Lab Manual

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Boiler Control and Burner Management Simulator

Version 4.02

Copyright c 2002

Laboratory Manual

Edutech

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Win BoilerSim Student Lab ManualTable of Contents

Topics PageIntroduction 3

1 Experiment - Boiler Start-Up1.1 Objective 51.1.1 Burner Management Description 51.2 Procedure 71.3 Discussion 14

2 Experiment - Boiler Drum Level Control - 3 Element Control / 1 ElementControl

2.1 Objective: 152.2.1 Procedure - 3 Element Drum Level Control: 162.2.2 Procedure - 1 Element Drum Level Control: 202.3 Discussion 22

3. Experiment - Inverse Response of Drum Level3.1 Objective 223.2.1 Procedure - Open Loop Drum Level Response -Feedwater Shrink / Swell Effects Disabled 223.2.2 Procedure - Open Loop Drum Level Response -Feedwater Shrink / Swell Effects Enabled 253.3 Discussion 26

4 Experiment - 3 Element Drum Level Control - Feedwater Shrink / SwellEnabled

4.1 Objective 274.2 Procedure 274.3 Discussion 28

5 Experiment - Drum Level Shrink Swell Due to Steam Flow Changes5.1 Objective 295.1.2 Procedure -Drum Level Steam 29Flow Shrink / Swell - Disabled5.1.3 Discussion 315.2.2 Procedure -Drum Level Steam 31Flow Shrink / Swell - Disabled5.2.3 Discussion 33

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6 Experiment - Boiler Air Fuel Control System6.1 Objective 346.1.2 Procedure - Cross Limiting Logic -Step Change in Fuel Flow 346.1.3 Discussion 366.2.2 Procedure - Cross Limiting Logic -Step Change in Air Flow 366.2.3 Discussion 366.3.2 Procedure - Cross Limiting Logic -All Controllers in Automatic - Step Increase in Steam Demand 376.3.3Discussion 386.4.2 Procedure - Cross Limiting Logic -All Controllers in Automatic - Step Decrease in Steam Demand 386.4.3 Discussion 396.5.2 Procedure - Changing the Air / Fuel Ratio 396.5.3 Discussion 41

7 Experiment - Changing the Dynamics of the Boiler7.1 Objective 417.1.2 Procedure 427.1.3 Discussion 447.2.2 Procedure - A "Faster" Boiler 447.2.3 Discussion 47

8 Suggestions for Additional Experiments 48

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Introduction

The lab manual contains 7 experiments that cover the most importantfundamental concepts of Boiler Control and Burner Management.

The experiments are organized as follows:

ExperimentObjectives

This section will identify those concepts that will be developed in theexperiment

ProcedureThis section will present the method of proceeding through theexperiment.

The following convention will be used to identify the where on the screen,the mouse should be clicked required when maneuvering through theprogram:

In the text of the lab manual, main menu items will be highlighted inBold, Italicized, and Underlined.

Shown below are the main menu items, as they will be highlightedin the text of the lab manual.FileControllerBoiler InitializeTrend RecorderEquipment SwitchesWindowHelp

Sub menu items are those items that appear after a main menuitem has been clicked on. In the text of the lab manual, the submenu items will be highlighted in Bold and Italicized only. Shownbelow are examples of highlighted sub menu items that appearwhen main menu item File has been clicked.

File Boiler VariablesExit

Where mouse clicks are required that are not menu or sub menuitems, the text will be highlighted in Bold only.

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The screen capture below will be used to illustrate the convention used inthe highlighting text in the lab manual:

Discussion SectionThis section will comment or explain the observations made atvarious steps in the procedures.

Menu ItemTrend Recorder

Sub-Menu ItemSteam Pressure

Not a Menu orSub-Menu ItemPause

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1 Experiment - Boiler Start-Up

1.1 Objective:

• Understand the equipment and logic associated with burner management• Proceed through a semiautomatic burner management startup from a cold

boiler state.• Understand those procedures required for safely igniting both the main and

pilot valves.

In this experiment you will be required to ignite the pilot and main burner underthe supervision of the Burner Management System (BMS). When successfully lit,the boiler steam pressure and steam flow will be slowly increased to operatingconditions.

1.1.1 Burner Management Description

The Burner Management system is shown below:

In the main gas line and pilot gas lines are double block and vent valves. Whenthe boiler is shutdown, the block valves are closed and the vent valves are open.Limit switches and their indicator lights show the state of the valves. In the caseof the block valves, the upper indicator light turning green indicates the valve isopen, while the lower indicator light turning green indicates the valve is closed.For the vent valves, the left most indicator light turning green indicates the valveis closed, while the right most indicator light turning green indicates the valve isopen. In addition, the body of an open valve turns light blue while a closed valvebody is white.

