BD Second Class Boiler Attendant cheat sheet
BD Second Class Boiler Attendant · Keep the key ideas within reach.
Boiler Laws, Rules and Regulations
Boilers exceeding 22.75 kg/hr steam capacity or 10 L water capacity typically require a certificate under boiler acts.
A Second Class Boiler Attendant certificate permits attendance on boilers up to a specified capacity (often 500 m² heating surface) under supervision.
First Class certificate holders may operate any boiler and supervise Second Class attendants.
Boiler inspections are mandated at intervals: internal inspection typically every 2 years, external every year, and hydrostatic test every 4-6 years depending on jurisdiction.
The boiler attendant must maintain a logbook recording pressure, water level, blowdown, and any irregularities each shift.
Operating a boiler without a valid certificate or with an expired inspection is a punishable offence under boiler regulations.
The attendant is responsible for immediate reporting of accidents, explosions, or serious defects to the Chief Inspector of Boilers.
License renewal requires proof of continuing service and may involve a refresher examination every 5 years.
Boiler Construction, Types and Classification
Fire-tube boilers: hot gases pass through tubes surrounded by water; limited to about 25 bar due to shell stress.
Water-tube boilers: water circulates inside tubes with hot gases outside; capable of high pressures above 100 bar.
Shell boilers (e.g., Lancashire, Cornish) have large water volume and are slow to steam but tolerate load swings.
Water-wall construction lines the furnace with tubes to increase radiant heating surface and protect refractory.
Mountings include safety valves, pressure gauge, water level indicators, feed check valve, blowdown valve, and fusible plug.
Accessories include economiser, air preheater, superheater, and feed pump; they improve efficiency but are not safety-critical.
A fusible plug, made of low-melting alloy, melts at about 230°C to warn of low water in fire-tube boilers.
Boiler classification by circulation: natural circulation (density difference) vs forced circulation (pump-driven).
Fuels, Combustion and Firing Equipment
Stoichiometric air for coal combustion is about 7-8 kg air per kg coal; excess air of 20-30% ensures complete combustion.
The three T's of combustion: Time, Temperature (above 800°C), and Turbulence (mixing) for complete burn.
Coal rank: anthracite (high carbon, low volatile) to lignite (low carbon, high moisture); bituminous is most common for boilers.
Fuel oil is atomised by pressure jet or steam/air atomiser to droplets under 100 µm for efficient burning.
Gas burners use a venturi or forced-draft mixer to entrain primary air; flame stability requires a minimum gas pressure.
Chain-grate stokers feed coal uniformly and remove ash continuously; spreader stokers throw coal over a grate.
Combustion efficiency is reduced by high excess air (heat lost up the stack) and by CO or smoke (incomplete combustion).
Flash point of fuel oil is the lowest temperature at which vapour ignites; it must be below the oil preheat temperature for safe atomisation.
Boiler Operation, Starting-up and Shutting-down Procedures
Pre-start checks: safety valve free, water level at normal, all valves in correct position, and no personnel inside.
Start-up: warm the boiler slowly (1-2 hours for large boilers) to avoid thermal stress; open air vent until steam appears.
Shutdown: reduce firing, blow down to control dissolved solids, and allow gradual cooling; never dump hot water suddenly.
During operation, maintain water level within the gauge glass; a low-water condition requires immediate fuel cut-off.
Blowdown procedure: open the valve slowly, hold for 10-30 seconds, then close; repeat as needed to control conductivity.
The attendant must check the safety valve lifting pressure at least once per shift by manual lifting lever.
When raising steam, ensure the superheater drain is open until steam flow is established to prevent overheating.
Emergency shutdown: trip fuel, close main steam stop valve, and open safety valve manually if pressure continues rising.
Boiler Feed Water Treatment and Feed Systems
Scale is mainly calcium and magnesium salts; it reduces heat transfer and can cause tube overheating.
Corrosion is caused by dissolved oxygen and low pH; deaeration and pH control (8.5-10.5) are essential.
