Patent Application
20180162758
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The field of this invention is to provide Zero Liquid Discharge ZLD (Solid Wastes) from desalination of saline water. Furthermore, ZLD operation is also often referred to as crystallization
Water significantly impacts the daily lives of each person on earth through its personal, industrial, and agricultural use. Water is loosely classified in this document as either “Fresh”, Saline, Contaminated Fresh, and Contaminated Saline Water. Fresh water is defined here as having acceptable levels of contaminants in the water for its use. Most fresh water is obtained through the “water cycle” by evaporating the water from the ocean and then depositing it over land as rain (fresh water). The rain waters the surface of the earth and the rest of it is temporally stored in streams, lakes, and replenished aquifers (Ground water). Some fresh water can be found in the polar ice caps and in non-replenished aquifers within the earth.
Saline water is defined as a water solution containing mostly dissolved salts that form electrolytes. Saline or Contaminated Saline water makes up most of earth's water and can be found in the oceans, streams (Especially streams near the ocean), and saline aquifers. Even with water conservation measures and improved means of better using the rain water, as the population grows there becomes a need to desalinate the abundant quantity of saline water to supplement earth's current fresh water supply.
Much of the source water on earth, that is considered fresh water and saline water, can be contaminated in a myriad of ways which is defined here as contaminated fresh water and contaminated saline water. Although some source water is directly usable or after desalination, much of it needs to be processed in some way to remove the contamination so as to provide useful water. In a general way, the myriad of contaminants in the water can be roughly divided into categories based on their size:
Based on size, contaminated fresh water is defined here as having any or all of the size range contaminants except for small quantities of Ionic Range Contaminants and fresh water as having only small quantities of any contaminants within acceptable limits. Based on size, saline water is defined here as only having solids dissolved in the water as ions with their size being in the Ionic Range Size as well as small quantities of other small contaminants suspended in the water. Contaminated saline water has any or all of the size range contaminants.
There are a number of water treatment process that will remove most of the water contaminants from the Macro Particle through the Molecular Sizes. Widely used water treatment processes, as described in numerous books and documents that remove Macro Particle through the Molecular Sizes contaminates from the water, are:
The water treatment for contaminated saline water or just saline water must use desalination processes to remove the ionic sized ions from it. The most common widely used desalination processes which are described in numerous books and documents are distillation, reverse osmosis, and electrodialysis. Some desalination techniques remove contaminants other than just the ionic contaminants as well. Some desalination processes including the ones just mentioned are discussed in numerous books and documents and are listed:
For large volume flow rate desalination operations, all the desalination processes currently in wide use have large amounts of saline waste water or contaminated saline waste water. For desalination plants near the ocean, the waste water could be disposed of in the oceans although there are environmental issues to overcome. For inland desalination plants, the question is: What to do with the large quantities of saline waste water for large volume flow rate operations? The volume flow rate of waste water probably would be too large to discharge into the ground, streams, or evaporation ponds. Furthermore, many governmental entities are considering the requirement of nearly Zero Liquid Discharge ZLD which means the waste is required to be a solid (In our case mostly solid salts). These solid wastes then could be economically buried in the ground, transported to the ocean using bulk carriers (Rail or barge), or sold.
The technologies to reduce the saline waste water or contaminated saline waste water to a solid are usually found under the title of Zero Liquid Discharge ZLD or salt manufacturing. To obtain ZLD or to manufacture salt, crystallizers that form solids from the liquid are used. The crystallizers typically operate by removing water from the salt solution by evaporation until the ionic chemicals in the remaining solution becomes supersaturated and solid crystals precipitate out forming solids as described in Non-Patent Literature Document [1]. The common process today is a twostep processes of (a) Brine Recovery that removes some water by thermal evaporation followed by (b) Crystallization that removes almost all the water using a thermal evaporation process so solids are formed. There does not currently seem to be any crystallizers (Most processes today use thermal evaporation for crystallization) to form ZLD wastes that are satisfactory for large volume flow rates and for affordable costs.
