GB2198720A - Process for preparing alpha-calcium sulfate hemihydrate - Google Patents
Process for preparing alpha-calcium sulfate hemihydrate Download PDFInfo
- Publication number
- GB2198720A GB2198720A GB08723624A GB8723624A GB2198720A GB 2198720 A GB2198720 A GB 2198720A GB 08723624 A GB08723624 A GB 08723624A GB 8723624 A GB8723624 A GB 8723624A GB 2198720 A GB2198720 A GB 2198720A
- Authority
- GB
- United Kingdom
- Prior art keywords
- flue gas
- heating
- calcium sulfate
- air pre
- calcium
- 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
Links
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
-
- 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
- C04B11/26—Calcium sulfate cements strating from chemical gypsum; starting from phosphogypsum or from waste, e.g. purification products of smoke
- C04B11/262—Calcium sulfate cements strating from chemical gypsum; starting from phosphogypsum or from waste, e.g. purification products of smoke waste gypsum other than phosphogypsum
- C04B11/264—Gypsum from the desulfurisation of flue gases
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
- Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Inorganic Chemistry (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Treating Waste Gases (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
A process for preparing alpha-calcium sulfate hemihydrate by pressureless heating of a suspension of calcium sulfate in the presence of a dehydration catalyst and subsequent filtration, washing and drying is carried out by a) the underflow of a hydrocyclone of a flue gas desulfurization plant is employed as the calcium sulfate dihydrate suspension; b) calcium chloride originating from the flue gas is employed as the dehydration catatyst; c) part of the mother filtrate rich in calcium chloride is re-circulated as dehydration catalyst and part of the mother filtrate rich in calcium chloride is dried in a spray-drier using a portion of the flue gas after the air pre-heating (LUVO); d) heating without pressure of the calcium sulfate dihydrate suspension is carried out using another portion of the flue gas after the air pre-heating (LUVO); e) the flue gas portions of the steps c) and d) are combined with the portion, if any, of the flue gas directly passed on after the air pre-heating (LUVO) and the combined flue gas portions are introduced into the flue gas desulfurization plant; and f) the hot washing water of the filtration is introduced into the flue gas desulfurization plant. The process is particularly suitable for flue gases rich in chloride contents. <IMAGE>
Description
PROCESS FOR PREPARING
ALPHA-CALCIUM SULFATE HEMIHYDRATE fihs present invention relates to a process or the preparation of alpha-calcium sulfate hemihydrate by pressure-less heating a suspension of calcium sulfate in the presence of a dehydration catalyst and subsequent filtration, washing and drying1
Alpha-calcium sulfate hemihydrate is formed upon heating aqueous suspensions of calcium sulfate dihydrate. As temperatures in excess of 100 "C must be employed for heating nguous suspensions without a dehydration catalyst, it is mostly required to carry out heating under an elevated pressure in an autoclave,
In the presence of dehydration catalysts such as suluric acid it is possible to reduce the temperature of the dehydration.Other dehydration catalysts such as larger amounts of dissolved calcium chloride, above all, increase the boiling point of the solution so that the deydration may also be effected out by heating without pressure,
After heating the calcium sulfate dihydrate suspension with concomitant reaction to form alphacalcium sulfate hemihydrate the suspension is filtered, and the residue is washed and dried, Washing and drying znust be effected as fast as possible, as otherwise the formed alpha-calcium sulfate hemihydrate will again react with the adherent water to form calcium sulfate dihydrate and set.As an alternative it is possible to add setting inhibitors to the alpha-calcium sulfate hernihydrate suspensions; however, said inhibitors must in turn be subsequently removed and mostly result in a deterioration of the setting property of the alphacalcium sulfate hemihydrate.
In the past it was mainly phosphogypsum as obtain- ed ?n 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 fact that in the meantime a desulfurization of flue gases is demanded by law, increasing amounts of flue gas gypsum are formed for which suitable applications are still being sought. However, in the future consd.rabl. amounts of flue gas gypsum will have to be disposed of under environment-compatible conditions.
Depending on the fossil fuel as initially employed the flue gas gypsum when being formed contains higher or lesser 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.
