CA1249414A - Process and reactor for making calcium sulfate hemihydrate - Google Patents
Process and reactor for making calcium sulfate hemihydrateInfo
- Publication number
- CA1249414A CA1249414A CA000520186A CA520186A CA1249414A CA 1249414 A CA1249414 A CA 1249414A CA 000520186 A CA000520186 A CA 000520186A CA 520186 A CA520186 A CA 520186A CA 1249414 A CA1249414 A CA 1249414A
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- CA
- Canada
- Prior art keywords
- reactor
- suspension
- calcium sulfate
- pipe
- steam
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B11/00—Calcium sulfate cements
- C04B11/02—Methods and apparatus for dehydrating gypsum
- C04B11/028—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained
- C04B11/032—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained for the wet process, e.g. dehydrating in solution or under saturated vapour conditions, i.e. to obtain alpha-hemihydrate
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B11/00—Calcium sulfate cements
- C04B11/02—Methods and apparatus for dehydrating gypsum
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The process for making calcium-sulfate hemihydrate from calcium sulfate dihydrate from a flue gas desulfurizing unit after a washing process involving lime comprises feeding a suspension substantially of calcium sulfate dihydrate drawn from the flue gas desulfurizing unit and a promoting agent into a continuous substantially vertical pipe-like reactor from above. This suspension is heated in the reactor to a reaction temperature which is greater than 100°C and an alpha calcium sulfate hemihydrate is drawn from the bottom portion of the reactor. The fluid height in the reactor is controlled by a regulator downstream of the outlet of the reactor. The suspension in the reactor is heated by steam which is introduced into the suspension and the heating with steam takes place at a plurality of positions distributed uniformly along the length of the reactor.
The process for making calcium-sulfate hemihydrate from calcium sulfate dihydrate from a flue gas desulfurizing unit after a washing process involving lime comprises feeding a suspension substantially of calcium sulfate dihydrate drawn from the flue gas desulfurizing unit and a promoting agent into a continuous substantially vertical pipe-like reactor from above. This suspension is heated in the reactor to a reaction temperature which is greater than 100°C and an alpha calcium sulfate hemihydrate is drawn from the bottom portion of the reactor. The fluid height in the reactor is controlled by a regulator downstream of the outlet of the reactor. The suspension in the reactor is heated by steam which is introduced into the suspension and the heating with steam takes place at a plurality of positions distributed uniformly along the length of the reactor.
Description
12~-3~
PROCESS AND REACTOR FOR MAKING CALCIUM
SULFATE HEMIHYDRATE
SPECIFICATION
Field of the Invention our present invention relates to a process and apparatus for making calcium sulfate hemihydrate or plaster of paris. ~
More particularly, the invention relates to the manufacture o alpha calcium sulfate hemihydrate or plaster of paris from calcium sulfate dihydrate or gypsum from a flue gas desulfurizing unit after a washing process to whlch lime is supplied, a suspension substantially of calcium sulfate dihydrate drawn from the flue gas desulfurizing unit and, possibly auxiliary agents controlling crystallization are fed into a continuous, substantially vertical pipe-like reactor from above. This suspension is heated in the reactor to a reaction temperature which is greater than 100C and an alpha calcium sulfate hemihydrate is drawn from the bottom portion of the reactor. The fluid height in the reactor is controlled (maintained constant) by a regulator downstream of the outlet of the reactor.
Background of the Invention A process for transforming the dihydrate to the hemihydrate has also been performed in a shell-and-tube heat exchanger whose outer wall contacts a heated medium. Such a reactor is relatively expensive and has a num~er of operating disadvantages. ~n the extensive surface area which contacts the suspension, a considerable amount of incrustation occurs, reducing the heat transfer rata and leading to a nonuniform flow distribution.
Obiects of the Invention It is an object of our invention to provide an ~improved process for making the hemihydrate of calcium sulfate, that is, or plaster of paris which obviates prior art drawbacks.
It is also an object of our invention to provide an improved apparatus, partisularly an improved reactor, for making calcium sulfate hemihydrate.
It is another object of our invention to provide an improved process and reactor for making calcium sulfate hemihydrate in which there is less incrustation in the reactor and thus a better heat transfer rate and flow distribution.
Summary of the Invention These objects and others which will become more readily apparent hereinafter, are attained in accordance with our invention in a process for making calcium sulfate hemihydrate from calcium sulfate dihydrate or gypsum from a
PROCESS AND REACTOR FOR MAKING CALCIUM
SULFATE HEMIHYDRATE
SPECIFICATION
Field of the Invention our present invention relates to a process and apparatus for making calcium sulfate hemihydrate or plaster of paris. ~
More particularly, the invention relates to the manufacture o alpha calcium sulfate hemihydrate or plaster of paris from calcium sulfate dihydrate or gypsum from a flue gas desulfurizing unit after a washing process to whlch lime is supplied, a suspension substantially of calcium sulfate dihydrate drawn from the flue gas desulfurizing unit and, possibly auxiliary agents controlling crystallization are fed into a continuous, substantially vertical pipe-like reactor from above. This suspension is heated in the reactor to a reaction temperature which is greater than 100C and an alpha calcium sulfate hemihydrate is drawn from the bottom portion of the reactor. The fluid height in the reactor is controlled (maintained constant) by a regulator downstream of the outlet of the reactor.
