215 terms

Power engineering study A1-2

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Draft.
Process of supplying combustion air to the boiler furnace.
Primary air.
Air admitted close to the burner tip or fuel bed. May be pre-mixed.
Secondary air.
Air necessary for complete combustion. Admitted closer to burner in the combustion zone.
Explain natural draft.
As air is heated, it decreases in mass. The cold air at the base of the intake will have more mass than the lighter heated air at the base of the chimney.
3 ways to increase natural draft. Note best option.
1. Chill outside air - not feasible.
2. Increase temp of gases - expensive and not thermally efficient.
3. Increase stack height - best choice, but costly and increased resistance to flue gas flow are concerns.
3 common chimney materials.
1. Reinforced concrete - more durable.
2. Brick - common brick is not heat resistant and needs a firebrick or clay lining.
3. Steel chimney - low initial cost, light. Disadvantages are higher maintenance cleaning and first third needs refractory lining.
Induced draft.
Increasing velocity of gases in the chimney, creating a partial vacuum and increasing air flow into the furnace. Accomplished by steam jet or fan.
Forced draft.
Forcing air into the furnace.
Balanced draft.
Forces air into the furnace and flue gases are removed by natural or mechanical means.
Advantages of mechanical draft.
1. independent of ambient air temp and chimney temp.
2. More accurate regulation which means better control of steam production and increased thermal efficiency.
3. Chimney height is only related to pollution and not draft related.
Types of draft control:
Register or damper control.
To control natural draft where air enters the furnace or chimney inlet. Chimney inlet is usually perforated so when closed, a slight draft is maintained to reduce gas build up.
Fan speed control.
When fan is steam turbine driven, speed can be controlled. For constant speed electric motors, outlet and inlet dampers are used.
Outlet damper control.
Acts as a throttle valve that restricts fan output. Located in fan outlet duct.
Inlet damper control.
Located directly at forced draft fan inlet. More complicated design but uses less power for low speed.
Variable speed coupling.
High initial cost but best regulation and efficiency.
Advantage of inclined manometer over u shape.
Greater movement over incline leg per movement in vertical leg. More accurate for small pressure changes.
Describe a diaphragm gage.
Pressure being measured is applied to a diaphragm. Movement of diaphragm is transmitted via push rod to cantilever spring attached to a pointer.
What code pertains to adequate openings for the admission of air into boiler room.
CSA code B-51. Specifies size of openings required when burning a number
Combustion.
Burning of fuel in a boiler furnace to produce heat.
Combustible elements of fuel.
Carbon, Hydrogen, and Sulphur.
Noncombustible elements of fuel.
Moisture, ash, carbon dioxide and other trace elements.
Theory of combustion?
1. Air for sufficient oxygen to combine with all combustible elements.
2. Turbulence to mix air and fuel.
3. Temperature must be sufficient to ignite fuel as it enters.
4. Furnace must be large enough to allow sufficient time for combustion before gases strike cooler areas of the heating surfaces.
Products of complete combustion?
Carbon plus oxygen make carbon dioxide.
Hydrogen plus oxygen make water vapor.
Sulphur plus oxygen make sulphur dioxide.
Products of incomplete combustion?
Carbon plus insufficient oxygen equals carbon monoxide.
Hydrogen plus insufficient oxygen forms free hydrogen's.
Sulphur plus insufficient oxygen forms free sulphur.
Why is sulphur considered an impurity?
Although it is a fuel, it tends to produce corrosive acids in the presence of water. Plus sulphur dioxide in the atmosphere contributes to acid rain.
Theoretical air?
The amount of air to provide just enough oxygen for complete combustion.
Excess air?
The amount of air above theoretical air to to mix all fuel particles with oxygen. Expressed as a percentage of theoretical air. Can vary from 10 to 60 percent.
Why is it desirable to minimize excess air?
Because air is heated to a high temperature and therefore carries a large amount of heat out the stack. Also, less power to fans if less air is required.
What happens with not enough excess air?
Incomplete combustion and formation of CO and free hydrogen. Will cause sooting of heating surfaces, and possibility of explosion if pockets of fuel build up.
