Stanley H. Huang

A review of conventional and emerging process technologies for the recovery of helium from natural gas

Helium is a unique gas with a wide range of important medical, scientific and industrial applications based on heliums extremely low boiling temperature, inert and non-flammable nature and small molecular size. The only practical sources of helium are from certain natural gas (NG) fields. As world demand for helium rapidly increases, the value of NG fields that contain it even in very small amounts is likely to rise significantly if the helium can be recovered efficiently. However, recovering the helium from the NG using conventional cryogenic distillation processes is expensive and energy intensive. We review the scope for improving the efficiency of the conventional helium recovery and upgrade processes, and evaluate the potential of emerging technologies based on adsorption or membrane separations for helium upgrade and purification. Helium recovery and purification processes are comparable in many ways with systems designed for hydrogen purification and thus, many of recent technological advances for H2 separation from CH4 N2 and CO2 may be applicable to a helium recovery process. Furthermore, some recent patents and pilot plant studies indicate there exist several opportunities for the development of advanced materials, such as helium-selective adsorbents, and optimized process operations for the recovery of helium from NG.

Influence of charge compensating cations on propane adsorption in X zeolites: experimental measurement and mathematical modeling

Separation of minor components is necessary prior to natural gas liquefaction. There are many methods to achieve this but one that has not been studied in great detail is adsorption of hydrocarbon gases on zeolite materials. A more comprehensive understanding of the fundamentals of hydrocarbon adsorption on zeolites is required in order to determine the efficacy of these materials in natural gas processing. This study investigates the influence of the charge compensating (non-framework) cation on the adsorption of propane on X zeolite by both dynamic experiments and mathematical modeling. This work presents a systematic experimental study examining the effects of the 5 typical types of charge compensating cations (Li+, Na+, K+, Ca2+, La3+) in X zeolites for saturated hydrocarbon adsorption. The dynamic experimental results reveal that for the X zeolites examined, all exhibited an affinity for propane, with LiX being the best, having a propane adsorption capacity of 15.5 wt%. Interestingly, unlike many non-zeolite solid sorbent materials, such as carbons, surface area and pore size alone do not necessarily determine propane adsorption capacity in these X zeolites. It has been shown that the charge compensating cation of the X zeolites of interest, in particular its valence, number of ions and size are the major factors affecting the propane adsorption capacity. Mathematical modeling equations are established by using mass balance in the adsorbent column, macroporous pellets and microporous crystals. The model-predicted results show a good match with our experimental results. The prediction results show that in our current experimental conditions, LiX has a slower adsorption rate than the other zeolites. The obtained adsorption equilibrium constants for all the X zeolites follow the same trend as their propane adsorption capacity, with LiX having the largest constant, suggesting a stronger binding energy between LiX and propane compared to the other zeolites.

Experimental studies of hydrocarbon separation on zeolites, activated carbons and MOFs for applications in natural gas processing

Separation of minor hydrocarbon components in natural gas is necessary prior to liquefaction to avoid operational (plugging of equipment) and product specification issues. While there have been many studies describing adsorption of gases on solid materials there have been relatively few focused on decreasing concentrations of light hydrocarbons in methane in non-equilibrium experimental configurations. In order to best understand the chemistry of competitive adsorption of saturated hydrocarbons for gas processing applications we investigated light hydrocarbon dynamic adsorption properties on 16 solid adsorbents of different structures and chemistries. The best adsorbents, as determined by adsorption capacity, were tested for their ability to separate higher molecular weight hydrocarbons from methane. It is found that for charged frameworks, the induced dipole moment between the adsorbent and adsorbate plays the most important role in adsorption capacity. For uncharged frameworks, pore size plays the critical role in adsorption: micropores are more effective than mesopores. For separation of mixtures of methane, ethane, propane and butane, the kinetics of adsorption must also be considered. Of the materials tested, a carbon derived from coal and activated with steam (carbon #5 (37771)), zeolite KX and zeolite 5A were the best in terms of adsorption and separation capability. These materials show promise for separating light hydrocarbons of similar chemical nature.

A Shortcut Thermodynamic Model for Simulating LNG Liquefaction Facilities

The thermodynamic Carnot engine was originally derived to describe the conversion of heat to work. A Carnot engine in reverse operation also acts as a model for heat pumps (refrigerators). This work describes the use of a non-ideal Carnot model to represent typical refrigeration systems, which can be of two-phase or single-phase operations, single-component refrigerant or mixed refrigerant configurations. It is demonstrated that a model using 50% Carnot efficiency is adequate for representing the performance of commercial LNG refrigeration systems. The non-ideal Carnot model is used to illustrate the end-flash system of an LNG plant, in lieu of rigorous simulations. This shortcut method not only reduces the development time, it also provides useful insights on behaviors of LNG facilities.

A Universal Methodology Based on SIMAR for Composing and Evaluating Expander - Based Processes

The expander-based processes for recovering intermediate components from natural gas streams have become the norm in gas processing industry since the early 1980’s. The improvements in machinery designs and innovative process configurations have pushed process efficiencies of this art to an unprecedented level. System Intrinsic Maximum Recovery (SIMAR) represents a methodology which was developed as a design tool to assist process engineers in composing and evaluating expander-based processes. The power of this methodology lies in its capability to distinguish process merits attributable to process configurations from impacts of refrigeration balances. This paper presents SIMAR in a systematic manner: from its procedural definitions to the recommended flow sequence for composing new processes. Along the way, representative examples including industrial cases are provided as illustrations.