A method for purifying flue gas and brine to purify disinfectant salt

Abstract

The present invention belongs to the technical field of salt-salt separation, and relates to a method for flue gas purification and brine purification and refined disinfection salt. The process technology of the method can realize an effective brine purification process according to the change of the original brine characteristics, and can control the SO in the flue gas to purify the 2 , flue gas moisture content and other indicators and SO 3 2‑ , calcium and magnesium ions, excess alkali and solid suspended matter content, so as to reduce the content of calcium, magnesium and other impurities in disinfection salt and increase the content of NaCl in disinfection salt. The present invention effectively utilizes solid-liquid-gas waste, recycles resources, realizes limited resources, unlimited utilization, energy saving and consumption reduction, and green and low-carbon advantages.

Description

Technical Field

[0001] The invention relates to the technical field of resource utilization and environmental protection, and in particular to a method for purifying flue gas and brine to purify and refine disinfection salt. Background Art

[0002] Disinfectant salt, as a substitute for traditional chlorine disinfection products, has gradually been favored by the water treatment industry. Disinfectant salt is based on the preparation of sodium hypochlorite solution by sodium hypochlorite generator. It is a recognized, technically mature, safe and reliable water treatment disinfection product. Therefore, it is widely used in sewage treatment in hospitals and livestock and poultry processing plants, advanced oxidation treatment of industrial sewage, tap water disinfection, swimming pool water disinfection, professional breeding, catering industry and other epidemic prevention and disinfection industries. In addition, sodium hypochlorite generators for online cleaning (CIP) or online disinfection (SIP) in the food industry have also begun to be used. Due to the characteristics of good disinfection effect and low cost, chlorination disinfection technology is still the mainstream disinfection technology, but it needs to be improved and optimized in the application mode of chlorination disinfection technology. At present, large and small water plants in various parts of the country are gradually transforming to "on-site preparation of sodium hypochlorite". At present, the content of calcium, magnesium and other impurities in salt is high, which does not meet the NaCl ≥ 99.2% of disinfection salt. Therefore, it is particularly important to improve flue gas purification and brine purification technology to prepare disinfection salt.

[0003] MVR mechanical thermal compression evaporation to produce disinfection salt requires a large amount of steam. Its public works - thermal power plant, in addition to producing steam and electricity, also produces a large amount of flue gas. The composition of flue gas is N 2 , O 2 , CO 2 , H 2 O, NOx, SOx, NH 3 , acid mist, heat energy, water vapor and smoke, etc. The flue gas has a high moisture content, and the condensed water of the flue gas is highly acidic. Direct discharge into the atmosphere will pollute the environment. It is also a waste of natural resources. The flue gas is purified to obtain purified flue gas. The main components of the purified flue gas are N 2 , O 2 , CO 2 and heat.

[0004] The salt making industry uses the lime flue gas brine purification process to fully utilize the CO in the flue gas. 2 Removing impurities from brine can not only reduce the pollution of flue gas to the environment, but also recover the heat of flue gas, achieve energy conservation and emission reduction, and reuse resources. However, there are still some problems, such as:

[0005] (1) The ventilation automatic regulating ball valve or butterfly valve leaks seriously due to acid and chloride ion corrosion; the brine with qualified indicators generates insoluble calcium carbonate due to leakage, which continues to react with flue gas to generate soluble calcium bicarbonate, affecting the quality of refined brine. The static sedimentation process affects the sedimentation of salt mud, and the automatic regulating ball valve or butterfly valve is difficult to maintain.

[0006] (2) The pH value of water vapor or steam condensate in lime flue gas is ≤2. If the water vapor content is high and the flue gas is passed for a long time, a large amount of water vapor or steam condensate will enter the reaction tank with the strong power of the compressed flue gas. + Prioritizes neutralization of OH - Producing water, reducing OH - With CO 2 The reaction produces CO 3 2- Effective content.