Approximate excess air percentages by fuel burnt?
Stroker firing coal - 30-35%
Pulverized coal - 15-20%
Fuel oil - 15%
Gaseous fuel - 10%
CSA B149.1
Installation code for natural gas burning appliances and equipment specifies standards for type, location, and size of outside air supply inlets.
Hydrocarbons in coal
Carbon combines with hydrogen to form hydrocarbon. Considered a volatile material as it passes off as gas was during combustion
Hog fuel
Byproducts of wood processing, such as bark, chips, and sawdust.
Biomass fuel
Residual organic materials such as sugar cane stalks and shells from nuts. Common to food industry and community waste processing.
Discuss fuel oil characteristics
Commercial number 1-6
1. Light, 2. medium domestic. 3. Light, 4. medium, 5. heavy industrial. As numbers go up, relative density, viscosity, and minimum flash point increase as well.
Advantages of fuel oil over coal
1. Less storage space required
2. More precise regulation of fuel admission
3. Less handling labor and equipment required.
4. Cleaner and more efficient to use
Advantages of natural gas as a fuel
1. No ash produced during burning.
2. Little handling equipment is required.
3. Excellent regulation of fuel feed to furnace.
4. Easily mixed with air.
5. Clean, no spills, mess, or residue.
6. No storage space is required
Disadvantages of natural gas
More expensive than coal and sometimes oil. Long piping from source to plant
Describe liquifies petroleum gases
Light hydrocarbon gas. Either butane, propane, or a mix. Moderate pressure will liquify the gas and it can store at 1/120th of space. It converts back to gas by reducing pressure and absorbing ambient heat.
Fuel heating value
When a unit amount of fuel is completely burned, the heat produced is called the fuel heating value. Measured in mass or volume
Average fuel heating values
Coal (bituminius). 25600 kj/kg.
Natural gas 37260 kj/m3
Fuel oil (light) 45360 kj/kg
Propane 93150 kj/m3
Butane 122200 kj/m3
List 3 types of mechanical stokers
1. Underfeed. Pushed up by blocks and rams. Particularly adapted to burning highly volatile coal. Custom air is supplied below grate through openings called tuyeres.
2. Crossfeed. Aka chain grate or bar grate. Gravity fed onto moving grate. Combustion air from draft fan under grate
3. Spreader or overfeed stoker. Coal is spread by a rotor with paddles that bats the coal out. Under grate draft fan
Advantage of pulverized coal
Mixes well with air. Allows cheaper grades to be burned and better combustion regulation
Raymond bowl mill
Coal is fed into a bowl with spring loaded rolls that grind coal to dust. Hot air picks up powdered coal and takes it to furnace.
What must be done to heavy oil before use in oil burner
Heated to 90 degrees while light oils are fine as is.
Air atomizing oil burner
Primary air at approx 103kPa to atomize oil. Secondary air mixes with this at burner
Steam atomizing oil burner
Used for larger than package type burners. Uses steam to atomize oil.
Mechanical atomizing oil burner
Oil is pumped under pressure through slots in a sprayer plate. Uses in both large and package boilers.
Rotary cup oil burner
Electric motor spins cup at 3500 r/min
Oil burner maintenance
Clean fuel lines for new installation. Keep burners clean. Always wear goggles when blowing out burners.
Oil burner operation tips
Lubricate louvres or registers linkage. Critical for air control. Too little air gives dark, heavy smoke, while too much air gives grey smoke.
Packaged boiler gas burner
Often for small firetube package boilers. Tube within a tube. Air is blown through central tube. Gas issues through small holes into the space at the end. Called an after mix or outside mix.
Pre mix gas burner
Small installation use. Gas controlled by needle valve and primary air from a controlling shutter at end of burner.
Ring type gas burner
For large boilers. Gas supplied to ring manifold.
Gas burner maintenance
Gas shut off cocks periodically lubricated and air registers checked and lubed. Flame should be stable. Blue with yellow tip. Gas burners cleaned whenever boiler is shutdown. Wire brush and solvents. Number of burners reduced at low loads to maintain proper gas pressure for remaining burners.
