WO2007030851A1

WO2007030851A1 - Introduction of solar heating energy for desalinating sea water

Info

Publication number: WO2007030851A1
Application number: PCT/AT2006/000378
Authority: WO
Inventors: Martin Hadlauer
Original assignee: Martin Hadlauer
Priority date: 2005-09-15
Filing date: 2006-09-13
Publication date: 2007-03-22
Also published as: AT502797B1; AT502797A4

Abstract

Disclosed is a sea water desalination system for producing service water and drinking water by means of a multistage distillation process, i.e. multistage flash (MSF) or multi-effect distillation (MED), while feeding heating energy. The inventive sea water desalination system is characterized in that distillate (5_1) is removed from the preheating column (6), is heated via one or several heating devices (1), and is then recirculated into the distillation circuit of the preheating column (6). The heated distillate (5_2) is recirculated via a chamber that is mounted upstream (7) while vapor is transferred (8) into a chamber (9) in order to finish heating the sea water.

Description

Solar thermal heat input for seawater desalination

The present invention relates to a special method for thermal heat input via solar panels in plants for the production of industrial and drinking water by means of a multi-stage distillation process according to the MSF (Mufti Stage Flash) or MED (Multi Effect Distillation) principle.

Systems based on the MSF or MED principle operate with high heat recovery by passing the inflowing seawater in series through the heat exchangers of the individual stages for condensate liquefaction, with afterheating in the amount of approximately one or two stage temperature intervals after leaving the topmost stage, or by introducing process steam into the first expansion stage. In the patent DE 3239 816 A1, a corresponding process with the devices for film and vacuum evaporation and the means for recondensation is described in detail. The heating heat is supplied, without going into the generation of more detail, via process steam introduction in the top step.

Generic systems can also be operated via thermal energy from solar systems. In solar-powered systems, a reheating of the seawater after exiting the preheating column usually takes place via coupler-type heat exchangers with media separation between the seawater circuit and the collector circuit. However, this heat exchanger is loaded on the secondary side of heavy deposits and thus maintenance-intensive. In order to keep the collector temperatures as low as possible, an attempt is made to use directly with seawater flowed through collectors. This results in the savings of the heat exchanger between seawater and collector cycle, but shifts the problem of corrosion and deposits on collectors and buffer memory. Through the development of appropriate collector materials made of plastics and composite materials, attempts are being made to minimize the problem of corrosion and deposits, and thus to enable economical use of solar energy. However, for many heat delivery systems such as solar panels or cooling circuits of heat engineering plants, the temperature of the incoming seawater from the preheating column is too high to still achieve efficient heat dissipation or the desired cooling target. This is especially true for the use of novel hybrid collectors for electricity and heat. In order to ensure appropriate cooling of the solar cells, the return temperature of the inflowing cooling medium should be substantially lower than the operating temperature of the uppermost preheating chamber. By keeping the return temperature low also results in the Advantage that buffer memory to compensate for the load fluctuations can be designed to be relatively small, since due to the difference of supply to return temperature, a higher energy storage potential is given.

The object of the present invention is now to eliminate the risk of corrosion and deposits in the collector circuit, without interposing a heat exchanger with media separation between primary and secondary circuit. In contrast to the above-mentioned solution variant, the development of special materials for collectors and buffer storage is not discussed, but a process engineering solution for avoiding direct contact of seawater in the collectors is offered. Another key objective is to keep the return temperature to the collectors low.

This is inventively achieved by a system according to the characterizing part of claim 1. In this case, distillate is removed from the preheating, passed through the (the) heat exchanger of the heater (s) and then returned to the distillate cycle of the preheating. The distillate recycling takes place either via a separate expansion chamber, or directly into one of the condensation stages of the preheating column. Crucial for the process engineering function is the admixture in the distillate stream of the preheating and not in the seawater cycle.

With this interconnection, it is possible to operate MWE systems exclusively via heating heat, to keep the return temperatures to the collectors low and to flow them through with deposit-free distillate. Depending on your preference, a wide range of combinations is possible with several heating system connections with different distillate withdrawals and returns, as well as the integration of compressor systems. Advantageous embodiments are characterized in the main claim and in the subclaims.

The basic version is to operate a system exclusively via thermal heat from thermal collectors. Distillate according to the invention is removed from the distillation column, heated in the collectors to about 115 to 165 ⁰ C and then introduced into a flash chamber with steam supply to the seawater circuit. This expansion chamber may be either the uppermost chamber of the preheating column, but may also be an outboard vapor deposition chamber via which the condensate is indirectly directed further into the uppermost chamber of the preheating column. The attachment of an external chamber fulfills the purpose of a small buffer memory to adjust load fluctuations from the collector circuit accordingly. Pressure equal to the outer distillate buffer, a chamber for the introduction of seawater and steam is connected upstream of the expansion chambers for seawater evaporation. The steam from the flash evaporation serves for the residual heating of the seawater emerging from the preheating column, which is then passed in descending order through the individual pressure stages of the flash evaporation. In order to be able to operate the system continuously during the night, a correspondingly large buffer memory is to be provided in the collector circuit, regardless of the buffer volume of the preheating column. The greater the difference between flow temperature and return temperature in the collector circuit, the smaller this buffer memory can be designed. Both from this point of view and the endeavor to keep the average collector temperature as low as possible, the distillate for the collector circuit from the bottom of the preheating column, or after emerging from the lowest stage recommended.

