DE29722931U1 - Deep well reactor for the continuous implementation of chemical reactions - Google Patents

Description

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71 755

"Deep shaft reactor for the continuous execution of chemical reactions" Description

The invention relates to a deep-shaft reactor for the continuous implementation of chemical reactions according to the generic term of claim 1

From US 4,744,909 a reactor is known which is built in the form of a deep shaft reactor and is suitable for carrying out the wet oxidation of sewage sludge.

The actual reactor is a double pipe system and essentially consists of two pipes that are coaxially guided into one another and lowered into a corresponding borehole. The outer pipe is sealed at its lower end by a base. The inner pipe has a significantly smaller diameter than the outer pipe and ends near the base of the outer pipe, leaving a gap. In this way, a flow path is created for a flowable medium that can flow through the interior of the inner pipe and the space between the inner pipe and the outer pipe. This creates two oppositely directed flow sections for this medium. The inner pipe and the outer pipe are each provided with a connection for the supply and discharge of the medium to be treated on the side of the pipes facing the earth's surface. Depending on which connection is connected to the supply line, the direction of flow through the reactor can be changed.

Since the reactor is designed for exothermic reactions, it must be ensured that the heat generated is dissipated sufficiently quickly to avoid local overheating of the reactor itself. A significant part of the heat generated is dissipated with the effluent flowing out of the reactor outlet, which is formed from the reaction products. Since the influent supplied at the inlet is usually at ambient temperature, heat is transferred from the heated

Effiuent, which flows on the outside of the inner tube, towards the colder influent, so that it is heated up to near the reaction temperature.

Depending on the type of reaction taking place and the amount of heat released, it may be that the removal of heat by the effluent alone is insufficient. This known reactor is therefore equipped with an additional cooling system that works through indirect heat exchange. For this purpose, another double pipe system is arranged inside the inner pipe, running coaxially to it, which is in principle constructed in the same way as the double pipe system consisting of the inner pipe and the outer pipe of the reactor. This means that there is again an outer heat exchanger pipe closed at the lower end by a base, inside which there is an inner heat exchanger pipe that is open at its lower end. The inner heat exchanger pipe ends near the base of the outer heat exchanger pipe, leaving a passage gap. In this way, a heat transfer medium (preferably water) can flow through the two heat exchanger pipes. The fresh cooling medium is expediently led from top to bottom through the heat exchanger inner pipe and then flows from bottom to top through the space between the heat exchanger inner and outer pipe back to the earth's surface. On its way back, indirect heat exchange takes place through the wall of the heat exchanger outer pipe with the process medium to be treated in the reactor, which is at process temperature.

In order to allow the chemical reaction (e.g. wet oxidation of sewage sludge) to take place, the reactants, i.e. sewage sludge on the one hand and oxygen or an oxygen-containing medium (e.g. air) on the other hand, must be brought together in sufficient quantities and under suitable conditions. In the case of wet oxidation, the values for the temperature and pressure for the oxidation process to take place are preferably close to the critical point of water, i.e. either slightly below or slightly above the critical values of pressure and temperature. During the oxidation process, it must be ensured that the pressure is kept above the vapor pressure of the water and the temperature is kept within specified limits in order to avoid damage to the reactor and to ensure that the reaction is maintained. The oxygen required for wet oxidation is

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the known reactor in parallel flow with the influent (sewage sludge) through the inner tube of the reactor. For this purpose, lances protrude from above into the inner tube, through which the oxygen is released into the influent at different depths, so that it mixes with it in the form of bubbles. One of these oxygen lances is even led down into the so-called reaction zone, in which the actual chemical reaction, i.e. wet oxidation in the example mentioned, takes place. This reaction zone is located at the lower end of the inner tube and can, under certain circumstances, extend into the beginning of the space between the inner tube and the outer tube. In a reactor with a depth of 1200 m, for example, the reaction zone begins at about 700 m. Such vertical shaft reactors, as used for the wet oxidation of sewage sludge, have the great advantage that the required pressure in the reaction zone (e.g. 80 to 150 bar) does not have to be generated by a correspondingly high pump output when feeding the reactants, but is essentially created as a hydrostatic pressure of the liquid column due to the system.

While the deep shaft reactor described above has a heat exchanger arranged within the actual reaction chamber, the deep shaft reactor known from US 4,803,054 has an external heat exchanger for indirect heat exchange between the medium to be treated and the cooling medium. Two reaction chambers arranged parallel to one another are provided, each consisting of a pair of pipes guided into one another, as used in the reactor according to US 4,744,909. The two pairs of pipes are surrounded by a common cooling jacket pipe at a distance from one another. The space between the two pairs of pipes within the cooling jacket pipe is filled with the cooling medium, which can be drawn off in the area of the upper end of the cooling jacket pipe. The fresh cooling medium is fed in through a coolant supply line running parallel to the two pairs of pipes containing the reaction zone, which ends open in the area of the lower end of the deep shaft reactor. In this way, the fresh coolant can be used near the hottest point in the reactor. In principle, it is also possible to reverse the coolant flow, i.e. to introduce the fresh coolant at the top end of the cooling jacket tube and to remove it at the bottom end of the reactor, in order to obtain the hottest possible coolant, the heat of which can be used for other purposes.

