An absorption tower for preparing ammonia water from liquid ammonia and its process

Abstract

The invention discloses an absorption tower for preparing ammonia water from liquid ammonia and an operating process thereof. The upper part of the absorption tower is provided with a spray device and a packing area, the tower kettle of the absorption tower is an ammonia water collecting cylinder, the middle part of the absorption tower is provided with a liquid ammonia heat exchange evaporator, the lower part of the liquid ammonia heat exchange evaporator is provided with a liquid ammonia inlet, the liquid ammonia inlet is connected to the shell side of the liquid ammonia heat exchange evaporator, the top of the shell side is connected to an air outlet pipe extending upward, the tube side of the liquid ammonia heat exchange evaporator comprises a plurality of vertically distributed heat exchange tubes, the top of the heat exchange tubes is connected to the upper part of the absorption tower, and the bottom is connected to the ammonia water collecting cylinder. The invention completes the process of gasifying liquid ammonia into ammonia gas inside the absorption tower by integrating the liquid ammonia heat exchange evaporator. The invention avoids the problem of local overheating and boiling caused by preparing ammonia water from liquid ammonia, reuses the spray liquid, fully utilizes the evaporation heat of the liquid ammonia, reduces the load of the cooling system required for the entire device, and saves the operating cost of the entire process.

Description

Technical Field

[0001] The present invention relates to the technical field of gasifying liquid ammonia into gaseous ammonia and then absorbing it into ammonia water, and in particular to an absorption tower for preparing ammonia water from liquid ammonia and a process thereof. Background Art

[0002] The traditional ammonia water preparation process generally uses gaseous ammonia or ammonia-containing gas, which is directly introduced into the absorption tower. The ammonia gas is then absorbed through the combined action of spraying desalted water and the filler area, forming ammonia water that falls back to the bottom of the absorption tower. With the further advancement of industrial integration, the preparation of ammonia water has gradually changed to directly introducing liquid ammonia into the absorption tower to prepare ammonia water.

[0003] Since liquid ammonia is a liquid, it cannot be directly introduced into the lower packing area of ​​the absorption tower like gas. The existing technology is to introduce liquid ammonia directly into the ammonia water in the bottom of the absorption tower. However, the volume per unit mass of liquid ammonia is about 1 / 800 of that of gaseous ammonia (under normal pressure), and the heat of solution per unit mass of gaseous ammonia is about 3 times that of liquid ammonia. Therefore, if liquid ammonia is directly introduced into the ammonia water, a large amount of heat per unit volume will accumulate in the ammonia water, causing a small-scale boiling of the ammonia water, which will directly affect the safety and stability of the equipment. To avoid the above situation, most companies still use liquid ammonia gasification equipment to convert it into ammonia gas, which is then introduced into the absorption tower to be prepared into ammonia water. Since the liquid ammonia gasification equipment itself requires an additional heating system, multiple sets of equipment are needed to achieve the preparation of ammonia water, resulting in a large number of ammonia absorption equipment and a large footprint. In addition, the liquid level of the ammonia evaporator and the supply of matching heat need to be adjusted to avoid large fluctuations in the ammonia water concentration.

[0004] Therefore, for those skilled in the art, there is an urgent need for an absorption tower for preparing ammonia water that is integrated with a liquid ammonia gasification system, which can ensure that the liquid ammonia can be fully gasified into ammonia gas and that the absorption tower is stable. Summary of the Invention

[0005] In response to the above-mentioned problems, the present invention aims to provide an absorption tower and process for preparing ammonia water from liquid ammonia, which has stable system operation, complete gasification of liquid ammonia into gaseous ammonia, sufficient absorption of gaseous ammonia, and high ammonia water production rate.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: an absorption tower for preparing ammonia water from liquid ammonia, the upper part of the absorption tower is provided with a spraying device and a packing area, the tower bottom of the absorption tower is an ammonia water collecting cylinder, the middle part of the absorption tower is provided with a liquid ammonia heat exchange evaporator, the lower part of the liquid ammonia heat exchange evaporator is provided with a liquid ammonia inlet, the liquid ammonia inlet is connected to the shell side of the liquid ammonia heat exchange evaporator, the top of the shell side is connected to the upwardly extending air outlet pipe, the tube side of the liquid ammonia heat exchange evaporator is a plurality of vertically distributed heat exchange tubes, the top of the heat exchange tubes is connected to the upper part of the absorption tower, and the bottom is connected to the ammonia water collecting cylinder, the top of the air outlet pipe is provided with a protective cover covering the air outlet pipe, and the air outlet pipe at the bottom of the protective cover is provided with an air vent connected to the upper part of the absorption tower.

