×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

utilizing waste heat to produce electricity

utilizing waste heat to produce electricity

utilizing waste heat to produce electricity

(OP)
I work in pulp & paper industry.  We loose a lot of energy (~150°F hot air and condensing steam), from dryers, through the roof vents.  

Could I use Kalina-cycle (ammonia/water) turbine or a Stirling engine to recover this heat and utilize it to produce electricity?  Any suppliers of the equipment?

RE: utilizing waste heat to produce electricity

There isn't much energy in hot air.  

The condensing steam should be used to preheat water or air in other processes.

RE: utilizing waste heat to produce electricity

I agree, probably not economically viable to use low grade waste heat to generate electricity.

Use it to preheat combustion air for boilers, or the make-up air for the driers.

RE: utilizing waste heat to produce electricity

Alas, I also agree the previous posts.  Payback costs for the capital investments required would be too long.

RE: utilizing waste heat to produce electricity

I have seen heat pumps used in this type of waste heat application to recover and boost the temperature so the the energy could be used in a practical mechanical application.

Pete PowerSmith

RE: utilizing waste heat to produce electricity

Lowest practical commercial temp I know of is 90 C ( 194 F) to drive a lithium bromide absorption air conditioner ( Yazaki).

RE: utilizing waste heat to produce electricity

Yazakis (lithium bromide)will produce rated tonnage at 175F if condensing temp is kept low, well within the range of existing heat-recovery equipment.

RE: utilizing waste heat to produce electricity

There is a company based in Phoenix Arizona which is commercializing sterling engines.  That design uses co2 as the working fluid.

However as a general rule it is more economical to conserve energy than to find new sources.

If you could convert this thermal waste to electricity you could hope to get an efficiency of 30 or 40%.  On the other hand if you were to install an air to air heat exchanger to preheat your drier make-up air you would be able to get an efficiency of around 80%, depending on what the outside air temperatures are and also how saturated the exhaust stream is.  You would need a strategy to handle defrosting of the HX if you are in a cold climate area.  The cost effectivenes of the HX will be tempered by the amount of ductwok modifications needed to connect the HX to intake and exhaust.

RE: utilizing waste heat to produce electricity

Well steam and air coming from the top threw vents and dryers will not give you that much energy for the installation costs and the required systems, and besudes most of the time they are sources of getting rid of contamination and cleaning the system

RE: utilizing waste heat to produce electricity

Apple.....

Give up on the idea of using "low-grade" heat to generate power.... your capital investment will be huge and the amount of power generated will be minimal

Perhaps you should consider a re-generative type of heater for the incoming(cold) air ?

A "pipe within a pipe" type heat exchanger (of fairly long length) for 150F might prove economic if prpoerly constructed.

At 150F, you are somewhat in the range where heat must be "thrown away" simply to get it out of the building.

If this application were the flue duct from a boiler, about 220F would be the minimum limit for the exhaust gas temperature (and even higher temps should be considered for high-sulfur fuels).

My opinion only

-MJC

  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources