Rapid Production of Methane Hydrates

NETL Develops a Method for Rapidly Producing Methane Hydrates

Natural gas, which is predominantly methane, is recognized as clean burning and an important bridge fuel to a future where renewable energy sources are more common. Natural gas currently accounts for nearly a quarter of the U.S. energy supply, and that share is expected to remain roughly constant over the next several decades. Energy demand during this time period is expected to continue growing, in the U.S. and in the world. The Energy Information Administration projects that the U.S. will need to increase its annual production of natural gas by roughly 10% over the next 25 years, in order to keep pace with rising consumption. 

Burning Methane Hydrate
 Burning methane hydrate

Methane hydrate—molecules of natural gas trapped in an ice-like cage of water molecules—represents a potentially vast methane resource for both the United States and the world. Recent discoveries of methane hydrate in arctic and deep-water marine environments have highlighted the need for a better understanding of this substance as a natural storehouse of carbon and a potential energy resource. 

The U.S. Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) released a preliminary assessment (2008) estimating that there are about 11,000 – 34,000 Tcf of methane in-place in the form of methane hydrate in the northern Gulf of Mexico. To put these numbers into context, note that the total U.S. natural gas resource, excluding hydrate, amounts to 2,074 Tcf. If one-third of the natural gas in-place in methane hydrate in sandy sediments of the Gulf of Mexico becomes technically recoverable, the U.S. could double its total natural gas resource. 

In May 2012, NETL sponsored a demonstration that carbon dioxide could be injected into and exchanged for natural gas recovered from a land-based methane hydrate formation. In March 2013, the Japanese Ministry of Economy Trade and Industry announced that a team aboard a drilling ship perched above the Eastern Nankai Trough had extracted methane gas from hydrates trapped 1,000 feet below the sea floor surface. While commercial production of methane hydrates maybe decades off, an economical way of bringing the resource to market, particularly from off-shore sources, will be needed.

NETL Patents New Nozzle Technology

An obstacle to exploiting the high storage capacity of methane hydrates was the length of time required to manufacture the methane hydrate ice crystals. Of particular difficulty was initiating and sustaining hydrate crystal nucleation. Hydrate nucleation refers to the process where hydrate nuclei grow and disperse until they attain the critical size. If the size of the nuclei is less than the critical size, the nuclei are unstable and may continue to grow or break in the aqueous solution. If the growing nuclei reach the critical size they then become stable and form hydrate crystals. This period from when the hydrate nuclei are forming and dissolving to the time when the nuclei reach the critical size is called the induction time. Induction times from hours to days are not uncommon. Having to maintain the water and forming gas at the required temperature and pressure conditions during long induction times translates to large capital costs. 

 NETL nozzle assembly
NETL Nozzle Assembly

The previous method involved injecting a water spray into a container or vessel holding methane gas. This is not effective or efficient in forming hydrates due to the induction time required to start forming the first crystals. The recently patented NETL process uses a nozzle (Figure 2) operating between 0 and 5°C and 900 to 1500 psi to inject a water/gas mixture into a containment vessel (Figure 3) where droplets encounter nucleation sites and hydrate crystal growth occurs. High-pressure water and methane gas within the nozzle assembly provide better atomization. Atomization improves with increased pressure; and production of micron-sized droplets can be achieved. By using four stages of atomization, the droplets and the gas bubbles trapped within the droplets get progressively smaller. When the droplets exit the nozzle the droplets are elongated and the gas within expands, breaking up the droplet and providing even further atomization. This high degree of atomization allows for new nucleation sites in the cell environment as these hydrates breaking up at the exit of the orifice of the nozzle. The NETL process results in nearly instantaneous hydrate formation. The high velocities of both the water and gas feeds within the small mixing zone eliminates any potential plugging within the nozzle (Figures 4 and 5).

 NETL 15-liter hydrate cell
NETL 15-liter Hydrate Cell

This process for rapid and continuous formation of methane hydrate could offer a safer, more cost-effective method for storing and transporting methane compared with conventional compressed and liquefied natural gas. This technology may be applicable to carbon dioxide sequestration, separation of mixed gases (e.g. , natural gas streams containing carbon dioxide and other gases impacting high methane content), cold energy storage, transportation fuels, and desalination processes.



 
 NETL designed Rapid Hydrate Formation Nozzle  powdered methane hydrate deposition over an ~ 30 minute period
NETL-designed Rapid Hydrate Formation Nozzle in the 15-liter Cell.
 Powdered methane hydrate deposition over an ~30 minute period.


Contact: Thomas Brown and Charles Taylor 

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