Rapid Simulation of Solid Deposition in Cryogenic Heat Exchangers To Improve Risk Management in Liquefied Natural Gas Production

Abstract

 A new tool is presented for assessing deposition risk in LNG production  Matching literature data, the tool represents an operational freeze-out incident well  Risk assessment reveals possible mitigation strategies and future research needs

Solubility of p-xylene in methane and ethane and implications for freeze-out at LNG conditions

“…error of 7.2 K, which improved to 3.1 K upon tuning the BIP to the SLE data. These results for p-xylene are consistent with the finding reported previously [4,6] that accurate solid-fluid phase equilibria calculations require different BIPs to those optimised for VLE calculations. This further indicates the need for additional measurements of melting temperatures in mixtures to improve models for the solubility of heavy compounds in hydrocarbon solvents.…”

“…A primary motivation of this work is to help improve the prediction of heavy hydrocarbon solubility in liquefied natural gas. At (4 MPa, 123 K), which approximates the effluent condition of a main cryogenic heat exchanger in an LNG plant, benzene becomes insoluble in liquid methane at a mole fraction concentration of 8 parts-per-million [4]. While p-xylene is normally present at far lower concentrations in natural gas than benzene, it is also far less soluble in LNG and hence predicting whether any trace amount present is likely to be problematic can be crucial.…”

“…These results were compared and found to be consistent with the only VLE data we are aware of for this system measured by Stepanova and Velikovskii [46] at 293.15 K, as shown in Figure 5. Also shown are comparisons with bubble-pressure predictions made using the Peng Robinson EOS implemented in the software ThermoFAST [4]. Figure 5(A) shows predictions made using a binary interaction parameter (BIP) for methane + p-xylene calculated using a group contribution method derived by Vitu et al [48].…”

“…However, carry-over of these C 5+ hydrocarbons into the vapour (overheads) product, even at trace concentrations, can result in freeze-out and consequently blockages in the main cryogenic heat exchanger. Such blockages can potentially become so severe that a shut down and warm-up of the plant is necessary, leading to a significant loss of production and revenue [2][3][4].…”

Hydrate nucleation and growth on water droplets acoustically-levitated in high-pressure natural gas

“…Thermodynamically stable at temperatures and pressures encountered in natural gas production or at oceanic or permafrost margins (2), hydrates are highly relevant to applications in conventional energy production from oil and gas reserves (flow assurance (3)), unconventional energy production from geological deposits of methane-hydrate (4,5) and to onshore processes related to gas storage (6) and water desalination (7). The kinetics of hydrate formation are critical to many of these applications, including optimising gas storage schemes, reducing the cost of hydrate management strategies for subsea gas production (8) or avoiding blockages in the cryogenic heat exchangers used to make liquefied natural gas (LNG) (9,10).…”