Loeffer Boiler Functions and Fuel Oils

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Questions and Answers

What is the function of the high-pressure feed pump in a Loeffer boiler?

To draw saturated steam from the evaporator drum

To deliver feed water to the evaporator drum (correct)

To circulate cold air through the boiler

To pass superheated steam to the turbine

What happens to the one-third of superheated steam in the Loeffer boiler system?

It is released into the atmosphere

It evaporates feed water

It circulates back to the economizer

It is sent to the turbine (correct)

Which component in the Loeffer boiler is responsible for evaporating the feed water?

Economizer

Superheater

Combustion chamber

Evaporator drum (correct)

What role does the steam-circulating pump play in the Loeffer boiler?

It draws saturated steam from the evaporator drum (C) Signup and view all the answers

Where does the feed water go after being forced through the economizer?

To the evaporator drum (D) Signup and view all the answers

What distinguishes fuel oil from other petroleum products?

It includes any liquid or liquefiable petroleum products used for generating heat. (B) Signup and view all the answers

Which grade of fuel oil is intended for vaporizing pot-type burners?

Grade no. 1 (C) Signup and view all the answers

What is the definition of motor gasoline?

A refined petroleum naphtha suitable for carburetors in engines. (C) Signup and view all the answers

What is kerosene primarily used for?

As an illuminant in wick lamps. (A) Signup and view all the answers

Which of the following statements about Liquefied Petroleum Gases (LPG) is incorrect?

It consists solely of butane and no other hydrocarbons. (A) Signup and view all the answers

How are diesel fuel oils classified?

By methods of production. (A) Signup and view all the answers

Which class of fuel oils is characterized as a mixture of two or more oil types?

Blended fuels (A) Signup and view all the answers

What is the flash point of kerosene as determined by the Abel tester?

Not below 22.8°C (D) Signup and view all the answers

What role does the external centrifugal pump play in the boiler operation?

It assists in the circulation of water due to reduced density difference. (B) Signup and view all the answers

What is a major disadvantage of the La-Mont type boiler?

Formation of bubbles that reduce heat flow. (C) Signup and view all the answers

How does the circulating pump distribute water within the boiler?

It uses a distributing header to direct water through nozzles. (C) Signup and view all the answers

What is the pressure range of the Benson boiler?

225 bar to 500 bar. (D) Signup and view all the answers

What is the purpose of the superheater tubes in the boiler?

To convert liquid water into superheated steam. (B) Signup and view all the answers

What is the primary advantage of a Benson boiler regarding its structure?

It is compact in size and lighter in weight. (C) Signup and view all the answers

What is the consequence of salts depositing in the transformation zone of the evaporator?

Necessity for periodic flashing of evaporator tubes. (D) Signup and view all the answers

Which statement correctly describes the density differences affecting circulation in the boiler?

Density differences are negligible at high pressures. (D) Signup and view all the answers

What does Q1 represent in the context of boiler operation?

The measure of boiler efficiency expressed as a percentage (C) Signup and view all the answers

What is the main function of the evaporator tubes in the boiler system?

To generate steam through heat exchange with hot flue gases. (C) Signup and view all the answers

How does a Benson boiler initially operate when starting from cold?

By circulating feed water through the system. (D) Signup and view all the answers

Which formula represents the energy loss due to dry flue gas?

Q2 = 0.24Wdg(tg - ta) (C) Signup and view all the answers

What happens when bubbles form and attach to the heating tubes in the La-Mont boiler?

They reduce heat flow and steam generation due to increased thermal resistance. (A) Signup and view all the answers

What is the significance of the specific heat value of 0.24 in the energy loss due to dry flue gas?

It is the specific heat of the flue gas at constant pressure (B) Signup and view all the answers

What method is used to prevent excessive heating of the tubes during operation?

Closing the valve that supplies superheated steam to the turbine. (D) Signup and view all the answers

What is the steam-raising capacity of a Benson boiler?

Around 150 tonnes/h and above. (D) Signup and view all the answers

Which factor is NOT included in the formula for energy loss due to evaporating and superheating moisture in fuel?

Weight of carbon in the fuel (D) Signup and view all the answers

What happens to the energy loss due to evaporating hydrogen when the temperature of the gas exceeds 575°F?

It is calculated using a different formula (D) Signup and view all the answers

What happens during the operation of the boiler above the critical pressure?

Bubble formation difficulty is eliminated. (B) Signup and view all the answers

What is a disadvantage of the Benson boiler related to evaporator tubes?

Salts deposit during water to steam transformation. (B) Signup and view all the answers

In the context of energy loss due to incomplete combustion, what do CO and CO2 represent?

Byproducts that can be further combusted (D) Signup and view all the answers

Which feature of the Benson boiler makes its erection easier?

All components are welded at the plant site. (A) Signup and view all the answers

What calculation is necessary to determine the proper value of $H_2$ in the energy loss equation?

Deduct a fraction of the moisture weight from the ultimate analysis (B) Signup and view all the answers

Which of the following is a direct consequence of energy loss due to unconsumed carbon?

