Peanut Processor

A Queensland peanut producer is a very large user of liquefied petroleum gas (LPG) and electricity for its operation. Through an energy assessment, ten emissions reduction opportunities were identified, including renewable projects, to help the manufacturer reduce its energy, costs and emissions. The assessment considered a range of energy projects from variable speed drives and compressed air reduction to major biomass and solar projects.

Significantly, the options identified offer potential energy cost savings of 89%, largely driven by the use of waste peanut shells to generate heat and electricity.

Summary of Opportunities

Dryer Plant VSDs

Part of the manufacturer’s production process is drying the peanuts, which requires significant energy consumption. The dryer plant supply is on a tariff with high demand charges in summer - and a higher tariff than the rest of the site. Three projects are recommended to reduce the impact of this high tariff and drive down energy consumption and costs. Each will also significantly reduce emissions.

While the plant only operates for five months a year, it has a number of large fans for dust collection and drying which may be suitable to retrofit with variable speed drives (VSDs).

Cleaner plant controls

The cleaner plant uses six 75 kilowatt (kW) fans as aspirator or stoner fans. It may be possible to install pressure based controls and VSDs on these fans, where the speed it controlled by pressure readings in the ducts. This allows the fan speed to be reduced when demand on the system is low. While the capital cost is significant at $125,000, it would save $47,199 each year in energy costs and have a payback period of only 2.3 years. It would also deliver important reductions in energy and emissions at 1,202 GJ in annual energy savings and 270 tonnes of CO₂-e.

The second improvement is to retrofit a VSD on the 90 kW HVAC suction fan of the intake cleaning plant. This would have a desirable payback period of 1.6 years and save 240 GJ of energy per annum.

Dryer silo VSDs

The plants refrigerated drying bins have 12 x 37 kW fans. It may be possible to reduce the fan speeds if sufficient flow can still be obtained at a slightly reduced speed of 2-5 hertz (Hz). This project has a potential payback period of just 1.6 years, despite its capital cost of $124,000. It would deliver very large energy savings of 1,757 GJ a year and an emissions reduction of 395 t CO₂-e.

Compressed Air Reduction

There are two major compressed air systems for the site’s two plants. Both systems have efficient VSD-based air compressors, which are programmed to operate at 750 kilopascals (kPA) to 800 kA. Since the compressors are already efficient, it may be worthwhile for the manufacturer to consider:

• Pressure set point reduction - each 6.9 kPA reduction in pressure reduces compressor power by 0.5%. Modern energy efficient plant operating procedures call for compressed air pressures to be as low as possible with pressure boosters and air storage installed near end users which require higher pressures. This reduces air leaks and artificial demand.
• A compressed air leak survey and repairs - these surveys use ultrasonic or thermographic devices which should be undertaken on a regular basis to reduce wasted air and power.
• Compressed air usage review - this involves evaluating the major end users of compressed air for replacement with more efficient electrical alternatives. If replacement isn’t possible, some other options to reduce compressed air usage include reducing pressure, pulsing times and frequency and changing nozzle types.

The business case undertaken as part of this assessment is for the pressure set point reduction only. This would have no capital cost and would result in $2,471 each year in energy cost savings. It would also reduce emissions by 15.8 t CO₂-e.

Demand Response (Diesel Generator)

An opportunity exists for the manufacturer to participate in a demand response program by using its existing diesel generator during times of high demand on the grid. By participating in a demand response program, the business could earn revenue for providing the grid with extra power or for reducing load during such events, while also reducing energy operating costs by reducing demand when wholesale electricity prices are high.

While the use of the diesel generator would increase emissions, this would only occur for a few hours each quarter and the income could be used to fund energy efficiency projects. This option would have a capital cost of $15,000 (for installation of remote control units on the generator) and offers a one year payback period.

Fuel Switching to Butane and Burner Upgrades

It may be possible to replace LPG with butane at the site as butane has recently become available in this region at about half the price of LPG. To burn butane instead of LPG, the manufacturer would likely need to increase the capacity of its LPG pipelines, as butane generally runs at a lower pressure. The oven burners would need to be replaced, although new burners would likely increase the efficiency of combustion as the existing burners are some 20 years old. This project would be paid back in 1.3 years, with cost savings totalling $326,000. It would reduce energy consumption by about 440 GJ a year.