High Pressure Boiler Design/ Draft, Combustion, High Pressure Boiler Fittings/ High Pressure Boiler Operation
Unit 12 - Chapters 51-55 Unit 13 - Chapters 56-61 Unit 14 - Chapters 62-65
Terms in this set (297)
Is steam generated in a hot water Boiler?
No, no steam is produced but it's still a boiler.
What is a boiler?
A pressure vessel in which a gas or vapour can be generated under pressure, or in which a liquid can be put under pressure, by the direct application of a heat source.
A wall, barrier or panel used to change the direction of flow of a liquid or gas.
How many blowdown valves on a high pressure boiler? Low Pressure?
a) Two. One fast opening and one slow opening valve.
b) One blowdown valve.
Boiler failure? Catastrophic boiler failure?
a) Tube rupture resulting in escaping steam or water and boiler shut down.
b) Combusting or boiler shell explosion.
Safety Valve? Safety relief valve?
a) A safety valve prevents the pressure from exceeding safe limits in a steam boiler.
b) A safety relief valve is used for liquids like in a hot water boiler. It bleeds off liquid then closes again.
The brickwork used to support a boiler and surround the combustion chamber. This is used in HRT boilers.
Vertical tubular boiler?
smaller sized FIRETUBE boiler with vertical tubes.
A water-filler section extending from the shell, which surrounds the firebox. Most locomotive boilers are equipped with water legs around the firebox.
First boiler ever?
Haycock boiler - 1720.
Chief aim in modern boiler design?
To design and produce boilers that are safe and efficient in operation and economical in fuel consumption.
The steam space of a boiler consists of what?
The portion of the boiler not filled with water.
The steam space of a boiler drum must be large enough to what?
Separate the water from the steam.
All parts of the boiler exposed to fire or flue gases must be covered by what?
A steam boiler should be compact in design in order to..
Reduce building costs.
Power boilers usually require how many blowdown valves?
2 blowdown valves.
High pressure boilers operate at pressures above..
What ultimately determines how efficient a firetube boiler is?
The number of passes the tubes make.
Capacity and operating pressure of a locomotive boiler?
6800 kg/hr, 2400 kPa surrounded by waterlegs on four sides.
Characteristics of a Firebox boiler?
-Compact, efficient and initially inexpensive.
- capacity of 6800 kg/h and up to 1720 kPa.
Most important language within a profession?
The terminology within that profession.
Shell VS Tube?
Shell - firetube
Drum - watertube
Make up water?
The water that does not derive from condensate or water returning from a previous point in the system.
High temperature hot water boiler V.S. Low pressure hot water heating boiler?
High temp. hot water - Temperature exceeds 121 C or a pressure of 1100 kPa.
Low press. Hot water - Temperature below 121 C or below 1100 kPa.
Lowest permissible water level :
Heating Boiler: Lowest visible part 25mm (1 inch) above the level.
Power Boiler: Lowest visible part 50mm (2inches) above the level.
H.R.T. : Lowest visible part of the gauge glass no less than 76 mm (3inches) above the highest point of the tubes, flues or crown sheet.
A PRV regulates pressure from lower to higher. True or False?
False. Higher to lower.
By code, what is required after a stop/check valve coming off a steam drum?
A stop valve must come after the stop/check valve, and before the header.
Usually a single coil pipe that prevents steam from entering a steam gauge which will damage it.
Describe the tubes in a modern HRT boiler.
- 76mm-102mm (3-4") diameter.
- tubes expanded at each end into the tubesheets.
- 2 pass design
- 454 to 6800 kg/h up to pressures of 1700 kPa
Which boiler has more stays, Locomotive or HRT?
What was the wetback Scotch boiler primarily designed for?
Types of Bent Tube boilers?
- 4 pass
- 3 pass
- 2 pass
- ( A, D, O )
What determines the capacity of a packaged boiler?
The length of it because the height is restricted according to transportation laws.
They are all bottom supported
Is a steam generating unit a boiler?
No, a steam generating unit refers to the boiler as well as all the components which obtain to its successful operation.
Difference between an altitude gauge and a standard gauge?
An altitude gauge measures height or altitude in units of inches of water or inches of mercury.
Distinct difference between safety valve and a safety relief valve?
Used when steam required for power generation or a process is at a temperature higher then that of saturation.
Advantages of an Air heater?
- improve combustion efficiency
- Assist in the burning of pulverized coal
A common problem with D-type water tube boilers is what?
