Chlorine drying waste sulfuric acid continuous dilution recovery system and control method thereof

Abstract

This invention discloses a continuous dilution and recovery system for chlorine-dried waste sulfuric acid and its control method, belonging to the technical field of waste sulfuric acid resource utilization in the chlor-alkali industry. The system includes a raw material supply unit, an enamel-lined kettle, a compressed air stirring and circulating cooling system, an external circulation heat exchanger, a reflux branch, a collection branch, a high-level dilute acid tank, and an automatic control unit. Chlorine-containing waste sulfuric acid with a sulfuric acid mass fraction of 75% is continuously fed into the enamel-lined kettle with production water at a mass flow ratio of 2:1 for mixing and dilution. After external circulation heat exchange, the mixture is divided; a portion is refluxed, and the other portion is collected as a product with a sulfuric acid mass fraction of approximately 50%. Closed-loop and interlocking control is implemented using temperature, concentration, and liquid level signals. This invention enables continuous, safe, and stable dilution and resource utilization of chlorine-containing waste sulfuric acid.

Description

Technical Field

[0001] This invention relates to the field of waste sulfuric acid resource utilization technology in the chlor-alkali industry, and more specifically, to a continuous dilution and recovery system and control method for chlorine-dried waste sulfuric acid. Background Technology

[0002] In the chlor-alkali production process, the chlorine drying section typically uses concentrated sulfuric acid with a mass fraction of approximately 98% to absorb moisture from the chlorine gas. After absorbing the moisture, the sulfuric acid mass fraction decreases to approximately 75%, and a small amount of chlorine gas dissolves, forming 75% chlorine-containing waste sulfuric acid. Because this waste sulfuric acid contains impurities such as chlorine, it is currently treated as hazardous waste in production, incurring corresponding disposal costs for the company and resulting in a waste of sulfur resources.

[0003] To recycle and utilize this byproduct waste sulfuric acid, some companies further dilute the chlorine-containing waste sulfuric acid (approximately 75% by mass) to about 50%, storing or selling it as a dilute sulfuric acid product. Current production methods typically employ intermittent preparation in enamel-lined reactors. A certain amount of water is first added to the reactor, followed by the slow addition of waste sulfuric acid, with manual operation and stirring to mix the acid and water. For example, using a 3m³ enamel-lined reactor, each reactor typically prepares 3 to 4 tons of dilute sulfuric acid, with a single reactor preparation time of approximately 2 hours. When preparing 30 tons of product, 8 to 10 reactor operations are usually required, with a total time of approximately 16 to 20 hours.

[0004] The above-mentioned intermittent dilution process has at least the following problems:

[0005] First, production continuity and efficiency are low. Due to the limitations of the effective volume of the enamel-lined reactor and the batch operation mode, after each batch of materials is completed, it is necessary to transfer, clean, or re-batch the materials, which makes it impossible to form a stable continuous feeding and continuous output. The production cycle is long and it is difficult to flexibly arrange production according to product demand.

[0006] Secondly, the operation is not very safe. When sulfuric acid is mixed with water, it releases a large amount of heat of dilution. During the manual addition of water and acid and stirring, operators need to be close to or in contact with highly corrosive materials. If the feeding speed, feeding sequence, or stirring is uneven, local high-temperature areas can easily form inside the reactor, leading to problems such as acid splashing, acid mist generation, and localized corrosion of the equipment.

[0007] Third, the stability of product concentration control is insufficient. The existing process mainly relies on manual metering, manual adjustment of feeding speed and batch stirring. The feed rate, mixing state and heat dissipation conditions are prone to change with the operator and operating conditions, resulting in fluctuations in the sulfuric acid mass fraction of the final dilute sulfuric acid product, making it difficult to consistently meet product quality requirements.

[0008] Fourth, there is a lack of continuous interlocking control for temperature and liquid level. Intermittent enamel-lined reactors typically control the results of single-reactor preparations, lacking continuous monitoring and linkage adjustment of the reactor temperature, external cooling status, product storage tank level, and abnormal operating conditions during the dilution process. When cooling capacity decreases or the storage tank approaches a high liquid level, timely adjustments cannot be made through reflux, material reduction, or stopping sampling.

[0009] In the prior art, CN103127873B discloses a continuous automatic dilution device and method for concentrated sulfuric acid. The device includes a controller, a concentrated sulfuric acid and water metering and feeding device, a mixing device, a cooling device, a sulfuric acid concentration detection device, and a dilute sulfuric acid tank. Continuous dilution of concentrated sulfuric acid is achieved through metering feeding, heat exchange cooling, and concentration detection. (CN103127873B disclosure text)

[0010] This technology is mainly for the continuous mixing and dilution of concentrated sulfuric acid with a mass fraction of approximately 98% and water. The properties of its raw materials, feed conditions and process conditions are different from those of the chlorine-containing waste sulfuric acid produced in the chlorine drying section. It does not include process configuration for the continuous treatment of chlorine-containing by-product waste sulfuric acid, external circulation cooling of the enamel kettle, reflux after heat exchange and product sampling and diversion.

