System and method for zero-discharge treatment of desulfurization wastewater for sintering and pelletizing equipment

Abstract

The present invention discloses a zero-discharge treatment system and method for desulfurization wastewater used in sintering and pelletizing roasting equipment. The system includes a flue gas purification main circuit connected to the sintering equipment or pelletizing roasting equipment and a desulfurization wastewater treatment bypass arranged in parallel with the flue gas purification main circuit. The desulfurization wastewater treatment bypass can extract flue gas with a temperature of 280 to 320°C in the flue gas purification main circuit to completely evaporate the desulfurization wastewater and return the obtained mixed flue gas to the flue gas purification main circuit after purification. The method uses the above-mentioned zero-discharge treatment system for desulfurization wastewater used in sintering and pelletizing roasting equipment to perform zero-discharge treatment of desulfurization wastewater. The zero-discharge treatment system and method for desulfurization wastewater used in sintering and pelletizing roasting equipment of the present invention can achieve zero discharge of desulfurization wastewater under the conditions of low investment cost and operation cost, stable system, and no influence on the quality and reuse of sintering / pellet ash. The investment cost can be saved by 80% compared with thermal concentration and crystallization, and the operation cost can be saved by 38%.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection treatment of sintering and pelletizing equipment, and more specifically, to a zero-discharge treatment system and method for desulfurization wastewater used in sintering and pelletizing roasting equipment. Background Art

[0002] On April 28, 2019, the Ministry of Ecology and Environment, together with the National Development and Reform Commission, the Ministry of Industry and Information Technology, the Ministry of Finance and the Ministry of Transport, jointly issued Document No. 35, "Opinions on Promoting the Implementation of Ultra-low Emissions in the Steel Industry", which stipulates that the hourly average concentrations of particulate matter, sulfur dioxide, and nitrogen oxides in the flue gas from the sintering machine head and pellet roasting shall not exceed 10, 35, and 50 mg / m3, respectively. The initial SO2 concentration in the flue gas from the sintering machine head and pellet roasting is related to the selected ore type and process. Usually, the initial SO2 concentration in the flue gas is 2000-4000 mg / Nm 3 , some can even reach 5000-6000mg / Nm 3 .

[0003] In view of the high initial SO2 concentration in the flue gas and strict emission limits, the sintering and pelletizing flue gas desulfurization must use wet desulfurization with high desulfurization efficiency, and the most commonly used wet desulfurization is limestone-gypsum wet desulfurization. Limestone-gypsum wet desulfurization has the advantages of high desulfurization efficiency and mature technology, but the disadvantage is that desulfurization wastewater is generated. In addition, the sintering and pelletizing flue gas must also meet the NO X Not more than 50mg / Nm 3 In order to meet the emission targets, an SCR denitrification device is usually installed in the flue gas purification system.

[0004] At present, there are three ways to achieve zero discharge of desulfurized wastewater: direct evaporation in the flue upstream of the main electrostatic precipitator, membrane method and thermal method of concentration and crystallization. The direct evaporation method in the flue upstream of the main electrostatic precipitator uses the original flue gas to evaporate the desulfurized wastewater, and the investment and operation costs are very low. However, the flue gas temperature here is only 120-160°C, and the desulfurized wastewater droplets cannot evaporate quickly, so they are easy to adhere to the inner wall of the flue, causing corrosion and scaling of the flue. Once a failure occurs, it will affect the normal operation of the sintering machine / pellet roasting machine. In addition, the impurities crystallized from the desulfurized wastewater will also be mixed with the ash collected by the main electrostatic precipitator, affecting the quality and reuse of the sintering / pellet ash. Although the membrane method and thermal method of concentration and crystallization have no effect on the sintering / pellet roasting equipment system, the investment and operation costs of the membrane method are very high. The investment and operation costs of the thermal method of concentration and crystallization are lower than those of the membrane method, but they are still at a high level. Summary of the invention

[0005] In view of the shortcomings of the existing technology, combined with the flue gas characteristics and flue gas purification process in the production process of sintering and pelletizing equipment, the present invention proposes a zero-emission treatment system and method for desulfurization wastewater, which can meet the zero-emission discharge requirements of desulfurization wastewater, has low investment and operating costs, high stability and does not affect the reuse of sintering / pellet ash.