Refractory and what areas commonly have it
Materials that can stand very high temperatures. Common in burner throat, inspection door openings, baffles, and combustion chambers.
Stoker units effect on refractory
Stoker units burning coal produce ash slag that will erode and corrode. Ash clinkers can firm and break away brick work.
Oil burner effect on refractory
Corrosion from ash from oil. Flame impingement on burner throat will break off pieces. Improper burner position may cause carbon build up on throat.
How is fuel flow controlled
1. Coal. Grate or stoker speed. Primary flow for pulverized.
2. Both oil and gas are either solenoid - on off or multi range control. Or modulating control valve.
Name 2 types of flue gas analyzers
Fyrite and Orsat.
Briefly describe Fyrite procedure
Insert test tube into chimney. 18 bulb strokes to get 60 ml sample. Invert unit and CO2 will be absorbed by fluid. Fluids good for several hundred readings.
How is CO2 in flue gas related to excess air
Inverse ratio.
Combustion boiler efficiency
The amount of boiler heat absorbed by water. Remainder goes out the stack. Keys are minimum excess air and clean boiler surfaces.
Fluidized bed combustion
In a utility steam generator, crushed coal is burned in a bed of limestone and ash. Air is blown from below the bed to keep it suspended.
FBC history
Patents as early as 1920's. Low oil cost and lax environmental laws kept interest low until the 1970's
Atmospheric fluidized bed combustion
Large industrial units generating up to 500 000 kg/h. Hope to increase to a million. 25 cm h2o pressure at fd fan and 16cm at base of bed. 1m depth of bed with 2-3 m/s velocity of particles in bed
Advantage of water tubes submerged in FBC bed
About 60% of heat transfer is from submerged tubes.
Why is 850c furnace temp an advantage
This lower temp limits nitrogen oxide production.
How does limestone reduce pollution in fbc
Limestone is coverted to calcium oxide and mixes with sulphur and forms gypsum. Can be captured in ash and repurposed for building supplies. 10% limestone reduces SOx by 80%
efficiency of combined cycle plant based on PFBC
about 5% higher efficiency than a conventional pulverized plant. One type with a comined gas/steam cycle uses a supercharged boiler where about one third of the electrical power is provided by the gas turbine, and two thirds by the steam turbine.
describe combined cycle plant process
coal and limestone are fed into furnace. The combustion or pressurizing air is delivered by the gas turbine compressors. The hot pressurized, combustion gases, after transferring most of their hear to the boiler, are passed through cyclones and granulator bed filter, to drive the gas turbine and its generator. The steam produced in boiler goes to steam turbines and condenser in a conventional power plant cycle
Potential advantages of combined cycle?
1. larger total electrical power output compared to gas turbine alone.
2. increase in overall efficiency of power generation.
Improved fluidization quality for a PFBC boiler occurs because the higher pressure brings a reduction in bubble size. Especially important for beds with fine particles.
PFBC drawbacks
1. complexity
2. erosion and/or corrosion/fouling of gas turbine blades
3. low furnace temps limit steam temp over the period heat supply
4. feeding of fuel and bed materials into the pressurized system
FBC Advantages
1. Fuel flexibility. Very tolerant of high moisture and ash content of up to 70%, which wouldn't burn in a traditional furnace.
2. Less maintenance. No slag. Due to lower operating temps in furnace, large clinkers are not produces and fry combustion residue is easier to dispose of than wet sludge. No soot blowing equipment.
3. Smaller plant size. up to 25% smaller and significant material and construction costs
4. Fuel preparation. No coal pulverizers. Either overbed nozzles, or feedthrough tubes.
5. Fuel Feed. Coal may be added by spreader stoker.
6. Pressurized Combustion chamber. more compact equipment and more efficient fuel to electricity processes
Disadvantages of FBC
1. High power requirements for combustion air. FD fan on an FBC unit - 225kW versus 75kW for stoker system.
2. Carryover. Gradual loss of fluidized bed including fuel particles, resulting in lower efficiency and high cost dust collectors.
