Low Pressure Boilers

AMERICAN TECHNICAL PUBLISHERS ORLAND PARK, ILLINOIS

Frederick M. Steingress Daryl R. Walker

SECTION 8.1 — Taking Over a Shift • List the tasks and procedures required when taking over a shift.

• Describe the blowdown procedures and tests typically performed each shift.

SECTION 8.2 — Startup and Shutdown • Describe a typical procedure for first-time startup of a boiler.

• Describe a typical procedure for routine startup of a boiler.

• Describe a typical procedure for routine shutdown of a boiler.

SECTION 8.3 — Maintenance • Describe common boiler maintenance rules.

• Describe common maintenance tasks.

SECTION 8.4 — Handling Boiler Conditions • List common boiler conditions that can occur.

• Describe appropriate responses to common boiler conditions.

Arrow Symbols AIR

GAS

WATER

STEAM

FUEL OIL

CONDENSATE

200

AIR TO GASES OF ATMOSPHERE COMBUSTION

A boiler operator must perform certain tasks and procedures to ensure the safe and efficient operation of the boiler. This involves testing and performing routine maintenance on boiler accessories as required. The ASME Code contains suggested procedures for testing boiler accessories. Boiler operation data, testing, and maintenance procedures must be recorded in a boiler room log.

SECTION 8.1 — TAKING OVER A SHIFT Boiler room equipment varies depending on the type and size of the plant.

The boiler operator is responsible for the safe operation of the boiler and supporting equipment. Established plant procedures are developed based on plant operation experience and by following manufacturer recommendations.

When taking over a shift, these plant procedures help ensure that the boiler operates safely and efficiently.

Preliminary safety checks are performed by the boiler operator to identify possible problems. The first task for a boiler operator when entering a boiler room is to check and log the water level of all the boilers on-line. The operator should then check and log the steam pressures, the condition of the flames, and the accessories. An accessory is a piece of equipment that is not directly attached to a boiler and is required for the boiler’s operation. All running accessories such as fuel oil pumps, feedwater pumps, and draft fans must be checked for proper operating temperature, pressure, and lubrication and the results should be logged.

After performing these initial safety checks, the boiler operator should have a shift log with a list of routine duties. The shift log helps to ensure quality and consistency when performing various tasks. It is developed in conjunction with the boiler log to ensure that critical duties, such as safety valve testing, are performed.

201

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When taking over a shift, any concerns are communicated by the boiler operator ending the shift to the boiler operator starting the next. This alerts the boiler operator of any special procedures that may be required during the shift. See Figure 8-1. Procedures commonly performed and logged during a shift include water column and gauge glass blowdown, bottom blowdown, low water fuel cutoff testing, and flame scanner testing.

TAKING OVER A SHIFT

Figure 8-1. Boiler operation information is communicated to the boiler operator starting a shift to specify any special procedures required.

Water Column and Gauge Glass Blowdown The water column and gauge glass are blown down to ensure an accurate boiler water level reading and to remove any sediment that may have accumulated in the water column. A boiler operator must observe the action of the water in the gauge glass. After blowing down the water column and gauge glass, the low water fuel cutoff should be blown down also. The boiler must be firing when the low water fuel cutoff is blown down to check for proper operation.

When blowing down the water column and gauge glass, the operator should carefully monitor the action of the water in the glass. See Figure 8-2. Water should enter the gauge glass quickly when the gauge glass blowdown valve is closed.

This indicates that the lines are free of sludge, sediment, or scale buildup. If the water returns sluggishly to its normal level, there may be an obstruction partially blocking the water flow.

If the apparent obstruction cannot be removed by blowing down, then it must be removed by other means. First, the boiler should be shut down and allowed to

Chapter 8 — Boiler Operation Procedures 203

cool. If the gauge glass is integrated with the low water fuel cutoff, the float (or probe) chamber should be opened and inspected. Mud, scale, or sediment deposits should be removed completely. The linkage should also be examined to ensure proper working order. All connecting piping should be inspected for any obstructions.

GAUGE GLASS BLOWDOWN

Bottom Blowdown Bottom blowdown is performed to remove sludge and sediment, to control high water, and to control the chemical concentration in the boiler.

Specific blowdown frequency varies depending on water characteristics and plant operations. In general, steam boilers should be blown down at least once every 24 hours. In addition, bottom blowdown should be performed just before cutting a boiler into service to help start cir- Figure 8-2. When blowing down the gauge culation in the boiler before picking glass, water should enter the gauge glass quickly when the gauge glass blowdown valve up the load. is closed.

Bottom blowdown is best performed during light loads to allow the maximum amount of sludge and sediment to settle to the bottom of the boiler drum. The water level should be at the normal operating water level (NOWL). Pressure should be on the boiler at all times during bottom blowdown. Bottom blowdown valves may involve either a slow-opening valve and a quick-opening valve or two slow-opening valves. A slow-opening valve is fully opened or closed by rotating the handwheel. A quick-opening valve is opened or closed by moving the valve lever. The quick-opening valve should be located closer to the boiler.

When a quick-opening valve and a slow-opening valve are used, the quickopening valve is opened first. See Figure 8-3. The slow-opening valve is opened to the full-open position. The flow through the valve as it opens and closes causes wear and tear. However, the valve is easy to replace because it can be isolated from the boiler. Precautions required of a boiler operator when blowing down a boiler include the following:

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• The boiler operator must always check the boiler water level before starting blowdown.

• The boiler operator must never walk away from an open blowdown valve. The operator should hold the valve handle until the valve closes.

• The bottom blowdown valves should be opened slowly to full-open position and closed slowly. If the bottom blowdown line has a quick-opening valve, it should be opened first and closed last.

• The water level in the gauge glass should never drop out of sight during bottom blowdown.

BOTTOM BLOWDOWN PROCEDURE 1

2

PERFORM BOTTOM BLOWDOWN UNDER LIGHT LOAD

4

MONITOR BOILER WATER LEVEL (OTHER BOILER OPERATOR PRESENT IF NECESSARY)

3

OPEN QUICKOPENING VALVE

5

OPEN SLOWOPENING VALVE

6

CLOSE SLOWOPENING VALVE

CLOSE QUICKOPENING VALVE

Figure 8-3. During bottom blowdown, the boiler should be under light load, and the water level should be at the NOWL.

Chapter 8 — Boiler Operation Procedures 205

Low Water Fuel Cutoff Testing BLOWING DOWN LOW A low water fuel cutoff is tested by BLOWDOWN VALVE WATER FUEL CUTOFFS either blowing down the cutoff or with an evaporation test. If the test involves blowing down the cutoff, it is blown down with the burner firing.

The blowdown valve is opened on the low water fuel cutoff. See Figure 8-4.

Water and steam leaving the chamber help to clean out any sludge and allow the float to fall. This shuts off the fuel valve as if there were a low water condition in the boiler. The low water fuel cutoff should be blown down every shift or daily, depending on plant operations.

An evaporation test is used to test Figure 8-4. When using blowdown to test a the low water fuel cutoff by inten- low water fuel cutoff, the blowdown valve is tionally causing a low water condi- opened to empty the cutoff chamber while the burner is firing. tion to occur. This is performed by securing the feedwater pump so no water is supplied to an operating boiler. The water level will gradually drop as steam is produced. Note: If the boiler has an automatic city water makeup feeder, it must also be secured. The evaporation test is a more reliable test than blowing down the cutoff. Under normal conditions, the water level in a boiler drops slowly. In an evaporation test, the water level also drops slowly.

WARNING: An evaporation test should be performed only under close supervision by authorized personnel with the boiler operating at low fire conditions.

The boiler operator must be in attendance as long as the feedwater supply to the boiler is secured. The low water fuel cutoff should activate before the water disappears completely from the gauge glass. The water must not be allowed to drop out of sight in the gauge glass.

A float that sticks during normal operation is more likely to be noticed with an evaporation test. During blowdown of a low water fuel cutoff, the force from the water and steam may cause the float to drop during the test even though the valve may stick during normal conditions. The burner should shut OFF when water is still visible in the gauge glass. If the low water fuel cutoff fails to shut the burner OFF, a boiler operator must closely monitor the boiler and be in constant attendance as long as it is firing until it can be taken off-line and checked.

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After blowing down the low water fuel cutoff, the burner should start with an automatic reset, or it must be started with a manual reset. This depends on the type of low water fuel cutoff being tested.

Flame Scanner Testing A flame scanner is tested with the burner firing to simulate a flame failure. See Figure 8-5. It is important to test a flame scanner because a flame failure can result in a furnace explosion from the ignition of accumulated fuel in the burner. To test a flame scanner, the scanner is loosened and removed from the burner assembly, and the scanner sensor is covered. After a short delay, the main fuel valve must close, and the flame failure alarm must sound. This indicates a successful test. The flame scanner is then cleaned as required and replaced. Finally, the programmer is reset by pressing the reset button, and the burner is monitored through a complete firing cycle.

FLAME SCANNER TESTING 1

2

LOOSEN FLAME SCANNER

4

BURNER STATUS DISPLAYED

FLAME FAILURE SIMULATED; BURNER SHUTS OFF

3

REMOVE FROM BURNER ASSEMBLY

5

COVER FLAME SCANNER SENSOR

6

REPLACE FLAME SCANNER

RESET BUTTON

RESET PROGRAMMER

Figure 8-5. When testing a flame scanner, the flame scanner sensor is covered to simulate a flame failure.

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SECTION 8.1 — CHECKPOINT

1. What is the first task a boiler operator must perform when taking over a shift?

2. What is the purpose of a shift log?

3. What is the purpose of bottom blowdown?

4. What is an evaporation test?

5. Why is it important to test a flame scanner?

SECTION 8.2 — STARTUP AND SHUTDOWN Boiler startup and shutdown operations can be dangerous. Proper procedures must be followed carefully. A first-time boiler startup occurs whenever a new boiler is installed or after major repairs have been made. Other common procedures include routine boiler startup and routine boiler shutdown.

First-Time Boiler Startup First-time boiler startup procedures should be followed as specified by the boiler manufacturer. Operators must check the condition of all accessory equipment and interlocks used to start and operate the boiler, such as pressure controls, the fuel train, and feedwater supply pumps. Routine first-time boiler startup procedures typically include the following: 1. When the boiler is closed, check and close the blowdown valves, the water column, and the gauge glass drains.

2. Open the boiler vent valves and gauge glass valves.

3. Fill the boiler with water at 70°F or above to a minimum level of approximately 2″ above the bottom of the gauge glass or enough to close the low water fuel cutoff contact in the combustion control circuit. See Figure 8-6.

If the water is too cold, high humidity can cause sweating that makes it difficult to see leaks. Fill the boiler slowly and vent it properly to prevent any pressure buildup from flashing warm water.

4. Blow down the water column(s) and the gauge glass(es). Ensure that the water returns to the proper level promptly.

5. Fuel piping, whether gas or fuel oil, should be pretested for leaks. The fuel oil pump sets should be started so oil can circulate and pressures can be adjusted to burner requirements. If gas is used, check the gas pressure and adjust the burner gas pressure regulator for proper pressure. If air has not been bled from the gas line, it should be bled by authorized utility company representatives.

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WARNING: The gas utility company should be contacted to supervise the bleeding and cleaning of gas lines.

6. When starting a boiler in inWATER LEVEL READING stallations where the fuel lines (gas and fuel oil) are new, precautions should be taken to ensure that piping is clean.

Foreign matter such as dirt, sand, gravel, thread cuttings, steel chips, welding beads, welding rods, rags, and wood chips can contaminate shutoff valve seats, control valves, pressure regulators, and burner nozzles. Foreign matter in the wrong place can cause serious problems. Strainers should be installed in fuel lines to remove Figure 8-6. Before starting a boiler for the first foreign matter. These strainers time, the boiler should have a minimum water should be checked frequently, level of approximately 2″ above the bottom of especially during the first few the gauge glass. days of operation. Strainers can clog quickly and impede the proper flow of fuel oil to the burner.

7. Start the burner in low fire according to procedures specified by the manufacturer. See Figure 8-7.

8. The boiler should be warmed up and the boiler metal temperature allowed to equalize. As the boiler begins to warm, it should be closely monitored for leaks and signs of expansion.

9. When all the air has been removed from the boiler, close the boiler vent. See Figure 8-8. Open the drains in the steam headers to warm as required.

10. Test the safety valve(s), check all combustion controls, and blow down the boiler.

Fuel oil heating systems require routine cleaning and maintenance before seasonal startup. During routine maintenance, a unit is thoroughly cleaned of any oil residue, the ignition electrodes are checked and replaced as needed, the fuel oil strainer is cleaned, and the unit is started and tested for proper operation and combustion.

Chapter 8 — Boiler Operation Procedures 209

Hydrostatic Tests STARTING BURNERS IN LOW FIRE A hydrostatic test is a water pressure test used on a boiler to check for leaks or damage due to a low water condition or after any extensive repairs.

These tests must be performed by authorized personnel. A hydrostatic test can be specifically requested by the boiler inspector or required to comply with state, local, or insurance company requirements to ensure the capability of the boiler to carry its rated pressure. To perform a hydrostatic test, the boiler is completely filled with water using the following procedure: 1. Remove and plug the whistle valve if the water column has one.

2. Close the main steam stop valve.

3. Remove the safety valve(s).

Then install blank flanges or Figure 8-7. During first-time boiler startup, the gag the safety valve(s). A gag burner is started in low fire according to proceis a clamp that prevents a safety dures specified by the manufacturer. valve from popping open without damaging the valve.

4. Open the boiler vent and fill BOILER VENTS the boiler. Close the boiler vent after water comes out.

5. Raise the pressure to 1Z\x times the MAWP. For low pressure boilers, the pressure is brought to 60 psi or 1Z\x times the design pressure, whichever is greater.

6. When the test is complete, replace the whistle valve.

7. Replace the safety valve(s) or remove the gag(s).

Water used for a hydrostatic test should be at ambient temperature but not less than 70°F. Water that is too Figure 8-8. A boiler vent is closed when prescold can cause the boiler to sweat, sure in the boiler reaches 10 psi to 15 psi.

210  LOW PRESSURE BOILERS

making leaks hard to find. Water that is too hot can evaporate or flash into steam when it leaks from the boiler.

Routine Boiler Startup When performing routine boiler startup procedures, all equipment should be prechecked for proper operation. The boiler operator must be sure to address any concerns listed in the boiler room log. If the system is cold, all condensate drains must be open to drain condensate to prevent water hammer. Routine boiler startup procedures typically include the following: 1. Check for a proper water level in the boiler (slightly below NOWL).

2. Check the main steam stop valve to ensure that it is closed. (In a single boiler system, the main steam stop valve should be open to allow the entire system to warm up at once.)

3. Open the boiler vent or the top try cock to vent the air from the boiler during warm-up.

4. Start the burner and keep it in low fire to allow the boiler to warm slowly.

5. Monitor the water level as the boiler is warmed. As the water warms, the level will rise slowly from thermal expansion.

6. When the steam pressure gauge records pressure on the boiler, blow down the gauge glass, water column, and low water fuel cutoff. Close the boiler vent when all the air has been removed from the boiler.

7. Test the flame scanner.

8. In a battery of boilers, when the boiler being started up is a few pounds below the header pressure, slowly open the main steam stop valve and allow the pressure to equalize. The main steam stop valve is opened slowly until it is wide open. See Figure 8-9.

9. Cut the boiler in on the line. The boiler should always be slightly below the header pressure when cutting in on the line. This prevents carryover because steam flows into the boiler for a short time.

Note: When opening a valve, it is good practice to open the valve completely, and then close the valve one to one-and-a-half turns. This helps ensure that the valve will not bind in the open position as the valve heats and expands. In many boiler plants, there is a bypass valve around the main steam stop valve to allow the steam lines to warm slowly and a drain valve between the main steam stop valves to drain condensate from the lines.

Routine Boiler Shutdown When shutting down a boiler, ensure that the remaining boilers on-line can carry the load before proceeding. Routine boiler shutdown procedures typically include the following:

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1. Secure the fire (shut the burner MAIN STEAM STOP VALVES OFF) in the boiler that is coming off-line.

2. Reduce the amount of forced draft to prevent things from cooling too quickly. If a brick refractory is used, fast cooling can cause damage from flaking of the surface of the brickwork.

Frequent fast cooling of the boiler tubes can cause the tubes to crack.

3. Monitor the water level in the boiler.

4. When the boiler has stopped steaming, close the main steam stop valve.

5. When the steam gauge shows approximately 1 lb to 2 lb of pressure, open the boiler vent to prevent a vacuum from Figure 8-9. The main steam stop valve is forming. opened slowly to allow the pressure to equalize Note: Do not close the main when a boiler is a few pounds below the header steam stop valve immediately be- pressure. cause the safety valve may pop open if pressure in the boiler increases. The boiler furnace will be hot, and the heat from the heating surfaces will continue to keep the boiler steaming for a short time.

SECTION 8.2 — CHECKPOINT

1. Why is it important to control the temperature of the water used to fill a boiler during a first-time startup?

2. Why is it important to install strainers in the fuel lines during a first-time boiler startup?

3. When should the main steam stop valve be opened during a routine boiler startup?

4. Why is it good practice to open a valve completely and then partially close it again during a routine boiler startup?

5. Why is it important to slowly cool down a boiler during a routine boiler shutdown?

6. When should the boiler vent be opened during a routine boiler shutdown?

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SECTION 8.3 — MAINTENANCE Proper maintenance of a boiler and associated boiler room equipment is critical for safe and efficient operation. The boiler operator is responsible for performing boiler maintenance tasks using established procedures. Established procedures ensure the overall quality of performed maintenance and reduce possible plant downtime. Specific maintenance tasks can be organized into the categories of daily, weekly, monthly, semiannual, and annual maintenance. Basic boiler maintenance is performed using standard rules: • Know the equipment. Information is available from authorized manufacturer representatives and from the manuals and drawings supplied with the equipment. This information should be filed for easy access by authorized personnel.

• Maintain equipment records. Equipment information, including manufacturer, model, serial number, and date of installation, should be listed on a form or in a computer database.

• Establish a routine boiler inspection schedule. The schedule should include daily, weekly, monthly, semiannual, and annual inspections or activities.

• Establish and use boiler room log sheets. Boiler room log sheets should be tailored to the specific equipment in the facility. They can help identify a developing problem and can be referenced when establishing an overall boiler maintenance program.

• Establish and maintain posted operating procedures. Update operating procedures as required, such as when new equipment is installed. A posted operating procedure can remind the boiler operator of tasks to be completed and can serve as a guide for less-experienced boiler operators in the plant.

• Maintain a clean boiler room. Keep all equipment clean to prevent problems.

• Maintain an adequate fresh air supply in the boiler room. Efficient burner operation requires an adequate amount of clean air. Filters must be kept clean.

• Maintain accurate fuel records. Fuel records can be used to identify extraordinary fuel demands, which indicate a problem.

• Practice required lockout/tagout procedures when a boiler is off-line. If there is more than one boiler connected to a common header taken off-line, establish a procedure for properly isolating the boiler and equipment for maximum safety.

Boiler maintenance procedures are specified by manufacturer recommendations and plant procedures. Many of these are specified in the boiler room log. Maintenance tasks completed can be recorded in the boiler room log or in a maintenance database. Information listed in a database includes basic equipment information such as nameplate data, date completed, and spare-part information. The part supplier and delivery time should be included for easy access by the boiler operator.

Chapter 8 — Boiler Operation Procedures 213

Boiler Room Logs A boiler room log is used to record information regarding operation of a boiler during a given period of time. See Figure 8-10. The number and frequency of the checks to be performed depend on the plant. Some plants maintain a log for every 8-hour period. Other plants maintain a log for a 24-hour period. Maintaining a boiler room log allows an operator to evaluate the past performance of a boiler.

In addition, boiler room log information can be useful in determining the cause of a malfunction or predicting a possible problem. Boiler operation data commonly recorded on a boiler room log includes the following: • steam pressure • water level • boilers on-line • condensate return temperature • feedwater temperature and pressure • fuel oil temperature and pressure • makeup water consumption • outside temperature Boiler operator duties are also sometimes recorded on a boiler room log. These duties include the following: • gauge glass blowdown • water column blowdown • low water fuel cutoff blowdown • flame scanner testing • safety valve testing • boiler blowdown • fuel on hand (gas meter readings for gas-fired boilers) • fuel consumed during shift • maintenance work Gauge Glasses A common maintenance concern is managing gauge glasses. Typical maintenance procedures include replacing or cleaning a gauge glass and repairing a leaky washer.

Gauge Glass Replacement. Checking the gauge glass is the quickest way to determine water level in a boiler. The gauge glass must provide an accurate indication of boiler water level. A broken or discolored gauge glass must be replaced immediately. For maximum safety, the boiler should be OFF and cool when the gauge glass is replaced. See Figure 8-11. A broken gauge glass on a boiler under pressure is replaced using a standard procedure:

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BOILER ROOM LOGS Date

8:00 AM

10:00 AM

12 PM

2:00 PM

4:00 PM

BOILER OPERATION DATA Boiler on Line Pressure (psi) Stack Temp Condensate Return Temp Feedwater Heater Temp Fuel Oil Tank Temp Fuel Oil Pump Suction Pressure Fuel Oil Pump Discharge Pressure Fuel Oil Temp at Burner Outside Temp BOILER OPERATOR DUTIES Blowdown Gauge Glass Water Column Low Water Cutoff Test Flame Scanner Safety Valve Test* *Tested once a month when boiler is coming off the line Fuel Oil Accessories Change Over Strainer & Clean Clean Fuel Oil Burner Fuel Oil Gauge Readings Start of Shift End of Shift Gal. Consumed Operator's Initials Special Instructions:

Figure 8-10. A boiler room log lists boiler operation data that can be used to increase boiler efficiency and identify potential malfunctions.

Chapter 8 — Boiler Operation Procedures 215

GAUGE GLASS REPLACEMENT 1

2

CLOSE VALVES TO GAUGE GLASS

3

OPEN BLOWDOWN VALVE

5

4

REMOVE GUARDS

6

REMOVE GAUGE GLASS AND WASHERS

8

7

INSTALL GAUGE GLASS AND WASHERS

9

REPLACE GUARDS

REMOVE NUTS

TIGHTEN NUTS WITH WRENCH

10

OPEN VALVES TO GAUGE GLASS

CLOSE BLOWDOWN VALVE

Figure 8-11. A broken or discolored gauge glass is replaced using a standard procedure for maximum safety.

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WARNING: Wear required personal protective equipment when changing a gauge glass.

1. Close the lower water valve and the upper steam valve to the gauge glass.

2. Open the gauge glass blowdown valve.

3. Remove the gauge glass guards.

4. Remove the gauge glass nuts.

5. Remove the gauge glass and washers.

6. Install the new gauge glass and new washers. If the glass must be cut to fit, allow Z\v″ less than the inside measurement for expansion from heat. Tighten the gauge glass nuts by hand and then use a wrench to tighten them by a quarter turn.

7. Replace gauge glass guards and slightly open the steam valve to the gauge glass to allow the glass to warm slowly.

8. Open the steam valve and water valve to the gauge glass completely.

9. Close the gauge glass blowdown valve and check for leaks.

10. If leaks are detected, secure the steam and water valves and open the drain valve to remove pressure before tightening the gauge glass nuts. Tighten the leaking nut with a wrench one flat of the nut at a time to ensure it is not overtightened. Test for leaks between each tightening.

Gauge Glass Cleaning. For maximum accuracy, a dirty gauge glass is replaced with a new one. However, a gauge glass can be cleaned if necessary to obtain accurate readings. A gauge glass is cleaned using the following procedure: 1. Secure the water and steam valves to the gauge glass.

2. Open the gauge glass blowdown valve and make sure the valves are not leaking steam or water.

3. Remove the gauge glass nuts and glass.

4. Use a cloth wrapped around a wooden dowel to clean the inside of the gauge glass. Never use an object that could scratch the glass. A scratch on the inside of the glass can promote etching by steam, create a weak spot, and possibly break the glass.

5. Use new gauge glass washers when reinstalling the glass.

6. Follow normal recommended gauge glass warm-up procedures.

Leaking Gauge Glass Washers. Leaking gauge glass washers can result in a false water level reading. In addition, leaking, worn gauge glass washers can cause the glass to wear quickly and eventually break.

Chapter 8 — Boiler Operation Procedures 217

Always close gauge glass steam and water valves and open the drain valve before attempting to tighten gauge glass nuts. Never attempt to repair a pressurized gauge glass. Safety goggles and gloves must be worn when working around a hot gauge glass. Increase pressure on the gauge glass washers by tightening the gauge glass nuts carefully. Tighten by turning each nut only one flat at a time and retest for leaks before tightening further. If tightening the gauge glass nuts does not stop the leak, the washers should be replaced.

Low Water Fuel Cutoffs Any maintenance and cleaning must be done while there is no pressure on the low water fuel cutoff. The internal mechanism of a low water fuel cutoff should be removed from the bowl at the recommended intervals to check and clean the float ball, the internal moving parts, and the bowl or water column of the boiler. A float ball should never be polished to a shine. Polishing removes material and will eventually cause a leak. At the same time, the pipe plugs from the boiler tees or crosses should be removed to ensure that the cross connecting piping is clean and free of obstructions. Low water fuel cutoff controls must be vertically aligned for proper performance throughout the life of the equipment. See Figure 8-12.

LOW WATER FUEL CUTOFF INSTALLATION

Figure 8-12. Low water fuel cutoff controls must be installed vertically for proper performance.

Burners and Controls Maintenance of a burner and its controls is crucial to maintain boiler efficiency.

See Figure 8-13. Spare burner parts should be kept clean and ready to be changed as necessary. When checking a burner and controls, examine the burner linkage, jackshafts, drive units, and cams. Make sure all linkages, linkage arms, and connections are tight. Lubricate or grease as required. If the burner and control parts cannot be repaired when the boiler is in operation, it should be noted in the boiler room log so repairs can be made when the boiler is taken out of service.

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BURNER MAINTENANCE AND TESTING

Figure 8-13. A burner is maintained and tested to ensure proper operation and maximum efficiency.

Usually, controls for the burner function properly for long periods of time.

Control malfunctions lead to uneconomical operation and damage in most cases, and often conditions can be traced directly to deficiencies in testing and maintenance. Normal operation of a boiler usually follows a distinct pattern. Entries in the boiler room log define this pattern. Any deviation from the pattern should be investigated. Changes in the readings can be gradual over a prolonged period, or they can be rapid over a short period. For example, a gradual change in readings, such as a slow increase in the flue gas temperature, can indicate a loss in heat transfer and soot buildup on fire-side surfaces, baffle leakage, or scale buildup on water-side surfaces. A sudden or rapid change in readings can indicate that the air-fuel ratio has changed due to a linkage slipping, a damper movement, or a change in fuel or air cam adjustment screws.

Feedwater Treatment Improper feedwater treatment is probably the largest direct cause of boiler failure.

When the boiler feedwater and the boiler water do not receive proper preparation and treatment, scale deposits, sludge deposits, corrosion, and pitting of boiler surfaces result. A feedwater treatment program developed by a water treatment

Chapter 8 — Boiler Operation Procedures 219

company addresses plant conditions, materials employed, pumps, lines, heat users, prevailing water chemistry, and other factors. The boiler operator must follow this program to keep the water-side surfaces in good condition.