[0006] To this end, one aspect of the present invention provides a zero-emission treatment system for desulfurization wastewater for sintering and pelletizing equipment, comprising a flue gas purification main circuit connected to the sintering equipment or the pelletizing equipment and a desulfurization wastewater treatment bypass arranged in parallel with the flue gas purification main circuit, wherein the desulfurization wastewater treatment bypass can extract flue gas with a temperature of 280 to 320°C in the flue gas purification main circuit to completely evaporate the desulfurization wastewater and return the resulting mixed flue gas to the flue gas purification main circuit after purification.

[0007] According to an embodiment of the zero-emission treatment system for desulfurization wastewater of sintering and pelletizing equipment of the present invention, the flue gas extraction position of the desulfurization wastewater treatment bypass is set at the outlet of the SCR denitrification unit in the main flue gas purification path, and the flue gas with a temperature of 280 to 320°C is the flue gas after denitrification.

[0008] According to an embodiment of the zero-emission treatment system for desulfurization wastewater of sintering and pelletizing equipment of the present invention, the desulfurization wastewater treatment bypass includes a desulfurization wastewater injection unit, a wastewater evaporation and dust removal unit and a wastewater evaporation and pressurization unit which are sequentially arranged in the bypass flue gas duct along the flue gas flow direction.

[0009] According to an embodiment of the zero-emission treatment system for desulfurization wastewater used for sintering and pelletizing equipment of the present invention, the desulfurization wastewater treatment bypass also includes flue baffles respectively arranged at the inlet and outlet of the bypass flue gas duct, and the desulfurization wastewater injection unit atomizes the desulfurization wastewater and sprays it into the bypass flue gas duct.

[0010] According to an embodiment of the zero-discharge treatment system for desulfurization wastewater of sintering and pelletizing equipment of the present invention, the return flue gas position of the desulfurization wastewater treatment bypass is arranged at the inlet of the induced draft unit in the flue gas purification main path.

[0011] According to an embodiment of the zero-emission treatment system for desulfurization wastewater used for sintering and pelletizing equipment of the present invention, the main flue gas purification path includes a main electrostatic precipitator unit, a main exhaust unit, a desulfurization unit, an SCR denitrification unit, an induced draft unit and a smoke exhaust unit which are sequentially arranged in the main flue gas duct along the flue gas flow direction, wherein the desulfurization wastewater entering the desulfurization wastewater treatment bypass for treatment comes from the desulfurization unit.

[0012] According to an embodiment of the zero-discharge treatment system for desulfurization wastewater of sintering and pelletizing equipment of the present invention, a rotary heat exchanger GGH and a supplementary combustion unit are further arranged in front of the SCR denitrification unit, and the desulfurization unit is a limestone-gypsum wet desulfurization tower.

[0013] Another aspect of the present invention provides a method for zero-discharge treatment of desulfurization wastewater for sintering and pelletizing equipment, and uses the above-mentioned zero-discharge treatment system for desulfurization wastewater for sintering and pelletizing equipment to perform zero-discharge treatment of desulfurization wastewater.

[0014] According to an embodiment of the zero-discharge treatment method for desulfurization wastewater of sintering and pelletizing equipment of the present invention, the desulfurization wastewater is sprayed into the desulfurization wastewater treatment bypass and flue gas with a temperature of 280-320°C is extracted from the flue gas purification main circuit to completely evaporate the desulfurization wastewater, and the obtained mixed flue gas is purified and returned to the flue gas purification main circuit for flue gas discharge, wherein the extracted flue gas volume is 5-10% of the flue gas volume of the sintering equipment or the pelletizing equipment.

