System and method for concentrating dilute phosphoric acid by leaching method

Abstract

The invention discloses a system and a method for concentrating dilute phosphoric acid by an immersion method, and belongs to the field of chemical industry. The system comprises a combustion chamber, an evaporator, an entrainment separator, an evaporator bottom valve, a sludge box and a sludge box bottom valve. By adopting the system and the method, the raw material-dilute phosphoric acid is added into the evaporator, hot gas from the combustion chamber is used for heating phosphoric acid in the evaporator to evaporate water, the dilute phosphoric acid is concentrated, and the concentrated phosphoric acid is discharged from the side outlet of the evaporator to serve as a target product-concentrated phosphoric acid debounded area. The device has a direct heating and concentrating function and can be used for heating dilute phosphoric acid to produce concentrated phosphoric acid, hot gas is in direct contact with a phosphoric acid solution, an indirect heat exchanger is not needed, a heat transfer surface does not exist, and scaling on the heat transfer surface is avoided; hot gas directly exchanges heat with the phosphoric acid solution without temperature difference, and the heat transfer efficiency is high.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical production, and in particular to a system and method for concentrating dilute phosphoric acid by immersion. Background Art

[0002] Phosphoric acid is an important intermediate chemical product. Its uses can be summarized into two aspects, namely fertilizer production and industrial phosphate production, and wet-process phosphoric acid is mainly used in fertilizer production.

[0003] The primary production process for wet-process phosphoric acid is the dihydrate process, which accounts for over 80% of the total. Dihydrate phosphoric acid products typically contain a P2O5 mass concentration of 22% to 30%. Domestic phosphoric acid production (equivalent to 100% P2O5) is nearly 17 million tons, with low-concentration phosphoric acid (containing a P2O5 mass concentration of 22% to 30%) (equivalent to 100% P2O5) reaching nearly 13.6 million tons, and actual production approaching 54.4 million tons. Due to its low concentration, it typically needs to be concentrated to a P2O5 mass concentration of over 40% to meet the requirements of fertilizer production and long-distance transportation.

[0004] A significant portion or all of the impurity compounds of iron, aluminum, and magnesium in phosphate rock dissolve in the reaction tank and enter the filtered acid. These compounds typically exist as ions or radicals, often in a saturated or supersaturated state. In existing systems for concentrating dilute phosphoric acid using indirect heat transfer, as the phosphoric acid concentration increases, the solubility of the salts formed by the impurities decreases, causing the compounds to crystallize and precipitate, forming scale on the heat exchange surfaces and inner walls of the indirect heat transfer evaporation pipes. This reduces heat transfer efficiency, hinders or even prevents the concentration operation, and creates problems for subsequent processes.

[0005] Therefore, it is necessary to improve the existing phosphoric acid concentration system and urgently need to provide a new system and method for heating and evaporating dilute phosphoric acid, which can produce concentrated phosphoric acid while shortening the process, reducing equipment scaling, and increasing the operating rate.

[0006] Patent content

[0007] The present invention aims to provide a system for concentrating dilute phosphoric acid by immersion. The raw material, dilute phosphoric acid, is added to an evaporator. Hot gas from a combustion chamber heats the phosphoric acid in the evaporator, evaporating the water and concentrating the dilute phosphoric acid. The concentrated phosphoric acid then exits the evaporator through a side outlet as the target product, concentrated phosphoric acid, in a delimited zone. This patent aims to provide a system and method for concentrating dilute phosphoric acid by immersion. This system and method utilize direct heating and concentration, and can be used to heat dilute phosphoric acid to produce concentrated phosphoric acid. Direct contact between the hot gas and the phosphoric acid solution eliminates the need for an indirect heat exchanger, eliminating heat transfer surfaces and preventing scaling. Direct heat exchange between the hot gas and the phosphoric acid solution eliminates temperature differences and results in high heat transfer efficiency.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] A system for concentrating dilute phosphoric acid by immersion method includes an evaporator. A combustion chamber is provided at one end of the top of the evaporator. The hot air outlet pipe of the combustion chamber is in the inner cavity of the evaporator and close to the input port of the dilute phosphoric acid. The other end of the top of the evaporator is a mist separator. The bottom outlet of the evaporator is connected to a sludge tank through the evaporator bottom valve.

