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CTL12-13 - Aerated & Diffusion Cell Thermal Instability Screening Test Apparatus

Test method to evaluate and quantify self-heating of bulked powders in stagnant or aerated environments.

Benefits

  • Designed to meet the specification in the 1990 Institute of Chemical Engineers book "Prevention of Fire & Explosions in Dryers", pages16 -18. (Author: John Abbott, ISBN-10: 0852952570)
  • Excellent screening-tool for examining self-heating effects within dryer, silos and bags
  • Simple to use glass test vessel enabling easy test configuration modification between either an aerated test or a diffusion test scenario
  • Internal pre-heating pipework configuration
  • Repeatable thermocouple location method
  • Multi-channel data acquisition system supplied ready configured

cell screeningcell screening

Figure 1: Aerated cell with pre-heated air (top entry)     Figure 2: Powder aerated cell set-up

The purpose of the Aerated cell test is to simulate the conditions in dryers in which a hot air stream passes through the material, whilst the diffusion cell test stimulates conditions in silos or bags and at the bottom of dryers where material can collect in bulk. The only difference between the two tests is that with the diffusion cell test, the lid is removed from the glass test-cell and there is no hot air stream passing through the material. Instead, heating occurs uniformly inside the oven so that the powder sample can be ramped-up to its target temperature gradually (typically 0.5 °C.min-1) thus enabling examination of the test sample for self-heating effects within the bulk of the product held within the test cell.

If the heat developed by a reaction of substance with oxygen, or by exothermic decomposition not lost rapidly enough to the surroundings, self-heating leading to self-ignition can occur. Self-ignition therefore occurs when the rate of heat production exceeds the rate of heat loss. The test procedure is useful as a preliminary screening test for powders being processed on plant.

Functional Specification & Deliverables

  • Mains supply: Volts 220 V - 240 V a.c / 7 A or 120 V a.c / 13 A
  • 30 litre fan assisted oven (400 °C capability)
  • Air flow meter fitted (adjusts flow through the pre-heating coil). Typical air flow is set to 0.6 l.min-1
  • Temperature controller (ramps oven at 0.5 °C.min-1)
  • Glass test vessel set each comprising cylinder closed at the base and top with sintered glass and a close fitting lid for aeration cell tests
  • Thermocouples for monitoring oven temperature at several places within the powder layer within the vessel (see figure 2)
  • Data acquisition software program (pre-installation on optional PC recommended) for conducting either the aerated cell test (with lid) or the diffusion cell test (no lid)
  • Thermocouple extension cables
  • Glass vessel support stand with pre-drilled thermocouple securing holes for repeatable alignment of thermocouples
  • 1 x instruction manual

Optional Extras

  • PC & LCD monitor (recommended)
  • Spare glassware
  • Thermocouples
  • Training