[0015] According to an embodiment of the zero-discharge treatment method for desulfurization wastewater of sintering and pelletizing equipment of the present invention, the desulfurization wastewater is atomized and sprayed into a desulfurization wastewater treatment bypass for complete evaporation, and the mixed flue gas obtained is pressurized after removing the impurities in the salt, and then merged with the main flue gas in the flue gas purification main path and discharged, wherein the temperature of the pressurized flue gas is 130-180°C.

[0016] The zero-emission treatment system and method for desulfurization wastewater of sintering and pelletizing roasting equipment of the present invention can achieve zero emission of desulfurization wastewater with low investment cost and operation cost, stable system, and no influence on the quality and recycling of sintering / pellet ash. The investment cost can be saved by 80% and the operation cost can be saved by 38% compared with thermal concentration and crystallization. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic structural diagram of a zero-discharge treatment system for desulfurization wastewater used in sintering and pelletizing equipment according to an exemplary embodiment of the present invention is shown.

[0018] Description of reference numerals:

[0019] 1-sintering equipment or pellet roasting equipment, 2-main electrostatic precipitator unit, 3-main exhaust unit, 4-desulfurization unit, 5-rotary heat exchanger GGH, 6-SCR denitrification unit, 7-flue baffle, 8-desulfurization wastewater injection unit, 9-wastewater evaporation and dust removal unit, 10-wastewater evaporation and pressurization unit, 11-induced draft unit, 12-smoke exhaust unit. DETAILED DESCRIPTION

[0020] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0021] Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0022] For sintering equipment or pellet roasting equipment without flue gas purification system (such as desulfurization and denitrification), the flue gas is discharged directly into the chimney after passing through the main electrostatic precipitator and the main exhaust fan. In order to meet the ultra-low emission standards of steel enterprises, sintering equipment or pellet roasting equipment usually installs limestone-gypsum wet desulfurization equipment and SCR denitrification equipment after the main exhaust fan, and exhausts the flue gas after overcoming the resistance of the flue gas purification system through the induced draft fan. However, since the original flue gas temperature of the sintering equipment or pellet roasting equipment is only 120-160°C, it cannot meet the denitrification temperature requirements of the SCR denitrification equipment. Therefore, a rotary heat exchanger GGH and a supplementary combustion system (not shown in the figure) are usually installed in front of the SCR denitrification equipment.

[0023] Based on the problems in the prior art, the present invention combines the flue gas characteristics and flue gas purification process in the production process of sintering and pelletizing equipment to propose a zero-emission treatment system and method for desulfurization wastewater that can meet the zero-emission discharge requirements of desulfurization wastewater and has low investment and operating costs, high stability, and does not affect the reuse of sintering / pellet ash.

[0024] Figure 1 A schematic structural diagram of a zero-discharge treatment system for desulfurization wastewater used in sintering and pelletizing equipment according to an exemplary embodiment of the present invention is shown.

[0025] like Figure 1 As shown, according to an exemplary embodiment of the present invention, the zero-emission treatment system for desulfurization wastewater for sintering and pelletizing equipment includes a flue gas purification main circuit connected to the sintering equipment or the pelletizing equipment 1 and a desulfurization wastewater treatment bypass arranged in parallel with the flue gas purification main circuit, wherein the desulfurization wastewater treatment bypass can extract flue gas with a temperature of 280 to 320°C in the flue gas purification main circuit to completely evaporate the desulfurization wastewater and return the resulting mixed flue gas to the flue gas purification main circuit after purification.

[0026] The flue gas purification main circuit performs dust removal, desulfurization and denitrification on the flue gas of the sintering equipment or the pellet roasting equipment 1 and discharges the treated flue gas. The present invention provides a desulfurization wastewater treatment bypass for zero-discharge treatment of desulfurization wastewater in the flue gas purification main circuit, extracts high-temperature flue gas in the flue gas purification main circuit to evaporate desulfurization wastewater, which can not only meet the requirement of zero discharge of desulfurization wastewater, but also control low investment cost and operation cost.

[0027] like Figure 1 The main flue gas purification circuit of the present invention includes a main electrostatic precipitator unit 2, a main exhaust unit 3, a desulfurization unit 4, an SCR denitrification unit 6, an induced draft unit 11 and a smoke exhaust unit 12 which are sequentially arranged in the main flue gas duct along the flue gas flow direction.

[0028] Among them, the main electrostatic precipitator unit 2 is used to perform electrostatic precipitator treatment on the flue gas to remove suspended smoke in the flue gas, such as a main electrostatic precipitator; the main exhaust unit 3 assists the flow of the flue gas and sends the flue gas into the desulfurization unit 4 for desulfurization treatment, such as a main exhaust fan; the desulfurization unit 4 is preferably a limestone-gypsum wet desulfurization tower, and the obtained desulfurization wastewater is collected and introduced into the desulfurization wastewater treatment bypass for treatment, that is, the desulfurization wastewater entering the desulfurization wastewater treatment bypass for treatment comes from the desulfurization unit 4; the induced draft unit 11 is used to overcome the resistance of flue gas purification and send the flue gas into the smoke exhaust unit 12, such as an induced draft fan; the smoke exhaust unit 12 discharges the flue gas into the atmosphere, such as a chimney.

[0029] In addition, in order to ensure the flue gas denitration temperature of the SCR denitration unit, a rotary heat exchanger GGH 5 and a supplementary combustion unit (not shown) are also provided in front of the SCR denitration unit 6. The inlet flue gas of the SCR denitration unit 6 passes through the rotary heat exchanger GGH 5 and the outlet flue gas of the SCR denitration unit 6 also passes through the rotary heat exchanger GGH 5 to achieve heat exchange. The structure and arrangement of the rotary heat exchanger GGH belong to the prior art and will not be described in detail here.

[0030] Preferably, the flue gas extraction position of the desulfurization wastewater treatment bypass in the present invention is set at the outlet of the SCR denitrification unit 6 in the flue gas purification main path, and the flue gas with a temperature of 280-320°C is the flue gas after denitrification; the return flue gas position of the desulfurization wastewater treatment bypass is set at the inlet of the induced draft unit 11 in the flue gas purification main path, so as to merge with the main flue gas in the flue gas purification main path and then be discharged.

[0031] Specifically, the desulfurization wastewater treatment bypass includes a desulfurization wastewater injection unit 8, a wastewater evaporation and dust removal unit 9 and a wastewater evaporation and pressurization unit 10 which are sequentially arranged in the bypass flue gas duct along the flue gas flow direction. Among them, the desulfurization wastewater injection unit 8 sprays the desulfurization wastewater generated by the desulfurization unit 4 into the bypass flue gas duct, and preferably sprays it in an atomized manner to improve the evaporation efficiency and evaporation effect, such as a desulfurization wastewater spray gun; the atomized desulfurization wastewater evaporates quickly in the bypass flue gas duct and crystallizes the impurities, and the impurities are brought into the wastewater evaporation and dust removal unit 9 with the flue gas and separated and purified, so that the crystallized impurities of the desulfurization wastewater can be recovered separately without affecting the quality and reuse of the sintering / pellet ash, such as a wastewater evaporation and dust removal device; the purified flue gas is pressurized by the wastewater evaporation and pressurization unit, and then returned to the flue gas purification main road and discharged, such as a wastewater evaporation fan.

[0032] In addition, the desulfurization wastewater treatment bypass of the present invention also includes flue baffles 7 respectively arranged at the inlet and outlet of the bypass flue gas duct, which can not only realize the online maintenance of the system, but also ensure that the system will not affect the normal operation of the sintering equipment or the pellet roasting equipment 1 under accident conditions.

