GB2403432A

GB2403432A - Distillation apparatus and method

Info

Publication number: GB2403432A
Application number: GB0412816A
Authority: GB
Inventors: Scott Alexander Barrie
Original assignee: Weir Westgarth Ltd
Current assignee: VWS Westgarth Ltd
Priority date: 2003-06-25
Filing date: 2004-06-09
Publication date: 2005-01-05
Anticipated expiration: 2024-06-09
Also published as: GB2403432B; GB0314805D0; GB0412816D0

Abstract

An apparatus 100 for removing at least a portion of a solute from a solution comprises a flash distillation plant 90 and a multiple-effect distillation plant 95, wherein condensed steam 20 exhausted from the heat input section 12 of the flash distillation plant is fed to the first effect 54 of the multiple-effect distillation plant to heat the solution. The apparatus is particularly for use in a process for desalination of sea water. The steam exhausted from the first effect may be returned to a boiler via a heat recovery steam generator. This arrangement increases the efficiency of the apparatus.

Description

DISTILLATION APPARATUS AND METHOD

FIELD OF INVENTION

The present invention relates to an improved apparatus and method for distillation, and in particular, but not exclusively, to an apparatus and method for desalination of sea water to produce potable water using combined multiple-stage flash distillation and multiple effect distillation processes.

BACKGROUND TO THE INVENTION

There are a number of locations throughout the world which have a shortage of natural potable water and which therefore require methods of producing potable water artificially. Due to the abundance of sea water, one of the preferred methods includes water desalination which involves removing the salt and other solutes from the sea water.

A number of desalination techniques are available but the general principle is the same, that is, most techniques involve a distillation process wherein sea water is vaporized and then condensed as fresh water.

Examples of distillation processes include: high temperature distillation such as flash distillation, multiple-stage flash distillation or multipleeffect distillation; low-temperature distillation such as waste heatrecovery distillation; and mechanical distillation such as vapour compression.

Like most industrial processes, every effort is made to ensure that plant efficiency is optimized, that is, providing an increased fresh water output for a minimised energy input with minimum energy wastage. However, there is often a compromise in situations where there is a demand for large quantities of fresh water and in such cases optimizing energy efficiency may be difficult to I achieve.

It is among the objects of the present invention to provide an improved apparatus and method of water desalination.

SUMMARY OF INVENTION

According to a first aspect of the present invention, there is provided an apparatus for removing at least a portion of a solute from a solution, said apparatus including a flash distillation plant and a multiple-effect distillation plant in combination, wherein condensed steam exhausted from a heat input section of the flash distillation plant is fed to a first effect of the multiple-effect distillation plant to drive the multipleeffect distillation plant. 3;

According to a second aspect of the present invention, there is provided an apparatus for removing at least a portion of a solute from a solution, said apparatus comprising: a steam source; a flash distillation plant; and a multiple-effect distillation plant, wherein steam supplied from the steam source is fed to a heat input section of the flash distillation plant to heat the solution for use in the flash distillation I process, and condensed steam exhausted from the heat input section is fed to a first effect of the multiple effect distillation plant to heat the solution for use in the multiple-effect distillation process.

It should be understood that condensed steam as used herein refers to steam which has given up some of its heat energy, for example, to heat the solution in the heat input section of the flash distillation plant.

Preferably, the flash distillation plant is a multiple-stage flash distillation plant.

Advantageously, the apparatus of the present invention is adapted for removing salt and other solutes from sea water to produce potable water.

In a flash distillation plant, the heat input section is generally referred to a brine heater.

Advantageously, the steam source may be steam exhausted from a gas turbine generator power plant wherein water is heated in a boiler to produce steam which is passed through gas turbine units to generate electricity. Alternatively, the steam source may be a direct steam source from a boiler or the like.

Preferably, condensed steam exhausted from the first effect of the multiple-effect distillation plant is returned to the boiler. Advantageously, where the steam source is exhausted steam from a power plant, the condensed steam exhausted from the first effect is returned to the boiler via a heat recovery steam generator apparatus. With such an arrangement, utilizing the heat from the steam exhausted from the power plant will result in an overall lower condensate temperature which will improve the overall efficiency of the entire system by reducing the outlet temperature of the heat recovery steam generator apparatus.

