By using 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.
Saving money on its energy bills turned out to be more than just a lot of hot air for flexible packaging manufacturer Shields Bag & Printing.
As a custom blown film extruder, Shields Bag extrudes, prints and converts film for flexible packaging products. The company produces more than 100 lines of products for clients all over the world, from produce bags to high graphic shrink-wrap. The company traces its roots back to 1935, when Frank Shields opened a print shop in Yakima, Wash. He and his sons built a successful commercial print shop, and in the mid-1950s, the company branched out into flexible packaging.
In 2011, Derek LaFramboise, environmental affairs manager for Shields Bag & Printing, learned that Cascade Natural Gas had government incentive money available for heat recovery projects. He began consulting with staff from the utility, as well as nearby Washington State University, about projects that might help Shields Bag capture waste heat and reduce its utility costs. Eventually, an energy audit was conducted as part of an overall review of the company’s operations.
In its final report back to the company, the utility noted that Shields Bag was releasing heated air from its oxidizer units. This meant heat - essentially, lost energy dollars - was being vented to the atmosphere but Shields Bag could recover it for other uses. The oxidizers treat the exhaust from the flexographic printing presses, using air heated to more than 550°F (288°C) to break down volatile organic compounds (VOCs) into carbon dioxide and water.
The utility suggested three ways Shields Bag could improve efficiency and reduce 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 incentive, as well as Washington State University funding for the project, Shields Bag began looking for a solution that would capture the waste heat and repurpose it.
The heat recovery inlet coil used at Shields Bag transfers surplus heat from the oxidizer exhaust to preheat the dryer oven intakes on the production side of the operation.
“When we started looking at our energy consumption, our natural gas usage was way up there,” LaFramboise says. “It prompted us to explore options to reduce the volume, and heat recovery was the option that lead us to the oxidizer modification.”
Shields Bag approached Megtec Systems, De Pere, Wis., a manufacturer of oxidizers and heat recovery systems. After reviewing the current setup, Megtec proposed installing a heat coil system filled with a water-glycol mix in the stacks of the oxidizer exhaust. The heat coil would capture the waste heat and make it available for transfer to other applications such as preheating the air inlets for the oxidizers themselves. By preheating the air using recovered heat, less gas would be needed to heat the oxidizers to their optimal temperatures.
But the solution did not stop there. While heating the intake inlets for the oxidizer would reduce the amount of gas needed to reach the right temperature, there would still be excess heat left in the recovery system that could be used for other applications. Working with Shields Bag, Megtec engineers also proposed using the coil system to transfer surplus heat from the oxidizer exhaust to preheat the dryer oven intakes on the production side of the operation 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 dryer ovens. With the amount of heat in the system, the recovery system also was able to preheat the dryer intakes for six of Shields Bag’s production lines.
Shields Bag opted for this 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 as needed with the startup of the new heat recovery system.
Shields Bag hired Megtec to install 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 preheating the air inlets for the oxidizers themselves.
Once the heat recovery system was active, Shields Bag experienced immediate returns on two fronts.
The company experienced a reduction in its natural gas consumption that ranges from 8,500 to 10,000 therms a month without any loss in production levels. The variations are the result of different lines being shut down at various times. 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 preheated 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 do not 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.
In addition, Shields Bag achieved other benefits and happily shares their lessons learn. “While many companies are seeking to ‘green’ their process and reduce their carbon footprint, knowing where to start is often the challenge,” says LaFramboise. Getting started often is as simple as asking for help. In the case of Shields Bag, asking about financial incentives resulted in the company looking for ways to reduce its energy use.
“Once you ask, it really gets the ball rolling,” LaFramboise says. “You start to see all kinds of other areas you can dig into.”
Additional benefits also become apparent. Because Shields Bag now is burning less natural gas, it also has reduced its emission of carbon dioxide and other compounds associated with burning natural gas.
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. PH