[0007] (3) During the ventilation purification process, SO 2 Large dissolution capacity, SO 2 With OH - The reaction generates SO 3 2- , SO 3 2- With Ca 2+ Produces insoluble CaSO 3 , CaSO 3 Unstable and continues to react to form slightly soluble CaSO 4 Therefore, SO 2 The large amount of dissolution but slow reaction affects the brine purification effect and the quality of refined brine, and reduces the OH - With CO 2 CO generation 3 2- Effective content. Summary of the invention

[0008] In order to solve the problem of high content of calcium, magnesium and other impurities in disinfection salt in the prior art, the present invention aims to provide a method for flue gas purification and brine purification and refined disinfection salt, by controlling the SO 2 , flue gas moisture content and other indicators and SO 3 2- , calcium and magnesium ions, excess alkali and solid suspended matter content, so as to reduce the content of calcium, magnesium and other impurities in disinfectant salt and increase the content of NaCl in disinfectant salt.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] A method for purifying flue gas and brine to purify disinfecting salt comprises the following steps:

[0011] The first step is to purify the flue gas once: the flue gas is introduced into NH 3 Catalytic removal of NO X , the denitrification rate reaches more than 92%, and then the smoke dust is removed to obtain purified flue gas 1. The main reaction principle is as follows:

[0012] 4NH 3 +4NO+O 2 =4N 2 +6H 2 O

[0013] 4NH 3 +2NO 2 +O 2 =3N 2 +6H 2 O

[0014] Ammonia (NH 3 ) as a reducing agent, in the presence of a catalyst, the NO in the flue gas is X Reduction to N 2 And the generated water, the denitrification rate is over 92%.

[0015] Main impurity components of purified flue gas 1: SO 2 :800-1400mg / m 3 、NO:20~45mg / m 3 NH 3 :8~15mg / m 3 、Dust ≤10mg / m 3 , Acid mist: 150-200mg / m 3 , Flue gas moisture content: 1.0~6.0%, NO 2 Not to be detected.

[0016] In the second step, the flue gas is purified twice: the flue gas 1 is purified by salt mud wet desulfurization to remove desulfurization, ammonia and dust to obtain purified flue gas 2. The main reaction principle is as follows:

[0017]

[0018] SO 2 +2OH - =SO 3 2- +H 2 O

[0019] Ca 2+ +SO 3 2- =CaSO 3 ↓

[0020]

[0021] CaCO 3 +H 2 SO 3 =CaSO 3 +CO 2 ↑+H 2 O

[0022] 2CaSO 3 +O 2 =2CaSO 4 ↓

[0023] Main impurity components of purified flue gas 2: SO 2 :20~45mg / m 3 、NO:18~44mg / m 3 NH 3 :0~4mg / m 3 , Acid mist: 30~80mg / m 3 , Flue gas moisture content: 15-25%, Dust ≤ 4mg / m 3 , NO 2 Not to be detected.

[0024] The third step is to purify the flue gas three times: the purified flue gas 2 is catalytically nitric to remove trace sulfur under compression to obtain purified flue gas 3. The main reaction principle is as follows:

[0025] 4NO+3O 2 +2H 2 O=4HNO 3

[0026] 2NO+O 2 =2NO 2

[0027] 4NO 2 +O 2 +2H 2 O=4HNO 3

[0028] 2HNO 3 +3SO 2 +2H 2 O=3H 2 SO 4 +2NO

[0029] Purify the main impurities in flue gas 3: SO 2 :10~32mg / m 3 、NO≤18mg / m 3 , Acid mist: 60~120mg / m 3 , Flue gas moisture content: 10~16%, Dust ≤1.0mg / m 3 , NH 3and NO 2 Not to be detected.

[0030] Step 4: 4-time flue gas purification: The purified flue gas 3 is passed into the liquid with the additive 1 added to neutralize the hydrogen ions of the wet flue gas to obtain the purified flue gas 4. The additive 1 is mainly bicarbonate, including one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide. The main reaction principle is as follows:

[0031] CO 2 +2OH - =CO 3 2- +H 2 O

[0032] CO 2 +CO 3 2- +H 2 O=2HCO 3 -

[0033] 2H + +CO 3 2- =H 2 O+CO 2 ↑

[0034] H + +HCO 3 - =H 2 O+CO 2 ↑

[0035] H + +OH - =H 2 O

[0036] Purify the main impurities in flue gas 4: SO 2 ≤6.0mg / m 3 、NO≤10mg / m 3 , Acid mist ≤2.0mg / m 3 , Dust ≤ 0.1mg / m 3 , smoke moisture content: 10~28%.

