How a coal-fired power station works
Follow a subcritical pulverised-coal drum boiler with reheat. Trace three separate fluid paths, see where heat goes, and distinguish generator output from net grid export.
In 60 seconds: how it works
A coal power station burns coal to boil water. The high-pressure steam spins a turbine that drives a generator.
- Coal is ground to a fine powder and burned in a large boiler.
- The heat turns water in the boiler tubes into high-pressure steam.
- The steam spins a turbine connected to a generator, which produces electricity. The steam is reheated between turbine stages.
- The used steam is cooled in a condenser, using cooling water or a cooling tower, and pumped back to the boiler.
- The smoke is cleaned and leaves through the chimney, and the ash is removed.
- A transformer raises the voltage so the electricity can travel to the grid.
Want the engineering detail? Explore the 3D model, then read the engineering notes and the types and variations.
By Power Stations Worldwide · Related reading updated · Preparation and review scope. Educational illustrations; no independent engineering peer review is claimed.
Explore the equipment in 3D
Rotate equipment, follow energy flows and inspect each component. Read the steps below at any time.
Choose a step to read the process. Activate the 3D model or start a guided tour to use the animation controls.
Subcritical pulverised-coal drum boiler with reheat and one closed regenerative feedwater heater. Enlarged original mill, furnace, drum, heating-surface, turbine and condenser cutaways show separate working-fluid, cooling-water and flue-gas paths. Fixed-state 16 MPa/540 °C parameters and losses are illustrative, not a calibrated plant or transient design. Motion is slowed for inspection. Coloured overlays reveal flow through enclosed equipment; gold pulses show net electrical energy transfer, not individual electrons.
How it works
- Coal’s chemical energy
- Furnace heat
- Water / steam circuit
- Turbine shaft
- Generator
- Grid electricity
In a conventional coal station, the furnace supplies heat and the steam turbine converts part of it into mechanical work. Coal is prepared and burned with air; heat passes through boiler-tube walls into the water circuit. The two streams stay separate: flue gas goes toward emissions controls and the stack, while steam goes to the turbine. Reheating steam between turbine sections can improve the cycle and limit moisture in its later stages.
This model keeps a subcritical drum, one reheat and a closed feedwater heater supplied by IP-turbine extraction. Heater drains return to the condenser; the remaining steam reaches two LP branches. Separate condenser cooling water rejects heat to the tower. Pumps, mills, fans and treatment auxiliaries reduce gross generation before net grid export. The dedicated cleanup lesson distinguishes NOx reduction, particle collection and SO₂ removal from CO₂ capture. A single illustrative LHV fuel balance supplies all readings; it is not a calibrated part-load or emissions model.
Reheat is part of the cycle. Cleanup is not cooling.
Simple explanation
Coal and air burn outside the boiler tubes. Water circulates through the water walls and drum; the drum separates steam from water. A superheater raises steam temperature before the high-pressure (HP) turbine. The illustrated 16 MPa pressure is below water’s 22.064 MPa critical pressure, so this remains a subcritical drum boiler. MPa means megapascals. [C1] [C4]
HP exhaust returns to a reheater, then expands through intermediate-pressure (IP) and low-pressure (LP) stages. A small, calculated IP extraction warms feedwater through a closed heater wall. Its drain and LP exhaust reach the condenser. Two pumps return water to the boiler; this loop is not the flue-gas path. [C2] [C5]
Condenser cooling water stays on the other side of tube walls and rejects heat at a tower. The separate gas path has selective catalytic reduction (SCR) for nitrogen oxides (NOx), an electrostatic precipitator (ESP) for particles and wet flue-gas desulfurisation (FGD) for sulphur dioxide (SO₂). They are not carbon dioxide (CO₂) capture equipment. [C7] [C8] [C9] [C10]
Selected: Whole plant. The same stage is highlighted in the diagram and optional 3D view.
Where does the fuel energy go?
