Heat Recovery Systems Reduce Waste Heat for Printing Plants
Throughout the printing industry, printers use diverse technologies to produce printed materials such as magazines and product labels. From lithography and flexography to screen printing, the many different printing processes share some common production and environmental challenges. Among these are the wise use of energy, maintenance of good indoor air quality and year-round control of temperature and humidity in the facility.
Two Midwestern printing plants, each dealing with different issues related to the expense of waste heat, found using air-to-air heat exchangers in a heat recovery system helped reduce the amount of waste heat and the price of their electric bills.
Printing Press Finds Energy Savings
A Wisconsin printer using flexographic printing equipment was experiencing air balance problems in the printing plant. Problems included drafts and high energy bills associated with negative air situations. Rather than simply addressing the air deficit with a traditional gas-fired makeup unit, an approach was formulated to capture much of the energy in the airstream with air-to-air heat exchangers.
In the Wisconsin plant, the web presses required approximately 23,000 cubic feet per minute (cfm) of air to dry the ink on the printed material. Air from the plant was drawn into the presses, warmed by electric heaters in the presses to about 160°F (71°C), and exhausted to the outside. The energy contained in that warmed airstream could be easily captured to help increase production and profits using air-to-air heat exchange.
Energy recovery technologies like air-to-air heat exchangers have been used in the printing industry to improve the overall production performance by reclaiming otherwise wasted energy. For the Wisconsin printer, there were many benefits to using an energy recovery system in the plant. Most importantly, the negative pressure problem in the plant was eliminated. In addition, gas-fired heaters that were needed to heat ambient air to maintain temperatures in the plant were shut down, reducing gas consumption and maintenance costs.
A major part of the energy savings stems from the fact that the electric heaters in the press do not have to operate as frequently. On a typical winter day, the heart recovery system raises the 32°F (0°C) outside air to 98°F (36°C), and this preconditioned air is supplied directly to the presses. Previously, much of the heating of the outside air had been done via electricity.
For the Wisconsin printer, more than $80,000 of annual energy savings could be achieved using the technology.
Free Heat from the Incinerator
At another large Midwestern printing plant, solvents used in ink from presses were generating harmful vapors. Two regenerative thermal oxidizers — with a combined 70,000 cfm exhaust — incinerate the VOCs. But rather than let all that heat go to waste and up the stack, the company decided to use it to heat its facility.
Two air-to-air heat exchangers, one on each incinerator, were installed to capture the exhaust heat and use it to heat outside air for plant makeup during the winter. Each heat exchanger is part of a complete packaged heat recovery system that includes supply and exhaust fans, dampers and filters.
Under design conditions, the system heats air from -10 to 130°F (-23 to 54°C) using 250°F (121°C) exhaust from one incinerator and 350°F (177°C) exhaust from the other. Combined, they can transfer more than 10.4 million BTUs per hour. The temperature to the space is controlled to a consistent 130°F (54°C) by modulating the hot gas flow through the heat exchanger.
Related: Other Heat Recovery Applications in the Printing Industry
Heat recovery ventilation systems have used been to control humidity in printing plants and ensure good indoor air quality.