NL7908431A - APPARATUS AND METHOD FOR DIRECT HEATING OF ANY SOLID CONTAINING PRESIDENT MEDIUM USING CONDENSATION HEAT. - Google Patents

Description

Ke / gn / 206 *

Short designation: Device and method for directly heating a liquid medium, which may contain solids, using condensation heat.

The invention relates to a method for directly heating a liquid medium, optionally containing solids, at a high temperature, using heat of condensation. The invention particularly relates to a method for directly heating, in particular, solutions and suspensions in water at temperatures of more than 150 ° C, preferably up to about 250 ° C, using condensation heat.

The invention further relates to a device which is particularly suitable for applying this method. The invention finally relates to the use of the method and the device for carrying out precipitation or leaching reactions.

It is often the task to carry out reactions in liquid medium, in particular aqueous medium, at high temperatures, in particular temperatures between 150 and 200 ° C. This is often the case with precipitation and leaching reactions. However, carrying out such reactions in this temperature range presents certain difficulties. For economic reasons, it is almost always necessary to recover the heat supplied to the system as much as possible. Preferably, equipment with a fixed exchange surface is used for the heat exchange. A pronounced problem consists in that caking on the heat transfer surfaces can occur, which adversely affects the heat transfer and whose removal is difficult and time consuming.

Problems also arise when the solution to be treated is already aggressive or becomes even more aggressive during the reaction. In these cases, the use of highly corrosion-resistant but mechanically low or hardly to be loaded materials is mandatory. An example of a high-temperature precipitation reaction is, for example, the high-temperature hydrolysis of iron, chromium and aluminum from the aqueous solutions of their sulfates. When these metals are precipitated at temperatures between 20 and 50 ° C, hydroxide sludge often results.

is particularly difficult to filter. However, it is known that these filtration difficulties do not occur when the precipitation reaction is carried out at temperatures between 180 ° and 250 ° C.

As stated above, carrying out the reaction is complicated by the fact that from the solution the hydroxides, calcium sulphate, silicon dioxide and optionally further compounds precipitate from the solution at an increasing temperature and therefore form deposits on the hot places, preferably on the heat exchange surfaces. At the same time, the acid concentration increases. This leads to a very strong corrosive load on the materials in the mentioned temperature range. In addition, operating temperatures of 20 to 50 bar occur at temperatures between 150 ° and 250 ° C in water-containing solutions.

The material problems require the use of materials such as Teflon and carbon, which no longer exhibit practical strength properties under the stated conditions of use. Other materials such as tahtalium and titanium 25 which are resistant to the corrosion occurring are so expensive that they can only be used economically as coating materials. In both cases, the forces must be absorbed by non-corrosion-resistant carbon steels. Since moving parts in the devices also have to be designed in a complicated manner, they should be avoided as much as possible. The combined use of plastic and steel allows heat exchange surfaces due to the high heat transfer resistance.

These material problems propose to the technician 35 the task of developing devices which are subjected as little as possible to mechanical stress and, therefore, above all to avoid moving parts.

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The same considerations apply to leaching reactions, for example for the leaching of finely ground minerals with bases or acids, optionally adding reactive gases such as oxygen or chlorine.

One can also think of a leaching of metal-containing solids, for instance of spent catalysts, which have been used at high temperatures and which contain valuable substances, such as non-ferrous metals or precious metals.

It is known to heat suspensions step by step. For example, German Patent Specification 19 37 392 discloses a method characterized in that the heating of the suspension takes place stepwise by heat transfer surfaces, in the first stage 15 or more heat exchangers by steam from an expansion plant heating, while the second stage is in the form of a double-tube exchanger, in which the suspension is further heated by indirect heat exchange and the refluxing suspension is cooled, and finally in a third stage the remaining required heat by heating with high-pressure steam, supplied by an organic heat carrier or by a salt heat carrier via heat exchange surfaces. This method has the drawback of the use of double-tube heat exchangers, which can lead to coagulation during leaching and precipitation reactions on the heat-exchange surfaces. Direct heat exchange processes have also already been proposed for the desalination of seawater, but as a rule foreign heat transfer agents are also used here in the heat exchange operations with the highest energy content.

