To better gauge its natural gas demand, the company began tracking hourly usage readings after the 2005 processing season at Toledo, and the following year at the other plants. Now the company knows its usage, which is correlated with the tonnage of product produced. This helps in gas contracting but also helps reduce peak loading plant-wide and in specific areas. Hirzel says this has helped to optimize evaporator configurations and better utilize cook kettles.
The kettles use large rotary coils that rapidly heat product but also create a large load demand. “By reading that meter every day, every hour, we quickly saw the effects of turning that coil on and opening the valve to let product in,” Hirzel says. Valve control and better synchronization of process flows have helped reduce peak loading.
Throughout its three plants, Hirzel introduced “surges” or intermediate product-holding areas to synchronize production speeds or flows from one step to the next. This smoothes production flows as it flattens-out energy demand spikes because equipment can be used at optimal efficiency.
Benchmarking and tracking consumption against product tonnage, Hirzel says that “at the two plants where we do our heaviest evaporation, we’ve reduced natural gas usage 15-20 percent.”
Economizing boiler heat
It’s become a little cheaper to feed Hirzel’s gas-fired boiler in the year-round Toledo plant thanks to an economizer. This is essentially a heat exchanger that recovers exhaust gases to preheat feed-water, which is routed to re-heat the boiler, but can be used for other purposes as well. An economizer is planned for the Ottawa plant, as well. However, Hirzel and plant engineers first want to analyze the plant’s total heat balance, the level of heat supply and its cost-justification.
Hirzel Canning installed variable-speed drives on as many machines as possible to save energy.
The company’s falling-film evaporators are another source of energy reduction. While not as intensive as the three- and four-stage evaporators used for tomato paste (which Hirzel does not produce), the company nonetheless has saved energy on its two-stage evaporators by capturing and re-routing heat from the first stage and feeding it to the second. Condensate recovered from the second stage is recycled for cooling systems and other plant water uses.
While Hirzel did not disclose costs, heat and condensate recovery systems vary widely with plant-specific retrofit and custom engineering requirements. According to industrial energy wonks at the at the U.S. Dept. of Energy, the average plant can save 20 percent on fuel costs related to steam product by using commercially available equipment and maintaining it properly.
“But food plant engineers need to consider factors of scale,” says Bill Wilson, a food plant veteran with more than 30 years at companies of all sizes (including Nestle and JR Simplot) and now senior industrial energy systems engineer at the Washington State University Extension Energy Program. “Heat recovery techniques that will work on a 1,000-hp boiler in a large plant may not work in a small plant.”
For example, a small boiler with intermittent bursts of feed water — say, 30-second bursts every five or 10 minutes — “generally cannot recover enough energy to justify an economizer,” Wilson says. He has posted energy-saving strategies for food plants of all sizes on the web at www.energyideas.org/TPFoodProcessing.aspx.
Back at Hirzel’s Ohio operations, improvements to motors, drives, compressed air systems, chillers and sub-metering of energy at the equipment level proceeds incrementally. For example, as old motors come due for replacement, Hirzel steps up to NEMA Premium standard-compliant models. (read Motors’ Next Big Act) These are being mated to variable-speed drives, which draw less energy while smoothing-out production flows.
Every day brings new challenges, says Hirzel. Due to fluctuations in agricultural supplies, “There will be days when we have to turn down our lines to two-thirds speed or shut one plant down and move production to another plant.” But the variable-speed drives adapt equipment to varying production rates, while reducing electrical requirements. At the Ottawa plant, more than one-third of all motors are controlled with variable-speed drives.
It’s the little steps Hirzel Canning takes that show what’s good for processing is also good for energy savings.