Patent Application
20250187950
Industrial systems, such as a natural gas refining plant, produce several wastewater streams (e.g., boiler blowdown, brackish water) that are typically discharged and get mixed with other upstream wastewater streams (e.g., produced water) in a water pond. Wastewater streams in a natural gas refining plant are made up of approximately 60% boiler blowdown, 20% produced water, 10% rain harvest, and 10% process wastewater. Moreover, wastewater treatment typically requires a lot of energy, thus produced waters are typically sent to ponds rather than being reused in the industrial process.
This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.
In one aspect, embodiments disclosed herein relate to a semi-closed loop salinity gradient energy harvesting system, including a first water stream drawn through a low salinity feed line by a first pump upstream of a salinity energy harvesting system and a second water stream drawn through a high salinity feed line by a second pump upstream of the salinity energy harvesting system. The semi-closed loop salinity gradient energy harvesting system also includes a mixed water exit stream drawn through a third pump immediately downstream of the salinity energy harvesting system and a separator system, configured to receive the mixed water exit stream and separate dissolved salts from the mixed water exit stream to produce a high salinity water exit stream and a pure water stream. The semi-closed loop salinity gradient energy harvesting system further includes a recycling line comprising a fourth pump configured to receive the high salinity water exit stream and combine the high salinity water exit stream with the second water stream.
In another aspect, embodiments disclosed herein relate to a method for treating and recycling wastewater, including producing a first water stream, producing a second water stream, where the second water stream has a higher salinity than the first water stream. The method for treating and recycling wastewater also includes pumping, using a first pump, the first water stream to a salinity energy harvesting system, pumping, using as second pump, the second water stream to the salinity energy harvesting system and operating the salinity energy harvesting system to produce a mixed water exit stream and a produced energy. The method for treating and recycling wastewater further includes pumping, using a third pump, the mixed water exit stream to a separator system, where the separator system is configured to receive the mixed water exit stream and separate dissolved salts from the mixed water exit stream to produce a high salinity water exit stream and a pure water stream. The separator system operates using the produced energy from the salinity energy harvesting system. The method further includes recycling, using a fourth pump, the high salinity water exit stream by combining the high salinity water exit stream with the second water stream.
Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.
Embodiments disclosed herein generally relate to a semi-closed-loop system to harvest salinity gradient energy from upstream water resources in industrial processes, using the harvested energy to treat downstream wastewater in a separator system, and subsequently recycling the treated wastewater back to the upstream water resources.
In industrial systems, such as a natural gas processing plant, several steps typically produce water as a by-product. This water is typically discharged into an evaporation pond and is largely either disposed of or allowed to evaporate into the atmosphere as industry does not deem it suitable for re-use opportunities. The present methods and systems advantageously re-use wastewater by using energy generated by salinity gradient harvesting technology to power a separation system which treats wastewater, allowing it to be recycled back into upstream processes.
The brackish water stream 124 in
Embodiments herein may recover wastewaters from a natural gas processing system. The first water stream may be boiler blowdown, pond water, fresh water, river water, or water streams originating from one or more upstream processes that have relatively low salinity. The first water stream of one or more embodiments has a salinity in a range of from 100 to 1000 g/kg, such as a lower limit selected from 100, 250 and 500 g/kg to an upper limit selected from 800, 900, and 1000 g/kg, where any lower limit may be paired with any upper limit.
In one or more embodiments, the second water stream may be seawater, produced water, brine water, or other water streams originating from one or more upstream processes that have relatively high salinity. The second water stream has a salinity in a range of from 50,000 to 150,000 g/kg, such as a lower limit selected from 50,000, 75,000 or 100,000 g/kg to an upper limit selected from 125,000 and 150,000 g/kg, where any lower limit may be paired with any upper limit. Other optional wastewaters may also be used for the first water stream or the second water stream.
Wastewaters from a natural gas processing system useful in the semi-closed loop energy harvesting system according to embodiments herein may include one or more of produced waters, process waters, and condensate (utility discharge waters). While numerous systems of differing configurations known in the art are used to purify, pressurize, and condense a raw natural gas into desired products (such as liquid natural gas (LNG) and compressed natural gas (NG), among other products), each of these natural gas processing systems generate wastewaters by removing water from the produced fluids and the raw natural gas. These natural gas processing systems also generate wastewaters, primarily in the form of condensate, resulting from the use of steam to drive turbines, as a heating fluid to provide heat to one or more heat exchangers, and other utility uses within the natural gas processing system.
Each of these natural gas processing wastewaters, both from the process side and the utility side of the natural gas processing system, may be collectively or individually accumulated, or a combination of collective and individual accumulation, and supplied to the energy harvesting system according to embodiments herein. For example, produced and process waters may be collectively accumulated and supplied while the condensate may be recovered and supplied by a separate system, such as a condensate collection system. As another example, each of the produced, process and utility wastewaters may be fed to a common collection system for subsequent supply to a salinity energy harvesting system according to embodiments herein. In yet other embodiments, each of the produced, process and utility wastewaters may be separately fed directly to a salinity energy harvesting system.
Keeping with
In one or more embodiments, the salinity energy harvesting system may be a RED or a PRO system. Both technologies use membranes to allow preferential transport of species by separating two reservoirs (streams) filled with fresh (lower salinity) and sea (higher salinity) water. In the case of PRO, the freshwater (low salinity) permeates to the highly-saline side through a semipermeable membrane, resulting in a pressure surge at the highly saline side which can be utilized to rotate turbine blades and produce electricity. While in the case of RED, the electricity is generated because of the transport of salt ions through ion permselective membranes, where the positive salt ions (e.g., sodium) permeate to the less-saline side, and the negative ions (e.g., chloride) permeate to the highly saline side.
