Preparation method of liquid fertilizer

Abstract

The invention discloses a preparation method of a liquid fertilizer, and belongs to the technical field of compound fertilizers. The method comprises the following steps: sulfur dioxide gas is fed into a gas inlet pipe, reacts with washing liquid sprayed by a first spray head, and sequentially penetrates through an inner-layer water curtain and an outer-layer water curtain; washing liquid of the absorption tower is output to the first nozzle and the heat exchanger respectively and is heated by the heat exchanger; the washing liquid reacts with oxygen, and mixed gas is sent to a second gas inlet; heating the ammonium sulfate dilute solution in an oxidation liquid storage tank; the ammonium sulfate dilute solution is heated and concentrated in a concentrator to obtain an ammonium sulfate concentrated solution, secondary steam is sent to a condenser, condensed non-condensable gas is sent to a second gas inlet, condensed clean condensate water is sent to an oxidation liquid storage tank for heat exchange, and non-clean condensate water condensed by the condenser is sent to a heat exchanger; the second spray head sprays and washes gas, and liquid output from the inner end of the second spray head downwards flows into the lower overflow weir; and liquid in the second condensate water storage tank is output to the upper overflow weir and the second spray head. And comprehensive utilization of heat and condensate water is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of compound fertilizers, and particularly relates to a method for preparing liquid fertilizer. Background Art

[0002] The preparation process of compound fertilizer is usually as follows: preparing concentrated sulfuric acid with pyrite or sulfur, preparing phosphoric acid with concentrated sulfuric acid and phosphate rock, preparing ammonium phosphate with phosphoric acid and ammonia, and preparing compound fertilizer with ammonium phosphate or directly with phosphoric acid (with ammonia). Sulfur dioxide is produced in the process of preparing concentrated sulfuric acid, which requires tail gas treatment.

[0003] In the prior art, sulfur dioxide can first react with ammonia water, then be oxidized to obtain ammonium sulfate, and finally be concentrated.

[0004] For example, the patent with application number CN201610202087.X discloses a process for ammonia desulfurization of large furnace tail gas, which includes the following steps: Step 1: SO2 absorption The flue gas from the large furnace contacts the ammonia absorbent in the absorption tower, and the following reaction occurs: NH3+H2O+SO2=NH4HSO3 2NH3+H2O+SO2=(NH4)2SO3 2(NH4)2SO3+H2O+SO2=2NH4HSO3 During the absorption process, ammonia is continuously added to the absorption tower; Step 2: Oxidation: The absorption liquid in the absorption tower is transferred to the oxidation tower, and oxygen is added to the oxidation tower, and the following reaction occurs: 2(NH4)2SO3+O2=2(NH4)2SO4 2NH4HSO3+O2=2NH4HSO4 NH4HSO4+NH3=(NH4)2SO4 During the oxidation process, oxygen is continuously added to the oxidation tower; Step 3, Concentration and Crystallization: The oxidized absorption liquid is heated and evaporated to form a supersaturated solution, and ammonium sulfate is crystallized from the solution. After filtration and drying, ammonium sulfate is formed. The absorption liquid is heated using flue gas waste heat as a heat source; Step 4: Remove the remaining dust by using an electrostatic precipitator to absorb the remaining dust in the flue gas.

[0005] In this patent, the tail gas after the absorption tower treatment usually contains trace amounts of SO2 and ammonia, and usually needs to be washed with water to meet the emission standards. In addition, during the oxidation process, the oxidation effect is not good at room temperature, and a large amount of oxygen needs to be introduced.

[0006] For example, the patent with application number CN200810233595.X discloses a method for recycling sulfur dioxide from sulfuric acid tail gas in the phosphorus chemical industry. The present invention uses ammonia water produced by the phosphorus chemical industry as a desulfurizer, removes the tail gas SO2 that has reached the standard for sulfuric acid removal, and improves the oxidation rate of the absorption liquid subsalt [including (NH4)2SO3, NH4HSO3] (from ≥98% to ≥99.5%). The ammonium sulfate solution obtained by oxidation is directly used as the raw material for the production of compound fertilizers in the enterprise. The method of the present invention includes absorption, regeneration, oxidation and concentration steps. The present invention does not produce SO2, so there is no need for the factory to have a sulfuric acid production device, nor is there any need to add sulfuric acid; the ammonium sulfate solution is directly used as the raw material for the production of compound fertilizers in the enterprise, and there is no need to build an ammonium sulfate production device; the construction of an attached ammonia station with pressure equipment is omitted; the process flow is greatly simplified, and the investment is more economical; at the same time, the processing volume of the enterprise's byproduct ammonia water is reduced, and the economic and social benefits are significantly improved.

