Vertical loading of bulk materials including cement products creates challenges for designers, manufacturers and operators of this equipment with regard to damage and dust. Damage to materials can result in poor process efficiency, and dust creation is both a health and safety and a legislative issue.
Typical vertical loading of materials is by shrouded free fall chutes with extraction, or by Cascade designs. However none of these solutions address the fundamental issues of material flow to avoid dust and damage.
The GraviLoad team have undertaken a complete review of the whole process. Typically the following problems are seen in Cascade systems :-
- They are limited in mass flow rate due to choking
- They behave as a free fall chute at low mass flow rates increasing dust, damage and edge wear
- Mass flow rates are limited by cone shipping size
- Material has to be forced from horizontal rectangular section on belt to vertical circular cross section, leading to
- Very high velocity change
- High dust generation at top of chute
- They encourage high velocity change at every cascade point increasing dust generation
The GraviLoad controlled flow chute uses spoon based elements and carefully designed geometry to address these fundamental limitations. Fig 1 shows a series of spoon based elements in a stack. These allow the material to flow cleanly from surface to surface, yet can stack telescopically to create a loading chute.
Furthermore the head chute is spoon based creating a smooth, controlled flow transition from belt to first chute element over a range of conveyor angles making tilting head chute systems more efficient and dust free.
The GraviLoad team have undertaken extensive design and test work to establish the correct geometry, and have worked with a University research team in bulk material handling to validate its models.
All our units are designed to meet the customer’s specifications and are designed in 3D solids, Finite Element Analysis tested and then modelled in our own Discrete Element Modelling ( DEM ) system to ensure that we get a “right first time” result. Fig 2 and Fig 3 show a head chute flow model and a spoon element tested in DEM.
In order to fundamentally test the performance of both systems a Cascade and GraviLoad chute of similar outlet cross section were designed and then subjected to DEM testing. Fig 4 shows the parameters that were to be analysed. :-
Fig 5 shows the velocity distribution comparison between the GraviLoad controlled flow chute and the conventional cascade chute at the same mass flow rate. The GraviLoad chute ( orange ) shows a highly controlled, stable flow with 2/3rds less slow moving particles and excellent high speed control compared to the Cascade chute ( green )
In summary Fig 6 shows that the GraviLoad chute achieves almost double the control of particle speed in the 1-2.5 m/s range and a 20 % mean weighted lower through the chute. Therefore dust generation will be minimised in the GraviLoad chute
Fig 7 shows the cascade chute at various mass flow rates. This clearly demonstrates the erratic nature of the velocity changes in the chute. At high mass flow rates the number of particles at low velocities increases showing the start of “choking” due to stationary flow. At low mass flow rates the higher velocities start to dominate indicating that the chute starts to behave as a free fall chute. Therefore as the flow rates change particularly at startup / shut down there is a large variation in velocities leading to an increase of dust and damage.
Fig 8 shows the same change in mass flow rate for the GraviLoad Chute. A highly controlled flow is achieved across the range indicating much improved dust / damage control.
Fig 9 and 10 show this mass flow rate issue within the DEM model outputs. Fig 9 shows the cascade chute as it starts to build up stationary material at high flow rates leading to choking and increased dust generation. Fig 10 shows the GraviLoad chute at the same flow rates – the flow remains controlled decreasing dust generation.
Fig 11 shows the summary of the development work. It can be clearly seen that the GraviLoad spoon system outperforms cascade chutes in all aspects of particle velocity control and therefore minimises damage and dust generation.
Whilst the GraviLoad system requires optimised geometry, it can be seen it is highly tolerant to mass flow rate changes. Other studies have been undertaken to also show that it is tolerant to frictional and other particle changes.
For optimum performance from a conveyor based input the following design issues should be considered :-
- Exit from the belt into the head chute and first chute element should be by a spoon based surface.
- The head chute can tilt for ship loader applications and the conveyor exit can be designed to allow optimised flow at different conveyor angles.
- Geometry should be arranged to minimise the velocity change from top to the bottom of the chute to reduce dust
- The outlet of the chute must be carefully designed preferably using more spoon surfaces to control the exit velocity and again minimise dust.
This is why all our chutes are designed to the customer’s specification and individually optimised for the application.
GraviLoad is working with a number of different materials and processes to reduce overall costs of chute systems. These are carefully matched to the material, environmental and life requirements.
Our fundamental approach is to avoid lining materials that are expensive initially, compromise the flowing surface, and are difficult to maintain over their life
Of particular interest in the cement industry is our Rotomould design of the spoon elements. This allows us more flexibility in the shape of the element, and can vary material thicknesses to suit wear requirements. Parts are created in a low pressure rotating mould from materials such as High Density Polyethylene ( HDPE ) and can have steel inserts added to improve wear performance.
We also fabricate from SSAB Hardox / Weldox materials to achieve high strength, low wear, low weight elements for particular applications.
Other applications of GraviLoad technology
The fundamental design of the geometry lends itself to other uses in material handling with applications in the cement industry. This is particularly the case in belt to belt transfer. Fig 12 below shows an inline belt to belt transfer. In this case material flow is ejected from the upper belt onto a spoon surface at a matched velocity. Other spoon faces may be used to match the height from inlet to outlet
Fig 13 below shows the same spoon based approach to right angle belts
The GraviLoad team have developed practical models using its own in house 3D print modelling capability. This allows scale models of particular applications to be physically tested to add more confidence to our “right first time” approach.
University research has been extended to larger scale models to continue to improve the capability of our technology.
The GraviLoad range of controlled flow chutes fundamentally addresses the limitations of conventional cascade chutes.
- They provide highly controlled flow over wide mass flow rates and different material properties generating less dust and damage
- We can offer the best material compromise for the bulk solid being used
- They are designed to exact application requirements
- They are fully designed and tested using FEA and DEM before manufacture
- Their performance has been externally validated
- Our integrated design offers low cost and high performance