Written by Rickdatech

Do you need to improve the mixing in your processor? Would it be a waste of time to add a mixing eductor or would adding one result in cheaper fuel? Over the years, the answer has always been subjective, leading to experimentation that may or may not have been fruitful. This test may change that and give you a clear quantitative answer. It’s really a simple test. Just before you shut down the processor for settling, take a sample of 100ml. After both the sample and the batch settle, compare the ratio of glycerin to biodiesel in both to each other. If they have the same ratio of biodiesel to glycerin, you have good mixing. If your sample has a higher percentage of glycerin than the batch, your mixing can be improved. The greater the difference in ratios, the worse your mixing is.

Inside your processor are little balls of glycerin that want to fall to the bottom of the tank. Mixing keeps them suspended evenly throughout the biodiesel and relatively small in size. Over time these balls touch each other and stick together forming a larger ball. The larger the ball the faster it falls. These little balls of glycerin not only contain glycerin, but also contain methanol and catalyst. The methanol and catalyst can dissolve in both the glycerin and the biodiesel, but at different levels. The glycerin can hold much more than the biodiesel. As the reaction proceeds the methanol in the biodiesel is used up, throwing off the balance of methanol between the glycerin and biodiesel. This imbalance forces the methanol out of the glycerin, into the biodiesel.

The two major factors are the size of the balls, and the distance the methanol needs to travel. The smaller the ball, the larger the total surface area between the biodiesel and glycerin. Passing the beads through the pump or a static mixer will chop up the balls into smaller balls making it easier for the methanol to flow in and out of it. The longer a ball of glycerin remains in the tank, the larger it will grow and the faster it will fall. If most of the glycerin is in the bottom of the tank, the top of the will run out of methanol and stop reacting short of it’s full potential. We pump mix drawing the biodiesel and glycerin from the bottom of the tank. As more and more glycerin settles out, the ratio of glycerin to biodiesel going to our pump and our sample port will also change. This means that when we draw a sample, it is an indication of how much of the glycerin we see settling in our tank. If we see more glycerin in our sample than we see in the full batch, then we know we have glycerin settling in our processor. There are some simple solutions to this, If you are using a high shear pump, can install a bigger pump using more energy or we can install a mixing eductor. If you are using a low shear pump, we can install a static mixer to reduce the size of the glycerin ball and slow settling that way.

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