EP0100328A1

EP0100328A1 - A method and means for reducing the need for energy supplied to distallation processes

Info

Publication number: EP0100328A1
Application number: EP83900443A
Authority: EP
Inventors: Björn ELMER
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-01-20
Filing date: 1983-01-18
Publication date: 1984-02-15
Also published as: WO1983002445A1; SE429647B; AU1110083A; SE8200293L

Abstract

Procédé de réduction des besoins en énergie fournie à des procédés de distillation, notamment dans le dessalement d'eau salée, se caractérisant par le fait que l'énergie thermique du distillat (11) et des résidus (12) formés lors du procédé est réduite en faisant passer le distillat et les résidus au travers d'un évaporateur (7) faisant partie d'un système séparé de pompe thermique (5, 6, 7(8, 9)), qui transfère l'énergie thermique au liquide brut (1) à distiller. Ce processus est effectué dans un dispositif du type comprenant au moins une colonne pourvue d'une zone de condenseur (2) et d'une zone d'évaporation (3), la zone de condenseur possédant un orifice d'entrée (1) pour le liquide brut et un orifice de sortie (4) pour le condensat et où est disposée, reliée à la colonne de distillation, une pompe thermique (5, 6, 7 (8, 9)), dont l'évaporateur (7) possède des conduites de sortie (11, 12) pour le condensat et le liquide résiduel, qui les traversent respectivement, le condenseur (5) de la pompe thermique étant traversé par le milieu à distiller avant ou après son orifice d'entrée à la zone d'évaporation (3).Method for reducing the energy requirements supplied to distillation processes, in particular in the desalination of salt water, characterized in that the thermal energy of the distillate (11) and of the residues (12) formed during the process is reduced by passing the distillate and residue through an evaporator (7) which is part of a separate heat pump system (5, 6, 7 (8, 9)), which transfers thermal energy to the raw liquid ( 1) to distill. This process is carried out in a device of the type comprising at least one column provided with a condenser zone (2) and an evaporation zone (3), the condenser zone having an inlet orifice (1) for the raw liquid and an outlet (4) for the condensate and where is arranged, connected to the distillation column, a heat pump (5, 6, 7 (8, 9)), whose evaporator (7) has outlet lines (11, 12) for the condensate and the residual liquid, which pass through them respectively, the condenser (5) of the heat pump being traversed by the medium to be distilled before or after its orifice for entering the zone d 'evaporation (3).

Description

A method and means for reducing the need for energy supplied to distillation processes

Background of the invention

The present invention relates to a method and means for reducing the need .for energy supplied to distillation processes, especially in the desalination of salt water.

Desalination of sea water may be accomplished in many different ways. In the most commonly used processes- the water is heated to evaporation, whereupon the salt-free water vapor is made to condens and the condensate, which consists of fresh water, is then collected in a convenient manner separate from the salty residual liquid in the distillation vessel.

In the production of fresh water from sea water, the theoretical " minimum amount of energy necessary to distil water from a salt solution of constant salinity corresoonds o to a temperature increase of 0.4 to 0.6 C (depending upon the salinity, temperature and pressure at which the distillation takes place), i.e. 1 kg of fresh water has an energy level which is about 0.4 to 0.6 kcal higher than 1 kg of water in a 3-4 % salt solution.

The theoretical energy requirement to gain 1 ton of fresh o water from two tons of a 3.43 % saltsolution at 25 C is

0.97 kWh, if in other words half the amount of raw water is transformed to distilled water, which as a comparison, corresponds to the heating of one gained ton of fresh water o by about 0.83 C, or that the same amount of water is pumped vertically upwardly a distance of 356 m.

In the production of fresh water from sea water in large plants of the multistage type, the energy used is between 120 and 50 kcal/kg of distillate (i.e. 240 - 100 times the theoretical minimum) , and in plants of the vapor compression type, which are used only to a limited extent in smaller units, it is possible to get down to about 15 kcal/kg of distillate i.e. about 30 times the theoretical minimum. This is largely due to the fact that both the end products and c the residues leave the plant with a surplus temperature.

