UNIT 3 - POWER PLANT ENGINEERING (ME-702(C)) - EXAM-FOCUSED SHORT NOTES

1.0 ENERGY RESOURCES & CONVERSION TECHNOLOGIES

1.1 Energy Sources: Classification & Inter-convertibility

• Primary Energy Sources: Naturally available in raw form (e.g., coal, crude oil, natural gas, uranium, sunlight, wind, hydro potential). Directly usable after minimal conversion.

• Secondary Energy Sources: Derived from primary sources through conversion (e.g., electricity, gasoline, diesel, hydrogen, refined fuels). Require transformation before end-use.

• Energy Inter-convertibility: Energy can change form but total quantity is conserved (First Law). Typical chain: Chemical (fuel) → Thermal (heat) → Mechanical (turbine rotation) → Electrical (generator). Direct conversion skips mechanical step (e.g., fuel cells, PV cells).

1.2 Direct Energy Conversion Methods

MagnetoHydroDynamic (MHD) Converter

• Working Principle: Direct conversion of thermal energy to electrical energy without moving parts. Hot, ionized combustion gases (plasma) pass through a magnetic field, inducing an electromotive force (EMF) across electrodes perpendicular to both flow and field (Faraday's Law).

• Schematic Flow: Combustion Chamber (with seed) → Nozzle (accelerates) → Duct (with transverse B-field & electrodes) → Diffuser → Seed recovery.

• Ionization (Seeding): Low-ionization-potential alkali metal (e.g., Potassium or Cesium) added to combustion gases (~1-2% by mass) to increase electrical conductivity.

• Key Components:

  • Combustor/Chamber: Burns fuel (coal/oil/gas) with preheated air and seed.

  • Nozzle: Accelerates plasma to high velocity (~1000 m/s).

  • Duct/Channel: Contains electrodes (anode/cathode) and magnet.

  • Electrodes: Collect current, subjected to high-temperature corrosion.

  • Load: External circuit connected to electrodes.

• Factors Limiting Commercial Use:

  1. Material Problems: Electrodes and duct walls face extreme temperatures (~2000°C) and corrosive plasma.

  2. Seed Recovery & Recycling: Complex, costly process to separate seed from slag and flue gas.

  3. Low Demonstrated Efficiency: ~25-30% (combined with steam bottoming plant ~40-45%), not competitive with modern ultra-supercritical thermal plants (~45-48%).

  4. High Investment Cost for magnets and channel.

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, with water as a by-product (for H₂ fuel).

• Basic Working Principle: Opposite of electrolysis. Fuel oxidized at anode, oxidant reduced at cathode. Ions move through electrolyte, electrons through external circuit.

  • Anode Reaction (H₂): $$\displaystyle H_2 \rightarrow 2H^+ + 2e^- $$

  • Cathode Reaction (O₂): $$\displaystyle \frac{1}{2}O_2 + 2H^+ + 2e^- \rightarrow H_2O $$

  • Overall: $$\displaystyle H_2 + \frac{1}{2}O_2 \rightarrow H_2O + \text{ Electricity + Heat} $$

• Thermodynamic Equations:

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

    • $$\displaystyle E^0 $$: Standard reversible voltage (~1.23 V for H₂/O₂ at 298K).

    • $R$: Gas constant, $T$: Temperature (K), $n$: electrons transferred (2), $F$: Faraday's constant.

  • Theoretical Efficiency (Based on HHV): $$\displaystyle \eta_{th} = \frac{\Delta G}{\Delta H} = \frac{nFE}{nFE + nFE_{loss}} $$ ≈ 83% at 298K for H₂.

  • Actual Efficiency: $$\displaystyle \eta_{actual} = \frac{V_{cell}}{1.48} $$ (for H₂, based on LHV) or $$\displaystyle \frac{V_{cell}}{1.25} $$ (based on HHV). Typical operating voltage: 0.6-0.8 V/cell.

• Types & Characteristics:

• Advantages: High efficiency (40-60%, up to 85% with CHP), modular, low emissions (NOx, SOx), silent, quick start (PEMFC).

• Applications: Distributed generation, backup power, transportation (fuel cell vehicles), portable power.

