WO2017046145A1

WO2017046145A1 - A flash vessel arrangement

Info

Publication number: WO2017046145A1
Application number: PCT/EP2016/071664
Authority: WO
Inventors: Tomas Skoglund
Original assignee: Tetra Laval Holdings & Finance S.A.
Priority date: 2015-09-17
Filing date: 2016-09-14
Publication date: 2017-03-23

Abstract

The invention relates to a flash vessel (10) arrangement for cooling a product flow comprising particles. The flash vessel (10) arrangement comprises a flash vessel (10) and an inlet pipe (20) fluidly connected to the flash vessel (10). The inlet pipe (20) is arranged to guide the product flow to the flash vessel (10). The flash vessel (10) arrangement further comprises a first throttle valve (30) arranged in the inlet pipe (20), the first throttle valve (30) being arranged to induce a first pressure drop of the product flow in the inlet pipe (20). The flash vessel (10) arrangement further comprises a second throttle valve (32) arranged downstream of the first throttle valve (30), the second throttle valve (32) being arrange to induce a second pressure drop of the product flow in the inlet pipe (20).

Description

A FLASH VESSEL ARRANGEMENT

Technical field

The present invention relates to a flash vessel arrangement for cooling a product flow comprising particles, and to a system for sterilizing and cooling a product flow comprising particles. The present invention also relates to a method for cooling a product flow comprising particles.

Background of the invention

In food processing industry, product flows are sometimes sterilized by using sterilization steam in order to the heat the product flow above the sterilization temperature and subsequently keep it at such temperature for a sufficiently long time. The product flow may e.g. be sterilized by indirect contact with the sterilization steam, e.g. by transferring the heat of the sterilization steam to the product flow in some kind of heat exchanger system, or by direct contact e.g. by injecting the sterilization steam into the product flow. In the latter case, the sterilization steam is added to the product flow, which results in an increased mass flow.

After the product in the product flow has been sterilized, it is often desirable to cool down the product flow, e.g. to a temperature being similar to that before the sterilization. In cases of direct steam sterilization as described above, it is also desirable to remove water corresponding to the added steam before the product flow is transferred to other downstream processing steps (such as e.g. packaging and transporting).

In order to solve the above two problems, i.e. to cool down the product flow and to remove a portion of the water in the product flow corresponding to the added sterilization steam, a flash vessel may be used. In a flash vessel, the static pressure is typically lower compared to the upstream processes (such as e.g. in a sterilization process). By having a static pressure lower than the vapor pressure of water at the desired outlet temperature of the product flow, water in the product flow may be evaporated and removed from the product flow, while the remaining portion of the product flow is cooled down (e.g. due to heat required by the evaporation). The static pressure of the flash vessel is typically achieved by a vacuum system having a vacuum pump, and the static pressure of the product flow is typically decreased by throttling the product flow in a throttle valve on its way to the flash vessel.

However, as the throttle valve typically reduced the flow cross sectional area, the velocity of the product flow is increased. The increased velocity of the product flow, especially if the product flow comprises particles, may damage the pipe and/or the throttle valve and/or the flash vessel.

Hence, there is a generally desire to improve the process of cooling down the product flow in a flash vessel in a way that reduces the risk of having the pipe, the throttle valve and/or the flash vessel damage by particles in the product flow. There is thus a need for improving the state of the art to provide arrangements and methods for cooling the product flow which at least partly solves these problems. Summary of the invention

It is an object of the present invention to improve the current state of the art, to solve the above problem and to provide an improved arrangement and/or method for cooling down a product flow. These and other objects are achieved by a flash vessel arrangement, a system and a method for cooling down a product flow comprising particles.

