A steam soot blowing device for a rotary air preheater

Abstract

The present invention relates to a steam soot blowing device for a rotary air preheater, which includes a steam soot blower, a barrel, and a nozzle assembly. The nozzle assembly includes a first nozzle assembly and a second nozzle assembly. The first nozzle assembly includes a throttle pipe that is connected to the barrel and has a throttle orifice disposed inside, and a spray head that is connected to the throttle pipe. The aperture of the throttle orifice is smaller than the diameter of the throttle pipe, and the inlet aperture of the spray head is smaller than its outlet aperture. The second nozzle assembly includes a distribution pipe that is connected to the barrel and nozzles that are connected to the distribution pipe. The jet velocity of the spray head is less than the jet velocity of the nozzles. The present invention improves the purging effect of ammonium bisulfate deposited ash. The high-temperature and low-velocity steam jet upstream heats and gasifies ammonium bisulfate in the deposited ash on the surface of the heat exchange element, making the dense deposited ash become a fluffy structure, reducing the hardness and adhesion strength of the deposited ash, improving the shearing and scouring effect of the high-velocity and low-temperature steam jet downstream on the deposited ash, and enhancing the removal effect of ammonium bisulfate deposited ash.

Description

Technical Field

[0001] The present invention relates to a rotary air preheater, and more particularly to a steam soot blower for a rotary air preheater. Background Art

[0002] Conventional coal-fired power plant boilers are typically equipped with a rotor rotary air preheater, which is divided into a flue gas compartment, a secondary air compartment, and a primary air compartment in the circumferential direction. The rotor consists of upper and lower layers of flat heat exchange elements. During rotation, it sequentially passes through the flue gas compartment, the secondary air compartment, and the primary air compartment, undergoing a periodic heat storage and heat release process: in the flue gas compartment, high-temperature flue gas passes through the heat exchange elements from top to bottom, the flue gas releases heat and its temperature decreases, while the heat exchange elements store heat and their temperature increases; in the secondary air compartment and the primary air compartment, cold secondary air and cold primary air pass through the heat exchange elements from bottom to top, the cold air absorbs heat and its temperature increases, while the heat exchange elements release heat and their temperature decreases. In the flue gas compartment, ammonia escaping from the upstream SCR denitration system and SO3 in the flue gas are likely to form ammonium bisulfate deposition ash on the surface of the cold-end heat exchange elements of the air preheater rotor, blocking the flue gas channels between the heat exchange elements.

[0003] To keep the channels between the heat exchange elements of the air preheater smooth, steam soot blowers are usually arranged above the hot-end heat exchange elements of the rotor in the flue gas compartment and below the cold-end heat exchange elements of the rotor. The steam jet is used to intermittently scour the surface of the heat exchange elements online, and the deposited ash on the surface is blown off by shearing. In the flue gas compartment, the flue gas flows through the heat exchange elements from top to bottom. The steam jet of the hot-end steam soot blower blows downward along the flow, and the steam jet of the cold-end steam soot blower blows upward against the flow. The steam pressure in the soot blower barrel is about 0.8 - 1.07 MPa, and the temperature is about 300 - 350 °C.

[0004] To improve the purging effect of ammonium bisulfate deposition ash between the heat exchange elements of the air preheater, various technical improvements have been tried for the steam soot blower:

[0005] Referring to the patent with the publication number CN208566739, it discloses a high-pressure water online cleaning device for a rotary air preheater, which combines high-pressure water and steam to form a two-fluid soot blower, and can separately spray high-pressure water and steam for soot blowing.

[0006] Referring to the patent with the publication number CN204881327 for a steam soot blower for a rotary air preheater and the paper "Optimization of the Soot Blower Purging Trajectory and Operation Mode of the Air Preheater", both propose a rake-type multi-nozzle soot blower based on a single-tube nozzle to increase the residence time of the steam purging section passing through the rotor heat exchange elements.

[0007] The patent with the publication number CN111623365 discloses a refined automatic soot blowing system and a soot blowing control method for a rotary air preheater, and proposes an on-line monitoring method for fouling and blockage of heat exchange elements, and automatically decides the operation of steam soot blowers according to the degree of fouling.

[0008] In the above-mentioned technology of steam soot blowers for air preheaters, CN204881327 increases the residence time of the heat exchange elements of the air preheater rotor in the circumferential steam purge section. However, for highly adhesive deposited ash containing ammonium bisulfate, the effect of conventional steam soot blowers is limited. The main reason is that when the jet steam reaches the surface of the heat exchange element, although the central jet velocity of 80 - 120 m / s is still retained, due to entraining the surrounding low-temperature flue gas, the temperature of the purge steam drops to about 100 - 150 °C. In the face of highly viscous deposited ash containing ammonium bisulfate, even though the steam jet has a strong scouring and shearing effect, due to the low temperature of the jet steam, it is impossible to weaken the strength of the deposited ash by heating and vaporizing the ammonium bisulfate in the deposited ash, which seriously reduces the purging effect of the steam soot blower on the deposited ash containing ammonium bisulfate. Summary of the Invention

[0009] The object of the present invention is to provide a steam soot blowing device for a rotary air preheater. Aiming at the problem of poor purging effect of the steam soot blower of the existing air preheater on the deposited ash containing ammonium bisulfate, based on the temperature distribution characteristics of the cold-end heat exchange elements of the air preheater rotor in the circumferential direction and the steam jet characteristics, a steam soot blowing device with a high-low speed nozzle assembly is proposed.

