Most coffee roasters are heated by a natural gas flame. Natural gas is a cheaper form of energy than electricity but it comes with inherent limitations. Since the flame requires a continual supply of oxygen it requires a lot of air which must be raised from ambient to combustion temperature, this is not the end of the energy waste. The coffee roasting is usually done in the exhaust gasses of the flame which, are not hot enough after passing through the Roasting Chamber, to break down the roasting smoke. That smell is similar to burnt toast, in the later stages, - imagine several kilo grams of burnt toast. Hence, an Afterburner is required to raise the temperature to over a 1000°F to break down the smoke. The large amount of air required by the flame means that a large amount of air must be raised from ambient temperature to over 1000°F. Consequently, the Afterburner burns, depending on the model, three times as much energy as the roaster (the equivalence of 6 home furnaces) just so that the neighbourhood will not see nor smell the roaster emissions. Of course the emissions from such burners are always present but the operators hope that they become sufficiently diluted by the outside air that they will not trigger calls to the environmental agency. Pollution awareness is upon us and some areas already require permits for coffee roasters with 5 kg or more capacity.
Are there alternatives?
There is, if the fabricator begins with a clean design slate rather than use off the shelf technologies. First, the amount of air needs to be reduced to greatly reduce the waste of energy. It is true that often the electricity is generated by the combustion of natural gas but the electrical companies have specialized equipment to remove and neutralize gas volatiles that individual roasters do not use. Nevertheless, the electrical Roastaire™'s biggest advantage is virtually eliminating the continual feeding of air to the roasting process. It is possible to recirculate the air with electrical heating because you do not need to feed a flame. The advantage, is that less energy is required to heat the returning air than to heat room temperature air (ambient) to roasting temperatures. There is less air to treat when neutralizing the emissions therefore it can be done on a continual basis. A minor advantage is that the oily smoke, as part of the re-circulation process, is burnt which helps to heat the roaster.
Does the design work?
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There wasn't a copyright on the photo but I am not attributing the photo because there is little benefit to kicking a hornet's nest.In 2010, it is reported that there were 1800 chimney fires, in the USA, that were attributed to coffee roasters. What heating method do you think was responsible for this incredible statistic?
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In the Roastaire the exhaust is passed through a second SmokEater© before it is discharged. It roasted hundreds of batches inside the Toronto and Vancouver convention centres without the use of a vent or chimney.
What is exhausted?
Only the air cooling the roasted coffee is exhausted after scrubbing it twice. More details about the design reasoning will be forthcoming when the topic of Bean Cooling is approached. In the interim here is some more information on an earlier NXT blogspot page.
