Fabrication of the second TGER prototype began in early March 2008 and was completed in three weeks. During fabrication, additional modifications were applied to the second prototype that could not be applied to the first. These modifications are discussed in more detail below.

a. Water circulation system. The material rinsing water was routed away from the main system through an intermediate sump pump and into a 500 gallon tank (see Fig. 6), and then routed back into the wash tank on the system using a sump pump. There were several reasons for this modification. First, the intermediate sump pump broke up any large debris (e. g. food slop and paper material) that passed through the sieve. This ensured that the re-circulated liquids would not cause any clogging of the plumbing. Using the large 500 gallon tank at ground level also made it easier and more efficient for the operators to monitor the fermentation process and add the necessary biocatalysts.

b. Rubber/flexible plumbing. The plumbing on the first TGER prototype was fabricated using standard two inch PVC pipe. When operating in freezing tem­peratures, water would collect in the pipes after operation, freeze overnight and cause the pipes to burst, causing significant delays in operation due to the time required to repair the pipes. The second TGER prototype therefore used a flex­ible rubber hose with quick disconnect fittings instead of pipes, allowing the water to be drained from the hoses after operation in order to prevent the pipes from freezing. Flexible hosing also eliminated the possibility of pipes breaking

due to excessive vibration of the TGER either while in operation or during transport.

c. Chiller. During testing of the first prototype, a chiller was needed to efficiently and quickly condense the distilled ethanol into a liquid state and collect it in the ethanol fuel tank. Due to design issues, the chiller could not be retrofitted on the first prototype but was included on the second. The chiller cooled a mixture of 50% water and 50% antifreeze and circulated it into a heat exchanger (condenser) where the ethanol vapor would condense into liquid ethanol, allowing the TGER to operate efficiently in hotter climates.

d. Reflux valve. The reflux valve is a programmable valve that automatically redi­rects condensed ethanol from the condenser to either the ethanol storage tank or back to the distillation column at a 5:2 time ratio. By redirecting condensed ethanol back into the distillation column at a 5:2 time ratio, the ethanol purity improved from 80% to 85%.

e. Pellet auger/elevator. An external pellet elevator was purchased in order to automate the process of supplying waste-derived pellet fuel into the downdraft gasifier (Fig. 7). On the original prototype, a technician was required to climb onto the top of the TGER in order to pour waste pellets from a bucket into the gasifier, a time consuming and unsafe process. The pellet elevator allowed the technician to dump the pellets into a large collection bin at ground level and the pellet elevator would automatically deliver the correct quantity of pellets into the gasifer based on data received from an infrared sensor suspended over the gasification chamber.

f. Centrifuge pump and basket filter configuration. On the original prototype, the centrifuge pump and basket filter had to be installed on their side. In order

Fig. 7 Pellet auger/elevator

to achieve optimal performance from the pump and filter it is necessary to install them upright. The frame on the second prototype was redesigned to accommodate an upright installation of both the pump and filter.