Low sulfur coal flue gas emission system and retrofit method

Abstract

The present application belongs to the technical field of flue gas purification, and particularly relates to a low-sulfur coal flue gas emission system and a transformation method. The emission system comprises an absorption tower, three layers of spray layers arranged in the upper inner cavity of the absorption tower from top to bottom, three circulating pumps respectively connected to the three layers of spray layers to extract slurry at the bottom of the absorption tower and spray the slurry through the three layers of spray layers, and slurry recirculation devices arranged between any two adjacent layers of spray layers. The technical scheme of the present application can achieve standard emission of the desulfurization system when the low-sulfur coal, i.e. the sulfur dioxide content, is low.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental protection flue gas purification, and particularly relates to a low-sulfur coal flue gas emission system and a transformation method. BACKGROUND

[0002] In order to reduce the amount of pollutants discharged in the industrial field, the State Council decided to first implement ultra-low emission in coal-fired power plants across the country. In order to implement the meeting spirit, the National Development and Reform Commission, the Ministry of Environmental Protection and the National Energy Administration jointly issued the "Work Plan for Implementing Ultra-Low Emission and Energy Saving Reconstruction of Coal-Fired Power Plants", to guide the ultra-low emission reconstruction work of coal-fired power plants.

[0003] Since the ultra-low emission reconstruction of coal-fired power plants began, localities have required key industries in the industrial field to follow the example of coal-fired power plants and promote the implementation of ultra-low emission reconstruction, such as steel, cement, petrochemical, non-ferrous, building materials, glass, ceramics and other non-electricity fields.

[0004] The national and local requirements for achieving ultra-low emission of pollutants are that the emission concentration of NO x is less than 50 mg / Nm 3 , the emission concentration of SO2 is less than 35 mg / Nm 3 , and the emission concentration of dust is less than 5 mg / Nm 3 . For desulfurization ultra-low emission reconstruction, in order to achieve the goal of SO2 emission concentration less than 35 mg / Nm 3 at the desulfurization outlet, the current mature high-efficiency desulfurization reconstruction technical schemes mainly include: increasing the slurry circulating pump, single-tower double-circulation, spiral coupling technology, double-tower double-circulation, and PH value zoning technology. The above technical schemes are suitable for high-sulfur coal reconstruction projects. Most of these schemes need to add a slurry circulating pump, or increase the absorption tower, or transform the absorption tower to raise it, and then accommodate the newly added spray layer or the space for the high-efficiency desulfurization device. The above existing reconstruction schemes increase the layout space of the reconstruction, increase the investment and operation cost of the reconstruction, prolong the construction and reconstruction period, and increase the construction difficulty. They are not suitable for flue gas reconstruction projects of some low-sulfur coal, especially low-sulfur coal ultra-low reconstruction projects. SUMMARY

[0005] The purpose of the present application is to provide a low-sulfur coal flue gas emission system and a transformation method, so as to realize that the desulfurization system can meet the emission standard when the low-sulfur coal, i.e. the sulfur dioxide content, is low.

[0006] In order to achieve the above purpose, the present application provides the following technical scheme:

[0007] A low-sulfur coal flue gas emission system, the emission system comprising:

[0008] An absorption tower, wherein three spray layers are arranged in the upper cavity of the absorption tower from top to bottom;

[0009] Three circulating pumps, wherein each of the three circulating pumps is connected to one of the three spray layers to extract the slurry at the bottom of the absorption tower and spray the slurry through the three spray layers;

[0010] A slurry recirculation device is arranged between any two adjacent spray layers.

[0011] The low-sulfur coal flue gas emission system as described above, wherein the slurry recirculation device is annular, a plurality of air holes are arranged on the circumference of the slurry recirculation device, and the air holes penetrate the slurry recirculation device along the axial direction of the slurry recirculation device.

[0012] Preferably, the slurry recirculation device comprises an upper surface and a lower surface arranged oppositely, the air holes penetrate the upper surface and the lower surface, the upper surface is arranged as an inclined surface, the lower surface is arranged as a horizontal surface, and the angle between the upper surface and the lower surface is 20°-40°.

[0013] The low-sulfur coal flue gas emission system as described above, wherein the slurry recirculation device is enclosed by ribs, a plurality of rib plates are arranged on the circumference of the slurry recirculation device, and the air holes are formed between any two adjacent rib plates.

[0014] Preferably, the surface of the slurry recirculation device is provided with a corrosion-resistant layer.

[0015] The low-sulfur coal flue gas emission system as described above, wherein each spray layer is provided with a plurality of slurry nozzles, the slurry nozzles are distributed in a circle layer in the radial direction of the spray layer, and the slurry nozzles close to the axial center of the spray layer are one-way double-head nozzles.

[0016] The low-sulfur coal flue gas emission system as described above, wherein a total of 7 circle layers of slurry nozzles are arranged on the spray layer, the total number of slurry nozzles in the first circle layer and the second circle layer is 84, the total number of slurry nozzles in the third circle layer to the seventh circle layer is 84, and the slurry nozzles in the third circle layer to the seventh circle layer are one-way double-head nozzles.

[0017] The low-sulfur coal flue gas emission system as described above, wherein a flue gas inlet is arranged on the lower sidewall of the absorption tower, the flue gas inlet is located between the lowermost spray layer and the liquid surface of the slurry at the bottom, a tray is further arranged in the absorption tower, the tray is arranged between the lowermost spray layer and the flue gas inlet, and a plurality of through holes are formed in the tray.

[0018] Preferably, the opening rate of the tray is 25%-35%.

[0019] The low-sulfur coal flue gas emission system as described above, optionally, the pH value of the slurry at the bottom of the absorption tower is 5.3-5.5, and the liquid level height of the slurry at the bottom is 6-8 m;

[0020] Preferably, a sulfur dioxide gas sensor is arranged at the flue gas inlet for detecting the sulfur content at the flue gas inlet, and the emission system further comprises a controller, the sulfur dioxide gas sensor and the three circulating pumps are electrically connected to the controller, and when the sulfur content at the flue gas inlet is greater than 400 mg / Nm 3 , the controller controls the two circulating pumps corresponding to the uppermost two layers of the spray layer to operate or the three circulating pumps to operate.

[0021] The present application also provides a method for reforming a low-sulfur coal flue gas emission system, the method comprising the following steps:

[0022] Step one, the speed of the speed reducer of the circulating pump corresponding to the three spray layers is increased from bottom to top, the speed reducer of the circulating pump corresponding to the lowermost spray layer of the original absorption tower is removed, the speed reducer of the circulating pump corresponding to the middle layer spray layer is moved to the position corresponding to the lowermost spray layer, and the speed reducer of the circulating pump corresponding to the uppermost spray layer is moved to the position corresponding to the middle layer spray layer; the speed reducer of the circulating pump corresponding to the uppermost spray layer is replaced, and the speed of the replaced speed reducer is greater than the speed of the speed reducer of the circulating pump corresponding to the uppermost spray layer of the original absorption tower;

[0023] Step two, a slurry recirculation device is additionally arranged between adjacent two layers of spray layers in the absorption tower.

[0024] The method for reforming a low-sulfur coal flue gas emission system as described above, optionally, the method further comprises the following steps:

[0025] Step three, all the slurry nozzles in the central region of the spray layer are replaced with one-way double-head nozzles, and 12 one-way double-head nozzles are additionally arranged in the central region.

[0026] Preferably, in step three, the slurry nozzles in the outermost first and second circles of the spray layer are not adjusted, all the slurry nozzles in the third to seventh circles are replaced with one-way double-head nozzles, and 12 one-way double-head nozzles are additionally arranged and uniformly distributed between the third to seventh circles of the spray layer.

[0027] More preferably, the cross-sectional outer contour shape of the spray layer is circular, the spray layer is equally divided into four fan-shaped regions with the axis of the spray layer as the center, 3 one-way double-head nozzles are additionally arranged in each fan-shaped region, and 6 slurry nozzles are adjusted.

[0028] Optionally, the method for retrofitting a low-sulfur coal flue gas emission system as described above may further include the following steps:

[0029] Step 4: Install a perforated tray inside the absorption tower between the bottom spray layer and the flue gas inlet.

[0030] Beneficial effects:

[0031] (1) The low-sulfur coal flue gas emission system of the present invention is a modification of the existing absorption tower. No modification is made to the original shape of the absorption tower or other systems. It makes full use of the existing equipment capacity, with low modification cost and short system modification period.

[0032] (2) The low-sulfur coal flue gas emission system of the present invention can not only remove sulfur dioxide, but also remove dust, thereby achieving deep purification of flue gas.

