Stationary Engineering: 3rd Engineers Essay Questions
It takes approximately 15 lb of air to burn 1 lb of coal. How much air is necessary to burn 1 ton of coal?
1 ton of coal = 2000 lb 15 lb air x 2000 lb coal = 30,000 lbs of air
A boiler is equipped with a superheater and has an automatic nonreturn valve. Explain how this boiler must be warmed up and cut in online:
1) Check for the following: a. Furnace is free and clear of all tools b. Boiler has proper water level c. Superheater drain is open d. Free-blow drain is open e. Drum vent is open 2) Follow the manufacturers recommendation, and light off the boiler; let it warm slowly 3) Monitor the water level in the boiler drum 4) When the boiler reaches approximately 25 psi, close the drum vent 5) When the boiler reaches approximately 85% of the line pressure, open the equalizing line around the main steam stop valve. Warm up the line and open the main steam stop valve slowly. Open the valve fully, then back it off slightly to keep it from jamming in the open position. 6) Open the automatic nonreturn valve. Bring up pressure on the incoming boiler slowly. When the steam pressure on the incoming boiler is approximately 1 lb higher than the line pressure, the automatic nonreturn valve will cut the boiler in online. -Then close free-blow drain 7) When 20% of the boilers steaming capacity is reached, the superheater drain valve may be closed. 8) Check the water level, condition of fire, and all operating temperatures and pressures. 9) Put the boiler on automatic control, and make sure they take over 10) Resume normal shift
List the auxiliaries commonly used in the operation of a condensing steam turbine:
1) Condenser: Condenses steam from the steam turbine exhaust, forming a vacuum. Lowers back pressure on steam turbine 2) Circulating water pumps: Provides condenser with cooling water needed to condense steam and maintain vacuum 3) Condensate pump: Removes condensate from the condenser hot well and discharges it to the feedwater heater to be reused 4) Air ejectors: Single- or two-stage ejectors used to remove air and Non condensable gases from the condenser, which increases the vacuum.
What is the procedure of cold startup of a boiler equipped with a superheater?
1) Inspect the fire side of the boiler to make sure it is clear of tools, rags, etc. 2) Check the water level of the boiler 3) Make sure the boiler vent, superheater drain, and free-blowing drain are open 4) Light off the boiler and warm up slowly. 5) Open the equalizing line around the main steam stop valve to equalize pressure and warm up the line. Then open the main steam stop valve, slowly. 6) Keep a close watch on the boiler water level 7) When steam pressure reaches 25 psi, close the boiler vent 8) Open the automatic nonreturn valve when steam pressure on the incoming boiler reaches 75-85% of line pressure 9) Test the flame failure control 10) Bring the boiler pressure up slowly and allow the automatic nonreturn valve to cut the boiler in online 11) Close the free-blowing drain 12) Close the superheater drain when adequate flow has been established (approximately 20% of boiler capacity) 13) Put all boiler controls on automatic and make sure they take over.
List four reasons for losing vacuum in a plant using a surface condenser. How could each condition be corrected?
1) Insufficient cooling water: increase water flow and check intake water line. If a cooling tower is the water source, check makeup water supply 2) Fouled air ejectors: Change over air ejectors and clean faulty ejector 3) Loss of water seal in hot well: Reestablish water seal 4) Waterlogged condenser: Check condenser condensate pump and return to service
Describe the location and purpose of the following: 1) Nonreturn valve, 2) Quick-opening valve, 3) superheater safety valve, 4) free-blowing drain, 5) expansion bend
1) Nonreturn valve: Found on main boiler steam line as close to the boiler as practicable. Cuts boiler in online and offline automatically, and protects system from draining in event of a failure on steam side of any one boiler. 2) Quick-open valve: Valve located on blowdown line closest to the boiler shell on boilers operating at 100 psi or higher. The quick-opening valve functions as a sealing valve. 3) Superheater safety valve: Located on outlet header of superheater. Superheater safety valve is set to pop before main safety valves to establish steam flow through superheater to prevent warping or burning out tubes. 4) Free-blowing drain: located on boiler main steam line between the two boiler stop valves. Used to remove condensate from steam line when warming up the line before boiler is cut in online. Also used to make sure automatic nonreturn valve is not leaking when performing a hydrostatic test on the boiler. 5) Expansion bend: Found on boiler main steam line. Allows for expansion and contraction. Also used on long runs of steam lines to allow for expansion and contraction in place of expansion joints.
How is an auxiliary steam turbine started?
1) Open the steam turbine exhaust valves and casing drains to allow the steam turbine to warm up 2) Check the oil level on all bearings 3) Open the feedwater suction and discharge valves on the pump 4) Crack the throttle valve enough to cause the steam turbine to spin. Secure the throttle and listen for rubbing noises. 5) If no rubbing occurs: a. Open the throttle and bring the steam turbine up to speed, b. Close the cylinder drains, and c. Make sure the governor takes over. 6) Test the overspeed trip manually, then reset the overspeed trip and bring the steam turbine back up to speed. 7) Check all bearings to ensure they are getting proper lubrication and cooling 8) Remove the other feedwater pump from service if necessary
Describe the three methods of heat transfer:
1) Radiation - Method of heat transfer that occurs when heat is transferred without a material carrier 2) Convection - Method of heat transfer that occurs as heat is transferred by currents through a fluid 3) Conduction - Method of heat transfer in which molecules come in direct contact with each other, and energy is passed from one molecule to another Heat always travels from a hot area to a cold area. There must be a temperature difference for heat to flow. The greater the difference in temperature is, the greater the movement will be.
