A system and method for absorbing sulfur dioxide from boiler flue gas using iodine

Abstract

The invention discloses a system and method for absorbing sulfur dioxide in boiler flue gas by using iodine. The system comprises a flue after a boiler booster fan, a washing tower packing layer, a washing tower, a washing liquid circulation pump, an absorption tower, an exhaust device, an iodine adding device and a waste liquid absorption device, etc. The washing tower packing layer is used to divide the washing tower into two parts, the outlet of the flue after the boiler booster fan is connected to the lower part of the washing tower, the outlet of the lower part of the washing tower is connected to the inlet of the washing liquid circulation pump, the outlet of the washing liquid circulation pump is divided into two strands, the first strand is connected to the inlet of the upper part of the washing tower, and the second strand is connected to the inlet of the waste liquid absorption device; two layers of absorption tower hood isolation layers are installed in the absorption tower, and the two layers of absorption tower hood isolation layers divide the absorption tower into three layers of upper, middle and lower. The invention is aimed at the complex composition of boiler flue gas. By setting a washing tower, most of the dust and nitrogen oxides in the flue gas can be washed, and the influence of these impurities on the absorption of sulfur dioxide by iodine can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of comprehensive utilization of boiler flue gas and hydrogen preparation, and specifically relates to a system and method for absorbing sulfur dioxide in boiler flue gas by utilizing iodine. Background Art

[0002] The use of sulfur-iodine cycle high-temperature hydrolysis to produce hydrogen requires the thermal decomposition of sulfuric acid into sulfur dioxide at a temperature above 850°C. Water, sulfur dioxide and iodine produce hydrogen iodide at a temperature of about 100°C, and hydrogen iodide decomposes into iodine and hydrogen at a temperature of 500°C. The current problems and difficulties in high-temperature hydrolysis to produce hydrogen and sulfur-containing coal combustion are:

[0003] (1) The high temperature of 850°C required for thermal decomposition of sulfuric acid into sulfur dioxide is difficult to meet.

[0004] (2) The economic efficiency of producing hydrogen by pyrolysis of sulfuric acid is poor.

[0005] Since coal contains sulfur dioxide, and the flue gas after coal combustion contains sulfur dioxide, sulfur dioxide is discharged into the atmosphere and causes air pollution, desulfurization measures must be taken. Obtaining sulfur dioxide from the flue gas of power station boilers to form an open sulfur-iodine cycle to produce hydrogen is an environmentally friendly and economical way to prepare hydrogen. However, this method currently has the following problems:

[0006] (1) The composition of boiler flue gas is complex, and the flue gas carries dust and nitrogen oxides. These impurities enter the Bunsen reaction of sulfur-iodine cycle hydrogen production, making it difficult to purify hydrogen iodide:

[0007] (2) Iodine is a relatively volatile substance. The escape of iodine vapor will cause pollution. At the same time, iodine is of high value. The escape of iodine vapor will increase the cost of hydrogen production.

[0008] (3) In the sulfur-iodine cycle for hydrogen production, the most economical way to separate sulfuric acid and hydrogen iodide is to achieve static stratification of sulfuric acid solution and hydrogen iodide solution by dissolving excess iodine, which will make the hydrogen production process discontinuous. Summary of the invention

[0009] The invention aims at the existing problems of producing hydrogen by absorbing sulfur dioxide from boiler flue gas, and provides a system and method for absorbing sulfur dioxide from boiler flue gas by utilizing iodine.

[0010] The present invention is achieved by adopting the following technical solutions:

[0011] A system for absorbing sulfur dioxide in boiler flue gas by using iodine, comprising a flue after a boiler booster fan, a scrubber packing layer, a scrubber, a scrubbing liquid circulation pump, an absorption tower, an absorption tower packing layer, an absorption tower wind cap isolation layer, an exhaust device, an iodine adding device and a waste liquid absorption device;

[0012] The packing layer of the washing tower is used to divide the washing tower into two parts, the outlet of the flue after the boiler booster fan is connected to the lower part of the washing tower, the outlet of the lower part of the washing tower is connected to the inlet of the washing liquid circulation pump, and the outlet of the washing liquid circulation pump is divided into two streams, the first stream is connected to the inlet of the upper part of the washing tower, and the second stream is connected to the inlet of the waste liquid absorption device;

[0013] Two layers of absorption tower wind hood isolation layers are installed in the absorption tower, and the two layers of absorption tower wind hood isolation layers divide the absorption tower into three layers: upper, middle and lower. One absorption tower packing layer is installed in each of the upper, middle and lower layers of the absorption tower, and the absorption tower packing layer divides the upper, middle and lower layers of the absorption tower into two layers, which are respectively called the lower-lower layer, the lower-upper layer, the middle-lower layer, the middle-upper layer, the upper and lower layers and the upper-upper layer. The outlet of the upper-upper layer is connected to the inlet of the exhaust device, the outlet of the upper layer of the washing tower is connected to the first inlet of the lower-lower layer, and the outlet of the iodine adding device is connected to the second inlet of the lower-lower layer.

