Heat Recovery | Shields Bag Reduces Natural Gas Consumption

Published: April 10, 2012

YAKIMA, WA | Saving money on its energy bills turned out to be a lot of hot air for flexible packaging innovator Shields Bag & Printing. 

As a custom blown film extruder, Shields Bag extrudes, prints, and converts film for flexible packaging products used in a wide range of industries. The company produces more than 100 lines of products that are shipped to clients all over the world, from produce bags to high graphic shrinkwrap.  

The company traces its roots back to 1935, when Frank Shields opened a print shop in Yakima. He and his sons built a successful commercial print shop, and in the mid-1950s branched out into flexible packaging.

In 2011, Shields brought in their local utility provider for an energy audit that was part of a greater review of the company’s operations. In their final report back to the company, the utility noted the company was releasing heated air from its oxidizer units—heat that represented lost energy dollars essentially being vented into the atmosphere. The oxidizers treat the exhaust from the flexographic printing presses, using heated air to break down volatile organic compounds (VOC) into carbon dioxide and water.  

Seeking Solutions

When the utility company delivered its final report to Shields Bag, three options were suggested for the company to improve its efficiency and reduce its energy waste from the oxidizers:

• Install a system that would capture the waste heat for other uses
• Install a new, more efficient oxidizer unit
• Replace the oxidizer with a biological system

A new system, whether it was a more efficient oxidizer or a biological system, was not seen as an effective solution for Shields Bag because of the capital costs. However, with the natural gas utility and Washington State Univ., offering financial incentives for a reduction in gas usage, the company began looking for a solution that would capture the waste heat from the oxidizers and re-use it for other purposes. 

“When we started looking at our energy consumption, our natural gas usage was way up there,” Derek LaFramboise, environmental affairs manager for Shields Bag & Printing, said. “It prompted us to explore options to reduce the volume, and heat recovery was the option that led us to the oxidizer modification.” 

MEGTEC proposed installing a heat coil system filled with a water-glycol mix in the stacks of the oxidizer exhaust that would capture the waste heat and make it available for transfer to other applications, such as pre-heating the air inlets for the oxidizers themselves. By pre-heating the air using recovered heat, less gas would be needed to heat the oxidizers to their optimal temperatures.

But MEGTEC’s solution did not stop there. The engineers also proposed using the coil system to transfer some of the heat from the oxidizer exhaust to pre-heat the dryer oven intakes on the production side as well. Again, by using the heat from the oxidizer exhaust to warm the air entering the oven intakes, less energy was required to achieve the optimal temperature for the operation of the dryer ovens.

Shields Bag opted for MEGTEC’s proposed solution, and its staff performed much of the installation in a two-phase approach that minimized production downtime. Engineers for MEGTEC worked on-site during the installation, providing assistance at critical times and with the start-up of the new heat recovery system.

The Payback

Shields Bag experienced immediate returns on two fronts once the heat recovery system was active.

The company experienced a reduction in its natural gas consumption by nearly 10,000 therms a month without any loss in production levels. The estimated cost of a therm of natural gas for an industrial user is $1 per therm, resulting in an estimated savings for Shields Bag of roughly $10,000 per month in energy costs. Not only is a savings in fuel usage recognized, this also provides a substantial drop in carbon emissions and products of combustion.

Additionally, the company has reported lower maintenance costs associated with heat controls for the oxidizer and the drying ovens. With the intake air pre-heated by the recovery system, less energy is needed to heat it to optimal temperatures and operators are making fewer adjustments to the control settings. Additionally, the warmers in the intake vents don’t need to operate as long. Supervisors on the line report the ovens better maintain consistent temperature and are more reliable since the installation was completed.

“It’s a lot like when you have your home furnace at 70 degrees. When it’s warming the air in the house, it clicks on and off just enough to keep the temperature constant,” LaFramboise said. “It’s when you open the doors and let in the cold outside air that the furnace has to work harder.”

For Shields Bag, saving money on its energy use is more than just a lot of hot air—saving money is a lot of hot air vented in the right direction.