Key points
Aggressive acids, high temperatures, high-viscous media and legislation encountered in biofuels production are imposing significant requirements on pump technology. The design, materials, drives and seals used for pumps are crucial for the economic efficiency of production plants. Christoph Pauly at KSB discusses the various pump systems suitable for the most diverse fluids pumped and ambient conditions.
​Numerous biodiesel production facilities have been built in Europe over the past few years and KSB has been a key supplier, with several thousand pumps being installed. The different processes employed to produce biodiesel all involve transesterification of oils and fats.
In principle, the overall process for the production of biodiesel can be divided into three stages. The whole process takes place without any pressure and at low temperatures, but each stage requires pumps specifically tailored to the particular requirements of the process.
Standard water pumps and standard chemical pumps
In the first stage metal pumps with shaft seals are used to handle the feedstock. Standard chemical pumps, or pumps with standard hydraulic systems designed for water applications can be used for this purpose.
Both pumps function in the same way for this application and the pump type selected is mostly based on the biodiesel plant operator's ‘background’: Operators from the chemical sector are most likely to opt for a standard chemical pump while investors with no chemical history will rather choose a lower-cost pump with standard hydraulic system for water applications.
No emissions – seal-less pumps
For the second stage, special pumps are required to handle/recover methanol. In Germany this process has to comply with the German Clean Air Act (TA-Luft).Therefore, pumps used must feature a high level of tightness to prevent larger amounts of methanol or catalyst leakage to the outside.
Standard chemical pumps – if provided with a double mechanical seal – may also be used at this stage, but this involves higher costs and more maintenance.
Leakage can be avoided by using seal-less pumps, with mag-drive pumps being commonly employed because their concept gives the advantage of having only two static seals, which ensures a high degree of security against leakage.
Pumps in duplex steel design for aggressive fluids
High demands are placed, in particular, on the materials of the pumps in the purification columns section. Depending on the process, aggressive acids are used to separate water and glycerine from biodiesel with the pumps being partly exposed to pure hydrochloric acid.
Special high-quality material must be used for the pumps because plain cast iron will not exhibit sufficient resistance to acids over the long term.
In comparison, pumps made of cast super duplex stainless steel are resistant to even the most aggressive of fluids. The pumps installed in the corrosive environments of the purification columns section are therefore made of duplex steel. This material is resistant to all kinds of fluids containing chloride and, therefore, to hydrochloric acid.
Non-clogging impeller pumps resist abrasion
The third stage in the biodiesel production process, the removal of glycerine, is yet another significant challenge to the pumps' technology. At this stage, salts with a concentration weight of 35%, and partly present even in crystalline form, are separated from the fluid. In order to resist the abrasion caused by the crystalline solids, non-clogging impeller pumps are used.
These centrifugal pumps in close-coupled or back pull-out design are specially designed for the handling of corrosive and abrasive fluids containing slurries. If necessary, the duplex steel used for the pumps can be subjected to a subsequent heat treatment to further increase their wear resistance.
Growing market for bioethanol
​Over the past few years there has a been a significant growth in the number of bioethanol refinery plants being built. Basically, the process can be divided into the actual ethanol production (fermentation) itself, the ethanol purification and the stillage treatment – a process which principally takes place in any brewery.
Europe's main feedstock for bioethanol production is cereals and sugar beet which are ground and mixed with water. The mixture is then pumped to the mash columns where the fermentation takes place.
At this stage, non-clogging impeller pumps are again used to ensure safe handling of the solids-laden fluid. Because of the fluid's high viscosity, the pumps require large impeller passages and correspondingly robust bearings.
Keep noise emissions low
Once again standard chemical pumps are used once more for the process following fermentation. They are designed to withstand temperatures up to 180°C encountered at this stage, whereas standard water pumps can only be used up to approximately 120°C.
Water plays an important role throughout the process with between 1.5 and 2 tons of water per ton of cereals is produced on average by evaporation.
That is why mainly pumps with standard hydraulic systems for water applications are used. To provide for the large flow rates required for cooling, cooling water pumps are also used.
These are pumps normally designed for the handling of cooling water in power plants. They deliver up to 2,800 m³ of water per hour, allowing for sufficient and fast cooling after the distillation phase.
In Germany seal-less pumps with mag drives are typically used for the alcohol storage tanks as ethanol also falls under the provisions of the German Clean Air Act (TA-Luft). Moreover, thanks to their drive concept, the seal-less pumps are particularly quiet when running, which is a great advantage given that ethanol production equipment is usually installed in the open air. With a view to applicable emission control regulations, it must therefore be ensured that noise emissions are kept low.
Food approval
A special characteristic in the production of bioethanol is that the plants must, at least in part, meet applicable food contact regulations. This means that the pumps also have to comply with the standards of the US Food & Drug Administration (FDA), i.e. they must be food-approved, which is why they are made of stainless steel.
Another characteristic is that many operators wish to install the pumps mounted on feet made of stainless steel so that the floor underneath can safely be hosed down with water without affecting the pumps.
Pump technology for the fuel of the future
As developments take place that allow a wider range of biomass feedstocks to be used for biodiesel or bioethanol, new processing technologies are emerging that are a challenge to the pump industry.
The high temperatures and aggressive fluids place special requirements on the materials used for the pumps, and to meet these pump manufacturers such as KSB are developing products to meet these demands.
