Method and device for producing solid caustic soda

Abstract

According to the method and device for producing the solid caustic soda, steam of a final concentration falling film evaporation furnace is used as a heat source for pre-concentration, in addition, a waste heat boiler is changed into a saccharification preheater, the saccharification reaction can be completed before alkali liquor enters a falling film pipe, and therefore the service life of the falling film pipe is prolonged; and the temperature of the alkali liquor entering the falling film tube is increased from 95 DEG C to 190 DEG C. After the fuel gas is directly heated, high-temperature molten salt is omitted as a heat carrier, heat loss caused by heat transfer of the heat carrier is reduced, and the problems that a molten salt pipeline is difficult to block and personal life and property safety is endangered due to molten salt leakage are solved, so that safe and stable operation of the system and the personal life and property safety are ensured.

Description

Technical Field

[0001] This application relates to the field of solid alkali production technology, and in particular to a method and apparatus for producing solid alkali. Background Technology

[0002] Solid alkali (solid sodium hydroxide) production involves evaporating water from liquid alkali to obtain molten alkali, which is then cooled and solidified. The heat source is steam generated from fuel gas, which is then used for indirect heating via film evaporation to concentrate the liquid alkali. This process is divided into two stages: rising film evaporation and falling film evaporation. Rising film evaporation is generally used as a pre-concentration stage, concentrating the alkali solution from approximately 30% to 40-60%. Falling film evaporation then introduces the pre-concentrated alkali solution from the top of the evaporator, where it is evenly distributed into numerous heating tubes by a distributor. Under gravity, the solution flows downwards in a film along the inner wall of the tubes. A high-temperature heat transfer medium (such as molten salt) is used for heating outside the tubes. The alkali solution is fully evaporated during its descent, reaching the bottom as molten alkali with a purity of over 98.5%. This method yields 98-98.5% molten (sodium) alkali, which is then shaped and packaged for sale as commercial alkali (barrel alkali, flake alkali, granular alkali, bead alkali, etc.). However, during the process of concentrating the alkali solution from ~50% to ~99%, the boiling point will rise sharply (reaching over 400°C), and the pressure of the saturated steam will be very high. In existing technologies, molten salt heated by gas (usually a mixture of potassium nitrate, sodium nitrate, etc., prepared in a certain proportion) is generally used as a heat carrier for final concentration. Molten salt as a heat medium can provide a stable temperature of 400°C or even higher under normal pressure. If the operating temperature range is 400-430°C, the high-temperature molten salt has strong corrosiveness. Once a leak occurs, it will endanger personal life and property safety, and it has been listed as a hazardous chemical for safety monitoring.

[0003] Meanwhile, the secondary steam in the final concentration process is usually excessive, resulting in high gas consumption and low thermal efficiency. Although there have been attempts to use the secondary steam from the final concentration as a heat source for pre-concentration, such as increasing the concentration of the alkali solution after pre-concentration to 62% so that the concentration of the alkali solution entering the final concentration reaches 62% to reduce the overall steam consumption, the operation is difficult in the production process and it has not been effectively promoted and applied.

[0004] On the other hand, in the production of liquid alkali using ion-exchange membrane electrolysis ( During the process, hypochlorite ( ) is generated in the electrolytic cell Under specific conditions (such as high temperature and low anolyte current efficiency), it will further react to generate chlorate ions. ). Chlorate ( Chlorate will corrode equipment. During the subsequent high-temperature concentration process of solid caustic soda, chlorate will decompose and release chlorine (Cl2) and oxygen (O2). The chlorine produced will dissolve in the molten caustic soda, resulting in an excessive chlorine content (in the form of NaCl) in the final solid caustic soda product. This affects the purity and grade of the product, failing to meet the needs of high-end users (such as those in the chemical fiber, pharmaceutical, and electronics industries). It is essential to effectively remove chlorate from the liquid caustic soda before it enters the evaporation and concentration section. A common method is "saccharification," which uses sugars (such as sucrose and glucose) as reducing agents to reduce chlorate to harmless chlorides under alkaline heating conditions. This reaction must be carried out in a hot alkaline solution. Under alkaline and heating conditions, these chlorides are oxidized by the strong oxidant chlorate ion (Cl2). It is oxidized and eventually produces sodium carbonate. Carbon dioxide (CO2) and water, etc. Chlorate is reduced: chlorate ion. Reduced to chloride ions Sodium chlorate (NaClO3) is converted into sodium chloride (NaCl), a common impurity in alkalis, while sugars are oxidized into smaller molecules of carbonates, carbon dioxide, and water. The generated CO2 escapes as bubbles, while NaCl and... It will exist as a trace impurity in the subsequent solidification process, and its impact is far less than that of chlorate.

[0005] The decomposition of chlorates releases chlorine (Cl2) and oxygen (O2). Strong oxidizing gases like Cl2 severely corrode the nickel-plated equipment used in evaporators, significantly shortening their lifespan and increasing maintenance costs and safety risks. This treatment unit is typically installed after the alkali solution has undergone preliminary pre-concentration (e.g., from 32% to approximately 48%). The chlorate content in the treated alkali solution can be reduced to extremely low levels (e.g., <10 ppm or even lower) before being sent to a falling film evaporator for final concentration into molten alkali.

[0006] However, in existing technologies, the chlorate saccharification reaction requires a temperature above 180℃. If the temperature in the pre-concentration stage does not reach this value, the chlorate saccharification reaction will be incomplete. This will cause the saccharification reaction to continue within the final concentration falling film tube, inevitably accelerating the corrosion rate of the falling film tube (made of nickel) by chlorate, thus reducing its service life. In large-scale industrial production, a reduced service life of core components such as the falling film tube can severely impact the normal operation of the system.

[0007] Due to the aforementioned technical issues, further improvements are needed to reduce gas consumption, extend the service life of the falling film pipe, ensure safe and stable operation, and protect personal safety and property. Summary of the Invention

[0008] The purpose of this invention is to provide a method and apparatus for producing solid alkali, so as to improve the safety of solid alkali production.

[0009] This application provides a method for producing solid alkali, the method comprising the following steps: A first concentration of alkaline solution and sugar solution is added for pre-concentration. The heat source for pre-concentration comes from steam generated by the final concentration falling film evaporator, resulting in a second concentration of alkaline solution and sugar solution. The alkaline solution and sugar solution of the second concentration are heated to cause the sugar solution and the alkaline solution of the second concentration to undergo a primary saccharification reaction, and then fed into the final concentration falling film evaporator; the heat source for heating comes from the flue gas generated by the final concentration falling film evaporator. The flue gas generated by the final concentration falling film evaporator is used to preheat the cold air entering the final concentration evaporator; The mixture after the initial saccharification reaction is subjected to a second saccharification reaction; the mixture after the second saccharification reaction is concentrated by falling film evaporation to obtain molten sodium alkali; The molten sodium alkali is flash-evaporated, cooled, shaped, and packaged.

[0010] In the above scheme, the final concentration secondary steam pressure is controlled above 50 kPaG, which can increase the pre-concentrated alkali concentration from 62% to 67%, not only ensuring full utilization of the final concentration secondary steam but also reducing the evaporation water volume of the final concentration. Replacing the waste heat boiler with a saccharification preheater ensures that the required temperature for the saccharification reaction is reached, guaranteeing that the saccharification reaction is completed before the alkali solution enters the falling film tube, thus extending the service life of the falling film tube. It also increases the alkali solution temperature entering the falling film tube from 95℃ to 190℃, creating conditions for subsequent direct gas heating. Eliminating the use of high-temperature molten salt as a heat carrier reduces heat loss from heat transfer, eliminates the difficulty of handling molten salt pipeline blockages, and prevents molten salt leaks from endangering personal safety and property, thereby ensuring the safe and stable operation of the system and the safety of personnel and property. This application is applicable to continuous, large-scale production, with high single-unit capacity, closed operation, and a high degree of automation.

[0011] In one specific implementation scheme, the pre-concentration using secondary steam generated by the final concentration falling film evaporator as a heat source specifically includes: The high-temperature, low-pressure secondary steam generated by the final concentration falling film evaporator is transported to the gas-liquid separation chamber for gas-liquid separation. The separated high-temperature and low-pressure secondary steam is cooled by a final concentrator and a final concentrator to obtain low-temperature and low-pressure secondary steam, which is then sent to the pre-concentrator evaporator to heat the alkaline solution of the first concentration.

[0012] In a specific feasible implementation, the following steps are also included: The alkali dust generated by the scraper of the caustic soda flake machine and the packaging machine is absorbed into the alkali absorption circulation tank by using liquid.

[0013] In a specific feasible implementation, the following steps are also included: The high-temperature, atmospheric-pressure secondary steam generated after flash evaporation in the flash distribution tank is cooled by a liquid spray pipe via a flash desuperheater and then sent to the alkali absorption circulation tank.