An alternative method of desalination having Zero Liquid Discharge ZLD (solid) waste is to transfer ions from the input saline water into another separate saline water system until solids precipitate out. Variations of this basic process can be found in relatively new patent applications and patents found in U.S. Patent Documents [1], [2], [3], [4], and [5]. One of the underlying issues with these patent documents and with bringing this basic process to widespread use is for the process that transfers ions from the input saline water to the separate saline water to not become fouled as the separate water solution becomes heavily concentrated in ions which can cause a precipitation of solids within the ion transfer process itself. A portion of this invention will provide means for the separate highly concentrated saline water not to precipitate ions during the operation of the ion transfer process but yet will provide means for the highly concentrated saline water to precipitate out solids at a new location and at a different time.
This invention has major components of (a) ion concentration, (b) combinations of prior art desalination processes and ion concentration processes to produce fresh water and nearly saturated saline water from a saline water input, and (c) combinations of prior art desalination processes and ion concentration processes to produce fresh water and supersaturated saline water operating in the metastable zone from a nearly saturated saline water input which is converted to solids by precipitation in a separate process. As background, a few comments and a reference are provided on prior art that is relevant to this invention. These are:
A. Useful Properties of Distillation and Reverse Osmosis: Distillation and reverse osmosis divides a single input stream of saline feed water into a stream of lower salinity water and a stream of higher salinity water which is sometimes referred to as waste water. Often a number of desalination processes are operated in series where the reject water from one desalination process feeds the next desalination processes and the fresh water from all the desalination processes operated in series are combined. In some realizations, a portion of the higher salinity stream of water is recirculated and added to the input saline water stream.
B. Useful Property of Electrodialysis and Capacitive Deionization: Electrodialysis and capacitive deionization has two distinct separate water streams. By transferring ions from one saline water stream to the other, one water stream is made less saline and the other independent water stream is made more saline. This process can be called an ion transfer process. If the desired ion concentration is not reduced enough in a single pass of the ion transfer process, several ion transfer processes can be operated in series or the two saline waters can be recirculated through a single ion transfer process to obtain the desired low salinity output water for desalination. The performance of the ion transfer processes can be limited as the ratio of the salinities of the reject more saline output water to the desired less saline water becomes high.
C. Precipitation: In the chemistry of sparingly soluble salts; if a solid salt is added to water, the solid will disassociate and ions will distribute themselves throughout the water until the solution becomes saturated. After the solution becomes saturated with ions, if more solid salts are added to the solution, no more solid salt will dissolve and the saturated solution and the additional solid salt added to the solution past the solution saturation point will coexist in equilibrium. Actually, the amount of solid salt dissolving into the water is equal to the amount of salt precipitating out of the water to a solid when the solution is saturated. However, the solution can exist in an unstable supersaturated state where the concentrations of the salt is greater than the concentrations of the salt in the water when the solution is saturated. If the solution is supersaturated and no solids are present, there is a region of ion concentrations above the saturated ion concentration that is called a metastable zone as described in Non-Patent Literature Document [2]. In the metastable zone, spontaneous formation of crystallization in the solution is impossible. However, crystal growth can take place in the metastable zone of ion concentrations given trigger mechanisms such as the presence of seed crystals but time is required for the crystal growth. For ion concentrations above this metastable zone, the ions can start precipitating out to form solids even when no seed crystals are present and often the solids called crystals form fairly rapidly. After crystal growth is initiated by adding seed crystals to the unstable supersaturated solution in the metastable zone having no solids present, solids start to precipitate to form crystals and continue to precipitate out into crystals until the saturation condition is reached which consists of both saturated saline water and solids. The rate of precipitation (crystallization) can play a role in forming solids from supersaturated saline water.