[0007] The patent has the following problems: steam needs to be introduced into the oxidation tower, which not only increases the amount of steam used, but also introduces water (increasing the amount of subsequent concentrated water); the absorption tower is unstable in its treatment of sulfur dioxide, and the concentration of sulfur dioxide is greater than 70 mg / m at some times. 3 ; Wastewater and exhaust gas are not treated. Summary of the invention

[0008] In order to solve the above problems, the embodiment of the present invention provides a method for preparing liquid fertilizer, which uses tail gas and ammonia gas from sulfuric acid synthesis as raw materials to prepare liquid ammonium sulfate; realizes the comprehensive utilization of heat and condensed water, and is more energy-efficient; treats condensed water and tail gas to avoid external discharge; the concentration of sulfur dioxide in the tail gas treated by the patent is less than 15mg / m 3 And the tail gas treatment effect is stable. The technical solution is as follows: An embodiment of the present invention provides a method for preparing a liquid fertilizer, the method comprising: S1: Sulfur dioxide gas is sent into the upper overflow weir 14 and downward into the air inlet pipe 13. The overflow liquid of the upper overflow weir 14 flows downward along the inner wall of the air inlet pipe 13 and contacts the gas. The gas reacts with the washing liquid sprayed by the first nozzle 15 in the air inlet pipe 13. The liquid in the air inlet pipe 13 flows downward to form an inner water curtain. The overflow liquid of the lower overflow weir 16 at the lower part of the air inlet pipe 13 forms an outer water curtain. The gas is discharged from the lower end of the air inlet pipe 13, and passes through the inner water curtain and the outer water curtain in sequence, and then passes upward through the demister 17 at the upper part of the absorption tower 1 and is discharged from the absorption tower 1. Finally, it is sent to the chimney through the fan, and ammonia water is added at the bottom of the absorption tower 1.

[0009] S2: The washing liquid at the bottom of the absorption tower 1 is output in two ways, one way is output to the first nozzle 15, and the other way is output to the heat exchanger 2. The heat exchanger 2 exchanges heat with the unclean condensed water output by the condenser 7 and heats the washing liquid to 40-55°C; the unclean condensed water after cooling is sent to the second condensate storage tank 10.

[0010] S3: The heated washing liquid is sent to the oxidation tower 3 to react with oxygen, and the dilute ammonium sulfate solution obtained by the reaction is sent to the oxidation liquid storage tank 4, and the mixed gas is sent to the second air inlet 18 of the absorption tower 1.

[0011] S4: The dilute ammonium sulfate solution is heated to 65-75° C. in the oxidizing liquid storage tank 4 and is heated by heat exchange with the clean condensed water output from the concentrator 5 ; the clean condensed water after cooling is sent to the second condensed water storage tank 10 .

[0012] S5: The heated dilute ammonium sulfate solution is heated and concentrated in the concentrator 5 to obtain a concentrated ammonium sulfate solution, the secondary steam is sent to the condenser 7, the non-condensable gas condensed by the condenser 7 is sent to the second air inlet 18, the clean condensed water condensed by the heated steam of the concentrator 5 is sent to the oxidizing liquid storage tank 4 for heat exchange, and the unclean condensed water condensed by the condenser 7 is sent to the heat exchanger 2. The concentration of the concentrated ammonium sulfate solution is 38-44wt%.

[0013] Among them, the second nozzle 19 in the second air inlet 18 sprays and washes the gas therein and the liquid output from its inner end flows downward into the lower overflow weir 16; the liquid in the second condensate storage tank 10 is output in two ways, one way is output to the upper overflow weir 14, and the other way is output to the second nozzle 19.