Due to the amount of energy required in practise in the desalination of sea water, the costs will be comparatively high, especially since there is often no cheap energy •_]_ available at places where the need of fresh water has to be filled by means of the distillation of sea water.

The object and main caracteristics of the invention

τ_5 The invention has for its object to provide a method of reducing the need for energy supplied to distillation processes, especially in the desalination of salt water, whereby the energy requirement may by considerably reduced while maintaining the production capacity. This has been

20 achieved in that the heat energy of the distillate and the residues, formed in the process, is lowered by passing both the distillate and the residues through the evaporation part of a separate heat pump, where the heat is given of, and that heat energy is transferred from said heat pump to the

25 medium to be distilled by passing said medium through the condensor of the heat pump.

The invention also comprises means for performing the method according to the inventio.n and of a kind comprising at least

30 one column with an evaporation zone provided with an inlet for raw liquid and with a condensor zone with an outlet for condensate, an the means is caracterised by a heat pump system with a separate energy transportation medium and the evaporator of which has out-going conduits for product 2 liquid and for residue liquid passing therethrough, whereas the condensor of the heat pump is passed through by the raw liquid conduit before the inlet of the raw liquid into the evaporation zone. Description of the drawings

The invention will be more closely described herebelow with referens to the embodiments diagra atically illustrated in figures 1 and 2 of the accompanying drawings.

Description of embodiments

Figure 1 shows, in diagrammatic form, an embodiment of a device for the distillation of liquids, for instace for the desalination of sea water, and this device comprises at least one. column to which raw water to be distilled is fed at 1. The raw water is passed in a conduit through a condensor two disposed in the upper portion of the column and will there take up heat energy in connection with condensation. The column also comprises an evaporator 3 to which the preheated raw water is sprayed. In the. evaporator 3 which is preferably disposed below the condensor 2 there will preferably be a sufficient low pressure for the raw water sprayed into the evaporator to boil, whereat the heat supplied by the preheating in the condensor 2 will be utilized for the evaporation, while at the same time the low temperature will reduce the risk of fur deposits.

The vapor thus formed in evaporator 3 will condensate in the condensor 2, and the condensate will leave the column through a condensate outlet 4. The raw liquid which thus has been supplied with condensation heat in the condensor 2, is transported from the condensor to the evaporator 3 by the intermediary of a heat exchanger 5 constituting the condensor of a heat pump system which forms a closed system separate from the distillation system and which also comprises an apparatus part 6 with compressor and valve and a second heat exchanger 7, which serves as the evaporator of the heat pump. The heat pump 5, 6, 7 may also take up heat from a third heat exchanger 8, an evaporator which takes up heat from some heat source (not shown) which is accesi in the vicinity and suitable from economical point of view, for instance solar heat, heat from surface sea water of a comparatively high temperature, cooling water etc.

The raw water may be supplied with further heat energy from the heat generated by the heat pump and its driving means e.g. cooling water and exhaust gases from a diesel engine which drives the heat pump (in the drawings symbolised by the conduit 10 and the heat exchange/condensor 9) .

The condensate from the product outlet 4 is passed via a conduit 11 through the heat exchanger/evaporator 7 and, furthermore the recidual liquid is passed through a conduit 12 which likewise passes through the heat exchanger/evaporator 7. The condensate and the recidual liquid will leave the heat exchanger with substantially the same temperature after giving of heat energy in the heat exchanger/evaporator 7.

A condition pertaining to the plant in its entirety should be that the temperatures of the product condensate and the residual liquid behind the evaporator 7 of the heat pump should be approximatly equal to, or even lower than, the temperature of the incoming raw liquid 1.

In the case that the distillation is most economical at a sub-atmospheric pressure, the column is prodived with a gas collecting chamber 13, intended to collect gases disolved in the raw liquid which do not condensate on the condensor 2 but have to be collected and pumped out by the aid of an evacuation pump 14. At the same time the pump 14 will maintain a sub-atmospheric pressure suitable for the process.

