BOILER SAFETY, TROUBLESHOOTING AND INSPECTION
The CB-Hawk boiler management control system ('''Figure 1''') combines the functions of a flame safeguard programmer with those of operating and firing rate controls. It also monitors the fuel pressure and temperature (if required) with solid-state sensors and provides a built-in safety limit control of those functions. This system is used on most types of steam or hot water boilers, including fire-tube, industrial water-tube, and commercial water-tube. The control system is designed to operate a gas, oil, or combination burner using a single modulation motor and provides the best results when used with a fully modulating burner.
'''Figure 1: CB-HAWK Boiler Management Control System'''
The burner and control system are in the starting condition when the following conditions exist:
The electrical portion of the boiler is made up of individual circuits with controls that are wired in a manner designed to provide a safe workable system. The program relay provides connection points for the interconnection of the various circuits.
The controls used vary depending upon the fuel oil or gas and the specific requirement of applicable regulatory bodies. Refer to the boiler wiring diagram to determine the actual controls provided.
The circuits and controls normally used in the circuits follow and are referred to in the following sequence of operation.
On a combination fuel unit, the gas/oil switch must be set for the proper fuel. The following sequence ('''Figure 2''') occurs with power present at the program relay (PR) input terminals and with all other operating conditions satisfied.
When the burner switch (BS) is turned "on," and controls wired in the "limit" and "fuel valve interlock" circuits are closed and no flame signal is present, the "blower motor start circuit" is powered, energizing the blower motor starter (BMS). The load demand light (LDL) turns on. When firing oil, the air compressor motor starter (ACMS) (if provided) is also powered. The air purge valve (APV) (Nos. 5 and 6 oil only) remains de-energized.
At the same time, the program relay signals the modulating damper motor (MDM) to open the air damper. The damper begins to open and drives to its full open or high fire position. Opening the damper motor allows a flow of purging air through the boiler prior to the ignition cycle.
On certain boilers, the circuitry will include a high fire switch (HFS). The purpose of the switch is to prove that the modulating damper motor (MDM) has driven the damper to the open position during the prepurge cycle. In this instance, the "high fire proving circuit" is used.
The controls wired into the "running interlock circuit" must be closed within 10 seconds after the start sequence. In the event any of the controls are not closed at this time, or if they subsequently open, the program relay will go into a safety shutdown.
At the completion of the high fire purge period, the program relay signals the modulating damper motor (MDM) to drive the air damper to its low fire position.
To ensure that the system is in low fire position prior to ignition, the low fire switch (LFS) must be closed to complete the "low fire proving circuit." The sequence will stop and hold until the modulating damper motor (MDM) has returned to the low fire position and the contacts of the low fire switch (LFS) are closed. Once the low fire switch is closed, the sequence is allowed to continue.
'''Figure 3: 833-2416 Sequence'''
The ignition transformer (IT) and gas pilot valve (GPV) are energized from the appropriate pilot ignition terminal.
The pilot flame must be established and proven by the flame detector (FD) within a 10 second period in order for the ignition cycle to continue. If for any reason this does not happen, the system will shut down and safety lockout will occur.
With a proven pilot, the main fuel valve(s) (OV or MGV) is/are energized and the main fuel valve light (FVL) in the panel is lighted. The main flame is ignited and the trial period for proving the main flame begins. It lasts 10 seconds for light oil and natural gas, and 15 seconds for heavy oil. At the end of the proving period, if the flame detector still detects main flame, the ignition transformer and pilot valve are de-energized and pilot flame is extinguished.
With main flame established, the program relay releases the modulating damper motor (MDM) from its low fire position to control by either the manual flame control (MFC) or the modulating control (MC), depending upon the position of the manual-automatic switch (MAS). This allows operation in ranges above low fire.
With the manual-automatic switch (MAS) set at automatic, subsequent modulated firing will be at the command of the modulating control (MC), which governs the position of the modulating damper motor (MDM). The air damper and fuel valves are actuated by the motor through a linkage and cam assembly to provide modulated firing rates.
The burner starting cycle is now complete. The (LDL) and (FVL) lights on the panel remain lit. Demand firing continues as required by load conditions.
The burner will fire until steam pressure or water temperature in excess of demand is generated. With modulated firing, the modulating damper motor (MDM) should return to the low fire position before the operating limit control (OLC) opens. When the limit control circuit is opened, the following sequence occurs:
The main fuel valve circuit is de-energized, causing the main fuel valve (MGV) or (OV) to close. The flame is extinguished. The control panel lights (LDL) and (FVL) are turned off. The blower motor continues to run to force air through the boiler for the post-purge period.
On a No. 6 oil burner, the air purge valve (APV) is powered from the blower motor start circuit via the contacts of the air purge relay (APR) to provide an air purge of the oil nozzle. The damper motor returns to the low fire position if it is not already in that position.
The blower motor start circuit is de-energized at the end of the post purge cycle and the shutdown cycle is complete.
