FLUE-GAS DESULFURIZATION OF LIGNITE-FIRED POWER-STATIONS WITH LIMESTONE OR FINE LIME

The environmental legislation which now applies to the whole of German y means that power stations must either be retrofitted with environmen tal protection technology if they are to continue in. operation, or be replaced by new power stations. Most of the flue gas desulphurization plants installed under these circumstances are operated with crushed Limestone. Low Permissible residual emissions and complete utilization of the FGD gypsum produced are placing high demands on the design of the plants and the absorbents to be used. After the commissioning of t he first desulphurization plants in March 1995 in the Janschwalde and Boxberg III power stations, which have been retrofitted, the initial o perating results are now available. With crushed limestone the critica l quality criteria for trouble-free and effective operation while main taining the required gypsum quality are not only the chemical composit ion but also, and in particular the whiteness and the particle size co mposition that must be maintained. The inclusion. of foreign substance s or bodies derived either ft om the limestone quarrying and productio n processes or from the means of transport has proved to be a problem which should not be underestimated. Impurities from hard flints, which can lead to abnormal wear or malfunctions in the desulphurization pla nts, also prove a problem when using the wet grinding process. Followi ng a technical and economic evaluation as a result of the special cond itions at the Lippendorf power station (high sulphur content, low resi dual emissions, usability of the gypsum) burnt lime (fine lime) will b e used as the absorbent. A pilot plant has been. operated at Lippendor f and has contributed decisively to the design of an industrially reli able process solution which meets the requirements of the licensing au thorities. It has been used for practical testing of special process e ngineering features and to optimize the part of the process dealing wi th the residual materials - gypsum and the waste water from flue gas d esulphurization. The official requirements for full utilization of the FGD gypsum produced are fulfilled in all VEAG power stations, and thi s has been confirmed during the practical operation of the retrofitted power stations at Janschwalde and Boxberg.