Mondelēz Gävle plant is located 180 km north of Stockholm and produce 35,000 tonne of coffee, which makes it the biggest roastery in Sweden (Mondelēz 2013 pers. comm.).
In 2012 a new generation of centrifugal roaster (capacity is 4 tonnes/hour) with pre-heating technology and equipped with catalytic exhaust cleaning was started up (installed in 2011). The machine features a roasting burner close to the roasting bowl and constant gap control to minimise heating losses.
Green beans are preheated using the exhaust gases to a maximum temperature of 100 °C. Thereby the roasting process uses less energy, resulting in significantly lower propane consumption.
The roasters (R1 and R2) shown in the Table below are centrifugal roasters with recirculation and catalytic exhaust gas cleaning. The yearly consumption for the three roasters and historical data about the weekly consumption of propane are shown in the Table and Figure, respectively.
Table: Accumulated annual propane consumption in kWh/tonne of green coffee (year 2013).
|
Roasters (capacity 4 tonne/h) |
Start-up |
Exhaust cleaning |
Propane consumption |
|
R 1 without preheater |
1981 |
catalytic |
376.14 kWh/t green coffee |
|
R 3 with preheater |
2012 |
catalytic |
279.14 kWh/t green coffee |
|
R2 without preheater |
1990 |
catalytic |
355.8 kWh/t green coffee |
Figure: Weekly consumption of propane in 2013.
Source: Mondelēz 2013
Assuming that the other factors that can affect the thermal energy use (roasting time and profile, type of catalyser etc.) are very similar between the three machines, the level of propane consumption for new roaster R3 with preheating technology is between 21.4% and 25.8% lower than the propane consumption in roasters R1 and R2 that are not equipped with preheaters.