Background of the Invention A process for transforming the dihydrate to the hemihydrate has also been performed in a shell-and-tube heat exchanger whose outer wall contacts a heated medium. Such a reactor is relatively expensive and has a num~er of operating disadvantages. ~n the extensive surface area which contacts the suspension, a considerable amount of incrustation occurs, reducing the heat transfer rata and leading to a nonuniform flow distribution.
Obiects of the Invention It is an object of our invention to provide an ~improved process for making the hemihydrate of calcium sulfate, that is, or plaster of paris which obviates prior art drawbacks.
It is also an object of our invention to provide an improved apparatus, partisularly an improved reactor, for making calcium sulfate hemihydrate.
It is another object of our invention to provide an improved process and reactor for making calcium sulfate hemihydrate in which there is less incrustation in the reactor and thus a better heat transfer rate and flow distribution.
Summary of the Invention These objects and others which will become more readily apparent hereinafter, are attained in accordance with our invention in a process for making calcium sulfate hemihydrate from calcium sulfate dihydrate or gypsum from a
-2-~24~
flue gas desulfurizing unit after a washing process with lime in which a suspension substantially of calciu~ sulfate dihydrate drawn from the flue gas desulfurizing unit and a promoting agent are fed into a continuous substantially vertical pipe-like reactor from above. This suspension is heated in the reactor to a reaction temperature which is greater than 100C and an alpha calcium sulfate hemihydrate is drawn from the bottom portion of the reactor. The fluid height in the reactor is controlled, for example, by a regulator downstream of the outlet of the reactor.
According to our invention the suspension in the reactor is heated by steam tsuperheated steam), which is ~ introduced into the suspension and the heating with steam takes place at a plurality of positions distributed uniformly along the len~th (height) of the reactor.
When the process is performed according to our invention the thermodynamic process parameters may be set very accurately. This is true for the pressure which varies with the fluid column or height in the heat exchanger pipe as well as ~or the temperature in the reactor and the residence time of the individual volume elements of the suspension in the reactor. The axial temperature profile can be well adjusted to the local operating pressure. It can operat~ with a comparatively gentle temperature rise in the suspension which results in the desired conversion and in good crystal growth.
:12~4~
According to a feature of our invention a mixing flow motion for improvement of the heat trans~er or heating is superposed on the general downward flow in the reactor in the vicinity of the heating. For example, the mixing flow motion for improving the heat transfer or heating can be provided by tangential introduction of steam into the reactor.
Alternatively or in addition, the mixing flow motion improving the heating is provided by continuously drawing a partial flow of the suspension from the reactor and feeding it back to the reactor. Steam is preferably introduced into this partial flow of suspension continuously drawn from and fed back to the reactor.
The calcium sulfate dihydrate suspension can be preheated with steam on introduction to the reactor.
Advantageously, the calcium sulfate dihydrate-suspension is heated before introduction into the reactor ~y superheated steam at 110C.
~'or preheating the delivered suspension and heating in the reactor, electricity ~enerating power plant steam which is at a pressure of about 8 bar and is superheated can be used.
Naturally, the calcium sulfate dihyd~ate can be concentrated before introduction into the reactor by a hydrocyclone and a crystallization promoting agent, for example, a dicarboxylic acid, for improving the crystallization yield can be added.
It is also possible within the scope of our invention to take a portion of the resultant alpha hemihydrate and feed it back to the upper portion of the reactor.
We have found it to be particularly advantage~us when the calcium sulfate dihydrate suspension fed to the reactor has a concentration o NaC1 of at least -10 g/l in the carrier fluid or liquid phase of the suspension.
It is known, that the con~ersion of calcium sulfate dihydrate into alpha calcium sulfate hemihydrate can be performed in the scrubbing liquid from the flue gas desulfurization unit without separation from the chloride lo component washed out of the flue gas as taught in German Patent 31 19 749. The CaC12 concentration does not substantially effect the operating conditions of the conversion. It has now been found surprisingly, that the operating pressure for the conversion and the required crystallization time can be considerably reduced when the calcium sul~ate dihydrate suspension contains NaCl in a concentration of at least 10 g/l in relation to the carrier fluid. Most surprisinglyr the relatively high salt content has no disadvantageous influence on the product quality. It is understood that the product hemihydrate is washed before drying to set the product properties.
When the flue gas desulfurization unit is located in a coastal region, sea water can be used as the carrier fluid for the calcium sulfate containing dihydrate suspension to provide the required NaCl content in a natural way~
It is also possible to use the sea water as the wash fluid in the flue gas desulfurization unit and the wash fluid containing the calcium sulfate dihydrate is then conducted
flue gas desulfurizing unit after a washing process with lime in which a suspension substantially of calciu~ sulfate dihydrate drawn from the flue gas desulfurizing unit and a promoting agent are fed into a continuous substantially vertical pipe-like reactor from above. This suspension is heated in the reactor to a reaction temperature which is greater than 100C and an alpha calcium sulfate hemihydrate is drawn from the bottom portion of the reactor. The fluid height in the reactor is controlled, for example, by a regulator downstream of the outlet of the reactor.
