Title: Reactor, gas lift pump for a reactor vessel, and also method for deactivating a reactor

The present invention relates to a reactor comprising: • a reactor vessel provided with a fluid comprising a bed with particles having a specific weight of > 1.1 kg/dm ³ ; and

• a gas lift pump arranged in the reactor vessel; the gas lift pump comprising:

• a vertical first tube (inner tube) having an open upper side and an open lower end; and

• a mouthpiece for blowing in a gas such as air; the open lower end of the first tube (inner tube) lying in the bed of particle material; the mouthpiece being provided at the lower end of the first tube (inner tube) in such a way that when gas is blown in, the gas blown into the first tube (inner tube) brings about a reduction in the density of the fluid in the first tube (inner tube).

Reactors of this type comprising a gas lift pump are generally known per se. A gas lift pump of this type consists generally of a tube having an open upper and lower end, a gas being supplied at the lower end. The supplied gas reduces in the tube the density (or, so to speak, specific weight) of the fluid located in the tube. After all, as a result of the supply of the gas, the fluid in the tube contains more gas than the fluid outside the tube. The difference in density inside and outside the tube results in an upward flow into the tube, also known as a lift flow. This upward flow also allows the entrainment of other particles which are drawn in at the underside of the tube. This is a generally known phenomenon which is used for, inter alia: keeping the layer of sand in sand filters moving; mixing and/or swirling heavy particles in a reactor vessel; aerating and/or mixing aerobic and anaerobic reactors; etc. Gas lift pumps are however not without their problems.

A known problem which occurs with a gas lift pump is that start-up thereof is rendered difficult as a result of the fact that a thick layer of settled particles is located around the lower end of the tube. A thick layer of settled particles of this type impedes drawing-in of liquid because the layer of settled particles is insufficiently permeable to liquid. The

upward flow is then substantially determined by the amount of supplied gas, although this may not be able or may only just be able (as a result of the relatively low density of the gas m relation to the particles) to cause particles to move upward A known solution to this problem is the provision of a few holes m the tube The purpose of these holes is to improve the drawmg-in of liquid, and this is possible as a result of the shorter distance between the holes and the upper side of the layer of particles. However, the holes must be "excavated" one by one. This "excavation" takes place gradually as a result of the fact that particles are released from the holes and entrained under the influence of the gas blown into the tube. This "excavation" is accordingly relatively time-consuming Furthermore, the course of this "excavation process" is often less than optimal.

Another known problem which occurs m a gas lift pump is that the pump has difficulty in raising heavy particles - i e particles having a relatively high specific mass - and is accordingly less suitable or unsuitable for use in a bed comprising heavy particles.

The object of the present invention is to provide an improved reactor of the type described at the outset, which improved reactor allows more effective operation.

According to the invention, this object is achieved by providing a reactor comprising: • a reactor vessel provided with a fluid comprising a bed with particles having a specific weight of > 1 05 kg/dm ³ , and

• a gas lift pump arranged in the reactor vessel; the gas lift pump comprising

• a vertical first tube (inner tube) having an open upper side and an open lower end, and

• a mouthpiece for blowing m a gas such as air; the open lower end of the first tube (inner tube) lying m the bed of particle material; the mouthpiece being provided at the lower end of the first tube (inner tube) in such a way that when gas is blown in, the gas blown into the first tube (inner tube) brings about a reduction in the density of the fluid in the first tube (inner tube), the gas lift pump further comprising a second tube (outer tube) having an open lower end,

the bottom part of the second tube (outer tube) being provided concentrically around the bottom part of the first tube (inner tube) to form a concentric channel around the bottom part of the first tube (inner tube); viewed in the vertical direction, the upper side of the second tube being lower than the upper side of the first tube; the upper side of the second tube (outer tube) being open and being located below the surface level of the fluid in the reactor; and the upper side of the second tube (inner tube) being located above the particles having a specific weight of > 1.05 kg/dm ³ (in particular being located above particles comprising particles having a specific weight of > 1.1 kg/dm ³ and more particularly being located above particles comprising particles having a specific weight of > 1.25 kg/dm ³ ) when the bed of particle material is at rest (i.e when the gas supply is inoperative).

