EP1791790A1

EP1791790A1 - Seawater desalination plant

Info

Publication number: EP1791790A1
Application number: EP05785071A
Authority: EP
Inventors: Peter Szynalski
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-09-17
Filing date: 2005-09-14
Publication date: 2007-06-06
Also published as: DE112005002873A5; MX2007003302A; AU2005284554A1; US20080017498A1; ZA200702018B; WO2006029603A1

Abstract

The invention relates to a seawater desalination plant comprising a cascade of evaporation bodies which are connected by a line system which guides the sea water containing salt. Each cascade can be impinged upon by low pressure. The seawater is guided to the evaporation bodies after having flown through the cascades, such that it can be successively evaporated. In order to improve the energy balance of the plant, an arrangement of heat exchangers (WT) is placed at least in the supply line of the sea water and a water pump (WP) is connected to one or several heat exchangers (WT).

Description

MEERWASSERENTSALZUHGSANLAGE

The invention relates to a seawater desalination plant.

It is known to operate seawater desalination plants, for example with the multi-stage flash method (MSF), which are based on the principle of vacuum evaporation: In order to use the required energy efficiently, commercial desalination processes are developed so that the distillation process is repeated in several stages becomes. Gradually, the pressure and temperature levels are lowered from level to level.

The inflowing salt water (saline feedwater) is heated after a small chemical treatment to prevent deposition, progressively in the preheating section (tube bundle heat exchanger) and reaches the end heater (Brine Heater). Within the final superheater, the water with the aid of Wär¬ meenergie (usually water vapor at 90 ⁰ C - heated 110 ⁰ C. A higher temperature is not desirable because, in particular, calcium sulfate (CaSO4) to solve at 115 ⁰ C from the salt water and heavy deposits. cause the system to be shut down.

The heated water is now forwarded to the first evaporation stage, de¬ ren ambient pressure is reduced, that a part of the water ver¬ flashes (flashing). At the tube bundle heat exchanger, the water vapor condenses and additionally heats the countercurrent salt water. The resulting distillate is collected and discharged separately. The remaining Brine is pumped further into the following boiler, where the same process takes place again at lower pressure and temperature levels.

Typical MSF plants have between 15 and 25 stages and produce between 4,000 - 100,000 m ³ / d fresh water. Another method for desalination of seawater is the multi-effect distillation (MED) and the methods based on reverse osmosis on a membrane (reverse osmosis or RO) in question.

The following should be noted about the energetic and economic assessment of seawater desalination plants.

Most of the large-scale seawater desalination plants built are distillation plants which require low-pressure steam as the heat source. From a thermodynamic and economic point of view, it therefore makes sense to combine seawater desalination plants and power plants in combined plants in which the high-pressure steam produced is used to produce electrical current in the turbo-generator , and the low pressure steam exhaust steam is used to supply the distillation plant.

The construction and operation of such a combined plant with power plant and seawater desalination require large financial expenditures. The operators must take into account many relevant factors if the technically and economically best plant combination is selected, and a fair apportionment of the total production costs in electricity and drinking water production costs is to take place.

The following table can help in the energetic assessment of seawater desalination processes:

In the energetic analysis, the membrane process (RO) is significantly better than the thermal processes (MSF, MED), since only in the case of the Distillation process thermal energy is needed. The bandwidths given in the table depend on the type of installation and the size of the installation, because with increasing system efficiency (system type) and increasing steam volume (system size), the specific energy requirement decreases.

The following table can help in the economic assessment of seawater desalination processes:

When considered economically, the membrane process (RO) does not score significantly better than the thermal process MED, since the maintenance costs are lower in the distillation processes. The filters used in the membrane process only have a lifespan of five years, which leads to high costs. The bandwidths given in the table do not depend on the type of installation and the size of the installation but on the type of energy used (gas, oil, nuclear energy).

For the process selection in the conception of a seawater desalination plant, therefore, different things have to be considered.

Based on the above-mentioned aspects, the selection criteria for the selected project goal can now be formulated.

1. Desalination of seawater to the highest possible state of purity

2. Energy consumption at the lowest possible level

3. Use of a good practice 4. Dimensioning option for medium consumption

5. Production possibility by means of freely accessible technology

6. Process improvement through new technologies For thermal processes, the following arguments speak:

- point 1, since a residual salt content of <50 ppm can be achieved,

- point 3, since as a proven technology in use for about 50 years, - point 4, because the required sizing procedures are now very mature, and

- Point 5, as there is a lot of background experience in the necessary metalworking.

For reverse osmosis procedures, the following argument holds:

- According to point 2, only electrical energy is necessary, but with the disadvantage of high running costs for maintenance and continuous operation, which is especially critical for small system sizes.

Finally, the choice is determined by the use of new techniques for process improvement. The technique of combined heat and power plants and heat pumps introduced in recent years is crucial for the selection of the MSF process as the basis of a new MSDP (Medium Size Desalination Plant) concept.

