Patent Application
20160332891
The present invention relates to a method and system for purifying produced water, especially from a wellhead.
Conventional oil/water separations and filtration processes deployed in, for example, the oil/gas industry, can only remove floating particulates and large oil droplets. Advanced demineralization technologies are then required in order to remove the salt and dissolved organics, in order to meet surface water discharge standards. Current desalination technologies for ion removal from sea water focus on membrane separation and thermal separation. Membrane-based desalination processes, such as reverse osmosis and electro dialysis are not cost or process-efficient for small or medium scale water desalination, for example in the neighborhood of less than 1,000 m3 per day. Furthermore, dissolved organics and the high concentration of suspended particulates in produced water seriously reduce the lifetime of the membranes that are utilized due to fouling. Therefore, sophisticated pretreatment is generally required to remove the floating particulates, dissolved metal ions and organics in order to prolong the lifetime of the membranes. Heat-based desalination methods, such as multi-stage flash desalination, multiple-effect evaporation with thermal vapor compression and mechanical vapor compression, are energy-intensive due to the high heat consumption during phase conversion, and are expensive to operate on a small scale. Other desalination methods such as freeze/thaw deionization can be used only in cold weather. Moreover, sophisticated pretreatment is generally required for prolonged operations for these technologies. Dissolved organics, metal oxides, and a large variation in salt concentration are the main factors in limiting the deployment of conventional desalination technologies for the purification or the cleaning of produced water at less than massive scales.
Therefore, there is a real need for being able to provide clean water for smaller scale operations in a cost-effective manner.
This need is realized by the method and system of the present application, which will be described subsequently with the aid of the accompanying schematic drawings, in which:
The method of the present application for purifying produced water includes the steps of providing produced water at a temperature of from 140 to 212° F.; conveying the hot water through the at least one humidification chamber portion; conveying ambient air through the at least one humidification chamber portion countercurrent to the direction of conveyance of the hot water therethrough to produce an up to 99% humid atmosphere in the humidification chamber portion, wherein concentrated produced water is also produced in the humidification chamber portion; withdrawing the concentrated produced water from the humidification chamber portion; conveying the humid air to at least one dehumidification/condensation chamber portion; allowing the humid air to cool in the dehumidification/condensation chamber portion, wherein fresh water is condensed out; and collecting the fresh water.
Applicant's system for purifying produced water comprises a humidification/dehumidification unit comprised of at least one humidification chamber portion capable of receiving hot produced water and, in a countercurrent direction, air; and at least one dehumidification/condensation chamber portion capable of receiving humid air from the humidification chamber portion, wherein concentrated produced water is capable of being withdrawn from the humidification chamber portion and clean or purified water is capable of being withdrawn from the dehumidification/condensation chamber portion.
Among other advantages Applicant's method and system for purifying or cleaning produced water provides flexibility in the capacity of produced water that can be processed, operation at atmospheric pressure, and the use of low cost process energy, for example in the form of solar, geothermal, and industry waste heat. Another advantage is that Applicant's process can be carried out below the boiling point of the liquid, unlike other typical thermal processes where extensive energy is used in heating and vaporizing water.
The method and system of the present application for purifying produced water will now be described in conjunction with
In the illustrated embodiment of Applicant's system 10, produced water, for example from a wellhead, is conveyed via the line 16, with the aid of the transfer pump 17, to the holding tank 18. An oil skimmer 19, such as a belt-type skimmer, may be disposed in the line 16 to remove any surface oil that remains in the produced water. Other separation devices or filters could also be provided in the line 16 for particulate matter or the like.
Although produced water from a wellhead or other ground source may have sufficient latent geothermal heat for the humidification/dehumidification process that is to take place in the unit 12, if additional heat, as measured for example by the sensor 20 in the line 16 and the sensor 35 in the line 25, is needed, the holding tank 18 can be provided with a heat exchanger as illustrated, which includes the cold medium return line 21, a source of heat 22, such as a solar collector, and a hot medium supply line 23. The currently preferred temperature range of the produced water that is to be supplied to the humidification/dehumidification unit 12 is 140-212° F., depending, among other factors, upon the humidity of the ambient air.
Hot water from the holding tank 18 is subsequently conveyed via the line 25, with the aid of a transfer pump 26, to the humidification/dehumidification unit 12, and in particular a distribution manifold 27, which is covered by a removable lid 28. By means of the distribution manifold 27, the heated produced water is conveyed to the tops of the humidification chamber portions 14, for example by being dripped onto the portions 14 from the top. To aid in the distribution of the water to the humidification chamber portions 14, deflectors 33 can be provided in the lid 28. In addition, a wier 34, such as a v-notched wier, or a similar obstruction, can be provided in the lid 28 above the humidification chamber portions 14, as shown in particular in
Thus, the heated water introduced into the humidification chamber portion 14 from the top, and the air introduced into the humidification chamber portion 14 from the bottom, encounter one another in a counter current manner, whereby as the air meets the heated produced water, the capacity of the air to carry water increases, and the water is evaporated while the air becomes humid. To increase residence time of the air and the produced water in the humidification chamber portion 14, packing material 36 can be disposed in the chamber portion 14, as illustrated in particular in
The humidified air is introduced into the top of the dehumidification chamber 15. As this air drops through the chamber portion 15, it loses heat. This effect can be accentuated by disposing Z-coils 38 in the dehumidification chamber portion 15, whereby the heat removed via the Z-coils 38 is available for return to the humidification chamber 14, or for other purposes. As the air cools in the dehumidification chamber portion 15, it loses its ability to hold as much water, resulting in dehumidification of the air, as a consequence of which fresh water “rains down” or is condensed in the dehumidification chamber portion 15. This very clean water is collected at the bottom of the chamber portion 15, such as in a collection vessel 40. In one specific embodiment, the clean water yield in the vessel 40 is approximately 10% of the produced water volume input into the humidification chamber portion 14.
The clean water collected in the vessel 40 can be withdrawn, for example at a low point drain indicated by the reference numeral 41. In addition, to further increase the yield of Applicant's process, the still somewhat moist air from the dehumidification chamber portion 15 can be passed through the air-cooled condenser or refrigeration unit 43 to further chill the air and thus release more fresh water. In one specific embodiment, this increased the total clean water yield to about 20% of the originally input produced water volume. The clean water from the collection vessel 40, as well as the clean water from the refrigeration unit 43, can be stored in the storage tank 44. When needed for various purposes, the water can be conveyed from the storage tank 44, for example via the transfer pump 45 and the check valve 46.
In order to monitor some of the operating parameters of Applicant's system, as mentioned above temperature sensors 20 and 25 can be provided in the supply lines 16 and 25 respectively. In addition, water level sensors 48 can be provided, for example to monitor the level of the concentrated produced water in the humidification chamber portions 14.
Although in the illustrated embodiment, the humidification chamber portions 14 and the dehumidification chamber portions 15 are shown as alternating with one another, any desired order or disposition of the chamber portions 14 and 15 is possible. Furthermore, whereas six dehumidification chamber portions 15 and five humidification chamber portions 14 are shown, the number of these chamber portions can be varied in any desired fashion.
It should be furthermore noted that Applicant's system is not sensitive to the quality of the input produced water. For example, produced water containing 400,000 ppm of dissolved solids (which is 13-14 times saltier than sea water) has been utilized without encountering any loss of efficiency.
The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.
