Working of Boiler – Explanation, Parts ...

What is a Boiler?

The boiler is commonly defined as a closed vessel in which water is heated until it converts to steam at the required pressure. The primary function of a boiler is to produce either hot water or steam. Hot water boilers heat water for domestic or commercial heating and hot water supply, while steam boilers generate steam to power turbines for power generation and various industrial heating applications.

To understand steam generation in a boiler, consider steam powering a turbine. When steam flows through the turbine blades, the force turns the blades and accelerates the turbine.

Steam contains significant energy because it incorporates the energy used to raise the water temperature, along with the latent heat of vaporization. This makes turbines efficient, and based on the fuel used to heat the water, they can also be highly energy-efficient. Boilers operate under pressure to heat different liquids for external use through the combustion of fossil fuels or energy from the sun.

Parts and Accessories of a Boiler

Boiler parts are categorized into two divisions:

Boiler Mounting

The essential components that define boiler performance include:

• Pressure Gauge: Measures the internal pressure of the boiler, located at the front.
• Water Level Indicator: Monitors the internal water level, fitted at the front with a glass tube and three cocks.
• Stop Valve: Controls steam flow from the boiler to the steam pipe.
• Safety Valve: Prevents boiler explosions due to high pressure, activating when internal pressure exceeds limits. Typically, two safety valves are present.
• Blow Off Cock: Used to empty the boiler of water and mud, generally located at the bottom of the drum.
• Grate: The area in the furnace where fuel burns.
• Feed Check Valve: Functions as a Non-Return Valve, fitted slightly below the normal water level to regulate water supply.

Boiler Accessories

These accessories enhance boiler efficiency, including:

• Super Heater: Superheats steam before it enters the turbine to prevent corrosion.
• Feed Pump: Pumps water into the boiler, operated by steam, electricity, or turbines.
• Air Preheater: Increases boiler efficiency by preheating the air.
• Economizer: Increases efficiency by allowing flue gases to pass through before being released into the atmosphere.

Working Principle of a Boiler

The working principle of a boiler is straightforward. The boiler serves as a closed vessel where water is stored. Hot gases formed from burning fuel in the furnace come into contact with the water vessel, facilitating heat transfer. Essentially, the boiler converts water into steam using heat energy. Various types of boilers are available for different applications.

Efficiency of Boiler

Boiler efficiency is defined as the total percentage of heat exported by the outlet steam compared to the total heat supplied by the fuel.

Boiler Efficiency (%) = (Heat Exported by Outlet Steam) / (Heat Supplied by the Fuel) * 100

Classification of Boiler

Classification is based on the following criteria:

According to the Relative Passage of Hot Gases and Water

• Fire-Tube Boiler: Hot combustion gases surround water.
• Water-Tube Boiler: Water flows through tubes surrounded by hot combustion gases.

According to the Arrangement of Water Circulation

• Forced Circulation: Water is circulated by pumping.
• Natural Circulation: Circulation occurs due to density differences.

According to Usage

• Locomotive: Used in railway engines.
• Marine Boiler: Used in ships.
• Stationary Boiler: Used in power plants.
• Portable Boiler: Movable and used temporarily at sites.

According to the Boiler's Position

• Inclined
• Horizontal

According to the Pressure Generated by the Steam

• Medium Pressure Boiler: Operates between 20-80 bars, generating power.
• Sub-Critical Boiler: Produces steam below critical pressure.
• Low-Pressure Boiler: Operates between 15-20 bars for heating.
• High-Pressure Boiler: Exceeds 80 bars.
• Supercritical Boiler: Produces steam over critical pressure.

According to Charge in the Furnace

• Pulverized fuel
• Supercharged fuel

A steam boiler heats water inside tubes surrounded by hot gases.

This type of boiler generates steam by applying heat energy to water. Earlier boilers operated at low to medium pressures (7 kPa to 290 psi), whereas modern boilers are designed for higher pressures. Steam boilers are crucial wherever steam is required, and their size and type depend on applications like mobile steam engines, including mini boilers for steam power. Power stations feature separate large steam-generating systems.

Types of Boiler

Fire Tube Boiler

The fire tube boiler consists of several tubes through which hot gases pass. These tubes are immersed in water inside a closed vessel. In a fire tube boiler, hot tubes heat the water, converting it into steam within the same vessel. Due to this design, fire tube boilers cannot produce steam at very high pressures, typically reaching a maximum pressure of 17.5 kg/cm² and a capacity of 9 Metric Tons of steam per hour.

Water Tube Boiler

The heating surfaces of a water tube boiler consist of numerous tubes, some exposed directly to flames and others to hot gases from burning fuel. Piping groups are equipped with baffles, creating several paths for hot gases to enhance heating efficiency. Heat is transferred to water in thin-section pipes, allowing water tube boilers to achieve higher working pressures than fire tube boilers.

Common Problems with Steam Boilers:

Wet Steam (Priming):

Causes:

Incorrect kettle hull, high water levels inside the kettle, improper combustion rates, high levels of dissolved solids, and high alkalinity.

Treatment:

Maintain low salt levels in the water, filter water effectively, and remove sediments periodically.

Blocked or Accumulated Scales:

Causes:

Poor water quality leads to mineral buildup, causing blockages in steam pathways.

Treatment:

Use treated water to prevent mineral accumulation.

Hearing Noises (Whistling or Knocking):

Causes:

Indicates air in the system, low water pressure, or lime buildup on the heat exchange.

Treatment:

Ensure proper gas pressure, piping, flame quality, air intake, and exhaust systems are functioning correctly.

Loss of Pressure:

Causes:

Steam leaks, possibly hidden, or issues in the return system (steam traps, check valves, or feed pumps).

Treatment:

Regular monitoring and maintenance of the boiler system.

Pressure Issues from Water Feeding:

Causes:

Intermittent water supply causing temperature variations and affecting steam production.

Treatment:

Implement a continuous water feeding system.

Use of Steam Boilers in Industry:

Steam boiler systems are among the safest and efficient methods to meet the steam requirements crucial for manufacturing in industrial facilities.

Industries that significantly benefit from steam boiler systems include:

• Hospitals and healthcare centers.
• Fermentation and distillation.
• Food and beverage industries.
• Commercial laundries.
• Textile industry.
• Pharmaceutical industries.
• Extraction of essential oils.

Methods of Storing Steam Boilers:

Inspect, wash, and dry the boiler before storage. Steam boilers can be stored either dry or wet.

Dry Storage:

• Use when storing the kettle for three months or longer.
• Cool water to just before boiling, but not below 83°C.
• Inspect and wash the kettle for repairs before storage.
• Dry all wet areas of the boiler.
• Place moisture-absorbing chemicals in the boiler and seal it to prevent moisture intrusion.
• In humid areas, oil treatment may be needed.

Wet Storage:

• Recommended for short-term storage, this method involves filling the boiler with treated water.
• Cool water to below atmospheric boiling point but not below 83°C.
• Inspect and wash the kettle for repairs before storage.
• Clean and dry all wet areas of the boiler.
• Fill the clean kettle with treated water to minimize corrosion.
• Maintain the water pressure above atmospheric levels.
• Add caustic soda and sulfites until water levels reach 450 ppm.
• Close drains and vents.
• Fill the kettle with treated service water before sealing.

We at Arabtec Boiler Company specialize in steam boilers, steam networks, maintenance, and water treatment, offering practical solutions for industrial needs with our skilled engineers and high-quality localized products that meet international standards.

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