The main heat exchanger is the key equipment to ensure the performance of the air separation plant. Its functions in the air separation plant of the molecular sieve pre-filtration process are as follows: recover the cooling capacity of the reflux gas, ensure that the heat exchange temperature difference is within the design range; provide sufficient expansion gas in front of the expander to make up for the cooling loss of the air separation plant; provide raw air for the lower tower under the design conditions; and the working medium is in the main heat exchanger The resistance value in meets the process requirements.
In the air separation plant, all factors affecting the performance of the equipment will be reflected in the main heat exchanger. Therefore, we always start from the suspected design of the main heat exchanger to carry out troubleshooting, and correctly analyze the external factors affecting the performance of the main heat exchanger is the shortcut to solve the problems of the air separation plant. According to the long-term practical experience, the main factors affecting the performance of the main heat exchanger are as follows:
1.Expander efficiency: the air compressor's exhaust volume is given by the process. If the expansion air volume increases, the positive flow air volume will decrease, which will reduce the heat load at the cold end of the main heat exchanger, and the cooling capacity will move up to the hot end. If there is excess cooling capacity at the hot end, the temperature difference at the hot end of the main heat exchanger will increase.
2.Molecular sieve adsorber: when the molecular sieve adsorber has insufficient filling amount, uneven bed, incomplete regeneration of molecular sieve, poor adsorption performance of molecular sieve, structural defects and other reasons, resulting in air short circuit, and molecular sieve leakage due to manufacturing problems, the adsorption of moisture and CO2 in the air will be affected, resulting in the increase of temperature difference and resistance at the hot end of the main heat exchanger.
3.Cooling loss: one part of the cooling loss of the distillation column system of the air separation plantis the loss of insufficient reheating of the main heat exchanger, and the other part is the cooling loss of the external environment of the equipment. The loss of reheating deficiency is determined by the temperature difference at the hot end of the main heat exchanger and set by the process flow; while the loss of cooling loss is estimated by experience, which is a process parameter. The difference between the set value of cooling loss and the actual value in operation also directly affects the temperature difference at the hot end of the main heat exchanger.