One example of an energy harvesting system useful in embodiments herein is shown in
The first water stream 202 may originate from the first upstream water source 220 including boiler blowdown, pond water, fresh water, river water, or water streams originating from one or more upstream processes that have relatively low salinity.
A semi-permeable membrane housing 224 includes a container and a semi-permeable membrane 226 dividing the container 224. The semi-permeable membrane 226 may be constructed of solid-state porous materials, lamellar materials, or two-dimensional materials. Examples of solid-state porous materials include porous alumina, polymer Janus particles, and perfluorinated NAFION™. An example of a lamellar material is carbon nitride. Examples of two-dimensional materials include graphene and graphene oxide. Examples of commercially available semi-permeable membranes suitable for this application include PCA PC-SK, Qianqiu, sPEEK 65, and FUMASEP FKD. The salinity of the high salinity fluid impacts the structure of the semi-permeable membrane. Generally, a multilayered semi-permeable membrane is used for high salinity fluids in PRO applications. In RED applications, ion selective membranes for sequential permeation of the salt ions are used.
Referring back to
The low salinity side of the semi-permeable membrane housing 228 is in fluid communication with the pressurized first water stream 211. The pressurized first water stream 211 provides a low salinity fluid to the low salinity side of the semi-permeable membrane housing 228 that permeates an amount of the low salinity fluid through the semi-permeable membrane 226. The remaining low salinity fluid that does not permeate exits to the low salinity side of the semi-permeable membrane housing 228 through a low salinity exit line 230. In some embodiments, the low salinity exit line 230 may be combined with the mixed water exit stream 208 and sent by the third pump 205 to the separator system 212, as illustrated in
The second water stream 204 may originate from the second upstream water source 222 including seawater, produced water, brine water, or other water streams originating from one or more upstream processes that have relatively high salinity.
Another example of a salinity energy harvesting system 206 useful for one or more embodiments is a reverse electrodialysis (RED) process. RED involves the transport of (typically, salt) ions through a series of alternating positively and negatively charged exchange membranes. Each of the membranes contains fresh water on one side and salt water on the other side. The positively charged anion exchange membranes allow only negatively charged ions to pass and the negatively charged cation exchange membranes allow only positively charged ions to pass. Therefore, positive and negative ions migrate in opposite directions, from salt water into fresh water, creating positive and negative poles, as in a battery. As a result, voltage is generated over each membrane and the total voltage of the system is the sum of the voltages over all membranes. Connecting the two poles by a conductor causes an electrical current to flow. In summary, the RED process harvests counterion fluxes across ion exchange membranes to generate a Nernst potential between two saline solutions of different concentrations.
Turning back to
The separator system 212 according to one or more embodiments may be any system capable of separating salt from a mixed water exit stream 208 to produce a high salinity exit stream 214 and a pure water stream 216. A “pure water” stream is defined herein as having a total dissolved solids (TDS) value of less than about 2000 ppm. In some embodiments, the pure water stream is recycled to a process in a natural gas refining plant, or the pure water stream is exported and/or sold.
Examples of separator systems useful in one or more embodiments disclosed herein may include, but are not limited to a membrane separator system, a membrane distillation system, a distillation system, or a deionization system.
The separator system of one or more embodiments may include a membrane separator system that relies on reverse osmosis technology, for example. In reverse osmosis systems, a contaminant, such as salt, is removed by passing a water stream through a semi-permeable membrane. Pressure exerted from the flowing water stream pushes the water stream through the semi-permeable membrane which removes dissolved salts. The dissolved salts are sent to a waste stream and a pure water stream is produced. The reverse osmosis process may include a series of semi-permeable membranes to improve the capacity to remove salt from the water stream.
The separator system of one or more embodiments may include a distillation system. The distillation process relies on differences in boiling points of different substances. During distillation, a saline water stream is heated to produce water vapor, which is then condensed to produce fresh water. There are several different types of distillation systems which may be used to desalinate water, including, but not limited to, a multistage flash distillation system, a multiple effect distillation system, a vapor compression distillation system, a membrane distillation system, and a dual purpose distillation system. The distillation system of one or more embodiments may be any of the example systems listed, or combinations therein.
The separator system of one or more embodiments may include a deionization system. A deionization system removes dissolved salts and minerals from a water stream using an electrically charged resin bed. The electrically charged resin bed may be positively or negatively charged, such that when the water stream is passed through the electrically charged resin bed, particles in the water stream having the opposite charge are attracted. The deionization system may include at least one positively and negatively charged resin beds in series to remove both negatively and positively charged ions, respectively. Deionization systems must be flushed to regenerate the electrical charge and remove collected ions.
Keeping with
Embodiments disclosed herein also relate to a method for treating and recycling wastewater.
Keeping with
Embodiments of the present disclosure may provide at least the following advantages. Energy requirement for water treatment applications, specifically wastewater treatment, pose a critical challenge. However, in this method and system, a semi-closed-loop system firstly harvests the salinity gradient energy of upstream water resources, then utilizes such harvested energy to treat the brackish water using a separator. Such an approach will result in a sustainable energy production, wastewater treatment, and ultimately upstream water recycling to be fed into other upstream applications. In summary, the semi-closed-loop salinity gradient energy harvesting system disclosed herein will result in a sustainable energy production, wastewater treatment, and ultimately water recycling to be fed into several upstream applications.
Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.
