Just ask the thousands of small scale producers across the U.S. who view wintertime as the "off season" of biodiesel production, largely due to the fuel washing difficulties that the cold weather brings with it.
Although these issues can affect the BioPro™ line of biodiesel processor's, it is still possible to successfully wash batches, if the user is aware of the difficulties that can arise and takes some simple steps to deal with them.
Before delving into how to deal with the problems, it's important to understand what these problems are.
Basically - all of the problems revolve around the cold. As you probably are well aware, biodiesel has a gel point that is higher then standard diesel, and this gel point can vary based on which feedstock you use. A more saturated feedstock will typically have a higher gel point.
In cold weather, the biodiesel in the machine may partially gel. The problem is exacerbated by the introduction of cold wash water, and the fact that the tank lid is removed for the wash. Biodiesel is not a very good thermal conductor, so because there is very little agitation in the tank during the wash, the heaters cannot heat all of the fuel efficently.
When biodiesel begins to gel, it can retain more water, and is much more prone to forming emulsions. When this occurs, it can result in too much fuel being pumped out during the wash, (due to the increased amount of water the sensor detects in the fuel), or too little may be pumped out, (due to the emulsion confusing the pump out sensor).
To help prevent these problems, we have provided a list of tips. It may not be necessary to implement all of these, as every situation is different. We encourage you to familiarize yourself with the following suggestions and implement those that are most feasible for you based on your own set of circumstances.
For the most part, the goal is to keep the heat in the fuel during the washing cycle.
The most obvious factor is the ambient temperature. Regardless of what other methods are employed, we do not recommend or endorse trying to brew biodiesel if the ambient temperature around the processor is less than 40-45 degress F.
A significant amount of heat is lost during the glycerin drop. To limit this loss, we recommend reducing the amount of time alloted for the glycerin drop to 16 hours. This may result in the loss of approximately a gallon or more of fuel being lost. However by reducing the "settling time" for the glycerin, the fuel is less apt to cool and thereby gel.
During the series of washes, an amount approximately 95% of the capacity of the processor is introduced to the fuel. If this water is cold, it will very effectively reduce the temperature of the fuel. (in addition water also has a specific heat almost twice that of biodiesel. Specific heat is a term that refers to how much heat is required to raise or lower the temperature of a given quantity of a substance.) while an Obvious solution is to use hot water for the wash. This, unfortunately is not always feasible for the user. If this is not an option try the following :
Typically at the start of the wash cycle the lid is removed from the main tank to allow water vapor to escape during the drying cycle. This works well but it is also a primary channel through which heat can escape. If possible, leave the main tank lid on for the bulk of the wash, only removing it for the drying segment ( which begins 18 hours into the wash cycle ).
The feedstock that you use in the winter should also be considered as well, as animal fats and hydrogenated oils will yield higher gel points. It is good practice to avoid using high gel point feedstocks in cold weather.
Vinegar is a cheap bit of insurance against emulsions in any weather, but especially in cold weather. If one gallon of vinegar ($2 - $3 ) is added to your wash vessel at the outset of the wash. It will help reduce the likelihood of emulsions forming. Adding vinegar to the wash water will not have adverse affect on the final quality of the fuel.
Despite these measures, at times you may encounter fuel that is cloudy at the end of a wash cycle. If this occurs it is not a cause for major concern. Simply drain off whatever water may be present at the bottom of the tank ( Water level may be below the window and not visible) and then turn on the heaters and stirrer for about 6 hours. This should clear up the fuel, and this problem will be alleviated as the weather turns warmer.