Open-Loop Refrigeration for Constant-Pressure NGL Recovery
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Solution Overview
Problem
Current cryogenic expansion processes for natural gas liquids (NGL) recovery, such as those using Joule-Thompson valves or turbo expanders, are inefficient in achieving high recovery rates of propane and ethane without expanding the gas, and often require multiple distillation columns.
Innovation Solution
An open loop mixed refrigerant process is employed using a single distillation column, where the overhead stream is cooled to partially liquefy and separated into a vapor stream and a liquid component serving as a refrigerant, enriching the reflux stream to enhance NGL recovery without gas expansion, allowing for higher temperatures and pressures within the column.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If Joule-Thompson valves or turbo expanders are used for gas expansion, then cooling effect is achieved, but process complexity and equipment cost increase
Solution Approach 1:
The patent extracts the expansion function from the traditional Joule-Thompson valve or turbo expander and relocates it to the distillation column itself. The feed gas is introduced at a specific tray in the distillation column where pressure reduction and partial condensation occur naturally through the pressure gradient and refrigeration effect, eliminating the need for separate expansion equipment.
Solution Approach 2:
The distillation column performs multiple functions simultaneously: it acts as both the separation column for NGL recovery and as the expansion device for pressure reduction. The column achieves both the cooling effect needed for condensation and the pressure drop needed for expansion in a single piece of equipment, reducing overall process complexity.
2Manufacturing precision
If multiple distillation columns are used for NGL recovery, then separation efficiency is improved, but device complexity and capital cost increase
Solution Approach 1:
The patent segments the distillation column into different functional zones with specific tray configurations. The column is divided into a rectification section above the feed point and a stripping section below, with different tray types and spacing optimized for their respective functions. This internal segmentation allows a single column to achieve the separation efficiency traditionally requiring multiple columns.
Solution Approach 2:
The patent introduces the dimension of vertical tray configuration and pressure gradient utilization within a single column to achieve multi-stage separation. By optimizing the number, type, and spacing of trays vertically throughout the column, and utilizing the pressure gradient from bottom to top, the system achieves enhanced separation efficiency without adding horizontal expansion through multiple columns.
3Productivity
If gas expansion is performed to achieve high NGL recovery, then recovery rate is improved, but loss of heavier hydrocarbons increases
Solution Approach 1:
The patent changes the parameters of the expansion process by controlling the pressure gradient and temperature profile within the distillation column. By optimizing the feed tray location, column pressure, and refrigeration temperature, the system achieves partial condensation that maximizes NGL recovery while minimizing heavier hydrocarbon losses through careful parameter optimization rather than aggressive expansion.
Solution Approach 2:
The patent implements a refrigeration system that provides feedback control to maintain optimal temperature and pressure conditions in the distillation column. The refrigeration unit adjusts its operation based on the condensation requirements, ensuring that the expansion and condensation process achieves high NGL recovery while preventing excessive heavier hydrocarbon losses through continuous parameter optimization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process achieves high recovery rates of propane and ethane, with up to 99% recovery of propane and 55% recovery of C2+ components, while operating at constant pressures and reducing losses of heavier hydrocarbons, thus improving the efficiency of NGL recovery.
Implementation Method 1
The overhead stream from the distillation column is condensed by making heat exchange contact with the mixed refrigerant
Implementation Method 2
The feed gas is cooled and partially liquefied in a main heat exchanger by making heat exchange contact with cooler process streams and with a refrigerant
Data Source
AI summary
The present invention relates to an improved process for recovery of natural gas liquids from a natural gas feed stream. The process runs at a constant pressure with no intentional reduction in pressure. An open loop mixed refrigerant is used to provide process cooling and to provide a reflux stream for the distillation column used to recover the natural gas liquids. The processes may be used to recover C3+ hydrocarbons from natural gas, or to recover C2+ hydrocarbons from natural gas.