Valve shownopen

Valve shownclosed

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When the Main Gas pushbutton is depressed after the pilot has beensuccessfully lit, Main Vent Valve 2 closes, but Main Block Valve 3 remains shut.Main Block Valve 1 can only be latched open in the field after the burnermanagement logic starts ignition of the main burner.

When Main Block Valve 1 is latched open after the Main Gas pushbutton hasbeen depressed, the action will open Main Block Valve 3 (Main Vent Valve 2 wasclosed when the Main Gas pushbutton was depressed).

To simulate the required field action, a command button with the caption "OpenValve" is located next to the valve. Clicking on this command button will simulatelatching the valve open in the field. This pushbutton can be used to close theMain Block Valve 1 shutting off the gas to the main burner.

The fan can be started or stopped from the burner management system windowby clicking the red Fan start pushbutton. In addition, it can be started or stoppedfrom the Boiler Controls and Monitoring window.

1.2 Procedure:1. From your Windows operating system, start the Win Boiler Sim program.

2. The program starts with the boiler in the cold shutdown state. The Boiler

Indicatescontroller inManual

Fuel Gascontrolleroutput at 10%,Low Fire State

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Controls and Monitoring window is displayed on the screen as shown below:

Notice all controllers are in manual. Notice the fuel gas controller is in the low firestate (fuel gas controller output - solid black bar - is at 10 %). The feedwaterpump and the forced draft (FD) fan are off. The pilot and main gas shutdownvalves are closed - the vent valve on the pilot and main gas are open (the blockand vent valves can be observed from the Burner Management System Window(click Window, click Burner Management System). Leave the BurnerManagement System Window open for the next step. You may have to move thewindow so that it doesn't hide the Boiler Controls and Monitoring window. Thiscan be done by left clicking the mouse with the cursor of the mouse somewherewithin the window (don't click on any switches) and dragging the window. Holddown the left click button when dragging.

3. Load the Boiler:In this step, you will be setting the load on the boiler to about 10%. This is donefrom the Boiler Controls and Monitoring Window by clicking Window and thenclicking Steam Demand Settings . Click the Base Demand scroll bar until thedemand has been set to 10%.

In this step, you have essentially created a load to discharge boiler steam flowafter the boiler has begun producing steam. Close the Variable DemandGenerator window by clicking on the Close command button in the lower righthand corner of the Variable Demand Generator window.

4. Select Trend Variables:In this step you will select those variables to be plotted on the trend recorder.From the Boiler Controls and Monitoring Window, click Trend Recorder. ClickSteam Pressure. Repeat and select by clicking Steam Flow, Drum Level,Feedwater Flow, Air Flow, Fuel Flow, and Steam Demand.

5. Set the drum level to Single Element:In this step you will select single element drum level control. At low loads this isan effective way to control the drum level. Essentially the feedwater flow control

Click here toraise demand1% for eachclick

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valve directly takes the output from the drum level controller. Set the level controlsystem to one element control by clicking Equipment Switches, clicking 3Element 1 Element Drum Level, and then clicking 1 Element Control.

6. Start the feedwater Pump:In this step you will start the feedwater pump. Because the feedwater controlvalve is closed, starting the pump will not result in any feedwater flow into thedrum. Some minimum flow will recirculate from pump discharge back to pumpsuction.

From the Boiler Controls and Monitoring Window, start the feedwater pumpby clicking Equipment Switches, clicking Feedwater Pump and thenclicking Start.

7. Set the drum level to Approximately 50%.In this step you will open the feedwater control valve using the manualadjustment on the drum level controller output. The feedwater controlleroutput is not used because the drum control is in single element mode, withthe output of the drum level controller directly adjusting the feedwater controlvalve. When the drum level begins to rise, you will reclose the feedwatervalve, setting the drum level to between approximately 50% and 70%. You

Drum levelmanualcontrolleroutput adjust.Click toincrease 1%per click

Click toincrease drumlevel set point1% per click

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will also set the drum level controller set point to 50%. The drum levelcontroller remains in manual mode.

The method to set the drum level is as follows:From the Boiler Controls and Monitoring Window, click on the drum levelcontroller output scroll bar (right arrow). This will cause the feedwater flow toincrease. Continuously clicking the right scroll bar will raise the feedwater flow(alternately drag the scroll bar to the right) to increase the drum levelcontroller output. Since steam is not being produced the level control valvemust be shut to stop the drum from being flooded. This is done by setting thedrum level controller output back to 0. Do this by dragging the scroll bar allthe way to the left until the drum level controller output is 0. If you need toreduce the drum level, this can be done by opening the boiler blowdownvalve. This is done as follows: from the Boiler Controls and MonitoringWindow, open the blowdown valve by clicking Equipment Switches, clickingBlowdown Valve and then clicking Open Blowdown Valve. The level willcontinuously drop. The boiler blowdown valve must be reclosed by doing thefollowing: from the Boiler Controls and Monitoring Window, open theblowdown valve by clicking Equipment Switches, clicking Blowdown Valveand then clicking Close Blowdown Valve.

