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#BoilerManual #ProtectingPressureParts #Section10 #Page11

Answers for protecting pressure parts

1. The two ways you can minimize overheating, thermal stress and corrosion in your boiler are:

........ 1. ___Balance the firing rate to the fluid flow.

........ 2. ___Monitor metal temperatures throughout the system. This will help avoid temperature imbalances which cause thermal stresses and corrosion.

2. The water should be a minimum of 70 F and must be within 100 F of boiler metal temperature.

3. It is very important that you DO NOT suddenly increase air flow to a tripped burner. Maintain the same air flow as at the time of the trip for an extended period of time. Prior to re-establishing the burner flame, you may have to post-purge the burner.

4. Dark and smokey flames indicate that fuel is not being completely burned. Once again, DO NOT suddenly increase air flow to the burners. Rather, you should reduce the FUEL FLOW so that it matches the existing air flow.

5. Anytime the boiler is fired, the furnace must have at least 33% of rated full load flow in the tube circuits.

6. You should make sure that the rate of change in the fluid temperature at the convection pass outlet does not exceed 200 F per hour. Any rate higher than this will lead to thermal stress problems.

7. You can detect a tube failure by monitoring the high makeup flow rate or by a discrepancy between feedwater flow and main steam flow.

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#BoilerManual #ProtectingPressureParts #Section10 #Page11

Answers for protecting pressure parts

1. The two ways you can minimize overheating, thermal stress and corrosion in your boiler are:

........ 1. ___Balance the firing rate to the fluid flow.

........ 2. ___Monitor metal temperatures throughout the system. This will help avoid temperature imbalances which cause thermal stresses and corrosion.

2. The water should be a minimum of 70 F and must be within 100 F of boiler metal temperature.

3. It is very important that you DO NOT suddenly increase air flow to a tripped burner. Maintain the same air flow as at the time of the trip for an extended period of time. Prior to re-establishing the burner flame, you may have to post-purge the burner.

4. Dark and smokey flames indicate that fuel is not being completely burned. Once again, DO NOT suddenly increase air flow to the burners. Rather, you should reduce the FUEL FLOW so that it matches the existing air flow.

5. Anytime the boiler is fired, the furnace must have at least 33% of rated full load flow in the tube circuits.

6. You should make sure that the rate of change in the fluid temperature at the convection pass outlet does not exceed 200 F per hour. Any rate higher than this will lead to thermal stress problems.

7. You can detect a tube failure by monitoring the high makeup flow rate or by a discrepancy between feedwater flow and main steam flow.

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#BoilerManual #OptimizingCombustion #Section9 #Page11

2,600 F is considered maximum. Somewhat lower temperatures may be desirable for fuels with high moisture content and low heating values.

COAL-ASH DEPOSITION

Ash deposition in various boiler zones is an important factor to be considered by the boiler operator. Initially, ash deposits on furnace walls act as insulation, thereby delaying the cooling of flue gases. This can cause an increase in steam temperature and is one factor that can cause the deposits to advance into normally cooler parts of the boiler. If the deposits are not removed during operation, accumulations forming on the furnace walls may cause excessive gas temperatures downstream, or in some cases, these accumulations may fall and damage pressure components. Accumulations in tube banks may block gas passes and require a boiler outage for cleaning.

The occurrence and severity of ash deposition depend largely on the coal-ash composition and amount of coal-ash, but can be strongly influenced by the method of firing, design of equipment, and operating conditions. Some of the influencing conditions are shown in Table 1.

ASH-DEPOSIT TYPES

A portion of the coal-ash and the combustion by-products is carried by the flue gases through the boiler, regardless of the method of coal firing. Much of the ash passes through the boiler without depositing, or in the case of the slag-tap-furnace, is removed as molten slag. The ash passing through the boiler is subject to various chemical reactions and physical forces which lead to deposition on tube surfaces. Flue-gas particles, metal temperatures, gas velocity, and flow patterns, as well as other factors,

such as particle size and composition, influence the amount and

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#BoilerManual #OptimizingCombustion #Section9 #Page11

2,600 F is considered maximum. Somewhat lower temperatures may be desirable for fuels with high moisture content and low heating values.

