UNIT 2: Power Plant Engineering - Comprehensive Study Notes

I. Energy Sources and Conversion Technologies

A. Classification of Energy Sources

• Primary Energy Sources: Naturally available in raw form (e.g., coal, crude oil, natural gas, uranium, solar radiation, wind, hydro, geothermal).

• Secondary Energy Sources: Derived from primary sources after conversion (e.g., electricity, gasoline, diesel, hydrogen, processed biomass).

• Inter-convertibility: Energy can be converted from one form to another, but with inherent losses (per 2nd law of thermodynamics). Example: Chemical (coal) → Thermal → Mechanical → Electrical.

B. Solar Energy Conversion

• Factors Affecting Solar Intensity:

  • Latitude: Decreases from equator towards poles.

  • Season & Earth-Sun Distance.

  • Atmospheric Conditions: Cloud cover, humidity, aerosols.

  • Duration of Sunshine.

  • Indian Regional Data (Approximate Annual Global Horizontal Irradiation - GHIs):

    • Rajasthan (Jaisalmer): 2100-2200 kWh/m²

    • Gujarat (Kutch): 2000-2100 kWh/m²

    • Tamil Nadu (Madurai): 1900-2000 kWh/m²

    • West Bengal (Kolkata): 1500-1600 kWh/m²

    • North-East States: 1400-1500 kWh/m²

• Comparison for Indian Conditions (Solar vs. Wind):

  | Parameter | Solar PV | Wind | |---------------------|-----------------------------------------------|-----------------------------------------------| | Capacity Factor | 15-22% (higher in NW India) | 25-35% (higher in coastal & peninsular zones)| | Land Requirement| ~2.5-3 acres/MW (ground mounted) | ~2.5 acres/MW (spacing included) | | Intermittency | Diurnal (day-night), seasonal (monsoon) | Variable, often stronger at night | | Best Sites (India)| Thar Desert (Rajasthan, Gujarat) | Tamil Nadu, Gujarat, Maharashtra, Karnataka | | Maturity | Very high, rapidly falling cost | Mature, cost-competitive |

• Advantages of Solar: Abundant, silent, no moving parts (PV), low maintenance, modular, suitable for distributed generation.

• Limitations: Intermittency (no sun at night), low conversion efficiency (15-22% PV), requires large area, initial cost (though decreasing), storage needed for 24x7 supply.

C. Wind Energy Conversion

• Factors Affecting Wind Velocity:

  • Pressure Gradient (Pressure Difference).

  • Coriolis Force (deflects wind direction).

  • Local Terrain & Friction (surface roughness).

  • Altitude (wind speed increases with height).

  • Indian Regional Data (Wind Power Density @ 80m hub height):

    • Excellent (>400 W/m²): Parts of Tamil Nadu (Coastal), Gujarat (Saurashtra).

    • Good (300-400 W/m²): Maharashtra, Karnataka, Rajasthan.

    • Moderate (200-300 W/m²): Rest of peninsular India, some coastal Odisha/AP.

• Advantages: Clean, renewable, land under turbines can be used for agriculture, cost-competitive.

• Limitations: Intermittent & variable, noise pollution, visual impact, threat to birds/bats, requires high wind speed sites (>6 m/s).

D. Hybrid Energy Systems

• Definition: Integration of two or more renewable energy sources (e.g., solar, wind, hydro, biomass) with or without energy storage and/or conventional backup to improve reliability and performance.

• Feasible Hybrid Options in India:

  1. Solar-Wind: Complementary generation profiles (wind stronger at night/monsoon, solar during day/clear sky). Reduces intermittency.

  2. Solar-Wind-Hydro: Hydro provides flexible, dispatchable power and storage (pumped hydro) to balance solar-wind variability.