This invention obtains fresh water and only solid waste from input saline water. This result is commonly known as desalination having zero liquid discharge (ZLD). The current common means of ZLD desalination is to use any common desalination process such as distillation, reverse osmosis, electrodialysis, etc. followed by brine recovery and crystallization which are both based on evaporation of water processes. This invention provides an alternative to the commonly used brine recovery and crystallization processes to produce only solid waste. This invention has major components of (a) new ion concentration process, (b) combinations of prior art desalination processes and new ion concentration processes to produce fresh water and nearly saturated saline water from a saline water input, (c) another combination of prior art desalination and new ion concentration processes to produce fresh water and supersaturated saline water having a salinity in the metastable zone from a nearly saturated saline water input, and (d) a separate process that precipitates out solids from the supersaturated saline water having a salinity in the metastable zone after seed crystals are introduced. Each of these processes are briefly discussed.
A base ion transfer process in which prior art electrodialysis and capacitive deionization with recirculation are examples is used as a fundamental element in the ion concentration process. The current common use of the base ion transfer process is to use the less saline output water and reject the more saline output water as waste. In this case, the more saline output water is the desired output. The ratio of the salinities of the more saline output water to the less saline output water is also limited to insure proper operation of the base ion transfer devices. Multiple base ion transfer processes are arranged so that the resultant outputs are nearly saturated saline water and even less saline output water than that of the input saline water. This arrangement is called the ion concentrator.
Multiple prior art desalination processes and ion concentrators are arranged to provide outputs of fresh water and nearly saturated saline water. The nearly saturated saline water is then passed to a precipitative crystallizer that uses combinations of desalination processes and ion transfer processes to produce more fresh water and supersaturated saline water having salinities in the metastable zone. The concentrated saline water having salinities in the metastable zone is passed to a precipitative tank where seed crystals are introduced, solids are formed from precipitation, and the now just saturated saline water is combined with the nearly saturated saline water of the input to the precipitative crystallizer for recirculation. On each new pass, the new nearly saturated saline water passing through the ion concentrator that supersaturate the saline water will dissolve any inadvertent crystallization left from the previous pass so that the crystals will not continue to grow in size as time goes on to foul the ion concentration process that supersaturates the saline water. After any inadvertent formed crystals are dissolved on this new pass, the nearly saturated saline water is then supersaturated for this new pass.
This invention obtains fresh water and only solid waste from input saline water where this process is commonly known as desalination having Zero Liquid Discharge (ZLD). Fresh water is defined as mostly pure water with only modest amounts of other contaminants in it and the input saline water is supply water that has been preprocessed leaving only the ions and a low concentration of other contaminants suspended in the water. The current common means of ZLD desalination is to use any common desalination process such as distillation, reverse osmosis, electrodialysis, etc. followed by brine recovery and crystallization which are both based on evaporation of water processes. This invention provides an alternative to the commonly used brine recovery and crystallization processes to produce only solid waste. This invention has major components of (a) new ion concentration process, (b) combinations of prior art desalination processes and new ion concentration processes to produce fresh water and nearly saturated saline water from a saline water input, (c) another combination of prior art desalination and new ion concentration processes to produce fresh water and supersaturated saline water having a salinity in the metastable zone from a nearly saturated saline water input, and (d) a separate process that precipitates out solids from the supersaturated saline water after seed crystals are introduced. Each of these processes are separately discussed.
The base ion concentrator 100 is shown in
Typically, the single stage base ion concentrator 100 is not sufficient to concentrate the desired more saline water to be nearly saturated saline water. To obtain higher saline water concentrations, multiple base ion concentrators 100 are concatenated in a concatenated concentrator 200 as shown in
An example of the concatenated concentrator 200 is provided.
Second Base Concentrator: The input saline water from the more saline water from the first base ion concentrator is divided into 2 equal parts yielding 237.5 kg fresh water and (25 kg+17 kg)/2=21 kg of salt dissolved in each storage tank. This base ion concentrator is operated with both separate water paths recirculating until there is 14.5 kg of salt ions transferred from the less saline water to the more saline water. The salinity of the less saline water then is (21 kg−14.5 kg)/(237.5+21 kg−14.5 kg)=2.66% and the salinity of the more saline water is (21 kg+14.5 kg)/(237.5+21 kg+14.5 kg)=13%. The ratio of these two salinities is 4.9 so the imposed limit on the ratio of salinities is satisfied.
