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 Infopetro -> Laws & Regulation


Proximate Analysis of Coal

  03/16/2007


This national standard is modified in relation to: (ISO 11722:1999, Solid mineral fuels-Hard coal-Determination of moisture in the general analysis test sample by drying in nitrogen, eqv), (ISO 1171:1997, Solid mineral fuels-Determination of ash content, eqv), (ISO 562:1998, Hard coal and coke - Determination of volatile matter, eqv).

Main difference is as follows:
- Added air drying method for determination of moisture
-Added fast ash method for determination of ash
-In determination of volatile matter, returning temperature is set to (900?0), 3 min.
This standard replaces GB/T 212- 1991 "Proximate analysis of coal?
This standard contains the following main changes in comparison with GB/T 212-1991:
- Deleted the toluene distillation method for determination of moisture (2.2 in 1991 version);
- Modified some conversion formulae for volatile matter result (4,5,6 in 1991 version; 5.5 and 7 of this version).
Annex A of this standard is normative.
This standard was proposed by former Coal Industry Bureau of People''s Republic of China.
This standard is under the jurisdiction of National Coal Standardization Technical Committee.
This standard was drafted by Assay Laboratory of China Coal Research Institute in combination with No.143 brigade of Yunnan Coalfield Geological Exploration Company.
Leading drafter of this standard: Lin Yujia, Chen Kequan, Han Liting.
The following is the previous versions of standard replaced by this standard :
- GB 212 - 1963, GB 212-1997, GN/ T 212-1991.


1 Scope

This standard specifies the method for determination of moisture, ash and volatile matter in coal and the calculation method of fixed carbon.
This standard is applicable to the lignite, bituminous coal and anthracites.

2 Normative reference documents

The following normative documents contain provisions which, through reference in this text, constitute provisions of this national standard. For dated reference, subsequent amendments to (excluding corrigeda), or revisions of, any of these publications do not apply. For undated references, the latest edition of the normative document referred to applies.
GB/T 218 Determination of carbon dioxide content in carbonate (eqv ISO 925)
GB/T 7560 Determination of mineral matter in coal (neq ISO 602)

3 Determination of moisture

This standard specifies two methods for determination of moisture. Among them, method A is applicable to all coal types, and method B is applicable to bituminous coal and anthracites only.
In arbitration analysis, for the case of using moisture in air dried basis coal sample for correction and converting basis, Method A shall be used to determine the moisture in air-dried sample.

3.1 Method A (method of drying in nitrogen)
3.1.1 Method brief
Weigh out a given amount of air-dried sample, place in 105-110 dry box, make it dried in dry nitrogen current till the mass remains constant. Then calculate the mass fraction of moisture according to the mass loss of coal sample.
3.1.2 Reagent
3.1.2.1 Nitrogen gas: purity of 99.9%, with oxygen content less than 0.01%.
3.1.2.2 Anhydrous calcium chloride:(HGB 3208): chemically pure, graniform.
3.1.2.3 Allochroic silicagel: industrial goods.
3.1.3 Instrument, equipment
3.1.3.1 Dry box of small space: tight body, with smaller free space, air inlet and outlet, also with automatic temperature control device, able to keep temperature within the range of 105-110.
3.1.3.2 Glass weighing bottle: diameter 40mm, height 25mm, with tight groundin cover (See Figure 1)
3.1.3.3 Desiccator: with allochroic silicagel or graniform anhydrous calcium chloride inside.
3.1.3.4 Drying tower: capacity 250mL, with drying agent inside.
3.1.3.5 Flowmeter: measurement range 100-1000mL/min.
3.1.3.6 Analytical balance: sensibility reciprocal 0.0001g.
3.1.4 Analysis step
3.1.4.1 Use weighing bottle dried and weighed in advance to weigh out (1?.1)g air-dried sample with size below 0.2mm, to the weighing accuracy of 0.0002g, and spread it evenly in the weighing bottle.
Figure 1 Glass weighing bottle