[0010] In the above system: an air inlet is provided on the combustion chamber, a primary air inlet is provided on the combustion chamber, and a secondary air inlet is provided on the cavity of the combustion chamber.

[0011] In the above system: the mist separator is of shutter type.

[0012] In the above system: an exhaust gas outlet is provided on the top of the mist separator.

[0013] In the above system, the hot air outlet pipe of the combustion chamber is immersed below the liquid level in the evaporator, and the height from the lowest point of the hot air outlet pipe to the liquid level is H, 40mm≤H≤450mm.

[0014] In the above system, the bottom of the evaporator is conical, and the concentrated phosphoric acid outlet is far away from the input port of the dilute phosphoric acid and close to the bottom outlet of the evaporator.

[0015] In some more specific technical solutions, the present invention is as follows:

[0016] A system for concentrating dilute phosphoric acid by immersion, comprising a combustion chamber, an evaporator, an entrainment separator, an evaporator bottom valve, a sludge tank, and a sludge tank bottom valve; a pipeline for dilute phosphoric acid, a raw material from the barrier zone, is connected to an evaporator side inlet A2, and an evaporator side outlet D2 is connected to a pipeline for concentrated phosphoric acid, a target product from the barrier zone;

[0017] In the above system, the evaporator is conical in shape, with outlet E2 at the bottom. The top of the evaporator is divided into two parts. One part is an air collecting box, which is equipped with a louvered entrainment separator. The top of the air collecting box is equipped with outlet C2. The other part is the base of the combustion chamber. The combustion chamber is installed at the top inlet B2 of the evaporator, and the hot air outlet pipe of the combustion chamber is immersed below the liquid level in the evaporator. The height from the hot air outlet D1 to the liquid level is H, which is ≤ 450mm. The side inlet A2 is arranged as close to the hot air outlet D1 as possible, and the side outlet D2 is arranged as far away from the side inlet A2 as possible and closer to the cone bottom outlet E2.

[0018] In the above system, the fuel pipe from the boundary area is connected to the fuel inlet A1 of the combustion chamber, the primary air pipe from the boundary area is connected to the primary air inlet B1 of the combustion chamber, and the secondary air pipe from the boundary area is connected to the secondary air inlet C1 of the combustion chamber. The air velocity in the hot air outlet pipe of the combustion chamber is V, and V≤60m / s.

[0019] In the above system: the evaporator top outlet C2 is connected to the tail gas pipeline of the delimited area; the evaporator cone bottom outlet E2 is connected to the sludge pipeline of the delimited area through the evaporator bottom valve, sludge box, and sludge box bottom valve;

[0020] A method for concentrating dilute phosphoric acid by immersion using the above system comprises the following steps:

[0021] (1) Raw material and fuel feeding: The raw material from the boundary zone - dilute phosphoric acid (containing P2O5 mass concentration ≥ 20%) enters the evaporator liquid phase from the side inlet A2; the fuel from the boundary zone enters the combustion chamber from the fuel inlet A1, and the primary air from the boundary zone enters the combustion chamber from the primary air inlet B1. The fuel and the primary air burn in the combustion chamber to produce hot air. The secondary air from the boundary zone enters the combustion chamber from the secondary air inlet C1. The secondary air promotes the full combustion of the fuel in the hot air and adjusts the hot air to the set temperature (temperature ≤ 800℃). The hot air reaching the set temperature leaves the combustion chamber from the hot air outlet D1 and directly enters the evaporator downward;

