(114d) New Process for Natural Gas Liquid (NGL) and Olefins Recovery From Low Pressure off-Gas Generated In Refineries and Petrochemical Plants

There are various   NGL(Natural Gas Liquid)   recovery units in North America  which are designed to recover olefins and NGL components like ethane, propane, butanes etc  by processing  the off-gas from various sources like the refinery or Petrochemicals Complex. There is an increased demand to install these units to recover valuable olefins & NGL and in return send the clean fuel gas for burning. 

The installation of the Off-Gas Processing units has both the economic and environmental benefits as the main polluting components from the off gas are separated and the value added products like natural gas, olefins and NGL are produced. The burning of methane rich gas produced from this unit without polluting and soot forming components is beneficial from an environmental point of view. 

The industry is presently using the modified version of cryogenic NGL recovery process typically used in the gas processing industry for treated natural gas. The industry has observed various disadvantages of using the modified conventional NGL process for this application. The existing processes have reported significant downtime due to maintenance issues with compressor, turbo expander, brazed aluminum heat exchangers etc. This is due to the nature of the off-gas which can have significant variations in the impurities, feed gas composition, flow rate etc.

The above clearly indicates that the Industry is presently striving for a new flexible, reliable and a safe process other than the conventional modified NGL recovery process.

Methods for removal of the individual contaminants in the off-gas are detailed in the paper. Various configurations of the off-gas plant and associated units are compared depending on the type of product and feed stock. Optimization strategies and environmental benefits are also discussed in the paper.