Cleaning a multi-effect evaporator

Abstract

A method and system for cleaning a multistage evaporator, the evaporator having a normal operational mode and a cleaning mode and having at least two groups of effects (2, 4), each group having one or more effects. In a normal operational mode, input vapor is introduced to a first group of effects (2), the first group comprising the hottest effects, and then vapor is delivered from the first group to a second group of effects (4), and optionally, from the second group of effects to a third group of effects (6) and so on depending on the total number of effects. Upon detection of a predetermined level of scale formation in the first group of effects, the evaporator is switched to a cleaning mode wherein the first group of effects (2) is physically separated from the other groups of effects and the input vapor is re-directed into the second group of effects (4). A cleaning agent is introduced into the physically separated first group of effects (2) until a predetermined level of cleanliness is achieved.

Claims

1. A method for cleaning a multistage evaporator, the evaporator having a normal operational mode and a cleaning mode and having at least a first group of effects and a second group of effects, each group having one or more effects, the first group of effects and the second group of effects being provided within a single chamber, a shutter being provided within the chamber to physically separate the first group of effects from the second group of effects, wherein in the operational mode, input vapor is introduced to the first group of effects, the first group of effects comprising the hottest effects; and vapor is delivered from the first group of effects to the second group of effects within the chamber; the method of cleaning comprising: In the cleaning mode, physically separating the first group of effects from the second groups of effects by shutting the shutter; re-directing the input vapor into the second group of effects during physical separation of the first group of effects; and introducing a cleaning agent into the physically separated first group of effects.

2. A method as claimed in claim 1, further comprising physically re-joining the first group of effects to the second group of effects, once a predetermined level of cleanliness has been achieved, and re-directing the input vapor back to the first group of hottest effects to resume the normal operational mode.

3. A method as claimed in claim 1, wherein the second group of effects comprises the group of effects nearest to the first group of hottest effects.

4. A method as claimed in claim 1, wherein input vapor is supplied on an input line, the method further comprising opening a valve provided between the input line and the second group of effects to re-direct input vapor to the second group of effects.

5. A method according to claim 1, comprising at least one further group of effects, the normal operational mode and cleaning mode comprising delivering the vapor from the second group of effects to the third group of effects within the chamber.

6. A method as claimed in claim 1, wherein each of the one or more effects is held at a different pressure than any other effect in the one or more effects.

7. A multi-effect evaporator having a normal operational mode and a cleaning mode, the evaporator comprising: At least a first group of effects and a second group of effects, each having one or more effects, the first group comprising the hottest group of effects; the first group of effects and the second group of effects being provided within a single chamber, an input inlet for introducing vapor to the first group of effects and wherein vapor is delivered from the first group of effects to the second group of effects within the chamber; wherein in the operational mode, input vapor is introduced by the input inlet to the first group of effects, the first group of effects comprising the hottest effects; and vapor is delivered from the first group of effects to the second group of effects; and wherein to provide a cleaning mode a shutter is provided within the chamber to physically separate the first group of effects from the second group of effects, the input inlet is operable to introduce vapor to the second group of effects during the physical separation of the first group of effects from the second group of effects, and the first group of effects is provided with a secondary inlet for the delivery of a cleaning agent to the first group of effects during the cleaning mode.

8. A multi-effect evaporator as claimed in claim 7 wherein a control unit is provided to switch the multi-effect evaporator from the normal operational mode to the cleaning mode when a predetermined level of scaling is detected in the first group of effects and/or to switch the multi-effect evaporator from the cleaning mode to the normal operational mode when a predetermined level of cleanliness is detected in the first group of effects.

9. A multi-effect evaporator as claimed in claim 7, wherein the second group of effects comprises the group of effects nearest to the first group of hottest effects.

10. A multi-effect evaporator as claimed in claim 7, comprising an input line to supply input vapor to the input inlet, and a valve provided between the input line and the second group of effects to re-direct in vapor to the second group of effects.

11. A multi-effect evaporator as claimed claim 7, comprising at least one further group of effects, wherein vapor is delivered from the second group of effects to the third group of effects within the chamber.

12. A multi-effect evaporator as claimed in claim 7, further comprising a vapor compressor to supply input vapor to the input inlet.

13. A multi-effect evaporator as claimed in claim 12, wherein the vapor compressor is a thermos-compressor, mechanical or other vapor compressor.

