The factors that affect the intensity of evaporation and boiling are: unit heat load (heat transfer per unit time and area), pipe geometry and relative height of liquid level (ratio of static liquid level height to pipe length). The experimental results show that the boiling heat transfer coefficient is larger when the relative height of liquid level is between 0.3 and 0.4 under the condition of certain tube geometry and heat load.DEAR Liquid air separation unit.The lower tower needs a larger reflux ratio to ensure the quantity and purity of pure liquid nitrogen, and then it is sent to the upper tower as reflux liquid. In this process, the unit cooling capacity of the expanded refrigerant is higher, and the expansion capacity is smaller on the premise of compensating the same cooling loss.The liquefier and subcooler transfer the cooling capacity to the tower, which can accelerate the accumulation of liquid. In this case, regardless of maintaining the liquid level of the lower tower for the time being, open the liquid air throttle valve to let as much liquid air entrained gas pass through the subcooler as possible to strengthen the heat exchange of the subcooler and recover more cooling capacity. Some oxygen generators do not even set up liquefier in the process design, only rely on the subcooler to be used as liquefier during start-up, starting from the upper tower to accumulate liquid.
In the start-up operation, as long as we connect the liquefier timely, we can avoid the liquefier to appear liquid prematurely. Usually, when the temperature condition of the switching heat exchanger is basically established and other equipment is cooled, it is better to close the bypass valve of the liquefier and connect the liquefier.DEAR Liquid air separation unit.Machinery industry, mainly used for metal cutting and welding. Oxygen is used as combustion supporting agent of acetylene to produce high temperature flame and melt metal. In national defense industry, liquid oxygen is often used as the combustion supporting agent of rocket. The combustible material soaked in liquid oxygen has strong explosiveness and can be used to make liquid oxygen explosive. In addition, in the medical sector, oxygen is also an indispensable material for first aid and adjuvant treatment of patients. Therefore, oxygen production is an indispensable part of the national economy.At the same time, the condensing evaporator also acts as a liquefier in the later stage of start-up. After expansion, the low-temperature air entering the upper tower cools the low-temperature pressure gas from the lower tower in the condensing evaporator, some of which condenses and then throttles to the upper tower to further reduce the temperature and become part of the low-temperature and low-pressure reflux gas, so that the accumulated liquid volume increases gradually.
DEAR Liquid air separation unit.Adjust the distillation condition of upper column, and strive to improve the average nitrogen purity. The average nitrogen purity indicates the oxygen loss rate. The average nitrogen purity depends on the purity of sewage nitrogen, because the proportion of sewage nitrogen is large. The purity of waste nitrogen is mainly guaranteed by the supply of qualified liquid nitrogen from the lower tower.For the full low pressure unit, the expansion can only be increased, which affects the distillation condition of the upper column and reduces the average purity of nitrogen. Therefore, when the expansion air flow into the tower is limited and the cooling capacity is insufficient, the argon fraction can only be reduced.DEAR Liquid air separation unit.Switching heat exchanger with water will also shorten the operation cycle. It is usually caused by improper operation of nitrogen water precooler. However, the slight water inflow is often due to the neglect of the blowing out of the water separator and the discharge of the condensed water in the air main pipe of the switching heat exchanger.
