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Optimising performance

Published by , Senior Editor
Hydrocarbon Engineering,

Accurate compressor performance monitoring is playing an increasingly important role in optimising production and maintenance activities. A recently completed case study at the ENI Versalis ethylene production facility in Priolo, Sicily offers unique insights into the real time detection of performance degradation, as well as compressor performance restoration, of a charge gas compressor (CGC) in an olefins plant.

In November 2017, turbomachinery experts from CCC and Versalis customised CCC’s Total Train Performance AdvisorTM(TTPA) to serve as an onsite Performance Monitoring System (PMS), which included CCC’s Compressor Performance AdvisorTM (CPA), Turbine Performance AdvisorTM (TPA), and intercooler monitor. The TTPA effectively diagnosed compressor fouling from polymerisation in two of the five compressor stages. The performance degradation caused by the fouling had created significant economic impact, increasing steam consumption and reducing throughput.

To financially justify addressing this situation, the team calculated the associated costs of the increased steam consumption and decreased efficiency, which led to supplementary collaboration with Nalco Champion, whose EC3144A anti-foulant solution was implemented in March 2018. Over a period of several weeks, the compressor’s efficiency was restored to an optimal range, and ENI realised record production at lower operating costs.

In examining this collaboration, this article will explore the relevant calculations, as well as system optimisations and integrations within the plant distributed control system (DCS) and historian, which afforded operations personnel enhanced key performance indicator (KPI) monitoring and improved the planning and execution of corrective actions.

System description

The CGC at ENI Versalis Priolo is composed of five compression stages driven by an extraction steam turbine, and a simplified process flow diagram (PFD) (Figure 1). Charge gas compressor fouling is a well-known issue, including fouling mechanisms such as radical polymerisation, Diels-Alder condensation, and thermal degradation due to coke. These processes are highly dependent on temperature and can result in coke-like deposits in the compressor, associated equipment, and adjacent piping and intercoolers.

Figure 1. Five-stage charge has compressor PFD at ENI Versalis Priolo

This can lead to severe decreases in compression process efficiency and intercooler heat transfer coefficients, as well as steam turbine efficiency, which can be directly affected by boiler feedwater quality and steam contamination. The performance monitoring system (PMS) identifies these fouling processes and evaluates severity by calculating the equivalent costs of increased energy consumption, providing justification for timely maintenance operations. Efficiency degradations in ENI’s CGC stages two and three required extra power consumption of approximately 2 MW to compensate for reduced throughput, with an economic impact of more than €2 million.

This article was originally published in the November issue of Hydrocarbon Engineering. To read the full version, sign in or register for a free trial subscription.

Written by Serge Staroselsky, CCC, alongside Gioacchino Mugnieco and Salvatore Avarino, ENI Versalis, as well as Roberto G. Presenti and Jan Van Bauwel, Nalco Champion.

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