[0014] A further improvement of the present invention is that it also includes an absorption tower concentrated liquid circulation pump, an absorption tower middle liquid circulation pump, an absorption tower clear liquid circulation pump and a clean water tank; the inlet of the absorption tower concentrated liquid circulation pump is connected to the lower-lower layer, and the outlet is divided into two branches, the first branch is connected to the lower upper layer, the inlet of the absorption tower middle liquid circulation pump is connected to the middle-lower layer, and the outlet is divided into two branches, the first branch is connected to the middle-upper layer, and the second branch is connected to the inlet of the absorption tower concentrated liquid circulation pump, the inlet of the absorption tower clear liquid circulation pump is connected to the upper and lower layers, and the outlet is divided into two branches, the first branch is connected to the upper upper layer, and the second branch is connected to the inlet of the absorption tower middle liquid circulation pump, and the outlet of the clean water tank is divided into two branches, the first branch is connected to the inlet of the absorption tower clear liquid circulation pump, and the second branch is connected to the inlet of the washing liquid circulation pump.

[0015] A further improvement of the present invention is that it also includes a separation device, a sulfuric acid storage tank and a hydrogen iodide purification and concentration device; the second outlet of the absorption tower concentrated liquid circulation pump is connected to the inlet of the separation device, the first outlet of the separation device is connected to the inlet of the sulfuric acid storage tank, and the second outlet of the separation device is connected to the inlet of the hydrogen iodide purification and concentration device.

[0016] A further improvement of the present invention is that it also includes a hydrogen iodide decomposition device and a hydrogen storage tank; the outlet of the hydrogen iodide purification and concentration device is connected to the inlet of the hydrogen iodide decomposition device, the first outlet of the hydrogen iodide decomposition device is connected to the inlet of the hydrogen storage tank, and the second outlet of the hydrogen iodide decomposition device is connected to the inlet of the liquid circulation pump in the absorption tower.

[0017] A further improvement of the present invention is that after the outlet of the washing liquid circulation pump is connected to the upper layer of the packing layer of the washing tower, it enters the upper space of the packing layer of the washing tower through the atomizing nozzle.

[0018] A further improvement of the present invention is that the flue gas from the rear flue of the boiler booster fan enters the lower space of the packing layer of the washing tower, passes through the packing layer of the washing tower and enters the upper space of the packing layer of the washing tower.

[0019] A further improvement of the present invention is that after the outlets of the absorption tower concentrated liquid circulation pump, the absorption tower intermediate liquid circulation pump and the absorption tower clear liquid circulation pump are respectively connected to the lower upper layer, the middle upper layer and the upper upper layer, they enter the lower upper layer, the middle upper layer and the upper upper layer space respectively through the atomizing nozzle, the flue gas discharged from the upper layer space of the washing tower packing layer enters the lower lower layer, passes through the lower absorption tower packing layer, absorbs sulfur dioxide by the atomized liquid in the lower upper layer, and then enters the middle lower layer through the lower absorption tower wind cap isolation layer, the flue gas entering the middle lower layer passes through the middle absorption tower packing layer, absorbs sulfur dioxide by the atomized liquid in the middle upper layer, and then enters the upper and lower layers through the upper absorption tower wind cap isolation layer, the flue gas entering the upper and lower layers passes through the upper absorption tower packing layer, absorbs sulfur dioxide by the atomized liquid in the upper upper layer, and is discharged to the exhaust device.

[0020] A further improvement of the present invention is that the hood of the hood isolation layer of the absorption tower is adjustable, and the amount of smoke passing through the hood can be adjusted by adjusting the hood.

[0021] A further improvement of the present invention is that a sampling detection device is provided at the outlet of the concentrated liquid circulation pump of the absorption tower, which can detect the concentration of the outlet mixed liquid. When the concentration of the mixed liquid meets the requirements, the mixed liquid is discharged to the separation device until the liquid level of the lower layer reaches the lower limit. After the liquid level of the lower layer reaches the lower limit, the mixed liquid of the middle and lower layers is discharged to the inlet of the concentrated liquid circulation pump of the absorption tower through the outlet of the absorption tower middle liquid circulation pump until the liquid level of the lower layer reaches the normal liquid level. After the liquid level of the middle and lower layers reaches the lower limit, the mixed liquid of the upper and lower layers is discharged to the inlet of the absorption tower middle liquid circulation pump through the outlet of the absorption tower clear liquid circulation pump until the liquid level of the middle and lower layers reaches the normal liquid level. When the liquid levels of the upper and lower layers reach the lower limit, the clean water tank injects clean water into the inlet of the absorption tower clear liquid circulation pump until the liquid levels of the upper and lower layers reach the normal liquid level.