The vibration involved.
What kinds of places would you often find electric boilers?
- Hospitals, Schools, Hotels etc.
- Places where there is an abundance of extra electricity available.
2 types of electric boilers?
- Electrode type
- Immersion heater type
Disadvantages of electric boilers?
- expensive to operate
- limited to 2100 kPa due to high temperatures on electrodes or elements.
What produces the heat in an electrode type electric boiler?
The current flowing through the water.
What is a key ingredient in the feedwater within an electric boiler?
Salt to conduct the electric current throughout it.
The amount of current is directly proportional to the length of the electrode submerged in the water. True or False?
Percent efficiency of electric boilers?
How does the water get heated in an immersion type boiler?
The electric current flows through a heating element which is entirely submerged beneath the boiler water level.
Operating voltage for an electrode boiler may be as high as ________ volts and at power ratings up to ________ kW.
16000 volts, 30 000 kW.
The amount of steam produced by an electrode type boiler depends on what?
The level of water in the basket.
What is NOT required on an electrode type electric boiler?
A low-water cutoff.
An immersion electric boiler capacity can be as high as ________ kW.
Control of the immersion heater boiler is done by turning on and off the what?
Number of Heating elements.
Thickness range for shells/drums?
6mm - 250mm
What is Boiler Construction?
The science of joining metal plates, tubing, and piping in required configurations so the vessel can withstand these pressure differences and stresses.
If you have 2 drums, same thickness but different diameter, which one can handle the higher pressure?
The one with the smaller diameter.
In a watertube boiler are the heads made in a dished or flat shape?
Dished. Flat heads are installed on firetube boilers and are often called " tubesheets ".
Most common type of joint weld used in boiler fabrication?
The butt-joint type, however, the lap joint is sometimes also used.
5 most common types of welded joints are:
Butt joint, corner joint, tee joint, lap joint and edge joint.
1) A _______ weld is used to make a butt joint and,
2) A _______ weld is used to make a lap joint.
1) Groove weld
2) Fillet weld
If the weld is applied to both sides of the pieces being welded, what is it called?
Double welded butt-joint.
What procedure must be followed after welding a drum/shell?
10 types of welding grooves?
Square groove, V-groove, J-groove, U-groove, Bevel groove, Double bevel groove, Double bevel, Double J, Double U and Double Vee.
What is a method of reducing the stresses within the metal while welding?
Heat treatment. ( temps. between 80-230 deg. C )
A second method of heat treatment?
- Post weld heat treatment OR " stress relieving ".
in the case of a boiler furnace, after it has been welded it can be stuck in a special furnace heating the piece to a specified temperature (up to 590 deg. C) and then slowly cooling it until it drops to below 315 deg. C.
Two types of riveted joints?
- lap joint
- butt joint
a) Circumferential seams = _________
b) Longitudinal seams = _________
a) Lap joints
b) Butt joints
Tubes for moderate pressure service are made from strips of steel, True or False?
Tubes used for high pressure service are usually seamless, True or False?
What is the most common method fastening tubes to drums or tube sheets?
To expand the tube into the tube hole in the drum or sheet.
Why are stays not normally required in water tube boilers?
Because water tube boilers are typically built without any flat surfaces.
What is the tool called that is used to expand the tubes against the tube sheet?
A tapered mandrel.
Describe a MANHOLE.
- Manholes are the openings to steam or mud drums and are usually elliptical in shape.
- Usual dimensions are 12" by 16" (305mm-406mm)
- By code they cannot be less then 15" ( 381mm)
Describe a MANWAY.
- An opening or " access port " to a confined space such as a boiler furnace.
Describe a HANDHOLE.
- Give access to smaller openings such as headers and waterlegs.
- Minimum dimensions for hand holes are 2 3/4" by 3 1/2" (70mm by 89mm)
For pressures less than ____ psi and temperatures less than ____ deg. C , manhole/handhole covers may be made of cast iron. If exceeding these limits they must be rolled, forged or cast ______ .
a) 250 psi
b) 450 degrees C
What are the two types of supports for boilers?
Top supported and bottom supported.
Tubes for high pressure service are usually made by what type of construction?
Pierce and roll construction.
What is the first pass of a groove weld in a butt-joint called?
A root weld.
What are 3 types of furnace walls in a boiler?
- Welded fin tube waterwall
- Tangent-tube wall
- Flat Stud tube wall
Define "draft" and state why we need it in boiler operation.
