The three possible sources for heat to be recovered are:
1/ Waste exhaust stream
2/ Condenser heat-exchanger
3/ Reflux cooling (if necessary)
The waste exhaust stream gases are a prime heat source that would otherwise be lost to atmosphere. I see possible, a variety of heat exchangers on the exhaust stack as good prospects.
Waste heat from the condenser is used to preheat the oil that is delivered to the retort. Obviously preheating this oil saves energy.
The likely uses for the recovered heat are:
1/ Preheated oil feed
2/ Preheated turk air intake
I tried preheating the bubbler but it hasn't worked as expected. In addition cooler is probably better for safety. I not proceeding with any gas jar heating either.
Preheating the oil for the continuous fed retort will increase efficiency and it will force any water present in the oil to fall into a trap. I envisage a target of 100'C to boil off residual water.
Preheating the turk air intake is thought to have significant heat saving benefit. The "Hot Blast" furnace principle was invented in 1828 which allowed greater fuel economy and efficiency.
The first part of the 3" exhaust flue. Due to the 3m+ vertical height and the overall weight of the pipe, some thought is given to allowing for expansion. There is 2 slip joins planned so that stress isn't transmitted to the turk pipe outlet. A flue damper butterfly will be recycled from an earlier prototype.
The hope is that the shear flue height will give ample draw without the need for additional induced draft or forced draft fans.
It appears that I need to add bracing to the building from which the upper exhaust will be mounted. A china mens' hat will adorn the flue top to prevent rain entering.
11Aug2013 Work continued on the exhaust with mounting brackets fabricated and welded to the building structure. Three meters of exhaust elevation will be trialed with extension added if extra draw is needed. One slip join is where the pipe exits the turk housing while the 2nd is where the pipe goes vertical.
12Aug2013 A fabricated flue damper and a chinamens' hat are amongst the work completed today. Can you guess what the chinamens' hat was recycled from?? The yellow handle is a major clue!
24Sept2013 The draught appears to be adequate thanks to the tall flue stack. This draw should also improve with heat. Google found some excellent pages about improving draught including flue insulation which I'll employ if need be.
29 Nov2013. Radiant heat from turk firing is recovered with the latest turk burner head. Effectively heat from the turk casing is captured in the 30mm gap between inner and outer steel layers. The preheating of the ingoing air will improve efficiency using "hot blast" principles concept.
4Dec2013 The feedstock preheating is in the design stages utilizing heat from the diesel condenser and retort-to-condenser pipework using a counter-current principle. The plan is for a gear pump to pump oil from the feedstock holding tank to the top of the reflux via the condenser/pipework route. The benefit is that heat from the outgoing vapor can be used to preheat ingoing feedstock which is a bargain because one needs to loose heat while other needs to gain.
25June2014 During the next run I'll be monitoring the exhaust temperature to see if a heat exchanger for the ingoing feedstock is possible.
2March2015 DIY Induced Draft (I.D.) fan made from a recycled convection oven fan. It is mains 240v powered with a pressed steel multi-blade centrifugal fan operating at fairly high speed. I cut the complete back panel out of the oven so mounting was super easy.
The unit will need a cover to protect from the weather. The electrical terminals are spade type live, neutral and earth/ground. I used 3core flex to run power taking care to be mindful of the flue heat. The flue already has a built-in damper so the draw can be adjusted to suit conditions.
Time will tell if the unit will withstand the rigorous conditions of hot flue gases. It may be that carbon may need cleaning from the fan blades at regular intervals or possibly the heat could travel up the motor shaft an deteriorate the windings. In the motor designs' defense, it is designed for oven use up to 250°C and features a secondary fan for motor cooling.
Update: the fan has survived 2 diesel making runs so far and is working well.