Calculation of liquid chlorine vaporization process

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This post was last edited by zyc88882011 on 2011-12-2 at 11:05. I. Process flow: This process is divided into three sections: the liquid chlorine storage tank feeding section, the liquid chlorine vaporization section, and the waste gas treatment section. The details are as follows: (I) Local area of the liquid chlorine storage tank feed: 1. First, confirm that the unloading port of the tank truck, the exhaust gas interface, and the nitrogen interface have been properly connected; then pressurize with nitrogen to 0.70 MPa to ensure that there are no leaks at the connection points. 2. Release pressure from the pipeline after confirming that there are no leaks at the connection points. Check the pressures of the tank truck and the storage tank to ensure that the pressure difference between them is within the range of 0.15~0.20 MPa. If the pressure in the tank truck is low, it can be increased by filling it with nitrogen, or the pressure in the storage tank can be reduced to address the issue (note: the pressure in the tank truck should be higher than that in the storage tank). 3. Once it is confirmed that the pressures and pressure differences between the tank truck and the storage tank are correct, open the feeding valve of the storage tank and the discharge valve of the tank truck to start feeding. During the feeding process, pay attention to maintaining the pressure difference between the tank truck and the storage tank; if the pressure difference is too low, feeding can be paused. Feeding can resume only after carrying out the procedures described in point 2. Meanwhile, during the pressurization and pressure relief process of the tank truck and the storage tank, their pressures must not exceed 0.65 MPa, nor must they be lower than 0.05 MPa. 4. After the unloading process from the tank truck is complete, close the unloading valve of the tank truck. Use nitrogen to push the material towards the storage tank; once that is done, close the feeding valve of the storage tank and open the feeding valve of the tank truck, using nitrogen to push the material back towards the tank truck. Finally, close the unloading valve of the tank truck. Note that during the material pressing process, the operating pressure must not exceed the pressure specified for the tank, and the valves must be operated slowly. 5. After the material compression is complete, slowly open the exhaust valve to evacuate the area, and at the same time open the nitrogen valve for gas replacement. The discharge valve can be removed only after the analysis tests show satisfactory results, thus completing the material discharge process from the tank truck. (II) Local area for liquid chlorine vaporization: 1. The liquid chlorine vaporizer is heated using a hot water circulation system; the water in the hot water tank is replenished with externally supplied softened water, with the level being maintained at a specific level (2/3). The water in Xunhua is heated by an external steam pipeline, with the water temperature maintained within the range of 40–45°C. The hot water circulation tank is drained regularly through the bottom drain outlet. 2. The liquid chlorine in the vaporizer of the liquid chlorine storage tank is pumped into the liquid chlorine vaporizer using an submersible pump; the outlet pressure of this submersible pump is maintained at around 0.65 MPa. The feed rate is adjusted based on signals transmitted by a level sensor, so as to keep the liquid level in the vaporizer at approximately 2/3 of its capacity. The vaporizer converts liquid chlorine into gas by heating it with circulating hot water supplied by a centrifugal pump; the flow rate of the incoming water is adjusted via a pressure sensor on the vaporizer, thereby controlling the amount of evaporation and keeping the pressure in the vaporizer at around 0.6 MPa. The vaporizer discharges waste regularly through the bottom drain port into the exhaust gas buffer tank, with strict control to keep the nitrogen trichloride content in the vaporizer at no more than 50 g/l. 3. The chlorine gas discharged from the vaporizer enters the chlorine gas buffer tank through a regulating mechanism. To prevent liquid chlorine carried by the chlorine gas from affecting the safety of operations in the subsequent system, the chlorine gas buffer tank is equipped with an outer casing through which hot water is circulated for insulation and heating (at 40–45°C), ensuring that any liquid chlorine introduced is completely vaporized. The pressure in the chlorine gas buffer tank is controlled via an inlet regulating valve (at 0.6 MPa). The chlorine gas discharged from the chlorine buffer tank is sent to the hydrogen chloride synthesis process. 4. Drainage operation of the liquid chlorine vaporizer: The outlet pressure should be between 50 and 80 Kpa. After drainage is complete, close the vaporizer’s drainage valve; then use nitrogen to pressurize the intermediate drainage tank to 0.15 MPa. Subsequently, transfer the material slowly into the residual chlorine absorption tank, where the residual chlorine is absorbed gradually using a 15% concentration of caustic solution. The caustic solution passes through an external cooler to ensure that the temperature in the absorption tank remains at or below 40°C and the pressure stays at or below 0.02 MPa. The exhaust gases are sent to the waste gas treatment tower. c. During the treatment of residual liquid, monitor the alkali content in the absorbed alkaline solution promptly; if this content is below 2%, the alkaline solution should be replaced immediately. (III) Exhaust gas treatment section: 1. Chlorine-containing exhaust gases generated in this process, such as those from tank truck unloading, tank feeding, pressure relief of equipment pipelines, nitrogen-sealed startup of