[0010] To achieve the above object, the technical solution adopted by the present invention is:

[0011] A steam soot blowing device for a rotary air preheater includes a steam soot blower and a barrel connected to the steam soot blower. The steam soot blowing device further includes a nozzle assembly connected to the barrel. The nozzle assembly includes a first nozzle assembly and a second nozzle assembly.

[0012] The first nozzle assembly includes a throttle pipe with one end connected to the barrel and a spray head connected to the other end of the throttle pipe. A throttle orifice is arranged inside the throttle pipe, and the diameter of the throttle orifice is smaller than the diameter of the throttle pipe. The inlet diameter of the spray head is smaller than its outlet diameter.

[0013] The second nozzle assembly includes a distribution pipe connected to the barrel and at least one nozzle connected to the distribution pipe. The steam jet velocity at the outlet of the spray head is smaller than the steam jet velocity at the outlet of the nozzle.

[0014] Preferably, the nozzle is a Venturi nozzle. The throat diameter of the Venturi nozzle is 6-10 mm, the outlet diameter is 8-12 mm, and the divergence angle is 10-15°.

[0015] Preferably, when multiple nozzles are connected to the distribution pipe, the center distance between two adjacent nozzles is equal to 0.5-1 times the purging radius of one nozzle, the purging trajectories of multiple nozzles overlap by 0.5-1 times the purging radius of one nozzle, and the purging radius of each nozzle is 50-100 mm.

[0016] Preferably, a resistance block is further provided inside the throttle pipe, and the resistance block is located downstream of the throttle orifice.

[0017] Preferably, the length of the throttle pipe is 400-500 mm, and the pipe diameter is 20-30 mm.

[0018] Preferably, the spray head includes a conical cavity with the bottom connected to the throttle pipe and a top surface covering the top of the conical cavity. Spray holes are provided on the top surface. If the spray head is a lotus-head spray head.

[0019] Further preferably, the top surface of the spray head is arc-shaped.

[0020] Even more preferably, when multiple groups of nozzle assemblies are provided, the arc length of the top surface of the spray head closer to the steam soot blower is greater than the arc length of the top surface of the spray head farther from the steam soot blower.

[0021] Even more preferably, the width of the top surface of the spray head is 1.0-1.5 times the jet purging radius of the nozzle, and the arc length of the top surface of the spray head is 1-6 times the jet purging radius of the nozzle.

[0022] Further preferably, the aperture diameter of the spray holes is 1-3 mm.

[0023] Further preferably, the total area of the spray holes is 40-60% of the area of the top surface.

[0024] Preferably, the first nozzle assembly, the second nozzle assembly and the gun barrel are connected and communicated through a tee pipe.

[0025] Preferably, the distance between the tee pipe and the gun barrel is 10-20 mm.

[0026] Preferably, multiple groups of nozzle assemblies are provided, and multiple groups of nozzle assemblies are distributed along the length direction of the gun barrel.

[0027] Further preferably, the spacing between adjacent two sets of the nozzle assemblies is equal, and the spacing between adjacent two nozzles is 1-2 m.

[0028] Preferably, the aperture of the throttling orifice closer to the steam soot blower is larger than that of the throttling orifice farther from the steam soot blower; the number of nozzles on the distribution pipe closer to the steam soot blower is not less than that on the distribution pipe farther from the steam soot blower.

[0029] Preferably, the centerlines of the throttling pipe, the distribution pipe and the nozzle are all perpendicular to the centerline of the gun barrel.

[0030] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0031] The nozzle assembly of the present invention improves the purging effect of ammonium bisulfate deposited ash. The high-temperature and low-speed steam jet upstream heats and gasifies ammonium bisulfate in the deposited ash on the surface of the heat exchange element, making the dense deposited ash become a fluffy structure, greatly reducing the hardness and bonding strength of the deposited ash, improving the shearing and scouring effect of the high-speed and low-temperature steam jet downstream on the deposited ash, and effectively enhancing the removal effect of ammonium bisulfate deposited ash. Description of the Drawings

[0032] Attached Figure 1 is the front view schematic diagram of the rotary air preheater in this embodiment;

[0033] Attached Figure 2 is the top view schematic diagram of the rotary air preheater in this embodiment;

[0034] Attached Figure 3 is the front view schematic diagram of the nozzle assembly in this embodiment;

[0035] Attached Figure 4 is the schematic diagram of the temperature distribution on the circumferences of the hot end and the cold end of the heat exchange element of the air preheater in this embodiment;

[0036] Attached Figure 5a is the cross-sectional view of the throttling pipe;

[0037] Attached Figure 5b is the cross-sectional view of the Venturi nozzle.

