Determination of total sulfur in the hottest coal

Determination method of total sulfur in coal

issued and implemented by the National Bureau of standards

this standard is applicable to the determination of total sulfur in lignite, bituminous coal and anthracite

this standard includes three methods for determining total sulfur in coal, namely gravimetric method, coulometric titration method and high temperature combustion neutralization method. In the arbitration analysis, the gravimetric method shall be used

1 gravimetric method (ESCA method)

1.1 key points of the method

mix the coal sample with aldrin, burn it at 850 ℃ to generate sulfate, and then make sulfate ions generate barium sulfate precipitation. Calculate the total sulfur content in the coal sample according to the weight of barium sulfate

1.2 instruments and equipment

1.2.1 analytical balance: accurate to 0.0002g

1.2.2 box type electric furnace: with thermocouple pyrometer, it can raise the temperature to 900 ℃, and can adjust the temperature for ventilation

1.2.3 porcelain crucible: capacity 30ml and 10 ~ 20ml

1.3 reagent

1.3.1 Aldrin: grind 2 parts of chemically pure light magnesium oxide (Hg 80) and 1 part of chemically pure anhydrous sodium carbonate (GB 63977) to less than 0.2mm, mix them evenly, and store them in closed containers

1.3.2 hydrochloric acid (GB 62277): chemically pure, specific gravity 1.19, prepared into 1:1 aqueous solution

1.3.3 barium chloride (GB 65278): chemically pure, 10% aqueous solution

1.3.4 methyl orange (Hgb 308959):0.2% aqueous solution

1.3.5 silver nitrate (GB 67077): analytically pure, 1% aqueous solution, stored in a dark bottle, and add a few drops of nitric acid

1.4 test steps

1.4.1 weigh 1g of analytical coal sample with particle size less than 0.2mm in a 30ml crucible (weigh 0.5g when the total sulfur content exceeds 8%) (accurate to 0.0002g) and 2G of aldrin, carefully mix them evenly, and then cover them with 1g of aldrin (accurate to 0.1g of aldrin)

1.4.2 move the crucible containing coal samples into a well ventilated box furnace. The electric furnace must be gradually raised from room temperature to 800 ~ 850 ℃ within 1 ~ 2H, and heated at this temperature for 1 ~ 2H

1.4.3 take out the crucible from the electric furnace, cool it to room temperature, and then carefully stir and mash the burning matter in the crucible with a glass rod (if there are black particles of unburned coal, continue to burn at 800 ~ 850 ℃ for 30min), then put it into a 400ml beaker, wash the inner wall of the crucible with hot distilled water, add the washing liquid into the beaker, add 100 ~ 150ml of freshly boiled distilled water, and stir it fully, If black particles of unburned coal are found floating on the liquid surface at this time, this determination is invalid

1.4.4 filter with medium speed qualitative filter paper by dumping method, pour and wash with hot distilled water for three times, then move the residue into the filter paper, wash carefully with hot distilled water for at least 10 times, and the total volume of washing solution is about 250 ~ 300ml

1.4.5 drop 2 ~ 3 drops of methyl orange indicator into the filtrate, then add 1:1 hydrochloric acid to neutral, and then add 2ml hydrochloric acid in excess to make the solution slightly acidic. Heat the solution to boiling, stir it continuously with a glass rod, drop 10ml of 10% barium chloride solution, keep it near boiling for about 2h, and finally the volume of the solution is about 200ml

1.4.6 after cooling or standing overnight, filter the solution with dense ashless quantitative filter paper, and wash it with hot distilled water until there is no chloride ion (tested with silver nitrate)

1.4.7 move the sediment together with the filter paper into a porcelain crucible with known weight. First ash the filter paper at low temperature, and then burn it in a box electric furnace with a temperature of 800 ~ 850 ℃ for 20 ~ 40min. Take out the crucible and cool it slightly in the air, then put it into a dryer to cool it to room temperature (about 25 ~ 30min), and weigh it

1.4.8 when preparing a batch of aldrin or changing any other reagent, a blank test should be carried out (the test should be carried out according to the test steps in article 1.4 of this standard except that no coal sample is added), and more than 2 samples should be measured at the same time. The difference between the maximum value and the minimum value of barium sulfate should not be greater than 0.0010g, and the arithmetic mean value should be taken as the blank value

1.5 result calculation

1.5.1 the determination result is calculated according to the following formula:

1.6 allowable difference

1.6.1 the maximum allowable difference of total sulfur determination shall not exceed the provisions in Table 1

