Flexibility of APG processing under composition variability

For citation: Kholyavkin V. O., Logvinenko E. V. Flexibility of APG processing under composition variability. Journal of International Academy of Refrigeration. 2026. No 3. p. 22-31. DOI: 10.17586/1606‑4313‑2026‑25‑3-22-31

Abstract
This paper evaluates the operational flexibility of an associated petroleum gas (APG) low-temperature rectification scheme by constructing operability windows in the space of two manipulated variables: process pressure (P) and the circulation rate of the pre-reflux (pre-cooling) loop (Gcir). A simulation campaign was performed for five representative APG compositions ranging from lean to heavy feeds. Feasibility was defined by simultaneous compliance with two product-quality constraints: propane mass fraction in the dry de-butanized gas stream,ω(C3)RG≤ 0.05, and ethane mass fraction in the unstable liquid hydrocarbon product,ω(C2)NGLu≤ 0.10. The results show that, within the investigated set-point range, a feasible operating domain exists only for the D (C4-rich) composition: 194 feasible points atP= 2.50–3.40 МПаandGcir = 1800–2700 kg/h, withω(C3)RG= 0.0397–0.0498,ω(C2)NGLu= 0.0669–0.0854, and process temperature −37.42 to −25.45 °C. For A and B, the ethane-in-liquid constraint is limiting, whereas for C and E the propane-in-gas constraint is limiting, resulting in no simultaneous feasibility. The operability maps provide quantitative evidence that two-parameter tuning (P, Gcir) is insufficient over a broad APG composition envelope and that an additional refrigeration degree of freedom is required, with upstream pre-cooling identified as the most straightforward modification to expand the operability window.