COAL-ASH DEPOSITION

Ash deposition in various boiler zones is an important factor to be considered by the boiler operator. Initially, ash deposits on furnace walls act as insulation, thereby delaying the cooling of flue gases. This can cause an increase in steam temperature and is one factor that can cause the deposits to advance into normally cooler parts of the boiler. If the deposits are not removed during operation, accumulations forming on the furnace walls may cause excessive gas temperatures downstream, or in some cases, these accumulations may fall and damage pressure components. Accumulations in tube banks may block gas passes and require a boiler outage for cleaning.

The occurrence and severity of ash deposition depend largely on the coal-ash composition and amount of coal-ash, but can be strongly influenced by the method of firing, design of equipment, and operating conditions. Some of the influencing conditions are shown in Table 1.

ASH-DEPOSIT TYPES

A portion of the coal-ash and the combustion by-products is carried by the flue gases through the boiler, regardless of the method of coal firing. Much of the ash passes through the boiler without depositing, or in the case of the slag-tap-furnace, is removed as molten slag. The ash passing through the boiler is subject to various chemical reactions and physical forces which lead to deposition on tube surfaces. Flue-gas particles, metal temperatures, gas velocity, and flow patterns, as well as other factors,

such as particle size and composition, influence the amount and

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#BoilerManual #Ramping #Section8 #Page11

9. Set the MW demand station rate of change and increse the station to its final end of ramp position. When the MW demand station is raised, thte ramp will begin. The 201's will be gradually opened to provide a linear increase in throttle pressure. Turbine first-stage pressure increases with throttle pressure and fuel flow is increased to maintain steam temperature.

The following will take place while the unit is ramping:

A. The 201 valves will start opening to pressurize the SSH above 500 psig {Pounds per Square Inch Gauge}

B. When SSH pressure exceeds the flashtank pressure, the 205 valve will close and be interlocked closed.

C. As the 201 valves open, the 207 valve will start closing to maintain the required flow through the PSH.

D. Excess boiler flow continues to be diverted to the flashtank through the 202 valve which is controlling boiler pressure.

E. When the superheater pressure reaches 2000 psi, the 201 valve is wide open. The 200s will start pulsing open to complete pressurization of the SSH.

F. The 202 valve will fully close.

G. Turbine load will increase as pressure and flow increase.

STARTUP VALVES DURING RAMP

To fully understand what happens during the ramp, we will discuss the graphs of several parameters as a function of startup time.

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#BoilerManual #Ramping #Section8 #Page11

9. Set the MW demand station rate of change and increse the station to its final end of ramp position. When the MW demand station is raised, thte ramp will begin. The 201's will be gradually opened to provide a linear increase in throttle pressure. Turbine first-stage pressure increases with throttle pressure and fuel flow is increased to maintain steam temperature.

The following will take place while the unit is ramping:

A. The 201 valves will start opening to pressurize the SSH above 500 psig {Pounds per Square Inch Gauge}

B. When SSH pressure exceeds the flashtank pressure, the 205 valve will close and be interlocked closed.

C. As the 201 valves open, the 207 valve will start closing to maintain the required flow through the PSH.

D. Excess boiler flow continues to be diverted to the flashtank through the 202 valve which is controlling boiler pressure.

E. When the superheater pressure reaches 2000 psi, the 201 valve is wide open. The 200s will start pulsing open to complete pressurization of the SSH.

F. The 202 valve will fully close.

G. Turbine load will increase as pressure and flow increase.

STARTUP VALVES DURING RAMP

To fully understand what happens during the ramp, we will discuss the graphs of several parameters as a function of startup time.

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#BoilerManual #BypassSystem #Section7 #Page11

Consult the appropriate lighter, burner, fan and air heater instructions for the correct procedure on purging the unit of any combustible gases and on lighting and controlling burners.Most furnace explosions occur during startup and low load periods. Whenever thee possibility exists for the accumulation of combustible gases or combustible dust in any part of the unit, no attempt should be made to light off until the unit has been thoroughly purged.

Insert the thermoprobes and begin firing. The thermal probes are retractable probes used to measure flue gas temperature entering the SSH during startup and low load operation {These were bi-metal K type thermocouples.} During startup, there is not sufficient steam flow through the superheaters to prevent overheating. The flue gas temperature entering the superheater section must not exceed 1000 F until 10% steam flow is passing through the superheater.

