ISO/TS 11725:2002 pdf download

ISO/TS 11725:2002 pdf download.Solid mineral fuels -Determination of
nitrogen – Semi-micro gasification method.
5.5 Sample boat, porcelain, of 8 ml capacity.
5.6 Silica boat, 25 mm x 15 mm x 130 mm, or as required, to contain the sample boat and any alkali that may
spill out during the pyrolysis of the sample.
6 Preparation of the test sample
The test sample is the general analysis test sample prepared in accordance with ISO 1988, ISO 2309, ISO 5069-2, ISO 9411-1 or ISO 9411-2 as appropriate. Expose the test sample for the minimum time required for the moisture content to reach approximate equilibrium with the laboratory atmosphere.
Before commencing the determination, mix the equilibrated sample for at least 1 mm.
If results are to be calculated other than on the “air-dried” basis (see clause 9) then, after weighing the test portion, determine the moisture content of a further portion of the test sample by the method described in ISO 331, ISO 687, ISO 1015 or ISO 5068 as appropriate.
7 Procedure
7.1 Preparation of the test portion
Transfer approximately 1 g of the powdered soda lime (4.5) to a clean, dry watch glass. Weigh to the nearest 0,1 mg, about 0,10 g of the sample, transfer to the watch glass and mix well with the soda lime.
Heat the sample boat (5.5) to 1 000 °C for a few minutes and allow to cool.
Carefully transfer the mixture to the sample boat to form an even layer. Cover with about 2 g of the activated alumina (4.6) and finally with about 0,1 g of the silica fibre (4.7), to reduce the loss of alkali during pyrolysis and hence prolong the life of the tube.
7.2 Preparation of the apparatus
Check that the apparatus is airtight, then raise the temperature of the main furnace (5.3.3) to 1 000 °C ± 5 °C and that of the steam-raising furnace (5.3.1)to 450 °C ± 5°C.
NOTE 1 This is conveniently carried out by fitting a manometer to the exit from the empty distillation flask and connecting a small hand pump to one of the tubes passing through the silicone rubber stopper at the inlet end of the pyrolysis tube. Close all other exits and inlets in the system of the pyrolysis tube and distillation flask and introduce air by means of the hand pump until there is a small positive pressure as shown by the manometer. Close the air inlet and observe the manometer for loss of pressure. If a pressure drop occurs, locate and rectify the source of the leak.
Ensure that water is passing through the condenser. Add 150 ml of the sodium hydroxide solution (4.2) to the distillation flask and raise it to the boiling temperature of approximately 125 °C using the heating mantle (5.4.3).
NOTE 2 One filling of the sodium hydroxide solution will serve several determinations. Renew once a day in apparatus which is in regular use.
Condition the apparatus, after placing a receiver under the end of the condenser, by introducing water at a rate of 2,5 ml/mm, by means of the peristaltic pump (5.3.5) and helium at a rate of 50 ml/mm, by means of the helium flow control apparatus (5.3.6). Maintain these conditions for 10 mm.
7.3 Gasification of the sample
Remove the receiver (discarding the contents), and replace with one into which 2 ml of the saturated boric acid solution (4.1) and 2 ml of the ammonia solution (4.3) have been transferred by means of a pipette. Adjust the receiver so that the delivery tube of the Liebig condenser (5.4.2) dips below the liquid level.
Turn off the peristaltic pump and remove the silicone stopper from the inlet end of the pyrolysis tube (5.3.4). Put the sample boat (5.5) containing the sample, into the silica boat (5.6), place at the inlet end of the pyrolysis tube and re-insert the silicone stopper. Carry out these operations as quickly as possible.
Re-introduce the water and maintain the helium flow as described in 7.2 for a maximum of 2 mm until traces of liquid water appear within the pyrolysis tube at the exit of the steam-raising furnace.
NOTE I If liquid water does not appear within 2 mm, the temperature of the steam-raising furnace is too high and should be reduced until the condition is met.
While maintaining the water and helium flows, transfer the silica boat to the pre-heater (5.3.2) zone of the pyrolysis tube, by means of the pusher rod (5.3.7). Withdraw the pusher rod and switch on the pre-heater.
For coals, set the pre-heater regulator to raise the temperature to 500 °C in 5 mm and then to 800 °C in a further 5 mm, or longer, until all the volatile matter has evolved.
For coke, set the pre-heater regulator to raise the temperature to 800 °C in 2 mm to 3 mm and maintain at this temperature for a total of 10 mm.
Switch off the pre-heater and push the silica boat into the heated zone of the main furnace. Withdraw the pusher rod and leave the boat in this position for 20 mm while still maintaining the water and helium flows.
Remove the receiver containing the distillate from the condenser and set it aside for titration (see 7.4). Switch off the water supply, disconnect the silicone rubber stopper, remove the boat and re-insert the stopper. Examine the residue in the boat. If unburnt sample is evident, discard the test.
If another determination is to be made, condition the system by passing water and helium through the empty pyrolysis tube for 10 mm as in 7.2. Collect the distillate in an empty receiver. Re-commence the procedure as at 7.3 using another test portion prepared as at 7.1.