In conventional flash distillation plant, the condensate from the heat input section is returned to the boiler where it is reheated and returned to the heat input section, either directly or indirectly via a power plant or the like. However, in use, the present invention utilises this condensate as the heating medium for a multiple-effect distillation plant which results in an increase in water production for a given mass of steam consumed, resulting in an overall increase in system efficiency.

Advantageously, the present invention provides an increase in water output of preferably around lot while requiring substantially no additional energy input than is required for a conventional flash distillation plant.

In one embodiment of the present invention the multiple-effect distillation plant may be located remotely from the flash distillation plant.

Conveniently, the multiple-effect distillation plant may be retro-fitted to an existing flash distillation plant to provide an apparatus in accordance with aspects of the present invention. In this way, the efficiency of a flash distillation plant can be improved with little interference to the flash distillation process.

Preferably, the condensed steam exhausted from the heat input section of the flash distillation plant is fed to the first effect of the multipleeffect distillation plant by at least one condensate pump and via insulated pipe-work. Thus, although an additional energy input may be required to drive the condensate pumps, the increased water output using the otherwise spent condensed steam to drive the multiple-effect distillation plant still increases the overall system efficiency.

According to a third aspect of the present invention, there is provided a method of removing a solute from a solution, said method comprising the steps of: supplying steam to a heat input section of a flash distillation plant to heat a solution to be distilled in a flash distillation process; and supplying condensed steam exhausted from the heat input section to a first effect of a multiple-effect distillation plant to heat a solution to be distilled in a multiple-effect distillation process.

Preferably, the method is adapted for use in removing salt and other solutes from sea water to produce

potable water.

IS Preferably also, the flash distillation plant is a multiple-stage flash distillation plant.

Conveniently, the steam may be supplied from a steam source such as a boiler or the like. Alternatively, the steam may be supplied from an exhaust of a gas turbine power plant.

Preferably, the method further comprises the step of returning the condensed steam exhausted from the multiple-effect distillation plant to be re-heated and supplied to the heat input section of the flash distillation plant.

In one embodiment of the present invention, steam enters the heat input section of the flash distillation plant at a temperature of around 115 to 120 degrees Celsius. Conveniently, condensed steam is exhausted from the heat input section and enters the first effect of the multiple-effect distillation plant at a temperature of around 100 to 120 degrees Celsius.

According to a fourth aspect of the present invention, there is provided a combined power and desalination apparatus, said apparatus comprising: a steam source; a power plant; a flash distillation plant; and a multipleeffect distillation plant, wherein steam supplied from the steam source is initially fed to the power plant to drive a generator and produce electricity, steam exhausted from the power plant being fed to a heat input section of the flash distillation plant to heat the solution for use in the flash distillation process, and condensed steam exhausted from the heat input section is fed to a first effect of the multiple-effect distillation plant to heat the solution for use in the multiple-effect distillation process.

Preferably, the apparatus further comprises a heat recovery steam generator unit which utilises condensed steam exhausted from the multipleeffect distillation plant.

Conveniently, the flash distillation plant is a multiple-stage flash distillation plant.

According to a fifth aspect of the present invention, there is provided a multiple-effect distillation plant adapted to be coupled to an exhaust of a flash distillation plant, wherein condensed steam from the exhaust of the flash distillation plant is utilised to drive the multiple-effect distillation plant.

According to a sixth aspect of the present invention, there is provided a multiple-effect distillation plant adapted to receive condensed steam from an exhaust of a flash distillation plant, wherein said condensed steam is utilised to drive the multiple effect distillation plant.

Conveniently, the input of a first effect of the multiple-effect distillation plant is adapted to receive condensed steam exhausted from the flash distillation plant.

According to a seventh aspect of the present invention, there is provided a method of improving potable water output from a water distillation process, said method comprising delivering condensed steam exhausted from a flash distillation plant to a multiple effect distillation plant to drive said multiple-effect distillation plant.