8. Set the drum level controller set point to 50 % by clicking on the vertical arrow(upper) to the left of the "M" manual / auto command button of the drum levelcontroller.

9. In addition to observing the operation of the Boiler from the Boiler Controlsand Monitoring window, the operation of the boiler can be observed byviewing the Boiler Dynamic Graphic Window. From the Boiler Controls andMonitoring window, click Window, and then click Boiler Dynamic Graphic.Click the Close button in the lower righthand corner to close the window.

10. Start Forced Draft (FD) fan.

In this step you will start the forced draft fan that supplies combustion air tothe boiler. When the fan is first started, no air is supplied because thecombustion air damper is closed.

From the Boiler Controls and Monitoring Window, start the fan by clickingEquipment Switches, clicking Fan and then clicking Start. Note that it ispossible to start the fan from the Burner Management System window aswell.

11. Establish Adequate Combustion Air.

Air flow will have to be established to the boiler. The air must be set to 70% orgreater in preparation for the purge step that is part of the liteoff sequence.

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From the Boiler Controls and Monitoring Window, click on the air flowcontroller output scroll bar right arrow. This will cause the air flow to increase.Continuously clicking the right scroll bar will raise the air flow (alternatively,drag the scroll bar to the right to open the combustion air damper). Set thedamper to 67% open to provide about 70% of maximum air flow (arequirement to satisfy the startup permissives of the Burner ManagementSystem).

12. Burner Management Status:

In this step you will observe the status of the burner management system. Ifthe Burner Management System window is closed, open from the BoilerControls and Monitoring window by clicking Window followed by BurnerManagement System.

Click toincrease airflow controlleroutput 1% perclick to 67%

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The states of the lamps and switches must be as follows:

Combustion Air Adequate Light Green/steadyCombustion Air Valve Open Light Green/steadyFuel Gas Low Fire Light Green/steadyBurner Ready Light Off (Grey)Fan Light Green/steadyPurge Light Off (Grey)Ignition Light Off (Grey)Main Gas Light Off (Grey)Fan Pushbutton On (Depressed)

The Enable switch should be OFF (disabling the alarms and shutdowns).Burner ignition cannot be started unless the lamp status indicatingpermissives have been met, as shown in the list on the previous page..

Note:

The "Combustion Air Adequate" may take a few seconds to indicate thepermissive has been met. This is due to the short lag in air flow reaching itsmaximum value after the combustion air damper has been fully opened. If thepermissives haven't been met repeat steps 3 to 12.

The valves should be in the following state:

Main Block Valve 1 Closed WhiteMain Vent Valve 2 Open Light Blue (Cyan)Main Block Valve 3 Closed WhitePilot Block Valve 1 Closed WhitePilot Vent Valve 2 Open Light Blue (Cyan)Pilot Block Valve 3 Closed White

13. From Burner Management System Window, click the Enable switch.The Main "Burner Ready" light will turn green/steady, The purge, ignition, andmain gas pushbuttons become visible allowing the burner ignition to proceed(any active shutdowns will prevent Burner Ready lamp from turning togreen/steady and the ignition from proceeding (purge, ignition, and main gaspushbuttons remain invisible). The alarms and shutdowns will be enabled (tocheck this, from the Boiler Controls and Monitoring window click Windowfollowed by Alarm and Shutdown Settings . Close the Alarm and Shutdownwindow by clicking Close in the lower right hand corner of the window).

14. In this step the boiler will be purged of any pockets of fuel gas that couldcreate a safety hazard. Essentially, air passes through the boiler forapproximately 10 seconds, enough time to adequately clear any pockets ofremaining fuel gas.

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15. From Burner Management System Window, click the red Purge pushbutton.The green "Purge" lamp will flash for 10 seconds. After 10 seconds, the lampwill stay green/steady indicating the Boiler has been purged and the ignitionmay proceed to the pilot ignition.

16. In this step the pilot burner will be ignited. The pilot and main burners of thisboiler have been supplied with a flame scanner that is wired into the burnermanagement system logic. The scanner detects proof of, and loss of flame. Aloss of flame alarm and shutdown occurs when both the pilot and main flameare lost.