An extended variant provides for connecting hybrid collectors in addition to the thermal collectors. These are tracked collectors with cooled solar cells, which are acted upon by mirrors with high radiation intensity. The hybrid collectors have a supporting effect on the distillation of distillate during the day, but are mainly used to generate electricity. In symbiosis with the desalination plant these collectors can be flowed through with deposit-free distillate at a low return temperature. Depending on the feed temperature (70-100 ⁰ C), the distillate at the corresponding temperature level of the Vorwärmkolonne is recycled to the distillate stream. This invention interconnection makes it possible to use hybrid collectors for industrial purposes. As a result, hydrogen can be generated via the solar power generated by these collectors.

Another variant also provides, instead of the thermal collectors use a compressor system for the base load. In this case, steam is removed from the distillation column and brought via the compressor unit in the chamber for residual heating of the preheated seawater. The hybrid collectors can now be integrated in the manner according to the invention. For example, this concept is ideal for retrofitting existing compressor-driven systems that operate according to a staged distillation process. Large buffer tanks are not necessary because the system can be kept in continuous operation via the compressor unit in a kind of base load. In the case of large-scale plants, it is conceivable to operate the compressor unit directly via a gas turbine plant, and cooling and waste heat are distilled off via a gas turbine. flowed heat exchanger according to the interconnection of the invention in the MWE plant bring.

The invention does not relate exclusively to the above-mentioned variants, but to all possible combinations resulting from these variants. The use of the inventive method of distillate removal from the preheating, heating via one or more heaters and return to the distillate of the preheating, is limited not only to distillation plants of seawater, but also to plants for the distillation of brackish water and biologically and chemically contaminated water for custom - and drinking water production.

Further features and details of the present invention will become apparent from the following description of the figures. Showing:

Fig. 1 is a schematic representation of an MSF-MED distillation plant with several heating connections in accordance with the usual state of the art, and a connection of collectors according to the interconnection of the invention.

2 shows two calculations of an MSF distillate column, one for seawater heating via a heating device 3 and the other for distillate heating with removal from the lowest stage and heating via a heating device 1.

Fig. 3 is a schematic representation of an MSF distillation plant with heat supply via solar panels according to the general state of the art.

Fig. 4 is a schematic representation of an MSF distillation plant with the inventive connection of thermal collectors.

Fig. 5 is a schematic representation of an MSF distillation plant, with the inventive connection of thermal collectors and hybrid collectors.

Fig. 6 is a schematic representation of an MSF distillation plant with steam supply via a compressor system and a connection of hybrid collectors.

7 is an illustration of a hybrid collector in the middle section.

Fig. 1 shows a schematic representation of a MSF-MED distillation plant with several heating connections 13, 3 according to the usual state of the art, and a connection of panels 1 according to the interconnection of the invention. The different methods for heating heat input are purely for comparison purposes and are not usually united in a single system. In the upper area is a MED process can be activated via film evaporation equipment. The MED vaporization is put into operation via the compressor 12 and overlaps the normal MSF process. The MSF process can now be operated independently via different possibilities of energy input. These are as follows:

a) heating heat is introduced via process steam 13 in the uppermost stage of the distillate. b) The preheated seawater 2 is heated by a heater 3. c) Distillate is removed according to the invention from the preheating column 6 and recycled to the uppermost stage.

Variant a is usually branched off when coupled to thermal power plants with a favorable possibility of process steam. Regardless of these couplings, process steam can also be taken from the MSF column. For this purpose, a further evaporation stage is provided after the lowest condensation stage. The vapor deposited in this stage is now compressed and introduced as process steam 13 in the uppermost stage. Basically, this plant is driven by technical work by compressors.

Variant b is a typical application for heat input via thermal collectors. Basically, three options should be set forth with the heater 3. On the one hand, this can be a heat exchanger with primary-side connection of a closed collector circuit, - on the other hand, an open collector circuit with direct seawater flow. In both cases, as mentioned above, relatively high heating temperatures are present, whereby problems with deposits from the seawater are to be expected.

Variation c represents the interconnection according to the invention for heat input via collectors 1. In the limiting case, the condensate can be taken from the uppermost stage of the preheating column 6 and returned to this stage after heating in the collectors 1. In this case, the temperature in the collectors is about the same as in the case of heating with direct seawater flow, but the problem with the deposits is solved. The distillate yield 14 is lower by the proportion of condensate vaporized in the introduction into the first (uppermost) stage than in variant b. At 20 MSF levels, a distillate loss of 12% is expected. This loss is measured against the savings on maintenance quite economically justifiable. In a distillate removal 5_1 from a lower stage, the distillate yield 14 decreases in Relative to the heat energy input accordingly. The exact behavior can not be estimated easily, but can only be determined by a calculation. As it turns out, the distillate removal at the lowest point at the exit from the preheating column 6 still achieves a very high desalting performance. The explanation is given based on the following calculation results.