The firing rate should be balanced across the width of the unit to ensure uniform heating. Gas tempering and recirculation are used from initial firing through initial turbine loading in order to maintain maximum furnace absorption with minimum gas temperature entering the superheater. Continue firing and circulate at minimum feedwater flow while periodically checking conductivity. If it exceeds two micromhos, transfer flow back to the condenser until the one micromho limit is again achieved. The fluid temperature at the convection pass outlet will begin to rise soon after firing is initiated. This hot water and eventually steam, passes to the flashtank where water/steam separation will take place {In this scenario, the flashtank is performing like the drum on a drum boiler furnace}.

As the PSH pressure reaches 300 psi, it will begin to boil out. The turbine stop valve, above seat drains and/or steam line drain valve, MS-2, should be open to allow proper drainage.

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#BoilerManual #BypassSystem #Section7 #Page11

Consult the appropriate lighter, burner, fan and air heater instructions for the correct procedure on purging the unit of any combustible gases and on lighting and controlling burners.Most furnace explosions occur during startup and low load periods. Whenever thee possibility exists for the accumulation of combustible gases or combustible dust in any part of the unit, no attempt should be made to light off until the unit has been thoroughly purged.

Insert the thermoprobes and begin firing. The thermal probes are retractable probes used to measure flue gas temperature entering the SSH during startup and low load operation {These were bi-metal K type thermocouples.} During startup, there is not sufficient steam flow through the superheaters to prevent overheating. The flue gas temperature entering the superheater section must not exceed 1000 F until 10% steam flow is passing through the superheater.

The firing rate should be balanced across the width of the unit to ensure uniform heating. Gas tempering and recirculation are used from initial firing through initial turbine loading in order to maintain maximum furnace absorption with minimum gas temperature entering the superheater. Continue firing and circulate at minimum feedwater flow while periodically checking conductivity. If it exceeds two micromhos, transfer flow back to the condenser until the one micromho limit is again achieved. The fluid temperature at the convection pass outlet will begin to rise soon after firing is initiated. This hot water and eventually steam, passes to the flashtank where water/steam separation will take place {In this scenario, the flashtank is performing like the drum on a drum boiler furnace}.

As the PSH pressure reaches 300 psi, it will begin to boil out. The turbine stop valve, above seat drains and/or steam line drain valve, MS-2, should be open to allow proper drainage.

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#BoilerManual #CycloneOperation #Section6 #Page11

Sequence 2, conditions for transferring the cyclone on or off management, are as follows:

Requirements:

1. Cyclone not tripped.

2. Cyclone not in test.

3. System in operate and management on.

4. Cyclone not selected management off.

To transfer the cyclone on to management, depress the Management On pushbutton. The red Select light will backlight red. The lower field will backlight red when the cyclone is on management.

The same process is followed for cyclone Management Off. However, it will be indicated with a green backlight.

Sequence 3 shows the requirements for transferring a cyclone into the enable or test mode, the cyclone is disabled so that its logic may respond to inputs from the test panel, but at the same time will not affect the condition of controlled devices. A single cyclone can be in the test mode while the other cyclones are in the operate mode, but a permissive for selecting the test mode is that the logic be in the shutdown state.

Requirements: Cyclone Enabled

1. System in operate.

2. Cyclone stopped and successfully shutdown.

3. Cyclone disabled not required.

With the requirements satisfied, the cyclone enable mode is established automatically. Anytime the cyclone is in the enabled mode and the system is in operate, the cyclone trip monitor will be on.

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#BoilerManual #CycloneOperation #Section6 #Page11

Sequence 2, conditions for transferring the cyclone on or off management, are as follows:

Requirements:

1. Cyclone not tripped.

2. Cyclone not in test.

3. System in operate and management on.

4. Cyclone not selected management off.

To transfer the cyclone on to management, depress the Management On pushbutton. The red Select light will backlight red. The lower field will backlight red when the cyclone is on management.

The same process is followed for cyclone Management Off. However, it will be indicated with a green backlight.

Sequence 3 shows the requirements for transferring a cyclone into the enable or test mode, the cyclone is disabled so that its logic may respond to inputs from the test panel, but at the same time will not affect the condition of controlled devices. A single cyclone can be in the test mode while the other cyclones are in the operate mode, but a permissive for selecting the test mode is that the logic be in the shutdown state.