The pilot in this boiler will be blown out causing a loss of flame alarm andshutdown if the main flame is not lit and the air flow is greater than 40% ofmaximum. In this step, the air flow must be set to less than 40%.

From the Boiler Controls and Monitoring Window, click on the air flowcontroller output scroll bar left arrow. This will cause the air flow to decrease.Continuously clicking the left scroll bar will lower the air flow (alternatively,drag the scroll bar to the left to close the combustion air damper). Set thedamper to 40% open to provide about 32% of maximum air flow. If the air flowis not reduced, then when igniting the pilot you will get a loss of flameshutdown at the end of the 10 second ignition period, requiring you to startthe liteoff sequence again.

From Burner Management System window, click the red Ignition pushbutton(clicking on the Ignition pushbutton before purge is complete, will not allowpilot ignition to proceed - the "Ignition" light will remain OFF - grey lamp, andignition transformer OFF. The ignition will automatically start after "PurgeComplete"). The 2 pilot block valves will open and the pilot vent valve willclose. The pilot must light before 10 seconds of ignition is complete and mustremain on for 2 seconds as detected by flame scanner. During the time thatthe ignition is on and before the pilot has been proven for 2 seconds, thegreen ignition light will flash. After the pilot light has been proven for 2seconds, the green flashing light will turn to steady green. When the pilot hasbeen proven the ignition of the main burner can proceed.

17. In this step the main burner will be ignited. From Burner Management SystemWindow, click the red Main Gas pushbutton.

With a proven pilot (step 16 above), the Main Block Valve 3 remains closedand Main Vent Valve 2 will close. The solenoid to Main Block Valve 1 will alsoenergize; however, in order to open Main Block Valve 1, an operator mustmanually unlatch the valve open. Main Block Valve 3 does not require anoperator to manually unlatch the valve - only Main Block Valve 1 requires this.The "Main Gas" lamp flashes green. The operator must unlatch and openMain Block Valve 1 before 10 seconds expires after clicking Main Gaspushbutton. On Win Boiler Sim, the unlatch is simulated by clicking on the

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Open Valve command button above Main Block Valve 1. When Main BlockValve 1 opens, Main Block Valve 3 will then open. The main burner requires 2seconds to be proven. When the burner is proven, the flashing green "MainGas" light stops flashing and remains steady green.

Note that clicking on the Main Gas pushbutton before the pilot is proven, willnot allow burner ignition to proceed. The "Main Gas" light will remain OFF -grey lamp, while the 2 Main Block Valves remain closed and Main Vent Valveopen. Only after the pilot is proven will the main burner ignition automaticallystart.

18. Return to the Boiler Controls and Monitoring window. You may or may notwant to close the Burner Management System window.

19. From the Boiler Controls and Monitoring window, click on the Steam PressureController set point button and raise the steam pressure set point to about 5%by clicking on the vertical arrow (upper) to the left of the "M" manual / autocommand button of the Steam Pressure Controller .

20. Click on the Auto/Manual pushbuttons starting with the feedwater controller,followed by the fuel gas controller, air flow controller, drum level controller,and finally steam pressure controller. The low combustion air alarm will be

Click to increasesteam pressurecontroller setpoint 1% perclick

Click to setcontrollers toautomatic

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triggered and require acknowledging. This is done by clicking the AlarmAcknowledge pushbutton in the lower left corner of the Alarm Acknowledgewindow. Close the window by clicking Close in the lower right hand corner ofthe window.

21. When the boiler variables are approximately at steady state (not changing),increase the steam pressure by another 5%. Continue this process until thesteam pressure is 50%.

22. If the Variable Demand Generator (steam demand is set from this window) isnot open then from the Boiler Controls and Monitoring window, click Windowfollowed by Steam Demand Settings. Increase the Base Demand from 10 to15 % (as in step 3). When the Boiler variables are at steady state, increasethe demand by another 5 %. Continue this process until the demand is 50%.

23. In this step you will switch the drum level control to 3 element mode. In thismode the output of the drum level controller is summed with the steam flowsignal and a bias. This combined signal becomes the set point for thefeedwater controller. The output from the feedwater controller is connected tothe feedwater control valve.

From the Boiler Controls and Monitoring window, click on the EquipmentSwitches followed by 3 Element 1 Element Level, followed by 3 ElementControl.

This completes experiment 1. The Boiler is at a steady state operating conditionof 50% steam flow and 50% steam pressure.

1.3 DiscussionThe National Fire Protection Association has standards for Burner Managementsystems. The NFPA 85 Chapter 2 Single Burner Boilers has been used as thebasis for Win Boiler Sim's Burner Management system.