[0014] The concentration of ammonia water is 15-25wt%; the pH of the washing liquid output to the heat exchanger 2 in step S1 is 5.8-6.2, and the density is 1.13-1.16g / cm 3 .

[0015] The spraying amount of the first nozzle 15 is 10-25 times that of the second nozzle 19 , and the flow rate of the second nozzle 19 is 1.5-3.0 times that of the liquid inlet of the upper overflow weir 14 .

[0016] Further, in step S3, the oxidation tower 3 contains an iron ion catalyst.

[0017] The air inlet pipe 13 is arranged at the top of the absorption tower 1, and is arranged vertically downward. It is coaxially arranged with the absorption tower 1, and its lower end reaches the middle of the absorption tower 1. An upper overflow weir 14 is coaxially arranged on the outer top, and a lower overflow weir 16 is coaxially arranged on the outer bottom, and its inner diameter is greater than or equal to 1m. The upper overflow weir 14 is closed and a first air inlet 20 is arranged on the top. The diameter of the lower overflow weir 16 is 1.5-3.0 times the outer diameter of the air inlet pipe 13.

[0018] The first nozzle 15 is coaxially arranged in the lower part of the air inlet pipe 13 and is arranged vertically upward. It is a swirl nozzle and the distance between it and the lower end of the air inlet pipe 13 is 0.8-1.5m.

[0019] The second air inlet 18 is arranged in the middle of the absorption tower 1, and is arranged obliquely downward from the outside to the inside. Its inner end extends into the absorption tower 1 and is located directly above the lower overflow weir 16, and a second nozzle 19 is arranged therein.

[0020] Furthermore, a heating jacket is provided on the oxidizing liquid storage tank 4 ; the clean condensed water output by the concentrator 5 is output in two ways, one way is output to the heating jacket, and the other way is output to the boiler; the boiler provides heating steam for the concentrator 5 .

[0021] Furthermore, the clean condensed water after being cooled by the heating jacket is output in two ways, one way is output to the second condensate storage tank 10, and the other way is output to the cooling tower of the condenser 7; the cooling tower and the condenser 7 form a circulating cooling structure.

[0022] Wherein, the sulfur dioxide gas is the tail gas of synthetic sulfuric acid. The technical solution provided by the embodiment of the present invention has the following beneficial effects: (1) Comprehensive utilization of heat and condensed water is achieved, which is more energy-efficient.

[0023] (2) The condensed water and exhaust gas are treated to avoid external discharge.

[0024] (3) The tail gas treatment effect is good, and the sulfur dioxide concentration of the tail gas after treatment is less than 15mg / m 3 The exhaust gas treatment effect is stable; the ammonia content meets the emission standards.

[0025] (4) The oxidation tower is specially designed. The overflow liquid from the upper overflow weir flows along the inner wall of the inlet pipe, lowering the temperature of the gas and moistening the gas (favorable for subsequent reactions). The first nozzle contacts the gas in countercurrent and forms a mist area in the inlet pipe, which not only allows the washing liquid to fully contact the gas, but also slows down the speed of the gas to improve the effect. The liquid flowing out from the lower end of the inlet pipe forms an inner water curtain, and the overflow liquid from the lower overflow weir forms an outer water curtain. It has the following functions: First, it allows the gas to fully contact the liquid; second, the outer water curtain is basically pure water, which closes the inner water curtain to avoid the overflow of ammonia in the inner water curtain; third, the outer water curtain forms a very large absorption surface, which can absorb the ammonia overflowing from the bottom of the absorption tower; fourth, in the process of the liquid flowing downward, it fully contacts with the air to achieve cooling and avoid high-temperature decomposition of hypohalite. In addition, the air flow velocity at the lower end of the air inlet pipe suddenly decreases, allowing the gas to go upward, reducing the amount of liquid carried upward and reducing the pressure of the demister; at the same time, the mist area in the air inlet pipe diffuses to form a larger area (forming a scattered mist area, mainly in the inner water curtain, with a small amount overflowing between the inner and outer water curtains), which can prevent the mist droplets from moving upward and the gas from moving downward. The gas first passes downward through the scattered mist area, and then passes upward through the scattered mist area, achieving full contact, further reducing the speed, and expanding the gas in the vertical direction (the distribution of the mist area is not completely uniform), allowing the gas to overflow at different heights of the water curtain, further improving the effect.

