WO1999001380A1

WO1999001380A1 - Method and apparatus for environmentally friendly desalting of sea-water

Info

Publication number: WO1999001380A1
Application number: PCT/HU1998/000062
Authority: WO
Inventors: Béla BOROS
Original assignee: Boros Bela
Priority date: 1997-07-04
Filing date: 1998-07-03
Publication date: 1999-01-14
Also published as: HUP9701148A2; HU9701148D0; HU218412B; AU8352198A; HUP9701148A3

Abstract

The characteristic feature of the invention is that the whole quantity of the saline solution is separated by evaporation into a low saline containing liquid (4-100 mg/l of saline content) with at least a fresh water quality and into a crystalline salt by strictly closed process, through the evaporation is done on a specifically increased surface on about 100 °C and the concentrated saline solution produced after the evaporation and condensation having a concentration of at least 15-20 % is crystallized. The purification apparatus, including a circulating pump (2) for saline solution a heat exchanger (15) connected to the circulating pump (2), a distillation unit (5), a settler tank (7) between the distillation unit (5) and a crystallizing unit (9), a second circulating pump (8), first output of this crystallizing unit (9) is connected to the liquid gathering tank (6) and the second output of this crystallizing unit (9) is connected to an additional settler tank (11) and the third output is connected to a crystalline salt tank (12), and the output of the additional settler tank (11) is connected back to the crystallizing unit (9) through the third circulating pump (13).

Description

METHOD AND APPARATUS FOR ENVIRONMENTALLY FR IENDLY DESALTING OF SEA-WATER

Subject of the invention is a method and an apparatus for environmentally friendly cleaning and/or processing of salt solutions especially sea- water. An enclose-loop control technology which is environmentally friendly and uses the waste heat rising from the operation of known equipment to separate salt solutions into a fresh-water quality liquid at least and a crystalline salt and/or salts. In the description salt solution means salts and/or poisonous compounds in solute state, which are formed either via natural processes or through technological processes.

As an introduction the polluting effect of the known methods is presented by some examples.

There are many methods and apparatus for the desalinizing of sea-water - generally with

30,000 - 45,000 mg/1 saline content - turning it into fresh water with a success rate of at most 4 - 1000 mg/1.

There are also known methods with the purpose of producing mainly table salt from salt solution or sea-water via water extraction either by natural means or by mechanical distillation such as vacuum-compressor distillation. The aim of both purposes of sea-water's conversion is to produce the required final product. In the known fresh-water producing technologies the increased concentrate and/or concentrated slain water produced as a byproduct is readily accepted (a process of reverse osmosis), but with the targeted salt production, by way of vacuum distillation, the improved quality water is still not utilized and is also treated as a byproduct

Of the many known desalinization methods the process of ion exchange and electrolysis is pushed into the background because of the relatively expensive electrical energy and the continuous requirements of chemicals. Among the other known methods the process of reverse osmosis is the most widespread, as it requires relatively less energy. The main disadvantage of this method is that the sea-water must be pre-treated, which requires many chemicals. This process involves, among others, decarbonisation with slaked lime, partial annealing with sodium carbonate and desilication with sodium aluminate and ferrous chloride. Furthermore the water needs to be flocculated through filters and finally strained through sand.

With the known evaporation processes steam is generated in traditional boilers and then channeled into the evaporator that is constructed with heating pipes. The steam created in the evaporator is led through the spray catchers to condense it, in modern methods, by utilizing the heat energy of the steam after which the condensed steam is led away. The vapour is circulated with any carrier gas (usually air) with the help of vacuum to increase the speed of evaporation and the thermal efficiency. It is standard practice to install a heat exchanger in the circulating system in which the condensation will occur. For example, to a solution such as this is that, the patents with registration numbers DE 3.435.614 and SU 1.139.708 apply.

