(197d) Solvent-free Adsorptive Separation technology for LNG pre-treatment

The pre-treatment of natural gas involves removing contaminants such as water, carbon dioxide (CO2), sulfur compounds (e.g., mercaptans, COS, hydrogen sulfide (H2S)), and mercury. This is followed by the recovery of natural gas liquids to produce lean feed gas or the removal of BTEX and heavy hydrocarbons if the gas is already lean. Pipeline-quality natural gas, common in North American LNG facilities, contains low levels of contaminants like heavy hydrocarbons (HHCs), water, and CO2, which must be reduced to <0.1 ppmv and <50 ppm, respectively, before liquefaction to prevent freezing and plugging of the coldbox, leading to production loss and downtime.

Lean natural gas feed poses a challenge for heavy hydrocarbon removal using conventional techniques due to insufficient reflux for separation in scrub columns. Fractionation is an expensive option for feeds with trace heavy hydrocarbon contaminants. In contrast, solvent-free, temperature-swing adsorption technology offers a lower lifecycle cost.

This paper discusses Honeywell UOP’s temperature-swing adsorption technologies, Dehydration and SeparSIV™. Molecular sieves in Dehydration technologies can remove both CO2 and H2O in one unit for feeds with less than 2.0 volume percent CO2. SeparSIV adsorbents selectively remove C5+ contaminants to meet LNG specifications while maintaining BTU value of the gas. The Dehydration unit can be retrofitted to a SeparSIV unit with minimal equipment modification for LNG facilities facing heavy hydrocarbon removal challenges.

We present two commercial examples demonstrating Honeywell UOP's design for removing contaminants such as water, CO2, heavy hydrocarbons, and BTEX using process design, modeling, and adsorbent expertise.

Customer 1: A greenfield facility with large capacity designed for CO2 and H2O removal, coupled with adsorption-based mercury removal and a SeparSIV unit for heavy hydrocarbon removal, offering a complete solvent-free LNG pre-treatment package.

Customer 2: In 2023, Honeywell UOP retrofitted an existing molecular sieve dehydration unit to a SeparSIV unit, which has been operating successfully without downtime.

These designs highlight the fundamentals and applications of temperature-swing adsorption technologies for processing lean natural gas feeds to meet LNG facility specifications, mitigating freezing issues and production bottlenecks.