[0033] The zero-discharge treatment method for desulfurization wastewater of sintering and pelletizing equipment of the present invention utilizes the above-mentioned zero-discharge treatment system for desulfurization wastewater of sintering and pelletizing equipment to perform zero-discharge treatment of desulfurization wastewater.

[0034] Specifically, the desulfurized wastewater is sprayed into the desulfurized wastewater treatment bypass and the flue gas with a temperature of 280-320°C is extracted from the flue gas purification main path to completely evaporate the desulfurized wastewater, and the obtained mixed flue gas is purified and returned to the flue gas purification main path for flue gas emission. The amount of flue gas extracted from the desulfurized wastewater treatment bypass can be adjusted according to the outlet flue gas temperature of the wastewater evaporation and boosting unit to meet the exhaust gas temperature requirement. For example, the amount of flue gas extracted can be 5-10% of the flue gas amount of the sintering equipment or the pelletizing equipment 1.

[0035] In order to achieve complete evaporation, the present invention atomizes the desulfurization wastewater and sprays it into the desulfurization wastewater treatment bypass for complete evaporation, removes the impurities in the obtained mixed flue gas and then pressurizes it, and then merges with the main flue gas in the flue gas purification main path and then discharges it, wherein the temperature of the pressurized flue gas is 130-180°C, which matches the flue gas temperature at the clean flue gas outlet of the rotary heat exchanger GGH and will not affect the final exhaust temperature.

[0036] The present invention will be further described below in conjunction with specific embodiments.

[0037] 450m 2 The flue gas volume of the sintering machine head is about 1600000Nm 3 / h, the sintering flue gas enters the desulfurization unit 4, the rotary heat exchanger GGH 5 and the SCR denitrification unit 6 in sequence after passing through the main electrostatic precipitator unit 2 and the main exhaust unit 3, and overcomes the resistance of the flue gas purification system through the induced draft unit, and is finally discharged into the atmosphere through the exhaust unit 12. The design temperature of the SCR denitrification unit of the sintering machine is 320℃, and the desulfurization wastewater generated by the desulfurization unit 4 is 10t / h.

[0038] A bypass flue gas duct is led out from the outlet flue of the SCR denitrification unit, and a desulfurization wastewater injection unit 8, a wastewater evaporation and dust removal unit and a wastewater evaporation and pressure-boosting unit 10 are arranged in sequence on the bypass flue gas duct along the flue gas flow direction. When the system is operating normally, the desulfurization wastewater is sprayed into the bypass flue gas duct after being atomized by the desulfurization wastewater injection unit 8, and the flue gas with a flue gas temperature of 320°C is extracted. The atomized desulfurization wastewater evaporates quickly in the bypass flue and crystallizes the impurities. The impurities are brought into the wastewater evaporation and dust removal unit 9 along with the flue gas. The purified flue gas is pressurized by the wastewater evaporation and pressure-boosting unit 10, and then sent to the flue before the induced draft unit 11 to merge with the main flue gas, and finally discharged through the exhaust unit 12. In addition, flue baffles are arranged before the desulfurization wastewater injection unit 8 and after the wastewater evaporation and pressure-boosting unit 10, respectively, to facilitate maintenance.

[0039] After calculation, the desulfurization wastewater treatment bypass of the present invention only needs to extract 80000-120000Nm 3 / h flue gas can meet the rapid and complete evaporation of the desulfurization wastewater generated by the sintering machine. The outlet flue gas temperature of the wastewater evaporation and boosting unit 10 is about 130-180°C, which matches the net flue gas outlet temperature of the rotary heat exchanger GGH 5 and does not affect the final exhaust gas temperature. In addition, the power of the wastewater evaporation and boosting unit 10 is about 200kW.