[0014] In a specific feasible implementation, the following steps are also included: The dilute alkali solution in the alkali absorption and circulation tank overflows into the residual liquid hopper of the caustic soda flake machine. After washing and diluting the molten alkali residue in the residual liquid hopper, it enters the alkali recovery tank of the alkali system for recycling.

[0015] In one specific implementation, the pre-concentration evaporator has a vacuum of -92 kPaG and an evaporation temperature of 105°C.

[0016] In one specific implementation, the flue gas generated by the final concentration falling film evaporator heats the air preheater from 250°C to 158°C before entering the chimney for exhaust; the cold air is preheated from 25°C to 135°C.

[0017] In one specific implementation scheme, the low-temperature, low-pressure secondary steam has a pressure of 50 kPaG and a temperature of 111°C.

[0018] Secondly, an apparatus for producing solid alkali is provided, the apparatus comprising: The pre-concentration main system includes a pre-concentration evaporator, which is used to heat an alkaline solution of a first concentration to an alkaline solution of a second concentration. The final concentration main system includes a saccharification preheater, a final concentration falling film evaporator, and a flash distribution tank. The saccharification preheater is used to perform a primary saccharification reaction on a second concentration of alkali solution and sugar solution to obtain a mixed solution. The final concentration falling film evaporator includes a saccharification reactor and a falling film tube. The saccharification reactor is used to perform a secondary saccharification reaction on the mixed solution obtained from the primary saccharification reaction, and the falling film tube is used to perform falling film evaporation and concentration on the mixture from the secondary saccharification reaction to obtain molten sodium alkali. The flash distribution tank is used to flash evaporate the molten sodium alkali. The flue gas auxiliary system is used to input the flue gas generated by the final concentration falling film evaporator into the saccharification preheater and heat the saccharification preheater, heat the air preheater, and the flue gas is mixed with the air preheated by the air preheater by the circulating fan and then into the burner to heat the final concentration falling film evaporator. The main system for forming and packaging caustic soda flakes includes a caustic soda flake machine and a packaging machine; wherein, the caustic soda flake machine is used to cool and form molten sodium caustic soda after flash evaporation; and the packaging machine is used to package the formed caustic soda flakes.

[0019] In the above scheme, the final concentration secondary steam pressure is controlled above 50 kPaG, which can increase the pre-concentrated alkali concentration from 62% to 67%, not only ensuring full utilization of the final concentration secondary steam but also reducing the evaporation water volume of the final concentration. Replacing the waste heat boiler with a saccharification preheater not only completes the saccharification reaction before the alkali solution enters the falling film tube, thus extending the service life of the falling film tube, but also increases the alkali solution temperature entering the falling film tube from 95℃ to 190℃. Using direct gas heating eliminates the need for high-temperature molten salt as a heat carrier, reducing heat loss from heat transfer and preventing difficulties in handling molten salt pipeline blockages and the dangers of molten salt leaks that could endanger life and property, thereby ensuring the safe and stable operation of the system and the safety of life and property.

[0020] In one specific implementation, the pre-concentration main system further includes a sugar solution tank, a pre-concentration separator, a pre-concentration alkali pump, a pre-concentration gas-blocking drain tank, a pre-concentration desuperheater, a pre-concentration surface condenser, and a pre-concentration vacuum pump, which are connected in sequence to the pre-concentration evaporator. The inlet of the pre-concentrating evaporator is connected to the first-efficiency alkali pump of the 50% alkali system and the sugar solution tank, respectively; the inlet of the pre-concentrating separator is connected to the outlet of the pre-concentrating evaporator; and the inlet of the pre-concentrating alkali pump is connected to the pre-concentrating separator. The shell-side inlet of the pre-concentrating evaporator is connected to the final concentration main system; the shell-side outlet of the pre-concentrating evaporator is connected to the atmosphere; the liquid inlet of the pre-concentrating gas-blocking drain tank is connected to the shell side of the pre-concentrating evaporator; the liquid outlet of the pre-concentrating gas-blocking drain tank is connected to the III-effect gas-blocking drain tank of the 50% alkali system; and the gas outlet of the pre-concentrating gas-blocking drain tank is connected to the shell side of the pre-concentrating evaporator. The inlet of the pre-concentrating desuperheater is connected to the pre-concentrating separator; the shell-side inlet of the pre-concentrating surface condenser is connected to the pre-concentrating desuperheater; the inlet of the pre-concentrating vacuum pump is connected to the shell side of the pre-concentrating surface condenser; the outlet of the pre-concentrating vacuum pump is connected to the atmosphere; the shell-side liquid outlet of the pre-concentrating surface condenser is connected to the main condensate tank of the 50% alkali system; the tube-side liquid inlet of the pre-concentrating surface condenser is connected to the circulating cooling water supply main pipe; and the tube-side liquid outlet of the pre-concentrating surface condenser is connected to the circulating cooling return water main pipe.

[0021] In one specific implementation scheme, the final concentration main system further includes a final concentration demister, a final concentration desuperheater, and a flash desuperheater; wherein... The inlet of the saccharification preheater is connected to the pre-concentration alkali pump; the inlet of the final concentration falling film evaporator is connected to the saccharification preheater; the inlet of the flash distribution tank is connected to the final concentration falling film evaporator; and the inlet of the flash desuperheater is connected to the alkali recovery pump of the 50% alkali system. The air inlet of the final concentration demister is connected to the final concentration falling film evaporator; the air inlet of the final concentration desuperheater is connected to the final concentration demister; and the air inlet of the flash desuperheater is connected to the flash distribution tank. The air inlet of the saccharification preheater is connected to the final concentration falling film evaporator.

[0022] In one specific implementation, the final concentration falling film evaporator includes a saccharification reaction chamber at the top, a furnace chamber in the middle, a gas-liquid separation chamber at the bottom, and multiple falling film tubes, wherein the falling film tubes are located in the furnace chamber and the lower part of the falling film tubes is inserted into the gas-liquid separation chamber. An alkali inlet pipe is provided on the saccharification reaction chamber, and a connecting pipe connected to multiple falling film pipes is provided on the top of the saccharification reaction chamber; a burner is installed on the burner interface that connects the saccharification reaction chamber to the furnace. The furnace is equipped with a flue gas outlet and a flue gas temperature measuring port, and the furnace is lined with a thermal insulation castable layer and a refractory castable layer. The gas-liquid separation chamber is equipped with a secondary steam outlet, a molten alkali outlet, and an inspection hole. The bottom of the gas-liquid separation chamber is equipped with a molten alkali temperature measuring port.

[0023] In one specific implementation, the flue gas auxiliary system includes an air preheater, a chimney, the circulating fan, the blower, and a burner connected in sequence. The air inlet of the air preheater is connected to the blower; the air inlet of the circulating fan is connected to the chimney; the air inlet of the burner is connected to both the air preheater and the circulating fan; the air inlet of the burner is connected to the main gas pipeline; and the burner is directly connected to the final concentration falling film evaporator. The air inlet of the air preheater is connected to the saccharification preheater; the air inlet of the chimney is connected to the air preheater; and the air outlet of the chimney is connected to the atmosphere.

[0024] In one specific feasible implementation, an auxiliary system for treating alkaline dust gas is also included; The alkaline dust gas treatment auxiliary system includes an alkaline dust absorption and circulation tank, an alkaline dust absorption and circulation pump, and a hydraulic vacuum jet pump connected in sequence. The inlet end of the alkali dust absorption circulation tank is connected to the hydraulic vacuum jet pump and the flash desuperheater, respectively; the inlet end of the hydraulic vacuum jet pump is connected to the alkali dust absorption circulation pump; the inlet end of the alkali dust absorption circulation pump is connected to the alkali dust absorption circulation tank. The air inlet of the hydraulic vacuum jet pump is connected to the caustic soda flake machine and the packaging machine.

[0025] In one specific feasible implementation, a caustic soda cooling water auxiliary system is also included; The caustic soda cooling water auxiliary system includes a cooling water collection tank, a cooling water heat exchanger, and a cooling water pump connected in sequence. The inlet end of the cooling water collection tank is connected to the caustic soda flake machine; the inlet end of the cooling water pump is connected to the cooling water collection tank; and the inlet end of the cooling water heat exchanger is connected to the cooling water pump. The inlet end of the cooling water heat exchanger is connected to the circulating cooling water main pipe; the outlet end of the cooling water heat exchanger is connected to the circulating cooling water return main pipe.

