DEMONSTRATION PLANT FOR PROCESSING FGD GYPSUM INTO ANHYDRITE

Objetivo

The principal aim is the demonstration of a novel 14 mtph FGD gypsum-based anhydrite production line which is characterized by low energy consumption, great environmental amenity and ease of operation. The anhydrite produced is used as a binder for self-levelling mortars in floor screeds and as a setting-time regulator in cement. Secondly, it will have to be demonstrated that the process is capable of treating the various types of FGD gypsum arising in power stations. This will include any such qualities as are off-specification (colour and chlorine content) for more conventional uses.
PRODUCT RESULTS
Tests regarding capacity, efficiency, and environmental load yielded satisfying results, except for the noise level, which will be reduced in the near future.

PRODUCT QUALITY
A high quality anhydrite, used as a binder for mortar, absorbs a small amount of water (a low water/gypsum factor). Besides, the resulting mortar must not bind too fast, because it takes time to pour out the mass and spread it evenly. Thirdly it must be able to withstand local pressure and vibration (high bending strength). And last but not least, the covering floor has to be hard enough to walk on within a reasonable time (high compressive strength) so work will not be delayed. The quality of the anhydrite of ROCAL meets the requirements of the German standard DIN 4208.

INVESTMENT COST
The investment for the ROCAL plant (inclusive of all the start-up costs) amounted to NLG 15.2 million, slightly below the estimate.

ECONOMIC EVALUATION
The process is interesting from an economical point of view :
- the energy efficiency is high;
- the investment costs are limited;
- the availability of the installation is high;
- the process is uncomplicated, keeping operation costs low;
- the installation has few rotating parts and does not need intensive maintenance;
- the installation does not take up much space;
- the product quality can be constantly and precisely regulated.

FUTURE DEVELOPMENTS
At this time two installations for processing FGD gypsum into anhydrite are under construction in Boxberg, Germany. These are similar to the installation in Geertruidenberg. ROCAL has contracts with GYVLON Handelsmaatschappij BV in the Netherlands and with GYVLON Handelgesellschafts GmbH in Germany, in which the purchase of the annual tonnage of anhydrite for the next 15 years has been agreed. GYVLON is currently expanding its existing network of production units for self-levelling floor screeds in the Netherlands, Germany, Belgium and Switzerland and is planning to set up a similar networkin Great Britain. GYVLON envisages sound marketing opportunities in the Scandinavian countries, France and Italy as well. It should be noted here that the Netherlands Ministry for Social Affairs and Employment strongly encourages the use of self-levelling floor screeds with a view to working conditions.
The production line to be demonstrated has a capacity of 10 mtph of anhydrite. The raw material is FGD gypsum with about 8% adherent moisture and a purity of 90% CaSO4.2H2O. The working principle of the process consists in the rapid and uniform heating of FGD gypsum to a temperature of around 800 deg. C. This transforms the gypsum to anhydrite (CaSO4.2H2O....> 800 deg. C...> CaSO4 + 2H2O), the so-called calcination.
The application of the countercurrent method in this step makes it possible for the temperatures of the off-gases and final product to be kept to 120 and 90 deg. C, respectively. As a result, the process is worked at a high thermal efficiency (over 70%). The rapid and uniform heating of the FGD gypsum produces an anhydrite crystal of low pore volume. Subsequent pulverising results in a anhydrite for self-levelling mortars that are particularly suitable for high-crush floor toppings. The wet FGD gypsum is fed to the process using the air from the final-product cooling.In this air the gypsum is dried and subsequently raised in temperature to about 500 deg. C by the discharge from the calcination step.
Finally, the FGD gypsum is heated to 800 deg. C to give anhydrite. The air required in the calcination is preheated by passing it countercurrently through the hot anhydrite. In this way low temperatures can be maintained in the off-gas and the product (120 and 90 deg. C, respectively). After calcining, the anhydrite is pulverized in a suitable grinding mill to a product with the required rheological properties.
The present process achieves an energy saving of about 20% over conventional methods, such as the sinter grate and rotary kiln. Tests on rotary kiln anhydrite from FGD gypsum have shown that the product is of insufficient quality for use in self-levelling mortars for floor screeds. The compression strengths measured on the floor toppings produced were too low.

Programa(s)

ENG-ENDEMO C - Programme (EEC) of demonstration projects and industrial pilot projects (EEC) in the energy field, 1985-1989

Tema(s)

8.5 - USE OF WASTE

Convocatoria de propuestas

Data not available

Régimen de financiación

DEM - Demonstration contracts

Coordinador

GYVLON HANDELMAATSCHAPPIJ BV

Aportación de la UE

Sin datos

Dirección

NIJVERHEIDSSTRAAT 24 POSTBUS 245
2800 Gouda
Países Bajos

Coste total