2 coulometric titration

2.1 key points of the method

the coal sample is burned and decomposed in the purified air flow under the high temperature of not less than 1150 ℃ and the action of catalyst. The generated sulfur dioxide is coulometrically titrated with iodine and bromine produced by electrolysis of potassium iodide and potassium bromide solutions. The electricity consumed by the electrogenerated iodine and bromine is integrated by the Coulomb integrator, and the milligrams of sulfur contained in the deformable viscosity model in the coal sample are displayed

2.2 instruments and reagents

2.2.1 instruments and equipment

the automatic sulfur analyzer based on the principle of coulometric titration includes the following parts:

a. sample sending program controller: the coal sample can move forward and backward according to the specified program

b. high temperature furnace: use silicon carbon tube or silicon carbon rod as heating element, and there is a high temperature zone (11505 ℃) no less than 90mm long. The combustion tube shall be resistant to temperature above 1300 ℃. Platinum Rhodium Platinum thermocouple is used. The burning boat is made of porcelain with temperature resistance above 1300 ℃

c. mixer and electrolytic cell: the rotating speed of the mixer is 500r/min, which is continuously adjustable. The electrolytic cell is about 12cm high, with a capacity of about 400ml, and is equipped with two platinum electrolytic electrodes with an area of 150mm2 and two platinum indicator electrodes with an area of 15mm2. The response time of indicating electrode shall be less than 1s

d. Coulomb integrator: the integral linearity within the range of electrolytic current 0 ~ 350mA should be 0.1%. A digital tube equipped with 5-6 digits displays the milligrams of sulfur or a printer equipped with no less than 5 digits

e. air purification system: about 1500ml/min of air supplied by the pump is purified and dried through a tube containing sodium hydroxide and discolored silica gel

2.2.2 reagent

2.2.2.1 potassium iodide (GB 127277): analytically pure

2.2.2.2 potassium bromide (GB 64977): analytically pure

2.2.2.3 glacial acetic acid (GB 6767678): analytically pure

2.2.2.4 tungsten trioxide: chemically pure

2.2.2.5 color changing silica gel: industrial product

2.2.2.6 sodium hydroxide (GB 62977): chemically pure

2.2.2.7 electrolyte: 5g potassium iodide, 5g potassium bromide, 10ml glacial acetic acid, 250 ~ 300ml distilled water

2.3 test preparation

2.3.1 after connecting the power supply, raise the temperature of the high-temperature furnace to 1150 ℃, and take another set of calibrated Platinum Rhodium Platinum thermocouple pyrometers to measure the position and length of the high-temperature zone in the combustion tube and the position of 600 ℃ pre decomposition

2.3.2 adjust the program controller so that the positions where the pre decomposition and extrusion technology suppliers can decompose at high temperature are at 600 ℃ and 1150 ℃ of the high temperature furnace respectively

2.3.3 fill the combustion tube with 3mm thick aluminum silicate wool, which is located at the rear end of the high temperature zone. Fill the outlet of the combustion tube with clean and dry glass fiber wool

2.3.4 assemble the program controller, high temperature furnace (with built-in combustion tube), Coulomb integrator, agitator, electrolytic cell and air purification system. The glass port to glass port of combustion pipe, piston and electrolytic cell shall be sealed with silicone rubber pipe

2.3.5 start the air supply and extraction pump and adjust the pumping speed to 1000ml/min. Then close the piston between the electrolytic cell and the combustion tube. If the pumping speed drops below 500ml/min, it means that the electrolytic cell, drying tube and other parts are air tight. Otherwise, it is necessary to recheck the electrolytic cell and other components

2.4 test steps

2.4.1 control the furnace temperature at 11505 ℃

2.4.2 adjust the pumping speed of the air pump to 1000ml/min. Under the conditions of gas supply and extraction, pour 250 ~ 300ml electrolyte into the electrolytic cell. After starting the mixer, turn the knob to the automatic electrolysis position

2.4.3 weigh about 0.05g (accurate to 0.0002g) of coal sample with particle size less than 0.2mg in the porcelain boat, and cover a thin layer of tungsten trioxide on the coal sample. Place the boat on the quartz tray for sample delivery, turn on the program controller, the quartz tray will automatically enter the furnace, and the coulometric titration will begin immediately. The integrator displays the milligrams of sulfur or the percentage of sulfur printed by the printer