1.3 Renewable Energy Sources for Indian Conditions

Solar Energy

• Solar Radiation Intensity Factors:

  • Geographical: Highest near Tropic of Cancer (India's latitude 8°-37°N). Clear sky regions (Rajasthan, Gujarat) receive >5.5 kWh/m²/day.

  • Seasonal: Max in summer (May-June), min in monsoon/winter.

  • Diurnal: Max at solar noon (~12-2 PM), zero at night.

  • Atmospheric: Cloud cover, humidity, aerosols, air mass reduce intensity.

• Conversion Technologies:

  1. Photovoltaic (PV): Direct conversion via semiconductor cells (Si, CdTe, CIGS). Output: DC → AC via inverter.

  2. Solar Thermal: Concentrates sunlight to generate heat → steam → turbine. Types: Parabolic Trough, Solar Tower, Dish-Stirling.

• Advantages for India: Abundant resource (300+ sunny days), decentralized (rooftop), low O&M cost, no fuel cost, silent.

• Limitations: Intermittency (day/night, weather), large land area for utility-scale, storage cost (batteries), module efficiency (15-22% commercial), dust/soiling.

Wind Energy

• Wind Velocity Dependence Factors:

  • Topography: Accelerates over hills, ridges, coastal areas, sea-land transitions.

  • Atmospheric Conditions: Pressure gradients, temperature gradients, monsoons.

  • Seasonal: Stronger in summer (Apr-Jun) in most of India; southwest monsoon in coastal regions.

• Wind Energy Conversion System (WECS) Components:

  • Rotor (Blades) → Gearbox (in geared type) → Generator (DFIG, PMSG) → Nacelle → Tower → Foundation → Grid Interface (Converter/Transformer).

• Limitations for India: Intermittency & variability, grid integration challenges (weak grids in remote areas), location-specific (needs >6 m/s avg. wind speed), noise pollution, bird/bat mortality, visual impact.

• Indian Wind Potential Zones: Tamil Nadu (largest installed), Gujarat, Maharashtra, Karnataka, Rajasthan. Potential: ~300 GW at 80m hub height (MNRE).

Comparative Analysis: Solar vs. Wind for India

1.4 Hybrid Energy Systems

• Definition: Integration of two or more renewable energy sources (e.g., solar, wind, hydro, biomass) with/without conventional backup (diesel/grid) and storage (battery, pumped hydro) to form a single, more reliable and stable power generation system.

• Need: Mitigate intermittency of single sources, improve capacity factor and reliability, reduce storage requirement, better resource utilization.

• Feasible Hybrid Options in India:

  1. Solar-Wind: Complementary generation profiles (wind stronger at night/monsoon, solar in day/summer). Common for distributed/isolated grids.

  2. Solar-Wind-Diesel: For remote islands/villages (e.g., Lakshadweep, Himalayan regions). Diesel backup for firm power.

  3. Solar-Wind-Hydro (Pumped Storage): Hydro provides storage and fast response. Excellent for grid-scale balancing (e.g., Kerala's 1000 MW solar-wind-pumped hydro project).

  4. Solar-Biomass: Biomass provides base load, solar peaks during day.

• Advantages: Enhanced energy security, reduced diesel consumption, lower levelized cost of energy (LCOE) for reliable power, minimized battery storage size.

2.0 THERMAL POWER PLANT (FOSSIL FUEL)

2.1 Coal Handling System

• Elements & Flow Path: Receiving (Rail/Wagon/Truck) → Unloading → Crushing (primary & secondary) → Screening → Conveying (belt conveyors) → Weighing (weigh feeders) → Storage (stockpiles - live & dead) → Reclaiming → Final Feeding to Boiler (via pulverizers or stokers).

• Schematic:

  DiagramSEARCH: "thermal power plant coal handling system layout"
  • Key Equipment: Wagon tippler, belt conveyors, crushers (jaw, hammer), vibrating screens, stacker-reclaimer, coal bunkers.

2.2 Fuel Burning Systems & Firing Principles

[!TIP] Exam Focus: Be ready to sketch a spreader stoker (overfeed) and an underfeed stoker. Compare based on coal type, air flow, and application.