Single or multi-stage methods of cooling solids containing liquids by means of expansion evaporation are known and are described, for example, in German patent application 2 361 236. The vapor generated in these cases is only precipitated by direct condensation, but not used for preheating solutions.

From the aforementioned literature, or from the general standard technique, methods or apparatuses which enable the reaction to be carried out in a high temperature range of up to about 250 ° C and which in particular precipitate or leach reactions in this process can be derived temperature range while avoiding the above drawbacks.

The requirements according to the invention can be met in that the heated liquid medium is partially evaporated by a one- or multi-stage expansion and heated directly in the countercurrent without the use of foreign heat transfer agents. medium is condensed.

An important feature of the method according to the invention therefore consists in that the cooling of the liquid medium, in particular solids, is effected by exclusively and consistently using one-stage, but preferably multi-stage expansion evaporation, whereby the use of any foreign heat transfer agent is omitted. In addition, the vapors formed during the expansion evaporation are directly condensed in the medium to be heated in countercurrent. Due to the direct heat transfer, optimal conditions for the heat exchange are created. The heat exchangers can therefore be built very small. The absence of heat exchange surfaces allows the use of corrosion-resistant coatings.

A preferred embodiment of the method according to the invention consists in that the liquid medium to be heated is heated to the reaction temperature to be reached after the last heating step has been flowed through by direct addition of additional steam directly in front of the reaction vessel or in the reaction vessel.

This increases consciously that the medium to be heated is diluted by the condensation of the vapors therein during the heating and by the supply of vapor in the last reaction step. As the expansion stages are run through, the solution is again significantly concentrated.

Preferably, after flowing through one or more expansion stages, the liquid medium is further cooled and concentrated by pressure reduction 790 84 31 5 and thereby almost reaches the initial concentration.

At relatively low temperatures, preferably at temperatures of about or less than 120 ° C 5 as well as at acceptable corrosive load and a low tendency to caked at these temperatures, the final cooling operation of the liquid medium after flowing through the expansion stage can be in a recuperator executed. Preferably, a plate exchanger of correspondingly corrosion-resistant materials is used for this purpose, which exhibits a high internal turbulence.

The device according to the invention for carrying out the method is characterized by the combination of the following features: a a pressure reaction vessel, b one or more heat exchangers with b 1 an expansion tank and b 2 one connected to the vapor space of the expansion tank. upright condensation-20 column, which has b 2.1 distribution and / or dripping bottoms, c a feed pump with volume flow controlled in dependence on the liquid level per heat exchange stage and reaction vessel 25 d a final cooling stage which is as d 1 expansion stage or as d 2 recuperator executed.

Preferred is a device that has more than one direct exchange stage. Within a reaction temperature range of about 180 to 250 ° C, it is recommended to use 2 to 3 direct heat exchange steps.

The reaction vessel used in the device according to the invention is coated on the product-contacting parts with correspondingly corrosion-resistant materials, which are resistant to high temperatures, for example, tantalum, titanium and Teflon. The force-absorbing structural parts are made of suitable temperature-resistant carbon steels.

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Preferably, the reaction vessel is characterized in that it has a centrally arranged flow tube, in the bottom opening of which a supply conduit for the heated liquid medium opens and in the bottom part of the reaction vessel outside the flow tube a conduit leading to the first heat exchanger. removal of treated medium is provided. The circulation in the reaction vessel is effected by the incoming streams.

The circulation can moreover be increased by an external cycle and a pump. The heated liquid to be treated or reacting rises in the centrally mounted flow tube and descends after leaving the flow tube between the inner wall of the reaction vessel and the flow tube, where the liquid is withdrawn from the reaction vessel and passed to a first heat exchanger. The liquid remaining in the reaction vessel circulates multiple times in the described sense. The circulation can be influenced by the shape of the rays.

