A system and method for producing liquid salt from industrial solid waste salt

Abstract

The application discloses a system for preparing liquid salt from industrial solid waste salt, comprising n-stage washing beds, wherein n is greater than or equal to 3; each of the washing beds is equipped with an industrial solid waste salt feeding pipe, a washing liquid discharging pipe, a washing liquid circulating discharging port and a clean water feeding pipe at the top, and is provided with a washing agent feeding pipe, a washing liquid circulating feeding port and a brine discharging pipe at the bottom; in the two adjacent washing beds, the washing liquid circulating discharging port at the top of the former washing bed is connected with the washing liquid circulating feeding port at the bottom of the latter washing bed; the washing liquid circulating discharging port at the top of the last-stage washing bed is connected with the washing liquid circulating feeding port at the bottom of the first-stage washing bed, thereby forming a circulating series pipeline; after the washing agent passes through the series-connected washing beds, the organic impurities in the waste salt are separated out through the recovered washing liquid, and the waste salt is emptied after being decomposed into harmless inorganic small molecules such as carbon dioxide and water through the limo cleavage; the purified waste salt is prepared into liquid salt products and is transported out; and the application has the advantages of greenness in the whole process.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection and relates to a system and method for preparing liquid salt from industrial solid waste salt, specifically a system and method for preparing liquid salt by washing and purifying industrial solid waste salt. Background Technology

[0002] With the rapid development of the pesticide, pharmaceutical, and fine chemical industries, the purification and treatment of by-product sodium chloride solid waste salt has become a bottleneck for the sustainable development of these industries. Due to the complex composition and large quantity of organic impurities in the by-product waste salt, its treatment is difficult and often involves high-temperature incineration, which consumes a large amount of energy and is therefore costly. Consequently, waste salt washing technology has emerged in recent years. Chinese patent CN109911918A first uses an organic solvent to wash away some of the organic impurities in the waste salt, and then uses saturated brine to wash away the remaining organic impurities. In other words, some of the organic impurities in the waste salt are transferred from the solid waste salt to the saturated brine. The saturated brine is then purified using a wet catalytic oxidation method under high temperature and pressure. However, it does not explain how to treat the organic impurities washed away by the organic solvent. Chinese patent application CN110560454A uses an organic solvent and saturated brine as a composite detergent. The waste salt is first washed once in the presence of the composite detergent, then the filtered solid salt is dried. The dried solid salt is then washed again with saturated brine in a multi-stage washing process, followed by multi-stage centrifugation to obtain purified solid salt. The mother liquor from the centrifugation is treated with oxidation evaporation to obtain condensate and evaporation mother liquor. This patent application does not disclose how to oxidize the centrifuged mother liquor containing high levels of organic impurities. Furthermore, the method disclosed in this patent application has a long process flow and includes multiple centrifuges (automated equipment) for separating solid salt and mother liquor. All of the above methods leave organic impurities from the waste salt in the brine, and then oxidize the organic impurities in the brine. This method is detrimental to the purification of brine because the oxidation process involves a chemical change and inevitably requires the addition of additional oxidizing agents, such as sulfuric acid, hydrogen peroxide, and sodium chlorate. These agents will leave some oxidation byproducts in the brine, ultimately reducing the purity of sodium chloride in the brine. Summary of the Invention

[0003] Currently, methods for purifying sodium chloride from industrial waste salt inevitably introduce impurities and cannot guarantee the purity of sodium chloride. To address these issues, the present invention aims to provide a system and method for preparing liquid salt by washing and purifying industrial solid waste salt.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A system for preparing liquid salt from industrial solid waste salt includes n-stage washing beds, where n≥3; each washing bed is equipped with an industrial solid waste salt inlet pipe, a washing liquid outlet pipe, a washing liquid circulation outlet, and a clean water inlet pipe at the top, and a detergent inlet pipe, a washing liquid circulation inlet, and a brine outlet pipe at the bottom of each washing bed; in adjacent washing beds, the washing liquid circulation outlet at the top of the preceding washing bed is connected to the washing liquid circulation inlet at the bottom of the following washing bed via a washing liquid circulation pipe; the washing liquid circulation outlet at the top of the final washing bed is connected to the washing liquid circulation inlet at the bottom of the first washing bed via a washing liquid circulation pipe. The system consists of interconnected pipes forming a continuous series circulation pipeline for continuous waste salt washing operations. The detergent feed pipe of each washing bed is connected to the main detergent feed pipe, and the washing liquid discharge pipe of each washing bed is connected to the main washing liquid discharge pipe. The outlet of the main washing liquid discharge pipe is connected to the methanol recovery system, and the methanol outlet of the methanol recovery system is connected to the feed end of the detergent feed pipe. The clean water feed pipe of each washing bed is connected to the main clean water feed pipe, and the brine discharge pipe of each washing bed is connected to the main brine feed pipe. The outlet of the main brine feed pipe is connected to the de-alcoholization system, and the methanol outlet of the de-alcoholization system is connected to the feed end of the detergent feed pipe.

