium-temperature flue gas inlet duct and a heat release side of a tubular air preheater system; a cold air inlet duct is connected with a hot air outlet duct via a heat absorption side of the tubular air preheater system, a medium-temperature air outlet duct, a medium-temperature air inlet duct and an air side rotary air preheater. The preheater can effectively increase the exhaust gas temperature at the rotary air preheater outlet, solve the problem of the influence of ammonium bisulfate ash blocking on the rotary air preheater, and has high safety and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of generator sets and relates to a combined air preheater. Background Art

[0002] Air preheaters are widely used in thermal power generating units. They can reduce the exhaust temperature of the unit, increase the temperature of the air required for combustion, and greatly improve the thermal efficiency of the boiler. Air preheaters are mainly divided into rotary air preheaters and tubular air preheaters. Rotary air preheaters have high heat exchange efficiency and small size. They are mainly used in large-capacity units of 300MW and above. Tubular air preheaters are simple to manufacture and have a low air leakage rate. They are mainly used in small units of 200MW and below.

[0003] After the implementation of the ultra-low emission policy, the NOx concentration is required to be no more than 50 mg / m 3 , the generator sets have been modified for denitration. The denitration system mainly uses SCR technology or SNCR+SCR technology, using ammonia to reduce NOx in the flue gas to N2. When ammonia cannot react completely, it will cause ammonia escape. The escaped ammonia will react with SO3 in the flue gas below 200°C to form ammonium bisulfate, which significantly increases the viscosity of the fly ash. The main problem faced by the rotary air preheater is the increase in resistance and the decrease in heat exchange efficiency due to ammonia escape.

[0004] In order to solve the problem of ammonium bisulfate blockage, a high-pressure water gun online flushing device was installed at the cold end of the air preheater, but the thickness of the ammonium bisulfate ash blockage reached more than 1m, and it was difficult to completely solve the ash blockage problem. Another option is to replace the low-temperature section of the air preheater with a large-channel heat exchange plate, which is conducive to online cleaning, but the large-channel heat exchange plate will reduce the heat exchange efficiency of the air preheater, increase the exhaust gas temperature at the air preheater outlet, and reduce the boiler efficiency.

[0005] Tubular air preheaters also have the problem of ammonium bisulfate clogging. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a combined air preheater, which can effectively increase the exhaust gas temperature at the outlet of the rotary air preheater, solve the problem of the influence of ammonium bisulfate ash blockage on the rotary air preheater, and has high safety and stability.

[0007] To achieve the above-mentioned object, the combined air preheater of the present invention comprises a rotary air preheater system, a tubular air preheater system, a cold air inlet duct and a medium-temperature air outlet duct, wherein the rotary air preheater system comprises a hot flue gas inlet duct, a hot air outlet duct, a flue gas side rotary air preheater, an air side rotary air preheater, a medium-temperature flue gas outlet duct and a medium-temperature air inlet duct;

[0008] The hot flue gas inlet duct is connected to the cold flue gas outlet duct via the flue gas side rotary air preheater, the medium-temperature flue gas outlet duct, the medium-temperature flue gas inlet duct and the heat release side of the tubular air preheater system; the cold air inlet duct is connected to the hot air outlet duct via the heat absorption side of the tubular air preheater system, the medium-temperature air outlet duct, the medium-temperature air inlet duct and the air side rotary air preheater.

[0009] A high-pressure water gun online flushing device is provided in the flue of the medium-temperature flue gas outlet.

[0010] High-power sonic soot blowers are arranged in the medium-temperature flue gas inlet duct and the cold flue gas outlet duct.

[0011] A plurality of air side baffle doors are arranged in the cold air inlet air duct, and the air side baffle doors are connected with baffle door actuators.

[0012] The tubular air preheater system is composed of a plurality of tubular air preheater modules, wherein each tubular air preheater module includes a shell and a plurality of heat exchange tubes and a plurality of tube sheets arranged in the shell, wherein the interior of the shell is divided into a plurality of closed channels by the tube sheets, wherein each heat exchange tube passes through all the tube sheets, and one closed channel corresponds to one air side baffle door; each air side baffle door is arranged at the entrance of the corresponding closed channel, each heat exchange tube is connected to the medium-temperature flue gas inlet flue and the cold flue gas outlet flue, and each closed channel is connected to the cold air inlet duct and the medium-temperature air outlet duct.

[0013] The heat exchange tube comprises a base tube, outer fins fixed on the outer wall of the base tube and inner fins fixed on the inner wall of the base tube.

[0014] The inner fins are evenly arranged on the inner wall of the base tube, the outer fins are evenly arranged on the outer wall of the base tube, and the outer fins are arranged in a staggered manner, the inner fins are arranged in a staggered manner, and the axes of the outer fins and the inner fins intersect with the axis of the base tube.