According to our invention the suspension in the reactor is heated by steam tsuperheated steam), which is ~ introduced into the suspension and the heating with steam takes place at a plurality of positions distributed uniformly along the len~th (height) of the reactor.
When the process is performed according to our invention the thermodynamic process parameters may be set very accurately. This is true for the pressure which varies with the fluid column or height in the heat exchanger pipe as well as ~or the temperature in the reactor and the residence time of the individual volume elements of the suspension in the reactor. The axial temperature profile can be well adjusted to the local operating pressure. It can operat~ with a comparatively gentle temperature rise in the suspension which results in the desired conversion and in good crystal growth.
:12~4~
According to a feature of our invention a mixing flow motion for improvement of the heat trans~er or heating is superposed on the general downward flow in the reactor in the vicinity of the heating. For example, the mixing flow motion for improving the heat transfer or heating can be provided by tangential introduction of steam into the reactor.
Alternatively or in addition, the mixing flow motion improving the heating is provided by continuously drawing a partial flow of the suspension from the reactor and feeding it back to the reactor. Steam is preferably introduced into this partial flow of suspension continuously drawn from and fed back to the reactor.
The calcium sulfate dihydrate suspension can be preheated with steam on introduction to the reactor.
Advantageously, the calcium sulfate dihydrate-suspension is heated before introduction into the reactor ~y superheated steam at 110C.
~'or preheating the delivered suspension and heating in the reactor, electricity ~enerating power plant steam which is at a pressure of about 8 bar and is superheated can be used.
Naturally, the calcium sulfate dihyd~ate can be concentrated before introduction into the reactor by a hydrocyclone and a crystallization promoting agent, for example, a dicarboxylic acid, for improving the crystallization yield can be added.
It is also possible within the scope of our invention to take a portion of the resultant alpha hemihydrate and feed it back to the upper portion of the reactor.
We have found it to be particularly advantage~us when the calcium sulfate dihydrate suspension fed to the reactor has a concentration o NaC1 of at least -10 g/l in the carrier fluid or liquid phase of the suspension.
It is known, that the con~ersion of calcium sulfate dihydrate into alpha calcium sulfate hemihydrate can be performed in the scrubbing liquid from the flue gas desulfurization unit without separation from the chloride lo component washed out of the flue gas as taught in German Patent 31 19 749. The CaC12 concentration does not substantially effect the operating conditions of the conversion. It has now been found surprisingly, that the operating pressure for the conversion and the required crystallization time can be considerably reduced when the calcium sul~ate dihydrate suspension contains NaCl in a concentration of at least 10 g/l in relation to the carrier fluid. Most surprisinglyr the relatively high salt content has no disadvantageous influence on the product quality. It is understood that the product hemihydrate is washed before drying to set the product properties.
When the flue gas desulfurization unit is located in a coastal region, sea water can be used as the carrier fluid for the calcium sulfate containing dihydrate suspension to provide the required NaCl content in a natural way~
It is also possible to use the sea water as the wash fluid in the flue gas desulfurization unit and the wash fluid containing the calcium sulfate dihydrate is then conducted
3~14 into a tower reactor where the crystal transformation of calcium sul~ate dihydrate to alpha calcium sulfate hemihydrate.
When sea water is not available according to the teaching of our invent on NaCl is introduced to the calcium sulfate dihydrate suspension from the flue gas desulfurization.
In order to keep the waste water which may have to be disposed of or treated at a mi~imum the calcium sulfate n dihydrate or gypsum suspension of the flue gas desulfurization unit can be concentrated first and the clear efficient obtained in the dewatering can be partially fed back to it. In this way substantial quantities of NaCl can be recycled. The NaCl containing recycled flow is adjusted to the dewatering of the calcium sulfate dihydrate suspension. It is particularly advantageous when a NaCl concentration of 30 g/1 in relation to the carrier fluid is used in the calcium sulfate dihydrate suspension.
According to our invention, a plurality of inlet connector pipes are positioned along the reactor wall spaced uniformly from each other and these inlet connector pipes are connected to a device for introducing steam.
Ad~antageously, the inlet connector pipes are connected tangentially to the reactor wall.
In another embodiment of our invention, each inlet connector pipe is associated with an outlet connector pipe that is connected tangentially to ~he reac~or wall and in the same direction as the inlet connector pipe. Each inlet - ~Z~
.
connector pipe and associated outlet connector pipe are connected to each other ~y a circulating pipe and the de~ice for introduction of steam is connected to the circulating pipe.
The flow in the circulating pipe can, if desired, be generated only by the injection of steam. In anather feature of our of our invention, a circulating pump is mounted in the circula~ing pipe. Because a partial flow of s~spension is continuously drawn from the reactor and is fed back by the circulating pipe again into the reactor, the downwardly directed flow in the reaction is superposed on a mixing motion for improvement of the heat transfer. Thus the danger of local overheating is reduced. Because of the tangential inflow and outflow, a high flow velocity in the reactor near the reactor walls results.
According to another feature of our invention, the inlet connector pipes and the outlet connector pipes are positioned vertically staggered or displaced and of course the spacing between each inlet connector pipe and the associated outlet connector pipe is exactly half as large as the spaclng between the neighboring inlet connector pipes. In this embodiment a circulating pump is mounted in the circulating pipe O
This has the advantage that the process according to our invention utilizes a reactor which has no internal structure. ~his reactor is distinguished by a very simple structure and construction. The reactor wall is assembled from a pluxality of short column rings or segments. The - :~2~
manufacture and assembly methods are advantageous. Because of the small surface area coming in contact with the suspension, the reactor does not have incrustation or other contamination problems. Moreover it is no problem to clean. An additional advantage is that the heating takes place at a plurality of positions distributed uniformly along the length of the reactor. In this way a very accurate axial temperature control and adjustment of the local operating pressure in the reactor is possible.
When, in accordance with the invention, an NaCl--containing calcium sulfate dihydrate suspension is provided, additional advantages result. Thus the required reactor height can be reduced about lO ~. Simultaneously, a reduction of the apparatus volume, because of the reduced crystallization time and residence time of the suspension in the reactor occurs. Thus the reactor can be constructed with less material and particularly also with reduced wall strength. The reduced weight affects advantageously the construction of the foundation and the required supporting structure for the reactor. Because of the reduced feed height the apparatus can operate with less powerful feed pump. All this leads to a more economical process.
By a "promoting agent" or "auxiliary agent" in this description, we mean an additive substance which assists in the production of the product of the reaction, that is the alpha hemihydrate. For example, one promoting agent which can be used is a dicarboxylic acid.
iz~
Brief Descri~tion of the Drawinq The above and cther objects, features and advantages of our invention will become more readily apparent from the following description, reference being made to the accompanying highly diagrammatic drawing in which:
FIG. l is a schematic diagram showing a reaction system for making calcium sulfate hemihydrate according to our invention;
FIG. 2 is a partially cutaway side elevational view of the reactor used for the process shown in FIG. 1 with heating devices; and FIG. 3 is a partially top plan partially cross sectional view through the reactor and accompanying heating devices shown in FIG. 2 taken along the section line III-III
of FIG. 2. - -Specific Description and Example The reactor shown in FIG.l acts to receive the - products of a flue gas desulfurization unit in a power plant which operates after a washing process involving calcium carbonate. Aqueous calcium sulfate dihydrate suspension from the flue gas desulfurization Ullit iS converted in this process by crystallization into an alpha calciu~ sulfate hemihydrate suspension which can be used to make a valuable construction material for use in subterranean and other applications.
The crystalline transformation of calcium sulfate dihydrate into alpha calcium sulfate hemihydrate is performed in a stationary pipe~ e substantially vertical reactor 1.
_g_ ~2~4~4 The reactor length (height~ is greater than 20 m.
The reactor 1 has no inner structure, i.e. is internal~y free from tubes, baffles or the like. A substantially vertical pipe 2 is connected to the reactor 1. The upper end of this substantially vertical pipe 2 is connected to an overflow pipe 3 which leads to the desulfurization unit. The reactor 1 has an upper inlet 4 for a calcium sulfate dihydrate containing suspension which is in this embodiment in the substantially vertical pipe 2, a lower outlet 5 for the alpha calcium sulfate hemihydrate and a connection to a feed back pipe 6. A
plurality of heating units 7 are mounted uniformly spaced along the reactor 1. The level is maintained constant via the ~ controller 30 regulating the valve 11.
The calcium sulfate dihydrate containing suspension is fed after concentration into a mixing space 9 by a feed pipe 8 from an unshown hydrocyclone unit or units. The delivered suspension is preheated by introduction of steam in this mixing space 9. The delivered suspension is continuously fed into the reactor 1 through the upper inlet 4.
Advantageously the delivered suspension has an NaCl concentration of 10 gjl relative to the carrier fluid.
The carrier fluid can, for example, also be sea water. The calcium sulfate dihydrate suspension can also have an auxiliary promoting agent added to improve the crystal yield from crystallization, for example carbox~lic acid. This promoting agent can be added by the feed pipe 10.
The alpha calcium sulfate hemihydrate formed in the crystallization can be discharged as a suspension from lo~er ~2~4~4~
outlet 5. The valve 11 connected downstream of the outlet 5 controls the fluid level in the reactor 1 is adjustable.
To perform the crystalline transformation the suspension is heated in the reactor 1. Ths heating occurs by steam which is introduced into the suspension. A plurality of heating units 7 are positioned at equal interv~ls alony the length of the reactor 1. In every heating unit 7 a portion of the flow of suspension in the reactor 1 is drawn from it by a circulating pump 12, heated with steam and fed back into the reactor 1. The steam heating uses power plant depleted steam which is at a pressure of 8 bar and which is superheated, delivered by steam pipe 14. The flow rat~ of steam is controlled by a steam regulator valves 15.