The first tube, which will be referred to in the present application also as the inner tube, is first surrounded at its bottom part by a second tube, which will also be referred to in the present application as the outer tube. This outer tube produces in the bottom part of the inner tube a concentric space which is open at the underside. The upper side of the outer tube is open and is located below the surface level of the fluid in the reactor.

Thus, the inner tube is able to draw in fluid, in particular liquid which may or may not be mixed with particles and/or gas, from the concentric space.

During start-up of the reactor, at the beginning of which the bed of particle material usually forms a settled, quiescent layer of particles, the concentric space allows a substantially unimpeded supply of fluid to the underside of the gas lift pump as a result of the fact that the upper side of the second tube (outer tube) is at rest above the layer of particles, or at least above the particles having a specific weight of > 1.05 kg/dm ³ , in particular is located above particles comprising particles having a specific weight of > 1.1 kg/dm ³ , and more particularly is located above particles comprising particles having a specific weight of > 1.25 kg/dm ³ . It is conceivable for lighter particles from among the particles to be located, when at rest, above the upper side of the second tube (outer tube). Lighter particles of this type impede the supply of fluid to the underside of the gas lift pump to a relatively low degree. The liquid which is thus drawn in at the underside of the inner tube entrains particles at the underside of the outer tube, as a

result of which the underside of the gas lift pump is excavated. This allows a more rapid and more reliable start-up of the reactor. (It will be noted that it is also possible for the upper side of the second tube (outer tube) to be located above the layer of particles both when the reactor is at rest and during operation thereof.)

It will be noted that in the case of a gas lift sludge bed reactor, the bed initially often consists entirely of particles having a relatively high specific weight (for example particles having a specific weight of > 1.5 kg/dm ³ ) such as brown coal particles, anthracite particles, pumice stone particles, etc. For a reactor height of 10 meters, the bed then has for example initially a height of 80 cm. During use of the reactor, biomass will (be able to) become deposited on these particles. The result of this is that the height of the bed, when the gas supply is switched off, will increase, for example to 1.5 meters or more, and that the specific weight of the particles (including the biomass) will decrease. The particles including biomass located at the top of the bed may then have a specific weight lower than 1.25 kg/dm or even lower than 1.05 kg/dm . According to the invention, these light particles can in this case themselves, when the gas supply is switched off, he above the upper side of the second tube (outer tube).

However, the invention also offers major advantages during normal operation, once start-up has already taken place, even if there are no excavation problems during startup

As a result of the fact that the inner tube can easily draw in liquid - which may or may not be mixed with particles - via the concentric space, the gas lift pump is able to convey a larger and/or higher turbulent volume flow upward through the inner tube. This provides a number of advantages during normal operation. The gas lift pump:

• can produce a higher output;

• is able to convey upward particles having a higher specific mass; and

• is able during the upward conveyance to subject the entrained particles more intensively to movements; this is advantageous with regard to purifying of said particles or mixing of said particles.

The reactor vessel thus contains a bed of particle material. Depending on the gas output of the gas lift pump and depending on the type of bed and particles, the particles will in this case not be suspended or scarcely be suspended or be suspended to a greater or lesser degree. In the case of suspending, the upper side of the bed will, depending on whether the particles are suspended to a greater degree, be at a higher level during operation of the reactor. When the reactor is deactivated, the suspended particles will then resettle to form a settled, quiescent layer of particles. If the particles are not suspended or are scarcely suspended during the operation, such as is the case with many sand filters, the upper side of the bed will be at substantially the same height during operation of the reactor as when the reactor is deactivated. In both cases, the upper side of the outer tube protrudes above the bed when the reactor is inoperative. If the particles are not suspended or are scarcely suspended, the upper side of the outer tube will, almost by definition, also protrude above the bed during operation of the reactor. In the cases of suspending, whether or not the upper side of the outer tube also protrudes above the fluidized bed during operation of the reactor will depend on the degree to which the outer tube protrudes above the quiescent bed. In the latter case, it is possible both for the upper side of the outer tube to lie m the (fluidized) bed during operation of the reactor and for said upper side to lie above the (fluidized) bed during operation of the reactor.

