Nashville Civic Design Center
Case Study: Biodiesel Buses At present, the Nashville Downtown Partnership operates a shuttle service that consists of 16 shuttle buses. Half of the shuttle buses are fueled by diesel and the other half are fueled by gasoline. The LunchLINE,1 a free shuttle service to 10 downtown stops available Monday through Friday between 11:00 a.m. and 1:30 p.m., utilizes two of the Downtown Partnership’s buses. The average route distance for the LunchLINE is one and a half to two miles. The average waiting time is 10 minutes. As the Nashville Downtown Partnership phases out all or some of their shuttle buses in the coming years, there are a number of options for achieving a more energy-efficient transit route: 1) Transition the 8 buses that run on diesel to biodiesel fuel and buy 8 diesel-hybrid buses or diesel buses that will run on biodiesel fuel, 2) Replace the whole fleet with diesel-electric buses or buses that run on biodiesel fuel, or 3) Replace all or some buses with hybrid-electric buses or electric buses.
The Vanderbilt Biodiesel Initiative
The following is VBI’s description and illustration of their biodiesel production system:
The Vanderbilt Biodiesel Initiative (VBI) converts waste vegetable oil from local restaurants and the university’s cafeterias into biodiesel fuel for use by the university’s diesel-fueled fleet (student activity vans, medical center buses, and landscaping machinery).2 Currently, the fuel costs approximately $1 per gallon to produce and VBI is only producing one-sixth (60 gallons per week) of the biodiesel production system’s capacity (360 gallons per week). With additional personnel and providers of waste oil, the organization would be able to realize its full capacity. Although the organization does not currently sell its biodiesel fuel to the public, the organization could be a potential resource for the Nashville Downtown Partnership’s bus fleet if the two organizations entered into a partnership. According to VBI, “Biodiesel is an alternative fuel created by the ‘transesterification’ of vegetable oil, a chemical process which exchanges the alcohol group of an ester compound with another alcohol. Pure vegetable oil or filtered waste vegetable oil is combined with methanol and a lye catalyst (we use potassium hydroxide) in specific proportions. Upon heating, a chemical reaction occurs producing biodiesel and glycerol (also known as glycerin, which is a great soap and de-greaser). One of the major advantages of biodiesel is that it can be used directly in any diesel engine or can be blended with petroleumbased diesel in any proportions.”3 The following is an illustration created by VBI that explains “The Biodiesel Reaction.”3
“This sketch roughly illustrates the current setup of our system, a 120 gallon batch processor. Waste vegetable oil, the main feedstock, is heated and mixed with methanol and KOH. After the reaction completes, a layer of glycerin settles to the bottom and is drained off, leaving biodiesel in the main reaction tank. To remove the impurities in the fuel, first the biodiesel is heated and the fumes are sent through a condenser to recover any unreacted methanol. Then Magnesol, a synthetic talc powder that attracts the impurities, is mixed in and then removed by centrifuge. The fuel is pumped through several filters to a storage tank, where it is ready to dispense.”2
1
Nashville Downtown Partnership. (2009). LunchLINE. Retrieved from http://www.parkitdowntown.com/getting_around/lunchline.php
2
Vandebilt Biodiesel Initiative. (2009). About us. Retrieved from http://studentorgs.vanderbilt.edu/biodiesel/aboutus.html
3
Vanderbilt Biodiesel Initiative. (2009). About biodiesel. Retrieved from http://studentorgs.vanderbilt.edu/biodiesel/aboutbiodiesel.html
Nashville Civic Design Center • Urban Design / Policy Brief • Biodiesel Buses • www.civicdesigncenter.org
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