[0022] A method for absorbing sulfur dioxide from boiler flue gas by using iodine, based on the system for absorbing sulfur dioxide from boiler flue gas by using iodine, comprises the following steps:

[0023] 1) Before starting the system, inject clean water into the inlet of the washing liquid circulation pump through the clean water tank until the water level at the bottom of the washing tower is at the normal water level;

[0024] 2) Inject clean water into the inlet of the clean liquid circulation pump of the absorption tower through the clean water tank until the liquid levels of the upper and lower layers reach the normal level;

[0025] 3) Start the absorption tower clear liquid circulation pump, inject water into the absorption tower middle liquid circulation pump inlet, and continue to inject clean water into the absorption tower clear liquid circulation pump inlet through the clean water tank until the upper and lower layer liquid levels and the middle and lower layer liquid levels reach the normal level;

[0026] 4) Start the absorption tower liquid circulation pump, inject water into the absorption tower concentrated liquid circulation pump inlet, until the upper and lower layer liquid levels, the middle and lower layer liquid levels and the lower and lower layer liquid levels are all at normal levels, and start the absorption tower concentrated liquid circulation pump;

[0027] 5) adding iodine to the lower layer through the iodine adding device until the iodine cannot be dissolved, i.e., saturation is reached;

[0028] 6) Start the scrubbing liquid circulation pump, and the flue gas containing sulfur dioxide from the flue after the boiler booster fan enters the lower layer of the scrubbing tower, the dust and soluble gas in the flue gas enter the scrubbing liquid, and other insoluble gases enter the absorption tower;

[0029] 7) When the dissolution of sulfur dioxide in the scrubbing liquid reaches saturation, the sulfur dioxide gas enters the lower layer of the absorption tower, and the sulfur dioxide gas reacts with iodine and water to generate hydrogen iodide and sulfuric acid. Iodine is continuously added to the lower layer through the iodine adding device to maintain a small amount of insoluble iodine in the lower layer;

[0030] 8) when the concentration of the lower layer solution meets the conditions for the stratification of hydrogen iodide and sulfuric acid solution, the concentrate is discharged to the separator by the absorber concentrate circulation pump, and when the lower layer liquid level reaches the minimum liquid level, the discharge of the concentrate to the separator is stopped, and water is replenished to the upper and lower layers, the middle and lower layers and the lower lower layers of the absorber by the clean water tank to maintain the normal liquid level of each layer, and iodine is continuously added to the lower layer by the iodine adding device to maintain the presence of a small amount of insoluble iodine in the lower lower layer, and the absorption of sulfur dioxide is continued;

[0031] 9) When the dust and nitrogen oxides in the exhaust gas from the scrubber exceed the standard, the scrubber liquid circulation pump discharges waste liquid to the waste liquid absorption device. When the liquid level in the lower layer of the scrubber reaches the minimum, the discharge of waste liquid is stopped, and water is added to the lower layer of the scrubber through the clean water tank to the normal liquid level, and the flue gas scrubbing continues;

[0032] 10) After the concentrated solution entering the separation device is separated into a sulfuric acid solution and a hydrogen iodide solution, the sulfuric acid solution is discharged into a sulfuric acid storage tank, and the hydrogen iodide solution enters a hydrogen iodide purification and concentration device for purification and concentration;

[0033] 11) The purified and concentrated hydrogen iodide solution enters the hydrogen iodide decomposition device and is decomposed into hydrogen and iodine. The hydrogen enters the hydrogen storage tank, and the remaining solution returns to the middle and lower layers of the absorption tower.

[0034] The system and method for absorbing sulfur dioxide from boiler flue gas by iodine provided by the present invention have at least the following obvious advantages:

[0035] (1) As boiler flue gas has complex components, a scrubber can be set up to wash away most of the dust and nitrogen oxides in the flue gas, reducing the impact of these impurities on the absorption of sulfur dioxide by iodine;

[0036] (2) In order to reduce iodine escape, the absorption tower is divided into three layers of absorption. The iodine lost from the lower layer is absorbed twice by the upper middle layer and the upper upper layer, which reduces the probability of iodine escaping from the system;

[0037] (3) A three-layer absorption is set up, and iodine is mainly placed in the lower layer. The liquid in the lower layer is also the first to contact the flue gas containing sulfur dioxide. Therefore, the lower layer is more likely to reach the concentration of hydrogen iodide solution and sulfuric acid solution for stratification, and stratification is easier to achieve;

[0038] (4) The solution returned from the hydrogen iodide decomposition device enters the middle and lower layers without affecting the concentration of the solution in the lower layer, so that the entire absorption, separation and decomposition can be carried out continuously.