Furthermore there are methods with the purpose of recovering the condensation heat. According to the patent registration number DE 3.509.590, for instance, the steam is utilized in performing mechanical work to create electrical energy. According to yet other methods the condensation heat, based on the principle of the counter flow heat exchanger, is used to heat up feed water as it is in patent registration number DE 3.331.775.

The common disadvantage of the known methods is that they each satisfy only one technical purpose and/or they can only be applied specifically. Their adaptation also requires different chemicals during the process - at hot procedures, the level of sulphates and/or hydrocarbonates, while at cold procedures, for example, the neutralization of the silica cause problems. These procedures or even the final product(s) themselves utilize materials that cause environmental pollution.

The main disadvantage of methods applied to desalinize sea-water is that although the purpose is to produce fresh water the desalinization process creates as a byproduct a condensed, highly concentrated, saline enriched liquid, (in a significantly higher concentration than the original unprocessed solution) most of which is usually released back into the environment endangering flora and fauna. This practice can swiftly and even irreversibly alter the ecological balance of the area resulting in an environmental catastrophe. Historical examples include the transformation of the Rhine river into a dead water and the destruction of rivers and their surrounds in Papua New Guinea due to CH solutions used in ore mining. Current threats include the Arabian gulf where the salinity of the sea-water is increasing significantly which can directly be attributed to the desalinization plants situated on its banks.

These examples prove the obvious one, i.e., that introducing the byproducts of salt and/or concentrates back into the environment is ecologically unsound. They also indicate the technological disadvantage whereby the salinity of the unprocessed water to be used by desalinizing plants is continuously rising as a result of the re-introduction of the byproducts. This means the plants can operate only with continually decreasing efficiency. The energy required to continue effective desalinization increases significantly due to the fact that the process of reverse osmosis on water with a higher saline content works only with a higher pressure. Hence, to continue to produce fresh water with the same level of quality, increased quantities of chemicals are required coupled with an increased demand for energy as well resulting in even higher levels of concentrated byproducts being released back into the environment.

The aim of this invention is to apply a process which eliminates the disadvantageous aspects of the known methods by utilizing a closed-circuit, environmentally friendly technology, in an effort to make redundant the polluting technologies and/or restore the ecology to its natural state.

My purpose, therefore, is the development and application of method(s) used for cleaning and/or processing saline solutions, specifically sea-water to produce the required final product, for example fresh water or crystalline salt, in a way that protects the environment and does not burden it with increased saline water, additional chemicals or emitted heat energy, thus allowing the ecological balance in the vicinity of operating desalinization plants to be slowly restored. I recognized that in developing and/or applying the invention the aim was not just to achieve the required final product, such as converting sea-water into fresh water or crystalline salt but from an ecological point of view the problem must be approached and solved in a complex way. Our natural environment can not be burdened further by the usual methods and a new environmentally friendly method is necessary.

Through this strictly closed technology invention I propose to fully separate saline liquids such as sea-water into crystalline salt(s) and at least a fresh-water quality, low saline liquid which contain poisonous materials in a minimum allowed quantities or none at all. Thus no matter which final product is the main goal they are produced in an environmentally friendly, useable and/or neutralized form.

The subject of the invention is a method for the environmentally friendly cleaning and/or processing of saline liquids, specifically sea-water, where they are converted into a liquid with at least a fresh- water quality, (at most 4-1000 mg/1 saline content), by evaporation and condensation. Meanwhile circulating the steam created during the evaporation process increases the temperature level of the unprocessed saline solution.

The separation is conducted in such a way that the evaporation is performed on a specifically increased surface between 65-110°C depending on the pressure value, but preferably in the vicinity of 105°C. After evaporation and condensation the resulting, concentrated salt solution, (with a concentration of at least 15-22 %), is crystallized with waste heat.

Firstly the saline solution to be evaporated is filtered to remove suspended pollutants. This filtering is achieved usually by mechanical means. Other more complex cleaning technologies are utilized only when, for example, there is a presence of alga. To remain true to my environmentally friendly method the cleaning and/or further utilization of the salt solution is done without the use of polluting materials. In water treating methods it is known that the scaling and/or precipitation of sulphates, hydrocarbonates can cause problems. Protection against these is also usually achieved by the use of chemical (or magnetic) pre- treatment.

