Liquid purification or separation – Processes – Including geographic feature
Reexamination Certificate
2001-11-15
2004-01-06
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Including geographic feature
C210S750000, C210S170050, C210S188000, C210S198100, C062S532000, C062S618000, C062S632000, C062S635000, C203S010000, C585S015000
Reexamination Certificate
active
06673249
ABSTRACT:
FIELD OF THE INVENTION
The inventions disclosed herein relate to desalination or purification of saline or otherwise polluted water using gas hydrates (referred to herein as “desalination” for simplicity but to be understood as encompassing other types of water purification). More particularly, the inventions relate to open-water systems (or partially open-water systems) for hydrate-based desalination or purification (although certain methodologies disclosed herein may also be used in fully land-based installations) and, in another aspect, to vaporization of Liquified Natural Gas (LNG),.
BACKGROUND OF THE INVENTION
Desalination or purification of saltwater or otherwise polluted water using hydrates is known in the art. For example, as illustrated in Max et al., U.S. Pat. No. 5,873,262, a hydrate-based fractionation column can be located in the open ocean. The column extends downward far enough for the lower portion of the column to be located at a depth where the water pressure is high enough and the water temperature is low enough for methane hydrate to form spontaneously (and remain stable) upon introducing a hydrate-forming substance (e.g., methane gas) into the lower portion of the column. The hydrate-forming substance combines with seawater, which enters the column freely through its open lower end, and forms naturally buoyant methane hydrate. The methane hydrate rises naturally within the column into a region where pressure and temperature conditions are such that the hydrate no longer is stable, and the hydrate dissociates (“melts”) naturally to release the hydrate-forming substance (e.g., methane gas) and fresh water which has been extracted from the saltwater via the hydrate. The fresh water is collected, e.g., for drinking or other purposes, and the hydrate-forming substance is captured and recycled for reuse in the process.
A variety of gas hydrate-forming substances are known in the art and include hydrocarbons besides methane (including but not limited to ethane, propane, butane, cyclopropane, cyclobutane, and mixtures thereof), carbon dioxide, and various mixtures of substances including one or more hydrate-forming substances. It is also known in the art that certain gas hydrate-forming substances can be mixed with the water to be treated in liquid form. (Therefore, unless otherwise specified, the inventions claimed herein in terms of a “hydrate-forming substance” are to be interpreted as encompassing any and all such species of gas hydrate-forming substances.)
The temperature of the water to be treated is an important parameter which bears on the formation of hydrate. The colder the water used for hydrate formation, the lower the pressure at which the hydrate will form for a given hydrate-forming substance. Additionally, for a given volume of water to be treated, using colder water allows more hydrate to be produced before the temperature rises (as a result of exothermic formation of the hydrate) to a level where hydrate will no longer form spontaneously at a given depth.
In some restricted bodies of marine and other water such as the Mediterranean Sea, surface water—particularly during the winter and spring—may be cooler than water at depth. In other areas where stratified watermasses or upwelling or downwelling watermasses occur, the coldest water in a local sea area may be found at a horizontal level somewhere between the surface and a water depth which provides the requisite pressure for hydrate formation.
Furthermore, depending on the hydrate-forming substance being used, the fractionation column may have to extend relatively deep into the body of water in order for the pressure at the depth where the hydrate-forming substance is introduced into the water to be treated is suitably high for hydrate formation. For example, U.S. Pat. No. 5,873,262 refers to feeding methane into seawater at depths exceeding 100 meters—a depth at which pressure exceeds 11 times atmospheric pressure (ten meters of water depth for each additional atmosphere of pressure). Therefore, the energy costs associated with pumping the methane gas (or other gaseous hydrate-forming substance) which has been released upon dissociation of the hydrate back down to depth represents a significant cost of operation.
With respect to vaporization of Liquified Natural Gas, the LNG industry is based on the formation of LNG as a means of transporting it to markets from a producer country, where transport of the gas by pipeline or other means is not possible or is commercially of less benefit. LNG is a man-made substance that is made by liquification of natural gas by a process of refrigeration and compression. It is commonly stored at its boiling temperature of about −162 degrees C. in highly insulated vessels that are pressurized slightly above atmospheric pressure (e.g., approximately 5 psig above atmospheric pressure). Vaporization of LNG during transport absorbs heat, which acts to keep the liquid cold. The vapor is vented, usually to fuel a combustion engine of some type, and the pressure and temperature in the vessel remains constant.
LNG is imported into the United States to make up a shortfall in North American natural gas production. In part, the transition from liquid petroleum fuels to natural gas is being driven by the fact that for a given unit of energy, natural gas is a cleaner source of fuel for combustion. Methane has the highest hydrogen-to-carbon ratio of any hydrocarbon, and it bums cleaner with fewer toxic emissions, which has caused it to be considered the combustible fuel “of the future.” This has led to environmental legislation requiring transition to gas fuels.
Because many natural gas pipelines in the United States are old and have bottlenecks that restrict transport of gas at peak periods, the import of natural gas, as LNG, directly to the target market without the construction of pipelines is an advantage over building new or expanding old pipelines.
When the LNG reaches its destination, it must be vaporized or converted back to a gaseous form in order to be distributed as gas and used as a combustion fuel. Presently, the energy requirement for the vaporization process is achieved by a process of “submerged combustion.” Energy must be expended to compensate for both the simple warming of the LNG/gas and the endothermic change of state from liquid to gas. In this method, the LNG is passed through a large assembly of pipes that are submerged in a water bath that is heated by combustion of some fuel (usually part of the gas load itself). The vaporization achieved using this process consumes fuel in relatively large and expensive apparatus that demands special maintenance, especially with respect to unwanted biosystems in the water bath.
As a byproduct of the combustion process that heats the vaporization water bath, exhaust is created, which contributes to pollution. Emissions are mitigated by bubbling exhaust through the water bath. However, this results in some of the combustion products becoming dissolved in the water, which commonly renders it acidic and produces a potential for corrosion and for a situation where the water bath may become a hazardous material.
No commercial products (of which I am aware) are derived from the existing thermal vaporization process during the vaporization of LNG.
SUMMARY OF THE INVENTION
The present inventions provide a number of different means by which to increase the efficiency and benefits of gas hydrate-based desalination or water purification. According to one aspect, the invention recognizes that in some instances, water that is the coldest—and hence most conducive to formation of gas hydrate—in a naturally occurring body of water may be found at depths other than that at which the hydrate formation region of an open-water (e.g., marine) hydrate fractionation desalination installation will be located. In particular, the coldest water may be found at depths above (i.e., less than) those which yield pressures necessary to support hydrate formation (and hence above the depths at which the hydrate formation region of the installati
Hoey Betsey Morrison
Marine Desalination Systems L.L.C.
LandOfFree
Efficiency water desalination/purification does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Efficiency water desalination/purification, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Efficiency water desalination/purification will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3198835