[0039] (4) The flue gas is washed and absorbed in three layers, making it cleaner and more environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention is a structural block diagram of a system for absorbing sulfur dioxide from boiler flue gas using iodine.

[0041] Description of reference numerals:

[0042] 1. Flue duct after boiler booster fan; 2. Packing layer of washing tower; 3. Washing tower; 4. Washing liquid circulation pump; 5. Absorption tower; 6. Packing layer of absorption tower; 7. Isolation layer of absorption tower wind cap; 8. Absorption tower concentrated liquid circulation pump; 9. Absorption tower intermediate liquid circulation pump; 10. Absorption tower clear liquid circulation pump; 11. Clean water tank; 12. Separation device; 13. Sulfuric acid storage tank; 14. Hydrogen iodide purification and concentration device; 15. Hydrogen iodide decomposition device; 16. Hydrogen storage tank; 17. Exhaust device; 18. Waste liquid absorption device; 19. Iodine adding device. DETAILED DESCRIPTION

[0043] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0044] like Figure 1 As shown, the present invention provides a system for absorbing sulfur dioxide in boiler flue gas by utilizing iodine, comprising a flue 1 after a boiler booster fan, a scrubbing tower packing layer 2, a scrubbing tower 3, a scrubbing liquid circulation pump 4, an absorption tower 5, an absorption tower packing layer 6, an absorption tower wind cap isolation layer 7, an absorption tower concentrated liquid circulation pump 8, an absorption tower intermediate liquid circulation pump 9, an absorption tower clear liquid circulation pump 10, a clean water tank 11, a separation device 12, a sulfuric acid storage tank 13, a hydrogen iodide purification and concentration device 14, a hydrogen iodide decomposition device 15, a hydrogen storage tank 16, an exhaust device 17, an iodine adding device 19 and a waste liquid absorption device 18.

[0045] The washing tower packing layer 2 is used to divide the washing tower 3 into two parts, the outlet of the flue 1 after the boiler booster fan is connected to the lower part of the washing tower 3, and the outlet of the lower part of the washing tower 3 is connected to the inlet of the washing liquid circulation pump 4. The outlet of the washing liquid circulation pump 4 is divided into two branches, the first branch is connected to the inlet of the upper part of the washing tower 3, and the second branch is connected to the inlet of the waste liquid absorption device 18; two layers of absorption tower hood isolation layers 7 are installed in the absorption tower 5, and the two layers of absorption tower hood isolation layers 7 divide the absorption tower 5 into three layers, namely, upper, middle and lower layers. One layer of absorption tower packing layer 6 is installed in each of the upper, middle and lower layers of the absorption tower 5, and the absorption tower packing layer 6 divides the upper, middle and lower layers of the absorption tower 5 into two layers, which are respectively called the lower-lower layer, the lower-upper layer, the middle-lower layer, the middle-upper layer, the upper and lower layers and the upper-upper layer. The outlet of the upper-upper layer is connected to the inlet of the exhaust device 17, the outlet of the upper layer of the washing tower 3 is connected to the first inlet of the lower-lower layer, and the outlet of the iodine adding device 19 is connected to the second inlet of the lower-lower layer.

[0046] The inlet of the absorber concentrated liquid circulation pump 8 is connected to the lower-lower layer, and the outlet is divided into two branches, the first branch is connected to the lower upper layer; the inlet of the absorber medium liquid circulation pump 9 is connected to the middle-lower layer, and the outlet is divided into two branches, the first branch is connected to the middle-upper layer, and the second branch is connected to the inlet of the absorber concentrated liquid circulation pump 8; the inlet of the absorber clear liquid circulation pump 10 is connected to the upper and lower layers, and the outlet is divided into two branches, the first branch is connected to the upper upper layer, and the second branch is connected to the inlet of the absorber medium liquid circulation pump 9; the outlet of the clean water tank 11 is divided into two branches, the first branch is connected to the inlet of the absorber clear liquid circulation pump 10, and the second branch is connected to the inlet of the washing liquid circulation pump 4.

