所謂側火建構的加熱系統。

側火的系統,基本上就是對流熱(熱風)比例較高的加熱系統。
1. 烘焙桶距離火焰較遠:
    由於採用燃燒效率高的火排,加熱空氣的效率極高,火焰則是避免直接碰觸到烘焙桶,藉由對流熱的比例提高許多,優點是在火力控制上比較直覺;豆子的膨脹較明顯,上色較淺。

2. 掉落銀皮的燃燒狀況減少:
    火焰的進入方向與烘焙桶的攪拌方向一致,半熱風烘焙桶前端多少會掉落銀皮被火焰燃燒的狀況減少;而直火烘焙桶直接掉落的銀皮,也因為咖啡豆在烘焙桶的位置集中於火焰的較遠端,銀皮燃燒的現象會減少,但是烘焙量較多時,也必須抽出銀皮收集盤清理銀皮。

3. 變頻風門的應用範圍較寬:
    這套側火系統採用直流變頻馬達的風機,可以提供穩定的轉速來對應抽風的壓力,抽風系統為:
設定抽風數值→偵測風管內的抽風壓力→傳送壓力數值→PID運算→調整馬達轉速→達到抽風數值
重複以上的調整,而抽風壓力會盡可能維持在一個範圍內上下浮動,這是因為烘焙桶攪拌生豆時造成的不穩定風流影響,搭配機械式壓差錶,來輔助烘豆者對數值的判斷。

下圖是側火烘豆機的剖面圖,可以看到冷空氣被火排加熱後進入烘焙室的路徑:



下圖是半熱風系統的剖面圖,空氣動線從烘焙桶後方進入,在由上方經風管移動:



下圖是直火烘焙桶,空氣從烘焙桶表面的孔洞進入,往上方的風管移動:



對流熱高的烘焙系統,仰賴保溫性強的烘焙室,烘焙桶的厚度也需要對應,過厚或過薄都會影響烘豆者的操控性,側火是我目前設計的烘豆機中較注重操控性的烘焙系統,從烘豆者能操作的範圍為前提製作。

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The Heating System of the so-called Side Heating(Fire) Construction

December 04, 2020

The side heating system, is basically with a high proportion ratio of convective heat (hot air).

1. The roasting drum which been set further away from the flame:

    When using the high-efficiency of the pipe burner(tube burner) which also heats up the air extremely, thus to avoids  the flame directly touching the roasting drum. Due to the ratio of convective current is greatly increased, the advantage is that the heat control is more intuitive,   expansion of the beans are evidently and the color is lighter.

2. The burning of chuff is reduced:

    The direction where the flame enters is same as rotation of the roasting drum, there are some  chuff dropped at the front end of the semi convection roasting drum and the chance to be burn by the flame is less.  However, the beans in the conduction roasting drum are concentrate on the far side of the flame, the chuff directly dropped by the conduction roasting drum also less burned. But when roasting in large quantities, the chuff collection tray must be taken out and clean regularly.

3. The wide range use of variable frequency damper:

    This side heating roaster adopts a fan with a DC variable frequency motor, which can provide a stable speed to correspond to the pressure of the air extraction. The air extraction system:

Set the suction value → Detect the suction pressure in the duct → Transmit the pressure value → PID calculation → Adjust the motor speed → Reach the suction value

Repeat the above adjustments, and the suction pressure will be kept within a range as close as possible. This is due to the unstable air flow caused by the rotation of roasting drum that stirring the green beans, the differential pressure gauge to assist the roaster determine the value. 

The diagram below is a cross-sectional view of the side-heated coffee bean roaster, illustrate the path of cold air entering the roasting chamber after being heated by the fire row:

The diagram below is a cross-sectional view of the semi-convection, air movement path which enters from the back of the roasting drum to the top through the air duct.

The diagram below is a conduction roasting drum, air enters through the holes on the surface of the roasting drum and moves to the upper air duct.

The roasting system with high convection heat relies on the roasting chamber with strong heat preservation. The thickness of the roasting drum also needs to be considered in corresponding towards the process, as too thick or too thin will affect the maneuverability of the roaster. The side heating roaster is my current design of roasting machines that need to pay more attention on maneuverability, this roasting system is made based on the roaster who is capable to manipulate.

※Thanks George for the English translation.

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