Maximize ethylene recovery
in ERU with DPPI
Ethylene is recovered from a light hydrocarbon feed through cooling and distillation in a dephlegmator. Current bottlenecks at our client’s facility are affecting the performance at the dephlegmator and too much ethylene is being sent to tail gas instead of downstream to a metathesis plant. Recovery is down and carbon emissions are up since the ethylene ends up being burned instead of being transformed into petrochemicals.
A Smart Operation Flow Diagram (SOFD) digital twin of the unit was created for the client. Connected to daily average operating data, the SOFD included design data and pertinent tools from our DPPI Digital Tool Box (DTB) including:
Energy and heat exchanger integration
Yield and energy optimization
Rotating equipment performance evaluation
Mass balance and margin
CO2 emissions, Scope 1, Scope 2 and Scope 3
By comparing design data and operations, we proposed initiatives to improve ethylene recovery.
A refrigerant loop is used to cool down the light hydrocarbons upstream from the dephlegmator. By increasing current refrigerant flow to the light ends cooler, separation can be improved, and ethylene losses decreased from 14 percent to 5 percent.
Two solutions were proposed:
The refrigerant loop compressor is working below its rated capacity. An oil seal leakage in the loop is accumulating in the knockout drum, tripping the compressor when it operates at higher capacity. Technip Energies proposes to repair the leakage or implement an automatic on-off valve to automatically drain the liquid at compressor aspiration to avoid tripping when operating at maximum capacity.
The refrigerant also is used to condense the column overhead. We found that this flow is higher than specification requirements because of abnormal heat input by the reboiler. Technip Energies proposes to review the APC tuning on the reboiler to decrease heat input and increase available refrigerant for the upstream cooler.
Ethylene is used for petrochemicals elaboration downstream. By maximizing its recovery from tail gas, the ethylene can be sold at a higher price. This operational improvement represents a potential margin gain for our client of about $3.8 million per year.
In addition to better profit margins, this initiative also will help decrease CO2 emissions since the ethylene that will not be burned will be replaced by lower carbon emitting molecules. The potential Scope 1 CO2 emission reduction is about 4 ktCO2 per year. Since the ethylene goes to a petrochemical plant, potential Scope 3 CO2 emission reduction is about 10 ktCO2 per year compared to a steam cracker.
By implementing our Digital Plant Performance Improvement (DPPI) tools and methodology, we assessed the ERU’s current operation, compared it to its original design and proposed initiatives to maximize ethylene recovery.