The task for the invention results from the improvement of the known processes for the production of drinking water from seawater (seawater desalination), in particular with regard to energy and the creation of a cost-effective and efficiently operated plant.

The solution of the problem is designed according to the features of claim 1 (method) and claim 10 (device).

In the subclaims advantageous developments are called. The further remarks describe a system with MSF technology for desalting salt, a downstream heat pump and a combined heat and power plant for generating the necessary thermal and electrical energy for operating the MSF stages and the necessary pumps and control devices.

The plant can thus be operated independently up to the supply of fossil fuels. A support or even complete operation by solar energies is possible. By suitable dimensioning a delivery of electrical energy is conceivable.

In the following, the invention is illustrated by way of example by way of drawings.

1 shows a scheme for vacuum evaporation,

FIG. 2 shows a schematic representation of the seawater desalination plant according to the invention,

FIG. 3 shows a table for the thermodynamic analysis of an MSF

Cascade, Figure 4 is a diagram of a heat pump,

FIG. 5 shows a diagram of a block heating station,

Figure 6 is a diagram for energy transport and

Figure 7 is a diagram for heat recovery.

The plant concept according to the invention is as follows.

The plant is based on the method of evaporation in order to allow desalting as free of residue as possible. As a basic method, the stepwise expansion or multi-stage flash technology is used: The construction of a chamber for Vakumverdampfung is shown in Figure 1. Here are represent: Seawater inlet: Seawater (salt water) coming from the previous stage, which forces the condensation of the steam in the heat exchanger

Seawater outlet heated seawater (salt water) is sent to the next stage

Residual water input coming from the previous stage, partially evaporated seawater, which is further evaporated

Residual water outlet: cooled, partially evaporated seawater, which could not be evaporated and is passed on to the next stage

Vacuum pump: Supply line to the vacuum pump, which supplies the necessary vacuum for evaporation via a control valve

To compensate for the inherent disadvantages of low volume compared to current systems, a heat pump and a cogeneration plant is used in heat energy generation, which have been developed in recent years technically crucial importance. The cogeneration plant is currently available as standard in heating systems and can provide heating energy and electricity at low cost through high efficiency. By utilizing environmental energy, the heat pump can reduce the necessary heating demand and is supplied with electrical energy by the combined heat and power plant. The combined heat and power supplies, etc. also the power for pumps, control systems .. The heat pump preferably operates at temperatures up to 6O ⁰ C, des¬ semi it is to be used very effectively in the lower stages of MSF chambers to reduce the temperature differences.

As improvements over conventional systems are

Dimensioning to actual needs, i. no overproduction Small footprint - advanced energy use

Use of the latest technologies in the heat exchanger sector Operation as a stand-alone station without otherwise necessary power station

Technical detail improvements

Use of energy recovery by the heat pump - Alignment of the temperature curves in the expansion stages between evaporation and heat recovery by condensation, thus avoiding losses Highly effective heat recovery through state-of-the-art heat exchangers

In the following, the functionality of the entire plant for seawater desalination is shown in a block diagram.

FIG. 2 shows the block diagram of a seawater desalination plant with a diesel generator DS, a heat pump WP and a few heat exchangers WT connected in the circuit. The heat exchanger WT are integrated in the liquid circulation of a cascade of cascade tanks K1, K2, Kn. The cascade container K1, K2, Kn are connected via pressure regulator DR with a vacuum pump VP, which generates the negative pressure for the evaporation of the seawater. The heat pump WP and the vacuum pump VP are operated by means of an energy station ES. The diesel generator DS generates the necessary electrical energy. The resulting heat energy is transferred via a heat exchanger WT to the liquid circuit for further heating of the seawater. The diesel generator DS can be coupled with systems for the use of solar energy and / or boil-off heat

The invention is based on the additional heat transfer from the raw water by means of the heat pump WP to the water to be heated in the cascade sections K1, K2, Kn. This saves heating energy and significantly increases the efficiency of the process. Furthermore, the heat pump WP can be switched and coupled to heat exchangers WT in such a way that the residual energy contained in the pure water is removed. taken and introduced into the heating process of the seawater (see Fig. 2). Thus, the necessary cooling can be supported on the withdrawal side of the pure water. At the same time, the surplus energy is used to minimize the energy required to heat up the seawater through energy sources.

Finally, a combination of the methods is possible by the heat pump WP is coupled as a preferably multi-stage arrangement on Wärmetau¬ shear WT both on the energy extraction side with the piping system of the raw water (seawater) and with the line system of pure water. For this purpose, several heat pumps WP can be used.

As a heat exchanger WT, tube bundle heat exchangers can be used here in a particularly advantageous manner, which are provided with an efficient heat transferring filler. This makes possible an improved forwarding of the heat to be recovered.

The special effect of the system can be demonstrated by a thermodynamic analysis.

The table according to FIG. 3 shows the thermodynamic analysis of an MSF cascade. The table shows the values for the thermodynamic analysis of an MSF cascade. Here, the seawater temperature rises when passing through 10 cascade stages from 31 to 89 degrees C. The temperature increase from stage to stage is 5 - 6 degrees C.