3.1.4.2 Uncap the weighing bottle, put it into dry box (3.1.3.1) which is filled with dry nitrogen gas and heated to 105-110 in advance. Dry 1.5h for bituminous coal, and 2h for lignite and anthracites.
Note: aerate 10min before putting weighing bottle into dry box, nitrogen flow subject to 15 ventilations per hour.
3.1.4.3 Take out weighing bottle from the dry box, immediately put on the cover, and put it into desiccator to cool it down to room temperature (about 20min), and then weigh it.
3.1.4.4 Carry on checking drying of 30min/time, till the coal sample shows mass loss below 0.0010g or mass increase after drying for 2 consecutive times. In the latter case, the mass just before the occurrence of mass increase should be taken as the basis for calculation. The moisture below 2% means no need of checking drying.

3.2 Method B( air drying method)
3.2.1 Method brief
Weigh out a given amount of air-dried sample, place in 105-110 dry box, make it dried in air current till the mass remains constant. Then calculate the mass fraction of moisture according to the mass loss of coal sample.
3.2.2 Instrument, equipment
3.2.2.1 Fan drying box: with auto temperature control device, and able to keep the temperature within the scope of 105-110.
3.2.2.2 Glass weighing bottle: Same as 3.1.3.2.
3.2.2.3 Desiccator: Same as 3.1.3.3
3.2.2.4 analytical balance: Same as 3.1.3.6
3.2.3 Analysis step
3.2.3.1 Use weighing bottle dried and weighed in advance to weigh (1?.1)g air-dried sample with size below 0.2mm, to the weighing accuracy of 0.0002g, and spread it evenly in the weighing bottle.
3.2.3.2 Uncap the weighing bottle, put it into fan drying box (3.2.2.1) which is filled with dry nitrogen gas and heated to 105-110 in advance. Under the continuous airblast, dry 1h for bituminous coal, and 1~1.5h for anthracites.
Note: Airblast in advance is to make temperature even. Airblast 3~5min before putting weighing bottle carrying coal sample into dry box.
3.2.3.3 Take out weighing bottle from the dry box, immediately put on the cover, and put it into desiccator to cool down to room temperature (about 20min), and then weigh it.
3.2.3.4 Carry on checking drying of 30min/time, till the coal sample shows mass loss below 0.0010g or mass increase after drying for 2 consecutive times. In the latter case, the mass just before the occurrence of mass increase should be taken as the basis for calculation. The moisture below 2% means no need of checking drying.
3.3 Result calculation
The calculation of moisture in air-dried sample is compliance with formula (1) :
(1)
Where:
Mad - the moisture of air-dried coal sample, the unit is percent (%);
M- the mass of the weighed air-dried coal sample, the unit is gram (g);
m1?the mass loss of coal sample after drying, the unit is gram (g);

3.4 Accuracy degree for determination of moisture
The repeatability for determination of moisture is stated as shown in Table 1:
Table 1
Moisture( Mad)/% Repeatability limit/%
<5.00 0.20
5.0010.00 0.30
>10.00 0.20 0.40

4 Determination of ash
This standard includes two methods for determining ash in coal - slow ash method and fast ash method. The slow ash method is arbitration method.
4.1 The slow ash method
4.1.1 Method brief
Weigh out air-dried coal sample of a given amount, put it into muffle furnace, heat to 815?0 at a certain speed, then incinerate and burn it till the mass maintains constant. Take percentage of residue mass occupied in the coal sample mass as the ash in the coal sample.
4.1.2 Instrument, equipment
4.1.2.1 Muffle furnace: Fireplace has enough constant temperature area, can keep the temperature of (815?0). The upper part of the furnace back wall is equipped with a chimney of diameter 25-30 mm. In the lower part, 20~30mm from the bottom of fireplace, an eyelet for the plugging of thermocouple is there, and an air hole of 20mm diameter can be found on furnace door.
The determination of muffle furnace constant temperature requires the close of furnace door, at least once per year. The pyrometer (including millivoltmeter and thermocouple) should be calibrated at least once per year.
4.1.2.2 Cupel: Porcelain, 45mm long, bottom length of 22mm, bottom width of 22mm, 14mm high (see Figure 2)

Figure 2 Cupel

4.1.2.3 Desiccator: Same as 3.1.3.3.
4.1.2.4 analytical balance: Same as 3.1.3.6.
4.1.2.5 Heat-proof porcelain plank or asbestos plank.