[0040] If a thermal concentration and crystallization system is set up separately to achieve zero discharge of desulfurization wastewater, the investment is about 20 to 25 million yuan, while the initial investment of this embodiment is less than 4 million yuan, the investment cost is low and the advantages are obvious. If a thermal concentration and crystallization system is used to treat 1 ton of wastewater, the cost is about 20 yuan, and the annual wastewater treatment cost is 1.6 million yuan (calculated based on an annual operating time of 8,000 hours), while the annual wastewater treatment cost of this embodiment is about 1 million yuan, and the operating cost is also low.

[0041] Therefore, the zero-emission treatment system and method for desulfurization wastewater used in sintering and pelletizing equipment of the present invention can meet the requirement of zero-emission of desulfurization wastewater, with low investment cost and operation cost and stable system, and does not affect the quality and reuse of sintering / pellet ash, and has good promotion and application value.

[0042] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A zero-discharge treatment system for desulfurization wastewater of sintering and pelletizing equipment, characterized in that: It includes a flue gas purification main circuit connected to the sintering equipment or the pellet roasting equipment and a desulfurization wastewater treatment bypass arranged in parallel with the flue gas purification main circuit, wherein the desulfurization wastewater treatment bypass can extract the flue gas with a temperature of 280 to 320°C in the flue gas purification main circuit to completely evaporate the desulfurization wastewater and return the obtained mixed flue gas to the flue gas purification main circuit after purification; The flue gas extraction position of the desulfurization wastewater treatment bypass is set at the outlet of the SCR denitrification unit in the flue gas purification main path, and the flue gas with a temperature of 280-320°C is the flue gas after denitrification; The desulfurization wastewater treatment bypass comprises a desulfurization wastewater injection unit, a wastewater evaporation and dust removal unit and a wastewater evaporation and pressurization unit which are sequentially arranged in the bypass flue gas duct along the flue gas flow direction; The desulfurization wastewater treatment bypass further includes flue baffles respectively arranged at the inlet and outlet of the bypass flue gas duct, and the desulfurization wastewater injection unit atomizes the desulfurization wastewater and then sprays it into the bypass flue gas duct; The return flue gas position of the desulfurization wastewater treatment bypass is arranged at the inlet of the induced draft unit in the flue gas purification main path; The main flue gas purification path comprises a main electrostatic precipitator unit, a main exhaust unit, a desulfurization unit, an SCR denitrification unit, an induced draft unit and a smoke exhaust unit which are arranged in sequence in the main flue gas duct along the flue gas flow direction, wherein the desulfurization wastewater entering the desulfurization wastewater treatment bypass for treatment comes from the desulfurization unit; A rotary heat exchanger GGH and a supplementary combustion unit are also arranged in front of the SCR denitration unit, and the desulfurization unit is a limestone-gypsum wet desulfurization tower.

2. A zero-discharge treatment method for desulfurization wastewater from sintering and pelletizing equipment, characterized in that: The zero-discharge treatment system for desulfurization wastewater used in sintering and pelletizing equipment as described in claim 1 is used to carry out zero-discharge treatment of desulfurization wastewater.

3. The zero-discharge treatment method for desulfurization wastewater used in sintering and pelletizing equipment according to claim 2 is characterized in that: The desulfurization wastewater is sprayed into the desulfurization wastewater treatment bypass and flue gas with a temperature of 280-320°C is extracted from the flue gas purification main path to completely evaporate the desulfurization wastewater. The obtained mixed flue gas is purified and returned to the flue gas purification main path for flue gas discharge, wherein the amount of extracted flue gas is 5-10% of the amount of flue gas from the sintering equipment or the pelletizing equipment.

4. The zero-discharge treatment method for desulfurization wastewater used in sintering and pelletizing equipment according to claim 3 is characterized in that: The desulfurization wastewater is atomized and sprayed into the desulfurization wastewater treatment bypass for complete evaporation, and the mixed flue gas is pressurized after removing the impurities in the mixed flue gas, and then merged with the main flue gas in the flue gas purification main path and discharged, wherein the temperature of the pressurized flue gas is 130-180°C.

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