Flue gas dehydration system

Abstract

The present invention relates to the technical field of heating furnaces, and discloses a flue gas dehydration system for a heating furnace, the system comprising a heating furnace, a high-temperature air preheater, a first low-temperature air preheater, a second low-temperature air preheater and an induced draft fan connected in sequence, and a blower connected to the first low-temperature air preheater and the second low-temperature air preheater respectively; wherein the high-temperature flue gas outlet of the first low-temperature air preheater is connected to the low-temperature flue gas inlet of the second low-temperature air preheater; the low-temperature flue gas outlet of the first low-temperature air preheater is connected to the high-temperature flue gas inlet of the second low-temperature air preheater. The flue gas dehydration system provided by the present invention can basically remove all the water in the flue gas of the heating furnace, can reduce the corrosion of the induced draft fan and the chimney, reduce the load of the induced draft fan, and improve the thermal efficiency of the heating furnace.

Description

Technical Field

[0001] The invention relates to the technical field of heating furnaces, and in particular to a flue gas dehydration system for a heating furnace. Background Art

[0002] In traditional petrochemical plants, heating furnaces are widely used equipment. The flue gas discharged from the heating furnace is generally transported to the chimney by the induced draft fan after completing heat exchange with the air in the air preheater, and finally discharged into the atmosphere. Since the fuel of the heating furnace contains sulfides, the flue gas discharged from the heating furnace contains a large amount of water vapor and a small amount of acidic gas. The acid mist formed by these acidic gases combined with water is brought into the induced draft fan by the flue gas, which is very easy to corrode the induced draft fan and also causes corrosion to the chimney. If it is directly discharged into the atmosphere, it is easy to form acid rain to pollute the environment. In addition, since the amount of flue gas discharged by the heating furnace is relatively large and the load of the induced draft fan is limited, the standby induced draft fan is often turned on in industrial production, resulting in poor fault tolerance of the heating furnace system.

[0003] Dehydrating the flue gas discharged from the air preheater can, on the one hand, reduce the emission of flue gas, thereby reducing the load of the induced draft fan; on the other hand, the acid gas can be removed during the dehydration process, which can effectively reduce the acid mist and smoke content in the flue gas, reduce the corrosion of the induced draft fan and chimney, and prevent the acid mist from being discharged into the atmosphere and polluting the environment.

[0004] However, in actual production, the temperature of the flue gas discharged by the air preheater is generally high, about 120-150℃, and the flue between the air preheater and the induced draft fan is relatively short. In this case, the dehydration operation of the flue gas mainly faces the following problems: 1) Lowering the exhaust temperature to condense water is convenient for removing moisture from the flue gas, but this will aggravate the dew point corrosion of the air preheater; 2) Since the flue gas contains a large amount of water vapor, a large amount of condensed water will be obtained by dehydrating the flue gas. If this part of water cannot be discharged in time, the accumulated water will easily damage the induced draft fan and cause equipment failure. In current industrial production, the amount of water condensed during the flue gas discharge process is generally small, and most of the water in the flue gas is discharged into the atmosphere with the flue gas, and the existing condensed water discharge port is difficult to meet the demand for large-scale flue gas dehydration; 3) The water condensed from the flue gas has a high temperature, strong acidity, and is dangerous. Direct discharge will not only cause heat waste, but also fail to meet environmental protection requirements.

[0005] CN1793766A discloses a tubular heating furnace, including a heating furnace body and a waste heat recovery system, wherein the waste heat recovery system includes an air preheater, wherein the air preheater is composed of two sections, a non-condensing air preheater and a condensing air preheater, and the waste heat recovery system is further provided with a condensate collection pool, an induced draft fan and a blower, wherein the condensate collection pool is directly arranged below the condensing air preheater, the condensate collection pool is connected to the induced draft fan, and the blower is connected to the condensing air preheater. Although this tubular heating furnace can recover part of the vaporization latent heat of acidic water vapor and further improve the thermal efficiency of the heating furnace, its exhaust gas temperature is about 100°C, and the acidic water vapor in the flue gas cannot be completely condensed, and the flue gas dehydration effect still needs to be further improved. Moreover, the condensing air preheater has the problem of uneven heat exchange, which is prone to local dew point corrosion, and because of the uneven heat exchange, the exhaust gas temperature is high, the thermal efficiency of the heating furnace is reduced, and most of the water in the flue gas is discharged into the atmosphere with the flue gas, and the amount of water removed by condensation is very small.

[0006] Therefore, there is an urgent need to provide a flue gas dehydration system with good dehydration effect, small induced draft fan load, good environmental performance and easy operation. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems in the prior art of severe corrosion and heavy load of the induced draft fan, acidic flue gas corroding the chimney, being discharged into the atmosphere to pollute the environment, and very little water removed from the flue gas. A flue gas dehydration system is provided, which can basically remove all the water in the flue gas of the heating furnace, and utilize the removed water to heat the air, so as to increase the thermal efficiency of the heating furnace by about 1.2%.