[0047] The second outlet of the absorber concentrate circulation pump 8 is connected to the inlet of the separation device 12 , the first outlet of the separation device 12 is connected to the inlet of the sulfuric acid storage tank 13 , and the second outlet of the separation device 12 is connected to the inlet of the hydrogen iodide purification and concentration device 14 .

[0048] The outlet of the hydrogen iodide purification and concentration device 14 is connected to the inlet of the hydrogen iodide decomposition device 15, the first outlet of the hydrogen iodide decomposition device 15 is connected to the inlet of the hydrogen storage tank 16, and the second outlet of the hydrogen iodide decomposition device 15 is connected to the inlet of the liquid circulation pump 9 in the absorption tower.

[0049] The outlet of the washing liquid circulation pump 4 is connected to the upper layer of the washing tower packing layer 2, and then enters the upper space of the washing tower packing layer 2 through the atomizing nozzle. The flue gas from the flue duct 1 after the boiler booster fan enters the lower space of the washing tower packing layer 2, passes through the washing tower packing layer 2 and enters the upper space of the washing tower packing layer 2.

[0050] After the outlets of the absorption tower concentrated liquid circulation pump 8, the absorption tower intermediate liquid circulation pump 9 and the absorption tower clear liquid circulation pump 10 are respectively connected to the lower upper layer, the middle upper layer and the upper upper layer, they enter the lower upper layer, the middle upper layer and the upper upper layer space respectively through the atomizing nozzle. The flue gas discharged from the upper layer space of the washing tower packing layer 2 enters the lower lower layer, passes through the lower absorption tower packing layer 6, absorbs sulfur dioxide by the atomized liquid in the lower upper layer, and then enters the middle lower layer through the lower absorption tower wind cap isolation layer 7. The flue gas entering the middle lower layer passes through the middle absorption tower packing layer 6, absorbs sulfur dioxide by the atomized liquid in the middle upper layer, and then enters the upper and lower layers through the upper absorption tower wind cap isolation layer 7. The flue gas entering the upper and lower layers passes through the upper absorption tower packing layer 6, absorbs sulfur dioxide by the atomized liquid in the upper upper layer, and is discharged to the exhaust device 17.

[0051] The hood of the absorption tower hood isolation layer 7 can be adjusted, and the amount of smoke passing through the hood can be adjusted by adjusting the hood.

[0052] The outlet of the concentrated liquid circulation pump 8 of the absorption tower is provided with a sampling detection device, which can detect the concentration of the outlet mixed liquid. When the concentration of the mixed liquid meets the requirements, the mixed liquid is discharged to the separation device 12 until the liquid level of the lower layer reaches the lower limit. When the liquid level of the lower layer reaches the lower limit, the mixed liquid of the middle and lower layers is discharged to the inlet of the concentrated liquid circulation pump 8 of the absorption tower through the outlet of the absorption tower middle liquid circulation pump 9 until the liquid level of the lower layer reaches the normal liquid level. After the liquid level of the middle and lower layers reaches the lower limit, the mixed liquid of the upper and lower layers is discharged to the inlet of the absorption tower middle liquid circulation pump 9 through the outlet of the absorption tower clear liquid circulation pump 10 until the liquid level of the middle and lower layers reaches the normal liquid level. When the liquid levels of the upper and lower layers reach the lower limit, the clean water tank 11 injects clean water into the inlet of the absorption tower clear liquid circulation pump 10 until the liquid levels of the upper and lower layers reach the normal liquid level.

[0053] The present invention provides a method for absorbing sulfur dioxide from boiler flue gas by using iodine.

[0054] The following steps are involved:

[0055] 1) Before starting the system, clean water is injected into the inlet of the washing liquid circulation pump 4 through the clean water tank 11 until the water level at the bottom of the washing tower 3 is at a normal water level;

[0056] 2) Inject clean water into the inlet of the absorber clean liquid circulation pump 10 through the clean water tank 11 until the liquid levels of the upper and lower layers reach the normal level;

[0057] 3) Start the absorption tower clear liquid circulation pump 10, inject water into the inlet of the absorption tower middle liquid circulation pump 9, and continue to inject clean water into the inlet of the absorption tower clear liquid circulation pump 10 through the clean water tank 11 until the upper and lower layer liquid levels and the middle and lower layer liquid levels reach normal levels;

[0058] 4) Start the absorption tower liquid circulation pump 9, inject water into the absorption tower concentrated liquid circulation pump 8 inlet, until the upper and lower layer liquid levels, the middle and lower layer liquid levels and the lower and lower layer liquid levels are all at normal levels, and start the absorption tower concentrated liquid circulation pump 8;