The selected case is 1000 MWth on an illustrative 25 megajoules per kilogram (MJ/kg) LHV basis. LHV excludes recovering water-vapour condensation heat from fuel products. The boiler transfers 90% of that input into main-steam and reheat duties; the other 10% is a grouped loss allowance, not a calculated pollutant stream. Gross output is before auxiliaries; net export is after auxiliaries and transformer loss. [C2]
| Measurement / budget | Power |
|---|---|
| Fuel LHV input | 1000.000 MWth |
| Boiler heat into main + reheat | 900.000 MWth |
| Boiler loss allowance | 100.000 MW |
| Reheat duty · included in boiler heat | 147.399 MWth |
| Closed heater · internal recovered heat | 130.411 MWth |
| HP shaft work | 110.120 MW |
| IP shaft work | 84.375 MW |
| Combined LP shaft work | 168.190 MW |
| Total turbine shaft work | 362.685 MW |
| Gross generator output | 355.431 MWe |
| Pump electrical consumption | 5.865 MWe |
| Other electrical auxiliaries | 21.326 MWe |
| Transformer loss | 1.641 MW |
| Net export | 326.599 MWe |
| Condenser heat · including heater drains | 542.887 MWth |
| Total unexported power | 673.401 MW |
Fuel input 1000.000 MW = net export 326.599 MW + unexported power 673.401 MW. Calculated unrounded residual: 0.00e+0 W.
Unexported power comprises boiler loss 100.000 MW, condenser heat 542.887 MW, generator loss 7.254 MW, pump-motor loss 0.293 MW, other auxiliary consumption 21.326 MW and transformer loss 1.641 MW. Pump fluid work 5.572 MW enters the cycle; only pump-motor loss is added to that environmental ledger. Do not add the full electrical pump load again. Internal reheat and feedwater heating are not additional external fuel.
Reference example: 1000 MWth fuel supplies 275.933 kg/s main steam and 326.599 MWe net export. It leaves 673.401 MW unexported. The example is invented, not an actual station rating. Rounding displayed values may obscure the unrounded checked balance.
Steam, extraction and return water
Main flow 275.933 kg/s; heater extraction 52.608 kg/s (19.07%); remaining LP flow 223.325 kg/s, split equally between two branches. Condenser return plus heater drains restores the full main flow.
| Point | p · MPa | T · °C | h · kJ/kg | s · kJ/(kg K) | x / phase | Flow · kg/s |
|---|---|---|---|---|---|---|
| Condenser liquid outlet | 0.010 | 45.81 | 191.81 | 0.6492 | 0.0000 · saturated-liquid | 275.933 |
| Condensate pump outlet | 0.100 | Not calculated | 191.92 | Not calculated | compressed-liquid | 275.933 |
| Boiler feed pump outlet | 16.000 | Not calculated | 212.00 | Not calculated | compressed-liquid | 275.933 |
| Heated feedwater (heater tubes) | 16.000 | 160.00 | 684.62 | 1.9247 | compressed-liquid | 275.933 |
| Economiser liquid outlet | 16.000 | 280.00 | 1232.70 | 3.0380 | compressed-liquid | 275.933 |
| Main superheated steam → HP | 16.000 | 540.00 | 3412.10 | 6.4493 | superheated-steam | 275.933 |
| HP outlet → reheater | 3.000 | 307.43 | 3013.02 | 6.5735 | superheated-steam | 275.933 |
| Reheated steam → IP | 3.000 | 540.00 | 3547.20 | 7.3493 | superheated-steam | 275.933 |
| IP outlet / heater extraction | 1.000 | 389.16 | 3241.42 | 7.4324 | superheated-steam | 275.933 |
| Combined LP exhaust (two equal branches) | 0.010 | 45.81 | 2488.30 | 7.8491 | 0.9600 · wet-steam | 223.325 |
| Heater shell drain before throttle | 1.000 | 179.88 | 762.52 | 2.1381 | 0.0000 · saturated-liquid | 52.608 |
| Flashed heater drain → condenser | 0.010 | 45.81 | 762.52 | 2.4385 | 0.2386 · wet-steam | 52.608 |
| Drum saturated-vapour region | 16.000 | 347.36 | 2580.80 | 5.2463 | 1.0000 · saturated-vapor | Not calculated |
p = absolute pressure; T = temperature; h = specific enthalpy (energy per unit mass); s = specific entropy; x = vapour mass fraction in a saturated mixture. A quality is not assigned to superheated HP/IP steam or compressed liquid. Pump-outlet temperature and entropy are not invented. Drum circulation is conceptual; its circulation flow is not equated to generated main-steam flow. LP exhaust wetness is a teaching result, not a qualified blade-moisture or erosion limit.