  3. Solar-Biomass: Biomass provides stable base load; solar reduces biomass fuel consumption during day.

  4. Wind-Solar-Diesel/Battery: For remote off-grid/mini-grid applications.

E. Direct Energy Conversion Systems

1. Magnetohydrodynamic (MHD) Converter

• Working Principle: Seeded combustion gases (ionized using alkali metal vapors like potassium) pass through a magnetic field. According to Faraday's law, an electromotive force (EMF) is generated perpendicular to both gas velocity and magnetic field, producing direct current.

• Sketch Description: A rectangular duct with electrodes on opposite walls, magnet poles creating perpendicular field. Hot ionized gas flows through.

  DiagramCANVAS: Rectangular channel, electrodes on side walls, magnet above/below, gas inlet/outlet, external load connected to electrodes.

• Factors Limiting Commercial Use:

  • Material Problems: Electrode corrosion at ~2000°C.

  • Seed Recovery & Cost: Potassium seed recovery is complex and expensive.

  • Low Efficiency at Practical Conditions: Combined cycle efficiency gains not yet commercially proven at scale.

  • High Initial Cost & Complexity.

2. Fuel Cells

• Definition: An electrochemical device that converts chemical energy of a fuel (H₂, hydrocarbons) and an oxidant (O₂ from air) directly into electricity and heat, without combustion.

• Working of Proton Exchange Membrane Fuel Cell (PEMFC):

  1. Anode: H₂ → 2H⁺ + 2e⁻ (oxidation).

  2. Electrolyte (PEM): Allows only H⁺ ions to pass.

  3. Cathode: ½O₂ + 2H⁺ + 2e⁻ → H₂O (reduction).

  4. Overall: H₂ + ½O₂ → H₂O + Electricity + Heat.

• Thermodynamic Equations:

  • Reversible Cell Potential (Nernst Equation): $$\displaystyle E = E^0 - \frac{RT}{nF} \ln \left( \frac{P_{H_2O}}{P_{H_2} P_{O_2}^{1/2}} \right) $$

  • Maximum Theoretical Efficiency: $$\displaystyle \eta_{max} = \frac{\Delta G}{\Delta H} = 1 - \frac{T \Delta S}{\Delta H} $$ (~83% for H₂-O₂ at 298K).

  • Actual Efficiency: $$\displaystyle \eta = \frac{V_{cell}}{1.48} \times 100\% $$ (1.48V is reversible voltage at 25°C).

• Applications: Transportation (fuel cell vehicles), stationary power (backup, remote), portable electronics, space programs.

F. Other Emerging/Non-Conventional Sources

• Tidal: Harnesses kinetic energy of tides. Predictable but site-specific (high tidal range), high infrastructure cost.

• Geothermal: Uses heat from Earth's core. High efficiency, base-load capable. Limited to tectonically active areas (e.g., Himalayas potential in India).

• Biomass: Organic matter (agro-waste, dung, wood). Carbon-neutral but requires large land/feedstock, combustion emissions.

[!TIP] For comparison questions, always frame answers around Availability in India, Technology Maturity, Cost (CAPEX/OPEX), Efficiency, Intermittency, Land/Environmental Impact.

II. Thermal Power Plants (Fossil Fuel Based)

A. Coal-Based Systems

1. Elements of Coal Handling System

• Receiving: Unloading from rail/road/ship (wagon tippler, grab crane).

• Storage: Outdoor (stacked) or indoor (silos). Provides buffer against supply disruptions.

• Crushing: Reduces coal size (to ~20mm) for pulverizers. Crushers: jaw, hammer, impact.

• Handling & Transport: Conveyors (belt), bucket elevators, drag chains.

• Feeding: To pulverizers or stokers. Gravimetric feeders for precise control.

  DiagramSEARCH: coal handling plant thermal power plant schematic

2. Fuel Burning Systems

• Overfeed vs. Underfeed Firing:

  • Overfeed Stoker: Coal fed above the grate. Grate moves, ash discharged at end. Advantage: Simpler, good for low-grade coal. Disadvantage: High excess air, lower efficiency.