[0026] (5) The temperature of the liquid in the absorption tower, heat exchanger, oxidation tower, oxidation liquid storage tank and concentrator is increased step by step to ensure the heat exchange effect.

[0027] (6) The amount of clean condensed water is large. It can be sent to the boiler before heat exchange and to the cooling tower after heat exchange. It can be flexibly adjusted according to water consumption.

[0028] (7) The heat and generation of condensed water were calculated and water balance was achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a principle block diagram of the liquid fertilizer preparation system provided by the present invention; Figure 2 is a schematic structural diagram of a system for preparing liquid fertilizer provided by an embodiment of the present invention; Figure 3 It is a schematic diagram of the structure of the absorption tower; Figure 4 The present invention is a flow chart of a method for preparing liquid fertilizer.

[0030] In the figure, 1 is an absorption tower, 2 is a heat exchanger, 3 is an oxidation tower, 4 is an oxidation liquid storage tank, 5 is a concentrator, 6 is an ammonium sulfate storage tank, 7 is a condenser, 8 is a first condensate storage tank, 9 is a third condensate storage tank, 10 is a second condensate storage tank, 11 is a water replenishment tank, 12 is a circulating pump, 13 is an air inlet pipe, 14 is an upper overflow weir, 15 is a first nozzle, 16 is a lower overflow weir, 17 is a demister, 18 is a second air inlet, 19 is a second nozzle, 20 is a first air inlet, 21 is an ammonia water inlet, 22 is an exhaust gas outlet, and 23 is a washing liquid outlet. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0032] Example 1 See also Figure 1-3 Embodiment 1 provides a system for preparing liquid fertilizer, which includes an ammonia water storage tank, an absorption tower 1, an oxidation tower 3, an ammonium sulfate storage tank 6, a fan, a chimney, a circulation pump 12, a concentrator 5, a heat exchanger 2, an oxidation liquid storage tank 4, a condenser 7, a first condensate storage tank 8, a second condensate storage tank 10, a third condensate storage tank 9 and a water replenishment tank 11. The tail gas outlet 22 of the absorption tower 1, the fan and the chimney are sequentially connected through pipelines to achieve desulfurization treatment.

[0033] Among them, the absorption tower 1 includes a demister 17, an air inlet pipe 13, an upper overflow weir 14 at the upper end of the air inlet pipe 13, a lower overflow weir 16 at the lower part of the air inlet pipe 13, a first nozzle 15 in the middle or lower part of the air inlet pipe 13, a second air inlet 18 in the middle of the absorption tower 1, and a second nozzle 19 in the second air inlet 18. The demister 17 is arranged at the upper part of the absorption tower 1, and can be specifically a wire mesh demister. The washing liquid outlet 23 at the bottom of the absorption tower 1 is connected to the circulation pump 12 through a pipeline, and the ammonia water inlet 21 at the bottom is connected to the ammonia water storage tank through a pipeline, and a tail gas outlet 22 (connected to the fan through a pipeline) is provided at the top. The air inlet pipe 13 is arranged at the top of the absorption tower 1, which is arranged vertically downward, and passes through the demister 17 downward to the middle of the absorption tower 1, and is coaxially arranged with the absorption tower 1. The upper overflow weir 14 is closed and a first air inlet 20 is provided at the top. The second air inlet 18 is arranged obliquely downward from the outside to the inside, and its inner end extends into the absorption tower 1 and is located directly above the lower overflow weir 16 .

[0034] Among them, the circulating pump 12 is divided into two outputs, one of which is connected to the cold water inlet of the heat exchanger 2 through a pipeline, and the other is connected to the first nozzle 15 through a pipeline. The hot water outlet of the heat exchanger 2, the oxidation tower 3 (specifically overflow output), the oxidation liquid storage tank 4, the concentrator 5 and the ammonium sulfate storage tank 6 are connected in sequence through pipelines; the tail gas outlet of the concentrator 5 is connected to the air inlet of the condenser 7 through a pipeline, and its steam inlet is connected to the steam network through a pipeline. Among them, the heat exchanger 2 is a common plate heat exchanger, a shell and tube heat exchanger or a heating tank. The concentrator 5 is a concentrating tank, which is provided with a steam heater. The non-condensable gas outlet of the condenser 7 and the tail gas outlet of the oxidation tower 3 are both connected to the second air inlet 18 through a pipeline. The oxidation liquid storage tank 4 is provided with a heating jacket. The inlet of the first condensate storage tank 8 is connected to the condensate outlet of the condenser 7 through a pipeline, and its outlet is connected to the hot water inlet of the heat exchanger 2 through a pipeline. The inlet of the third condensate storage tank 9 is connected to the condensate outlet of the concentrator 5 through a pipeline; the outlet of the third condensate storage tank 9 is divided into two outputs, one is connected to the inlet of the heating jacket through a pipeline, and the other is connected to the boiler of the steam network through a pipeline. The cold water outlet of the heat exchanger 2 is connected to the inlet of the second condensate storage tank 10 through a pipeline; the outlets of the heating jacket are connected to the water replenishment tank 11 through a pipeline. The outlet of the water replenishment tank 11 is divided into two outputs, one is connected to the inlet of the second condensate storage tank 10 through a pipeline, and the other is connected to the water replenishment port of the cooling tower of the condenser 7 through a pipeline. The second condensate storage tank 10 is divided into two outputs, one is connected to the upper overflow weir 14 through a pipeline, and the other is connected to the second nozzle 19 through a pipeline.

[0035] Furthermore, in the embodiment of the present invention, a pH meter and a density meter are provided at the bottom of the absorption tower 1, a thermometer is provided in the oxidation tower 3, and a density meter is provided in the concentrator 5, so as to control the production process.

[0036] The inner diameter of the air intake pipe 13 in the embodiment of the present invention is greater than or equal to 1.0 m.

[0037] The lower overflow weir 16 in the embodiment of the present invention is coaxially arranged at the lower end of the air inlet pipe 13 .

[0038] The first nozzle 15 in the embodiment of the present invention is coaxially arranged at the lower inner part of the air inlet pipe 13 and is arranged vertically upward, and is a swirl nozzle.

[0039] Specifically, the inner diameter of the absorption tower 1 in the embodiment of the present invention is 5-8 m, and the height is 10-18 m. The inner diameter of the air inlet pipe 13 is 1.5-3.0 m.

[0040] Example 2 Example 2 provides a system for preparing liquid fertilizer, and its structure is basically the same as that of Example 1. The inner diameter of the absorption tower 1 is 6m, and its height is 10m. The inner diameter of the air inlet pipe 13 is 1.8m. The inner diameter of the oxidation tower 3 is 3.5m, and its height is 10m. The diameter of the concentrator 5 is 2m, and the heat exchange area is 32m 2 The heat exchange area of ​​heat exchanger 2 is 25m 2 The heat exchange area of ​​condenser 7 is 60m 2 The volume of ammonium sulfate storage tank 6 is 50m 3 The volume of the third condensate storage tank 9 is 5m 3 The volume of the first condensate storage tank 8, the second condensate storage tank 10 and the water replenishment tank 11 is 3m 3 .

[0041] The air flow rate of the first air inlet 20 is 1.5*10 5 m 3 / h, the temperature is about 72℃, and the concentration of sulfur dioxide is 540-590mg / m 3 The concentration of sulfur dioxide at the tail gas outlet 22 is 12.9 mg / m 3 About (92-day average, highest 14.3 mg / m 3 ), the temperature is 31°C. The concentration of ammonium sulfate in the ammonium sulfate storage tank 6 is 38-44wt%, and the density is 1.18-1.21g / cm 3 , the sub-salt content is less than 0.1wt%. The temperature of the non-clean condensed water at the hot water outlet of the heat exchanger 2 is 40-55°C, and the reaction temperature of the oxidation tower 3 is 42-55°C. The temperature of the washing liquid output from the washing liquid outlet 23 is 33-35°C, the temperature of the condensed water (clean condensed water) output from the concentrator 5 is greater than 80°C, and the temperature of the condensed water (non-clean condensed water) output from the condenser 7 is greater than 60°C.

