This story is told in the hope that it may be of some use to those of you who are going through the process of improving and upgrading walnut harvesting and drying equipment. These notes were originally prepared for a NZWIG field day.
Our Walnut Harvesting Story – Nelson Hubber.
(more or less in the order that it happened)
Believe it or not we dried our first walnuts in a bedroom. (Very proud I was)
Then came the drying racks. We have a very warm sunny place to put them. In recent years birds have become a big problem, they even try to carry nuts off the racks.
Big capacity but simple washer
It was obvious that any kind of large scale harvesting system would pick up rubbish as well as nuts so I built a washer that could handle it. To my mind the washing equipment comes before the harvesting equipment. You have to have an idea of what sort of harvester you’re going to have and once you know that you have to have a suitable cleaning and washing system in place before you get the harvester. Ours is made from a 1800 litre reject plastic tank. It has baffles to slow and control the speed at which the nuts travel through, rather than an archimedes screw, and a water blaster to make a good job of the cleaning process. I noticed that the action of the nuts rubbing against each other in the basket rollers was very helpful in removing bits of dried hulls etc so I tried to duplicate the process in the washer. (and also in our harvester)
For harvesting we used basket rollers like everyone else.
I thought that a small Rousset three wheel harvester like this would be suitable for us but they stopped making them and I didn’t put much effort into trying to find a second hand one. Rousset have decided to reintroduce a similar model and it will be coming out soon I think. This seems to be a suitable size for our orchards.
Harvesters that I tried out
Harvester that I made
Tried out various harvesting systems and decided to build a harvester based on a Bag A Nut spiky roller because it was the most likely one to successfully work first time off. (Which it did) I remember that my heart was in my mouth when we tried it first. As soon as they are picked up the machine starts cleaning the nuts in the white tube on the side.
Added blower to either blow leaves away in front of the machine or blow nuts from around the trees.
We harvested between 9.5 and 10 tonnes with this machine this year. (2017) It works best when the orchard is mown and flat. This year some nuts did get stuck in the soft ground and longer grass and consequently it wasn’t able to pick them up. In the 2016 season it was the leaves at the end of the season that were the problem.
We have about 900 trees and I think this machine will continue to be adequate for our needs. Generally it works well.
The first box. During a harvest I borrowed a blower off our son and quickly built a box to surface dry the nuts before they were bagged and dried at SST. I drilled holes in plywood for the bottom grille.
The drying boxes got bigger and better.
The built in drying boxes, below, have mesh bottoms and air is blown in from the barn or cycled through the drying shed. The barn tends to collect solar energy and be warm and dry. In the 2016 season we dried about 4 tonnes right down the the requirements of the factory using only warm ambient air from the barn. In the 2017 season there were only 3 afternoons in April that were dry enough for this to occur. (65% or better humidity)
In the 2016 season we had 2 drying bins and in 2017 we have 4.
Centrifugal carpet drying fans.
We have 6 of these fans from 3 brands, The orange ones from Fanwarehouse (online) deliver the most air and are the cheapest but are the noisiest. The yellow German ones from Accurate Instruments are the quietest and most expensive. The blue ones are from Topmaq. (online and in ChCh). Pice for all is in the $400 to $500 (incl) range each.
Centrifugal fans are required to force the air through the nuts. Axial propellor type fans stall more easily when pressure is required.
2017 Season 2 mobile bins
Two additional bins, identical to the drying bins, were also made for the 2017 season.
These were used for;
1/ Collecting nuts from the washer
2/ Ambient air pre-drying the nuts.
Ambient Air Pre-drying
Bins containing wet nuts from the washer are placed in a warm spot and an air chamber and fan put on top of them. This forces ambient air down through the bin and air dries the surface water off the nuts.
The air chamber and fan are taken off the bin and then it’s put into the dehumidified drying shed. Our system wouldn’t have handled the wet 2017 season without pre-drying, it reduces the amount of moisture that gets into the drying shed.
This pre-drying setup dries the nuts at the top of the box first. In the drying shed the airflow is in the opposite direction and the nuts at the bottom dry first. Helps to balance the drying out.