Draft: A differential in pressure which will produce a flow of air. Drafts in boilers are used to supply combustion air to the boiler furnace.
Primary air V.S. Secondary air?
Primary - The air being mixed with the fuel before being admitted to the furnace.
Secondary - The remaining air leftover necessary for complete combustion, supplied close to the burner in the combustion zone.
What is tertiary air?
An additional layer of air introduced at the end of the combustion zone to ensure that the fuel is burned completely.
What action promotes thorough mixing between the primary and secondary air?
counter-acting rotations of the two. (Clockwise and counter-clockwise)
Two groups of draft equipment are:
- Natural draft equipment
- Mechanical draft equipment
As a percent, how efficient can dust collectors be when removing dust from flue gases?
Most durable type of chimney? Most popular type of chimney?
Most durable - Concrete type.
Most popular - Steel type.
3 types of mechanical draft equipment?
Induced draft, forced draft, and balanced draft.
What are two types of induced draft equipment?
- Steam jet
- Induced fan
What are 2 purposes of the louvres inside a windbox?
1) Give the air a swirling motion in order to obtain better mixing of the fuel and air.
2) Prevents other burners from starving for air while that burner or other burners are put out of service.
What type of pressure is essential to keep the furnace at in a balanced draft system?
Always keep the pressure at the furnace slightly below atmospheric so the hot flue gases have a path to exit.
If a fan runs at a constant speed, how do you vary the air flow?
By register or damper control (inlet or outlet dampers)
Describe fan speed control. (steam)
Variable speed fan control through an automatic control system where there is a steam driven turbine throttling the fan speed.
Most efficient type of fan control?
Variable speed coupling.
What is the use of aspirating air in a pressurized furnace?
Aspirating air is used as 'sealing' air that allows for removal of an oil burner or an auto gas lighter while the boiler is in service.
3 types of draft measuring equipment?
- U-tube manometer
- Inclined U-tube manometer
- Diaphragm draft gauge
Boiler draft is typically indicated in what kind of units?
Millimetres of water
What does the CSA code B-51 specify?
This code specifies the size of openings required into a boiler room when burning a given number of heat units in a given time.
Complete combustion is absolutely necessary for what 2 reasons?
- Environmental reasons
- Safety Reasons
3 combustible elements common to a Power Engineer?
Hydrogen, Carbon and Sulphur.
A few common non-combustible materials?
Moisture, ash, CO2 and many other trace elements.
By WEIGHT, what are the composition percentages of air?
oxygen - 23%
nitrogen - 77%
What are the 2 factors that determine the ideal amount of excess air?
- The composition and condition of the fuel fired.
- The method used for burning the fuel.
Excess air percentages for: Stoker fired coal, Pulverized coal, fuel oil and gaseous fuel.
O2 percentages for: Stoker fired coal, Pulverized coal, fuel oil and gaseous fuel.
Fuel oils are classified into grade numbers according to what three characteristics?
Relative density, viscosity and flash point.
What is a good indication of the fire hazard involved in the storage and pumping of an oil?
It's flash point.
What is the possible range of excess air required in common processes?
10-60% or even higher in some cases.
Grades 1 and 2 require heating before being fired in a boiler furnace. True or False?
False, they do not need heating as they have a relatively low viscosity and relative density.
What is the most popular grade of fuel oil for domestic, small commercial and industrial boiler purposes?
Grade 2 oil.
For higher grade oils that require heating, what is the ideal temperature before they can be satisfactorily burned?
Roughly 95 degrees C.
2 Gaseous fuels used in combustion for boilers?
- Natural gas (methane)
- Liquefied petroleum gas
Approximate hydrocarbon contents of natural gas?
2 possible hydrocarbons for LPG?
Butane and propane or a mixture of the two
Approximate space occupied of a LPG in comparison of liquid VS gas?
1/120th of the space as a liquid VS its gaseous state.
At atmospheric pressure the boiling point for: Butane =
Butane: 0 deg. C
Propane: -42 deg. C
3 types of mechanical stokers?
Underfeed, overfeed and cross-feed.
Crossfeed is also referred to as a what?
Chain grate or bar grate stoker.
Overfeed stoker also referred to as a what?
A spreader stoker.
Hog fuel may be burned with coal simultaneously. True or False?
What kind of oil burner would you typically see on larger packaged boilers?
A Rotary cup oil burner.