| Section | Duty |
|---|---|
| Economiser: compressed-liquid heating | 151.233 MWth |
| Water walls: remaining liquid heating + evaporation | 371.985 MWth |
| Superheater: dry steam → main steam | 229.383 MWth |
| Reheater | 147.399 MWth |
Engineering details
One bounded steady calculation uses SI units. ṁ is mass flow (kg/s), Q̇ heat-transfer rate (W), P power (W), v specific volume (m³/kg), Δp pressure rise (Pa), η efficiency, β extraction fraction and ω angular speed (rad/s). Use enthalpies in J/kg and entropies in J/(kg K) internally; table values are divided by 1000. Neglect fluid kinetic/potential energy, piping heat and pressure drops. [C2]
P_fuel = ṁ_fuel LHV · Q̇_boiler = η_boiler P_fuel
h_out = h_in − η_turbine(h_in − h_out,is)
“is” denotes the ideal isentropic endpoint at the specified outlet pressure. HP expansion uses the narrow NIST 3 MPa/280–290 °C entropy bracket; the actual HP outlet uses 300–310 °C enthalpy interpolation. IP uses the 1 MPa/360–370 °C ideal bracket and 380–390 °C actual bracket. These local interpolations are not a full steam-property solver. Use the actual IP entropy for subsequent LP expansion. [C4]
x_LP,is = (s_IP − s_f)/(s_g − s_f)
h_LP,is = h_f + x_LP,is(h_g − h_f)
Subscripts f and g denote saturated liquid and vapour at 10 kPa; the actual LP endpoint follows the same turbine-efficiency equation. Apply the quality relation only inside the saturation region, not to superheated steam. Illustrative HP/IP/LP efficiencies are each 0.85. Reheat raises HP exhaust to 540 °C at 3 MPa, drawing heat from the same boiler. [C2] [C4]
w_pump = v_f Δp / η_pump
β = (h_heated-feed − h_pump)/(h_IP − h_heater-drain)
Condensate pumping raises 0.010→0.100 MPa; boiler feed pumping raises 0.100→16 MPa. Both use illustrative hydraulic efficiency 0.80 and motor efficiency 0.95. Their fluid work raises feed enthalpy once. Extracted 1 MPa steam condenses to saturated liquid outside 16 MPa heater tubes. Heated feedwater is 160 °C, below extraction saturation 179.878 °C: the positive terminal difference is 19.878 K. This is a heat balance, not an area or pressure-vessel design. Drains throttle isenthalpically to the condenser and partly flash. [C2] [C4]
ṁ_main = Q̇_boiler / [(h_main − h_heated-feed) + (h_reheat − h_HP)]
P_shaft = ṁ_main[(h_main − h_HP) + (h_reheat − h_IP) + (1−β)(h_IP − h_LP)]
Q̇_condenser = ṁ_main[(1−β)(h_LP − h_f) + β(h_heater-drain − h_f)]
The condenser receives both LP exhaust and heater drains. Boiler duties comprise economising to 280 °C liquid, remaining liquid heating/evaporation at the 16 MPa drum, superheat to 540 °C and reheat. Heat crosses walls; combustion products never become the turbine's working fluid. The density-driven circulation illustration uses no invented circulation ratio. [C1] [C4] [C5]
P_gross = 0.98 P_shaft
P_aux = P_pump,electric + 0.06 P_gross
P_net = 0.995(P_gross − P_aux) · η_net = P_net/P_fuel
Generator efficiency 0.98, other auxiliaries 6% of gross and transformer efficiency 0.995 are illustrative constants. The 6% allowance groups mills, fans, cooling and treatment loads but excludes the two explicitly calculated pumps. There is no assumed emissions-removal efficiency or measured gas concentration. Station-service takeoffs are omitted from the diagram and 3D wiring; the gross-to-transformer-input reduction is auxiliary consumption, not a loss attributed to the breaker. At positive load, physical n = 120f/p = 3000 rpm, where f = 50 Hz and p = two total poles. Torque τ = P_shaft/ω with ω = 2πn/60. [C2] [C3]