2 shows two computations of an MSF distillate column with distillate heating via a heating device 1, on the one hand a variant A with distillate removal from the uppermost stage, and on the other hand a variant B with distillate removal from the lowest stage. For the uppermost stage, a seawater temperature of 85 ° C is used in both cases. The supply of sea water in the Vorwärmkolonne 6 occurs by definition at a temperature of 25 ⁰ C. In both cases, the heating is carried out of the distillate in the heater 1 to a predetermined temperature of 120 ° C. When the distillate yield 14 is kept constant, a comparison of the heat to be supplied via the heating device 1 is made. As you can see, the efficiency of distillate extraction drops from variant A to variant B in about 100% to 66%. In this sense, efficiency is understood to mean the amount of distillate obtained in relation to the heat energy introduced. An essential aspect, that still a comparatively high efficiency of 66% is achieved, is explained by the fact that due to the differently sized countercurrent mass flows in the heat exchangers, less steam is needed for the residual heating of the seawater 2, since the preheating to a comparatively higher temperature ( 81 ⁰ C instead of 79 ° C) takes place. Which removal height is chosen depends on the collector behavior. High-quality thermal collectors can be coupled most efficiently to Variant A - Hybrid collectors with cooled solar cells according to Variant B. In general, there is a wide range of options for interconnecting different collector types in parallel and in series. It should also be borne in mind that with the integration of buffer storage for the night, the volume for variant B is about half as large as for variant A.

The prior art shown in Fig. 3 is a well-known process of MSF (Multi Stage Flash) distillation equipment for recovering service water according to a thermal process. The heat from the collector 1 is passed from a buffer memory 4 via a heat exchanger 3 to the preheated seawater 2.

4 shows a schematic representation of an MSF distillation plant with the inventive connection of thermal collectors 1. The removal of distillate 5_1 from the preheating column 6 for the collector circuit is carried out at a medium stage temperature. The return of the heated distillate 5_2 to the preheating column 6 takes place via an upstream expansion chamber 7 with steam supply line 8 into a condensation chamber 9 for residual heating of the seawater. The interposition of a buffer memory 4 ensures that the system can be kept in operation day and night. Apart from the pumps, the system is only driven thermally.

5 shows a schematic representation of an MSF distillation plant, with the inventive connection of thermal collectors 1 and hybrid collectors 10. The distillate decoupling 5_1 for both collector circuits takes place at the exit from the preheating column 6. From the thermal collectors 1, the heated distillate via a buffer memory 4 introduced into the expansion chamber 7. The hybrid collectors 10 pass the heated distillate 5_2 directly into one of the upper stages of the preheating column 6. Ideally, the distillate introduction is variably selectable in that stage in which approximately the temperature of the supplied distillate (5_2) prevails. Apart from the pumps, the system is only driven thermally.

FIG. 6 shows a schematic representation of an MSF distillation plant which is operated in the base load via a compressor installation 11. The connection of the hybrid collectors 10 is used primarily for power generation. According to the invention, the distillate 5_1 is withdrawn on leaving the preheating column and, after being heated by the hybrid collectors 10, is returned to one of the upper stages of the preheating column 6. Due to the low feed temperature, the hybrid collectors 11 can not independently operate the MWE plant without compressor assistance, but make a significant contribution to increasing the distillate output.

7 shows a representation of a hybrid collector in the middle section. A large part of the radiation is conducted via the mirror 15 onto a cooled solar cell module 16. The radiation reflected at the solar cells is absorbed in the thermal absorber 17. In order to cool the solar cells sufficiently, the temperature of the incoming cooling medium, in this case distillate from the preheating column, must be kept low.

In the features of the invention shown schematically in all figures, it should be noted that the individual components and leads can be made in all different variants and materials.

Claims

claims

1. Distillation plant according to the MSF (Multi Stage Flash) or MED (Multi Effect Distillation) method with solar thermal heat input, characterized in that distillate (5_1) is removed from the preheating column (6), via one or more heating devices (1, 10, ...) is heated, and then returned to the distillate cycle of the preheating column (6).

2. MSF / MED distillation plant according to claim 1, characterized in that the return of the heated distillate (5_2) takes place via an upstream chamber (7) with vapor transfer line (8) into a chamber (9) for rest warming of the seawater.

3. MSF / MED distillation plant according to one of claims 1 to 2, characterized in that the distillate removal (5_1) after exiting the preheating column (6).

4. MSF / MED distillation plant according to one of claims 1 to 3, characterized in that the introduction of the distillate (5_2) is variably switchable in different stages of the preheating column (6).

5. MSF / MED distillation plant according to one of claims 1 to 4, characterized in that a plurality of circuits for distillate heating with different removal and return points from and to the preheating column (6) are coupled.

6. MSF / MED distillation plant according to one of claims 1 to 5, characterized in that a compressor unit (11) is coupled to maintain the base load.

7. MSF / MED distillation plant according to claims 1 and 6, characterized in that hybrid collectors (10) without a buffer memory (4) to be coupled to the distillation unit.