[0037] The fifth step is the purification of raw brine flue gas method: lime milk and mother liquor are added to the raw brine to prepare first-grade brine, and the purified flue gas 4 is passed through to remove calcium to obtain purified brine and salt mud; the specific method is to add lime milk and discharged mother liquor to the raw brine to prepare first-grade brine, which is input into the annular coil, and at the same time, the automatic regulating ball valve or butterfly valve is opened to pass the purified flue gas 4 to undergo carbonization reaction, and the reaction time of the annular tube is 8 to 20 minutes, and the purified brine is transported to the top of the reaction tank, and the residual gas is discharged; the salt mud is dehydrated after 2 to 3 cycles of sedimentation-washing-sedimentation washing, and then transported to the salt mud pool of the power plant to remove the micro-chlorine to obtain purified salt mud, which is used for wet desulfurization.

[0038] Among them, the relationship between the amount of hydroxide and calcium ions in the first-grade brine is M = [nOH - / 2nCa 2+ ], 1.22≤M≤1.28; before the automatic regulating ball valve or butterfly valve is closed, deliver weak alkaline sodium carbonate or sodium bicarbonate solution for 2 to 5 minutes, and use weak alkaline solution to seal to prevent acid mist or acidic gas or liquid from corroding the ball valve or butterfly valve.

[0039] Step 6: Purified brine testing: brine purification qualification index Ca 2+ ≤5.0mg / L, Mg 2+ ≤2.0mg / L, CO 3 2- ≤0.35g / L, OH - ≤0.12g / L, SO 3 2- ≤1.0mg / L.

[0040] After the purified brine is tested and found to be qualified, the refined brine is obtained by sedimentation. The main reaction principle is as follows:

[0041] CO 2 +2OH - =H 2 O+CO 3 2-

[0042] Ca 2+ +CO 3 2- =CaCO 3 ↓

[0043] If it is unqualified, add auxiliary material 2 to react and prepare refined brine. Auxiliary material 2 is soda ash, first-grade refined brine, filtrate and flue gas.

[0044] Qualified index of refined brine: Ca 2+ ≤5.0mg / L, Mg 2+ ≤2.0mg / L, CO 3 2- ≤0.35g / L, OH -≤0.12g / L, suspended solids SS ≤1.0mg / L, SO 3 2- ≤1.0mg / L.

[0045] Step 7: The refined brine is subjected to MVR mechanical thermal compression evaporation to produce disinfectant salt. The qualified indicators of disinfectant salt are shown in the following table:

[0046]

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] It is difficult to completely remove SO from flue gas during production. 2 After the method of the present invention adopts multi-stage flue gas purification, SO 2 The low content effectively improves the efficiency of the flue gas brine purification process and improves the quality of refined brine.

[0049] The method of the present invention adopts multi-stage flue gas purification, and the acidity of the flue gas after purification is low. In addition, the weak alkaline solution sealing technology is adopted in industrial production, which greatly reduces the corrosion degree of the ball valve or butterfly valve of the equipment and reduces the maintenance cost. The refined brine has excellent quality after purification, and qualified disinfection salt products can be obtained by one evaporation, which reduces energy consumption, improves production efficiency, and realizes the transformation of waste into treasure.

[0050] The disinfection salt product prepared by the method of the present invention has extremely low calcium and magnesium contents, can avoid the generation of scale such as calcium carbonate, and prevent equipment clogging; the product does not agglomerate without adding an anti-caking agent such as potassium ferrocyanide, thereby ensuring product quality while avoiding the potential adverse effects of the anti-caking agent on the life of the sodium hypochlorite generator, water quality, and human health.