[0026] In one specific implementation, the caustic soda flake forming and packaging main system includes the caustic soda flake machine, the packaging machine, and the palletizer connected in sequence. The liquid inlet of the caustic soda flake machine is connected to the flash evaporation distribution tank and the alkali dust absorption and circulation tank, respectively; the feed inlet of the packaging machine is connected to the caustic soda flake machine; the feed inlet of the palletizer is connected to the packaging machine. The liquid inlet of the caustic soda flake machine is connected to the cooling water heat exchanger. Attached Figure Description

[0027] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments provided according to this disclosure and should not be construed as limiting the scope of this disclosure.

[0028] Figure 1 This is a schematic diagram of the process flow for the gas-fired direct heating method for producing solid alkali provided by the present invention.

[0029] Figure 2 This is a schematic diagram of the general process flow of the gas-fired direct heating method for producing solid alkali provided by the present invention.

[0030] Figure 3 A schematic diagram of the process flow of the pre-concentration main system provided by the present invention.

[0031] Figure 4 A schematic diagram of the process flow of the final concentration main system provided by the present invention.

[0032] Figure 5 This is a schematic diagram of the process flow of the main system for forming and packaging caustic soda flakes provided by the present invention.

[0033] Figure 6 This is a schematic diagram of the process flow of the flue gas auxiliary system provided by the present invention.

[0034] Figure 7 This is a schematic diagram of the process flow of the alkaline dust gas treatment auxiliary system provided by the present invention.

[0035] Figure 8 This is a schematic diagram of the process flow of the caustic soda cooling water auxiliary system provided by the present invention.

[0036] Figure 9 This is a schematic diagram of the general apparatus structure for the gas-fired direct heating method for producing solid alkali provided by the present invention.

[0037] Figure 10 This is a schematic diagram of the specific device structure of the pre-concentration main system provided by the present invention.

[0038] Figure 11 This is a schematic diagram of the specific device structure of the final concentration main system provided by the present invention.

[0039] Figure 12 This is a schematic diagram of the specific device structure of the main system for forming and packaging caustic soda flakes provided by the present invention.

[0040] Figure 13 This is a schematic diagram of the specific device structure of the flue gas auxiliary system provided by the present invention.

[0041] Figure 14 A schematic diagram of the specific device structure of the alkaline dust gas treatment auxiliary system provided by the present invention.

[0042] Figure 15 A schematic diagram of the specific device structure of the caustic soda cooling water auxiliary system provided by the present invention.

[0043] Figure 16 This is a schematic diagram of the specific structure of the final concentration falling film evaporator provided by the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this application clearer, the application will now be described in further detail with reference to the accompanying drawings.

[0045] It should be noted that, unless otherwise defined, the technical or scientific terms used in one or more embodiments of this specification should have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms "first," "second," and similar terms used in one or more embodiments of this specification do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word covers and is equivalent to the element or object listed following the word, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0046] refer to Figure 1 and Figure 2 As shown, Figure 1 A flowchart of a method for producing solid alkali according to an embodiment of this application is shown. Figure 2 A schematic diagram of an apparatus for producing solid alkali using direct combustion of natural gas, provided in an embodiment of this application, is shown.

[0047] The apparatus for producing solid alkali using natural gas, as provided in this application embodiment, mainly includes three main systems and three auxiliary systems. The three main systems are: a pre-concentration main system 1, a final concentration main system 2, and a flake caustic soda forming and packaging main system 3. The three auxiliary systems are: a flue gas auxiliary system 4, an alkali dust gas treatment auxiliary system 5, and a flake caustic soda cooling water auxiliary system 6. The specific workflows of the above six systems can be found in [reference needed]. Figures 2-8 The following is combined with Figures 1-8 The method for producing solid alkali provided in the embodiments of this application is described in detail. The method includes the following steps: Step 001: Add the first concentration of alkaline solution and sugar solution for pre-concentration. The heat source for pre-concentration comes from the steam generated by the final concentration falling film evaporator to obtain the second concentration of alkaline solution and sugar solution. Specifically, the first concentration mentioned above can be 50%, that is, 50% alkali solution is added to the pre-concentrating evaporator 1-1. The steam (secondary steam) generated by the final concentration falling film evaporator 2-2 is used as a heat source for pre-concentration. During the heating process, the pressure and temperature are controlled to achieve heat balance (for example, the vacuum degree of pre-concentration evaporation is -92 kPaG, and the evaporation temperature is 105°C). Sugar solution is added to the pre-concentrating evaporator 1-1 to ensure thorough mixing with the alkali solution. After pre-concentration, a mixture of alkali solution and sugar solution with a second concentration is obtained. The second concentration can be 67%. It should be understood that the second concentration is greater than the first concentration.

[0048] In the specific utilization of secondary steam, the high-temperature, low-pressure secondary steam generated by the final concentration falling film evaporator 2-2 is transported to the gas-liquid separation chamber for gas-liquid separation. Then, the separated high-temperature, low-pressure secondary steam is cooled by the final concentration demister 2-4 and the final concentration desuperheater to obtain low-temperature, low-pressure secondary steam, which is then sent to the pre-concentration evaporator 1-1 to heat the alkaline solution of the first concentration. For example, the low-temperature, low-pressure secondary steam has a pressure of 50 kPaG and a temperature of 111°C.

[0049] Step 002: Heat the second concentration of alkaline solution and sugar solution to cause the sugar solution and the second concentration of alkaline solution to undergo a primary saccharification reaction, and then send them to the final concentration falling film evaporator; the heat source for heating comes from the flue gas generated by the final concentration falling film evaporator. Specifically, the boiling point of the 67% alkali solution at a pressure of 50 kPaG is 189°C. The flue gas (final concentrated flue gas) is heated to the temperature required for the saccharification reaction (above 180°C) in the saccharification preheater 2-1, while the temperature of the final concentrated flue gas is reduced from 505°C to 250°C; the 67% alkali solution is preheated from 105°C to 190°C and undergoes the initial saccharification reaction with the sugar solution.

[0050] Step 003: Use the flue gas generated by the final concentration falling film evaporator to preheat the cold air entering the final concentration evaporator; Specifically, the flue gas is preheated from 250°C to 158°C before entering the chimney and being discharged; the cold air is preheated from 25°C to 135°C.

[0051] The combustion gas used in the combustion chamber can be natural gas, coal gas, hydrogen, or other combustible gases.

[0052] Step 004: Perform a second saccharification reaction on the mixture after the initial saccharification reaction; concentrate the mixture after the second saccharification reaction by falling film evaporation to obtain molten sodium alkali; Specifically, the 67% alkali solution enters the top saccharification reaction chamber 2-2-1 of the final concentration falling film evaporator 2-2 and is further heated for a second saccharification reaction to ensure complete saccharification. It then enters the falling film tube 2-2-4 in the middle of the final concentration falling film evaporator 2-2 for falling film evaporation and concentration, thus obtaining 98%~98.5% molten sodium alkali. The temperature of the 98% molten sodium alkali is 370℃.

[0053] When heating the final concentration falling film evaporator 2-2, the alkaline solution in the falling film tube 2-2-4 in the middle of the final concentration falling film evaporator 2-2 is concentrated by falling film evaporation using the heat source provided in step 003. High-temperature, low-pressure secondary steam and flue gas can also be obtained. The steam can be used as a heat source in step 001 after processing, and the flue gas can be used as a heat source in step 002.

[0054] Step 005: Flash evaporate the molten sodium alkali, cool and shape it, and then package it.

[0055] Specifically, 98% molten sodium alkali is flash-evaporized in flash distribution tank 2-3 and then enters caustic soda flake machine 3-1. After cooling and forming, caustic soda flakes are obtained and then bagged and packaged in caustic soda flake packaging machine 3-2.

[0056] In addition to the steps described above, the method provided in this application may also include the following steps: Step 006: Use liquid to absorb the alkaline dust generated during cooling, molding, and packaging into the alkaline absorption circulation tank.

[0057] Specifically, dilute alkali (or condensate) is used to completely absorb the alkali solution into the alkali absorption circulation tank in a hydraulic jet pump. Step 007: The high-temperature, atmospheric-pressure secondary steam generated after flash evaporation is cooled by a liquid spray pipe through a flash desuperheater and sent to the alkaline solution absorption circulation tank.

[0058] Specifically, the high-temperature, atmospheric-pressure flash steam is at atmospheric pressure and 370℃. A small amount of high-temperature, atmospheric-pressure secondary (superheated) steam is cooled by spraying with dilute alkali (or condensate) through flash desuperheaters 2-6, so that the high-temperature, atmospheric-pressure secondary (superheated) steam condenses and enters the alkali absorption circulation tank.

[0059] Step 008: The dilute alkali solution in the alkali absorption circulation tank overflows into the residual liquid hopper of the caustic soda flake machine. After washing and diluting the molten alkali residue in the residual liquid hopper, it enters the alkali recovery tank for recycling.