As a result of the concentric arrangement of the outer tube around the bottom part of the inner tube, particles at the underside of the gas lift pump are drawn in uniformly around the underside of the gas lift pump. There is m this regard no need for the outer tube to lie concentrically around the inner tube over the entire length thereof, or at least the open upper side of the outer tube does not have to extend concentrically around the inner tube. However, owing to design-related considerations, it is preferable for the outer tube to extend concentrically around the inner tube over the entire length thereof.

According to the invention, with a view to effective drawing of particles into the inner tube as a result of the upward lift flow, it is advantageous if, viewed in the vertical direction, the open lower end of the first tube (inner tube) is lower than the open lower end of the second tube (outer tube). At the underside of the inner tube, liquid which is drawn from the outer tube as a result of the lift flow will then entrain particles more

effectively as a result of the fact that the outer tube does not, viewed in a horizontal direction, completely cover the lower end of the inner tube but rather leaves it partly exposed.

According to the invention, in order to ensure, in particular during start-up but also during normal operation, effective drawing-in of fluid, in particular liquid, via the second tube (outer tube), it is advantageous if, where d is the diameter of the open lower end of the first tube (inner tube), where D is the diameter of the open lower end of the second tube (outer tube), and where Z is the, viewed in the vertical direction, distance between the open lower end of the first tube (inner tube) and the open lower end of the second tube (outer tube), the following applies: 0.1 (D-d) < Z < 0.4 (D-d). In particular, it is in this case advantageous if Z has a value of approximately 0.2 (D-d).

According to the invention, m order to ensure that a sufficient output of fluid, in particular liquid, can be drawn in via the outer tube, it is advantageous if, where d is the diameter of the open lower end of the first tube (inner tube), and where D is the diameter of the open lower end of the second tube (outer tube), the following applies: 0.5 D < d < 0.7 D. In particular, it is in this case advantageous if d has a value of approximately 0.6 D.

According to the invention, it is advantageous if the mouthpiece is provided below the open lower end of the first tube (inner tube) and is directed toward the interior of the first tube (inner tube) in such a way that, during operation, all of the blown-m gas is directed into the first tube (inner tube). This allows a certain degree of resuspension of particles to be forced at the underside of the gas lift pump as soon as the gas stream is activated during start-up of the reactor. It also ensures that the gas blown into the concentric space does not generate any (undesirable) lift flow

According to the invention, m order to rule out any risk of (undesirable) lift flow m the concentric space, it is advantageous if the mouthpiece is provided in the first tube (inner tube). The mouthpiece will then be provided in the interior of the bottom portion of the first tube (inner tube).

According to the invention, the excavation during start-up of the reactor can be further improved if one or more holes, which produce a fluid connection between the concentric channel and the interior of the first tube (inner tube), are provided in the wall of the first tube (inner tube) at a distance above the lower end of the second tube (outer tube). Via these holes, free drawing of fluid, in particular liquid, from the concentric channel is possible right from the beginning of start-up. Furthermore, these holes contribute during normal operation - separately from the start-up phase - to the capacity for upward conveyance, thus allowing particles having a higher specific mass to be conveyed more easily upward through the inner tube.

According to a further embodiment of the invention, the particles comprise one or more of the following particles:

• filtering sand such as garnet sand and/or quartz sand;

• basalt; • granular activated carbon;

• biomass, on a carrier or not on a carrier;

• crystals;

• minerals;

• brown coal; • pellets;

• pumice stone;

• anthracite;

• etc.

According to the invention, garnet sand can have a grain size of from 0.6 - 3 mm, with a specific weight of approximately 4.1 kg/dm ³ and a dump volume of approximately 2.3 kg/dm ³ . According to the invention, quartz sand can have a grain size of from 0.6 -

3 mm, with a specific weight of from approximately 2.5 to 2.6 kg/dm and a dump volume of from approximately 1.5 to 1.6 kg/dm ³ .

According to still a further embodiment, the fluid comprises water.