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A deep shaft reactor is usually installed in such a way that its outermost cladding pipe is connected to the surrounding soil via a concrete casing. Since significant temperature differences occur during operation of the deep shaft reactor, especially when starting up and shutting down the reactor, strong thermally induced stresses or length changes also occur in the area of the outermost pipe. Due to the undefined friction conditions between the outermost pipe wall and the concrete casing, the mechanical stresses caused by this are particularly critical.

The object of the present invention is to improve a generic deep-shaft reactor in such a way that temperature changes during different operating phases of the reactor do not lead to undesirably large mechanical stresses in the area of the outermost pipe shell and the concrete casing.

This object is achieved according to the invention in that an outer protective tube is provided which surrounds the at least one pair of pipes guided into one another at a distance and is in turn directly surrounded by the concrete casing, and this protective tube is designed as a heat insulation tube. Advantageous further developments of the invention arise from the subclaims 2 to 11,

The invention is explained in more detail below with reference to the figures: They show: Fig. 1 a deep shaft reactor according to the invention with direct cooling and

Fig. 2 shows a deep shaft reactor according to the invention with external

indirect cooling system.

The deep shaft reactor shown schematically in Fig. 1 (the length is shown much too short in relation to the diameter) extends from the ground to a depth of e.g. 1200 to 1500 m. The borehole in which the reactor is housed has a diameter that is typically in the range of 500 to 900 mm. The core of the reactor is a pair of pipes 1, 2 that are guided coaxially into one another while leaving a hollow space. Since the inner pipe 1 is at a distance from the outer pipe 2

, the cavity formed between them is designed as an annular space 3. The outer pipe 2 is sealed at its lower end with a bottom 4 to the outside. The inner pipe 1 ends near this bottom 4 and is open at the bottom. At the upper end of the inner pipe 1, a feed line 5 is attached, through which an influent to be treated in the reactor can be introduced. This influent can flow downwards through the inner pipe and then enters the annular space 3, thus reversing the flow direction and flowing back towards the earth's surface, finally being discharged at the upper end of the outer pipe 2 through a discharge line 6 as effluent after the chemical reaction taking place in the reactor has been carried out.

γ to be able to be withdrawn. Of course, it is also possible to reverse the flow direction of the medium to be treated, i.e. to introduce the influent through line 6 and to withdraw it again through line 5. A characteristic of the deep shaft reactor is that there are two opposing flow sections, namely on the one hand the flow through the interior of the inner pipe 1 and on the other hand the flow through the annular space 3 between the inner pipe 1 and the outer pipe 2. While flowing through these two flow sections, a heat exchange between the two flow sections can take place through the wall of the inner pipe 1. Usually, a reactant (e.g. air or oxygen) that is to react with the influent is introduced through a separate reactant line 7, which ends openly in the reactor before the reaction zone. The reactant line 7 runs parallel to the longitudinal axis of the reactor. In the present case, the reactor is equipped with a cooling system that provides direct cooling. For this purpose, a coolant supply line 9 is arranged inside the inner tube 1 parallel to the reactant line 7, which also runs parallel to the longitudinal axis of the reactor and preferably extends down into the area of the reaction zone. The coolant introduced can thus exit into the reactor directly at the point where heat is generated and mix with the reactants in order to achieve sufficient cooling. The coolant (e.g. water or part of the influent that has not yet been treated and preheated or part of the withdrawn and cooled effluent) is withdrawn from the reactor together with the effluent through the discharge line 6. The deep shaft reactor according to the invention also has a protective tube 8 that is arranged at a distance from the outer tube 2, so that an annular gap 12a exists between these two tubes 2, 8. The protective tube 8 is in turn surrounded on the outside by a concrete casing 13, which fills the gap between

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the protective pipe 8 and the inner surface of the borehole is completely closed. By providing this protective pipe 8 and not directly covering the outer pipe 2 with the concrete casing 13, it is possible, if necessary, to pull out the core components of the reactor, i.e. the pair of the two coaxially guided pipes 1, 2 and the lines 7, 9 arranged therein and, if necessary, to inspect or even repair them.