[0038] In the above drawings:

[0039] 1. Rotor; 10. Central sleeve; 11. Flue gas compartment; 12. Primary air compartment; 13. Secondary air compartment; 130. Cold secondary air inlet duct; 131. Hot secondary air outlet duct; 14. Seal; 15. Heat exchange element; 150. Cold end bottom surface; 151. Cold end top surface; 152. Hot end top surface; 20. Steam soot blower; 21. Barrel; 22. Throttle pipe; 220. Throttle orifice; 221. Resistance block; 23. Nozzle; 24. Distribution pipe; 25. Venturi nozzle; 26. Three-way pipe; 30. Heating area; 31. Blowing area; 4. Ammonium bisulfate deposition temperature range. Detailed implementation manners

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0042] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0043] As Figure 1 , 2A rotary air preheater with a steam soot blowing device is shown, which includes a rotor 1 rotating around a central sleeve 10. Inside the rotor 1, flue gas compartments 11, primary air compartments 12, and secondary air compartments 13 are circumferentially distributed. The flue gas compartments 11, primary air compartments 12, and secondary air compartments 13 are separated by sector seals 14. A metal heat exchange element 15 is provided on the rotor 1. During the rotation process, it sequentially passes through the flue gas compartments 11, secondary air compartments 13, and primary air compartments 12, undergoing a periodic heat storage and heat release process: In the flue gas compartments 11, high-temperature flue gas passes through the heat exchange element 15 from top to bottom, the flue gas releases heat and the temperature decreases, while the heat exchange element 15 stores heat and the temperature increases; in the primary air compartments 12 and secondary air compartments 13, cold primary air and cold secondary air pass through the heat exchange element 15 from bottom to top, the cold air absorbs heat and the temperature increases, while the heat exchange element 15 releases heat and the temperature decreases.

[0044] The air preheater further includes a steam soot blowing device, which is arranged in the cold secondary air inlet duct 130 of the secondary air compartment and is close to the seal 14 on the side of the flue gas compartment 11.

[0045] As Figure 3 shown: The steam soot blowing device includes a steam soot blower 20, a barrel 21 connected to the steam soot blower 20 and extending radially along the rotor 1, and multiple groups of nozzle assemblies connected to the barrel 21.

[0046] The total length of the barrel 21 is equal to the radius of the rotor 1. It is equally spaced at intervals of 1 - 2m and divided into n segments. According to the segmented length, n groups of nozzle assemblies are arranged at intervals from the inside to the outside along the radius of the rotor 1, that is, from the end of the barrel 21 close to the central sleeve 10 to the outermost side of the rotor 1, the nozzle assembly numbers increase from the first group to the nth group. The barrel 21 is movably arranged in the radial direction of the rotor 1, and the moving stroke of the barrel 21 in the radial direction of the rotor 1 is the distance between adjacent two nozzle assemblies.

[0047] The nozzle assemblies include a first nozzle assembly and a second nozzle assembly. In the rotation direction of the rotor, the first nozzle assembly is located upstream of the second nozzle assembly. Among them:

[0048] The first nozzle assembly includes a throttle pipe 22 connected to one end of the barrel 21 and a spray head 23 connected to the other end of the throttle pipe 22. A throttle orifice 220 and a circular resistance block 221 located downstream of the throttle orifice 220 are provided inside the throttle pipe 22. The throttle orifice 220 and the resistance block 221 are connected to the throttle pipe 22 by nuts. The aperture of the throttle orifice 220 is smaller than the inner diameter of the throttle pipe 22, and the inlet diameter of the spray head 23 is smaller than its outlet diameter. The length of the throttle pipe 22 is 400 - 500mm, and the inner diameter is 20 - 30mm.

[0049] In this embodiment: The spray head 23 includes a quadrangular pyramid-shaped cavity with its bottom communicating with the throttle pipe 22, and an arc-shaped top surface covering the top of the conical cavity. Spray holes are formed on the top surface. The distance between the top surface of the spray head 23 and the lower surface of the cold-end heat exchange element 15 is 10 - 15 mm. The spray holes are evenly and densely distributed on the top surface of the spray head 23, with a diameter of about 1 - 3 mm. The total area of the spray holes is about 40% - 60% of the area of the top surface of the spray head 23. Specifically, a shower-head type spray head can be used. In addition, the width of the arc-shaped top surface of the spray head 23 in the radial direction of the rotor 1 is 1.0 - 1.5 times the jet steam purging radius of the Venturi nozzle 25, and the arc length is 1 - 6 times the jet steam purging radius of the Venturi nozzle 25, and the arc length increases as the nozzle assembly number increases.

[0050] After the high-pressure and high-temperature steam in the gun barrel 21 passes through the throttle orifice 220, the resistance block 221, and the spray head 23, under the isenthalpic principle of adiabatic non-work, it expands and decompresses into low-pressure and relatively high-temperature steam. The steam temperature in the spray head 23 is about 300 °C, and the pressure is slightly higher than the static pressure of the external cold secondary air by 200 - 500 Pa. The steam jet velocity at the outlet of the spray holes on the top surface of the spray head 23 is about 20 - 30 m / s, converging into a vertically upward low-speed and high-temperature steam jet. The jet velocity entering the channel of the cold-end heat exchange element 15 of the rotor 1 is about 15 - 23 m / s, forming a steam heating area in the circumferential direction. The low-speed and high-temperature steam jet velocities of different numbered nozzle assemblies are equal, and the flow rate is set by the diameter of the throttle orifice 220 in the throttle pipe 22. As the nozzle assembly number increases from the first group to the nth group, the diameter of the throttle orifice 220 gradually increases.

