Power Eng 3rd Class cheat sheet

Sensible heat: Q = m·cp·ΔT; latent heat uses enthalpy of vaporization/condensation instead of cp.

Steam tables give saturation temperature/pressure pairs; superheated steam needs both pressure and temperature to fix state.

First Law for steady flow: q − w = Δh + ΔKE + ΔPE (per unit mass); for a boiler w = 0, so q ≈ Δh.

Thermal efficiency of a Rankine cycle = (h1 − h2) − (h4 − h3) divided by (h1 − h4), using pump and turbine enthalpies.

Conduction: Q = k·A·ΔT/L; convection: Q = h·A·ΔT; radiation: Q = ε·σ·A·(T1⁴ − T2⁴) with T in kelvin.

Overall heat-transfer coefficient U combines series resistances: 1/UA = 1/(hA) inside + wall resistance + 1/(hA) outside.

LMTD = (ΔT1 − ΔT2)/ln(ΔT1/ΔT2); use it with Q = U·A·LMTD for heat exchangers.

Entropy increases in any real (irreversible) process; isentropic efficiency compares actual to ideal work.

Absolute pressure = gauge pressure + atmospheric pressure; vacuum readings are subtracted from atmospheric.

Theoretical (stoichiometric) air is the minimum O2 needed for complete combustion; excess air = (actual air − theoretical)/theoretical × 100%.

Typical excess-air targets: ~15% for gas/oil, ~20–30% for coal; too little gives CO and smoke, too much wastes heat up the stack.

Combustion products: C + O2 → CO2; 2H2 + O2 → 2H2O; incomplete combustion yields CO, so CO in flue gas signals air deficiency.

Drum water level must be maintained near normal water level (NWL); low water can expose tubes and cause overheating and failure.

Safety valve setting must not exceed the boiler's maximum allowable working pressure (MAWP); it protects against overpressure.

Blowdown removes dissolved solids and sludge; bottom blowdown also removes sediment, surface (continuous) blowdown controls dissolved solids.

A boiler's evaporative capacity is expressed as kg/h of steam; equivalent evaporation normalizes to 100 °C feedwater at 100 °C.

Draft is measured in pascals or mm of water column; balanced draft keeps furnace slightly negative.

Forced-draft fan supplies combustion air; induced-draft fan pulls flue gas out and maintains furnace negative pressure.

Air preheater recovers stack heat to warm combustion air, raising boiler efficiency by lowering exit gas temperature.

Economizer heats feedwater using flue gas; it lowers stack loss but must stay above acid dew point to avoid corrosion.

Superheater raises steam temperature above saturation; attemperation (spray) controls final steam temperature.

Sootblowers remove ash/fouling from tube surfaces; fouling raises gas-side resistance and reduces heat transfer.

Steam traps remove condensate while holding back steam; failed-open traps waste steam, failed-closed traps cause water hammer.

Deaerator removes dissolved O2 and CO2 by heating water to saturation and venting; it also serves as feedwater storage.

Ash-handling and dust-collection systems (baghouse, ESP) control particulate emissions; ESP efficiency depends on resistivity and field strength.

Gate valves are for on/off isolation with low pressure drop; globe valves are for throttling and give higher pressure drop.

Check valves allow flow in one direction only and prevent backflow; they are not used for throttling.

Safety (relief) valves open at set pressure; they must be tested and sealed, never used as a control valve.

Steam traps and drain valves must be installed at low points and before valves to remove condensate and avoid water hammer.

Pipe expansion is handled by loops, bends, or expansion joints; anchors and guides direct movement and prevent stress.

Water hammer results from rapid valve closure or trapped condensate; prevention is slow closing and proper drainage.

Pressure ratings of flanges and fittings drop as temperature rises; select by design pressure and temperature together.

A pressure-reducing valve maintains downstream pressure; a bypass and safety valve downstream are commonly required.

Centrifugal pump head-capacity curve slopes down; operating point is where the pump curve meets the system curve.

Cavitation occurs when local pressure falls below vapor pressure; NPSH available must exceed NPSH required.

Affinity laws: flow ∝ speed, head ∝ speed², power ∝ speed³ for a given impeller.

Positive-displacement pumps deliver nearly constant flow regardless of pressure; a relief valve is required on the discharge.

Reciprocating compressors are positive displacement; centrifugal compressors suit large flows at high volume.

Turbine efficiency = actual work / isentropic work; steam turbines use enthalpy drop across stages.

Pump power ≈ (ρ·g·Q·H)/efficiency; compressors use polytropic or isentropic power relations.

Vibration, high bearing temperature, and abnormal noise signal misalignment, imbalance, or bearing wear.

A control loop has a sensor/transmitter, controller, and final control element; the controller compares measurement to setpoint.

PID control: proportional responds to error, integral eliminates offset, derivative anticipates rate of change.

