GB2198721A - Process and device for preparing alpha-calcium sulfate hemihydrate - Google Patents
Process and device for preparing alpha-calcium sulfate hemihydrate Download PDFInfo
- Publication number
- GB2198721A GB2198721A GB08723625A GB8723625A GB2198721A GB 2198721 A GB2198721 A GB 2198721A GB 08723625 A GB08723625 A GB 08723625A GB 8723625 A GB8723625 A GB 8723625A GB 2198721 A GB2198721 A GB 2198721A
- Authority
- GB
- United Kingdom
- Prior art keywords
- calcium sulfate
- sulfate hemihydrate
- alpha
- flue gas
- suspension
- 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.)
- Granted
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/46—Sulfates
- C01F11/466—Conversion of one form of calcium sulfate to another
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/48—Sulfur compounds
- B01D53/50—Sulfur oxides
- B01D53/501—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
- B01D53/502—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound characterised by a specific solution or suspension
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Inorganic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Health & Medical Sciences (AREA)
- Geology (AREA)
- Biomedical Technology (AREA)
- Environmental & Geological Engineering (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Treating Waste Gases (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
Alpha-calcium sulfate hemihydrate is prepared by heating a suspension of calcium sulfate dihydrate from a flue gas desulfurization plant and subsequently immediately drying the suspension of alpha-calcium sulfate hemihydrate formed by passing the suspension into a spray-drier.
Description
PROCESS AND DEVICE FOR PREPARING AtPdA'-CAtCIUN SULFATE HEMIHYDRATE The present invention relates to a process for the preparation of alpha-calcium sulfate hemihydrate by heating a suspension of calcium sulfate dihydrate from a flue gas desulfurization plant and subsequent immediate drying of the formed suspensions of alphacalcium sulfate hemihydrate.
Alpha-calcium sulfate hemihydrate is formed upon heating aqueous suspensions of calcium sulfate dihydrate. As tempsrdtures in excess of 100 'C must be employed, it is required to carry out heating under an elevated pressure in an autoclave. In the presence of dehydration catalysts such as larger amounts of calcium chloride#dissolved in the suspension the operation may be carried out under a pressureless condition.
After heating the calcium sulfate dihydrate suspension and the reaction to form alpha-calcium sulfate hemihydrate the suspension is filtered, and the filter residue is dried, Drying must be effected as fast as possible, as otherwise the alpha-calcium sulfate hemihydrate formed will again react with the adherent water to form calcium sulfate dihydrate and set. If the solution contains dissolved calcium chloride as a dehydrating catalyst, it must be removed from the filter residue by washing same with hot water.
In the past it was mainly phosphogypsum as obtained in the production of phosphoric acid or gypsum as recovered otherwise from chemical reactions that was used for preparing alpha-calcium sulfate hemihydrate.
Due to the tact that in the meantime a desulfurization of flue gases is being demanded by law, increasing amounts of flue gas gypsum are formed for which suitable applications are still being sought.
However, in the future considerable amounts of flue gas gypsum will have to be disposed of under environmentcompatible conditions, Depending on the fossil fuel as initially employed, the flue gas gypsum when being formed contains higher or lssser amounts of chloride which, depending on how the flue gas gypsum is further processed, may either be removed therefrom or remains in the flue gas gypsum.
From the DE-OS 31 19 749 there has been known a process for preparing calcium sulfate hemihydrate from flue gas gypsum wherein the calcium slfita firs; formed is oxidized to form calcium sulfate dihydrate, and the resulting calcium sulfate dihydrate is then converted into calcium sulfate hemihydrate, said conversion bring carried out in the oxidized washing liquid or part thereof. This reaction in the autoclave is followed by a conventional mechanical dehydration such as that using a vacuum filter and a fluidized stream dryer.
It is the object of the present invention to convert the gypsum formed in flue gas desulfurization plants into a usable final product in a manner as simply and inexpensively as possible, for example into alpha-calcium sulphate hemihydrate which might be used, to a reduced extent, as material for building purposes, however to a considerable extent as a mortar in mining.
If alpha-calcium sulfate hemihydrate is to be employed as a building material, the chloride contents thereof must not be in excess of 100 ppm, whereas somewhat higher amounts of chloride contents will not interfere with a use as mining mortar, Now it was surprisingly found that the above object can be attuned with particular ease and at low cost by carrying out the step of drying the suspension of alpha-calcium sulfate hemihydrate in a spray-dr ' er .
A suspension of alpha-calcium sulfate hemihydrate so far has never been subjected to spray-drying, since this method was deemed to be absolutely inappropriate for reasons of energy cost. Furthermore, flue gas gypsum from flue gas desulfurization units was always separate in the solid state and was only then subject- ed to furthar prc: ing as a solid mass having a moisture content of about 10%.
In the process according to the invention the step of separating the flue gas gypsum from the suspension is forgone. The suspension is rather pumped, for example as hydroplane underflow, into an autoclave and there in heated at a temperature at which the calcium sulfate dihydrate is converted into alpha-calcium sulfate hemihydrate.
According to the invention the suspension thus formed of alpha-calcium sulfate hemihydrate is directly dried in a spray-drier, with view to energy cost this becomes possible by that spray-drying is carried out by using flue gas after the LUVO (air pre-heating). Flue gas after the LUVO in general has a temperature of between 100 'C and 170 'C. It is preferred to employ a flue gas of from 130 'C to 160 'C after the LUDO.
