Demonstration and Commercial Implementation of Energy Efficient Drying for Walnuts

Infrared Walnut Drying - Saves Energy while Reducing Product Loss Due to Over and Under Drying Nuts

Industrial and Agricultural Innovation

The Regents of the University of California, on behalf of the Davis Campus

Recipient

Davis, CA

Recipient Location

3rd

Senate District

4th

Assembly District

beenhere

$998,576

Amount Spent

closed

Completed

Project Status

Download Project

Project Result

The Infrared (IR) walnut drying unit was installed at Emerald Farms and showed reduced drying times of 10-22% and removed 3.5-4% moisture from high and low moisture walnuts. Considering that the unsorted walnuts generally consume more energy for drying than sorted, and the added energy savings from reducing heat loss, IR drying could save up to 25 percent of energy use without affecting quality. The IR pre-dried walnuts maintained the color values stipulated by the California Walnut Industry after storing for 6 months. The pilotscale and commercial scale dryers were demonstrated to walnut producers, growers, and dryer equipment manufacturers. Even though the technology can be used for other nuts, the technology has not been installed or demonstrated at other facilities as there has not been strong interest from industry, attributed to the economics of a short drying season.

The Issue

The walnut drying process, the most energy intensive step in nut processing, is a large consumer of natural gas and electricity. Even though the processors have attempted different approaches to reduce energy consumption for walnut drying, the average energy consumption is still high. Walnut drying requires an average of 12 therms of natural gas or 13 gallons of propane and 24 kWh of electricity per ton of dried nuts and inefficient operations may even use twice this much.

Project Innovation

This project demonstrates a novel infrared technology for walnut drying at pilot and commercial scales to achieve up to 25 percent energy (natural gas and electricity) savings and reduce walnut drying time. This new technology uses infrared as an efficient heat source to quickly remove the surface and shell moisture of walnuts, followed by the final drying using hot air. Nuts are required to meet strict USDA standards for moisture content. With traditional methods, walnuts are washed and then moved to large drying bins where hot air is circulated for 12 to 24 hours. The wettest nuts are dried to the safe storage moisture to prevent mold development, resulting in 6 to 8 hours of additional drying time. As a result, nuts with low moisture are over dried. In addition to energy savings, the new infrared technology will improve product quality, and decrease product loss due to over drying. This new technology could also be used for drying other types of nuts.

Project Benefits

As walnut drying is one of the most energy intensive processes, consuming natural gas for heating and electricity for blowers and motors. The IR drying technology demonstrated overall energy savings compared to current drying technology and the potential to produce a superior product. This technology has the potential of increasing the revenue in walnut production by reducing energy costs and producing a quality product by avoiding over-drying of nuts. These can have a major effect on the environmental and economic sustainability of the walnut industry.* [br /]
[br /]
This technology reduces natural gas consumption and reduces GHG emissions, as the infrared emitters do not produce any NOx.[br /]
[br /]
* https://piet.ucdavis.edu/wp-content/uploads/2013/09/Energy-analysis-of-…

Affordability

This technology demonstrated a reduction in energy consumption for walnut drying by up to 25 percent, compared to currently used practices, while also improving the quality of the final product.