The synchronous generator produces three-phase AC directly. Excitation supplies the rotor magnetic field; stationary windings carry the output through switchgear and a transformer. A transformer changes AC voltage, not AC to DC. The ESP may have its own local rectified auxiliary supply, but that is not an AC/DC/AC conversion stage in the generator's export route. This page does not calculate voltage/current waveforms, protection settings or excitation dynamics. [C3] [C9]
Cooling and emissions cleanup: different jobs
A condenser rejects cycle heat through tube walls; tower cooling water does not become boiler feedwater. The tower's visible plume depicts condensed water droplets. Stack-gas arrows show combustion-product direction, not a measured plume, concentration or clearance. No visible smoke does not imply zero emissions.
- SCR: ammonia reagent and a catalyst reduce NOx to nitrogen and water under suitable gas conditions. The chosen hot-side arrangement is after the economiser and before the air heater; other arrangements exist. [C7]
- ESP: corona charging moves particles to collection plates; rapping releases collected dust to ash hoppers. This targets particles, not CO₂. [C9]
- Wet FGD: alkaline limestone slurry absorbs SO₂; a mist eliminator limits entrained droplets and forced oxidation supports gypsum handling. This does not imply all pollutants are removed or constitute CO₂ capture. Separate carbon-capture equipment is not modelled. [C8] [C10]
What the cutaways can—and cannot—show
The original editable scene shows roller/classifier mill internals, burner air/fuel separation, water-wall headers, drum separators, superheater/reheater walls, fixed stators and turning turbine/generator rotors, condenser tubes, bearings, supports and access platforms. Stacker slew is constrained around its pivot; bucket rotation is distinct from boom motion. Placing a flow marker inside a tube illustrates direction, not local velocity. [C1] [C5] [C6]
One scene unit represents roughly 5 metres, but distances are compressed and internals/cutaway openings enlarged. Blade counts, proportions and clearances are pedagogical, not OEM dimensions. Pipe/shaft connections and selected moving/fixed regions are checked against authored geometry; no complete interference, stress, pressure-vessel, thermal-hydraulic, emissions, safety or standards-compliance assessment is claimed. The fixed-state model omits real part-load efficiency, startup/shutdown, steam pressure drops, air/fuel composition, ash rates, wetness limits and cooling-weather response.
Download the editable Coal Blender scene · Download the optimized browser model
Check your understanding
1. Why does the reheater not count as another fuel input?
The same coal boiler supplies main-steam and reheat heat. Both duties share its single fuel budget; adding reheat as new fuel would double-count an internal transfer.
2. Does all main steam pass through the LP turbines?
No. A calculated IP extraction supplies the closed heater. The remaining fraction goes to two LP branches; the extracted mass returns as heater drains to the condenser.
3. Does the cooling tower clean flue gas or capture CO₂?
No. It rejects condenser heat through a separate water loop. SCR, ESP and wet FGD have separate pollutant-specific functions, and the model includes no CO₂ capture equipment.
