SQUEEZING ENERGY FROM LOW GRADE HEAT

    Chemical engineers have been trying to find ways to squeeze energy from low grade heat for some time now.  An example of low grade heat may be water at 90 ⁰C. Michio Ikura at the Canmot Energy Technology Center in Nepean, Ontario may have found a way to do just that.  After experimenting with pyroelectrical materials, Ikura says that he has found a way to produce low cost electricity from water that was once thought to be zapped of its useful energy.  Pyroelectrical materials are those that produce a direct current when exposed to temperature changes.  The material that Ikura used was a 25 micrometers thick copolymer (vinylidene fluoride and trifluoroethylene) with an aluminum coating on each side.  10 to 20 of these sheets are sandwiched together and exposed to pulses of hot and cold water as shown below:

    Scale up of this experiment is expected to produce electricity at $0.03-$0.05/kWh with the equipment cost spread over a 20 year time period.   The implications for this technology could mean a whole new way of thinking about heat integration.  Typically, water at temperatures below 100 ⁰C, was considered to be "used up" in terms of heat energy.  The reality of course is much different.  Assuming an ambient temperature of 30 ⁰C, one gallon of water at 90 ⁰C contains over 900 KJ of energy that would traditionally have been wasted unless the plant contains a very cool stream that needs heating.

Reference:  Chemical Engineering, McGraw-Hill Company, July 1998, p. 29