Delayed coking unit heating furnaceThe delayed coking unit heating furnace is a tubular heating furnace. In order to make the device run more reasonably and achieve the best economic benefits, the device is partially transformed and upgraded, and the thermal efficiency of the heating furnace is improved by increasing the heating area of the oil phase, improving the heat exchange coefficient, reducing the air leakage volume, reducing the exhaust gas temperature and other transformation measures, so as to achieve a good purpose of energy saving and consumption reduction, saving costs and increasing revenues.
The delayed coking unit heating furnace is a tubular heating furnace, and the fuel used is refinery gas. The transformation design scheme of the heating furnace is to increase the operating load of the heating furnace as much as possible by changing the arrangement of the radiant coil and the convection coil under the premise of not making great changes to the furnace equipment body, so as to meet the requirements of the large-load production operation of the device. At the same time, the problems that seriously affect the thermal efficiency of the coking heating furnace, such as the main flue baffle of the heating furnace is stuck, the heat dissipation loss on the surface of the furnace is large, the burner flame is easy to lick the furnace tube, and the furnace leaks air, so as to improve the thermal efficiency of the coking furnace and dig deep into the energy-saving potential of the coking device.
Furnace operation problems and analysisDue to the increased processing load, the furnace is at the upper limit of the operating load and is therefore a major bottle diameter to increase the processing capacity of the unit.
1.Convection section: There are unreasonable points in the original design of the steam section pipe, resulting in excessive steam load and low process medium load; At the same time, there is more dust accumulation outside the tube, and the thermal resistance is large, which affects the heat exchange effect. Radiation section: The calculated heat load of the original design shielding section is too large, resulting in the reduction of the heat load of the radiation section, resulting in a small average thermal intensity of the radiant tube design. In the actual production process, in order to make the furnace outlet temperature reach 500, the actual heat load of the furnace tube must exceed the design load, especially the surface thermal strength of the 4 10th furnace tube from the bottom up is very high, resulting in the fast coking speed of the furnace tube, and the oxidation and skin explosion of the outer wall of the furnace tube are serious, which affects the long-term operation of the device.
2.The heat dissipation loss of the furnace body is large, and the air leakage volume is large: the temperature of the wall outside the convection chamber and radiation room is high, and the local temperature reaches 110; There are a total of 80 fire doors on the side wall of the radiation room, which has a large amount of heat dissipation and air leakage; With the change of temperature, the sealing baffle of the main flue of the heating furnace deforms and freezes the rotating shaft, which is in a fully open state for a long time, resulting in a large heat loss of flue gas.
3.There are potential safety hazards in the burner: the structure of the burner is that there is one permanent lamp nozzle in the center, two main rows of three combustion nozzles on both sides, and the air distribution comes from the bottom of the burner. When the air distribution of the main burner is large, it is easy to cause the flame to be too high or automatically extinguished, and if the air distribution is small, the flame will float and it is easy to lick the furnace tube. During the combustion process, the fuel gas of the main combustion nozzles on both sides and the air distribution at the bottom form a negative pressure area in the center where the ever-bright lamp is located, and the ever-bright lamp is often extinguished.
4.Corrosion intensification at low temperatures: In the past few years, the refinery has increased the depth of heavy quality and treatment, and the sulfur content of the refinery gas and the fuel consumption itself have increased, resulting in the rising sulfur dioxide and sulfur trioxide levels in the flue gas. The sulfur content of the flue gas causes corrosion at low temperatures.
Retrofit processing analysis1.Process change: The superheated steam pipe in the convection chamber is changed from 4 rows to 2 rows, and the lower 2 rows (4 in total) are replaced with oil pipes. Add 2 tubing to the top of the radiation chamber. By reducing the number of steam coils, increasing the heating area of the process medium, reducing the thermal intensity of the radiant furnace tubes, optimizing the operation of the furnace with minimal changes to the furnace, and extending the operation cycle of the furnace under the condition of stable operation of the unit. On the one hand, it reduces the superheat of steam, on the other hand, it increases the heating area of the oil and reduces the thermal strength of the surface of the furnace tube. The addition of 28 sonic sootblowers reduced the deposition of flue gas dust and improved the heat transfer coefficient. The heat transfer coefficient increases, and the thermal efficiency of the furnace increases. Superheated steam vents the low point of the pipeline to increase drainage and drainage to prevent water hammer caused by steam with water, resulting in damage to the pipeline, and avoid water evaporation to absorb the heat of the convection chamber and cause energy waste.
