Steam Traps and Boilers
1. Explain in detail about the different types of steam traps, Mountings and Accessories in the steam
Boilers.
2. Describe in Detail about the steam generation methods and discuss the uses of steam in process
industry
elaborately.
3. Sketch the basic flow diagram of a steam power plant cycle showing by product generation
of electric power and process steam?
4. Explain the steam generation process in the water gas fired boiler with a neat sketch
each question have 20 marks
1. Types of Steam Traps, Mountings, and Accessories in Steam Boilers
Steam Traps: A steam trap is a device used to discharge condensate and non-condensable gases from
steam systems while preventing the escape of live steam. The steam trap operates based on
temperature, pressure, or a combination of both. Common types include:
Thermostatic Steam Traps: Operate based on the temperature difference between steam and
condensate. They use a thermally sensitive element to open or close the valve. Example: Bellows-
type, Capsule-type traps.
Mechanical Steam Traps: Work by the principle of the density difference between steam and
condensate. The most common is the float type, where a float rises with condensate to open the
valve, allowing the steam to escape.
Inverted Bucket Steam Traps: The inverted bucket floats in the condensate, and its position
regulates the valve. When condensate accumulates, the bucket rises, and the valve opens. It is
suitable for high-pressure systems.
Float and Thermostatic Steam Traps: Combination of mechanical float operation and
thermostatic control to provide an efficient discharge of both condensate and non-condensable
gases.
Mountings: Mountings are the safety devices that are installed on steam boilers for their proper
operation and to ensure safe and efficient functioning.
Water Level Indicators: These show the water level in the boiler to avoid dry-running.
Pressure Gauges: They display the steam pressure inside the boiler.
Safety Valve: Automatically releases steam if the pressure inside the boiler exceeds a certain limit,
preventing damage or explosion.
Blow-off Valve: Used to remove sediment or scale from the bottom of the boiler.
Steam Stop Valve: Used to control the flow of steam from the boiler to the system.
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Accessories: Accessories in steam boilers are additional components that enhance the performance of
the system.
Economizer: Recovers heat from the exhaust gases to preheat the feedwater before it enters the
boiler, improving efficiency.
Air Preheater: Preheats the combustion air before it enters the furnace to improve fuel
combustion efficiency.
Superheater: Increases the temperature of the steam above its saturation temperature, increasing
the energy content of the steam.
Deaerator: Removes dissolved gases, such as oxygen, from the feedwater to prevent corrosion in
the system.
2. Steam Generation Methods and Uses of Steam in the Process Industry
Steam Generation Methods: Steam is primarily generated in boilers by heating water to its boiling
point. The different methods include:
Fire-tube Boilers: Hot gases pass through tubes submerged in water. Heat is transferred to the
water, converting it into steam. They are widely used for lower pressure systems.
Water-tube Boilers: Water circulates through tubes that are exposed to heat. This design is more
suitable for high-pressure steam generation and is commonly used in large-scale plants.
Fluidized Bed Boilers: Uses a bed of inert particles (like sand) fluidized by air, where coal is burned
in the bed. This method is effective in burning various fuels efficiently.
Electric Boilers: Uses electrical energy to heat water and generate steam. These boilers are
typically used in smaller operations or when there is a need for clean steam generation.
Uses of Steam in the Process Industry: Steam plays a crucial role in a variety of industrial applications:
Heat Transfer: Steam is used for heating, cooking, and pasteurizing in the food and beverage
industry.
Power Generation: Steam turbines are used to generate electricity in power plants.
Mechanical Drive: Steam is used in pumps, compressors, and turbines for driving mechanical
processes in industries like oil refining, chemical manufacturing, etc.
Chemical Reactions: In the chemical industry, steam is essential for distillation, drying, and other
heat-driven chemical reactions.
Sterilization: Steam is used to sterilize equipment and utensils in pharmaceutical and food
processing industries.
Drying and Evaporation: Steam is used to evaporate water from products such as textiles, paper,
and chemicals.
3. Basic Flow Diagram of a Steam Power Plant Cycle (Electric Power and Process
Steam Generation)
The steam power plant cycle consists of four key components: the boiler, turbine, condenser, and pump.
Below is a basic flow diagram of the cycle:
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1. Boiler: Water is converted to steam in the boiler by heating. The fuel (e.g., coal, oil, gas) is
combusted, producing heat to boil the water.
2. Turbine: High-pressure steam enters the turbine, where it expands, causing the turbine blades to
rotate. This mechanical energy is converted into electrical energy via a generator.
3. Condenser: After the steam passes through the turbine, it enters the condenser, where it is cooled
and condensed back into water.
4. Pump: The condensate water is pumped back into the boiler to repeat the cycle.
Electric Power Generation: The turbine is connected to a generator that produces electricity.
Process Steam Generation: In some cases, steam from the boiler is diverted to the process plant for
industrial heating and other applications, apart from power generation.
4. Steam Generation Process in a Water Gas Fired Boiler
A water gas fired boiler uses water gas (a mixture of carbon monoxide and hydrogen) as a fuel to
generate steam. The process includes:
1. Water Gas Generation: Water gas is produced by passing steam over hot carbon (from coal or
coke) in a gasifier, generating a mixture of carbon monoxide and hydrogen.
2. Combustion: The water gas is combusted in the furnace of the boiler. The heat generated from
this combustion raises the temperature of water circulating in the tubes of the boiler.
3. Steam Generation: The heat from the combustion gases is transferred to the water in the boiler
tubes, converting the water into steam.
4. Superheating: The steam can be passed through a superheater, increasing its temperature before
it is used in turbines or sent to industrial processes.