It has been shown that already 15 to 20% of the flue gas after the LUVO are sufficient for completely spray-drying the suspension of alpha-calcium sulfate henlhydrats formed in the same unit. It has further been shown that upon this spray drying etep more than 90% of the formed alpha-calcium sulfate hemihydrate is obtained as a dry powder, whereas the fines as entrained by the current of air are re-circulated into the flue gas desulfurization plant to form seed crystals for the formation of new flue gas gypsum. The remaining portion of the flue gas after the LUVO is completely sufficient to heat the suspension of calcium sulfate dihydrate in an autoclave and to cause the conversion into alpha-calciu: sulfate hemihydrate to take place.
The re-united flue gas stream is still hot er.ou'#h to be at a temperature above the dew point. It may be directly introduce into the flue gas desulfurization plant in the usual manner. The consumption of energy from the flue gas after the LUVO for spray-drying and the reaction of calcium sulfate dihydrate to form alpha-calcium sulfate hemihydrate result in an accordingly lessee consumption of energy of evaporation in the flue gas desulfurization and in the desired cooling of the flue gas for the stage of the desulfurization.
In the case that the flue gas after the LUVO has already been cooled to such a low temperature which is no longer high enough to provide sufficient energy for heating the suspension of calcium dihyarate, this reaction may be effected also by using steam which is always available in power plants. This is all the more applicable to plants operating at a low chloride level wherein the reaction of calcium sulfate dihydrate may be carried out under elevated pressure and at a higher temperature to form alpha-calcium sulfate hemihydrate.
It is a particular advantage of the process according to the present invention that this process works free from producing any waste water, since all solids of the flue gas gypsum are discharged in the solid state together with the alph2-calcium sulfate hemihydrate, while the water is completely discharged in the form of steam together with the purified waste gases. In the process according to the invention the purified flue gases may either be passed into accordingly suitable cooling towers at sufficiently low temperatures below the dew point, or they may be reheated in the usual manner to such a degree that they may be introduced into conventional stacks without causing troubles.
If in the process according to the invention a fossils fuel having extremely low chloride levels is employed, an alpha-calcium sulfate hemihydrate having a correspondingly low chloride content of, for example, less than 100 ppm, is formed, which may be used as building material and for construction purposes as well as mining mortar. Thin mining mortar, with respect to its weight and volume, is only a fraction of the amount of coal conveyed from the mine to the. power plant.
Thus, the alpha-calcium sulfate hemihydrate formed according to the invention may be advanced by return transportation to the mine as mining mortar at particularly low cost. Apart from the fact that this mining mortar is put into a meaningful use, the process according to the present invention also meets the requirement of that the waste and residual materials of coal combustion are to be carried back to the place where they came from, namely into the mine.
However, the process according to the invention can be employed also with chlort containing fuels from which, then, a chloride-containing alpha-calcium sulfate hemihydrate is obtained.
In the case of a flue gas having high chloride contents It has further been shown that upon passing the flu. gas after the LUVO to a spray-drier located upstream of the flue gas desulfurizer part of the chloride contents is absorbed by the limestone residue having remained in the suspension and, thus, is removed together with the dry product from the flue gas. This results in a reduced chloride load of the flue gas desulfurization plant. Thus, according to the invention it is possible, more specifically with fuels rich in chloride, to optimize the conditions in the flue gas desulfurization plant.
Th. particular advantages of the above-described variants ensue from that the process works without producing waste water, the steps of filtering, drying, pelletizing, calcining and grinding are omitted and the process works energy-neutral.
Claims (4)
1. A process for preparing alpha-calcium sulfate hemihydrate by heating a suspension of calcium sulfate dihydrate from a flue gas desulfarization plant and subsequent immediate drying of the suspension formed of alpha-calcium sulfate hemihydrate, characterized in that the suspension of alpha-calcium sulfate hemihydrate is passed into a .spray-drier for the purpose of being dried.
2. A process as claimed in claim 1 substantially as herein described.
3. A device for preparing alpha-calcium sulfate hemihydrate substantially as herein described.
4. The invention substantially as herein described.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19863634204 DE3634204C1 (en) | 1986-10-08 | 1986-10-08 | Process for the preparation of alpha calcium sulfate hemihydrate |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8723625D0 GB8723625D0 (en) | 1987-11-11 |
| GB2198721A true GB2198721A (en) | 1988-06-22 |
| GB2198721B GB2198721B (en) | 1990-05-09 |
Family
ID=6311260
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8723625A Expired - Fee Related GB2198721B (en) | 1986-10-08 | 1987-10-08 | Process for preparing alpha-calcium sulfate hemihydrate. |
Country Status (2)
| Country | Link |
|---|---|
| DE (1) | DE3634204C1 (en) |
| GB (1) | GB2198721B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102013200122A1 (en) | 2013-01-08 | 2014-07-10 | Henkel Ag & Co. Kgaa | Water-resistant binder based on calcium sulfate |
| DE102013200119A1 (en) | 2013-01-08 | 2014-07-10 | Henkel Ag & Co. Kgaa | Water-resistant binder based on α-CaSO4 · 0.5 H2O |
| CN108821620B (en) * | 2018-08-23 | 2024-02-02 | 湖南金凤凰建材家居集成科技有限公司 | Continuous production equipment for producing high-strength gypsum by free water crystal transformation method |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3119749C2 (en) * | 1981-05-18 | 1984-11-08 | Steag Ag, 4300 Essen | Process for the production of calcium sulfate hemihydrate from flue gas gypsum |
-
1986
- 1986-10-08 DE DE19863634204 patent/DE3634204C1/en not_active Expired
-
1987
- 1987-10-08 GB GB8723625A patent/GB2198721B/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| GB8723625D0 (en) | 1987-11-11 |
| GB2198721B (en) | 1990-05-09 |
| DE3634204C1 (en) | 1988-05-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19931008 |