NO793653L - PROCEDURE FOR DIRECT HEATING OF Aqueous MEDIUM - Google Patents

Description

The invention relates to a method for directly heating any liquid medium containing solids to high temperatures while utilizing the heat of condensation.

It particularly relates to a method for directly heating particularly aqueous solutions and suspensions to temperatures greater than 150°C, preferably to approx. 250°C,

during utilization of the condensation heat.

The invention further relates to an implementation of

the method according to the invention suitable device.

The invention relates to final use of the method and device for carrying out folding or leaching reactions.

The task is often to carry out reactions in a liquid medium, especially an aqueous medium, at high temperatures, especially at temperatures between 150 and 250°C. This is often the case in folding or leaching reactions. Carrying out such reactions in this temperature range, however, entails various difficulties. For economic reasons, it is almost always necessary to recover the amount of heat supplied to the system to the greatest extent possible. Apparatus with fixed exchange surfaces is preferably used for heat exchange.

A particular difficulty lies in the fact that it must be calculated

with deposits on the heat exchanger floats, which reduces the heat transfer and whose removal is difficult and labor-intensive.

Further difficulties arise when the solutions to be treated are already aggressive or become aggressive during reaction. In such cases, the use of materials that are particularly corrosion-resistant, but mechanically little or hardly influenced.

An example of a folding reaction proceeding at high temperature is e.g. the high temperature hydrolysis of iron, chromium and

aluminum from aqueous solutions of their sulfates.

If one precipitates these metals at temperatures between

2 0 and 50°C, hydroxide sludge is often formed which is very difficult to filter. It is known, however, that these filtration difficulties do not occur when the heating is carried out approximately in the range from 180 to 250°C.

As mentioned above, carrying out the reaction is made more difficult by the fact that the solution precipitates hydroxides, calcium sulphate, silicon dioxide and possibly further compounds with increasing temperature, whereby deposits occur in hot places, i.e. preferably on the heat exchanger floats. At the same time, the acid concentration rises. In the aforementioned temperature range, this leads to a strong corrosive attack on the materials. In addition, at temperatures from 150 to 250°C in aqueous solutions, operating pressures of up to 50 bar occur.

These material problems force the use of materials, e.g. teflon and carbon, which under the stated conditions of use no longer have useful holding properties. Other materials such as tantalum or titanium, which would be able to withstand the corrosion stresses, are too expensive so that they can only be used as plating materials in an economical way. In both cases, the compressive forces must be absorbed by non-corrosion-resistant carbon steels. As moving parts in the devices must also be carried out in a manner similar to the work area, these should be avoided if at all possible. Plastic/steel combinations make heat exchanger surfaces impossible due to the additional heat transfer resistance.

These material problems present the chemical engineer with the task of developing devices that are as little as possible exposed to mechanical stress and therefore particularly to avoid moving parts.

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

Hereby, consideration must also be given to a leaching of metal-containing solids, e.g. of used catalysts that have been used at high temperatures, and materials such as e.g. contains non-ferrous metals or precious metals.

It is known to heat suspensions stepwise. DE-PS 1937392 describes, for example, a method which is characterized by the heating of the suspension taking place in stages over heat transfer surfaces, whereby in the first stage one or more heat exchangers are heated with steam from an expansion plant, while the second stage is carried out as a double tube exchanger in which the suspension by indirect heat exchange is further heated and the returning suspension is cooled, and finally a third step where the remaining required amount of heat is supplied by heating with high-pressure steam using an organic heat carrier or a salt heat carrier, through heat exchanger surfaces.

This method has the disadvantage of using double-tube heat exchangers, whereby deposits can form on the heat exchanger floats during leaching or precipitation reactions.

Direct heat exchange for desalination of seawater has also been proposed. However, here as a rule, in the exchanger stages with the highest energy content, heat transfer agents introduced into the system are used.

One- or multi-stage methods for cooling liquids containing solids using expansion evaporation are known and are described, for example, in DE-OS 2361236. In these cases, the water vapor formed is only precipitated by direct condensation, but not used for preheating solutions.

However, there are no methods or devices known in the above-mentioned literature and from the general state of the art that allow reactions to be carried out in a high temperature range up to approx. 2 50°C and which enables precipitation or leaching reactions in this temperature range by avoiding the above-mentioned disadvantages.

In the method according to the invention, the set task is solved in that the heated, liquid medium is partly vaporized by one- or multi-stage expansion and, without the use of a heat transfer agent foreign to the system, is immediately condensed in the medium which is to be heated in a countercurrent flow.