According to an eighth aspect of the present invention, there is provided an apparatus for supplying condensed steam exhausted from a flash distillation plant to a first effect of a multiple-effect distillation plant.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure l is a diagrammatic representation of a known multiple stage flash distillation plant; Figure 2 is a diagrammatic representation of a known multiple-effect distillation plant; Figure 3 is a diagrammatic representation of a desalination apparatus in accordance with an embodiment of the present invention; Figure 4 is a block diagram representation of the desalination apparatus shown in Figure 3; and Figure 5 is a block diagram representation of a desalination apparatus in accordance with an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is first made to Figure 1 in which there is shown a diagrammatic representation of a known multiple-stage flash (MSF) distillation plant, generally indicated by reference numeral 10, used to remove salt and other solutes from sea water.

In the MSF plant 10, sea water or brine is heated in a heat input section or brine heater 12 wherein the brine passes through a bank of tubes 14 upon which steam condenses, thus heating the brine within the tubes 14.

The steam is supplied from a source 16 such as a boiler plant or a steam exhaust stream from a power plant or the like. The steam enters the brine heater at 18 and condensed steam exits the brine heater 12 at 20, wherein the condensed steam is returned to the boiler or the like to be reheated and recycled.

The brine is heated at atmospheric pressure and once leaving the brine heater 12 the brine is flowed into a first stage 22 which is maintained at a pressure lower than atmospheric such that when the heated brine enters the first stage 22 of the MSF plant 10, a portion will be immediately vaporised or flashed, dropping out the salt and other solutes contained therein. Thus, the flash distillation process utilises the fact that the boiling temperature of a liquid reduces as the ambient pressure is reduced. The vaporized brine is then condensed on a cooling tube bundle 24 and the condensate, which will be distilled potable water, is run-off.

The brine which remains in the liquid phase and which has cooled is then fed to a second stage 26 which is maintained at a lower pressure than the first stage 22 such that vaporization will again occur at a lower temperature, and the produced vapour will be condensed on a further cooling tube bundle 28. This process is then repeated through a number of stages until substantially all the brine supplied to the MSF plant 10 is flash distilled.

As noted above, in each stage the vaporized brine is condensed on a cooling tube bundle 24, 28, through which brine flows from a brine source 30 to the brine heater 12. Thus, the brine acts as the cooling medium for the tube bundles 24, 28 and is consequently pre-heated before entering the brine heater 12, resulting in improved overall heat transfer to the brine and improved plant efficiency.

Reference is now made to Figure 2 of the drawings in which there is shown a diagrammatic representation of a known multiple-effect distillation (MED) plant, generally indicated by reference numeral 50, used to remove salts and other solutes from sea water.

Steam 52 is supplied to a first effect or cell 54 of the MED plant 50 where the steam flows through a tube bundle 56. This first effect 54 is maintained at a pressure below atmospheric such that when brine is sprayed 58 into the first effect 54, contact with the tube bundle 56 will result in thin film vaporization of a portion of the brine, thus dropping out a portion of the salt and other solutes therefrom. The vaporization of the brine on the tube bundle 56 will condense the steam 52 flowing therethrough, which steam will further be condensed by the unvaporised brine 60 collected within the first effect 54. The condensed steam is removed from the first effect 54 and returned to a boiler plant or the like to be reheated and reused in the MED plant 50.

The vaporized brine 62 from the first effect 54, which will be lower in temperature than the steam 52 supplied to the first effect 54, is then fed to a second effect 64 where the vaporized brine flows through a second tube bundle 66. This vaporized brine 62 therefore acts as a heating medium to vaporise additional brine ]3 sprayed 68 into the second effect 64 of the MED plant 50.

To ensure that the additional brine sprayed 68 into the second effect 64 is vaporized, the second effect 64 is maintained at a lower pressure than the first effect 54.

Vaporisation of the additional brine in the second effect 64 results in condensation of the vaporised brine 62 flowing through the tube bundle 66, wherein the condensed brine 62 is run off as distilled potable water 70. The vaporised brine 72 in the second effect 64 is flowed to a third effect or cell 74 where the vaporization process is repeated, which process is continued through the required number of effects, with each subsequent effect being maintained at a progressively lower pressure and producing condensed distilled water which is run off for consumption.

Vaporised brine 76 from the final effect 77 of the MED plant 50 is flowed through a heat exchanger 78 where it is used to pre-heat inlet brine 80 which is to be supplied to the effects of the plant 50 to be sprayed over the corresponding tube bundles. Pre-heating the brine 80 in this way assists to improve the overall efficiency of the MED plant 50 and also condenses the vaporized brine 76 from the final effect 76.