[0042] Example 3 See also Figure 1-4 Embodiment 3 provides a method for preparing liquid fertilizer, using the system disclosed in Embodiment 1, the method comprising the following steps: S1: The sulfur dioxide gas is sent into the upper overflow weir 14 and flows downward into the air inlet pipe 13. The overflow liquid of the upper overflow weir 14 flows downward along the inner wall of the air inlet pipe 13 and contacts the gas to cool and moisten. The gas reacts with the washing liquid (ammonia water and sub-salt solution, etc.) sprayed by the first nozzle 15 in the air inlet pipe 13. The liquid in the air inlet pipe 13 (including the overflow liquid of the upper overflow weir 14, the spray liquid of the first nozzle 15 and the liquid after the reaction) flows downward to form an inner water curtain. The overflow liquid of the lower overflow weir 16 at the lower part of the air inlet pipe 13 (the liquid after the spray liquid of the second nozzle 19 contacts the gas) forms an outer water curtain. The gas is discharged from the lower end of the air inlet pipe 13, and passes through the inner water curtain and the outer water curtain in sequence, then passes through the demister 17 at the upper part of the absorption tower 1 upward and is discharged from the absorption tower 1, and finally sent to the chimney through the fan. Ammonia water is added at the bottom of the absorption tower 1, and the concentration of ammonia water is 15-25wt%. In this patent, condensed water is introduced into the upper overflow weir 14 and the second nozzle 19 to dilute the washing liquid. To ensure the effect, the concentration of ammonia water is required to be relatively high, preferably 15-20wt%. Among them, sulfur dioxide gas is the tail gas of synthetic sulfuric acid, which has the characteristics of high temperature, no dust and large flow rate.

[0043] S2: The washing liquid at the bottom of the absorption tower 1 is output in two ways, one way is output to the first nozzle 15, and the other way (can be output after reaching certain requirements, the requirements are: the pH of the washing liquid is 5.8-6.2, the density is 1.13-1.16g / cm 3 Under this condition, the liquid is easy to flow, the oxidation effect in the oxidation tower 3 is good, and the amount of oxygen used can be reduced) is output to the heat exchanger 2, and the heat exchanger 2 exchanges heat with the unclean condensed water output by the condenser 7 and heats the washing liquid to 40-55°C. The unclean condensed water after cooling is sent to the second condensate storage tank 10. In this step, since the sub-salt is easy to decompose, it is best to be carried out in a closed container, and a heat exchanger is generally used for heating.

[0044] S3: The heated washing liquid is sent to the oxidation tower 3 to react with oxygen (preferably a catalyst is added, the catalyst is an iron ion catalyst, and the amount is less than 0.5%), and the dilute ammonium sulfate solution obtained by the reaction is sent to the oxidation liquid storage tank 4, and the mixed gas (including water vapor, unreacted oxygen, overflowed ammonia and sulfur dioxide produced by decomposition, etc.) is sent to the second air inlet 18 of the absorption tower 1. In this step, since the temperature is increased and the pH of the washing liquid is controlled, the conversion rate is basically 100% and the oxygen utilization rate is high.

[0045] S4: The dilute ammonium sulfate solution is heated to 65-75°C in the oxidation liquid storage tank 4, and is heated by heat exchange with the clean condensed water output from the concentrator 5; the clean condensed water after cooling is sent to the second condensed water storage tank 10. In this step, since it does not contain nitrite, it can be carried out in an open container and the solution can be stored at the same time (concentrator 5 is carried out in batches).

[0046] S5: The heated dilute ammonium sulfate solution is heated and concentrated in the concentrator 5 to obtain a concentrated ammonium sulfate solution. The secondary steam (including water vapor, ammonia and sulfur dioxide produced by decomposition, etc., with a high temperature, even if there is unconverted nitrite, it will decompose) is sent to the condenser 7, and the non-condensable gas condensed by the condenser 7 is sent to the second air inlet 18. The clean condensed water (temporarily stored in the third condensate storage tank 9) after condensation of the heated steam in the concentrator 5 is sent to the oxidizing liquid storage tank 4 for heat exchange, and the unclean condensed water (temporarily stored in the first condensate storage tank 8) after condensation by the condenser 7 is sent to the heat exchanger 2. The concentration of the concentrated ammonium sulfate solution is 38-44wt%.