Describe 3 methods for identifying overheated bearings:
1) Smell: When the oil in journal bearings starts to overheat, it gives off a distinct odor, and/or changes color 2) Feel: If the operator touches a journal bearing and cannot keep a hand on it, it is running hot. 3) Noise: Journal bearings squeal when they are overheated.
How is an auxiliary steam turbine removed from service?
1) Use the manual overspeed trip to secure steam to the steam turbine. 2) When the steam turbine stops spinning, secure the exhaust valve and open all cylinder drains 3) If the steam turbine is driving a feedwater pump, secure the suction and discharge valves 4) Reset the overspeed trip for the next startup
How do you start a non-condensing turbine?
1. Fill all grease cups and oil the governor and other miscellaneous parts. 2. Open drains on the header, separator, casing, and exhaust lines. If these are equipped with traps, open the bypass line. 3. Slowly open the exhaust-line shutoff valve. 4. If the turbine has a pressure lubricating system with an auxiliary oil pump, start the pump. 5. Inspect the bearings for ample flow of oil; check the oil pressure and see if the pump is operating properly; 3 to 5 psi is sufficient. 6. Turn on the cooling water for the bearings or oil cooler. 7. Open the throttle quickly to start the turbine. During this time observe the turbine carefully for signs of unusual noises and rubbing by careful listening or check vibration monitoring equipment if available. 8. Slowly bring the turbine up to speed, approximately 300 rpm, and operate it at this speed for a period of 15 to 30 minutes. 9. Trip the emergency valve by hand to see that it closes properly. 10. Open the throttle wide and allow the governor to regulate the speed; keep a close check to prevent overspeeding. Note: If the governor will not control the speed at no load, the hand throttle may be used until the load is on. 11. Inspect the bearings to make certain that they are getting oil. Oil should be up to the level recommended by the manufacturer. Usually the level drops when oil fills all the various cavities in the system. 12. The drains, which were opened before the turbine was started, should now be closed or arranged to discharge through the trap. 13. Gradually increase the load on the turbine while keeping a close check on the oil, cooling-water, and bearing temperatures.
How is a boiler prepared for an annual inspection
A boiler is prepared for annual inspection using specific procedures to prevent injury to plant personnel or damage to the boiler. The procedure is as follows: 1) Take the boiler off-line 2) Allow the boiler to cool slowly 3) Make sure the drum vent is open and there is no vacuum on the boiler 4) Secure all main steam stop valves and feedwater valves to the boiler by locking and tagging out. 5) Make sure the free-blowing drain between the stop valves is open, proving the stop valve nearest the steam header is not leaking 6) Never dump a hot boiler. Sludge will bake on the heating surface 7) Never dump the boiler until it is ready to be flushed 8) After dumping and flushing out the boiler, secure, lock, and tag out bottom blowdown valves. Note: If vent is on a common with another boiler, lock it out too 9) Overhaul the bottom blowdown valves 10) Clean the fire & water side of the boiler 11) Open up feedwater regulators and low water fuel cut offs and clean them. 12) Remove all plugs and cross Ts Note: Never enter the steam and water drum with a conventional drop light. Use a spotlight or low-voltage droplight. Never allow anyone into a boiler until you, personally, have checked to see that all valves are secured, locked and tagged out 13) After checking to make sure the boiler is clean on the fire side and water side, notify the boiler inspector that the boiler is ready. Be prepared to assist the boiler inspector during inspection and point out any problems that are cause for concern. All defects should be reported to the boiler inspector. 14) After inspection is complete, close up the boiler and check the fire side and water side for tools 15) Use new gaskets when closing up the boiler
Describe the operation of a centrifugal pump:
A centrifugal pump uses centrifugal force to develop a pressure rise for moving a liquid. The centrifugal pump imparts kinetic energy to the liquid, which overcomes potential energy. As the liquid passes through the rotating impeller, the kinetic energy overcomes potential energy and gives it centrifugal force. Once a liquid is thrown from the impeller, the casing directs the liquid to its proper destination.
Describe how a deaerating feedwater heater functions: Work on this
A deaerating feedwater heater functions by having steam and water mix together in the shell. There is a vent condenser on top of the shell. Condensate and makeup water enter, passing through tubes before entering the shell below. Work on this
What is the function of the feedwater injector?
A feedwater injector is a secondary means of supplying feedwater to a boiler. It is not an efficient means of feeding water to the boiler. It can only lift water about 20' under ideal conditions. The maximum temperature of the water a feedwater injector can handle is 130-150°F. The feedwater injector works on the principle that kinetic energy is greater than potential energy. Steam passing through a nozzle drops in pressure, expands, and increases in velocity. It entrains the water, and velocity or kinetic energy forces open the check valve on the feedwater line, discharging the water into the boiler.
What causes a feedwater pump to become steam bound and how is this condition corrected?
A feedwater pump becomes steambound when the feedwater temperature gets too hot, or there is not enough net positive suction head on the suction line. Water entering the suction side of the feedwater pump flashes into steam. To correct these conditions, cold water must be added to the feedwater heater to lower its temperature, or water level in the deaerator must be increased, respectively. The operator must then determine the cause of the increase in feedwater temperature, or the drop in level and take necessary corrective action.
What is the function of a grid valve?
A grid valve is used on steam turbines, and extracts steam from one or more stages for plant process. Steam flow is regulated by a positioning control that actuates a servo-motor connected by linkage to a grid valve and governor system that controls the steam turbine speed. The grid valve is used to maintain pressure in the extraction line but will close or throttle back if the steam turbine load requires more steam. If not enough steam is supplied from the extraction line, a steam regulator will open, and steam will be supplied from an auxiliary steam line.
Why must leaks on the bottom blowdown line be promply repaired?