[0051] The second nozzle assembly includes a distribution pipe 24 communicating with the gun barrel 21 and at least one Venturi nozzle 25 communicating with the distribution pipe 24. The distribution pipe 24 can adopt a rake blowpipe. One to five Venturi nozzles 25 of the same type are arranged on each distribution pipe 24. As the nozzle assembly number increases from the first group to the nth group, the number of Venturi nozzles 25 on the distribution pipe 24 gradually increases. The throat diameter of the Venturi nozzle 25 is about 6 - 10 mm, the outlet diameter is about 8 - 12 mm, and the divergence angle is 10 - 15°. Under the isentropic principle of adiabatic pressure reduction and expansion to do technical work, the outlet steam jet velocity reaches 1 - 2 times the Mach number, and the temperature rapidly drops to about 100 - 150 °C. Appropriately reducing the expansion distance between the throat and the outlet of the Venturi nozzle 25 makes the outlet steam jet in an incomplete expansion state, with the steam jet temperature greater than 120 °C and the pressure about 0.2 - 0.3 MPa, higher than the surrounding ambient atmospheric pressure. The distance from the outlet of the Venturi nozzle 25 to the lower surface of the cold-end heat exchange element 15 is about 400 - 600 mm. The purging radius of the steam jet of a single Venturi nozzle 25 on the lower surface of the heat exchange element 15 is about 50 - 100 mm. The center distance between two adjacent Venturi nozzles 25 is equal to 0.5 - 1 purging radius of the steam jet. The purging trajectories of the steam jets of the Venturi nozzles 25 in the same group overlap by 0.5 - 1 purging radius, forming a steam purging area along the circumference. After entraining a large amount of surrounding cold secondary air along the way, the central velocity of the steam jet when it reaches the lower surface of the heat exchange element 15 drops to about 100 - 150 m / s, and the temperature of the steam jet gradually decreases, and the jet temperature is maintained close to 100 °C by gradually releasing the latent heat of vaporization of the steam.

[0052] The throttle pipe 22, the distribution pipe 24 and the gun barrel 21 are connected by nuts through a tee pipe 26. The distance between the tee pipe 26 and the gun barrel 21 is 10 - 20 mm. The centerlines of the throttle pipe 22, the distribution pipe 24 and the Venturi nozzle 25 extend along the axial direction of the rotor 1, and the centerline of the gun barrel 21 extends along the radial direction of the rotor 1.

[0053] After the boiler steam is throttled and depressurized, it enters the gun barrel 21 of the steam soot blower 20. After further depressurization and expansion by the high- and low-speed nozzle assembly, two kinds of vertically upward steam jets, namely low-speed high-temperature and high-speed low-temperature, are formed at multiple radial positions of the rotor 1 in the cold secondary air duct. Flowing in the same direction as the cold secondary air, they enter the channels of the cold-end heat exchange element 15 of the upper rotor 1 from bottom to top. During the circumferential rotation of the heat exchange element 15, it first passes through the heating area formed by the low-speed high-temperature steam jet to gasify the ammonium bisulfate in the ash deposited on the surface of the heat exchange element 15, and then passes through the purging area formed by the high-speed low-temperature steam jet to remove the deposited ash. The gasified ammonium bisulfate and the stripped deposited ash enter the boiler furnace with the hot secondary air.

[0054] The barrel 21 is radially from the inside to the outside of the rotor 1. The central angle corresponding to the circumferential arc length of the fan-shaped heating areas of the first to the nth nozzle assemblies is approximately the same. And the residence time of the cold-end heat exchange element 15 of the rotor 1 in each steam heating area is not less than 0.2 s, and the residence time in each steam purging area is not less than 0.2 s. The barrel 21 can be advanced intermittently and retracted directly. The advancement step length is 0.5 to 1 times the steam purging radius of the Venturi nozzle under the lower surface of the heat exchange element. A smaller multiple increases the overlap of the purging trajectories. The residence time of each step makes the air preheater rotor rotate 1 to 2 weeks. According to the degree to which the differential pressure on the flue gas side of the air preheater shown by the unit DCS online analyzer is higher than the design value, the steam soot blower is put into operation once at different time intervals of every 8 hours, 1 day, and 1 week. The greater the degree to which the flue gas differential pressure is higher than the design value, the shorter the soot blowing interval should be.

[0055] The following specifically elaborates on the design of the steam jet parameters of the steam soot blowing device in this embodiment:

[0056] Mark the throttle tube as 1, the Venturi nozzle as 2. Mark the inlet of the throttle tube as (1, 0), the throttle orifice as (1, 1), and the outlet of the throttle tube as (1, 2); mark the inlet of the Venturi nozzle as (2, 0), the throat of the Venturi nozzle as (2, 1), and the outlet of the Venturi nozzle as (2, 2).

[0057] The steam flow rates of the throttle tube and the Venturi nozzle can be calculated using Equations (1) to (3) according to the critical steam state at the throttle orifice and the throat position 1 of the Venturi nozzle. Among them, h0 is obtained by looking up the enthalpy-entropy diagram based on the steam pressure P0 and temperature T0. After obtaining the critical pressure P1 at the throttle orifice and the throat position of the Venturi nozzle using the isentropic principle, look up the enthalpy-entropy diagram to obtain the steam enthalpy h1 and specific volume v1. The designed steam flow rate G1 of a single throttle tube or Venturi nozzle is:

[0058]

[0059]

[0060]

[0061] Where: A1 is the cross-sectional area of the throat of the throttle tube or Venturi nozzle; c1 is the steam velocity at the throat of the throttle tube or Venturi nozzle; v1 is the steam specific volume; h0 is the stagnation steam enthalpy in the barrel; P1 is the critical steam enthalpy at the throat of the throttle tube or Venturi nozzle; P0 is the stagnation steam pressure in the barrel; P1 is the critical steam pressure at the throat of the throttle tube or Venturi nozzle; γ is the adiabatic coefficient of superheated steam.