14. A multi-effect evaporator as claimed in claim 7, wherein each of the one or more effects is held at a different pressure than any other effect in the one or more effects.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention shall now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic diagram of a multi effect evaporator according to one embodiment of the present invention;

(3) FIG. 2 is a schematic diagram of a multi effect evaporator according to another embodiment of the present invention; and

(4) FIGS. 3a and 3b are schematic diagrams of a multi effect evaporator according to yet another embodiment of the present invention, shown in a normal operational mode and a cleaning mode respectively.

DETAILED DESCRIPTION

(5) The present invention relates to an improved method of cleaning multi effect evaporator and to an evaporator having a normal operational mode and a cleaning mode.

(6) FIG. 1 of the accompanying drawings provides a schematic drawing of a multi-effect evaporator according to one embodiment of the present invention. The evaporator has an input stream for delivering hot feed water, such as sea water, to a first effect 2 (or group of effects). Water is evaporated in the effect and the vapour is delivered to the next effect (or group of effects) 4 which is held at a lower pressure than the last. The boiling temperature of water decreases as pressure decreases, so vapor evaporated in one vessel can be used to heat the next. Vapor produced in the second effect 4 then passes to a third effect (or group of effects) 6 before the final product is removed from the system.

(7) It is to be appreciated that three effects, or group of effects, are shown in the accompanying figures but the evaporator may include more effects, or groups of effects or only two effects or groups of effects, i.e. a hot and a cold effect or group of effects.

(8) The first group of effects (or single effect) is subjected to the hottest temperatures and thus scale formation is greatest in this group/effect. Therefore, the present invention provides the evaporator with a cleaning mode wherein the first effect or group of effects are physically separated from the other groups of effects at periodic intervals. This is achieved by shutting of the taps 10, 12 and opening of tap 14 so that the input stream is redirected into the second effect or group of effects 4 with the first effect, or group of effects, being isolated from the rest of the evaporator. A cleaning agent is then introduced into the physically separated first group of effects (2) by opening a tap 20 in a cleaning agent fluid line until a predetermined level of cleanliness is achieved.

(9) Once a predetermined level of cleanliness has been achieved in the first effect (or first group of effects) the taps 20 and 14 are shut and taps 10 and 12 re-opened so that the input stream is re-directed back to the first group of hottest effects (2) to resume the normal operational mode.

(10) FIG. 2 illustrates one embodiment for providing the physical separation between the hottest effect, or group of effects 2, and the adjacent or second effect 4. The hottest effect 2 is provided in a separate chamber 200 and the second and further effects (or group of effects) are housed within another chamber 400. The chambers 200, 400 are connected by pipework that is sealable with a tap 12 to allow temporary physical separation of the first group of effects from the second and subsequent group of effects. In this manner, during normal operation, the taps 10 and 12 are open and tap 14 is shut so that the input stream passes feed into the first group of effects 2 and vapor passes from the first group along the pipeline to the second group of effects 4 and from the second group of effects to the third groups of effects 6. In the cleaning mode, taps 10 and 12 are shut and tap 14 opened thereby redirecting the input stream directly into the second group of effects 4 housed in the second chamber 400. Bypassing of the chamber 200 enables the first group of effects, which will experience the worst scaling, to be cleaned by introducing cleaning agent by opening a separate cleaning fluid pipeline having tap 20.

(11) The apparatus preferably includes a control unit (not shown) which monitors scale build-up in the first effect, or group of effects, to switch the multi-effect evaporator from the normal operational mode to the cleaning mode when a predetermined level of scaling is reached and/or to switch the multi-effect evaporator from the cleaning mode to the normal operational mode when a predetermined level of cleanliness is detected in the first group of effects.

(12) FIGS. 3a and 3b illustrate another embodiment of the present invention wherein the at least three effects, or groups of effects, are provided in a single chamber 300 which has means, such as a slidable shutter, for sealing the first part of the chamber housing the first effect, or group of effects 2 from the second and third effect, or group of effects 4,6. FIG. 3a shows the shutter in the open configuration and the evaporator is able to perform in the normal operational mode with feed being delivered to the first effect 2 before the second and then third effects. When a predetermined level of scaling is detected in the first effect (or group of effects), the evaporator is switched into cleaning mode causing the shutter to shut and seal off the part of the chamber 300 that contains the first effect (or group of effects) to allow temporary physical separation of the first group of effects from the other effects, as shown in FIG. 3b. This part of the chamber can then be cleaned while the other part of the chamber, containing the other effects, or group of effects, continues to operate normally.