[0008] In order to achieve the above object, the present invention provides a flue gas dehydration system, the system comprising a heating furnace, a high-temperature air preheater, a first low-temperature air preheater, a second low-temperature air preheater and an induced draft fan connected in sequence, and a blower connected to the first low-temperature air preheater and the second low-temperature air preheater respectively;

[0009] The first low-temperature air preheater is provided with a first low-temperature air preheater high-temperature flue gas outlet and a first low-temperature air preheater low-temperature flue gas outlet; the second low-temperature air preheater is provided with a second low-temperature air preheater high-temperature flue gas inlet and a second low-temperature air preheater low-temperature flue gas inlet;

[0010] Wherein, the high-temperature flue gas outlet of the first low-temperature air preheater is connected to the low-temperature flue gas inlet of the second low-temperature air preheater; the low-temperature flue gas outlet of the first low-temperature air preheater is connected to the high-temperature flue gas inlet of the second low-temperature air preheater;

[0011] A flue is provided between the second low-temperature air preheater and the induced draft fan, and a deliquated water bag is provided on the flue; wherein the flue is divided into a first flue between the second low-temperature air preheater and the deliquated water bag and a second flue between the deliquated water bag and the induced draft fan;

[0012] Wherein, at least one transverse baffle is arranged in the first flue, and at least one oblique baffle is arranged below the transverse baffle; and at least one defoaming net is arranged in the second flue.

[0013] Through the above technical solution, the present invention has the following beneficial technical effects:

[0014] 1) The flue gas dehydration system provided in the present invention makes the temperature of the flue gas discharged from the second low-temperature air preheater more uniform through the cross connection between the first low-temperature air preheater and the second low-temperature air preheater; by arranging a dehydration water bag, a flue with sieve holes, a transverse baffle, an inclined baffle and a defoaming net, it is basically possible to safely, conveniently and quickly remove all moisture and smoke entrained in the flue gas, thereby improving the thermal efficiency of the heating furnace by about 0.4%;

[0015] 2) The flue gas dehydration system provided in the present invention realizes the pressure balance between the neutralization tank and the dehydration water bag by setting a pressure balance pipeline, thereby avoiding the increase of dehydration resistance and dehydration difficulties caused by negative pressure;

[0016] 3) The flue gas dehydration system provided by the present invention can effectively observe the conditions in the dehydration water bag and the neutralization tank by setting up a liquid level gauge on one side of the dehydration water bag and the neutralization tank. At the same time, a filter is set at the bottom of the dehydration water bag to filter out impurities such as smoke and dust to prevent them from blocking the drainage pipeline;

[0017] 4) The flue gas dehydration system provided in the present invention injects alkali solution into the neutralization tank through the alkali solution storage tank and the alkali solution injection pump to neutralize the acidity of water, thereby realizing safe, convenient and environmentally friendly treatment of the removed condensed water;

[0018] 5) The flue gas dehydration system provided in the present invention utilizes the removed condensed water to heat the air, which can increase the thermal efficiency of the heating furnace by about 0.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of a flue gas dehydration system;

[0020] Figure 2 It is a schematic diagram of the structure of a flue with sieve holes;

[0021] Figure 3 is a schematic diagram of the structure of the transverse baffle;

[0022] Figure 4 This is a schematic diagram of the heating furnace system in Comparative Example 1.

[0023] Description of Reference Numerals

[0024] 1. Heating furnace 2. High temperature air preheater 31. First low temperature air preheater

[0025] 32. Second low-temperature air preheater 4. Induced draft fan 5. Blower

[0026] 51. Blower inlet air duct 52. Blower outlet air duct 6. Deliquification water bag

[0027] 61. Liquid level gauge for deliquescence water bag 62. Drain gate valve 63. Filter

[0028] 64, stop valve 71, transverse baffle 72, oblique baffle

[0029] 73. Defoaming net 81. Mixing flue 82. Dehydration flue

[0030] 83. Flue with sieve holes 84. Inclined flue 9. Chimney

[0031] 10. Neutralization tank 101, pressure balance pipeline 102, balance gate valve

[0032] 103. Glass plate level gauge 104. Remote level gauge 105. pH online monitor

[0033] 106, sampling pipeline 107, sampling gate valve 11, alkali solution storage tank

[0034] 111. Alkali injection funnel 112. Alkali injection gate valve 113. Water injection pipeline

[0035] 114. Water injection gate valve 115. Alkali solution storage tank level gauge 12. Alkali solution injection pump

[0036] 121. Alkali solution regulating valve 122. Alkali solution flow meter 123. Alkali solution return pipeline

[0037] 124, alkali solution return valve 13, heat exchanger 14, wastewater delivery pump

[0038] 141. Wastewater return pipeline 142. Wastewater return gate valve 143. Wastewater outlet regulating valve

[0039] 144. Wastewater flow meter 15. Air suction port 16. Wastewater treatment pipeline

[0040] 3. Low temperature air preheater DETAILED DESCRIPTION

[0041] The present invention provides a flue gas dehydration system, the system comprising a heating furnace 1, a high-temperature air preheater 2, a first low-temperature air preheater 31, a second low-temperature air preheater 32 and an induced draft fan 4 connected in sequence, and a blower 5 connected to the first low-temperature air preheater 31 and the second low-temperature air preheater 32 respectively;

