Under the design working condition, the positive and return air volume of the Heat section of the switching heat exchanger (or cooler) is basically equal. While in the cold section, the return flow volume must be larger than the positive flow air volume, and keep a certain proportion relationship, so that the temperature difference of the cold end is within the required range of moisture and carbon dioxide self-elimination, and the temperature difference of the hot end should be appropriate. In actual operation, when the temperature condition fluctuates, the method of changing the air volume or the distribution of product gas volume is also often used to adjust.
When the middle temperature deviation occurs between two groups of switching heat exchanger (or between two groups of refrigerators), air inlet stop valve (or thin film butterfly valve) can be used for adjustment. The group with lower temperature in the middle part is larger, increasing air ventilation. In this way, the required cooling volume increases while the return flow volume remains unchanged, which will lead to insufficient cooling volume, thus the temperature in the middle part can rise. Lower the air inlet stop valve (or thin film butterfly valve) for the group with higher temperature in the middle to reduce the air ventilation. Due to sufficient cooling, the temperature in the middle can be reduced. When adjusting, pay attention to keep the total amount of air basically unchanged. 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, this is the bias caused by the lack of air volume, we should try to increase the air intake, generally used in rough tone.
The oxygen and nitrogen of the product are recirculation gases. Changing the flow distribution can also achieve the purpose of adjusting the temperature working condition. Each unit group of the switching heat exchanger is generally equipped with a product regulating valve (the cooler does not exist). For example, the 10 unit groups of the switching heat exchanger of the domestic 6000m 3/h air separation plant are equipped with an oxygen outlet butterfly valve, each group also has a pure nitrogen outlet butterfly valve. Turn on the big product regulating valve for the unit group with higher temperature in the middle part, and increase the excess of the product, that is, increase the cooling capacity, which can lower the temperature in the middle part; turn off the small product regulating valve for the unit group with lower temperature in the middle part, reduce the excess of the product, that is, reduce the cold volume, which can make the temperature in the middle rise. Adjust the distribution of excess quantity of products according to the temperature of the middle part, but the total quantity of products should not be changed. When the temperature of each unit group is unbalanced, the two groups with the highest and the lowest temperature in the middle should be adjusted first. The distribution of adjusted product quantity should not be too large, generally around ± 2%. In practice this method adjusting central temperature, or compare trouble the, so only for fine-tuning.
Increasing air excess or reducing product excess will cause the expansion of temperature difference at the cold end, the reduction of temperature difference at the hot end, and the rise of temperature at the circulation outlet (or the middle outlet, as shown in the curve 3 in figure 45 (the backflow is smaller than the forward flow, which refers to the thermal segment ). When reducing the air volume or increasing the excess of the product, it will lead to the reduction of the temperature difference at the cold end, the expansion of the temperature difference at the hot end and the reduction of the temperature at the outlet of circulation (or the middle outlet, as shown in curve 1 in figure 45 (the backflow is larger than the forward flow ). Curve 2 shows the situation of backflow-forward flow (referring to the thermal segment. Therefore, when increasing air ventilation or reducing product ventilation, attention should be paid to the expansion of the temperature difference between the cold end and the middle part; while when reducing air ventilation or increasing product ventilation, pay attention to the cold damage of the hot end. When necessary, it should be supplemented by the adjustment of circulation.
The above-mentioned method of adjusting temperature condition by changing air volume or product gas volume distribution is essentially the adjustment of cooling balance between groups, just transfer a group of excess cold capacity to the group with insufficient cold capacity. If the central temperature of each group tends to increase (or decrease), then the refrigerating capacity of the expansion machine should be increased (or decreased) to adjust.