A leaky bottom blowdown line is costly and also very dangerous. Leaky bottom blowdown lines cause a loss of chemically treated boiler water. This requires more makeup water to be added to the boiler, which requires more chemicals. If the leak in the bottom blowdown line is not repaired, the hole can enlarge and result in an overheated boiler if the feedwater pump cannot supply enough water to the boiler. If the line ruptures, serious boiler damage would result. The ASME code requires any repair to the bottom blowdown line to be supervised by a boiler inspector.
What are common causes of a low-water condition?
A low water condition can be caused by: 1) Feedwater pump failure 2) No water in feedwater heater 3) Failure of makeup water valve 4) Malfunction of feedwater regulator 5) Leaky bottom blowdown valves 6) Boiler Pressure overcoming feedpump pressure 7) Boiler tube failure. Tip: Just imagine the water traveling as it travels through the system
Why would a safety valve fail to open at its set pressure?
A safety may fail to open at its set pressure because of corrosion. The operator should lower the boiler pressure below its set pressure and pop the safety by hand. If the safety valve pops, the operator should bring the pressure back up and make sure the safety valve is operating properly. If the safety valve does not pop by hand at its set pressure, a new boiler should be warmed up and cut in online. The malfunctioning boiler should be taken out of service and the faulty safety valve replaced.
How is a steam pressure gauge protected against excessive temperature?
A steam pressure gauge is protected from the temperature of live steam by a siphon installed between the boiler and the steam pressure gauge. The siphon forms a water leg so that live steam cannot enter the Bourdon tube in the steam pressure gauge
What is a steam separator and steam trap? How is each used?
A steam separator is a device used to remove moisture from steam and allows steam to pass through. It is located in the steam and water drum to remove moisture trapped in the steam before the steam enters the main steam line. It is also located before the throttle valve of prime movers. In plants having reciprocating engines it is called a receiver separator. A steam trap is an automatic device that removes air and water from a steam line without loss of steam. It is located on main steam headers, on the end of steam lines, on heat exchangers, and where steam lines make a 90° turn going up. Steam traps are found on all heat exchangers where steam condenses when giving up its heat.
What is the purpose of a steam separator?
A steam separator removes moisture and impurities from the steam before the steam enters a reciprocating steam engine or a steam turbine. This prevents damage to the cylinder head or blades of the steam turbine.
Define running condensing:
A steam turbine or reciprocating steam engine is running condensing when it exhausts into a condenser. The condenser condenses steam forming a vacuum. This reduces the back pressure and water rate to increase efficiency.
What is the purpose of a surface blowdown? Describe its location:
A surface blowdown removes impurities from the surface of the boiler water This reduces surface tension and prevents foaming, priming and carryover. The surface blowdown discharges into the blowdown tank. A surface blowdown is located on the steam and water drum at the NOWL
Describe the function and location of a surface condenser:
A surface condenser is used to create a vacuum on the exhaust end of a steam turbine or reciprocating steam engine. 1) This reduces the backpressure, 2) lowering the water rate, and 3) increases the efficiency of the steam turbine or reciprocating steam engine. The exhaust steam and cooling water of a surface condenser do not mix. Water flows through the tubes that are surrounded by exhaust steam. Surface condensers are classified as single-pass or multipass, depending on whether the cooling water makes one or more passes before leaving the condenser.
What is the function of a telltale hole?
A telltale hole alerts the boiler operator of a broken staybolt. A telltale hole is a 3/16" hole drilled into a boiler staybolt and extends 1" into the boiler water. The stay bolt is used on firetube boilers to hold the inner and outer wrapper sheets of the boiler together to keep the flat surfaces from bulging. If a staybolt shears (breaks), water would come through the telltale hole. The operator must replace the staybolt as soon as possible. Staybolts are subjected to shear stress in addition to severe corrosion, which results in leaks. (wrapper sheets?)
According to ASME code, when must a boiler have two main steam stop valves? What type of valves may be used?
ASME code states that high-pressure boilers in battery that have a manhole opening must have two main steam stop valves and a free-blowing drain between them. These valves should be os&y gate valves that show whether they are open or closed by the position of their spindle. They should always be either wide open or closed. The ASME code further states that an automatic nonreturn valve may be used in place of one stop valve, but must be located as close to the boiler as practical.
What test must be performed on a new or repaired boiler?
All new boilers and boilers that have had extensive repair work on their steam and water side, or have had a low water condition develop should be given a hydrostatic test.
What is the purpose of an air heater? Describe two types:
An air heater increases combustion efficiency by supplying preheated primary and secondary air to the furnace. It also increases the life of the firebrick and furnace refractory. Air heaters are located in the breeching and reclaim heat from gases of combustion that would otherwise be lost to the atmosphere. The two basic types of air heaters are the convection and regenerative air heaters. The convection air heater can be of tubular or plate design. In the tubular convection air heater, gases of combustion pass through the tubes while air being heated flows around the tubes. The air being heated makes several passes over tubes to increase transfer of heat. The plate convection air heater uses plates instead of tubes. They both use the counterflow principle where gases of combustion and air to be heated flow in opposite directions. The regenerative air heater is found in larger boiler installations, and because of the many moving parts, they require more care and maintenance. They consist of a large round casing divided into three zones: the gases of combustion zone, sealing zone, and air zone. A slow-moving rotor consisting of honeycomb plates rotates through the three zones. The air for combustion is forced through the air heater to the furnace by the forced draft fan. Air heaters, because of their location, are continually bombarded with soot and fly ash. They must be kept clean for maximum efficiency. This is accomplished by soot blowers.
What is an automatic non-return valve? Where is it located?