[0022] (2) Concentration of dilute phosphoric acid and discharge of finished products: Hot air from the hot air outlet D1 of the combustion chamber is introduced into the liquid phosphoric acid in the evaporator in the form of large bubbles. The large bubbles rotate rapidly in the liquid phosphoric acid and split into small bubble groups. The small bubbles quickly transfer heat to the liquid phosphoric acid. The heat transfer is very rapid and is completed within one hundredth of a second. The liquid phosphoric acid in the evaporator is heated by the hot air. It first enters a temperature rise stage and then enters a constant temperature (temperature ≥ 100°C) evaporation stage. The heat transferred by the hot air to the liquid phosphoric acid is completely converted into the latent heat of vaporization of evaporating water. The concentration process is continuous. Dilute phosphoric acid is added continuously and quantitatively. When the liquid phosphoric acid enters the constant temperature (temperature ≥ 100°C) evaporation stage and the concentration reaches the requirement (containing P2O5 mass concentration ≥ 40%), the liquid phosphoric acid as the target product - concentrated phosphoric acid (containing P2O5 mass concentration ≥ 40%) is continuously discharged from the side outlet D2 of the evaporator to the delimiting area.

[0023] (3) Exhaust gas defoaming and sludge removal: The exhaust gas (temperature ≥ 100°C) evaporated from the evaporator is defoamed by the mist separator and flows upward to the boundary area from the top outlet C2. The removed liquid flows downward and returns to the evaporator as recovered phosphoric acid. When there is sludge in the evaporator, the evaporator bottom valve is opened to put the sludge into the sludge box. The sludge in the sludge box is sent to the boundary area through the sludge pipeline by regularly opening the sludge box bottom valve.

[0024] A method for concentrating dilute phosphoric acid by immersion, comprising feeding dilute phosphoric acid, heating air with fuel combustion, immersing hot air to heat and concentrate the phosphoric acid, discharging the concentrated phosphoric acid, defoaming the phosphoric acid-containing hot air to separate the phosphoric acid, and removing sludge from the concentrated phosphoric acid. The production process includes feeding raw materials and fuel, concentrating the dilute phosphoric acid and discharging the finished product, defoaming the tail gas, and removing sludge. The steps are as follows:

[0025] (1) Raw material and fuel feeding: The raw material from the boundary zone - dilute phosphoric acid (containing a P2O5 mass concentration of 20% to 30%) enters the evaporator liquid phase from the side inlet A2; the fuel from the boundary zone enters the combustion chamber from the fuel inlet A1, and the primary air from the boundary zone enters the combustion chamber from the primary air inlet B1. The fuel and the primary air burn in the combustion chamber to produce hot air. The secondary air from the boundary zone enters the combustion chamber from the secondary air inlet C1. The secondary air promotes the full combustion of the fuel in the hot air and adjusts the hot air to the set temperature (temperature 600℃ to 800℃). The hot air that reaches the set temperature leaves the combustion chamber from the hot air outlet D1 and directly enters the evaporator downward;

[0026] (2) Concentration of dilute phosphoric acid and discharge of finished products: Hot air from the hot air outlet D1 of the combustion chamber is introduced into the liquid phosphoric acid in the evaporator in the form of large bubbles. The large bubbles rotate rapidly in the liquid phosphoric acid and split into small bubble groups. The small bubbles quickly transfer heat to the liquid phosphoric acid. The heat transfer is very rapid and is completed within one hundredth of a second. The liquid phosphoric acid in the evaporator is heated by the hot air. It first enters a temperature rise stage and then enters a constant temperature (temperature 100°C to 124°C) evaporation stage. The heat transferred by the hot air to the liquid phosphoric acid is completely converted into the latent heat of vaporization of evaporating water. The concentration process is continuous. Dilute phosphoric acid is added continuously and quantitatively. When the liquid phosphoric acid enters the constant temperature (temperature 100°C to 124°C) evaporation stage and the concentration reaches the required value (containing P2O5 mass concentration of 40% to 55%), the liquid phosphoric acid as the target product - concentrated phosphoric acid (containing P2O5 mass concentration of 40% to 55%) is continuously discharged from the side outlet D2 of the evaporator to the demarcation zone.

[0027] (3) Exhaust gas defoaming and sludge removal: The exhaust gas (temperature 100℃~130℃) evaporated from the evaporator is defoamed by the mist separator and flows upward to the boundary area from the top outlet C2. The removed liquid flows downward and returns to the evaporator as recovered phosphoric acid. When there is sludge in the evaporator, the evaporator bottom valve is opened to put the sludge into the sludge box. The sludge in the sludge box is sent to the boundary area through the sludge pipeline by regularly opening the sludge box bottom valve.