Sketch: (Unfortunately, I can't provide a sketch here, but I can guide you through it if needed.)
A simple diagram will show the boiler with a furnace, water gas feed, combustion chamber, and
water tubes. The steam produced exits the boiler and is used for power generation or sent to
industrial processes.
Would you like further clarification or a more detailed explanation of any of these topics?
6. Describe the fluidized bed combustion process and how it compares with pulverized coal and
stoker firing.
Name the major advantages of fluidized bed combustion.
7. Explain the Rankine cycle and obtain an expression for the Rankine cycle efficiency. Comment on
the reasons
for considering Rankine cycle as an ideal cycle for steam power plant.
6. Fluidized Bed Combustion Process and Comparison with Pulverized Coal and
Stoker Firing
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Fluidized Bed Combustion (FBC): In fluidized bed combustion, solid particles (usually sand or
limestone) are suspended or "fluidized" by an upward flow of air. This process creates a bed of material
that behaves like a fluid and allows for efficient combustion. The combustion process occurs when fuel
(such as coal, biomass, or waste) is injected into the fluidized bed, where it mixes thoroughly with the
hot bed material, allowing for uniform combustion at lower temperatures.
Process:
1. Air Supply: Air is supplied through the bed of particles (which could be sand, limestone, etc.),
causing the bed to fluidize.
2. Fuel Injection: Fuel is injected into the bed where it mixes with the particles and combusts. The
fluidized bed maintains a uniform temperature, leading to efficient combustion.
3. Heat Transfer: The heat generated in the bed is transferred to water tubes or heat exchangers to
produce steam.
Comparison with Pulverized Coal and Stoker Firing:
Pulverized Coal Firing:
Operation: In pulverized coal combustion, coal is ground into fine powder and then mixed
with air before being burned in a furnace.
Efficiency: Pulverized coal furnaces operate at higher temperatures and pressures, leading to
higher efficiency, but they also require more complex equipment for coal grinding and air
mixing.
Emissions: Higher NOx and particulate emissions, requiring stringent control measures.
Stoker Firing:
Operation: In stoker firing, coal is fed onto a moving grate where it burns in layers. The air is
supplied beneath the grate to support combustion.
Efficiency: The combustion process in stoker firing is relatively slow and can be inefficient in
terms of heat transfer, leading to lower overall combustion efficiency compared to FBC.
Emissions: Higher emissions compared to FBC, especially at lower combustion temperatures.
Advantages of Fluidized Bed Combustion:
1. Lower Combustion Temperature: FBC operates at lower temperatures (typically 800-900°C)
compared to pulverized coal (1200-1500°C), reducing the formation of NOx (nitrogen oxides).
2. Fuel Flexibility: FBC can efficiently burn a variety of fuels, including low-quality coals, biomass, and
industrial waste.
3. Enhanced Heat Transfer: The fluidized particles in the bed allow for more effective heat transfer,
improving the efficiency of the combustion process.
4. Lower Emissions: Due to lower combustion temperatures, the emission of NOx is reduced.
Additionally, sulfur can be captured by limestone added to the bed, reducing SOx emissions.
5. Reduced Ash Problems: The combustion process in FBC reduces ash deposition problems that
occur in conventional coal combustion methods.
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6. Efficient Combustion: The thorough mixing of the fuel with the bed material ensures more
complete combustion, leading to better efficiency.
7. Rankine Cycle and Expression for Efficiency
Rankine Cycle: The Rankine cycle is a thermodynamic cycle that converts heat into mechanical energy,
typically used in steam power plants. It consists of four main stages:
1. Isentropic Compression: The working fluid (typically water) is compressed from low pressure
(saturated liquid) to high pressure in a pump. This requires work input but increases the pressure
and temperature of the fluid.
2. Isobaric Heat Addition: The compressed liquid enters a boiler, where heat is added at constant
pressure. This heat transforms the liquid into high-pressure steam.
3. Isentropic Expansion: The high-pressure steam is expanded through a turbine, doing work by
rotating the turbine blades. During expansion, the steam loses pressure and temperature.
4. Isobaric Heat Rejection: The low-pressure steam exits the turbine and enters a condenser, where
it is cooled and condensed back into liquid at constant pressure.
Rankine Cycle Efficiency: The efficiency of the Rankine cycle can be derived by comparing the work
output from the turbine to the heat input in the boiler.
Work Output (Turbine Work):
Wturbine = h1 − h2
where h1 is the enthalpy of the steam entering the turbine and h2 is the enthalpy of the steam
exiting the turbine.
Heat Input (Boiler Heat):
Qin = h3 − h4
where h3 is the enthalpy of the steam entering the boiler, and h4 is the enthalpy of the water
leaving the boiler.
Heat Rejection (Condenser Heat):
Qout = h4 − h1
Thermal Efficiency: The thermal efficiency (ηthermal ) of the Rankine cycle is the ratio of the work
output to the heat input:
Wturbine h1 − h2
ηthermal = =
h3 − h4
Qin
Reasons for Considering the Rankine Cycle as an Ideal Cycle for Steam Power Plants:
1. High Efficiency: The Rankine cycle is designed to optimize the conversion of heat into mechanical
energy, making it highly efficient in large-scale power generation.
2. Simple Operation: It has relatively simple components—pump, boiler, turbine, and condenser—
that are straightforward to operate and maintain.
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3. Established Technology: The Rankine cycle is widely used and understood, with well-established
components that can be scaled up for large power plants.
4. Adaptability: It is adaptable to various fuel types, from coal and natural gas to nuclear power,
making it a flexible choice for steam power generation.
Would you like further details on any specific part of these processes?
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