[0007] A liquid level gauge is provided on the side of the liquid ammonia heat exchange evaporator of the present invention, and the liquid level gauge is connected to the shell side of the liquid ammonia heat exchange evaporator. The liquid level height of the liquid ammonia introduced into the liquid ammonia heat exchange evaporator is controlled by the liquid level gauge, and the input amount of the liquid ammonia is further regulated to maintain the smooth operation of the entire device.

[0008] Both ends of the liquid ammonia heat exchange evaporator of the present invention are provided with vertically installed tower kettle connecting exhaust pipes, the top of the tower kettle connecting exhaust pipe is connected to the upper part of the absorption tower, and the bottom is connected to the ammonia collecting cylinder. The top height of the tower kettle connecting exhaust pipe is higher than the shell side of the liquid ammonia heat exchange evaporator and lower than the exhaust pipe, and the top of the tower kettle connecting exhaust pipe is provided with a protective cover; the main purpose of the tower kettle connecting exhaust pipe is to connect the tower kettle and the tower top to avoid excessive ammonia pressure in the tower kettle; at the same time, in order to facilitate the heat exchange of sprayed ammonia water, the top of the exhaust pipe is protected by the protective cover to prevent the ammonia water from directly falling into the tower kettle through the exhaust pipe.

[0009] The liquid ammonia heat exchange evaporation device of the present invention is provided with a support plate in the middle, and the middle part of the heat exchange tube is fixed on the support plate; since the heat exchanger itself is composed of multiple vertically distributed heat exchange tubes, the entire liquid ammonia heat exchange evaporation device is fixed by the support plate.

[0010] The absorption tower of the present invention is provided with a gas discharge port at the top, and an ammonia detection instrument is provided on the connecting pipeline of the gas discharge port; the ammonia content of the gas discharged from the top is monitored by the ammonia detection instrument; the input amount of liquid ammonia or the actual working condition of the spray liquid inside the tower body is timely regulated.

[0011] The present invention provides an operating process of an absorption tower for preparing ammonia water from liquid ammonia, comprising the following steps:

[0012] 1) According to the actual size of the absorption tower, determine the total height of the liquid ammonia heat exchange evaporation device as H and the designed liquid ammonia flow rate as F D And the designed ammonia concentration is C D ;

[0013] 2) The absorption tower enters the working state, desalted water is introduced into the spray device, liquid ammonia is introduced into the liquid ammonia inlet, and the prepared ammonia water is discharged from the tower kettle;

[0014] 3) The actual height of liquid ammonia in the liquid ammonia heat exchange evaporator is measured by the liquid level meter as h, and the density of ammonia water is measured by the mass flow meter. The actual ammonia concentration is calculated as C T ; The actual ammonia flow rate into the liquid ammonia heat exchange evaporator is detected by the flow meter, and the actual ammonia flow rate is f T The conversion formulas of the three are as follows:

[0015]

[0016] Among them, AA is the actual area margin of the liquid ammonia heat exchange evaporator, AA = (actual heat exchange area / theoretically calculated heat exchange area - 1) · 100%; a = 50%, b = 12%; the value detected by the instrument is compared with the value obtained by the conversion formula to maintain the smooth operation of the entire device.

[0017] During the operation of the absorption tower, the process of the present invention maintains the actual ammonia flow rate f T Unchanged, real-time monitoring of the actual ammonia concentration C T and the designed ammonia concentration C D The size of ∣C T -C D ∣≈0;

[0018] 1) If the actual ammonia concentration C T Lower than the designed ammonia concentration C D , then reduce the amount of desalted water entering the spray device;

[0019] 2) If the actual ammonia concentration C T Lower than the designed ammonia concentration C D , then increase the amount of desalted water entering the spray device.