2.5 allowable difference

the same as 1.6.1

3 high temperature combustion neutralization method

3.1 key points of the method

the coal sample is burned at high temperature in the oxygen flow, so that all forms of sulfur in the coal are oxidized and decomposed into sulfur oxides, and then captured in the hydrogen peroxide solution to form a sulfuric acid solution. Drip it with sodium hydroxide solution to calculate the total sulfur content in the coal sample

3.2 instruments, materials and reagents

3.2.1 instruments and materials

3.2.1.1 high temperature furnace: it is required that the furnace temperature can maintain a high temperature zone of 80 ~ 100mm long (12005 ℃). The pyrometer should be calibrated in advance

3.2.1.2 combustion tube: temperature resistance above 1300 ℃. The total length of the pipe is about 750mm. The outer diameter of one end is 22mm, the inner diameter is 19mm, and the length is about 690mm. The outer diameter of the other end is 10mm, the inner diameter is about 7mm, and the length is about 60mm

3.2.1.3 burning boat: made of high-temperature porcelain or corundum, 77mm long, 12mm wide on the top and 8mm high

3.2.1.4 thermocouple: Platinum Rhodium Platinum thermocouple

3.2.1.5 nickel chromium wire push rod: the nickel chromium wire with a diameter of about 2mm and a length of about 650mm is rolled into a spiral shape at one end to form a circular pad with a diameter of about 10mm, which is used to propel the combustion boat

3.2.1.6 nickel chromium wire hook: nickel chromium wire with a diameter of about 2mm and a length of about 650mm, bend one end into a small hook for taking out the combustion boat

3.2.1.7 silicone rubber tube: the outer diameter is 11mm, the inner diameter is 8mm, and the length is about 30mm. It is connected to the fine diameter end of the combustion tube as a connection to the absorption system

3.2.1.8 T-shaped glass tube: install a No. 3 rubber stopper on the horizontal end of the T-shaped tube as a closed combustion tube. A rubber turning cap is installed on the other end in the horizontal direction, and the rubber turning cap passes through a small hole so that the nickel chromium wire push rod can pass through the small hole and pass through the horizontal direction of the T-shaped tube. The rubber tube is connected to the vertical direction of the T-shaped tube for oxygen

3.2.1.9 flowmeter: it can measure the oxygen flow of more than 350ml per minute

3.2.1.10 absorption bottle: 250ml or 300ml conical bottle

3.2.1.11 gas filter: glass fused plate sintered from glass sand. The model of fused plate G1 ~ G3 is connected to one end of the air outlet of the absorption bottle

3.2.1.12 drying tower: 250ml, containing 3 alkali asbestos and 3 calcium chloride

2 1

3.2.1.13 gas storage barrel: capacity 30 ~ 50L

3.2.1.14 acid burette: 25ml and 10ml

3.2.1.15 alkali burette: 25ml and 10ml

3.2.2 reagent

3.2.2.1 oxygen

3.2.2.2 hydrogen peroxide (Hg 77): analytical purity, concentration 30%

3.2.2.3 alkali asbestos: granular (grade III)

3.2.2.4 tungsten trioxide; Chemically pure

3.2.2.5 mixing indicator: 0.125 g of methyl red (Hg 76) is dissolved in 100ml of ethanol, 0.083 g of methylene blue (Hgb 339460) is dissolved in 100ml of ethanol, stored in brown bottles respectively, and mixed according to the same volume before use

3.2.2.6 sodium hydroxide: 0.03mol/l solution

preparation of sodium hydroxide solution: weigh 6G of high-grade pure sodium hydroxide (GB 62977), dissolve it in 5000ML of distilled water cooled after boiling, mix it evenly, put it into a bottle, and plug it tightly with a rubber stopper. Weigh about 0.2g standard coal sample (accurate to 0.0002g), put it in the combustion boat, and then cover it with a thin layer of tungsten trioxide catalyst. Then carry out the test according to the test steps in Clause 3.4, and finally record the dosage of sodium hydroxide solution during titration. The titration degree of sodium hydroxide solution (grams/ml of sulfur) is calculated by formula (3):

3.2.2.7 hydroxy mercuric cyanide solution: weigh about 6.5g of hydroxy mercuric cyanide, dissolve it in 500ml distilled water, fully stir it, place it for a moment, filter it, add 2-3 drops of mixed indicator to the filtrate, neutralize it to neutral with dilute sulfuric acid solution, and store it in a brown bottle. This solution should be used within a week

3.3 test preparation

3.3.1 the instrument and equipment include three main parts, namely, the oxygen purification system, the combustion device and the mouth of oxidation products (dioxygen and guaranteed cost and minimum)