Third Base Concentrator: The input saline water from the more saline water from the second base ion concentrator is divided into 2 equal parts yielding 118.75 kg fresh water and (21 kg+14.5 kg)/2=17.75 kg of salt dissolved in each storage tank. This base ion concentrator is operated with both separate water paths recirculating until there is 12.5 kg of salt ions transferred from the less saline water to the more saline water. The salinity of the less saline water then is (17.75 kg−12.5 kg)/(118.75+17.75 kg−12.5 kg)=4.23% and the salinity of the more saline water is (17.75 kg+12.5 kg)/(118.75+17.75 kg+12.5 kg)=20.3%. The ratio of these two salinities is 4.8 so the imposed limit on the ratio of salinities is satisfied.
Combine the Less Saline Outputs from All Base Ion Concentrators: The total fresh water from the less saline water outputs of all of the three base ion concentrators is (475 g+237.5 kg+118.75 kg)=831.25 kg. The total weight of salt dissolved in the fresh water is (8 kg+6.5 kg+5.25 kg)=19.75 kg. The salinity of the less saline output water then is (19.75 kg/(831.25 kg+19.75 kg)=2.3%
Example Summary:
Although the objective of having a nearly saturated saline water output is obtained by the concatenated concentrator 200 shown in
The next part of this invention, defined as desalinate/concentrate process 1 as shown in
The next part of this invention, defined as precipitative crystallizer process 2 as shown in
Backtracking now to the supersaturated saline water being formed in the very first ion concentrator 300 of the precipitative crystallizer 2, this supersaturated saline water is output to one of a plurality of precipitative tanks 430 after the salinity has reached a metastable zone threshold where spontaneous precipitation would occur. Seed crystals are applied to the supersaturated saline water in the precipitation tank 430 and solids precipitate out. After this precipitation process is complete, the now only saturated saline water is filtered to remove any suspended precipitated solids and then combined with the other nearly saturated saline water in combiner 420. The solids can be disposed of as waste. To determine if the salinity of the supersaturated saline water is at the metastable zone threshold, measurements of the concentrations of the ions can be made and with a smart processor one can determine if a cation and anion combination is at the metastable zone threshold for that combination. Alternately, one can detect if precipitation has begun by looking for particles starting to appear in the supersaturated water. It is critical that little precipitation of solids occur while the supersaturated saline water is being formed so as to not foul the processes. Even if a small quantity of solids inadvertently form during a first ion concentration process 300, on the next pass of receiving nearly saturated saline water, these solids will dissolve early in the process while the feed water is still slightly unsaturated before this small quantity of solids could grow larger when the nearly saturated saline water is supersaturated. This operation and fact is critical to the success of the precipitative crystallizer 2.
If there are small quantities of other suspended contaminants other than ions in the input saline water, a small quantity of these could end up in the fresh water ports. However, most of the small quantities of suspended contaminants other than ions in the input saline water will end up in the precipitation tank. The filter that filters the saturated saline water containing suspended precipitated solids will also filter out these other contaminants other the ions and keep them in the precipitation tank. These other non-ionic contaminants as well as the precipitated-out solids can then be removed for disposal.
All the processes in the ion concentrators 300, desalinate/concentrate process 1, and precipitative crystallizer process 2 can be implemented in a different manner but achieve the same results. A plurality of (a) base ion concentrator processes, (b) desalination processes, (c) storage tanks, and (d) combiners, defined in the concentrators 300, desalinate/concentrate process 1, and precipitative crystallizer process 2, can be made available. Under the control of a smart controller not shown, the saline water can be shifted between any available base ion concentrator, any available desalination process, any available storage tank, and any combiner to process the saline water so that the end result is the same as shown in the processes defined by ion concentrators 300, desalinate/concentrate process 1, and precipitative crystallizer process 2.