[0006] The number of stages in the washing bed is 3≤n≤50, preferably 4≤n≤35.

[0007] Industrial solid waste salt enters the washing bed through the industrial solid waste salt feed pipe, which is equipped with a waste salt feed valve.

[0008] Detergent enters the washing bed from the bottom through the detergent inlet pipe, which is equipped with a detergent inlet valve.

[0009] The washing liquid circulation pipeline is equipped with a washing liquid circulation valve.

[0010] The washing liquid discharge pipe is equipped with a washing liquid discharge valve.

[0011] Clean water enters the washing bed from the top through the clean water inlet pipe to dissolve the solid salt after washing. The clean water inlet pipe is equipped with a clean water inlet valve.

[0012] The brine is discharged from the bottom of the washing bed through the brine discharge pipe, which is equipped with a brine discharge valve.

[0013] The methanol recovery system includes a series of equipment and energy sources required for distillation, such as intermediate tanks, feed pumps, evaporators, distillation columns, condensers, reflux tanks, reflux pumps, storage tanks, and corresponding valves, control systems, steam, and circulating cooling water. The recovered methanol is returned to the detergent feed main. The methanol recovery system is connected to an oxygen-based cracking unit, which sends the distillation residue to the unit for catalytic oxidation purification. In the presence of oxygen, the residue is catalytically oxidized and decomposed into harmless inorganic small molecules such as carbon dioxide and water before being discharged into the air.

[0014] The described de-alcoholization system includes a series of equipment and energy sources required for distillation, such as intermediate tanks, feed pumps, evaporators, distillation columns, condensers, reflux tanks, reflux pumps, storage tanks, and corresponding valves, control systems, steam, and circulating cooling water. Methanol removed from the de-alcoholization system is returned to the detergent feed main; the de-alcoholized brine is transported as a liquid salt product.

[0015] Another object of the present invention is to provide a method for preparing liquid salt from industrial solid waste salt, comprising the following steps:

[0016] Step (1): Load the industrial solid waste salt to be treated into the washing beds of each stage;

[0017] Step (2): Open all washing beds except the last two (n-1th level washing bed B). n-1 Final stage washing bed B n The washing liquid circulation valve between (B) and the connection to the final stage washing bed (B) n The washing liquid circulation valve outside the washing liquid circulation valve between the first-stage washing bed (B1) and the n-1th-stage washing bed B n-1 Washing liquid discharge valve XD n-1 The detergent feed valve JC1 of the primary washing bed B1, and the primary washing bed B1 and the (n-1)th stage washing bed B n-1 The adjacent two-stage washing beds are connected in series to form a washing pipeline. The detergent is introduced into the first-stage washing bed B1 from the bottom and washes the industrial solid waste salt from bottom to top through the first-stage washing bed B1. Then it is discharged from the top of the first-stage washing bed B1 and enters each of the series washing beds from bottom to top, washing the industrial solid waste salt in each stage of the washing bed step by step, and then passes through the (n-1)th stage washing bed B1. n-1 The washing liquid outlet pipe discharges into the washing liquid main pipe;

[0018] After the first-stage washing bed B1 has finished washing industrial solid waste salt, open the washing liquid circulation valve between the first-stage washing bed B1 and the second-stage washing bed B2, and connect the final-stage washing bed (B1). n The washing liquid circulation valve outside the washing liquid circulation valve between the first washing bed (B1) and the first washing bed (B2) will circulate the remaining n-1 stages of the washing bed (from the second washing bed B2 to the last washing bed B). n The washing pipeline is connected in series. The detergent is introduced into the second-stage washing bed B2 from the bottom. The detergent enters each washing bed in series from bottom to top, washing the industrial solid waste salt in each washing bed step by step, and then passes through the final washing bed B in the washing pipeline. n The washing liquid outlet pipe discharges into the washing liquid main pipe; while washing the industrial solid waste salt in the washing bed step by step, the solid salt washed in the first washing bed B1 is dissolved with clean water, and the resulting washing brine enters the washing brine main pipe, and then the industrial solid waste salt to be treated is added to the first washing bed B1.