In order to keep the thermal effect on the protective tube caused by the heat released during the reaction as small as possible, the invention provides for the protective tube 8 to be designed as a heat-insulating tube. This can be done, for example, by using a material with a comparatively low thermal conductivity to manufacture the protective tube 8. The protective tube 8 is preferably designed as a double-jacket tube. A solution in which vacuum insulation is arranged in the space between the inner and outer jacket of the double-jacket tube is particularly preferred. In this way, it can be ensured that the temperature increase of the protective tube 8 during reactor operation remains significantly lower than the temperature increase of the outer tube 2. This also keeps the mechanical stresses caused by thermal expansion correspondingly low.

From Fig. 1 it can also be seen that the upper part of the protective pipe 8 is surrounded by two further pipes spaced apart from one another. Firstly, this is the anchor pipe 14, which serves to protect the groundwater. It extends from the earth's surface to the groundwater horizons that are found in the respective local geological conditions. Secondly, there is the so-called standpipe 15, which serves to absorb the drilling forces and to secure the borehole against collapse and extends approximately 40 m into the ground. After the drilling work has been completed, it offers additional protection for the groundwater near the surface in the event that the media to be treated in the reactor should escape from the reactor in an uncontrolled manner due to damage to the reactor.

Another embodiment of the present invention is shown in Fig. 2. Functionally identical parts of the deep shaft reactor are provided with the same

Reference symbols have been given to the same as in Fig. 1, so that this does not need to be discussed separately. The main difference between the two embodiments is that in Fig. 2 there is no direct heat exchange between the cooling medium and the media to be treated, but rather an indirect heat exchange is provided. For this purpose, the pair of coaxially interleaved pipes 1, 2 are surrounded by a cooling jacket pipe 10 at a distance. Similar to the reactor known from US 4,803,054, several pairs of interleaved pipes 1, 2 could be arranged together within this cooling jacket pipe. At the upper end of the cooling jacket pipe 10 there is a connection 16 for the supply or discharge of the cooling medium (preferably water). Furthermore, a coolant line 11 is arranged parallel to the outer tube 2 of the reactor, which serves to supply or discharge the coolant depending on the desired flow direction of the coolant and preferably extends to near the lower end of the outer tube 2 and is open at the bottom. The cooling jacket tube 10 is sealed at the bottom by a base in the same way as the outer tube 2 of the reactor. In this way, the flow of the cooling medium can be guided in the same way as the flow of the medium to be treated in the reactor (inside the inner tube 1 and the outer tube 2). This means that when the cooling medium is introduced into the cooling jacket tube 10 through the connection 16, it heats up more and more as it flows down as it approaches the actual reaction zone and then, when it reaches its maximum temperature, can be drawn out of the reactor from the lower part of the reactor through the coolant line and reused to utilize the heat it contains. The coolant line 11 is expediently designed as a heat insulation pipe, similar to the protective pipe 8, in order to avoid heat losses as much as possible. Between the cooling jacket pipe 10 and the protective pipe 8, there is an annular gap 12b in the design of Fig. 2, in a similar manner to that between the outer pipe 2 and the protective pipe 8 in Fig. 1.

A preferred embodiment of the invention provides for the gap 12a or 12b to be evacuated in order to further limit the heating of the protective tube 8. It is expedient to introduce a means for absorbing hydrogen into the gap 12a or 12b, because in the event that the tubes rust and hydrogen is produced as a result, this hydrogen should not permeate into the evacuated gap. More cost-effective, although in

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From an insulation point of view, it is less effective to fill the annular gap 12a or 12b with dry air or nitrogen. Here too, the heat losses are relatively low. Temperature differences during start-up and shut-down lead to the gas density in the annular gap 12a or 12b changing accordingly. If the gap 12a or 12b is sealed to the outside, different operating conditions lead to corresponding pressure changes. This pressure indicator can also be used to monitor leaks in the gap 12a or 12b by connecting appropriate pressure indicators to this cavity. For practical reasons, the pressure of the gas in the gap should be kept low, because otherwise the sealing on the surface becomes unnecessarily complicated. Low pressures lead to smaller heat losses, but on the other hand to significant pressure differences between the gap and the cooling jacket pipe 10 and the protective pipe 8. This makes the use of higher-strength materials or thicker-walled pipes necessary.

An inert atmosphere in the gap reduces the corrosion potential accordingly. Therefore, a gas filling in the annular space 12b or 12a should be as dry as possible. Nitrogen is generally preferable to the use of air due to the lower rust potential.

Another way to monitor leaks is to analyze the gas in the gap 12a or 12b. For this purpose, for example, a pipe is inserted into the gap 12a or 12b that reaches approximately to the bottom of the reactor. The gap 12a or 12b is periodically or continuously flushed with an inert gas and the escaping flushing gas is analyzed for foreign components.

