Variable load operation of air separation unit is to dynamically adjust the equipment operation parameters according to the fluctuation of gas load. Under the premise of ensuring product purity and stable working conditions, it is the core operation to adapt to production demand and reduce energy consumption. It is divided into two working conditions: load reduction and load increase. The whole process follows the regulation principle of "small amplitude, slow and step-by-step".
The variable load operation takes the adjustment of the processing air volume as the core benchmark. The operators first fine tune the air compressor load according to the consumption demand of oxygen, nitrogen and argon products, and control the gas volume increase and decrease at 0.5%~1% of the total gas volume each time, so as to avoid the sudden change of gas volume impacting the distillation condition. Adjust the operation parameters of the expander synchronously. By changing the expansion air volume to match the cooling capacity balance of the system, appropriately increase the expansion bypass volume when the load is reduced, and increase the cooling capacity of the expander when the load is increased to offset the cooling capacity fluctuation caused by the change of working conditions.
Subsequently, the key valves of the distillation system were precisely regulated, and the liquid nitrogen, liquid oxygen throttle valves and reflux valves were fine tuned to stabilize the pressure, temperature difference and liquid level of the upper and lower columns, so as to ensure the distillation separation accuracy. The core parameters such as product purity, tower pressure and hot end temperature difference are monitored in real time throughout the whole process, and the fluctuation range of parameters is strictly controlled. The adjustment process should be gradual and orderly, and the buffer time for stable working conditions should be reserved to prevent the imbalance of working conditions caused by large-scale operation.
At present, the mainstream air separation equipment can rely on the automatic control system, preset the working condition parameters, realize the accurate automatic control of variable load, and take into account the production stability and energy-saving benefits.