The alpha calcium sulfate hemihydrate suspension is discharged from the lower outlet 5 and fed into a surge tank 16 with an air vent 17. With some of the suspension present in the surge tank 16 the variations in continuous operation can be compensated.
From the surge tank 16 a mass flow of alpha calcium sulfate hemihydrate corresponding to the delivered suspension is fed by a feed pump 18 to a mechanical dewatering unit (not shown). A portion of the flow of the alpha calcium sulfate suspension is returned by the feedback pipe 6 from the surge tank 16 into the upper part of the reactor 1 ~y a pump 19.
The crystalli3ation is favorably influenced by this recirculation.
The structure of the heating devices 7 can be seen particularly well in FIGS. 2 and 3. The heating device 7 of - ~2~14 which only one is shown in these figures comprises a circulatin~ pipe 13, a circulating pump 12 and a device 2-2 ~or feeding steam. The circulating pipe 13 connacts an inlet connector pipe 20 and an outlet connector pipe 21 which are ~oth connected to-the reactor wall 23-tangentially and in the same direction in the cross sectional view of FIG.3.
The reactor wall 23 can be constructed from short column rings or sections. The inlet connector pipe 20 and the outlet connector pipe 21 are attached vertically staggered.
The apparatus is structured so that the spacing h is exactly half as large as the spacing H between the neighboring inlet connector-pipes 20 and 20a. The feed direction of the circulating pump 12 is so chosen that the suspension is fed from below upwardly into the circulating pipe 13. The fed in steam quantity is adjustable and regulatable by the steam regulator 15. Ths local suspension temperature in the circulating pipe 13 acts as a guide for regulation of the steam input flow rate. A controller 31 is provided for each heating unit to this end.
The conditions for the reaction are such that the calcium sulfate dihydrate suspension has a solid content of from 100 to 800 y/1 on introduction to the reactor 1 and after preheating in the mixing space 9 to 110 C enters the reactor 1 through the upper inlet 4. The crystalline transformation is performed at a p~ of between 3.7 and 8.8, advantageously from 4.5 to 5.5, and a temperatur~ hetween 120 and 130. A suitable fluid column or fluid height is set in the reactor l. The residence time is from 10 to 20 z~
minutes in this embodiment.
An investigation a~ the crystalline transformation from calcium sulfate dihydrate to alpha calcium sulfata hemihydrate was performed in the laboratory. In the crystalline transformation-a crystallization time of five minutes at a pressure of 3 bar was measured in a NaCl free wash fluid. Performing the crystallization with sea water as the carrier fluid the crystallization time was reduced to 3.5 minutes. The operating pressure was 1.7 bar, also a considerable reduction.
When sea water is not available according to the teaching of our invent on NaCl is introduced to the calcium sulfate dihydrate suspension from the flue gas desulfurization.
In order to keep the waste water which may have to be disposed of or treated at a mi~imum the calcium sulfate n dihydrate or gypsum suspension of the flue gas desulfurization unit can be concentrated first and the clear efficient obtained in the dewatering can be partially fed back to it. In this way substantial quantities of NaCl can be recycled. The NaCl containing recycled flow is adjusted to the dewatering of the calcium sulfate dihydrate suspension. It is particularly advantageous when a NaCl concentration of 30 g/1 in relation to the carrier fluid is used in the calcium sulfate dihydrate suspension.
According to our invention, a plurality of inlet connector pipes are positioned along the reactor wall spaced uniformly from each other and these inlet connector pipes are connected to a device for introducing steam.
Ad~antageously, the inlet connector pipes are connected tangentially to the reactor wall.
In another embodiment of our invention, each inlet connector pipe is associated with an outlet connector pipe that is connected tangentially to ~he reac~or wall and in the same direction as the inlet connector pipe. Each inlet - ~Z~
.
connector pipe and associated outlet connector pipe are connected to each other ~y a circulating pipe and the de~ice for introduction of steam is connected to the circulating pipe.
The flow in the circulating pipe can, if desired, be generated only by the injection of steam. In anather feature of our of our invention, a circulating pump is mounted in the circula~ing pipe. Because a partial flow of s~spension is continuously drawn from the reactor and is fed back by the circulating pipe again into the reactor, the downwardly directed flow in the reaction is superposed on a mixing motion for improvement of the heat transfer. Thus the danger of local overheating is reduced. Because of the tangential inflow and outflow, a high flow velocity in the reactor near the reactor walls results.
According to another feature of our invention, the inlet connector pipes and the outlet connector pipes are positioned vertically staggered or displaced and of course the spacing between each inlet connector pipe and the associated outlet connector pipe is exactly half as large as the spaclng between the neighboring inlet connector pipes. In this embodiment a circulating pump is mounted in the circulating pipe O
This has the advantage that the process according to our invention utilizes a reactor which has no internal structure. ~his reactor is distinguished by a very simple structure and construction. The reactor wall is assembled from a pluxality of short column rings or segments. The - :~2~
manufacture and assembly methods are advantageous. Because of the small surface area coming in contact with the suspension, the reactor does not have incrustation or other contamination problems. Moreover it is no problem to clean. An additional advantage is that the heating takes place at a plurality of positions distributed uniformly along the length of the reactor. In this way a very accurate axial temperature control and adjustment of the local operating pressure in the reactor is possible.