Two Dimplex 40 litre domestic dehumidifiers are installed in the drying shed. Its important to note that the drying shed can be completely enclosed when the dehumidifiers are used. Or dry ambient air from the barn used when the humidity in the outside ambient air is low enough. (then the dehumidifiers turned off and the air exhausted out through a door)
The drying shed was kept to 22 degrees celsius or more ( most of the time ) using a domestic oil column heater.
Notes on Dehumidifiers
The two dehumidifiers that I installed couldn’t cope with the wet 2017 season so I hired two more. A 120litre one for a week and a 65 litre one for 4 weeks. The 120 litre one was fairly useless. It’s interesting to note that if you were to buy the 65 litre one it would cost $3500 new. By itself it consistently removed about the same amount of water as the two Dimplex ones, but they only cost $1000 (incl) in total for the two. (And I could have bought two more Dimplexs for the cost of the hire)
The litre rate of the dehumidifiers refers to the theoretical amount of water they can remove in a 24 hour period at about 28 to 30 degrees celsius and 80% humidity
Using this method we successfully dried 9.5 to 10 tonnes in the 2017 season using about $1360 (GST excl) of electricity.
More notes on Dehumidifiers
The dehumidifiers that I’ve used are condensate ones that rely on air temperatures typically being between 20 and 30 degrees celsius for good performance. Below this temperature range the performance drops off rapidly.
Topmaq in ChCh have the best value 80 litre commercial condensate dehumidifiers that I know of ($1299 incl) The Dimplex 40 litre ones are the largest capacity domestic ones. ($500 to $650 incl, they are regarded as being noisy but it doesn’t matter for walnuts)
Absorption desiccant dehumidifiers are an alternative. They work much better at lower temperatures and dew points but they cost much more for equivalent capacity.
Dehumidifiers should be of a type that can be set to turn off at about 40% humidity. Once I understood our system I found it hard not to over dry the nuts, especially during the night when I wasn’t around to check so dehumidifiers that sense the humidity and turn off are necessary. (40% is the lowest setting on the Dimplex)
The diagram shows how our fans are set up. Our drying room is attached to our barn which is warm and dry on sunny days. Air flow on barn side of wall. Fans are here so that warm ambient air can be taken from the barn if the situation arrises.
Changes for Next Season
I didn’t work out the average number of days it took to dry each bin but I think that in 2017 it was probably about 4. (Varies from as low as 2 days and up to 5) If each bin holds 380kg, takes 4 days to dry and there are 4 bins then it would take 26 days to dry 10 tonnes.
The system didn’t handle the 10 tonne crop quickly enough in 2017 so in the future I intend to insulate the shed to increase the temperature stability which will make the dehumidifiers work better. I expect that in normal years there will be more opportunities to use dry ambient air which would improve the situation. We will also have 4 dehumidifiers, one for each bin. Higher capacity dehumidifiers can also be used if we think it necessary. I like this system because it doesn’t burn fossil fuels and the fans and dehumidifiers that we’ve used are relatively inexpensive. Another feature is that you can build capacity as your crop increases.
Bin to box nut transfer and storage
I intend to make a conveyor system to transfer nuts from the drying bins to the storage boxes. It takes about 26 large storage boxes to hold 10 tonnes. For storage we have a 20 foot container that can hold 20 large storage boxes. (about 7.5 tonnes)
Nelson Hubber, July 2017
We recently purchased these two commercial dehumidifiers on TradeMe. They were part of a container lot bought in to dry buildings after the Christchurch earthquakes. These two were never used. They are rated at 120 litres in 24 hour period and can be set to turn on or off at a preset humidity. Their model number is NB-75120URBC and you can find out about them on this web site http://www.newbridgeservices.com.au/industrial-dehumidifires/
We plan to use them for the 2018 harvest and will then have one dehumidifier for each of our drying bins.
Other Drying Systems
Other drying systems such as Brenmuhl’s shown here with the red fan or Horsbrugh’s French made Rousset drying tower should be considered.