3. Poor combustion control at low operating rates. Cannot be avoided without adding expensive control equipment.
What is necessary before coal can be burned in an inert bed?
Bed must be heated up to 600 C. either with auxiliary flame or hot air. Typically takes one hour.
AFBC operating temp and pressure example?
17000 kPa and 540 C
How do you adjust working bed height?
Changing limestone feed and bed drain rate.
Where might FBC become mainstream?
Power and petrochemical facilities
FGD?
Flue gas desulphurization
2 causes for acid rain
NOx and SOx emissions from boilers contribute to acid rain
Two systems that the vast majority of power plants in the world are equipped with for effective removal of fine dust.
Electrostatic precipitators or fabric filters.
3 problems associated with regular FGD plants
Expensive to build, troublesome to operate and maintain.
3 processes that FBC emerged from?
Classifying, chemical reactor, and drying applications
FCC
Fluid catalytic cracker in oil refineries
2 subgroups of AFBC
Bubbling, and circulating
3 factors that effect the desulphurization process in AFBC
1. Amount of limestone added.
2. depth of bed.
3. time in the limestone flux.
Only limiting factor for FBC fuel
Fuel must have sufficient heating value to sustain combustion.
Name four fuels for FBC
wood, heavy oil tarsand, coal mine tailings, waste gas refuse, shredded scrap tires.
Another PFBC design uses compressed air as the cooling medium.
It is then mixed with pressurized combustion products, after they have been cleaned. The mix then expands through the turbine, and any leftover heat energy passes to a waste heat boiler. About 60% of power is from the gas turbine and the remainder is from the steam turbine.
Why would FBC windbox be divided into multiple compartments
For separate fluidization of fuel bed for startup, and for load reduction with either underbed or overbed firing.
ASME code requirements for safety valves
each steam boiler shall have at least one safety valve, and if boiler has over 46.4 m2 (500 ft2) of water heating surface, then at least two safety valves will be installed. All boilers must be fitted with an approved type of pop safety valve of sufficient capacity to discharge all steam that the boiler can evaporate without allowing pressure to rise more than 6% above allowable working pressure. Min 13mm, max 1120mm.
What ASME codes are referenced regarding safety and relief valves
ASME I, IV, and VII. All boilers must be fitted with an approved type of pop safety valve of sufficient capacity to discharge all steam the boiler can evaporate, without permitting pressure to rise more than 6% above allowable working pressure.
describe safety valve process
held shut by means of a spring which holds safety valve disc tightly against its seat. When set pressure is reached (popping pressure), the disc will be raised slightly from its seat and steam will begin to escape. Valve has a manual lever.
What is the pop valve lip
The disc has a lip that is behind the seal. This increases the surface area after the disc starts to lift, ensuring the valve will do its job.
Blowdown of safety valve
The differences between the pressure at valve opening and closing. ASME 1-pg72.1 states it must be a minimum of 14 kPa (2psi) and max blowdown will allow the safety valve to close at a pressure not lower than 96% of set pressure of safety valve.
How is blowdown adjusted?
There are escape ports around the lip at the disc. An adjustable ring allows the ports to be more open or closed. The more open, the quicker steam can escape, and the faster pressure will reduce.
How is blowdown adjustment protected
A cap screw is installed and held in place with a seal installed by the boiler inspector.
How can popping pressure be adjusted
Increase or decrease of 5% are allowed as per ASME S1. Back off lock nut, adjusting screw up or down to decrease, or increase pressure from spring. Must have boiler inspector permission.
Safety valve installation
Should be upright with spindle vertical. Connected to boiler with no intervening connection, pipe, or fitting. Discharge pipe should be separately supported to allow for expansion.
How do superheater and reheater valves fit in with drum valves
Superheater and reheater valves are set to pop first, and close after drum valves so there will be a flow of steam maintained until fires can be shut down, or pressure reduced. ASME 1 pg 68
What safety valve is used on boilers over 8000 kPa?