When, in accordance with the invention, an NaCl--containing calcium sulfate dihydrate suspension is provided, additional advantages result. Thus the required reactor height can be reduced about lO ~. Simultaneously, a reduction of the apparatus volume, because of the reduced crystallization time and residence time of the suspension in the reactor occurs. Thus the reactor can be constructed with less material and particularly also with reduced wall strength. The reduced weight affects advantageously the construction of the foundation and the required supporting structure for the reactor. Because of the reduced feed height the apparatus can operate with less powerful feed pump. All this leads to a more economical process.
By a "promoting agent" or "auxiliary agent" in this description, we mean an additive substance which assists in the production of the product of the reaction, that is the alpha hemihydrate. For example, one promoting agent which can be used is a dicarboxylic acid.
iz~
Brief Descri~tion of the Drawinq The above and cther objects, features and advantages of our invention will become more readily apparent from the following description, reference being made to the accompanying highly diagrammatic drawing in which:
FIG. l is a schematic diagram showing a reaction system for making calcium sulfate hemihydrate according to our invention;
FIG. 2 is a partially cutaway side elevational view of the reactor used for the process shown in FIG. 1 with heating devices; and FIG. 3 is a partially top plan partially cross sectional view through the reactor and accompanying heating devices shown in FIG. 2 taken along the section line III-III
of FIG. 2. - -Specific Description and Example The reactor shown in FIG.l acts to receive the - products of a flue gas desulfurization unit in a power plant which operates after a washing process involving calcium carbonate. Aqueous calcium sulfate dihydrate suspension from the flue gas desulfurization Ullit iS converted in this process by crystallization into an alpha calciu~ sulfate hemihydrate suspension which can be used to make a valuable construction material for use in subterranean and other applications.
The crystalline transformation of calcium sulfate dihydrate into alpha calcium sulfate hemihydrate is performed in a stationary pipe~ e substantially vertical reactor 1.
_g_ ~2~4~4 The reactor length (height~ is greater than 20 m.
The reactor 1 has no inner structure, i.e. is internal~y free from tubes, baffles or the like. A substantially vertical pipe 2 is connected to the reactor 1. The upper end of this substantially vertical pipe 2 is connected to an overflow pipe 3 which leads to the desulfurization unit. The reactor 1 has an upper inlet 4 for a calcium sulfate dihydrate containing suspension which is in this embodiment in the substantially vertical pipe 2, a lower outlet 5 for the alpha calcium sulfate hemihydrate and a connection to a feed back pipe 6. A
plurality of heating units 7 are mounted uniformly spaced along the reactor 1. The level is maintained constant via the ~ controller 30 regulating the valve 11.
The calcium sulfate dihydrate containing suspension is fed after concentration into a mixing space 9 by a feed pipe 8 from an unshown hydrocyclone unit or units. The delivered suspension is preheated by introduction of steam in this mixing space 9. The delivered suspension is continuously fed into the reactor 1 through the upper inlet 4.
Advantageously the delivered suspension has an NaCl concentration of 10 gjl relative to the carrier fluid.
The carrier fluid can, for example, also be sea water. The calcium sulfate dihydrate suspension can also have an auxiliary promoting agent added to improve the crystal yield from crystallization, for example carbox~lic acid. This promoting agent can be added by the feed pipe 10.
The alpha calcium sulfate hemihydrate formed in the crystallization can be discharged as a suspension from lo~er ~2~4~4~
outlet 5. The valve 11 connected downstream of the outlet 5 controls the fluid level in the reactor 1 is adjustable.
To perform the crystalline transformation the suspension is heated in the reactor 1. Ths heating occurs by steam which is introduced into the suspension. A plurality of heating units 7 are positioned at equal interv~ls alony the length of the reactor 1. In every heating unit 7 a portion of the flow of suspension in the reactor 1 is drawn from it by a circulating pump 12, heated with steam and fed back into the reactor 1. The steam heating uses power plant depleted steam which is at a pressure of 8 bar and which is superheated, delivered by steam pipe 14. The flow rat~ of steam is controlled by a steam regulator valves 15.
The alpha calcium sulfate hemihydrate suspension is discharged from the lower outlet 5 and fed into a surge tank 16 with an air vent 17. With some of the suspension present in the surge tank 16 the variations in continuous operation can be compensated.
From the surge tank 16 a mass flow of alpha calcium sulfate hemihydrate corresponding to the delivered suspension is fed by a feed pump 18 to a mechanical dewatering unit (not shown). A portion of the flow of the alpha calcium sulfate suspension is returned by the feedback pipe 6 from the surge tank 16 into the upper part of the reactor 1 ~y a pump 19.
The crystalli3ation is favorably influenced by this recirculation.
