Design of Sampling Systems

Researchers have developed a specification to enable Australian coal operators to design reliable and accurate sampling systems suited to their individual needs.

Many sampling systems installed in Australian coal mines are unreliable, inaccurate and require a high degree of operator intervention. Their construction is also inappropriate ? based on laboratory style equipment, light-weight conveyor systems and non-site standard motors, positioners and electric switch gear.

PROJECT OBJECTIVE

The primary objective of this project was to develop a generic functional specification for the design and installation of coal sampling systems that address the mechanical, electrical and safety standards necessary for the systems to operate as key components of modern coal quality management systems. The specification was prepared as a pro-forma document (in software as well as hard copy) so project engineers could customise the specification to suit their requirements.

A secondary objective was to prepare summary justifications for equipment selection drawn from the site audits to help site engineers in the formal justification process.

FINDINGS

A formalised set of questions was generated and forwarded to seven major companies involved in the design, supply and maintenance of sampling equipment for the Australian coal industry. Three companies provided comprehensive responses to the questions.

Researchers audited 13 existing sampling plants at six different sites to determine how well the sampling system addressed sampling protocol, mechanical/electrical/control system availability, housekeeping and cost. The result reflected consensus on a number of issues but also highlighted significant differences in opinion regarding some others.

Key conclusions from the survey are:

• There was universal agreement that the coal industry is not currently being well served by the existing system of design and installation of sampling systems. The basic reason appears to be due to lack of technical know-how on behalf of the client combined with commercial pressure on the service provider to supply the lowest cost system without due regard to technical and engineering issues.
• One form of contract used is an initial detailed engineering study to tightly define the specification of the installation followed by a competitive tender for supply and installation. However, survey respondents argued that a more flexible EPCM style of arrangement with a reputable service provider could also provide a satisfactory technical and operating solution, but at a lower cost.
• It is possible to design in flexibility of sampling systems to allow for future changes in sampling requirements, but there will always be a trade-off with cost.
• There was widespread disagreement regarding the most suitable form of individual sampling elements. The researchers felt this was cause for concern, because they believe there are valid technical reasons why one form of sampling element should be preferred over another, such as roll crushers in preference to impact type crushers.
• There was agreement that, in the past, the general maintenance of samplers had not been successful, but other than a requirement for regular inspections and audits, there was little agreement regarding the best means to address these problems.
• Access to critical areas of sampling systems was one of concern, especially with the need to address safety issues while still providing ready access to the system. It was suggested that on-line control charts could be used and sensors could be used more appropriately to indicate blockages.
• The area of safety should be extended beyond the immediate sampling system to include broader issues such as location of sampling systems in towers without suitable access and routine cleaning, and lifting devices to allow safe handling of sampling drums and maintenance items.
• One response included a very useful discussion of criteria that need to be established to define the material that is to be sampled. Of importance are issues such as the need to define the actual physical topsize of material likely to be sampled rather than nominal topsize, as it only requires a few lumps of oversize material out of thousands of tonnes of coal being sampled to create a blockage.