[0033] (3) The low-sulfur coal flue gas emission system of the present invention has low energy consumption, no power equipment or electrical devices in the absorption tower, low system maintenance cost, and is easy to maintain and repair. Attached Figure Description

[0034] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0035] Figure 1 This is a schematic diagram of a low-sulfur coal flue gas emission system according to an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the internal structure of a portion of the absorption tower in a low-sulfur coal flue gas emission system according to an embodiment of the present invention.

[0037] Figure 3 for Figure 2 A partial cross-sectional structural diagram of the slurry recirculation unit;

[0038] Figure 4 for Figure 2 Another structural schematic diagram of the medium slurry recirculation device;

[0039] Figure 5 This is a schematic diagram showing the distribution of slurry nozzles on the spray layer in an embodiment of the present invention;

[0040] Figure 6 for Figure 5 A magnified view of a portion of the image;

[0041] Figure 7 This is a schematic diagram of the tray from another perspective in an embodiment of the present invention.

[0042] Icon labels:

[0043] 1-absorption tower; 11-spray layer; 12-slurry nozzle; 12a-new nozzle; 12b-shifted nozzle; 12c-reversed nozzle; 12d-adjusted nozzle; 13-flue gas inlet; 14-bottom slurry; 2-circulating pump; 3-slurry recirculation device; 3a-upper surface; 3b-lower surface; 31-vent hole; 32-rib plate; 33-corrosion-resistant layer; 34-notch; 4-tray; 41-through hole. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0045] The present application will be described in detail below with reference to the embodiments. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0046] The present application provides a low-sulfur coal flue gas emission system, which can realize standard emission of the desulfurization system when the low-sulfur coal, i.e., the sulfur dioxide content, is low.

[0047] As shown in Figure 1 and Figure 2 , the low-sulfur coal flue gas emission system of the present application comprises:

[0048] An absorption tower 1 is provided with three layers of spray layers 11, which are arranged in the upper inner cavity of the absorption tower 1 from top to bottom.

[0049] Three circulating pumps 2 are respectively connected to the three layers of spray layers 11 to pump out the bottom slurry 14 of the absorption tower 1 and spray through the three layers of spray layers 11. A slurry recirculation device 3 is arranged between any two adjacent spray layers 11.

[0050] The low-sulfur coal flue gas emission system of the present application is provided with a slurry recirculation device 3 between any two adjacent spray layers 11, which mainly prevents flue gas escape and effectively reduces the erosion of the tower wall. The SO2 concentration on the cross section of the absorption tower 1 is high on both sides and low in the middle, and the slurry spray density near the inner wall of the absorption tower 1 is much lower than that at the center of the absorption tower 1. At the same time, when the slurry is sprayed onto the inner wall of the absorption tower 1, a liquid film is formed along the inner wall of the absorption tower 1, and the mass transfer effect of the gas-liquid contact surface is very poor. A part of the flue gas leaves the absorption tower 1 without sufficient gas-liquid contact, which causes the "escape" of the flue gas along the inner wall of the absorption tower 1, thereby affecting the flue gas desulfurization efficiency of the entire desulfurization system. After arranging the slurry recirculation device 3, the airflow can be strengthened to flow to the center, and the formation of the flue gas corridor can be effectively avoided.

[0051] In addition, in order to ensure the uniformity of the slurry spray in the absorption tower 1, the arrangement of the slurry nozzles 12 should be uniform and meet certain coverage rate. It is unavoidable that the slurry sprayed by the slurry nozzles 12 will wash the tower wall. After arranging the slurry recirculation device 3, the washing of the tower wall can be effectively avoided and weakened.

[0052] Since part of the sprayed slurry is sprayed to the side wall of the absorption tower 1, and this part of the slurry flows to the slurry at the bottom of the absorption tower 1 along the wall of the absorption tower 1 due to gravity, it does not participate in the desulfurization reaction, that is, this part of the slurry is completely wasted. At the same time, since the slurry is sprayed by the slurry circulating pump 2 to the slurry nozzles 12 at the upper part of the absorption tower 1, part of the power of the circulating pump 2 does not play its due role, which increases the operating power consumption of the desulfurization system. Reusing the slurry sprayed to the side wall of the absorption tower 1 can improve the utilization rate of the slurry, reduce the operating power consumption of the system, and increase the performance of the desulfurization system. Therefore, the slurry recirculation device 3 is arranged in the absorption tower 1, that is, a slurry recirculation device 3 is arranged on the tower wall below each spray layer 11. After the slurry flows through the slurry recirculation device 3, the slurry is re-converged and introduced into the flue gas in the absorption tower, so that the slurry is contacted again, and the gas-liquid contact time is increased. According to the parameters and the spray amount of the original absorption tower 1, two slurry recirculation devices 3 can be arranged between the uppermost spray layer 11 and the middle spray layer 11 and between the middle spray layer 11 and the lowermost spray layer 11, respectively, so as to increase the spray amount and improve the flue gas purification efficiency.

