WO2015036523A1

WO2015036523A1 - Method and arrangement for foam extinguishing

Info

Publication number: WO2015036523A1
Application number: PCT/EP2014/069469
Authority: WO
Inventors: Tomas Skoglund; Fredrik Innings; Göran Pantzar
Original assignee: Tetra Laval Holdings & Finance S.A.
Priority date: 2013-09-13
Filing date: 2014-09-12
Publication date: 2015-03-19

Abstract

A device for separating foam from gas in a deaeration process comprises a spray nozzle arranged to provide a spray curtain preventing foam from entering a vacuum outlet arranged to evacuate the gas.

Description

METHOD AND ARRANGEMENT FOR FOAM EXTINGUISHING

Technical Field

The present invention relates to separation and extinguishing of foam, in particular in relation to deaeration systems.

Technical Background

During processing of liquid foodstuff (liquid in the following) it is often desired to remove air trapped in the liquid. Air content may affect the taste, colour and shelf- life of the final product, and therefore the liquid is deaerated. The utilization of deaeration is well known, and it may be used for other liquids than liquid foodstuff, which is also true for the application of the present invention as it will be described in the present specification.

When deaerating liquids it is a common side effect that significant amounts of foam are generated. Since the final goal is a deaerated liquid, the generation of foam is a problem. Deaeration is a well known process and there are several different techniques for accomplishing it. The liquid to be deaerated is introduced into a deaeration vessel, which may be referred to as a separation vessel. In the separation vessel the pressure is very low, to the extent that for the prevailing temperature the pressure is so low that the liquid starts to boil. When boiling air, as well as other gases, trapped in the liquid will be entrained by bubbles and leave the liquid. The deaerated liquid leaves the separation vessel at a lower end thereof, while the released gases leave via a vacuum exit at an upper end of the separation vessel. In order to prevent steam from leaving the vacuum exit a condensation unit may be arranged, such that the liquid contained in the steam is returned to the bulk of liquid being deaerated.

Foam may be formed as a result of different processes and different liquids will behave differently, yet two common effects are that the foam either is generated as it is introduced to the separation vessel, or as a result of the boiling. The generated foam will be prone to follow the gases out through the vacuum exit, either by being entrained in the flow or simply since so much foam is generated so that a top portion is pushed into the vacuum exit. The foam comprises gas but also liquid, and any foam leaving through the vacuum exit corresponds to a loss of liquid, i.e. product. Wasting product in this way has the direct effect of lost product, but it also results in an increased load on purification plants. Thus there exist enough drawbacks for foam extinguishing to be an issue.

For the purpose of better understanding the problem of foam a short description of one deaeration technique is given herein below. Common approaches to extinguish foam are to reduce the pressure in the separation vessel to a pressure corresponding to 4-8 °C below the boiling point (i.e. where liquid having a temperature being 4-8 °C lower than the actual temperature in of the liquid present in the separation vessel would boil), resulting in an increase boiling of the liquid. The bubbles will become fragile and easily crack. This established technique is energy consuming. Other existing methods include the use of ultrasound pulses, hot air, etc, yet for large-scale applications these are generally not efficient enough.

The present invention aims at providing an improved method and device for extinguishing and/or separating foam.

Summary

To that end the present invention relates to a method of extinguishing foam, comprising the step of providing a local spray curtain preventing foam from entering a vacuum outlet where gas is removed. The method is performed in a separation vessel having the pressure P2 containing deaerated liquid and foam generated by the deaeration, and gas released from the liquid. The separation vessel has an inlet where the liquid to be deaerated enters and an outlet through which deaerated liquid exits, and a third exit corresponds to the already mentioned vacuum outlet. There is a benefit in the inventive way of extinguishing the foam locally instead of trying to perform a full foam extinction, which generally would be more energy demanding. According to the invention only foam trying to escape with the evacuated gases is extinguished, thus keeping the effort to a minimum.

In one or more embodiments a spray nozzle may arranged inside a vacuum line and is directed towards the vacuum outlet. The use of a spray enables a good penetration of the foam, and having the spray nozzle arranging inside the vacuum line facilitates an excellent control of the effect of the spray. There is also a natural benefit in having the spray directed towards the vacuum outlet, i.e. upstream towards the separation vessel, in that the sprayed liquid is not as readily entrained with the evacuated gas.

