Boiler Water Treatment and Fireside Cleaning Systems

Focus on Dissolved Compounds in Boiler Water

  • Emphasis on the importance of managing dissolved compounds rather than just removing solids and sludge.
  • Continuous process blowdown control is used to manage water quality.

Types of Dissolved Compounds in Boiler Water

  • Common types of dissolved compounds include:
    • Sodium compounds
    • Carbonates
    • Bicarbonates
    • Chlorides
    • Others (implied to be numerous)
  • Presence of these compounds is influenced by:
    • Amount of makeup water
    • Effectiveness of water treatment
    • Internal chemical reactions occurring in the boiler

Effects of Dissolved Compounds

  • Dissolved compounds can impact:
    • Steam disengagement from water
    • Foaming in the boiler
    • Priming during steam production
  • Concentration of impurities is left behind when steam disengages from water.

Continuous Blowdown Control

  • Continuous blowdown (CBD) helps to manage dissolved solids in boiler water.
  • It involves removing a small amount of water continuously to maintain quality.
  • Conductivity measurements are used to control blowdown rate.
    • Higher electrical conductivity indicates increased dissolved impurities.

Monitoring and Guidelines for Conductivity

  • Conductivity readings are crucial for controlling blowdown rates.
  • ASME recommended guidelines provide rough estimates for conductivity based on operating pressure:
    • In the PowerLab, conductivity target is approximately 3,500 μS/cm.
    • Conductivity tolerances decrease with higher boiler pressure (more stringent requirements for purity).

Factors Influencing TDS and Blowdown Rate

  • Total Dissolved Solids (TDS) in boiler water depends on:
    • Type and concentration of impurities in makeup water.
    • Ratio of makeup water to condensate return.
    • Rate of steam production.
  • Overall blowdown rate is typically expressed as a percentage.
    • Example: If 5,000 kg of feed water with a blowdown rate of 250 kg/hour, the blowdown rate is 5%.
    • For systems without precise flow meters, estimates are obtained by comparing steam flow and feed water flow.

Regulations on Blowdown Systems

  • Blowdown systems must adhere to ASME B31 code regulations.
  • Blowdown systems operate continuously and control dissolved solid concentrations in boiler water.
  • Differences between blowdown and blowoff systems:
    • Blowdown systems are designed for continuous operation and enduring pressure, while blowoff systems are for occasional use.

Blowoff Piping and Valves

  • Blowoff piping design must include:
    • Isolation valve (one required).
    • Throttling (needle) valve for precise control.
  • Isolation valve is typically fully open during operation and can be closed during shutdowns.

Maintenance of Blowdown Systems

  • Regular inspections are vital for safety and efficiency:
    • Look for leaks, cracks, or corrosion signs.
    • Immediate repair or replacement is crucial to avoid dangerous failures.
  • Importance of operator vigilance to ensure proper functioning of systems.

Overview of Fireside Cleaning Systems

  • Transition to discussing fireside cleaning systems:
    • Objective is to maintain cleanliness of the boiler's furnace and associated surfaces.
  • Types of deposits that cause fouling include:
    • Ash from solid fuels
    • Soot from incomplete combustion
  • Importance of cleaning for:
    • Heat transfer efficiency
    • Steaming capacity
    • Maintaining proper draft within the boiler.

Methods for Fireside Cleaning

  • Types of outages for cleaning:
    • Major outage: Long-term shutdown for intensive cleaning.
    • Minor outage: Short-term shutdown for moderate cleaning.
    • In-service cleaning: Cleaning performed while the boiler is operational, utilizing specialized systems.

In-Service Cleaning Techniques

  • Common methods include:
    • Soot blowers: Operate using steam, air, or water to dislodge ash and soot from surfaces.
    • Acoustic cleaning: Utilizes sound waves to loosen debris without damaging tubes.
    • Pneumatic cleaning: Involves mechanical hammers that impact and shake loose residue.
    • Falling shot: Drops balls onto surfaces to dislodge buildup.

Operation of Soot Blowers

  • Soot blowers can be:
    • Automatic or manual.
    • Triggered based on time intervals or differential pressure measurements.
  • High-pressure steam is preferred for cleaning to reduce corrosion risk compared to using water.

Mechanical Maintenance of Soot Blowers

  • Importance of routine maintenance includes checking operation and calibrating measurement devices for accuracy.
  • Considerations for thermal shock and corrosion when using different cleaning mediums (water, steam, air).

Types of Soot Blowers

  • Stationary Soot Blowers: Fixed position within the boiler, designed for certain cleaning tasks.
  • Retractable Soot Blowers: Designed to extend into the boiler during operation, equipped for cleaning.
  • Description of operational mechanics involving lance movement and cleaning execution.

Special Circumstances in Cleaning

  • Acoustic cleaning advantages: Reduces wear and tear, no risk of damaging tubes.
  • Use of explosives as a last resort for particularly stubborn deposits, with necessary regulatory oversight.