When a Del Monte Foods plant operating in Modesto, Calif., was required to reduce NOx emissions to less than a limit of 30 parts per million (ppm) in the 1990s, several special considerations had to be made in order to meet the needs of its seasonal production schedule. Specifically, the boiler, with a 10:1 turndown target, would have to operate with a near full load for three months of the year, but less than 20,000 pounds per hour for re-manufacturing during the rest of the year.
One of several unique features included with the initial bid saved the plant from having to purchase and install a new 300-horsepower fan. Instead, Benz Air Engineering installed a 250-horsepower variable speed drive to control an existing combustion air fan. It also added a 5-horsepower flue gas recirculation fan, which was also controlled by a variable speed drive. These solutions better met the needs of the plant. And, since the 250-horsepower fan operated at less than 400 watts of power, it is estimated the variable fan solution saved as much as $7,000 per month.
There were several other breakthroughs provided by Benz Air with its Compu-NOx solution. For example, Del Monte Foods' initial turndown requirement was 10:1, but the Compu-NOx solution delivered a boiler turndown of 15:1 while maintaining very tight and responsive boiler controls. This, combined with a unique feedwater control that eliminated an old pneumatic control, enabled Benz Air to increase boiler efficiency that resulted in an estimated annual savings of $100,000 in natural gas.
Highlights from the Initial Retrofit
• Reduced NOx emissions to 22 ppm, well below the 30 ppm requirement.
• Reduced CO emissions to 50 ppm, well below the 400 ppm requirement.
• Increased efficiency to ensure low NOx and CO levels attained with .8% O2.
• Meet all emission requirements at full capacity, and with a 25:1 turndown.
Since the initial retrofit, Benz has returned to Del Monte Foods several times to help the plant meet new requirements. To date, Benz has assisted in increasing plant efficiency to greater than 93 percent, reducing NOx emissions to less than 6 ppm, and earning more than $265,000 in efficiency rebates.