[0051] The compressed disinfectant salt product prepared by the method of the present invention has uniform particle size, a hardness range of 6-8kg, and a dissolution rate of ≤6g / min. The stability of the solubility of the sodium chloride solution required by the sodium hypochlorite generator is ensured by controlling the dissolution rate, and the disinfectant salt can be prevented from being caking during the dissolution process. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0053] Example 1 Flue gas purification 1 Purification of brine to produce disinfectant salt

[0054] Flue gas denitrification and dust removal produced by boiler combustion obtains purified flue gas 1, and the first-grade brine prepared from raw brine is passed through the purified flue gas 1, and the pH is automatically controlled online: 10.4-10.8 is the reaction end point, and the ventilation time is 7.5h. The refined brine obtained after the sedimentation of the purified brine is subjected to MVR mechanical thermal compression evaporation to produce disinfectant salt.

[0055] SCS-900 flue gas emission continuous monitor for tracking monitoring.

[0056] Table 1 Results of various indicators for flue gas purification and brine purification to produce disinfectant salt

[0057]

[0058] Example 2 Flue gas purification 2 Purification of brine to produce disinfectant salt

[0059] Flue gas produced by boiler combustion is denitrated and dusted to obtain purified flue gas 1, which is then desulfurized, deammonified and dusted to obtain purified flue gas 2. The first-level brine prepared from raw brine is passed through purified flue gas 2, and the pH is automatically controlled online: 10.4-10.8 is the reaction end point. The ventilation time is 5.5h. The refined brine obtained after the sedimentation of the purified brine is evaporated by MVR mechanical thermal compression to produce disinfectant salt.

[0060] SCS-900 flue gas emission continuous monitor for tracking monitoring.

[0061] Table 2 Results of various indicators of flue gas purification and brine purification for disinfection salt production

[0062]

[0063] Example 3 Flue Gas Purification 3 Purification of Brine to Prepare Disinfectant Salt

[0064] The flue gas produced by boiler combustion is denitrated and dusted to obtain purified flue gas 1, and then desulfurized, ammonia-removed and dust-removed to obtain purified flue gas 2. Nitrate is catalytically removed under compression to obtain purified flue gas 3. The first-level brine prepared from the original brine is passed through the purified flue gas 3, and the pH is automatically controlled online: 10.4-10.8 is the reaction end point, and the ventilation time is 3.0h to obtain purified brine. The refined brine obtained after the sedimentation of the purified brine is evaporated by MVR mechanical thermal compression to produce disinfectant salt. The SCS-900 flue gas emission continuous monitor is used for tracking and monitoring.

[0065] Table 3 Results of various indicators of flue gas purification 3 brine purification to make disinfection salt

[0066]

[0067] Example 4 Flue gas purification 4 Brine purification to produce disinfectant salt Results of various indicators

[0068] The flue gas produced by boiler combustion is denitrated and dusted to obtain purified flue gas 1, which is then desulfurized, deammonified and dusted to obtain purified flue gas 2. Purified flue gas 2 is catalytically denitrated to remove trace sulfur under compression to obtain purified flue gas 3. Purified flue gas 3 is passed into the liquid with additive 1 added to neutralize the wet flue gas hydrogen ions to obtain purified flue gas 4. The original brine is used to prepare the first-level brine to purify flue gas 4. The pH is automatically controlled online: 10.4-10.8 is the reaction end point, and the ventilation time is 2.0h to obtain purified brine. The refined brine obtained after the sedimentation of the purified brine is subjected to MVR mechanical thermal compression evaporation to produce disinfectant salt. The SCS-900 flue gas emission continuous monitor is used for tracking and monitoring.

[0069] Table 4 Results of various indicators for flue gas purification and brine purification to produce disinfection salt

[0070]

[0071] The usage of the vent valve in Examples 1, 2, 3, and 4 is shown in Table 5.

[0072] Table 5 Comparison of the degree of leakage of the vent valve due to corrosion in Examples 1, 2, 3, and 4

[0073]

[0074] The quality of the disinfectant salt prepared in Examples 1, 2, 3 and 4 is shown in Table 6.