An essential characteristic of the method according to the invention thus consists in the fact that the cooling of the particularly solid-containing liquid medium is effected by the exclusive and consistent use of one, but preferably multi-stage expansion evaporation, whereby the use of any heat transfer agent foreign to the system is avoided. Thereby, the water vapor formed during the expansion evaporation is directly condensed in the medium which is to be heated in a countercurrent flow. The direct heat transfer provides optimal conditions for exchange. The heat exchangers can therefore be built very small. In the absence of heat exchanger surfaces, the use of corrosion-resistant coatings is first made possible.

A preferred embodiment of the method according to the invention consists in that the liquid medium to be heated after passing through the last preheating step is heated by direct input of additional steam before the reactor or in the reactor to the achievable reaction temperature.

It is thereby taken into account that the medium to be heated is diluted by condensation of the water vapor in it during the course of the heating and by the addition of steam in the final reaction step. During the passage of the expansion steps, the solution is again largely concentrated.

Preferably, the liquid medium after flowing through the expansion step(s) is cooled and concentrated again by pressure reduction and thus almost reaches the initial concentration.

In the area of relatively low temperatures, preferably

at temperatures at or below 120°C as well as at tolerable corrosion stresses and little tendency for the formation of deposits in this temperature range, the final cooling of the liquid medium can be carried out after passing through the expansion step(s) in a recuperator. Preferably, a plate exchanger of corresponding corrosion-resistant materials, which exhibits a high internal turbulence, is used.

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

a a pressure reactor,

b one or more heat exchanger stages with, among other things, an expansion tank and

b2 one with the vapor space in the expansion vessel in connection with a standing condensation column,

which exhibits

b 2.1 distribution and/or contact efforts,

c a feeding pump with depending on liquid level

adjustable volume flow for each heat exchanger stage and reactor,

d a cooling stage which is formed as dl expansion stage or as

d2 recuperator.

A device that contains more than one direct heat exchanger stage is preferred. Within a temperature range of the reaction of approx. 180 to 250°, it is recommended to use two to three direct heat exchanger stages.

The reactor used in the device according to the invention is coated with corresponding temperature- and corrosion-resistant materials, e.g. tantalum, titanium or Teflon. Building parts that take up mechanical stress are made of corresponding temperature-resistant carbon steel.

Preferably, the reactor is characterized by the fact that it contains a flow tube arranged in the middle, in which lower opening opens a supply line for the liquid, heated medium and in the lower reactor area outside the flow tube is set aside for a leading line to the first heat exchanger stage for discharge of the treated medium . The circulation in the reactor is formed by incoming currents. Circulation can be further increased by an external circuit and a pump. The heated liquid to be treated or converted rises in the centrally arranged flow pipe upwards and sinks downwards after the outlet from the flow pipe between the inner reactor wall and the flow pipe, from where it is withdrawn from the reactor and supplied to the first heat exchanger stage. The liquid in the reactor circulates several times in the specified manner. The circulation process can be influenced by the design of the drive jets.

In a further embodiment of the device, a further supply line for steam and/or reaction gas opens into the lower opening in the flow pipe. Both streams are fed in regulated in relation to the required heating and/or reaction conditions. With the addition of steam, the medium is further heated and by reducing the density of the liquid medium, the speed of the circulation flow and thus the circulation ratio is increased. The same applies to the reaction gas added at this point, e.g. oxygen and chlorine. The residence time distribution in the reactor can be influenced via an externally arranged pump and/or by adjusting the degree of slenderness of the reactor.

If precipitation reactions are carried out in the device according to the invention, it is particularly advantageous that the circulation flow in the reactor in the precipitation product contains germs which favor the formation of coarse grains, whereby the filtration of solids contained in the liquid medium is facilitated.

The reactor contains no mechanically affected material parts that come into contact with the product. The material in the inner surfaces of the device can be selected exclusively with a view to corrosion resistance. All product-touched walls can be coated with plastic that has the least possible adhesion property for deposits. Thereby, the inner surfaces of the device in the upper part can be poorly insulated and thus kept moist to effectively counteract deposits.

If the reaction proceeds at a high rate and exhibits only a small reaction enthalpy, the reactor can also be formed as a tube reactor in combination with a small loop reactor.

The liquid medium leaving the reactor at the highest temperature level is fed to the first heat exchanger stage. Appropriately, the expansion steps thereby have such a low liquid content and thus such a low residence time that the equilibria set in the reactor are maintained.