[0042] The first low-temperature air preheater 31 is provided with a first low-temperature air preheater high-temperature flue gas outlet and a first low-temperature air preheater low-temperature flue gas outlet; the second low-temperature air preheater 32 is provided with a second low-temperature air preheater high-temperature flue gas inlet and a second low-temperature air preheater low-temperature flue gas inlet;

[0043] Wherein, the high-temperature flue gas outlet of the first low-temperature air preheater is connected to the low-temperature flue gas inlet of the second low-temperature air preheater, and the low-temperature flue gas outlet of the first low-temperature air preheater is connected to the high-temperature flue gas inlet of the second low-temperature air preheater;

[0044] A flue is provided between the second low-temperature air preheater 32 and the induced draft fan 4, and a deliquated water bag 6 is provided on the flue; wherein the flue is divided into a first flue between the second low-temperature air preheater 32 and the deliquated water bag 6 and a second flue between the deliquated water bag 6 and the induced draft fan 4;

[0045] In the first flue, at least one transverse baffle 71 is provided, and at least one oblique baffle 72 is provided below the transverse baffle 71; in the second flue, at least one defoaming net 73 is provided. The specific structure of the system is as follows: Figure 1 shown.

[0046] At present, in industrial production, multi-stage air preheaters are generally used to indirectly exchange heat between air and flue gas to reduce the exhaust temperature. At the same time, corrosion-resistant materials are used to prepare air preheaters to solve the dew point corrosion problem. At present, the most commonly used corrosion-resistant air preheater is the cast iron plate air preheater. Due to the large heat exchange area of ​​the cast iron plate air preheater, the flue gas temperature discharged from the two flue gas outlets of the cast iron plate air preheater is uneven, one temperature is low, about 80°C, and the other temperature is high, about 105°C. The flue gas with low exhaust temperature causes serious dew point corrosion problems on the heat exchange surface near the flue gas outlet of the air preheater; the moisture entrained in the flue gas with high exhaust temperature exists in the form of gas. Since the flue between the air preheater and the induced draft fan is relatively short, it is difficult to condense and remove the moisture before the flue gas enters the induced draft fan, making the induced draft fan and the chimney susceptible to corrosion. In addition, the uneven mixing of flue gas with temperature difference will affect the accuracy of exhaust temperature measurement and increase the difficulty of system regulation.

[0047] The inventor of the present invention has found through research that, while the heat exchange area of ​​the cast iron plate air preheater remains unchanged, the cast iron plate air preheater can be divided into two and set up as two units. By cross-connecting the two low-temperature air preheaters, the temperature difference of the flue gas discharged from the two flue gas outlets of the cast iron plate air preheater can be reduced, so that the temperature of the flue gas with a low exhaust temperature can be increased, and the temperature of the flue gas with a high exhaust temperature can be reduced, thereby solving the dew point corrosion problem of the cast iron plate air preheater caused by the low local flue gas exhaust temperature and the dehydration difficulty caused by the high local flue gas exhaust temperature.

[0048] In the present invention, the temperature of the flue gas discharged from the low-temperature flue gas outlet of the first low-temperature air preheater is 120-130°C, preferably 123-127°C, and the temperature of the flue gas discharged from the high-temperature flue gas outlet of the first low-temperature air preheater is 127-147°C, preferably 133-141°C; the temperature of the flue gas discharged from the low-temperature flue gas outlet of the second low-temperature air preheater is 86-94°C, preferably 88-92°C, and the temperature of the flue gas discharged from the high-temperature flue gas outlet of the second low-temperature air preheater is 88-96°C, preferably 90-94°C.

[0049] When only one cast iron plate air preheater is used for heat exchange while the heat exchange area remains unchanged, the flue gas temperatures discharged from the two flue gas outlets of the cast iron plate air preheater are about 80°C and 105°C respectively. After two cast iron plate air preheaters are set, the flue gas temperatures discharged from the two flue gas outlets of the second low-temperature air preheater 32 are about 86-94°C and 88-96°C respectively. Since the temperatures of the flue gas discharged from the two flue gas outlets of the second low-temperature air preheater 32 are both above the dew point corrosion temperature (84°C), the dew point corrosion problem of the cast iron plate air preheater caused by the low local exhaust temperature is solved. Because the temperature of the flue gas discharged from the two flue gas outlets of the second low-temperature air preheater 32 is below 99°C (at this temperature, water is mainly in liquid form, which is conducive to separation from the flue gas), by setting a transverse baffle 71, an oblique baffle 72 and a defoaming net 73 in the pipeline between the second low-temperature air preheater 32 and the induced draft fan 4, moisture can be quickly removed from the flue gas, thereby reducing the emission of flue gas and reducing the load of the induced draft fan 4. The deliquescence water bag 6 set in the flue can collect condensed water and discharge the condensed water from the system in time to reduce the burden on the flue.