An automatic nonreturn valve cuts a boiler in online automatically, takes a boiler off-line automatically and prevents the system from being drained of steam in case of failure on the steam side of a boiler It can be closed manually but can only open by a difference in pressure across the valve. It is located on the main boiler steam line as close to the boiler as practical, replacing one of the boilers' main steam stop valves.
What is an economizer? Where is it located? What are some problems encountered in its use?
An economizer is a heat exchanger used to heat feedwater before it enters the boiler drum. An economizer reclaims heat from gases of combustion that would otherwise be lost to the atmosphere. Economizers are used mostly on large watertube boilers. They may be a unit type outside the boiler casing or an integral type inside the boiler casing. Economizers are located in the direct path of gases of combustion. Water passes through tubes that are surrounded by gases of combustion. To overcome the restriction to the gases of combustion, induced draft fans are required. Economizer tubes must be kept clean and free of soot. Soot restricts heat transfer and draft if built up too much. The temperature of the gases of combustion must be high enough to prevent sweating of tubes, which causes corrosion. In addition, economizers must be inspected for leaks, which when combined with soot also causes corrosion.
Explain how to replace a tubular gauge glass with the boiler in service. Include all safety precautions:
Assuming the gauge glass is broken, the following procedure is performed, using the proper PPE: 1) Using the chain-operated shut-off valves, secure steam/water to the gauge glass 2) Open the gauge glass blowdown valve 3) Remove the gauge glass nuts and washers 4) Check to make sure no broken glass has fallen into the line going to the water side of the gauge glass 5) Obtain new gauge glass and gauge glass washers. Cut glass to size, if necessary. Must be ¼" shorter than inside length between top and bottom connections 6) Install the new gauge glass, using new washers 7) Tighten the gauge glass nuts hand-tight, then about one-quarter turn with a wrench 8) Crack the steam valve to the gauge glass to warm up the glass 9) When glass is warmed up, open the steam & water valves wide, then close GG blowdown valve. Check for leaks.
What is the procedure followed if popping or blowback pressure on a safety valve must be adjusted?
Before making any changes affecting popping or blowback pressure on a boiler, the boiler inspector must be notified. In order to make any adjustments, the seals must be broken. All safety valves have a nameplate that shows the popping pressure and blowback. Any changes require a new nameplate, showing new popping pressure and blowdown. Obtain one from the safety valve manufacturer and reattach it to the safety valve. New seals must also be installed.
How are the steam valves set on a duplex reciprocating feedwater pump? Really look into this
Before the steam valves can be set, the pump must be placed in mid-position, which is done as follows: 1) Secure valves. Steam admission/exhaust valves and feedwater suction/discharge valves. (2 on the steam side, 2 on the water side) 2) Open drains on the steam and water sides 3) Bar the pump toward the steam side as far as it will go. 4) Scribe a mark on the steam piston rod flush with the packing gland 5) Bar the pump in the opposite direction as far as it will go. 6) Scribe a mark on the steam rod again, flush with the packing gland. 7) With dividers, find the center and mark the steam piston between the two marks. 8) Bar the pump toward the steam side, lining the last mark flush with the packing gland 9) The rocker arm should be perpendicular to the steam piston rod. One side of pump is now in mid-position. 10) Repeat steps 1-9 on other side of the pump The pump is now ready to have the valves set. Note: when barring the pump over, bar it against the crosshead or spool piece, never against the rocker arm. With the pump in mid-position, proceed to set the valves. a. Mark and remove the valve chest cover b. Move the slide valve so that it covers all ports. c. Move the valve in one direction as far as it will go. d. Measure the steam port opening. e. Move the valve in the opposite direction as far as it will go. f. Measure the steam port opening. Note: The steam port openings should be equal, with about ½ of a port open on each side when the D slide is at its end position. This distance is the lost motion. The lost motion allows the pump to make a full stroke, and it also prevents the pump from striking the head. After setting the lost motion nut, move one valve to uncover a port, otherwise the pump cannot start. Once in motion, the duplex reciprocating feedwater pump can never stop with all the ports covered.
What is the prupose of blowing down the water column, gauge glass, and low water fuel cutoff each shift?
Blowing down the water column and gauge glass removes sludge or sediment that could result in an inaccurate indication of the boiler water level. Blowing down the low water cutoff also removes sludge and sediment and verifies that the control is operative. Blowing down the low water cutoff does not replace the evaporation test that should be performed once a month as recommended by the ASME code.
What is caustic embrittlement? How can it be prevented?
Caustic embrittlement is the internal breakdown or cracking of the boiler metal as a result of high alkalinity in the boiler water. The high alkaline material tends to build up along seams, tube ends, and riveted joints. Caustic embrittlement can be prevented by maintaining proper alkalinity of boiler water at all times. This is accomplished by using caustic soda or soda ash and careful control of boiler blowdowns. A continuous blowdown system is most helpful in controlling proper boiler water treatment.
How do economizers and air heaters affect draft?
Economizers and air heaters are located in the direct path of the gases of combustion and restrict their flow. Both forced and induced draft fans are used to overcome this.
Explain how to allow for expansion and contraction of the main steam line between the boiler and steam header:
Expansion bends are used (designing bends in the lines, twists and turns that account for expansion and contraction)
Why is feedwater heated before it enters the steam and water drum?
Feedwater is heated before it enters the steam and water drum for the following reasons: 1) Fuel consumption is reduced. For every 10°F rise in feedwater temperature using exhaust steam or heat from gases of combustion, there is approximately a 1% savings in fuel 2) Thermal shock to the boiler is reduced, which extends the life of the boiler 3) The boiler capacity is increased slightly
What causes foaming and priming in a boiler? How is this condition corrected?
