## Friday, April 28, 2017

### Cider Press; sizing calculations

I am going to use the cider press discussed yesterday to introduce readers to some of the fundamentals of industrial engineering and Theory of Constraint.

It is inevitable that some step in any given process will become the metronome that paces the output.  Sometime it is a random station (meaning the industrial engineer did not do their job).  Sometimes it is a malingering worker.  Sometimes is due to an incapable process that requires much rework (painting is an example).  Sometimes it is inspection when defects saturate the repair capacity and the amount of "re-inspection" bogs down the system output.

It is desirable to use some intelligence to select the station that will be the bottleneck.  That way the person sizing the components in the system can configure it to "armor" the bottleneck station.  "Armoring" entails doing everything economically possible to protect the bottleneck's run-time and quality-of-output.

In this case, the most expensive piece of equipment is the centrifuge (washing machine) so it makes sense to configure the system to make this the "bottleneck".  The intelligent solution is to do everything possible to ensure that the centrifuges receives "service" at the expense of all the other stations.

Suppose the engineer (you) assumes a 10 minute spin cycle and 5 minutes to unload-reload.    Further, assume that 9 cubic feet will hold 6 bushels (240 pounds) of crushed apples.  That means that  at a minimum the crusher must be able to shred 240 pounds of apples in 10 minutes.  Since the crusher is inexpensive relative to the centrifuge, it makes sense to buy significantly greater "over-speed" to recover from hiccups.

One possible sequence of operations, starting from when the centrifuge finishes its 10 minutes spin cycle is:
1. Open lid to centrifuge
2. Hook rope loops of bag with cherry picker, lift and rotate away from centrifuge.
3. Slide pre-fill hopper over opening of centrifuge (probably need some kind of roller track, it weighs over 240 pounds.
4. Drop bag out of pre-fill hopper into centrifuge
5. Close lid
6. Start centrifuge  (Does that look like less than five minutes to you?  It does to me)
7. Push pre-fill hopper back into place
8. Insert the mesh bag.  You will need two because the first one is still hanging on the hook
9. Start grinder
10. Dump spent pomace (crushed apples) out of the used bag.
11. Shake bag.
12. Rinse bag
13. Hang bag on hook near grinder for next cycle.
14. Load six bushels of apples into the hopper feeding the crusher.
15. Stand next to centrifuge waiting for it to finish its cycle.  This is the "loafing" position.  Physically it saves walk time (which is dead-time) after the centrifuge finishes cycling.  Psychologically it reinforces the idea that the entire process is "serving" the centrifuge.
So how much cider might this set-up produce an hour?

Using three gallons of cider to the bushel, you would expect 18 gallons of cider per cycle (remember, you are processing six bushels a batch).  At fifteen minutes per cycle you should get 4 * 18 gallons per hour or about 70 gallons of cider an hour.

Just to illustrate the significance of details like the pre-fill hopper:  The person engineering the system might be tempted eliminate the pre-fill hopper and have the operator load the bag into the centrifuge and have the grinder deposit the shredded apples directly into the centrifuge.  The point is that the centrifuge cannot be spinning when the operator is inserting the bag.  The centrifuge cannot be spinning as the grinder fills the centrifuge's drum.  Realistically, eliminating the pre-fill hopper will add another 10 minutes to the 15 minute cycle time and will lower the output to about 45 gallons per hour.

With this kind of capacity, it might make sense to mount it on a trailer with a gas generator and do custom processing. At 24 bushels to the hour, it would take about 15 hours (two work days) to process the apples from a 100 tree orchard, figuring 3 bushels to the tree.  The cider pressing season is about four months long, mid-September to mid-January.  That would be a lot of cider!