[0011] Therefore, there is an urgent need to provide a continuous dilution and recovery system and control methods for chlorine-dried waste sulfuric acid to solve the above problems. Summary of the Invention

[0012] The purpose of this invention is to solve the technical problems mentioned in the background section, and to provide a continuous dilution and recovery system and control method for chlorine drying waste sulfuric acid.

[0013] The above-mentioned objective of the present invention is achieved as follows: a continuous dilution and recovery system for chlorine drying waste sulfuric acid, used to continuously dilute chlorine-containing waste sulfuric acid with a sulfuric acid mass fraction of 75% generated in the chlorine drying section into a dilute sulfuric acid product with a sulfuric acid mass fraction of 50%, comprising a raw material supply unit, a dilution and mixing unit, an external circulation cooling and distribution unit, a product storage unit and an automatic control unit.

[0014] The raw material supply unit includes a 75% waste sulfuric acid feed pump, a 75% waste sulfuric acid flow meter, a production water supply pipeline, a production water flow meter, an acid feed regulating valve, and a water feed regulating valve.

[0015] The dilution and mixing unit includes an enamel-lined kettle, a compressed air stirring system, a circulating water cooling system, and a circulating cooling water regulating valve. The circulating water cooling system is connected to the jacket or coil of the enamel-lined kettle.

[0016] The external circulation cooling and distribution unit includes a 50% acid transfer pump, a heat exchanger, an external circulation pipeline, a reflux regulating valve, and a 50% sulfuric acid regulating valve. The heat exchanger is connected to the circulating cooling water pipeline. The external circulation pipeline is sequentially connected to the outlet of the enamel-lined reactor, the 50% acid transfer pump, and the heat exchanger. The outlet of the heat exchanger is connected to a reflux branch and a sampling branch. The reflux branch is connected to the enamel-lined reactor via the reflux regulating valve, and the sampling branch is connected to the product storage unit via the 50% sulfuric acid regulating valve.

[0017] The product storage unit includes a dilute acid high-level tank and a level gauge;

[0018] The automatic control unit is connected to the 75% waste sulfuric acid flow meter, the production water flow meter, the first temperature detection element installed in the enamel kettle, the second temperature detection element installed at the heat exchanger outlet, the level gauge, the acid feed regulating valve, the water feed regulating valve, the circulating cooling water regulating valve, the reflux regulating valve, and the 50% sulfuric acid regulating valve, respectively. It is used to control the feed ratio of 75% chlorine-containing waste sulfuric acid and production water according to the flow detection signal, control the circulating cooling water regulating valve, the reflux regulating valve, and the 50% sulfuric acid regulating valve according to the temperature detection signal, and control the product output according to the level detection signal.

[0019] As a preferred technical solution of the present invention, the 75% waste sulfuric acid flow meter and the production water flow meter are used to detect the mass flow rate of the corresponding materials. The automatic control unit controls the mass flow rate F1 of 75% chlorine-containing waste sulfuric acid and the mass flow rate F2 of production water according to the mass flow rate to satisfy: 75%×F1=50%×(F1+F2), so that F1:F2=2:1.

[0020] As a preferred technical solution of the present invention, the volume of the enamel-lined kettle is 3m3, the compressed air stirring system is used to continuously mix 75% chlorine-containing waste sulfuric acid and production water in the enamel-lined kettle, and the circulating water cooling system is used to remove the dilution heat generated during the dilution process through the jacket or coil.

[0021] As a preferred technical solution of the present invention, the heat exchanger is used to forcibly cool the dilute sulfuric acid flowing out of the enamel-lined kettle by circulating cooling water. The automatic control unit adjusts the reflux regulating valve to allow part of the dilute sulfuric acid cooled by the heat exchanger to flow back to the enamel-lined kettle so that the temperature of the dilute sulfuric acid in the enamel-lined kettle does not exceed 45°C, and controls the output of the dilute sulfuric acid product by adjusting the 50% sulfuric acid regulating valve.

[0022] As a preferred technical solution of the present invention, the dilute acid high-level tank is a fiberglass storage tank with a volume of 25m3; the automatic control unit performs high and low liquid level interlock control according to the detection signal of the liquid level gauge: when the liquid level of the dilute acid high-level tank reaches the set high limit, the opening of the 50% sulfuric acid regulating valve is reduced or the 50% sulfuric acid regulating valve is closed; when the liquid level of the dilute acid high-level tank reaches the set low limit, the product output is reduced or the feed rate is increased.

[0023] As a preferred technical solution of the present invention, an online sulfuric acid concentration detector is installed at the heat exchanger outlet or on the extraction branch. The online sulfuric acid concentration detector is connected to the automatic control unit. The automatic control unit adjusts the acid feed regulating valve and the water feed regulating valve according to the detected sulfuric acid mass fraction, so that the sulfuric acid mass fraction of the extracted dilute sulfuric acid product is maintained in the range of 49% to 51%.

