What are the optimal settings for sludge drying in terms of requiring the smallest amount of reagent and ensuring maximum energy efficiency without damaging the equipment?
We are using the fluidized bed drying system. The water content we achieve in our dried sludge is less than 10%.
The centrifuges are the better way to drying the sludge.
Not always is the sludge drying process necessary, but in many cases it is the only solution. ¾ Sludge drying process diminishes volume of sludge making the transportation cost lower and the sludge storage easier; increases sludge calorific value; makes it hygienic (without pathogenic organisms); stabilizes it and improves its structure. ¾ There is quite a big variety of technical solutions of dryers among which contact and convective dryers are most popular. The choice of sludge drying facility should be dependent on the type of sludge and the method of sludge utilization. It should be emphasized that not all drying facilities are able to dry sludge only partially (less than 85-90% of DS) and, after all, not always there is a necessity to dry sludge up to 90% of DS or more.
I think that there is no "optimal" settings from the point of view of drying process. In any case you need to use a given amount of energy (heat) to evaporate 1 kg of water in the raw sludge. I can calculate for you the minimum quantity of energy to dry cold sludge with temp. T1 and initial x% of water to final hot sludge with temperature T2 and final water content y%. I say minimum heat quantity because in real device and in real process you loose some of it and the use of the heat (heat use efficiency) is less than 100%. The optimal settings you ask about can come only from the specific dryer construction (e.g. construction material etc.) and the highest temperature of the drying medium (air in fluidized bed dryer) should be stated to achieve the dry sludge of expected thermal degradation level. In the extreme case you could use the air heated to 500 C, dry and burn partially the sludge inside the dryer.