NGL RECOVERY PLANT FEED GAS COOLING BY EJECTOR REFRIGERATION – DESIGNED FOR HOT CLIMATE

Abstract

Typical NGL plant compresses its feed to a high pressure (3040 kPa). The feed gas compressors’ discharge reaches approximately 150 OC. After that, the feed is cooled by three-stage propane vapour compression refrigeration cycle. This paper examines various options for thermal power cooling in such plants in order to eliminate part of the propane chilling system. Since most of the new plants are located in desert climates, typical designs based on absorption refrigeration are not very efficient. Design proposed in this work employs ejector refrigeration and it is based on 45 OC air as a cooling media (summer conditions in hot climates). Performance factor has been defined as the total cooling provided by the refrigeration system over the total cooling required in the 1st cooling stage of the NGL Recovery Plant. Cooling based on a single N-pentane ejector cycle with N-pentane has COP of 0.342 and performance factor (ƞ) of 0.842. Multistage ejector N-pentane refrigeration system has COP of 0.714 and performance factor (ƞ) of 1.053. For a typical 750 Million scf/d NGL plant, the new design saves $12 Millions in capital costs and $1.5 in annual electricity cost.