14.01.2010 | Author / Editor: C. Pinches, United Kingdom / Marcel Dröttboom
Accurate weighing is essential to the bulk materials industry to maintain a positive bottom line. Tracking, weighing and moving large quantities of aggregate material requires precise measurement. A belt weighing system maximizes the use of raw materials, controls inventories and aids in the manufacturing of a consistent product.
Hanson is one of the UK’s largest suppliers of construction materials. Each week Hanson‘s UK business delivers an average of 750000 tonnes of aggregates, asphalt and cement and 80000 cubic meters of ready-mixed concrete by rail, water and road. At the Machen site in South Wales, the company required accurate loading of rail wagons directly from the quarry for delivery to London and the South East.
Hanson’s load out system fills the hopper wagons at a rate of 700 tonnes per hour on a 900 mm conveyor belt travelling at 1.6 m/s. If the hopper wagons are loaded accurately they should hold 66 tonnes and be loaded by the conveyor in less than six minutes. Underloading is inefficient and increases transportation costs. Overloading is expensive and time consuming as excess material must be unloaded and is often unrecoverable.
Accuracy was obviously important to Hanson however independent verification of the weigh accuracy was a prerequisite for operations staff. A legally documented weight could then be used both for the rail operator and for the receiver of the dispatched material. Hanson requested that the weigh system employed should be capable of being approved by the National Measurement Office for custody transfer certification to meet the independent verification required.
Siemens provided a belt scale system, approved by the International Organization of Legal Metrology (OIML), which includes a belt scale, integrator, speed sensor and static test weights for calibration. In addition, an out-of-range indicator, with a non-resettable remote totalizer and a ticket printer are required to verify and record the transaction under the OIML approval conditions.
The belt scale included in this package is a two-idler MMI system for high accuracy (± 0.25percent over the totalized range) custody transfer, and for use on applications with fast-moving belts, short idler spacing and light or uneven belt loading. It includes stainless steel parallelogram load cells with 300percent overload protection that provide instant response to vertical loading, eliminating any influences generated by the horizontal movement of the belt. With belt speeds up to 4 m/s the belt scale handles loading of the hopper wagons fast and efficiently.
The integrator, of type BW500, is standard on the approved belt package. This microprocessor based integrator monitors rate, load, totalized weight and speed, and offers communications with many industry standard protocols, such as Profibus DP.
The International Organization of Legal Metrology is an intergovernmental treaty organization including 58 member states, which develops metrological guidelines for measuring instruments that are accepted worldwide.
The OIML R 50 Certificate, issued for the MMI/BW500 OIML package, attests the conformity of the instrument type with the requirements of the international recommendation. However, having such a certificate alone does not allow the use of equipment into metrological applications. Equipment must also carry European Community Type Approval Certification to the Measuring Instrument Directive. MID 2004/22/EC became law on October 30, 2006. The European Union Measuring Instrument Directive covers automatic weighing instruments such as belt scales to create a single approval for measuring instruments within all of the Europe Community.
Accordingly, on Friday 23 February 2009 staff from the Product Certification team of the National Measurement Office attended the site testing of the belt scale package at Hanson Aggregates, Machen Quarry. Once the equipment test was completed an EC Type Approval Certificate was issued.
With only two idlers, the costs of the system offered by Siemens are significantly less than other three, four or six idlers belt scales on the market. In addition, the package physically weighs up to three times less, so shipping costs are lower. There is no need to hire specialist lifting equipment to move the scale package into place or to cut and rejoin the belt. The installation time is dramatically reduced as the belt scale is designed to Conveyor Equipment Manufacturer Association (CEMA) standards, allowing for simple drop-in installation with no conveyor modification required. The stainless steel triple beam load cell design makes the MMI suited for harsh conditions, with high moisture and corrosion resistance, and suitability for aggregates of all sizes. With fewer idlers and fewer surfaces for product build-up to occur, maintenance costs are lower.
It is important to the overall accuracy of the system to use ‘Scale Quality’ idlers. Scale quality idlers are high precision machined idlers with minimal roller run out and frame deflection. A precise alignment is still required as with any successful belt scale installation but this process is simplified using the scale’s two independent weighbridges. Static test weights may be used for routine verification of calibration in between custody transfer certification cycles. Use of a roller test chain is not required, saving significant costs and down time. The Siemens MMI/BW500 OIML package offers an economical and reliable solution for certified custody transfer, production output and inventory or to regulate product load out. For this aggregate producer it also keeps its product shipments and costs on track.
Mr. C. Pinches, Siemens AG, United Kingdom
This article is protected by copyright. You want to use it for your own purpose? Infos can be found under www.mycontentfactory.de (ID: 332535)
Leave a comment