According to a first aspect of the present invention, a flash vessel arrangement for cooling a product flow comprising particles is provided. The flash vessel arrangement comprises:

a flash vessel,

an inlet pipe fluidly connected to said flash vessel, said inlet pipe being arranged to guide the product flow to said flash vessel;

a first throttle valve arranged in said inlet pipe, said first throttle valve being arranged to induce a first pressure drop of the product flow in said inlet pipe,

wherein said flash vessel arrangement further comprises

a second throttle valve arranged downstream of said first throttle valve, said second throttle valve being arrange to induce a second pressure drop of the product flow in said inlet pipe. Hereby, the static pressure of the product flow can be reduced to that of the flash vessel in at least two stages. Thus, by having at least two throttle valves arranged on the inlet pipe, the decrease in static pressure of the product flow can be better controlled and more adapted to the requirements of the surrounding components. For instance, the local peak velocity of the product flow inside the throttle valves will be lower, as the minimum cross sectional area of the throttle valves can be made larger as compared to having only one throttle valve (i.e. as compared to the case of decreasing the static pressure of the product flow in only one stage). Hence, particles in the product flow will have a lower local peak velocity and upon their impact with surrounding components inside the inlet pipe and/or any one of the throttle valves, will cause less damage.

It should be noted that, in addition to cool the product flow, the flash vessel is also arranged to separate a portion of the water in the product flow (i.e. the portion of the product flow which is evaporated).

It should be understood that the first and the second throttle valves are arranged to reduce the static pressure of the product flow prior to the product flow enters the flash vessel.

It should be understood that by stating that the second throttle valve is arranged downstream of the first throttle valve, the second throttle valve is arranged closer to the flash vessel as compared to the first throttle valve (i.e. the product flow will first pass through the first throttle valve and subsequently the second throttle valve as it is transferred to the flash vessel).

According to at least one example embodiment, said first and said second throttle valves are arranged such that said first pressure drop of the product flow is substantially the same as said second pressure drop of the product flow.

Hereby, the local peak velocity in the flash vessel arrangement (such as e.g. inside the throttle valves) can be kept close to its minimum. The adaptation of the throttle valves depends on the throttle valves chosen, and is known to a person skilled in the art. For example, in embodiments where each of the throttle valves comprises a contraction, the size of the contraction is varied such that the two pressure drops are essentially equal. However, according to at least one alternative example embodiment, said first and said second pressure drop together make up a combined induced pressure drop, and said first pressure drop of the product flow is between 25 % - 75 % of the combined induced pressure drop.

That is, the second pressure drop make up for the remaining part of the combined induced pressure drop, i.e. it is also between 25 % and 75 %.

Hereby, the local peak velocity of the product flow in the first and the second throttle valves may be adapted. For example, in cases when letting the first throttle valve induce a larger part of the combined induced pressure drop (e.g. 75 % of the combined induced pressure drop), the local peak velocity of the first throttle valve will be higher compared to the local peak velocity of the second throttle valve chosen to occur at the first throttle valve or at the second throttle valve

According to at least one example embodiment, said flash vessel arrangement comprises a vacuum pump for generating a sub-atmospheric static pressure inside said flash vessel, and an outlet pipe for transporting the product flow out from said flash vessel. The vacuum pump may e.g. be used at the startup of the process i.e. in order to generate an initial sub- atmospheric static pressure. After the sub-atmospheric static pressure has been reached, and further into the process of cooling down the product flow, the sub-atmospheric static pressure may be generated by a condenser. In the latter case, the vacuum pump may function as a condenser pump for removing condensate and non-condensable gases.

Hereby, the static pressure inside the flash vessel can be adapted to the desired static pressure, while the product flow, preferably in liquid form, can be transported out from the flash vessel and further downstream to other processes.

According to at least one example embodiment, said vacuum pump is arranged to generate a flash vessel static pressure of approximately 0.3-0.8 bar. According to at least one example embodiment, said vacuum pump is arranged to generate a flash vessel static pressure of approximately 0.5 bar. Hereby, the outlet product flow from the flash vessel typically adopts a temperature close to 80 °C, being the temperature of saturated liquid at 0.5 bar (81 .35 °C).

According to at least one example embodiment, said flash vessel arrangement comprises at least one additional throttle valve arranged between said first and said second throttle valves, or arranged downstream of said second throttle valve.

Hereby, the static pressure of the product flow can be reduced in at least three stages. Thus, the local peak velocity in the throttle valves can be further decreased.

According to at least one example embodiment, said first throttle valve comprises a first throttle valve orifice, and said second throttle valve

comprises a second throttle valve orifice. According to at least one example embodiment, said second throttle valve orifice is larger than said first throttle valve orifice.