[0059] 5) adding iodine to the lower layer through the iodine adding device 19 until the iodine cannot be dissolved, i.e., saturation is reached;

[0060] 6) Start the washing liquid circulation pump 4, the flue gas containing sulfur dioxide from the flue 1 after the boiler booster fan enters the lower layer of the washing tower 3, the dust and soluble gas in the flue gas enter the washing liquid, and other insoluble gases enter the absorption tower 5;

[0061] 7) When the dissolution of sulfur dioxide in the scrubbing liquid reaches saturation, the sulfur dioxide gas enters the lower layer of the absorption tower 5, and the sulfur dioxide gas reacts with iodine and water to generate hydrogen iodide and sulfuric acid, and iodine is continuously added to the lower layer through the iodine adding device 19 to maintain a small amount of insoluble iodine in the lower layer;

[0062] 8) when the concentration of the lower layer solution satisfies the conditions for the stratification of hydrogen iodide and sulfuric acid solution, the concentrate is discharged to the separator 12 by the absorber concentrate circulation pump 8, and when the lower layer liquid level reaches the minimum liquid level, the discharge of the concentrate to the separator 12 is stopped, and water is replenished to the upper and lower layers, the middle and lower layers and the lower lower layer of the absorber by the clean water tank 11 to maintain the normal liquid level of each layer, and iodine is continuously added to the lower layer by the iodine adding device 19 to maintain the presence of a small amount of insoluble iodine in the lower lower layer, and the absorption of sulfur dioxide is continued;

[0063] 9) When the dust and nitrogen oxides in the exhaust gas from the scrubber exceed the standard, the scrubbing liquid circulation pump 4 discharges the waste liquid to the waste liquid absorption device 18. When the liquid level in the lower layer of the scrubber 3 reaches the lowest, the discharge of the waste liquid is stopped, and the lower layer of the scrubber 3 is replenished with water to the normal liquid level through the clean water tank 11, and the flue gas scrubbing is continued;

[0064] 10) After the concentrated solution entering the separation device 12 is separated into a sulfuric acid solution and a hydrogen iodide solution, the sulfuric acid solution is discharged into a sulfuric acid storage tank 13, and the hydrogen iodide solution enters a hydrogen iodide purification and concentration device 14 for purification and concentration;

[0065] 11) The purified and concentrated hydrogen iodide solution enters the hydrogen iodide decomposition device 15 and is decomposed into hydrogen and iodine. The hydrogen enters the hydrogen storage tank 16, and the remaining solution returns to the middle and lower layers of the absorption tower 5.

[0066] Example:

[0067] For a 350MW unit, if the sulfur content of flue gas is 5g / m3 and the total flue gas volume is 1.3 million m3 / h, theoretically, it can produce 100,000 mol / h and 2,240 m3 of hydrogen / h. 1 m3 of hydrogen is worth 22,000 yuan at 10 yuan. It can produce 100,000 mol / h and 9.8 t / h of sulfuric acid. 1 ton of sulfuric acid is worth 4,900 yuan at 500 yuan. The heat required to decompose hydrogen iodide is 17,002.6 mj / h, which accounts for less than 1% of the heat of boiler flue gas, and has good economic benefits.