[0020] During the operation of the absorption tower, the limit working liquid level of the liquid level gauge in the liquid ammonia heat exchange evaporation device is set to H J And H J <H, when the actual height of liquid ammonia h≥H J When , close the liquid ammonia input valve and suspend the input of liquid ammonia.

[0021] The advantages of the present invention are as follows: the present invention completes the process of gasifying liquid ammonia into ammonia gas inside the absorption tower by integrating the absorption tower with the liquid ammonia heat exchange evaporation device; the gaseous ammonia is evenly distributed in the absorption tower, and further fully contacts with the filler and spray liquid on the upper part of the absorption tower, and is then prepared into ammonia water. In the process of falling, the ammonia water exchanges heat with the liquid ammonia in the shell side through the tube side of the liquid ammonia heat exchange evaporation device, thereby avoiding the problem of local overheating and boiling caused by the preparation of ammonia water by liquid ammonia, reusing the spray liquid, and making full use of the evaporation heat of the liquid ammonia, reducing the cooling system load required by the entire device, and saving the operating cost of the entire process.

[0022] The entire device is controlled by a control system. In order to ensure that liquid ammonia is fully vaporized into ammonia gas and ammonia gas is fully absorbed to prepare ammonia water, a complete set of processes is used to control the device to ensure stable operation of the entire device. The operation of preparing ammonia water from liquid ammonia in a set of absorption towers is truly realized. The overall process is precisely regulated. When the actual operating parameters and theoretical parameters change, the corresponding operating steps can be used for regulation to maintain stable and efficient operation of the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the overall structural diagram of the absorption tower of the present invention;

[0024] Figure 2 This is an enlarged structural diagram of the liquid ammonia heat exchange evaporation device of the present invention;

[0025] Figure 3 It is an enlarged top cross-sectional view of the structure of the liquid ammonia heat exchange evaporator of the present invention;

[0026] Figure 4 It is a process control schematic diagram of the absorption tower control system of the present invention.

[0027] Among them, 1 ammonia collection cylinder, 2 spray device, 3 packing area, 4 liquid ammonia heat exchange evaporation device, 5 liquid ammonia inlet, 6 outlet pipe, 7 gas discharge port, 8 liquid level gauge connection port, 9 shell side, 10 heat exchange tube, 11 protective cover of outlet pipe, 12 vent, 13 tower kettle connecting exhaust pipe, 14 tower kettle connecting exhaust pipe protective cover, 15 support plate. DETAILED DESCRIPTION

[0028] The present invention will be described in further detail below with reference to the accompanying drawings and specific implementation methods.

[0029] Example 1: Figure 1 、 2As shown in Figure 3, the present invention discloses an absorption tower for preparing ammonia water from liquid ammonia, wherein a spray device 2 and a packing area 3 are provided at the upper part of the absorption tower, the tower bottom of the absorption tower is an ammonia water collecting cylinder 1, a liquid ammonia heat exchange evaporator 4 is provided at the middle part of the absorption tower, a liquid ammonia heat exchange evaporator 4 is provided at the lower part thereof, a liquid ammonia inlet 5 is provided, the liquid ammonia inlet 5 is connected to the shell side 9 of the liquid ammonia heat exchange evaporator 4, the top of the shell side 9 is connected to an air outlet pipe 6 extending upward, the tube side of the liquid ammonia heat exchange evaporator 4 is a plurality of vertically distributed heat exchange tubes 10, the top of the heat exchange tube 10 is connected to the upper part of the absorption tower, and the bottom is connected to the ammonia water collecting cylinder 1, a protective cover 11 covering the air outlet pipe is provided at the top of the air outlet pipe 6, and an air vent 12 is provided on the air outlet pipe 6 at the lower part of the protective cover to connect to the upper part of the absorption tower.

[0030] A liquid level gauge connection port 8 is provided on the side of the liquid ammonia heat exchange evaporator 4 to connect to the liquid level gauge, and the liquid level gauge is connected to the shell side 9 of the liquid ammonia heat exchange evaporator 4; the liquid level height of the liquid ammonia introduced into the liquid ammonia heat exchange evaporator 4 is controlled by the liquid level gauge, and the input amount of liquid ammonia is further regulated to maintain the smooth operation of the entire device.

