Steam Boil out procedure for cleaning new water tube boiler
1. As the steam drum pressure reaches at 50% of working pressure the alkali boil out ( internal cleaning of Boiler ) commences. Hold the temperature and the pressure for 8 hours. Take sample from CBD once in 2 hours.
2. The effectiveness of Alkali boil out will be identified by change in phosphate ppm and Oil and Fe2O3 content from the initial value.
After alkali boil out is completed, generally the boiler is stopped and depressurised to commence flushing. But in this case, since refractory dry out activity is also carried out along with boil out, it is advised to go for an extended boil out so that the refractory dry out activity can be completed.
3. Now the flue gas temperature can be brought down by reducing the firing rate.
4. Rate of reduction in flue gas inlet temperature to Boiler will be at the rate of 50 Deg C / Hr. When the flue gas temperature drops to 250 Deg C, stop ID Fan and adjust the stack cap to maintain Kiln pressure below ABC as 3 to 5 mmWC. At this time online flushing can be carried out by opening the CBD, IBD. Pressure can be reduced to 10 kg / cm2.
5. At the above pressure take a blow down from the bottom header valves one by one for not more than 10 seconds per drain valve. While this is being done it must always be ensured that the drum level does not fall below the normal working level and the water level is always visible in the level gauge.
6. Gradually increase the opening of the start up vent valve, to relieve the steam drum pressure to 5 kg / cm2.
7. Constantly watch the flue gas temperature at Boiler inlet. In case the temperature shoots up beyond 250 Deg C, stop draining and investigate to take remedial action.
8. Fully open the steam drum vent gradually when the drum pressure falls to 2 kg /cm2. Take sample from CBD piping and analyse for pH, conductivity, phosphates, oil contents and Fe2O3.
9. Open CBD valve and drain water to blow down tank. Dilute the blow down tank content with water and divert the solution to a pre-determined safe location.
10. After draining the content from the steam drum, start draining from evaporator module and bottom headers respectively. Also drain from support tube bottom header and water wall bottom headers subsequently. Close all the drain valves.
11. After the Boiler cools down, fill in the water into the Boiler up to the drum Normal water level and flush.
12. Repeat this operation a few times till the quality of boiler water and the feed water are very close.