According to a further aspect, the present invention relates to a method for deactivating

a reactor according to the invention, wherein in a first step, in which a gas supply is maintained, the gas supply is first reduced to a level such that the particles impede the supply of liquid via the bed along the lower end of the second tube (outer tube); and wherein, in a second step following the first step, this level of gas supply or a lower level of gas supply is maintained until particles located in the second tube (outer tube) have become substantially discharged from said second tube (outer tube) to the first tube (inner tube) under the influence of the gas; wherein, m a third step following the second step, the gas supply is closed off.

Deactivating the reactor in this way ensures that during restarting of the reactor as few particles as possible are located in the outer tube, in particular in the concentric channel at the underside of the gas lift pump. This is achieved as a result of the fact that during the deactivation the gas supply is first lowered, so the particles settle to form a bed which substantially closes off the underside of the gas lift pump. This closure causes fluid to be drawn into the inner tube via the outer tube by way of the still remaining but less strong lift flow. This, in turn, causes particles located in the fluid in the outer tube to become discharged by way of circulation of the fluid through the outer tube. As a result of the fact that the upper side of the outer tube protrudes in this case above the bed of particles, drawing-in of new particles with the fluid via the outer tube will decrease and may be eliminated altogether.

It is in this case particularly advantageous if the second step is continued until both the second tube (outer tube) and the first tube (inner tube) contain substantially no particles.

According to still a further aspect, the present invention relates to a gas lift pump for a reactor vessel provided with a fluid comprising a bed of particulate material, the gas lift pump comprising:

- a first tube (inner tube) which in use is arranged vertically and has an open upper side and an open lower end; and

- a mouthpiece for blowing in a gas such as air; the mouthpiece being provided at the lower end of the first tube (inner tube) in such a way that when gas is blown in during use, the gas blown into the first tube (inner tube)

brings about a reduction in the density of the fluid in the first tube (inner tube), resulting in an upward lift flow of fluid into the first tube (inner tube); the gas lift pump further comprising a second tube (outer tube) having an open lower end; viewed in the vertical direction, the upper side of the second tube being lower than the upper side of the first tube; the bottom part of the second tube (outer tube) being provided concentrically around the bottom part of the first tube (inner tube) to form a concentric channel around the bottom part of the first tube (inner tube); and the upper side of the second tube (outer tube) being open in such a way that at the upper side of the second tube (outer tube) fluid can be drawn in as a result of suction caused by the upward lift flow through the first tube (inner tube).

Further embodiments of this gas lift pump are described m Claims 17-24. Advantages of the gas lift pump according to this third aspect of the invention will become clear from the above-described reactor according to the invention.

The present invention will be described hereinafter in greater detail with reference to the examples indicated schematically in the drawings, in which: • Figure 1 is a schematic view of a first reactor according to the invention at the beginning of the start-up phase;

• Figure 2 is a corresponding schematic view, the start-up phase being at a more advanced stage;

• Figure 3 is a corresponding view, the first reactor being in a normal phase of operation;

• Figure 4 is a corresponding view, the first reactor being in a deactivation phase; and

• Figure 5 is a schematic view of a second reactor according to the invention during normal operation.

Two different applications of the invention will be described hereinafter. The first application (Figures 1-4) relates to the activation (once the gas supply has been terminated) of what is known as an airlift reactor such as that sold by the Applicant

under the brand name Circox®. The second application relates to the improvement during operation of the gas lift pump, as a result of which the principle of the gas lift pump may readily be applied to a bed comprising relatively heavy particles, such as in a sand bed filter comprising, for example, garnet sand.

In Figures 1 to 4 inclusive, reference numeral 10 denotes a first reactor according to the invention. This reactor vessel contains a fluid, the upper surface of which, also known as the liquid level, is denoted by reference numeral 18. The fluid comprises a bed with particles 17 which are schematically illustrated as being triangular. The upper side of the bed is denoted schematically by reference numeral 19. This first reactor is of the type in which the bed of particles is fluidized during operation. This is, by way of example, a bed comprising biomass-carrying particles.

A gas lift pump is located m the reactor vessel 10. This gas lift pump comprises an inner tube 11 and an outer tube 12 placed concentrically around said inner tube. The inner tube 11 and the outer tube 12 jointly delimit a concentric channel 21. This concentric channel 21 extends, m particular, along the bottom part of the inner tube 11.

