DE2850104A1 - METHOD FOR DIRECTLY WARMING A LIQUID MEDIUM USING THE CONDENSATION HEAT, AND DEVICE FOR CARRYING OUT THE METHOD - Google Patents

Description

Th. Goldschmidt AG, Essen

Process for the direct heating of a liquid medium using the Heat of condensation and device for carrying out the process

Claims: Pages 2 to 6 Description: Pages 7 to 26 Illustrations: Pages 27 to 28

030021/0484

The invention relates to a method for direct heating an optionally solids-containing liquid medium to high temperatures using the condensate ion swarm.

It relates in particular to a method for the direct heating of, in particular, aqueous solutions and suspensions to temperatures> 150 C / vorzugswi
Utilization of the condensation heat.

to temperatures> 150 C / preferably up to about 250 C, below

The invention also relates to one for carrying out the according to the invention Method particularly suitable device.

Finally, the invention relates to the use of the method and the device for carrying out precipitation or leaching reactions.

It is often the task of liquid reactions Medium, in particular aqueous medium, to be carried out at high temperatures, in particular temperatures between 150 and 250 ° C. This is often the case with precipitation or leaching reactions the case. Carrying out such reactions in this temperature range brings various difficulties with himself. For economic reasons, it is almost always necessary to reduce the heat supplied to the system as much as possible largely recovered. Apparatus with a fixed exchange surface is preferably used for the heat exchange.

$ 30021/0484

A particular difficulty is that encrustations are expected on the heat transfer surfaces must, which affect the heat transfer and the removal of which is difficult and expensive.

Additional difficulties arise when the solution to be treated is already aggressive or during the reaction becomes even more aggressive. In these cases, the use is particularly resistant to corrosion, but mechanically Little or hardly stressable materials are mandatory.

An example of a high temperature expiring Precipitation reaction is e.g. the high temperature hydrolysis of Iron, chromium and aluminum from the aqueous solutions of their sulfates.

If these metals are precipitated at temperatures between 20 and 50 C, hydroxide sludges are often formed, which are extraordinary difficult to filter. It is known, however, that these filtration difficulties do not occur when the precipitations are carried out approximately in the range from 180 to 250.degree.

Carrying out the reaction is, as stated above, made more difficult by the fact that the temperature rises from the solution the hydroxides, calcium sulfate, silicon dioxide and possibly other compounds precipitate and are attached to the hot

030021/0484

- Q -

Places, i.e. preferably on the heat exchange surfaces, incrustations produce. At the same time, the acid concentration increases. This results in the temperature range mentioned to a very strong corrosive stress on the materials. In addition, at temperatures of 150 to 250.degree operating pressures of up to 50 bar occur in aqueous solutions.

These material problems force the use of materials, e.g. Teflon and carbon, which are listed below Conditions of use no longer show any usable strengthening properties. Other materials, such as tantalum or titanium, which would withstand the stresses of corrosion are so expensive that they are only economical as cladding materials can be used. In both cases, the forces must pass through non-corrosion-resistant carbon steels recorded v / earth. Since moving parts in the apparatus also have to be designed in a similarly complex manner, these should as far as possible to be avoided. The plastic-steel composite construction makes heat exchange surfaces impossible because of the additional heat transfer resistance.

These material problems present the process engineer the task of developing devices that are mechanically stressed as little as possible, and therefore in particular to forego moving parts.

030021/048 *

Similar considerations apply to leaching reactions, e.g. for the leaching of finely ground minerals with alkalis or acids, optionally with the addition of reactive gases such as oxygen or chlorine.

This also includes leaching of metal-containing solids, e.g. from spent catalysts that are involved in have been used at high temperatures and contain valuable materials such as non-ferrous or precious metals.

It is known to heat suspensions in stages. It is a method in DE-PS 19 37 3 92, for example described, which is characterized / that the heating of the suspension is gradual through heat transfer surfaces takes place through it, wherein in the 1st stage one or more heat exchangers through exhaust steam from an expansion system are heated, while the 2nd stage is designed as a double tube exchanger in which the suspension further heated by indirect heat exchange and the returning suspension is cooled and finally in a 3rd stage the remaining heat required Heating with high pressure steam using an organic heat transfer medium or a salt heat transfer medium using heat exchange surfaces through, is made.

