Heat recovery

Heat recovery is a process where waste heat from hot stream is transferred directly or indirectly to some colder temperature target which can be fluid or solid.

To be technically and economically profitable the recovered energy has to

Decrease primary energy consumption
Produce recovered energy with the competitive price level (considering CAPEX and OPEX) compared to the energy produced with the primary energy sources

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Temperature and humidity – importance for dryer’s heat recovery efficiency

It is a common rule that increased humidity level in dryer’s exhaust air flow improves heat recovery rate. Besides this there is a fact that increased temperature difference between hot and cold fluid flows increases heat transfer as Newton’s law of cooling defines. However, the scale of influence of these two factors is not so obvious for all designers. In this article is presented with an example the importance of these parameters.

How much increased water content in dryer section exhaust air will improve the heat recovery efficiency?

Exhaust air flow from the dryer section is normally adjusted by maintaining constant water content in air flow. In some situations, exhaust air flow needs to be decreased thus causing decrease for the heat recovery process. Decreased humidity level decreases energy efficiency by means of lower heat recovery rate and higher specific heat consumption of the drying process.

How much energy can be recovered from the dryer section exhaust air flow?

Essential part of energy efficient dryer section operation is a properly dimensioned heat recovery system. In green field projects the design of the heat recovery system is almost the standard, but in rebuild cases there is need for tailor-made design is needed to maximize the benefit of the heat recovery system.