  • Underfeed Stoker: Coal fed below the grate. Grate stationary, ash discharged through holes. Advantage: Better combustion control, less excess air. Disadvantage: More mechanical complexity.

• Pulverized Fuel System: Coal ground to fine powder (70-80% < 75µm) in pulverizers (ball, bowl, impact). Mixed with air and burned in furnace as a suspension fire. Advantages: High combustion efficiency (~99%), flexible load response, low excess air, larger boiler size possible.

3. Fluidized Bed Combustion (FBC) System

• Working Principle: Air blown at high velocity through a bed of coarse sand/limestone + fuel particles. At critical velocity, bed particles suspend (fluidize), creating a turbulent mixing zone. Combustion occurs at 800-900°C (lower than pulverized fuel).

  DiagramSEARCH: bubbling fluidized bed boiler schematic

  • Bubbling FBC (BFBC): Air velocity just above fluidization. Distinct bed surface.

  • Circulating FBC (CFBC): Higher velocity, solids carried out, separated by cyclone, returned.

• Advantages of FBC:

  • Fuel Flexibility: Can burn low-grade coals, lignite, biomass, waste.

  • In-situ Desulfurization: Limestone (CaCO₃) added, captures SO₂ as CaSO₄.

  • Lower NOₓ: Low combustion temperature reduces thermal NOₓ.

  • Higher Heat Transfer: Turbulent bed has high surface area.

B. Gas Turbine Plants

• Simple Open Cycle: Air compressed → fuel added & burned → hot gases expand in turbine → exhaust to atmosphere. Low thermal efficiency (~30%) due to high exhaust heat loss.

• Reheating in Gas Turbines:

  • Process: Turbine exhaust gases are reheated in a second combustion chamber (reheater) before expanding in a second-stage turbine.

  • How it Improves Efficiency:

    1. Increases average temperature of heat addition (T_max), moving cycle closer to ideal Brayton cycle.

    2. Reduces compressor work per unit output (as mass flow through high-pressure turbine is lower).

    3. Allows higher pressure ratios without excessive turbine inlet temperature.

  • Result: Significant increase in net work output and thermal efficiency (can reach ~40-45% in combined cycle).

C. Auxiliary Systems & Plant Performance

1. Feed Water Treatment Plant

• Purpose: Remove dissolved gases (O₂, CO₂) and impurities (salts, silica, minerals) to prevent corrosion, scale formation, and turbine blade deposits.

• Stages:

  • Mechanical Filtration: Remove suspended solids.

  • Deaeration: Remove dissolved O₂ & CO₂ using steam stripping in deaerator.

  • Chemical Treatment: Lime-soda process, phosphate treatment.

  • Demineralization (Ion Exchange): Final polishing. Cation exchanger (H⁺ form) → Anion exchanger (OH⁻ form) → Pure H₂O.

    DiagramSEARCH: feed water treatment plant thermal power plant

2. Plant Heat Balance (Energy Balance)

• Concept: Accounting of all energy inputs (fuel LHV, feedwater enthalpy) and outputs (electrical output, losses: stack, radiation, cooling water, auxiliaries).

• Example (Simplified):

  • Input: Heat supplied by fuel = $$\displaystyle m_f \times LHV $$

  • Output: Net electrical output + Heat loss in flue gas + Radiation/convection losses + Heat carried by ash/slag + Heat in cooling water.

  • Thermal Efficiency: $$\displaystyle \eta_{th} = \frac{\text{Net Electrical Output}}{\text{Heat Input}} = \frac{W_{net}}{m_f \times LHV} $$

  DiagramCANVAS: Sankey diagram showing energy flows in a thermal power plant: fuel input (100%), boiler efficiency ~90%, turbine cycle efficiency ~35-40%, net output ~33-36%, major losses: flue gas, cooling water, radiation.