Low-water fuel cutoff (LWCO) shuts off fuel on low drum level; it must be tested regularly and is a critical safety device.

Flame scanners (flame safeguards) prove main flame and pilot; loss of flame signal must trip fuel within the trial-for-ignition time.

Pressure and temperature transmitters output 4–20 mA; 4 mA is live zero so a broken wire is detectable.

Safety interlocks trip the burner on high pressure, low water, low fuel pressure, or loss of combustion air.

A deadweight tester calibrates pressure gauges; gauges should be checked against a known standard.

Boiler trips and alarms must be annunciated; bypassing a safety device requires formal authorization and documentation.

Ohm's law: V = I·R; power: P = V·I = I²·R for DC and resistive AC loads.

Three-phase power = √3·V_L·I_L·power factor; power factor correction reduces reactive current and line losses.

Motor full-load current rises with load; overload relays protect motors from sustained overcurrent.

Circuit breakers and fuses protect against short circuit and overload; earthing/grounding protects personnel.

Lockout/tagout (LOTO) isolates energy sources before maintenance; verify zero energy before work.

Motor starters (DOL, star-delta, VFD) control starting current; VFDs vary frequency to control speed.

Insulation resistance testing (megger) checks winding insulation; low readings indicate moisture or degradation.

Standby generators and emergency power must be tested under load; automatic transfer switches switch between sources.

Scale forms from hardness (Ca, Mg) salts; softening or demineralization removes scale-forming ions.

Dissolved oxygen causes pitting corrosion; deaeration plus oxygen scavenger (e.g., sulfite) controls it.

pH control: boiler water typically alkaline (around 10–11) to limit corrosion; too high promotes caustic embrittlement.

Conductivity or TDS indicates dissolved solids; continuous blowdown controls them to prevent carryover.

Silica can carry over into steam and deposit on turbine blades; limit silica in boiler water.

Phosphate treatment precipitates hardness as sludge, removed by blowdown.

Condensate return should be monitored for corrosion products and contamination; returning clean condensate saves energy.

Chemical dosing must match load and water quality; over-dosing or under-dosing both cause problems.

Refrigeration cycle: compressor raises pressure, condenser rejects heat, expansion valve drops pressure, evaporator absorbs heat.

COP = refrigeration effect / work input; higher COP means more efficient cooling.

Superheat at evaporator outlet protects the compressor from liquid slugging; subcooling at condenser outlet improves capacity.

Refrigerant pressure–temperature relationship: saturation pressure corresponds to evaporating or condensing temperature.

Chillers use chilled water or direct expansion; cooling towers reject condenser heat to atmosphere.

HVAC comfort depends on dry-bulb temperature, humidity, and air movement; psychrometrics relates them.

Air handling units use filters, coils, and fans; dirty filters reduce airflow and increase energy use.

Compressor high discharge pressure often indicates fouled condenser or non-condensable gases.

Boiler and pressure-vessel codes set design, materials, welding, inspection, and stamping requirements; follow the applicable code edition.

Periodic inspection and hydrostatic testing verify integrity; records must be retained and available.

Safety valves must be set, sealed, and tested per code; tampering is prohibited.

Confined-space entry requires permit, atmospheric testing, ventilation, attendant, and rescue plan.

Hot-work permits control welding/cutting near flammables; fire watch and extinguisher required.

Lockout/tagout and energy isolation are mandatory before maintenance on rotating or electrical equipment.

Operators must hold the required certification/qualification for the boiler class and plant.

Report accidents and near misses; statutory notifications apply to serious incidents.

Preventive maintenance schedules reduce unplanned outages; lubrication, alignment, and inspection are core tasks.

Log readings (pressure, temperature, level, flow) at defined intervals to trend performance and detect drift.

Startup sequence typically includes checks, purge, pilot light-off, main flame, and gradual load increase.

Shutdown sequence: reduce load, stop fuel, purge, and maintain water level during cooldown.

Root-cause analysis (5 Whys, fishbone) identifies underlying causes of failures rather than symptoms.

Spare-parts and consumables inventory must match critical equipment; critical spares avoid long downtime.

Shift handover should document abnormal conditions, ongoing work, and outstanding permits.

Energy efficiency monitoring compares actual fuel/steam ratio to baseline; deviations trigger investigation.

Steam turbine stages: impulse (pressure drop across nozzles) and reaction (pressure drop across moving blades).

Turbine overspeed trip protects against loss of load; it must be tested regularly.

Condenser vacuum improves turbine efficiency by lowering exhaust pressure and increasing enthalpy drop.

Gas turbine efficiency rises with firing temperature and pressure ratio; compressor fouling reduces output.

Diesel engines: compression ignition; power depends on fuel rate and air supply; turbocharging increases output.

Governor controls prime-mover speed by adjusting fuel/steam input to match load.