submersible pumps, equipment sewage discharge, and equipment maintenance and replacement, are all routed to the exhaust gas buffer tank. After being absorbed by alkali solution in the exhaust gas treatment tower, these gases are exhausted into the atmosphere via the fan at the top of the tower; the pressure at the fan inlet is maintained at -3.5 Kpa. 2. The alkaline solution is discharged in a measured amount into the circulation tank through the lower alkaline solution tank; a measured amount of water is added to the alkaline solution circulation tank, and the alkaline solution circulation pump is started to circulate and mix the solutions. Analysis shows that water addition should be stopped when the concentration of the mixed alkali solution reaches 10–15%. Start the alkali solution circulation pump to convey the chlorine-containing waste gas discharged by the alkali absorption system to the waste gas treatment tower. Periodic analysis is conducted to measure the alkali content and the sodium hypochlorite content in the circulation liquid; when the alkali content reaches a pH value of 8–10, the alkaline solution is routed to another circulation tank in order to continue absorbing chlorine-containing waste gases. 3. The absorbent solution converted into sodium hypochlorite solution is pumped to the lower tank containing sodium hypochlorite for sale. II. Key operating points and precautions: 1. It is strictly prohibited to operate the equipment under overpressure or when it is in a faulty condition. 2. The escape of chlorine gas is strictly prohibited. 3. Operate strictly in accordance with the prescribed procedures to eliminate all types of violations. 4. Strictly carry out the regular cleaning of the carburetor and the testing for nitrogen trichloride. 5. The plant area is equipped with chlorine scavengers, protective gas masks, safety goggles, and oxygen respirators to handle emergencies should they occur. 6. The liquid chlorine storage area is not equipped with a backup tank; in the event of a malfunction in the liquid chlorine storage tank, the liquid chlorine can be transferred to the backup tank. During operation, an submersible pump can be used to pump the liquid chlorine from the tank that has leaked into the backup tank. (Pressurizing the leaking tank is strictly prohibited.) 7. During the discharge of residual liquid and the absorption process, the pressure in all containers must not exceed the pressure values specified by the process; at the same time, it is necessary to ensure that material transfer and absorption take place in a liquid phase. III. Process Conditions: Equipment Name – Industrial Control Objectives
Hot water tank: Liquid level at 2/3; Water temperature at 40–45°C. Hot water pump: Flow rate of Q=5 m3/h, head of H=25 m; Motor power: 1.5 KW.
Liquid chlorine storage tank: Liquid level at 2/3; Operating pressure ≤0.65 MPa. Submersible pump: Flow rate of Q= m3/h, head of H= m; Motor power in KW.
Liquid chlorine evaporator: Operating pressure ≤0.65 MPa; Heating water temperature at 40–45°C; Liquid level ≤2/3.
Chlorine gas buffer tank: Operating pressure ≤0.65 MPa; Heating water temperature at 40–45°C (set value: 42°C).
Waste gas treatment tower: Pressure at the top of the tower at 3–5 KPa (actual void fraction). Buffer tank before the waste gas compressor: Operating pressure at -30–+50 KPa.
Chlorine compressor: Inlet pressure at -30–+50 KPa.
a. Maintain the liquid level in the vaporizer at 30%, reduce the pressure to around 0.2 MPa, and then discharge the material into the intermediate waste tank. Exit temperature ≤50°C; buffer tank after the exhaust gas machine; operating pressure: 50–80 KPa; top fan of the tower; vacuum degree: 5–10 KPa; motor power in KW. For the alkali solution circulation tank, the liquid level should be ≤80%, and the alkali concentration should be 10–15%. The flow rate of the alkali solution circulation pump is Q = m3/h, with a height of 30 m; motor power in KW. For the alkali solution circulation cooler, the exit temperature of the alkali solution should be ≤40°C. In the lower tank for the alkali solution, the liquid level should also be ≤80%, with a capacity of m3. The operating pressure for chlorine gas is 0.7 MPa (absolute pressure); according to the data sheet, its boiling point is 22°C. The capacity is in m3, with a pH value of approximately 8–10. The amount of ineffective chlorine is 4–7%. IV. Process calculations: (I) Liquid chlorine vaporizer: 1. Operating parameters: For the sodium hypochlorite storage tank, the liquid level should be ≤80%. The temperature of the circulating hot water is 40–45°C; at this temperature, the saturated vapor pressure of chlorine is 1.27 MPa. Therefore, the pressure in the vaporizer should be no less than 1.4–1.5 MPa. The set pressure for the safety valve should be between 0.75 and 0.80 MPa. 2. Heat exchange area: The heat of vaporization of liquid chlorine at 22°C and a pressure of 0.7 MPa is approximately 250 kJ/kg. With an evaporation rate of 10 tons per day, the hourly evaporation rate is 0.417 tons. Thus, the steam generation amount is Q_steam = 0.417 * 250 * 1000 = 104,250 kJ/hr, which is equivalent to 24,940 kcal/hr. The temperature difference between the inlet and outlet of the circulating hot water is assumed to be 10°C (inlet at 42°C, outlet at 32°C). Therefore, the required amount of circulating hot water is M = 24,940 / (1 * 10 * 1000) = 2.494 tons/hr. 3. Pipeline calculations: At 22°C and a pressure of 0.7 MPa, the density of chlorine gas is approximately 23 kg/m3. Hence, the flow rate of chlorine gas is V = 0.417 * 1000 / 23 = 18.13 m3/hr. Assuming a gas flow velocity of u = m/s, the pipe diameter is d = … 4. Steam requirement: Heat losses are considered to be 1.2 times the actual demand. Thus, m = 1.2 * 24,940 / 539 = 55.5 kg/hr. The SEO rules remain unchanged; for further discussions, you can contact me via QQ at 282985864