Taking the Heat
Bakeries find better ways to capture an oven’s waste heat and divert it to other systems to keep natural gas costs from going up in smoke.
BakingBusiness.com, Dec. 13, 2011
by Dan Malovany
POWER Engineers
After New Horizons Baking Co. decided to replace the aging proofer and oven in its Norwalk, OH, plant, John Widman primarily focused on calculating how much more efficient the new systems would be than the old ones.

Discussions about return on investment, however, quickly turned to sustainability as well when Mr. Widman, the company’s senior vice-president of operations, learned that installing a heat recovery system in the oven’s stack could be used to heat and provide steam to the proofer on the bakery’s 5,000-doz-buns-an-hour line.

“I told Tim Brown, president of our company, ‘We have an opportunity here to be greener,’” Mr. Widman recalled.

Although the idea piqued his interest, Mr. Widman still wasn’t totally sold on the concept until later in the process. In fact, the idea of putting in such new technology made him a little nervous. “I have to tell you, it was a bit scary because we had never done it this way, and I’m always leery about new things,” he said. “I don’t want to be the one who shows the industry that something doesn’t work.”

New Horizons relied on its oven and proofer supplier, Baking Technology Systems (Bake-Tech), Tucker, GA, and the heat recovery system installer, Air Management Technologies (AMT), Lewisburg, PA, to do the legwork. “They did all of the drawings and spec’ed out the equipment” Mr. Widman said, “but I kept my fingers crossed until we actually started it up and showed it actually worked.”

That was 18 months ago, and so far, the system has worked as planned, according to Mr. Widman. “I cannot afford to have my proofer not heated up, but this system has functioned flawlessly,” he said.

PERPETUAL DIVIDENDS.

While more efficient lighting fixtures and water conservation programs reduce energy costs, heat recovery is the money saver that keeps on saving, observed Jeff Dearduff, veteran bakery engineer and chairman of the American Society of Baking.

Mr. Dearduff, who oversaw a recent heat recovery system installation, noted the exhaust leaves the oven chamber around 300°F. Instead of sending it to the atmosphere, it can be used to heat a secondary medium — usually food-grade propylene glycol — that can be routed to proofer heating coils, process water heaters and even fermentation room systems. The glycol is recycled through a closed-loop system so there is no effect on oven airflow or pressure.

“The idea of using the waste heat from the oven stack simply allows you to get a full bang for the buck on each cubic foot of natural gas or other fuel that you are purchasing,” Mr. Dearduff explained. “By using this waste heat, you are not buying fuel for steam boilers, water heaters and other systems. It is this full use of the purchased fuel and overall reduction of fuel purchases that becomes the sustainable feature. If you factor your fuel purchases into the entire business unit’s productivity, you can calculate a cubic foot of fuel per pound of finished product formula. This can be reported as a monetary savings and a conservation of natural resources, which makes the big customers very happy.”

Scott Houtz, AMT’s president, said heat recovery is just common sense. “When you look up to the roof of a bakery and see these heat plumes, you just think, ‘What a waste of energy,’” he noted.

In addition to providing heat to bakery equipment, the system can preheat cold outside air to warm the bakery during winter months. “Sometimes it’s a little tough to swallow that you are burning gas inefficiently to heat air when you can do it basically for free,” Mr. Widman said.

The glycol tanks and other main parts of the system can be installed outside of the bakery and are tolerant enough to operate in either extreme heat or cold, according to Mr. Houtz. The actual heat exchanger sits inside the stack with a damper arrangement that can divert all, some or none of the oven exhaust through the heat exchange coils, depending on the bakery’s needs.

“If we need only 50% of the heat coming out of the oven, the damper will modulate accordingly to match up our heat loss through the loop to make up that load,” Mr. Houtz said.

In the case of a system failure, he added, the damper can be fully opened so it doesn’t disrupt the baking process.

DOWN TO THE CORE.

Throughout the baking industry, talk about such sustainability efforts is heating up, mainly because of the advances in new technology that has become available in recent years. Many of these recovery systems can now capture 95 to 98% of the heat and steam coming out of the stack.

Another energy-saving system, the patent-pending Condenser Oxidizer Recuperative Exchanger (CORE) can reduce fuel consumption up to 50% and replace costly oven stack oxidizers, according to Jim Pezzuto, president of ERB CORE, a division of the Ensign Group, Pelham, NY.

Traditionally, oven oxidizers burn volatile organic compounds such as ethanol to prevent them from being released into the atmosphere. CORE captures ethanol, a byproduct of baking yeast-raised products, and diverts it to the oven, where it’s reused as a biofuel, Mr. Pezzuto said.

CORE also recaptures water vapor from the exhaust to convert into steam for proofers or supplying hot water for washing pans and equipment inside the bakery. “We’re exploring the possibility of using it with a small electrical generator or a gas turbine to provide electricity,” Mr. Pezzuto noted. “We’re trying to wring every last Btu out of that stack and send it for reuse.”

With CORE, only carbon dioxide, which can eventually be directed for greenhouse usage, comes out of the stack at a temperature of 85°F or less. The 50% savings includes energy saved not only by reusing heat and vapor but also by not having to use or install a boiler. “That’s another chunk of fuel that you are saving, and it goes into our calculation as well,” Mr. Pezzuto said.

Energy savings is only part of the overall equation with heat recovery projects. To maximize efficiencies, the accompanying software program can track information on the amount of Btus being used and the amount of energy that’s available for future use.

“It is truly a management system so you can go back and measure what you are specifically saving in natural gas usage,” Mr. Widman said.

This story is sponsored by POWER Engineers, which has one of the most comprehensive teams of engineers and specialists serving the baking and snack industry. As an extension of its clients' engineering teams, the company provides program management, integrated solutions and full facility design for the baking and snack industry. Learn more at www.powereng.com/food.