Gravel-bed filter

The arrangement and distribution of anodes in gravel and activated charcoal filters is different. Cathodic protection of activated charcoal filters is basically feasible but requires a large number of electrodes and high protection current densities that are twice those for gravel bed filters, so that an electrically insulating layer can be deposited on the steel wall. 

Another approach [12.10] uses the technology developed for the gravel bed filter. It operates at a pressure drop of 1.5 kPa and has given absorption efficiencies of 97 to 99%. 

Wherever such a precleaned waste water is to be further treated, for instance by extraction or distillation, the solids content has to be reduced to a much lower level. This is done not only in the pressurized gravel bed filters which have been standard equipment for decades already although they tolerate only small... 

In the Swedish BWR plant Barseback, a so-called vented containment was employed for the first time, consisting of a 10,000 m gravel bed filter to which the gas-steam mixture from the containment would be directed in the event of a severe accident. The steam will condense on the initially cold pebble surfaces, resulting in an effective retention of aerosols and iodine. However, for various reasons this solution proved not to be optimal. 

The clinker cooler has three grates and is equipped with a hammer crasher between the 2nd and 3rd grate. Hot air is taken out just at the beginning of the 2nd grate and is used to dry coal in a roller mill with a capacity of 30 tonnes/hour. At the end of the 2nd and 3rd grate exhaust gases are taken out and cleaned in a gravel bed filter. 

By using these fairly clean, dry and hot gases, we were able to build a simple heat exchanger with standard components. The gases, with an average temperature of 230°C, are taken out after the gravel bed filter into a by-pass loop. By controlhng the speed of the fans the water temperature is held at a desired... 

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