The structure of the heating devices 7 can be seen particularly well in FIGS. 2 and 3. The heating device 7 of - ~2~14 which only one is shown in these figures comprises a circulatin~ pipe 13, a circulating pump 12 and a device 2-2 ~or feeding steam. The circulating pipe 13 connacts an inlet connector pipe 20 and an outlet connector pipe 21 which are ~oth connected to-the reactor wall 23-tangentially and in the same direction in the cross sectional view of FIG.3.
The reactor wall 23 can be constructed from short column rings or sections. The inlet connector pipe 20 and the outlet connector pipe 21 are attached vertically staggered.
The apparatus is structured so that the spacing h is exactly half as large as the spacing H between the neighboring inlet connector-pipes 20 and 20a. The feed direction of the circulating pump 12 is so chosen that the suspension is fed from below upwardly into the circulating pipe 13. The fed in steam quantity is adjustable and regulatable by the steam regulator 15. Ths local suspension temperature in the circulating pipe 13 acts as a guide for regulation of the steam input flow rate. A controller 31 is provided for each heating unit to this end.
The conditions for the reaction are such that the calcium sulfate dihydrate suspension has a solid content of from 100 to 800 y/1 on introduction to the reactor 1 and after preheating in the mixing space 9 to 110 C enters the reactor 1 through the upper inlet 4. The crystalline transformation is performed at a p~ of between 3.7 and 8.8, advantageously from 4.5 to 5.5, and a temperatur~ hetween 120 and 130. A suitable fluid column or fluid height is set in the reactor l. The residence time is from 10 to 20 z~
minutes in this embodiment.
An investigation a~ the crystalline transformation from calcium sulfate dihydrate to alpha calcium sulfata hemihydrate was performed in the laboratory. In the crystalline transformation-a crystallization time of five minutes at a pressure of 3 bar was measured in a NaCl free wash fluid. Performing the crystallization with sea water as the carrier fluid the crystallization time was reduced to 3.5 minutes. The operating pressure was 1.7 bar, also a considerable reduction.
Claims (15)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a process for making calcium sulfate hemihydrate from calcium sulfate dihydrate from a flue gas desulfurizing unit after a washing process involving lime comprising feeding a suspension substantially of said calcium sulfate dihydrate drawn from said flue gas desulfurizing unit agent into a continuous substantially vertical pipe-like reactor from above, heating said suspension in said reactor to a reaction temperature which is greater than 100° C, drawing said calcium sulfate hemihydrate from a bottom portion of said reactor, and controlling the fluid height in said reactor, the improvement which comprises effecting the heating of said suspension in said reactor by introducing steam into said suspension takes place at a plurality of positions distributed uniformly along the height of said reactor.
2. The improvement according to claim 1, further comprising superposing a mixing flow motion for improving said heating on a generally downwardly directed flow of said suspension in said reactor in the vicinity of each of said positions of heating in said reactor.
3. The improvement according to claim 2 wherein said mixing flow motion for improving said heating is induced by tangentially introducing said steam into said reactor.
4. The improvement according to claim 2 wherein said mixing flow motion is induced by drawing a partial flow of said suspension continuously from said reactor and subsequently feeding said partial flow back into said reactor.
5. The improvement according to claim 4 wherein said steam is injected into said partial flow of said suspension continuously drawn from and subsequently fed back to said reactor.
6. The improvement according to claim 1 which additionally comprises preheating said suspension by said steam at a temperature of about 110°C before introducing said suspension to said reactor.
7. The improvement according to claim 6 wherein said steam is superheated power plant steam.
8. The improvement according to claim 7, further comprising the step of maintaining in said suspension fed to said reactor a NaCl concentration of at least 10 g/l in the liquid phase of said suspension.
9. The improvement according to claim 8 wherein said carrier fluid is sea water.
10. In a reactor for making calcium sulfate hemihydrate from calcium sulfate dihydrate from a flue gas desulfurizing unit after a washing process involving lime comprising a substantially vertical pipe-like reactor wall, an upper inlet for said calcium sulfate dihydrate suspension, and a lower outlet for said calcium sulfate hemihydrate, the improvement wherein a plurality of inlet connector pipes are positioned uniformly spaced along said reactor wall and said inlet connector pipes are connected with a device for introducing steam to said reactor.
11. The improvement according to claim 10 wherein said inlet connector pipes are connected tangentially to said reactor wall.
12. The improvement according to claim 11 wherein each of said inlet connector pipes is associated with an outlet connector pipe which is connected tangentially to said reactor wall and is directed in the same direction as said inlet connector pipe associated therewith, said inlet connector pipe and said outlet connector pipe being connected with each other by a circulating pipe and said device for introduction of said steam being connected to said circulating pipe.
13. The improvement according to claim 12 wherein a circulating pump is provided in said circulating pipe.
14. The improvement according to claim 13 wherein said inlet connector pipes and said associated outlet connector pipes are positioned vertically staggered and the distance between said inlet connector pipe and said associated outlet connector pipe is exactly half the distance between neighboring ones of said inlet connector pipes.