[0050] Preferably, the high-temperature air preheater 2 is provided with a high-temperature air preheater air inlet and a high-temperature air preheater air outlet, the first low-temperature air preheater 31 is provided with a first low-temperature air preheater air inlet and a first low-temperature air preheater air outlet, and the second low-temperature air preheater 32 is provided with a second low-temperature air preheater air inlet and a second low-temperature air preheater air outlet; wherein, the first low-temperature air preheater air inlet and the second low-temperature air preheater air inlet are respectively connected to the blower outlet air duct 52, the first low-temperature air preheater air outlet and the second low-temperature air preheater air outlet are respectively connected to the high-temperature air preheater air inlet, and the high-temperature air preheater air outlet is connected to the heating furnace air inlet.

[0051] Preferably, the high-temperature air preheater 2 is also provided with a high-temperature air preheater flue gas inlet and a high-temperature air preheater flue gas outlet, and the first low-temperature air preheater 31 is also provided with a first low-temperature air preheater high-temperature flue gas inlet connected to the first low-temperature air preheater high-temperature flue gas outlet, and a first low-temperature air preheater low-temperature flue gas inlet connected to the first low-temperature air preheater low-temperature flue gas outlet; the second low-temperature air preheater 32 is also provided with a second low-temperature air preheater high-temperature flue gas outlet connected to the second low-temperature air preheater high-temperature flue gas inlet, and a second low-temperature air preheater low-temperature flue gas outlet connected to the second low-temperature air preheater low-temperature flue gas inlet; wherein, the high-temperature air preheater flue gas inlet is connected to the heating furnace flue gas outlet, and the high-temperature air preheater flue gas outlet is respectively connected to the first low-temperature air preheater high-temperature flue gas inlet and the first low-temperature air preheater low-temperature flue gas inlet, and the second low-temperature air preheater high-temperature flue gas outlet and the second low-temperature air preheater low-temperature flue gas outlet are connected to the induced draft fan 4.

[0052] In the present invention, taking the first low-temperature air preheater 31 as an example, the high / low temperature inlets / outlets are explained: the flue gas inlet / outlet arranged on the side close to the air inlet of the first low-temperature air preheater is the low-temperature flue gas inlet / outlet of the first low-temperature air preheater, and conversely, the flue gas inlet / outlet arranged on the side close to the air outlet of the first low-temperature air preheater is the high-temperature flue gas inlet / outlet of the first low-temperature air preheater. The amount of flue gas discharged from the high-temperature air preheater flue gas outlet entering the high-temperature flue gas inlet of the first low-temperature air preheater and the amount entering the low-temperature flue gas inlet of the first low-temperature air preheater are preferably equal. The amount of air discharged from the blower 5 entering the air inlet of the first low-temperature air preheater and the amount entering the air inlet of the second low-temperature air preheater are preferably equal.

[0053] Preferably, the first flue includes a mixing flue 81 and a dehydration flue 82, wherein the diameter of the mixing flue 81 is larger than that of the dehydration flue 82; wherein the present invention does not specifically limit the shape of the first flue, and the flue is preferably rectangular or square. The mixing flue 81 is arranged at the bottom of the second low-temperature air preheater 32, wrapping the high-temperature flue gas outlet of the second low-temperature air preheater and the low-temperature flue gas outlet of the second low-temperature air preheater, and is used to mix the flue gas discharged from the high-temperature flue gas outlet of the second low-temperature air preheater and the low-temperature flue gas outlet of the second low-temperature air preheater; the dehydration flue 82 is arranged between the mixing flue 81 and the deliquescence water bag 6, and plays a dehydration role by arranging a transverse baffle 71 and an oblique baffle 72 in the dehydration flue 82. In the present invention, the connection between the dehydration flue 82 and the mixing flue 81 is called the entrance of the dehydration flue 82.

[0054] Preferably, in order to improve the mixing effect of the flue gas, a flue 83 with a sieve hole is provided in the mixing flue 81, such as Figure 2 As shown. One end of the flue 83 with mesh holes is connected to the bottom of the second low-temperature air preheater 32 and is located between the high-temperature flue gas outlet of the second low-temperature air preheater and the low-temperature flue gas outlet of the second low-temperature air preheater, and the other end is connected to the entrance of the dehydration flue 82. The flue 83 with mesh holes can change the flow direction of the flue gas, so that the temperature of the flue gas discharged from the two exhaust ports is more uniform.

[0055] Preferably, the flue 83 with sieve holes is a circular flue, the opening direction of the sieve holes is perpendicular to the outer surface of the flue 83 with sieve holes, and the shape is preferably circular.

[0056] Preferably, the mesh holes are evenly arranged along the circumferential direction of the flue 83 with mesh holes, and the aperture of the mesh holes gradually decreases from top to bottom along the axial direction of the flue 83 with mesh holes, the largest mesh hole aperture at the top is about 15-30 mm, and the smallest mesh hole aperture at the bottom is about 10-18 mm. The upper part refers to the end connected to the bottom of the second low-temperature air preheater 32.

[0057] In the present invention, the temperature of the flue gas obtained after the flue gas discharged from the high-temperature flue gas outlet of the second low-temperature air preheater and the low-temperature flue gas outlet of the second low-temperature air preheater is mixed through the flue 83 with mesh holes is 87-95°C, preferably 90-92°C. Since the temperature of the flue gas discharged from the second low-temperature air preheater 32 is lower than 99°C, the water in the flue gas exists in liquid form. In the flue connecting the second low-temperature air preheater 32 and the induced draft fan 4, a transverse baffle 71, an oblique baffle 72 and a defoaming net 73 are arranged, which can basically remove all the water droplets entrained in the flue gas.

