A continuous vanadium precipitation method based on heat exchanger preheating and straight-through steam heating

Abstract

This invention discloses a continuous vanadium precipitation method based on heat exchanger preheating and direct steam heating. Vanadium solution is preheated in a heat exchanger, and then pumped to a vanadium precipitation reactor. Direct steam heats the slurry in the reactor to initiate the vanadium precipitation reaction. The inlet temperature of the vanadium solution in the heat exchanger is 30–45°C, and the outlet temperature is 75–90°C. The heat exchanger is a BEM-type double-tube horizontal heat exchanger, with steam flowing through the shell side and vanadium solution through the tube side, in a co-current flow. The pressure drop in the shell side of the heat exchanger is allowed to be ≤70 kPa. This method ensures stable and uniform preheating of the vanadium solution before pumping it to the vanadium precipitation reactor. By controlling the temperature of the preheated vanadium solution, the temperature difference between the vanadium solution and the slurry in the reactor is reduced, effectively avoiding uneven reaction and spoilage caused by temperature fluctuations. This also reduces the amount of direct steam required for the vanadium precipitation reaction, ensuring continuous, stable, and efficient operation of the vanadium precipitation process and reducing the generation of wastewater per ton of vanadium at the source.

Description

Technical Field

[0001] This invention relates to a method for vanadium precipitation with acidic ammonium salts, and more particularly to a continuous vanadium precipitation method based on heat exchanger preheating and direct steam heating. Background Technology

[0002] Preparation of ammonium polyvanadate ((NH4)2V6O) by precipitation of vanadium with acidic ammonium salts 16 The preparation process of vanadium polyvanadate can be divided into batch and continuous methods. Traditional batch ammonium salt precipitation of vanadium suffers from problems such as low vanadium content in the vanadium solution, large wastewater generation per ton of vanadium, and long production cycles. To address these issues, a continuous vanadium precipitation process using acidic ammonium salts with high-concentration vanadium solution has been developed. The main preparation steps include: continuously feeding a preheated vanadium-containing solution, ammonium sulfate solid or solution, and concentrated sulfuric acid into a vanadium precipitation reactor in a specific ratio; precisely controlling the pH and temperature of the precipitation system to promote the formation of ammonium polyvanadate; and finally obtaining the ammonium polyvanadate product after the vanadium concentration in the supernatant drops below 0.3 g / L through filtration, washing, and drying. In this process, preheating the vanadium solution effectively reduces the temperature difference between it and the reaction slurry, preventing large temperature fluctuations within the reactor and ensuring the stable progress of the vanadium precipitation process. Vanadium concentration is one of the key factors affecting the wastewater generation per ton of vanadium. In the vanadium precipitation process, for every 1 g / L increase in vanadium concentration, approximately 0.4 mg / L of wastewater can be reduced. 3 The amount of vanadium wastewater generated per ton of vanadium is also significantly affected by the heating method of the vanadium solution and the slurry in the reactor.