In this invention the specifically increased surface is preferable coated by the same and/or similar material to teflon known and used at nonsticky frying pans, which prevents the sticking and/or binding of the salt crystals to the surface. This, preferably a plastic, cover ensures that the salt crystals do not precipitate on the surface but roll down from it and leave with the concentrated salt solutions to be crystallized in the crystalliser. One of the advantages of this invention is that the neutralization and/or separation of the salt solution(s) are conducted in industrial processes, pre-treatment and/or in any part of the whole closed technological process. For example, salt solutions for extracting electrolytes, compounds containing paint material(s) or metal(s) and/or salt(s) from mines.

Another advantage of this method is that the waste heat created by the operation of known equipment, especially internal-combustion engines and turbines, can be utilized for evaporation and/or crystallizing. The 105°C temperature required for evaporation can be obtained by the use of this waste heat. As a result the method can be put to very practical use in naval ships, power stations or industrial plants.

Following evaporation and condensation we are left with distilled steam, which through recirculation serves to preheat the as yet untreated salt solution, and a saline solution with 15-25% concentration. This saline solution is further heated to at least 108°C to achieve crystallization. At this temperature the salt releases the crystal water and the separation of salt and water is achieved. Through the circulation of the vapour created during crystallization, (as in the evaporation), the crystallized concentrated saline solution is also preheated. A significant part of the heat quantity required for continuous operation of the process can be recovered from the distillate by a heat exchanger and/or can be realized by utilization of other waste heat(s).

It is also the subject of the invention an apparatus for the environmentally friendly cleaning and/or processing saline solutions especially sea-water, including the circulating pump for salt solution and one of the branches of the heat exchanger connected to the pump directly or indirectly. Its output is directly connected to the input of a distillation unit. One of the outputs of the distillation unit is equipped by a liquid gathering tank through the other branch of the heat exchanger, the other output is equipped by a settler tank. The bottom of the settler tank is connected to the input of a crystallizing unit through the second circulating pump. The first output of this unit is connected to the liquid gathering tank and the second output is connected to an additional settler tank and the third output is connected to a tank for the crystalline salt. The output of the additional settler tank is connected back to the crystallizing unit through the third circulating pump.

In a preferable installation of the apparatus there is a filter unit between the first circulating pump and one of the branches of the heat exchanger.

According to a further preferable solution of this invention there is a preliminary heater with a thermostat T between one of the branches of the heat exchanger and the distillation unit, which automatically provides the heat required for maintaining the process.

Suitably, the upper - less concentrated - part of the concentrate having been gathered in the settler tank is conducted back to the distillation unit by the forth circulating pump.

With another practical utilization of the method one of the branches of an additional heat exchanger is installed between the crystallizing unit and liquid gathering tank, its other branch is installed between the settler tank and the crystallizing unit. One of the possible arrangement of the apparatus according to this invention is shown in details according to the enclosed drawing, where

Figure 1 is representing the sketchy construction.

Figure 1 shows the subject of this invention, the apparatus for environmentally friendly cleaning and/or processing saline solutions, preferably sea-water, including a first circulating pump (2) for circulating the saline solution (1), one of the branches of a heat exchanger (3) connected to the pump directly or indirectly. One of the outputs of the heat exchanger (3) is connected to the input of the distillation unit (5) directly or through the preliminary heater (4). One of the outputs of the distillation unit (5) is connected to the liquid gathering tank (6) through the other branch of the heat exchanger (3), its other output is connected to the settler tank (7). The bottom of the settler tank (7) is connected to the input of a crystallizing unit (9) through the second circulating pump (8). The first output of this crystallizing unit (9) is connected to the liquid gathering tank (6) directly or indirectly through one of the branches of the additional heat exchanger (10) and the second output is connected to an additional settler tank (1 1) and the third output is connected to a crystalline salt tank (12). The output of the additional settler tank (11) is connected back to the crystallizing unit (9) through the third circulating pump (13).

