NIEDERFISCHBACH – How can cost effectiveness and operation reliability be combined with high product quality? In pneumatic transport one can only achieve that with system solutions tuned to the specific technical requirements. To find the adequate solution one should avail of the full range of conveying solutions.
The high demands on the automation level and the cost effectiveness of industrial facilities are a constant challenge for manufacturers of pneumatic conveying systems. The priority here is to find a suitable system solution to meet the demands of the transported material and the manifold application conditions. For that reason, KLEIN Anlagenbau AG developed various pneumatic conveying systems, each of which is optimized for the respective application. Some of these systems were optimised for the transport of silica sand, in particular in foundries or in the railway sector. Others are suitable for the transport of a wide range of pourable, granular and powdery bulk material for applications such as in the construction material industry, the glass industry or the chemical and painting industry.
The main focus in the transport of silica sand – in particular in foundries – is on highest possible conveying capacities, smooth and gentle transport, low wear of the conveying system as well as low compressed air consumption. For these demands KLEIN Anlagenbau AG developed the pressure vessel conveyor SP-HL. This conveyor operates with very short conveying cycles to achieve a quasi-continuous conveying flow. In comparison with conventional conveyors of different sizes, the SP-HL with its rapid sequence of conveying cycles is particularly advantageous with regards to cost efficiency and compact size as well as energy consumption. The rapid sequence of conveying cycles results in a smooth plug-flow with low conveying velocities, the key factor when it comes to wear.
On top of the conveyor SP-HL there is the inlet housing with its lateral sand feed pipe and the vertically inserted exhaust pipe connection. An inlet cone closure with an integrated vent valve is installed between the pressure vessel and the inlet housing. A self-actuating outlet valve at the bottom of the pressure vessel is equipped with an inductive minimum probe. The conveying pipe is installed to the connection flange; additional air is fed into the conveying pipe via an aeration flange.
During the development phase of the SP-HL, its capacity and its energy consumption were monitored. The achievable capacity with low conveying velocities depends on the conveying pipe length. The conveying capacity remains constant until up to 40 m conveying distance and constantly decreases in dependence of the conveying pipe length exceeding 40 m. To achieve high capacities, two SP-HL conveyors can be combined to a tandem system feeding one conveying pipe. Conveying capacities up to 24 t/h can thus be achieved with conveying pipes of max. 60 m. With conveying pipe distances of more than 60 m, the capacity decreases.
The energy consumption, too, is an important factor in the transport of silica sand. Thanks to its principle of a continuous plug-flow considerable energy savings of 40 to 50 % can be achieved with an SP-HL in comparison with conventional pressure vessel conveyors. Though the SP-HL was originally designed for the transport of silica sand it is also used to transport e. g. perlite in the building materials industry and spray grain or chamotte in the stoneware industry. In contrast to the transport of silica sand, other pourable bulk materials and in particular powdery bulk materials are usually transported by means of the dense phase conveying principle. For this kind of application, too, KLEIN offers a large range of pressure vessels matching the specific requirements.
Higher conveying rates
The different conveying principles of dense or dilute phase are differentiated in accordance to their proportion of transported material and consumed compressed air volume, the dense phase conveying principle having the highest material ratio in proportion to the consumed compressed air volume. Especially for the transport of materials that are complicated to transport, KLEIN offers a loading control, the so-called μ-control. With the installation of such a μ-control, the flow properties of the transported material and the expected wear are taken into account. With the μ-control, the pressure level in the conveying system is continuously monitored by means of pressure sensors and the loading of the conveying air flow with transported material controlled fully-automatically.
In a typical conveying process of a pressure vessel conveyor without loading control transported material is introduced into the conveying pipe when the ventilation phase of the conveyor starts. With the increase of transported material in the conveying pipe, the conveying pressure rises until either the conveyor vessel is empty or the conveying pipe clogs. In order to avoid cloggings, the pressure rise is adjusted by pre-setting the conveying air flow and the conveying pressure at the conveyor, so that the conveying vessel is empty before the critical conveying pressure is reached. A long pressurization and an unincisive conveying cycle are characteristic for this process. In a conveying process with load control, the conveying air conditions are optimally adjusted when the pressure level is just below the clogging limit and the operating level is reached as quickly as possible. Should the conveying pressure rise unexpectedly during operation so that the conveying pipe is prone to clog, the loading control will take corrective action. The material feeding into the conveying pipe is interrupted and additional air introduced into the pipe if necessary, in order to purge the pipe until the pressure (the so-called μ-pressure) is falling below the pre-set level again. After that, the material transport is continued automatically. This may repeat several times until the conveying vessel is empty. As a consequence, the conveying pressure may in practise oscillate around the pre-set μ-pressure but below the critical pressure level. A short pressurization and a distinct conveying cycle with high load are characteristic for this process.
Conveying systems equipped with a loading control do not need to be pre-adjusted to the most complicated operating mode expected, but can be highly optimized. However, the loading control does not only make sense with materials that are difficult to be pneumatically transported, but also offers advantages in standard applications: On the one hand, higher conveying rates can be realised with the risk of cloggings being reduced
to a minimum, as the systems reacts independently and automatically to impending operating malfunctions and can thus prevent them. On the other hand, the higher load of the conveying air flow offers significant saving potential with regards to compressed air consumption.
Another advantage lies in the fact that due to the lower conveying velocity wear of the conveying pipes is reduced considerably. Typical conveying velocities in dense phase conveying processes range between 10 m/s to max. 25 m/s. As the conveying velocity should be considered squared in different approaches, already comparatively slight reductions may offer a considerable advantage to the operator with regards to a reduction of expected maintenance costs.