[0060] Specifically, the dilute alkali solution overflowing from the alkali absorption circulation tank enters the conical residual liquid hopper of the caustic soda flake machine 3-1. After washing and diluting the molten alkali residue, the dilute alkali flows by gravity into the alkali recovery tank of the 50% alkali system for recycling.

[0061] The above preparation method specifically includes the following principles: 1. Pre-concentration working mechanism: Using the secondary steam of final concentration as a heat source, 50% alkali is pre-concentrated to increase the concentration of alkali entering the final concentration, thereby reducing energy consumption.

[0062] 2. Principle of saccharification reaction: Sodium chlorate reacts with glucose at 180-200℃. The chemical reaction formula is as follows:

[0063] 3. Final Concentration Working Mechanism: The final concentration falling film evaporator 2-2-2 utilizes direct combustion of natural gas to heat the wall of the falling film evaporator 2-2. The alkali solution flows down the wall of the falling film evaporator 2-2-4 and evaporates on the wall, generating secondary steam. Blades located in the upper section of the falling film evaporator 2-2-4 rotate rapidly under the influence of the fast-flowing secondary steam, throwing the alkali solution splashed onto the center of the falling film evaporator 2-2-4 back onto the wall, maintaining a uniform alkali solution coating on the upper section of the wall. As the alkali solution flows down the wall of the falling film evaporator 2-2-4 from top to bottom, the evaporation rate increases, the secondary steam flow rate increases, and the alkali solution becomes increasingly viscous. Consequently, the splashing generated during falling film evaporation decreases, therefore, no blades are installed in the lower section of the falling film evaporator 2-2-4.

[0064] 4. Caustic soda flake formation mechanism: High-temperature molten sodium alkali enters the arc-shaped pot 3-1 of the caustic soda flake machine. A cooling water device is installed inside the drum. The drum rotates slowly. After the part immersed in the arc-shaped pot is cooled down, the molten sodium alkali forms a thin layer that condenses on the surface of the drum. Under the uniform rotation of the drum, a continuous thin layer is formed. After leaving the arc-shaped pot, it is further cooled to below 60°C and then scraped off by a scraper to form caustic soda flakes that enter the silo. After packaging and stacking, it is stored in the warehouse.

[0065] 5. Working mechanism of alkali dust gas treatment: A certain amount of alkali dust gas will be generated during the scraping and packaging of caustic soda flakes. The alkali dust gas is drawn into the hydraulic vacuum jet pump 5-3 to create a negative pressure, so that it is completely dissolved in dilute alkali.

[0066] The method provided in this application includes five process routes, as follows: (1) The pre-concentration main system 1 includes five process lines: 1) Alkali solution line: 50% alkali solution from the 50% alkali solution system I efficiency alkali pump enters the tube side of the pre-concentration evaporator 1-1 for evaporation and concentration, and 67% alkali solution and secondary steam enter the pre-concentration separator 1-3 for gas-liquid separation, and 67% alkali solution enters the pre-concentration alkali pump 1-5.

[0067] 2) Sugar solution line: Glucose powder is added to sugar solution tank 1-2, and then cooling water or pure water is added in proportion and stirred with compressed air to dissolve and store in sugar solution tank 1-2. The sugar solution from sugar solution tank 1-2 is added to pre-concentration evaporator 1-1 according to the alkali inlet flow rate ratio, and is thoroughly mixed in pre-concentration evaporator 1-1.

[0068] 3) Heating Steam Line: Secondary steam from the final concentration desuperheater 2-5 of the main final concentration system 2 enters the shell side of the pre-concentrating evaporator 1-1, where it condenses while heating the tube-side alkaline solution. The condensate is discharged through the pre-concentrating gas-blocking drain tank 1-5 and then enters the 50% alkaline solution system's third-effect gas-blocking drain tank. The secondary steam returns to the shell side of the pre-concentrating evaporator 1-1. Non-condensable gases are vented from the shell side of the pre-concentrating evaporator 1-1.

[0069] 4) Vacuum circuit: The secondary steam after gas-liquid separation in the pre-concentrator 1-3 is de-cooled by condensate spray in the pre-concentrator desuperheater 1-6, and then enters the shell side of the pre-concentrator surface condenser 1-7 for condensation. The condensate enters the main condensate tank of the 50% alkali solution system. Non-condensable gases are extracted and vented by the pre-concentrator vacuum pump 1-8.

[0070] 5) Circulating water line: Circulating cooling water from the circulating cooling water supply main enters the tube side of the pre-concentrated surface condenser 1-7, where the shell side secondary steam is condensed, and the circulating cooling return water returns to the circulating cooling return water main.

[0071] (2) The final concentration main system 2 includes three process lines: 1) Alkali Solution Flow: 67% alkali solution from the pre-concentration alkali pump 1-4 of the pre-concentration main system 1 enters the saccharification preheater 2-1 for preheating and initial saccharification reaction. It then enters the saccharification reaction chamber 2-2-1 at the top of the final concentration falling film evaporator 2-2 for a second saccharification reaction, bringing the saccharification reaction closer to completion. Next, it enters the falling film tube 2-2-4 of the final concentration falling film evaporator 2-2 for evaporation and concentration, obtaining 98% molten alkali. This molten alkali and secondary steam enter the gas-liquid separation chamber 2-2-3 at the bottom of the final concentration falling film evaporator 2-2 for gas-liquid separation. The resulting 98% molten alkali is then forced into the flash distribution tank 2-3 under the pressure of the secondary steam for flash evaporation.

[0072] 2) Secondary Steam Line: The secondary steam separated in the gas-liquid separation chamber 2-2-3 at the bottom of the final concentration falling film evaporator 2-2, after being demisted by the final concentration demister 2-4, returns to the gas-liquid separation chamber 2-2-3 at the bottom of the final concentration falling film evaporator 2-2 via the same route. The secondary steam is de-cooled by condensate spray in the final concentration desuperheater 2-5. The flash steam after flashing in the flash distribution tank 2-3 is de-cooled and condensed in the flash desuperheater 2-6 by 40% dilute alkali from the alkali recovery pump of the 50% alkali system or by condensate spray.

[0073] 3) Flue Gas Flow: Cold air is compressed by blower 4-4 and enters air preheater 4-1 for preheating. Flue gas from chimney 4-2 is compressed by circulating fan 4-3 and mixed with preheated hot air in the pipeline. It is then ignited with fuel gas in burner 4-5 on final concentration falling film evaporator 2-2 installed in final concentration main system 2, and burned in furnace 2-2-2 of final concentration falling film evaporator 2-2. The flue gas after combustion enters saccharification preheater 2-1 to preheat 67% alkali solution. After preheating the alkali solution, the flue gas in furnace 2-2-2 of final concentration falling film evaporator 2-2 exchanges heat with the alkali solution in falling film pipe 2-2-4 in the middle of final concentration falling film evaporator 2-2, and then enters air preheater 4-1 to preheat air. After preheating the air, the flue gas enters chimney 4-2 and is discharged at a specified height.

[0074] (3) The main system for forming and packaging caustic soda flakes includes four process lines: 1) Caustic soda flakes line: High-temperature 98% molten caustic soda from the final concentration main system 2 flash distribution tank 2-3 enters the caustic soda flake machine 3-1 for forming and cooling, then enters the packaging machine 3-2 for bagging and packaging, and then enters the palletizer 3-3 for palletizing and warehousing.

[0075] 2) Liquid alkali line: 40% dilute alkali from the flash desuperheater 2-6 of the final concentration main system 2 enters the alkali dust absorption circulation tank 5-1 for storage, and non-condensable gas is discharged in the alkali dust absorption circulation tank 5-1. After being pressurized by the alkali dust absorption circulation pump 5-2, the 40% dilute alkali enters the hydraulic vacuum jet pump 5-3 simultaneously with the alkali dust gas from the caustic soda flake machine 3-1 and the packaging machine 3-2. While absorbing and dissolving the alkali dust gas, it also creates a local slight negative pressure on the caustic soda flake machine 3-1 and the packaging machine 3-2 to ensure that the alkali dust gas does not fly into the atmosphere. The 40% dilute alkali from the hydraulic vacuum jet pump 5-3 enters the alkali dust absorption circulation tank 5-1 for storage. The 40% dilute alkali flows fully into the conical hopper of the caustic soda flake machine 3-1 to dissolve the splashed molten alkali. The dissolved alkali enters the alkali recovery tank of the 50% alkali system.

[0076] 3) Caustic soda cooling water line: Condensate or pure water is added and stored in cooling water collection tank 6-1. The cooling water for caustic soda enters the cooling water heat exchanger 6-2 via cooling water pump 6-3 for cooling, and then enters the caustic soda machine 3-1 to cool the caustic soda flakes. The caustic soda cooling return water enters cooling water collection tank 6-1 for storage.

