The present invention generally concerns water purification, and more specifically, the purification of water containing toxic species, using thermal and thermocatalytic processes and apparatus.
It is often necessary to purify water by removing inorganic, organic, and biological species from the water before it can be used or consumed. Methods for removing particulate and chemical species from water are well known, and include distillation, reverse osmosis, freezing, ionization, photocatalytic treatment, and carbon filtration. Examples of such methods are disclosed in U.S. Pat. Nos. 5,007,994; 5,227,053; 5,133,858; and 4,717,476. In addition, there are many well-known methods for destroying bacteria in water, including boiling, using submicron filtration, and disinfectant processes using chlorine, bromine, iodine, or other strong oxidizers. Treatment with heat or disinfectants may also be used sterilize water containing harmful viral agents.
In many instances, it is desired to have access to a portable means for purifying water. For example, it is often impractical for campers, hikers, mountain climbers, and others who are outdoors for extended period of time, to rely on treated water that they would be required to carry throughout an outing extending over several days. In these instances, it will be preferable to rely on local water sources, such as streams or lakes, which typically contain various particulate and mineral contaminants, including dirt, salt, algae, etc., and also may contain bacterial or viral contaminants. Although the methods and devices discussed above might be used to purify water flowing in a stream or lake water, some of the methods are unsuitable for portable use, because, e.g., they require heavy or bulky equipment, or substantial mechanical or electrical power. In view of the problem, several portable water purification devices have been developed, including those disclosed in U.S. Pat. Nos. 5, 273,649; 5,268,093; 5,244,579; and 3,635,799.
A related but more troubling problem arises during military conflicts when it is necessary to provide potable water to troops in the field. A land force may intend to use local groundwater or surface water after it has been purified, while a pilot that has been shot down will be forced to use any available source of water that can be found. During warfare, untreated water is potentially contaminated with a variety of toxic species, including chemical warfare agents such as Sarin, mustard gas, phosgene, and cyanogen chloride. In addition, water may contain biological warfare agents such as Anthrax, or other biological toxins, including E. coli, salmonella, hepatitis, and Norwalk virus. The portable water treatment devices disclosed in the prior art patents noted above do not adequately remove or deactivate (i.e., reduce to a less toxic species) such toxic species, and while large scale water purification systems may be capable of removing or deactivating such toxins, they are impractical for use on the battlefield, or by individuals separated from their support personnel, such as a downed pilot. It would therefore be desirable to provide a water purification apparatus that is small, lightweight and easy to operate, yet capable of purifying water containing some or all of the foregoing toxic species, as well as more common contaminants such as dirt, salt, algae, and the like. Furthermore, it is desirable that this apparatus comprise components that are readily serviceable in the field.
The present invention addresses the foregoing problems by providing a process and associated apparatus for purifying water and is particularly useful in removing from water toxic inorganic, organic, and/or biological species such as Sarin, mustard gas, phosgene, cyanogen chloride, Anthrax spores, E. coli bacteria, Girardia cysts, Hepatitis virus, and Norwalk virus. The process includes a purification step that employs a hydrolysis catalyst to cause steam contacting the catalyst to thermocatalytically deactivate at least 90% of the organic or biological species, changing them to less toxic organic species or non-viable biological species, respectively, thereby purifying the steam. The apparatus can be configured in different embodiments, including lightweight portable versions suitable for recreational and/or military uses.
According to a first aspect of the invention, a process is provided for removing toxic inorganic, organic, and/or biological-species from water, wherein such species have a size less than 10 xcexcm and a concentration of less than 50,000 parts per million (ppm). The process begins by heating the contaminated water to convert a portion of it into steam, preferably at least 20%, and most preferably at least 50%. The steam is then made to contact a hydrolysis catalyst at a sufficient temperature to thermocatalytically deactivate at least 90% of the organic and/or biological species, converting them to less toxic organic species or non-viable biological species, respectively, thereby purifying the steam. The hydrolysis catalyst preferably comprises a metal oxide, such as titanium oxide or magnesium oxide. The steam is then condensed and cooled to produce purified water. The steam is preferably made to contact the hydrolysis catalyst by circulating the steam through a passage comprising a surface coated or covered with the catalyst, or containing a replaceable element comprising the catalyst. The temperature of the region in which the steam is exposed to the hydrolysis catalyst is preferably at least 100xc2x0 C., and most preferably at least 300xc2x0 C.
