Baker Hughes, a GE Company
15:00 - 15:30
Thursday, 19 September 2019
T3.9 EZ Start: Depressurization of Refrigeration Compression System Without Venting
In the refrigerant compression systems (e.g. propane, propylene, deep refrigerant, Mixed Refrigerant, etc.) the settle out pressure reached after a shutdown may be very high for many reasons, affecting the startup capability of the driver especially single shaft gas turbine. Hence, for a successful start up vent is required with a consequence loss of working fluid and the need to make up and/or rebuilt the mixture during compressor loading. For example:
- If enough refrigerant liquid is present in the suction drums and the compressor is maintained under the sun for enough time, liquid can vaporize completely pressurizing the compressor system up to the saturation pressure at the ambient temperature. In this condition, a successful start up can be accomplished only by venting the compressor system down to the starting pressure.
- The settle out pressure reached after a shutdown may be too high respect to the installed driver capability (e.g. propane compressor with Frame 7 + helper motor) and vent is required for a successful start up.
- Due to the leakages from the discharge isolation and/or check valves, the compression system may be pressurized up to the accumulator pressure. Hence, vent is required to perform a successful start up.
BHGE patented a solution called EZ Start which allows depressurizing the compression system without venting and therefore recovering completely the refrigerant vapor as liquid using the liquid -vapor equilibrium condition existing in all the accumulators of closed loop refrigerant systems. The solution is performed by reducing the pressure of the existing accumulator, or an additional smaller dedicated one, by cooling\subcooling the existing liquid through the vaporization of a cryogenic fluid (e.g. LNG, N2, etc.) in a cryogenic evaporator. As the temperature of accumulator decreases also the pressure decreases and vapor from the compressor system is drown out, condensed and accumulated in equilibrium with its vapor inside the accumulator. Based on the composition of the refrigerant mixture (one component of a mixture of components) an optimum liquid cryogenic refrigerant may be selected to reduce the pressure down to 1bara and even less.
Once depressurized, compressor can be successfully started up to minimum operating speed. Then the condensed mixture can be reinjected into the compression system during the loading phase optimizing the compressor loading time (same mixture as used before) and the plant start up time to reestablish the full production.
A very important adding value of the EZ Start is also the positive impact on the environment, since venting and the relevant pollution are drastically reduced and even avoided. Hence the existing and/or new plant can be optimized in terms of start up and environment pollution reduction.
Another important aspect of the EZ Start is the limited impacts in terms of CAPEX respect to great benefits gained using this system. In fact, the EZ Start is supposed to be a standalone package set up by a few additional equipment: a small accumulator, to collect the mass of refrigerant trapped in the compressor system, circulation pumps, cryogenic evaporator and a two-phase separator.