After cleaning an oil burner, what should you do?
Hang them vertically with the burner tips immersed in kerosene or any type of solvent.
What kind of gas burner would you typically see on large boilers?
Ring type gas burner.
Ideal flame color characteristics?
Blue flame with yellow tips.
How often should a gas burner be cleaned?
Whenever the boiler is shut down for routine maintenance and inspection.
What is the most commonly used type of refractory?
What determines fuel flow speed for solid fuels?
Adjustments to the primary air flow (pulverized coal), or the grate or stoker speed.
The higher the amount of excess air, the higher the amount of CO2 in the flue gases. True or False?
False, the higher the amount of excess air the LOWER the amount of CO2 there will be in the flue gases.
What is the name of one common flue gas analyzer used on heating boilers?
The Fyrite analyzer.
4 types of flue gases that are of most interest according to environmental standards?
Nitrous oxides, carbon dioxide, carbon monoxide, and sulphur dioxide.
What is a 'Peltier Cooler' ?
An electrochemical device that produces a cool surface that condenses any moisture out of the flue gas before it reaches the measuring sensor.
2 different ways flue gas readings are portrayed?
Either in percentages or in PPM's.
To ensure a Fyrite analyzer is properly purged to take a fresh reading, how many bulb strokes are made to clear the rubber hose and top reservoir?
Sample capacity of the Fyrite analyzer?
What type of flue gas analyzer uses a chemical absorber?
The Orsat analyzer.
How do you calculate whether or not you have an adequate amount of excess air?
By using your readings of CO2 and O2, you could either do a calculation or read it from a table or graph.
What unwanted deposit is formed on refractory in coal fired burners?
Ash slag which will corrode and erode the refractory.
What is ' Combustion Efficiency ' ?
The indication of what percentage of heat is actually absorbed into the water from the combustion.
What 2 things must be known to determine the boiler efficiency?
- The percentage of CO2 in the flue gases leaving the boiler.
- The net stack temperature. ( temperature of flue gases V.S. temperature of the combustion air )
Aside from too much excess air, what else could increase the stack temperature?
- Scale formation (waterside) or soot and ash deposits (fireside).
High pump pressure is required in what type of fuel oil burner?
The mechanical fuel oil atomizer.
Describe the basic concept behind FBC.
- Method of burning crushed coal in a bed of limestone particles and ash.
- Air blows up from beneath the bed of limestone/ash keeping the bed in a fluidized motion.
Limestone and coal fully combust to produce an inert compound called calcium sulphate. What popular by-product is created from calcium sulphate?
List 5 major benefits of FBC.
- Increased power generation efficiency
- SOx and NOx emission regulations met
- Less expensive than a flue gas de-sulphurization plant
- Less effluent disposal
- Lower combustion temperature
Two types of FBC units are:
a) Atmospheric fluidized bed combustion
b) Pressurized fluidized bed combustion
Large industrial AFBC units have achieved to produce as much as _________ kg/h of steam and anticipate to produce ________ kg/h of steam in the future.
500 000 kg/h and 1 000 000 kg/h.
Two sub-groups of AFBC units?
- Bubbling bed
- Circulating bed
Bubbling mass is maintained at a depth of ___ metre in a AFBC unit.
What is the name of the piece of equipment that takes care of "carryover"?
Typical velocity of fluidizing air?
Common furnace temperature is ______ deg. C
850 deg. C
About ___ % limestone reduces SO2 emissions by ___% in AFBC systems.
10% and 80%.
In comparison to a conventional pulverized coal plant, a PFBC system is ___% more efficient.
One type of gas/steam cycle using a PFBC boiler is capable of generating ____ of the electrical power by the gas turbine and ____ by the steam turbine.
1/3 and 2/3.
The steam generator can be reduced by up too ___% in comparison to a regular unit.
What is one major danger of running a FBC system at a low operating rate?
Poor combustion control, risk of incomplete combustion.
The inert bed material (limestone) must be preheated to at least ______ deg.C before operation. This usually takes about _____ hour(s)
600 deg.C/ 1
The operator must be aware of ________ when starting up the FBC system. To control this you could slow down the feed rate of the fuel.
2 common scenarios that can cause the boiler to exceed its operating pressure.
- sudden loss of load demand
- failure of the automatic controls
Everyone boiler must have at least ONE pressure safety valve, and if the water heating surface exceeds ____ then two or more safety valves shall be installed.