Hereby, the first and the second pressure drop can be adapted to be same or close to the same.

According to at least one example embodiment, said second throttle valve orifice is between 5 % and 15 % larger than said first throttle valve orifice.

However, according to one alternative embodiment, said second throttle valve orifice is smaller than said first throttle valve orifice.

According to at least a second aspect of the present invention, a system for sterilizing and cooling a product flow comprising particles is provided. The system comprises:

a flash vessel arrangement according to the first aspect of the invention,

a sterilization arrangement arranged upstream of said first throttle valve, said sterilization arrangement being arranged to inject sterilization steam into said inlet pipe for sterilizing the product flow.

Hereby, the at least two throttle valves are arranged between the sterilization arrangement and the flash vessel. According to at least one example embodiment, the at least two throttle valves are arranged in the pipe, e.g. the inlet pipe to the flash vessel, between said sterilization arrangement and said flash vessel.

Effects and features of this second aspect of the present invention are largely analogous to those described above in connection with the first aspect of the inventive concept. Embodiments mentioned in relation to the first aspect of the present invention are largely compatible with the second aspect of the invention.

According to at least a third aspect of the present invention, a method for cooling a product flow comprising particles is provided. The method comprises the steps of:

providing a product flow comprising particles in an inlet pipe, said product flow having a first static pressure and a first velocity,

throttling said product flow in a first throttle valve to induce a first pressure drop of said product flow whereby said product flow adopts a second static pressure after said first throttle valve being lower than said first static pressure, and whereby said product flow adopts a first local peak velocity inside said first throttle valve being higher than said first velocity, downstream of said first throttle valve, throttling said product flow in a second throttle valve to induce a second pressure drop of said product flow whereby said product flow adopts a third static pressure after said second throttle valve being lower than said second static pressure, and whereby said product flow adopts a second local peak velocity inside said second throttle valve being higher than said first velocity,

downstream of said second throttle valve, transferring said product flow from said inlet pipe into a flash vessel.

The method thus improves the process of cooling down the product flow in a flash vessel in a way that reduces the risk of having equipment damage by particles in the product flow since the local peak velocities inside the throttle valves are reduced.

Effects and features of this third aspect of the present invention are largely analogous to those described above in connection with the first aspect of the inventive concept. Embodiments mentioned in relation to the first aspect of the present invention are largely compatible with the second aspect of the invention.

In other words, the static pressure may be reduced in at least two stages, and the local peak velocities in each of the throttle valves may be reduced compared to using only one throttle valve. According to at least one embodiment, said first local peak velocity in said first throttle valve occurs in the first throttle valve orifice, and said second local peak velocity in said second throttle valve occurs in the second throttle valve orifice.

According to at least one example embodiment, said first pressure drop and said second pressure drop in said step of throttling said product flow in a first throttle valve and said step of throttling said product flow in a second throttle valve, are substantially equal.

For example, the size of the first valve orifice and the second valve orifice are adapted to achieve a substantially equal pressure drop over the first and the second throttle valve, respectively.

According to at least one example embodiment, said first and said second pressure drop together make up a combined induced pressure drop, and wherein said first pressure drop in said step of throttling said product flow in a first throttle valve is between 25 % - 75 % of said combined induced pressure drop.

According to at least one example embodiment, said method further comprises the steps of:

prior to providing the product flow comprising particles in an inlet pipe, sterilizing said product flow by injecting sterilization steam into said inlet pipe.

This may e.g. be made by a sterilization arrangement mentioned above.

According to at least one example embodiment, the particles comprised in the product flow have a mean size of between 1 μηι to 200 μηι.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, step, etc.]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc.,

explicitly stated otherwise.

Brief description of the drawings

The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a schematic view of a flash vessel arrangement in accordance with at least one embodiment of the invention;

Fig. 2 is a schematic view of a flash vessel arrangement in accordance with at least one embodiment of the invention;

Fig. 3 is a schematic view of a system comprising a sterilization arrangement and a flash vessel arrangement in accordance with at least one embodiment of the invention; and

Fig. 4 is a flow chart illustrating a method for cooling, and possibly sterilizing, a product flow in accordance with at least one embodiment of the invention.

