Determination method of coal coke total sulfur instrument

In a 1250 ° C tube furnace, coke is burned and decomposed in the air stream under the action of a catalyst, and sulfur in the coke forms sulfur oxides. Sulfur dioxide is absorbed by the potassium iodide solution, and the iodine produced by electrolysis of potassium iodide solution is titrated. The total sulfur content in coke/coal is calculated according to the electricity consumed by electrolysis.

Coke total sulfur testing equipment consists of:

High-temperature tube furnace: heated with a silicon carbide rod or silicon carbon tube, with a temperature control device, so that the furnace temperature can be maintained within the range of 1250 ° C ± 10 ° C.

Combustion tube: made of high-temperature porcelain, corundum or quartz, with a total length of about 750mm, an outer diameter of 22mm at one end, an inner diameter of 19mm, a length of about 690mm, and an outer diameter of 10mm at the other end, an inner diameter of about 7mm, and a length of about 60mm.

Burning boat: made of high temperature porcelain or corundum, with a length of 77mm, an upper width of 12mm, a lower width of 9mm, and a height of 8mm.

Absorbent flask: conical flask, volume 250mL.

Nickel-chrome wire hook: about 2mm in diameter, 650mm in length, with one end bent into a small hook.

Silicone rubber tube: outer diameter 11mm, inner diameter 8mm, length about 80mm.

Reagents and materials required for coke total sulfur testing equipment:

Tungsten trioxide HG 10-1129

Color changing silicone HG /T 2765.4 industrial products

Sodium hydroxide GB/T629 Chemically pure

electrolyte

The configuration of electrolyte in the use of coke total sulfur instrument:

Weigh 5.0g each of potassium iodide GB/T1272 and potassium bromide GB/T649, dissolve in 250-300ml of water and add glacial acetic acid GB/T676 10ML to the solution

Burning boat: plain porcelain or corundum products, with a sample length of 60mm and a temperature resistance of more than 1200 ° C.

The composition of the automatic sulfur determination instrument of the coke sulfur determination device:

High-temperature furnace: can be heated to above 1200 ° C, and has a high-temperature constant temperature zone of at least 70mm long (1150 ± 10) ° C, with a platinum-rhodium-platinum thermocouple temperature measurement and temperature control device, and the furnace is equipped with a reducer combustion tube with a temperature resistance of more than 1300 ° C.

Electrolytic cell and electromagnetic stirrer: The electrolytic cell is (120~ 180) mm high and has a capacity of not less than 400mL. There are platinum electrolytic electrode pairs with an area of about 150mm and platinum indicator electrode pairs with an area of about 15mm. The indicator electrode response time should be less than 1s, and the electromagnetic stirrer speed should be about 500r/min and continuously adjustable

Coulomb integrator: The integration linearity error should be less than 0.1% within the range of electrolytic current (0-350) mA, and it is equipped with a (4-6) digit digital display or printer.

The sample feeding program controller can move forward and backward flexibly according to the prescribed program.

The air supply and purification device consists of an electromagnetic pump and a purification tube. The air supply volume is about 1500mL/min, the air extraction volume is about 1000mL/min, and the purification tube is filled with sodium hydroxide and color-changing silica gel.

Determination method of coke total sulfur: 

Test preparation:

The tube type high temperature furnace was heated to 1150 ℃, and the position, length and position of the high temperature zone in the combustion tube were measured by another set of platinum germanium-platinum thermocouple pyrometers.

Adjust the sample feeding program controller so that the pre-decomposition and pyrolysis positions of the coal samples are at 500 ℃ and 1150 ℃, respectively.

Fill the outlet of the combustion tube with washed and dried glass fiber wool; fill the aluminum silicate cotton with a thickness of about 3 mm at about (80-100) mm from the outlet end.

The program controller, tubular high temperature furnace, Coulomb integrator, electrolytic cell, electromagnetic stirrer and air supply and purification device are assembled together. The connection between the combustion tube, piston and electrolytic cell should be mouth-to-mouth and sealed with silicone rubber tube.

Start the pumping and air supply pumps, adjust the pumping flow to 1000 mL/min, and then close the piston between the electrolytic cell and the combustion tube. If the pumping volume can be reduced to less than 300 mL/min, it proves that the components and interfaces of the instrument are airtight and can be measured. Otherwise, check the components and interfaces of the instrument.

Instrument calibration:

Calibration method: Use certified coal reference material and calibrate the automatic sulfur meter according to one of the following methods.

Multi-point calibration method: calibrate with at least three certified coal reference materials whose sulfur content can cover the sulfur content range of the tested sample;

Single-point calibration method: calibrate with a reference material similar to the sulfur content of the tested sample.

Calibration procedure: according to GB/T 212 determination of coal standard material air drying base moisture, calculate its air drying base total sulfur S.. standard value.

According to the above steps, the sulfur content of the coal reference material is measured with the calibrated instrument. Each reference material is measured at least 3 times, and the average value of the three measurements is the sulfur measurement value of the coal reference material.

The sulfur measurement value of the coal reference material and the air drying base standard value are input to a sulfur meter (or automatically read by the instrument) to generate a correction coefficient.

Notes: Some instruments may require manual calculation of the correction factor before entering the instrument.

calibration validity verification

In addition, (1 to 2) coal reference materials or other control samples were selected and calibrated with a sulfur detector.

Determination of its total sulfur GBT 214-2007 Determination method of total sulfur in coal; GBT 2286-2008 Determination method of total sulfur content in coke; SNT 1083.3-2002 Determination instrument method of sulfur content in coke - coulometric titration. If the difference between the measured value and the standard value (control value) is within the uncertainty range (control limit) of the standard value (control value), the calibration is valid, otherwise the reason should be found and re-calibrated.

Determination steps of coke total sulfur: 

The tubular high temperature furnace was heated and controlled at (1150 ± 10) ° C.

Start the air supply pump and suction pump and adjust the pumping flow to 1000mL/min. Under pumping, add the electrolyte to the electrolytic cell and start the electromagnetic stirrer.

Put a small amount of coal samples for non-determination in the porcelain boat,

Perform the endpoint potential adjustment test as described above. If the displayed value of the Coulomb integrator is 0 after the test, it should be measured again until the displayed value is not 0.

Weigh an air-dried coal sample (0.05 ± 0.005) g (calibrated to 0.0001g) with a particle size of less than 02mm in a porcelain boat, and cover the coal sample with a thin layer of tungsten trioxide. Place the porcelain boat on the quartz tray for sample feeding, turn on the sample feeding program controller, and the coal sample is automatically fed into the furnace. Coulomb titration begins immediately. After the test, the Coulomb integrator shows the milligram number or mass fraction of sulfur, or is printed by the printer. Calibration Check

During the measurement of the instrument, the stability of the sulfur detector and the validity of the calibration should be checked regularly (after every 10 to 15 measurements) using coal reference materials or other control samples. If the measured value of coal reference materials or other control samples exceeds the uncertainty range of the standard value (control limit), the instrument should be re-calibrated according to the above steps, and the samples since the last inspection should be re-measured.

 Result calculation

When the Coulomb integrator finally shows the number of milligrams of sulfur,

The mass fraction of total sulfur is calculated according to formula (2)

 St,ad=m1/m *100

In the formula:

 St, ad--total sulfur mass fraction in general analytical coal samples,%;

M1 - Coulomb integrator display value in milligrams (mg);

M---Coal sample quality, in milligrams (mg)