Preferably, the heat exchanger stage or a majority of these are formed in such a way that they contain a cyclone-shaped steam chamber with a collection chamber arranged underneath for the at least partially expanded liquid medium and that the steam chamber is connected over a chimney pipe, which is covered at the upper end with a drip cap with the condensation column , whereby the condensing column is separated from the vapor space of the expansion stage so that the heated liquid medium is diverted to a collection space which is connected to a feed pump with the heat exchanger stage at the next highest energy level or the reactor, each having a line

a) for the liquid medium to be heated and which exits at the top of the condensation column, b) for the liquid medium to be expanded and exits into the top of the vapor space and c) each a diversion line for the partially expanded, cooled liquid medium, which exits out in

the top of the vapor space of the heat exchanger stage at the second lowest energy level or in the cooling stage above an expansion valve.

The heat exchange takes place in the heat exchanger stage described above so that heated liquid medium is injected into the cyclonic steam room after flow through an expansion valve. The steam released thereby flows through the chimney as in the condensation column and releases its reaction enthalpy to the liquid medium to be heated at the second lowest temperature level, which is fed into the top of the condensation column. The liquid to be heated thereby trickles down over the distribution and sieve trays arranged in the condensation column. The heated liquid flows over a bottom that separates the condensation column from the vapor space, in a standpipe, from which dosed volume flows are supplied via a feed pump to the reactor depending on the liquid level. At the downstream heat exchanger stage, the heated liquid medium is fed into the top of the heat exchanger column at a higher temperature level.

The at least partially expanded and partially cooled liquid medium collects under the steam space in a collection space and is supplied to the next heat exchanger stages at the next lowest temperature level depending on the liquid level. If, however, it concerns the last heat exchanger stage, the reaction material is withdrawn and supplied to the final cooling stage.

If the liquid medium is a suspension with increased viscosity or the suspended particles have an increased tendency for sedimentation, a device is preferably used which is characterized by the fact that the heat exchanger stage or a majority of these have a cyclone-like steam chamber with a collection chamber arranged underneath for the at least partially expanded liquid medium, whereby a flow pipe is arranged in the collection chamber, in which there is a circulation stirrer, and the steam chamber is connected via a steam line to a condensation column and opens into a flow pipe located in the sump of the condensation column and each a line

a) for the liquid medium to be heated, which exits at the top of the condensation column, b) for the liquid medium to be expanded and exits at the top of the vapor space and c) for the partially expanded, cooled liquid medium exiting into the top of the vapor space of the heat exchanger stage at the second lowest energy level or in the de-cooling final stage.

In the heat exchanger stage characterized in this way, it is appropriate to separate the vapor space from the condensation column so that the cooled suspension is collected in a circulated sump with the least possible liquid content. The heated suspension is collected in a circulated sump that works as a pump source.

In these cases, it is expedient to use no distributor or strainer bottoms in the condensation column, but downward sloping guide plates, whereby the formation of deposits on these plates is counteracted by the trickling down suspension to be heated.

In the top area, the condensation columns and/or the reactor preferably contain degassing devices for diverting excess of any used reaction gases or non-condensed gases which are not reacted during the reaction or which are formed by side reactions.

The device according to the invention has a cooling stage on the input side which can be operated with negative pressure.

This can be adapted according to the heat exchanger steps. In the condensation column, however, water is fed into the upper area, whereby the water is diverted together with condensed steam in a suitable manner at the foot of this. The cooled medium can be taken from the collection space located under the expansion zone bg and added to the final processing which no longer belongs to the invention, e.g. a filtering.

If, under the conditions prevailing in the cooling stage, there is no reason to fear formation of the deposit and/or corrosive damage, a recuperator can be used at this point, especially in the form of a plate exchanger with high internal turbulence.

The device according to the invention and the method that can be carried out in this device shall be illustrated on

basis of the following drawings, where

fig. 1 schematically shows the device consisting of reactor, heat exchanger stage and cooling stage, and

fig. 2 shows a heat exchanger step in a special suspension with higher viscosity and/or significant sedimentation rate, adapted device.

In fig. 1, the high-temperature reactor is denoted by 1. It exhibits a flow pipe 2, into which a supply line for the highly heated liquid medium opens. Supply lines are also assumed. 4 for a possibly required reaction gas and for hot steam 5 for supplying the amount of energy required to reach the reaction temperature. The liquid medium to be treated rises in the flow pipe 2 according to impulses from the introduced liquid and according to driving forces caused by the other introducing currents upwards, whereby a circulation flow is set up. After discharge from the flow pipe 2, the liquid medium sinks downwards. The average residence time, flow rate and degree of slenderness of the reactor are selected in such a way that the reaction ends in the liquid medium when it leaves the reactor via line 6.