[0053] As Figure 3 and Figure 4As shown, in an optional embodiment of the present application, the slurry recirculation device 3 is in a ring shape, and a plurality of air holes 31 are arranged at intervals in the circumferential direction of the slurry recirculation device 3, and each of the plurality of air holes 31 penetrates the upper and lower sides of the slurry recirculation device 3 in the axial direction of the slurry recirculation device 3. In this way, after the slurry at the inner wall of the absorption tower 1 flows to the slurry recirculation device 3, the slurry is re-converged and poured into the flue gas in the absorption tower 1 through the air holes 31, so that the slurry is in contact with the flue gas again, which increases the gas-liquid contact time, and effectively avoids and reduces the erosion of the slurry to the tower wall of the absorption tower 1.

[0054] In a preferred embodiment of the present application, the slurry recirculation device 3 comprises an upper surface 3a and a lower surface 3b arranged oppositely, and the air holes penetrate the upper surface 3a and the lower surface 3b, the upper surface 3a is arranged in an inclined surface, the lower surface 3b is arranged in a horizontal surface, and the included angle between the upper surface 3a and the lower surface 3b is 20°-40° (such as 20°, 25°, 30°, 35° or 40°).

[0055] In a specific embodiment of the present application, the slurry recirculation device 3 is made by surrounding with a rib, and a plurality of rib plates 32 are arranged at intervals in the circumferential direction of the slurry recirculation device 3, and each of the plurality of rib plates 32 forms an air hole 31. In this embodiment, the slurry recirculation device 3 is made by surrounding with a rib, which has a relatively simple structure and is light in quality, and is easy to assemble.

[0056] Further, a manhole is provided in the side wall of the absorption tower 1, the manhole is arranged adjacent to the slurry recirculation device 3, the slurry recirculation device 3 is correspondingly provided with a notch 34, the notch 34 penetrates the upper and lower sides of the slurry recirculation device 3 in the axial direction, and the manhole and the notch 34 can facilitate the user to install, check and maintain or replace the slurry nozzles on the spray layer. Optionally, the manhole is provided with a plurality of (preferably two or three) manholes, and the plurality of manholes are distributed in the circumferential direction of the absorption tower 1, and the notch 34 is correspondingly provided with a plurality of notches.

[0057] Preferably, the surface of the slurry recirculation device 3 is provided with a corrosion-resistant layer 33. The provision of the corrosion-resistant layer 33 can effectively prevent the slurry from corroding the slurry recirculation device 3, thereby ensuring the service life of the slurry recirculation device 3.

[0058] The present application differentiates the arrangement of the slurry nozzles 12 on the spray layer 11, mainly aiming at the non-uniformity of the flue gas flow field in the absorption tower 1, which causes the high flow velocity in the central region and the low flow velocity in the wall-attached region. The uniform arrangement of the slurry nozzles 12 on the original design of the spray layer 11 causes the mismatch between the slurry amount and the flue gas amount, the slurry amount in the central region is insufficient, and the slurry amount in the wall-attached region is not fully utilized. Therefore, the density of the slurry nozzles 12 needs to be increased at the high flow velocity region, that is, the slurry nozzles 12 are arranged more to increase the local flue gas resistance, and the number of the slurry nozzles 12 is reduced at the low flow velocity region. In this way, the flue gas velocity in the original high flow velocity region is reduced, and the flue gas velocity in the low flow velocity region is increased, so as to achieve the relative uniformity of the flow velocity in the absorption tower 1, and improve the utilization rate of the slurry, thereby improving the desulfurization performance of the system.

[0059] Through numerical simulation calculation of the absorption tower 1, the original spray layer 11 is optimized according to the numerical simulation calculation, the arrangement of the slurry nozzles 12 on the spray layer 11 is adjusted, the one-way double-head high-efficiency nozzle is locally increased in the central region of the absorption tower 1, and the coverage rate is improved, so as to further improve the desulfurization efficiency. Compared with the traditional slurry nozzle, the one-way double-head high-efficiency nozzle generates smaller atomized particle size through secondary atomization, increases the specific surface area of the liquid droplets in contact with the flue gas, and strengthens the mass transfer effect. Under the same pressure condition, the use of the high-efficiency nozzle can obtain higher desulfurization and dust removal efficiency.