3. Cooling Towers

• Function: Reject waste heat from condenser cooling water to atmosphere via evaporation and sensible heat transfer.

• Types:

  • By Air Flow:

    • Natural Draft: Hyperbolic shape creates chimney effect. Large, low operating cost.

    • Mechanical Draft: Fans force air. Induced Draft (fan at outlet, negative pressure) most common. Smaller footprint.

  • By Water Flow:

    • Wet Cooling: Water evaporates, high heat rejection, drift losses.

    • Dry Cooling: Air-cooled heat exchangers (fin tubes). No water loss, high cost, lower efficiency in hot climates.

    • Hybrid: Combination.

D. Recent Trends

• Boiler Size: Trend towards supercritical (SC) and ultra-supercritical (USC) parameters (pressure > 22.1 MPa, temp > 593°C) for higher efficiency (45-48%) and lower emissions.

• Selection: Focus on fuel flexibility (biomass co-firing), low-NOₓ burners, advanced materials for high temperatures.

• Operations: Digitalization, AI/ML for performance optimization, predictive maintenance, flexible operation for grid support with renewables.

III. Nuclear Power Plants

A. Nuclear Reactor Fundamentals

• Nuclear Fission: Heavy nucleus (U-235, Pu-239) absorbs a neutron, becomes unstable, splits into two lighter nuclei (fission products), releasing 2-3 fast neutrons and ~200 MeV energy per fission.

• Chain Reaction: Released neutrons cause further fissions. Controlled by moderator (slows neutrons) and control rods (absorb neutrons).

B. Reactor Types & Characteristics

1. Pressurized Heavy Water Reactor (PHWR - CANDU)

• Working:

  • Fuel: Natural Uranium (0.7% U-235) oxide pellets.

  • Moderator & Coolant: Heavy Water (D₂O). Kept at high pressure (100-130 bar) to prevent boiling.

  • Pressure Tube Design: Fuel channels (pressure tubes) pass through a low-pressure calandria containing moderator. Allows on-power refueling.

  • Heat Transfer: Primary D₂O coolant in pressure tubes carries heat to steam generators. Secondary light water loop produces steam.

  DiagramSEARCH: PHWR CANDU reactor schematic diagram

• Advantages: Uses natural uranium (no enrichment), excellent neutron economy, on-power refueling, high capacity factor.

• Disadvantages: Heavy water production costly, tritium production/leakage risk, larger size than PWR for same power.

2. Advanced Gas-Cooled Reactor (AGR)

• Description: Second generation of UK's Magnox reactors. Uses enriched uranium (2.5-3.5% U-235) fuel in stainless steel cladding. Moderator: Graphite. Coolant: Carbon dioxide (CO₂) at high pressure (~40 bar). Steam generators inside the concrete pressure vessel.

• Fission Context: Graphite moderator slows neutrons to thermal energies to sustain fission in enriched uranium. CO₂ coolant removes heat. Thermal reactor.

3. Thermal vs. Fast Breeder Reactors (FBR)

C. Reactor Components & Control

1. Functions of Moderators

• Primary Function: Slow down fast neutrons (from fission) to thermal energies where fission cross-section for U-235 is highest.

• Characteristics of Common Moderators:

  | Moderator | Advantages | Disadvantages | |-----------------|-----------------------------------------|-------------------------------------------| | Light Water | Cheap, good heat transfer | High neutron absorption, requires enriched fuel | | Heavy Water | Very low neutron absorption, allows natural U | Very expensive, tritium production | | Graphite | Low absorption, stable at high temp | Low density, requires large volume, fire risk (Chernobyl) | | Beryllium | Low absorption, good reflector | Toxic, expensive, swelling under radiation |

2. Principles of Reactor Control

• Control Rods: Made of neutron absorbers (B₄C, Ag-In-Cd, Hf). Inserted/withdrawn to control reactivity.