[0058] Preferably, the transverse baffles 71 are provided in two pieces, and the two transverse baffles 71 are staggered and spaced apart in the extension direction of the first flue. Specifically, the two transverse baffles 71 are respectively provided on the left and right sides of the dehydration flue 82, and spaced apart in the extension direction of the dehydration flue 82, such as Figure 1 The transverse baffle 71 is perpendicular to the extension direction of the dehydration flue 82, and is used to change the flow direction of the flue gas and increase the flow speed of the flue gas.

[0059] Preferably, the transverse baffle 71 is connected to the first flue by welding. In order to prevent the acidic condensate accumulated on the transverse baffle 71 from corroding the weld, reducing the connection strength between the transverse baffle 71 and the flue, and thus damaging the transverse baffle 71, preferably, tear holes are provided on the transverse baffle 71, wherein the tear holes are provided on the side where the transverse baffle 71 is connected to the flue, preferably 4-6 circular holes with a hole diameter of 10-20 mm are provided, such as Figure 3 In order to reduce the friction between the smoke and the transverse baffle 71 , preferably, a layer of polytetrafluoroethylene coating is provided on the transverse baffle 71 .

[0060] Preferably, in the direction perpendicular to the extension of the first flue, the ratio of the area of ​​the transverse baffle 71 to the cross-sectional area of ​​the first flue is 1:3-4, preferably 1:4. The larger the ratio of the area of ​​the transverse baffle 71 to the cross-sectional area of ​​the first flue, the greater the change in the flow rate of the flue gas. In order to reduce the impact force of the flue gas on the transverse baffle 71 and extend the service life of the transverse baffle 71, it is preferred to limit the ratio of the area of ​​the transverse baffle 71 to the cross-sectional area of ​​the first flue to between 1:3-4.

[0061] In the present invention, multiple transverse baffles 71 are provided, preferably two transverse baffles 71 are provided, and further preferably, the area of ​​the second transverse baffle 71 is larger than the area of ​​the first transverse baffle 71. The second transverse baffle 71 refers to the transverse baffle 71 closest to the deliquidation water bag 6. Such a setting can gradually increase the flow rate of the flue gas. The greater the flow rate, the better the dehydration effect when colliding with the oblique baffle 72.

[0062] Preferably, the oblique baffle 72 is arranged below the transverse baffle 71 closest to the deliquidation water bag 6 and is located above the deliquidation water bag 6, and the acute angle between the oblique baffle 72 and the transverse baffle 71 is 30-60°, preferably 45-60°.

[0063] In the present invention, after the flue gas contacts the transverse baffle 71, the flow direction of the flue gas will change to a certain extent, so that the flow direction of the flue gas changes to an "S" shape. The oblique baffle 72 is arranged below the transverse baffle 71, so that the flue gas with changed flow direction can hit the oblique baffle 72 almost vertically. After the flue gas hits the transverse baffle 71, the gravity of solid impurities such as water droplets and smoke dust is much greater than that of the flue gas, so the water droplets and solid impurities such as smoke dust entrained in the flue gas can be removed after the collision. The water falling off the oblique baffle 72 can "clean" the flue gas in the process of falling, so that the smoke dust, sulfide, carbon dioxide and other substances in the flue gas are dissolved in the water as much as possible, thereby achieving the purpose of purifying the flue gas.

[0064] Preferably, in order to improve the dehydration effect, the oblique baffles 72 are provided in 2-5 pieces, and the multiple oblique baffles 72 are arranged in parallel; in order to reduce the flow resistance of water, preferably, a layer of polytetrafluoroethylene coating is provided on the oblique baffles 72.

[0065] The water removed from the oblique baffle 72 will also cause the flue gas to re-entrain some water during the process of "cleaning" the flue gas. In order to prevent the water entrained in the flue gas from corroding the induced draft fan 4 and the chimney 9, the inventors set a defoaming net 73 in the second flue to remove the water in the flue gas again.

[0066] Preferably, the acute angle between the defoaming net 73 and the extension direction of the second flue is 30-60°, preferably 45-60°. The acute angle between the defoaming net 73 and the extension direction of the second flue refers to the acute angle between the lower end of the defoaming net 73 and the extension direction of the second flue. The defoaming net 73 is used to intercept water droplets entrained in the flue gas. The intercepted water droplets form large droplets under the action of capillary action and gravity and flow into the deliquescence water bag 6, which can prevent the acidic water droplets entrained in the flue gas from causing corrosion to the induced draft fan 4 and the chimney 9 and polluting the environment.

[0067] Preferably, the number of the defoaming net 73 is one.

[0068] In order to facilitate the collection of condensed water removed in the flue, preferably, the deliquescence water bag 6 is arranged at the lowest point of the flue between the second low-temperature air preheater 32 and the induced draft fan 4.

[0069] Since the position of the defoaming net 73 is higher than the deliquated water bag 6, in order to allow the water intercepted by the defoaming net 73 to flow smoothly into the deliquated water bag 6, preferably, an inclined flue 84 is provided between the defoaming net 73 which is farthest from the deliquated water bag 6 and the deliquated water bag 6.