[0060] As shown in Figure 5 and Figure 6 , in the optional embodiment of the present application, each spray layer 11 is provided with a plurality of slurry nozzles 12, the plurality of slurry nozzles 12 are distributed in the radial direction of the spray layer 11 in the form of a ring layer, and the slurry nozzles 12 close to the axial region of the spray layer 11 are all one-way double-head nozzles. It should be noted that the one-way double-head nozzle is a high-efficiency nozzle (i.e., a one-way double-head high-efficiency nozzle).

[0061] In the specific embodiment of the present application, there are 7 rings of slurry nozzles 12 on the spray layer 11, along the radial direction of the spray layer 11 from outside to inside, the slurry nozzles 12 in the first ring and the second ring are not adjusted, and the total number of the slurry nozzles 12 is 84, of which there are 52 slurry nozzles 12 in the first ring and 32 slurry nozzles 12 in the second ring; the original number of the slurry nozzles 12 in the third ring to the seventh ring is 72, and 12 are newly added on this basis, so that the total number of the slurry nozzles 12 is 84, of which there are 36 slurry nozzles 12 in the third ring, 24 slurry nozzles 12 in the fourth ring, 12 slurry nozzles 12 in the fifth ring, 8 slurry nozzles 12 in the sixth ring, and 4 slurry nozzles 12 in the seventh ring. And the slurry nozzles 12 in the third ring to the seventh ring are all one-way double-head high-efficiency nozzles. Such adjustment scheme improves the slurry amount and eliminates the flue gas hollow phenomenon that occurs when the original slurry nozzles are arranged.

[0062] As shown in Figure 5 and Figure 6As shown, the detailed adjustment of the nozzle scheme is as follows: the spray layer 11 is equally divided into four 90-degree sector areas, and three one-way double-head high-efficiency nozzles are added to each sector area, and six nozzles are adjusted, and the whole tower is symmetrically adjusted, and a total of twelve one-way double-head high-efficiency nozzles are added, so that the flue gas entering the absorption tower can flow relatively uniformly, and the mixing of the slurry and the flue gas is improved, which not only achieves uniform mixing and absorption, but also makes the flue gas temperature drop to the saturation temperature as soon as possible. The nozzle adjustment in each sector area is mainly in area ①, area ②, area ③, area ④ and area ⑤, and the nozzle adjustment in different sector areas is symmetrically centered on the center of the spray layer. Take the nozzle adjustment in one of the sector areas as an example for detailed description. Specifically, in area ①, one one-way double-head high-efficiency nozzle is added (i.e. new nozzle 12a), and the original nozzles in this area are shifted outward (i.e. shifted nozzle 12b) to make them evenly distributed; in area ②, one one-way double-head high-efficiency nozzle is added (i.e. new nozzle 12a), and the original nozzles in this area are shifted outward (i.e. shifted nozzle 12b) to make them staggered, and the shifting distance can be determined according to the actual size of the spray layer 11. At the same time, the length of the shifted nozzle 12b is shortened; in area ③, the positions of the two nozzles (one long pipe nozzle and one short pipe nozzle) are switched (i.e. switched nozzle 12c); in area ④, one one-way double-head high-efficiency nozzle is added (i.e. new nozzle 12b), and the original nozzles in this area are shifted outward (i.e. shifted nozzle 12b), and the length of the shifted nozzle 12b is adjusted, and the shifted nozzle 12b is adjusted from a short pipe nozzle to a long pipe nozzle; in area ⑤, the length of the nozzle is adjusted (i.e. adjusted nozzle 12d), and the nozzle is adjusted from a short pipe nozzle to a long pipe nozzle.

[0063] It should be noted that the slurry nozzles 12 on each layer of the spray layer 11 are adjusted in this manner, and will not be described again.

[0064] As shown in Figure 1 and Figure 7 In an optional embodiment of the present application, the lower side wall of the absorption tower 1 is provided with a flue gas inlet 13, and the flue gas inlet 13 is located between the lowermost spray layer 11 and the liquid surface of the bottom slurry 14; the absorption tower 1 is also provided with a tray 4, and the tray 4 is arranged between the lowermost spray layer 11 and the flue gas inlet 13, and the tray 4 is provided with a through hole 41.