[0024] As a preferred technical solution of the present invention, the 50% acid transfer pump includes a first transfer pump and a second transfer pump. The first transfer pump and the second transfer pump are connected in parallel between the outlet of the enamel kettle and the heat exchanger, forming a conveying structure with one pump in use and one in standby.

[0025] This invention also provides a continuous dilution and recovery control method for chlorine-dried waste sulfuric acid, employing a continuous dilution and recovery system including an enamel-lined kettle, an external circulation heat exchanger, a reflux branch, a collection branch, a product storage unit, and an automatic control unit, comprising the following steps:

[0026] S1. Continuous feeding: 75% sulfuric acid waste sulfuric acid and production water produced in the chlorine drying section are continuously fed into the enamel kettle. The feeding ratio is controlled according to the mass flow rate F1 of 75% sulfuric acid waste sulfuric acid and the mass flow rate F2 of production water, so that F1:F2=2:1.

[0027] S2. Mixing, dilution and preliminary cooling: 75% chlorine-containing waste sulfuric acid and production water are continuously mixed in the enamel-lined kettle by agitation with compressed air, and circulating cooling water is introduced through the jacket or coil of the enamel-lined kettle for preliminary cooling so that the temperature of the dilute sulfuric acid in the enamel-lined kettle does not exceed 50°C.

[0028] S3. External circulation cooling and distribution: The dilute sulfuric acid in the enamel kettle is sent to the heat exchanger for forced cooling through a 50% acid transfer pump. The dilute sulfuric acid at the outlet of the heat exchanger is divided into two paths. One path is returned to the enamel kettle through the reflux regulating valve, and the other path is sent to the dilute acid high-level tank as a dilute sulfuric acid product with a sulfuric acid mass fraction of 50% through the 50% sulfuric acid regulating valve.

[0029] S4. Interlocking control: Adjust the opening of the 50% sulfuric acid regulating valve according to the liquid level detection signal of the dilute acid high-level tank, and adjust the circulating cooling water flow rate, return flow rate and product output rate according to the temperature detection signals of the enameled kettle and the heat exchanger outlet.

[0030] As a preferred technical solution of the present invention, the heat exchanger uses circulating cooling water to cool dilute sulfuric acid. The inlet temperature of the circulating cooling water does not exceed 32°C and the return temperature does not exceed 40°C. The temperature of the dilute sulfuric acid returning to the enamel kettle is not more than 45°C by adjusting the return flow rate.

[0031] As a preferred technical solution of the present invention, when the temperature of dilute sulfuric acid in the enamel kettle or at the outlet of the heat exchanger reaches the preset alarm temperature, the automatic control unit performs the following interlock control: reducing or closing the opening of the 50% sulfuric acid regulating valve, increasing the opening of the reflux regulating valve, reducing the feed flow rate of 75% chlorine-containing waste sulfuric acid and production water, and issuing a temperature abnormality alarm; the preset alarm temperature is 55°C.

[0032] Compared with existing technologies and batch dilution processes, this invention controls the mass flow rate ratio of 75% chlorine-containing waste sulfuric acid and production water, ensuring that the two materials continuously enter the enamel-lined reactor at a ratio of F1:F2=2:1. Continuous mixing and heat dissipation are achieved through compressed air stirring, enamel-lined reactor jacket or coil cooling, and external circulation heat exchange. The dilute sulfuric acid, after heat exchange, returns to the enamel-lined reactor via a reflux branch and is sent to a high-level dilute acid tank via a collection branch. This transforms batch preparation into continuous feeding, continuous heat exchange, and continuous collection, reducing material transfer, re-mixing, and waiting time. In Example 1, 30 tons of dilute sulfuric acid can be produced continuously within approximately 20 hours. Simultaneously, the closed-loop conveying and automatic control reduce the opportunity for manual contact with highly corrosive acids. Combined with enamel-lined reactor stirring, jacket or coil cooling, and external circulation reflux, the risks of localized overheating, acid splashing, and acid mist generation are reduced.

[0033] This invention establishes a closed-loop control system for feed ratio, dilution temperature, product concentration, and storage tank level by incorporating a first temperature sensing element inside the enamel-lined reactor, a second temperature sensing element at the heat exchanger outlet, an online sulfuric acid concentration detector, and a level gauge in the dilute acid high-level tank. The automatic control unit adjusts the circulating cooling water flow and return flow based on temperature signals to ensure the temperature of the dilute sulfuric acid inside the enamel-lined reactor does not exceed 50°C and the temperature of the dilute sulfuric acid after cooling by the heat exchanger does not exceed 45°C. When the online concentration detector is installed, the acid feed regulating valve and water feed regulating valve are adjusted to maintain the product sulfuric acid mass fraction within the range of 49% to 51%. In Example 1, the measured product sulfuric acid mass fraction was 50.2%. Simultaneously, the high and low level interlocking of the dilute acid high-level tank can regulate the product extraction rate or the feed rate for preparation. When the temperature reaches the 55°C alarm value, the system can reduce or shut down product extraction, increase the return flow rate, reduce the feed flow rate, and issue an alarm, thereby improving the temperature control stability, product quality stability, and ability to handle abnormal conditions during continuous operation.

