1. What is reflux ratio? What effect does it have on distillation?
Answer: reflux ratio refers to the ratio of the amount of downflow liquid and the amount of rising steam in the distillation column. The purity of the distillation product depends on the reflux ratio when the number of trays is fixed. When the reflux ratio is large, the purity of nitrogen in the gas phase is high and the purity of oxygen in the liquid phase is low; when the reflux ratio is small, the purity of nitrogen in the gas phase is low and the purity of oxygen in the liquid phase is high.
2. What are the causes of molecular sieve water accidents?
Answer: 1. When the liquid level of the air cooling tower is higher than 3500mm, the water exceeds the height of the air inlet pipe, and a large amount of water enters the molecular sieve adsorber with the air;
2. When the resistance of the air-cooled tower rises above 7kpa, liquid suspension will form in the air-cooled tower, which will cause fluctuation of the bottom water level, fluctuation of the resistance of the air-cooled tower, and water will enter the molecular sieve adsorber with air;
3. The disordered procedure of molecular sieve switching causes the air to suddenly pass through the molecular sieve adsorber for air defense, the air flow speed in the air cooling tower is accelerated rapidly, and the water enters the molecular sieve adsorber with the air;
4. The air pressure of the instrument is reduced, and the self-regulation of the pneumatic valve is out of control, resulting in the rise of the water level;
5. The flow of cooling water and chilled water is too large, which makes the air cooling tower suspended at night.
3. What are the preventive measures for expander accidents?
Answer: 1. The temperature alarm value of the front bearing of the expander is 70 ℃, and the interlock value is 75 ℃;
2. When the rotating speed of the expander exceeds the alarm value, the return valve gradually opens, and when it exceeds the interlock value, the expander stops;
3. The booster flow is lower than the minimum alarm value, the expander return valve is fully open;
4. When the inlet temperature of expander is less than - 180 ℃, the inlet valve is closed.
4. What are the operation precautions of booster expander?
Answer: 1. Under no circumstances is it allowed to remove the interlock to start the expander;
2. Control the inlet temperature of expander to be no less than - 118 ℃;
3. It is not allowed to start the expander when the bypass valve fcv401 of the supercharger is closed. Precooling shall be carried out first when the expander is used for the first time or put into use in hot state.
5. What impurities are in the air?
A: in addition to oxygen and nitrogen, there are a small amount of water vapor, carbon dioxide, acetylene, other hydrocarbons and a small amount of dust and other solid impurities in the air.
6. Why should impurities be removed in the process of air separation?
Answer: with the cooling of air, the frozen water and carbon dioxide will be deposited in the low-temperature heat exchanger, turbo expander or distillation tower, which will block the channels, pipelines and valves; acetylene accumulation in liquid oxygen may cause explosion; dust will wear the operating machinery. In order to ensure the long-term stable and reliable operation of air separation equipment, special purification equipment must be set up to remove these impurities.
7. How to judge whether the heating regeneration of molecular sieve is complete?
Answer: first of all, it is required that the gas pressure and flow required for heating the molecular sieve meet the requirements of the process. Heating regeneration process can be judged by regeneration curve. The "peak temperature of cold blowing" is a sign of whether the regeneration of the whole bed is complete.
8. What is oxygen release rate?
Answer: it refers to the proportion of the oxygen (gaseous and liquid) products produced by the oxygen generator that have not been used but have been emptied. Oxygen release rate is an important index of the adaptability and production organization level of the reaction equipment. The more oxygen release rate is, the more energy waste is, the worse comprehensive economic benefit is. Therefore, it is necessary to reduce the oxygen release rate by various means.
9. What are the forms of air precooling system?
Answer: 1. Air cooling tower with low temperature water;
2. Indirect cooling system of low temperature water
3. Air and chiller direct heat exchange system;
4. Waste nitrogen evaporation cooling system;
5. Directly use the aftercooler to cool
10. What is molecular sieve? What kinds are there? What are its characteristics?
A: molecular sieve is a synthetic crystal of aluminosilicate. There are also natural ones, commonly known as stylolite. At present, the commonly used types are a, X and y. Main characteristics of molecular sieve:
1. It has strong adsorption capacity and good selective adsorption performance;
2. High dryness, good drying ability for high temperature gas;
3. It has good stability and can maintain normal adsorption capacity under 200 ℃. The service life of molecular sieve is longer.
4. The adsorption capacity of molecular sieve to water is very strong, followed by acetylene and carbon dioxide.
11. What are the characteristics of the air separation equipment in the molecular sieve adsorption and purification process? What should be paid attention to during operation?
Answer: the air separation equipment of molecular sieve purification process mainly focuses on giving full play to the refrigeration capacity of the expander, reasonably distributing the cooling capacity and comprehensively cooling the equipment during startup. It can be divided into three stages: cooling setting, liquid accumulation and working condition adjustment.
matters needing attention:
1. The molecular sieve used for the first time needs to be activated for regeneration in order to remove the adsorbed water and carbon dioxide during transportation and filling. Activation temperature is generally higher than 200 ℃ and lower than 250 ℃. When the outlet temperature reaches 80 ℃, it can be cooled. Activation time shall not be less than two cycles;
2. When the molecular sieve is started, the gas supply process shall be slow, and the vent valve shall be closed carefully to prevent the molecular sieve in the bed from being damaged due to pressure fluctuation;
3. When two expanders need to be started, the return valve of the booster shall be fully opened to reduce the pressure of the first operating expander, and then the two expanders shall be loaded at the same time to prevent the later starting booster from surging;
4. Pay attention to the temperature control in the middle of the heat exchanger;
5. Pay attention to the work of air cooling tower to ensure that the air after precooling meets the design requirements.