Detailed description of preferred embodiments of the invention

Fig. 1 shows a flash vessel arrangement 1 in accordance with one embodiment of the present invention. The flash vessel arrangement 1 comprises a flash vessel 10 and an inlet pipe 20 fluidly connected to the flash vessel 10. The inlet pipe 20 in Fig. 1 is divided into three portions 22, 24, 26 separated by a first throttle valve 30, and a second throttle valve 32. The flash vessel 10 is fluidly connected to a vacuum system 1 2 having a vacuum pump 14, and to an outlet system having an outlet pump 18.

The functioning of the flash vessel arrangement 1 will now be described with reference to Fig. 1 .

In the first portion 22 of the inlet pipe 20, a product flow comprising particles is provided. The product flow in said first portion 22 is provided at a certain flow rate and at a first static pressure determined by some process upstream of the inlet pipe 20, e.g. a sterilization arrangement (see Fig. 3). The product flow is subsequently throttled in the first throttle valve 30 in order to induce a first pressure drop of the product flow in the inlet pipe 20. Hereby, the static pressure of the product flow will be reduced. Hence, after the product flow has passed the first throttle valve 30, it enters the second portion 24 of the inlet pipe 20 with a second static pressure being lower than the first static pressure.

Subsequently, the product flow is throttled in the second throttle valve 32 in order to induce a second pressure drop of the product flow in the inlet pipe 20. Hereby, the static pressure of the product flow will be further reduced. Hence, after the product flow has passed the second throttle valve 32, it enters the third portion 26 of the inlet pipe 20 with a third static pressure being lower than the second static pressure of the product flow prior to the second throttle valve 32. Downstream of the second throttle valve 32, and from the third portion 26 of the inlet pipe 20, the product flow enters into the flash vessel 10. In the flash vessel 10, a certain amount of the product flow will be evaporated and subsequently leave the flash vessel 10 via the vacuum system 12, while the remaining portion of the product flow, typically in liquid form, will thereby be cooled and leave the flash vessel 10 via the outlet system 1 6.

The physical phenomena which the product flow undergoes as it is throttled through the first and second throttle valves 30, 32 are rather complex. The physical phenomena are often described with physical relationships like the Bernoulli's equation, the Navier-Stokes equation and the laws of thermodynamics. A thorough description of the physical phenomena is too cumbersome to include in this description why the process of throttling the product flow is described in a simplified way in the following sections.

When the product flow pass through one of the throttle valves, the cross-sectional area is reduced (as compared to the cross sectional area of the inlet pipe 20 before the throttle valve 30, 32), whereby the velocity of the product flow increases (since the mass flow of the product flow is constant over the throttle valve). As no work or heat is added or extracted from the throttle valves 30, 32, the static pressure of the product flow decreases as the velocity of the product flow increases. Where the cross sectional area of the throttle valve is at its minimum, the velocity of the product flow peaks (i.e. a local peak velocity of the product flow). This is schematically indicated in Fig. 1 by the narrow passage 31 of the first throttle valve 30, also referred to as a first throttle valve orifice 31 , and the narrow passage 33 of the second throttle valve 32, also referred to as a second throttle valve orifice 33. Subsequently, as the product flow leaves any one of the throttle valves 30, 32, the velocity of the product flow decreases (as the cross sectional area is again increased) and the static pressure of the product flow recovers slightly. Due to different losses (e.g. frictional losses and/or losses due to turbulence), the static pressure of the product flow is not recovered to its pre-throttle valve value.

By having at least two throttle valves 30, 32 arranged on the inlet pipe 20, as compared to having only one throttle valve, the static pressure can be reduced to that of the flash vessel in two stages instead of only one stage. Hereby, the local peak velocity of the product flow inside the throttle valves 30, 32 will be lower, as the minimum cross sectional area of the throttle valves can be made larger. Furthermore, as indicated in Fig. 1 , the second throttle valve orifice 33 is larger than the first throttle valve orifice 31 . This is advantageous, as it allow for a throttle valve design where the pressure drop over each of the throttle valves may be made equal.