This method has the disadvantage of using double tube heat exchangers, whereby in leaching or precipitation

330021/0484

reactions on the heat exchange surfaces can cause incrustations.

Direct heat exchange processes have also been proposed for the desalination of seawater. However Here too, heat transfer media from outside the system are usually used in the exchange stages with the highest energy content used"

Single or multi-stage process for cooling solids-containing liquids using flash evaporation are known and are described, for example, in DE-OS 23 61 236. The resulting vapors are in in these cases only precipitated by direct condensation / but not used to preheat solutions .

The aforementioned literature as well as the general status of However, no methods or devices can be found in technology, which carry out reactions in one allow high temperature range up to about 25O ° C to carry out and in particular precipitation or leaching reactions in this temperature range while avoiding the above enable the disadvantages described.

In the method according to the invention, the Problems solved in that the heated liquid medium

partially evaporated by single or multi-stage expansion and without the use of non-system heat transfer media directly in the countercurrent to be heated Medium is condensed.

An essential feature of the method according to the invention is therefore that the cooling of the particular solids-containing liquid medium by exclusive and consequent use of a single, but preferably multi-stage, flash evaporation is effected, with the use of any non-system heat transfer medium is dispensed with. The vapors formed during the flash evaporation are directly fed into the countercurrent Medium to be heated condensed. Through the direct Heat transfer, optimal conditions for the exchange are created. The exchangers can therefore be very small be built. The elimination of the heat exchange surfaces means that corrosion-resistant coatings are used only made possible.

A preferred embodiment of the method according to the invention consists in that the liquid medium to be heated after flowing through the last preheating stage through direct Feeding of additional steam directly upstream of the reactor or in the reactor to the reaction temperature to be reached is heated.

1) 30021/0 * 8 *

It is consciously accepted that the heating up Medium through the condensation of the vapors in it during the warm-up process and through the addition of steam in the final reaction stage is diluted. When going through the relaxation stages, the solution is largely concentrated again.

The liquid medium is preferably after flowing through the Expansion stage Cn) cooled further by reducing the pressure and concentrated and thus almost reached the initial concentration.

In the range of relatively low temperatures / preferably at Temperatures around or <120 C as well as corrosive if justifiable Stress and a low tendency to crust formation in this temperature range can result in the final cooling of the liquid medium after flowing through the expansion stage (s) be made in a recuperator. A plate exchanger is preferably used here from accordingly corrosion-resistant materials with high internal turbulence.

The device according to the invention for carrying out the method is characterized by the combination of the following features:

a pressure reactor,

b 'with one or more heat exchange stages

«30021/048 *

b 1 an expansion tank and

b 2 a condensation column connected to the vapor space of the expansion tank, which

b 2.1 has distribution and / or trickle inserts,

c a feed pump with a volume flow regulated depending on the liquid level for each heat exchange stage and reactor,

d a cooling final stage, which as d 1 relaxation stage or as

d 2 recuperator is formed.

A device which contains more than one direct exchange stage is preferred. Within a temperature range the reaction from about 180 to 25O ° C, it is advisable to Use 2 to 3 direct heat exchange stages.

The reactor used in the device according to the invention is at the parts in contact with the product with correspondingly high-temperature and corrosion-resistant materials, e.g. tantalum, titanium or Teflon, coated. Absorbing the forces Components are made from appropriately temperature-resistant carbon steels.

The reactor is preferably characterized in that it has a centrally arranged flow tube in which lower opening a feed line for the heated liquid medium opens and in the lower reactor area outside the

030021/0484

Flow tube a line leading to the first heat exchange stage is provided for discharging the treated medium is »The circulation in the reactor is generated by the incoming currents. The circulation can also be carried out by an external circuit and a pump can be boosted. The heated liquid to be treated or reacting rises in the middle arranged flow tube and sinks after leaving the flow tube between the inner reactor wall and the flow tube down, where it is removed from the reactor and fed to the first heat exchange stage. The one in the reactor Lingering liquid circulates several times in the sense described. The circulation ratio can be determined by the design the propulsion jets are influenced.