[0034] This invention can convert chlorine-containing waste sulfuric acid (approximately 75% sulfuric acid by mass) generated in the chlorine drying section into dilute sulfuric acid product (approximately 50% sulfuric acid by mass), reducing disposal costs and sulfur resource loss caused by treating waste acid as hazardous waste, and realizing the resource utilization of by-product waste acid. The system is based on an existing 3m³ enamel-lined reactor, 75% waste sulfuric acid feed pump, heat exchanger, flow meter, level gauge, and dilute acid high-level tank. A process modification is implemented using a first and second transfer pump to form a standby external circulation conveying structure, reducing the need for new equipment and supporting engineering. Combined with a 25m³ fiberglass dilute acid high-level tank, it also allows for advance stockpiling during sales off-peak periods at a low flow rate of 1.0 ton / hour of 75% waste sulfuric acid and 0.5 ton / hour of production water. According to the implementation plan, the investment for new pipelines, cables, and installation modifications is approximately 50,000 yuan, offering advantages such as high equipment utilization, low modification investment, and flexible production scheduling. Attached Figure Description

[0035] Figure 1 This is a flowchart of a method for controlling the continuous dilution and recovery of chlorine-dried waste sulfuric acid according to the present invention. Detailed Implementation

[0036] The present invention will be further described below in conjunction with its system configuration, control method, and specific operating conditions. It should be noted that the following embodiments are used to illustrate the technical solution of the present invention and are not intended to limit the scope of protection of the present invention.

[0037] See Figure 1This embodiment is used to treat chlorine-containing waste sulfuric acid generated in the chlorine drying process. The chlorine drying process typically uses concentrated sulfuric acid (98% by mass) to absorb moisture from the chlorine gas, resulting in chlorine-containing waste sulfuric acid with a sulfuric acid mass fraction of approximately 75%. This chlorine-containing waste sulfuric acid contains a small amount of dissolved chlorine. In this embodiment, production water is continuously added to dilute it to a 50% sulfuric acid mass fraction product, which is then stored in a high-level dilute acid tank.

[0038] The continuous dilution and recovery system of this embodiment includes a raw material supply unit, a dilution and mixing unit, an external circulation cooling and distribution unit, a product storage unit, and an automatic control unit.

[0039] The raw material supply unit includes a 75% waste sulfuric acid feed pump, a 75% waste sulfuric acid flow meter, a production water supply pipeline, a production water flow meter, an acid feed regulating valve, and a water feed regulating valve. The inlet of the 75% waste sulfuric acid feed pump is connected to the chlorine-containing waste sulfuric acid storage or conveying pipeline in the chlorine drying section, and the outlet is connected to the feed inlet of the enamel-lined reactor. In one specific embodiment, the 75% waste sulfuric acid feed pump is an existing P-0405 pump. The production water supply pipeline is connected to the water inlet of the enamel-lined reactor. The 75% waste sulfuric acid flow meter and the production water flow meter respectively detect the flow rates of the two materials, and the acid feed regulating valve and the water feed regulating valve are used to regulate the feed rates of the two materials, respectively.

[0040] In this implementation, flow control is based on mass flow rate. Let the mass flow rate of 75% chlorine-containing waste sulfuric acid be F1, and the mass flow rate of the production water be F2. Based on the material balance relationship:

[0041] 75% × F1 = 50% × (F1 + F2)

[0042] Therefore, F1:F2 = 2:1, meaning the mass flow rate of the produced water is 0.5 times the mass flow rate of the 75% chlorine-containing waste sulfuric acid. When using volumetric flow rate measurement on-site, the volumetric flow rate is converted to mass flow rate based on the density of the corresponding material, and then proportionally controlled by the automatic control unit. In this example, the density of 75% chlorine-containing waste sulfuric acid is approximately 1.67 g / cm³, and the metering results from both the acid and water sides are converted to mass flow rate before being used in the control.

[0043] The dilution and mixing unit includes an enamel-lined kettle, a compressed air stirring system, a circulating water cooling system, and a circulating cooling water regulating valve. The enamel-lined kettle receives 75% chlorine-containing waste sulfuric acid and production water, serving as a continuous mixing and dilution container. In one specific embodiment, the volume of the enamel-lined kettle is 3 m³. The compressed air stirring system introduces compressed air into the enamel-lined kettle, ensuring thorough mixing of the waste sulfuric acid and production water, reducing local concentration differences in the acid-water mixture, and minimizing localized heat release concentration.

[0044] The circulating water cooling system is connected to the jacket or coil of the enamel-lined reactor, and the circulating cooling water regulating valve is used to regulate the flow rate of circulating cooling water entering the jacket or coil. A first temperature sensing element is installed inside the enamel-lined reactor, transmitting the temperature signal of the dilute sulfuric acid inside the reactor to the automatic control unit. During the initial stage of continuous feeding, the circulating water cooling system removes the heat generated during the dilution process, ensuring that the temperature of the dilute sulfuric acid inside the enamel-lined reactor does not exceed 50°C.

