The block diagram in this document represents the layout of a typical waterless, modular Biodiesel processing facility. This illustration includes the pipe to pipe solution, optional blending module and raw material tank farm. Tank farms and total build out of plant are available as a single package via a Turnkey solution. Pipe to pipe included items are green.
Following the block diagram is a step-by-step description of the waterless Biodiesel process describing each step in the system and its purpose. Certain modules reflect choices of equipment that are driven by personal preference or choice of process.
Process Flow Description
The basic process for any catalyst induced transesterification process involves migrating ester chains from a triglyceride molecule, and reconnecting the ester chains with a methanol or ethanol molecule, thus creating a methyl ester molecule. It is this methyl ester molecule that is Biodiesel. Various chemical and mechanical actions work together to make the trans-esterification process occur. The catalyst used is a strong base, either sodium or potassium. Once the ester chains are broken off, the left over glycerin molecule is a byproduct of the reaction. The mass balance is shown following this description.
1. Raw materials holding tanks:
Tanks depicted in the upper left corner, hold the following supplies; The raw materials storage tanks hold;
- Vegetable feedstock, (soy, rapeseed, etc.)
- The second feedstock tank (optional) contains blending oil, (rendered fats, waste cooking oil, or other suitable material) this tank may also be used to store a secondary vegetable oil.
- Catalyst or methoxide, can be either potassium, or sodium and is mixed with methanol forming a methylate. Using methylate is a safe and easy method of handling and blending catalyst into the process that does not require open mixing of methanol with the caustic. Operators are not exposed to either methanol, or catalyst materials.
2. Optional Centrifuge and Blending Module:
The system can process two or more feedstocks of similar or dissimilar acid values, by using the optional blending module (shown in yellow). Combined acid value must be less than ≤ 5. Acid value is an indicator for FFA (free fatty acid) level. FFA is approximately 50% of acid value.
Shown in the diagram as the yellow group just below the left feedstock tank. The centrifuge, also optional, may be included with the blending module offering further flexibility in feedstock selection. The blending unit simply blends and meters the various components together. The centrifuge separates water and other unwanted material from the incoming feedstock. For example, this combination would be used when working with a combination of soy and chicken fat.
3. Dosing Module:
Just below the methanol tank is the methanol catalyst mixing station. It is at this station that the concentrated methoxide solution is blended with methanol to the exact proportions needed for the specific process recipe. Metering is done via closed loop control from the computer module. Process parameters and real time feedback are available on the computer control screen where operators can monitor flow rates at any given moment. Dosing ratios are metered using mass flow meters that are keyed into the mass of feedstock entering the system.
4. Drying Station:
Water has been described as the bane of the Biodiesel industry. It causes soap to be formed in the transesterification process, and also causes the finished fuel to be unstable. This process is totally waterless, and to further deter any moisture contamination, two drying stations areused. The first drying station, depicted as a green box, following the line from the blending unit, re-circulates and heats the oil under vacuum to remove any residual moisture in the incoming feedstock. The second drying station, the methanol removal unit is discussed later in this document.
5. First Pass Transesterification Reactor:
Immediately after the drying station the dosing mix of methanol and catalyst enter a special mixing tube and then enter the reactor. This system features a two stage transesterification process which accelerates conversion efficiency and maximizes yield. Approximately 90% of the feedstock oil is transesterified in the first pass. With other Biodiesel processes there is always a trade off between quality fuel and increased throughput. A dual station transesterification process offers no trade off or sacrifice of fuel quality for throughput. The secret involves the proprietary reaction tank design, and in the cutting of the fuel after the first transesterification reactor. The result is high throughput and high quality fuel.
6. Glycerin Removal:
Initial separation of glycerin from product stream is done using a settling tank. It is located directly after the first reaction station. The glycerin is then pumped to the glycerin storage tank, (6a) shown in the upper right corner of the diagram. Glycerin contains approximately 2% methanol. This small amount helps to keep the glycerin liquid as ambient temperatures drop. The glycerin storage tank is the tank in the upper right corner of the illustration
7. Second Pass Transesterification Reactor:
Immediately after the glycerin removal station the second dosing mix of methanol and catalyst enter a special mixing tube and then enter the reactor. This mix is a slightly different mixture of catalyst. All metering is computer controlled. The second pass reactor further pushes the reaction enabling the process to fully react any remaining mono, di, or triglycerides.
8. Glycerin Removal/Settlement Tanks:
This step sends the product mix on to settling tanks (2, 3, 4) after second pass reactor. Trace amounts of biodiesel, methanol, and the remaining catalyst are carried away with the glycerin byproduct to the glycerin holding tank (6a) in the upper right area of the diagram.
9. Ion Exchange Waterless Wash:
Following the settling tanks, the biodiesel moves to the ion exchange towers. One of the principle reasons many customers choose this system is for the waterless wash. Rohm & Haas pioneered the waterless wash in collaboration with several biodiesel processor designers to create a unique active ion resin material known as Amberlite. Rohm & Haas has expended a great amount of research and development to create a unique purification system.
Amberlite resembles coffee grounds and functions much like coffee grounds in a percolator. The biodiesel stream enters the top of the percolator and trickles down through the cylinder of Amberlite. The active Ion material on the Amberlite reacts with the unwanted material in the biodiesel. The chemical reaction renders the catalyst neutral, and the resultant material attaches itself to the Amberlite, thus removing it completely from the fuel. The final product is pure and absolutely dry. The Amberlite needs replacing at the rate of about 1 metric ton for every 250,000 gallons of biodiesel processed. Once its lifespan is over, Amberlite is neutral, and non-toxic. It is not a hazardous waste, and may be used as landfill. The Amberlite can be changed without shutting down the process. Tanks are arranged in a configurable series and may be serviced with out shutting down the process.
10. Polish Filter:
The polishing filter removes any extremely fine particles that may have passed through the processor. Various levels of particulate filters are available. Filters are configured such that filter elements can be changed with out shutting down the process.
11. Methanol Recovery:
Following the polish module, the product stream enters the methanol recovery unit. This unit heats the oil to over 100 c while under vacuum. The oil then filters down over heated dispersion plates to facilitate removal of methanol. Recovered methanol is then routed back to the main methanol storage unit.
12. Storage Tanks:
Following the methanol recovery, the biodiesel is ready for sale or storage. Typical parameters for storage require the fuel to be kept at temperatures above 38 degrees Fahrenheit. Biodiesel should not be stored for more than six months prior to use. Nitrogen blankets may be used to help protect your finished product. Heated tanks may be necessary if fuel is to be stored for any length of time in climates colder than 40 degrees Fahrenheit.