The reactor is preferably built in such a way that the attacking solid particles remain in the circulation flow and cannot settle, the introduced gases remain further in the circulation flow in finely divided form and thus circulate unreacted and newly formed gases that accumulate at the top of the reactor, can be diverted via an expansion valve, all product-touched parts, thus also the steam or gas space at the top of the reactor, are lined with corrosion-resistant material and all forces are absorbed by a corrosion-resistant, load-bearing construction. At the top of the reactor is a pressure reduction valve 7 for diverting any excess reaction gases used or any inert gases present.

After the reaction, the liquid medium leaves the reactor via the line 6 to the reducing valve part 8. The quantity flow of the liquid medium is regulated depending on the liquid level in the reactor 1. During the steam expansion, the treated liquid medium is frozen in its reaction equilibrium position and a according to the reduced press a corresponding temperature. The gas-liquid-solids mixture formed after the expansion valve flows into a cyclonically formed vapor chamber 9. The cooled liquid with the solid particles collects in the bag 10. The separation of solids-containing liquid and vapor does not have to be complete, the liquid droplets that may have been entrained are returned the reactor. The vapors flow through the chimney pipe 11, which is covered by a drip cap 12, into the condensation column 13, which contains distributor bottoms 14 and strainer bottoms 15. The rising steam flows countercurrently to it over the line 16 by means of the dosing pump 17 at the top of the condensation column 13 supplied liquid medium to be heated, and emits its enthalpy of condensation to this. The liquid medium heated to a higher temperature level flows after passing the condensation column 13 over the bottom 18 in the sump container 19 and is fed from there by means of the dosing pump 20 into the line 3, which leads to the high-temperature reactor. The condensation column 13 has a similar degassing device 41 for non-condensable gases as in the reactor. The cooled liquid which has accumulated in the bag 10 is now supplied via line 21 to the next degassing stage, preferably after passing through the last degassing stage added in the final cooling stage 22. The bag 10 is dimensioned so that the sedimentation process is suppressed. The level in the bag 10 is regulated by withdrawal through the feed pump. In the final cooling stage 22, the steam formed after the reduction valve 23, which flows in the condensation columns, is condensed by counter-flowing cooling water, which is supplied via line 25 to the top of the condensation column. The chimney pipe 26 is led through a bottom 27 in the final cooling stage. The heated cooling water is discharged over the line 28. The cooled liquid medium collects in the collecting chamber 29 and is drawn out over the line 30 and is further worked up as e.g. filtered, centrifuged or similar.

In fig. 2 shows a heat exchanger stage in which the condensation column 13 and the cyclonic formed steam chamber 9 do not form a structural unit, but are only connected to each other by a steam pipe 31. The liquid medium fed from a heat exchanger stage at the second highest temperature level above the line 42 into the steam chamber 9 expands by steam generation. The cooled liquid medium reaches the bag 32. In the bag 32 there is an inner tube in which a stirrer 33 is immersed, which causes a forced circulation of the liquid medium cooled at a lower temperature level. In the case of high turbulence, the extraction flow is taken from the circulating medium via line 43 and diverted to a stage at the second lowest temperature level. Because of the forced circulation, extraction of suspensions with a significant sediment ion rate is made possible in particular. The steam flowing out of the steam chamber 9 is led through the line 31 to the collecting chamber 34 in the condensation column 13. The collecting chamber has an inner pipe 35, at the lower end of which the steam line 31 opens. This also causes a circulation of the sump which is present in the collecting chamber 34. The condensation column contains obliquely downward sloping guide plates 36, over which the liquid medium, in this case the suspension, flows, which is supplied to the top of the condensation column 13 via the line 37. With this design of the plates in the condensation column, the formation of deposits is avoided, as any precipitated substances on the guide plates 36 is washed away by the downward flowing liquid medium. The condensation column 13 also preferably has a degassing device 38 in the top area. The heated liquid medium (suspension) is withdrawn from the collection space 34 between the wall of the collection space and the wall of the inner tube above the line 39 and is supplied to a dosing group 40, which is in connection with either the heat exchanger stages on the nest highest temperature level or the high temperature reactor.

It is self-evident to a person skilled in the art that in the supply lines and possibly in the discharge lines in the device according to the invention, pre-regulation devices, especially liquid level control devices, serving branch and/or shunt lines can be provided.

The device can be mastered in a simple way in terms of control technology so that a continuous working method is possible with relatively little equipment and a high space-time yield. Due to the lack of moving parts (except the dosing pump), high demands must not be made on the mechanical properties of the materials used. It is therefore possible to select materials that are optimally adapted to the reaction conditions, especially corrosive attack by the medium.