4.1.3 Analysis step
4.1.3.1 From the cupel which in advance was burned to the degree of contact mass, weigh out (1?.1)g air-dried sample of below 0.2 mm to the weighing accuracy of 0.0002g, spread evenly in the cupel, make the mass per square centimeter below 0.15g.
4.1.3.2 Put cupel into the constant temperature zone below 100 in muffle furnace, close the furnace door and keep a gap of about 15mm. In not les than 30min, slowly raise the furnace temperature to 500 and keep this temperature for 30min. Continue to raise the temperature to (815?0) , and burn under this temperature for 1h.
4.1.3.3 Take out the cupel from the stove, put on the heat-proof porcelain plank or asbestos plank, cool it down in air for about 5min, then move it into desiccator to cool down to room temperature (about 20 min), and then weigh.
4.1.3.4 Carry on checking drying of 20min/time, till the mass shows change no more than 0.0010g after burning for 2 consecutive times. The mass after the last burning shall be taken as the basis for calculation. The ash content below 15% means no need of checking drying.

4.2 Fast ash method
This standard includes two methods of fast ash method: Method A and Method B.
4.2.1 Method A
4.2.1.1 Method brief
Put the cupel with coal sample on the conveyer belt of ash rapid determination instrument which was preheated to (815?0). The coal sample is automatically transported into the instrument for complete ashing and then sent out. Take the percentage of residue mass occupied in the coal sample mass as the ash in the coals ample.

4.2.1.2 Special instrument: Fast ash determination instrument (See Annex A)
4.2.1.3 Analysis step
a) Preheat fast ash determination instrument to (815?0).
b) Start the conveyer belt and set its speed to about 17mm/min or other proper speed.
Note: The new fast ash determination instrument should undergo the contratest against slow ash method with respect to different coal types, and adjust the transmission speed of conveyer belt according to the result of this contratest.
c) From the cupel which in advance was burned to the degree of contact mass, weigh out (0.5?.01)g air-dried sample of 0.2 mm, to the weighing accuracy of 0.0002g, spread evenly over the cupel, make the mass/square centimeter below 0.08g.
d) Put the cupel with coal sample on the conveyer belt of fast ash determination instrument, it is automatically sent into the furnace.
e} When cupel is sent out from the furnace, take it and put on the heat-proof porcelain plank or asbestos plank, and cool down in air for about 5min, then move it into desiccator to cool down to room temperature (about 20 min), and then weigh.
4.2.2 Method B
4.2.2.1 Method brief
Put the cupel with coal sample from outside into muffle furnace preheated to (815 ?0), and keep burning till the mass is constant. Take the percentage of residue mass occupied in the coal sample mass as the ash in the coal sample.
4.2.2.2 Instrument, equipment: Same as 4.1.2.
4.2.2.3 Analysis step
a} From the cupel which in advance was burned to the degree of contact mass, weigh out (1?.1)g air-dried sample of below 0.2 mm to the weighing accuracy of 0.0002g, spread evenly in the cupel, make the mass/square centimeter below 0.15g. Place the cupel with coal sample by rows on the heat-proof porcelain plank or the asbestos plank in advance.
b} Heat muffle furnace to 850, open furnace door and slowly push the heat-proof porcelain plank or asbestos plank, which carries the cupels, into muffle furnace. After 5~10min, when coal sample no long emits smoke, at a speed of less than 2cm/min push the rest cupels in sequence into the intensely hot part inside the furnace (if the coal sample catches fire and deflagration happens, the test should be discarded).
c) Close furnace door, keep it burning at (815?0) for 40min.
d} Take out the cupel from the furnace, keep it in the air for about 5min to cool down, then move it into desiccator to cool down to room temperature (about 20min), and then weigh.
e} Carry on checking drying of 20min/time, till the mass shows change no more than 0.0010g after burning for 2 consecutive times. The mass after the last burning shall be taken as the basis for calculation. In case of unstable result during checking drying, use slow ash method to re-determine. The ash content below 15% means no need of checking drying.
4.3 Result calculation
The calculation of ash in air-dried sample is compliance with formula (2):
(2)
Where:
Aad ?the ash in air-dried coal sample, the unit is percent(%);
mweight of the weighed air-dried coal sample, the unit is gram (g).
m1-- Mass of residue after burning, the unit is gram (g);

4.4 Accuracy degree of ash determination
The repeatability and reproducibility for ash determination is stated as shown in Table 2::
Table 2


5 Volatile matter determination method
5.1 Method brief
Weigh out air-dried sample of a given amount, put in the porcelain crucible with cover, and heat it for 7min at (900?0) in a manner of isolating air. The result of deducting the moisture in this coal sample from the percentage of mass loss occupied in coal sample mass is the volatile matter.
5.2 Instrument, equipment
5.2.1 Volatile matter crucible: porcelain crucible with tight cover, with shape and size shown in Figure 3. The total mass of crucible is 15-20g.

Figure 3 Volatile matter crucible
5.2.2 Muffle furnace: equipped with the pyrometer and attemperator, able to keep temperature within 900?0, and with enough constant temperature area for 900?. The heat capacity of this furnace refers to the following, at initial temperature of 920, put into crucible stool and several crucibles with room temperature, after furnace door is closed, 900?0 is recovered within 3min. On the back wall of furnace, there are a line vent holes and an eyelet for plugging thermocouples. The eyelet position should allow the thermojunction of thermocouple, inserted into the furnace, to lie between the crucible bottom and the furnace bottom, and keep a distance of 20~30mm from furnace bottom.

The determination of muffle furnace constant temperature requires the close of furnace door, at least once per 6 months. For the calibration of pyrometer (including millivoltmeter and thermocouple), at least once per 6 months.
5.2.3 Crucible stool: made of nichrome wire or other heat-proof metal wires. Its specification and size should be able to allow all crucibles stay within constant temperature area of muffle furnace, and allow crucible bottom next to the thermojunction of thermocouple (See Figure 4).
5.2.4 Crucible stool clip: see Figure 5.

Figure 4 Crucible stool


Figure 5 Crucible stool clip


5.2.5 Desiccator: Same as 3.1.3.3.
5.26 Analytical balance: Same as 3.1.3.6.
5.2.7 Wafer machine: The spiral type or the lever type wafer machine, able to wafer coal cake of 10mm diameter.
5.2.8 Stop-watch.
The above is Figure 4, Figure 5

5.3 Analysis step
5.3.1 From the crucible with cover, which in advance was burned to the degree of constant mass under 900, weigh out (1?.1)g air-dried sample with size below 0.2 mm (to the weighing accuracy of 0.0002g), then softly shake the crucible to make coal sample spread evenly, put up the cover, and place it on the crucible stool
For lignite and long flame coal, the coal cake should be wafered in advance, and cut into pieces of 3mm.

5.3.2 Preheat muffle furnace to 920 or so. Open furnace door, send the stool carrying crucible into the constant temperature area quickly, close furnace door immediately, and heat for accurate 7min. After the crucible and stool are put inside, the recovery of furnace temperature to 900?0 is required, henceforth the temperature of 900?0,should be maintained, otherwise this test will be discarded. Heating time includes the temperature recovery time.
5.3.3 Take out crucible from the stove, keep it in the air to cool off for 5min or so, then move into the desiccator to cool down to room temperature (about 20min), and then weigh.