[0015] Width of tubular air preheater module

[0016] Length of tubular air preheater module

[0017] Spacing between adjacent tube sheets

[0018] Wherein, D is the diameter of the base tube, u is the flue gas velocity between the heat exchange tubes, P is the flue gas pressure, and ρ is the flue gas density.

[0019] The design temperature of the flue gas outlet of the rotary air preheater system is 200℃ at 50% load;

[0020] The design temperature of flue gas inlet of tubular air preheater system is 200℃ at 50% load;

[0021] The internal fins are designed to enhance the heat transfer coefficient in the base tube by 1.90 times;

[0022] The strengthening effect of the external fins on the heat transfer coefficient outside the base tube is designed to be 2.30 times.

[0023] The present invention has the following beneficial effects:

[0024] During specific operation, the combined air preheater of the present invention combines the flue gas side rotary air preheater, the air side rotary air preheater and the tubular air preheater system to increase the exhaust temperature of the rotary air preheater outlet, solve the effect of ammonium bisulfate ash blocking on the rotary air preheater, and provide a high safety and stability system.

[0025] Furthermore, the volume of the tubular air preheater system is reduced by using inner and outer fins, and the air side baffle door is used for group cutting to increase the tube wall temperature, thereby solving the effect of ammonium bisulfate ash blockage on the tubular air preheater system.

[0026] Furthermore, the outlet design flue gas temperature of the rotary air preheater system is 200°C at 50% load, ensuring that no ammonium bisulfate ash blockage occurs above 50% load, and slight ash blockage occurs below 50% load, but the ash blockage thickness does not exceed 0.3m, and the ash blockage is eliminated by using a high-pressure water gun online flushing device.

[0027] Furthermore, the inner and outer walls of the heat exchange tubes are provided with fins, which greatly increases the heat exchange efficiency of the heat exchange tubes and can reduce the volume of the tubular air preheater system to 50% of the traditional volume. The angle of the inner fins is parallel to the flue gas flow direction, which increases the heat exchange effect while slightly increasing the flow resistance. Although the outer fins will increase the resistance, the original resistance on the air side is low, and the increased resistance is also within an acceptable range.

[0028] The inlet flue gas temperature of the tubular air preheater system is 200°C at 50% load, so that the ammonium bisulfate ash blockage basically occurs in the tubular air preheater system. The tubular air preheater is divided into several independent channels. If ammonium bisulfate ash blockage occurs, the corresponding air side damper doors can be closed in sequence. No cold air flows outside the heat exchange tubes in the closed independent channels, and the heat exchange tubes are filled with hot flue gas above 200°C. The hot flue gas is used to evaporate the ammonium bisulfate in the heat exchange tubes, and then a high-power sonic soot blower is used to solve the ash blockage problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the present invention;

[0030] Figure 2A top view of a tubular air preheater system in the present invention;

[0031] Figure 3 It is a top view of the tubular air preheater module 13 of the present invention;

[0032] Figure 4 It is a side view of the tubular air preheater module 13 of the present invention;

[0033] Figure 5 is a cross-sectional view of the heat exchange tube 15 in the present invention;

[0034] Figure 6 It is a side view of the heat exchange tube 15 in the present invention.

[0035] Among them, 1-1 is a rotary air preheater on the flue gas side, 1-2 is a rotary air preheater on the air side, 2 is a high-pressure water gun online flushing device, 3 is a hot flue gas inlet duct, 4 is a hot air outlet duct, 5 is a medium-temperature flue gas outlet duct, 6 is a medium-temperature air inlet duct, 7 is a medium-temperature flue gas inlet duct, 8 is a cold air inlet duct, 9 is a high-power sonic soot blower, 10 is a medium-temperature air outlet duct, 11 is a cold flue gas outlet duct, 12 is an air side baffle door, 13 is a tubular air preheater module, 14 is a baffle door actuator, 15 is a heat exchange tube, 15-1 is a base tube, 15-2 is an outer fin, 15-3 is an inner fin, 16 is a tube sheet, and 17 is a shell. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0037] refer to Figures 1 to 6 The combined air preheater described in the present invention comprises a rotary air preheater system, a tubular air preheater system, a cold air inlet duct 8 and a medium-temperature air outlet duct 10, wherein the rotary air preheater system comprises a hot flue gas inlet duct 3, a hot air outlet duct 4, a flue gas side rotary air preheater 1-1, an air side rotary air preheater 1-2, a medium-temperature flue gas outlet duct 5 and a medium-temperature air inlet duct 6; the hot flue gas inlet duct 3 is connected to the cold flue gas outlet duct 11 via the flue gas side rotary air preheater 1-1, the medium-temperature flue gas outlet duct 5, the medium-temperature flue gas inlet duct 7 and the heat release side of the tubular air preheater system; the cold air inlet duct 8 is connected to the hot air outlet duct 4 via the heat absorption side of the tubular air preheater system, the medium-temperature air outlet duct 10, the medium-temperature air inlet duct 6 and the air side rotary air preheater 1-2.