[0077] 4) Circulating water line: Circulating cooling water from the circulating cooling water main enters the cooling water heat exchanger 6-2 to cool the caustic soda cooling water, and the circulating cooling return water returns to the circulating cooling return water main.

[0078] In a specific example, the above method uses the following parameters to prepare solid alkali: A method for producing solid alkali by direct heating of gas, the process flow is as follows: Figures 1 to 8 As shown, it includes the following steps: (1) 50% alkali solution from the 50% alkali solution system I-efficiency alkali pump enters the tube side of the pre-concentrating evaporator 1-1. The low-temperature, low-pressure secondary (saturated) steam after final concentration and cooling is used as a heat source to enter the shell side of the pre-concentrating evaporator 1-1 (the pressure and temperature are controlled to achieve heat balance, and sugar solution is added in the tube side of the pre-concentrating evaporator 1-1 to mix it thoroughly with the alkali solution). Pre-concentration is carried out under the conditions of vacuum degree of -92kPaG and evaporation temperature of 105℃ to obtain 67% alkali solution and secondary steam. The 67% alkali solution obtained after gas-liquid separation enters the pre-concentrating separator 1-3 for gas-liquid separation. After gas-liquid separation, the 67% alkali solution enters the pre-concentrating alkali pump 1-4. (2) The 67% alkali solution delivered by the concentrated alkali pump 1-4 enters the saccharification preheater 2-1. The 67% alkali solution is preheated from 105℃ to 190℃ by the final concentrated flue gas, and the final concentrated flue gas is reduced from 505℃ to 250℃. The preheated 67% alkali solution enters the saccharification reaction chamber 2-2-1 at the top of the final concentrated falling film evaporator 2-2 and is further heated. After the saccharification reaction is carried out again, the saccharification reaction tends to be complete.

[0079] (3) Cold air is delivered into air preheater 4-1 by blower 4-4, and preheated to 135°C by saccharification preheating flue gas, and then enters burner 4-5 to be fully mixed and burned with fuel gas to provide heat source for final concentration; (3) Cold air is delivered into air preheater 4-1 by blower 4-4 and preheated to 135°C by saccharification preheating flue gas. After the flue gas temperature drops from 250°C to 158°C, it enters chimney 4-2 for exhaust. A small portion of the flue gas in chimney 4-2 is drawn into burner 4-5 by circulating fan 4-3 and fully mixed with the fuel gas for combustion, providing a heat source for final concentration. (4) After the saccharification reaction is complete, the alkaline solution enters the falling film tube 2-2-4 of the final concentration falling film evaporator 2-2. The heat source is provided by direct combustion of gas for falling film evaporation and concentration, and 98-98.5% high temperature (370℃) molten (sodium) alkali and high temperature (370℃), low pressure (50kPaG) secondary (superheated) steam are separated into gas and liquid in the gas-liquid separation chamber 2-2-3 at the bottom of the concentration falling film evaporator 2-2. (5) The high-temperature (370℃) and low-pressure (50kPaG) secondary (superheated) steam obtained from gas-liquid separation is defoamed by the final concentrator demister 2-4 and de-temperatured by the final concentrator desuperheater 2-5. The resulting low-temperature (111℃) and low-pressure (50kPaG) secondary (saturated) steam provides a heat source for pre-concentration. (6) The 98% molten (sodium) alkali obtained by gas-liquid separation is flashed in flash distribution tank 2-3 and then enters caustic soda flake machine 3-1. After cooling and forming, caustic soda flakes are obtained. Then, they are bagged and packaged by caustic soda flake packaging machine 3-2, and finally stacked by palletizer 3-3 and transported into the warehouse. (7) The alkali dust generated during the scraping process of the caustic soda machine 3-1 and the packaging process of the packaging machine 3-2 is completely absorbed by dilute alkali (or condensate) in the hydraulic vacuum jet pump 5-3 and enters the alkali absorption circulation tank 5-1. (8) A small amount of high-temperature (370℃) and atmospheric-pressure flash vapor after flashing in flash distribution tank 2-3 is cooled by spraying with dilute alkali (or condensate) through flash desuperheater 2-6, so that the high-temperature (370℃) and atmospheric-pressure flash vapor condenses and enters alkali absorption circulation tank 5-1. (9) The dilute alkali solution in the alkali absorption circulation tank 5-1 overflows into the conical residual liquid hopper of the caustic soda flake machine 3-1. After washing and diluting the molten alkali residue, the dilute alkali flows into the 50% alkali system alkali recovery tank for recycling.

[0080] The design specifications for solid alkali products are as follows: 1. Design parameters for raw materials in solid alkali production: 1) 50% alkaline solution: (w / w%) (GB / T209-2018) NaOH ≥ 50.0%, Na₂CO₃ ≤ 0.50%, NaCl ≤ 0.05%, Fe₂O₃ ≤ 0.005%; 2) Glucose: (w / w%) (GB / T20880-2018) C6H12O6·H2O≥99.0%, pH=4.0~6.5, chloride≤0.01%, moisture≤10.0%; 3) Natural gas: (GB17820-2018) Higher heating value ≥34.0 MJ / Nm 3 Total sulfur content ≤20mg / Nm 3 Hydrogen sulfide concentration ≤6mg / Nm 3 The mole fraction of carbon dioxide is ≤3%.

[0081] 2. Raw material consumption indicators for solid alkali production: 1) 50% alkali solution: 2000 kg / t (98% alkali); 2) Glucose: 3.00 kg / t (98% alkali); 3) Natural gas: 75 Nm 3 / t (98% alkali).

[0082] 3. Quality indicators for solid alkali products: (w / w%) (GB / T209-2018) NaOH ≥ 98.0%, Na2CO3 ≤ 0.80%, NaCl ≤ 0.05%, Fe2O3 ≤ 0.008%.

[0083] To facilitate understanding of the effects of the methods provided in the embodiments of this application, their parameters are compared with those of existing solid alkali preparation methods.

[0084] 1. Comparison of control parameters:

[0085] 2. Comparison of consumption parameters:

[0086] As can be seen from the above methods, the method provided in this application embodiment has the advantages of low energy consumption, low cost, high processing efficiency, energy saving and environmental protection, complete reaction, and high product recovery rate and purity, making it suitable for industrial promotion and application. Controlling the final concentration secondary steam pressure above 50 kPaG can increase the pre-concentrated alkali concentration from 62% to 67%, not only ensuring full utilization of the final concentration secondary steam but also reducing the amount of evaporation water in the final concentration. Replacing the waste heat boiler with a saccharification preheater 2-1 not only completes the saccharification reaction before the alkali solution enters the falling film tube 2-2-4, thus improving the service life of the falling film tube 2-2-4, but also increases the alkali solution temperature entering the falling film tube 2-2-4 from 95℃ to 190℃. Using direct gas heating eliminates the need for high-temperature molten salt as a heat carrier, reducing heat loss from heat carrier heat transfer, preventing difficulties in handling molten salt pipeline blockages, and eliminating the dangers of molten salt leakage to personal safety and property, thereby ensuring the safe and stable operation of the system and the safety of personal safety and property.

[0087] By using combustible gases (such as natural gas, coal gas, and hydrogen) to directly heat the alkali solution in the falling film tube 2-2-4 within the final concentration falling film evaporator 2-2, the molten salt system is eliminated, thus eliminating its investment and operating costs. The pressure of the secondary steam in the final concentration is increased, meeting the prerequisite for increasing the alkali concentration from the pre-concentration stage. This increases the amount of water evaporated during pre-concentration and decreases the amount evaporated during final concentration, balancing the heat provided by the secondary steam in the final concentration with the heat required for pre-concentration, ultimately reducing natural gas consumption. The waste heat boiler is replaced with a saccharification preheater 2-1, increasing the alkali inlet temperature of the falling film tube 2-2-4 in the final concentration falling film evaporator 2-2 (and adding the sugar solution simultaneously with the alkali inlet during pre-concentration, ensuring thorough mixing). This allows the saccharification reaction to occur before the alkali solution enters the falling film tube 2-2-4 in the final concentration falling film evaporator 2-2, effectively extending the service life of the falling film tube 2-2-4 (eliminating the molten salt system also eliminates the frictional corrosion of the falling film tube 2-2-4 by the molten salt).

[0088] This invention selects appropriate equipment according to the requirements of each process step. While ensuring that individual equipment meets the process requirements such as complete reaction, it achieves overall optimization of the device. It can meet the needs of large-scale industrial production and has the advantages of simple structure, complete functions, easy operation, and advanced and mature technology. The whole set of equipment has the advantages of low purchase cost, low production energy consumption, and high processing efficiency, making it suitable for industrial promotion and application.