[0068] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A system for absorbing sulfur dioxide from boiler flue gas using iodine, characterized in that: The invention comprises a flue after a boiler booster fan (1), a washing tower packing layer (2), a washing tower (3), a washing liquid circulation pump (4), an absorption tower (5), an absorption tower packing layer (6), an absorption tower wind cap isolation layer (7), an exhaust device (17), an iodine adding device (19), a waste liquid absorption device (18), an absorption tower concentrated liquid circulation pump (8), an absorption tower intermediate liquid circulation pump (9), an absorption tower clear liquid circulation pump (10), a clear water tank (11), a separation device (12), a sulfuric acid storage tank (13), a hydrogen iodide purification and concentration device (14), a hydrogen iodide decomposition device (15) and a hydrogen storage tank (16); The scrubbing tower packing layer (2) is used to divide the scrubbing tower (3) into two parts, the outlet of the flue (1) after the boiler booster fan is connected to the lower part of the scrubbing tower (3), the outlet of the lower part of the scrubbing tower (3) is connected to the inlet of the scrubbing liquid circulation pump (4), the outlet of the scrubbing liquid circulation pump (4) is divided into two streams, the first stream is connected to the inlet of the upper part of the scrubbing tower (3), and the second stream is connected to the inlet of the waste liquid absorption device (18); Two layers of absorption tower wind cap isolation layers (7) are installed in the absorption tower (5), and the two layers of absorption tower wind cap isolation layers (7) divide the absorption tower (5) into three layers: upper, middle and lower. Each of the three layers of the absorption tower (5) is equipped with an absorption tower packing layer (6), and the absorption tower packing layer (6) divides each of the three layers of the absorption tower (5) into two layers, which are respectively called the lower-lower layer, the lower-upper layer, the middle-lower layer, the middle-upper layer, the upper-lower layer and the upper-upper layer. The outlet of the upper-upper layer is connected to the inlet of the exhaust device (17), the outlet of the upper layer of the washing tower (3) is connected to the first inlet of the lower-lower layer, and the outlet of the iodine adding device (19) is connected to the second inlet of the lower-lower layer. The inlet of the absorber concentrated liquid circulation pump (8) is connected to the lower layer, and the outlet is divided into two branches, the first branch is connected to the lower upper layer; the inlet of the absorber medium liquid circulation pump (9) is connected to the middle lower layer, and the outlet is divided into two branches, the first branch is connected to the middle upper layer, and the second branch is connected to the inlet of the absorber concentrated liquid circulation pump (8); the inlet of the absorber clear liquid circulation pump (10) is connected to the upper and lower layers, and the outlet is divided into two branches, the first branch is connected to the upper upper layer, and the second branch is connected to the inlet of the absorber medium liquid circulation pump (9); the outlet of the clean water tank (11) is divided into two branches, the first branch is connected to the inlet of the absorber clear liquid circulation pump (10), and the second branch is connected to the inlet of the washing liquid circulation pump (4); The second outlet of the absorber concentrated liquid circulation pump (8) is connected to the inlet of the separation device (12), the first outlet of the separation device (12) is connected to the inlet of the sulfuric acid storage tank (13), and the second outlet of the separation device (12) is connected to the inlet of the hydrogen iodide purification and concentration device (14); The outlet of the hydrogen iodide purification and concentration device (14) is connected to the inlet of the hydrogen iodide decomposition device (15), the first outlet of the hydrogen iodide decomposition device (15) is connected to the inlet of the hydrogen storage tank (16), and the second outlet of the hydrogen iodide decomposition device (15) is connected to the inlet of the liquid circulation pump (9) in the absorption tower.

2. A system for absorbing sulfur dioxide from boiler flue gas using iodine according to claim 1, characterized in that: After the outlet of the washing liquid circulation pump (4) is connected to the upper layer of the washing tower packing layer (2), the washing liquid enters the upper layer space of the washing tower packing layer (2) through the atomizing nozzle.

3. A system for absorbing sulfur dioxide from boiler flue gas using iodine according to claim 1, characterized in that: After the flue gas from the rear flue (1) of the boiler booster fan enters the lower space of the packing layer (2) of the scrubbing tower, it passes through the packing layer (2) of the scrubbing tower and enters the upper space of the packing layer (2) of the scrubbing tower.

4. The system for absorbing sulfur dioxide from boiler flue gas using iodine according to claim 1, characterized in that: The outlets of the absorption tower concentrated liquid circulation pump (8), the absorption tower intermediate liquid circulation pump (9) and the absorption tower clear liquid circulation pump (10) are connected to the lower upper layer, the middle upper layer and the upper upper layer respectively, and then enter the lower upper layer, the middle upper layer and the upper upper layer space respectively through the atomizing nozzle. The flue gas discharged from the upper layer space of the scrubbing tower packing layer (2) enters the lower lower layer, passes through the lower absorption tower packing layer (6), absorbs sulfur dioxide by the atomized liquid in the lower upper layer, and then enters the middle lower layer through the lower absorption tower wind cap isolation layer (7). The flue gas entering the middle lower layer passes through the middle absorption tower packing layer (6), absorbs sulfur dioxide by the atomized liquid in the middle upper layer, and then enters the upper and lower layers through the upper absorption tower wind cap isolation layer (7). The flue gas entering the upper and lower layers passes through the upper absorption tower packing layer (6), absorbs sulfur dioxide by the atomized liquid in the upper upper layer, and then is discharged to the exhaust device (17).

5. The system for absorbing sulfur dioxide from boiler flue gas using iodine according to claim 1, characterized in that: The hood of the hood isolation layer (7) of the absorption tower is adjustable, and the amount of smoke passing through the hood can be adjusted by adjusting the hood.