Feedwater Pumps Feedwater pumps require little maintenance during normal operation. Periodic checks should be made for proper bearing temperatures and any unusual vibration. See Figure 8-14. Lubrication procedures should follow manufacturer recommendations. Feedwater pump service should coincide with other scheduled maintenance to minimize effects on plant operations. During service, the bearings should be checked for wear and lubricant replaced or added. Flexible couplings should be opened and checked for wear and alignment. The coupling should be washed thoroughly and reassembled with new lubricant. The pump seals should also be inspected and, if necessary, replaced. If boiler room log entries indicate feedwater pump performance has significantly decreased, an overhaul of the pump may be required according to manufacturer specifications.

FEEDWATER PUMPS

Figure 8-14. Feedwater pumps should be checked periodically for proper bearing temperatures and any unusual vibration.

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Proper installation impacts feedwater pump life more than any other factor.

When installed, the feedwater pump should be very carefully leveled, grouted, and aligned before it is piped. After piping is installed, the feedwater pump should be checked again for proper alignment.

Safety Valves There is no routine maintenance involved with safety valves. However, they are routinely tested to ensure proper operation. Safety valves are commonly tested on a low pressure steam boiler by SAFETY VALVE TESTING lifting the safety valve try lever.

See Figure 8-15. With the boiler pressure at a minimum of 5 psi, lift the safety valve to wide open position. Discharge the steam for 5 sec to 10 sec. Then release the try lever. The disk should snap to the closed position against the valve seat. Malfunctioning safety valves must be replaced as soon as possible. Replacement safety valves must comply with the ASME Boiler and Pressure Vessel Code and all design specifications of the boiler. Any adjustments or repairs to a safety valve must be performed by an authorized manufacturer representative.

Figure 8-15. Safety valves are routinely

Boiler Inspections tested to ensure proper operation and must A boiler inspection is performed as be serviced by an authorized manufacturer a part of plant procedures and/or representative. requirements by an inspection agency. The boiler inspector thoroughly examines the boiler and related equipment for corrosion, overheating, and other possible damage. See Figure 8-16. Then a written report is filed and a new boiler certificate is issued after boiler inspection requirements are met. An inspection date appointment is made to minimize plant downtime. The boiler operator must be present during the boiler inspection.

Before inspection, the boiler must be taken off-line. Close, lockout, and tagout the main steam stop valve. Open the boiler vent to prevent vacuum buildup in the boiler. Then close, lockout, and tagout the feedwater line valve to the boiler. If applicable, the makeup water valve is also closed.

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When the boiler is cool enough to dump, use the bottom blowdown valve to empty the boiler. After the boiler is empty, close, lockout, and tagout the bottom blowdown valve to ensure that hot water and flash steam cannot back up into the boiler. The boiler is cool enough to dump when the heating surface is cool enough to touch. Never dump a boiler that is hot because sludge and sediment may bake on the heating surfaces.

As soon as the boiler has been dumped, open the handholes, remove the manhole cover, and thoroughly flush and wash out the water side. See Figure 8-17. Do not dump a boiler unless it can be flushed immediately. If a boiler is dumped and not immediately flushed, the sludge and sediment may air-dry on the heating surfaces, making the boiler extremely difficult to clean.

As the water side is cleaned, look for signs of scale, pitting, or fuel oil.

After cleaning the water side, the fire side must be inspected and cleaned thoroughly. Remove all soot and carefully examine the entire fire side.

Look for signs of blisters or bags on the heating surface. Check the condition of the brickwork (if present) and make any needed repairs.

BOILER INSPECTIONS

Figure 8-16. During a boiler inspection, check tube sheets, tubes, and other internal parts for corrosion, overheating, and other damage.

HANDHOLES

Figure 8-17. Handhole covers are removed to provide access to boiler parts during a boiler inspection.

“Authorized Inspector” is an industry term for a person qualified to perform boiler inspections. Usually, this person has received a commission from the National Board of Boiler and Pressure Vessel Inspectors. An inspector can help a boiler operator maintain a safe and efficient operation.

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Frequently, the boiler inspec- INTERNAL SURFACE CLEANING tor requires all of the plugs to be removed at the water column and the low water fuel cutoff controls opened so the inside float chamber can be inspected. After both the fire side and water side of the boiler have been cleaned, notify the inspector that the boiler is ready for inspection. See Figure 8-18.

Boiler inspection dates are usually the same every year. Contact the Figure 8-18. All internal surfaces are exposed boiler inspector several weeks in and cleaned prior to a boiler inspection. advance to schedule the inspection to prevent having the boilers down for an unnecessary period of time. When the boiler inspector is in the plant, have anything ready that may be needed. For example, the boiler inspector may need a ladder and a low voltage droplight. Arrange for additional personnel to assist if necessary to save time. Anything that appears to be a potential problem should be conveyed to the boiler inspector. Follow any recommendations the boiler inspector makes.

WARNING: The inside of a boiler is a confined space. A confined-space permit may be needed for a boiler inspection. All the regulations and precautions regarding confined space entry must be followed.

Boiler Layup Boiler layup is the preparation of a boiler for out-of-service status for an extended period of time. Wet layup is the storage of a boiler filled with warm, chemically treated water. Wet layup is used when the boiler may be needed on short notice.

