3.4.4 Open the rubber stopper of the absorption bottle and clean the gas filter 2-3 times with distilled water. Use ear wash balls to pressurize, otherwise the washing solution is not easy to flow out. Add 3-4 drops of mixed indicator to each absorption bottle and titrate with sodium hydroxide solution. The solution changes from peach red to steel gray, which is the endpoint of titration. Record the amount of sodium hydroxide solution used.

3.4.5 Blank test

Load a thin layer of tungsten trioxide (without coal sample) into the combustion boat and measure the blank value according to the above test steps.

3.5 Result Calculation

3.5.1 Calculate the measurement results according to equation (4):

(4)

Table 2

In the formula, SfQ - total sulfur content in the analyzed coal sample,%;

V1- The amount of sodium hydroxide solution used for coal sample determination, mL;

V0- The amount of sodium hydroxide solution used in blank determination, mL;

D - Titration of sodium hydroxide solution, mass concentration of sulfur, g/mL;

G - Coal sample weight, g.

3.6 Tolerance

3.6.1 The allowable deviation for total sulfur determination shall not exceed the provisions in Table 2.

Note: If the titration method of sodium hydroxide solution is not used in the experiment, sulfuric acid and sodium hydroxide standard solutions need to be prepared and calibrated. The final result should be multiplied or divided by a coefficient, that is, if SfQ<1%, the result should be divided by 1.05; If SfQ>4%, multiply the result by 1.05; SfQ=1% to 4%, the result remains unchanged.

a. Preparation and calibration of sulfuric acid standard solution: Take 4mL of high-grade pure sulfuric acid (GB 625-77), slowly add it to distilled water, and dilute to 5000mL. Accurately weigh approximately 0.1g portions of high-grade pure anhydrous sodium carbonate that has been pre baked to constant weight at 130 ℃, and place them in 300mL beakers. Dissolve in about 100mL of distilled water, then add 3-4 drops of mixed indicator and titrate with sulfuric acid prepared above until the solution turns steel gray. Boil this solution for 5 minutes, remove carbon dioxide, cool it, and when the solution turns green again, continue to titrate with the sulfuric acid solution prepared above until the solution turns steel gray. Record the amount of sulfuric acid used to calculate the standard concentration of the sulfuric acid solution.

b. Preparation and calibration of sodium hydroxide standard solution: Weigh 6g of high-grade pure sodium hydroxide (GB 629-77), dissolve it in 5000mL of distilled water that has been boiled and cooled, mix well, put it into a bottle, and cover it tightly with a rubber stopper.

Accurately measure several portions of 20mL sodium hydroxide solution using a pipette, place them in a 300mL beaker, dilute with boiled distilled water to a volume of about 100mL, add 3-4 drops of mixed indicator, then titrate with sulfuric acid standard solution until the solution turns steel gray, boil the solution to remove possible carbon dioxide, and continue titrating until it reaches steel gray, which is the endpoint of titration. Record the amount of sulfuric acid solution used. The concentration of sodium hydroxide solution is calculated according to equation (5):

? (5)

c. Calculate the measurement results according to equation (6):

(6)

In the formula, SfQ - total sulfur content in coal sample,%;

V - The amount of sodium hydroxide solution used for coal sample determination, mL;

V0- The amount of sodium hydroxide solution used in blank determination, mL;

N - Equivalent concentration (mass concentration) of sodium hydroxide solution;

0.016- grams of sulfur per milligram equivalent (12 millimoles);

G - Coal sample weight, g.

② The calibration method for chlorine in coal: Generally, the chlorine content in raw coal is very low and may not be calibrated. However, for raw coal with chlorine content higher than 0.02% and clean coal with zinc chloride ash reduction, chlorine calibration should be carried out according to the following methods:

Add 10mL of hydroxymercuric cyanide solution to the solution titrated to the endpoint of sodium hydroxide standard solution to cause a displacement reaction between chloride ions and hydroxymercuric cyanide, resulting in the solution becoming alkaline and appearing green. Use sulfuric acid standard solution for reverse titration, record the amount of sulfuric acid solution, and calculate the total sulfur result according to equations (7) and (8):

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX?????????????????? (7)

Or object (8)

In the formula, SfQ - total sulfur content in the analyzed coal sample,%;

N1- the equivalent concentration of sodium hydroxide solution;

V1- amount of sodium hydroxide solution used for coal sample determination, mL;

V10- Amount of sodium hydroxide solution used for blank determination, mL;

N2- equivalent concentration of sulfuric acid;

V2- Amount of sulfuric acid, mL;

D - Titration of sodium hydroxide solution, grams of sulfur per milliliter;

0.016- grams of sulfur per milligram equivalent;

G - Coal sample weight, g.

_____________________?

Additional notes: