GB/T 39836-2021Test methods for slagging indexes in coal combustion (English PDF)

4.1 Method summary

The one-dimensional furnace carries pulverized coal with a certain amount of air flow during the test. After entering the hearth, it will catch fire and burn when the furnace wall emits heat, so that it burns out. One-dimensional furnace can realize the suspension combustion test of pulverized coal and air under dynamic conditions. The burning pulverized coal flow moves downwards along the height of the hearth. Use silicon carbide rods as slagging probes to sample when pulverized coal is burned in one-dimensional furnace. Then use a blade to cut the slag sample on the surface of the silicon carbide rod to determine the slag type. Calculate corresponding slag type assignment to obtain the probe slagging index.

4.2 Test devices

The schematic diagram of the one-dimensional furnace test device is shown in

Figure 1. The one-dimensional furnace test bench is mainly composed of powder feeding system, heating and temperature control system, combustion furnace body system, air smoke system and sampling analysis system. The one-dimensional furnace body adopts a vertically arranged electric heating building block structure. It is mainly composed of ignition section, stable combustion section and burnout section. Connect the powder feeder to the ignition section. The end of the burnout section is connected to the flue gas cooler, followed by dust collector and induced draft fan. Ash trough is at the bottom of the furnace body, used to collect the ash residue from the combustion of pulverized coal airflow. The outside of the furnace is covered with refractory and thermal insulation materials to ensure that the temperature of the outer wall of the furnace is <=60°C. The residence time of pulverized coal particles in the furnace is controlled at 2s~10s. It can meet the burning-out requirements of pulverized coal particles in the furnace. The air leakage rate of the whole one-dimensional furnace test device (that is, the percentage of the leaked air mass in the flue gas mass at the inlet of the device) is controlled within 5%.

The pulverized coal burner is installed on the top of the hearth. The primary air carries pulverized coal into the top of the hearth. The secondary air is arranged around the primary air and fed from the top of the hearth. The flow of primary air and secondary air can be measured and controlled by flow meter. Use hot air to send powder. The air preheater can adjust the temperature of the hot air Where, n - Pulverized coal uniformity coefficient (take n=1); Vdaf - Dry ash-free volatile matter of pulverized coal, %.

4.4.1.3 Requirements for deviation of pulverized coal fineness

The deviation of pulverized coal fineness is calculated according to formula (4):

R90 allowable deviation increases with the increase of Vdaf: When Vdaf is less than 15%, deltaR90=1~2; when Vdaf=15%~25%, deltaR90=2~3; when Vdaf is greater than 25%, deltaR90=3~4.

4.4.2 Test preparation

According to the specified conditions of test conditions in GB/T 39833, preheat each section of the furnace body to the set temperature. Start the induced draft fan and the blower one after another. Adjust hot air temperature and excess air coefficient. Start the power feeder to adjust the amount of pulverized coal. After the furnace temperature and flue gas composition of the pulverized coal combustion in the one-dimensional furnace are stabilized, according to the ignition position of the test coal, insert six silicon carbide slagging rods (probes) into the selected measuring hole along the flame stroke. Make each slagging rod at the initial stage of ignition, the highest flame temperature, the median temperature and the furnace outlet.

4.4.3 Probe sampling

Maintain the stable operating conditions of the pulverized coal combustion of the one-dimensional furnace. Wait for a sufficient amount of ash and slag layer to deposit on the slagging probe. The continuous slagging time of the probe sampling is determined by the ash content of the coal. Generally, it is 20min~30min.

4.4.4 Observation of slag type

After the test, pull out the slagging probe carefully. Keep it as it is. After cooling, use a blade to scrape the slag sample on the surface of the silicon carbide rod. Observe and record its slag type characteristics.

4.5 Data processing and calculation methods

theta - Characteristic temperature value corresponding to slag type, in Celsius (°C).

5.1 Method summary

According to the percentage of each component of coal ash (expressed as oxide), calculate the individual slagging index of coal: mass ratio of SiO2 to Al2O3 (SiO2/Al2O3), mass ratio of SiO2 in coal ash (G) and base/acid ratio (B/A).

Comprehend the softening temperature (ST) and mass ratio of SiO2 to Al2O3, mass ratio of SiO2 in coal ash and base/acid ratio. Conduct weighted calculation of comprehensive slagging index of coal (R) to judge its slagging characteristics.

The determination of softening temperature (ST) and precision is carried out according to GB/T 219. The components of coal ash (expressed as oxides): the content determination of SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O and TiO2 and precision are implemented in accordance with GB/T 1574.

5.2 Data processing and calculation methods

Comprehend the softening temperature and mass ratio of SiO2 to Al2O3, mass ratio of SiO2 in coal ash and base/acid ratio. According to empirical coefficient weighted average method of formula (6), calculate the comprehensive slagging index (R): Where, R - Comprehensive slagging index; B/A - Base/acid ratio of coal ash;

SiO2/Al2O3 - Mass ratio of SiO2 to Al2O3 of coal ash; ST - Softening temperature of coal ash, in Celsius (°C); G - Mass ratio of SiO2 in coal ash.

NOTE: Method R is based on the weighted average method of empirical coefficients obtained from the statistics of a large number of coal samples of China's 300MW~600MW units.