Requirements: Cyclone Enabled

1. System in operate.

2. Cyclone stopped and successfully shutdown.

3. Cyclone disabled not required.

With the requirements satisfied, the cyclone enable mode is established automatically. Anytime the cyclone is in the enabled mode and the system is in operate, the cyclone trip monitor will be on.

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#BoilerManual #CycloneDescription #Section5 #Page11

This assumes that a specific fuel and air combination will result in complete combustion while ignoring any heat loss to the surroundings. While this can never be achieved in actual operation, it is desirable to gear plant operations toward the goal of efficient and complete combustion. The benefits will be seen throughout the boiler system.

The heat of combustion (BTU value) of the fuel is the major factor which determines the flame temperature. This is a property inherent to the fuel and over which the operator has no control. However, other variables are controllable and will have the effect of raising the flame temperature. Increasing the temperature of the combustion air or fuel (reduce moisture) will increase flame temperature. The adiabatic flame temperature will be at a maximum with zero excess air (although some excess air is required to insure that all the fuel is burned). Excess air is not involved in the combustion process and only dilutes the temperature of the products of combustion.

The secondary (combustion) air temperature required depends greatly on the moisture content of the fuel and the boiler load. The greater the amount of moisture in the fuel, the higher the combustion air temperature required to dry the fuel. Similarly, high boiler loads require increased combustion air temperature to ensure self-sustaining combustion. In order to ensure adequate combustion over the entire load range, certain adjustments are required at windbox temperatures below 300 F. Primary and tertiary air is limited to minimum flow until the windbox temperature exceeds 300 F The lighter will remain in service for extra heat input and to stabilize ignition until the windbox temperature exceeds 300 F. Total air flow per cyclone also compensates for combustion air temperature (along with excess air) throughout the load range.

Other factors which affect secondary air temperature are sootblowing schedule or pattern, and air heater pluggage or leakage. Sootblowing patterns directly affect the flue gas temperature at the economizer outlet

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#BoilerManual #CycloneDescription #Section5 #Page11

This assumes that a specific fuel and air combination will result in complete combustion while ignoring any heat loss to the surroundings. While this can never be achieved in actual operation, it is desirable to gear plant operations toward the goal of efficient and complete combustion. The benefits will be seen throughout the boiler system.

The heat of combustion (BTU value) of the fuel is the major factor which determines the flame temperature. This is a property inherent to the fuel and over which the operator has no control. However, other variables are controllable and will have the effect of raising the flame temperature. Increasing the temperature of the combustion air or fuel (reduce moisture) will increase flame temperature. The adiabatic flame temperature will be at a maximum with zero excess air (although some excess air is required to insure that all the fuel is burned). Excess air is not involved in the combustion process and only dilutes the temperature of the products of combustion.

The secondary (combustion) air temperature required depends greatly on the moisture content of the fuel and the boiler load. The greater the amount of moisture in the fuel, the higher the combustion air temperature required to dry the fuel. Similarly, high boiler loads require increased combustion air temperature to ensure self-sustaining combustion. In order to ensure adequate combustion over the entire load range, certain adjustments are required at windbox temperatures below 300 F. Primary and tertiary air is limited to minimum flow until the windbox temperature exceeds 300 F The lighter will remain in service for extra heat input and to stabilize ignition until the windbox temperature exceeds 300 F. Total air flow per cyclone also compensates for combustion air temperature (along with excess air) throughout the load range.

Other factors which affect secondary air temperature are sootblowing schedule or pattern, and air heater pluggage or leakage. Sootblowing patterns directly affect the flue gas temperature at the economizer outlet

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#BoilerManual #Lighters #Section4 #Page11

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Alt = Labeled Fig. 7 Oil on. The image is on its side such that the bottom is along the right edge of the page and the top is along its left, and it utilizes the mechanical symbols identified in the printed key on page 7. This image is identical to Fig. 5 except the solenoid conditions show what has occurred for the Oil On condition.

#BoilerManual #Lighters #Section4 #Page11

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Alt = Labeled Fig. 7 Oil on. The image is on its side such that the bottom is along the right edge of the page and the top is along its left, and it utilizes the mechanical symbols identified in the printed key on page 7. This image is identical to Fig. 5 except the solenoid conditions show what has occurred for the Oil On condition.

