The Arizona desert is an ideal place to try some of these things. The sun shines 330 days a year on those solar cells (as well as the four other solar power systems), and water is scarce in a desert community an hour south of Phoenix that suddenly has swelled in population.
"We had a vision three years ago that it would be possible to take Casa Grande off the grids," he says – meaning removing the plant as much as possible from supply systems for electricity, water and natural gas. The results are:
- Electricity: 5 megawatts of electricity is generated on the site, accounting for half the plant's needs.
- Water: 75 percent of the process water is reused. Toilets, drinking water, floor drains are supplied by and return waste water to municipal systems.
- Heat: All of the plant's steam is generated by the boiler; overall natural gas needs have been reduced 80 percent.
- Waste: For the past nine months, the plant has sent zero waste to landfills.
Some other bullet-point results, as reported by PepsiCo:
- 67 percent of the plant's energy is generated by renewable sources.
- The collective actions make for a 50 percent reduction in greenhouse gases.
Let's look at some of the utility replacements separately.
Five distinct solar power systems installed throughout the property produce 5 MW of electricity, about half of what the plant needs. The biggest contributors are two solar fields of single axis tracking photovoltaic (PV) systems with more than 18,000 solar panels, which were installed on 36 acres of the facility's agricultural property.
The ownership of those is interesting. About half the solar arrays are dedicated to the plant, but they are owned by Solar Power Partners Inc., which develops, owns and operates solar energy systems. The other half is owned by Arizona Public Service Inc., the local electric utility. All the land belongs to the Casa Grande plant.
There is enough open field to have constructed solar arrays to supply all of the plant's needs, and PepsiCo apparently considered it. But the contract with Arizona Public Service and the need to string high-voltage overhead power lines made that decision not feasible.
The three additional solar power systems installed by the plant include:
- Single-axis PV systems that cover about two-thirds of the front parking lot – not only generating electricity but also shading employees' cars.
- A dual-axis PV tracking system by SolFocus, slightly different from and smaller than those on the 36 acres.
- 10 Stirling engine dual-axis tracking systems in a field behind the plant. In a Stirling engine, the heat of the sun is concentrated by parabolic mirrors onto the engine. The heat creates cyclic compression and expansion of helium within the engine, moving a piston back and forth. That movement drives a flywheel, which ultimately drives an electrical generator. These Stirling engines are among the more leading-edge – and trickier – technologies being employed at Casa Grande.
That's where the electricity comes from, but a key component also was to reduce electrical needs. Frito-Lay has its own "department of energy," which carries out energy audits of each of the company's facilities each year. Casa Grande also employs such traditional "low-hanging fruit" strategies as variable frequency drives and higher-efficiency lighting systems.
A 60,000 lb./hr. biomass boiler burns wood chips from old pallets and agricultural waste from surrounding communities. It produces all the steam needed for the manufacturing plant and reduces natural gas use by more than 80 percent.
It was a hugely expensive item – Halvorsen wouldn't say how much, but he said it won't provide a classical three- or four-year payback.
Once again, the first step was to reduce the plant's need for heat. In one example, a system suctions off the rinse water from potatoes just before they enter fryers. With less water needed to be boiled off, the thermal load on the fryers was reduced.
"We've also installed high-efficiency oven burners, high-efficiency boiler controls and waste heat recovery systems off the Doritos ovens," Halvorsen adds.
By the way, the ash produced by the biomass boiler is collected and sold to Scotts Co. to be made into fertilizer.
PepsiCo installed a water recovery and reuse system that combines membrane bioreactor and low-pressure reverse osmosis technologies to recycle approximately 75 percent of the plant's process water.
Interestingly, the membrane bioreactor failed within two hours of its startup because of fouling. "That was an incredible disappointment," Halvorsen recalls. But a carbon filtration system fixed the problem and it has worked well since.
Once again, the first step was to reduce the plant's need for water. Frito-Lay engineers redesigned the cooking process for corn used in tortillas. Forty percent of the water from one batch is left in the tanks for the next batch, saving both water and much of the energy to heat it.
But non-process water and waste water systems rely on municipal systems.
Purely green initiatives
There are plenty of energy-generating technologies at work in Casa Grande. And every kilowatt and therm produced responsibly on-site replaces a traditionally produced kilowatt or therm off-site, which lowers the plant's upstream greenhouse gas responsibilities.
Beyond those obvious paybacks are some softer green initiatives. As far back as 2010, the Casa Grande facility sent less than 1 percent of its overall waste to landfills through extensive recycling and using food waste for cattle feed. For the past nine months, no waste has been sent to landfills.
Employees are exhorted to reduce, reuse and recycle. There are vending-like machines throughout the plant that give employees credits for recycling empty beverage containers. Plus, employees are active in "adopt-a-highway" and other local ecological efforts.
Being a big but somewhat isolated plant – the plant supplies seven southwestern states – fleet efficiency is of keen interest to the Casa Grande plant. This location – and parents Frito-Lay and PepsiCo – have reduced diesel fuel use through driver training and by making changes to trucks, such as new idling technology and increased aerodynamics. New trucks are more energy efficient, many of them either hybrids or using natural gas. The plant soon will be getting some plug-in electrical vehicles.
Frito-Lay will leverage key learnings from the Casa Grande plant and apply them to other facilities where appropriate. Company officials say every Frito-Lay plant is identifying projects and approaches to get closer to "near net zero" and to significantly reduce its environmental footprint.