Pre-commissioning checks include systematic checking of erection and field quality assurance log sheets. Checking each product as per the commissioning check list before starting of any commissioning activity will enable smooth commissioning of the boiler.
The hydraulic test of boiler superheater, reheater and piping like main steam and reheater form a portion of pre-commissioning activity. The hydraulic test of these components is required to be carried out in stages. The first stage will include economizer, steam drum, water walls, superheaters, interconnecting pipes, and all headers including main steam header.
The boundary for the first stage will include
- Isolation vale at economizer inlet
- The stop valve at final superheater outlet
- Isolation valve on the soot blowing steam line
- Isolation and bypass valves in the desuperheating spray control station
- Boiler drain line valves
- Vent line isolation valves
The second stage, which is a low pressure section, will include the entire reheater, the interconnecting piping, headers in this section, all the vents, and all drains.
Trial running of equipment like fans, pumps, dampers, valves, gates, mills, etc. is essential to ensure the smooth commissioning of the boiler. The simulation testing of all interlocks, controls and protection in the controls instrumentation area of the boiler also forms a part of pre-commissioning activity.
The trial running of all rotating equipment is by running the equipment for a period of eight hours continuously with all interlocks, controls, and protection. During this period all parameters like vibration, bearing temperature, etc. are locally also checked. If any rotating equipment needs any correction or servicing, the same is done and again a full trial run of eight hour is taken up.
The pre-commissioning checks on dampers, valves, gates, etc. involves checking each one physically for free movement, clearances, full travel, full closure, and operation both by hand and by the prime mover provided.
Pre-commissioning checks also include other tests necessary to ensure proper performance of the boiler during commissioning and thereafter.
These tests carried out are
- Gas tightness test
- Air tightness test on boiler and connected ducts
- Gas distribution test in electro static precipitator (ESP)
- Air load test in ESP
- Simulation test in all instrumentation, control, interlock ,and protection areas
Besides the readiness of the boiler and its auxiliaries, the boiler requires availability of various services for starting commissioning activities and further operation. Checking the status of all these services for its readiness also forms a part of pre-commissioning checks.
These services include
- Water treatment plant
- 6.6 KV and 0.4 KV supply
- Cooling water system
- Fuel handling system
- Ash plant system
- Coal plant
- Operating laboratory personnel and instruments
- Testing facility
- Compressed air system
- Firefighting system
Once these pre-commissioning checks are carried out, then the preparation for commissioning of the boiler starts. This again encompasses many checks and preparation in all the areas of the boiler. Some boiler commissioning engineers include these activities also in pre-commissioning activity, as it very difficult to draw a clear demarcation.