Torsion bar safety valve. Can be machined to much finer specification
ASME Code states that each steam heating boiler shall have one or more officially rated safety valves of the spring pop type, adjusted and sealed to discharge at a pressure not to exceed ____
103 kPa
Safety valve capacity cannot be more than ____ above max allowable working pressure while operating at max capacity with steam valves closed
34 kPa
ASME code section 4 for mounting safety valves on heating boilers
1. Valve mounted vertical and at highest point.
2. Connected directly to a tapped, flanged, or to a fitting connected to boiler by short nipple, y base, or a valveless header connecting steam outlets or water outlets in the same boiler.
3. Discharge pipe is short and straight. Internal cross sectional area is at least same as valve outlet. No valve on discharge pipe. Proper drainage to avoid water collection. No chance to scald operator.
Define safety relief valve for heating boiler
ASME sec 4 states that each heating boiler will have a safety relief valve set at or below it's maximum working pressure.
How do safety relief valves differ from safety valve on a steam boiler?
Hot water heating boiler safety relief valves Are similar to their steam cousins but don't pop due to escaping water not having the same lifting effect. Also they do not have an adjusting ring and bottom guides are not permitted.
main causes of frequent opening or spilling of relief valve are:
1. Scale accumulated on valve seat. Hard water will scale at temps above 65C.
2. Pressure in supply line varies and at times exceeds the valve setting.
3. relief valve is defective or insufficient for boiler.
Lever test for safety valve
Pull the try lever on safety valve to wide open and allow steam to escape for 5-10 seconds. Release lever alowing it to snap back into place. This determines valves ability to operate, but not the pressure valve will open at. ASME reccomends this test monthly and be recorded in boiler log.
When should lever test be avoided?
on low pressure boilers, min 35kPa should be present to avoid material interfering with disc seating.
Pop Test for safety valve
Raise steam pressure in boiler until at value set for safety valve. This tests operation and exact pressure.
Pop Test procedure
Steam discharge and feedwater supply valves should be closed and accuracy of steam gage checked. On auto fire boilers, bypass operating control and high limit control. Valve should open oat 103kPa but +- 14 kPa is acceptable. If it doesn't open at 117, shut down and release pressure to atmosphere, or steam header. Apply try lever test and repeat. If still no sucess, replace valve. Never strike valve to assist.
How often is pop test recommended?
Once per year. Preferably at beginning of the heating season if boiler is only used for space heating purposes.
Who can repair safety valves?
ASME recommends manufacturer or authorized repair representative, but provinicial regs allow a fully qualified boiler operator to do so with written permission from chief inspector.
Temperature relief device
protects domestic hot water system from dangerously high water temperatures. opens when water rises to about 99C. One type uses a fusible plug that melts and has to be replaced. Another uses a rod that expands and contracts and will close of at 71C
Combination pressure temperature relief valve
Uses both a spring for pressure and wax filled sensor probe that can expand and open valve.
Most common form of direct technique for indicating liquid level?
Gage glass. Tubular gage glass is simplest and least costly. Will have isolating valves at top and bottom. Will be surrounded by metals rods or shield in case of failure.
What is a safety shut off gage valve
In case of gage glass failure, this valve has a stainless steel ball which closes off fluid passage when glass breaks. In case of failure, there will be a sudden rush of water which will cause ball to seat and shut off flow.
Tubular gage glass restrictions
1. Limited to lower temps and pressures. Less than 2800 kPa
2. non-toxic and non-hazardous material.
3. limited to max 750mm in length. If longer, use two overlapping runs.
Boiler glass installation must be high enough to ______, and low enough so ________?
Completely cover all parts of heating surface to prevent overheating.
That water is not carried over with the steam.
What is the benefit of using a water column between gage glass and boiler?
Acts as a reservoir to dampen agitation in water. It also traps any sludge or sediment and prevents collection in the glass. Also provides a place for try cocks, high/low level alarms, and controls.
Regulations require the the bottom of gage glass be ______ above the top of the highest heating surface
76MM. Heating boilers have a lowest permissible water level marked by manufacturer. Lowest visible level in gage glass should be 50mm above this. Same for watertube boilers.
What temps and pressures can armored gage glass withstand?
exceeding 250C and up to 70000 kPa
How is glass treated to withstand caustic elements?