[0028] Beneficial effects of the present invention:

[0029] The present invention provides a system and method for concentrating dilute phosphoric acid by immersion method, which has the function of direct heating and concentration, can be used to heat dilute phosphoric acid to produce concentrated phosphoric acid, and can be widely used in industrial production processes.

[0030] The combustion chamber and entrainment separator are both installed on top of the evaporator, featuring a compact design and small footprint. The hot gas comes into direct contact with the phosphoric acid solution, eliminating the need for an indirect heat exchanger. This eliminates the need for a heat transfer surface, preventing scaling on the heat transfer surface and making construction materials easier to source. Direct heat exchange between the hot gas and the phosphoric acid solution eliminates temperature differences, resulting in high heat transfer efficiency.

[0031] The air velocity in the hot air outlet pipe of the combustion chamber is controlled within the range of 45m / s to 60m / s, which can prevent backfire and excessive mist entrained in the exhaust gas.

[0032] The evaporator is conical and has a sludge box underneath, so the evaporator can operate continuously for a long time without clogging. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the process flow in the present invention

[0034] Among them, there are combustion chamber 1, evaporator 2, mist separator 3, evaporator bottom valve 4, sludge box 5, and sludge box bottom valve 6. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of this patent will be clearly and completely described below in conjunction with the drawings in the embodiments of this patent. Obviously, the described embodiments are part of the embodiments of this patent, not all of the embodiments. The components of the embodiments of this patent generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this patent provided in the drawings is not intended to limit the scope of the patent claimed for protection, but merely represents selected embodiments of this patent. Based on the embodiments in this patent, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this patent. The embodiments of this patent are described in detail below, and examples of the embodiments are shown in the drawings, where the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain this patent, and should not be understood as limitations on this patent.

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0037] A system for concentrating dilute phosphoric acid using the immersion method comprises an evaporator 2. A combustion chamber 1 is located at one end of the top of the evaporator. The hot air outlet pipe of the combustion chamber is located within the inner cavity of the evaporator 2 and near the inlet port for the dilute phosphoric acid. An entrainment separator 3 is located at the other end of the top of the evaporator. The bottom outlet of the evaporator 2 is connected to a sludge tank 5 via an evaporator bottom valve 4. The combustion chamber 1 is provided with an air inlet and a primary air inlet, and the cavity of the combustion chamber 1 is provided with a secondary air inlet. The entrainment separator 3 is a louvered type. An exhaust gas outlet is located at the top of the entrainment separator 3. The hot air outlet pipe of the combustion chamber 1 is submerged below the liquid level in the evaporator 2. The height from the lowest point of the hot air outlet pipe to the liquid level is H, with a range of 40 mm ≤ H ≤ 450 mm. The bottom of the evaporator 2 is conical, with the concentrated phosphoric acid outlet located away from the inlet port for the dilute phosphoric acid and near the bottom outlet of the evaporator 2.

[0038] like Figure 1 As shown, the system includes a combustion chamber 1, an evaporator 2, an entrainment separator 3, an evaporator bottom valve 4, a sludge tank 5, and a sludge tank bottom valve 6; the raw material from the boundary zone, the dilute phosphoric acid pipeline, is connected to the side inlet A2 of the evaporator 2, and the side outlet D2 of the evaporator 2 is connected to the target product from the boundary zone, the concentrated phosphoric acid pipeline;

[0039] The evaporator 2 is conical in shape, with an outlet E2 at the bottom. The top of the evaporator 2 is divided into two parts. One part is the air collecting box, which houses the louvered entrainment separator 3. The top of the air collecting box is provided with an outlet C2. The other part is the base of the combustion chamber 1. The combustion chamber 1 is mounted at the top inlet B2 of the evaporator 2, and the hot air outlet pipe of the combustion chamber 1 is immersed below the liquid level in the evaporator 2. The height from the hot air outlet D1 to the liquid level is H = 350mm. The side inlet A2 is arranged as close to the hot air outlet D1 as possible, and the side outlet D2 is arranged as far away from the side inlet A2 as possible and closer to the cone bottom outlet E2.