[0062] The steam pressure at the nozzle outlet is about 200-500Pa higher than the external environment pressure. The steady flow steam before and after the throttling shrinkage hole in the throttling tube belongs to an isenthalpic process of adiabatic expansion without work. After the steam enthalpy is determined by the stagnation steam pressure P0 and temperature T0 in the barrel, the steam temperature and specific volume v after decompression expansion are obtained on the enthalpy-entropy diagram according to the steam pressure at the nozzle outlet. 1,2 , the steam velocity c of the injection hole on the top surface of the nozzle is calculated using formula (4): 1，2 for:

[0063]

[0064] Where: v 1,2 A is the specific volume of steam at the injection hole on the top surface of the nozzle; 1，2 is the surface area of the top of the nozzle; φ is the flow area ratio of the injection hole.

[0065] The steady flow steam before and after the throat of the Venturi nozzle belongs to the isentropic process of adiabatic expansion and technical work. The enthalpy and entropy values are determined by the stagnation steam pressure P0 and temperature T0 in the barrel. Assume that the steam pressure P0 at the outlet of the Venturi nozzle is 2,2 The initial value is the critical pressure P at the throat of the Venturi nozzle 2,1 0.5 times, the steam enthalpy, temperature and specific volume at the outlet of the Venturi nozzle are obtained from the enthalpy-entropy diagram, the outlet steam jet velocity is calculated using formula (5), the outlet steam flow rate is calculated using formula (6), and the flow deviation between the throat and the outlet of the Venturi nozzle is calculated using formula (7). When the deviation is greater than 5%, the outlet steam pressure is adjusted to 1.1 times the previous value, and the outlet steam flow rate is calculated again by checking the enthalpy-entropy diagram; when the deviation is less than -5%, the outlet steam pressure is adjusted to 0.9 times the previous value, and the outlet steam flow rate is calculated again by checking the enthalpy-entropy diagram; until the deviation between the two is no more than ±5%, the steam pressure, temperature and velocity at the nozzle outlet are determined:

[0066]

[0067]

[0068]

[0069] Where: h 2,2 is the steam enthalpy at the outlet of the Venturi nozzle; c 2,2 is the steam velocity at the outlet of the Venturi nozzle; A 2,2 is the outlet area of the Venturi nozzle; v 2,2 G is the specific volume of steam at the outlet of the Venturi nozzle; 2,2 is the steam flow rate at the outlet of the Venturi nozzle; G 2,1 is the steam flow rate at the throat of the Venturi nozzle; ξ is the steam flow deviation.

[0070] The steam at the outlet of the Venturi nozzle is a free jet. After determining the distance between the outlet of the Venturi nozzle and the lower surface of the heat exchange element at the cold end of the rotor, the steam purging radius of a single Venturi nozzle is calculated using Equation (8), the central velocity is calculated using Equation (9), the flow rate of the jet along the way is calculated using Equation (10), and the jet temperature is calculated using Equation (11). When the calculated value of the jet temperature is lower than 100 °C, the steam on the periphery of the jet gradually releases the latent heat of vaporization to make the jet temperature approach but not exceed 100 °C:

[0071]

[0072]

[0073]

[0074]

[0075] Where: R is the steam purging radius of the Venturi nozzle; R2 is the outlet radius of the Venturi nozzle; s is the distance from the outlet of the Venturi nozzle to the lower surface of the heat exchange element at the cold end of the rotor; θ is the diffusion angle of the Venturi nozzle; c is the velocity of the purging central jet; G is the flow rate of the jet in the steam purging section; T a is the central jet temperature in the steam purging section; T e is the ambient temperature; T 2,2 is the steam temperature at the outlet of the Venturi nozzle.

[0076] After obtaining the steam flow rates of the throttle pipes and Venturi nozzles in each group of nozzle assemblies, the steam consumption G of the steam soot blower is calculated using Equation (12): total :

[0077]

[0078] In the formula: G 1，j is the steam flow rate of the throttle pipe of the j-th group of nozzle assemblies; G 2，j，i is the steam flow rate of the i-th Venturi nozzle of the j-th group of nozzle assemblies; n is the total number of nozzle assemblies; m j is the total number of Venturi nozzles of the j-th group of nozzle assemblies; j is the number of the group of nozzle assemblies; i is the number of the Venturi nozzle.

[0079] The resistance on the flue gas side of the air preheater recorded online by the unit's DCS can reflect the degree of blockage of the channels of the heat exchange elements of the air preheater rotor by the ammonium bisulfate-deposited ash. However, due to being affected by factors such as the operating load too much, it is still necessary to evaluate from aspects such as the steam heating and purging effects of the steam soot blower itself.

[0080] (1) The nozzle assembly on the gun barrel forms a steam heating area and a purging area on the lower surface of the heat exchange element at the cold end of the air preheater rotor. The central angles corresponding to the circumferential arc lengths of each area can be calculated by Equation (13) and Equation (14) respectively. The central angles corresponding to the n heating areas should be close, and the central angles corresponding to the n purging areas should be close:

[0081]

[0082]

[0083] (2) The residence times of the heat exchange elements of the air preheater rotor passing through the steam heating areas and purging areas of each nozzle assembly in the circumferential direction can be calculated by Equation (15) and Equation (16) respectively. The residence times of the n heating areas should be close, and the residence times of the n purging areas should be close:

[0084]

[0085]

[0086] (3) According to the steam flow rates of the throttle tube and the Venturi nozzle, the heating steam flow rate and the purging steam flow rate of different groups of nozzle assemblies can be calculated by Equation (17) and Equation (18) respectively:

[0087] M 1,j =G 1，1,j (17)

[0088]

[0089] (4) After obtaining the heating steam flow rate and the purging steam flow rate of each group of nozzle assemblies, according to the heating and purging areas on the circumference of the radial position of the air preheater rotor where each group of nozzle assemblies is located, the steam reception amount per unit area of the heat exchange element on the circumference is calculated by Equation (19) and Equation (20):

[0090]

[0091]

[0092] (5) Using the relative deviation method, the relative deviation of the heating steam reception amount per unit area of the heat exchange element of the n groups of nozzle assemblies is calculated by Equation (21), and the relative deviation of the purging steam reception amount per unit area of the heat exchange element of the n groups of nozzle assemblies is calculated by Equation (22). Conventionally, it is required that the relative deviation of the heating steam amount is less than ±10%, and the relative deviation of the purging steam amount is less than ±20%:

[0093]

[0094]

[0095] In the formula: ɡ 1，j is the central angle corresponding to the j-th group of heating zones; A rc，j is the arc length of the j-th group of heating zones; R r，j is the radius of the air preheater rotor corresponding to the j-th group of nozzle assemblies; ɡ 2，j is the central angle corresponding to the j-th group of purging zones; R i is the steam purging radius of the Venturi nozzle; Δτ 1，j is the time for the heat exchange elements at the cold end of the rotor to pass through the j-th group of heating zones; Δτ 2，j is the time for the heat exchange elements at the cold end of the rotor to pass through the j-th group of purging zones; c rpm is the rotational speed of the air preheater rotor; M 1，j is the heating steam flow rate of the j-th group of nozzle assemblies; G 1，1，j is the steam flow rate at the throttling orifice of the j-th group of nozzle assemblies; M 2，j is the purging steam flow rate of the j-th group of nozzle assemblies; G 2，1，j,i is the steam flow rate at the throat of the i-th Venturi nozzle of the j-th group of nozzle assemblies; SFUA 1，j is the amount of heating steam received by the heat exchange elements per unit area at the cold end of the rotor at the j-th group of nozzle assemblies; SFUA 21，j is the amount of purging steam received by the heat exchange elements per unit area at the cold end of the rotor at the j-th group of nozzle assemblies; RD 1，j is the relative deviation of the heating steam amount of the j-th group of nozzle assemblies; RD 2，j is the relative deviation of the purging steam amount of the j-th group of nozzle assemblies.

[0096] Taking the air preheater of a 1000MW unit as an example for further illustration.

[0097] 1), A 1000MW unit is equipped with 2 34-VI(T)-2000-SMR type rotor rotary 3-compartment air preheaters. The diameter of the air preheater rotor is 16400mm, and the diameter of the central sleeve is 1560mm; the air preheater rotor is divided into upper and lower 2 layers of the rotor hot end and the rotor cold end: the material of the upper layer of heat exchange elements is low-carbon steel, with a height of 1100mm and a thickness of 0.5mm; the lower layer of heat exchange elements is enameled Corten steel, with a height of 1000mm and a thickness of 1.2mm, and the flow porosity is about 78%.

[0098] 2), The central angle of the flue gas compartment is 165°, the secondary air compartment is 100°, the primary air compartment is 50°, and the total of 3 sector seals is 45°; the air preheater rotor rotates along the flue gas compartment - secondary air compartment - primary air compartment, with a rotational speed of 1.2r / min. The temperature of the cold secondary air in the cold secondary air inlet duct at the bottom of the secondary air compartment under the full load of the unit is 23°C, and the static pressure is 0.103140MPa.

[0099] 3) Under the rated load of the unit, the circumferential temperature distributions of the top surface of the rotor hot-end heat exchange element, the top and bottom surfaces of the rotor cold-end heat exchange element are calculated, as shown in Figure 4 the figure. In the flue gas bunker, the inlet flue gas temperature is 364.8 °C, and the outlet flue gas temperature is 1231. °C. The ammonium bisulfate in the flue gas condenses and deposits on the surface of the rotor cold-end heat exchange element in the temperature range of about 150 - 190 °C. When the heat exchange element of the air preheater rotor leaves the flue gas bunker and enters the secondary air bunker, the temperature of the heat exchange element reaches the highest, and an ammonium bisulfate deposition area is formed in the area about 400 - 600 mm upward from the lower surface of the heat exchange element.

[0100] 4) In the cold secondary air duct at the bottom inlet of the secondary air bunker, near the seal between the flue gas bunker and the secondary air bunker, a steam soot blower of this embodiment is arranged. The length of the gun barrel is consistent with the radial length of the air preheater rotor, which is 7420 mm. The length of the gun barrel is 7420 mm. A total of 5 groups of nozzle assemblies are set from the gun head near the central sleeve to the outside of the air preheater rotor, and the distance between adjacent nozzle assemblies is 1484 mm.