Reduced overall energy output (D) Signup and view all the answers

What is the formula for overall turbo-alternator efficiency (η ota)?

η ota = Electrical energy sent out / Heat supplied to steam in boiler × 1000 (B), η ota = ηt × ηc × ηg (D) Signup and view all the answers

How is heat rate (HR) expressed mathematically?

HR = Heat added to steam in boiler / Electrical energy sent out (A) Signup and view all the answers

What must be multiplied to the overall efficiency if a plant has multiple turbines?

Range factor (B) Signup and view all the answers

Which factor impacts boiler efficiency primarily?

Physical size and operating pressure (A) Signup and view all the answers

What does the gross-on-gross efficiency represent?

The ratio of gross calorific value to gross heat supplied (D) Signup and view all the answers

What is the relationship between overall station efficiency (η0) and boiler efficiency (ηb)?

η0 = ηb × ηota (D) Signup and view all the answers

What type of efficiency is calculated after excluding energy consumption from boiler auxiliaries?

Net on gross efficiency (A) Signup and view all the answers

Which statement is true about larger boilers compared to smaller ones?

Larger boilers generally have higher efficiency due to operating conditions. (A) Signup and view all the answers

Study Notes

Power Plant with Renewable Energy - Lecture 3 - Boilers

Course Name: Power Plant Design with Renewable Energy
Course Description: This course studies fundamental concepts in the design and installation of various power plants (steam, diesel electric, geothermal, etc.) and renewable energy generation (solar, wind, tidal, hydro-electric, biomass, OTEC, etc.).
Course Units: Lecture - 3 units; Computational Laboratory - 1 unit; Contact Hours per week - Lecture - 3 hours; Computational Laboratory - 3 hours
Prerequisites: Combustion Engineering (a-D, c-D, e-D, h-D)
Course Outcomes: Students will be able to identify components of different power plants, evaluate their performance, explain renewable energy types, and design simple power plants considering constraints (economic, environmental, health, safety, social, ethical).
Course Outline: Covers Steam Power Plants, Variable Load Problems, Diesel Electric Power Plants, Gas Turbine Power Plants, Hydro-electric Power Plants, Geothermal Power Plants, Combined Cycle Power Plants, Renewable Energies (solar, wind, tidal, hydro-electric, biomass, OTEC, etc.), Power Plant Economics(various cost components, pie chart analysis, plant cost comparison), and Co-generation and Energy Management System.
Laboratory Equipment: None specified

Boiler Performance Calculations

Factor of Evaporation (FE): FE quantifies how efficiently a boiler converts water into steam, relating heat input to latent heat of vaporization.
FE Formula: FE = (h_s - h_fw) / h_fg, where:
- h_s = enthalpy of steam
- h_fw = enthalpy of feedwater
- h_fg = latent heat of vaporization at standard atmospheric conditions (970.3 Btu/lb or 2257 kJ/kg or 539 kcal/kg)
Equivalent Evaporation (EE): EE quantifies a boiler's steam generation capacity at a standard temperature and pressure, allowing for direct comparison among various boiler systems.
EE Formula: EE = m_s × FE, where m_s = amount of steam generated.
Equivalent Specific Evaporation (ESE): ESE is a refined measure of steam generation efficiency, focusing on the amount of steam produced per unit of energy input, considering specific operating conditions.
ESE Formula: ESE = (EE) / (m_f), where m_f = amount of fuel burned in the furnace.
ASME Evaporation Units (AEU): Designed to efficiently remove solvents from liquid mixtures through evaporation while optimizing performance and following safety/quality standards.
ASME EU Formula: ASME EU = m_s(h_s - h_fw)
Rated Boiler Horsepower (Rated Bo Hp): A unit of measurement that quantifies a boiler's capacity to generate steam. Comparing results across different systems.
Rated Bo Hp Formula: Rated Bo Hp = (Total Heating Surface) / k, where
- k = 12 sq ft for fire-tube boilers
- k = 10 sq ft for water-tube boilers

Developed Boiler Horsepower (Dev Bo Hp)

Dev Bo Hp: A measure of a boiler's actual steam-generating capacity under specific operating conditions, essential for understanding performance and efficiency in various industrial applications.
Dev Bo Hp Formula: Dev Bo Hp = [m_s(h_s-h_fw)] / c, where
- c = 33,475 Btu/hr = 35,316 kJ/hr = 8,433 kcal/hr

Percent Rating Developed (% Rating Dev)

% Rating Dev: A metric for expressing a boiler's operational efficiency relative to its maximum design output, in terms of developed horsepower (Dev Bo Hp).
**% Rating Dev Formula: ** % Rating Dev = (Dev Bo Hp / Rated Bo Hp) × 100

Higher Heating Value (HHV) vs. Lower Heating Value (LHV)

HHV (Higher Heating Value): Also known as gross calorific value, HHV measures the total energy released when a fuel is burned, including energy contained in water vapor (which condenses releasing heat of vaporization).
LHV (Lower Heating Value): Also known as net calorific value, LHV accounts for the energy lost in vaporizing water during combustion. It assumes water remains vaporized (not recovering latent heat).