[0070] Preferably, the flue gas flows through the defoaming net 73, enters the induced draft fan 4, and finally is discharged into the chimney 9, and the flue gas is discharged into the atmosphere by the chimney 9. Among them, the present invention uses the four-fold arrangement of the flue 83 with sieve holes, the transverse baffle 71, the oblique baffle 72 and the defoaming net 73, so that the water content in the flue gas is less than 2-10wt%, preferably less than 3-6wt%, after the flue gas flows through the defoaming net 73, and basically all the water entrained in the flue gas can be removed, so that the flow rate of the flue gas can be reduced by 37300-38500m 3 / h, thereby reducing the load of the induced draft fan 4.

[0071] Since the amount of condensed water removed is relatively large, in order to facilitate observation of the dehydration amount, preferably, a dehydration water bag level gauge 61 is provided on the dehydration water bag 6. The dehydration water bag level gauge 61 is used to observe the liquid level in the dehydration water bag 6, which can solve the problem of being unable to observe the water accumulation at the bottom of the air preheater in the prior art.

[0072] At present, in industrial production, the water in the flue gas is generally not specially removed, and only the condensed water accumulated at the bottom of the air preheater is discharged. However, the present invention can basically remove all the water droplets entrained in the flue gas through the cross connection between the first low-temperature air preheater 31 and the second low-temperature air preheater 32 and the setting of the flue 83 with sieve holes, the transverse baffle 71, the oblique baffle 72 and the defoaming net 73, thereby reducing the load of the induced draft fan 4 and improving the fault tolerance of the heating furnace system. This part of condensed water removed from the flue gas is not only large in quantity, but also high in temperature, generally around 80°C. Using this part of water to heat the air entering the first low-temperature air preheater 31 and the second low-temperature air preheater 32 can not only recover heat to improve the thermal efficiency of the heating furnace, but also increase the temperature of the air entering the first low-temperature air preheater 31 and the second low-temperature air preheater 32, further avoiding the occurrence of local dew point corrosion.

[0073] Because the removed condensed water contains sulfide and the pH value is usually around 3, the condensed water needs to be neutralized before the heat of the condensed water is recovered to prevent the acidic condensed water from corroding the equipment. Preferably, the system also includes a neutralization tank 10 and an alkali liquid storage tank 11, and the neutralization tank 10 is connected to the deliquated water bag 6 and the alkali liquid storage tank 11, respectively, for neutralizing the condensed water from the deliquated water bag 6 and the alkali liquid from the alkali liquid storage tank 11 to obtain wastewater.

[0074] Preferably, a drain gate valve 62, a filter 63 and a stop valve 64 are sequentially arranged on the pipeline connecting the deliquated water bag 6 and the neutralization tank 10. When the condensed water flowing into the deliquated water bag 6 reaches a certain amount through the deliquated water bag level gauge 61, the drain gate valve 62 and the stop valve 64 can be opened to allow the condensed water collected in the deliquated water bag 6 to flow into the neutralization tank 10. The filter 63 is preferably a Y-type filter, which can filter out solid impurities such as smoke and dust in the deliquated water bag 6. In practical applications, the filter 63 can be cleaned regularly.

[0075] Since the bottom of the second low-temperature air preheater 32 is a negative pressure environment, in order to reduce the resistance of the water in the deliquidation water bag 6 to flow into the neutralization tank 10, preferably, the system also includes a pressure balancing pipeline 101, wherein the pressure balancing pipeline 101 is arranged between the neutralization tank 10 and the second flue, and a balancing gate valve 102 is arranged on the pressure balancing pipeline 101.

[0076] Among them, the pressure balancing pipeline 101 is used to balance the pressure of the neutralization tank 10. During the operation of the system, the pressure balancing pipeline 101 is in a normally open state. When the deliquidation condition of the deliquidation water bag 6 is not good as observed by the deliquidation water bag level gauge 61, it is necessary to check and confirm whether the pressure balancing pipeline 101 is open, or clean the filter 63 in time.

[0077] Preferably, the neutralization tank 10 is also provided with a glass plate level gauge 103 and a remote level gauge 104, wherein the glass plate level gauge 103 is used to observe the liquid level in the neutralization tank 10 on site, and the remote level gauge 104 is used to transmit the liquid level signal in the neutralization tank 10 to the DCS screen in the central control room, so as to remotely control the liquid level in the neutralization tank 10.

[0078] In order to conveniently control the amount of alkali solution added, preferably, a pH online monitor 105 and a sampling pipeline 106 are also provided on the neutralization tank 10, and a sampling gate valve 107 is provided on the sampling pipeline 106. The pH online monitor 105 can transmit the pH signal in the neutralization tank 10 to the DCS screen in the central control room for remote observation and control of the pH value of the water in the neutralization tank 10. The sampling pipeline 106 is used to collect samples in the neutralization tank 10 for testing and analysis.