[0038] A high-pressure water gun online flushing device 2 is arranged in the medium-temperature flue gas outlet flue 5, and high-power sonic soot blowers 9 are arranged in both the medium-temperature flue gas inlet flue 7 and the cold flue gas outlet flue 11.

[0039] A plurality of air side damper doors 12 are arranged in the cold air inlet duct 8, and the air side damper doors are connected to the damper door actuator 14; the tubular air preheater system is composed of a plurality of tubular air preheater modules 13, wherein each tubular air preheater module 13 includes a shell 17 and a plurality of heat exchange tubes 15 and a plurality of tube sheets 16 arranged in the shell 17, wherein the interior of the shell 17 is divided into a plurality of closed channels by each tube sheet 16, wherein each heat exchange tube 15 passes through all the tube sheets 16, and one closed channel corresponds to one air side damper door 12; each air side damper door 12 is arranged at the entrance of the corresponding closed channel, each heat exchange tube 15 is connected with the medium-temperature flue gas inlet flue 7 and the cold flue gas outlet flue 11, and each closed channel is connected with the cold air inlet duct 8 and the medium-temperature air outlet duct 10.

[0040] The heat exchange tube 15 includes a base tube 15-1, outer fins 15-2 fixed on the outer wall of the base tube 15-1, and inner fins 15-3 fixed on the inner wall of the base tube 15-1. The inner fins 15-3 are evenly arranged on the inner wall of the base tube 15-1, and the outer fins 15-2 are evenly arranged on the outer wall of the base tube 15-1. The outer fins 15-2 are arranged in a staggered manner, and the inner fins 15-3 are arranged in a staggered manner. The axis of each outer fin 15-2 and the axis of each inner fin 15-3 intersect with the axis of the base tube 15-1.

[0041] Width of tubular air preheater module 13

[0042] Length of tubular air preheater module 13

[0043] The spacing between adjacent tube sheets 16

[0044] Wherein, D is the diameter of the base tube 15 - 1 , u is the flue gas flow rate between the heat exchange tubes 15 , P is the flue gas pressure, and ρ is the flue gas density.

[0045] The design temperature of the flue gas outlet of the rotary air preheater system is 200℃ at 50% load; the design temperature of the flue gas inlet of the tubular air preheater system is 200℃ at 50% load;

[0046] The inner fins 15-3 are designed to enhance the internal heat transfer coefficient of the base tube 15-1 by 1.90 times; the outer fins 15-2 are designed to enhance the external heat transfer coefficient of the base tube 15-1 by 2.30 times.

[0047] The specific working process of the present invention is:

[0048] The rotary air preheater and the tubular air preheater are combined together. The hot flue gas enters the flue gas side rotary air preheater 1-1 through the hot flue gas inlet flue 3 and becomes medium-temperature flue gas, and then flows out through the medium-temperature flue gas outlet flue 5. The medium-temperature air enters the air side rotary air preheater 1-2 through the medium-temperature air inlet duct 6 and becomes hot air, and then flows out through the hot air outlet duct 4. The outlet design flue gas temperature of the rotary air preheater system is 200°C at 50% load, ensuring that ammonium bisulfate ash blockage does not occur at a load above 50%, and slight ash blockage will occur below 50% load, but the ash blockage thickness does not exceed 0.3m, and the ash blockage is removed by an online flushing device 2 using a high-pressure water gun.

[0049] Cold air enters the tubular air preheater module 13 through the cold air inlet duct 8 and the air side baffle door 12, and flows out through the medium temperature air outlet duct 10 after heat exchange to become medium temperature air. The medium temperature flue gas enters the tubular air preheater module 13 through the medium temperature flue gas inlet flue 7, and flows out through the cold flue gas outlet flue 11 after becoming cold flue gas. The inner and outer wall surfaces of the heat exchange tube 15 in the tubular air preheater module are provided with inner fins 15-3 and outer fins 15-2, which greatly increase the heat exchange efficiency of the heat exchange tube 15 and can reduce the volume of the tubular air preheater to 50% of the traditional volume. The angle of the inner fin 15-3 is parallel to the flue gas flow direction, which increases the heat exchange effect while slightly increasing the flow resistance. Although the outer fin 15-2 will increase the resistance, the original resistance on the air side is low, and the increased resistance is also within an acceptable range. The inlet flue gas temperature of the tubular air preheater system is 200°C at 50% load, so that the ammonium bisulfate ash blockage basically occurs in the tubular air preheater system. The tube sheet 16 and the shell 17 separate the tubular air preheater module into several independent channels. If ammonium bisulfate ash blockage occurs, the corresponding air side damper door 12 can be closed in sequence. No cold air flows outside the heat exchange tube 15 in the closed independent channel. The heat exchange tube 15 is filled with hot flue gas above 200°C. The hot flue gas is used to evaporate the ammonium bisulfate in the heat exchange tube 15, and then the high-power sonic soot blower 9 is used to solve the ash blockage problem. The closing time of each air side damper door 12 is not less than 8 hours.