In a further embodiment of the device, a feed line for steam and / or reaction gas also opens into the lower opening of the flow tube. Both streams are fed in regulated according to the required heating and / or the reaction equations. The supply of steam heats the medium further and, by reducing the density of the liquid medium, increases the speed of the circulating flow and thus the circulation ratio. The same applies to the reaction _{gas 7} fed in at this point, for example oxygen or chlorine. The residence time distribution in the reactor can be influenced by means of an externally arranged pump and / or by adjusting the degree of slenderness of the reactor.

030021/040 *

If precipitation reactions are carried out in the device according to the invention / turn out to be particularly favorable found out that the circulating stream in the reactor contains germs in the precipitation product / which promote coarse grain formation / thereby facilitating the filtration of the liquid medium containing solids.

The reactor has no mechanically stressed material parts that come into contact with the product. the Materials of the inner surfaces of the apparatus can only be selected with regard to corrosion resistance will. All walls in contact with the product can be clad with plastic, which has the lowest possible adhesion properties for incrustations. It is difficult to insulate the inner surfaces of the apparatus in the upper part keep it moist / to effectively counter possible incrustations *

If the reaction takes place at high speeds and has only a low reaction enthalpy, the reactor can also as. Tube reactor in combination with a small loop reactor be trained.

The liquid medium leaving the reactor at the highest temperature level is now fed to the first heat exchange stage. The levels of relaxation are expediently so low Liquid content and thus such low residence

030021/048 *

times that the equilibria established in the reactor are maintained stay.

Preferably, the heat exchange stage or a plurality of the same is designed in such a way that it has a cyclone-like design Has vapor space with a collecting space arranged underneath for the at least partially expanded liquid medium and the vapor space via a Kaitiinrohr, which at the top The end is covered by a drip hood, with the condensation column is in connection, the condensation column being so separated from the vapor space of the expansion stage is that the heated liquid medium is diverted to a collecting space, which is connected to the via a feed pump Heat exchange stage of the next higher energy level or the reactor is connected, and one line each

a) for the liquid medium to be heated, which opens into the top of the condensation column,

b) for the liquid medium to be relaxed, which is in the head of the The vapor space opens, and

c) a discharge line for the partially relaxed, cooled liquid medium, which is located in the head of the vapor space of the Heat exchange stage of the next lower energy level or in the cooling stage via an expansion valve flows into

having.

030021/0484

The heat exchange takes place in the heat exchange stage described above in such a way that in the cyclone-like Vapor chamber the heated liquid medium is injected after passing through a relief valve. The vapors released in the process flow through the chimney pipe into the condensation column and give off their enthalpy of reaction to the liquid medium to be heated from the next lower temperature level, which is in the top of the condensation column is fed in. The liquid to be heated trickles over the distribution and sieve trays, which are arranged in the condensation column. The heated liquid overflows a base, which separates the condensation column from the vapor space, into a standpipe, from which it is connected via a feed pump depending on the liquid level metered volume flow is fed to the reactor. At the downstream heat exchangers the heated liquid medium is correspondingly higher in the top of the column of the heat exchange stage Temperature levels fed.

The at least partially expanded and partially cooled liquid medium collects under the vapor space in a collecting space and will be the next lower to the next heat exchange stage Temperature levels supplied depending on the liquid level. However, if it is the last heat exchange stage, the reaction mixture is drawn off and fed to the final cooling stage.

