Fusebox EPFL

Reduce Water Consumption / Water from Air

Water is not only delivered to a process plant through pipes. A lot of water comes bound to grain into a process plant, and whether it is rice, maize or wheat, at some point of the whole process it undergoes a drying process to extend the shelf life. If this process is done with hot air, what happens with the saturated air that has absorbed the water from the dried cereals? Is it just discharged into the environment, why don't we retrieve the water? I think water consumption is an important factor in large industrial process plants. It might doesn't play such a big role in western countries, where tap water is plentiful and not many really care as long it is not turned into waste water. But in developing countries it might have a huge impact and if you can make potable water from humid process air maybe even in western countries. If you search in google there are a lot of attempts to generate water from humid ambient air. So i think retrieving water from a process flow, where humid air is generated in a large amount, should be possible. Maybe it is even possible to use the water for pasta production or at least as process water.

edited on Mar 6, 2014 by Gian Nutal Schädli

Ian Roberts Mar 5, 2014

Utilising removed water from drying processes is a good idea. How much water is removed when drying? How would you recuperate it? How much water would be needed to make the recuperation cost effective for the owner? 

When you have humidity in the gas stream of a dryer you can also recuperate energy.

Gian Nutal Schädli Mar 6, 2014

The amount of water removed depends on the grain. If we dry 1000kg to maize with a water content from 35% to 15%, around 235kg water has been removed. I think for rice the undried water content is around 25%, so if the water content is decreased to 15%, the water removed from 1000 kg rice would be about 115 115 kg. With a throughput of 10t/h maize, 2.35t/h water is removed!

Now of course we can't recuperate all the water. The easiest way for recuperation is just to cool it down until it reaches the dew point and then collect the condensate, obviously this method is limited to the ambient air temperature and relative humidity. Then we still could increase the pressure to increase the dew point temperature, but this needs energy as well. Now there has been a lot of research in recovery of water from atmospheric air (see paper). A solid or a liquid desiccant is used to absord the moist air, afterwards the water is recuperated by evaporation and subsequently condensing, where solar irradiation is used to evaporate the water. 

  • Combination of cooling and pressure increase to condense the water
  • absorption of the moist air by a desiccant, followed by evaporation and condensation. 

The challenge is to combine everything into a cost effective system. Well, I have no idea how much water is needed to make the recuperation attractive to  the owner. I think in general the additional amount of energy used has to be as small as possible, so most of it should come from renewable energy like solar power. As I also like the idea from Andy Lauper "Drying process - including solar technology". I think a sophisticated sytem right from the start of the drying process is necessary to make it cost effective for the owner. For example with the idea from Andy Lauper, the energy saved for the drying process could be used for recovering water from the moist air.

Combining the idea from Andy Lauper & Andreas Bruun

Now the idea from Andreas Brunn made me recall a short documentary (see youtube clip - only german). As can be seen in the documentary the people in these countries are really eager to adapt new concepts and ideas. As Nadina already mentioned a drying step could improve the idea from Andreas in terms of shelf life. With the idea from Andy the drying could be done in those regions (they have a lot of sun) without the need of much fuel. Finally the water could be retrieved to water their fields. So the children would have real perspectives in their villages to work as a farmer.

 

 

 

Andreas Baumann Mar 7, 2014

The amount of water that could be recuperated during drying are quite impressive. You also combined several ideas to have a small-scale unit for drying based on solar energy that you rent to farmers. This implies that you could use the recuparated water for growing the crops that enter your equipment. This could then be a chance to grow food in regions where water is scarce. Do you have an idea of the relation between the water that is needed for crop growing and the water that you recuparate with your system?