Issue 11, p. 353 (2022)

  Oral

ISO 13909 compliant contractual payment station coal sampling plant: process design and equipment selection for chemical, physical and moisture sampling

  • M. Nyokong  
  • W. P. Slabbert

The paper discusses the process design and mass balance highlights to illustrate the ISO 13909 compliance of a 4-year-running contractual payment station sampling plant. The plant is used to sample - 60mm coal supply to a coal fired power station infrastructure belonging to the South African National Power Utility. Payment parameters are proximate analysis (Calorific Value, Ash-, Sulphur content), physical (size and abrasion index) and moisture content. Over and above ergonomic physical samples and timeous moisture samples, the plant also delivers the crushed chemical sample in triplicate for buyer-, seller- and referee analysis.

The lot period was defined as 24 hours production while the system compliance was designed around mass-based sampling. Production varies over a wide range of throughout tonnages from 800-3600 ton/h as dictated by complex boiler and silo operational requirements. The plant required a unique operational philosophy to adapt the number of primary increments (and corresponding time interval) per sublot size to the varying production rates which over a fix lot period results in varying lot size. Furthermore, a contractual grade, calibrated, 6-idler belt scale is used to measure the instantaneous conveyor load which in turn controls the cutter speed via a programmable logic controller (PLC) prompted variable speed drive (VSD) setpoint to sample fixed increment mass to represent fixed production mass interval.

The primary belt end crosscut sampler boasts a unique articulated joint design sample chute to fit down the high sample tract; eliminating the delineation errors associated with the previous competitor design.

Keywords: ISO 13909 compliant, Sampling Plant, chemical-, physical-, moisture sampling, time-based lot, mass-based sampling interval.

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