In one or several embodiments a spray cone formed by the nozzle is arranged to be symmetrical and to match a diameter of the vacuum outlet such that the entire outlet is covered. Using a conical spray, and preferably a hollow cone, is an efficient way of obtaining a good coverage of the, generally though not necessarily, cylindrical vacuum line. To obtain a match of the diameter basically translates to not having the spray nozzle arranged to close to the vacuum outlet. For each cone angle there will be a position for the nozzle where the perimeter of the cone will impact the perimeter or the vacuum outlet. In one or more embodiments the nozzle is not arranged closer to the outlet than where the perimeter of the cone will impact the perimeter or the vacuum outlet. The nozzle may be arranged further downstream the vacuum pipe, i.e. farther away from the vacuum outlet, though not necessary it may still be an added advantage to have it as close to the vacuum outlet as possible.

In one or more preferred embodiments the spray nozzle is fed with already deaerated liquid, and this liquid may be collected from deaerated liquid having left the deaeration vessel already. Using deaerated liquid removes the risk of diluting or polluting the contents of the separation vessel.

In one or more embodiments a feed line may be arranged between the spray nozzle and a position downstream a pump arranged in the outlet line. In this way the necessity of an extra pump for building spray pressure may not exist. Rather, it may be preferred to add an adjustable valve to the feed line in order to tune the performance of the spray nozzle.

Brief Description of the Drawings

Fig. 1 is a schematic layout of a first embodiment of the present invention.

Fig. 2 is a detailed view showing an alternative embodiment.

Detailed Description

In Fig. 1 there is shown a general layout of a device 100 involving a first embodiment of the present invention. Several of the components shown in Fig. 1 are optional, so it actually corresponds to a combination of several embodiments. Starting from the upstream position the product to be deaerated is fed through a feed line 102, to the left in the drawing. The pressure PI may generally be elevated in the feed line 102, compared to atmospheric in general and compared to a pressure P2 inside the separation vessel 104 in particular. In fact, the pressure inside the separation vessel 104 is typically residing in an area of 0-10 °C above the boiling point of the product/liquid contained in the separation vessel (again meaning that if the temperature of the liquid in the separation vessel increased by 0-10 °C the liquid would start to boil). Preferably the temperature may be 0-5 °C above the boiling point, or the lower part of the interval may even vary between 0.1- 1 °C above the boiling point to ensure that no boiling occurs. A nucleation valve 106 or, using a more general expression, an expansion valve 106 separates the feed line 102 from the separation vessel 104, and as the product passes the expansion valve 106 it will experience a sudden pressure drop, either causing the product to flash boil or to the generation of gas bubbles in the product. The pressure drop represents the initiation of deaeration, and as the product enters the separation vessel the partly deaerated product 108 will collect at the bottom of the separation vessel 104 while the released gases 110 will reside in the remaining part of the tank 104. An interface surface is depicted by a delimiter line 112. The deaerated product 108 will be pumped out through an exit 114 at the bottom of the tank 104 and the gases will be evacuated through an arrangement 116 in the top of the separation vessel, driven by a vacuum pump (not shown). The arrangement 116 may in the one embodiment merely comprising a pipe extending from the separation vessel 104.

A side effect of the deaeration process is that considerable amounts of foam, indicated at 118, will be generated, a side effect that is unwanted for several reasons, as previously mentioned in the background section.

Extinguishing of the foam may merely imply that the foam is separated from the rest of the product flow, yet in most cases it is desired to extinguish the foam such as to capture the product bound thereto. In that sense the present application will relate to both separation of foam (from product) and to extinguishing foam.