030021/0484

285QIQ4

Is the liquid medium a suspension with increased viscosity or increased tendency of the suspended particles to sediment / it is preferable to use a device which is characterized in that the heat exchange stage or a plurality thereof is cyclonic Has vapor space with a collecting space arranged underneath for the at least partially expanded liquid medium, wherein A flow pipe is arranged in the collecting space, in which a circulating stirrer is located, and the vapor space via a steam line connected to a condensation column and into a flow tube located in the bottom of the condensation column opens and one line each

a) for the liquid medium to be heated, which is in the head of the Condensation column opens,

b) for the liquid medium to be relaxed, which is in the head of the The vapor space opens, and

c) for the partially relaxed, cooled liquid medium, which is in the head of the vapor space of the heat exchange stage of the next lower energy level or in the final cooling stage flows out.

In the case of the heat exchange stage marked in this way, it makes sense to to separate the vapor space from the condensation column so that the cooled suspension in a circulated sump with The smallest possible liquid content is stored. The heated suspension is circulated in a sump, which works as a pump reservoir, collected.

■ 030021/0434

In these cases it is expedient to use it in the condensation column no distribution or sieve bottom, but downwardly inclined guide plates, with an encrustation of these Sheets through the trickling down suspension to be heated is counteracted.

The condensation columns and / or the reactor preferably contain degassing devices for discharge in the head area the excess of any reaction gases or non-condensable gases used during the reaction were not implemented or which resulted from side reactions.

The device according to the invention has an input side Äbkühlungsstufe on, which are operated with negative pressure can. This can be designed according to the heat exchange stages be. In the condensation column, however, water is fed in at the top, which in a suitable manner together at the foot is withdrawn with the condensed vapors. The cooled liquid medium can be taken from the collecting space located below the relaxation zone and the final, processing according to the invention, e.g. a filtration, can no longer be fed.

Is encrustation and / or corrosive damage under the conditions prevailing in the final cooling stage A recuperator, in particular in the form of a plate exchanger, can no longer be feared at this point

030021/0484

285Q1Q4

high internal turbulence.

The device according to the invention and that in this device Feasible procedures are to be explained in more detail with the aid of the following figures.

Figure 1 shows schematically the reactor, heat exchange stage and final cooling stage.

Figure 2 shows a heat exchange stage in a special, suspensions with higher viscosity and / or considerable Sedimentation rate, adapted design.

In Figure 1, the high-temperature reactor is labeled (1). It has a flow pipe (2) into which a feed line (3) for the highly heated liquid medium flows out. There are also provided feed lines (4) for any reaction gas required and (5) for heating steam for supplying the amount of energy required to reach the reaction temperature. The liquid to be treated Medium rises in the flow pipe (2) as a result of the momentum of the entering liquid and as a result of the driving forces that caused by the other incoming currents, upwards, whereby a circulating flow is established. After leaving the flow pipe (2), the liquid medium sinks to the bottom. Mean residence time, flow velocity and slenderness of the reactor are chosen so that the reaction in the liquid medium is completed when

Ö30021 / 048 *

this leaves the reactor via line {6).

The reactor is preferably built so that the impinging Solid particles remain in the circulating flow and cannot settle, as do the gases introduced in the circulating flow linger in finely divided form and thus circulate, unreacted or newly formed gas components that are in the Collect at the top of the reactor, all parts in contact with the product can be drained off via an expansion valve, so also the vapor or gas space at the top of the reactor with corrosion-resistant Material are lined and all forces are absorbed by a corrosion-resistant, load-bearing construction will. At the top of the reactor there is a pressure reducing valve (7) with drainage if necessary excess reaction gas used or any inert gases present.

After the reaction, the liquid medium leaves the reactor via line (6) to the reducing valve (8). The mass flow of the liquid medium is regulated depending on the liquid level in the reactor (1). Through the vapor relaxation the treated liquid medium is frozen in its reaction equivalence position, and it arises a temperature corresponding to the reducing pressure. The gas-liquid-solid mixture formed after the expansion valve flows into a cyclone-like vapor space (9). The cooled liquid with the solid particles collects in the sack (10). the