Referring now to Figure 3, an embodiment of a desalination apparatus in accordance with the present invention will be described. The desalination apparatus, generally indicated by reference numeral 100 in the diagrammatic representation of Figure 3, includes an MSF plant 90, somewhat similar to that as shown in Figure 1, and an MED plant 95, similar to that as shown in Figure 2, in combination. For convenience, the components of the apparatus 100 of Figure 3 share the same reference numerals with those like components of Figures 1 and 2.

As described above with reference to Figure 1, condensed steam 20 exiting the brine heater 12 of an MSF plant 10 is conventionally returned to the boiler or the like to be reheated and recycled. However, in the embodiment of the present invention shown in Figure 3, condensed steam from an MSF plant 90 is fed, via condensate pumps 102 and insulated pipes 104, to the first effect 54 of an MED plant 95. Thus, the heat in the condensed steam 20 exhausted from the MSF plant 90 is used to drive the MED plant 95, without the requirement for any additional energy input. This novel and inventive combination of MSF and MED plants 90, 95 by using the condensed steam 20 as the heating medium for the MED plant 95 results in an increase in water production for a given mass of steam consumed, thus increasing the overall system efficiency.

As shown in Figure 3, the condensed steam 106 is returned to be reheated and recycled.

Reference is now also made to Figure 4 of the drawings in which there is shown a block flow diagram representation of the desalination apparatus 100 as shown in Figure 3. In the embodiment shown, steam 112 is produced in a boiler plant 114 and is fed to a multiple stage flash (MSF) distillation plant 90 where the steam is used to heat brine for use in a multiple-stage flash distillation process. Condensed steam 20 exhausted from the MSF plant 90 is fed to the first effect of a lO multiple-effect distillation (MED) plant 95 where it is used to heat brine for use in a multiple-effect distillation process. Finally, condensed steam 106 from the MED plant 95 is returned to the boiler plant 114 to be reheated and recycled in the desalination apparatus 100.

An embodiment of a desalination and power apparatus in accordance with an aspect of the present invention is shown in Figure 5, wherein the apparatus is generally identified by reference numeral 130. In this embodiment, steam 132 is produced in a boiler plant 134 and is expanded through a gas turbine generator 136 to produce electricity. The exhausted steam 138 from the power plant 136 is fed to a multiple-stage flash (MSF) distillation plant 140 where it is used to heat brine in a brine heater (see Figure 1) to produce potable water.

The condensed steam 142 exhausted from the brine heater of the MSF plant 140 is supplied to a multiple-effect distillation (MED) plant 144 where it is used to vaporise brine in a first effect (see Figure 2) and to drive the MED plant 144 to produce additional potable water.

Exhausted condensed steam 146 from the MED plant 144 is then used to drive a heat recovery steam generator (HRSG) unit 148 in order to produce additional electricity.

Finally, condensed steam 150 is returned to the boiler plant 134 to be reheated and recycled in the apparatus 130.

It should be understood that the embodiments hereinbefore described are merely exemplary of the present invention, and that various modifications may be made thereto without departing from the scope of the invention.

Claims

CLAIMS: 1. An apparatus for removing at least a portion of a solute from a

solution, said apparatus including a flash distillation plant and a multiple-effect distillation plant in combination, wherein condensed steam exhausted from a heat input section of the flash distillation plant is fed to a first effect of the multiple-effect distillation plant to drive the multiple-effect distillation plant.
2. An apparatus for removing at least a portion of a solute from a solution, said apparatus comprising: a steam source; a flash distillation plant; and a multiple-effect distillation plant, wherein steam supplied from the steam source is fed to a heat input section of the flash distillation plant to heat the solution for use in the flash distillation process, and condensed steam exhausted from the heat input section is fed to a first effect of the multiple effect distillation plant to heat the solution for use in the multiple-effect distillation process.
3. An apparatus as claimed in claim 2, wherein the flash distillation plant is a multiple-stage flash distillation plant.
4. An apparatus as claimed in claim 2 or 3, adapted for removing salt and other solutes from sea water to produce