[0040] The fuel pipeline from the boundary zone is connected to the fuel inlet A1 of the combustion chamber 1, the primary air pipeline from the boundary zone is connected to the primary air inlet B1 of the combustion chamber 1, and the secondary air pipeline from the boundary zone is connected to the secondary air inlet C1 of the combustion chamber 1. The air velocity in the hot air outlet pipe of the combustion chamber 1 is V, V = 50m / s;

[0041] The top outlet C2 of the evaporator 2 is connected to the tail gas pipeline of the delimited area; the cone bottom outlet E2 of the evaporator 2 is connected to the sludge pipeline of the delimited area through the evaporator bottom valve 4, the sludge box 5, and the sludge box bottom valve 6;

[0042] The method for concentrating dilute phosphoric acid by immersion using the above system includes the following steps. More than one fuel can be used. Natural gas is used as an example:

[0043] (1) Raw material and fuel feeding: The raw material from the boundary zone - dilute phosphoric acid (containing 30% by mass concentration of P2O5) enters the liquid phase of evaporator 2 from the side inlet A2; natural gas from the boundary zone enters combustion chamber 1 from fuel inlet A1, and primary air from the boundary zone enters combustion chamber 1 from primary air inlet B1. Natural gas and primary air burn in combustion chamber 1 to produce hot air. Secondary air from the boundary zone enters combustion chamber 1 from secondary air inlet C1. The secondary air promotes the full combustion of natural gas in the hot air and adjusts the hot air to the set temperature (temperature 700°C). The hot air reaching the set temperature leaves combustion chamber 1 from hot air outlet D1 and directly enters evaporator 2 downward;

[0044] (2) Concentration of dilute phosphoric acid and discharge of finished product: Hot air from the hot air outlet D1 of the combustion chamber 1 is introduced into the liquid phosphoric acid of the evaporator 2 in the form of large bubbles. The large bubbles rotate rapidly in the liquid phosphoric acid and split into small bubble groups. The small bubbles quickly transfer heat to the liquid phosphoric acid. The heat transfer is very rapid and is completed within one hundredth of a second. The liquid phosphoric acid in the evaporator 2 is heated by the hot air. It first enters a temperature rise stage and then enters a constant temperature (temperature 120°C) evaporation stage. The heat transferred by the hot air to the liquid phosphoric acid is completely converted into the latent heat of vaporization of evaporating water. The concentration process is continuous. Dilute phosphoric acid is added continuously and quantitatively. When the liquid phosphoric acid enters the constant temperature (temperature 120°C) evaporation stage and the concentration reaches the required level (containing 54% by mass of P2O5), the target product, concentrated phosphoric acid (containing 54% by mass of P2O5), is continuously discharged from the side outlet D2 of the evaporator 2 to the delimiting area.

[0045] (3) Exhaust gas defoaming and sludge removal: The exhaust gas (temperature 121°C) evaporated from the evaporator 2 is defoamed by the mist separator 3 and flows upward to exit the evaporator 2 from the top outlet C2 to the boundary area. The removed liquid flows downward and returns to the evaporator 2 as recovered phosphoric acid. When there is sludge in the evaporator 2, the evaporator bottom valve 4 is opened to put the sludge into the sludge tank 5. The sludge in the sludge tank 5 is sent to the boundary area through the sludge pipeline by regularly opening the sludge tank bottom valve 6.

[0046] The results of the patent application are shown in the following table

[0047] Performance evaluation results of 3 tons of concentrated phosphoric acid (P2O5 is calculated as 100%) / hour immersion method for concentrating dilute phosphoric acid

[0048] project parameter project parameter <![CDATA[Raw material - dilute phosphoric acid containing P2O5, wt%]]> 30 Evaporated water, t / h 4.45 Raw material - dilute phosphoric acid consumption, t / h 10 Exhaust gas temperature, ℃ 121 Hot air outlet immersion height H, mm 350 Target product - concentrated phosphoric acid Temperature, ℃ 120 Hot air outlet pipe velocity, m / s 50 <![CDATA[Target product - concentrated phosphoric acid containing P2O5, wt%]]> 54 <![CDATA[Natural gas consumption, m 3 > 466 Target product - concentrated phosphoric acid amount, t / h 5.55 Hot air temperature, ℃ 700 .