47 m squared ( 500 ft. squared )
Safety Relief Valve V.S. Safety Valve?
Safety Relief Valve: a) found anywhere on the boiler b) there is no isolating valve between the boiler and the relief valve c) not found on steam boilers.
Safety Valve: a) found on steam boilers on the steam drum b) they typically have an exhaust line going to the roof
By code, the safety valve must be capable of bleeding off the steam in time before the boiler over pressurizes to above ___ % the maximum allowable working pressure.
Why is the spring exposed on a safety valve?
To prevent the high temperature of the steam from destroying the mechanical properties of the spring.
Superheater/ reheater safety valves are set to pop before and close after drum safety valves. True or False?
What ASME section refers to rules governing superheater/reheater safety valves?
ASME section 1
What is the next step after an adjustment and lock nut has been set on a safety valve?
The cap is put in place and the inspector attaches his seal to a wire passing through a hole preventing access to the adjustment nut.
If a safety valve is to be tested for correct operation, how much pressure does the boiler have to be at?
75% of the boiler operating pressure.
How many seats does a safety valve have?
2. They are double-seated.
What happens when the huddling chamber outlet is closed too much?
Pressure under the lip is greater; boiler pressure must drop a lot before the spring closes the valve.
What about when the huddling chamber outlet is open too wide?
Pressure under the lip is minimal and the valve will close with very little drop in pressure.
What is the special name for the difference between the pressure which the valve opens/closes?
Blowdown of the safety valve.
Minimum allowable blowdown?
Maximum allowable blowdown?
The safety will close at a pressure no lower than 96% of the set pressure of the safety valve.
A threaded adjustable angular ring vary's the amount of port opening. What happens if it's screwed upwards? downwards?
Upwards: Blowdown is longer.
Downwards: Blowdown is shorter.
To increase BLOWOFF pressure?
Screw the adjusting nut down-compressing the spring.
To decrease BLOWOFF pressure?
Screw the adjusting nut upwards-releasing some of the pressure on the spring.
Popping pressure may be decreased or increased by ___% by changing the compression of the spring.
A lever test tells you whether or not the valve will operate at its set pressure. True or False?
False. It only tells you whether or not it's free to let steam exit.
Do not perform a lever test on low pressure boilers operating below ___ kPa.
35 kPa (5 psi)
Torsion bar safety valves are installed on boilers operating at _____ kPa and higher.
What are the minimum and maximum seat diameters of safety valves according to the ASME codes?
Minimum - 13mm
Maximum - 110mm
Which ASME code refers to the mountain of Safety and Safety Relief valves?
ASME section IV
It is ok to attach the safety valve to an internal pipe in the boiler. True or False?
Safety valves should be adjusted and sealed to discharge at a pressure not to exceed _____ psi.
When fuel systems are burning at maximum capacity, the pressure in the boiler cannot exceed ___ psi past its maximum allowable working pressure without a safety valve popping.
How man safety relief valves should a hot water heating boiler have?
At least one that discharges at or just below the maximum allowable working pressure for that boiler.
As far as design goes, what are the key differences between the safety valve and safety relief valve?
Safety relief valves aren't fitted with blowdown adjustment rings, and bottom guides are not permitted.
Where must you connect a safety relief valve on a system or tank?
It can go anywhere
(reasonably close to the heater or tank though)
4 possible reasons why a safety relief valve could be leaking?
1) Scale has formed on the seat of the valve because the heater used operates at temperatures higher than 65 deg.C and the water is hard.
2) The pressure in the supply line is exceeding the setting of the valve.
3) Valve is defective or being improperly used.
4) System becomes water logged.
2 Common places the safety relief valve is placed?
- cold water supply line
- hot water discharge line
Where would you typically see a temperature relief device?
A domestic hot water system.
Two types of arrangements for temperature relief devices?
a) A device which contains a fusible plug which melts at about 99 deg.C and hot water is released.
b) A device that uses to expansion and contraction of a rod and tube arrangement to open it at 99 deg.C and 71 deg.C
It is common to install a combination of temperature and pressure relief devices on one system
Before performing a pop test what is one of the first things you should do?
Verify the accuracy of the steam pressure gauge.
3 examples of direct measurement?
- Gauge Glass
- Float Gauge
4 examples of indirect measurement?
- Bubbler systems
- Differential pressure level meters
- Electrical capacitance level gauges
- Ultrasonic level gauges
3 types of gauge glasses?