5.4 Classification of coke residue characteristics
The classification of characteristics of coke residue from the determination of volatile matter shall be in line with following provision
(1)Powdery- all of powder, no agglutinating grains.
(2)Agglutinating- all or basically becomes powder once touched by a finger, where the bigger conglomeration become powder by soft touch.
(3)Weakly caking- becomes small pieces once pressed by a finger.
(4)Caking without fusion- broken into small pieces once firmly pressed by finger, no luster on the top surface of coke residue, with somewhat silver white luster on undersurface.
(5)Caking with fusion without expansion- flat even piece of coke residue forms flat pieces, indistinct boundary of coal grain, visible silver white metal luster on the top surface of coke residue, even more visible silver white luster on the lower surface.
(6)Caking with slight-expansion and fusion- not broken if pressed by hand, with silver white metal luster on the top surface and undersurface of coke residue , but smaller inflated bulb on its surface (or minute bubbles)
(7)Caking with medium-expansion and fusion - silver white metal luster on top surface and undersurface, obvious inflation but the height not over 15mm.
(8)Caking with strong-expansion and fusion- silver white metal luster on top surface and undersurface, height over 15mm.
For the sake of simplicity, the above ordinal number is used as the code of each characteristics of coke residue.

5.5 Result calculation
The volatile matter of air-dried coal sample is calculated according to formula (3) :
(3)
where:
Vad volatile matter in air-dried coal sample, the unit is percent(%)
mmass of the air-dried sample, the unit is gram (g);
m1mass loss of coal ample after heating, the unit is gram (g);
Mad?moisture of air-dried sample, the unit is percent;(%)

5.6 Accuracy degree of volatile matter determination
The repeatability and reproducibility for determination of volatile matter is stated as shown in Table 3:


6 The calculation of the fixed carbon
The calculation of air dried basis fixed carbon is in compliance with formula (4):
(4)
Where:
FCadof FCad- air dried basis fixed carbon, the unit is percent (%);
Mad?The moisture in air-dried coal sample, the unit is percent (%);
Aad?The ash in air-dried coal sample, the unit is percent (%);
Vad?The volatile matter in air-dried coal sample, the unit is percent (%);

7 The air dried basis volatile matter is converted to the dry ash-free basis volatile matter and dry mineral basis volatile matters
7.1 Dry ash-free basis volatile matter
(5)
(6)
When carbon dioxide content in carbonate of air-dried coal sample is more than 2%-12%, then:
(7)
Where, Var? Volatile matter of dry ash-free basis, the unit is percent (%);
(CO2)adThe mass fraction of carbon dioxide (in line with GB/T 218) in carbonate of air dried basis, the unit is percent (%);
(CO2)ar?mass fraction of carbon dioxide in coke residue to coal sample, the unit is percent (%);
7.2 Dry mineral-matter-free basis volatile matter
(8)
When carbon dioxide content in carbonate of air-dried coal sample is 2%-12%, then:
(9)
When carbon dioxide content in carbonate of air-dried sample is more than 2%-12%, then:
(10)
Where Var?Volatile matter in dry ash-free basis, the unit is percent (%);
(CO2)admass fraction of mineral (in line with GB/T 7560) in air dried basis, the unit is percent (%);


Annex A
(normative annex)
fast ash determination instrument
A1 Fig. A1 is a kind of quite suitable ash fast determination instrument, composed of three parts, namely horseshoe electric tube furnace, conveyer belt and controller, with structure and size of each part shown as follows:


Figure A1 Fast ash determination instrument


1- Electric tube furnace; 2- Conveyer belt; 3- Controller
a} The horseshoe electric tube furnace: fireplace is about 700mm long, bottom width of about 75mm, height of about 45mm, with open mouth on both ends, axial rake of about 5?Its constant temperature zone is required to be: (815?0)) part is about 140mm long, 750-825 part of about 270mm long, outlet temperature below 100.
b} Chain-type automatic conveyer (conveyer belt for short): made of heat-proof metal, with adjustable transmission speed, non deformable and no sloughing under 1000.
c} Controller: Mainly includes the temperature controller and conveyer belt speed controller. The temperature controller is able to control temperature within (815?0); conveyer belt speed controller is able to control the conveying speed between15-50mm/ min.
A2 Any fast ash determination instrument meeting following requirements is qualified for use:
a} High-temperature furnace can be heated to (815?0) and have a constant temperature zone of enough length;
b} Enough air in the furnace for coal sample combustion;
c} Enough retention time of coal sample in furnace for ensuring complete ashing;
d} The occurrence where the oxysulphide from oxidization of sulfur in coal contacts with calcium oxide from decomposition of carbonate, is prevented or minimized.



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