Vegetable Oil Firing

Penland’s Vegetable Oil Firing By John Britt

Many potters consider themselves environmentalists and yet they fail to consider the effects of their craft on the environment. As we participate in the demand for electricity, minerals and petroleum, we also share in the blame for their environmental effects. One of the most common rationalizations is that we are only using the scraps of industry and are therefore not the primary cause. For Sam Clarkson this rationalization soon became unsatisfactory and he decided to take some positive action to reconcile his love of pottery with his concern for the environment.

As a production potter, he wanted to minimize both the cost and the detrimental effects of burning hydrocarbons while pursuing his passion for high-fire pottery. For a time he experimented with wood firing, using scrap wood from a molding factory. He reasoned that the wood was a scrap product and would have been burnt in an incinerator anyway. This solution worked well for a while, but wood firing is extremely labor intensive and still produces large amounts of soot emissions.

While searching for another solution, Sam heard a story on NPR, about a car that ran on biodiesel, a mixture of approximately 80-90% vegetable oil with 10-20% ethanol alcohol. It is produced from a chemical reaction that is catalyzed by the introduction of lye into the vegetable oil. He reasoned that if it were possible to run a car on vegetable oil, surely it should be possible to fire a small kiln with it.

So, while in graduate school at Penn State, he experimented with vegetable oil fuel in a small 7 cu. ft. kiln. After some initial success, he longed to experiment with a larger kiln to test the viability of this method in a production setting.

His chance came in the fall of 2001 while team-teaching an eight-week concentration at Penland School of Crafts with Alleghany Meadows. Although the focus of the course was functional dinnerware, he and Alleghany convinced the twenty students to embark on the experimental project, firing Penland’s noborigama with used vegetable oil.

Many people who fire noborigama kilns, fire with wood until cone 8 and then finish off with diesel fuel. Switching to diesel fuel allows them to quickly and easily reach the final temperature and eliminates fly ash at the upper end of the firing. We thought that we could adapt this method of a wood/fuel/salt firing but substitute diesel fuel with vegetable oil. We wanted to start the kiln with wood until it reached approximately cone 1. This would give us enough time to get some early ash deposits and also establish enough heat to ignite the oil.

One of advantage of used vegetable oil is that it is a waste product of the massive fast food industry. Some restaurants, kitchens and fast food chains have contracts with companies which process their used oil and sell it for use in cosmetics, livestock feed, pet food, heating, etc. Yet, there are thousands of smaller restaurants and kitchens across the country that just throw out their used oil as waste. That means there are millions of gallons of vegetable oil that could potentially be available as fuel.

Aside from being readily available and free, the most important reason for using vegetable oil is that the hydrocarbon, soot and nitrogen emissions are very low. Tests show that biodiesel emissions are substantially lower in carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen dioxide and a host of other emissions than petroleum diesel emissions. In fact, the amount of carbon dioxide emitted into the air by burning, is the same amount that is theoretically absorbed by growing the next crop of soybeans or corn.

Canola and corn oil are two of the most popular vegetable oils used in fryers across American. Canola oil has one of the highest yields of any of the oil crop, around 200 gallons per acre. We used approximately 20 gallons per firing for a 100 cu ft chamber.

Most of the oil we used on the first two firings was new, as we did not want to collect and store a lot of used oil until we were sure it would work. After we found it was possible we collected 25 gallons of used canola oil from the Penland kitchen fryer, thanks to the generosity of the head chef, “Big John” Renick. After it was screened, this oil worked just as well as the new oil, although it did have a more familiar smell of French fries.

Vegetable oil should be stored in a cool dry location in dark containers. The containers should also be as full as possible to minimize contact with air and moisture. This is important as the oil may become very smelly if microorganisms are allowed to grow in the containers.

We purchased a reconditioned 50-gallon oil drum to store the vegetable oil. With the help of the studio assistants, Steve Schaeffer and John Arsenault, I set out to construct a burner and oil delivery system that was efficient enough to fire the kiln to cone 10.

The 50-gallon drum was elevated to approximately 6 feet by a stand made of 2 x 4’s. The drum had both a 4-inch and a 2-inch female threaded opening which were placed at the bottom. This allowed us to easily attach treaded pipe for the delivery system. It also allowed the oil to be fed by gravity and kept our delivery pipes overhead, out of the path of workers. In the top of the drum, we cut a 6-inch hole with an acetylene torch. This hole remained open and is where we poured in the vegetable oil.

The burners were constructed from 5 inch wide “I” beam metal that was laid on its side and cut into 12-inch sections, then welded together in a stepped configuration. It had three “steps” that extended about 15 inches into the fire-box. This was so that the heat of the firebox would be conducted to the metal drip burner plates. As the oil drips down the burner steps, it gets successively hotter and hotter, until it vaporizes and ignites. A shut-off valve is used to control the flow of oil.

Another supply line feeds water onto the burner, which serves two purposes. It causes the oil to dissipate and flow down the metal burner channel and it creates hydrogen reduction in the chamber. Hydrogen is far more reactive as a reducing agent than is carbon. When water combines with red-hot carbon it produces carbon dioxide and hydrogen. This carbon hydrogen is also known as ‘water gas”.

The Chinese have used hydrogen reduction since the Han Dynasty in the production of gray bricks. It is still used today in some woodfired kilns in Jingdezhen. The water was either dripped down the interior walls of the kiln or introduced through channels in the kiln as it reached peak temperature. The kiln was then shut-off and sealed.

Our water delivery system was constructed with a standard water hose that went into a fitting that reduced it to 3/8 inch copper tubing. We controlled the water with a shut-off valve at the hose and a needle valve at each burner. This had to be adjusted regularly as the water pressure fluctuated frequently. During the firing it sounded a lot like water dripping into a hot frying pan, with the accompanying smell of cooking pancakes.

After several attempts we determined that we needed four oil drip burners. In order to have more control the flame, we placed two of the oil burners in the front of the main firebox and the other two burners in the stoke holes of the main ware chamber. Each had separate feed lines to maintain equal pressure. Sam, together with the students and a good dose of patience and perseverance, were able to find a good mix of fuel, water and air. The kiln reached temperature and was well reduced throughout.

Firing kilns with used vegetable oil has great potential as an alternative energy source. It will require substantially more research and experimentation before this method is perfected. One area of research could explore a stainless steel injection burner system that would spray in the vegetable oil with compressed air. We found that vegetable oil is easy to obtain, cheap and produces sufficient heat to fire to cone 10. It requires only a small investment in burners, supply lines and storage drums. Hopefully, this and other alternative fuel sources will help potters address the impending shortfalls of petroleum fuel and its associated pollutants.