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 sulphato 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 a8 a building material, the chloride contents thereof must not be excess of 100 ppm, whereas somewhat higher amounts of chloride contents will not interfere with a use as mining mortar1
Now it was surprisingly found that the above object can be attained with particular ease and at low cost by a) using the underflow of a hydrocyolone of a flue gas desulfurization plant as the calcium sulfate dihydrate suspension: b) using calcium chloride originating from the flue gas as dehydration catalyst: c) re-circulating part of the mother filtrate rich in calcium chloride as dehydration catalyst and drying part or the mother filtrate rich in calcium chloride in a spray-drier using a portion of the flue gas after the air pre-heating (LUVO); d) carrying out heating without pressure of the calcium sulfate dihydrate suspension using another portion of the flue gas after the air pre-heating (LWO) a) combining the flue gas portions of the steps c) and d) with the portion, if any, of the flue gas directly passed on after the air pre-heating (LUVO) and introducing the combined flue gas portions into the flue gas droulfurization plant; f) introducing the hot washing water of the fil- tration into the flue gas desulturization plant.
The process according to the present invention is preferably used for flue gases which are rich in chloride content. Drying of the alpha-caloium sulfate hemihydrate is alternatively effectedalso by utilizing flue gas after air pre-heating, while, however, it may also be carried out by utilizing air from the air preheater or steam from the power plant1 The flue gases from the drier are preferably introduced into the flue gas desulturization unit. Thereby deducting ng the flue gases becomes dispensable, since most finely divided dust forms crystallization nuclei for the flue gas desulfurization. Temperature and the contents of water vapor of the flue gases also will not adversely affect the operation of the flue gas desulfuration unit.
One advantage of the process according to the invention consists of that the separation of the flue gas gypsum, as so far usual can be forgone. In the process according to the invention the underflow of a hydrocyclone of a flue gas desulfurization plant is directly employed.
Thie suspension obtained as the underflow of a hydrocyclone also contains part of the chloride as precipitated in the flue gas desulfurization step, which chloride in the next step acts as a dehydration catalyst in the next step. In order to be able to operate without the application of pressure, further calcium chloride originating from the flue gas is introduced into the dehydration. To this end, a portion of the mother filtrate rich in calcium chloride is returned according to step c).
When, in the course of the process, further amounts of chloride from the flue gas desulfurization plant are introduced into the dehydration step, an equivalent portion pf the mother filtrate may be removed from 'the cycle. According to the invention, this portion of the mother filtrate is dried in a spray drier utilizing a portion of the flue gas from the air pre-heatin (LUVO).
Also, pressureless heating of the calcium sulfate dihydrate suspension with the dehydration catalyst calcium chloride ie carried out utilizing another portion of the flue gas after air pre-heating (LUVO).
The flue gas portions of spray-drying and of pressureless heating are combined with the directly passed portion, if present, of the flue gas after the air preheating, and the combined flue gases are introduced into the flue gas desulfurization plant. The temperature, the water vapour contents and most finely divided dust particles as possibly present from spraydrying do not ad-ver6ely affect the following flue gas desulfurization.
The step of drying the alpha-calcium sulfate hemihydrate must be carried out very fast to avoid a rehydration. Thus, said drying may basically be carried out by utilizing flue gas after the air pre-heating.
Nevertheless, further variants comprise the use, of air from the air pre-heating or of steam from the power plant. In any event the flue gases from the drier may be subsequently introduced into the flue gas desulfur- ization unit where they do not interfere with the process and are subjected to the following purification steps,
The hot washing water of the filtration may also be introduced into the flue gas desulfurization unit, if so desired.Thus, the process according to the invention has the , particular advantage of being operated without producing any waste water and to provide" as the only products, a usable low-chloride alpha-calcium sulfate hemihydrate and a small amount of solid calcium chloride contaminated by some gypsum which can either be readily disposed of or be further processed.
Another advantage of the process according to the invention is that in the flue gas desulfurization units substantially lower amounts of chloride are accumulated in the suspensions than is the case in conventional processes. Due thereto the conditions in the flue gas desulfurization unit may be optimized with respect to the involved materials.
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.
By the process according to the invention it is possible to obtain an alpha-calcium sulfate heihydrate having a chloride content of less than 100 ppm, which may be used as building material and for construction purposes. However, more particularly, the alphacalcium sulfate hemihydrate obtained according to the present invention is used as a mining mortar. This 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, Another advantage of the process according to the invention consiets of that the process works energy-neutral and, above all, the waste heat is optimally exploited.
The process operation according to the present invention is schematically illustrated by the diagram shown in the attached Figure 1.