Foaming in a boiler results from high surface tension caused by impurities on the surface of the water or high total dissolved solids. It can lead to priming or carryover of water into the main steam line. Correcting this condition requires the boiler surface to be blown down to remove surface impurities, then a bottom blowdown to reduce total dissolved solids in the boiler water.
Why is fuel oil in boiler water dangerous? How can fuel oil get into a boiler?
Fuel oil in boiler water can settle out on boiler heating surfaces and lead to the formation of blisters, bags, or burned out tubes. Fuel oil also increases surface tension in the steam and water drum, leading to foaming, priming, or carryover. Fuel oil can get into boiler water by leaking heating coils in fuel oil tanks.
What happens when baffles deteriorate in watertube boilers?
If baffles were leaking, the gases of combustion would take the path of least resistance. There would be an increase in the chimney temperature and the boiler would have trouble maintaining its proper steam pressure
Describe the procedure required to increase the working pressure of a boiler?
If increasing the working pressure of the boiler does not exceed its MAWP, and does not require resetting the safety valves, make the necessary adjustments to the operating controls based on the type in the plant. If, however, the increase in pressure exceeds the MAWP of the boiler, nothing can be done to increase the pressure. If the safety valves must be reset, the boiler inspector must be notified. Changing the popping pressure requires a new safety valve nameplate. This must come from the safety valve manufacturer. The safety valve manufacturer should also make the changes and reseal the valves or if necessary, replace the safety valves with new valves of the proper capacity.
What are water temperature considerations from an open feedwater heater?
If the water temperature in an open feedwater heater gets too high, the feedwater pump could become steam bound. This could cause a low water condition to develop in the boiler, which could lead to overheating or burned out tubes. If the water is allowed to get too cold, oxygen would not be vented from the feedwater heater and would enter the boiler, leading to pitting. In addition, cold water can cause thermal shock to the boiler heating surface. Finally, if the oil separator malfunctions, oil could get in the boiler, causing foaming to develop that would lead to priming and carryover. Oil on the heating surfaces of the boiler could also cause overheating of the boiler heating surface
Why are a steam strainer and separator located before a steam turbine?
If there is no steam strainer or separator in line before the steam turbine throttle valve, the steam turbine blades traveling at high velocity would be seriously damaged by loose particles of matter or water in the steam.
What procedure should be followed if a safety valve leaks after testing?
It should be popped by hand to try to clear the seat of any rust or scale particales. If after two or three attempts it still leaks, another boiler should be warmed up and cut in online. The boiler with the leaky safety valve should be taken out of service and cooled slowly. When the pressure is off the boiler, the safety valve should be removed and sent back to the manufacturer for an overhaul or replaced with a new safety valve. If there is only one boiler in the plant, the boiler should be taken out of service as soon as possible. Under no circumstances should the boiler be left unattended until the safety valve has been repaired or replaced.
What should be done if there is a possibility that the main boiler steam pressure gauge is not accurate?
Obtain a steam pressure gauge that is known to be accurate. Install it on the inspectors' test connection that is alongside the boiler steam pressure gauge and compare readings. If the boiler steam pressure gauge is not accurate, it must be removed and recalibrated using a deadweight pressure-gauge tester if one is available. If one is not available, the boiler steam pressure gauge must be sent out for repairs or replaced with a new one. As soon as a steam pressure gauge has been installed, remove and carefully store the one that was used for testing so it will always be on hand. Note: Do not lose the water in the siphon while working on the boiler steam pressure gauge or the new steam pressure gauge may be damaged by live steam.
Describe the operation of commonly used feedwater heaters:
Open feedwater heater: It is located on the suction side of the feedwater pump but at a higher elevation. Exhaust steam and condensate returns come into intimate contact with each other and oxygen, and other noncondensable gases are driven off and vented to atmosphere. The open feedwater heater is equipped with an internal overflow to prevent flooding the system and an oil separator to remove oil present in the returns. The feedwater pump takes its suction from the feedwater heater and delivers water to the boiler. Economizer: It is located between the feedwater pump and boiler in the direct path of the gases of combustion. Water passes through the tubes that pick up heat that would otherwise be lost to atmosphere. Economizers must be kept free of soot deposits or fly ash, which would act as insulation and retard heat transfer or even cause restriction to draft flow. This is accomplished by using soot blowers. Economizers are used mostly in larger boilers that have a fairly constant load to prevent sweating, which would lead to corrosion. Feedwater must be heated to drive off oxygen and other noncondensables, reduce thermal shock to the boiler, increase boiler life, reduce fuel consumption, and increase plant thermal efficiency if using exhaust steam or gases of combustion.
Describe 3 ways fuel oil is atomized:
Pressure atomizing burners, (mechanical) require fuel oil at the proper temperature and pressure to atomize the fuel oil. They are either plug-and-tip or sprayer plate atomizing burners. In the plug-and-tip burner, fuel oil enters the burner tube and is forced through the plug channel where atomization takes place. The fuel oil leaves the burner tip rotating at a high velocity. In the sprayer plate burner, fuel oil enters the burner tube where it is forced through the sprayer plate channel where atomization takes place. The atomized fuel oil leaves the burner tip spinning at a high velocity. Air or steam atomizing burners use either air or steam to atomize fuel oil. Air atomizing burners require an air compressor to atomize the fuel oil. They are inside-mixing burners and are used primarily in small installations. Steam atomizing burners are either outside-mixing or inside-mixing. In the outside-mixing burner, fuel oil and steam mix outside the burner. In the inside-mixing burner, fuel oil and steam mix inside the burner. Steam is used in both cases to atomize the fuel oil, which is supplied at pressures and temperatures lower than that in the pressure atomizing burners. The fuel oil pressure is approximately 50 psi, and the steam must be 20 psi higher than the fuel oil. The steam and fuel oil do not mix until the steam is directed across the path of the fuel oil, flowing outside or inside the burner nozzle, depending on the type used. The rotary cup atomizing burner can burn a wide range of fuel oil at low pressures and temperatures. It is ideal for automatic operation. Atomization is accomplished by a fuel oil discharged from a spinning cup and high-velocity air supplied by the primary air fan.
