Effective silo volume measurement can create cost savings and improved inventory control. Katrien Geerinckx reports.
Traditional methods of inventory measurement of bulk solids inside silos and warehouses include either single-point level measurement technologies such as capacitance switches and mechanical rotary paddles, which are used as alarms switches, or continuous level measurement such as ultrasonic, radar, laser, plumb bobs (manual or electronic), and ropes. These technologies yield estimates of the levels of stored bulk solids but provide unreliable measures of volume, especially in large silos and warehouses.
Limitations
Due to the limitations of basing estimates on sampling a single point on the material surface, these technologies have inherent accuracy error that can be on the order of 20 per cent or more, and which may translate into higher investments in safety stock, excess ordering costs, and non-optimal usage of storage capacity.
Nuclear technology has been used for real-time inventory measurement, but has rarely been adopted because of major on-site complications related to licensing, safety, material deterioration, and other factors.
These limitations can be overcome by acoustic volume mapping instrumentation, which utilises 3D scanning technology to provide precise silo volume measurement.
Acoustic volume mapping
The CONTOUR acoustic volume mapping device from Magnetrol, accurately detects random surface irregularities and material build-up on silo walls, enabling the visualisation of true consumption over time. More importantly, the accurate volumetrics generated by acoustic volume mapping allow inventory managers to realise cost savings from two sources: the reduction of stock levels, which can decrease inventory carrying costs; and the removal of labour-intensive inventory management processes.
Many companies deploy inventory policies that maintain a minimum stock over a set period of time. These minimum inventory levels cushion against demand spikes and supply disruptions.
If real inventory drops below the minimum without being measured as such, the chance of stock-out is higher than the supply chain was designed for.
To avoid this situation, the minimum inventory level is inflated by the maximum possible positive measurement error, guaranteeing that any stock-outs are not due to measurement error.
This scenario of overcompensating with higher levels of safety stock clearly illustrates the disadvantages of imprecise level instrumentation technologies applied to the task.
Therefore, better awareness of inflows, outflows, and current stock levels would allow companies to reduce required safety stock, while protecting them against supply chain changes and loss of inventory while providing greater accuracy in reporting bulk material assets.
Decreased carrying stocks
With its ability to significantly improve the accuracy of volume measurement in a wide range of inventory environments, acoustic volume mapping technology can decrease carrying costs of safety stock.
Furthermore, by reducing average inventory levels, utilisation of existing storage space can be further optimised, allowing for additional capacity to increase production.
Reducing labour costs
Implementing acoustic volume mapping eliminates the need for manual volume measurement, which is the case in a variety of bulk solids and powders inventory scenarios where traditional process level instrumentation is used currently. For example, if one manual volume measurement is taken every day in each of two silos, it would take two man-hours per day, or 730 man-hours per year. Assuming a cost of EUR15 per hour for a technician to perform this function, the annual labour cost would equal EUR10,950.
Acoustic volume mapping's ability to provide automated real-time measurement removes this cost entirely.
Additional benefits
A number of qualitative benefits arise from moving to the precise volumetrics of acoustic volume mapping, resulting in a holistic inventory management solution.
Among them are more accurate accounting, better awareness of yields, and alerts to unexpected inventory changes (as can be experienced from theft or damaging events).
CONTOUR works with almost every solid and bulk powder material, such as coal, cement, sand, aggregates, fly ash, chemicals, fertilisers, food, grain and plastic pellets.
In addition to bins and silos, the systems allow measuring in previously difficult-to-measure vessels or containers, such as bunkers, hoppers, pits, open bins, bulk storage rooms and warehouses.
Magnetrol manufactured the first liquid level switch to accurately and safely detect motion of liquid in boilers and feedwater systems.
The company was also responsible for introducing the first pneumatic valve controller, supporting the growth of the nuclear power industry with new standards in safety and performance.
For more information at www.engineerlive.com/epe
Katrien Geerinckx is with Magnetrol International, Zele, Belgium. www.contour.magnetrol.com