Main book references
Actual accessible passages, not just metadata, were read on . Only the named passages were checked. The page is not independently engineering peer reviewed; software and geometry checks are not installation approval.
- [C1] Babcock & Wilcox. Steam: Its Generation and Use. 42nd ed., 2015. Editor Gregory L. Tomei. ISBN 9780963457028. Lawful publisher sample: actual Chapter 1, printed pp. 1–1 through 1–4, checked for water-wall heating, drum separation and circulation. Full pulveriser, reheat and cleanup chapters were not accessible beyond the table of contents; those details are cross-checked with primary supplements rather than invented book citations.
- [C2] US DOE. Thermodynamics, Heat Transfer, and Fluid Flow. DOE-HDBK-1012/1-92, Vol. 1, June 1992. Actual handbook, printed pp. 79–82, 84 and 90–91: steady turbine, pump, heat-exchanger and cycle balances. The extraction/reheat equations here are original derivations for the selected architecture.
- [C3] H. H. Woodson and J. R. Melcher. Electromechanical Dynamics. Part I, Wiley/MIT, 1968. Actual MIT-hosted chapter, §4.1.8/equation 4.1.95, checked for the synchronous pole/speed relation.
Supplementary technical sources
- [C4] A. H. Harvey. NISTIR 5078, Thermodynamic Properties of Water: Tabulation from the IAPWS Formulation 1995. 1998. Actual Table 3, printed pp. 38–39, 46–47, 58–59, and Table 2, printed pp. 11, 13, 15. Exact source points and narrow interpolation brackets support the 1/3/16 MPa states, 10 kPa condensation and critical-pressure distinction; this is not a full property solver.
- [C5] B&W. Radiant-boiler brochure E101-3193A, ©2018. Actual brochure, printed pp. 4–7, checked for circulation, drum separators and heating-surface arrangement. Geometry is original; no product rating or compliance is adopted.
- [C6] B&W. Roll Wheel pulveriser brochure E101-3143D, ©2019. Actual brochure, printed p. 6, checked for primary-air/classifier/roller/drive principles. The model is a generic original cutaway, not a copied proprietary design.
- [C7] US EPA. Selective catalytic reduction, EPA-452/F-03-032, 2003. Actual fact sheet, theory printed p. 3: reagent, catalyst, NOx reduction and possible hot-side placement. No historical removal/cost figures adopted.
- [C8] US EPA. Flue-gas desulfurisation, EPA-452/F-03-034, 2003. Actual fact sheet, theory printed p. 3: wet alkaline slurry, mist separation, forced oxidation and gypsum.
- [C9] US EPA. Dry wire/plate electrostatic precipitator, EPA-452/F-03-028, 2003. Actual fact sheet, theory printed pp. 3–4: charging, plates, rapping, hoppers and local auxiliary power. No quantified emissions model.
- [C10] DOE/NETL. Carbon Capture overview. Primary CO₂-separation overview, accessed 3 October 2026. Carbon capture requires a separate process; the pictured cleanup train is not such a process.
Inside the engineering
Follow the machinery, the working fluids and the electrical connection.
Mechanical
A constrained stacker/reclaimer, conveyors, mills and supported air/fuel ducts prepare combustion. HP, IP and two LP sections share a coaxial generator train; stators, housings, bearings and supports stay fixed. Condensate and boiler feed pumps return water through a closed extraction heater and economiser.
Thermal & chemical
Burners transfer heat across water-wall, superheater and reheater tubes. A drum separates steam below critical pressure. SCR plus reagent reduces NOx; the ESP collects particles; wet FGD targets SO₂. This is not CO₂ capture. Condenser tube walls isolate cooling water; tower droplets are not stack emissions.
Electrical
A two-total-pole, 50 Hz synchronous generator runs at 3000 rpm in the positive teaching case, separately slowed for display. Three-phase AC passes switchgear and a transformer directly to the grid. One LHV fuel balance accounts for boiler losses, generator losses, separately calculated pumps, other auxiliaries, transformer loss and net export; the isolated zero-fuel case has no power flow.