[0089] The above method has the advantages of low energy consumption, low cost, energy saving and environmental protection, complete saccharification reaction which increases the life of falling film tube 2-2-4, and high alkali recovery rate, making it suitable for industrial promotion and application. As can be seen from the above description, the scheme disclosed in this application achieves complete saccharification reaction and stable product quality by adopting the above method; the system has a small material throughput, and the segmented concentration further reduces the system's material throughput; the equipment has a long service life, reducing energy consumption. Safety is significantly improved, as molten salt is not required. It features a high degree of automation, closed operation, and significant environmental benefits. The process is simplified, resulting in lower equipment investment and higher single-unit capacity for continuous, large-scale production.

[0090] Based on a general inventive concept, the present invention also provides an apparatus for the above-described method, with reference to... Figure 9 As shown, the apparatus includes a pre-concentration main system 1, a final concentration main system 2, and a caustic soda flake forming and packaging main system 3 connected in sequence. The apparatus also includes a flue gas auxiliary system 4 connected to the final concentration main system 2, an alkali dust gas treatment auxiliary system 5 connected to the caustic soda flake forming and packaging main system 3, and a caustic soda flake cooling water auxiliary system 6. The alkali dust gas treatment auxiliary system 5 and the caustic soda flake cooling water auxiliary system 6 can be added as optional components to the solid alkali production apparatus of this application.

[0091] The flue gas auxiliary system 4 provides the high-temperature flue gas after combustion of the fuel gas required for the final concentration main system 2; the alkali dust gas treatment auxiliary system 5 provides the alkali dust gas treatment required for the caustic soda flake forming and packaging main system 3; and the caustic soda flake cooling water auxiliary system 6 provides the caustic soda flake cooling water required for the caustic soda flake forming and packaging main system 3.

[0092] In a specific configuration, the pre-concentration main system 1 includes a pre-concentration evaporator 1-1, which evaporates and concentrates the alkaline solution of the first concentration to the alkaline solution of the second concentration. The final concentration main system 2 includes components such as a saccharification preheater 2-1, a final concentration falling film evaporator 2-2, and a flash distribution tank 2-3. Specifically, the saccharification preheater 2-1 is used to perform a primary saccharification reaction on the second concentration of alkali solution and sugar solution to obtain a mixed solution; the final concentration falling film evaporator includes a saccharification reactor and a falling film tube 2-2-4; wherein, the saccharification reactor is used to perform a secondary saccharification reaction on the mixed solution obtained from the primary saccharification reaction, and the falling film tube 2-2-4 is used to perform falling film evaporation and concentration on the mixture from the secondary saccharification reaction to obtain molten sodium alkali; the flash distribution tank 2-3 is used for flash evaporation of the molten sodium alkali. The flue gas auxiliary system 4 is used to input the flue gas generated by the final concentration falling film evaporator 2-2 into the saccharification preheater 2-1 and heat the saccharification preheater 2-1, and heat the air preheater 4-1. The flue gas is mixed with the air preheated by the air preheater 4-1 by the circulating fan 4-3 and then mixed and burned in the burner 4-5. The high-temperature flue gas generated evaporates and concentrates the alkaline solution in the falling film tube 2-2-4 of the final concentration falling film evaporator 2-2. The main system 3 for forming and packaging caustic soda flakes includes equipment such as a caustic soda flake machine 3-1 and a packaging machine 3-2; among them, the caustic soda flake machine 3-1 is used to cool and form molten sodium caustic soda after flash evaporation; the packaging machine 3-2 is used to package the formed caustic soda flakes.

[0093] In the above scheme, the final concentration secondary steam pressure is controlled above 50 kPaG, which can increase the pre-concentrated alkali concentration from 62% to 67%, not only ensuring full utilization of the final concentration secondary steam but also reducing the evaporation water volume of the final concentration. Replacing the waste heat boiler with a saccharification preheater 2-1 not only completes the saccharification reaction before the alkali solution enters the falling film tube 2-2-4, thus extending the service life of the falling film tube 2-2-4, but also increases the alkali solution temperature entering the falling film tube 2-2-4 from 95℃ to 190℃. Using direct gas heating eliminates the need for high-temperature molten salt as a heat carrier, reducing heat loss from heat carrier transfer, eliminating the difficulties in handling molten salt pipeline blockages, and preventing molten salt leaks that could endanger personal safety and property, thereby ensuring the safe and stable operation of the system and the safety of personal safety and property.

[0094] like Figure 10 As shown, in a specific feasible implementation, the pre-concentration main system 1 further includes a sugar solution tank 1-2, a pre-concentration separator 1-3, a pre-concentration alkali pump 1-4, a pre-concentration gas-blocking drain tank 1-5, a pre-concentration desuperheater 1-6, a pre-concentration surface condenser 1-7, and a pre-concentration vacuum pump 1-8, which are connected in sequence to the pre-concentration evaporator 1-1; that is, in this embodiment, the pre-concentration main system 1 includes a pre-concentration evaporator 1-1, a sugar solution tank 1-2, a pre-concentration separator 1-3, a pre-concentration alkali pump 1-4, a pre-concentration gas-blocking drain tank 1-5, a pre-concentration desuperheater 1-6, a pre-concentration surface condenser 1-7, and a pre-concentration vacuum pump 1-8, which are connected in sequence. The inlet of the pre-concentrating evaporator 1-1 (alkali solution and sugar solution) is connected to the first-efficiency alkali pump of the 50% alkali system and the sugar solution tank 1-2, respectively; the inlet of the pre-concentrating separator 1-3 (alkali solution + secondary steam) is connected to the outlet of the pre-concentrating evaporator 1-1; and the inlet of the pre-concentrating alkali pump 1-4 (alkali solution) is connected to the pre-concentrating separator 1-3. The shell side (secondary steam) inlet of the pre-concentrating evaporator 1-1 is connected to the final concentrating desuperheater 2-5 of the final concentrating main system 2; the shell side (non-condensable gas) outlet of the pre-concentrating evaporator 1-1 is connected to the atmosphere; the liquid inlet of the pre-concentrating gas-blocking drain tank 1-5 (condensate + secondary steam) is connected to the shell side of the pre-concentrating evaporator 1-1; the liquid outlet of the pre-concentrating gas-blocking drain tank 1-5 (condensate) is connected to the III-effect gas-blocking drain tank of the 50% alkali system; the gas outlet of the pre-concentrating gas-blocking drain tank 1-5 (secondary steam) is connected to the shell side of the pre-concentrating evaporator 1-1. The inlet of the pre-concentrating desuperheater 1-6 (secondary steam) is connected to the pre-concentrating separator 1-3; the inlet of the shell side (secondary steam) of the pre-concentrating surface condenser 1-7 is connected to the pre-concentrating desuperheater 1-6; the inlet of the pre-concentrating vacuum pump 1-8 (non-condensable gas) is connected to the shell side of the pre-concentrating surface condenser 1-7; the outlet of the pre-concentrating vacuum pump 1-8 (non-condensable gas) is connected to the atmosphere; the outlet of the shell side (condensate) of the pre-concentrating surface condenser 1-7 is connected to the main condensate tank of the 50% alkali system; the inlet of the tube side (circulating cooling water supply) of the pre-concentrating surface condenser 1-7 is connected to the main circulating cooling water supply pipe; and the outlet of the tube side (circulating cooling return water) of the pre-concentrating surface condenser 1-7 is connected to the main circulating cooling return water pipe.

[0095] like Figure 11 As shown, in a specific feasible implementation, the final concentration main system 2 includes a saccharification preheater 2-1, a final concentration falling film evaporator 2-2, a flash distribution tank 2-3, a final concentration demister 2-4, a final concentration desuperheater 2-5, and a flash desuperheater 2-6 connected in sequence. The alkali inlet of saccharification preheater 2-1 is connected to the pre-concentration alkali pump 1-4 of the pre-concentration main system 1; the alkali inlet of final concentration falling film evaporator 2-2 is connected to saccharification preheater 2-1; the molten alkali inlet of flash distribution tank 2-3 is connected to final concentration falling film evaporator 2-2; the alkali inlet of flash desuperheater 2-6 is connected to the alkali recovery pump of the 50% alkali system. The inlet of the final concentration demister 2-4 (secondary steam) is connected to the final concentration falling film evaporator 2-2; the inlet of the final concentration desuperheater 2-5 (secondary steam) is connected to the final concentration demister 2-4; the inlet of the flash desuperheater 2-6 (flash steam) is connected to the flash distribution tank 2-3; and the (flue gas) inlet of the saccharification preheater 2-1 is connected to the final concentration falling film evaporator 2-2. Additionally, the final concentration desuperheater 2-5 is connected to the shell side (secondary steam) inlet of the pre-concentration evaporator 1-1.