Why must a safety valve discharge outlet not be reduced or restricted in any way?
Restriction or reduction of discharge piping would cause back pressure, preventing the safety valve from relieving the required pounds of steam it is rated for.
How can it be determined if the safety valves on a boiler have enough relieving capacity?
Safety valves are rated in number of pounds of steam per hour they are capable of relieving at a given pressure. Three equations can be used: 1) The first method is determined by the fuel burned per hour. W = (C x H x 0.75) / h Where W = steam lbs/hr c = quantity of fuel burned per hour H = heating value per unit of fuel h = constant, the latent heat of steam 2) The second method is by determined by the square feet of heating surface in the boiler: For firetube boilers: W = (8 x HSb) + (14 x HSww) For watertube boilers: W = (8 x HSb) + (16 x HSww) Where HSb = boiler heating surface ft² HSww = Waterwall heating surface in furnace ft² 3) The third method is obtained by performing an accumulation test on the boiler
How is scale in a boiler caused and prevented?
Scale in a boiler is caused by improper feedwater treatement. All raw water contains some amount of scale-forming salts. If the boiler water is tested daily and proper chemicals (caustic soda and phosphates) are added in correct amounts, the scale forming salts change to a nonadhering sludge. This nonadhering sludge is removed by the bottom blowdown valves. By proper testing, chemical control, surface blowdown, and bottom blowdown, scale should not form on any boiler heating surface.
What steps must be taken if the safety valve does not pop with excessive boiler pressure?
Secure all burners to the boiler and allow pressure in the boiler to drop below the safety valve popping pressure, then pop all safety valves manually. Relight the boiler and bring the pressure up to safety valve popping pressure. If the safety valves pop, proceed with normal operation. When the boiler is down for annual inspection, have the safety valves removed and sent to the manufacturer for a complete overhaul. When the safety valves are put back on the boiler and before the boiler is put back in service, establish a safety valve testing procedure. The safety valves will stick to their seats because of corrosion buildup if there is a lack of testing.
Why must a steam turbine rotor rotate during cooldown?
Small steam turbines are allowed to cool while they are idle. Large steam turbines are equipped with a turning gear to keep the rotor moving slowly to prevent warping during cooling
Why is Steam extracted from a steam turbine?
Steam is extracted from a steam turbine for plant process. This is reclaiming latent heat that would otherwise be lost in the condenser to the cooling water, which also increases steam turbine and plant efficiency.
What is superheated steam?
Superheated steam is steam at a higher temperature than its corresponding pressure. When more heat is added to saturated steam (with constant pressure), it becomes superheated steam.
Why does the auxiliary lubricating pump operate after the steam turbine has been secured?
The auxiliary lubricating oil pump is kept running to keep the bearings cool and help the rotor cool slowly
What is the function of a thrust bearing on a steam turbine?
The axial clearance between the moving and stationary blades of the steam turbine and steam nozzles and moving blades is very critical. The thrust bearing keeps the rotor in its proper fixed position to prevent damage to the steam turbine.
List all the parts of a centrifugal pump:
The basic parts of a centrifugal pump and their function are: 1) Casing: Outer part of the pump that directs water flow from the pump 2) Impeller: Rotating element that imparts centrifugal force to the liquid 3) Impeller shaft: Supports the impeller and transmits rotational force to the impeller from the drive 4) Shaft bearings: Support the impeller and shaft in a fixed axial and radial position 5) Packing glands/mechanical seals: Prevent leakage of liquid between the casing and the shaft
Why is an approved blowdown tank required on a steam boiler?
The blowdown tank must be built according to the ASME Unfired Pressure Vessel Code. When a steam boiler is blown down, the blowdown tank is subjected to the steam boiler pressure and temperature even though it is vented to atmosphere. In addition, the blowdown tank is also subjected to thermal shock
What is the function of the bottom blowdown line? Where and how is it connected to a boiler?
The bottom blowdown line is used to control high water, remove sludge and sediment, control chemical concentration, and dump the boiler for cleaning and inspection The bottom blowdown lines are connected to the lowest part of the water side of a firetube boiler and the mud drum of a watertube boiler. The lines must run full size with no reducers or bushings. If they are exposed to direct furnace heat, they must be protected by a refractory pier or wrapped with protective insulation. Piping may not be exposed to freezing or corrosive conditions. The opening in the boiler setting should be arranged to provide for free expansion and contraction, and blowdown lines must be exposed for easy inspection.
What procedure must be followed if the water level in the gauge glass is not visible, and the burner is still operating:
The burner must be secured immediately, and absolutely no feedwater can be admitted to the boiler. The boiler must be taken off-line and allowed to cool slowly, then it must be inspected for damage that may have resulted from overheating. Before the boiler is put back into service, the cause of the low-water condition must be determined and corrected.
What are the requirements of the discharge line of a safety valve?