[0031] Example 2: Figure 1 、 2 As shown in Figure 3, vertically installed tower kettle connecting exhaust pipes 13 are provided at both ends of the liquid ammonia heat exchange evaporator 4. The top of the tower kettle connecting exhaust pipe 13 is connected to the upper part of the absorption tower, and the bottom is connected to the ammonia collecting cylinder 1. The top height of the tower kettle connecting exhaust pipe 13 is higher than the shell side 9 of the liquid ammonia heat exchange evaporator 4 and lower than the air outlet pipe 6. A protective cover 14 is provided on the top of the tower kettle connecting exhaust pipe 13; the main purpose of the tower kettle connecting exhaust pipe 13 is to connect the tower kettle and the tower top to avoid excessive ammonia pressure in the tower kettle; at the same time, in order to facilitate the heat exchange of sprayed ammonia, the top of the tower kettle connecting exhaust pipe 13 is protected by a protective cover to prevent ammonia from falling directly into the tower kettle through the exhaust pipe.

[0032] A support plate 15 is provided in the middle of the liquid ammonia heat exchange evaporation device 4, and the middle part of the heat exchange tube 10 is fixed on the support plate 15; since the heat exchanger itself is composed of multiple vertically distributed heat exchange tubes 15, the entire liquid ammonia heat exchange evaporation device is fixed by the support plate 15.

[0033] Example 3: Figure 1 、 2 As shown in Figure 3, a gas discharge port 7 is provided at the top of the absorption tower, and an ammonia detection instrument is provided on the connecting pipeline of the gas discharge port 7; the ammonia content of the gas discharged from the top is monitored by the ammonia detection instrument; the input amount of liquid ammonia or the actual working condition of the spray liquid inside the tower body is timely regulated.

[0034] Example 4: Figure 2 and 4 As shown, an operating process of an absorption tower for preparing ammonia water from liquid ammonia includes the following steps:

[0035] 1) According to the actual size of the absorption tower, determine the total height of the liquid ammonia heat exchange evaporation device 4 as H and the designed liquid ammonia flow rate as F D And the designed ammonia concentration is C D ;

[0036] 2) The absorption tower enters the working state, desalted water is introduced into the spray device, liquid ammonia is introduced into the liquid ammonia inlet 5, and the prepared ammonia water is discharged from the tower kettle;

[0037] 3) The actual height of liquid ammonia in the liquid ammonia heat exchange evaporator 4 is measured by the liquid level meter as h, and the density of ammonia water is measured by the mass flow meter. The actual ammonia concentration is calculated as C T ; The actual ammonia flow rate is f T The conversion formulas of the three are as follows:

[0038]

[0039] Where AA is the actual area margin of the liquid ammonia heat exchange evaporator, AA = (actual heat exchange area / theoretically calculated heat exchange area - 1) · 100%; a = 50%, b = 12%. By comparing the values ​​detected by each instrument with the values ​​obtained by the conversion formula, the corresponding valve switches of the instrument are adjusted in a timely manner to ensure the smooth operation of the entire equipment and avoid safety accidents.

[0040] 4) During the operation of the absorption tower, maintain the actual ammonia flow rate f T Unchanged, real-time monitoring of the actual ammonia concentration C T and the designed ammonia concentration C D The size of ∣C T -C D ∣≈0;

[0041] ① If the actual ammonia concentration C T Lower than the designed ammonia concentration C D , then reduce the amount of desalted water flowing into the spraying device through the regulating valve;

[0042] ② If the actual ammonia concentration C T Lower than the designed ammonia concentration C D , the amount of desalted water entering the spraying device is increased through the regulating valve.

[0043] Example 5: Figure 2 and 4 As shown, the limit working liquid level of the liquid level gauge in the liquid ammonia heat exchange evaporation device is set to H J And H J <H, when the actual height of liquid ammonia h≥H J When the liquid ammonia input valve is closed, the input of liquid ammonia is suspended.

