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Aux. Boilers
Term | Definition | |
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What are the 4 types of Auxiliary Boilers | 1-Water Tube, 2-Fire Tube, 3-Natural Circulation, 4-Force Circulation | |
Water Tube Boiler | A boiler in which wtr. circulates thru. the tubes & combustion or exhaust gases surround the tube | |
Natural Circulation boiler (Horizontal fire tube) | Circulation of water within the boiler is achieved strictly by differing densities *Associated with tank type fire tube boilers | |
Fire Tube Boiler | A boiler in which combustion or exhaust gases circulate through the tubes and water surrounds the tubes Also called a tank boiler | |
Flame Scanner | A device positioned at the end of a sight tube that is used to prove establishment of a flame for light-off and confirm continuous flame during the combustion cycle | -Thruough the flame safeguard relay, shuts down the boiler on lost of flame. -May be sensitive to ultraviolet(UV), infrared (IR) or visible light(photocell) |
Flame Safeguard Control | -Control of automated boilers via programmed sequencing -Starts boiler automatically on a fall in steam pressure (to lowest acceptable) as sensed by a pressure switch or pressure controller -Stops boiler automatically on a rise in steam pressure | (to highest acceptable) |
Flame Safeguard Control Start Sequence | -Initiates program sequence on fall in steam pressure -Starts burner motor -Executes pre-purge of furnace of combustible gases with forced draft air and with no fuel delivery (oil solenoid closed) for a timed interval | -Proper pre-purge rerquires proper damper position &proper air flow -initiates an ignition trail with oil dely. by opening oil solenoid & achieving spark ignition by energizing ignition transformer. |
Flame Safeguard Control Stop Sequence | -Initiates program sequence on rise in steam pressure…to design… -Executes post-purge of furnace of combustible gases with forced draft air and with no fuel delivery by closing oil solenoid and de-energizing ignition transformer | (only if ignition is continuous)for a timed interval -Stops burner motor |
Flame Safeguard Control Flameout | -In the event of a flameout, the flame safeguard relay will immediately shutdown the boiler -Resetting the flame safeguard relay will be required before an attempted light-off -Depress the reset only once before investigating the cause of the flameout | -Repeated resets may cause an explosion due to repeated ignition trails |
(Photocell) Optical readers are generally used on? | Large industrial furnaces and boilers. | |
Optical Flame sensors can? | See the flame & generate voltage. Voltage is in the range of 2 to 5 volts (DC) | |
Optical readers use a photocell when? | -When exposed to ultraviolet light will actually generate a voltage from the light source. -The greater the intensity of the light, the larger the voltage generated | |
Optical flame sensors are | Optical flame sensors are very sensitive to any dust or debris that can accumulate in the burning chamber. | -The sensor window must have full exposure to the flame or else it can't "see" the intensity &thus won't generate a voltage to send to the controller |
In the optical flame the sensor window must have? | Full exposure to the flame or else it cannot "see" the intensity and thus will not generate a voltage to send to the controller | |
In a Boiler Feedwater, controlling pH will? | Reduce corrosion rates | |
The Boiler feed water has to be? | Specially conditioned to avoid problems in the boiler and downstream components | The water required for boiler feed purposes i.e. for steam generation should be of very high quality and thus requires a lot of treatment |
Boiler feed water required for boiler feed purposes i.e. for steam generation should be? | Of very high quality and thus requires a lot of treatment | |
Boiler feed water Untreated, containing impurities may lead to what problems in boilers? | -Boiler corrosion & components, ie O2 & CO2 have to be removed, usually by use of a deaerator. -Feedwater has to be alkalized to a pH of 9 or higher. *Reduce oxidation. *Support the forming of a stable layer of magnetite on the water-side surface. | -Protect the material underneath from further corrision |
Boiler feedwater Scale and Sludge causes: | -Deposits reduce the heat transfer in the boiler, reduce the flow rate and eventually block boiler tubes Any none-volatile salts & mineral that would remain in solute form when the feedwater is evaporated have to be removed | -Make-up water added to replace any losses of feedwater have to be demineralized/deionized water. |
Auxiliary Boiler Ops. Flame Safeguard | *Prevents restart upon component failure *Flame scanners/photocells output is proportional to flame size | |
Auxiliary Boiler Ops. Feed Water | Feed that is too hot can cause a loss of suction resulting in loss of feed flow to the boiler | |
Auxiliary Boiler Ops. Pre-Purge | Damper position and proper air flow | |
Auxiliary Boiler Ops. Automated Boiler | Steam pressure rises to setpoint fuel valve will close causing the flame to go out | |
Auxiliary Boiler Maintenance | *Maintenance -Manually shut fuel valve to prevent uncontrolled fuel leaks *Maintenance Schedule Scotch boiler-Fusible plugs located at center of crown sheet in combustion chamber Steam Atomizer-Utilizes to steam to assist in atomization of fuel | -Tube replacement-Must be rolled, beaded, & seal welded Safety Valves -Must open and shut quickly to prevent wire drawing |
Automated Boiler Controls (46CFR Requires the following control systems) | -Program control system -Operating control system -Flame Safeguard control system -Limit Control system -Combustion Control System -Fuel Supply Control System -Ignition System | -Non Automated Flameout requires both visual and audible alarms for flame out |
Auxiliary Boiler Maintenance Hydrostatic testing | -Occurs after all major repairs -Test at 150% of operating pressures -Several hydro test pressure calculation on board *Frequent Cycling -Operating band is too small -Results in rapid soot buildup | |
Auxiliary Boiler Maintenance Maintenance Tasks | *Photo Cell -Remove -Clean -Inspect -Reinstall -Test *Ignition Electrode -Check -Clean -Set Gap | |
Forced Circulation Boiler (Water tube, waste heater economizer) | -Circulation of water within the boiler is achieved mechanically by means of a boiler water circulating pump | -Associated with water tube waste heat economizers, where tubes are horizontally arranged or helically and spirally coiled (on a horizontal plane) |