[0065] Preferably, the tray 4 is arranged at an intermediate position between the lowermost spray layer 11 and the flue gas inlet 13.

[0066] In this embodiment, the tray 4 is added between the flue gas inlet 13 and the lowermost spray layer 11, and the tray 4 is a common component for increasing the efficiency of the desulfurization system, which can uniformly distribute the flue gas in the tower, prolong the desulfurization reaction time, and reduce the consumption of the device.

[0067] The flue gas enters the flue gas inlet of the absorption tower 1 to form a vortex area, and the flue gas passes through the holes of the tray from bottom to top to reduce the flow rate and uniformly pass through the spray area of the absorption tower 1. After the tray 4 is arranged, the flow rate of the gas entering the absorption tower 1 is well distributed, and most of the flow rate is within the average flow rate range; without the tray 4, the flow rate distribution range of the gas is relatively wide.

[0068] The tray 4 is arranged in the absorption tower, which is equivalent to adding a spray layer 11 to increase the spray density. In order to prevent the deflection of the flue gas, the absorption tower without the tray 4 needs to fully consider the influence of the non-uniformity of the flue gas flow rate in the absorption tower 1 on the design of the spray nozzle of the spray layer. The flue gas flow rate is non-uniform in the same cross section of the tower, and the flow rate is high in some areas and low in some areas. Therefore, compared with the absorption tower 1 without the tray 4, the tray 4 can effectively reduce the liquid / gas ratio.

[0069] The arrangement of the tray 4 can improve the utilization rate of the absorbent. Since the tray 4 can maintain a certain height of liquid film, the residence time of the flue gas in the absorption tower 1 is increased. When the gas passes through, the gas-liquid contact can fully absorb part of the pollution components in the gas, thereby effectively reducing the liquid / gas ratio, improving the utilization rate of the absorbent, and reducing the flow rate and power consumption of the circulating slurry pump 2. In addition, the arrangement of the tray 4 not only improves the absorption efficiency of the slurry for SO2, but also has a certain buffering effect. When the flue gas load changes, the operation of the absorption tower 1 is stable, and the fluctuation of the SO2 removal rate caused by the fluctuation of the boiler operation is avoided, thereby providing a reliable guarantee for stable desulfurization efficiency.

[0070] For projects with a small liquid / gas ratio, the scheme of the present application is to add a tray 4 between the flue gas inlet 13 and the lowermost spray layer 11. The distance between the flue gas inlet 13 and the lowermost spray layer 11 of the absorption tower 1 is 2.5 m or more, and there is space to add the tray 4. The opening rate of the tray 4 is 25%-35% (25%, 27%, 30%, 32% or 35%). When the opening rate of the tray 4 is 30%, the resistance is 700 Pa when three slurry circulating pumps 2 are fully opened. The addition of the tray 4 can improve the desulfurization efficiency and has a synergistic dust removal effect, but has the problem of large running resistance. When the air fan has a large wind pressure margin, this scheme can be considered.

[0071] The present application can ensure that the desulfurization process of the low-sulfur coal flue gas emission system is stably and efficiently operated by comprehensively adjusting the liquid level of the slurry in the absorption tower, the pH value of the slurry and the operation mode of the slurry circulating pump. Specifically, the pH value of the bottom slurry 14 in the absorption tower 11 is controlled to be 5.3-5.5 (such as 5.3, 5.4 or 5.5) to improve the SO2 absorption rate, and the liquid level height of the bottom slurry 14 is controlled to be 6-8 m (such as 6 m, 6.5 m, 7 m, 7.5 m or 8 m) to improve the output of the circulating pump 2 corresponding to the liquid level, enhance the nozzle atomization effect, and thus improve the desulfurization efficiency.

[0072] Further, a sulfur dioxide gas sensor is arranged at the flue gas inlet for detecting the sulfur content at the flue gas inlet, and the emission system further comprises a controller, the sulfur dioxide gas sensor and the three circulating pumps are electrically connected to the controller, and when the sulfur content at the flue gas inlet is greater than 400 mg / Nm 3 , the controller controls the two circulating pumps corresponding to the uppermost two spray layers to operate or the three circulating pumps to operate. In this way, the ultra-low emission requirement can be effectively ensured.