[0019] This process is repeated continuously in a cycle.

[0020] Step (3): The washing liquid in the washing liquid main pipe enters the methanol recovery system, and the methanol in the washing liquid is recovered by distillation. The distillation residue enters the oxygen cracking unit and is purified by catalytic oxidation in the presence of oxygen and catalyst.

[0021] The washing brine in the main washing brine pipe enters the de-alcoholization system, where trace amounts of methanol are removed by distillation to obtain liquid salt product.

[0022] In step (1), the industrial solid waste salt has a water content of ≤10%, a sodium chloride content of ≥97.4% (dry basis), a magnesium ion content of ≤0.2% (dry basis), a calcium ion content of ≤0.65% (dry basis), and a TOC value of 1000~100000mgC / kg (dry basis).

[0023] The specific filling method for industrial solid waste salt is as follows: close the detergent inlet valve, washing liquid outlet valve, washing liquid circulation valve, clean water inlet valve, and brine outlet valve of each washing bed, open the waste salt inlet valve of each washing bed, and load the industrial solid waste salt to be treated into each washing bed; after the waste salt is loaded, close the waste salt inlet valve.

[0024] In step (1), each washing bed is filled with industrial solid waste salt.

[0025] In step (2), the detergent is methanol. Among alcohols, methanol has the lowest boiling point and does not form an azeotrope with water, making it easy to separate and recover from the aqueous phase after subsequent water washing of the salt. However, alcohols with more than two carbon atoms, such as ethanol, have high boiling points and readily form an azeotrope with water. This results in the washing salt water only yielding an azeotrope of alcohol and water through distillation, rather than obtaining pure alcohols. Therefore, in order to form a closed-loop system for preparing liquid salt from industrial solid waste salt and recycling methanol, this invention can only use methanol.

[0026] The detergent flows from bottom to top through the washing bed, avoiding channeling caused by the liquid phase flowing from top to bottom, thus ensuring sufficient contact between the detergent and the waste salt. The residence time of the detergent in each stage of the washing bed is 1–10 minutes; the washing temperature is room temperature, and the washing pressure is 0.1 MPa–0.3 MPa (gauge pressure).

[0027] The method for preparing washing brine is as follows: After the industrial solid waste salt in a certain washing bed is washed, open the brine discharge valve and the clean water inlet valve of the washing bed, and introduce clean water. After the solid salt in the washing bed is completely dissolved, close the clean water inlet valve, and the brine enters the washing brine main pipe. After the brine in the washing bed is completely discharged, close the brine discharge valve.

[0028] The continuous cyclic washing process is as follows: the n-1 stage washing beds between the primary washing bed and the (n-1)th stage washing bed are connected in series, and the industrial solid waste salt in each stage washing bed is washed step by step; after the industrial solid waste salt in the primary washing bed in the n-1 stage washing bed is washed, the connection between the primary washing bed and its next stage washing bed is disconnected, the washed solid salt in the primary washing bed in the n-1 stage washing bed is prepared into washing brine, the washing brine is discharged, and then industrial solid waste salt is loaded; at the same time, the n-2 stage washing beds (excluding the primary washing bed) in the n-1 stage washing bed are connected in series with the remaining stage washing bed to form a new series of n-1 stage washing beds, and the industrial solid waste salt in the new series of n-1 stage washing beds is washed step by step.

[0029] Specifically, when n=3, the continuous cyclic washing is carried out in the following order: industrial solid waste salts B1 and B2 are washed step by step, industrial solid waste salts B2 and B3 are washed step by step + B1 is used to prepare washing brine, industrial solid waste salts B3 and B1 are washed step by step + B2 is used to prepare washing brine, and industrial solid waste salts B1 and B2 are washed step by step + B3 is used to prepare washing brine.

[0030] When n≥4, continuous cyclic washing is performed in the following order: B1, B2, ..., B n-1 Industrial solid waste salt is washed in stages: B2, B3, ..., B n Industrial solid waste salt is washed in stages, followed by the preparation of wash brine using B1, and then B3, ..., B... n B1 Industrial solid waste salt is washed in stages + B2 is used to prepare washing brine, ..., B1, B2, ..., B n-1 Industrial solid waste salt is washed in stages + B5 is used to prepare washing brine, ...

[0031] In step (3), the distillation column of the methanol recovery system has 10 to 15 theoretical plates, a reflux ratio of 0.1 to 0.3, and the mass fraction of methanol obtained by distillation is ≥99.95%, with a methanol recovery rate of 90% to 95%.