Alignment of prime mover to driven equipment prevents vibration and coupling wear.

Cooling and lubrication of bearings are essential; high temperature indicates inadequate flow or wear.

Pressure gauges must be selected for the range; a gauge should read near mid-scale at normal operating pressure.

Thermocouples and RTDs measure temperature; RTDs are more accurate at low temperatures, thermocouples suit high temperatures.

Flow measurement: orifice plate uses differential pressure; accuracy depends on straight pipe runs and tapping.

Level measurement: differential pressure, float, or radar; density changes affect DP level accuracy.

Control valves fail-safe position (fail-open or fail-closed) is chosen based on process safety.

Alarm and trip setpoints must be below mechanical limits and above normal operating range.

Calibration records and traceability are required for safety-critical instruments.

Interlock testing before startup confirms trips function; document results.

Motor nameplate gives voltage, current, power factor, speed, and insulation class; operate within ratings.

Star-delta starting reduces starting current but also reduces starting torque.

VFDs control motor speed and can cause harmonics; filters and proper grounding mitigate issues.

Earth fault protection detects leakage current to ground; residual current devices protect personnel.

Cable sizing considers current-carrying capacity and voltage drop; long runs need larger conductors.

Batteries and UPS support critical controls during power loss; test capacity periodically.

Arc-flash hazards require PPE and safe work procedures; de-energize before opening panels.

Phase imbalance and single-phasing damage motors; protection relays detect them.

Feedwater temperature affects boiler efficiency; economizer and deaerator raise it.

Condensate polishing removes corrosion products and dissolved solids for high-pressure boilers.

Amine dosing raises condensate pH to protect return lines from carbonic acid corrosion.

Chloride and sulfate limits protect against stress-corrosion cracking in high-pressure boilers.

Blowdown rate is set by allowable dissolved solids; automatic blowdown uses conductivity control.

Sampling points must be representative; cool samples before testing.

Iron and copper in feedwater indicate corrosion; investigate source.

Chemical storage and handling require labeling, secondary containment, and PPE.

Cooling tower approach = leaving water temperature minus wet-bulb temperature; lower approach means better performance.

Chiller efficiency expressed as kW per ton of refrigeration; lower is better.

Air filters classified by MERV; higher MERV captures finer particles but increases pressure drop.

Duct static pressure controls fan speed in variable-air-volume systems.

Steam and hot-water heating coils require traps and vents to remove air and condensate.

Compressor oil management: oil separators and proper charge prevent oil logging and wear.

Refrigerant leak detection protects personnel and environment; some refrigerants are asphyxiants.

Economizer cooling uses outside air when conditions allow, reducing mechanical cooling.

Permit-to-work systems control high-risk tasks; permits specify hazards and controls.

Isolation certificates confirm equipment is de-energized and drained before maintenance.

Emergency response plans cover fire, leak, and evacuation; drills verify readiness.

Personal protective equipment selection follows hazard assessment (heat, chemical, electrical).

Noise and heat stress are occupational hazards requiring monitoring and controls.

Environmental limits on emissions (NOx, SOx, particulate) require monitoring and reporting.

Waste and effluent disposal must follow regulations; record manifests.

Management of change (MOC) reviews modifications before implementation.

Boiler efficiency can be estimated by direct method (heat output/heat input) or indirect (losses) method.

Stack loss is the largest boiler loss; it rises with excess air and exit gas temperature.

Heat rate = fuel energy input / useful output; lower heat rate means better efficiency.

Performance tests require steady load and calibrated instruments.

Trending vibration and temperature predicts failures before breakdown.

Work orders should record cause, action, and parts used for history.

Training and competency records support safe operation and audits.

Energy audits identify savings from insulation, traps, and combustion tuning.

Compressor volumetric efficiency falls as clearance volume and pressure ratio increase.

Intercooling between stages reduces work and improves efficiency.

Surge in centrifugal compressors is reversed flow at low flow; anti-surge control recycles flow.

Compressor discharge temperature rises with pressure ratio; cooling and lubrication control it.

Air dryers remove moisture; dew point depends on dryer type.

Reciprocating compressor valves and rings wear; monitor pressure and temperature.

Compressor efficiency compares actual power to ideal isentropic power.

Safety valves and relief devices protect compressors and receivers from overpressure.

Control valve flow characteristic: linear, equal-percentage, quick-opening; equal-percentage suits wide range.

Valve sizing uses Cv, which relates flow to pressure drop and specific gravity.

Cavitation in liquid control valves causes noise and damage; avoid by limiting pressure drop.

Positioners improve valve response and accuracy.

Actuator air failure position must be defined for safety.

Valve stroke testing verifies travel and calibration.

Stiction causes poor control; regular maintenance prevents it.

Bypass valves allow maintenance without shutdown; use with care.

Generator output depends on excitation (voltage) and prime-mover input (frequency/load).

