Operation of the reboiler in the fractionation tower
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The heat load of the reboiler is 7,000 kW. After being pumped out from the bottom of the distillation column through the reboiler pump, the fluid passes through a heat exchanger; the designed temperature at the inlet to the reboiler after heat exchange is 318°C, while the temperature at the outlet of the reboiler is 308°C. Why is it designed this way? The furnace is currently operating normally, but the flue damper opening is less than 10%; the negative pressure is too low (with a higher absolute value), and the oxygen level is too high. Adjusting the frequency of the blower helps to reduce the oxygen level, but this results in even lower negative pressure. Additionally, the exhaust gas temperature is very high, resulting in low thermal efficiency. How should this be adjusted?
Check whether the opening of your flue dampers is correct, and whether the opening of the exhaust fan is too large
The frequency of the blower was reduced by 7%, which caused a slight decrease in oxygen levels. The opening degree of the flue dampers is indeed quite low; however, the adjustment of these dampers is unstable. Shouldn’t it have been adjusted properly from the start when the furnace was started up? It’s very difficult to make adjustments now, and there are many concerns involved. . .
If the negative pressure is too low, it will increase the suction force of the furnace, resulting in a high oxygen content and high flue gas temperatures. All these indicate that the opening degree of the flue dampers is too large; try to reduce it further. Butterfly valves do not provide very precise control – in our installations, we can sometimes close them by two or three positions, but this is only for reference!
The temperature at the inlet of the furnace is higher than that at the outlet; check first whether there is a problem with the instruments. The latter possibility is that the thermocouple has coked; another possibility is that there is an issue with your pressure control – too low a pressure can cause the medium in the furnace to vaporize, leading to a phase change, but this possibility is likely small! Your furnace has a high oxygen level and low negative pressure; it seems that there is a poor coordination between your blower and the flue dampers. The owner can try to reduce the air supply to the furnace as much as possible while ensuring normal combustion, and then increase the flue dampers when the oxygen level drops in order to raise it