Overall Boiler Efficiency (e_o)

e_o is a critical metric that quantifies a boiler's effectiveness in converting fuel energy into usable steam
e_o Formula: e_o= [ms(hs-hfw)+mrs(hro-hri)+mbo(hbo-hfw)]/m₄HHV - m₄=amount of steam reheated

Boiler and Furnace Efficiency (e_bf)

ebf quantifies the effectiveness of a boiler or furnace in converting fuel energy (specifically steam or hot water) into usable thermal energy
**ebf Formula: ** ebf = ms(hs-hfw) / (m₄HHV –m,HV)

Net Efficiency of a Steam Generating Unit (ε_net)

measures a steam generator's effectiveness in converting fuel energy into useful steam work output
ε_net formula: ε_net=[m_s(h_s - h_aux) *ms(hs-hfw)]/m₄HHV

Gross Station Heat Rate (GSHR)

A critical measure used in the energy sector to evaluate the efficiency of a power plant in terms of the thermal energy required to generate electrical energy
GSHR Formula: GSHR= (Gross heat supplied by fuel)/ (Gross work output)

Net Station Heat Rate (NSHR)

A metric used to evaluate a power plant's efficiency in converting fuel energy to electrical energy, considering all internal energy losses.
NSHR Formula: NSHR = [Heat supplied by fuel, m₄HHV] / [(kW – hr generated) - (kW – hr used by auxiliaries)]

Overall (Gross) Station Efficiency (η_o)

A key performance metric to assess power plant efficiency in converting fuel energy into electrical energy, representing the ratio of total output generated to total input from fuel combustion.
η_o Formula: η_o= (kW – output at generator terminals) / (Heat supplied by fuel)

Grate Efficiency (e_gr)

Measures the effectiveness of a boiler's grate system in converting fuel into usable energy, crucial for evaluating solid fuel-fired boiler performance.
e_gr Formula: e_gr = 1 - (mc * HV_c) / m₄HHV

Boilers - Definition and Types

Definition: A steam generator is a closed pressure vessel specifically designed to produce steam at a consistent pressure, using various heat sources, according to process requirements.
Steam Types: Wet, dry saturated, or superheated steam.
Modern Power Plants: Typically use one boiler per turbine to simplify the piping systems and enhance boiler and turbine control.
Pressure Design: Boilers can operate at critical pressure, above, or below it.
- Supercritical: Operate above critical pressure (once-through boilers).
- Sub-critical: Operate below critical pressure (drum boilers).
Maintenance: Balancing the steam generation rates with steam consumption rates to maintain constant pressure. The primary fuel source in thermal power stations is coal.
Boilers in Power Generation: Burning fuel to produce steam that drives a turbo-generator generating electricity.

Boilers - Classification (Fire and Water Tube)

Fire-tube Boilers: Hot combustion gases pass through tubes surrounded by water. Cost-effective for smaller applications with lower steam demands. Relatively simple design and operation, but typically limited to lower pressures.
Water-tube Boilers: Water circulates through tubes heated externally by hot gases in a combustion chamber. More efficient for higher steam demands and pressures than fire-tube boilers. More complex design but can operate at higher pressures. Can be further classified into various types (A, D, O, Yarrow, Stirling, Thornycroft, La Mont, Benson).

Boiler Components

Water-Tube:
- Steam Drum: Collects and separates steam from water.
- Mud Drum: Collects impurities in water.
- Water Walls: Tubes surrounding the furnace absorbing heat from combustion gases.
- Riser Tubes: Carry heated water from mud drum to steam drum.
- Downcomers: Return cooler water from steam drum to mud drum.
- Furnace: Combustion chamber where fuel is burned.
- Economizer: Preheats feedwater with waste heat from flue gases.
- Superheater: Increases steam temperature above saturation.
- Headers: Distribute water and steam to various boiler components.

Boiler Types (Examples)

Cornish: Simple horizontal fire-tube boiler
Lancashire: Twin flue tubes improvement over the Cornish boiler for higher efficiency in water heating and steam generation.
Locomotive: Horizontal cylindrical fire-tube boiler design
Scotch Marine: Marine application, large shell with multiple curved fire tubes used for large steam demand to power ships
Cochran: Vertical multi-tubular fire-tube boiler, compact design and efficient steam generation. Suitable for medium-sized industrial or commercial use and produces consistent steam supply.
A-type, D-type, O-type, Yarrow, Stirling, Thornycroft, La Mont, Benson: Diverse water-tube designs optimized for specific applications (pressures, capacities) in power plants. (Detailed further in 2. Water Tube Boilers section )

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Description

This quiz covers the functions and components of the Loeffer boiler, including feed pumps and steam circulation. Additionally, it explores various fuel oils, their classifications, and specific uses. Test your knowledge on these critical subjects in boiler technology and fuel properties.