Synchronization requires matching voltage, frequency, and phase before paralleling.

Load sharing between generators is controlled by governor droop settings.

Protective relays (overcurrent, differential, reverse power) isolate faults.

Earthing of generator neutral limits fault current.

Excitation systems control reactive power and voltage.

Black-start capability allows restart without grid power.

Regular testing of generators and switchgear ensures reliability.

Total dissolved solids limits depend on boiler pressure; higher pressure requires lower TDS.

Alkalinity control prevents foaming and caustic attack.

Hardness in boiler water indicates softener breakthrough; act promptly.

Dissolved oxygen limits are tight for high-pressure boilers.

Iron and copper limits protect against deposition.

Silica limits depend on pressure and turbine requirements.

pH and conductivity are routine tests; log results.

Chemical feed rates should be adjusted to test results, not fixed.

Steam traps: thermodynamic, thermostatic, and mechanical types; select by application.

Flash steam forms when high-pressure condensate drops in pressure; recover it.

Condensate receivers and pumps return condensate to the deaerator.

Steam headers need drains at low points and before valves.

Insulation reduces heat loss and protects personnel.

Air in steam systems reduces heat transfer; vents remove it.

Water hammer from condensate must be prevented by proper trapping and drainage.

Steam quality (dryness) affects turbines and processes.

Pressure-relief device sizing uses required capacity and set pressure.

Inspection intervals are set by code and service conditions.

Repairs to pressure parts require qualified welders and procedures.

Records of inspections and repairs must be kept.

Non-destructive testing (radiography, ultrasonic, dye penetrant) verifies integrity.

Hydrostatic test pressure is typically a multiple of design pressure per code.

Operators must not alter safety devices or setpoints.

Incident reporting and investigation are required.

Condition monitoring: vibration, oil analysis, thermography.

Planned maintenance reduces reactive work.

Failure modes and effects analysis (FMEA) prioritizes risks.

Criticality ranking guides spare parts and inspection.

Root-cause analysis prevents recurrence.

Contractor management requires induction and supervision.

Documentation and drawings must be current.

Continuous improvement uses performance data.

Dry-bulb temperature measures sensible heat; wet-bulb reflects evaporative cooling.

Relative humidity = actual vapor pressure / saturation vapor pressure.

Dew point is the temperature at which condensation begins.

Enthalpy of moist air includes sensible and latent components.

Humidification and dehumidification change moisture content.

Cooling coils condense water when below dew point.

Psychrometric charts relate dry-bulb, wet-bulb, humidity, and enthalpy.

Comfort depends on temperature, humidity, and air movement.

Fuel properties: calorific value, density, viscosity, sulfur, ash.

Burners atomize liquid fuel for complete combustion.

Air-fuel ratio control maintains efficient combustion.

Flame stability depends on burner design and fuel quality.

Ignition systems and pilots must be proven.

Furnace dimensions affect residence time and combustion.

Fuel oil heating reduces viscosity for atomization.

Gas fuel requires pressure regulation and leak detection.

Fan laws: flow ∝ speed, pressure ∝ speed², power ∝ speed³.

Dampers and inlet vanes control flow; VFDs save energy.

Fan balance and alignment prevent vibration.

Bearing temperature and lubrication are monitored.

Draft losses occur in ducts, air preheater, and economizer.

Balanced draft maintains slight negative furnace pressure.

Fan surge/stall occurs at low flow; avoid.

Air leakage reduces efficiency.

Thermostatic traps respond to temperature; mechanical traps to density.

Failed-open traps waste steam; failed-closed traps flood.

Trap testing by sound, temperature, or ultrasonic.

Strainers protect traps from debris.

Bypass around traps aids maintenance.

Condensate quality affects trap selection.

Group trapping can hide failures.

Regular trap surveys save energy.

Journal bearings support radial loads; thrust bearings axial loads.

Oil film separates surfaces in hydrodynamic bearings.

Bearing temperature rise indicates inadequate lubrication or overload.

Vibration analysis detects bearing defects.

Alignment reduces bearing load.

Grease and oil selection depends on speed and temperature.

Contamination accelerates wear; filter oil.

Condition monitoring extends bearing life.

Burner management system (BMS) sequences purge, light-off, and shutdown.

Pre-purge removes unburned fuel before ignition.

Trial-for-ignition time limits unburned fuel if no flame.

Flame failure response must trip fuel.

Interlocks prevent unsafe operation.

Regular testing of BMS is required.

Documentation of setpoints and tests.

Bypassing BMS is prohibited without authorization.

Electrical isolation and LOTO before work.

Test for zero energy before touching conductors.

Use insulated tools and PPE.

Arc-flash boundaries must be respected.

Grounding protects against fault current.

Overcurrent protection sized to conductors.

Regular inspection of panels and cables.

Report electrical incidents.