The device according to the invention contains no heat exchanger surfaces. The heat and substance exchange processes flow immediately over the phase boundary vessels. The device provides large phase interface surfaces. Combined with a good degassing of all appliances, excellent heat transfer conditions are achieved, despite the use of materials that have a poor heat conduction coefficient, which allows for a very compact construction method.

Since heat exchanger surfaces are missing, the device according to the invention allows continuous treatment of solutions that contain a large amount of substances that form deposits.

A difficult and frequently occurring substance that forms deposits is e.g. calcium sulfate.

For the person skilled in the art, it is self-evident that the device according to the invention can be used particularly advantageously for the treatment of very large volume flows, as certain parts of the plant are introduced in other large-scale technical processes under other conditions and therefore in general a small proportion of measurement and regulation technology decreases with increasing size of the devices.

Claims (15)

1. Method for direct heating of a possibly solid substance containing liquid medium to high temperatures using condensation heat, characterized by the fact that the heated liquid medium is partially vaporized during one or more stages of expansion and, without the use of a heat transfer agent external to the system, immediately condenses in it in countercurrent led medium to be heated. 2. Method according to claim 1, characterized in that the liquid medium, after passing through the last preheating step by direct feeding of additional steam immediately before or in the reactor, is heated to the reaction temperature to be achieved. 3. Method according to claim 1, characterized in that the liquid medium, after passing through the expansion step(s), is cooled by lowering the pressure and condensed. 4. Method according to claim 1, characterized in that the liquid medium, after passing through the expansion stage(s), is cooled in the recuperator. 5. Method according to claim 4, characterized in that a recuperator with high turbulence is used. 6. Method according to one or more of the preceding claims, characterized in that an aqueous solution is used as liquid medium. 7. Device for carrying out the method according to claims 1-6, characterized by the combination of the following characteristics: a a pressure reactor, b one or more heat exchanger stages with bl an expansion vessel and b2 one with the vapor space of the expansion vessel in connected standing condensation column, which exhibits b2.1 distribution and/or strainer inserts, c a feed pump with depending on the liquid level adjustable volume flow for each heat exchanger stage and reactor, d a cooling stage which is formed as a dl expansion stage or as a d2 recuperator. 8. Device according to claim 7, characterized in that the reactor has a centrally arranged flow tube, in the lower opening of which a line for the liquid medium to be heated flows out, and in the lower reactor area outside the flow tube, a first heat exchanger stage leading line for discharge of the treated medium. 9. Device according to claim 8, characterized in that a further line for steam and/or reaction gas opens into the lower opening of the flow tube. 10. Device according to claim 7, characterized by the fact that the heat exchanger stage or a majority of these have a cyclone-like formed steam chamber with a collection chamber arranged underneath. at least partially expanded liquid medium, and the vapor space is connected via a pipe, which is uncovered at the upper end with a drop cap with the condensation column, whereby the condensation column is separated from the vapor space's expansion stage so that the heated liquid medium is diverted to a collecting space which is connected via a feed pump with the heat exchanger stage from the second highest energy level or the reactor, and each has a supply line a) for the liquid medium to be heated, which exits at the top of the condensation column, b) for the liquid medium to be expanded and exits at the top of the steam room and c) each a diversion for the partially expanded, cooled liquid medium, which opens into the top of the steam room in the heat exchanger stage from the second highest energy level or in the cooling stage above an expansion valve. 11. Device according to claim 7, characterized by the fact that the heat exchanger stage or a majority of these have a cyclone-like steam chamber with a collection chamber for at least partially expanded liquid medium arranged underneath, whereby a flow pipe is arranged in the collection chamber, in which a stirrer is located, and the steam room are connected above-a- steam pipe: with a condensation column and a flow pipe opening located in the sump of the condensation column, and each a supply line a) for the liquid medium to be heated and which opens at the top of the condensation column, b) for the liquid medium which is to be expanded and which opens at the top of the vapor space and c) for the partially expanded, cooled liquid medium that opens at the top of the vapor space in the heat exchanger stage from the next highest energy level or in the cooling stage. 12. Device according to claim 7, characterized by the fact that it exhibits a final cooling stage which is formed as a vacuum expansion stage. 13. Device according to claim 7, characterized in that it has a recuperator with high internal turbulence as the final cooling stage. 14. Device according to one or more of claims 7-11, characterized in that the condensation column and/or the reactor in the top area have expansion devices. 15. Application of the method according to claims 1-6, and the device according to claims 7-14, for precipitation or leaching reactions.