[0003] Publication No. CN115072778A discloses a continuous reaction crystallization process for ammonium polyvanadate. A pre-adjusted vanadate solution with a pH of 4-7 is heated to 70-80°C via a preheater, then transported to a crystallizer where solid ammonium sulfate is added. After dissolution, dilute sulfuric acid is added to adjust the pH. Forced circulation and temperature control are achieved using a circulating pump and heat exchanger to promote continuous vanadium precipitation. Although this method avoids direct steam heating of the reaction slurry, the slurry in the crystallizer has a high solids content (5-50%). Using a heat exchanger to heat the slurry can easily lead to pipe blockage and reduced heat transfer efficiency, affecting the stable operation of the system. Publication No. CN117602671A discloses a method and apparatus for improving the quality stability of ammonium polyvanadate, in which acidic vanadate solution is pumped at 50-70°C... 3 After being preheated to 65-75°C by a heat exchanger at a flow rate of / h, a precipitant is added and the solution is transported to the vanadium precipitation mother tank. The pH of the slurry in the vanadium precipitation mother tank is maintained at 1.7-1.9 and the temperature at 85-90°C by automatically controlling the opening of the acid addition valve and the steam valve, so as to achieve continuous vanadium precipitation. After multi-stage sedimentation, solid-liquid separation and washing, ammonium polyvanadate is obtained. However, this method has the following drawbacks: the large temperature difference between the vanadium solution and the slurry in the mother tank after preheating reduces the stability of the process and increases the amount of wastewater generated per ton of vanadium. Furthermore, the preheated vanadium solution after adding the precipitant is a solid-liquid mixture, which cannot be uniformly and quantitatively transported to the vanadium precipitation mother tank in industrial applications. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a continuous vanadium precipitation method based on heat exchanger preheating and direct steam heating that can effectively control the vanadium precipitation temperature difference.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: vanadium liquid is preheated by passing it into a heat exchanger, and then the preheated vanadium liquid is pumped to a vanadium precipitation reactor, where steam is directly introduced to heat the slurry in the reactor to carry out the vanadium precipitation reaction; the inlet temperature of the vanadium liquid in the heat exchanger is 30-45℃, and the outlet temperature of the vanadium liquid is 75-90℃; the heat exchanger adopts a BEM type double-tube horizontal heat exchanger, wherein steam flows through the shell side and vanadium liquid flows through the tube side, the vanadium liquid and steam flow in the same direction, and the pressure drop in the shell side of the heat exchanger is allowed to be ≤70kPa.

[0006] Furthermore, the BEM type double-pass horizontal heat exchanger has a single-pass tube length of 2500mm, an inner shell diameter of 600mm, an outer tube diameter of 25mm, a tube wall thickness of 1.5mm, and 240 tubes; the baffles are single-arch type, with at least 3 baffles and their cross-sectional direction is perpendicular to the direction of the vanadium liquid inlet pipe.

[0007] Furthermore, in the BEM type double-tube horizontal heat exchanger, an equilateral triangular liquid inlet with a side length of 10-25mm is opened at the center of the baffle plate below the shell side.

[0008] Furthermore, the steam pressure is 0.8 MPa and the steam temperature is 170.5–220 °C.

[0009] Furthermore, the concentration of the vanadium solution is 30–60 g / L, and the inlet pressure of the vanadium solution is 0.4–0.7 MPa.

[0010] The beneficial effects of adopting the above technical solution are as follows: This invention combines the preheating of vanadium liquid with heat exchanger and the direct steam heating of slurry in the vanadium precipitation reactor, so that vanadium liquids of different concentrations and flow rates are preheated stably and uniformly and pumped into the vanadium precipitation reactor. By controlling the temperature of the preheated vanadium liquid, the temperature difference between the vanadium liquid and the slurry in the reactor is reduced, effectively avoiding uneven reaction and the generation of bad material caused by temperature fluctuations. It also reduces the amount of direct steam required for the vanadium precipitation reaction, ensuring the continuous, stable and efficient operation of the vanadium precipitation process while reducing the generation of vanadium wastewater per ton of vanadium from the source.

[0011] This invention optimizes key structural parameters of the heat exchanger, including heat exchange tube length, number of tube passes, number of heat exchange tubes, and number of baffles, to construct a vanadium liquid preheating system, reducing the temperature difference between the vanadium liquid and the vanadium precipitation reaction slurry from the source. The optimized heat exchanger provides stable and uniform preheating of the vanadium liquid, accurately raising its temperature to near the actual temperature of the slurry in the reactor. Subsequently, a direct steam supply method is used to supplement heating and temperature regulation of the slurry, forming a composite heating and temperature difference control strategy. This invention effectively suppresses temperature fluctuations caused by insufficient preheating, avoiding uneven vanadium precipitation reactions or material spoilage accidents, and ensuring the stable and smooth operation of continuous vanadium precipitation reactions. This invention achieves stable and efficient process operation while reducing the generation of vanadium wastewater per ton of vanadium at the source. Attached Figure Description

[0012] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0013] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is a schematic diagram of the heat exchanger described in this invention.