030021/0484

285G104

Separation of solids-laden liquids and vapors does not need to be perfect because any liquid droplets that may be entrained are returned to the reactor will. The vapors flow through the chimney pipe (11), which is covered by a drip hood (12), into the Condensation column (13) which contains distribution trays (14) and trickle trays (15). That flows to the rising vapors Liquid to be heated and fed to the top of the condensation column (13) via the line (16) by means of the metering pump (17) Against the medium and gives off its enthalpy of condensation to it. The heated to a higher temperature level liquid medium runs after passing the condensation column Ci 3) through the bottom (18) into the sump container (19) "and will from there by means of the metering pump (20) into the line (3), which leads to the high-temperature reactor, fed. the The condensation column (.13) has a degassing device similar to the reactor (41) for non-condensable gases. The cooled liquid that has accumulated in the sack (10) Has,; is now via the line (21) of the next degassing stage or after passing through the last degassing stage of the Cooling final stage (22) supplied. The sack (10) is like this dimensioned so that sedimentation processes are suppressed. The status in the sack (TO) is determined by the removal by the Regulated feed pump. In the final cooling stage (22) the vapors formed after the reducing valve (23), which flow into the condensation column (24), through countercurrent Cooling water, which is fed to the top of the condensation column (24) via the line (25), condenses. That

030 021/04 «*

Chimney pipe (26) is guided through a base (27) of the cooling end stage (22). The heated cooling water is over the line (28) discharged. The cooled liquid medium collects in the collecting space (29) and is via the line (30) withdrawn and further processed, such as filtered, centrifuged or the like.

Figure 2 shows a heat exchange stage in which the condensation column (13) and the cyclone-like one Vapor space (.9) do not form a structural unit, but are only connected to one another by a steam pipe (31). That from a heat exchange stage of the next higher temperature level via the line (42) into the vapor space (9) liquid medium relaxes with development of vapors. The cooled liquid medium enters the sack (32). In the sack (32) there is an inner tube, into which a stirrer (33) is immersed causes liquid medium cooled to a lower temperature level. At high * Turbulence, the extraction flow is withdrawn via line (43) and to a stage of the next lower temperature level derived. The forced circulation especially enables the discharge of suspensions with a considerable sedimentation speed enables. The steam emerging from the vapor space (9) flows through the line (31) into the collecting space (34) of the Condensation column (13). The collecting space (34) has an inner tube (35), in the lower end of which the steam line (31) flows out. This in turn causes the sump to circulate

030021/0 * 84

285Q104

acts, which is located in the collecting space (34). The condensation column (13) has diagonally downwardly inclined guide plates (.36), over which the liquid medium, in this If the suspension flows, which is fed to the top of the condensation column (13) via line (37). By this design of the sheets in the condensation column prevents the formation of incrustations, since possible precipitations on the baffles (36) from the downward flowing liquid medium. are washed away. The condensation column (13) in turn preferably has one in the head area Degassing device (38). The heated liquid medium (suspension) is in the collecting space (34) between the wall of the Collecting space and inner pipe wall removed via the line (39) and fed to a metering pump (40), which is in connection either with the 'heat exchange stage next higher temperature level or with the high temperature reactor.

It is a matter of course to the person skilled in the art that in the supply lines and, if appropriate, the discharge lines of the device according to the invention the regulation, in particular the liquid level regulation, serving branch and / or bypass lines are provided could be.

The device can be controlled in a very simple manner, so that with relatively little Effort and high space-time yield a continuous mode of operation is possible. Due to the lack of moving parts (with the exception of the dosing pumps) must be connected to the mechanical

G30Ö21 / 0484

Properties of the materials used do not meet high requirements be asked. It is therefore possible to reduce the reaction conditions, especially the corrosive attack of the medium to select optimally adapted materials.

The device according to the invention does not contain any heat exchange surfaces. The heat and mass transfer processes take place directly over phase interfaces. The device creates large phase interfaces. Combined with good degassing of all devices, this results in despite the use of materials that have poor coefficients of thermal conductivity, excellent heat transfer conditions that allow a very compact design.

Since there are no heat exchange surfaces, only the inventive Device for the continuous treatment of solutions which contain large amounts of crusting agents. A difficult and frequently occurring crust former is e.g. calcium sulfate.