potable water.
5. An apparatus as claimed in claim 2, 3 or 4, wherein the steam source is steam exhausted from a gas turbine generator power plant.
6. An apparatus as claimed in claim 2, 3 or 4, wherein the steam source is a direct steam source.
7. An apparatus as claimed in any one of claims 2 to 6, where the steam source is provided from a boiler.
8. An apparatus as claimed in claim 7, wherein condensed steam exhausted from the first effect of the multiple-effect distillation plant is returned to the boiler.
9. An apparatus as claimed in claim 7 or 8, wherein condensed steam exhausted from the first effect is returned to the boiler via a heat recovery steam generator apparatus.
10. An apparatus as claimed in any one of claims 2 to 9, wherein the multiple-effect distillation plant is located remotely from the flash distillation plant.
11. An apparatus as claimed in any one of claims 2 to 10, wherein the multiple-effect distillation plant is lO adapted to be retro-fitted to an existing flash distillation plant.
12. An apparatus as claimed in any one of claims 2 to 11, wherein condensed steam exhausted from the heat input section of the flash distillation plant is fed to the first effect of the multiple- effect distillation plant by at least one condensate pump.
13. An apparatus as claimed in any one of claims 2 to 12, wherein condensed steam exhausted from the heat input section of the flash distillation plant is fed to the first effect of the multiple- effect distillation plant via insulated pipe-work.
14. A method of removing a solute from a solution, said method comprising the steps of: supplying steam to a heat input section of a flash distillation plant to heat a solution to be distilled in a flash distillation process; and supplying condensed steam exhausted from the heat input section to a first effect of a multiple-effect distillation plant to heat a solution to be distilled in a multiple-effect distillation process.
15. A method as claimed in claim 14, adapted for use in removing salt and other solutes from sea water to produce

potable water.
16. A method as claimed in claim 14 or 15, wherein the flash distillation plant is a multiple-stage flash distillation plant.
17. A method as claimed in claim 14, 15 or 16, wherein the steam is supplied from a steam source.
18. A method as claimed in claim 17, wherein the steam source is a boiler.
19. A method as claimed in claim 17 or 18, wherein the steam source is an exhaust of a gas turbine power plant.
20. A method as claimed in any one of claims 14 to 19, S further comprising the step of returning condensed steam exhausted from the multiple-effect distillation plant to be re-heated and supplied to the heat input section of the flash distillation plant.
21. A method as claimed in any one of claims 14 to 20, wherein steam supplied to the heat input section of the flash distillation plant is at a temperature of around to 120 degrees Celsius.

Is
22. A method as claimed in any one of claims 14 to 21, wherein condensed steam exhausted from the heat input section is supplied to the first effect of the multiple effect distillation plant at a temperature of around 100 to 120 degrees Celsius.
23. A combined power and desalination apparatus, said apparatus comprising: a steam source; a power plant; a flash distillation plant; and a multiple-effect distillation plant, wherein steam supplied from the steam source is initially fed to the power plant to drive a generator and produce electricity, steam exhausted from the power plant S being fed to a heat input section of the flash distillation plant to heat the solution for use in the flash distillation process, and condensed steam exhausted from the heat input section is fed to a first effect of the multipleeffect distillation plant to heat the solution for use in the multipleeffect distillation process.
24. A combined power and desalination apparatus as claimed in claim 23, further comprising a heat recovery steam generator unit which utilizes condensed steam exhausted from the multiple-effect distillation plant.
25. A combined power and desalination apparatus as claimed in claim 23 or 24, wherein the flash distillation plant is a multiple-stage flash distillation plant.
26. A multiple-effect distillation plant adapted to be coupled to an exhaust of a flash distillation plant, wherein condensed steam from the exhaust of the flash distillation plant is utilised to drive the multiple effect distillation plant.
27. A multiple-effect distillation plant as claimed in claim 26, wherein the input of a first effect of the multiple-effect distillation plant is adapted to receive condensed steam exhausted from a flash distillation plant.
28. A multiple-effect distillation plant adapted to receive condensed steam from an exhaust of a flash distillation plant, wherein said condensed steam is utilised to drive the multiple-effect distillation plant.

IS
29. A method of improving potable water output from a water distillation process, said method comprising delivering condensed steam exhausted from a flash distillation plant to a multiple-effect distillation plant to drive said multiple-effect distillation plant.
30. An apparatus for supplying condensed steam exhausted from a flash distillation plant to a first effect of a multiple-effect distillation plant.