In a further embodiment of the device 20, a supply pipe for steam and / or reaction gas also opens into the bottom opening of the flow tube. Both streams are fed regularly depending on the required heating and / or the reaction equations. The medium is further heated by the steam supply, and by reducing the density of the liquid medium, the speed of circulating and thereby the circulation is increased. The same applies to the reaction gas supplied at this location, for example oxygen and chlorine. The residence time in the reaction vessel can be influenced by means of an externally mounted pump and / or by adjusting the degree of slenderness of the reaction vessel.

When precipitating reactions are carried out with the device according to the invention, it has been found to be particularly advantageous if in the circulation flow in the reaction vessel germs are present in the precipitate product which promote the formation of coarse grains, so that the solids-containing media are filtered. is facilitated.

The reaction vessel has no mechanically loaded parts that come into contact with the product. The materials of the interior surfaces of the device can only be selected on the basis of its corrosion resistance.

All walls that come into contact with the product can be coated with plastic which exhibit the least possible adhesion properties compared to cakings. In addition, it is difficult to insulate the interior surfaces of the device in the upper part and to keep it moist in order to prevent possible deposits as much as possible.

If the reaction proceeds at high speeds and shows only a small enthalpy of reaction, the reaction vessel can also be designed as a tube reaction vessel in combination with a small loop reactor.

The highest temperature liquid medium leaving the reaction vessel is now fed to the first heat exchanger. The expansion devices preferably have such a low liquid content and, therefore, a so long residence time that the equilibria set in the reaction vessel are maintained.

Preferably, the one or more heat exchangers are designed in such a way that they exhibit a cyclonic shaped vapor space with a collecting space arranged underneath for the at least partially expanded liquid medium, while the vapor space is provided by means of a flue pipe, which is the top end is covered by a dropper cap, communicating with the condensation column, the condensation column is separated from the vapor space of the expander in such a way that the heated liquid medium is discharged to a collection space, which is connected by means of a feed pump the heat exchanger of the next higher energy level or with the reaction vessel and each having a conduit: a) for the liquid medium to be heated, which opens at the top of the condensation column, b) for the liquid medium to be expanded, which opens at the top of the vapor space and c) each a discharge for the partly e Expanded, cooled liquid medium, which discharges into the top of the vapor space of the heat exchanger with the subsequent lower energy level or into the cooling device through 790 8 4 31, through an expansion valve. i

The heat exchange takes place in the heat exchanger described above such that the heated liquid medium 5 is injected into the cyclone-shaped vapor space after passing through an expansion valve.

The vapors released thereby flow through the flue into the condensation column and release their reaction enthalpy to the lower temperature liquid medium to be heated, which is introduced into the top of the condensation column. The liquid to be heated drips over distribution and sieve bottoms that are placed in the condensation column. The heated liquid passes over a bottom separating the condensation column from the vapor space in a standing tube, from which the liquid is supplied to the reaction vessel via a feed pump with a volume flow dosed in dependence on the liquid level. In the subsequent heat exchangers, the heated liquid medium is similarly introduced into the top of the column of the higher temperature heat exchanger.

The at least partially expanded and partially cooled liquid medium collects under the vapor space in a collection space and is fed to the subsequent heat exchanger with a lower temperature level depending on the liquid level. However, when it concerns the last heat exchanger, the reaction product is discharged to the last cooling device. When the liquid medium is a suspension with an increased viscosity or with a high tendency of the suspended particles to sediment, it is preferred to use a device which is characterized in that the one or more heat exchangers thereof have a cyclonic vapor space with a collecting space disposed beneath it. in front of . exhibit the at least partially expanded liquid medium 35, while in the collection space a flow tube is arranged, in which a circulation stirrer is located, while the vapor space is connected by means of a vapor pipe to a condensation column and in a container present in the condensation column receptacle flow pipe and each has a 790 8 4 31 4 9 pipe a) for the liquid medium to be heated, which opens into the top of the condensation column, b) for the liquid medium to be expanded, which opens into the top of the vapor space, and * c) for the partially expanded, cooled liquid medium, which opens into the top of the vapor space of the heat exchanger with the subsequent lower energy level or into the final cooling device.

