Go through it.. not around it


I wrote this late last night.. I didn’t get a chance to post it but better late..

Tonight I roasted some coffee (shhh don’t tell you know who). It's been 5 weeks to the day that I roasted the last batch on the Petroncini before dismantling it for the move. 

The first batch was a throwaway test to see how the new setup behaved. The Afterburner (AB) sat comfortably at 420C+ rising to 445’ish towards the end. Difficult to see any visible smoke from the stack (since it was dark outside)

but downwind aromas were minimal and not unpleasant. Score 1 for DT.

The flue system has changed dramatically from the original (expensive) installation where the two flues (hot gases and cooling tray outlet) joined together after the AB. DT said it would never work. Flue guy said it would. Guess who was right. Way too much backpressure in the flue caused by the cooling tray outlet causing the hot gases to be pushed back down through the AB causing the temperature to rise quickly to over the safety cutoff of 500C. 

Just as bad was when the AB was running and the cooling fan wasn’t. The back-pressure in the stack was sufficient to cause the hot gases to take a sharp left hand turn and travel down the cooling duct, back up through the cooling tray and into the roastery.

Neither good.

Luckily the flue guy came back and disconnected the two flues, put a temporary cap on the join and jerry rigged a cooling outlet with flexible flue liner out the door. 

That was yesterday. Today DT finished the wiring for the VSD Inverter drive to enable a variable speed on the exhaust fan.

The Petroncini has never behaved like a traditional drum roaster with increased air flow acting to cool the roasting chamber. It always behaved in reverse.  So much energy in the combustion chamber meant any increased airflow (via the crude baffle adjuster in the exhaust duct) meant more heat into the chamber. Not now.

Correct (as well as possible with a differential pressure manometer) setting of the new and very shiny deflector plate relative to the end of the burner tube made a massive difference to the behaviour with air flow adjustments. Now the VSD drive sits at 50Hz and when it’s pushed up to max 60Hz the volume of air flowing through the combustion chamber is enough to act to cool the roasting chamber.. like a traditional roaster.

What else can I tell ya ? Plenty tbh. Bottom line is we’re almost back on line. Few niggles to sort out and tidy to placate you know who if they should visit (which of course they will). Hopefully that’ll be done by the end of the week and the temporary fixes will be a thing of the past.

It’s been a journey. Not one I’d like to repeat soon. I heard someone say that the way to grow is face your challenges. Go through them, not around them.

Right now I’m not sure I want to grow anymore.

The web store will soon be back on line with coffees available for purchase. Honest. Thanks for everyone’s patience and support during the move. Special thanks to our roaster friends who have wither roasted some coffee for us or allowed us to use there machines. I owe you all much respect and gratitude. You know who you are.

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