July/August | Volume 32, No. 4

The Green Future of LNG
By Haluk Alper, MyCelx Technologies Corporation


Illustration 1: Corrosive effects of Mercury on Aluminum.
Source: Corrosion of type 6061-T6 aluminum in mercury and mercury vapor by S.J. Pawel and E.T. Manneschmidt


Illustration 2: Liquid Metal Embrittlement, LNG Plant
– Skikda, Algeria

When all the factors such as greenhouse warming potential, water demand in production and usage, energy density and availability are considered, it is clear that natural gas will become the predominant energy source for the next few decades, replacing coal and oil in many cases.

Ironically, the adoption of natural gas as the predominant energy source could actually render the current grouping of green alternatives economically and ecologically viable. Current green energy alternatives are not really very green or economically viable when measured by the same parameters as above, such as energy density, etc. (Energy density is the total amount of energy per unit volume.) They have to be subsidized. The barrier to economic viability is the discontinuous nature of energy delivery leading to the need for storage to meet demand when needed. This often involves the use of costly and pollution-creating storage devices such as batteries. These discontinuous sources of energy can be rendered green by eliminating the need to store energy with a continuous secondary source of energy, which can be used to augment during downtimes. Liquefied natural gas (LNG) is the logical candidate to fulfill this function as it is plentiful, there are vast reserves of it, and it is relatively greener than other continuous sources of energy at the cost of a relatively minor loss in energy density (see Table 1).

There are two major impediments to the adoption of LNG as the next generation “greener” fuel. The first impediment has to do with the ultimate fate of the fracking water and the environmental impact it will have. At this point in time, multiple studies have been conducted but are inconclusive as it has been difficult to determine the diffusion profile of the unrecoverable fracking water. The second impediment is the emerging recognition of the ubiquitous presence of mercury. A recently constructed natural gas power plant in Australia discovered high levels of mercury.  Because of this, the project costs have increased by over 60%, now totaling over $5 billion, and delayed production by almost five years. There are multiple other recent examples as well. Concentrations of mercury vary from region to region, but it is always there. Areas of Southeast Asia, Europe and Eurasia, for example, can have anywhere from 70 to 3,500 µg/m3 of mercury according to a recent report by the Natural Resources Defense Council. The worldwide production of natural gas is 3.3 trillion cubic feet per year. Each 1,000 µg/m3 generates 6 million pounds of mercury. This can theoretically contribute from nearly 2 million to 21 million pounds of mercury from this region alone. Some of this mercury is removed in the production process; approximately one-third is burned off into the atmosphere at the thermal oxidizers, and the fate of the rest is unknown although it is safe to assume that some of it ends up in the product. Mercury in the production process and in the end product is highly undesirable due to its corrosive effects on equipment and its detrimental effects to living things and ecosystems, especially after it is transformed to highly toxic organic states, which can accumulate in the food web.


Table 1: Energy density

The presence of mercury has been an issue in production (see Illustrations 1 and 2) and is now becoming an obstacle in the adoption of LNG in sectors, which are eager to switch.  One such sector is commercial shipping. Commercial shipping has found it very difficult to comply with sulfur and nitrogen oxide emissions with the type of fuels they use (Bunker C or marine diesel oil). These fuels are rich in sulfur and highly polluting. Natural gas practically eliminates this concern (see Table 2), however, ships are composed primarily of metal and the concern of mercury embrittlement of metal must be addressed before adoption.

Propulsion
Mercury is generated with the gas and attempts to remediate are currently limited to the production process, in many cases, as an unintended and undesirable secondary effect of other processes.  In the production of LNG it is vital to remove all traces of water, hydrocarbons and other compounds, which are liquids at room temperature. If these materials pass through to the liquefication process it can result in inefficiency or even catastrophic failure. Therefore, in the production of natural gas, multiple redundant processes exist for the removal of these liquids. Mercury is often dragged along. The first significant remediation process is coalescence, whereby all the liquids, which can be physically coalesced are removed and results in a variable mixture referred to as condensate, which is approximately 50% water and 50% assorted hydrocarbons. Some mercury is removed at this stage. After coalescence, polishing processes are employed, using molecular sieves to polish out any traces of water and activated carbon to polish out any residual liquid hydrocarbons. Sometimes the carbon is modified with sulfides, colloidal precious metals or bromides in order to polish out residual mercury. Some mercury is removed at this stage. After the liquefication process, the gas is usually processed through a reverse osmosis membrane to recover any residual liquefiable hydrocarbons and to discard and burn off non-liquefiable hydrocarbons at the thermal oxidizer. We know that the coalescing and polishing process steps are only partially effective because measurements of mercury at the thermal oxidizer can often be as high as 1ppm and concentrations in the retained gas can be equally high.


Table 1: Energy density

In order to eliminate the mercury impediment, we must understand why multiple redundant coalescence and polishing processes, and even process steps designed to react with gaseous mercury, are not effective. As with many grand mistakes in science, which can last for centuries, the problem lies in the very basic, fundamental assumptions. All of the process steps, which directly or indirectly remove mercury, are predicated on the mercury behaving either as a gas or as a liquid (sulfide modified granular media, coalescence, respectively). MyCelx has discovered that the mercury present in LNG is in a unique state. This realization has broad implications for mercury remediation technologies and we believe this explains the shortcomings of the current approaches. MyCelx is in the process of developing elements, which remove mercury by exploiting its true nature present in LNG.

As the use of LNG increases, it will be important to remove mercury during the production process in order to avoid catastrophic failure, as a worst-case scenario, and to avoid its release into the environment as an ongoing consideration. It is also possible that natural gas will develop a pricing structure similar to premium and economy gasoline based on the amount of mercury present in the end product. The ability to polish residual mercury out of processed LNG will become important to adding value, and thus profitability, to the end product. MyCelx has completed initial developmental phases and will be pilot testing elements for these applications in the near future. MyCelx is dedicated to removing one of the major hurdles to the implementation of LNG as a cleaner energy source on its own, and also one, which can be used to replace the need for batteries and storage devices through real-time augmentation of discontinuous green energy technology.


For more information contact:

MyCelx Technologies Corp.
Tel: 1 770 534 3118 | Fax: 1 770 534 3117
Email: alper@mycelx.com | Website: www.mycelx.com