With the heat exchanger characterized in this way, it is recommended to separate the vapor space from the condensation column in such a way that the cooled suspension is collected in a stirred receptacle with the lowest possible liquid content. The heated slurry is collected in a stirred receptacle, which acts as a pump space.

In these cases it is advisable not to use dividing or sieve bottoms in the condensation column, but downwardly inclined slate plates, in which a build-up on these plates is prevented by the downwardly dripping, heated suspension.

The condensation columns and / or the reaction vessel preferably contain at the top degassing devices for discharging the excess any used reaction gases or non-condensable gases which are not converted during the reaction or which are produced by side reactions.

The device according to the invention initially has a cooling device which can operate under reduced pressure. This can be designed in accordance with the heat exchangers. In the condensation column, however, water is supplied at the top, which is suitably discharged at the bottom together with the condensed vapor. The cooled liquid medium can then be withdrawn from the collection space present under the expansion space and be fed to the final treatment which no longer belongs to the invention, for instance to a filtering operation.

If under the conditions prevailing during the last cooling there is no fear of caking and / or corrosive attack, a recuperator can be added at this location. 790 8431

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10 suitable / in particular one in the form of a plate exchanger with a high internal turbulence.

The device according to the invention and the methods feasible in this device are elucidated on the basis of the following images: Fig. 1 schematically shows the device consisting of a reaction vessel, a heat exchanger and a last cooling device, Fig. 2 shows a heat exchanger embodiment adapted in particular to suspensions with a high viscosity and / or considerable sedimentation speed.

Fig. 1 shows a high temperature reaction vessel 1. This reaction vessel is provided with a flow tube 2 into which a feed 3 for the liquid medium heated to high temperature 15 flows. Furthermore, a supply 4 for any required reaction gas and a supply 5 for steam for supplying the required energy to reach the reaction temperature are provided. The liquid medium to be treated rises upwards in the flow tube 2 due to the impulses of the entering liquid and due to the driving forces caused by the other entering flows, so that a circulation flow is created. After leaving the flow tube 2, the liquid medium drops. The average residence time, flow rate and slenderness of the reaction vessel are chosen such that the reaction of the liquid medium is completed when it leaves the reaction vessel through line 6.

The reaction vessel is preferably constructed so that the solid particles present or formed remain in the circulating stream and cannot settle, further the gases supplied in the circulating streams remain in finely divided form and therefore circulate, unreacted or newly formed gas constituents which collect in the top of the reaction vessel can be discharged through an expansion valve, all parts in contact with the product, as well as the vapor or gas space at the top of the reaction vessel, are coated with a corrosion-resistant material and all forces are removed by a 790 8431

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corrosion-resistant, load-bearing construction. In the top of the reaction vessel there is a pressure reducing valve 7 with an outlet for any excess reaction gas used or any inert gases present.

After the reaction, the liquid medium leaves the reaction vessel via the line 6 to the regulator 8.

The flow rate of the liquid medium is controlled depending on the liquid height in the reaction vessel 1. The reaction equilibrium of the treated medium is frozen by the vapor expansion and a temperature corresponding to the reduced pressure is established. The gas-liquid-solid mixture formed after the pressure reducing valve flows to a cyclonic shaped vapor space 9. The cooled liquid with the solid particles collects in the bag 10. The separation of the liquid-loaded liquid and the vapor need not be completely since any liquid droplets entrained are returned to the reaction vessel. The vapor flows through the chimney pipe 11, which is covered by a drip hood 12, to the condensation column 13, which is provided with dividing bottoms 14 and drip bottoms 15. The ascending vapor flows in countercurrent with the pipe 16 using the metering pump 17. liquid medium to be heated in the top of the condensation column 13 and releases its condensation enthalpy 25 thereon. The liquid medium heated to a higher temperature flows after passing through the condensation column 13 over the bottom 18 to the receptacle 19 and from there is pumped into the line 3 by means of the metering pump 20, which line leads to the high-temperature reaction vessel.