The pump 14 may also increase the efficiency of the plant if it handles a larger quantity of gas than the minimum of what is needed for removing gases disolved in the water, whereby the through-flow will increase through the condensor zone 2. The pump 14 will thereby transport water vapor to a further heat exchanger/condensor 15 where the energy will be transferred to the raw water which thereafter will proceed to the evaporator 3. (In this case the pump 14 will also serve as a heat pump) . If the liquid condensed in the heat exchanger/condensor 15 is sufficiently clean, it will be supplied after the separation and removal of non-condensing gases, to the product water and removed through the product conduit 11.

In the example illustrated in figure 1 there may also be provided in the column a low pressure pump 16 with a pump motor 17, said pump being provided for the purpose of considerably increasing the rate of evaporation and condensation and thereby increasing the amount of product water per hour if necessary. The pump is of a well known type with a large volume capacity at a low pressure differential.

Figure 2 is a diagram of a modified embodiment of a device according to the invention. As in the previously described device this device comprises at least one column with a raw water inlet 21 which passes in to and through a condensor 22 in the upper portion of the column. The raw water thus heated by condensation taking place in the condensor is thereafter conducted to a spray ramp 23a through which the raw water is sprayed out into an evaporator provided in the lower portion of the column. A sub-atmospheric pressure is maintained in this evaporator which will cause the raw liquid sprayed into the evaporator to be evaporated, whereat the vapor will flow upwardly and will be at least partly condensated as product water in the condensor 22 from which the water is removed from the column through a product water outlet 24.

In the evaporator there is also provided a first heat exchanger 25 which serves as the condensor in a heatpump system comprising a heatpump 26 with a valve and a second heat exchanger 27 which operates as the evaporator of the heat pump. The heat pump may also take up heat from a third heat exchanger 28 which in turn takes up heat from an external heat source (not shown) in the vicinity.

Additional heat, energy may be supplied to the process by heat generated by the heat pump with its driving means, e.g. heat from cooling water and from exhaust gases from a diesel engine which drives the heat pump and which is symbolised in the drawing by the fourth heat exchanger 29 provided in the evaporator.

The condensator from the product outlet 24 is conducted via a conduit 31 through the heatexchanger/evaporator 27 and, furthermore, the residual liquid is conducted through a conduit 32 which likewise passes through the heat exchanger/evaporator 27. Thereafter, the condensate and the recidual liquid will leave the heat exchanger 27- with substantially the same temperature after - having given of heat .energy in the heat exchanger.

A condition pertaining to the plant in its entirety should be that the temperatures of the product condensate and the recedual liquid behind the evaporator 27 of the heat pump should be substantially equal to, or even lower than the temperature of the incoming raw liquid 21.

In the same as in the embodiment according to figure 1 the column is provided in its upper portion with a gas collecting chamber 33 which communicates with the product water conduit 31 via an evacuation pump 34. In the conduit between the evacuation 34 and the product water conduit 31, there is provided a further heat exchanger 35 in which water vapor from the gas collecting chamber 33 will be condensed. In similarity with the above-mentioned first and second heat exchangers 25 and 29, resp. the heat exchanger 35 is provided in the evaporator space, so that the heat exchangers contribute to the evaporation of the raw water sprayed into the evaporator. Furthermore, as in the device according to figure 1, a sub-atmospheric pressure contributing to the evaporation is maintained in the evaporator portion 23 by the aid of the evacuation pump 34 and also by the aid of a low pressure pump 36 with motor 37 disposed in the column.

Thus the device according to figure 2 differs from the one according to figure 1 substantially only in that the heat exchangers 25, 29 and 35 are adapted to give of there heat inside the evaporator 23 instead off to the raw water conduit as is the case in the embodiment of figure 1. By the design illustrated in figure 2 the device may be made more compact than is the case according to figure 1.

In both embodiments the evaporator may be filled with filling elements in order t.o increase the active surface in the evaporator 3,23.

According to the invention a heat pump system separate from the distillation system is used for transferring heat energy from the end product, residual liquids and possibly from surrounding heat energy sources to the heating side. Since the heat pump is capable of transferring many times larger amount of energy from a lower to a higher temperature level than what has to be supplied to the pump in the form of mechanical energy, and since furthermore, the pump is capable of utilizing its own heat losses, the energy gain will increase correspondingly compared to if the energy supplied to the heat pump should be directly utilized for heating.