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With the boiler at 50% steam pressure and 50% steam flow, the Boiler Controlsand Monitoring window should look like that below:

The previously described start up procedure is for educational purposesonly. There are many variations of startup procedures and the user mustfollow the regulations for his / her jurisdiction when starting up a boiler.

2 Experiment - Boiler Drum Level Control - 3 Element Control / 1 ElementControl2.1 Objective:• Understand the differences between three element and single element drum

level control.• Understand the effects on drum level of changes in steam demand.

In the first experiment on burner management systems and start up, you wentthrough a complete start up from a cold boiler state to a steady state operating

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point. This took a significant amount of time to complete. In this experiment, youwill use a feature of Win Boiler Sim that allows you to set or initialize the boiler toan immediate steady state operating point. This will enable you to quickly see theeffect of changing various boiler control parameters and disturbances withouthaving you to go through a complete start up.

2.2.1 Procedure - 3 Element Drum Level Control:1. From your Windows operating system, start the Win Boiler Sim program.

The program starts with the boiler in the cold shutdown state. The BoilerControls and Monitoring window is displayed on the screen as shown onpage 10.

2. From the Boiler Controls and Monitoring window, Click Window.

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3. Click Boiler Dynamics. Continuously click the right hand arrow of the SelectBoiler Dynamics Scroll Bar and select the set of boiler dynamics shownbelow.

4. From the Boiler Dynamics window, click File5. Click Accept Dynamics and Return6. Click Yes to close the Boiler Dynamics window.

The Boiler Dynamics window allows the boiler to behave with differentresponses. In effect, the response can be shaped to create different sizes ofboilers, for example a large slow boiler or a small fast boiler.

The previous steps in this procedure have selected a set of dynamics that willchange how the boiler drum responds to changes in feedwater flow andsteam demand. The parameters have been chosen so that the drum level willnot display any shrink or swell effects.

The following step will initialize the boiler.

7. From the Boiler Controls and Monitoring window, Click Boiler Initialize, clickSelect Steady State Operating Conditions.

Click File

Click to selectthe set ofdynamicsshown

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8. Continuously click the right hand arrow of Select Boiler Initialize Set andfind the set of operating conditions where the comment is "50% OperatingPoint (50% steam flow, demand, and pressure)."

Click to selectoperatingconditions

Click File

Click on Boiler Initialize

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9. On the Boiler Initialization window menu Click File10. Click Accept Initial Conditions and Return11. Click Yes

The above steps have set the Boiler to a steady state operating point of 50%steam pressure, steam demand, steam flow, etc.

The following steps select the variables to be plotted on the trend recorder.

12. From the Boiler Controls and Monitoring window, click Trend Recorder13. Click Steam Flow14. Repeat steps 12 and 13 to select , Drum Level, Feedwater Flow, and Steam

Demand

In the following steps you will create a step increase in steam demand

15. On the Boiler Controls and Monitoring window, click the trend recorder Pausecommand button at the bottom of the screen underneath the trend recorder.This will halt the simulation and hold all variables at their current value (thePause button will have red text saying "Paused".

16. From the Boiler Controls and Monitoring window click Window followed bySteam Demand Settings

17. Continuously the Click top of Base Demand Scroll bar until Base Demand isset to 60% (an increase of 10%). This step increase in base demand will beapplied when the simulation is unpaused.

18. Click Close to close the Variable Demand Generator.

19. From the Boiler Controls and Monitoring window click Paused, starting thesimulation.

The response should look similar to that on the next page:

Click toincrease BaseDemand to60%

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Drum Level Transient on Steam Demand Step Change - 3 Element ControlNo shrink swell effects enabled. Demand 50% to 60% step change

Notice that shortly after the change in demand corresponding to an increasedload such as that of a steam turbine, steam flow (red) begins to increase followedby the feedwater flow (blue). The feedwater flow reacts relatively quickly due tofeedforward action of the steam flow on feedwater flow. The minimum drum level(green) transient is relatively small (minimum drum level about 38% or 12 %transient)

2.2.2 Procedure - 1 Element Drum Level Control:

The experiment will be repeated but with the drum level controller switched tosingle element (see figure below). No change will be made to the controllertuning constants.

1. Repeat steps 1. through 18. In section 2.2.1 - the 3 element controlprocedure. After step 18, the simulation should be paused.