15. A reactor for making calcium sulfate hemihydrate from calcium sulfate dihydrate from a flue gas desulfurizing unit after a washing process involving lime comprising:
a substantially vertical pipe-like reactor wall;
an upper inlet for said calcium sulfate dihydrate;
a lower outlet for said calcium sulfate hemihydrate;
a plurality of inlet connector pipes positioned uniformly spaced connected tangentially to said reactor wall;
a plurality of outlet connector pipes each of which is associated with one of said inlet connector pipes, is connected vertically staggered with respect to the associated one of said inlet connector pipes and is oriented in the same direction as said inlet connector pipe associated therewith;
a circulating pipe connecting each of said inlet connector pipes and said outlet connector pipes;
a device for introducing steam connected to each of said circulating pipes; and a circulating pump in each of said circulating pipes.
a substantially vertical pipe-like reactor wall;
an upper inlet for said calcium sulfate dihydrate;
a lower outlet for said calcium sulfate hemihydrate;
a plurality of inlet connector pipes positioned uniformly spaced connected tangentially to said reactor wall;
a plurality of outlet connector pipes each of which is associated with one of said inlet connector pipes, is connected vertically staggered with respect to the associated one of said inlet connector pipes and is oriented in the same direction as said inlet connector pipe associated therewith;
a circulating pipe connecting each of said inlet connector pipes and said outlet connector pipes;
a device for introducing steam connected to each of said circulating pipes; and a circulating pump in each of said circulating pipes.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19853536321 DE3536321A1 (en) | 1985-10-11 | 1985-10-11 | Process and reactor for producing alpha-hemihydrate gypsum from calcium sulphate dihydrate from flue gas desulphurisation plants operating by the wet scrubbing process with lime |
| DEP3536321.5-45 | 1985-10-11 | ||
| DE19863622277 DE3622277A1 (en) | 1986-07-03 | 1986-07-03 | Process for preparing alpha-hemihydrate plaster from calcium sulphate dihydrate (gypsum) from flue gas desulphurisation plants |
| DEP3622277.1 | 1986-07-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1249414A true CA1249414A (en) | 1989-01-31 |
Family
ID=25836906
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000520186A Expired CA1249414A (en) | 1985-10-11 | 1986-10-09 | Process and reactor for making calcium sulfate hemihydrate |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1249414A (en) |
| IT (1) | IT1197489B (en) |
| NL (1) | NL8602538A (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9676684B2 (en) | 2011-03-01 | 2017-06-13 | Fort Hills Energy L.P. | Process and unit for solvent recovery from solvent diluted tailings derived from bitumen froth treatment |
| US9791170B2 (en) | 2011-03-22 | 2017-10-17 | Fort Hills Energy L.P. | Process for direct steam injection heating of oil sands slurry streams such as bitumen froth |
| US10041005B2 (en) | 2011-03-04 | 2018-08-07 | Fort Hills Energy L.P. | Process and system for solvent addition to bitumen froth |
| US10125325B2 (en) | 2011-02-25 | 2018-11-13 | Fort Hills Energy L.P. | Process for treating high paraffin diluted bitumen |
| US10226717B2 (en) | 2011-04-28 | 2019-03-12 | Fort Hills Energy L.P. | Method of recovering solvent from tailings by flashing under choked flow conditions |
| US11261383B2 (en) | 2011-05-18 | 2022-03-01 | Fort Hills Energy L.P. | Enhanced temperature control of bitumen froth treatment process |
-
1986
- 1986-10-07 IT IT21932/86A patent/IT1197489B/en active
- 1986-10-09 CA CA000520186A patent/CA1249414A/en not_active Expired
- 1986-10-09 NL NL8602538A patent/NL8602538A/en not_active Application Discontinuation
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10125325B2 (en) | 2011-02-25 | 2018-11-13 | Fort Hills Energy L.P. | Process for treating high paraffin diluted bitumen |
| US9676684B2 (en) | 2011-03-01 | 2017-06-13 | Fort Hills Energy L.P. | Process and unit for solvent recovery from solvent diluted tailings derived from bitumen froth treatment |
| US10041005B2 (en) | 2011-03-04 | 2018-08-07 | Fort Hills Energy L.P. | Process and system for solvent addition to bitumen froth |
| US10988695B2 (en) | 2011-03-04 | 2021-04-27 | Fort Hills Energy L.P. | Process and system for solvent addition to bitumen froth |
| US9791170B2 (en) | 2011-03-22 | 2017-10-17 | Fort Hills Energy L.P. | Process for direct steam injection heating of oil sands slurry streams such as bitumen froth |
| US10226717B2 (en) | 2011-04-28 | 2019-03-12 | Fort Hills Energy L.P. | Method of recovering solvent from tailings by flashing under choked flow conditions |
| US11261383B2 (en) | 2011-05-18 | 2022-03-01 | Fort Hills Energy L.P. | Enhanced temperature control of bitumen froth treatment process |
Also Published As
| Publication number | Publication date |
|---|---|
| IT1197489B (en) | 1988-11-30 |
| NL8602538A (en) | 1987-05-04 |
| IT8621932A0 (en) | 1986-10-07 |
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