Frequently the saline solution (1) contains mechanical pollution, thus, in a special installation of the apparatus, there is a filter unit (15) between the first circulating pump (2) and one of the branches of the heat exchanger (3).

If necessary it should be practical the top of the settler tank (7) to be conducted back to the distillation unit (5) by the forth circulation pump (14). On the Figure it can be seen that the other branch of the additional heat exchanger (10) is installed between the settler tank (7) and the crystallizing unit (9). The apparatus of the investment is working as follows. Mechanical filtering of the saline solution (1), preferably sea-water, is done in the filtering unit (15). The saline solution (1) filtered to remove suspended pollutants is conducted into the distillation unit (5) by the circulating pump (2) through the branch of heat exchanger (3) and preferably through the preliminary heater (4). The saline solution (1) (sea- water) with an original temperature of 6- 25 degree C is heated to practically higher than 70 degree C, preferably about 90 C degree C, through the branch of the heat exchanger (3) and then it is conducted to the distillation unit (5) through the preliminary heater (4). In the distillation unit (5) the evaporation is done on the specifically increased surface.

The saline solution (1) the temperature of it has been increased by method described above is conducted onto the specifically increased evaporation surface by a flow rate of 1.5-20 m/s, preferably by 2-5 m/s. The evaporation is performed on the trays (16), preferably placed under each other, by a steam with about 100 degree C temperature and 0.1-0.5 bar pressure. The saline solution (1) may be conducted into the distillation unit (5) by the gravity and/or by injection as well.

Consequently the evaporation of the salt solution (1) in the distillation unit (5) is performed on preferably 100 degree C temperate. In order to prevent the precipitating or gathering together of the saline crystals generated on the specifically increased surfaced trays (16), the heat transfer surfaces are covered by adhesion inhibitor material preferably by plastic, earth metal or rare earth material. One of the outputs of the distillation unit (5), where the sterile steam leaves, hands the most part of it's heat quantity to the evaporated saline solution (1) streaming in one of the branches of heat exchanger (5) and then goes to the liquid gathering tank (6) in water state. The saturated saline solution (1), preferably with a 15-25 % concentration, is arriving to the settler tank (7) through the other output of the distillation unit (5) at about 100 degree C temperature. In the bottom of the settler tank (7) the saturated saline solution (1) is more concentrated than on the top. Thus it should be practical to use a forth circulating pump (14), if necessary, to connect to the top of the settler tank (7) and the distillation unit (5). The bottom of the settler tank (7) is connected to the output of the crystallizing unit (9) directly through the circulating pump (8) or preferably through one of the branches of the additional heat exchanger (10) the other branch of the additional heat exchanger (10) is installed between the output of the crystallizing unit (9) and the liquid gathering tank (6). The steam created in the crystallizing unit (9), where the separation of salt and water is performed on at least 108 degree C temperature, is heating the saturated saline solution (1), with a temperature of nearly 100 degree C, of the settler tank (7) in the additional heat exchanger (10). Additional preliminary heater unit (4) can be installed in front of the crystallizing unit (9) if necessary similarly to the distillation unit (5). The outlet of the settler tank (11) conducts the non crystallized saline solution (1) back to the crystallizing unit (9) through the third circulating pump (13). The third output of the crystallizing unit (9) is the crystalline salt storage tank.

