8.2 Requirement for Industrial Applications
115
have been compiled important considerations and examples which can be used as
guideline for implementation of industrial applications.
8.2.1 Economical Aspects
We should keep in mind, whatever the performances of a small-scale implementation
of a cavitation process, that the scale-up will be performed on the base of economic
considerations. For instance, in the second half of 2015, the average price of industrial
consumers in Europe was 0.119 euro/kWh and accounted for a sizable share of annual
expenditure. Thus, many companies tend to improve their energy efficiency to reduce
costs and their carbon footprint.
The treatment of large flows requires data on input energy per volume treated
(kWh/L) and the needed intensity to successfully lead the chemical process, i.e. the
actual output power per area (W/cm
2 ) of the cavitation devices. The introduction
of a high power has technical limits and is not always the guarantee of success
because there is a level beyond which the performances decline. The exposure time
to cavitation should be minimized and there is a trade-off between input power
and processing time which must be determined before scaling-up. This operation
is usually performed with a semi-pilot system. Otherwise, the power consumption
depends on the choice of the technology. For example, when cavitation is provided
by piezoelectric transducers, the yields between output/input powers can range from
50 to 60% for clean-type transducers to 80% for bar probes.
8.2.2 Choosing a Technology
The choice of cavitation phenomenon in process intensification has technical limitations which must be taken into account from the origin of the scaling project.
Depending on the expected objectives, bubble collapse can be carried out either by
hydrodynamic cavitation or by ultrasonic cavitation.
Hydrodynamic cavitation is useful for processes that require low cavitation energy
and is easily carried out at ambient temperature. This technique has the shortcoming
of inducing a consequent loss of energy which must be compensated by a highly
dimensioned pumping circuit and adequate geometry of the system. Although the
erosion phenomenon is important for some applications, hydrodynamic cavitation is
the cheapest technique compared to ultrasonic devices with regard to the generated
cavitation energy, the rudimentary equipment and the low maintenance load (Carpenter et al. 2016). An innovative design of cavitator for process intensification was
reported by Kumar and Pandit (1999), who used a high-speed homogenizer consisting
of an impeller inside a cage-like stator with numerous slots where cavitation generates. Another rotor- and stator-based design was described by Badve et al. (2013),
with a high-speed rotation cylindrical rotor with indentations generating cavitation
115
have been compiled important considerations and examples which can be used as
guideline for implementation of industrial applications.
8.2.1 Economical Aspects
We should keep in mind, whatever the performances of a small-scale implementation
of a cavitation process, that the scale-up will be performed on the base of economic
considerations. For instance, in the second half of 2015, the average price of industrial
consumers in Europe was 0.119 euro/kWh and accounted for a sizable share of annual
expenditure. Thus, many companies tend to improve their energy efficiency to reduce
costs and their carbon footprint.
The treatment of large flows requires data on input energy per volume treated
(kWh/L) and the needed intensity to successfully lead the chemical process, i.e. the
actual output power per area (W/cm
2 ) of the cavitation devices. The introduction
of a high power has technical limits and is not always the guarantee of success
because there is a level beyond which the performances decline. The exposure time
to cavitation should be minimized and there is a trade-off between input power
and processing time which must be determined before scaling-up. This operation
is usually performed with a semi-pilot system. Otherwise, the power consumption
depends on the choice of the technology. For example, when cavitation is provided
by piezoelectric transducers, the yields between output/input powers can range from
50 to 60% for clean-type transducers to 80% for bar probes.
8.2.2 Choosing a Technology
The choice of cavitation phenomenon in process intensification has technical limitations which must be taken into account from the origin of the scaling project.
Depending on the expected objectives, bubble collapse can be carried out either by
hydrodynamic cavitation or by ultrasonic cavitation.
Hydrodynamic cavitation is useful for processes that require low cavitation energy
and is easily carried out at ambient temperature. This technique has the shortcoming
of inducing a consequent loss of energy which must be compensated by a highly
dimensioned pumping circuit and adequate geometry of the system. Although the
erosion phenomenon is important for some applications, hydrodynamic cavitation is
the cheapest technique compared to ultrasonic devices with regard to the generated
cavitation energy, the rudimentary equipment and the low maintenance load (Carpenter et al. 2016). An innovative design of cavitator for process intensification was
reported by Kumar and Pandit (1999), who used a high-speed homogenizer consisting
of an impeller inside a cage-like stator with numerous slots where cavitation generates. Another rotor- and stator-based design was described by Badve et al. (2013),
with a high-speed rotation cylindrical rotor with indentations generating cavitation