Loeffer Boiler Functions and Fuel Oils

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

Recommended Reading List:

• Variety of technical articles on different aspects of power plant design, steam generation, and efficiency related subjects. These are provided as a list of links and not as a detailed content.
• Reference lists to other technical sources

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 )