6. The system for absorbing sulfur dioxide from boiler flue gas using iodine according to claim 1, characterized in that: The outlet of the concentrated liquid circulation pump (8) of the absorption tower is provided with a sampling detection device, which can detect the concentration of the outlet mixed liquid. When the concentration of the mixed liquid meets the requirements, the mixed liquid is discharged to the separation device (12) until the liquid level of the lower layer reaches the lower limit. When the liquid level of the lower layer reaches the lower limit, the mixed liquid of the middle and lower layers is discharged to the inlet of the concentrated liquid circulation pump (8) of the absorption tower through the outlet of the absorption tower middle liquid circulation pump (9) until the liquid level of the lower layer reaches the normal liquid level. When the liquid level of the middle and lower layer reaches the lower limit, the mixed liquid of the upper and lower layers is discharged to the inlet of the absorption tower middle liquid circulation pump (9) through the outlet of the absorption tower clear liquid circulation pump (10) until the liquid level of the middle and lower layer reaches the normal liquid level. When the liquid levels of the upper and lower layers reach the lower limit, the clean water tank (11) injects clean water into the inlet of the absorption tower clear liquid circulation pump (10) until the liquid levels of the upper and lower layers reach the normal liquid level.

7. A method for absorbing sulfur dioxide from boiler flue gas using iodine, characterized in that: The method is based on a system for absorbing sulfur dioxide from boiler flue gas using iodine as described in claim 1, and comprises the following steps: 1) Before starting the system, clean water is injected into the inlet of the washing liquid circulation pump (4) through the clean water tank (11) until the water level at the bottom of the washing tower (3) is at a normal water level; 2) injecting clean water into the inlet of the clean liquid circulation pump (10) of the absorption tower through the clean water tank (11) until the liquid levels of the upper and lower layers reach the normal liquid level; 3) starting the absorption tower clear liquid circulation pump (10), injecting water into the inlet of the absorption tower middle liquid circulation pump (9), and simultaneously continuing to inject clean water into the inlet of the absorption tower clear liquid circulation pump (10) through the clean water tank (11), until the liquid levels of the upper and lower layers and the middle and lower layers reach normal levels; 4) starting the absorption tower liquid circulation pump (9), injecting water into the inlet of the absorption tower concentrated liquid circulation pump (8), until the upper and lower layer liquid levels, the middle and lower layer liquid levels and the lower and lower layer liquid levels all reach normal liquid levels, and starting the absorption tower concentrated liquid circulation pump (8); 5) adding iodine to the lower layer through the iodine adding device (19) until the iodine cannot be dissolved, i.e., saturation is reached; 6) Start the scrubbing liquid circulation pump (4), and the flue gas containing sulfur dioxide from the flue (1) after the boiler booster fan enters the lower layer of the scrubbing tower (3), the dust and soluble gas in the flue gas enter the scrubbing liquid, and other insoluble gases enter the absorption tower (5); 7) When the sulfur dioxide in the scrubbing liquid reaches saturation, the sulfur dioxide gas enters the lower layer of the absorption tower (5), reacts with iodine and water to generate hydrogen iodide and sulfuric acid, and iodine is continuously added to the lower layer through the iodine adding device (19) to maintain a small amount of insoluble iodine in the lower layer; 8) When the concentration of the lower layer solution meets the conditions for the separation of hydrogen iodide and sulfuric acid solution, the concentrate is discharged to the separation device (12) through the absorber concentrate circulation pump (8). When the liquid level of the lower layer reaches the lowest level, the discharge of the concentrate to the separation device (12) is stopped, and water is replenished to the upper and lower layers, the middle and lower layers, and the lower-lower layers of the absorber through the clean water tank (11) to maintain the normal liquid level of each layer. At the same time, iodine is continuously added to the lower layer through the iodine adding device (19) to maintain the presence of a small amount of insoluble iodine in the lower-lower layer, and the absorption of sulfur dioxide continues; 9) When the dust and nitrogen oxides in the exhaust gas from the scrubbing tower exceed the standard, the scrubbing liquid circulation pump (4) discharges the waste liquid to the waste liquid absorption device (18). When the liquid level in the lower layer of the scrubbing tower (3) reaches the lowest level, the discharge of the waste liquid is stopped, and water is added to the lower layer of the scrubbing tower (3) through the clean water tank (11) to the normal liquid level, and the flue gas scrubbing is continued; 10) After the concentrated solution entering the separation device (12) is separated into a sulfuric acid solution and a hydrogen iodide solution, the sulfuric acid solution is discharged into a sulfuric acid storage tank (13), and the hydrogen iodide solution enters a hydrogen iodide purification and concentration device (14) for purification and concentration; 11) The purified and concentrated hydrogen iodide solution enters the hydrogen iodide decomposition device (15) and is decomposed into hydrogen and iodine. The hydrogen enters the hydrogen storage tank (16), and the remaining solution returns to the middle and lower layers of the absorption tower (5).

Images