On anti-surge control for pressurized turbine expanders

“The \"anti-surge curve for booster turbine expanders\" refers to the mechanism for preventing pulsation in boosters, and the characteristics curves of turbine compressors can be used as a reference. If you are involved in design, you can find information on the principles of turbine expanders and turbine compressors on this forum ； If on-site control is required, a base point can be set during operation; once it is adjusted to be as close as possible to the pulsation point, it can be used as a reference point for future use. This method is often used (for reference).

In my opinion, the anti-surge curve of a pressurized turbine expander is determined based on pressure and pressure difference; that is, a certain pressure corresponds to a maximum flow rate. Given the wide operating range, in practice the method of controlling flow at the maximum rate is often used, whereby the anti-surge bypass valve opens automatically when the flow rate falls below this maximum value. After the manufacturer provides the theoretically calculated value, users use it to make on-site measurements for adjustments, but many users generally do not do this.

Yes, it is generally set only according to the flow interlock provided by the manufacturer. After all, the variable load operation of the expander in air separation systems is not very common. Surge in booster turbine expander systems often occurs at the beginning of operation when the temperature has not reached the designed conditions, especially when two expanders are in use.

The original surge curve is given by F=aP+b, while the anti-surge curve is given by F1=a1P+b1, where P represents PF1. The value by which F1 is greater than F depends on the requirements of the process; the line thus obtained represents the anti-surge curve! I hope this helps!

Thank you all. For the anti-surge systems of your pressure-driven turbine expanders, does it stop the expander when surge occurs, or is there a gradual adjustment?

In some mature foreign technologies, surge protection control is divided into three parts: linear control, proportional control, and full opening. Calculations are performed based on flow rate, pressure, and temperature; linear control is used when the system is in the linear control range, while proportional control takes over from linear or full opening control once the system enters the proportional control range. The third part is the forced regulation, which is controlled by a solenoid valve; when power is supplied, it opens completely. When the inlet flow rate is low, it is usually opened fully to allow all flow to be returned. If surge still occurs, a shutdown command is issued after a few seconds delay. Such a sophisticated surge control system is generally used in large turbine units; for small and medium-sized expanders, there is no need for such complexity.

The surge curve is F=aP+b

1. The anti-surge flow rate of the booster is determined under conditions where the inlet pressure, inlet temperature, and speed are all at their rated values; when these conditions vary, the anti-surge flow rate is adjusted accordingly. 2. Adjusting the booster return valve can prevent surging.

In domestic expanders, the pressurization side generally only prevents surge by simply controlling the outlet pressure or flow rate of the expander; it does not represent true surge prevention control, and efficiency has to be sacrificed in order to avoid surge. The anti-surge control for imported booster expanders operates on the same principle as that of compressors, with calculations being based on flow rate and pressure ratio; for details, refer to the anti-surge control principle for compressors. However, all imported compressors undergo surge testing on-site, while for some imported boost expanders, the manufacturers conduct surge testing in the factory and prepare the anti-surge control curves.