Main types and variations
The model illustrates a pulverised-coal steam plant. Subcritical, supercritical and ultra-supercritical describe steam conditions; fluidised-bed describes the furnace, so those categories can overlap. Gasification combined cycle changes the conversion route more fundamentally. These labels do not identify the grade of coal being burned.
Subcritical steam cycle
The boiler operates below water’s critical pressure, where liquid water and steam can coexist during boiling. A typical drum boiler separates steam from circulating water, then superheats the steam before the turbine. The term describes pressure conditions, rather than whether the furnace burns pulverised fuel or uses another combustion arrangement.
What changes in practice
The steam drum and circulation system shape plant layout and operation. Raising steam conditions can improve cycle efficiency, but requires equipment designed for the higher stresses.
Mitsubishi Power: Steam power plants and boiler designs (PDF)
Supercritical steam cycle
At pressures above water’s critical pressure, heating does not cross a distinct liquid-to-vapour boiling boundary. A once-through boiler raises the fluid to the turbine’s required inlet conditions. This statement applies to that high-pressure heating path; the complete cycle still includes lower-pressure expansion, cooling and condensation.
What changes in practice
Higher operating conditions can extract more electricity from the same fuel input. Flow control and suitable boiler materials remain essential to managing heat transfer safely.
Maharashtra Directorate of Steam Boilers: Supercritical boilers
Ultra-supercritical steam cycle
Ultra-supercritical is an industry description for especially demanding steam conditions within the supercritical family, not a new phase of water. Higher steam temperatures and pressures increase the demands on boiler tubes, turbine parts, valves and welds. Advanced ultra-supercritical research pushes these material requirements further.
What changes in practice
Improved thermal efficiency can reduce fuel consumption per unit of electricity. Creep resistance, corrosion and fabrication capability constrain the materials and conditions engineers can select.
Fluidised-bed combustion
Upward-flowing air suspends and mixes a bed of hot solids with the fuel. Heat passes into boiler surfaces, and limestone can capture sulfur within the furnace. In a circulating design, separated solids return to the bed. The downstream steam turbine still converts boiler heat into electricity.
What changes in practice
Thorough mixing supports fuel flexibility and in-furnace sulfur control. Bed solids, ash and the remaining flue-gas pollutants still need appropriate handling and treatment.
Integrated gasification combined cycle
A gasifier converts coal into synthesis gas, mainly a combustible mixture of carbon monoxide and hydrogen. After particles and other contaminants are removed, this gas fuels a combustion turbine. Heat recovery supplies a steam turbine, combining gasification equipment with a gas-and-steam power cycle.
What changes in practice
Fuel cleanup happens before the gas turbine. Gasifiers, cleanup systems and often oxygen-production equipment add complexity; gasification alone does not mean carbon dioxide is captured.
Worth knowing
- Coal produces more carbon dioxide per unit of electricity than any other major source.
- Many countries are closing or converting coal plants.
- Biomass plants often use a very similar boiler and steam cycle.
See real examples
The atlas includes 2,333 coal records worldwide.
Show on the mapRelated answers
Textbook references
Suggested technical background for this topic. These books are further reading, not proof that every explanation was checked against every edition. See the full bibliography and review scope.
- Steam: Its Generation and UseBoilers, combustion, steam generation and emissions control.
- Thermodynamics: An Engineering ApproachRankine cycle efficiency, reheat and regeneration.
Sources
- EIA: Use of coal ↗
- US EPA: Air-pollution control equipment ↗
- Babcock & Wilcox: checked Steam 42 publisher sample ↗
- EIA: How electricity is generated ↗
Cutaways reveal enclosed equipment. Layouts, dimensions, materials and animation speeds are illustrative; this is an educational model, not a plant design. The fixed-state calculation is not a transient combustion, emissions, pressure-vessel or safety simulation.