Steam Flow

Feedwater FlowDrum Level

Steam Demand

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2. Before restarting the paused simulation switch to 1 element drum level controlas follows:

3. From the Boiler Controls and Monitoring window, click Equipment followedby 3 element / 1 element drum level followed by 1 element control

4. From the Boiler Controls and Monitoring window click Paused, restarting thesimulation.

The response should look similar to that below:

Drum Level Transient on Steam Demand Step Change - 1 Element Control, Noshrink swell effects enabled, Demand 50 to 60% step change

Notice that the feedwater (blue) increase occurs after the drop in level due to theaction of the level controller output rather than the action of feedforward onsteam flow (red). The minimum drum level transient (approximate minimum levelof 32%) is significantly greater than (about 18% vs 12% ) for 3 element control.

3 Element/ 1 Element Comparison of Responses

Steam Flow

Feedwater Flow

Drum Level

Steam Demand

Steam Flow

Feedwater Flow

Drum Level

Steam Demand

Steam Flow


Steam Demand

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2.3 DiscussionOne element control is not as effective in controlling drum level as three elementcontrol when large changes in steam demand occur. With 3 element controlsteam flow changes adjust the feedwater flow to the drum providing tighter(smaller deviation from set point) drum level control.

3. Experiment - Inverse Response of Drum Level3.1 Objectives:• To determine the effect of a step change in feedwater flow, with no shrink /

swell effects enabled.

In this experiment the steam flow and demand will be initialized to 50% and thefeedwater controller output will be put into manual mode. This will allow the userto observe the effects on drum level due to a step change in feedwater flow.

The first time the step change is made, the shrink swell effects will be disabled.The experiment will be repeated after shrink swell effect on feedwater flow hasbeen enabled. The user will be able to observe the shrink effect on the drumlevel of quenching the drum level with relatively cooler feedwater.

3.2.1 Procedure - Open Loop Drum Level Response - Feedwater Shrink /Swell Effects Disabled

1. From the Boiler Controls and Monitoring window, Click Window2. Click Boiler Dynamics. Continuously click the right hand arrow of the SelectBoiler Dynamics Scroll Bar and select the set of boiler dynamics shown below(this is the same set of dynamics as for the previous part of the experiment).

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6. From the Boiler Controls and Monitoring window click Boiler Initialize, clickSteady State Operating Conditions.

7. Continuously click the right hand arrow of Select Boiler Initialize Set andfind the set of operating conditions where the comment is "50% OperatingPoint (50% steam flow, demand, and pressure)."

8. From the Boiler Initialization window, click File9. Click Accept Initial Conditions and Return10. Click Yes

11. From the Boiler Controls and Monitoring window click Trend Recorder.12. Click Drum Level13. Repeat the previous two steps and select Feedwater Flow, Feedwater

Controller Output for the trend recorder

14. Click on A, the feedwater controller Auto / Manual command button. This willswitch the controller to manual allowing you to manually step increase thefeedwater flow.

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15. Left Click and drag to the right the Feedwater Horizontal Scroll Bar. Themanual controller output will step change the feedwater.

The plot should look like that on the next page:

FeedwatercontrollerAuto/Manualcommandbutton

FeedwaterHorizontalScroll Bar

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Step Change to Feedwater Control Valve, (feedwater controller in Manual)Boiler demand and steam flow constant at 50%. No Inverse response effect ofdrum level when feedwater increasing.

This is the response of the drum level for a step increase in feedwater flow. Thelevel control system is open looped. That is, there is no feedback to correct thedrum level. The drum will eventually fill up, the "drum high level" trip willshutdown the boiler.

3.2.2 Procedure - Open Loop Drum Level Response - Feedwater Shrink /Swell Effects Enabled

In this experiment, the shrink / swell effects of feedwater will be enabled.The effect of an increase in feedwater flow will be examined on boiler drum level.This is a real phenomenon, that makes drum level more difficult to control. It iscounterintuitive (opposite of "common sense"), because normally increasing themass flow of water into a vessel should increase the level.

1. From the Boiler Controls and Monitoring window, click WindowClick Boiler Dynamics2. Continuously click on the right hand side Select Boiler Dynamics Scroll Bar

and select the boiler dynamics shown on the following page.

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3. Repeat steps 3. to 15. in section 3.2.1

The plot should look like that below:

Step Change to Feedwater Control Valve, (feedwater controller in Manual)Boiler demand and steam flow constant at 50%

The increase in feedwater flow results in a transient decrease in drum level dueto the quenching effect of the relatively cool feedwater flow followed by a rise indrum level.3.3 DiscussionInverse response of drum level on changes to feedwater flow, occurs when therelatively cool feedwater has a quenching effect on the steam and water mixturein the drum. This quenching results in a temporary drop in drum level when thefeedwater is increased. This results in a degradation of drum level control. If thedrum level controller is tuned too tightly it will respond to further increasefeedwater flow when this temporary drop in level occurs.

