Boiler Drum & Steam-Water Separation

The steam drum in a modern boiler serves multiple purposes and contains various components known as drum internals. Here’s a breakdown of the purposes and functions of the steam drum and its internals:

1. Steam Storage: The steam drum provides a space for storing steam, allowing for quick and smooth adjustment to load changes. It ensures a steady supply of steam to meet varying demands.
2. Water Separation: Within the steam drum, equipment such as steam separators or steam driers are installed. These devices remove any water droplets carried along with the steam, ensuring that only dry steam passes through to the superheaters, turbines, or other downstream equipment. Separating water from steam helps protect the turbine blades from erosion and damage.
3. Impurity Removal: Equipment installed within the steam drum helps remove impurities from the steam. These impurities can include dissolved solids, suspended particles, and other contaminants. By removing these impurities, the steam drum prevents them from depositing on surfaces such as turbine blades, which could lead to reduced efficiency and potential damage.
4. Blowdown: The steam drum provides a location for the removal of heavy concentrations of impurities from the boiler water. This is achieved through a blowdown line connected to the bottom of the drum. Periodically, a portion of the water is discharged to eliminate the buildup of impurities, maintaining the water quality within acceptable limits.
5. Feedwater Distribution: The steam drum facilitates the distribution of feedwater into the water circuits of the boiler. Feedwater, which typically enters the drum from an external source, is evenly distributed to different sections of the boiler for heating and steam generation.
6. Water Treatment: Within the steam drum, there may be equipment and lines for introducing water treatment chemicals. These chemicals help control the water chemistry, preventing scale formation, corrosion, and other water-related issues. They are added to maintain the desired water quality and protect the boiler and its components.

SEPARATION OF STEAM AND WATER

Certainly! Here’s an explanation of steam-water separation in a utility boiler drum.

Primary Separation:

• The steam-water mixture from the riser portions of the circuit enters the steam drum.
• Internal devices, such as baffles and cyclone separators, aid in primary separation.
• The steam, being lighter, rises to the upper portion of the drum.
• Water droplets, being heavier, fall to the bottom of the drum.

Secondary Separation:

• The steam-water mixture undergoes secondary separation within the steam drum.
• Specialized steam drum internals, like demisters or mist eliminators, are used.
• These internals capture and collect remaining fine water droplets in the steam.
• Coalescence and drainage mechanisms help remove water droplets, improving steam dryness.

Steam Scrubbing:

• Steam scrubbing focuses on removing or reducing contaminants from the steam.
• Additional equipment or processes are incorporated within the steam drum for this purpose.
• Filters, chemical treatment systems, or other purification methods may be used.
• The aim is to eliminate impurities carried over from water and protect downstream equipment.

Dry Steam Outlet:

• After the separation process, dry and high-quality steam exits the steam drum.
• The dry steam is directed to superheaters, turbines, or other parts of the boiler system.
• Dry steam ensures efficient and reliable operation of downstream equipment.

Continuous Operation:

• Steam-water separation in the drum occurs continuously during boiler operation.
• The separation process helps maintain steam quality and prevents water carryover.
• Efficient separation contributes to optimal performance and longevity of the boiler system.

By following these steps of separation, the utility boiler drum ensures the delivery of dry, high-quality steam while minimizing water content and removing impurities. This ensures the efficient and safe operation of the boiler and associated equipment.