The heat pump used for the plant is of known type. FIG. 4 shows the functional diagram of a heat pump. The heat pump is integrated as a per se known assembly in the field of seawater desalination plant. In this case, it is driven by the electric supply by means of a diesel generator. This can be part a combined heat and power plant.

A station for power generation is designed as a diesel generator DS. FIG. 5 shows the functional diagram of a diesel generator DS. The diesel generator DS supplies the required heat energy for the operation of the MSF stages and the electric power for the heat pump WP, the vacuum pump VP and the entire system. This is thus, in addition to the required fuel, completely self-sufficient, and can also be operated away from developed areas.

The construction of the diesel generator is described in more detail in FIG. The figure contains the elements

1. Heating water heat exchanger

2. Exhaust gas heat exchanger 3. Lubricating oil cooler

4 cooling water pump

5. Exhaust silencer

6 .. gas engine

7. Generator 8. Control cabinet

9. Lubricating oil tank

10. Starter battery

11. Soundproof hood

An extension of the seawater desalination system according to the invention results from heat pump arrangements.

By expanding the previously described concept of a simple passage, it is envisaged to build a closed circuit. It is necessary to recycle the heat energy supplied on the hot side of the seawater desalination plant on the cold side of the seawater desalination plant, otherwise the necessary temperature difference for the return condensation can not be applied. Therefore, the heat pump WP cold water side is fed from the outlet of the cascade K1 of the evaporator. The heat pump WP hereby cools the cleaned water and transports the - otherwise lost - energy back to the hot side of the K2 kas, Kn evaporator. There, the energy thus gained is available again for heating the seawater to be purified. Thus, a significant energy saving is made possible. While in previous systems, the Küh¬ treatment is carried out using fresh water and the energy is thus discharged into the sea and thus lost.

FIGS. 6 and 7 show the energy balance of such a system. FIG. 6 shows that the evaporation energy can be recovered from the condensation energy. The temperature increase necessary for the evaporation is applied by means of introduced evaporation energy. At the same time condensation energy is released again during the condensation of the pure water, whereby the temperature drops again. Although both processes take place at different temperature levels, the energy released can be used to replace the required energy. In the form according to the invention, this is utilized according to FIG. 7 in that a heat pump is integrated in the region of the discharge of the pure water via a heat exchanger (see FIG. 2). The energy obtained there can be introduced into the cascade section for heating the water to be evaporated. FIG. 7 shows the temperature reduction of the seawater via the cascade stages (condensation stages). The temperature of the pure water reached at the end of the cascade stages is further lowered via a heat exchanger of the heat pump. The amount of heat gained is introduced by means of the heat pump at an elevated temperature level in addition - and at the same time reduction - the necessary heating power for the evaporation wie¬ in the cascade stages.

Claims

claims

1. desalination plant with a cascade of Verdampfungskör¬ pern, one of these salty seawater feeding line system, each cascade can be acted upon by a negative pressure and / or includes a heater, wherein the seawater is fed to the evaporation bodies after passing through the cascades, so that the Meer¬ water is successively evaporated, and a cascade pure water ent¬ taking second conduit system, characterized by the arrangement of heat exchangers (WT) in the supply line of Meer¬ water and a heat pump (WP), which connected to one or more of the heat exchanger (WT) is.

2. seawater desalination plant with a cascade of Verdampfungskör¬ pern, one of these salty seawater feeding line system, each cascade can be acted upon by a negative pressure and / or includes a heater, the seawater is fed after passing through the cascades the evaporation bodies, so that the sea water is successively evaporated, and a cascade pure water ent¬ taking second conduit system, characterized by the arrangement of heat exchangers (WT) in the area of removal of the still warm pure water and their connection to a heat pump (WP), with one or more heat exchangers ( WT) in the field of

Supply of still unheated or teilerhitztem sea water is coupled.

3. seawater desalination plant according to claim 1, characterized in that the heat pump (WP) has a heat exchanger (WT) in the region of

Removal of the still warm pure water with a heat exchanger (WT) coupled in the supply of still unheated seawater.

4. seawater desalination plant according to claim 1 to 3, characterized in that the heat pump one or more heat exchangers in the field of

Removal of the still warm pure water with a heat exchanger in the supply of already teilerhitztem sea water between two cascades coupled.

5. seawater desalination plant according to claim 1 to 3, characterized in that a heat exchanger (WT) is coupled in the region of the supply of largely er¬ heated seawater with a heat generator.

6. seawater desalination plant according to claim 5, characterized in that the heat generator is a diesel generator (DS).

7. seawater desalination plant according to claim 1 to 6, characterized in that the heat pump is operated by means of the diesel generator (DS) generated e- lectric energy.

8. seawater desalination plant according to claim 1 to 6, characterized in that a highly efficient Rohrbündelwärmetau shear with heat-transferring filler is used as the heat exchanger (WT).