• Chemical Shim: Dissolved neutron absorber (e.g., boric acid) in coolant (PWR).

• Burnable Absorbers: Rods or pellets (Gd₂O₃, B₄C) in fuel matrix that deplete over time.

• Reactivity Control: Maintains reactor at criticality (k_eff = 1). Insertion of negative reactivity to shut down (scram).

D. Safety & Reliability

• Reliability Features:

  • Multiple, Independent, Diverse Safety Systems: Redundancy (2/3/4 trains) and diversity (different principles).

  • Defense-in-Depth: Physical barriers (fuel cladding, reactor pressure vessel, containment) + safety systems.

  • Passive Safety Systems: Rely on natural forces (gravity, convection) without active components/power (e.g., AP1000).

  • Containment Structure: Massive reinforced concrete/steel dome to prevent radioactive release.

  • Emergency Core Cooling System (ECCS): Floods core with water if LOCA occurs.

  • Redundant Power Supply: Grid, diesel generators, batteries.

IV. Hydroelectric Power Plants

A. Hydraulic Turbines

• Classification & Characteristics:

  | Type | Principle | Head (m) | Flow (m³/s) | Specific Speed (Ns) | Efficiency | Example | |----------------|----------------|--------------|-----------------|-------------------------|----------------|------------------| | Impulse | Kinetic energy | High (>300) | Low | Low (10-30) | ~90% | Pelton Wheel (high head, low flow) | | Reaction | Pressure + Kinetic | Low-Medium | Medium-High | Medium-High (50-1000+) | ~90-94% | Francis (medium head/flow) <br> Kaplan/Bulb (low head, high flow) |

• Turbine Selection Factors:

  1. Available Head (H): Primary determinant.

  2. Design Discharge (Q): Flow rate.

  3. Speed (N): Grid frequency (f) and number of poles (p): $$\displaystyle N = \frac{120f}{p} $$.

  4. Specific Speed (Ns): $$\displaystyle N_s = N \sqrt{P} / H^{5/4} $$ (imperial) or metric equivalent. Indicates turbine type.

  5. Efficiency & Cost: Trade-off between efficiency and capital cost.

  6. ** cavitation Susceptibility:** Especially for reaction turbines.

B. Site Selection & Plant Layout

• Parameters for Site Selection:

  • Hydrological: High, reliable rainfall/snowmelt, large catchment area, high annual runoff, low silt load.

  • Topographical: Narrow gorge with steep sides for dam, suitable tailrace path.

  • Geological: Sound rock foundation for dam & powerhouse, earthquake zone consideration.

  • Economic: Proximity to load center (to reduce transmission cost), accessibility, land availability, environmental & social impact (displacement).

C. Small Hydro Power (SHP)

• Definition: Hydro plants with installed capacity ≤ 25 MW (India's definition).

• Comparison:

  | Feature | Micro Hydro (≤ 100 kW) | Pico Hydro (< 10 kW) | |-------------------|-----------------------------------------|------------------------------------------| | Application | Village/mini-grid, isolated communities | Single household/small shop, off-grid | | Head/Flow | Very variable, often high head | Very low head/flow, run-of-river common | | Turbine | Turgo, Crossflow, Pelton | Propeller, Crossflow, Water wheel | | Civil Works | Minimal, often no dam | Weir, penstock, small powerhouse | | Cost/Complexity| Low, simple O&M | Very low, often DIY/maintained locally |

D. Auxiliary Structures

• Spillways:

  • Function: Safely pass excess flood water over or around the dam to prevent overtopping and failure.

  • Types:

    1. Overflow (Ogee) Spillway: Crest follows downstream profile of overflowing nappe. Most common for gravity dams.

    2. Side Channel Spillway: Flow enters a channel parallel to dam axis. For narrow valleys.

    3. Shaft (Morning Glory) Spillway: Circular, vertical inlet shaft leading to horizontal tunnel. For narrow, steep sites.

    4. Chute (Open Channel) Spillway: Steeply sloping open channel from crest to river.

V. Power Plant Economics and Operation

A. Fundamental Load & Performance Factors

• Maximum Demand (MD): Highest instantaneous load during a given period (e.g., daily, monthly, annual). Unit: kW or MW.