Claims

1. A system for concentrating dilute phosphoric acid by immersion, characterized in that: The system comprises an evaporator (2), wherein a combustion chamber (1) is provided at one end of the top of the evaporator, and a hot air outlet pipe of the combustion chamber is located in the inner cavity of the evaporator (2) and close to an input port of dilute phosphoric acid; the other end of the top of the evaporator is a mist separator (3); and the bottom outlet of the evaporator (2) is connected to a sludge tank (5) via an evaporator bottom valve (4).

2. The system for concentrating dilute phosphoric acid by immersion method according to claim 1, characterized in that: The combustion chamber (1) is provided with an air inlet and a primary air inlet, and the cavity of the combustion chamber (1) is provided with a secondary air inlet.

3. The system for concentrating dilute phosphoric acid by immersion method according to claim 1, characterized in that: The mist separator (3) is of shutter type.

4. The system for concentrating dilute phosphoric acid by immersion method according to claim 1, characterized in that: The top of the mist separator (3) is provided with an exhaust gas outlet.

5. The system for concentrating dilute phosphoric acid by immersion method according to claim 1, characterized in that: The hot air outlet pipe of the combustion chamber (1) is immersed below the liquid level in the evaporator (2), and the height from the lowest point of the hot air outlet pipe to the liquid level is H, 40mm≤H≤450mm.

6. The system for concentrating dilute phosphoric acid by immersion method according to claim 1, characterized in that: The bottom of the evaporator (2) is conical, and the concentrated phosphoric acid outlet is far away from the input port of the dilute phosphoric acid and close to the bottom outlet of the evaporator (2).

7. A method for concentrating dilute phosphoric acid by immersion using the system of claim 1, the method comprising the following steps: (1) Raw material and fuel feeding: The raw material dilute phosphoric acid from the boundary zone enters the evaporator liquid phase; the fuel from the boundary zone enters the combustion chamber, the primary air from the boundary zone enters the combustion chamber, the fuel and air burn in the combustion chamber to produce hot air, the secondary air from the boundary zone enters the combustion chamber, the secondary air promotes the full combustion of the fuel in the hot air and adjusts the hot air to a set temperature of ≤800℃, and the hot air reaching the set temperature enters the evaporator downward; (2) Concentration of dilute phosphoric acid and discharge of finished products: Hot air is introduced into the liquid phosphoric acid in the evaporator in the form of large bubbles. The large bubbles rotate rapidly in the liquid phosphoric acid and split into small bubble groups. The small bubbles quickly transfer heat to the liquid phosphoric acid. The liquid phosphoric acid in the evaporator is heated by the hot air. It first enters the temperature rise stage and then enters the constant temperature evaporation stage. The heat transferred by the hot air to the liquid phosphoric acid is completely converted into the latent heat of vaporization of evaporating water. The concentration process is continuous. Dilute phosphoric acid is added continuously and quantitatively. When the liquid phosphoric acid enters the constant temperature evaporation stage and the concentration reaches the required level, the liquid phosphoric acid is taken as the target product - concentrated phosphoric acid to the deboundary zone. (3) Exhaust gas defoaming and sludge removal: The exhaust gas evaporated from the evaporator is defoamed by the mist separator and then flows upward to the boundary area. The removed liquid flows downward and returns to the evaporator as recovered phosphoric acid. When there is sludge in the evaporator, the evaporator bottom valve is opened to put the sludge into the sludge box. The sludge in the sludge box is sent to the boundary area through the sludge pipeline by regularly opening the sludge box bottom valve.

8. The method according to claim 7, characterized in that The mass concentration of the dilute phosphoric acid in step (1) is ≥20%.

9. The method according to claim 7, characterized in that In step (2), the constant temperature is ≥100° C.; the concentration requirement is that the P2O5 mass concentration is ≥40%; and the P2O5 mass concentration of the target product, concentrated phosphoric acid, is ≥40%.

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