The final design of the Green Machine consists of several key components: a pump, a solar array, tubing, microreactors, an immersion heater and a collection bin. The system consists of 750 microreactors in parallel which will produce exactly 1 gallon of biodiesel in a 24 hour period as specified. Each microreactor will be 7 cm long and the reactants will have a residence time of 30 seconds. The immersion heater contains racks on different levels. The microreactors will be stacked 30 high and 25 across within the immersion heater. The heater itself will be maintained at a uniform temperature of 80˚C, requiring 106.1 kW of power. The dimensions of the immersion heater are 120 in. by 100 in. by 8 in. The pump used will be a Harvard Pump 33 Dual Syringe Pump because it operates well at low flow rates and can handle the pressure drop within each microreactor of 1156 Pa, which is less than the specified maximum of 1,300 Pa [ref 8]. This pump can operate at 45 W which is more than enough to overcome these pressure drops. The system will pump the reactants at a molar ratio of 25:1 for methanol to soy oil, resulting in a total flow rate of 0.0035 mL/min. The flow rates of methanol and soy oil are 0.0027 mL/min and 0.00084 mL/min respectively. Lastly, the solar array will be 108 m2 in area, making it capable of providing 108 kW of power to run both the pump and the immersion heater.
The image below shows the final design of the Green Machine. Although this is just a basic set up, it clearly takes into account all of the necessary calculations and specifications as discussed above. In this design, the pump rests on a column, feeds tubing into the immersion heater, pumps the fluids through the microreactors, and then more tubing empties the biodiesel into a collection bin. The solar array is mounted on the column upon which the pump rests. Although it cannot be seen in the schematic, the column is at an upward angle so that the array is exposed more directly to the sun. Additionally, the system is to be constructed so that the solar array is at a southerly exposure point where it will receive the most sunlight (provided it is built in the Maryland area). This design sufficiently meets all performance specifications laid out earlier.
In a future post, we'll discuss exploring the reasons why the microreactors failed to yield biodiesel.