For the person skilled in the art, it goes without saying that the inventive device for the treatment of very large volume flows can be used particularly advantageously, because individual plant components are introduced into other large-scale processes under different conditions and because the actually small share for the measurement and control technology still decreases with increasing size of the apparatus.

6t0021 / 0iS4

Blank page

Claims (15)

285Q104 claims 1. Procedure for direct heating of a possibly Liquid medium containing solids to high temperatures using the heat of condensation, characterized in that the heated liquid medium partially evaporates by means of single or multi-stage relaxation and without the use of non-system heat transfer media directly in the countercurrent Medium to be heated is condensed. 2. The method according to claim 1, characterized in that the liquid medium after flowing through the last preheating stage by direct feeding in of additional steam immediately before or in the reactor on the to be reached Reaction temperature is heated. 3. The method according to claim 1, characterized in that the liquid medium is cooled and concentrated after flowing through the expansion stage Cn) by reducing the pressure will. 4. The method according to claim 1, characterized in that the liquid medium is cooled in a recuperator after flowing through the expansion stage Cn). 030021/0484 5. The method according to claim 4, characterized in that a recuperator is used with high turbulence. 6. The method according to one or more of the preceding claims, characterized in that as a liquid Medium an aqueous solution is used. 7. Device for performing the method according to claims 1 to 6, characterized by the combination following features: a pressure reactor, b one or more heat exchange stages with b 1 an expansion tank and b 2 one with the vapor space of the expansion tank related condensation column, which b 2.1 has distribution and / or trickle inserts, c a feed pump with a volume flow regulated depending on the liquid level for each heat exchange stage and reactor, d a cooling final stage, which as d 1 relaxation stage or as d 2 recuperator is formed. 8. Apparatus according to claim 7, characterized in that the reactor has a centrally arranged flow tube a feed line for the heated liquid medium opens into the lower opening and in the lower reactor 030021/0484 rich outside the flow pipe leading to the first heat exchange stage line for the discharge of the treated medium is provided. 9. Apparatus according to claim 8, characterized in that A feed line for steam and / or reaction gas also opens into the lower opening of the flow tube. 10. Apparatus according to claim 7, characterized in that the heat exchange stage or a plurality of the same a cyclone-like vapor space with a collecting space arranged underneath for the at least partially expanded Has liquid medium and the vapor space over a Tube, which is covered at the upper end by a drip hood, is in connection with the condensation column, whereby the condensation column from the vapor space of the relaxation sstufe is separated in such a way that the heated liquid medium is diverted to a collecting space, which is connected to the heat exchange stage of the via a feed pump next higher energy level or the reactor is connected, and one feed line each a) for the liquid medium to be heated, which is in the head the condensation column opens, b) for the liquid medium to be relaxed, which is in the head of the vapor space opens, and c) one derivation each for the partially tensioned, cooled 030021/0484 liquid medium, which in the head of the vapor space of the heat exchange stage of the next lower energy level or flows into the cooling stage via a relief valve, having. 11. The device according to claim 7, characterized in that the heat exchange stage or a plurality of the same one cyclonic vapor room. with a collecting space arranged underneath for the at least partially relaxed liquid medium, a flow pipe in which there is a circulating stirrer and the vapor chamber is arranged in the collecting chamber via a steam line with a condensation column is connected and opens into a flow tube located in the bottom of the condensation column and one feed line each a) for the liquid medium to be heated, which ends in the top of the condensation column, b) for the liquid medium to be relaxed, which opens in the head of the vapor space, and c) for the partially expanded, cooled liquid medium in the head of the vapor space of the heat exchange stage the next lower energy level or in the cooling send stage opens. 12. The device according to claim 7, characterized in that it has a cooling end stage, which is used as a vacuum relaxation stage is trained. 030021/0484 13. Apparatus according to claim 7, characterized in that it has a recuperator with high internal turbulence as the final cooling stage. 14. The device according to one or more of claims 7 to 11, characterized in that the condensation columns and / or the reactor has degassing devices in the head area. 15. Application of the method of claims 1 to 6 and the Apparatus of claims 7 to 14 for precipitation or leaching reactions. © 30021/04 «*