According to at least one example embodiment, the cross sectional area of the inlet pipe 20 is between 50 mm and 100 mm, such as e.g.

between 60 mm and 80 mm. That is, the cross sectional area of the first portion 22, the second portion 24, and the third portion 26 is between 50 mm and 100 mm, such as e.g. between 60 mm and 80 mm. According to one embodiment the cross sectional area of the first throttle valve orifice is between 10 mm and 40 mm, such as e.g. between 20 mm and 30 mm, and the second throttle valve orifice is between 20 mm and 50 mm, such as e.g. between 25 mm and 35 mm. In such embodiments, the mass flow of the product flow may be chosen to be between 18 000 kg/h to 30 000 kg /h, such as e.g. between 20 000 kg/h to 26 000 kg /h. Furthermore, in such

embodiments the pressure may for example be reduced from approximately 4.5 bar and approximately 140 °C prior to the first throttle valve 30 (i.e. after a sterilization arrangement) to approximately 0.5 bar and approximately 80 °C in the flash vessel 10. Thus, preferably the combined induced pressure drop over the first and the second throttle valves 30, 32 is approximately 4.0 bar, and each of the first and the second throttle valves 30, 32 induce a pressure drop of approximately 2.0 bar.

Depending on inter alia, the density difference of the fluid (i.e. the product flow) before and after each of the throttle valves, the velocity of the fluid in the inlet pipe after each throttle may be slightly higher compared to the velocity of the fluid prior to each of the throttle valves. For example the velocity in the first portion 22 of the inlet pipe 20 may be slightly lower compared to the velocity of the fluid in the second portion 24 of the inlet pipe 20, the latter being slightly lower compared to the velocity of the fluid in the third portion 26 of the inlet pipe 20.

It should be noted that if the static pressure inside the inlet pipe 20 is reduced below that of the vapor pressure of the fluid, a portion of the fluid (i.e. the product flow) will evaporate causing an at least temporary existing two- phase product flow. Such two-phase flow may cause an increase of the product flow velocity as the density of the fluid is reduced (i.e. the volume of the fluid is increased).

The static pressure inside the flash vessel is typically that of saturated liquid at the desired outlet temperature.

Fig. 2 shows a flash vessel arrangement 1 ^' in accordance with one embodiment of the present invention. The flash vessel arrangement 1 ' is largely similar to the flash vessel arrangement 1 shown in Fig. 1 , and the same reference numerals refer to the same or similar elements and

components. For the sake of brevity, only the elements which differ from the embodiment shown in Fig. 1 are described with reference to Fig. 2 below.

In Fig. 2, the flash vessel arrangement 1 ^' comprises an additional throttle valve 34 arranged between the first and the second throttle valves 30, 32, or arranged downstream of the second throttle valve 32. The variable position of the throttle valve 34 is indicated by the dashed lines. Hereby, the product flow may undergo a pressure drop in at least three steps (instead of in two steps as shown in Fig. 1 ), and the local peak velocity at each of the throttle valves, 30, 32, 34 may be further reduced.

In Fig. 3 a system 100 for sterilizing and cooling a product flow is shown. The system 100 comprises a flash vessel arrangement 1 , as shown in Fig. 1 and a sterilization arrangement 200 arranged upstream of the first throttle valve 30. The sterilization arrangement 200 is arranged to inject sterilization steam into the inlet pipe 20 (or into a pipe being arranged prior to, and in fluid communication with, the inlet pipe 20). The sterilization steam may e.g. be injected into the inlet pipe 20 via a sterilization pipe arranged fluidly connected to the inlet pipe 20 by an injector (not shown).

In such system 100, a product flow may e.g. be heated from

approximately 80 °C up to around 140 °C, by injecting sterilization steam into the pipe with the product flow. Hereby, the product flow is sterilized.

Subsequently, a corresponding amount to the added sterilization steam is removed in the flash vessel, as the product flow is cooled down to its temperature prior to the sterilization arrangement (i.e. to approximately 80 °C). As explained with reference o Fig. 1 and Fig. 2, in between the

sterilization arrangement and the flash vessel, the product flow is guided through at least two throttle valve undergoes at least two pressure drops

Fig. 4 shows a flow chart of an exemplary method for cooling a product flow comprising particles in accordance with at least one embodiment of the invention. The method may, but need not, be performed utilizing a flash vessel arrangement as shown in any one of Figs. 1 -3.

