Municipal waste processing

Heat consumption for evaporation of water is roughly 2.4 GJ/t(water). Most often the actual heat consumption goes to 4 GJ/t(water). The additional heat consumption is the addition of various losses:

• wall losses to the surrounding
• solids that are heated up
• gases that are heated too

These losses can actually vary quite a lot depending on the design constraints.

For example, the maximum temperature might be limited (fire risks for example), and the exhaust temperature could not go below a certain limit (say 100°C). Therefore, the heat consumption will increase if the maximum allowed temperture is decreased. This is because of an increase gas volume leaving the dryer at about 100°C.

There are also various drying systems that can have different efficiencies. Co-current or counter-current drying, direct or indirect drying, rotary dryer, flash dryer, ...

The nature of the product being dried can also play a big role. It is relatively easy to evaporate "surface water". But materials, like patatoes, are more difficults to dry because water has to go through the barrier of the material itself before evaporating. Therefore, a "drying curve" should be measured in the labaoratory, in principle. When a material is hard to dry, the heat consumption will increase.

The amount of water itself influences also the efficiency since more water means less solids and usually also more surface water that is easier to dry.

Since I don't know much about municipal wastes, I cannot give more precise information.  

Dear LALbatros,

        Sound good.Thanks for ur valuable reply.This is a generic evaporation formula and is a basic drying factor.Infact we need to develop more on this to get more specific values for municipal wastes.

Somebody might be having hands on experience in their plant for procesing solid wastes,kindly help me out with the design calculations.

Anybody?

Regards,

Kesav