The method of the investment can be put to very practical use. For cleaning and/or processing saline solution the method provides to produce the final products i.e. the fresh water quality liquid and crystalline salt by closed environmentally friendly technology. This requires few energy which can be provided mostly by waste heat created by known equipment. The method of the investment completes and makes economical and environmentally friendly the plants producing preferably fresh water by known method. The method can preferably be put to very practical use in naval ships spending long period on the sea, in producing boiler water in big quantity for thermal power station or producing irrigation water from sea-water. Field of application of the method of the investment is wide, because it can be used not only to treat sea-water but detoxicate industrial sewage especially, to process saturated saline solution of plants or neutralize electrolytes of galvanic plants as well. It can be used practically to convert artesian water into irrigation or drinking water as well, because the underground cisterns are containing saline in big quantity, but the present methods can not solve the problem of treating or using of the salt concentrate as the byproduct of desalinizing. In the water cleaning technologies this is the biggest process causing pollution all over the world especially from the Mediterranean to the desert climate territories, which problem can be solved by the method of this investment. List of references

saline solution first circulating pump heat exchanger preliminary heater distillation unit liquid gathering tank settler tank second circulating pump crystallizing unit additional heat exchanger additional settler tank crystalline salt tank third circulating pump forth circulation pump filter unit tray

Claims

1. Method for environmentally friendly cleaning and/or processing of saline solutions especially sea-water, in which the saline solution is evaporated and condensed into at least a fresh water quality liquid with a success rate of at most 4-1000 mg/1 of saline content, while the temperature of the saline solution to be evaporated is increased by streaming of the steam arose from the evaporation, is c h a ra c t erized by th at the whole quantity of the saline solution is separated into a low saline containing liquid with at least a fresh-water quality and into a crystalline salt by a strictly closed process, through the evaporation is done on a specifically increased surface on about 100 degree C and the concentrated saline solution produced after the evaporation and condensation having a concentration of at least 15-20 % is crystallized.

2. The method according to the claim 1 is c h a ra ct erized by th at the evaporated saline solution is filtered to remove suspended pollutants.

3. The method according to the claim 1 or 2. is ch ara c terized by th at the cleaning and/or processing of the saline solution is performed without using any further environmentally pollutants or chemicals.

4. The method according to any of the claims 1. -3. is ch a racterized by that the waste heat rising from the operation of known equipment for evaporation and/or crystallization, such as heat engine, internal combustion engine or turbine, is utilized too.

5. The method according to any of the claims 1-4. is c h ra cterized by th at the produced concentrated saline solution after the evaporation and condensation is crystallized by heating it up to at least 108 C degree.

6. The method according to the claim 5. is c h a ra c te rized by that the concentrated saline solution is preheated by circulation of the steam generated in the process of crystallization.

7. Apparatus for cleaning and/or processing saline solutions preferably sea- water, including a circulating pump for saline solution and one of the branches of a heat exchanger connected to the circulating pump directly or indirectly, an output of this heat exchanger is connected to the input of a distillation unit, and one of the outputs of the distillation unit is channeled into a liquid gathering tank through the other branch of the heat exchanger, the other output of the distillation unit is channeled into a settler tank, ch a racterized by th at the bottom of the settler tank (7) is connected to the input of a crystallizing unit (9) through the second circulating pump (8), first output of this crystallizing unit (9) is connected to the liquid gathering tank (6) and the second output of this crystallizing unit (9) is connected to an additional settler tank (11) and the third output is connected to a crystalline salt tank (12), and the output of the additional settler tank (1 1) is connected back to the crystallizing unit (9) through the third circulating pump (13).

8. The apparatus according to the claim 7. is c h a ra cte rize d by that there is a filter unit (15) between the first circulating pump (2) and one of the branches of the heat exchanger (15).

9. The apparatus according to any of the claim 7. or 8. is c h a ra c te rized by th at there is a pre-heater (4) between one of the branches of heat exchanger (3) and the distillation unit (5).

10. The apparatus according to any of the claims 7.-9. is c h a ra c te rized by th at the top of the settler tank (7) is channeled back to the distillation unit (5) through the forth circulating pump (14).

11. The apparatus according to any of the claims 7.-10. is c h a ra ct e rized by th at one of the branches of the additional heat exchanger (10) is installed between one of the outputs of the crystallizing unit (9) and the liquid gathering tank (6), the other branch of the additional heat exchanger (10) is installed between the settler tank (7) and the crystallizing unit (9).