Dry layup is the storage of a boiler with all the water drained. Dry layup is used when the boiler is expected to be out of service for a long period of time or if the water in the boiler has a possibility of freezing. Both wet layup and dry layup require the boiler to be thoroughly cleaned on both fire and water sides. Soot from gas, fuel oil, coal, and ash may contain sulfur and must be removed. When combined with water, sulfur reacts to form sulfuric acid, which corrodes boiler metal.

In wet layup, the boiler is closed with new gaskets installed on handholes and manholes. The boiler is filled to the top with chemically treated water to reduce the possibility of corrosion and oxygen pitting. The water is heated to 100°F to reduce condensation.

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In dry layup, the water side must be dry to prevent corrosion and pitting from residual moisture. A moisture-absorbing agent (quicklime or silica gel) is placed in the boiler. Approximately 2 lb of quicklime or 10 lb of silica gel are used per 1000 gal. capacity. Quicklime or silica gel may be placed on desiccant trays inside the drums or inside the shell to absorb moisture from the air. The manhole is then reinstalled with a new gasket. All valves are closed to seal the boiler from moisture. The moisture-absorbing agent must be checked periodically and replaced as needed.

SECTION 8.3 — CHECKPOINT

1. Why is it important to use established procedures?

2. When cutting a replacement gauge glass, why is it necessary to cut it a shorter length than the inside length?

3. What are possible causes of a gradual increase in flue gas temperature?

4. What is the purpose of a boiler inspection?

5. How are wet layup and dry layup different?

SECTION 8.4 — HANDLING BOILER CONDITIONS Certain boiler conditions that occur can result in serious injury if proper actions are not taken immediately. The boiler operator must be thoroughly familiar with the actions required. In addition, boiler operation is critical to plant heat and process needs, and downtime must be kept to a minimum. According to incident reports from The National Board of Boiler and Pressure Vessel Inspectors, the most frequent causes of boiler incidents are operator error and poor maintenance.

The boiler operator must be able to quickly handle boiler conditions that occur such as water level control, boiler overpressure, flame failures, feedwater pump failure, furnace explosions, and general troubleshooting tasks.

Water Level Control One of the most important concerns with operating a boiler is maintaining the proper water level. Low water conditions and high water conditions are both dangerous.

Low Water Conditions. A low water condition is a condition that occurs when the water in a boiler is below the NOWL as indicated by the gauge glass. Even though it is considered a low water condition to have water below the NOWL, it does not become dangerous until the water drops out of sight in the gauge glass. The low water fuel cutoff is positioned and adjusted to secure the burner when the boiler water level falls to approximately 1″ above the lowest gauge glass water level.

If the water level is observed lower than this, the boiler operator must manually

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secure the burner and feedwater valve immediately. Some plants have an audible alarm and light to signal a low water condition in a boiler.

Water should not be added until the actual water level in the boiler is determined.

The lowest visible part of the gauge glass must be a minimum of 1″ above the lowest permissible water level recommended by the boiler manufacturer. As long as the heating surface is covered with water, it is safe to add water to the boiler.

WARNING: Water must not be added to a boiler if water is not present in the gauge glass. The fuel and feedwater must be secured immediately. Adding water could cause a boiler explosion.

If the boiler is truly low on water and must be shut down, then it must be inspected for damage after cooling. The low water fuel cutoff and feedwater systems must be inspected and repaired as required. A low water condition can damage the boiler drum, the furnace, and the tubes from overheating. The cause must be determined whenever a low water condition occurs. The boiler must be removed from service and inspected. The feedwater supply must be checked for proper function. The boiler drum, fittings, and accessories should be checked for leaks.

If multiple boilers are on-line and one has a low water condition, both the fuel to the burner and the feedwater of the boiler with the low water condition must be secured. The NOWL of all boilers on-line must be monitored.

High Water Condition. A high water condition is a condition caused by an excessive amount of water in a boiler as indicated by the gauge glass. When this condition occurs, the gauge glass should be blown down to ensure an accurate reading, and the water level must be checked again using the gauge glass.

The immediate danger with a high water condition is the possibility of carryover of water in the steam. This can result in water hammer and damage to steam lines.

In the event of high water, a bottom blowdown is performed to bring the water level to the NOWL. The burner firing rate should be reduced. After the NOWL is restored in the boiler, the cause of the high water condition should be determined.

The feedwater regulator must be checked for proper operation.

Boiler Overpressure Boiler overpressure is a condition that occurs when a boiler is operating at or above its maximum allowable working pressure (MAWP). In an overpressure condition, the pressure controls and safety valve have failed. The safety valve pressure must be set at or below the MAWP. The safety valve must open at the safety valve pressure setting. In an overpressure situation, the burner should be shut off immediately if the boiler is still firing, the boiler pressure is above its

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MAWP, and the safety valve is not open. Do not open the safety valve manually, as this could cause a boiler explosion. Allow the boiler to cool and determine what caused the overpressure condition and why the safety valve and pressure controls did not operate properly.

Flame Failures Flame failure is a boiler condition that occurs when the flame in the boiler furnace has been unintentionally lost. Flame failure causes vary from a malfunction in the ON/OFF pressure control, fuel contamination, or inadequate draft from a draft fan switch or a motor failure. Flame failure can result in a furnace explosion from the buildup and ignition of fuel. The flame scanner is tested to ensure that a burner would shut down in the event of a flame failure. When a scanner is tested, the burner should shut OFF. The flame scanner is then cleaned and reinstalled if it works. The combustion control programmer is reset for automatic control, and it should properly control the burner through the firing cycle. The fuel supply must be checked if the programmer is functioning properly.

