(3a) Optimizing Turbomachinery for Maximum Process Performance: Methodology and Case Study for Turboexpander Control in Ethylene Plant

Turbomachinery is highly integrated into industrial plants, acting as the primary mover of key process units. Turbomachinery control directly impacts Key Performance Indicators (KPIs) including safety, process, reliability, production, yield, energy consumption, environmental emissions and maintenance costs. However, in existing assets, controls are often based on antiquated hydro-mechanical methods or simplistic implementations that significantly limit production rates, process availability, energy optimization and emission reduction efforts. Understanding and quantifying these limitations is key to justifying improvement projects for existing assets.

This paper presents a new methodology for executing turbomachinery optimization studies. Leveraging knowledge, advanced analytics tools and collaborative engineering processes, this method has proven effective in multiple installations, including the control optimization study of an ethylene plant’s cryogenic expander-recompressors discussed in this paper. By analyzing the correlation between production yield and expander control design, CCC determined the most effective primary and constraint control objectives. Compressor dimensional or non-dimensional analysis then identified shortfalls in control system design and an optimal operating point. The use of advanced data analytics software in combination with thermo-properties database provides effective tools to study turbomachinery operation through extensive time periods.

The paper further presents CCC proven strategy for optimal control of cryogenic expanders in ethylene plants. Implemented with CCC’s patented design, this coordinated control of guide vanes, the JT valve and recompressor antisurge valve maximizes production and economic return.