[0047] The second nozzle 19 in the second air inlet 18 sprays and washes the gas therein and the liquid outputted from the inner end thereof flows downward into the lower overflow weir 16. The liquid in the second condensate storage tank 10 is outputted in two ways, one to the upper overflow weir 14 and the other to the second nozzle 19, which can be flexibly adjusted as needed.

[0048] Among them, the spraying amount of the first nozzle 15 (for the main reaction) is 10-25 times the spraying amount of the second nozzle 19, and the flow rate of the second nozzle 19 is 1.5-3.0 times the liquid inlet amount of the overflow weir 14 (less amount), ensuring water balance while ensuring the absorption effect.

[0049] The air inlet pipe 13 is arranged at the top of the absorption tower 1, and is arranged vertically downward. It is coaxially arranged with the absorption tower 1, and its lower end is to the middle of the absorption tower 1. The upper overflow weir 14 is coaxially arranged on the outer top, and the lower overflow weir 16 is coaxially arranged on the outer bottom, and its inner diameter is greater than or equal to 1m. The upper overflow weir 14 is closed and has a first air inlet 20 (for feeding sulfur dioxide gas) on its top. The diameter of the lower overflow weir 16 is 1.5-3.0 times the outer diameter of the air inlet pipe 13 to avoid the overlap of the inner water curtain and the outer water curtain, and can also control the outflow of the lower overflow weir 16. The first nozzle 15 (can be multiple, evenly distributed) is coaxially arranged at the lower part of the air inlet pipe 13, and is arranged vertically upward. It is a swirl nozzle, and the distance between it and the lower end of the air inlet pipe 13 is 0.8-1.5m. The second air inlet 18 (for sucking in the gas discharged from the oxidation tower 3 and the concentrator 5 with negative pressure) is provided in the middle of the absorption tower 1, and is arranged obliquely downward from the outside to the inside, with its inner end extending into the absorption tower 1 and located directly above the lower overflow weir 16, wherein a second nozzle 19 is provided.

[0050] Furthermore, a heating jacket is provided on the oxidation liquid storage tank 4. The clean condensed water output by the concentrator 5 is output in two ways, one way is output to the heating jacket, and the other way is output to the boiler, which can be flexibly adjusted according to needs. The boiler provides heating steam for the concentrator 5.

[0051] Furthermore, the clean condensed water (temporarily stored in the water supply tank 11) after being cooled by the heating jacket is output in two ways, one way is output to the second condensed water storage tank 10, and the other way is output to the cooling tower of the condenser 7. The cooling tower and the condenser 7 form a circulating cooling structure.