The program relay is now ready for subsequent recycling, and when steam pressure or water temperature drops to close the contacts of the operating control, the burner again goes through its normal starting and operating cycle.
The program relay will recycle automatically each time the operating control closes, or after a power failure. It will lockout following a safety shutdown caused by failure to ignite the pilot, or the main flame, or by loss of flame. Lockout will also occur if flame or flame simulating condition occurs during the pre-purge period.
The control will prevent startup or ignition if limit circuit controls or fuel valve interlocks are open. The control will lock out upon any abnormal condition affecting air supervisory controls wired in the running interlock circuit.
If the burner will not start, or upon a safety lockout, the trouble shooting section in the operating manual and the technical bulletin should be referred to for assistance in pinpointing problems that may not be readily apparent.
The program relay has the capability to self-diagnose and to display a code or message that indicates the failure condition. Refer to the control bulletin for specifics and suggested remedies. Familiarity with the program relay and other controls in the system can be obtained by studying the contents of the manual and this bulletin.
Knowledge of the system and its controls will make troubleshooting much easier. Costly down time or delays can be prevented by systematic checks of the actual operation against the normal sequence to determine the stage at which performance deviates from normal. Following a routine may possibly eliminate overlooking an obvious condition, often one that is relatively simple to correct.
Remember, a safety device, for the most part, is doing its job when it shuts down or refuses to operate. Never attempt to circumvent any of the safety features.
Preventive maintenance and scheduled inspection of all components should be followed. Periodic checking of the relay is recommended to see that a safety lockout will occur under conditions of failure to ignite either pilot or main flame,
Safety shutdown (lockout) occurs if:
If the burner will not start or operate properly, refer to the troubleshooting chart below ('''Table 1''') for assistance in pinpointing problems that may not be readily apparent.
The program relay has the capability to self-diagnose and to display a code or message that indicates the failure condition. Knowledge of the system and its controls will make trouble shooting much easier. Costly down-time or delays can be prevented by systematic checks of actual operation against the normal sequence to determine the stage at which performance deviates from normal. Following a routine may possibly eliminate overlooking an obvious condition, often one that is relatively simple to correct.
If an obvious condition is not apparent, check the continuity of the circuits with a voltmeter or test lamp. Each circuit can be checked and the fault isolated and corrected.
Most fire detection technology focuses on detecting heat, smoke (particle matter) or flame (light) – the three major characteristics of fire. All of these characteristics also have benign sources other than fire, such as heat from steam pipes, particle matter from aerosols, and light from the sun. Other factors such as air temperature and air movement further confound the process of fire detection by masking the characteristic of interest. In addition, smoke and heat from fires can dissipate too rapidly or accumulate too slowly for effective detection. In contrast, because flame detectors are optical devices, they can respond to flames in less than a second. This optical quality also limits the flame detector as not all fires have a flame. As with any type of detection method, its use must match the environment and the risk within the environment.
There are three types of flame detectors currently available: ''infrared (IR)'', ''ultraviolet (UV)'', and a ''combination of UV and IR''. The spectrum below shows the relationship between these frequencies and visible light.
Infrared detectors have been available for many years; however, it has only been in recent times that technology has allowed for stable, accurate detection to occur. There are two types of infrared detectors: ''single frequency'' and ''multi-spectrum''.
The basic principles of operation for a single frequency IR detector are:
Strengths of the single frequency IR detector are:
Limitations of the single frequency IR detector are:
The basic principle of operation for a multi spectrum IR detector is:
Strengths of the multi-spectrum IR detector are:
Limitations of multi spectrum IR detector are:
IR detectors are sensitive to most hydrocarbon fires (liquids, gases, and solids). Fires such as burning metals, ammonia, hydrogen and sulphur do not emit significant amounts of IR in the detector’s sensitivity range to activate an alarm. IR detectors are suitable for applications where hydrocarbon fires are likely to occur and high concentrations of airborne contaminants and/or UV radiation sources may be present. The detector should be used with caution when the presence of hot objects and the potential for ice buildup on the detector are likely.
A UV detector uses a sensor tube that detects radiation emitted in the 1,000 to 3,000 angstrom (one ten-billionth of a meter) range. It is important to note that ultraviolet radiation from the sun that reaches earth starts at 2,800 angstroms. If the detector’s sensor has a wide range, then it will be triggered by the sun’s rays, which means it is only suitable for indoor use. There are sensors available with a range of 1,800 to 2,500 angstroms. Virtually all fires emit radiation in this band, while the sun’s radiation at this band is absorbed by the earth’s atmosphere. The result is that the UV flame detector is solar blind. The implication of this feature is that the detector can be used indoors and outdoors. In response to UV radiation from a flame that falls within the narrow band, the sensor generates a series of pulses that are converted by the detector electronics into an alarm output.