[0045] The external circulation cooling and distribution unit includes a 50% acid transfer pump, a heat exchanger, external circulation piping, a reflux regulating valve, and a 50% sulfuric acid regulating valve. The outlet of the enamel-lined reactor is connected to the 50% acid transfer pump via the external circulation piping. The outlet of the 50% acid transfer pump is connected to the acid-side inlet of the heat exchanger. The acid-side outlet of the heat exchanger is connected to both the reflux branch and the extraction branch. The reflux branch returns to the enamel-lined reactor via the reflux regulating valve, and the extraction branch is connected to the dilute acid high-level tank via the 50% sulfuric acid regulating valve.

[0046] The cooling side of the heat exchanger is connected to the circulating cooling water pipeline, and the circulating cooling water regulating valve is used to adjust the flow rate of the circulating cooling water on the cooling side of the heat exchanger. A second temperature sensing element is installed at the heat exchanger outlet to detect the temperature of the dilute sulfuric acid after cooling by the heat exchanger. Under a specific operating condition, the inlet temperature of the circulating cooling water does not exceed 32℃, the return temperature does not exceed 40℃, and the temperature of the dilute sulfuric acid at the heat exchanger outlet is controlled below 45℃.

[0047] Once the liquid level in the enamel-lined reactor reaches the set level, the 50% acid transfer pump is activated, causing the dilute sulfuric acid in the reactor to enter the heat exchanger for forced external circulation cooling. The cooled dilute sulfuric acid is divided into a reflux portion and a collection portion. The reflux portion returns to the enamel-lined reactor through a reflux regulating valve to continuously remove heat and enhance mixing within the reactor; the collection portion enters the dilute acid high-level tank through a 50% sulfuric acid regulating valve. By adjusting the reflux and collection rates, the material quantity, temperature, and continuous operation status of the system within the enamel-lined reactor are maintained stable.

[0048] In one specific embodiment, the 50% acid transfer pump includes a first transfer pump and a second transfer pump. The first and second transfer pumps are connected in parallel between the outlet of the enamel-lined reactor and the heat exchanger. During normal operation, one of them acts as the operating pump, and the other as a standby pump. When the operating pump needs maintenance or fails, it is stopped and the standby pump is started to maintain the continuous delivery capacity of the external circulation cooling circuit.

[0049] The product storage unit includes a dilute acid high-level tank and a level gauge. In one specific embodiment, the dilute acid high-level tank is a 25 m³ fiberglass storage tank used to store 50% dilute sulfuric acid product that has been cooled by a heat exchanger and delivered through the outflow branch. The level gauge monitors the liquid level in the dilute acid high-level tank in real time and transmits the liquid level signal to the automatic control unit.

[0050] The automatic control unit uses a DCS or PLC controller. It receives detection signals from the 75% waste sulfuric acid flow meter, the production water flow meter, the first temperature sensing element, the second temperature sensing element, and the level gauge, and outputs control signals to the acid feed regulating valve, water feed regulating valve, circulating cooling water regulating valve, reflux regulating valve, and 50% sulfuric acid regulating valve. The automatic control unit controls the acid-water feed ratio according to F1:F2=2:1; controls the circulating cooling water flow and reflux flow according to the temperature inside the enamel reactor and the heat exchanger outlet temperature; and controls the product output according to the level in the dilute acid high-level tank.

[0051] The continuous dilution and recovery control method of this embodiment includes the following steps.

[0052] Step S1, continuous feeding. Start the 75% waste sulfuric acid feed pump to allow chlorine-containing waste sulfuric acid with a sulfuric acid mass fraction of 75% to enter the enamel-lined reactor; simultaneously, open the production water supply pipeline to allow production water to enter the enamel-lined reactor. The automatic control unit reads the mass flow signals from the flow meters on both sides and maintains F1:F2 at a ratio of 2:1 through the acid feed regulating valve and the water feed regulating valve.

[0053] Step S2, Mixing, Dilution, and Preliminary Cooling. The compressed air stirring system is activated to continuously mix 75% chlorine-containing waste sulfuric acid with production water in the enamel-lined reactor. The circulating water cooling system is activated to remove the heat of dilution through the enamel-lined reactor jacket or coils. The first temperature detection element monitors the temperature inside the enamel-lined reactor. When the temperature approaches the set upper limit, the automatic control unit increases the opening of the circulating cooling water regulating valve; when the temperature is within the set range, the circulating cooling water flow rate is maintained to ensure that the temperature of the dilute sulfuric acid inside the enamel-lined reactor does not exceed 50°C.

[0054] Step S3, External Circulation Cooling and Distribution. When the liquid level in the enamel-lined reactor reaches the set level, the 50% acid transfer pump is started to transport the dilute sulfuric acid from the enamel-lined reactor to the heat exchanger. The circulating cooling water on the cooling side of the heat exchanger is turned on to force the dilute sulfuric acid to cool within the heat exchanger. The second temperature detection element detects the temperature of the dilute sulfuric acid at the heat exchanger outlet, and the automatic control unit adjusts the circulating cooling water regulating valve and the reflux regulating valve according to this temperature.