[0079] Preferably, the neutralization tank 10 and the alkali liquid storage tank 11 are connected via an alkali liquid injection pump 12, and an alkali liquid regulating valve 121 and an alkali liquid flowmeter 122 are provided on the pipeline connecting the neutralization tank 10 and the alkali liquid injection pump 12. An alkali liquid return pipeline 123 is provided between the outlet of the alkali liquid injection pump 12 and the alkali liquid storage tank 11, and an alkali liquid return gate valve 124 is provided on the alkali liquid return pipeline 123. The purpose of such a setting is to accurately control the injection amount of the alkali liquid, and then regulate the entire neutralization process.

[0080] In order to facilitate adding alkali to the alkali solution storage tank 11, preferably, an alkali injection funnel 111 and an alkali injection gate valve 112 are provided on the upper part of the alkali solution storage tank 11. The alkali injection funnel 111 and the alkali injection gate valve 112 are used to inject high-concentration alkali solution into the alkali solution storage tank 11.

[0081] In order to facilitate the injection of water into the alkali solution storage tank 11 , preferably, a water injection pipeline 113 is further provided on the alkali solution storage tank 11 , and a water injection gate valve 114 is provided on the water injection pipeline 113 , and the concentration of the alkali solution can be adjusted through the water injection pipeline 113 .

[0082] In order to conveniently control the liquid level in the alkali solution storage tank 11 , preferably, an alkali solution storage tank liquid level gauge 115 is also provided on the alkali solution storage tank 11 .

[0083] In the present invention, the temperature of the wastewater obtained after the alkali solution treatment is about 80°C. In order to make full use of this part of heat, preferably, the system also includes a heat exchanger 13 and a wastewater delivery pump 14, wherein the heat exchanger 13 is arranged at the outlet of the blower 5, and is used to recover the heat of the wastewater in the neutralization tank 10 to heat the air entering the first low-temperature air preheater 31 and the second low-temperature air preheater 32, and the wastewater delivery pump 14 is used to transport the wastewater in the neutralization tank 10 to the heat exchanger 13.

[0084] Preferably, a wastewater return pipeline 141 is provided between the outlet of the wastewater delivery pump 14 and the neutralization tank 10, and a wastewater return gate valve 142 is provided on the wastewater return pipeline 141. The wastewater return pipeline 141 is used to control the liquid level of the neutralization tank 10 to be not less than 30% to prevent air from entering; and can increase the disturbance of the liquid in the tank to make the liquid in the tank more evenly mixed. The wastewater return gate valve 142 is used to adjust the amount of wastewater returned.

[0085] Preferably, a wastewater outlet regulating valve 143 and a wastewater flow meter 144 are provided on the pipeline connecting the wastewater delivery pump 14 and the heat exchanger 13 .

[0086] In the present invention, air enters the blower inlet duct 51 through the air suction port 15, and then enters the blower 5. The air coming out of the blower 5 exchanges heat with the wastewater from the neutralization tank 10 in the heat exchanger 13. After heat exchange, the air discharged from the heat exchanger 13 enters the flue gas dehydration system through the first low-temperature air preheater air inlet and the second low-temperature air preheater air inlet through the blower outlet duct 52, and the wastewater discharged from the heat exchanger 13 is transported to the sewage treatment system through the sewage treatment pipeline 16.

[0087] The present invention will be described in detail below through examples. The sum of the heat exchange areas of the first low-temperature air preheater and the second low-temperature air preheater in Example 1 is equal to the heat exchange area of ​​the low-temperature air preheater 3 in Comparative Example 1. The flue gas at the outlet of the convection section of the heating furnace is the flue gas directly discharged from the flue gas outlet of the heating furnace.

[0088] Example 1

[0089] according to Figure 1 The flue gas dehydration system shown in the figure is operated, wherein the heating furnace fuel gas consumption is 10645m 3 / h, the flue gas temperature at the outlet of the convection section of the heating furnace is 280℃, and the flow rate is 158300m 3 / h, the water content is 24wt%. The flue gas temperature coming out of the high-temperature air preheater is 170℃, and it is evenly divided into two paths to enter the first low-temperature air preheater. The temperature coming out of the low-temperature exhaust port of the first low-temperature air preheater is 125℃, and the temperature coming out of the high-temperature exhaust port of the first low-temperature air preheater is 138℃; the temperature coming out of the low-temperature exhaust port of the second low-temperature air preheater is 89℃, and the temperature coming out of the high-temperature exhaust port of the second low-temperature air preheater is 91℃; the temperature of the mixed flue gas is 90℃, and the water content in the flue gas discharged from the chimney is 4wt%.

[0090] The temperature of the air sucked in by the blower from the air inlet is 33°C and the flow rate is 169000m 3 / h, the temperature of the air after heat exchange through the heat exchanger is 36℃, the temperature coming out of the second low-temperature air preheater is 102℃, the temperature coming out of the first low-temperature air preheater is 142℃, and the temperature coming out of the high-temperature air preheater is 262℃.

[0091] The amount of condensed water collected in the deliquified water bag is 32t / h, and the temperature is 90℃; the flow rate of condensed water flowing into the neutralization tank is 32t / h, the amount of alkali solution injected is 2t / h, and the temperature of the wastewater obtained after neutralization with alkali solution is 80℃. The flow rate of wastewater transported to the heat exchanger is 34t / h, the temperature entering the heat exchanger is 80℃, and the temperature after heat exchange is 40℃.

