With most plants now searching for ways to
minimize energy waste, one of the most common questions I hear is whether
there’s enough heat in an oven or furnace exhaust stream to make it worth
recapturing. Obviously, everything has to be approached on a case-by-case
basis, but here are some facts, figures and guidelines that may help you make
an informed decision.
Over the years of writing columns for Process Heating, I’ve had a number of items worth communicating
that are just too brief to fill an entire column. This is a collection of those
little bits and pieces. Just because something is small doesn’t mean it
shouldn’t see the light of day.
In
2006, as part of its “Save Energy Now” program, the U. S. Department of Energy
funded “Energy-Savings Assessments” of process heating applications in many
industrial plants. The assessments are conducted by engineering professionals
who have completed the DOE’s training to become BestPractices Qualified
Specialists.
Over the last few columns, I’ve beaten the energy conservation drum pretty hard. But energy costs remain fairly high, and many companies are still struggling with their impact on profitability, so please indulge me one more swing of the drumstick. This time, I’ll look at some ways to quickly assess efficiency and energy savings in process heating equipment.
The definition of oven or furnace efficiency is pretty straightforward -- it’s the thermal energy put into the product, divided by the total thermal energy consumed to carry out the process.
We all know that in convection ovens and furnaces, air is heated by a burner or electrical elements and then is pushed or pulled over and through the workload by a circulating fan. Coming into contact with the workpieces, the air transfers some of its heat to the product before going out the exhaust or being recirculated to the heating chamber.
It’s a well-established fact that setting up combustion systems for too much excess air (or dilution air) wastes fuel. You can use this relationship to calculate just how much you can save by decreasing excess air:
% Fuel Savings = 100 x [1- (Available Heat, High XS Air/Available Heat, Low XS Air)]
Visits to a number of plants this year have identified a common problem when it comes to energy conservation in their ovens and furnaces. They’ve got institutional amnesia -- as organizations, they don’t remember what they need to do to keep their equipment running at top efficiency.
Over the past few months, I’ve been involved in a number of plant process energy assessments. The results have been a mixed bag -- confirmation of prior expectations, some surprises and an exposure to a wide spectrum of attitudes toward energy conservation.