[0055] After being distributed, the dilute sulfuric acid from the heat exchanger outlet is divided in two parts: a portion returns to the enamel-lined reactor via a reflux regulating valve, and the other portion is sent to the high-level dilute acid tank via a 50% sulfuric acid regulating valve. During continuous operation, the reflux portion is used to maintain stable temperature and liquid level inside the enamel-lined reactor, while the output portion is used to form the product output. By adjusting the reflux and output rates, the temperature of the dilute sulfuric acid returning to the enamel-lined reactor is kept below 45°C.

[0056] Step S4, Liquid Level Interlock Control. The automatic control unit reads the detection signal from the level gauge of the dilute acid high-level tank. When the liquid level in the dilute acid high-level tank reaches the set high limit, the automatic control unit reduces the opening of the 50% sulfuric acid regulating valve or closes the 50% sulfuric acid regulating valve to reduce the product output and prevent the dilute acid high-level tank from exceeding the liquid level. When the liquid level in the dilute acid high-level tank reaches the set low limit, the automatic control unit reduces the product output or increases the acid water preparation feed rate to restore the liquid level in the dilute acid high-level tank to the set range.

[0057] In another specific embodiment, an online sulfuric acid concentration detector is installed at the heat exchanger outlet or on the extraction branch. The online sulfuric acid concentration detector detects the sulfuric acid mass fraction of the extracted dilute sulfuric acid and transmits the detection result to the automatic control unit. When the detected sulfuric acid mass fraction is below 49%, the automatic control unit decreases the opening of the water feed regulating valve or increases the opening of the acid feed regulating valve; when the detected sulfuric acid mass fraction is above 51%, the automatic control unit increases the opening of the water feed regulating valve or decreases the opening of the acid feed regulating valve, maintaining the product sulfuric acid mass fraction within the range of 49% to 51%.

[0058] When the temperature of dilute sulfuric acid inside the enamel reactor or at the heat exchanger outlet reaches 55°C during continuous production, the automatic control unit executes an abnormal operating condition interlock: reducing or closing the 50% sulfuric acid regulating valve, increasing the opening of the reflux regulating valve, reducing the feed flow rate of 75% chlorine-containing waste sulfuric acid and production water, and issuing a temperature abnormality alarm. Operators check the operating status of the circulating cooling water, heat exchanger, and transfer pump based on the alarm. After the temperature returns to the set range, the product output and acid water feed rate are gradually restored.

[0059] Example 1: Continuous dilution to produce 30 tons of dilute sulfuric acid.

[0060] This embodiment uses the aforementioned 3m³ enamel-lined reactor, external circulation heat exchanger, and 25m³ fiberglass high-level dilute acid tank. The raw material is chlorine-containing waste sulfuric acid with a sulfuric acid mass fraction of 75% produced from the chlorine drying section, with a density of approximately 1.67 g / cm³. The dilution water is production water. Before startup, approximately 1 ton of dilute sulfuric acid with a sulfuric acid mass fraction of 50% is added to the enamel-lined reactor as a base liquid, and the compressed air stirring system is turned on.

[0061] Start the 75% waste sulfuric acid feed pump and control the mass flow rate F1 of the 75% chlorine-containing waste sulfuric acid to 2.0 tons / hour; simultaneously, open the production water supply pipeline and control the mass flow rate F2 of the production water to 1.0 tons / hour, so that F1:F2=2:1. Turn on the circulating water cooling system of the enamel-lined reactor jacket to control the temperature inside the enamel-lined reactor below 50℃.

[0062] When the liquid volume in the enamel-lined reactor reaches approximately 2.5 tons, start the 50% acid transfer pump to send the dilute sulfuric acid from the reactor into the heat exchanger. Circulating cooling water is introduced into the cooling side of the heat exchanger, controlling the inlet temperature to not exceed 32℃ and the return temperature to not exceed 40℃, ensuring the dilute sulfuric acid temperature at the heat exchanger outlet is below 45℃. The dilute sulfuric acid from the heat exchanger outlet flows back to the enamel-lined reactor at a flow rate of approximately 1.5 tons / hour, and then enters the high-level dilute acid tank via the extraction branch at a flow rate of approximately 1.5 tons / hour.

[0063] After approximately 20 hours of continuous operation, the system produced about 30 tons of dilute sulfuric acid in the high-level dilute acid tank. When the tank level reached the set limit of approximately 25 tons, the automatic control unit adjusted the opening of the 50% sulfuric acid regulating valve to maintain a balance between the product output and the system feed rate. Sampling and testing revealed a sulfuric acid mass fraction of 50.2%, falling within the control range of 49% to 51%.

[0064] Example 2: Utilizing sales gaps for low-volume continuous inventory replenishment.

[0065] In cases where there are no customers picking up goods temporarily but advance stocking is required, the same system as in Example 1 is used. The mass flow rate of 75% chlorine-containing waste sulfuric acid is controlled at 1.0 ton / hour, and the mass flow rate of production water is controlled at 0.5 ton / hour, maintaining an acid-to-water mass flow rate ratio of 2:1. Compressed air agitation and jacketed circulation cooling are activated, and external circulation heat exchange is started according to the temperature of the enamel-lined reactor. The dilute sulfuric acid cooled by the heat exchanger is gradually fed into a 25 m³ fiberglass high-level dilute acid tank for storage.

[0066] When the dilute acid high-level tank reaches the set high limit, the automatic control unit reduces or closes the product dispensing regulating valve; when the liquid level drops to the set low limit, product dispensing resumes or supplementary feed is added. Through a low-flow, start-stop continuous operation mode, dilute sulfuric acid is stocked during sales off-peak periods.

[0067] Example 3: Interlocking procedures for abnormal heat exchanger cooling.

[0068] During normal system operation, the second temperature sensing element continuously monitors the temperature of dilute sulfuric acid at the heat exchanger outlet. When the circulating cooling water is briefly interrupted or the heat exchange capacity decreases, causing the detected temperature to rise to 55°C, the automatic control unit triggers a temperature anomaly alarm and executes the following controls sequentially or simultaneously: closes or reduces the 50% sulfuric acid regulating valve, suspends or reduces product dispensing; increases the opening of the reflux regulating valve to return the high-temperature dilute sulfuric acid to the enamel-lined reactor and continue circulating; reduces the feed flow rate of 75% chlorine-containing waste sulfuric acid and production water to reduce additional dilution heat; and prompts operators to check the heat exchanger, circulating cooling water pipeline, and 50% acid transfer pump.

[0069] After the temperature returns to the set operating range, the automatic control unit gradually restores the circulating cooling water flow rate, acid water feed rate, and product output rate, so that the system can return to a continuous and stable operating state.

[0070] Through the above implementation method, 75% chlorine-containing waste sulfuric acid is continuously diluted to 50% dilute sulfuric acid product under closed conveying, continuous proportioning, enamel-lined kettle mixing, and external circulation heat exchange conditions, and then sent to the high-level dilute acid tank for storage through the product outlet branch. The system utilizes flow rate, temperature, concentration, and liquid level signals to form automatic control and interlocking control, reducing the risk of local overheating caused by manual contact with acid and intermittent operation, while improving product concentration stability and continuous production capacity.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A continuous dilution and recovery system for waste sulfuric acid from chlorine drying, used to continuously dilute chlorine-containing waste sulfuric acid with a sulfuric acid mass fraction of 75% generated in the chlorine drying section into a dilute sulfuric acid product with a sulfuric acid mass fraction of 50%, characterized in that, It includes a raw material supply unit, a dilution and mixing unit, an external circulation cooling and distribution unit, a product storage unit, and an automatic control unit; The raw material supply unit includes a 75% waste sulfuric acid feed pump, a 75% waste sulfuric acid flow meter, a production water supply pipeline, a production water flow meter, an acid feed regulating valve, and a water feed regulating valve. The dilution and mixing unit includes an enamel-lined kettle, a compressed air stirring system, a circulating water cooling system, and a circulating cooling water regulating valve. The circulating water cooling system is connected to the jacket or coil of the enamel-lined kettle. The external circulation cooling and distribution unit includes a 50% acid transfer pump, a heat exchanger, an external circulation pipeline, a reflux regulating valve, and a 50% sulfuric acid regulating valve. The heat exchanger is connected to the circulating cooling water pipeline. The external circulation pipeline is sequentially connected to the outlet of the enamel-lined reactor, the 50% acid transfer pump, and the heat exchanger. The outlet of the heat exchanger is connected to a reflux branch and a sampling branch. The reflux branch is connected to the enamel-lined reactor via the reflux regulating valve, and the sampling branch is connected to the product storage unit via the 50% sulfuric acid regulating valve. The product storage unit includes a dilute acid high-level tank and a level gauge; The automatic control unit is connected to the 75% waste sulfuric acid flow meter, the production water flow meter, the first temperature detection element installed in the enamel kettle, the second temperature detection element installed at the heat exchanger outlet, the level gauge, the acid feed regulating valve, the water feed regulating valve, the circulating cooling water regulating valve, the reflux regulating valve, and the 50% sulfuric acid regulating valve, respectively. It is used to control the feed ratio of 75% chlorine-containing waste sulfuric acid and production water according to the flow detection signal, control the circulating cooling water regulating valve, the reflux regulating valve, and the 50% sulfuric acid regulating valve according to the temperature detection signal, and control the product output according to the level detection signal.

2. The chlorine drying waste sulfuric acid continuous dilution and recovery system according to claim 1, characterized in that, The 75% waste sulfuric acid flow meter and the production water flow meter are used to detect the mass flow rate of the corresponding materials. The automatic control unit controls the mass flow rate F1 of 75% chlorine-containing waste sulfuric acid and the mass flow rate F2 of production water according to the mass flow rate to satisfy: 75%×F1=50%×(F1+F2), so that F1:F2=2:

1.