• Load Factor (LF): Ratio of average load to maximum demand over a period.

$$\text{Load Factor} = \frac{\text{Average Load}}{\text{Maximum Demand}} = \frac{\text{Total Energy (kWh)}}{\text{MD} \times \text{Time (h)}}$$

*   **Significance:** Measures how uniformly load is utilized. High LF (>0.7) indicates good utilization, lower cost per unit.

• Diversity Factor (DF): Ratio of sum of individual maximum demands to simultaneous maximum demand of the system.

$$\text{Diversity Factor} = \frac{\sum \text{Individual Peak Loads}}{\text{System Peak Load}}$$

*   **Significance:** Always **≥ 1**. Reflects non-coincidence of peaks. Higher DF means lower required station capacity.

• Plant (Capacity) Factor (PF): Ratio of actual energy produced to maximum possible energy (if run at full capacity continuously).

$$\text{Plant Factor} = \frac{\text{Actual Annual Energy Output (kWh)}}{\text{Rated Capacity (kW)} \times 8760 \text{ h}}$$

*   **Significance:** Measures how fully plant capacity is used. Includes scheduled outages. PF ≤ LF.

[!TIP] Common Pitfall: Confusing Load Factor and Diversity Factor. LF = Avg Load / MD (for one entity). DF = Sum of MDs / System MD (for multiple entities). LF ≤ 1, DF ≥ 1.

B. Load Analysis Curves

• Load Duration Curve (LDC): Loads arranged in descending order vs. time (percentage or cumulative hours). Area under curve = total energy.

  • Use: Determines base load (left, flat part) and peak load (right, steep slope) plants needed.

• Power Duration Curve: Same as LDC but power (kW/MW) on Y-axis instead of load (same thing for fixed period).

  DiagramCANVAS: Schematic of Load Duration Curve: Y-axis: Load (MW), X-axis: % of time (or hours). Steep right side (peak), flatter left side (base).

C. Tariffs and Costing

• Types of Tariffs:

  1. Flat Rate: Fixed charge per unit energy consumed. Ignores demand.

  2. Block Rate: Different rates for different consumption blocks (slab system). Progressive.

  3. Two-Part Tariff: Fixed Charge (₹/kW of MD) + Running Charge (₹/kWh). Most common for industrial/commercial. Recovers fixed and variable costs.

  4. Power Factor Tariff: Incentive/penalty based on PF (cos φ). Low PF increases system losses, so penalized.

D. Depreciation & Financial Analysis

• Purpose: Allocate capital cost of plant over its useful life.

• 1. Straight Line Method (SLM):

  • Equal annual depreciation.

  • $$\displaystyle D_{annual} = \frac{P - S}{n} $$

  • Where P = Initial cost, S = Salvage value, n = life (years).

• 2. Sinking Fund Method (SFM):

  • Annual deposit (A) into a fund earning interest (i) to accumulate to (P-S) in n years.

  • Formula: $$\displaystyle A = (P - S) \left[ \frac{i}{(1+i)^n - 1} \right] $$

  • Total Depreciation in kth year: $$\displaystyle D_k = A(1+i)^{k-1} $$

  • Book Value at end of kth year: $$\displaystyle BV_k = P - \sum_{j=1}^{k} D_j $$

  DiagramCANVAS: Sinking fund method table: Year, Deposit (A), Interest Earned, Total Fund, Book Value.

  [!TIP] Numerical Focus: Sinking fund problems are frequent. Remember: $A$ is constant, but $$\displaystyle D_k $$ increases yearly. Book value decreases non-linearly.

E. Comparative Assessment of Power Plants