Hello,
We have increased water make-up on our 150MW coal fired power plant. Water consumption tendency indicates we cannot wait until next planned outage son we need to stop the plant, cool it down, locate and repair failed tube, and restart until planned outage.
As every hour offline counts, we want to define the best/quickest way to locate the failed tube.
Our plan is to cool boiler keeping negative furnace pressure with induced and forced draft fans in service, and open manholes and inspection ports in order to try to locate failed tube in the furnace; but, according to noise, temperature and pressure behavior, it seems that the failed tube belongs to secondary superheater (vertical arrangement of tubes located above furnace).
As the drum water level will be kept whitin normal range, any leak in furnace will be easily found, but, in order to find the failed tube in the superheating section (roof tubes, backpass, primary, secondary, and tertiary superheater) we want to put some water in with the feedwater pumps. We have done this in the past, after long outages with boiler tubes at ambient temperature.
In this case we want to establish a minimum cool down time in order to put water in the superheater section, we have indication of metal temperature in these components and water/steam temperature in the boiler, so we monitor cooling down process. Any suggestions? cooling down tube metal to 200°F will be enough? 250? 300? or reaching a water-metal temperature difference below 50°F? 100°F?. Every 50°F difference requires cooling the boiler down for an additional day approximately.
Thanks in advance for you time
By the way, we are not located in USA so ASME B&PV is not mandatory here (but widely used)
Javier Guevara E.
Projects, Mechanical Engineer
We have increased water make-up on our 150MW coal fired power plant. Water consumption tendency indicates we cannot wait until next planned outage son we need to stop the plant, cool it down, locate and repair failed tube, and restart until planned outage.
As every hour offline counts, we want to define the best/quickest way to locate the failed tube.
Our plan is to cool boiler keeping negative furnace pressure with induced and forced draft fans in service, and open manholes and inspection ports in order to try to locate failed tube in the furnace; but, according to noise, temperature and pressure behavior, it seems that the failed tube belongs to secondary superheater (vertical arrangement of tubes located above furnace).
As the drum water level will be kept whitin normal range, any leak in furnace will be easily found, but, in order to find the failed tube in the superheating section (roof tubes, backpass, primary, secondary, and tertiary superheater) we want to put some water in with the feedwater pumps. We have done this in the past, after long outages with boiler tubes at ambient temperature.
In this case we want to establish a minimum cool down time in order to put water in the superheater section, we have indication of metal temperature in these components and water/steam temperature in the boiler, so we monitor cooling down process. Any suggestions? cooling down tube metal to 200°F will be enough? 250? 300? or reaching a water-metal temperature difference below 50°F? 100°F?. Every 50°F difference requires cooling the boiler down for an additional day approximately.
Thanks in advance for you time
By the way, we are not located in USA so ASME B&PV is not mandatory here (but widely used)
Javier Guevara E.
Projects, Mechanical Engineer