[0096] Please refer to the above. Figure 16 When arranging the final concentration falling film evaporator, such as Figure 16As shown, the final concentration falling film evaporator (2-2) includes a saccharification reaction chamber 2-2-1 at the top, a furnace chamber 2-2-2 in the middle, a gas-liquid separation chamber 2-2-3 at the bottom, and multiple falling film tubes 2-2-4 (the number of falling film tubes is determined by the solid alkali production capacity). The falling film tubes 2-2-4 are located in the furnace chamber 2-2-2, and their lower parts are inserted into the gas-liquid separation chamber 2-2-3. An alkali inlet pipe 2-2-5 is installed on the saccharification reaction chamber 2-2-1, and a connecting pipe 2-2-6 at the top connects to multiple falling film tubes 2-2-4. The lower parts of the falling film tubes 2-2-4 are inserted into the gas-liquid separation chamber 2-2-3. A burner (4-5) is installed on the burner interface 2-2-7 that connects the saccharification reaction chamber 2-2-1 to the furnace chamber 2-2-2. The furnace chamber 2-2-2 is equipped with a flue gas outlet 2-2-8, a flue gas temperature measuring port 2-2-9, an inner lining of insulating castable layer 2-2-10, and a refractory castable layer 2-2-11. The gas-liquid separation chamber 2-2-3 is equipped with a secondary steam outlet 2-2-12, a molten alkali outlet 2-2-13, an inspection hole 2-2-14, and a molten alkali temperature measuring port 2-2-15 at the bottom.

[0097] like Figure 13 As shown, in an optional embodiment, the flue gas auxiliary system 4 includes an air preheater 4-1, a chimney 4-2, a circulating fan 4-3, a blower 4-4, and a burner 4-5 connected in sequence.

[0098] The air preheater 4-1 (air) inlet is connected to the blower 4-4; the circulating fan 4-3 (flue gas) inlet is connected to the chimney 4-2; the burner 4-5 (air) inlet is connected to both the air preheater 4-1 and the circulating fan 4-3; the burner 4-5 (gas) inlet is connected to the gas main; and the burner 4-5 is directly connected to the final concentration falling film evaporator 2-2. The (flue gas) inlet of the air preheater 4-1 is connected to the saccharification preheater 2-1 of the final concentration main system 2; the (flue gas) inlet of the chimney 4-2 is connected to the air preheater 4-1; and the (flue gas) outlet of the chimney 4-2 is connected to the atmosphere.

[0099] like Figure 14 As shown, in an optional scheme, the alkaline dust gas treatment auxiliary system 5 includes an alkaline dust absorption and circulation tank 5-1, an alkaline dust absorption and circulation pump 5-2, and a hydraulic vacuum jet pump 5-3 connected in sequence. The inlet of the alkali dust absorption circulation tank 5-1 (alkali solution) is connected to the hydraulic vacuum jet pump 5-3 and the flash desuperheater 2-6 of the final concentration main system 2, respectively; the inlet of the hydraulic vacuum jet pump 5-3 (alkali solution) is connected to the alkali dust absorption circulation pump 5-2; the inlet of the alkali dust absorption circulation pump 5-2 (alkali solution) is connected to the alkali dust absorption circulation tank 5-1. The air inlet of the hydraulic vacuum jet pump 5-3 (alkali dust gas) is connected to the caustic soda flake machine 3-1 and the packaging machine 3-2 of the caustic soda flake forming and packaging main system 3.

[0100] like Figure 15 As shown, in an optional embodiment, the caustic soda cooling water auxiliary system 6 includes a cooling water collection tank 6-1, a cooling water heat exchanger 6-2, and a cooling water pump 6-3 connected in sequence.

[0101] The inlet end of the cooling water collection tank 6-1 (cooling return water for caustic soda flakes) is connected to the caustic soda flake machine 3-1 of the main caustic soda flake forming and packaging system 3; the inlet end of the cooling water pump 6-3 (cooling water supply for caustic soda flakes) is connected to the cooling water collection tank 6-1; the inlet end of the cooling water heat exchanger 6-2 (cooling water supply for caustic soda flakes) is connected to the cooling water pump 6-3. The inlet end of the cooling water heat exchanger 6-2 (circulating cooling water supply) is connected to the circulating cooling water supply main pipe; the outlet end of the cooling water heat exchanger 6-2 (circulating cooling water return) is connected to the circulating cooling water return main pipe.

[0102] like Figure 12 As shown, in one optional embodiment, the caustic soda flake forming and packaging main system 3 includes a caustic soda flake machine 3-1, a packaging machine 3-2, and a palletizer 3-3 connected in sequence; The liquid inlet of the caustic soda flake machine 3-1 (molten caustic soda and dilute caustic soda) is connected to the flash distribution tank 2-3 of the final concentration main system 2 and the caustic dust absorption and circulation tank 5-1 of the caustic dust gas treatment auxiliary system 5, respectively; the feed end of the packaging machine 3-2 (caustic soda flakes) is connected to the caustic soda flake machine 3-1; the feed end of the palletizer 3-3 (bagged caustic soda flakes) is connected to the packaging machine 3-2; The liquid inlet of the caustic soda machine 3-1 (caustic soda cooling water supply) is connected to the cooling water heat exchanger 6-2 of the caustic soda cooling water auxiliary system 6.

[0103] As can be seen from the above description, the apparatus for producing solid alkali provided in the embodiments of this application may include three main systems and three auxiliary systems (such as...). Figure 9As shown), there are three main systems: pre-concentration main system 1, final concentration main system 2, and caustic soda flake forming and packaging main system 3; and three auxiliary systems: flue gas auxiliary system 4, alkali dust gas treatment auxiliary system 5, and caustic soda flake cooling water auxiliary system 6. The above-mentioned methods for preparing solid alkali can be achieved through the aforementioned systems. During preparation, combustible gas (such as natural gas, coal gas, or hydrogen) is used to directly heat the alkali solution in the falling film tubes of the final concentration falling film evaporator for falling film evaporation and concentration, eliminating the need for the molten salt system and thus eliminating its investment and operating costs. The pressure of the secondary steam in the final concentration is increased to meet the prerequisite for increasing the concentration of alkali produced from the pre-concentration, thereby increasing the amount of water evaporated in the pre-concentration and decreasing the amount of water evaporated in the final concentration. This balances the heat provided by the secondary steam in the final concentration with the heat required for pre-concentration, ultimately achieving the goal of reducing natural gas consumption. The waste heat boiler is replaced with a saccharification preheater, increasing the alkali inlet temperature of the falling film tubes in the final concentration falling film evaporator (and adding the sugar solution at the same time as the alkali is introduced into the pre-concentration process, ensuring thorough and uniform mixing of the sugar and alkali solutions). The saccharification reaction is completed before the alkali solution enters the falling film tubes of the final concentration falling film evaporator, effectively improving the service life of the falling film tubes (eliminating the molten salt system also eliminates the frictional corrosion of the falling film tubes by the molten salt).

[0104] One or more embodiments of this specification are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments of this specification should be included within the scope of protection of this disclosure.

[0105] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for producing solid alkali, characterized in that, Includes the following steps: A first concentration of alkaline solution and sugar solution is added for pre-concentration. The heat source for pre-concentration comes from steam generated by the final concentration falling film evaporator, resulting in a second concentration of alkaline solution and sugar solution. The alkaline solution and sugar solution of the second concentration are heated to cause the sugar solution and the alkaline solution of the second concentration to undergo a primary saccharification reaction, and then fed into the final concentration falling film evaporator; the heat source for heating comes from the flue gas generated by the final concentration falling film evaporator. The flue gas generated by the final concentration falling film evaporator is used to preheat the cold air entering the final concentration evaporator; The mixture after the initial saccharification reaction is subjected to a second saccharification reaction; the mixture after the second saccharification reaction is concentrated by falling film evaporation to obtain molten sodium alkali; The molten sodium alkali is flash-evaporated, cooled, shaped, and packaged.

2. The method for producing solid alkali according to claim 1, characterized in that, The process of adding a first-concentration alkaline solution and sugar solution for pre-concentration, wherein the heat source for pre-concentration is steam generated by the final concentration falling film evaporator, specifically includes: The high-temperature, low-pressure secondary steam generated by the final concentration falling film evaporator is transported to the gas-liquid separation chamber for gas-liquid separation. The separated high-temperature and low-pressure secondary steam is cooled by a final concentrator and a final concentrator to obtain low-temperature and low-pressure secondary steam, which is then sent to a pre-concentrator evaporator to heat the alkaline solution of the first concentration.

3. The method for producing solid alkali according to claim 2, characterized in that, It also includes the following steps: The alkaline dust generated during cooling, molding, and packaging is absorbed by a liquid and then transferred to an alkaline solution absorption and circulation tank.