Strengths of the UV detector are:
Limitations of the UV detector are:
UV detectors are sensitive to most fires, including hydrocarbon (liquids, gases, and solids), metals (magnesium), sulphur, hydrogen, hydrazine, and ammonia. The UV detector is the most flexible general purpose optical fire detector available. They are fast, reliable, have few false alarm sources, and respond to virtually any fire.
A UV/IR detector consists of an UV and single frequency IR sensor paired to form one unit. The two sensors individually operate the same as previously described, but additional circuitry processes signals from both sensors. This means the combined detector has better false alarm rejection capabilities than the individual UV or IR detectors.
Strengths of the UV/IR detector are:
Limitations of UV/IR detector are:
Since the UV/IR detector pairs two sensor types, it will typically only detect fires that emit both UV and flickering IR radiation. UV detectors will respond to virtually all fires including hydrocarbon (liquids, gases, and solids), metals (magnesium), sulfur, hydrogen, hydrazine and ammonia. IR detectors typically only respond to hydrocarbon fires. Since the IR detector is not sensitive to burning metals, ammonia, hydrogen, and sulfur, the combined unit will not respond to these fires.
The detector is suitable for applications where hydrocarbon fires are likely and other sources of radiation may be present (X-rays, hot surfaces, and arc welding). They maintain constant protection while arc welding takes place. The UV/IR detectors are highly reliable with fast response times and low propensity to false alarms
Boilers are inspected annually to ensure they are safe to operate. The inspector checks safety controls to make sure they work properly and inspects inside the boiler, both the waterside and fireside. The inspector looks for signs of problems that should be investigated, such as:
Before the inspector arrives, you can take the following steps to ensure the boiler passes the inspection:
Fuel oil-fired boilers are especially susceptible to corrosion on the fireside and leaks in the fuel train. If the boiler firing level is too low, condensation can occur in the stack and cause corrosion.
When bringing a boiler online with other boilers, make sure the operating temperature and pressure are the same as the other boilers online before opening the supply and return isolation valves. When bringing a boiler online, crack the valves and check for unusual noises or vibrations prior to fully opening the valves. For steam boilers, be sure to drain condensate from the steam feed line prior to opening the steam outlet valve to avoid slugging condensate into the steam main.
MODEL 300 COMBUSTION ANALYZER
To avoid damaging the probe assembly due to excessive heat, remove probe from stack at or before the prescribed time listed below. Allow probe to cool to room temperature before reinserting it back into the stack.
Note that the high-temperature extended-probe options have unlimited exposure times up to 2,000°F (1,093°C).
Perform testing using the operating instructions that come with the analyzer.
Automatic low-high water control equipment must be serviced on a daily basis when the boiler is in operation. A high frequency of boiler failures is the result of low water, and can be attributed to a careless boiler operator. A procedure must be established at your facility to regularly clean the glass gauge column by "blowing down" the column at the start of the facility day, during non-peak operating periods, and at the conclusion of the facility day or shift. This ensures ability to determine the level of water in the boiler.
A major reason for damages incurred to low-pressure steam boilers is the low water within the boiler. If the condition of low water exists it can seriously weaken the structural members of the boiler, and result in needless inconvenience and cost. Low-pressure boilers can be protected by installing an automatic water level control device.
Steam boilers are usually equipped with automatic water level control devices. It must be noted, however, that most failures occur due to low water on boilers equipped with automatic control devices. The water control device will activate water supply or feedwater pumps to introduce water at the proper level, interrupt the gas chain and ignition process when the water reaches the lowest permissible level, or perform both functions depending on design and interlocking systems. No matter how automatic a water control device may be, it is unable to operate properly if sediment scale and sludge are allowed to accumulate in the float chamber.
Accumulations of matter will obstruct and interfere with the proper operation of the float device, if not properly maintained. To ensure for the reliability of the device, procedures must be established in your daily preventive maintenance program to allow "blow-down" the float chamber at least once a day. Simply open the drain for three to five seconds, making certain that the water drain piping is properly connected to a discharge line in accordance with city building codes. This brief drainage process will remove loose sediment deposits, and at the same time, test the operation of the water level control device. If the water level control device does not function properly it must be inspected, repaired, and retested to guarantee proper operation.
There are two very effective tests for low water controls on steam boilers. The first is the quick drain or blowdown test, which should be performed at a time other than a peak steam generating period. As the water is drained from the column the firing sequence is interrupted, the low water alarm signal activates, and the boiler operation shuts down.
The second and more costly method is the slow-drain test. By opening the blowdown valves, the water level can be checked to determine the water level in the column, gauge glass, and boiler. The boiler should shut down while you determine the level in the gauge glass.
As a safety precaution, the low water float chamber of hot water boilers should be tested daily, at the beginning of the shift, at the end of the shift, and once during non-peak firing periods. Time of tests and the boiler controls tested should be recorded on your boiler room log.
Annually, or as required, a thorough inspection of all low water control parts shall be performed. The annual inspection should include opening and cleaning the water chamber.