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Optimization of the startup procedure for the ammonia cryocooler in the acetic acid plant at the Yongcheng Industrial Park of Henan Energy and Chemical Group. Author/Source: Date: 2018-05-09. Clicks: 108. During operation, the ammonia cryocooler in the Yongcheng Industrial Park’s acetic acid plant encounters problems due to issues related to the design of the turbine. After the cryocooler is started up, the moving and stationary parts of the turbine expand as a result of heat, but their expansion coefficients differ, which leads to collisions between these parts within the turbine. This results in excessive vibration in the turbine, causing it to shut down and preventing the plant from operating properly, thus threatening the progress of starting up the subsequent systems. During the startup process of the ammonia cryocooler, there is a large amount of nitrogen in the system; therefore, a significant quantity of liquid ammonia must be added to replace this nitrogen and cool the system. Each startup results in substantial losses of ammonia, with around 8 tons of liquid ammonia being lost each time, resulting in high startup costs. After numerous discussions and analyses by the technical staff, it was decided to make the following optimizations to the starting and stopping process of this compressor: 1. A differential expansion gauge will be installed on the turbine itself of the ammonia chiller, in order to monitor the differential expansion value of the unit and determine the position of the moving and stationary parts of the turbine. This helps to decide the appropriate time to apply load to the turbine, ensuring that it can operate properly. In response to the problem of high vibration during the startup of the turbine in ammonia refrigeration units, the relationship between the turbine cylinder temperature, steam volume, turbine expansion amount, and turbine expansion differential was analyzed, thereby determining the appropriate timing for increasing the load on the compressor. This ensures that the expansion differential of the unit remains within a reasonable range of -3mm to 3mm, preventing collisions between the moving and stationary parts of the turbine. The time for releasing steam from the turbine and connecting it to the piping system is set to 5 minutes after entering the warm-up mode 2; this ensures that, at low speeds, the turbine casing (the stationary parts) can be preheated quickly, thereby helping to reduce the gaps between the moving and stationary parts of the turbine. Increase the high-speed warm-up time of the turbine by about 1 hour; the high-speed warm-up speed is approximately 6200 RPM. Regulations have been established regarding the outlet pressure of ammonia refrigeration units; before reaching normal operating speed, the system pressure must not exceed 0.5 Mpa. This ensures that during the high-speed warming-up of the turbine, there is no risk of collision between the moving and stationary parts due to high turbine load. 2. During the startup and operation of the ammonia chiller system, the nitrogen that enters the system through the dry gas seal is the main source of nitrogen in the ammonia system. During startup, the pressure difference of 0.2 Mpa between the primary seal gas for the dry gas seal and the balance pipe is reduced to 0.12 Mpa. Control the flow rate of the primary seal air in the high-pressure cylinder at around 120 Nm3/h, and that of the primary seal air in the low-pressure cylinder at around 50 Nm3/h, thereby reducing the amount of nitrogen entering the system. Before starting the chiller, keep the pressure in the chiller system at 20 Kpa to reduce the starting resistance of the unit and the amount of nitrogen used. Before the chiller is warmed up at high speed, no liquid ammonia is added to the system; in order to prevent a high temperature at the outlet of the low-pressure cylinder, the final outlet pressure of the compressor is controlled to be no more than 0.5 Mpa. During high-speed warm-up of the unit, once the compressor outlet pressure reaches 0.5 Mpa, the anti-surge valves FV046240 and FV046242 should be closed promptly to increase the pressure difference between the compressor inlet and outlet; meanwhile, the nitrogen used for the primary seal of the dry gas seal should be replaced with process gas. After switching the dry gas seal to process gas, promptly close the compressor outlet pressure relief control valve, and at the same time open the ammonia injection valve at the inlet of the ammonia chiller to supply liquid ammonia, thereby cooling the compressor inlet. Additionally, ammonia is added to the ammonia chiller system to increase the outlet pressure of the chiller. When the outlet pressure of the ammonia chiller reaches around 0.8 Mpa, open the pressure relief control valve PV04518 of the outlet condenser E04501 of the ammonia chiller to release the nitrogen that cannot be condensed at the compressor outlet, thereby removing nitrogen from the ammonia chiller system and reducing ammonia losses. Improvement effects: 1. By installing a differential expansion gauge on the turbine, it is ensured that during the startup process of the ammonia chiller, the moving and stationary parts of the turbine remain within acceptable limits; this prevents collisions between these parts, ensures the proper operation of the unit, improves its startup efficiency, and increases the success rate of its startup. 2. During the startup of the ammonia chiller, the amount of ammonia lost during each startup has been reduced – from around 8 tons previously to 1.5–2.5 tons now – thereby decreasing ammonia loss and environmental pollution during startup.