[0032] In the oxygen cracking unit, the catalyst is a molecular sieve catalyst supported on metal oxides as active components. The active components are one or two of copper oxide, iron oxide, nickel oxide, cobalt oxide, zinc oxide, manganese oxide, chromium oxide, yttrium oxide, cerium oxide, and lanthanum oxide. The molecular sieve support is one of HZSM-5, MCM-41, KIT-6, Y, and USY. The loading of the active components is 5-25%. The catalyst is cylindrical, honeycomb, hollow columnar, clover-shaped, or strip-shaped.

[0033] The temperature for catalytic oxidation purification is 350–450℃, and the air volume hourly space velocity is 3000–10000 h⁻¹. -1 The concentration of the distillation residue in the air after vaporization is 1000–5000 mg / m³.3 The VOC content in the gas discharged from the oxygen pyrolysis unit is ≤40 mg / m³. 3 .

[0034] The distillation column of the dealcoholization system has 25 to 40 theoretical plates and a reflux ratio of 0.5 to 2.

[0035] The liquid salt product contains 260–290 g / L of sodium chloride, ≤15 mgC / kg of TOC, and ≤10% methanol. -7 kg / L. Liquid salt can be used directly as a raw material for the production of soda ash.

[0036] In the dealcoholization system, the obtained methanol mass fraction is ≥99.95%.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] This invention employs a fixed waste salt washing device to establish a novel system for producing liquid salt from waste salt. The first-stage washing bed to the (n-1)th stage washing bed are connected in series to form a simulated moving bed. When the industrial solid waste salt in the first-stage washing bed is washed, the waste salt in the second to nth stage washing beds still contains TOC (Total Organic Carbon). Since the TOC content of the waste salt in each washing bed exhibits a tiered distribution, the original second-stage washing bed is transformed into a new first-stage washing bed, which is then connected in series with the nth-stage washing bed to maintain a constant total number of washing stages. This process is repeated to create a simulated moving washing bed. Compared to traditional processes, this invention achieves cascade washing, avoiding the centrifugal separation of waste salt and detergent during the washing process. This not only reduces the use of moving equipment such as centrifuges and agitators but also reduces detergent volatilization during centrifugation, making the process safer.

[0039] This invention can avoid the high-concentration, high-salt organic wastewater that occurs when using saturated brine and organic solvents as a mixed washing liquid, thereby avoiding the formation of secondary pollution sources and having the advantage of being green throughout the entire process.

[0040] This invention allows organic matter remaining in waste salt to remain in the washing liquid, and then uses a physical method of distillation to separate the detergent and organic impurities. This avoids the chemical changes required to treat high concentrations of organic impurities in brine, thus preventing unnecessary secondary pollution of the brine. The invention separates organic impurities from the waste salt from the washing liquid and decomposes them into harmless inorganic small molecules such as carbon dioxide and water using an oxygen-induced cracking method before releasing them into the air.

[0041] This invention converts waste salt into liquid salt for sale, avoiding the salt drying process, saving energy, and greatly shortening the waste salt treatment process, thus significantly reducing treatment costs. Attached Figure Description

[0042] Figure 1This invention relates to a system for preparing liquid salt from industrial solid waste salt;

[0043] In the diagram, B1 to B5 are washing beds, FY1 to FY5 are waste salt feed valves, JC1 to JC5 are detergent feed valves, L1 to L5 are washing liquid circulation valves, XD1 to XD5 are washing liquid discharge valves, QS1 to QS5 are clean water feed valves, and XS1 to XS5 are brine discharge valves. Detailed Implementation

[0044] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0045] Example 1

[0046] like Figure 1 As shown, a system for preparing liquid salt from industrial solid waste salt includes five washing beds B1 to B5, namely, first-stage washing bed B1, second-stage washing bed B2, third-stage washing bed B3, fourth-stage washing bed B4, and final-stage washing bed B5. Each washing bed is equipped with four connection ports at the top: top first connection port, top second connection port, top third connection port, and top fourth connection port, and three connection ports at the bottom: bottom first connection port, bottom second connection port, and bottom third connection port.

[0047] In two adjacent washing beds, the top first connection port (i.e., the washing liquid circulation outlet) of the previous washing bed is connected to the bottom first connection port (i.e., the washing liquid circulation inlet) of the next washing bed via a washing liquid circulation pipe. From the first washing bed B1 to the last washing bed B5, the washing liquid circulation pipes connecting the two adjacent washing beds are equipped with washing liquid circulation valves, numbered L1 to L4 in sequence. The top first connection port of the last washing bed B5 is connected to the bottom first connection port of the first washing bed B1 via a washing liquid circulation pipe, forming a circulating series pipeline. A washing liquid circulation valve L5 is provided in the washing liquid circulation pipe connecting the last washing bed B5 and the first washing bed B1.