The reference numerals have the following mean- ings:
1 Flue gas desulfurizatton unit;
2 Spray drier;
3 Reactor for heating and dehydrating the calcium
sulfate dihydrate to form alpha-calcium sulfate
hemihydrate;
4 Fan for the waste air from the spray drier;
5 Drier for alpha-calcium sulfate hemihydrate;
6 Band filter; 7 Raw gas after the air pre-heating (LUVO); 8 Puriiisd gas;
9 Conduit for the suspension of flue gas gypsum
(hydrocyclone underflow): 10 Dry alpha-calcium sulfate hemihydrate; 11 Solid calcium chloride (possibly contaminated with
some gypsum); 12 Hot washing water; 13 Mother filtrate.
Claims (5)
1. A process for preparing alpha-calcium sulfate
hemihydrate by pressureless heating of a suspension of
calcium sulfate in the presence of a dehydration
catalyst and subsequent filtration, washing and drying,
characterized in that
a) the underflow of a hydrocyclone of a flue gas
desulfurization plant is employed as the calcium
sulfate dehydrate suspension;
b) calcium chloride originating from the flue gas is
employed as the dehydration catalyst;
c) part of the mother filtrate rich in calcium
chloride is re-circulated as dehydration catalyst and
part of the mother filtrate rich in calcium chloride is
dried in a spray-drier using a portion of the flue gas
after the air pre-heating (tWO):: d) heating without pressure of the calcium sulfate dihydrate suspension is carried out using another
portion of the flue gas after the air pre-heating
(LWO);
e) the flue gas portions of the steps c) and d) are
combined with the portion, if any, of the flue gas
directly passed on after the air pre-heating (LUVO) and
the combined flue gas portions are introduced into the
flue gas desulfurization plant and
f) the hot washing water of the filtration is intro
duced into the flue gas desulfurization plant.
2. The process according to claim 1, characterized in
that flue gases rich in chloride contents are employed.
3. The process according to claims 1 or 2, character
ized in that the step of drying the alpha-calcium
sulfate hemihydrate is carried out utilizing flue gas
after the air pre-heating, air from the air pre
heating or steam from the power plant.
4. The process according to claim 3, characterized in
that the waste gases from the drying step are intro
duced into the flue gas desulfurization unit.
5. A process as claimed in claim 1 substantially as herein described.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19863634207 DE3634207A1 (en) | 1986-10-08 | 1986-10-08 | METHOD FOR PRODUCING ALPHA CALCIUM SULFATE SEMI-HYDRATE |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8723624D0 GB8723624D0 (en) | 1987-11-11 |
| GB2198720A true GB2198720A (en) | 1988-06-22 |
| GB2198720B GB2198720B (en) | 1990-05-09 |
Family
ID=6311261
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8723624A Expired - Fee Related GB2198720B (en) | 1986-10-08 | 1987-10-08 | Process for preparing alpha-calcium sulfate hemihydrate |
Country Status (2)
| Country | Link |
|---|---|
| DE (1) | DE3634207A1 (en) |
| GB (1) | GB2198720B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2002088045A1 (en) * | 2001-05-01 | 2002-11-07 | National Gypsum Properties, Llc | Method of producing calcium sulfate alphahemihydrate |
| CN108926981A (en) * | 2017-05-24 | 2018-12-04 | 沈阳铝镁设计研究院有限公司 | The desulfurization of aluminium hydroxide production process flue gas and afterheat utilizing system and method |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19755885B4 (en) * | 1997-12-05 | 2007-10-31 | Vattenfall Europe Generation Ag & Co. Kg | Method and device for improved task of a demixed gypsum suspension on a filter cloth of a vacuum belt filter system |
| DE19908776C2 (en) * | 1999-02-19 | 2002-05-23 | Ver Energiewerke Ag | Process and arrangement for producing high-purity alpha-calcium sulfate hemihydrate |
-
1986
- 1986-10-08 DE DE19863634207 patent/DE3634207A1/en not_active Withdrawn
-
1987
- 1987-10-08 GB GB8723624A patent/GB2198720B/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2002088045A1 (en) * | 2001-05-01 | 2002-11-07 | National Gypsum Properties, Llc | Method of producing calcium sulfate alphahemihydrate |
| US6652825B2 (en) * | 2001-05-01 | 2003-11-25 | National Gypsum Properties Llc | Method of producing calcium sulfate alpha-hemihydrate |
| CN108926981A (en) * | 2017-05-24 | 2018-12-04 | 沈阳铝镁设计研究院有限公司 | The desulfurization of aluminium hydroxide production process flue gas and afterheat utilizing system and method |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3634207A1 (en) | 1988-04-21 |
| GB2198720B (en) | 1990-05-09 |
| GB8723624D0 (en) | 1987-11-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19931008 |