[0050] The air side is divided into several independent channels in order to reduce the influence of the operation on the unit when closing the air side damper door 12. The relationship between the number n (recommended n ≥ 5) of the air side damper doors 12 and the load rate during operation is:

[0051] 100*(1-1 / n)≤D≤100*(1-1 / 2n)

[0052] Wherein, D is the load rate. When the air side damper doors 12 are closed sequentially within this load range, the tubular air preheater system can still maintain a good heat exchange effect and has little impact on the unit.

[0053] The present invention provides the upper limits of the length a, width b of a single tubular air preheater module 13 and the distance L between two adjacent tube sheets 16, so as to avoid vibration of the tubular air preheater system.

Claims

1. A combined air preheater, characterized in that: The invention comprises a rotary air preheater system, a tubular air preheater system, a cold air inlet duct (8) and a medium-temperature air outlet duct (10), wherein the rotary air preheater system comprises a hot flue gas inlet duct (3), a hot air outlet duct (4), a flue gas side rotary air preheater (1-1), an air side rotary air preheater (1-2), a medium-temperature flue gas outlet duct (5) and a medium-temperature air inlet duct (6); The hot flue gas inlet duct (3) is connected to the cold flue gas outlet duct (11) via the flue gas side rotary air preheater (1-1), the medium temperature flue gas outlet duct (5), the medium temperature flue gas inlet duct (7) and the heat release side of the tubular air preheater system; the cold air inlet duct (8) is connected to the hot air outlet duct (4) via the heat absorption side of the tubular air preheater system, the medium temperature air outlet duct (10), the medium temperature air inlet duct (6) and the air side rotary air preheater (1-2); A high-pressure water gun online flushing device (2) is provided in the medium-temperature flue gas outlet flue (5); A high-power sonic soot blower (9) is arranged in both the medium-temperature flue gas inlet flue (7) and the cold flue gas outlet flue (11); A plurality of air side baffle doors (12) are arranged in the cold air inlet duct (8), and the air side baffle doors (12) are connected to baffle door actuators (14); The tubular air preheater system is composed of a plurality of tubular air preheater modules (13), wherein each tubular air preheater module (13) comprises a shell (17) and a plurality of heat exchange tubes (15) and a plurality of tube sheets (16) arranged in the shell (17), wherein the interior of the shell (17) is divided into a plurality of closed channels by the tube sheets (16), wherein each heat exchange tube (15) passes through all the tube sheets (16), and one closed channel corresponds to one air side baffle door (12); each air side baffle door (12) is arranged at the entrance of the corresponding closed channel, each heat exchange tube (15) is connected to a medium-temperature flue gas inlet duct (7) and a cold flue gas outlet duct (11), and each closed channel is connected to a cold air inlet duct (8) and a medium-temperature air outlet duct (10); The heat exchange tube (15) comprises a base tube (15-1), an outer fin (15-2) fixed on the outer wall of the base tube (15-1), and an inner fin (15-3) fixed on the inner wall of the base tube (15-1); Each inner fin (15-3) is evenly arranged on the inner wall of the base tube (15-1), each outer fin (15-2) is evenly arranged on the outer wall of the base tube (15-1), each outer fin (15-2) is arranged in a staggered manner, each inner fin (15-3) is arranged in a staggered manner, and the axis of each outer fin (15-2) and the axis of each inner fin (15-3) intersect with the axis of the base tube (15-1); The design temperature of the flue gas outlet of the rotary air preheater system is 200℃ at 50% load; The design temperature of the flue gas inlet of the tubular air preheater system is 200℃ at 50% load.

2. The combined air preheater according to claim 1, characterized in that: Width of tubular air preheater module (13) Length of the tubular air preheater module (13) The spacing between adjacent tube sheets (16) Wherein, D is the diameter of the base tube (15-1), u is the flue gas flow rate between the heat exchange tubes (15), P is the flue gas pressure, and ρ is the flue gas density.

3. The combined air preheater according to claim 1, characterized in that: The inner fins (15-3) are designed to enhance the heat transfer coefficient inside the base tube (15-1) by 1.90 times; The strengthening effect of the external fins (15-2) on the external heat transfer coefficient of the base tube (15-1) is designed to be 2.30 times.

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