#BoilerManual #AirAndGasFlow #Section3 #Page11

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Alt = The image is sideways with the bottom being along the right edge and the top being along the left edge, and contains both Figures 7 and 8. When image is rotated, Figure 7 is an outline of a furnace labeled Fig. 7 Furnace and convection pass; on the right is labeled Fig. 8 Flue gas flow. Follow the text walk-through on the pages for each of these images, respectively.

#BoilerManual #AirAndGasFlow #Section3 #Page11

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Alt = The image is sideways with the bottom being along the right edge and the top being along the left edge, and contains both Figures 7 and 8. When image is rotated, Figure 7 is an outline of a furnace labeled Fig. 7 Furnace and convection pass; on the right is labeled Fig. 8 Flue gas flow. Follow the text walk-through on the pages for each of these images, respectively.

#BoilerManual #FluidCirculation #Section2 #Page11

last tube bank, stringer tubes carry the water upward to the economizer outlet headers in the penthouse. The stringer tubes serve the dual purpose of carrying the fluid to the outlet headers and of supporting the horizontal convection pass banks.

Economizer tubes are often subject to corrosion, both internal and external. External corrosion is caused by the condensation of water vapor in the flue gas. [Inserting a reminder from high school science class that water is called the universal solvent for good reason, and the purer the water is, the more aggressive it is as a solvent.} External corrosion can be minimized when tube metal temperatures are kept above the dew point and tube surfaces are kept free of corrosive deposits. Internal corrosion is usually caused by oxygen in the feedwater or improper pH {the acid/alkalinity measurement}. Feedwater conditions must be kept within certain limits to prevent the deposition of solids from the make-up water {the water from the lake that the plant is next to, which the power plant also puts through its own treatment facility first} and to prevent the corrosion, erosion and deposition of metals within the cycle {metalic deposits are largely in the form of iron pyrites}. Solids are kept to a minimum by use of a condensate polishing system. Oxygen and carbon dioxide levels are kept low with mechanical deaeration and lower with hydrazine {make note of that hydrazine injection. It's at parts-per-million level but that stuff is still damn toxic hazmat}. In order to control iron in the system, maintain the pH level in the range of 9.3 - 9.5 at 77 F. Both internal and external corrosion of the economizer can be minimized if the temperature of the entering feedwater is kept above 240 F. Feedwater temperature entering the economizer should be approximately 481 F at full load.

To permit the natural circulatio of water through the cyclones and other hot slag areas if the flow of the feedwater stops, a natural circulation line, Figure 11, is provided between the economizer inlet and the downcomer to the convectino pass enclosure. The valve in this line, Figure 12, functions similar to a non-return valve. During normal operation, the fluid pressure differential across the economizer, cyclones and furnacekeeps the valve closed. If the flow of the feedwater stops, the pressure differential falls and the valve opens, but only if the valve stem is in the open position. The valve stem is actuated by a limitorque motor operator connected to a reliable source of energy which will be available at all times, even in the event of loss of all external station power (blackout).

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#BoilerManual #FluidCirculation #Section2 #Page11

last tube bank, stringer tubes carry the water upward to the economizer outlet headers in the penthouse. The stringer tubes serve the dual purpose of carrying the fluid to the outlet headers and of supporting the horizontal convection pass banks.

Economizer tubes are often subject to corrosion, both internal and external. External corrosion is caused by the condensation of water vapor in the flue gas. [Inserting a reminder from high school science class that water is called the universal solvent for good reason, and the purer the water is, the more aggressive it is as a solvent.} External corrosion can be minimized when tube metal temperatures are kept above the dew point and tube surfaces are kept free of corrosive deposits. Internal corrosion is usually caused by oxygen in the feedwater or improper pH {the acid/alkalinity measurement}. Feedwater conditions must be kept within certain limits to prevent the deposition of solids from the make-up water {the water from the lake that the plant is next to, which the power plant also puts through its own treatment facility first} and to prevent the corrosion, erosion and deposition of metals within the cycle {metalic deposits are largely in the form of iron pyrites}. Solids are kept to a minimum by use of a condensate polishing system. Oxygen and carbon dioxide levels are kept low with mechanical deaeration and lower with hydrazine {make note of that hydrazine injection. It's at parts-per-million level but that stuff is still damn toxic hazmat}. In order to control iron in the system, maintain the pH level in the range of 9.3 - 9.5 at 77 F. Both internal and external corrosion of the economizer can be minimized if the temperature of the entering feedwater is kept above 240 F. Feedwater temperature entering the economizer should be approximately 481 F at full load.