[0073] The present application also proposes a method for reforming a low-sulfur coal flue gas emission system, the reforming method comprising the following steps:

[0074] Step one, the speed of the speed reducer of the circulating pump corresponding to the three spray layers is increased from bottom to top, the speed reducer of the circulating pump 2 corresponding to the lowermost spray layer 11 is removed, the speed reducer of the circulating pump 2 corresponding to the middle layer spray layer 11 is shifted to the position corresponding to the lowermost spray layer 11, the speed reducer of the circulating pump 2 corresponding to the uppermost spray layer 11 is shifted to the position corresponding to the middle layer spray layer 11, the speed reducer of the circulating pump 2 corresponding to the uppermost spray layer 11 is replaced, and the speed of the replaced speed reducer is greater than the speed of the speed reducer of the circulating pump corresponding to the uppermost spray layer of the original absorption tower;

[0075] Step two, a slurry recirculation device 3 is additionally arranged between the adjacent two spray layers 11 in the absorption tower 1.

[0076] The reconstruction method of the present application shifts and replaces the speed reducer of the slurry circulating pump 2, according to the relationship that the rotation speed is in a first order relationship with the flow rate and the rotation speed is in a second order relationship with the head, the higher the rotation speed of the pump, the greater the flow rate and the head generated. A low-sulfur coal desulfurization project generally sets three slurry circulating pumps 2, A pump (corresponding to the lowermost spray layer), B pump (corresponding to the middle spray layer), and C pump (corresponding to the uppermost spray layer) with increasing head. During the reconstruction, the speed reducer of the existing A pump is removed, the speed reducer of the existing B circulating pump is shifted to the current A pump position, the speed reducer of the existing C circulating pump is shifted to the current B pump position, and the speed reducer of the uppermost slurry circulating pump C is replaced. After the reconstruction, the slurry circulating pump pressure is used to replace the flow rate, and under the condition that no efficiency-improving components are arranged in the tower, the flow rate of the corresponding slurry circulating pump 2 is improved, the existing liquid-gas ratio is improved, and the purpose of increasing the circulating slurry amount is achieved, thereby improving the desulfurization efficiency.

[0077] The reconstruction method of the present application further includes the following steps:

[0078] Further, the reconstruction method of the present application further includes the following steps:

[0079] Preferably, in step three, the outermost first and second circles of the spray layer are not adjusted, the third to seventh circles of the spray layer are replaced with single-direction double-head high-efficiency nozzles, and 12 single-direction double-head high-efficiency nozzles are added and uniformly distributed between the third to seventh circles of the spray layer.

[0080] More preferably, the cross-sectional outer contour shape of the spray layer 11 is circular, and the spray layer 11 is divided into four 90-degree fan-shaped regions with the center of the spray layer 11 as the center, three single-direction double-head high-efficiency nozzles are added to each region, and six slurry nozzles 12 are adjusted. The third aspect of the reconstruction method of the present application differentiates the arrangement of the slurry nozzles of the spray layer, can realize relatively uniform flow rate in the absorption tower, and improves the utilization rate of the slurry, thereby improving the desulfurization performance of the system. Moreover, the reconstruction method is relatively simple to operate and has low operation cost. The specific adjustment scheme of the slurry nozzles 12 can be referred to the above description, which will not be repeated here.

[0081] Further, the reconstruction method of the present application further includes the following steps:

[0082] Step four: a perforated tray is arranged between the lowermost spray layer and the flue gas inlet in the absorption tower.

[0083] The reconstruction method of the present application can make the flue gas in the absorption tower uniformly distributed by additionally arranging the perforated tray between the lowermost spray layer and the flue gas inlet, prolong the desulfurization reaction time, and reduce the device consumption. The specific arrangement of the tray can refer to the above description, and will not be described one by one here.