2.Furnace wall lining replacement: The upper part of the side wall, end wall and top of the radiation chamber are all replaced with 220mm thick high-alumina ceramic fiber module composite lining, and the lower part of the side wall is 2500mm. The height is backed by heat-insulating refractory castables and ceramic fiberboard B-12 and B-14, and the fire-facing surface is high-alumina refractory bricks. The surface of the radiation chamber lining is sprayed with high-temperature radiation paint. Reduce heat loss and improve thermal efficiency. The number of fire doors has been reduced from 72 to 8, and the manhole and explosion-proof doors have been updated. By reducing the opening area, the amount of air leakage is reduced, and the heat loss is reduced. Replace the main flue baffle, adopt external support bearing, electro-hydraulic valve form, and it is not easy to jam.
3.Burner replacement: changed from bottom firing to side firing, the position has not changed, the heat is reflected through the furnace wall, but the top hole of the burner is facing the furnace wall. Prevent flames from adding to the furnace tube and prevent the furnace tube from coking.
4.Replace the air preheater: improve the corrosion resistance of the equipment through material upgrades. Regularly measure the corrosion temperature of the heating furnace flue gas, select the appropriate exhaust gas temperature, and reduce the equipment corrosion caused by the preheater. Increase the air heat exchange area and improve the thermal efficiency of the heating furnace.
Energy-saving transformation effect of coking furnaceCombined with the actual observation on site, the effect of the furnace after the transformation is better than before the transformation, and the thermal efficiency is increased from the original 90% to 91%, which mainly achieves the following good results:
1.Heating furnace convection chamber 1The temperature of 0MPa superheated steam is 330 350, which is lower than before the transformation. The convection flue gas temperature of the coking furnace is 340 360, and the flue gas outlet temperature of the convection chamber reaches about 400 before the transformation, which has decreased significantly. The results show that the heat extraction effect of the convection chamber is significantly improved. The maximum temperature of the surface of the furnace tube and the furnace chamber is greatly reduced, indicating that the surface thermal strength of the furnace tube is greatly reduced, and the adjustment of the process makes the heat load distribution of the convection chamber and the radiation chamber more reasonable. The sootblower runs regularly and is in good condition.
2.The maximum temperature of the outer wall of the tube box on the east and west sides of the convection chamber furnace decreased from 110 to 55 before the transformation, and the temperature of the outer wall of the radiant chamber also decreased from 60 80 to 40 50 before the transformation, indicating that the insulation effect of the new lining of the radiant chamber was good. The new main flue baffle switch is in good action, and there is no jamming, which reduces the heat loss of flue gas.
3.The new burner is in good use.
Problems after the renovation of the heating furnace1.The sampling and analysis results of the oxygen content of the exhaust flue gas are 2 times higher than that of the ** analyzer instrumentMore than 5%, it is necessary to calibrate the instrument to control the actual oxygen content of the flue gas in the range of 2 4%.
2.The calculated thermal efficiency of the furnace is lower than the design value for two main reasons:
2.1. After the transformation, the heat exchange effect of the air preheater does not reach the design index, and the exhaust gas temperature is high.
2.2. After the transformation, the coking processing capacity did not reach the design value of 1.3 million tons per year, and the self-produced steam volume was also lower than the design 84t h, only 2-4t h, resulting in a decrease in the thermal efficiency of the convection chamber and an increase in the exhaust gas temperature.
3.The small flue baffle on the west side of the north road of the coking furnace is Kaser, which cannot be automatically adjusted normally.