[0092] Calculations show that in Example 1, the load of the induced draft fan is 56%, the energy consumption of the heating furnace is 210 kgEO / t, and the thermal efficiency is 95.5%.

[0093] Comparative Example 1

[0094] according to Figure 4 A flue gas dehydration system is shown in FIG. 1, wherein the heating furnace fuel gas consumption is 11000m 3 / h, the flue gas temperature at the outlet of the convection section of the heating furnace is 280℃, and the flow rate is 196200m 3 / h, the water content is 24wt%. The temperature from the high temperature air preheater is 170℃, the temperature from the low temperature air preheater low temperature exhaust port is 80℃, and the temperature from the high temperature exhaust port of the low temperature air preheater is 105℃; the temperature of the mixed flue gas is 100℃, and the water content in the flue gas discharged from the chimney is 20wt%.

[0095] The temperature of the air blown by the blower is 33°C and the flow rate is 176000m 3 / h, the temperature out of the low-temperature air preheater is 120°C, and the temperature out of the high-temperature air preheater is 260°C. The amount of condensed water discharged from the bottom of the low-temperature air preheater is 3t / h.

[0096] Through calculation, it can be known that in comparative example 1, the load of the induced draft fan is 68%, the energy consumption of the heating furnace is 212.6 kgEO / t, and the thermal efficiency is 94.3%.

[0097] By comparing Example 1 with Comparative Example 1, it can be seen that the flue gas dehydration system provided by the present invention can not only reduce the corrosion of the induced draft fan and reduce the load of the induced draft fan, but also improve the thermal efficiency of the heating furnace by 1.2%.

[0098] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A flue gas dehydration system, the system comprising a heating furnace, a high-temperature air preheater, a first low-temperature air preheater, a second low-temperature air preheater and an induced draft fan connected in sequence, and a blower connected to the first low-temperature air preheater and the second low-temperature air preheater respectively; The first low-temperature air preheater is provided with a first low-temperature air preheater high-temperature flue gas outlet and a first low-temperature air preheater low-temperature flue gas outlet; The second low-temperature air preheater is provided with a second low-temperature air preheater high-temperature flue gas inlet and a second low-temperature air preheater low-temperature flue gas inlet; Wherein, the high-temperature flue gas outlet of the first low-temperature air preheater is connected to the low-temperature flue gas inlet of the second low-temperature air preheater; the low-temperature flue gas outlet of the first low-temperature air preheater is connected to the high-temperature flue gas inlet of the second low-temperature air preheater; A flue is provided between the second low-temperature air preheater and the induced draft fan, and a deliquated water bag is provided on the flue; wherein the flue is divided into a first flue between the second low-temperature air preheater and the deliquated water bag and a second flue between the deliquated water bag and the induced draft fan; Wherein, at least one transverse baffle is arranged in the first flue, and at least one oblique baffle is arranged below the transverse baffle; and at least one defoaming net is arranged in the second flue.

2. The system according to claim 1, wherein: The transverse baffle is provided in two pieces, and the two transverse baffles are staggered and spaced apart in the first flue along the extension direction of the first flue.

3. The system according to claim 2, wherein: The transverse baffle is provided with tear holes, and in a direction perpendicular to the extension of the first flue, the ratio of the area of ​​the transverse baffle to the cross-sectional area of ​​the first flue is 1:3-4.

4. The system according to any one of claims 1 to 3, wherein: The oblique baffle is arranged below the transverse baffle closest to the deliquated water bag and is located above the deliquated water bag. The acute angle between the oblique baffle and the transverse baffle is 30-60°.

5. The system according to claim 4, wherein: The acute angle between the oblique baffle and the transverse baffle is 45-60°.

6. The system according to claim 4, wherein: The acute angle between the defoaming net and the extension direction of the second flue is 30-60°.

7. The system according to claim 6, wherein: The acute angle between the defoaming net and the extension direction of the second flue is 45-60°.

8. The system according to claim 1, wherein: The first low-temperature air preheater and the second low-temperature air preheater are cast iron plate-type air preheaters.

9. The system according to claim 4, wherein: The system also includes a neutralization tank and an alkali solution storage tank. The neutralization tank is connected to the deliquated water bag and the alkali solution storage tank respectively, and is used to neutralize the condensed water from the deliquated water bag and the alkali solution from the alkali solution storage tank to obtain waste water.

10. The system according to claim 9, wherein: The neutralization tank and the alkali solution storage tank are connected via an alkali solution injection pump; an alkali solution return pipeline is provided between the alkali solution injection pump outlet and the alkali solution storage tank, and an alkali solution return gate valve is provided on the alkali solution return pipeline.

11. The system according to claim 10, wherein: The system further comprises a pressure balancing line, which is arranged between the neutralization tank and the second flue.

12. The system according to claim 9, wherein: The system further comprises a heat exchanger, which is arranged at the outlet of the blower and is used to recover the heat of the waste water in the neutralization tank to heat the air entering the first low-temperature air preheater and the second low-temperature air preheater.

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