Factors affecting the thermal efficiency of heating furnace and improvement measures

Exhaust temperature

From the overall operation of the furnace, the greatest heat loss of the furnace is taken away by the exhaust smoke. If the smoke temperature is reduced, the heat released by the smoke can be effectively reduced, so as to improve the heat efficiency of the furnace. The waste heat recovery system of the device is now equipped with an acoustic ash cleaner. In daily operation, the air preheater is used for the acoustic ash blowing of heat pipe to reduce the ash and scale accumulation of heat pipe and convection pipe and improve the efficiency of the preheater, but the effect on reducing the exhaust temperature is not obvious. During the maintenance shutdown in 2019, in addition to the transformation of the heating furnace burner, the heat pipe of the heating furnace waste heat recovery air preheater will be replaced. After the normal operation of the furnace, the exhaust temperature is 162.9℃, which exceeds the 140℃ specified in the Furnace Pipe Rules. The heat loss of the furnace is calculated as 3068KJ/kg fuel. The main reason for the analysis may be that the baffle of the flue gas direct-discharge duct of the furnace may not be closed properly, and part of the flue gas is pumped back into the air preheater again, resulting in the mismatch of smoke and air volume. According to the actual situation on site, it is planned to remove the original heat pipe preheater and replace a new air preheater at the place where the original heat pipe preheater is to reduce the exhaust temperature of the heating furnace to 110℃. In addition, the natural ventilation burner of F202 in the heating furnace waste heat recovery system is replaced with a forced ventilation burner, and the annular air duct and auxiliary air duct, fast-opening air door and baffle valve are added. The combustion-supporting air entering F202 furnace is introduced into the air preheater and then sent to F202 furnace after preheating. After the modification, the thermal efficiency of the furnace is expected to increase from 90.8% to 92.8%.

Oxygen content

The oxygen content of flue gas directly affects the thermal efficiency and safe and stable operation of heating furnace. The flue gas oxygen content is high, the thermal efficiency is low, the furnace tube is easy to oxidize; The low oxygen content of flue gas makes it easy to cause incomplete combustion. During the thermal efficiency test of the furnace, the oxygen content on-line instrument display data of the furnace are all greater than the oxygen content data of the flue gas inlet of the air preheater, the oxygen content instrument may be installed in an unreasonable position or the test is not accurate. The content of oxygen in flue gas is the main parameter that affects the combustion effect of heating furnace. The inaccurate determination of oxygen content is easy to cause insufficient fuel gas combustion, increase the loss of incomplete combustion, and decrease the thermal efficiency of heating furnace.

Operation management

Improve the operating efficiency of the automatic control system of the heating furnace, strengthen the stable control of various parameters such as the total volume, branch flow and temperature inside the heating furnace, and improve the operating efficiency of the heating furnace. There is one induced draft fan in the hydrogenation unit. Under the current practical situation, the opening degree of the flue damper of three reheating furnaces is optimized, the inlet temperature of the air preheater is controlled well, the service life of the air preheater is improved, and the exhaust temperature of the reheating furnace is reduced. In addition, operators should be regularly trained and tested to improve their operational skills and theoretical level, improve operators' understanding of the field heating furnace system, and enhance their operation guarantee technology.