The condensation column 13, like the reaction vessel, has a degassing device 41 for non-condensable gases.

The cooled liquid that collects in the bag 10 is then transported through the line 21 to the next degassing device or after passing through the last degassing device to the last cooling device 22.

The bag 10 is designed in such a way that sedimentation processes are prevented. The position in the bag 10 is controlled by means of the discharge by the feed pump. In the last 790 84 31 12 cooling device 22, the vapors formed after the reducing valve 23 "and flowing to the condensation column 24 are condensed by countercurrently moving cooling water which is supplied through the conduit 25 to the top of the condensation column 24. The chimney pipe protrudes through a bottom 27 of the last cooling device 22. The heated cooling water is discharged via the pipe 28. The cooled liquid medium collects in the collection space 29 and is discharged through the pipe 30 and further processed, for example filtered, centrifuged or subjected to such an operation »

Fig. 2 shows a heat exchange device, the condensation column 13 and the cyclonic vapor space 9 of which do not form a structural unit, but are only connected to each other by a vapor line 31. The liquid medium brought from the heat exchanger of the subsequent higher temperature into the vapor space 9 via the conduit 42 expands to form vapor. The cooled liquid medium ends up in the bag 32. In this bag 32 there is an inner tube, into which a stirrer 33 is inserted, which creates a forced circulation of the liquid medium cooled to a lower temperature level. At a high turbulence, the effluent flow is withdrawn from the circulating medium via the pipe 43 and is led to a device with the subsequent lower temperature level. Due to the forced circulation, especially the discharge of slurry is made possible with a considerable sedimentation rate. The vapor originating from the vapor space 9 flows through the line 31 to the collection space 34 of the condensation column 13. The collection space 34 has an inner tube 35, in the lower end of which the vapor line 31 opens. As a result, a circulation of the mixture contained in the collection space 34 is again established. The condensation column 13 has inclined downwardly inclined guide plates 36, over which the liquid medium, in this case the suspension, flows, which is fed via the conduit 37 to the top of the condensation column 13. This formation of these slates in the condensation column avoids the build-up of cakings, as any deposits on the slates 710 84 31 13 36 are washed off by the downflowing liquid medium. Preferably, the column 13 again has a degassing device 38 at the top. The heated liquid medium (suspension) is discharged in the collection space 34 between the wall of the collection space and the wall of the inner tube via the pipe 39 to a dosing pump 40. This dosing pump is again connected to the heat exchanger with the next higher temperature or to the reaction vessel.

It goes without saying for those skilled in the art that branch pipes and / or bypass lines serving in the supply and optionally the discharges of the device according to the invention may be provided, especially for the liquid level control.

The device can be controlled in a simple manner by means of control technology, so that soot is relatively inexpensive and effortless, with a high space-time yield, a continuous process is possible. Due to the absence of moving parts (apart from the dosing pumps), high demands are not made on the mechanical properties of the materials used. It is therefore possible to choose materials that are best adapted to the reaction conditions, especially with regard to the corrosive attack by the medium.

The device according to the method is not provided with heat-exchange surfaces. The heat and dust exchange processes run directly via phase separation surfaces. The device provides large phase interfaces. Combined with good degassing of all devices 30, despite the use of materials with poor heat conduction coefficients, excellent heat transfer conditions are obtained which enable a very compact construction.

Since heat exchange surfaces are absent, the device according to the invention allows the continuous treatment of solutions containing substantial cake-forming substances. A difficult and common biscuit-forming substance is, for example, calcium sulfate.

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It goes without saying for the skilled person that the device according to the invention can be used with great advantage for the treatment of very large volume flows, since separate parts of the device are customary in other technical processes and under different circumstances and since the section for measurement and control technology is decreasing with increasing size of the devices.

790 8431

Claims (15)

Method for the direct heating of a liquid medium, optionally containing solids, at a high temperature, using heat of condensation, characterized in that the liquid medium partly evaporates by one or more stages of expansion and without the use of foreign materials. heat transfer agents are condensed directly in the medium to be heated in countercurrent. 2. Process according to claim 1, characterized in that the liquid medium to be heated is heated to the reaction temperature to be reached immediately before or in the reaction vessel after the last heating step has been flowed through, by direct addition of additional vapor. 3. A method according to claim 1, characterized in that the liquid medium to be heated is cooled and concentrated after passing through the one or more expansion stages. 4. Method according to claim 1, characterized in that the liquid medium is cooled in a recuperator after flowing through the one or more expansion stages. Method according to claim 4, characterized in that a recuperator with a high internal turbulence is used. Method according to one or more of the preceding claims, characterized in that a solution in water is used as the liquid medium. 7. Device for carrying out the method according to any one of claims 1 to 6, characterized by the combination of the following features: a a pressure reaction vessel, b one or more heat exchangers with b 1 an expansion tank and b 2 one with the vapor space of the expansion vessel-communicating condensation column, which has 790 84 31 b 2.1 distribution and / or dripping bottoms, c a feed pump with dependency. ... volume flow controlled from the liquid level per heat exchange stage and reaction vessel, 5. a final cooling stage that is designed as d 1 expansion stage or as d 2 recuperator. 8. Device according to claim 7, characterized in that the reaction vessel has a centrally arranged flow tube, in the bottom opening of which a supply conduit for the heated liquid medium opens and in the bottom part of the reaction vessel outside the flow. tube a conduit leading to the first heat exchanger for discharging treated medium is provided. 9. Device according to claim 8, characterized in that a supply pipe for steam and / or reaction gas also opens into the bottom opening of the flow tube. 10. Device according to claim 7, characterized in that the one or more heat exchangers have a cyclonic vapor space with a collecting space for the at least partially expanded liquid medium arranged underneath, while the vapor space is provided by means of a flue pipe, which is the top end is covered by a drip cap, communicating with the condensation column, the condensation column being separated from the vapor space of the expander in such a way that the heated liquid medium is discharged to a collection space which is connected by means of a feed pump with the heat exchanger of the next higher energy level or with the reaction vessel and each having a supply line: a) for the liquid medium to be heated, which opens into the top of the condensation column, b) for the liquid medium to be expanded, which opens at the top of the vapor space, and c) each a discharge for the The partially expanded cooled liquid medium, which opens into the top of the vapor space of the heat exchanger with the subsequent 790 84 31 lower energy level or into the cooling device by means of an expansion valve. 11. Device as claimed in claim 7, characterized in that the one or more exchangers have a cyclonic vapor space with a collecting space arranged below it for the at least partially expanded liquid medium, wherein a flow tube is arranged in the collecting space, in which a circulating stirrer is located , and the vapor space is connected to a condensation column by means of a vapor pipe and opens into a flow tube present in the collection column of the condensation column and each has a pipe a) for the liquid medium to be heated, which opens into the top of the condensation column, 15 b) for the liquid medium to be expanded which flows into the top of the vapor space and c) for the partially expanded, cooled liquid medium, which flows into the top of the vapor space of the heat exchanger with the subsequent lower energy level or in the last cooling device opens. Device according to claim 7, characterized in that it has a final cooling device which is designed as a vacuum expansion device. 13. Device according to claim 7, characterized in that the last cooling device has a recuperator with a high internal turbulence. Inriditing according to any one of claims 7 to 11, characterized in that the condensation columns and / or the reaction vessel have degassing devices at the top. Method for carrying out precipitation or leaching reactions, characterized in that the method according to one of claims 1 to 6 and the device according to any one of claims 7 to 14 is used. 790 84 31