The lower end 15 of the outer tube 12 is, viewed in the vertical direction, higher than the lower end 14 of the inner tube 11. A mouthpiece 20, along which gas, in this case air, is blown m, is located centrally below the inner tube 11. In the figures, air bubbles are illustrated schematically as circles and denoted by reference numeral 16.

Figure 1 shows that the bed of particle material, when this reactor is deactivated and the fluid is at rest, has precipitated to form a relatively compact bed of particles. This precipitated, relatively compact bed of particles closes off the underside of the gas lift pump. The upper end of the outer tube 12 protrudes above the upper side 19 of the bed in this rest state. As soon as gas, such as air, is then blown in via the mouthpiece 20, fluid, in particular liquid, will be drawn into the concentric channel via the upper end of the outer tube 12 in order to be drawn at the underside of the concentric channel 21 into the inner tube 11 by way of the lift flow generated in the interior of the inner tube 11. If there are no holes 13 m the side wall of the inner tube 11, this can take place only along the bottom of the lower end 14 of the inner tube 11. However, the provision of the holes 13 ensures right from the outset that fluid can be drawn into the interior of the

inner tube 11 unimpeded via the holes 13 (see the arrows α in Figure 1) by way of the upward lift flow.

After a certain amount of time, the gas lift pump will have become completely excavated at the underside, so the flow of fluid is also drawn in along the bottom via the lower end 14 of the inner tube 11 (see the arrows β in Figure 2).

On further continuation of the start-up, the bed of particles will ultimately become suspended to a certain degree, depending on the process operated in the reactor The upper side 19 of the bed then rises and can, depending on inter alia the described process, even rise above the lower end of the inner tube 11 and outer tube 12. This is represented in Figure 3. In this state, the gas lift pump will also draw in fluid, in particular liquid, via the bed of particle material (see arrows γ in Figure 3)

If the reactor must then be deactivated, the gas supply will, as is indicated schematically in Figure 4, first be lowered to a level such that the bed of particle material starts to thicken, wherein the upper side 19 of the bed will usually descend. The result of the thickening is that the particles close off the underside of the gas lift pump, as a result of which fluid can still be drawn in only via the concentric channel, delimited between the outer tube 12 and inner tube 11, as is indicated schematically in Figure 4 by arrows α and β. As a result of maintaining the gas supply in this case for a further amount of time and in the meantime lowering it further if appropriate, the concentric channel 21 contains relatively few particles 17. After all, particles located in the concentric channel 21 will be drawn out of this concentric channel 21 and be discharged via the inner tube 11. Thus, when the reactor is deactivated, the concentric channel 21 can contain substantially no particles. This allows, on restarting, fluid to be supplied from the outset unimpeded to the inner tube 11 via the concentric channel.

For further illustration of the invention, the following dimensions may be specified, with reference to Figure 1, for the configuration of the gas lift pump according to the invention:

• the diameter d (in cm) of the inner tube as a whole: 2 to 100 cm;

• the diameter D (in cm) of the outer tube as a whole follows from: d = 0.6*D, with

a spread in the range of: 0 5*D < d < 0.7*D;

• the distance X (in cm) between the upper end of the inner tube and the upper end of the outer tube follows from- X = 3*(D-d), with a spread in the range of 2*(D-d) < X ≤ 4*(D-d); • the distance Z (in cm) between the lower end of the inner tube and the lower end of the outer tube follows from: Z = O 2*(D-d), with a spread in the range of: 0.1*(D-d) ≤ Z < 0.4*(D-d);

• the distance Y (in cm) between the lower end of the inner tube and the base of the reactor follows from: Y = 0.33*d, with a spread in the range of 0 l *d < Y < 0.5*D. This distance can optionally be greater, although there is then a greater risk that sediment will remain at the bottom of the reactor.