Flame failures in gas-fired boilers are commonly caused by insufficient pressure in gas lines. Flame failures in fuel oil-fired boilers are commonly caused by cold fuel oil, water in the fuel oil, air in fuel oil lines, clogged fuel oil strainers, clogged burner tips, and loss of fuel oil pressure. A flame failure must be addressed immediately. Fuel to the burner must be secured quickly, and the furnace is purged to prevent an accumulation of fuel.

Feedwater Pump Failures A feedwater pump must be capable of delivering feedwater to a boiler. A low water condition can result without an adequate supply of feedwater. Feedwater pump failure can have many different causes: • overheated feedwater supplied to the feedwater pump • a worn or damaged feedwater pump impeller • motor failure from single phasing, overheating, or some other malfunction • a blockage or restriction in a feedwater supply line • worn or damaged feedwater pump bearing(s) • leakage from the feedwater pump housing Steambound Feedwater Pumps Feedwater pumps are designed to pump liquids, not steam. Water vaporizes when the temperature is too high or the pressure is too low. A steambound feedwater pump is a pump where the entering feedwater flashes to steam and causes the pump to quit pumping. To correct a steambound feedwater pump, water fed to

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the pump must be cooled. Water that is drawn from a condensate return tank may be cooled by adding water from the makeup system. Cool water can be carefully poured directly on the feedwater pump without spilling water on the motor if the problem persists. Steam traps on the condensate return line should also be tested for proper operation. See Figure 8-19.

Furnace Explosions A furnace explosion is the instantaneous combustion of flammable gases or vapors accumulated in a furnace. This accumulation can occur from leaking fuels or a flame failure. Any signs of leaking fuels must be addressed immediately.

The cause of a flame failure must STEAM TRAP TESTING be determined. The boiler must be inspected for physical damage, and the flame scanner must be checked for proper function.

Before relighting the burner, the combustion control programmer must go through a purge cycle. The purge cycle must completely empty the fuel from the furnace. One method of purging is to shut off the gas to the pilot, disconnect the power from the ignition transformer, and shut off the fuel oil valve. Start the programmer to complete a cycle. The burner motor will operate, and the fan will blow out any buildup of fuel oil vapor. Then open the fuel oil valve, reconnect the power, Figure 8-19. Steam traps should be checked for open the gas valve, and allow the proper operation when determining the cause burner to go through a firing cycle. of a steambound feedwater pump.

WARNING: Never bypass a purge cycle in order to start a burner that has misfired. This could cause additional unburned fuel to accumulate in the furnace, possibly leading to a furnace explosion.

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The fuel to the burner must be secured, and the proper plant personnel and authorities should be notified if the cause of a furnace explosion cannot be determined. Water should not be added to a boiler until proper operation of the boiler has been verified. If any odor of gas is detected, the burner should be shut down and not allowed to light to avoid a furnace explosion. If accessible, gas lines should be checked for leaks by applying a mixture of soapy water with a paint brush. Bubbles will appear where gas is leaking. Gas leak detection equipment may be required to further isolate the location of leaks. Repairs on gas lines and equipment must be performed by authorized personnel.

Boiler and pressure vessel inspector reports usually do not include data on furnace explosions because a boiler explosion does not normally affect the pressure vessel. Furnace explosions are normally investigated by a fire inspector. There have been many boiler service technicians and boiler operators injured or killed from furnace explosions. However, the frequency of furnace explosions is decreasing every year, mainly due to the solid-state combustion controls that do not allow a purge cycle to be bypassed.

A boiler explosion can cause catastrophic damage.

Boiler Troubleshooting Boiler troubleshooting must identify a problem and restore steam to all loads as soon as possible. Standard troubleshooting steps provided by the manufacturer are followed to isolate and remedy problems. See Figure 8-20.

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BOILER OPERATION TROUBLESHOOTING Problem Burner Stays In Low Fire

Solution 1. Pressure or temperature above modulating control setting 2. Manual-automatic switch in wrong position 3. Inoperative modulating motor (see Section F) 4. Defective modulating control 5. Binding or loose linkage, cams, set screws, etc.

Shutdown Occurs During Firing

1. Loss or stoppage of fuel supply 2. Defective fuel valve; loose electrical connection 3. Flame detector weak or defective 4. Lens dirty or sight tube obstructed 5. If the programmer lockout switch has not tripped, check limit circuit for an opened safety control.

Pilot Flame, But No Main Flame

1. Insufficient pilot flame 2. Gas fired unit A. Manual gas cock closed B. Main gas valve inoperative C. Gas pressure regulator inoperative 3. Oil fired unit A. Oil supply cut off by obstruction, closed valve, or loss of

Figure 8-20. Troubleshooting steps from the manufacturer provide a guide to correcting boiler problems.

WARNING: Troubleshooting procedures must be performed only by personnel familiar with the boiler and related equipment. Familiarity with the operation of the boiler and related equipment makes troubleshooting easier.

Costly downtime can be reduced by a systematic comparison between normal operating characteristics and a performance that deviates from normal.

Starting with the most obvious cause in a logical step-by-step sequence offers the greatest efficiency when troubleshooting.

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SECTION 8.4 — CHECKPOINT

1. Why is a low water condition dangerous?

2. Why is a high water condition dangerous?

3. What are possible causes of overpressure?

4. What are possible causes of a furnace explosion?

5. When is an appropriate time to add water during a low water condition?

6. What is the proper response to an overpressure condition?

7. How can a steambound feedwater pump be returned to service?

Additional Activities 1. Take the Quick Quizzes™ for Chapter 8.

2. Review the related Media Library clips.

3. Review the Flash Cards for Chapter 8.

4. Review the related Master Math™ applications.

5. Review Chapter 8 Study Guide questions.