4. The method for producing solid alkali according to claim 3, characterized in that, It also includes the following steps: The high-temperature, atmospheric-pressure secondary steam generated after flash evaporation is cooled by a liquid spray pipe through a flash desuperheater and then sent to the alkaline solution absorption circulation tank.

5. The method for producing solid alkali according to claim 3, characterized in that, It also includes the following steps: The dilute alkali solution overflowing from the alkali absorption and circulation tank is sent to the residual liquid hopper of the caustic soda flake machine. After washing and diluting the molten alkali residue in the residual liquid hopper, it enters the alkali recovery tank for recycling.

6. The method for producing solid alkali according to claim 3, characterized in that, The pre-concentration has a vacuum degree of -92 kPaG and an evaporation temperature of 105°C.

7. The method for producing solid alkali according to claim 3, characterized in that, The flue gas is preheated from 250°C to 158°C before entering the chimney and being discharged into the atmosphere; the cold air is preheated from 25°C to 135°C.

8. The method for producing solid alkali according to claim 2, characterized in that, The low-temperature, low-pressure secondary steam has a pressure of 50 kPaG and a temperature of 111°C.

9. An apparatus for producing solid alkali, characterized in that, include: The pre-concentration main system includes a pre-concentration evaporator, which is used to heat an alkaline solution of a first concentration to an alkaline solution of a second concentration. The final concentration main system includes a saccharification preheater, a final concentration falling film evaporator, and a flash distribution tank. The saccharification preheater is used to perform a primary saccharification reaction on a second concentration of alkali solution and sugar solution to obtain a mixed solution. The final concentration falling film evaporator includes a saccharification reactor and a falling film tube. The saccharification reactor is used to perform a secondary saccharification reaction on the mixed solution obtained from the primary saccharification reaction, and the falling film tube is used to perform falling film evaporation and concentration on the mixture from the secondary saccharification reaction to obtain molten sodium alkali. The flash distribution tank is used to flash evaporate the molten sodium alkali. The flue gas auxiliary system is used to input the flue gas generated by the final concentration falling film evaporator into the saccharification preheater and heat the saccharification preheater, heat the air preheater, and the flue gas is mixed with the air preheated by the air preheater by the circulating fan and then into the burner to heat the final concentration falling film evaporator. The main system for forming and packaging caustic soda flakes includes a caustic soda flake machine and a packaging machine; wherein, the caustic soda flake machine is used to cool and form molten sodium caustic soda after flash evaporation; and the packaging machine is used to package the formed caustic soda flakes.

10. The apparatus for producing solid alkali according to claim 9, characterized in that, The pre-concentration main system also includes a sugar solution tank, a pre-concentration separator, a pre-concentration alkali pump, a pre-concentration gas-blocking drain tank, a pre-concentration desuperheater, a pre-concentration surface condenser, and a pre-concentration vacuum pump, which are connected in sequence to the pre-concentration evaporator. The inlet of the pre-concentrating evaporator is connected to the first-efficiency alkali pump of the 50% alkali system and the sugar solution tank, respectively; the inlet of the pre-concentrating separator is connected to the outlet of the pre-concentrating evaporator; and the inlet of the pre-concentrating alkali pump is connected to the pre-concentrating separator. The shell-side inlet of the pre-concentrating evaporator is connected to the final concentration main system; the shell-side outlet of the pre-concentrating evaporator is connected to the atmosphere; the liquid inlet of the pre-concentrating gas-blocking drain tank is connected to the shell side of the pre-concentrating evaporator; the liquid outlet of the pre-concentrating gas-blocking drain tank is connected to the III-effect gas-blocking drain tank of the 50% alkali system; and the gas outlet of the pre-concentrating gas-blocking drain tank is connected to the shell side of the pre-concentrating evaporator. The inlet of the pre-concentrating desuperheater is connected to the pre-concentrating separator; the shell-side inlet of the pre-concentrating surface condenser is connected to the pre-concentrating desuperheater; the inlet of the pre-concentrating vacuum pump is connected to the shell side of the pre-concentrating surface condenser; the outlet of the pre-concentrating vacuum pump is connected to the atmosphere; the shell-side liquid outlet of the pre-concentrating surface condenser is connected to the main condensate tank of the 50% alkali system; the tube-side liquid inlet of the pre-concentrating surface condenser is connected to the circulating cooling water supply main pipe; and the tube-side liquid outlet of the pre-concentrating surface condenser is connected to the circulating cooling return water main pipe.

11. The apparatus for producing solid alkali according to claim 10, characterized in that, The final concentration main system also includes a final concentration demister, a final concentration desuperheater, and a flash desuperheater; wherein... The inlet of the saccharification preheater is connected to the pre-concentration alkali pump; the inlet of the final concentration falling film evaporator is connected to the saccharification preheater; the inlet of the flash distribution tank is connected to the final concentration falling film evaporator; and the inlet of the flash desuperheater is connected to the alkali recovery pump of the 50% alkali system. The air inlet of the final concentration demister is connected to the final concentration falling film evaporator; the air inlet of the final concentration desuperheater is connected to the final concentration demister; and the air inlet of the flash desuperheater is connected to the flash distribution tank. The air inlet of the saccharification preheater is connected to the final concentration falling film evaporator.

12. The apparatus for producing solid alkali according to claim 11, characterized in that, The final concentration falling film evaporator includes a saccharification reaction chamber at the top, a furnace chamber in the middle, a gas-liquid separation chamber at the bottom, and multiple falling film tubes, with the falling film tubes located in the furnace chamber and the lower part of the falling film tubes inserted into the gas-liquid separation chamber. An alkali inlet pipe is provided on the saccharification reaction chamber, and a connecting pipe connected to multiple falling film pipes is provided on the top of the saccharification reaction chamber; a burner is installed on the burner interface that connects the saccharification reaction chamber to the furnace. The furnace is equipped with a flue gas outlet and a flue gas temperature measuring port, and the furnace is lined with a thermal insulation castable layer and a refractory castable layer. The gas-liquid separation chamber is equipped with a secondary steam outlet, a molten alkali outlet, and an inspection hole, and the bottom of the gas-liquid separation chamber is equipped with a molten alkali temperature measuring port.

13. The apparatus for producing solid alkali according to any one of claims 9 to 12, characterized in that, The flue gas auxiliary system includes an air preheater, a chimney, a circulating fan, a blower, and a burner connected in sequence. The air inlet of the air preheater is connected to the blower; the air inlet of the circulating fan is connected to the chimney; the air inlet of the burner is connected to both the air preheater and the circulating fan; the air inlet of the burner is connected to the main gas pipeline; and the burner is directly connected to the final concentration falling film evaporator. The air inlet of the air preheater is connected to the saccharification preheater; the air inlet of the chimney is connected to the air preheater; and the air outlet of the chimney is connected to the atmosphere.

14. The apparatus for producing solid alkali according to claim 13, characterized in that, It also includes an auxiliary system for treating alkaline dust gas; The alkaline dust gas treatment auxiliary system includes an alkaline dust absorption and circulation tank, an alkaline dust absorption and circulation pump, and a hydraulic vacuum jet pump connected in sequence. The inlet end of the alkali dust absorption circulation tank is connected to the hydraulic vacuum jet pump and the flash desuperheater, respectively; the inlet end of the hydraulic vacuum jet pump is connected to the alkali dust absorption circulation pump; the inlet end of the alkali dust absorption circulation pump is connected to the alkali dust absorption circulation tank. The air inlet of the hydraulic vacuum jet pump is connected to the caustic soda flake machine and the packaging machine.

15. The apparatus for producing solid alkali according to claim 14, characterized in that, It also includes the caustic soda cooling water auxiliary system; The caustic soda cooling water auxiliary system includes a cooling water collection tank, a cooling water heat exchanger, and a cooling water pump connected in sequence. The inlet end of the cooling water collection tank is connected to the caustic soda flake machine; the inlet end of the cooling water pump is connected to the cooling water collection tank; and the inlet end of the cooling water heat exchanger is connected to the cooling water pump. The inlet end of the cooling water heat exchanger is connected to the circulating cooling water main pipe; the outlet end of the cooling water heat exchanger is connected to the circulating cooling water return main pipe.

16. The apparatus for producing solid alkali according to claim 15, characterized in that, The main system for forming and packaging caustic soda flakes includes the caustic soda flake machine, the packaging machine, and the palletizer connected in sequence. The liquid inlet of the caustic soda flake machine is connected to the flash evaporation distribution tank and the alkali dust absorption and circulation tank, respectively; the feed inlet of the packaging machine is connected to the caustic soda flake machine; the feed inlet of the palletizer is connected to the packaging machine. The liquid inlet of the caustic soda flake machine is connected to the cooling water heat exchanger.

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