[0101] 5) The diameter of the gun barrel is 50 mm. The relevant design parameters of the 5 groups of nozzle assemblies are shown in Table 1: The first group is located at a radius of 2264 mm in the rotor radial direction, with 1 Venturi nozzle and 1 throttle orifice with a diameter of 5.4 mm; the second group is located at a radius of 3748 mm, with 2 Venturi nozzles and 1 throttle orifice with a diameter of 7.0 mm; the third group is located at a radius of 5232 mm, with 2 Venturi nozzles and 1 throttle orifice with a diameter of 8.2 mm; the fourth group is located at a radius of 6716 mm, with 3 Venturi nozzles and 1 throttle orifice with a diameter of 9.2 mm; the fifth group is located at a radius of 8200 mm, with 4 Venturi nozzles and 1 throttle orifice with a diameter of 10.3 mm. The distance from the outlet of the Venturi nozzle to the lower surface of the rotor cold-end heat exchange element is 500 mm.

[0102] Table 1 Design parameters of nozzle assemblies:

[0103]

[0104] 6) The steam pressure in the gun barrel is 0.78 MPa, and the temperature is 310 °C. After being decompressed and expanded through the throttle orifice or the throat of the Venturi nozzle, the steam pressure at the outlet of the throttle pipe is 0.103 MPa, and the temperature is 302 °C. The steam pressure at the outlet of the Venturi nozzle is 0.2 MPa, and the temperature is 150.5 °C. The detailed data are shown in Table 2.

[0105] Table 2 Changes in steam parameters of the soot blower:

[0106]

[0107] 7) The steam jet velocity at the Venturi nozzle outlet is 547 m / s. The central velocity reaching the lower surface of the heat exchange element at the cold end of the rotor is reduced to 156 m / s, and the jet velocity at 1 / 4 radius is 65 m / s. The purging radius is 58 mm. The steam jet velocity at the throttle pipe outlet is 25 m / s, and the velocity entering the heat exchange element channel of the cold end rotor is reduced to 19.2 m / s. The purging steam flow rate of the steam soot blower is 46.7 kg / min, and the heating steam flow rate is 16.0 kg / min. The total is 62.7 kg / min. Radially on the air preheater rotor, the relative deviation of the steam flow rate received by the heat exchange elements per unit area in 5 heating areas is -1.7% to 2.0%, and the relative deviation of the steam flow rate received by the heat exchange elements per unit area in the purging area is -16.6% to 16.4%. The detailed data are shown in Table 3.

[0108] Table 3 Steam jet parameters of the soot blower:

[0109]

[0110]

[0111] 8) Consistent with the steam purging radius length of the Venturi nozzle, the advancing step of the gun barrel is 58 mm, the advancing speed is 0.806 mm / s, the advancing stroke is 1484 mm, and the time for one purging is 1842 s.

