Fan delivered for tobacco processor
We regularly supply fans for a North Brabant client that works with tobacco products. Especially when tobacco is moist, it can be very corrosive, with even stainless steel 304 no longer being sufficiently resistant.
The high-pressure fan we supplied was therefore specially designed for this difficult environment. This is because the extracted air from the dryer is hot and humid, and contains highly corrosive particles of tobacco.
Measures against corrosion due to aggressive air flow
Several measures have been taken to prevent corrosion:
- The shaft penetration is by means of a gas-tight shaft seal with barrier gas connection;
- All stainless steel parts are glass beaded to a flawless finish, preventing any material from sticking;
- The fan is fitted with a drain nipple that allows any condensation formed to be drained away.
| Reference | Order 77457 |
| Fan type | Series 16 Type MH13 |
| Flow rate m3/h | 5.100 |
| Static pressure at 60° C (Pa) | 4.660 |
| Static pressure at 20° C (Pa) | 4.100 |
| Maximum temperature supply gas (°C) | 85 |
| Speed (o/min) | 2557 |
| Motor power, absorbed ( kW) | 9 |
| Motor power, maximum (kW) | 18.5 |
| Materials | Parts in contact with gas flow: stainless steel-316 (1.4401) Other parts: Steel S235JR (1.0037) |
The pictures below show two renders of the supplied fans. It can also be seen why a good seal is so important, if corrosive gases can reach the bearings and inside of the motor a lot of rusting occurs very quickly with all its consequences.
Extraction of moist air and condensation
Another aspect of aggressive gases comes from a somewhat unexpected source: namely, water vapour. When extracting air from ovens or drying plants, the fan is often a lot cooler than the gas flowing through it, especially the walls in direct contact with the outside air. Water vapour in hot air with very high humidity will then quickly cool and condense, after which the water accumulates in the fan. This is also the case with this fan, as the air comes from a dryer with a temperature of 60° C.
Depending on the application, there are various solutions for this, the simplest being a drain nipple at the bottom of the fan that actively drains the condensation water. Preventing condensation completely is also possible but quickly makes the fan much more complex. Think of thermal insulation of the fan so that the temperature difference is minimal, or mixing dry air, or providing the fan with tracing.
Fan supplied for roasting coffee
We also supplied a high-pressure flue gas outlet for a well-known coffee roaster for the gases released during roasting. Roasting coffee is a precise and complex process in which various chemical reactions take place in the coffee beans due to the high temperature. This forms the aromas that characterise coffee, with different acids playing an important role in shaping the flavour.
Although the final product is also eagerly consumed at Naaykens’, acids, volatile organic compounds and fine (burnt) particles are therefore released as residual gases during this process. The fan that extracts these gases naturally also has to be able to withstand this gas flow with various reactive components.
In the photos below, you can clearly see the stainless steel of the fan housing and the inspection hatch. The additional reinforcement strips are also clearly visible for the very high pressure.
A shaft seal is also used at this installation, fitted with carbon seal rings with stainless steel locking springs and a barrier gas connection. High-quality pressure-resistant graphite seals of Sigraflex type are also used at the flanges.
| Reference | Order 79619 |
| Fan type | Series 2300 Type PA3600 |
| Flow rate m3/h | 18.000 |
| Static pressure at 130° C (Pa) | 12.000 |
| Maximum temperature supply gas (°C) | 225 |
| Speed (o/min) | 2900 |
| Motor power, absorbed at 130° C ( kW) | 88.7 |
| Motor power, maximum (kW) | 135 |
| Materials | Fan parts in contact with the gas flow: stainless steel-304 (1.4401) Other parts: St37 |
Extra power for cold starts
For fans that move hot air, in some cases the motor has to be run at a higher power rating than the power it consumes during normal operation, e.g. during a cold start at rated speed. This is because hot air is much thinner than the same air at room temperature. The density of air relative to temperature is easily derived from the general gas law (PV = nRT). For equal pressure and volume, a doubling of temperature is accompanied by a halving of density. Because far fewer molecules need to be set in motion, the force on the impeller is much lower, and hence the force the motor has to deliver.
For the above application, the temperature of the air is 130° C. This also means that the density of the air is only 73% compared to outside air and the power input at 20° C is 38% higher than at working temperature.
So, without the use of variable speed drives or valves, the motor will have to be substantially larger than necessary at the high operating temperature, to start at 20C.
Corrosion-resistant fans for ammonia-rich environment fertiliser / fertiliser plant
We recently delivered the fan below for a fertiliser producer, which comes in a highly polluted environment. To prevent corrosion, a more economically advantageous fully galvanised finish and robust paint finish was chosen here instead of having this fan made entirely of stainless steel.
A large inspection hatch has also been designed here with 4 handy strength knobs making it easy to regularly check the condition of the fan on the inside.
Galvanised piping for corrosive dust, with insulated fan
Another customer was looking for a filter system for extracting zeolite powder, which can be acidic in some states. Here, the filter was placed in front of the fan due to limited space in height, instead of the typical Pat-Jet Easy Access construction where the fan is directly on the filter housing.
This fan is part of a total solution for this client, where we provided a turn-key solution for a production process where production regularly had to be stopped due to high levels of dust in the air.
In this installation, pay particular attention to the use of different types of pipework; thick-walled galvanised pipe was chosen before the filter because of the greater dust load. Between the filter and the fan, the dust load (and risk of corrosion) is obviously much lower and standard pipe material can be used.
Insulated fan for low-noise operation
Also clearly visible here is the filter casing: insulating it greatly dampens the noise produced – which is nice for nearby workers. We often work with specialised insulation companies that can fit fans with both thermal and sound insulation.
| Reference | Order 85033 |
| Fan type | Series 53 |
| Flow rate m3/h | 30.000 |
| Static pressure at 20° C (Pa) | 2.800 |
| Speed (o/min) | 1750 (frequency-controlled) |
| Motor power, absorbed (kW) | 29 |
| Motor power, maximum (kW) | 30 |
| Materials | Fan parts in contact with the gas flow: stainless steel-304 (1.4401) Other parts: St37 |
Hot-dip galvanised impellers for mushroom farms
Perhaps this is an industry you would not expect, but in mushroom farms, the air released is corrosive due to the use of ammonia, among other things. The high humidity of the air in which mould thrives also causes problems if the fan is colder than the air sucked in, given that condensation will quickly occur.
See here, for example, a fan returned by a customer, here the heavy rust is clearly visible.
For this customer, we therefore completely rebuilt the impeller and hub and hot-dip galvanised them.
So, now you have a bit of an idea of what Naaykens’ can do for aggressive gas streams. Do you also have a gas stream with corrosive components? We would be happy to help!