[0052] The concentration of the ammonium sulfate concentrated solution finally obtained is 38-44wt%, which meets the use standard of liquid fertilizer; the concentration of the nitrite is less than 0.1wt%.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing liquid fertilizer, characterized in that: The method comprises: S1: Sulfur dioxide gas is fed into the upper overflow weir (14) and flows downward into the air inlet pipe (13). The overflow liquid of the upper overflow weir (14) flows downward along the inner wall of the air inlet pipe (13) and contacts the gas. The gas reacts with the washing liquid sprayed from the first nozzle (15) in the air inlet pipe (13). The liquid in the air inlet pipe (13) flows downward to form an inner water curtain. The overflow liquid of the lower overflow weir (16) at the lower part of the air inlet pipe (13) forms an outer water curtain. The gas is discharged from the lower end of the air inlet pipe (13), passes through the inner water curtain and the outer water curtain in sequence, then passes upward through the demister (17) at the upper part of the absorption tower (1) and is discharged from the absorption tower (1). Finally, the gas is fed to the chimney through the fan and ammonia water is added at the bottom of the absorption tower (1). S2: The washing liquid at the bottom of the absorption tower (1) is output in two ways, one way is output to the first nozzle (15), and the other way is output to the heat exchanger (2). The heat exchanger (2) exchanges heat with the unclean condensed water output from the condenser (7) and heats the washing liquid to 40-55° C. The unclean condensed water after cooling is sent to the second condensate storage tank (10); S3: sending the heated washing liquid to the oxidation tower (3) to react with oxygen, sending the dilute ammonium sulfate solution obtained by the reaction to the oxidation liquid storage tank (4), and sending the mixed gas to the second air inlet (18) of the absorption tower (1); S4: The dilute ammonium sulfate solution is heated to 65-75° C. in the oxidation liquid storage tank (4), and is heated by heat exchange with the clean condensed water output from the concentrator (5); the clean condensed water after cooling is sent to the second condensed water storage tank (10); S5: the heated dilute ammonium sulfate solution is heated and concentrated in the concentrator (5) to obtain a concentrated ammonium sulfate solution, the secondary steam is sent to the condenser (7), the non-condensable gas condensed by the condenser (7) is sent to the second air inlet (18), the clean condensed water condensed by the heated steam of the concentrator (5) is sent to the oxidation liquid storage tank (4) for heat exchange, and the unclean condensed water condensed by the condenser (7) is sent to the heat exchanger (2), and the concentration of the concentrated ammonium sulfate solution is 38-44wt%; The second nozzle (19) in the second air inlet (18) sprays and washes the gas therein and the liquid output from its inner end flows downward into the lower overflow weir (16); the liquid in the second condensate storage tank (10) is output in two ways, one way is output to the upper overflow weir (14), and the other way is output to the second nozzle (19).

2. The method for preparing liquid fertilizer according to claim 1, characterized in that: The concentration of ammonia water is 15-25wt%; the pH of the washing liquid output to the heat exchanger (2) in step S1 is 5.8-6.2, and the density is 1.13-1.16g / cm 3 .

3. The method for preparing liquid fertilizer according to claim 1, characterized in that: The spraying amount of the first nozzle (15) is 10-25 times the spraying amount of the second nozzle (19), and the flow rate of the second nozzle (19) is 1.5-3.0 times the liquid inlet amount of the upper overflow weir (14).

4. The method for preparing liquid fertilizer according to claim 1, characterized in that: In step S3, an iron ion catalyst is present in the oxidation tower (3).

5. The method for preparing liquid fertilizer according to claim 1, characterized in that: The air inlet pipe (13) is arranged at the top of the absorption tower (1), and is arranged vertically downward. It is coaxially arranged with the absorption tower (1), and its lower end reaches the middle of the absorption tower (1). An upper overflow weir (14) is coaxially arranged on the outer top, and a lower overflow weir (16) is coaxially arranged on the outer bottom, and its inner diameter is greater than or equal to 1m; the upper overflow weir (14) is closed and a first air inlet (20) is arranged on the top; the diameter of the lower overflow weir (16) is 1.5-3.0 times the outer diameter of the air inlet pipe (13).

6. The method for preparing liquid fertilizer according to claim 1, characterized in that: The first nozzle (15) is coaxially arranged in the lower part of the air inlet pipe (13), and is arranged vertically upward. It is a swirl nozzle, and the distance between it and the lower end of the air inlet pipe (13) is 0.8-1.5m.

7. The method for preparing liquid fertilizer according to claim 1, characterized in that: The second air inlet (18) is arranged in the middle of the absorption tower (1), and is arranged obliquely downward from the outside to the inside. Its inner end extends into the absorption tower (1) and is located directly above the lower overflow weir (16), and a second nozzle (19) is arranged inside it.

8. The method for preparing liquid fertilizer according to claim 1, characterized in that: The oxidizing liquid storage tank (4) is provided with a heating jacket; the clean condensed water output by the concentrator (5) is output in two ways, one way is output to the heating jacket, and the other way is output to the boiler; the boiler provides heating steam for the concentrator (5).

9. The method for preparing liquid fertilizer according to claim 8, characterized in that: The clean condensed water after being cooled by the heating jacket is output in two ways, one way is output to the second condensed water storage tank (10), and the other way is output to the cooling tower of the condenser (7); the cooling tower and the condenser (7) form a circulating cooling structure.

10. The method for preparing liquid fertilizer according to claim 1, characterized in that: The sulfur dioxide gas is tail gas from synthetic sulfuric acid.

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