- Tubular (simplest and least costly)
- Armored-type (type)
2 types of isolating valves on gauge glasses?
- Slow closing valves
- Quick closing valves
Explain the common safety feature used on glass gauges and one main disadvantage of this feature.
- Consists of a stainless steel ball which closes off the passage for water when the glass breaks.
- One disadvantage of this feature is the fact it requires more maintenance.
Maximum allowable length of a gauge glass?
750 mm/ 75 cm
Steam generating boilers must be equipped with at least ONE gauge glass. True or False?
How often should a gauge glass be drained to clear away any sediment or sludge?
At least daily.
Advantages of connecting a gauge glass to a water column? (4)
- Column acts as a reservoir to dampen agitation in the water.
- Column traps sludge and sediment rather than the glass itself.
- The column is a good place to attach alarms and controls for the boiler.
- Try cocks can also be installed as an alternative for when the gauge glass breaks.
Limits and restrictions of a tubular gauge glass?
- Limited to low temperatures and pressures.
- Restricted to non-toxic and non hazardous material.
A.S.M.E. codes for the lowest visible point of a gauge glass on a firetube boiler who's crown sheet is 36" (914mm) or less? Or more?
Less than 36" : 2" of space (51 mm)
More than 36" : 3" of space (76 mm)
The consumer must calculate the lowest permissible level for a packaged steam boiler. True or False?
False. It is provided by the manufacturer, and whatever this measurement is the lowest visible level in the gauge glass should me 25mm or more above this point.
3 causes of gauge glass failure?
- High PH from alkalinity causes thinning to the glass
- Condensate formed in the glass due to cooling of the steam dissolves silica within the glass to weaken it.
- Misalignment of fittings causes weakness
What should you use as a lubricant for the washers and nuts when replacing a gauge glass?
only tighten the nuts hand tight
Protocol for when the gauge glass leaks and the nuts need to be tightened?
- DO NOT tighten the nuts when the glass is under pressure. Close the steam and water valves and open the drain before tightening the nuts.
At what pressure should a Armored type gauge glass be used?
2800 kPa (406 psi)
Certain armored type gauge glasses are suitable for temperatures exceeding ____ deg.C and pressures up to _______ kPa. What are the 2 specific types?
250 deg.C , 70 000 kPa. Transparent and Reflex.
Special material used to protect transparent gauge glass surfaces?
The transparent gauge glass itself is also resistant to what?
mechanical and thermal shock.
When tightening the U-bolts on the armored gauge glasses, what method is recommended?
The crossover method, starting in the middle.
Reflex gauge glasses are typically used for what kind of liquids?
Clean, colourless, non-viscous, and non-corrosive liquids such as light and heavy hydrocarbons.
To let the new piece of glass slip into place easily for an armoured gauge glass, what chemical should be applied to the contact surfaces?
In a bicolour gauge glass, what does red indicate? What about green?
- Red indicates steam space
- Green indicates water space
A boiler operating at 13 800 kPa may have a gauge glass that reads 20% inaccurately, with the reading actually being lower in the glass then in the boiler. How come?
- The temperature of water in the gauge glass is lower then the temperature of water in the boiler. The water is the glass is also denser.
When testing the gauge, why don't you open the valves all the way?
You don't want the ball's to seat on the valves.
How often is the operator advised to change the gauge glasses?
Every couple years, depending on the wear (etching, thinning)
The _________ remote water level indicator is a popular indirect instrument.
A remote indicator uses a __________ which measures head pressure and steam pressure to operate shutters and give a coloured indication.
On an Igema remote indicator, the glass contains a special liquid lighter then water. To prevent contamination of this liquid _____ _____ are installed on both connections to the glass.
Advantage of a remote indicator?
No mechanical parts.
What are 5 main steam drum internals?
- Primary and secondary separators
- Internal feed lines for feedwater
- Continuous blowdown for dissolved solids
- Chemical feed lines for corrosion/impurities and ongoing water treatment.
Mechanical separators are required in low pressure boilers. True or False?
False, at low pressures steam naturally separates from the moisture.
The ___ _____ is an early form of separator.
The Dry pipe.
Primary and secondary separators remove most of the moisture from the steam, while the ______ _______ remove most of the contaminants in the steam.
How are the separators installed?
In single or double rows.
The water in the mixture between steam/water can range between ___ to ___ times as heavy in mass
2 - 25 times as heavy.
- Acceptable circulation ratio?
