BS ISO 502:2015 pdf download – Coal — Determination of caking power — Gray-King coke test
5.1 Furnace, horizontal electric, 50 mm internal diameter and 300 mm long, with one end closed and the other carrying a plug of insulating material which is bored centrally with a hole 25 mm in diameter. The winding of the furnace shall be such that the middle 200 mm is at a uniform temperature within ±5 °C at both 300 °C and 600 °C. Alternatively, the furnace may be constructed from an electrically-heated aluminium-bronze block, with one or several, bores of 25 mm diameter. The furnace shall be insulated and located in a cover of metal or other suitable material, and shall be equipped with a suitable thermocouple, lying above the retort tube when the latter is in position and with the junction at the centre of the furnace. An indicator shall be provided for showing the furnace temperature with an accuracy of ±5 °C. A suitable means of controlling the energy input shall also be provided to permit an increase in temperature at a rate of 5 °C/min. A multiple tube furnace to allow simultaneous determinations is convenient. The furnace may be of the fixed type or mounted on rails. Suitable furnaces are shown in Figure 2 and Figure 3. 5.2 Retort tube (see Figure 4), a heat-resistant glass or transparent silica tube, 20 mm internal diameter and 300 mm long, closed at one end, with a side arm, 8 mm internal diameter and 50 mm long, sealed in at a distance of about 20 mm from the open end. The tube shall be smooth and either of uniform bore or with a slight taper (19 mm to 21 mm) such that the open end is the larger.
5.3 Distance rod, with a flat disk at one end to assist in the packing of the coal and to indicate the free end of the coal sample in the retort tube.
5.4 Receiver and outlet tube A glass vessel of adequate size, suitably supported and attached to the side arm of the retort tube, fitted with an outlet tube leading to atmosphere or to a piece of small bore silica tubing at the end of which the gas leaving the receiver can be burned through Bunsen burner (in a fume cabinet) to ensure toxic fumes are burnt before venting to the atmosphere through the fume cabinet. The receiver may conveniently be a U-tube which can be immersed in water. The outlet shall be open to the atmosphere to prevent pressure build-up. Fumes are toxic and it is recommended that the process is carried out in a fume cupboard. The tar receiver should be cleared on a regular basis, by placing tar in a heat resistant crucible and burning off in a furnace.
WARNING — THE FUMES ARE TOXIC AND DUE CARE SHOULD BE EXERCISED IN THEIR DISPOSAL.
6 Preparation of sample
The coal used for the determination of the Gray-King coke type is the analysis sample ground to pass a sieve of 212 μm aperture. If necessary, expose the sample in a thin layer for the minimum time required for the moisture content to reach approximate equilibrium with the laboratory atmosphere. Before commencing the determination, mix the air-dried sample thoroughly for at least 1 min, preferably by mechanical means. The sample shall be prepared on the same day as the determination is carried out.
7.1 Coals with a Gray-King coke type within the range A to G 2 (see 10.3) Raise the temperature of the furnace until it is steady at 325 °C. Weigh on a scoop 20,0 g ± 0,1g of the sample and transfer it to the retort tube (5.2), held in such a manner that the coal cannot enter the side arm. Complete the transfer with a soft brush and allow the coal to fall to the far end of the retort tube. Hold the tube horizontally, insert the distance rod (5.3) so that the face of the disk is 150 mm from the closed end of the retort tube and spread the coal into a layer of uniform depth by shaking and turning. Withdraw the distance rod and insert a flattened pad of asbestos wool or a notched asbestos disk to retain the coal in position. Without disturbing the position of the coal, close the open end of the retort tube with a heat-resisting stopper. Connect the receiver (5.4) to the side arm and insert the retort tube in position in the furnace (5.1) so that the centre of the coal layer coincides with the centre of the furnace. If the furnace is mounted on rails, clamp the retort tube in a horizontal position and run the furnace into position.