The method comprises a first step, S1 , of providing a product flow comprising particles in an inlet pipe, the product flow having a first static pressure and a first velocity. The first step S1 , may comprise providing a product flow comprising particles with a mean size of between 1 μηι to 200 μηι.

In other words, the static pressure of the product flow at the inlet pipe is a first static pressure, and the velocity of the product flow is a first velocity (the latter being the velocity of the product flow) In a subsequent step, S2, the product flow is throttled in a first throttle valve inducing a first pressure drop of the product flow. Hereby, the product flow adopts a second static pressure after the first throttle valve being lower than the first static pressure. Inside the first throttle valve, as the product flow is throttled, it adopts a first local peak velocity being higher than the first velocity. It should be noted that the first throttle valve has a first throttle valve orifice where the cross sectional area of the first throttle valve is at its minimum. The first local peak velocity are referring to the state of the product flow at the first throttle valve orifice.

In a subsequent step, S3, the product flow is throttled in a second throttle valve inducing a second pressure drop of the product flow. Hereby, the product flow adopts a third static pressure after the second throttle valve being lower than the second static pressure. Inside the second throttle valve, as the product flow is throttled, it adopts a second local peak velocity being higher than the first velocity. It should be noted that similar to the first throttle valve, the second throttle valve has a second throttle valve orifice where the cross sectional area of the second throttle valve is at its minimum second local peak velocity are referring to the state of the product flow at the second throttle valve orifice.

In a subsequent step, S4, the product flow is transferred from the inlet pipe into a flash vessel. Prior to the step S4, the flash vessel has preferably been arranged in operative mode, e.g. by operating the vacuum system until the desired static pressure (e.g. a sub-atmospheric pressure) of the flash vessel has been reached.

It should be noted that, as explained above with reference to Fig. 1 , the product flow will adopt a static pressure in the portion of the inlet pipe between the first and the second throttle valves (i.e. in the second portion 22 of the inlet pipe 20) being referred to as the second static pressure. The product flow will also adopt a velocity in the portion of the inlet pipe between the first and the second throttle valves (i.e. in the second portion 22 of the inlet pipe 20) which is very similar to the first velocity.

Similarly, the product flow will adopt a static pressure in the portion of the inlet pipe between the second throttle valve and the inlet to the flash vessel (i.e. in the third portion 24 of the inlet pipe 20) which is referred to as the third static pressure. The product flow will also adopt a velocity in the portion of the inlet pipe between the second throttle valve and the inlet to the flash vessel (i.e. in the third portion 24 of the inlet pipe 20) which is very similar to the fist velocity. As mentioned above, in case of formation of a two- phase flow, the velocity after the second throttle may be higher than the first velocity due to formation of steam.

According to at least one example embodiment, step S2 and step S3 may be performed such that the first pressure drop and the second pressure drop of the product flow are substantially equal. This is preferably done by adapting the first and the second valves, such as e.g. the first throttle valve orifice and the second throttle valve orifice, in accordance with the desired pressure drop. For example, if the product flow is approximately 25 000 kg/h and the main pipe diameter is around 65 mm, the first throttle orifice may e.g. be between 20 mm and 30 mm, and the second throttle orifice may e.g. be between 25 mm and 35 mm. In particular, if the first and the second pressure drop each should be approximately 1 .73 bar, the first throttle orifice is preferably chosen to be around 26 mm and the second throttle orifice to be around 30 mm.

According to at least one example embodiment, the first and the second pressure drops together make up a combined induced pressure drop, and the first pressure drop of the product flow is adapted to be between 25 % - 75 % of the combined induced pressure drop. Again, this is preferably carried out by adapting the first and the second valves, such as e.g. the first throttle valve orifice and the second throttle valve orifice, in accordance with the desired pressure drop.

In a fifth optional step, SO, occurring prior to the first step S1 , the product flow is sterilized by injecting sterilization steam into the inlet pipe. This optional fifth step, SO, may be performed utilizing a sterilization arrangement 200 in the same manner as described on connection with Fig. 3.