[0044] Example 6: Matching instructions for implementing the flow chart

[0045] like Figure 2 and 4 As shown: This process is applied to a 5t / h 15% (mass) ammonia water preparation unit:

[0046] The liquid ammonia from the boundary area (1.6MPa, 40℃, 0.75t / h) is reduced in pressure to 0.6MPa by the FV001 liquid ammonia flow regulating valve and then enters the shell side of the liquid ammonia heat exchange evaporator of the ammonia absorption tower, where it exchanges heat with the hot ammonia water (71℃ reduced to 53℃) in the tube side and is vaporized to obtain gaseous ammonia. The gaseous ammonia enters the lower packing layer through the gas outlet pipe of the shell side and comes into countercurrent contact with the dilute ammonia water and circulating ammonia water from the upper packing layer. 80-90% of the gaseous ammonia is absorbed by the dilute ammonia water and circulating ammonia water in the lower packing layer, and the remaining small amount of gaseous ammonia enters the upper packing layer and comes into countercurrent contact with the desalted water (controlled by the FV002 desalted water flow regulating valve, with a valve upstream pressure of 1.6MPa, 25-40℃, 4.25t / h) from the upper packing layer. All the gaseous ammonia is completely absorbed by the desalted water in the upper packing layer.

[0047] The desalted water passes through the upper packing layer, where it comes into contact with a small amount of ammonia vapor to produce dilute ammonia water (1.5%-3.0%). This water then merges with circulating ammonia water (0.6MPa, 40°C, 5.00t / h, 15%) before entering the lower packing layer, where it comes into contact with a larger amount of ammonia vapor to produce hot ammonia water (0.6MPa, 71°C, 10.00t / h, 15%). The water then passes through the tube side of the liquid ammonia heat exchange evaporator, providing heat to the shell-side liquid ammonia through falling film heat exchange. The water is then cooled to 53°C before being delivered to the reactor. The hot ammonia water leaving the reactor is pumped up (with a head of 20m) and cooled to 40°C in a water cooler. It is then split into two paths: one path serves as circulating ammonia water and dilute ammonia water, entering the lower packing layer as an absorbent for ammonia vapor; the other path serves as finished ammonia water (0.8MPa, 40°C, 5.00t / h, 15%) and is delivered to the boundary area.

[0048] The desalted water flow control system is a cascade control system, with AIC001 ammonia concentration as the primary control loop and FIC002 desalted water flow as the secondary control loop. By introducing a closed secondary control loop, not only can interference acting on the secondary control loop be quickly overcome, but interference acting on the primary control object, ammonia concentration, can also be overcome more quickly. The secondary control loop features pre-adjustment, coarse adjustment, and rapid adjustment; the primary control loop features post-adjustment, fine adjustment, and slow adjustment, and can completely overcome interference effects not fully overcome by the secondary control loop. Therefore, by setting up the desalted water flow control system as a cascade control system, the primary and secondary control loops cooperate and complement each other, fully utilizing their control capabilities and significantly improving the control quality of ammonia concentration.

[0049] Similarly, the circulating ammonia flow control system is also a cascade control system, with TIC001 ammonia temperature as the main control loop and FIC003 circulating ammonia flow as the secondary control loop, so that the ammonia temperature TIC001 out of the tower remains stable, thereby improving the absorption effect of the ammonia absorption tower.

[0050] The heat exchange area of ​​the liquid ammonia heat exchange evaporator is 35.5m 2 (Area margin is 100%), heat exchange tube size is Φ25*2, effective tube length is 2m, under design conditions (5t / h, 15% ammonia product concentration), the calculated liquid level value LI001B of the liquid ammonia heat exchange evaporator is 1m, and the measured value LIA001A should also be 1m. If the deviation between the two values ​​LDI001 is large, the cause should be investigated, especially if the measured value is higher than the calculated value. If instrument measurement failure has been eliminated, it indicates poor heat exchange performance of the device. If operation cannot be maintained, the heat exchange tube bundle of the equipment should be cleaned.

[0051] To ensure safety, a high-level interlock S001 (typically set at 90%-95% of the effective length of the heat exchange tubes, i.e., the total height) is set. Once triggered, it closes the liquid ammonia flow control valve FV001. Under low-load conditions, with a 2.5t / h ammonia product concentration of 20%, the calculated liquid level value LI001B of the liquid ammonia heat exchange evaporator is 0.49m, and the measured value LIA001A under stable conditions should also be 0.49m. Under high-load conditions, with a 7.5t / h ammonia product concentration of 10%, the calculated liquid level value LI001B of the liquid ammonia heat exchange evaporator is 1.51m, and the measured value LIA001A under stable conditions should also be 1.51m.

