The design of the aggregate drying and heating system of the asphalt mixing station is the core of the heating system design of the whole mixing station. We calculated the thermal engineering analysis and calculation by calculating the relationship between the water content of the aggregate, the air excess coefficient, and the relationship between the exhaust gas temperature and the fuel consumption rate. The design of the heating system successfully developed the research and development of the field heat regeneration equipment.
1 Overview
Heat composition during drying and heating of asphalt mixing plant
1.11 burners must ensure that the fuel (diesel or heavy oil) is fully combusted, that is, the amount of air must be rich - that is, the air excess factor must be greater than 1, and the excess air needs due to the negative pressure at the end of the drying cylinder and the leaking of the seal. Consumes a certain amount of heat.
1.22 The heat loss of the outer wall of the drying cylinder, such as the outer wall of the drying cylinder, has a thermal insulation layer, and the heat loss is relatively small. This analysis does not consider this part of the heat loss.
1.33 Flue gas emissions should take away heat
1.44 The heat required for the drying and heating of the aggregate, including the heat required for the aggregate to be heated from the normal temperature to the required temperature and the moisture in the aggregate is heated and vaporized.
1.5 This paper analyzes the relationship between aggregate moisture content, air excess coefficient and exhaust gas discharge temperature and fuel consumption rate through thermal engineering calculation.
2 burner combustion temperature calculation
2.1 Theoretical combustion temperature, which can be calculated as follows:
(°C)(1)
Where: Qd - fuel calorific value, taking heavy oil as an example, Qd = 40892.5 (kJ / kg)
Q1—Physical heat brought into the fuel Qd=C1M1T1 (kJ/kg)
Q2—Physical heat brought in by combustion air (kJ/kg)
Cm—specific heat of the flue gas at theoretical temperature (kJ/Nm3.K)
Vy—the amount of flue gas (Nm3/kg), which can be calculated by Vy=10.8×α+0.58 for heavy oil combustion.
—-air excess coefficient
C1—heavy oil specific heat (kJ/kg.K); M1—heavy oil quality (kg); T1—heavy oil temperature (°C)
Ck-air specific heat (kJ/Nm3.K); Vk-air quantity (Nm3/kg)
Burning heavy oil = 10.8 × α; T1 - air temperature, 20 ° C.
2.2 actual combustion temperature t = ηtm (°C) (2)
Where: η - furnace temperature coefficient, take 0.8.
2.3 cases: such as α = 1.3, heavy oil temperature T1 = 125 ° C, heavy oil specific heat C1 = 2.093 (kJ / kg. K),
The average specific heat Ck=1.302 (kJ/Nm3.K) at an air temperature of 20 °C,
Take Cm=1.604 (kJ/Nm3.K)
Then the theoretical combustion temperature tm = 1771 ° C, the actual temperature t = 0.8 × 1771 = 1416 ° C
3 drying cylinder exhaust emissions and specific heat calculation
3.1 Total exhaust emissions U=Uy+Us(Nm3/h)(3)
Where: Uy—the amount of smoke emitted (Nm3/h),
Us—the amount of water vapor discharged (Nm3/h),
M—cold aggregate flow rate (t/h), δ—cold aggregate moisture content, q—fuel consumption per ton of hot aggregate (kg/t),
Γs—steam specific gravity 0.804 (kg/m3)
1 Overview
Heat composition during drying and heating of asphalt mixing plant
1.11 burners must ensure that the fuel (diesel or heavy oil) is fully combusted, that is, the amount of air must be rich - that is, the air excess factor must be greater than 1, and the excess air needs due to the negative pressure at the end of the drying cylinder and the leaking of the seal. Consumes a certain amount of heat.
1.22 The heat loss of the outer wall of the drying cylinder, such as the outer wall of the drying cylinder, has a thermal insulation layer, and the heat loss is relatively small. This analysis does not consider this part of the heat loss.
1.33 Flue gas emissions should take away heat
1.44 The heat required for the drying and heating of the aggregate, including the heat required for the aggregate to be heated from the normal temperature to the required temperature and the moisture in the aggregate is heated and vaporized.
1.5 This paper analyzes the relationship between aggregate moisture content, air excess coefficient and exhaust gas discharge temperature and fuel consumption rate through thermal engineering calculation.
2 burner combustion temperature calculation
2.1 Theoretical combustion temperature, which can be calculated as follows:
(°C)(1)
Where: Qd - fuel calorific value, taking heavy oil as an example, Qd = 40892.5 (kJ / kg)
Q1—Physical heat brought into the fuel Qd=C1M1T1 (kJ/kg)
Q2—Physical heat brought in by combustion air (kJ/kg)
Cm—specific heat of the flue gas at theoretical temperature (kJ/Nm3.K)
Vy—the amount of flue gas (Nm3/kg), which can be calculated by Vy=10.8×α+0.58 for heavy oil combustion.
—-air excess coefficient
C1—heavy oil specific heat (kJ/kg.K); M1—heavy oil quality (kg); T1—heavy oil temperature (°C)
Ck-air specific heat (kJ/Nm3.K); Vk-air quantity (Nm3/kg)
Burning heavy oil = 10.8 × α; T1 - air temperature, 20 ° C.
2.2 actual combustion temperature t = ηtm (°C) (2)
Where: η - furnace temperature coefficient, take 0.8.
2.3 cases: such as α = 1.3, heavy oil temperature T1 = 125 ° C, heavy oil specific heat C1 = 2.093 (kJ / kg. K),
The average specific heat Ck=1.302 (kJ/Nm3.K) at an air temperature of 20 °C,
Take Cm=1.604 (kJ/Nm3.K)
Then the theoretical combustion temperature tm = 1771 ° C, the actual temperature t = 0.8 × 1771 = 1416 ° C
3 drying cylinder exhaust emissions and specific heat calculation
3.1 Total exhaust emissions U=Uy+Us(Nm3/h)(3)
Where: Uy—the amount of smoke emitted (Nm3/h),
Us—the amount of water vapor discharged (Nm3/h),
M—cold aggregate flow rate (t/h), δ—cold aggregate moisture content, q—fuel consumption per ton of hot aggregate (kg/t),
Γs—steam specific gravity 0.804 (kg/m3)
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