3. The chlorine drying waste sulfuric acid continuous dilution and recovery system according to claim 1, characterized in that, The enamel-lined kettle has a volume of 3 m3. The compressed air stirring system is used to continuously mix 75% chlorine-containing waste sulfuric acid with production water in the enamel-lined kettle. The circulating water cooling system is used to remove the dilution heat generated during the dilution process through the jacket or coil.

4. The chlorine drying waste sulfuric acid continuous dilution and recovery system according to claim 1, characterized in that, The heat exchanger is used to forcibly cool the dilute sulfuric acid flowing out of the enamel-lined kettle by circulating cooling water. The automatic control unit adjusts the reflux regulating valve to allow part of the dilute sulfuric acid cooled by the heat exchanger to flow back to the enamel-lined kettle so that the temperature of the dilute sulfuric acid in the enamel-lined kettle does not exceed 45°C, and controls the output of dilute sulfuric acid product by adjusting the 50% sulfuric acid regulating valve.

5. The chlorine drying waste sulfuric acid continuous dilution and recovery system according to claim 1, characterized in that, The high-level dilute acid tank is a fiberglass storage tank with a volume of 25m³. The automatic control unit performs high and low level interlock control based on the detection signal of the level gauge: when the level of the high-level dilute acid tank reaches the set high limit, the opening of the 50% sulfuric acid regulating valve is reduced or the 50% sulfuric acid regulating valve is closed; when the level of the high-level dilute acid tank reaches the set low limit, the product output is reduced or the feed rate is increased.

6. The chlorine drying waste sulfuric acid continuous dilution and recovery system according to claim 1, characterized in that, An online sulfuric acid concentration detector is installed at the outlet of the heat exchanger or on the extraction branch. The online sulfuric acid concentration detector is connected to the automatic control unit. The automatic control unit adjusts the acid feed regulating valve and the water feed regulating valve according to the detected sulfuric acid mass fraction, so that the sulfuric acid mass fraction of the extracted dilute sulfuric acid product is maintained within the range of 49% to 51%.

7. The chlorine drying waste sulfuric acid continuous dilution and recovery system according to claim 1, characterized in that, The 50% acid transfer pump includes a first transfer pump and a second transfer pump. The first transfer pump and the second transfer pump are connected in parallel between the outlet of the enamel kettle and the heat exchanger, forming a conveying structure with one pump in use and one in standby.

8. A method for continuous dilution and recovery control of chlorine-dried waste sulfuric acid, characterized in that, A continuous dilution and recovery system, comprising an enamel-lined autoclave, an external circulation heat exchanger, a reflux branch, a product collection branch, a product storage unit, and an automatic control unit, includes the following steps: S1. Continuous feeding: 75% sulfuric acid waste sulfuric acid and production water produced in the chlorine drying section are continuously fed into the enamel kettle. The feeding ratio is controlled according to the mass flow rate F1 of 75% sulfuric acid waste sulfuric acid and the mass flow rate F2 of production water, so that F1:F2=2:

1. S2. Mixing, dilution and preliminary cooling: 75% chlorine-containing waste sulfuric acid and production water are continuously mixed in the enamel-lined kettle by agitation with compressed air, and circulating cooling water is introduced through the jacket or coil of the enamel-lined kettle for preliminary cooling so that the temperature of the dilute sulfuric acid in the enamel-lined kettle does not exceed 50°C. S3. External circulation cooling and distribution: The dilute sulfuric acid in the enamel kettle is sent to the heat exchanger for forced cooling through a 50% acid transfer pump. The dilute sulfuric acid at the outlet of the heat exchanger is divided into two paths. One path is returned to the enamel kettle through the reflux regulating valve, and the other path is sent to the dilute acid high-level tank as a dilute sulfuric acid product with a sulfuric acid mass fraction of 50% through the 50% sulfuric acid regulating valve. S4. Interlocking control: Adjust the opening of the 50% sulfuric acid regulating valve according to the liquid level detection signal of the dilute acid high-level tank, and adjust the circulating cooling water flow rate, return flow rate and product output rate according to the temperature detection signals of the enameled kettle and the heat exchanger outlet.

9. The continuous dilution and recovery control method for chlorine-dried waste sulfuric acid according to claim 8, characterized in that, The heat exchanger uses circulating cooling water to cool the dilute sulfuric acid. The inlet temperature of the circulating cooling water does not exceed 32°C and the return temperature does not exceed 40°C. The temperature of the dilute sulfuric acid returning to the enamel-lined kettle is kept below 45°C by adjusting the return flow rate.

10. The method for continuous dilution and recovery control of chlorine-dried waste sulfuric acid according to claim 8, characterized in that, When the temperature of dilute sulfuric acid inside the enamel-lined reactor or at the outlet of the heat exchanger reaches the preset alarm temperature, the automatic control unit performs the following interlock control: reduces or closes the opening of the 50% sulfuric acid regulating valve, increases the opening of the reflux regulating valve, reduces the feed flow rate of 75% chlorine-containing waste sulfuric acid and production water, and issues a temperature abnormality alarm; the preset alarm temperature is 55℃.

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