Patent Application
20170072335
Field of the Invention
This invention relates to a method and apparatus for purifying contaminated fluid such as water which incorporate a vacuum distillation unit.
Description of Related Arts
In recent years water has become an increasingly important commodity. Global droughts coupled with population expansions within arid regions have left many communities without this natural resource for drinking and irrigation purposes. This has occurred while large volumes of water are being disposed of everyday in many industries because the quality of the water and its contaminants are not suitable for human consumption. Although the use of mechanical filtration such as reverse osmosis membrane systems have proven effective to clean water in the lower total dissolved solids ranges below 50,000 ppm, they have not proven effective at TDS levels above these limits. This is primarily due to the mechanical inability of the filters to handle high volumes of solids that are in solution within the water. When TDS levels exceed 50,000 ppm range one of the only proven methods to remove these solids and achieve a water quality suitable for discharge or reuse is distillation. Although distillation is very effective in removing high volumes of these solids it has not proven to be very energy efficient. For this reason many companies have explored the use of vacuum distillation to reduce the BTU requirements to bring the water to high enough temperatures to vaporize. Although this method has proven to be more thermally efficient than conventional distillation it still incorporates the use of tube and shell heat exchangers to bring the water to high enough temperatures. Boilers using flames generated by a fuel/air source transfer heat directly to a system of coils to capture as much of the fuels BTUs to heat the water are typically used. These boilers although well insulated cannot recover all of the BTUs that are generated before the air mass is moved out of the chamber and exhausted by the system. This thermal inefficiency has limited the commercial application of these systems on a large scale basis. It is for this reason that the need to find a more efficient system exists. This is increasingly apparent in the oil and gas industry where millions of gallons of this valuable resource are used and disposed of everyday in a process referred to as fracking. During frack operations large volumes of fresh water are used to help unlock the hydrocarbons that are trapped deep within the earth. This water is then recovered from the well where it has mixed with minerals and salts from the earth. Because the TDS levels are typically above the 50,000 ppm range this water is then disposed of by pumping it into deep reservoirs within the earth. This invention makes use of direct contact heat generated from the shear effect of a rotating and static plate design. These types of heaters have been used in many different industries to heat various fluids. However they have never been applied for the purpose of distillation. Part of the reason for this is fear that the corrosive nature of most contaminated fluids would limit the effectiveness of their application. To prevent this corrosive nature a secondary media such as antifreeze would need to be heated by the direct contact heater and with the use of a tube and shell heat exchanger the media would transfer the heat to the water. However this energy transfer reduces the thermal absorption characteristics of the water. During research and testing it was discovered that if the water were pre-filtered to a submicron level low enough to remove all of the suspended solids from the water then the water could be run into the direct contact heater without damage to the unit. In addition the use of a preset relief valve prevented the vacuum from being pulled directly on the heater. This is important to keep positive pressure on the cavity of the heater and to prevent the water from boiling off and allowing the solids to precipitate inside of the heater causing damage to the unit. It was also discovered that by using an engine driven by natural gas that the heat could be recovered from the engine cooling system to further enhance the effectiveness of the energy transfer and would provide maximum BTU transfer into the water thereby reducing the operating cost of the distillation unit. This proved to be extremely effective to assist in preheating the water prior to its introduction into the direct contact heater. This helped to drop the differential temperature between the entry of the water and the exit of the water into the vacuum distillation unit. This system reduced the thermal loses to that of the radiant heat from the engine case and small amounts of the engine exhaust system. This system proved to be so effective that it doubled the BTU absorption of the water. This allowed twice the volume of water to be distilled for the same fuel volume as that used in a conventional boiler system. In one embodiment this system has proven to be very effective in the distillation of oilfield produced water, bringing it to a dischargeable quality at a very low energy consumption. This also allows the brine to be condensed and the salt recovered from the system. It should be understood that the use of these (DHG) dynamic heat generators have not been used in this application because of the contaminates contained within the water. Waters that have high levels of (TSS) total suspended solids tend to be very abrasive and wear quickly on the tight tolerances within the heat generator. This required the heat generators to be used to heat a clean fluid media such as oil or Glycol and using a tube and shell heat exchanger. The BTUs are indirectly transferred to the water thus preventing wear or damage to the DHG. The problem with this method is the heat loss associated with this thermal transfer.
Consequently there is a need for a high volume energy efficient vacuum distillation system that is effective for fluids that have a high content of dissolved solids.
The present invention utilizes a dynamic heat generator to heat the fluid which has been passed through an initial filter for example a submerged membrane having a filter size of about 0.01 micros for example. This provides sufficient clean water to allow the use of a dynamic heat generator in conjunction with a vacuum distillation unit. The dynamic heat generator can be used in direct contact with the fluid thereby radically improving the thermal efficiencies and reducing heat losses. The heated fluid is then directly feed into the vacuum distillation unit. A relief valve is used to prevent vacuum from reaching the dynamic heat generator that could cause rapid pressure drops thereby allowing scale to precipitate within the dynamic heat generator instead of in the vacuum distillation unit.
The FIGURE illustrates a fluid purifying and vacuum distillation system according to an embodiment of the invention
As shown in the FIGURE, a system 10 according to an embodiment of the invention includes a source of fluid to be treated flowing in an inlet pipe 11. Pipe 11 is connected to an initial filter 12 which may be of the type having a submerged membrane having a filter size of about 0.01 micros for example. However any type of known micro filter may be used.
Fluid from filter 12 is directed to a preheater 14 having coils that are heated by cooling fluid or gases via a conduit 18 from a combustion type engine 17 which also serves as the power source for dynamic heat generator 16.
Consequently fluid exiting preheater 14 is heated to a certain degree prior to entering dynamic heat generator 16 via tubing 15. Dynamic heat generators are well known in the art, see for example U.S. Pat. No. 7,959,814, and include a pocketed rotor and end plates, a drive shaft and a group of rotating plates. Fluid entering the generator is heated by shearing force. A source of dynamic heat generator is Island City LLC located in Merrill, Wis.
The drive shaft of the generator is driven by a combustion engine 17. Heated fluid leaves the generator 16 via a conduit 19 which leads directly to a vacuum pot 20. A relief valve 21 is positioned in conduit 19 upstream of vacuum pot 20. Air and water vapor leave the upper portion of vacuum pot 20 by virtue of a vacuum pump 25 via conduit 22. Output from the vacuum pumps enter a condenser unit 26 in the vapor stage and is condensed and collected in a tank 30. Solids that accumulate in the bottom portion of vacuum pot 20 can be pumped out as a slurry by pump 23 connected to a holding tank or other receptacle 24 via conduit 29.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be herein without departing from the spirit and scope of the invention as defined by the appended claims.
