Kenny Foggo, Abdie Solutions, discusses the en-masse ‘eleveyor’ rising in popularity at many grain-handling facilities due to its array of benefits over more traditional conveyors and elevators.
The en-masse machine is a combination of an elevator (i.e., a machine to move bulk materials vertically) and a conveyor (i.e., a machine to move bulk materials laterally); which leads to it commonly being referred to as an ‘eleveyor’. The en-masse is becoming increasingly popular as the machine of choice in the design of new installations as well as chosen as the best solution to replace existing screw conveyors, drag-link chain conveyors and belt and bucket elevators which are reaching end-of-life or require upgrading (for example, increased capacity requirements or conforming to ATEX requirements). The en-masse can offer many benefits, including: size, ATEX compliance, and cost.
Practical benefits
Many plants and facilities look to upgrade their existing bulk materials conveying equipment because of increased production demand for their product(s). Increasing production capacity without increasing the floorspace available for production equipment can be a challenge. However, one key benefit in the design of an en-masse eleveyor allows for significantly higher machine throughputs whilst maintaining (or reducing) the overall dimensions of the casing. This is particularly beneficial where the vertical section of the machine passes through floor levels where the size of the opening in the floor is unable to be increased without major structural steelwork modifications. A recent project which Abdie Solutions undertook for William Grant & Sons in the Mash House at one of their Speyside distilleries, demonstrated the possibility of replacing a 4000 kg/hr belt and bucket elevator with a 6500 kg/hr en-masse eleveyor. The floor penetrations in the Mash House had been designed for the existing elevator with dimensions (in the vertical section) of 737 mm deep x 276 mm wide. The new, higher throughput capacity, machine (a Guttridge 150 en-masse eleveyor) had dimensions in the vertical section of 468 mm deep x 258 mm wide.
With smaller size also comes less weight, which is a further benefit for the team of engineers tasked with the mechanical installation of the machine. Smaller, lighter machines are particularly beneficial in congested facilities where a machine needs to be installed in a tight space with limited access for lifting equipment.
Safety benefits
In the world of bulk goods handling – and in particular grain handling – ATEX is one of the biggest safety considerations. ATEX control measures for conveying machinery and systems can be categorised into one of two principles: explosion prevention; or explosion mitigation. As is almost always the case in the assessment and control of risk: prevention is better than cure.
To understand how simple and effective the ATEX control measures for an en-masse are, first a description of the ATEX control measures commonly used for a belt and bucket elevator:
The atmosphere inside a belt and bucket elevator – conveying grain – will almost always be classified as ATEX zone 20 (an area in which an explosive mixture is continuously present or present for long periods). This is because the calorific energy stored in the grain dust combined with the motion of the belt leads to the dust becoming airborne, often in a concentration which constitutes a highly explosive atmosphere. In this atmosphere, are metal bucket whizzing up and down metal elevator legs making for a very high-risk scenario.
Belt and bucket elevators can of course be designed to be ATEX compliant. ATEX zone 20 rated elevators nowadays are fitted with belt alignment sensors to prevent the rotating belt and buckets from contacting the sides of the casing. They are also fitted with an underspeed rotation sensor on the idle shaft to detect a breakage in the belt or blockage causing the belt to slip on the drive pulley; these two additional features are prevention measures. These measures do not however mitigate against all possible sources of ignition inside a belt and bucket elevator (for example, a bucket detaching from the belt). Therefore, prevention measures alone are often not sufficient, and a mitigation measure is also required. The most common mitigation measure comes in the form of explosion relief panels and, when installed indoors, flameless venting on the explosion panel.
By contrast, the atmosphere inside an en-masse conveying grain will usually be classified as zone 21 (an area in which an explosive mixture is likely to occur in normal operation). Whilst conveying, the machine moves the bulk material ‘en masse’ (ie. as a mass of product without air space for dust and oxygen to mix).
Additionally, the chain rotation speed is far lower – than the belt rotation speed in an elevator – so any inadvertent contact between metal chain and metal casing does not have the capability of becoming a source of ignition. This means that an underspeed rotation sensor on the idle shaft is the only preventative measure needed to meet ATEX safety requirements, with no mitigation measures required at all. The fundamental conveying principle of the en-masse harmonises perfectly with the safety requirements of conveying a potentially explosive bulk material.
Commercial benefits
An en-masse can be designed with a very short horizontal section – used purely as an inlet into the eleveyor – and in this type of configuration it can be used to simply replace an elevator. However, the en-masse is at its most cost-effective when configured with a horizontal conveying element as well as a vertical conveyor element. The en-masse is unique in being able to use one drive unit in a system which would otherwise have needed two (one for the horizontal element and one for the vertical element), reducing the electrical hardware needed to build and maintain a facility and reducing the power consumption needed to run the conveying equipment. A true ‘2-in-1’ design. The small size-to-throughput ratio allows for lower raw material costs for the manufacturer to produce the eleveyor, and its minimal weight helps reduce time and costs associated with installation.
The safety principles which the en-masse is designed upon allow for minimal explosion prevention hardware and no explosion mitigation hardware. Belt alignment sensors as well as explosion panels and flameless vents can add considerable cost to the initial purchase of an elevator. Removing the need for these reduces the initial capital cost of the machine and removes additional complexity which could contribute to higher maintenance costs and downtime required to maintain the additional safety hardware.
On the flip side
There is however, not always one perfect solution. There are a few considerations to bear in mind which may exclude the en-masse from the shortlist of solutions.
Additional space at the inlet of the machine is required to house the idle sprocket and chain tensioning mechanism. Unlike a screw conveyor, an en-masse cannot have its inlet positioned at the very end of the machine. The space required between the end of the machine and the centre of the inlet varies from around 800 mm on a Guttridge 75 en-masse, up to 1300 mm on a Guttridge 300 en-masse.
Another drawback of the en-masse is the lack of self-cleaning capability. The principle of an en-masse requires a ‘mass’ of product to be conveyed in one slug, with the pressure of new bulk material being added at the inlet forcing material out at the outlet. Although the eleveyor is fitted with ‘cleaning flights’ to help clear any remaining bulk material at the end of a conveying run, there will always be bulk material residue left behind. An en-masse is therefore not suitable for a system conveying bulk materials where subsequent batches cannot be contaminated from the previous batch.
The future
In recent years, two of the most significant influences for engineering projects in the grain-handling industry are: increasing production capacity; and increasing safety and adherence to ATEX legislation. The en-masse eleveyor is uniquely positioned to tackle both challenges and in doing so provide an elegant and cost-effective solution which is fit for purpose. The en-masse may not suit all applications, but it is a valuable resource in the Bulk Material Handling Engineer’s toolbox of solutions.
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