The skilled person realizes that a number of modifications of the embodiments described herein are possible without departing from the scope of the invention, which is defined in the appended claims.

Claims

1 . A flash vessel (10) arrangement for cooling a product flow comprising particles, said flash vessel (10) arrangement comprising:

a flash vessel (10),

an inlet pipe (20) fluidly connected to said flash vessel (10), said inlet pipe (20) being arranged to guide the product flow to said flash vessel (10); a first throttle valve (30) arranged in said inlet pipe (20), said first throttle valve (30) being arranged to induce a first pressure drop of the product flow in said inlet pipe (20),

wherein said flash vessel (10) arrangement further comprises a second throttle valve (32) arranged downstream of said first throttle valve (30), said second throttle valve (32) being arrange to induce a second pressure drop of the product flow in said inlet pipe (20).

2. A flash vessel (10) arrangement according to claim 1 , wherein said first and said second throttle valves (30, 32) are arranged such that said first pressure drop of the product flow is substantially the same as said second pressure drop of the product flow.

3. A flash vessel (10) arrangement according to claim 1 , wherein said first and said second pressure drop together make up a combined induced pressure drop, and wherein said first pressure drop of the product flow is between 25 % - 75 % of the combined induced pressure drop.

4. A flash vessel (10) arrangement according to any one of the preceding claims, further comprising a vacuum pump for generating a sub- atmospheric static pressure inside said flash vessel (10), and an outlet pipe for transporting the product flow out from said flash vessel (10).

5. A flash vessel (10) arrangement according to claim 4, wherein said vacuum pump is arranged to generate a flash vessel (10) static pressure of approximately 0.5 bars.

6. A flash vessel (10) arrangement according to claim 1 , further comprising at least one additional throttle valve arranged between said first and said second throttle valves (30, 32), or arranged downstream of said second throttle valve.

7. A flash vessel (10) arrangement according to any one of the preceding claims, wherein said first throttle valve (30) comprises a first throttle valve orifice, and said second throttle valve (32) comprises a second throttle valve orifice, and wherein said second throttle valve orifice is larger than said first throttle valve orifice.

8. A system for sterilizing and cooling a product flow comprising particles, said system comprising:

a flash vessel (10) arrangement according to any one of claims 1 -7, a sterilization arrangement arranged upstream of said first throttle valve (30), said sterilization arrangement being arranged to inject sterilization steam into said inlet pipe (20) for sterilizing the product flow.

9. A method for cooling a product flow comprising particles, said method comprising the steps of:

providing a product flow comprising particles in an inlet pipe (20), said product flow having a first static pressure and a first velocity,

throttling said product flow in a first throttle valve (30) to induce a first pressure drop of said product flow whereby said product flow adopts a second static pressure after said first throttle valve (30) being lower than said first static pressure, and whereby said product flow adopts a first local peak velocity inside said first throttle valve (30) being higher than said first velocity, downstream of said first throttle valve (30), throttling said product flow in a second throttle valve (32) to induce a second pressure drop of said product flow whereby said product flow adopts a third static pressure after said second throttle valve (32) being lower than said second static pressure, and whereby said product flow adopts a second local peak velocity inside said second throttle valve (32) being higher than said first velocity,

downstream of said second throttle valve (32), transferring said product flow from said inlet pipe (20) into a flash vessel (10).

10. A method according to claim 9, wherein said first pressure drop and said second pressure drop in said step of throttling said product flow in a first throttle valve (30) and said step of throttling said product flow in a second throttle valve (32), are substantially equal.

1 1 . A method according to claim 9, wherein said first and said second pressure drop together make up a combined induced pressure drop, and wherein said first pressure drop in said step of throttling said product flow in a first throttle valve (30) is between 25 % - 75 % of said combined induced pressure drop.

12. A method according to any one of claims 9-1 1 , further comprising the steps of:

prior to providing the product flow comprising particles in an inlet pipe (20), sterilizing said product flow by injecting sterilization steam into said inlet pipe (20).

13. A method according to any one of claims 9-12, wherein said particles has a mean size of between 1 μηι to 200 μηι.