A protective coating of transparent mica is applied. Prolonged exposure changes it to opaque. Needs replacing.
Reflex glass gage
best suited for clean, colorless, non-viscous, and non-corrosive fluids, including light and heavy hydrocarbons. Has special optical properties that create a sharp line of demarcation at liquid level.
Bicolor glass gage
Point level method of indication. A number of sealed circular glasses, or double bullseye assemblies with spotlights connected at the back. Steam space is indicated in red, while water space is green. Mirrors can be used so it can be viewed at floor level.
Why is gage glass error normal
Can be up to 20%. Depends on the difference of Water in the gage and its connection, and water in the drum. Affected by ambient temp, velocity of air around gage, amount of gage surface, length of gage glass, and level of liquid in the glass.
describe replacing regular gage glass
1. shut off steam and water valves on gage and open drain.
2. remove nuts and glass.
3. crack open gage glass valves to blowout any shards. wear protective gear.
4. install new glass. Apply graphite to washers to avoid spinning glass. Cross tighten hand tight unless using o rings.
5. Heat glass slowly by cracking steam valve and leaving drain valve open.
Gage glass installation cautions
1. if remote chains are not available, wear a face shield during first run in case of sudden failure.
2. If new glass leaks, always close valves and open drain so as not to tighten under pressure.
3.
describe extra steps taken for flat glass with mica
When glass is removed, threads on studs should be coated with graphite and the nuts run down.
Remove remaining gasket material. Caution not to create low spots.
Clean both ends so gasket material will not plug valves on gage.
Apply molybdenum disulphide on contact surfaces of new glass to slip into place easily.
Install new asbestos gasket, new mica and new glass on one side.
Testing directly connected gage glass
1. close water valve and open drain valve. Steam blowing through proves connection and glass are clear.
2. Close gage glass steam valve and open gage water valve, then drain valve. Water flow proves lower connection clear.
3. Close drain valve on gage and open steam valve to put back in service.
Why must valves only be partially opened during testing of gage glass?
If fully open, the surge of steam or water would trigger the ball safety shutoff mechanism. When only partially open, there is a pin that extends through the valve seat so flow is not restricted.
General format for testing gage glass
Assuming steam and water are open. Start on column before gage.
1. Open drain and steam should blow through.
2. Close steam and open water and drain and water should flow through.
3. Open steam and repeat for gage.
Testing water column and glass on low pressure boiler. No shutoff allowed between boiler and column.
1. Shut off gage steam to prevent steam from bypassing through the gage glass.
2. Open column drain. Steam and water will blow through and the column to drain.
3. Close the column drain valve and open the drain on the gage glass to prove that the steam connection and glass are clear.
4. Close the gage steam valve, and open the gage water valve to prove that the water passages on the gage glass are clear.
Fire it back up
How often should water column and gage glasses be blown down?
Every shift. Except on large boilers where constant blow down will shorten the life of the mica and increase maintenance costs.
Name two types of remote water level indicators
Hopkinsons remote water-level indicator and Igema remote water-level indicator
The main operating element of a Hopkinson remote water level indicator is a?
Diaphragm
When a differential head meter is used to measure water level in a boiler steam drum, the connection to the steam space forms the _____ or reference leg of the meter
Constant
Dirt traps are installed on an "Igema" remote water-level indicator to prevent indicating liquid ______
Contamination
A great advantage of an Igema level indicator over a Hopkinson unit is?
No moving parts
3 Cautions while replacing gage glass
1. Shut off steam and water valves.
2. Crack open gage glass valves to blow out any glass debris while wearing a face shield.
3. Heat glass slowly by cracking open steam valve. Not heating glass slowly will result in failure.
describe Hopkinson remote water level function
A large sensitive diaphragm with the top side attached to the steam space of boiler and bottom to the water side.
Why are gage glass valves designed to be quick closing
In case of glass failure, and to make remote operation easier.
Purposes of steam drum?
1. Storage of steam to handle load increases quickly.
2. separators to remove water.
3. Remove impurities from steam and water to keep surfaces clean, ie turbine blades.
4. distribution of feedwater and chemicals into boiler.
