Optimum design of turbo expander final-paper

OPTIMUM DESIGN OF TURBO-EXPANDER ETHANE RECOVERY PROCESS
Originally Issued: March 2007 Updated: December 2008 Abstract—This paper explores methods for determining the optimum design of turbo-expander ethane (C2 ) recovery processes, focusing on constrained maximum recovery (C-MAR), a new methodology. C-MAR—successor to the system intrinsic maximum recovery (SIMAR) methodology introducedrecently— uses a set of curves developed to benchmark C2 recovery applications based on the popular gas sub-cooled process (GSP) and external propane (C 3 ) refrigeration (–35 °C). Using the C-MAR curves, a process engineer can quickly determine the optimum design and estimate the performance and cost of various C2 recovery opportunities without performing time-consuming simulations. Moreover, the C-MARcurves enable alternative process configurations to be compared against GSP performance. Keywords—C-MAR, compressor, ethane, expander, refrigeration, SIMAR, turbo-expander
INTRODUCTION necessary to move to sub-SIMAR operations, and additional steps are required. This paper presents a new approach to eliminate the aforementioned shortcomings of SIMAR. The new method is called C-MAR, which stands forconstrained maximum recovery. C-MAR redefines the reference case by adopting the gas sub-cooled process (GSP), a well-known industrial design [6], as the benchmark case and by incorporating a fixed refrigeration temperature of –35 °C, the practical lower bound of propane (C 3 ) refrigeration circuits. Since this new reference case is a realistic industrial design, its results are more readilytransferable to industrial applications (for example, cost estimates). The technical background for the development of C-MAR is described in some detail in this paper. SIMAR methodology is discussed and illustrated. C-MAR’s usefulness and applications are demonstrated in real cases using the Enhanced Natural Gas Liquid (NGL) Recovery ProcessSM (ENRP) [1, 7, and 8] (employing a stripping gas system)and the lean reflux process. [9]

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Wei Yan, PhD
wyan@bechtel.com

Lily Bai, PhD
lbai@bechtel.com

Jame Yao, PhD
jxyao@bechtel.com

Roger Chen, PhD
rjchen@bechtel.com

ince its acceptance by the industry in the 1970s, the expander-based process has become the mainstay technology in ethane (C2 ) recovery applications. [1] Despite the great technical and commercial successof this technology, a systematic methodology for determining the optimal system design has remained elusive until recently. Design optimization was approached as an art to be mastered; to this end, a new process engineer would typically spend several years gaining experience and acquiring the necessary expertise. The steep and frustrating learning curve was not conducive to extending this artbeyond the province of process specialists to general engineers. Recently, a methodology called SIMAR, which stands for system intrinsic maximum recovery, was described in papers presented at a key technical conference. [2, 3] These works and subsequent follow-up papers [4, 5] identified a systematic approach to arrive at the optimal design for a given feed stream. Although SIMAR greatly facilitatesthe design procedures by reducing a two-dimensional (2-D) search to a single dimension, its reference case is a hypothetical scenario in which infinite amounts of refrigeration are available to the system. In many real cases, the refrigeration supply is limited and costly. Therefore, it is

Doug Elliot, PhD
delliot@bechtel.com

Chevron Energy Technology Company

Stanley Huang, PhDshhuang@chevron.com

TECHNICAL BACKGROUND FOR DEVELOPMENT OF C-MAR ollowing a general categorization and discussion of expander-based C2 recovery processes, SIMAR methodology is explored in this section. A scenario in which liquefied

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ABBREVIATIONS, ACRONYMS, AND TERMS
1-D 2-D one-dimensional two-dimensional methane ethane propane...