Stamford Bio-Gas

For gasification of biosolids to begin, a testing facility would need to be found or created. We found that it would be more beneficial to us if we created a scale model gasifier. With the scale model we will have total control and greater flexibility in research and testing.

Jeffrey Fournier, from Carlin Contracting Company, designed a scale model of a downdraft gasifier. The model is approximately 8' x 12' horizontal and less than 10' vertical. It feeds at a rate of approximately 20kg per hour. The model has been constructed so that it can be easily broken down to make design modifications and is mounted onto a 16' trailer for easy transportation.

The reactor is the main component to the gasifier. It consists of three main sections: the metered feed stock delivery, the shaker grate, and the ash removal system. To begin the process, the biosold pellets are releashed into the metered feed stock delievery system in set quantities. The pellets are ignited once inside the reactor to begin the gasification process. Air is constantly entering and exiting the reactor throughtout the process, but only in small amounts to keep a low amount of oxygen inside at all times. With low amounts of oxygen, the pellets never ignite on fire, therefore preventing combustion.

After about 20 minutes, the pellets turn into a carbon fuel conprised mostly of hydrogen, carbon monoxide, and carbon dioxide also known as sythesis gas or syngas. There is a bioproduct of ash that is also created in the gasification process and it is removed using the shaker grate. The shaker grate vibrates, causing the ash to move down through the reaction zone. Then the ash removal system, driven by a standard generator at 25 rpm, uses an auger to take the ash and char out of the reactor.

Above are pictures of our gasifier. From left to right: a drawing of the reactor showing the details of the components inside, second is a live picture of the reactor, and the third is a photo of the hopper where the pellets are releashed into.

The vortex particular seperator removes suspended particulates from the hot syngas coming from the gasifier. When the gas enters the seperator, it spins around a pipe located in the center of the sperator in a circular motion similar to that of a cyclone. As the air spins, the velocity increases causing the particles in the air to fall to the bottom of the seperator and a cleaner gas flows out the top towards other filters.

The heat exchanger is responsible for cooling off the gas. Using a standard room air conditioner, water is cooled and then pumped through coils running throughout the heat exchanger. The gas leaves the vortex and enters the heat exchanger at a temperature between 600 to 700 degrees C, where it flows over the coils to be cooled down to a temperature around 75 to 100 degrees C.

Above are two pictures of the heat exchanger. The first is an actual photo showing the heat exhanger and the air conditioner unit that cools the water. The second image is a drawing showing the inside of the heat exchanger and how the coils run through to cool down the gas.

Our gasification unit has three filters responsible for removing suspended particles with in the gas stream along with moisture and tar. Each filter can be changed out for testing to find which product works the best. The first filter referred to as the coarse filter, uses larger media filters to collect the larger particles in the gas. Some examples that are used in the coarse filter are chunks of hard wood and wood chips. The second filter referred to as the moisture filter, removes the water vapor from the gas. Steel mesh, insulation, and different coarses of nylon buffing pads are used in the moisture filter. The fine filter is the last place the gas travels through before being tested in different types of motors. For this filter we purchased a HEPA filter that has rechangable cartiridges. The fine filter is used as a protective device to remove any tiny particles. With the testing done so far, we have found the wood chips and the nylon pads give us the cleanest results.

Our gasifier has been design to function completly on its own. There is a generator located on the unit that supplies power to the shaker, auger, air conditioner, water recirculation pump, and blower. The generators motor runs on gas produced from the gasifier itself. While on the testing site in Stamford, we do not use the generator, but we have proven it to be very effective if the unit was to even be transported and power was not avaible.

Above are two pictures of the showing the generator and the motor used to power the generator.

When the gas produced is not being used on testing motors, it is burned off into the air. The gas is ignited and sent to one of two flares avaible. The first flare is located on the unit itself. The other is mounted onto a nearby storage trailor, and also contains a bio-filter which utilizes charcoal and wood chips to reduce the smoke and odor produced when the gas is burned. When the gas leaves the flare it appears clear, but as shown below when a piece of paper is held over the flare, it ignites into flames.

Shown above are images of the two different type of flares. The first photo is of the flare mounted on the trailor. The second picture is showing the piece of paper being burned by the ignited gas coming from the flare located on the unit itself.