List typical drum internals
1. Steam separators.
2. Chemical feedlines.
3. Feedwater lines.
4. Blowoff lines.
Do water and steam separate easier at higher or lower pressure?
Lower pressure. Typically need no mechanical help.
How does a dry pipe work. Where is it typically employed?
Changes direction of flow of water and steam mixture, causing water to fall back into drum. Early form of separator still found on some low pressure boilers.
The third step of steam separation, aka steam scrubbing, removes _____ from the steam
contaminants
The cyclone steam separator was developed to remove the steam from the mixture of steam and water in the steam drum, and to provide the _______ with steam-free water
Downcomers
The water in the mixture will have a mass of between _____ times the mass of steam in the mixture
2 and 25
Briefly describe cyclone separator action.
Steam and water from risers swirls into the cyclone at high velocity. Centrifugual force pushes water to outside and steam rises up through the center, passing through a small corrugated scrubber. Directional vanes at bottom direct water into the sperarator drum. Water velocity overcomes the head of water outside the cyclone.
Cyclone steam separator
No moving parts. Converts circulating force into centrifugal force to separate steam and water. Permits a reasonably wide variation in the drum water level, without affecting circulation or steam quality.
Turbo separator
Steam and water enters near the top of the drum. Baffles direct down wall to the turbo separator. Spinner blades impart spin allowing steam up the center into a secondary separator. The turbo separator does not have a water seal, unlike cyclone separator. Turbo has no capacity limit and is not affected by water level changes.
The secondary separators are generally rows of closely fitted ______ located directly above the primary separators. These plates cause the steam to change direction many times and the water deposited on the plates drains from the bottom of the assembly to the water in the drum
corrugated metal plates
Dryers
Located at top of drum. Generally a wire or mesh screen. Remove water and contaminants before steam is taken away.
Most boilers use an _______ feedwater pipe
internal
Internal feedwater pipe is designed to reduce
risk of thermal shock and excessive agitation. Smaller boilers may use a baffle and larger may use a perforated tube.
Continuous blowdown pipe
several cm below water level, where highest concentration of dissolved solids is thought to be found.
How is continuous blowdown regulated
according to periodic boiler water tests, a special regulating or metering valve equipped with an indicator.
Chemical feed pipe
Pipe along length of boiler, perforated and placed to ensure rapid mixing of chemicals with entering feedwater.
The most efficient operation of a fan occurs when
The speed be only sufficient enough to supply the required amount of air
In a balanced draft system, combustion gases are removed from the boiler furnace by the
Induced draft fan
The differential between the pressure at the furnace inlet and the pressure at the furnace exit of a natural draft boiler is
greater in winter time
The types of draft systems employed with boiler furnaces include
Balanced draft, forced draft, induced draft
Furnace explosions resulting from a buildup of combustibles during shutdown in the boiler may be prevented by
Using a perforated chimney inlet damper
When using mechanical fuel oil atomization
Hi pump pressure is required
The combustible elements in a typical fuel include
Hydrogen, carbon and sulfur
The formation of carbon monoxide in the furnace is undesirable because it
Is a combustible compound and represents a waste of fuel
In coal the volatile matter is comprised of
Hydrocarbons
Before fuel oil can be properly burned it must be
Atomized
In the FBC system fuel is kept in suspension by means of
Air that is used for combustion
In a typical SPC unit, the Coal & lime stone are fed to the furnace and suspended in an updraft of fluid izing air from the
Forced draft fan
NO x emissions in a fluidized bed furnace are reduced by
Reducing combustion temperature
The two main types of fluidised bed combustion are
Atmospheric and pressurised fluidised bed combustion
If the safety valve on a boiler pops and the only pressure gauge indicates well below pop pressure, you should
Reduce boiler pressure and get the gauge checked
True or false. According to code, no isolating valve may be placed between the boiler steam drum and the safety valve
True
True or false. According to code, no valve may be in the discharge line if it discharge line is used
True
The safety valve on a boiler must be of sufficient capacity to discharge all the steam the boiler can produce without allowing the pressure to rise more than
6% above the maximum allowable working pressure
Raising the blowdown ring on a pop safety valve will
Increase the amount of blowdown
The ASME code states that when the water level is at the lowest visible level in the gauge glass there she'll be a minimum of water over the top row of tubes or the crown sheet in a fire tube boiler. According to cold, this minimum level is
76 millimeters
If shut off valves are installed on a water column, they should be sealed in the open position and must be
Outside screw and yoke rising spindle gate valves
To protect the flat glass water gauges from erosion, the glass plates are lined with
Mica
True or false. Small boilers typically use a short feed pipe that discharges against a baffle
True
Purpose of the separators in the steam drum of a water tube boiler is to
Remove moisture and impurities from the steam
The CBD valve is normally a needle valve, equipped with
A position indicator
At lower pressures, steam
Readily rises and separates from the water
List four drum internals
Corrugated scrubber. Baffle. Internal chemical feed pipe. Separator.
