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Aux. Boilers

TermDefinition
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)
Created by: Rafael Leon
 

 



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