[0048] The second connection port at the top of each washing bed is connected to an industrial solid waste salt feed pipe. The industrial solid waste salt enters the washing bed through the industrial solid waste salt feed pipe. The industrial solid waste salt feed pipe is equipped with a waste salt feed valve. The waste salt feed valves corresponding to washing beds B1 to B5 are FY1 to FY5 in sequence.

[0049] The second connection port at the bottom of each washing bed is connected to a detergent feed pipe. The detergent feed pipes of each washing bed are connected in parallel to the detergent feed main pipe. The detergent enters the washing bed through the detergent feed pipe. The detergent feed pipe is equipped with a detergent feed valve. The detergent feed valves corresponding to washing beds B1 to B5 are JC1 to JC5 in sequence.

[0050] Each washing bed has a washing liquid discharge pipe connected to the third connection port at the top. The washing liquid discharge pipes of each washing bed are connected in parallel to the main washing liquid discharge pipe. Each washing liquid discharge pipe is equipped with a washing liquid discharge valve, and the washing liquid discharge valves corresponding to washing beds B1 to B5 are XD1 to XD5 respectively. The outlet end of the main washing liquid discharge pipe is connected to the methanol recovery system, and the methanol outlet of the methanol recovery system is connected to the inlet end of the main washing agent feed pipe.

[0051] The fourth connection port at the top of each washing bed is connected to a clean water inlet pipe. The clean water inlet pipes of each washing bed are connected in parallel to the main clean water inlet pipe. Clean water enters the washing bed through the clean water inlet pipe to dissolve the solid salt after washing. The clean water inlet pipe is equipped with a clean water inlet valve. The clean water inlet valves corresponding to washing beds B1 to B5 are QS1 to QS5 in sequence.

[0052] Each washing bed has a brine outlet pipe connected to its bottom third connection port. These brine outlet pipes are connected in parallel to the main brine pipe. Brine is discharged from the bottom of the washing bed through these outlet pipes. Each outlet pipe is equipped with a brine outlet valve, with the valves for washing beds B1 to B5 being XS1 to XS5 respectively. The outlet end of the main brine pipe is connected to the de-alcoholization system, and the methanol outlet of the de-alcoholization system is connected to the inlet end of the detergent feed main pipe.

[0053] The methanol recovery system includes a series of equipment and energy sources required for distillation, such as intermediate tanks, feed pumps, evaporators, distillation columns, condensers, reflux tanks, reflux pumps, storage tanks, and corresponding valves, control systems, steam, and circulating cooling water. The bottom outlet of the distillation column in the methanol recovery system is connected to an oxygen-containing cracking unit. The residual liquid after recovering methanol in the distillation column enters the oxygen-containing cracking unit, where it is catalytically oxidized and decomposed into harmless inorganic small molecules such as carbon dioxide and water in the presence of oxygen before being discharged into the air.

[0054] The de-alcoholization system includes a series of equipment and energy sources required for distillation, such as intermediate tanks, feed pumps, evaporators, distillation columns, condensers, reflux tanks, reflux pumps, storage tanks and corresponding valves, control systems, steam and circulating cooling water. The de-alcoholized brine is transported as a liquid salt product.

[0055] Considering that the washing liquid entering the methanol recovery system and the washing brine entering the de-alcoholization system both contain salt, salt may be deposited during the evaporation process. Cleaning the reboiler is quite difficult. Since methanol is volatile and does not require a large heat transfer area, using an evaporation kettle instead of a reboiler can reduce equipment investment costs.

[0056] Those skilled in the art can connect the equipment in the methanol recovery system and the de-alcoholization system based on common knowledge in the field.

[0057] Example 2

[0058] In this embodiment, the industrial solid waste salt to be treated is sodium chloride solid waste salt, a by-product of herbicide production in a pesticide factory. The water content in the waste salt is 1.1%, the dry basis content of sodium chloride is 98.5%, there are no other impurity ions, and the total TOC is 87201 mgC / kg (dry basis).

[0059] Based on the system of Example 1, liquid salt is prepared from industrial solid waste salt, and the steps are as follows:

[0060] Step (1): Close all detergent feed valves JC1~JC5, all detergent discharge valves XD1~XD5, all brine discharge valves XS1~XS5, all clean water feed valves QS1~QS5, and all detergent circulation valves L1~L5. Open all waste salt feed valves FY1~FY5. Industrial solid waste salt is loaded into washing beds B1~B5 through industrial solid waste salt feed pipes. After each washing bed is full of industrial solid waste salt, close the waste salt feed valves FY1~FY5.