Figure 5 shows a second reactor 30 according to the invention This is a sand filter reactor. The sand can comprise any suitable filtering sand, although m this case it comprises in particular garnet sand such as garnet sand having a grain size of from 0.6 - 3 mm, with a specific weight of approximately 4.1 kg/dm ³ and a dump volume of approximately 2 3 kg/dm ³ In the case of a sand filter reactor, the bed 31 is formed by a layer of sand which can be a few meters, for example 3-4 meters, thick and this bed forms a filter bed 31. The liquid to be purified is usually supplied m the filter bed and then flows up through the filter bed in order in the meantime to be filtered. In the meantime, the filter bed itself moves in the downward direction m order at the bottom of the filter bed to extract dirty sand from the bed, to return purified sand to the bed and usually to deposit this purified sand at the top of the bed. In a filter bed of this type, little or no fluidization occurs, so the upper side 32 of the filter bed 31 is substantially invariably at the same level during operation of the reactor and when the reactor is not in use The use of a gas lift pump for keeping the filter bed moving and purifying the particles of sand is known per se.

The gas lift pump according to the invention, such as has already been discussed with reference to Figures 1 -4, is ideal for a filter bed reactor of this type (which filter bed can in accordance with the invention also consist of a material other than sand). In the case of the reactor 30 in Figure 5, the same reference numerals have therefore been used for the gas lift pump as in Figures 1-4. Furthermore, in this case too, the gas

bubbles are indicated schematically as circles 16. The sand particles are indicated schematically in Figure 5 as triangles 34. In order to prevent sand particles from falling into the concentric space 21 between the inner tube 11 and outer tube 12 after leaving the inner tube 11 at the upper end, a cap 33 is provided below the upper end of the inner tube 11 but above the upper end of the outer tube 12. There may however also be no cap.

Use of the gas lift pump according to the invention in a filter bed reactor (in which no or little fiuidization occurs), such as a sand filter bed reactor, has the advantage that this gas lift pump is able to convey upward particles having a high specific weight, has a high output, and also improved washing properties. It will however be clear that these advantages (upward conveyance of particles having a high specific weight, high output, improved washing properties/mixmg properties) can also advantageously be used during normal operation of other types of reactors such as reactors in which the bed of particle material is fluidized to a greater or lesser degree. Furthermore, it will be clear that use of the gas lift pump according to the invention leads to improved start-up in the case of both filter bed reactors and other types of reactors.

Figures 1 -5 show that the gas supply pipe 20 terminates in the base of the reactor, so that m this case the mouthpiece (where gas streams out into the reactor) is then located in the base It will however be clear that the supply pipe 20 can also protrude above the base of the reactor and even can extend into the bottom portion of the inner pipe. In the latter case, the mouthpiece will then be in the interior of the inner tube 11. The mouthpiece may, for example, be located in a range of from 50 cm below the lower end 14 of the inner tube to approximately 50 cm above the lower end of the inner tube 11; more particularly, the mouthpiece will be in a range of from 20 cm below the lower end

14 of the inner tube to approximately 20 cm above the lower end of the inner tube 11.

List of reference numerals used

10 = first reactor 11 = first tube/inner tube;

12 = second tube/outer tube;

13 = hole in the wall of the inner tube;

14 = lower end of the inner tube;

15 = lower end of the outer tube; 16 = gas bubble;

17 = particle;

18 = upper surface of the fluid/liquid level

19 = upper side of the bed;

20 = mouthpiece; 21 = concentric channel;

30 = second reactor;

31 = bed/filter bed;

32 = upper side of the bed 31 ;

33 = cap; 34 = sand particle;

α = drawing-in of fluid via the concentric channel 21 and hole(s) 13; β = drawing-in of fluid via the concentric channel 21 and along the bottom of the lower end 14 of the inner tube 11; γ = drawing-in of fluid via the bed and along the bottom of the lower ends 15,

14 of the outer tube 12 and inner tube 11; d = diameter (in cm) of the inner tube 11 ;

D = diameter (in cm) of the outer tube 12;

X = vertical distance (m cm) from the upper end of the outer tube 12 to the upper end of the inner tube 11 ;

Y = vertical distance between the lower end 14 of the inner tube 11 and the base of the reactor;

Z = vertical distance (in cm) between the lower end 14 of the inner tube 11 and the lower end 15 of the outer tube 12;