In order to enable the use of comparatively thin-walled pipes, the annular space 12a or 12b can also be filled with a suitable liquid that hinders heat conduction as much as possible, so that the hydrostatic pressure of the medium to be treated (in the design according to Fig. 1) or the cooling medium in the cooling jacket pipe 10 (in the design according to Fig. 2) is counteracted by a corresponding hydrostatic pressure in the annular space 12a or 12b. Water, for example, is suitable as a filling liquid, especially if this water is mixed with a rust inhibitor. In principle, the heat losses are greater when liquids are used for gap filling than when gases are used. The use of oil with a particularly low

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Thermal conductivity. Since temperature changes within the liquid filling inevitably lead to corresponding thermal volume changes, it is recommended to connect the annular gap 12a or 12b to an expansion vessel with sufficient buffer volume.

Instead of an expansion vessel, it can also be provided that the liquid filling in the space 12a or 12b is only carried out up to a minimum distance from the ground and that a gas cushion is formed above it, which is displaced or compressed accordingly when the volume of the liquid filling increases. The gas cushion thus represents an integrated expansion vessel.

In order to suppress natural circulation of the gas or liquid filled into the gap 12a or 12b as a result of an existing temperature gradient, which inevitably occurs depending on the height, it is advisable to provide fittings in the gap 12a or 12b that prevent free flow. For example, ring-shaped metal sheets can be used for this purpose. In this way, the thermal influence on the protective tube 8 can be further reduced. In order to detect leaks on the cooling jacket tube or on the outer tube 2, the gap 12b or 12a can be permanently connected to an appropriate measuring device or can be connected as required. Such a measuring device could, for example, react to changes in the pH value or the electrical conductivity of the liquid filling.

Claims (11)

-10- Protection claims 1. Deep shaft reactor for the continuous implementation of chemical reactions, with at least one pair of tubes (1, 2) which are guided into one another while leaving a hollow space (annular space 3), of which the outer tube (2) is sealed at one end towards the outside (bottom 4) and the inner tube (1) is open at this end, with a line connection for the supply line (5) of an influent or the discharge line (6) of an effluent formed by the chemical reaction being provided at the other end of each of the two tubes (1, 2). &iacgr;&ogr; is arranged so that the influent in two opposite Flow sections (interior of the inner pipe 1 and annular space 3 between the inner pipe 1 and the outer pipe 2) with indirect heat exchange between the flow sections (through the wall of the inner pipe 1) through the reactor, further comprising an outer protective pipe (8) which surrounds the at least one pair of pipes (1, 2) guided into one another at a distance from one another, and a concrete casing (13) placed directly around the protective pipe (8) and at least one reactant line (7) running inside the reactor, which ends openly in front of the reaction zone of the reactor and through which a reactant capable of reacting with the influent can be introduced, and a cooling system for removing heat from the reactor, characterized in that
that the protective tube (8) is designed as a heat insulation tube. 2. Reactor according to claim 1,
characterized, that the protective tube (8) is designed as a double-jacket tube with a vacuum insulation arranged between the inner and the outer tube jacket. 3. Reactor according to one of claims 1 to 2,
characterized, that the reactor has a direct cooling system, wherein a coolant supply line (9) runs within the at least one pair of tubes (1, 2) guided into one another over a part of its axial length and the coolant can be removed together with the effluent after the heat absorption and wherein there is an intermediate space (12a) between the protective tube (8) and the at least one pair of tubes (1, 2) guided into one another. 4. Reactor according to one of claims 1 to 2, characterized, that an indirect heat exchanger is provided as the cooling system, wherein the at least one pair of tubes (1, 2) guided into one another is surrounded by a common cooling jacket tube (10) which has a connection (16) for the supply or discharge of a cooling medium and a coolant line (11) running essentially over the entire length of the cooling jacket tube (10) in the latter for the discharge or supply of the coolant, wherein there is an intermediate space (12b) between the cooling jacket tube (10) and the protective tube (8). 5. Reactor according to one of claims 3 to 4,
characterized,
that the intermediate space (12a or 12b) is evacuated. 6. Reactor according to claim 5,
characterized, that a hydrogen-absorbing agent is introduced into the intermediate space (12a and 12b). 7. Reactor according to one of claims 3 to 4,
characterized, that the intermediate space (12a or 12b) is filled with a gas, in particular with air or nitrogen. 8. Reactor according to one of claims 3 to 4,
characterized, that the intermediate space (12a or 12b) is filled with a liquid, in particular with inhibited water. -12- 9. Reactor according to claim 8, characterized in that the intermediate space (12a or 12b) is connected to an expansion vessel. 10. Reactor according to one of claims 7 to 9, characterized in that internal components are provided within the intermediate space (12a or 12b) to suppress a natural circulation of the filled gas or the filled liquid triggered by a temperature gradient. 11. Reactor according to one of claims 1 to 10, characterized in that a measuring device for detecting leaks is connected or can be connected to the intermediate space (12a or 12b).