2.3 Advanced Combustion Technologies: Fluidized Bed Combustion (FBC)

• Working Principle: Solid fuel particles (coal, biomass) are suspended in an upward stream of air (or gas) at a velocity between minimum fluidization and transport velocity. The bed behaves like a fluid—exhibiting high mixing, heat transfer, and uniform temperature.

• Schematic:

  DiagramSEARCH: "bubbling fluidized bed boiler schematic"

  • Bed: Sand/limestone + fuel.

  • Air Distributor: Supports fluidization.

  • Combustion Zone: In-bed heat release.

  • Cyclone Separator (CFBC only): Recirculates solids.

• Types:

  • Bubbling Fluidized Bed Combustion (BFBC): Velocity ~1-2 m/s. Distinct bed surface, bubbles. Simpler, smaller units (50-100 MW).

  • Circulating Fluidized Bed Combustion (CFBC): Velocity ~5-10 m/s. Solids entrained, separated by cyclone, recirculated. Larger units (>100 MW), better heat transfer, longer particle residence.

• Advantages:

  • Fuel Flexibility: Can burn low-grade coals, lignite, biomass, waste (high ash/fuel flexibility).

  • In-situ SOx Control: Limestone (CaCO₃) added to bed captures SO₂ → CaSO₄ (sorbent utilization 80-90%).

  • Low Combustion Temperature: 850-950°C → Low NOx formation (thermal NOx suppressed).

  • High Heat Transfer Coefficient → Smaller boiler size for same capacity.

2.4 Gas Turbine Power Plant

• Simple Open Cycle: Air Compressor → Combustor → Gas Turbine → Exhaust. Efficiency limited by low pressure ratio and high exhaust temperature loss.

• Reheating in Gas Turbines:

  • Concept: Expand high-temperature gas in a high-pressure (HP) turbine stage, then reheat in a second combustor before expanding in a low-pressure (LP) turbine stage.

  • Cycle Improvement (T-s diagram): Increases average temperature of heat addition, reduces compressor work fraction of total work output.

  • How it Improves Thermal Efficiency:

    1. Increases net work output (more expansion stages).

    2. Reduces compressor work fraction (same compressor work but more turbine work).

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

  • Result: Higher cycle efficiency (by 2-5 percentage points) and higher power output for same turbine inlet temperature.

• Regeneration & Intercooling (Brief):

  • Regeneration: Uses exhaust heat to preheat compressed air before combustion → reduces fuel consumption.

  • Intercooling: Cools air between multi-stage compression → reduces compressor work.

  • Combined Effect (Regenerative-Intercooled-Reheat): Maximizes efficiency but increases complexity/cost.

2.5 Feed Water Treatment Plant

• Need for Purity: Prevent scale formation (insulation, hot spots, reduced heat transfer), corrosion (dissolved O₂, CO₂, acids), and erosion (suspended solids).

• Elements/Processes (Typical Flow):

  1. Screening: Removes coarse debris.

  2. Aeration: Strips CO₂, O₂, other gases.

  3. Chemical Treatment:

     • Lime-Soda Process: Precipitates Ca²⁺, Mg²⁺, silica as hydroxides/carbonates. (For high-hardness water).

     • Ion Exchange: Cation exchanger (H⁺ form) removes Ca²⁺, Mg²⁺, Na⁺; Anion exchanger (OH⁻ form) removes Cl⁻, SO₄²⁻, HCO₃⁻. Produces deionized water.

  4. Filtration: Removes suspended precipitates (sand filters, cartridge filters).

  5. Deaeration: Thermal deaerator (heats water to saturation temp, strips O₂/CO₂ with steam) → O₂ < 7 ppb, CO₂ < 7 ppb.

• Final Output: High-Purity Feedwater (conductivity < 0.2 µS/cm, dissolved solids < 100 ppb) to boiler.

2.6 Plant Heat Balance

• Definition: Quantitative accounting of all heat inputs and heat outputs in a power plant over a given period (usually annually). Basis for calculating thermal efficiency.