The process can be repeated using water that has already been partially purified by the present method, as the xe2x80x9ccontaminatedxe2x80x9d water input to the process, until a desired level of purity in the water output from the process is achieved. The overall efficiency of the process is enhanced by using a counterflow heat exchanger to preheat the water that is input to the process and to cool condensed water that has been purified by the process.
According to a second aspect of the invention, apparatus are defined for purifying water according to the process discussed above. The apparatus include a vaporizing device that converts at least 20% of the water into steam, thereby removing a substantial portion of any inorganic species (such as salt, dirt, etc.) present in the water, and deactivating a substantial portion of any biological species present in the water. The purified steam is then condensed to form liquid water in a condenser, which may optionally include an evaporative subcooler.
According to another aspect of the invention, the vaporizing device preferably comprises a preheater, a boiler, and a superheater. The preheater heats the water to a temperature less than boiling before the water enters the boiler, and in the boiler, at least a portion of the preheated water is converted to steam. In the superheater, the steam is superheated at a higher-than-atmospheric pressure. The vaporizing device preferably is heated using a gas-fired heat source that burns a fuel such as butane. Preferably, the preheater comprises a counterflow heat exchanger having xe2x80x9cmesochannelsxe2x80x9d that transfers heat between an incoming supply of water and exiting condensed water to preheat the water entering the boiler.
Various embodiments are provided, including one that has a catalytic reactor in which the thermocatalytic reaction is performed. The catalytic reactor is preferably made of metal with a surface comprising a hydrolysis catalyst, such as a metal oxide. Optionally, a replaceable catalyst element comprising a suitable hydrolysis catalyst is disposed within the catalytic reactor. The reaction between the steam and the hydrolysis catalyst causes a thermocatalytic reaction that deactivates a substantial portion of any organic toxins present in the steam to produce purified steam. The purified steam then enters a condenser that cools the steam, forming liquid water.
Components of the apparatus are preferably arranged so as to maximize the overall heat efficiency of the apparatus. In one preferred embodiment, the apparatus comprise a primary boiler and condenser, and a secondary boiler and condenser. The primary boiler generates superheated steam, which is condensed in the primary condenser at an elevated temperature and pressure (i.e., above 100xc2x0 C. and above atmospheric pressure). The secondary boiler is disposed in thermal communication with the primary condenser, so that heat is transferred from the superheated steam/superheated condensed water in the primary condenser to water in the secondary boiler through thermally conductive surfaces of the primary condenser and the secondary boiler, which preferably share a common wall or shell.
According to another aspect of the invention, portable apparatus are provided for purifying water with a portable heating device, such as a hiking or camping stove. A first preferred embodiment includes a core boiler section and a series of concentric shells that are offset from one another so as to form adjacent annular volumes respectively comprising a condenser and reservoir. The core boiling section is heated with the flame from the portable heating device, thereby converting a portion of unpurified water in the boiler that has been received through a passageway connecting the boiler to the reservoir into steam. The steam exits the boiler, and is condensed, forming liquid water, which is cooled in the condenser. This cooled liquid water can be removed through a tap connected to the condenser.
The reservoir provides sufficient capacity to store extra water that absorbs heat from the condenser shell, thereby improving the condensation and cooling efficiency of the apparatus and preheating the water in the reservoir. The boiler may also comprise a surface area coated with a hydrolysis catalyst or defining a region in which a replaceable hydrolysis catalyst element is disposed. When steam generated by the boiler passes over the hydrolysis catalyst, a thermocatalytic reaction occurs, resulting in the destruction or deactivation of a majority of any toxic organic species present in the unpurified water. The portable apparatus further preferably include a counterflow heat exchanger that preheats the water entering the boiler and cools the water exiting the condenser.
According to yet another aspect of the invention, the portable apparatus include a secondary boiler and secondary condenser, in addition to the primary boiler, primary condenser, and water reservoir discussed above. The primary boiler is supplied with pressurized water, and operates under a pressure substantially above atmospheric, enabling superheated steam to be produced and maintained at a temperature well above the boiling temperature of water at atmospheric pressure, thereby enhancing the purification efficacy. The steam is condensed in a primary condenser, producing condensed superheated water that enters a secondary boiler operating at a lower pressure than the primary boiler. The water is again converted into steam, and cooled in the secondary condenser by transferring heat to water stored in the water reservoir.
In an optional configuration of this portable apparatus, the primary boiler also includes a surface area coated with a suitable hydrolysis catalyst, or contains a replaceable catalyst element, enabling a thermocatalytic reaction to occur in the manner described above.