The first step in the biodiesel manufacturing process is to heat the feedstock oil to the required process temperature of between 60 and 64°C. The following description gives a step-by-step explanation of the handling of the vegetable oil, the use of all valves and the control of the pumps. The pre-heating vessel is equipped with a plate heat exchanger through which hot water circulates at 75° C and an immersed spiral made of flexible INOX pipe through which hot water circulates at 60°. Also immersed is a spiral through which the methoxide is conveyed for pre-incineration before being fed into the reactor.
The maximum volume is 1,700 litres of fuel oil. The volume of oil for one barrel of biodiesel is 1000 litres. The oil remaining in the pre-heater provides a thermal buffer for the volume required for the next batch and is also used to ensure the pre-heating of the methoxide.
The transfer of the preheated oil takes place at a temperature above 60°C. We can assume a drop in temperature due to the cold metal of the reactor body. Therefore a transfer at 64 to 65° C is better than pumping only at 55 to 60° C. For safety and safe operation in view of the presence of methanol, the maximum oil temperature limit is 65° C. This will give the best biodiesel formation reaction at around 60-63°C.
After transferring the oil from the preheater to the reactor, and transferring the methoxide, the complete cycle of the preheating process is completed and the preheater can be filled with the volume of oil required for the next batch. The reactor is filled with 1000 litres of oil preheated to 60°C and 200 litres of KOH-Methoxide (otherwise known as Methylate).
The total process takes 2 hours. The production capacity of the reactor is 1000 litres per hour or 10,000 litres per 24 hours.
Biodiesel cleaning - decanting glycerine
The transesterification reaction replaces methanol with glycerol.
Separation of phases with normal gravity sedimentation
- Slow solution with 10,000 litres in 24 hours
- Very clear dividing line
Easy to separate 100% glycerine and 100% biodiesel requires keeping the temperature at 60°C.
The sedimentation tanks have a volume of 15,000 litres, but a protective guard must be kept at the top of the tank to protect it from overflow. Therefore the maximum filling volume is 14,000 litres. The bottom always has a glycerine layer, to avoid a mixture of biodiesel and glycerine during draining and maintaining the phase separation line. The bottom drain of the tank is 15 to 25 cm high, which corresponds to about 2000 litres. Therefore the full fill volume is 12,000 litres. Each barge will produce a crude biodiesel/glycerine blend of 1,100 litres. Thus the maximum number of barges that can be transferred to a decanter will be 10 to 11, depending on the filling of the bottom level in the start-up phase.
Composition of the glycerol phase
The glycerol phase is a by-product of biodiesel production. The composition depends on the purity of methanol and methoxide, impurities, FFA and water content in the feedstock oil. Also the settling time parameter and temperature influence the composition of crude glycerol.
glycerol 65 — 85 'Yo, w/w
soaps/ soaponiums 5 to 25 %, w/w
methanol 10 %, w/w
This glycerol can be used as a feed supplement for animals, where the methanol is removed by distillation. This is an option that can be done in the future. The first choice is to sell crude glycerine to customers in Europe who purify glycerine to a pharmaceutical grade quality.
Impure glycerine can also be introduced into the fermentation reactors of biogas plants.
Crude glycerol is also a feed supplement for animals. It is recommended for feeding animals. For cows it increases milk production and the chickens will also grow faster.
All the raw glycerine from the biodiesel settling process is collected in a 15 m3 tank.
The transfer of biodiesel from the decanters to the wash tank
After 10 to 11 barrels of raw biodiesel produced, the upper biodiesel phase must be transferred to the wash tank. All 15 m3 tanks (decanters, glycerine storage tank, washing tank and drying tank) are connected to the centrifugal pump on the inlet and discharge side. With this pump it is possible to make any transfer of biodiesel from, and to all the other 15 m3 vessels.
Biodiesel water washing process :
Crude biodiesel contains residual caustic KOH, glycerine, possibly impurities from used cooking oil, soaps and methanol. By washing with water, cleaning is very effective. The water wash solution always gives the same good quality biodiesel. The disadvantage of this process is the remaining 1% water in the biodiesel - so a drying is needed afterwards as an additional procedure.
Wash water is prepared with an organic acid (citric) to increase reactivity in the washing process and to avoid reaction with soap formation. Pumping the water/biodiesel mixture can easily give a saponification reaction. The acid concentration is adjusted to give a neutral pH after washing in the range of 7 to 9 pH. The washing time is 10 to 20 minutes, followed by 24 hours of waiting time for the water to settle. The best settling of the water will be at temperatures around 55 to 60°C. The thermal agent water is set at 60°C.
Biodiesel drying - water removal
After washing and 23 hours of sedimentation inside wash tank 5 (320) the biodiesel is not clearly transparent. A very easy optical indication for the stage of the drying process. Biodiesel and water are not mixable, but up to 0.2% water can be bound within the molecular structure of biodiesel.
Continuously blowing dry air from the bottom of the vessel into the biodiesel will reduce the moisture in the biodiesel over the 1-day process cycle to obtain a clear and transparent picture of the biodiesel with water content below 50 ppm.
For drying, two air sources are available. The compressor, with a working pressure of 6 - 8 bar, and the air blower which can produce a maximum of 300 mbar, but much more air volume with less energy consumption.
The dry biodiesel is ready for additive dosing, final filtration and drainage to the underground storage tank outside. Before emptying it is checked whether additive dosing is necessary. Usually the following additives are used:
- Antifreeze to make biodiesel usable in winter
- Antioxidant stabilisers
Addition of additives in the final phase of the biodiesel manufacturing process is possible in the drying vessel.
Biodiesel filtration and emptying to storage tank :
The dried biodiesel in the drying vessel is ready to be transferred to the storage vessel. On it's way the biodiesel will pass through the filter unit which consists of two different filters:
Filter 1: filter bag 1 my
Filter 2 : candle filter 1 my
The high volume pump transfers biodiesel at 300 l/min through the pair of filters and will flow to the 60,000 litre biodiesel storage tank outside.
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