Natural Gas Liquids Recovery/Dewpoint Control
Problem
Natural gas is processed to remove heavy hydrocarbons (C3+) to meet pipeline specifications for dewpoint and Btu value. Recovery of natural gas liquids (NGLs) is desirable because these hydrocarbons have greater value as a chemical feedstock than as fuel. Refrigeration and turbo-expander plants traditionally have been used for NGL recovery. These plants have high capital and operating costs and are not suited to use on offshore platforms.
Membrane Solution
Membranes offer a simple and low-cost solution for removal and recovery of heavy hydrocarbons from natural gas. The VaporSep® process is based on a high-flux membrane that selectively permeates heavy hydrocarbons compared to methane. These hydrocarbons permeate the membrane and are recovered as a liquid after recompression and condensation. The residue stream from the membrane has a lower dewpoint and Btu value. The membrane also permeates water vapor preferentially, so the residue gas is dehydrated, eliminating the need for a conventional dehydration system. The membrane system is compact, skid-mounted, and can be easily and inexpensively installed into existing facilities. The membrane systems are particularly well suited for offshore platforms because of their compact size, low weight, and simple low maintenance design.
Application Example
In crude oil production, the pressurized oil from the wellhead is progressively depressurized in flash vessels to remove entrained light hydrocarbons. The light gases are collected and compressed in a multi-stage compressor. These gases are saturated with
C3+ hydrocarbons. The system can be integrated
into this process to increase oil recovery. The feed to the system is compressed
gas from the low-pressure separator. The membrane preferentially permeates the heavy hydrocarbons present in the gas, which are then recycled to the front of the compressor. These heavy hydrocarbons are then removed as additional oil.
The MTR membrane system significantly increases oil production without changing operating conditions. The system payback time because of the increased oil production can be as low as 6 months.
Benefits
NGL recovery being field demonstrated at a US Gulf Coast refinery
- Recovers NGLs from associated and natural gas at the wellhead
- Removes heavy hydrocarbons and water vapor, which reduces hydrocarbon and water dewpoint in the pipeline gas
- Permits unattended operation at remote locations
- Overcomes space and weight limitations on off-shore platforms
- Simplifies operation with few or no moving parts
- Operates at ambient temperature
- Minimizes installation cost due to skid-mounted construction
System Performance
- Feed flow rate: 0.2 to 50 MMscfd
- Feed NGL content: 5% to 50%
- NGL recovery: up to 95%
- Dewpoint reduction: 20°F to 100°F
- Typical payback time: 6 to 18 months
Application Areas
- Wellhead liquids recovery
- Associated gas liquids recovery
- Dewpoint control (water and hydrocarbon)
- Flare gas recovery
- Turbo-expander plant debottleneck
- Propane refrigeration plant debottleneck