Fundamental principles for sizing and design of gravity separators for industrial refrigeration

Throughout the past decades, the industrial refrigeration industry has developed various “rule of thumb” methods for sizing gravity liquid separators for ammonia and other common refrigerants. However, to date a uniform systematic approach or an agreeable standard has not been established. For commonly used refrigerants such as ammonia, the large installed base of separators can be used as a benchmark for sizing separators. But, when using a less common refrigerant such as CO2, the designer faces new challenges. In this paper, a systematic approach is presented for sizing horizontal and vertical gravity liquid separators for industrial refrigeration applications. To compute separation velocities and separation distances, a theoretical model is presented. The model is used as a basis for comparison with observations from 85 operating gravity separators surveyed in the field. Criteria and formulas are presented for estimating the required liquid volume for storage. An example is provided demonstrating the use of the methods presented in this paper.

► Model for sizing and design of horizontal and vertical gravity separators for industrial refrigeration.
► Discussion of entrainment model versus gravity model.
► Determining separation height and length; and computation of separation velocity, ballast and surge volume.
► Recommendations for droplet sizes based on field observations.
► Example for sizing a separator using Ammonia and Carbon Dioxide as a refrigerant, including comparison.