• Heat Balance Diagram (Simplified):

  
  HEAT INPUTS:
  
  1. Fuel Heat Input (LHV basis) = m_fuel * LHV_fuel
  
  2. (Optional) Auxiliary steam, hot air recirculation
  
  HEAT OUTPUTS:
  
  1. Net Power Output (electrical) = 3600 * MWh (converted to kJ)
  
  2. Heat in Steam (to process/turbine) = m_steam * (h_steam - h_feedwater)
  
  3. Heat Loss in Flue Gas = m_fluegas * Cp_fluegas * (T_stack - T_ambient)
  
  4. Radiation & Unaccounted Losses (~0.5-1% of input)
  
  

• Efficiency Calculation:

$$\eta_{thermal} = \frac{\text{Net Electrical Output (kJ)}}{\text{Total Heat Input from Fuel (kJ)}} \times 100\%$$

*   **Gross Efficiency:** Based on gross power output (before station auxiliaries).

*   **Net Efficiency:** Based on net power output (after deducting station consumption ~5-8%).

• Major Losses: Flue gas loss (largest, 6-10%), radiation, unburnt carbon (in ash), moisture in fuel/air.

2.7 Recent Trends in Boiler Technology

• Increase in Boiler Size & Parameters:

  • Subcritical: < 22.1 MPa, 540/540°C. Older plants.

  • Supercritical (SC): > 22.1 MPa, 540-560°C. Efficiency ~40-42%.

  • Ultra-Supercritical (USC): > 25 MPa, 600°C/600°C (or 620°C/620°C). Efficiency ~43-45%. Current global trend.

• Selection Criteria:

  • Fuel Type: Indian coals (high ash, low volatile) favor tangentially fired or CFBC.

  • Capacity: Larger units (660 MW, 800 MW) have lower specific cost (₹/MW) and auxiliary consumption.

  • Efficiency Target: USC for high efficiency, lower fuel cost & emissions.

  • Emissions: Low-NOx burners (LNB), OFA (Over Fire Air), FGD (Flue Gas Desulfurization), SCR (Selective Catalytic Reduction) for NOx.

• Operational Trends:

  • Flexibility: Ramp rates, part-load efficiency, frequent start-stop (for renewable integration).

  • Digitalization: AI/ML for optimization, predictive maintenance, digital twins.

  • Low-NOx Combustion: Advanced LNB, staged combustion, reburning.

3.0 NUCLEAR POWER PLANT

3.1 Nuclear Fission Phenomenon

• Basic Reaction: $$\displaystyle ^{235}_{92}U + ^1_0n \rightarrow ^{236}_{92}U^* \rightarrow \text{Fission Fragments} + 2-3\, ^1_0n + \text{Energy (}\approx 200\,\text{MeV/fission)} $$.

• Chain Reaction: Neutrons from one fission cause subsequent fissions. Criticality states:

  • Subcritical: Neutron population decreases.

  • Critical: Neutron population steady (k_eff = 1). Normal operation.

  • Supercritical: Neutron population increases (k_eff > 1). Start-up or power increase.

• Role in AGR: Uses enriched uranium (2.5-3.5% U-235) fuel. Graphite moderator, CO₂ coolant. Fission provides heat.

3.2 Reactor Types & Characteristics

Pressurized Heavy Water Reactor (PHWR)

• Working Principle: Natural uranium (0.7% U-235) fuel (UO₂ pellets in Zr-4 clad). Heavy water (D₂O) used as both moderator and coolant. High neutron economy allows natural uranium.

• Schematic/Layout:

  DiagramSEARCH: "PHWR pressure tube calandria diagram"

  • Calandria: Large cylindrical vessel filled with moderator (D₂O) at atmospheric pressure.

  • Pressure Tubes: Horizontal tubes through calandria carrying fuel channels. Coolant (D₂O) flows under high pressure (≈ 100 bar) inside pressure tubes.

  • Fuel Channel: Fuel bundles (37 elements) inside pressure tube. Separator/steamer in inlet/outlet headers.

  • On-Power Refueling: Can add/remove fuel bundles while reactor is critical (using remote machines).

• Key Feature: Pressure Tube Design vs. Pressure Vessel (PWR). Allows larger core, online refueling.