[0061] Step (2), B1, B2, B3, B4 industrial solid waste salt stage washing: Open washing liquid circulation valves L1, L2, L3, washing liquid discharge valve XD4, and detergent feed valve JC1, and introduce methanol from the bottom into the first washing bed B1. The methanol washes the industrial solid waste salt from bottom to top through the first washing bed B1, and then discharges from the top of the first washing bed B1. It then enters the series washing beds B2 to B4 in sequence, and washes the industrial solid waste salt from bottom to top through each washing bed. Finally, it enters the washing liquid main pipe through the washing liquid discharge valve XD4.

[0062] B2, B3, B4, B5 industrial solid waste salt staged washing + B1 preparation of washing brine: After the industrial solid waste salt in washing bed B1 is washed, close the detergent feed valve JC1 of the first-stage washing bed B1, the washing liquid circulation valve L1 connecting the first-stage washing bed B1 and the second-stage washing bed B2, and the washing liquid discharge valve XD4 of the fourth-stage washing bed B4. Open the detergent feed valve JC2 of the second-stage washing bed B2, the washing liquid circulation valve L4 connecting the fourth-stage washing bed B4 and the final-stage washing bed B5, and the washing liquid discharge valve XD5 of the final-stage washing bed B5. Methanol is introduced into the second-stage washing bed B2 from the bottom, washing the industrial solid waste salt from bottom to top through washing bed B2, and then discharged from the top of washing bed B2, sequentially entering the series-connected washing beds B3, B4, and B5, flowing from bottom to top through each washing bed. The industrial solid waste salt is washed in stages, and then enters the washing liquid main pipe through the washing liquid discharge valve XD5 of the final washing bed B5. While the industrial solid waste salt in washing beds B2, B3, B4 and B5 is washed in stages, the brine discharge valve XS1 and the clean water inlet valve QS1 of the first washing bed B1 are opened. Clean water is introduced through the clean water inlet pipe to prepare the washing brine. The salt concentration in the washing brine is controlled to be ≥27%. After the clean water has completely dissolved the solid salt washed with methanol in the first washing bed B1, the clean water inlet valve QS1 is closed. The washing brine enters the washing brine main pipe through the brine discharge pipe. After the washing brine in the first washing bed B1 is completely discharged, the brine discharge valve XS1 is closed. Then the waste salt inlet valve FY1 is opened to add the industrial solid waste salt to be treated into the first washing bed B1. Then the waste salt inlet valve FY1 is closed.

[0063] B3, B4, B5, B1: Step-by-step washing of industrial solid waste salt + B2: Preparation of washing brine: After the industrial solid waste salt washing in the second-stage washing bed B2 is completed, close the detergent feed valve JC2 of the second-stage washing bed B2, the washing liquid circulation valve L2 connecting the second-stage washing bed B2 and the third-stage washing bed B3, and the washing liquid discharge valve XD5 of the final-stage washing bed B5. Open the detergent feed valve JC3 of the third-stage washing bed B3, the washing liquid circulation valve L5 connecting the final-stage washing bed B5 and the first-stage washing bed B1, and the washing liquid discharge valve XD1 of the first-stage washing bed B1. Methanol is introduced into the third-stage washing bed B3 from the bottom, washing the industrial solid waste salt from bottom to top through the washing bed B3, and then discharged from the top of the washing bed B3, sequentially entering the series-connected washing beds B4, B5, and B1. The industrial solid waste salt is washed step by step through various washing beds from bottom to top. The washing liquid then enters the main washing liquid pipe through the washing liquid discharge valve XD1 of the first washing bed B1. While the industrial solid waste salt in washing beds B3, B4, B5 and B1 is being washed step by step, the brine discharge valve XS2 and the clean water inlet valve QS2 of the second washing bed B2 are opened. Clean water is introduced through the clean water inlet pipe to prepare the washing brine. The salt concentration in the washing brine is controlled to be ≥27%. After the clean water has completely dissolved the solid salt in washing bed B2, the clean water inlet valve QS2 is closed, and the washing brine enters the washing brine main pipe. After the washing brine in washing bed B2 is completely discharged, the brine discharge valve XS2 is closed. Then the waste salt inlet valve FY2 is opened, and the industrial solid waste salt to be treated is added to washing bed B2. Finally, the waste salt inlet valve FY2 is closed.