Continuouslyclick to select theboiler dynamicsshown

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4 Experiment - 3 Element Drum Level Control - Feedwater Shrink / SwellEnabled4.1 Objective:• To determine the effects on drum level control when feedwater shrink swell

effects are enabled

In this experiment, the drum level will be operated closed loop in 3 elementmode. The boiler will be initialized to steady state. A steam demand stepincrease will be created. The resultant boiler level transient will be compared tothe transient when the drum shrink swell effect disabled - Experiment 2, section2.2.1.

4.2 Procedure1. From your Windows operating system, start the Win Boiler Sim program.

The program starts with the boiler in the cold shutdown state. The BoilerControls and Monitoring window is displayed on the screen as shown onpage 6.


3. Click Boiler Dynamics. Continuously click the right hand arrow of the SelectBoiler Dynamics Scroll Bar and select the set of boiler dynamics shownbelow.

Continuouslyclick to select theboiler dynamicsshown

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4. Repeat steps 4 to 19 described in section 2.2.1

The response should look similar to that below:

Drum Level Transient on Steam Demand Step Change - 3 Element ControlFeedwater shrink / swell effects enabled

Demand 50% to 60% step change

4.3 DiscussionNotice that shortly after the change in demand corresponding to an increasedload such as that of a steam turbine, steam flow begins to increase followed bythe feedwater flow. The feedwater flow reacts relatively quickly due tofeedforward action of the steam flow on feedwater flow. The minimum drum leveltransient is larger than that which occurred with feedwater shrink / swell disabled,shown in section 2.2.1, (minimum drum level about 33% or 17 % transient,compared with 38% and 12% for transient with shrink / swell disabled). Theshrink / swell effect makes control of the drum level more difficult.

Inverse Response Disabled /Enabled Comparison

Steam Demand

Steam FlowFeedwater Flow

Drum Level

Inverse Response Disabled Inverse Response Enabled

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5 Experiment - Drum Level Shrink Swell Due to Steam Flow Changes5.1 Objective:• To determine the effects on drum level control when steam flow shrink swell

effects are enabled

In this part of the experiment, the level control system will be set to 1 elementand placed in manual mode (no feedback from the controller to compensate thechange in level). In the first part of the experiment, the shrink swell factor onsteam flow will be set to 0.0 to disable the effect. The steam demand will then beincreased from 50 to 60%. In the second part of the experiment, the shrink / swellfactor on steam flow will be enabled. Again, the steam demand will then beincreased from 50 to 60%. The drum level responses will then be compared.

5.1.2 Procedure -Drum Level Steam Flow Shrink / Swell - Disabled1. From your Windows operating system, start the Win Boiler Sim program.

The program starts with the boiler in the cold shutdown state. The BoilerControls and Monitoring window is displayed on the screen as shown below:


Click to selectBoiler Initialize

Click to selectTrend Recordervariables

Click to selectEquipmentSwitches

Drum LevelAuto/ManualCommandButton

Click to selectWindow

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3. Click Boiler Dynamics. Continuously click the right hand arrow of the SelectBoiler Dynamics Scroll Bar and select the set of boiler dynamics shownbelow. This set of dynamics will disable shrink / swell effects.


7. Click Boiler Initialize , click Select Steady State Operating Conditions.8. Click Select Boiler Initialize Set and find the set of operating conditions

where the comment is 50% Operating Point (50% steam flow, demand, andpressure).

9. From the Boiler Initialization window, click File10. Click Accept Initial Conditions and Return11. Click Yes12. From the Boiler Controls and Monitoring window click Trend Recorder.13. Click Drum Level14. Repeat the previous two steps and select Steam Flow, Steam Demand for

the trend recorder15. Click Equipment Switches16. Click 3 Element / 1 Element Drum Level17. Click 1 Element Control

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18. Click the drum Level controller Auto / Manual command button. This willswitch the controller to manual preventing the feedwater from increasing,thereby isolating the effect of steam flow on drum level.

19. Pause the simulation20. Click Window21. Click Steam Demand Settings and increase the Base Demand settings to

60%22. Click Close to close the Variable Demand Generator window.23. Click Unpause to restart the simulation and observe the transient. It should

look as follows:

5.1.3 DiscussionNotice that the drum level decreases with increasing steam flow. This is to beexpected when the steam flow and feedwater flow is not balanced, with thesteam flow greater than the feedwater flow.

5.2.2 Procedure -Drum Level Steam Flow Shrink / Swell - Enabled1. From your Windows operating system, start the Win Boiler Sim program.

The program starts with the boiler in the cold shutdown state. The Boiler Controlsand Monitoring window is displayed on the screen as shown on the next page:


3. Click Boiler Dynamics. Continuously click the right hand arrow of the SelectBoiler Dynamics Scroll Bar and select the set of boiler dynamics shown onthe next page. This set of dynamics will enable steam flow shrink / swelleffects.