What is indicated by carbon monoxide or such appearing in the flue gases
Incomplete combustion due to insufficient air supply
True or false. Mechanical draft systems on boilers are more accurately regulated then systems employing natural draft
True
In an enclosed boiler room, a small cast iron boiler with an input of 422000 kilojoules is required to have
Adequate are openings from outside
the furnace of a boiler in a balanced draft system will be kept at
Slightly negative pressure
A mechanical draft system would you use as a fan to supply air to the wind box and a fan to expel flue gases to the stack is called
Balanced draft
True or false. In a natural draft boiler, the furnace draft will increase as the atmospheric air temperature is reduced
True
Low fuel oil pressure in an oil burner system will
Reduce burner flame stability
Sulfur dioxide is composed of
One atom sulfur and two atoms oxygen
When more air is supplied than the amount theoretically required for complete combustion, it is called
Excess air
The main purpose of combustion control is too
Ensure the proper ratio of air and fuel supply to the furnace
Air is largely comprised of an inert gas that will not combined with the combustible elements of a fuel. This gas is
Nitrogen
In a fluidized bed combustor, by adding three times the theoretical quantity of lime required for the reactions, sulfur dioxide emissions may be reduced by
80 - 90%
True or false. Fluidised bed combustion reduces the amount of clinker formation due to the reduced combustion temperatures
True
In a combined cycle power plant using a pressurized bed combustor, the flue gases from the furnace go to
The gas turbine
After checking a safety valve using the try lever, the valve continues to simmer after closing. In order to close the valve fully the operator should
Operate the test lever two or three times in order to allow the disc to seat
The superheater & reheater safety valves are set to open
Before and to close after the drum safety valve
Two safety valves are required on a high pressure boiler when the heating surface is larger than
47 square meters
When fired to maximum capacity with the main steam stop valve closed, the allowable rise and pressure in a boiler with allowable working pressure of 2900 kiloPascals will be
174 kiloPascals. This is 6% of the allowable working pressure
The safety valve capacity of a steam heating boiler shall be such that, with the fuel burning equipment installed and operating at the full capacity and all steam outlets closed, the pressure can not rise above the maximum allowable working pressure by an amount of
34 kilopascal
The lifting leaver is used to determine that the safety valve
Will open, release steam and close
In the event the gauge glass steam valve is accidentally closed during normal operation, the result will be
A rapid increase in apparent water level
Cheering normal boiler operation the gage glass generally indicates water level
Lower than the actual level in the boiler drum
Advantages of mounting a gauge glass on a water column instead of directly to the boiler include
The Colin provides a place for installation of high and low level alarms and controls. The column traps a nice lunch or settlement and prevents collection in the gauge glass. Also acts as a reservoir to dampen agitation in the water
True or false. The asme code states that when the water level is at the lowest visible level in a gauge glass, there she'll be at least 50 millimeters of water over the top row of tubes or the crown cheat in a fire tube boiler
False
The chemical injection line is usually located near the
Internal feed pipe
In a water tube boiler steam drum, what collects condensation from the secondary separators
Drain pots
In a steam boiler drum, secondary separators normally consist of
Rows of closely fitted corrugated metal plates
In a modern boiler drum, steam separation usually takes place in
3 steps