[0014] In the diagram, 1-vanadium liquid outlet, 2-vanadium liquid inlet, 3-steam inlet, 4-vent, and 5-condensate outlet. Detailed Implementation

[0015] Figure 1 As shown, the continuous vanadium precipitation method based on heat exchanger preheating and direct steam heating includes the following steps: (1) The concentration of the vanadium liquid is 30-60 g / L. The vanadium liquid is introduced into the heat exchanger for preheating. The inlet temperature of the vanadium liquid is 30-45℃, the outlet temperature of the vanadium liquid is 75-90℃, and the inlet pressure of the vanadium liquid when it flows through the heat exchanger is 0.4-0.7 MPa. Figure 2 As shown, the heat exchanger is a BEM-type double-pass horizontal heat exchanger, consisting of a shell and heat exchange tubes and baffles located inside the shell. It has a vanadium liquid outlet 1, a vanadium liquid inlet 2, a steam inlet 3, a vent 4, and a condensate outlet 5. The heat exchange tubes have a single-pass length of 2500 mm, the shell's inner diameter is 600 mm, the tubes' outer diameter is 25 mm, the tube wall thickness is 1.5 mm, the tubes are made of 316 stainless steel, and there are 240 tubes. The baffles are single-arch type, with at least three baffles, and their cross-sections are perpendicular to the vanadium liquid inlet tube direction, i.e., perpendicular to the vanadium liquid flow direction of vanadium liquid inlet 2. A triangular liquid inlet with a side length of 10–25 mm is opened at the center of the baffle below the shell side. Steam flows through the shell side, and vanadium liquid flows through the tube side, with the vanadium liquid and steam flowing in the same direction. The allowable pressure drop in the shell side of the heat exchanger is ≤70 kPa.

[0016] (2) The preheated vanadium liquid is pumped to the vanadium precipitation reactor, and steam is directly passed through to heat the slurry in the reactor, so that the slurry in the reactor is kept boiling to carry out the vanadium precipitation reaction; the steam pressure is 0.8 MPa and the steam temperature is 170.5~220℃; after the vanadium precipitation reaction, ammonium polyvanadate can be generated.

[0017] (3) After adopting the above method, the amount of vanadium wastewater produced by conventional processes is reduced from 30m³. 3 Reduced to 25m 3 the following. Example 1

[0018] Vanadium solution with an initial vanadium concentration of 30 g / L and a temperature of 30 °C was subjected to a 70 m... 3 The vanadium solution is continuously pumped to a heat exchanger at a flow rate of / h, using 170.5℃ steam as the heat fluid to heat the vanadium solution. The outlet temperature of the vanadium solution is maintained at 80℃ by controlling the steam flow rate. Subsequently, this preheated vanadium solution, ammonium sulfate solution, and concentrated sulfuric acid are continuously pumped to a crystallization reactor at a specific flow rate. Steam is continuously supplied to keep the slurry in the reactor boiling. After a period of time, the mixture is filtered and washed to produce ammonium vanadate. Compared to the direct heating method in the intermittent vanadium precipitation process, the steam condensate wastewater is reduced from 3.5m³... 3 Reduced to 1.3m 3 . Example 2

[0019] Vanadium solution with an initial vanadium concentration of 38 g / L and a temperature of 43 °C was subjected to a 75 m... 3 The vanadium solution is continuously pumped to a heat exchanger at a flow rate of / h, using 180℃ steam as the heat fluid to heat the vanadium solution. The outlet temperature of the vanadium solution is maintained at 90℃ by controlling the steam flow rate. Subsequently, this preheated vanadium solution, acidic ammonium sulfate solution, and concentrated sulfuric acid are continuously pumped at a certain flow rate into a crystallization reactor. Steam is continuously supplied to keep the slurry in the reactor boiling. After a period of time, the mixture is filtered and washed to obtain ammonium vanadate. Compared with the direct heating method of intermittent vanadium precipitation process, the steam condensate wastewater can be reduced from 3.5m³... 3 Reduced to 1.1m 3 . Example 3