Advanced Gas Cooled Reactor (AGR)

• Working Principle: Second generation of British gas-cooled reactors. Graphite moderator, Carbon Dioxide (CO₂) coolant (pressure ~40 bar). Enriched uranium (2.5-3.5% U-235) fuel in stainless steel clad.

• Features vs. Magnox (First Gen):

  • Higher operating temperature (≈ 650°C vs 400°C) → higher thermal efficiency (~40% vs 30%).

  • Enriched fuel → smaller core, longer refueling outage.

  • Stainless steel cladding → better corrosion resistance, higher temperature capability.

  • Still uses graphite moderator (large, expensive).

Fast Breeder Reactor (FBR)

• Principle: No moderator. Relies on fast neutrons (E > 0.1 MeV). Uses Plutonium-239 (from U-238) as primary fuel, and U-238 (fertile) in blanket to breed more Pu-239 via:

$$^{238}_{92}U + n \rightarrow ^{239}_{92}U \xrightarrow{\beta^-} ^{239}_{93}Np \xrightarrow{\beta^-} ^{239}_{94}Pu$$

*   **Breeding Ratio > 1:** More fissile material produced than consumed.

• Coolant: Liquid Sodium (Na). Excellent heat transfer, low neutron absorption, high boiling point (allows atmospheric pressure operation). Disadvantage: Chemically reactive (fire hazard).

• Comparison with Thermal Reactors:

  | Aspect | Thermal Reactor (PWR/PHWR) | Fast Breeder Reactor (FBR) | | :--- | :--- | :--- | | Neutron Spectrum | Thermal (slowed by moderator) | Fast (no moderator) | | Fuel | U-235 (enriched) or Natural U | Pu-239 + U-238 (blanket) | | Fuel Utilization | Low (~0.5-1% of natural U) | Very High (~60-70% of U-238) | | Waste | Long-lived transuranics | Can burn transuranics (actinides) | | Safety | Negative reactivity feedbacks (Doppler, void) | Positive sodium void coefficient (major safety challenge). | | Status | Commercial (mature) | Prototype/experimental (India's PFBR, Russia's BN-800). |

3.3 Moderators

• Functions: 1. Slow down fast fission neutrons to thermal energies (≈ 0.025 eV) where fission cross-section for U-235 is high. 2. Minimize neutron absorption (low absorption cross-section).

• Types & Characteristics:

3.4 Reactor Control & Safety

Principles of Reactor Control

1. Control Rods:

   • Material: High neutron absorption (B₄C, Ag-In-Cd alloy, Hf).

   • Mechanism: Insertion ( scram/emergency shutdown) or withdrawal (power increase). Driven by electromagnets, hydraulic, or gravity.

2. Chemical Shim (Soluble Boron): Dissolved boric acid in coolant (PWR). Provides fine, uniform reactivity control. Concentration adjusted as fuel burns.

3. Moderator Temperature Coefficient (MTC): Change in reactivity with moderator temp. Negative MTC (most designs) is desirable: as moderator heats up, density ↓, neutron moderation ↓ → reactivity ↓ → inherent safety.

Reliability Features for Nuclear Power Plants

• Multiple Physical Barriers: 1. Fuel matrix (UO₂), 2. Fuel cladding (Zircaloy), 3. Reactor pressure vessel, 4. Containment building (reinforced concrete + steel liner).

• Redundant & Diverse Safety Systems: Multiple, independent trains for critical functions (e.g., 3 independent ECCS trains). Diverse means (e.g., high-pressure injection, low-pressure injection, accumulators).

• Emergency Core Cooling System (ECCS): Defense-in-depth to maintain core cooling during Loss-of-Coolant Accident (LOCA). Includes:

  • High-Pressure Cooling Systems (HPCS)

  • Accumulators (borated water tanks, spring-loaded)

  • Low-Pressure Cooling Systems (LPCS/LPCI)

  • Core Spray System

• Passive Safety Features: Rely on natural forces (gravity, convection, pressure difference) without active components/pumps. Examples: Gravity-driven water tanks, passive containment cooling, natural circulation core cooling (AP1000, EPR).