The discharge line of a safety valve must be free to expand and contract and not put strain on the body of a safety valve to ensure its proper operation and prevent distortion to the valve. No valves can be installed on the discharge line, as to potentially obstruct the free-flow of steam discharge from the valve, or create a back-pressure Safety valve discharge lines must steer clear of cat-walks, or anywhere someone might get scolded by the discharge of steam
Describe the condition that develops in economizers if the feedwater temperature is too low:
The economizer is located in the direct path of gases of combustion. Its purpose is to heat the feedwater before it enters the steam and water drum. If the feedwater temperature is too low, it will create sweating of the economizer tubes. This causes corrosion of the economizer, and soot + leaking water will form sulfuric acid which will further corrode the economizer metal
What would cause a reciprocating feedwater pump to not provide enough water to a boiler? look into the answer
The following could cause a reciprocating feedwater pump to not provide enough water to a boiler: 1) No water in the open feedwater heater 2) Pump suction or discharge valves closed 3) Suction or pump discharge valves worn, leaking, or not seating properly 4) Worn rings or liner in the water cylinder 5) Steam admission valves worn or not set properly 6) Steam piston rings worn or broken 7) Steam cylinder worn 8) Pump has become steam bound look into each of these components
Describe the procedure to follow when performing a hydrostatic test:
The following procedure is followed to perform a hydrostatic test: 1) Secure the main steam stop valves 2) Open the free-blowing drain between the main steam stop valves 3) Remove high and low water level whistle alarm and plug the opening. 4) Remove and blank-flange or gag the safety valve 5) Fill the boiler with ambient 70°F water until it comes out of the drum vent. 6) Close the drum vent 7) Use a hand pump to bring the pressure up to 1½ x the safety valve setting 8) Look for signs of pressure dropping 9) Lower the pressure to the safety valve setting 10) Carefully examine the boiler for leaks or bulging of metal 11) After testing, reduce the pressure to 0 psi 12) Replace the high-low water level whistle alarm and replace the safety valve or remove gags 13) Check the fire side for any tools, lights, ladders, etc.
How does a governor control the speed of a steam turbine?
The governor used on steam turbines driving auxiliaries is a mechanical governor. The mechanical governor consists of a speed-sensing element that through linkage controls the speed of the steam turbine shaft. The speed-sensing element consists of weights mounted on the steam turbine shaft. The centrifugal force tends to move the weights out as the speed of the turbine increases. Through linkage, this tends to close down the steam to the steam turbine. As the steam turbine speed decreases, the weights move in and the linkage opens the steam valve to the steam turbine. There is a separate overspeed trip. It consists of a pin mounted in the steam turbine shaft and is held by spring tension. If the steam turbine exceeds its safe operating speed by 10%, centrifugal force causes the pin to pop out and hit an emergency trip that secures the steam to the turbine.
What is the heating surface of a boiler?
The heating surface of the boiler is any part of the boiler that has water on one side and heat from gases of combustion on the other
Why is high vacuum desirable in a condenser for a condensing steam turbine?
The higher the vacuum in the condenser is, the lower the back pressure will be on the steam turbine. This allows the steam to expand further, extracting more heat from the steam. It also reduces the steam turbine water rate to increase its efficiency
What is the function of an overspeed trip on a steam turbine? When is it tested and how often?
The overspeed trip on a steam turbine shuts the steam turbine down to prevent it from destroying itself from excessive speed. It secures steam to the steam turbine when it exceeds its design speed by 10%. The over speed trip should be tested when warming up a steam turbine before putting it in service, and should also be tripped when taking a steam turbine out of service.
Describe the operation of a reciprocating feedwater pump?
The reciprocating feedwater pump operates on the principle that the steam piston must be 2 to 2½ times larger in area than the water piston. This is why a reciprocating feedwater pump using steam at 100 psi can develop 250 psi of water pressure at the pump discharge When the steam piston moves through each stroke, a specific amount of water is discharged
Should the rotor of a steam turbine be moving or stationary during the warm-up period?
The rotor and blades of a steam turbine must be slowly moving as soon as steam is admitted to the steam turbine to prevent the rotor from bowing or warping. The rotor is only supported by two bearings. One is at the throttle and one is at the exhaust end. By having the rotor in motion, it is heated up evenly.
Why does a boiler safety valve pop open rather than open slowly?
The safety valve prevents the boiler from exceeding its MAWP. It must open fully and remain open until there is a definite drop in pressure (blowdown). It must then close tightly without chattering The safety valve is designed to pop open by means of the huddling chamber, which provides steam pressure with a larger area to work on. This increases the total upward force, which overcomes the valve spring force, which keeps the valve in a closed position
Which safety valves should be set to pop first, the safety valves on the boiler or the safety valves on the superheater?
The safety valves on the superheater must be set to pop before the safety valves on the boiler. This ensures steam flow through the superheater tubes to prevent them from overheating
Describe the procedure followed when taking over a shift:
The shift operator should report to work at least 30 minutes before the shift begins. This should give the shift operator enough time to check all the equipment for proper operating conditions before relieving the operator on duty. The procedure for taking over a shift is as follows: 1) Check the water level in all boilers that are on-line 2) Blow down the water column, gauge glass, and LWCO on all boilers online 3) Check the boiler steam pressure 4) Check the condition of the fires 5) Check all running auxiliaries for proper temperature, pressure, and lubrication 6) Ask the operator being relieved if any difficulties occured during that shift 7) Check the boiler log for any orders left by the chief engineer 8) If everything is in order, relieve the operator and take over the shift. Note: Once the boiler operator takes over a shift, that boiler operator is held responsible for any problems that occur. If a boiler drops a tube or a pump burns out a bearing 5 minutes into the shift, the boiler operator on duty will be held responsible.
What maintains the speed of an auxiliary steam turbine operating at 3600 RPM?