[0020] Vanadium solution with an initial vanadium concentration of 48 g / L and a temperature of 40 °C was subjected to a 100 m... 3 The vanadium solution is continuously pumped to a heat exchanger at a flow rate of / h, using 200℃ steam as the heat fluid to heat the vanadium solution. The outlet temperature of the vanadium solution is controlled to 75℃ by controlling the steam flow rate. Subsequently, this preheated vanadium solution, ammonium sulfate solution, and concentrated sulfuric acid are continuously pumped at a certain flow rate into a crystallization reactor. Steam is continuously supplied to keep the slurry in the reactor boiling. After a period of time, the mixture is filtered and washed to produce ammonium vanadate. The steam condensate wastewater can be treated from 3.5m³. 3 Reduced to 1.6m 3 . Example 4

[0021] Vanadium solution with an initial vanadium concentration of 60 g / L and a temperature of 45 °C was subjected to an 80 m... 3 The vanadium solution is continuously pumped to a heat exchanger at a flow rate of / h, using 220℃ steam as the heat fluid to heat the vanadium solution. The outlet temperature of the vanadium solution is controlled to 85℃ by controlling the steam flow rate. Subsequently, this preheated vanadium solution, acidic ammonium sulfate solution, and concentrated sulfuric acid are continuously pumped at a certain flow rate into a crystallization reactor. Steam is continuously supplied to keep the slurry in the reactor boiling. After a period of time, the mixture is filtered and washed to produce ammonium vanadate. The steam condensate wastewater can be treated from 3.5m³. 3 Reduced to 1.5m 3 .

Claims

1. A continuous vanadium precipitation method based on heat exchanger preheating and direct steam heating, characterized in that: Vanadium liquid is preheated in a heat exchanger, and then pumped to a vanadium precipitation reactor. Steam is directly introduced to heat the slurry in the reactor to carry out the vanadium precipitation reaction. The inlet temperature of the vanadium liquid in the heat exchanger is 30-45℃, and the outlet temperature is 75-90℃. The heat exchanger is a BEM type double-tube horizontal heat exchanger, in which steam flows through the shell side and vanadium liquid flows through the tube side. The vanadium liquid and steam flow in the same direction, and the pressure drop in the shell side of the heat exchanger is ≤70kPa.

2. The continuous vanadium deposition method based on heat exchanger preheating and direct steam heating according to claim 1, characterized in that: The BEM-type double-pass horizontal heat exchanger has a single-pass tube length of 2500mm, an inner shell diameter of 600mm, an outer tube diameter of 25mm, a tube wall thickness of 1.5mm, and 240 tubes. The baffles are single-arch type, with at least 3 baffles, and their cross-section is perpendicular to the direction of the vanadium liquid inlet pipe.

3. The continuous vanadium precipitation method based on heat exchanger preheating and direct steam heating according to claim 2, characterized in that: The BEM type double-tube horizontal heat exchanger has an equilateral triangular liquid inlet at the center of the baffle plate below the shell side, with a side length of 10-25mm.

4. The continuous vanadium precipitation method based on heat exchanger preheating and direct steam heating according to claim 1, characterized in that: The steam pressure is 0.8 MPa and the steam temperature is 170.5–220 °C.

5. A continuous vanadium precipitation method based on heat exchanger preheating and direct steam heating according to any one of claims 1-4, characterized in that: The concentration of the vanadium solution is 30–60 g / L, and the inlet pressure of the vanadium solution is 0.4–0.7 MPa.

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