[0064] Similarly, the multi-stage washing beds connected in series are continuously circulated and washed according to the above process, namely, industrial solid waste salts B4, B5, B1, and B2 are washed in stages + brine is prepared by B3, industrial solid waste salts B5, B1, B2, and B3 are washed in stages + brine is prepared by B4, industrial solid waste salts B1, B2, B3, and B4 are washed in stages + brine is prepared by B5, and industrial solid waste salts B2, B3, B4, and B5 are washed in stages + brine is prepared by B1.

[0065] The washing conditions are the same for each washing bed: the washing temperature is room temperature, the washing pressure is 0.18 MPa (gauge pressure), and the residence time of methanol in the washing bed is 10 min.

[0066] Step (3): The washing liquid in the washing liquid main pipe enters the methanol recovery system. Methanol in the washing liquid is recovered by atmospheric distillation. The distillation column has 15 theoretical plates, a reflux ratio of 0.3, and the methanol mass fraction obtained by distillation is 99.96%, with a recovery rate of 93%. The methanol is returned to the detergent feed main pipe and enters the washing bed for washing industrial solid waste salts. The distillation residue enters the oxygen cracking unit (filled with HZSM-5 cylindrical catalyst loaded with 5% copper oxide and 15% cobalt oxide), and the air volume hourly velocity is controlled at 10000 h⁻¹ at a temperature of 400℃. -1The concentration of the distillation residue in the air after vaporization is 1500 mg / m³. 3 The gas discharged from the oxygen cracking unit undergoes catalytic oxidation purification treatment, resulting in VOC concentrations ≤ 40 mg / m³. 3 ;

[0067] The washing brine in the main washing brine pipe contains approximately 3% methanol. This washing brine is then connected to a de-alcoholization system. The de-alcoholization system has a distillation column with 40 theoretical plates and a reflux ratio of 2. Trace amounts of methanol are removed from the washing brine through distillation, and the resulting liquid salt product is shipped out. The liquid salt product contains 290 g / L sodium chloride and 7.2 × 10⁻⁶ methanol. -8 The concentration of methanol is 12.9 mgC / kg, and the total organic matter content (TOC) is 12.9 mgC / kg. 99.96% of the methanol obtained from the deethanolination is returned to the detergent feed manifold and fed into the washing bed for washing industrial solid waste salts.

Claims

1. A system for preparing liquid salt from industrial solid waste salt, characterized in that: It includes n-stage washing beds, where n≥3; each stage of the washing bed is equipped with an industrial solid waste salt feed pipe, a washing liquid discharge pipe, a washing liquid circulation discharge port, and a clean water feed pipe at the top, and a detergent feed pipe, a washing liquid circulation inlet, and a brine discharge pipe at the bottom of each stage of the washing bed. In two adjacent washing beds, the washing liquid circulation outlet at the top of the previous washing bed is connected to the washing liquid circulation inlet at the bottom of the next washing bed via a washing liquid circulation pipe; the washing liquid circulation outlet at the top of the last washing bed is connected to the washing liquid circulation inlet at the bottom of the first washing bed via a washing liquid circulation pipe, forming a circulating series pipeline. The detergent feed pipe of each washing bed is connected to the detergent feed main pipe, the washing liquid discharge pipe of each washing bed is connected to the washing liquid discharge main pipe, the outlet end of the washing liquid discharge main pipe is connected to the methanol recovery system, and the methanol outlet of the methanol recovery system is connected to the feed end of the detergent feed main pipe; the clean water feed pipe of each washing bed is connected to the clean water feed main pipe, the brine discharge pipe of each washing bed is connected to the brine feed main pipe, the outlet end of the brine feed main pipe is connected to the de-alcoholization system, and the methanol outlet of the de-alcoholization system is connected to the feed end of the detergent feed main pipe.

2. The system for preparing liquid salt from industrial solid waste salt according to claim 1, characterized in that: The number of stages in the washing bed is 3 ≤ n ≤ 50.

3. The system for preparing liquid salt from industrial solid waste salt according to claim 2, characterized in that: The number of stages in the washing bed is 4 ≤ n ≤ 35.

4. The system for preparing liquid salt from industrial solid waste salt according to claim 1, characterized in that: The industrial solid waste salt feed pipe is equipped with a waste salt feed valve; the detergent feed pipe is equipped with a detergent feed valve; the detergent circulation pipe is equipped with a detergent circulation valve; the detergent discharge pipe is equipped with a detergent discharge valve; the clean water feed pipe is equipped with a clean water feed valve; and the brine discharge pipe is equipped with a brine discharge valve.