The speed of auxiliary turbines are maintained by a mechanical governor. The Speed of a generating turbine is maintained by a hydraulic governor. Both turbines are equipped with overspeed trips.
What are the advantages of a superheater used with a steam turbine?
The superheater increases the temperature of the steam but not the pressure. By increasing the heat of the steam before it enters the steam turbine, the superheater cuts down condensation losses and makes it possible to extract more heat from the steam to increase the thermal efficiency of the steam turbine.
How does boiler drum pressure compare to the superheater outlet pressure during normal operation of a boiler equipped with a superheater?
The superheater outlet pressure is always slightly lower (approximately 5 lb) than the boiler drum pressure. Unless there is a difference in pressure, there could be no steam flow. In order for any flid to flow, there must be a pressure differential and the flow is always from the high-pressure area to the low-pressure area.
List three commonly used fuels and their Btu content:
The three most commonly used fuels in bolers are coal, fuel oil, and natural gas. The follow Btu contents are approximate values and vary depending on where the fuels come from: 1) Bituminous coal: 12,000 Btu/lb Anthracite coal: 15,000 Btu/lb 2) No. 6 fuel oil: 150,000 Btu/gal No.4 Fuel oil: 146,000 Btu/gal 3) Natural gas: 100,000 Btu/therm
Describe the two basic types of superheaters. Where are they located on a boiler?
The two basic types of superheaters are radiant and convection The radiant superheater is located among the generating tubes and receives most of its heat by radiation. The convection superheater, located in the second to last pass of the gases of combustion leaving the boiler, receives most of its heat by convection. The radiant superheater temperature decreases with an increase in boiler load, while the convection superheater increases with an increase in boiler load. To maintain a fairly constant superheater temperature, boilers have been designed to have convection superheaters in series with a radiant superheater.
Describe the wet method of boiler lay-up:
The wet method of boiler lay-up is as follows: 1) Thoroughly clean the fire side and water side of the boiler to prevent corrosion 2) Inspect the fire side and water side for tools or rags 3) Close the steam and water side using new gaskets 4) Fill the boiler using chemically treated water at about 100°F until water comes out of drum vent. Close the vent 5) Maintain a pressure in the boiler slightly above atmospheric. (nitrogen is often used)
Define boiler efficiency:
Thermal efficiency and boiler efficiency are synonymous. It is the ratio of heat output to heat input, or the amount of fuel needed to produce a certain amount of heat. It is expressed mathematically as follows: TE = {Ws [Hs - (Tfw - 32)]} / (Wf - C) Where TE = Thermal Efficiency Ws = Steam lbs/hr Hs = Enthalpy of steam Tfw = Feedwater temperature 32 = Base temperature from which total heat is calculated Wf = lbs/gal of fuel per hour C = Btu content per unit of fuel
Describe two types of feedwater regulators. State where each is used:
Thermoexpansion feedwater regulators are found mostly on large boilers in which the feedwater pumps run continuously. They consist of an inclined tube called a thermostat that is located at the NOWL. The top of the thermostat is connected to the steam side of the boiler, and the bottom to the water side. The inclined tube then registers the amount of water in the boiler. The top of the inclined tube is free to expand and contract and is connected by linkage to a valve in the feedwater line. The bottom of the inclined tube is fixed and cannot move. As the water level drops in the boiler, it also drops in the inclined tube, and steam takes its place. This causes the tube to expand slightly and the linkage moves the feedwater valve toward an open position. When the water level rises, it also rises in the inclined tube, replacing the steam, and causes the tube to contract, and the linkage causes the valve in the feedwater line to close up. By using an inclined tube rather than a vertical tube, there is a larger surface of steam and water, making the regulator more sensitive. The inclined tube feedwater regulator is mechanical and works on the principle of expansion and contraction. The Float type feedwater regulators are used on package firetube and watertube boilers where the feedwater pumps run intermittently. They are also located at the NOWL of the boiler. They consist of a float in a float chamber, which connects to mercury tubes or micro switches. There are two mercury tubes or micro switches because the regulator is often a combination feedwater regulator and low water cut out. The top of the float chamber is connected to the uppermost part of the steam space and the bottom of the chamber is connected to the water side of the boiler, well below the NOWL. The float chamber will have the same water level as the boiler. As the water level drops in the boiler, the float in the chamber starts to move down and the linkage causes the mercury tube to tilt. This completes an electrical circuit, and the feedwater pump starts up and pumps water into the boiler. With a rise in water level, the float through the same linkage moves up, causing electrical circuit to break, shutting down the feedwater pump. If for some reason the feedwater pump fails to pump water to the boiler, the float drops lower and the second mercury tube tilts and breaks the electrical circuit to the burner, shutting off the burner on a low water condition. The float chamber is also fitted with a blowdown valve to keep the chamber free of sludge and sediment and also to test the control for operation.
How is a low water fuel cutoff tested?
To test a low water fuel cutoff, it should be blown down once a shift. It should also be tested using an evaporation test once a month. When it is blown down, the burner should shut down. The evaporation test is done by securing all feedwater pumps to that boiler and allowing the water level to drop slowly. The boiler operator must watch the water level in the gauge glass to make sure the burner shuts off properly.
Why is a steam valve under pressure never opened quickly?
When steam flows from a high-pressure area to a low-pressure area, it drops in pressure and increases in velocity. 1) This leads to water hammer and could lead to a pipe rupture. 2) If the steam valve is connected to the boiler, it can lift water from the boiler into the steam line. 3) It could cause a reciprocating pump or reciprocating steam engine to break its cylinder head. 4) In a steam turbine, the water impinging on the steam turbine blades would cause severe erosion of the blades.