- Most common ratio?
1) 3:1 to 20:1
2) 5:1 is common
The cyclone steam separator has no moving parts. True or False?
True. It utilizes the circulation force into a centrifugal force in which separates the steam from the water.
Cyclone separator is a primary or secondary separator?
Secondary separators are typically made up of...
rows of closely fitted corrugated metal plates located directly above the primary separators. They work by making the steam change direction numerous times separating the moisture from the steam.
Located at the very top of the drum would be the...
Chevron scrubbers/dryers. Usually just a wire mesh screen picking up any droplets of water.
On large boilers the feed water pipe extends the length of the drum and is perforated for what 2 main reasons?
- Reduces the risk of thermal shock
- Reduces the amount of excess turbulence
Where is the CBD located in the steam?
Several centimetres below water level since the more concentrated water is usually far below the surface.
The chemical feed pipe extends the length of the drum just like the feed water pipe. True or False?
Some smaller boilers have a short pipe which discharges against a baffle in the steam drum. This pipe acts as a what?
Internal feed pipe.
What would be 2 majorly unfortunate outcomes if we didn't have sootblowers?
- Soot and ash would act as insulation reducing heat transfer rate lowering boiler efficiency/capacity.
- Deposits would obstruct the passages of the flue gases, resulting in an increase of draft power required.
Sootblowers are installed in the convection and radiant zones of the system. Give 5 specific examples of these areas.
- Furnace walls
- Air heater
2 mediums available for soot blowing?
Steam and air.
Between these two mediums, which one is more convenient?
Steam because it is readily available.
In solid fuel boilers what are the 2 systems available for sootblowing?
Retractable and stationary
The wall blower is designed to remove slag. what is slag?
A retractable sootblower uses a short stroke lance with special openings penetrating the furnace walls _____ to ______ mm in diameter. The lance produces approximately a ____ m radius.
25-51mm , 1.5m radius
Long retractable soot blowers are typically used for which sections?
Convection and radiant sections.
While the lance traverses the boiler, it rotates forming what kind of pattern?
Helical blowing pattern.
When soot blowing, the boiler should operate at minimum ____ % and the furnace pressure should be what?
50% and below atmospheric to prevent blowback at inspection ports.
When would you use a stationary sootblower?
When there is not enough space for a single nozzle type and the flue gases run at a moderately low temperature.
Which systems would you use shot cleaning in?
Economizer, air heater, superheater tubes.
Iron shot pellets usually ___ mm in diameter fall by _______ between surfaces.
What determines what type of blowdown system a plant has?
The type of external water treatment system.
What determines what type of water treatment a system has?
The boiler operating pressure.
A boiler operating above roughly 5000 kPa retrieves its water from what sources?
This type of system would use demineralized water from a cation-anion exchange system, reverse osmosis or an evaporator.
In the case of a utility boiler operating well below 5000 kPa, what kind of treatment system would be used? How often would the CBD be used? and the Intermittent blowdown?
1) Sodium Zeolite/ Hot or cold lime softening
2) CBD runs CONTINUOUSLY
3) Intermittent blowdown should be performed once a day.
3 resources that will explain furthermore the guidelines according to boiler care.
a) Section 7 of the ASME Boiler/Pressure Vessel Code
b) B31.1 Code on Power Piping
c) CSA B51 Code
2 sources dissolved and suspended solids?
a) Leftover solids from external water treatment
b) From the chemicals injected into the boiler as part of the internal water treatment
What type of valve regulates the CBD?
A needle valve usually equipped with a valve position indicator (vernier valve).
On a demineralizing treatment system, how much would the valve usually be open?
Almost or completely closed under normal operation.
On regular treatment systems, what should the CBD valve be set to in relation to the steam flow rate?
CBD flow should be set to equal 1% or more than overall boiler steam flow rate.
Where are the suspended solids in a...
- Firetube boiler?
- Watertube boiler?
a) Bottom of the shell
b) The mud drums
3 major components to an intermittent blowdown system?
- Blow off tank
- Blow down piping
- Blow down valves
What combination of things would damage the sewer piping if the blowdown tank wasn't involved?
Pressure, Vaporization and High Temperatures.
Which code states requirements for the installation of a blow off tank operating at or above 103 kPa?
CSA code B51
Temperature may not exceed _____deg.C at the blowoff tank outlet.
ASME Code B31.1 on Power Piping specifies what regulations?
