Boiler Steam Blowing Procedure In Thermal Power Plant

Steam blowing is an old method for physically removing any residue from the superheater and its connected pipelines. Typically, these materials consist of scales and loose minerals that may have become stuck along the production, storage, or installation processes.

Principal Of Steam Blowing

The idea behind steam blowing is to apply heat shock to remove the scales. In due course, the dynamic velocity of the increasing steam will push these scales forward. Ensure these things before you start the boiler for steam-blowing

1. The alkali boil-out has been finished.
2. The instrument calibration and safety interlocks are in order, except for the water level interlock, which needs to be temporarily isolated.
3. It is recommended to avoid installing the NRV and flow nozzle at the beginning and to remove the thermowell from the steam line.
4. The steam line’s spring hangers are all correctly loaded.
5. The temporary steam line has been correctly set up and fastened to begin steam blowing.
6. Make sure you have the plan for fixing the target plates available.
7. The necessary target plates should be manufactured and stored for quick repairs.
8. The plates used as targets must be made of aluminum.

PROCEDURE FOR STEAM BLOWING

Here is how steam blowing is done:

1. Keep the bed temperature between 800-950°C and increase the boiler pressure over 35 kg/cm^2. Operate with a single compartment.

2. If temporary blowing valves are provided, open them immediately in addition to the main steam stop valve. When the steam pressure goes below about 16 kg/cm², the primary steam stop valve must remain open to keep the flow to the atmosphere.

3. Slump the boiler and gradually lower the firing rate. The main steam stop valve must be shut once the boiler’s pressure hits 16 kg/cm².

4. After one hour, the boiler should start with one chamber, and the bed temperature should be between 800 and 950°C.

The steam-blowing process can be restarted when the pressure hits 35 kg/cm². The next process breaks the scale attached to the contours due to the temperature differential and removes it with additional blows.

OPERATIONAL PRECAUTIONS SHOULD BE TAKEN DURING STEAM-BLOWING

1. During the steam-blowing activity, the initial opportunity to fire the unit at a considerable rate is typical. The unit must be brought up considerably slower during the inspection of all equipment and closely monitoring expansion movements.

2. Blowouts can cause the water level in the drum gauge glass to change abruptly. The feed regulating station needs to be examined to ensure effective remote operation. An adequate supply of D.M. water is imperative.

3. No more than 450°C of flue gas temperature may pass through the entrance of the convection superheater.

4. The diameter of the linked piping should be at least equal to the temporary discharge piping’s diameter, and it must be adequately supported to resist reaction forces when steam is blowing.

5. The discharge piping needs to be redirected in a way that doesn’t put people or equipment in danger. Demarcate the region.

6. You can fix the target plate after three free blows.

7. The turbine supplier will advise you on whether to continue or stop blowing, depending on the condition of the target plate.

8. Allow enough time between blows to achieve maximum thermal shock and remove scale and other deposits from pressure parts and the steam line.

9. Once the steam blowing has been cleared, the boiler must be turned off, and the steam line cooled to finish welding the NRV, flow nozzle, and thermowell onto the main steam line.

10. Disconnect the temporary steam line and attach the permanent line to the TG.

11. Once the job is done, the boiler is prepared to have the safety valve floated.

The blowing is often finalized under the following circumstances:

• No indentation over 0.8 mm in diameter
• Impressions more than 0.4 mm in diameter, limited to a maximum of 2 per 2500 mm² on the target plate surface

• Impressions greater than 0.2 mm, not exceeding ten instances per 2500 mm² of the target plate surface

• Impressions under 0.2 mm

• According to the specifications of a turbine provider

The previously mentioned technique of steam blowing is referred to as the puffing method. Occasionally, another technique, the continuous blowing method, is also employed. The process is identical To the puffing method, where the pressure remains constant during the blowing process. Emphasis on the boiler is situated at a lower elevation in this instance. The temporary pipeline is dismantled upon steam-blowing completion, and the primary steam line is connected to the ESV. All auxiliary pipelines, such as the ejector steam line, gland steam line, and extraction line, are also cleansed using steam. A suitable loop is established under low pressure, and steam is utilized.

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