To permit the natural circulatio of water through the cyclones and other hot slag areas if the flow of the feedwater stops, a natural circulation line, Figure 11, is provided between the economizer inlet and the downcomer to the convectino pass enclosure. The valve in this line, Figure 12, functions similar to a non-return valve. During normal operation, the fluid pressure differential across the economizer, cyclones and furnacekeeps the valve closed. If the flow of the feedwater stops, the pressure differential falls and the valve opens, but only if the valve stem is in the open position. The valve stem is actuated by a limitorque motor operator connected to a reliable source of energy which will be available at all times, even in the event of loss of all external station power (blackout).

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@Su_G #BoilerManual #UnitDescription #Section1 #Page11

8 - Convection Pass - A gas tight enclosure which houses the primary superheater (PSH), secondary superheater (SSH), reheater superheater (RSH pendant and horizontal) and economizer.

9 - Sootblower (IR) - Mechanical device located in the furnace area and used to maintain the heat absorbing capacity of the furnace walls by clearing tube surfaces of deposits.

10-Sootblower (IK) - Mechanical device located in the convection pass areas (on the sidewalls) of the unit and used in order to clear deposits on tubes and maintain heat absorption capability.

11-Penthouse - Sealed and pressurized enclosure above the boiler roof which houses outlet headers, interconnecting piping, main steam and reheat lines.

12-Slag Tank - For storage and removal of molten coal/ashwhich flows from the furnace floor.

13-Economizer - A heat recovery device designed to transfer heat from the products of combustion (flue gas) to the entering feedwater.

14-Superheater - A group of tubes which absorb heat from the products of combustion (flue gas) to raise the temperature of the vapor passig through the tube above the temperature corresponding to its pressure.The superheater is divided into the primary superheater (PSH) and secondary supeheater (SSH).

15- Reheater - A heat transfer tube bank for heating steam after it has surrendered some of its original heat energy doing work in the high-pressure section of a steam turbine. The reheater is divided into pendant (hanging) and horizontal sections.

16- Gas Recirculation - Recirculated flue gas introduced in the vicinity of the initial burning zone of the furnace and used for steam temperature control.

17- Gas Tempering - Recirculated flue gas introduced near furnace outlet and used for control of gas temperature.

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@Su_G #BoilerManual #UnitDescription #Section1 #Page11

8 - Convection Pass - A gas tight enclosure which houses the primary superheater (PSH), secondary superheater (SSH), reheater superheater (RSH pendant and horizontal) and economizer.

9 - Sootblower (IR) - Mechanical device located in the furnace area and used to maintain the heat absorbing capacity of the furnace walls by clearing tube surfaces of deposits.

10-Sootblower (IK) - Mechanical device located in the convection pass areas (on the sidewalls) of the unit and used in order to clear deposits on tubes and maintain heat absorption capability.

11-Penthouse - Sealed and pressurized enclosure above the boiler roof which houses outlet headers, interconnecting piping, main steam and reheat lines.

12-Slag Tank - For storage and removal of molten coal/ashwhich flows from the furnace floor.

13-Economizer - A heat recovery device designed to transfer heat from the products of combustion (flue gas) to the entering feedwater.

14-Superheater - A group of tubes which absorb heat from the products of combustion (flue gas) to raise the temperature of the vapor passig through the tube above the temperature corresponding to its pressure.The superheater is divided into the primary superheater (PSH) and secondary supeheater (SSH).

15- Reheater - A heat transfer tube bank for heating steam after it has surrendered some of its original heat energy doing work in the high-pressure section of a steam turbine. The reheater is divided into pendant (hanging) and horizontal sections.

16- Gas Recirculation - Recirculated flue gas introduced in the vicinity of the initial burning zone of the furnace and used for steam temperature control.

17- Gas Tempering - Recirculated flue gas introduced near furnace outlet and used for control of gas temperature.

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