5. The system for preparing liquid salt from industrial solid waste salt according to claim 1, characterized in that: The methanol recovery system is connected to the oxygen cracking unit, and the distillation residue is sent to the oxygen cracking unit for catalytic oxidation purification treatment.

6. A method for preparing liquid salt based on the system for preparing liquid salt from industrial solid waste salt as described in claim 1, characterized in that: Includes the following steps: Step (1): Load the industrial solid waste salt to be treated into the washing beds of each stage; Step (2): Open all washing liquid circulation valves except for the washing liquid circulation valve between the last two washing beds and the washing liquid circulation valve connecting the last washing bed and the first washing bed, the washing liquid discharge valve of the n-1th washing bed, and the detergent feed valve of the first washing bed. The two adjacent washing beds between the first washing bed and the n-1th washing bed are connected in series to form a washing pipeline. The detergent is introduced into the first washing bed from the bottom and washes the industrial solid waste salt from bottom to top through the first washing bed. Then it is discharged from the top of the first washing bed and enters each of the connected washing beds from bottom to top to wash the industrial solid waste salt in each washing bed step by step. Then it is discharged into the washing liquid main pipe through the washing liquid discharge pipe of the n-1th washing bed. After the first-stage washing bed for industrial solid waste salt is completed, open all washing liquid circulation valves except for the washing liquid circulation valve between the first-stage and second-stage washing beds and the washing liquid circulation valve connecting the final-stage washing bed and the first-stage washing bed. Connect the remaining n-1 stages of washing beds in series to form a washing pipeline. Introduce the detergent into the second-stage washing bed from the bottom, and then allow the detergent to enter each stage of the series from bottom to top, washing the industrial solid waste salt in each stage of the washing bed step by step. The waste salt then passes through the final-stage washing bed B in the washing pipeline. n The washing liquid outlet pipe discharges into the washing liquid main pipe; While the industrial solid waste salt in the washing bed is being washed in stages, the solid salt washed in the first washing bed is dissolved in clean water. The resulting brine enters the brine main pipe, and then the industrial solid waste salt to be treated is added to the first washing bed. This process is repeated continuously in a cycle. Step (3): The washing liquid in the washing liquid main enters the methanol recovery system, where methanol is recovered by distillation. The distillation residue enters the oxygen cracking unit for catalytic oxidation purification in the presence of oxygen and a catalyst. The VOC content in the gas discharged from the oxygen cracking unit is ≤40 mg / m³. 3 ; The washing brine in the main washing brine pipe enters the de-alcoholization system, where methanol is removed by distillation to obtain liquid salt product.

7. The method for preparing liquid salt according to claim 6, characterized in that: The industrial solid waste salt has a water content of ≤10%, a sodium chloride content of ≥97.4% dry basis, a magnesium ion content of ≤0.2% dry basis, a calcium ion content of ≤0.65% dry basis, and a TOC value of 1000~100000 mgC / kg dry basis.

8. The method for preparing liquid salt according to claim 6, characterized in that: In step (2), the detergent is methanol; the residence time of the detergent in each washing bed is 1 to 10 minutes; the washing temperature is room temperature; and the washing pressure is 0.1 MPa to 0.3 MPa gauge pressure.

9. The method for preparing liquid salt according to claim 6, characterized in that: In step (3), the distillation column of the methanol recovery system has 10 to 15 theoretical plates and a reflux ratio of 0.1 to 0.3; the distillation column of the deethanolination system has 25 to 40 theoretical plates and a reflux ratio of 0.5 to 2.

10. The method for preparing liquid salt according to claim 6, characterized in that: In step (3), the catalyst is a molecular sieve catalyst with a metal oxide as the active component; the active component is one or two of copper oxide, iron oxide, nickel oxide, cobalt oxide, zinc oxide, manganese oxide, chromium oxide, yttrium oxide, cerium oxide, and lanthanum oxide; the molecular sieve is one of HZSM-5, MCM-41, KIT-6, Y, and USY; and the loading of the active component is 5-25%. The temperature for catalytic oxidation purification is 350–450℃, and the volume hourly space velocity (VHSV) of the air is 3000–10000 h⁻¹. -1 The concentration of the distillation residue in the air after vaporization is 1000–5000 mg / m³. 3 The VOC content in the gas discharged from the oxygen pyrolysis unit is ≤40 mg / m³. 3 .

11. The method for preparing liquid salt according to claim 6, characterized in that: In step (3), the liquid salt product contains 260–290 g / L of sodium chloride, ≤15 mgC / kg of TOC, and ≤10 mgC / kg of methanol. -7 kg / L.

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