Water hardness is measured in ppm or mg/L as CaCO3; softeners replace Ca/Mg with sodium via ion exchange.
Blowdown controls dissolved solids; conductivity is used as an indicator (e.g., limit 3000-4000 µS/cm for shell boilers).
Feed pumps: centrifugal for high flow, positive displacement (reciprocating) for high pressure; injectors use steam to lift water.
An economiser recovers heat from flue gas to preheat feed water, improving efficiency by 5-10%.
Oxygen scavengers (e.g., sodium sulphite) remove residual oxygen; hydrazine is used in high-pressure systems.
Feed water temperature should be above 80°C to reduce oxygen solubility and thermal shock.
Steam Generation, Steam Systems and Steam Traps
Saturated steam temperature depends on pressure: at 10 bar (gauge) it is about 184°C.
Superheated steam has higher temperature than saturation at the same pressure, improving efficiency and reducing condensation.
Steam traps remove condensate and air while retaining steam; types: thermodynamic, thermostatic, and mechanical (float).
A failed-open trap wastes steam; a failed-closed trap causes water hammer and flooding.
Steam quality is the mass fraction of vapour in a mixture; boiler steam should be >99% dry.
Water hammer is caused by condensate slugs accelerated by steam; prevention includes proper trapping and drainage.
Steam header pressure should be maintained within ±5% of design for stable process operation.
Flash steam forms when high-pressure condensate is discharged to lower pressure; it can be recovered for low-pressure use.
Boiler Safety, Protective Devices and Emergency Procedures
Safety valves must be set to lift at or below the design pressure; typically two valves are required for boilers above certain size.
Low-water cut-out (LWCO) automatically cuts fuel when water level falls below the safe limit; it must be tested regularly.
A fusible plug fails at about 230°C, releasing steam to the firebox to warn of low water.
Boiler explosion causes: low water, overpressure, defective safety valve, or scale-induced overheating.
First aid for burns: cool with running water for at least 10 minutes, cover with sterile dressing, do not apply ointments.
Emergency procedures: on low water, cut fuel immediately, do not feed water until the boiler has cooled.
Pressure gauge and water level indicators must be checked each shift; a broken gauge glass is an emergency.
All protective devices (LWCO, safety valve, pressure switch) require periodic testing as per regulations.
Boiler Inspection, Testing and Maintenance
Hydrostatic test: fill with water, pressurise to 1.5 times design pressure, hold for 30 minutes, inspect for leaks.
Steam test: operate at full pressure to verify safety valve lifting and overall integrity; typically done after major repairs.
Internal inspection: examine firebox, tubes, shell for scale, corrosion, cracks; requires cooling and cleaning.
External inspection: check insulation, fittings, supports, and visible leaks without opening the boiler.
Repairs to pressure parts require approval from the Inspector and must be done by qualified welders.
Non-destructive testing (NDT) includes ultrasonic thickness measurement, dye penetrant, and magnetic particle inspection.
Maintenance schedule: daily blowdown, weekly safety valve test, monthly LWCO test, annual internal inspection.
After any repair, a hydrostatic test is mandatory before returning the boiler to service.
Boiler Efficiency, Heat Balance and Energy Conservation
Boiler efficiency = (heat output in steam) / (heat input in fuel) × 100%.
Direct method: measure fuel and steam; indirect method: sum losses (dry flue gas, moisture, radiation, unburnt).
Major losses: dry flue gas (5-15%), moisture in fuel (2-10%), radiation (1-2%), unburnt carbon (1-5%).
Excess air optimisation: reduce O2 in flue gas to 3-5% (coal) or 2-3% (gas) to minimise stack loss.
Economiser and air preheater recover waste heat, improving efficiency by 5-15%.
Blowdown heat recovery can save 1-3% of fuel by using flash steam or heat exchangers.
Regular scale removal improves efficiency: 1 mm scale increases fuel consumption by 2-5%.
Heat balance: heat input = heat in steam + stack loss + radiation + blowdown + unaccounted losses.