What does REA or FGD gypsum mean? This is the German and the respective English abbreviation of the gypsum, which is produced during the process of catching the sulphur dioxide (SO2) in the sulphur cleaning installations of the thermal power stations. The sulphur content in the lignite coal of the Eastmaritsa basin is about 2,5%, which presumes a lot of gypsum from the thermal power stations in the process of sulphur cleaning.
Why FGD gypsum?
- Because there is plenty of it
- Because it costs nothing
- Because it is as good as the natural one
- Because it is the end of the cycle of a solution to a essential environmental problem
In that way all of us become part of a chain, which results in the production of construction materials with excellent properties.
- Where does Technogips take the raw material from? From the sulphur cleaning installations of 7th and 8th bloc of Thermal power station Maritsa East 2, with which it has signed a 25 year contract.
- How much raw gypsum per year is necessary for the production? About 360 000 tons.
In the tables below, you can see the basic indicators of the FGD gypsum compared to the natural one.
Analysis of the content of harmful substances in the FGD and natural gypsum
A detailed scientific analysis on that topic has been made in 1991 in Germany and was ordered by the Federal Union of the Gypsum Manufacturers (the so called “Beckert” study, Beckert et. Al 1991). The waste gypsum from the thermal power stations, working on brown coal, as well as the natural gypsum had been examined in medical and hygiene institutes. The content of residual elements, radioactivity, polycyclic elements and dioxins in the raw gypsum and the gypsum processed in a final product (e.g. gypsum plasterboard) had been compared. The specialists had determined that there were no polycyclic compounds and dioxins neither in the natural gypsum, nor in the one from the thermal power stations (FGD gypsum). All the determined residual elements were in extremely small quantities and there was no presence of artificial radioactive substances. All the values of the natural radioactive substances were far below the admissible norms of the radioactivity, measured in the usual construction products. The conclusion is that the gypsum from the thermal power stations, as well as the natural one is suitable for the production of construction materials.
The content of different chemical substances in both types of gypsum is shown in the table below:
| Element | Max.content in the natural gypsum (mg/kg) | Max. content in the gypsum from the thermal power stations (mg/kg) | Max. concentration in the gypsum dust (yg/m3) | Admissible values (yg/m3) | Max. concentration in the gypsum dust |
|---|---|---|---|---|---|
| Arsenic | 4 | 3 | 0,024 | 100 | 1/4000 TRK |
| Beryllium | 0,7 | 0,6 | 0,004 | 2 | 1/500 TRK |
| Lead | 21 | 22 | 0,130 | 100 | 1/800 MAK |
| Cadmium | 0,5 | 0,3 | 0,003 | * | |
| Chrome | 25 | 10 | 0,150 | 100 | 1/700 TRK |
| Cobalt | 4 | 2 | 0,024 | 100 | 1/4000 TRK |
| Copper | 14 | 9 | 0,084 | 1000 | 1/12000 MAK |
| Manganese | 130 | 200 | 1,200 | 500 | 1/400 MAK |
| Nickel | 13 | 13 | 0,078 | 500 | 1/6000 TRK |
| Mercury | 0,09 | 1,3 | 0,008 | 100 | 1/12000 MAK |
| Selen | 0,5 | 16 | 0,096 | 100 | 1/1000 MAK |
| Tellurium | 0,2 | 0,3 | 0,002 | 100 | 1/50000 MAK |
| Thalium | 0,2 | 0,4 | 0,002 | 100 | 1/50000 MAK |
| Vanadium | 26 | 8 | 0,156 | 50 | 1/300 MAK |
| Zinc | 40 | 50 | 0,300 | 5000 | 1/1700 MAK |
The minimal availability of residual elements in the FGD gypsum could be explained by the fact that during the sulphur cleaning process, the heavy metals from the coal or the black oil adhere to the ash. The ash or the dust is caught by the electric filters before the sulphur cleaning process. In this way the treated smoke barely contains any residual elements. In some countries the ash that has been caught by the filters is used in the road construction, avoiding the water supply areas.
Requirements of the gypsum industry to the FGD gypsum
The requirements have been determined and adopted by Eurogypsum in 1991:
| Property | Requirement |
|---|---|
| Free humidity | ≤ 10 M.-% |
| CaSO4 x 2H2O | ≥ 95* M.-% |
| MgO water soluble | ≤ 0,1 M.-% |
| Chloride | ≤ 0,01 M.-% |
| Na2O | ≤ 0,06 M.-% |
| Sulphur dioxide (SO2) | ≤ 0,25 M.-% |
| pH-value | 5 to 9 |
| Colour | White to yellowish |
| Smell | Neutral |
| Toxic components | None |
* Lower purity (up to 80%) caused by inert contaminants, depending on the area of appliance is not a disadvantage.
A stricter criteria for the water-soluble magnesium oxide is being discussed (< 0,01)
- Colour digressions, depending on the area of application are also admissible.
Requirements of the cement industry for the FGD gypsum according to DIN 1164:
| ROI | < 5 % |
|---|---|
| CO2 | < 2,5 % |
| insoluble residue | < 3,0 % |
| MgO | < 5,0 % |
| SO3 | < 3,5 - 4,5 % |
| Additives | < 5 % |
| Chloride | < 0,1 % |
About 2 million tons of FGD gypsum are used in the German cement industry every year, as a regulator of the setting times.