From the vaporization temperature (saturation temperature) of liquid oxygen, if the liquid oxygen surface is too high, the greater the static pressure difference between the upper and lower liquid oxygen surface, the higher the average pressure of liquid oxygen and the corresponding saturation temperature. In order to maintain the heat transfer temperature difference of the condensing evaporator, it is necessary to increase the pressure of the lower tower. From this point of view, we do not want to make the plate unit too high.DEAR Air separation plant.When the temperature of the air entering the unit increases, not only the heat load of the accumulator (or switching heat exchanger) increases, but also the amount of water brought in increases, which increases the burden of self cleaning. With the increase of water freezing, the heat transfer efficiency is reduced. When the heat transfer area of the heat exchanger is fixed, the increase of the heat load and the poor heat transfer effect will inevitably lead to the increase of the temperature difference between the cold end and the hot end.
If the temperature of the product channel and circulation channel in the middle of the switching heat exchanger is uniform, and the temperature deviation in the middle of other channels is very large, it is due to the bias flow caused by insufficient air volume. It is necessary to try to increase the air intake volume, which is generally used in rough adjustment. The product oxygen and nitrogen are backflow gases. Changing their flow distribution can also achieve the purpose of adjusting the temperature condition.The liquid air and liquid nitrogen throttled from the lower tower to the upper tower are used as the reflux liquid to participate in the distillation of the upper tower. It is hoped that the proportion of gasification (called "gasification rate Y") will be reduced as much as possible when entering the upper tower. The liquid out of the lower tower is the saturated liquid corresponding to the lower tower pressure, the saturation temperature of liquid nitrogen is about - 177 ℃, and the saturation temperature of liquid air is about - 173 ℃.
When the gas expands in the expander, only the enthalpy drop caused by external work is considered in calculating the refrigeration capacity of the expander. In fact, when the pressure decreases, the molecular potential energy also increases, so a part of the throttling effect should be produced, which should be the cooling capacity. This part of refrigerating capacity is not calculated separately, but the total throttling effect refrigerating capacity of the unit is expressed by the total enthalpy difference between the low-pressure gas at the time of leaving the unit and the pressure gas at the time of entering the unit. When the refrigeration capacity of expander is adjusted, the refrigeration capacity of throttling effect is not affected.DEAR Air separation plant.The cooling of each equipment is carried out in stages, so the cooling is uniform and the thermal stress is small. In addition, in the second cooling stage, the cooling capacity of each equipment in the cooling tower is large, which makes the expander run for a long time at a higher inlet temperature, so as to give play to the large cooling capacity of the turbo expander at high temperature and shorten the start-up time.
In the ideal case, the work done by expansion can be equal to the work consumed by compression. It is a reversible adiabatic expansion process, and the entropy value before and after expansion remains unchanged, which is called isentropic expansion. The actual expander expansion will have loss, which is also an irreversible process, and the entropy also increases.DEAR Air separation plant.In the past, it was thought that the explosion of fractionator was caused by acetylene. The efficiency of acetylene adsorption could reach 98% when liquid air and liquid oxygen adsorbers were installed in the explosion-proof system. After years of practice and research abroad, it is found that in addition to acetylene, there are saturated and unsaturated hydrocarbons hydrocarbons, such as ethane, ethylene, propane and propylene, which are enriched in liquid oxygen.When the air separation column changes from normal temperature to low temperature, the phenomena of pipe cracking and valve sticking often occur. The main reasons are that the installation prestress is too large and the cold compensation is not good. In order to reduce the installation prestress and cold deformation stress, the following measures should be taken in the installation: when piping, it should be large first and then small, difficult first and then easy, small pipe should give way to large pipe, heat pipe should give way to cold pipe.