[0075] Table 6 Comparison of disinfectant salt indicators prepared in Examples 1, 2, 3, and 4

[0076]

Claims

1. A method for purifying flue gas and brine to purify disinfectant salt, characterized in that: The steps include: The first step is to purify the flue gas once: NH3 is introduced into the flue gas to remove NO through catalysis. X , the denitrification rate reaches more than 92%, and then the smoke dust is removed to obtain purified flue gas 1; In the second step, the flue gas is purified twice: the flue gas 1 is purified by using salt mud wet desulfurization to remove sulfur, ammonia and dust to obtain purified flue gas 2; In the third step, the flue gas is purified three times: the purified flue gas 2 is catalytically nitric acid-free to remove trace sulfur under compression to obtain purified flue gas 3; Step 4: purify the flue gas 4 times: the purified flue gas 3 is passed into the liquid containing the auxiliary material 1 to neutralize the hydrogen ions of the wet flue gas to obtain the purified flue gas 4; the main impurity components of the purified flue gas 4 are: SO2≤6mg / m 3 、NO≤10mg / m 3 , Acid mist ≤2.0mg / m 3 and dust≤0.1mg / m 3 , smoke moisture content: 10~28%; the auxiliary material 1 includes one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide; The fifth step is purification by raw brine flue gas method: raw brine is added with lime milk and mother liquor to prepare first-grade brine, and purified flue gas 4 is passed through to remove calcium to obtain purified brine and salt mud; the specific method is to add lime milk and discharged mother liquor to raw brine to prepare first-grade brine, which is input into the annular coil, and the automatic regulating ball valve or butterfly valve is opened at the same time, and the amount of purified flue gas 4 is carbonized, and the reaction time of the annular tube is 8-20 minutes, and the purified brine is transported to the top of the reaction tank, and the residual gas is discharged; before the automatic regulating ball valve or butterfly valve is closed, sodium carbonate or sodium bicarbonate solution is transported for 2-5 minutes to prevent acidic gas or acidic liquid from corroding the ball valve or butterfly valve; Step 6: Purification of brine testing: If the purified brine is qualified, it is further precipitated to obtain refined brine; if it is unqualified, auxiliary material 2 is added to react and prepare refined brine; the auxiliary material 2 includes soda ash, first-grade brine, filtrate and flue gas; the qualified index of refined brine: Ca 2+ ≤5.0mg / L, Mg 2+ ≤2.0mg / L, CO3 2- ≤0.35g / L, OH - ≤0.12g / L, SS≤1.0mg / L and SO3 2- ≤1.0mg / L; Step 7: The refined brine is subjected to MVR mechanical thermal compression evaporation to produce disinfectant salt; The disinfection salt indicators are as follows: non-pressed moisture content ≤0.1%, NaCl ≥99.8%; 0.3≤pressed moisture content ≤0.7%, NaCl ≥99.2%; total calcium and magnesium ion amount ≤2.0mg / kg, iodine ≤1.0mg / kg, barium ≤15mg / kg, lead ≤0.2mg / kg, total mercury ≤0.1mg / kg, arsenic ≤0.1mg / kg, cadmium ≤0.1mg / kg, potassium ferrocyanide <1.0mg / kg, water insoluble matter ≤0.01%.

2. The method for flue gas purification and brine purification and refining disinfection salt according to claim 1, characterized in that: In the second step, the main impurity components of flue gas 2 are purified: SO2: 20~45mg / m 3 、NO:18~44mg / m 3 、NH3: 0~4mg / m 3 , Acid mist: 30~80mg / m 3 , Flue gas moisture content: 15~25% and dust ≤4mg / m 3 , NO2 shall not be detected.

3. The method for flue gas purification and brine purification and refining disinfection salt according to claim 1, characterized in that: In the third step, the main impurity components of the flue gas 3 are purified: SO2: 10~32mg / m 3 、NO≤18mg / m 3 , Acid mist: 60~120mg / m 3 , Flue gas moisture content: 10~16% and dust ≤1.0mg / m 3 , NH3 and NO2 shall not be detected.

4. The method for flue gas purification and brine purification and refined disinfection salt according to claim 1, characterized in that: In the fifth step, the amount of hydroxide and calcium ion in the first-grade brine is expressed as M=[nOH - / 2nCa 2+ ], 1.22≤M≤1.28.

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