[0084] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A low-sulfur coal flue gas emission system, characterized in that, The emission system includes: An absorption tower, wherein three spray layers are provided inside the absorption tower, and the three spray layers are arranged from top to bottom in the upper inner cavity of the absorption tower; Three circulating pumps are connected to the three spray layers respectively to extract the slurry from the bottom of the absorption tower and spray it through the three spray layers. The speed of the reducer of the circulating pump corresponding to the three spray layers increases sequentially from bottom to top. A slurry recirculation device is provided between any two adjacent spray layers; The slurry recirculation device has a ring structure, and multiple vent holes are arranged circumferentially on the slurry recirculation device. All of the multiple vent holes penetrate the slurry recirculation device along the axial direction of the slurry recirculation device. The slurry recirculation device includes an upper surface and a lower surface arranged opposite to each other, the vent hole penetrates the upper surface and the lower surface, the upper surface is arranged as an inclined surface, the lower surface is arranged as a horizontal surface, and the included angle between the upper surface and the lower surface is 20°-40°. The slurry recirculation device is made of reinforcing bars, and multiple reinforcing plates are arranged circumferentially on the slurry recirculation device, with the ventilation hole formed between any two adjacent reinforcing plates; Each spray layer is provided with multiple slurry nozzles, which are arranged in concentric circles in the radial direction of the spray layer, and the slurry nozzles near the axial center of the spray layer are all unidirectional double-headed nozzles. The spray layer has a total of 7 rings of slurry nozzles. The spray layer is divided into four 90-degree fan-shaped areas. Along the radial direction of the spray layer from the outside to the inside, there are a total of 84 slurry nozzles. Among them, the first ring has 52 slurry nozzles, the second ring has 32 slurry nozzles, and the third to seventh rings have a total of 84 slurry nozzles. Among them, the third ring has 36 slurry nozzles, the fourth ring has 24 slurry nozzles, the fifth ring has 12 slurry nozzles, the sixth ring has 8 slurry nozzles, and the seventh ring has 4 slurry nozzles. All the slurry nozzles in the third to seventh rings are unidirectional double-headed high-efficiency nozzles.

2. The low-sulfur coal flue gas emission system as described in claim 1, characterized in that, The surface of the slurry recirculation device is provided with an anti-corrosion layer.

3. The low-sulfur coal flue gas emission system as described in any one of claims 1-2, characterized in that, The lower side wall of the absorption tower is provided with a flue gas inlet, which is located between the bottom spray layer and the liquid surface of the bottom slurry. The absorption tower is also equipped with a tray, which is located between the bottom spray layer and the flue gas inlet, and the tray has multiple through holes.

4. The low-sulfur coal flue gas emission system as described in any one of claims 3, characterized in that, The tray has an opening ratio of 25%-35%.

5. The low-sulfur coal flue gas emission system as described in any one of claims 1-2, characterized in that, The pH value of the slurry at the bottom of the absorption tower is 5.3-5.5, and the liquid level of the slurry at the bottom is 6-8m.

6. The low-sulfur coal flue gas emission system as described in any one of claims 5, characterized in that, A sulfur dioxide gas sensor is installed at the flue gas inlet to detect the sulfur content at the flue gas inlet. The emission system also includes a controller, and the sulfur dioxide gas sensor and the three circulating pumps are electrically connected to the controller. The controller determines that the sulfur content at the flue gas inlet is greater than 400 mg / Nm³. 3 The system controls the operation of either the two circulating pumps corresponding to the top two spray layers or the three circulating pumps.

7. A method for retrofitting a low-sulfur coal flue gas emission system, implemented based on any one of claims 1-6, characterized in that, The modification method includes the following steps: Step 1: The speed of the reducers of the circulating pumps corresponding to the three spray layers increases sequentially from bottom to top. Remove the reducer of the circulating pump corresponding to the bottom spray layer of the original absorption tower, move the reducer of the circulating pump corresponding to the middle spray layer to the corresponding position of the bottom spray layer, and move the reducer of the circulating pump corresponding to the top spray layer to the corresponding position of the middle spray layer; replace the reducer of the circulating pump corresponding to the top spray layer, and the speed of the replaced reducer should be greater than the speed of the original reducer of the circulating pump corresponding to the top spray layer of the absorption tower. Step 2: Install a slurry recirculation device between two adjacent spray layers inside the absorption tower; Step 3: Replace all the slurry nozzles in the central area of ​​the spray layer with unidirectional double-headed nozzles, and add 12 unidirectional double-headed nozzles in the central area. In step three, the slurry nozzles in the outermost first and second rings of the spray layer are not adjusted. All the slurry nozzles in the third to seventh rings are replaced with unidirectional double-headed nozzles, and 12 new unidirectional double-headed nozzles are added, evenly distributed between the third and seventh rings of the spray layer. The cross-sectional outer contour of the spray layer is circular. The spray layer is divided into four fan-shaped regions with the axis of the spray layer as the center. Each fan-shaped region is equipped with 3 unidirectional double-headed nozzles and 6 slurry nozzles are adjusted.

8. The method for retrofitting a low-sulfur coal flue gas emission system as described in claim 7, characterized in that, The modification method also includes the following steps: Step 4: Install a perforated tray inside the absorption tower between the bottom spray layer and the flue gas inlet.

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