Through this invention heat energy at a low temperature in the end products residual products leaving the plant is utilized by means of a heat pump, and this energy as well as a large portion of its own energy consumption including suitable energy from the surrounding is used in the process. Due to its nature the invention may also be applied to most of already existing plant.

In the desalination of sea water the heat energy of the fresh and salt water leaving the plant is utilized by the aid of a heat pump, so that this heat energy, together with the heat generated by the heat pump and its driving means, may be utilized in the process at an increased temperature level.

This also means that it will be possible to have the distillate and residues leaving the plant at lower temperatures than they had at the entry into the plant. The difference in energy represented by the lowering of temperature between the incoming raw liquid and the outgoing product and residues will then be utilized for gaining pure water from the salt water.

If this alternative is chosen, it will be possible also to utilize the heat energy of e.g. the surrounding or adjacent ocean as additional energy in the process.

The invention has been described in connection with plants for the desalination of sea water but is not limited thereto but may be applied also to other types of liquid distillation. Also, the invention is not limited to the embodiments shown in the drawings and described with reference thereto, but modifications are possible within the scope of the appended claims.

Claims

1. A method reducing the need for energy supplied to distillation processes, especially in the desalination of

5 salt water, c h a r a c t e r i z e d i n that the heat energy of the distillate and the residues formed in the process is lowered by passing both the distillate and the residues through the evaporation part 0 (7:27) of a separate heat pump, where heat is given of, and that energy is transferred from said heat pump (5,6,7(8,9) ;25,26,27(28,29) ) to the medium to be distilled by passing said medium through the condensor (5,25) of the heat pump. 5

2. A method according to claim 1 c h a r a c t e r i z e d i n that the heat energy of the distillate and the residues is lowered at least to the extent that their temperature when 0 leaving the process will be substantially equal to the temperature of the incoming raw liquid.

3. A method according to claim 1 c h a r a c t e r i z e d i n 5 that the temperature of the distillate and the residues is lowered to a level lower than the temperature of the incoming raw liquid.

4. A method according to any of claims 1 - 3 _Q C h a r a c t e r i z e d i n that water vapor which escapes (14,34) at the upper portion (13,33) of the process vessel is pumped to a heat exchanger (15,35) wherein the medium to be distilled is heated, whereat the water vapor condensed in this heat exchanger is supplied to a condensate conduit.

5. A method according to anyone of the preceding claims c h a r a c t e r i z e d i n that the heat pump (5,6,7;25,26,27) takes up additional heat from adjacent heat sources (8:28).

6. A method according to anyone of the preceding claims c h a r a c t e r i z e d i n that heat energy from the driving means (6;26) of the heat pump (5,6,7(8,9) ;25,26,27 (28,29) ) and heat energy generated by the heat pump itself is supplied to the medium to be distilled when said medium passes the heat exchanger/condensor (9;29).

7. Means for reducing the need for energy supplied to distillation processes in accordance with the method claimed in claim 1 and of the kind comprising at least one column provided with a condensor zone (2;22) and an evaporation zone (3 23) , the condensor zone having an inlet (1;21) for raw liquid and an outlet (4;24) for condensate c h a r a c t e r i z e d b y a heat pump system (5,6,7(8,9) ;25,26,27(28,29) ) with a separate transportation medium, the evaporator (7;27) of said heat pump system having outgoing conduits (11,12;31,32) for product liquid and recidual liquid, respectively, passing therethrough whereas the condensor (5;25) of the heat pump is arranged to having the medium to be distilled to pass therethrough and to give of heat to said medium.

3. Means according to claim 7, c h a r a c t e r i z e d i n that the medium to be distilled further passes through heat exchangers (9,15;29,35) for the supply of further heat to said meduim.

9. Means according to claim 7 or 8, c h a r a c t e r i e d i n that the raw liquid conduit passes through the condensor (5) of the pump and possibly through said further heat exchangers (9,15) before the inlet of the raw liquid into the evaporation zone (3) .

10. Means according to claim 7 or 8, σ h a r a c t e r i z e d i n that the condensor (25) of the heat pump and possibly also said further heat exchangers (29,35) are provided in the evaporation zone (23) .