[0112] The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly. It should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A steam soot blower for a rotary air preheater, comprising a steam soot blower and a gun barrel communicated with the steam soot blower, characterized in that: The described steam soot blower further includes a nozzle assembly communicated with the barrel, and the nozzle assembly includes a first nozzle assembly and a second nozzle assembly. The first nozzle assembly includes a throttle pipe with one end communicated with the barrel, and a spray head communicated with the other end of the throttle pipe. A throttle orifice is arranged inside the throttle pipe, and the aperture of the throttle orifice is smaller than the diameter of the throttle pipe. The inlet aperture of the spray head is smaller than its outlet aperture. The second nozzle assembly includes a distribution pipe communicated with the barrel, and at least one nozzle communicated with the distribution pipe. The nozzle is a Venturi nozzle, and the steam jet velocity at the outlet of the spray head is smaller than the steam jet velocity at the outlet of the nozzle. The steam jet parameters of the described steam soot blower are designed according to the following formula: The steam flow rates of the throttle pipe and the Venturi nozzle are calculated by using formulas (1) to (3) according to the critical steam state at the throttle orifice and the throat position of the Venturi nozzle. Wherein: h0 is obtained by looking up the enthalpy-entropy diagram according to the steam pressure P0 and temperature T0. After obtaining the critical pressure P1 at the throttle orifice and the throat position of the Venturi nozzle by using the isentropic principle, the steam enthalpy h1 and specific volume v1 are obtained by looking up the enthalpy-entropy diagram. The steam flow rate G1 of a single throttle pipe or Venturi nozzle is designed as: Wherein: A1 is the cross-sectional area of the throat of the throttle pipe or Venturi nozzle; c1 is the steam velocity at the throat of the throttle pipe or Venturi nozzle; v1 is the steam specific volume; h0 is the stagnation steam enthalpy in the barrel; P1 is the critical steam enthalpy at the throat of the throttle pipe or Venturi nozzle; P0 is the stagnation steam pressure in the barrel; P1 is the critical steam pressure at the throat of the throttle pipe or Venturi nozzle; γ is the adiabatic coefficient of superheated steam. The steam pressure at the nozzle outlet is higher than the external ambient pressure. The steady-flow steam before and after the throttling orifice in the throttle pipe undergoes an isenthalpic process of adiabatic expansion without doing work. After determining the steam enthalpy from the stagnation steam pressure P0 and temperature T0 in the barrel, according to the steam pressure at the nozzle outlet, the steam temperature and specific volume v after pressure reduction and expansion are obtained by looking up in the enthalpy-entropy diagram. 1,2 , and the steam velocity c of the injection holes on the top surface of the nozzle is calculated using Equation (4). 1，2 It is: Where: v 1,2 is the specific volume of steam at the injection holes on the top surface of the nozzle; A 1，2 is the surface area of the top of the nozzle; φ is the proportion of the flow area of the injection holes The steady-flow steam before and after the throat of the Venturi nozzle belongs to an isentropic process of adiabatic expansion to do technical work. The enthalpy value and entropy value are determined by the stagnation steam pressure P0 and temperature T0 in the barrel. Let the steam pressure P at the outlet of the Venturi nozzle 2,2 The initial value is 0.5 times the critical pressure P 2,1 at the throat of the Venturi nozzle. The steam enthalpy, temperature and specific volume at the outlet of the Venturi nozzle are obtained from the enthalpy-entropy diagram. The outlet steam jet velocity is calculated by Equation (5), the outlet steam flow rate is calculated by Equation (6), and the flow rate deviation between the throat and the outlet of the Venturi nozzle is calculated by Equation (7). When the deviation is greater than 5%, the outlet steam pressure is adjusted to 1.1 times the previous value, and the enthalpy-entropy diagram is rechecked to calculate the outlet steam flow rate; when the deviation is less than -5%, the outlet steam pressure is adjusted to 0.9 times the previous value, and the enthalpy-entropy diagram is rechecked to calculate the outlet steam flow rate; until the deviation between the two is not greater than ±5%, the steam pressure, temperature and velocity at the nozzle outlet are determined: where: h 2,2 is the enthalpy of the steam at the venturi nozzle outlet; c 2,2 is the velocity of the steam at the venturi nozzle outlet; A 2,2 is the outlet area of the venturi nozzle; v 2,2 is the specific volume of the steam at the venturi nozzle outlet; G 2,2 is the steam flow rate at the venturi nozzle outlet; G 2,1 is the steam flow rate at the throat of the venturi nozzle; ξ is the steam flow rate deviation, The steam at the outlet of the Venturi nozzle is a free jet. After determining the distance between the outlet of the Venturi nozzle and the lower surface of the heat exchange element at the cold end of the rotor, the steam purging radius of a single Venturi nozzle is calculated by formula (8), the center velocity is calculated by formula (9), the flow rate of the jet along the way is calculated by formula (10), and the jet temperature is calculated by formula (11). When the calculated value of the jet temperature is lower than 100 °C, the steam on the periphery of the jet gradually releases the latent heat of vaporization to make the jet temperature close to but not higher than 100 °C. Where: R is the steam purging radius of the Venturi nozzle; R2 is the outlet radius of the Venturi nozzle; s is the distance from the outlet of the Venturi nozzle to the lower surface of the heat exchange element at the cold end of the rotor; θ is the diffusion angle of the Venturi nozzle; c is the velocity of the central jet of the purge; G is the jet flow rate of the steam purging cross-section; T a is the central jet temperature of the steam purging cross-section; T e is the ambient temperature; T 2,2 is the steam temperature at the outlet of the Venturi nozzle, After obtaining the steam flow rates of the throttle pipes and Venturi nozzles in each group of nozzle assemblies, calculate the steam consumption G of the steam soot blower using Equation (12). total : Where: G 1，j is the steam flow rate of the throttling pipeline of the j-th nozzle assembly; G 2，j，i is the steam flow rate of the i-th Venturi nozzle of the j-th nozzle assembly; n is the total number of nozzle assemblies; m j is the total number of Venturi nozzles of the j-th nozzle assembly; j is the number of the nozzle assembly; i is the number of the Venturi nozzle.

2. The steam soot blowing device for a rotary air preheater according to claim 1, characterized in that: When a plurality of the nozzles are communicated with the distribution pipe, the center distance between two adjacent nozzles is equal to 0.5-1 times the purging radius of one nozzle, and the purging trajectories of the plurality of nozzles overlap by 0.5-1 times the purging radius of one nozzle.

3. The steam soot blowing device for a rotary air preheater according to claim 1, characterized in that: A resistance block is further arranged inside the throttle pipe, and the resistance block is located downstream of the throttle orifice.

4. The steam soot blower for a rotary air preheater according to claim 1, characterized in that: The spray head includes a conical cavity with the bottom communicated with the throttle pipe, and a top surface covering the top of the conical cavity. Spray holes are arranged on the top surface.

5. The steam soot blowing device for a rotary air preheater according to claim 1, characterized in that: The first nozzle assembly and the second nozzle assembly are communicated with the barrel through a tee pipe.

6. The steam soot blowing device for a rotary air preheater according to claim 1, characterized in that: A plurality of groups of the nozzle assemblies are arranged, and the plurality of groups of nozzle assemblies are distributed along the length direction of the barrel.

7. The steam soot blower for a rotary air preheater according to claim 6, characterized in that: The distance between two adjacent groups of nozzle assemblies is equal.

8. The steam soot blower for a rotary air preheater according to claim 1, characterized in that: The aperture diameter of the throttling orifice near the steam soot blower is larger than that of the throttling orifice far from the steam soot blower; the number of nozzles on the distribution pipe near the steam soot blower is not less than that on the distribution pipe far from the steam soot blower.

9. The steam soot blowing device for a rotary air preheater according to claim 1, characterized in that: The centerlines of the throttling pipe, the distribution pipe, and the nozzles are all perpendicular to the centerline of the gun barrel.

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