4.0 HYDROELECTRIC POWER PLANT

4.1 Site Selection Criteria

1. Hydrology: High & reliable rainfall/snowmelt, large catchment area, favorable flow duration curve (high % of time flow > minimum).

2. Topography: Narrow gorge/canyon for dam, steep gradient (head), minimal excavation. Suitable dam site with sound abutments.

3. Geology: Sound rock foundation (granite, gneiss) at shallow depth, low seismicity (earthquake zone), no active faults.

4. Access & Proximity: Access roads/rail, near load center to minimize transmission loss/cost.

5. Environmental & Social Impact: Minimal displacement, forest submergence, impact on aquatic ecology, sedimentation rate.

4.2 Hydraulic Turbines

• Classification by Net Head (H) & Design Discharge (Q):

• Factors for Turbine Selection: Net Head (H), Design Discharge (Q), Efficiency map, Cavitation risk (Thoma's cavitation parameter σ), Cost, Part-load operation.

4.3 Small Hydro Power (Micro & Pico Hydro)

• Definitions (Capacity-based, typical):

  • Small Hydro (SHP): ≤ 25 MW (India's definition).

  • Micro Hydro (MHP): 100 kW – 1 MW.

  • Pico Hydro (PHP): < 100 kW (often < 5 kW for very small).

• Comparison: Micro vs. Pico Hydro Machines:

4.4 Spillways

• Definition & Purpose: Structure to safely pass excess flood water from reservoir downstream, protecting dam from overtopping. Must handle Probable Maximum Flood (PMF).

• Types & Selection:

• Selection Criteria: Dam type & foundation, available head & valley geometry, flood magnitude, cost, sediment passage.

5.0 POWER PLANT ECONOMICS & OPERATION

5.1 Key Performance & Load Indices

5.2 Load & Power Duration Curves

• Load Duration Curve (LDC): Loads arranged in descending order vs. time percentage. Constructed from load curve (load vs. time).

  • Interpretation: Shows firm capacity (load for 100% time), peak load, load variability.

  • Use: Determines installed capacity needed for a given loss-of-load probability (LOLP).

• Power Duration Curve: Same as LDC but power (MW) on Y-axis. Directly related to hydro power planning—shows time for which a given power level is available.

• Use in Hydro Planning: For hydro-thermal coordination. The "firm power" from hydro is the horizontal portion of the power duration curve after subtracting thermal capacity.

5.3 Tariffs & Costing

• Types of Tariffs:

  1. Flat Rate: Fixed charge per unit (kWh) irrespective of consumption/demand. Simple, but no load management.

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

  3. Two-Part Tariff: Fixed charge (based on MD or connected load) + Energy charge (per kWh). Most common for industrial/commercial. Recovers fixed & variable costs.

  4. Power Factor Tariff: Incentive/penalty based on power factor (cos φ). Encourages consumers to improve PF (reduce reactive power draw).

• Objectives: Cost recovery (capital + O&M), load management (shift peak), promote efficiency, cross-subsidization.

5.4 Depreciation & Replacement Cost

• Straight Line Method (SLM):

  • Equal depreciation charge every year.

  • Formula: $$\displaystyle D_{SL} = \frac{P - S}{n} $$

    • $P$: Initial cost, $S$: Salvage value, $n$: Useful life (years).

  • Book Value after $t$ years: $$\displaystyle BV_t = P - t \cdot D_{SL} $$

• Sinking Fund Method (SFM):

  • Annual deposit $A$ invested at interest rate $i$ to accumulate to $(P-S)$ in $n$ years.

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

  • Book Value after $t$ years: $$\displaystyle BV_t = P - (P-S) \cdot \frac{(1+i)^t - 1}{(1+i)^n - 1} $$

• Numerical Example (Nov 2023 Pattern):

  A power plant costs Rs. 90,000, salvage Rs. 5,000, life 15 years, interest 6%.

  SLM: $$\displaystyle D = (90000 - 5000)/15 = \boxed{Rs. 5,667 \text{ per year}} $$

  SFM: $$\displaystyle A = (85000) \times \frac{0.06}{(1.06)^{15} - 1} = 85000 \times \frac{0.06}{2.3966 - 1} = 85000 \times 0.0430 = \boxed{Rs. 3,655 \text{ per year}} $$

5.5 Numerical Problem Solving (Load & Energy)

• Given: Peak loads of 4 regions: 10 MW, 5 MW, 8 MW, 7 MW. Diversity Factor (DF) = 1.5. Annual Load Factor (LF) = 0.6.