Materials, Pressure ratings, and required sizes for blowdown piping.
What is ' allowance ' ?
The ability to expand and contract during drastic temperature changes between the boiler and all the blowdown piping.
Every ______ pressure steam boiler must be equipped with ____ approved blowdown valve(s) which should be of the slow opening type.
AT LEAST 5 TURNS FROM FULL-CLOSED TO FULL OPEN
- High pressure
Every plant is different but what is the deciding factor for a start up procedure in every plant?
The role the steam plays for that type of plant.
4 parts to a basic start up preparation?
- Quick overlook of the boiler components.
- Feedwater, Fuel and Draft
- Boiler dry out (old)
- Boiling out (new)
Before closing up the boiler and filling it, it must be inspected __________ and __________.
Internally and Externally
Before filling the boiler, what is very important to be check?
The blowdown valves are CLOSED and the vent valve is OPEN.
In Winter time, what is important to check on the draft equipment?
That the intake screens are clear if the system uses an external source. Frost can form on the screens.
Important considerations when doing a boiler dry out:
- Do not heat the furnace too much so the moisture in the refractory flashes to steam, slowly build temperature.
- Leave a vent open to prevent pressure build up.
- Maintain water level.
- Dry out may take several hours or even days.
Considerations when boiling out a boiler?
- If not boiler out- all the grease, debris and oil could impede on water circulation or destroy instruments.
- Use detergent type chemicals and blow down any concentrated debris.
Types of alkaline solutions used for boiling out a boiler?
- Soda ash
- Caustic Soda
- Trisodium Phosphate
- Sodium Silicate
3 major areas of attention for boiler START-UP are:
- Boiler warm-up
- Steam header warm-up.
What is the basic sequence for ignition of most systems?
1) Pre-purge the furnace
2) Reduce air flow for stable ignition
3) Pilot burner ignition
4) Main burner ignition
Some boilers have automatic systems while others have completely manual systems. What kind of system do MOST boilers have?
A combined system; half auto/half manual.
If a boiler has a superheater, what valve is essential to open when starting up the boiler?
The vent valve to the superheater so it does not overheat due to lack of steam flow.
Deciding factors how long a boiler takes to get to normal operating status?
- Size of the boiler
- Length of time its been shut down
What do "hotspots" on the furnace walls indicate?
That refractory has fallen away.
Steam headers should be warmed up gradually to avoid ________ ______ and to remove _________. If this procedure is not done, what will result because of this?
1) Thermal Stress
3) Water hammer
a) High pressure turbines/processes
b) Intermediate pressure turbines and processes
c) Pressure steam for heating/auxiliary equipment
a) 10 250 kPa
b) 2410 kPa
c) 620 kPa
Easiest way to warm up Boiler/header piping?
- Open the boiler stop valve
- Open the header drains
The process of "cutting" a boiler into the header is described in which ASME code?
ASME code section VII (7)
Procedure for cutting into a header is as follows:
- Open drain on non-return valve
- Open header valve SLIGHTLY to drain condensate and warm up line
- Open header valve all the way
- When boiler pressure is just below header pressure, open stop/check slightly
- After check valve opens, open stop/check all the way. Close drain
How often should the low-water alarm be checked?
Beginning of every shift.
Causes of foaming or priming?
- Wide fluctuation of water level
- High level of TDS or TSS or oil
Causes of smoking in the stack?
- Air intake might be blocked with snow or ice
- Burner nozzle may be dirty (oil fired)
- Fuel oil temperature might be too low (oil fired)
- Fuel air ratio might be incorrect (gas or oil firing)
Gas fired boilers require regular sootblowing. True or False?
You must record the CBD setting in the daily log. True or False?
If alarms/cutoffs fail, and you shut down the boiler automatically, what should you proceed NOT to do?
- Do not feed water into the boiler raise the water level
- Do not open the safety valve or vent to release pressure
4 reasons why accidents occur in boilers?
- The misconception an automatic fired boiler doesn't need supervision
- Lack of training/knowledge
- Inadequate maintenance
- Low water incidents because of safety controls or poor operation
2 types of boiler explosions:
- Furnace explosions
- Pressure explosions
What is RCM?
Reliability Centered Maintenance
Number one cause of furnace explosions?
What are the 3 types of logs?
- Boiler operations (daily log book)
- Rounds Logs (every hour or so)
- Maintenance logs (recordings should be done in the operators log book and a maintenance log)
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