According to the first embodiment of the present invention foam 118 trying to escape the separation vessel 104 via the gas outlet 115 and the arrangement 116 is sufficiently prevented from this by the arrangement of a spray curtain 128 formed from a liquid spray covering the outlet. "Covering" should be construed as that there is essentially no way for the foam to enter through the arrangement 116 without passing the spray curtain 128, and the spray curtain will extinguish the foam or at least prevent to foam from entering the arrangement 116. Consequently, instead of extinguishing the foam in the entire separation vessel, the spray curtain 128 will extinguish the foam locally, only in the area where it is necessary. In the preferred embodiment a nozzle 126 is arranged inside the arrangement 116 (e.g. inside a vacuum line) and sprays towards the gas outlet 115. This will make the bubbles burst while gas may pass through. The gas continues towards the vacuum pump, the path indicated by the arrow V.

The spray may be provided as a spray cone which either touches upon the arrangement 116 in the area of the opening (as illustrated in Fig. 1) or, in other embodiments, impacts with a circumferential wall of the arrangement 116 further downstream. This is schematically illustrated in the detail view of Fig. 2. The suggested approach will readily provide an adequate extinguishing of foam in an area where it is the most needed.

From Figs. 1 and 2 it is apparent that the liquid sprayed with the nozzle 126 ends up in the separation vessel. It is therefore desired that that the spray liquid does not interfere with the product being deaerated. This may be accomplished in several ways, yet a solution is to use the actual product being deaerated in the tank. Another solution may be to use another liquid not interfering with the product, such another liquid may be sterile water. In the embodiment of Fig. 1 this is accomplished by pulling deaerated liquid from a position downstream the outlet 114, preferably downstream a pump 124 in which way a separate pump for providing the spray is made redundant. The pipe 122 transporting the deaerated liquid may be provided with valve 132 means in order to tune the flow, a functionality which also may be provided by the nozzle 126. It is often the case that the pressure immediately downstream the pump 124 is more than enough to drive the spray, yet if necessary an additional pump (not shown) may be added to the line 122. In other embodiments one or more components of the liquid product is used as spray liquid.

Having described the invention, and a few embodiments thereof in detail it is important to emphasize that the context of deaerators, materials used, components used etc. are considered to be well known. For that reason the detailed description has focused on the gist of the invention. Still the examples given are examples only, and they should not be construed as limiting to the present invention as defined by the claims to follow.

Claims

1. A method of extinguishing foam, comprising the steps of, in a separation vessel having the pressure P2 containing deaerated liquid and optionally foam generated by the deaeration as well as gas released from the liquid,

providing a spray curtain preventing foam from entering a vacuum outlet (115) through which gas is evacuated.

2. The method of claim 1, wherein a spray nozzle is arranged inside a vacuum line used to evacuate gas from the separation vessel and directed towards the vacuum outlet.

3. The method of any preceding claim, wherein a spray cone formed by the nozzle is arranged to be symmetrical and positioned to match a diameter of the vacuum outlet such that the outlet is covered.

4. The method of any preceding claim, wherein the spray curtain is arranged such that a spray cone impacts onto the walls of the arrangement (116) leading downstream from the vacuum outlet (115).

5. The method of any preceding claim, further comprising the step of feeding the spray with deaerated liquid.

6. The method of claim 5, further comprising the step of collecting the deaerated liquid in an outlet line leading from the separation vessel and leading it to the spray nozzle via a feed line (122).

7. A device for separating foam from gas in a deaeration process, comprising a spray nozzle arranged to provide a spray curtain preventing foam from entering a vacuum outlet arranged to evacuate the gas.

8. The device of claim 7, wherein a vacuum line (116) extends from the vacuum outlet, and wherein the spray nozzle is arranged inside the vacuum line.

9. The device of claim 8, wherein the spray nozzle is arranged concentrically in the vacuum line.

10. The device of any one of claims 7-9, wherein the spray nozzle is arranged to provide a spray the direction of the vacuum outlet.

11. The device of any one of claims 7-10, where the spray curtain is a cone- shaped spray, preferably in the form of a hollow cone.

12. The device of claim 11, wherein the nozzle is arranged such that the cone- shaped spray impacts the walls of the vacuum line adjacent the vacuum outlet or upstream thereof.

13. The device of any preceding claim, wherein the spray nozzle is fed with deaerated liquid, preferable deaerated liquid collected downstream an outlet for deaerated liquid leaving the separation vessel.