• Step 1: Station Maximum Demand (MD_station)

$$DF = \frac{\sum \text{Individual Peaks}}{\text{Station Peak}} \Rightarrow 1.5 = \frac{10+5+8+7}{\text{MD}}$$

$$\text{MD} = \frac{30}{1.5} = \boxed{20 \text{ MW}}$$

• Step 2: Annual Energy Supplied

$$\text{Avg Load} = LF \times \text{MD} = 0.6 \times 20 = 12 \text{ MW}$$

$$\text{Annual Energy} = \text{Avg Load} \times \text{Hours per year} = 12 \times 8760 = 105,120 \text{ MWh} = \boxed{105.12 \text{ GWh}}$$

6.0 AUXILIARY SYSTEMS & COMPONENTS

6.1 Cooling Systems: Cooling Towers

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

• Types:

  1. Natural Draft: Hyperbolic shape creates stack effect (hot air rises). No fans. Large capacity (500+ MW). Low O&M, high capital cost.

  2. Mechanical Draft:

     • Forced Draft: Fan at inlet (air side). Positive pressure.

     • Induced Draft: Fan at outlet (air side). Negative pressure, more common.

     • Forced-Induced: Fans at both ends. Better control.

• Working Principle (Induced Draft): Hot water from condenser sprayed over fill (increases air-water contact). Air drawn by fan through fill, evaporates some water, cools remaining water. Drift eliminators capture water droplets. Cooled water collected in basin, recirculated.

• Components: Fill (film or splash), Drift eliminators, Basin, Fans, Nozzles/Distributors, Make-up water system.

• Key Parameter: Approach = (Tower outlet temp - Wet-bulb temp). Lower approach = better cooling, higher cost.

6.2 Ash Handling Systems (Brief)

• Need: Handle large quantities of ash (30-50% of coal) from boiler (bottom ash, fly ash). Reduce pollution, recover for by-products.

• Types:

  1. Mechanical: Hydraulic rams, conveyors, bucket elevators. For bottom ash.

  2. Hydraulic: High-pressure water jets sluice ash to sump → pumps → ash pond. Common for fly ash (wet system).

  3. Pneumatic: Compressed air conveys dry fly ash. Allows fly ash utilization (cement). More expensive.

6.3 Dust Collection Systems (Brief)

• Cyclones: Inertial separation. Removes coarse particles (>10 µm). Low efficiency, used as pre-cleaner.

• Electrostatic Precipitators (ESPs): Corona discharge ionizes particles → collected on plates. High efficiency (>99.9% for >1 µm), handles large volumes, dry collection. Major equipment for fly ash.

• Bag Filters (Fabric Filters): Physical filtration through fabric bags. Very high efficiency (>99.99% for fine particles). Used where ESP performance drops (low resistivity fly ash). Higher pressure drop.

7.0 INTEGRATED & COMPARATIVE STUDIES

7.1 Comparative Analysis of Power Plants

7.2 Overall Power Plant Selection Factors

1. Resource Availability: Primary determinant (coal mines, river, wind/solar resource, uranium).

2. Economic Viability (LCOE): Levelized Cost of Electricity (₹/kWh) over plant life. Includes capex, O&M, fuel, financing.

3. Grid Stability & Load Following: Need for baseload (thermal, nuclear, hydro), peaking (gas, hydro), intermittent (solar, wind) with backup/storage.

4. Government Policies & Incentives: Carbon pricing, renewable purchase obligations (RPO), subsidies, import duties, nuclear liability act.

5. Social & Environmental Acceptability: Land acquisition, displacement, emissions (carbon, local pollutants), waste disposal (ash, nuclear, solar panels), water use.

END OF UNIT 3 NOTES
Aligned with Dec 2025 & Nov 2023 RGPV question patterns. Focus on definitions, sketches, comparisons, and numerical problems.