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Highly Selective Pressure Swing Adsorption Technology Recovers Valuable Components from Waste Streams
Many polyolefin plant designs use a polymer degassing step to remove unreacted monomer, solvents, and additives from the product polymer fluff before it is processed in downstream pelletizing operations. When nitrogen is used as the stripping gas, the operation produces a low-pressure gas stream that typically contains nitrogen and valued hydrocarbons that can be recovered and recycled to the plant. If the gas is not processed for recovery, it is typically flared. The flaring step results in volatile organic compounds, NOX, and CO2 emissions. Flaring can also be costly, roughly equal to the value of the purchased nitrogen.
With assistance from AMO, Air Products and Chemicals has developed a single unit operation to recover these gases. Pressure swing adsorption (PSA) is combined with partial condensation to essentially recover 100% of the hydrocarbons from the vent gas. In addition, PSA produces a high purity N2 stream, with nearly 100% recovery of nitrogen. The recovered nitrogen can be recycled to the stripping operation or used elsewhere in the facility. Air Products' high recovery system eliminates waste streams and therefore emissions.
In this new process, the vapor stream from the partial condensation section flows into a PSA unit. Within the PSA, specially selected adsorbent materials extract hydrocarbons, thereby refining the nitrogen to a high purity with minimal pressure drop. Over time the adsorbent material in the bed becomes saturated and must be regenerated. Lowering the pressure in the saturated bed desorbs the hydrocarbon components from the adsorbent material in the PSA. The hydrocarbons are released and recovered in a low-pressure tail gas, which is recycled back to the compressor suction so the hydrocarbons are not lost. This technology provides a significant opportunity for energy and cost savings and reduced waste.
Impact of Commercialized Technology
|Energy Savings (Trillion Btu)||0.022||0.081||0.089||0.100||0.111||0.111||0.111||0.111||0.111|
- Developed by Air Products and Chemicals.
- Commercialized in 2003.
- Installed in three locations in Texas.
Can be used by chemical and refining industries, including polyethylene and polypropylene production processes that use N2 for degassing the polymer fluff and for treating refinery off-gas streams. Could be adapted to recover valuable products from other waste streams throughout the industry.
- Recovers hydrogen, nitrogen, and hydrocarbons for reuse.
- Is flexible enough to operate using an external refrigeration source.
Can collect and separate for reuse exit streams from certain processes, eliminating the emissions and need for disposal. Can save energy and costs by eliminating flaring of waste streams, which is typically part of disposal.
Profitability and Productivity
Reduces operating and emission costs by eliminating flaring and increases productivity by reusing products in the feed streams.