[0052] It should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any combination or equivalent transformation based on the above embodiments falls within the scope of protection of the present invention.

Claims

1. An absorption tower for preparing ammonia water from liquid ammonia, wherein the upper portion of the absorption tower is provided with a spraying device and a packing area, and the bottom of the absorption tower is an ammonia water collecting cylinder, characterized in that: A liquid ammonia heat exchange evaporator is provided in the middle of the absorption tower, a liquid ammonia inlet is provided at the lower part of the liquid ammonia heat exchange evaporator, the liquid ammonia inlet is connected to the shell side of the liquid ammonia heat exchange evaporator, the top of the shell side is connected to the outlet pipe extending upward, the tube side of the liquid ammonia heat exchange evaporator is a plurality of vertically distributed heat exchange tubes, the top of the heat exchange tubes is connected to the upper part of the absorption tower, and the bottom is connected to the ammonia collecting cylinder, the top of the outlet pipe is provided with a protective cover covering the outlet pipe, and the outlet pipe at the lower part of the protective cover is provided with an air vent connected to the upper part of the absorption tower.

2. The absorption tower according to claim 1, wherein A liquid level gauge is provided on the side of the liquid ammonia heat exchange evaporator, and the liquid level gauge is connected to the shell side of the liquid ammonia heat exchange evaporator.

3. The absorption tower according to claim 1, wherein Both ends of the liquid ammonia heat exchange evaporator are provided with vertically installed tower kettle connecting exhaust pipes, the top of the tower kettle connecting exhaust pipe is connected to the upper part of the absorption tower, and the bottom is connected to the ammonia collection cylinder. The top height of the tower kettle connecting exhaust pipe is higher than the shell side of the liquid ammonia heat exchange evaporator and lower than the exhaust pipe, and the top of the tower kettle connecting exhaust pipe is provided with a protective cover.

4. The absorption tower according to claim 1, wherein A support plate is provided in the middle of the liquid ammonia heat exchange evaporator, and the middle of the heat exchange tube is fixed on the support plate.

5. The absorption tower according to claim 1, wherein A gas discharge port is provided on the top of the absorption tower, and an ammonia detection instrument is provided on the connecting pipeline of the gas discharge port.

6. An operating process for an absorption tower for preparing ammonia water from liquid ammonia as claimed in claim 1, characterized in that: The described operation process comprises the following steps: 1) According to the actual size of the absorption tower, determine the total height of the liquid ammonia heat exchange evaporation device as H and the designed liquid ammonia flow rate as F D And the designed ammonia concentration is C D ; 2) The absorption tower enters the working state, desalted water is introduced into the spray device, liquid ammonia is introduced into the liquid ammonia inlet, and the prepared ammonia water is discharged from the tower kettle; 3) The actual height of liquid ammonia in the liquid ammonia heat exchange evaporator is measured by the liquid level meter as h, and the density of ammonia water is measured by the mass flow meter. The actual ammonia concentration is calculated as C T ; The actual ammonia flow rate into the liquid ammonia heat exchange evaporator is detected by the flow meter, and the actual ammonia flow rate is f T The conversion formulas of the three are as follows: Among them, AA is the actual area margin of the liquid ammonia heat exchange evaporator, AA = (actual heat exchange area / theoretically calculated heat exchange area - 1) · 100%; a = 50%, b = 12%.

7. The operating process according to claim 6, characterized in that: During the operation of the absorption tower, the actual ammonia flow rate f T Unchanged, real-time monitoring of the actual ammonia concentration C T and the designed ammonia concentration C D The size of ∣C T -C D ∣≈0; 1) If the actual ammonia concentration C T Lower than the designed ammonia concentration C D , then reduce the amount of desalted water entering the spray device; 2) If the actual ammonia concentration C T Lower than the designed ammonia concentration C D , then increase the amount of desalted water entering the spray device.

8. The operating process according to claim 6, characterized in that: During the operation of the absorption tower, the limit working liquid level of the liquid level gauge in the liquid ammonia heat exchange evaporation device is set to H J And H J <H, when the actual height of liquid ammonia h≥H J When , close the liquid ammonia input valve and suspend the input of liquid ammonia.

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