32

4. Click to selectBoiler Initialize



Drum LevelAuto/ManualCommandButton

Click to selectWindow

33

4. Repeat steps 4 to 23 from Procedure section 5.1.2

After step 23 has been completed the response should look like that below.

5.2.3 DiscussionIn the plot, the drum level transiently rises a few percent after the steam flowbegins increasing. This is a counterintuitive result. No additional feedwater isentering the drum, yet the drum level transiently rises.

The reason for transient rise is due to the increased fuel firing and resultantincrease in boiling. This results in a decrease in water/steam density and amomentary rise in drum level. With an imbalance between feedwater flow andsteam flow, the drum level eventually falls.

The shrink / swell effects have been analyzed in isolation. In fact the steam / flowshrink swell and feedwater shrink swell are somewhat self-compensating.

Inverse Response Disabled /Enabled Side By Side Comparison

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6 Experiment - Boiler Air Fuel Control System6.1 Objective:• To understand the air / fuel control system and how cross limiting protects a

boiler from producing a fuel rich mixture• To observe the effects of excess air on boiler efficiency

In the first part of the lab, the action of the cross-limiting logic will bedemonstrated. The boiler will be initialized to steady state. The fuel flow controllerwill be put into manual and the controller output will be increased in a stepwisemanner manually.

6.1.2 Procedure - Cross Limiting Logic - Step Change in Fuel Flow1. From your Windows operating system, start the Win Boiler Sim program.

The program starts with the boiler in the cold shutdown state. The Boiler Controlsand Monitoring window is displayed on the screen as shown below:

2. From the Boiler Controls and Monitoring window, Click Window. To view the




Click to selectWindowfollowed by AirFuel ControlFuel Flow

Controller AutoManualCommandButton

35

air / fuel control window when doing experiment 3, click Air Fuel Control.

3. From the Boiler Controls and Monitoring window, click Boiler Initialize , clickSelect Steady State Operating Conditions.

4. Click Select Boiler Initialize Set and find the set of operating conditionswhere the comment is 50% Operating Point (50% steam flow, demand, andpressure).

5. From the Boiler Initialization window, click File6. Click Accept Initial Conditions and Return7. Click Yes8. From the Boiler Controls and Monitoring window click Trend Recorder.9. Click Air Flow10. Repeat the previous two steps and select Fuel Flow, Fuel Flow Controller

Out11. Click on the Auto/Manual command button (A) for the fuel gas flow controller

putting the controller into Manual12. Click and drag to the right the scroll bar of the fuel flow controller, creating a

step increase the fuel flow controller output.

Air Fuel Control System

36

The response should resemble that shown below:

6.1.3 DiscussionAs the fuel flow increases, the air flow controller set point also increases. Thishappens because the air flow controller set point receives the output from thehigh selector FY2A. Since the firing rate (one of the inputs to the high selector)remains constant, the increasing fuel flow gets selected causing the set point ofthe air flow controller to increase. This will ensure that fuel flow increases cannotoccur without an accompanying increase in air flow. Leaving the boiler in thisstate will result in a shutdown on high steam pressure.

6.2.2 Procedure - Cross Limiting Logic - Step Change in Air FlowIn the second part of the lab, the air flow controller will be put into manual and thecontroller output will be increased in a stepwise manner manually.

1. Repeat steps 1 to 8 in Procedure section 6.1.22. Click Air Flow.3. Repeat the previous two steps and select Fuel Flow, Air Flow Controller

Out4. Click on the Auto/Manual command button (A) for the air flow controller

putting the controller into Manual5. Click and drag to the right, the scroll bar of the air flow controller, creating a

step increase the air flow controller output.

The response should resemble that shown below:

6.2.3 DiscussionThe increase in air flow results in no accompanying rise in fuel flow. Air flow isallowed to lead fuel flow. The fuel flow controller set point is set by the outputfrom the low selector FY2B. One of the inputs to FY2B is from the air flowmeasurement while the other is from the firing rate. Since the input from air flowrises while the firing rate remains constant, the low selector output remainsconstant. Fuel flow set point eventually begins to increase due to the drop in

Fuel FlowControllerOutput Air Flow

Air Flow

Air FlowControllerOutput

Fuel Flow

Air Flow

37

steam flow caused by the additional air flow. The drop in steam flow results in adrop in pressure with a subsequent rise in firing rate and ultimately fuel flow.

6.3.2 Procedure - Cross Limiting Logic - All Controllers in Automatic - StepIncrease in Steam DemandIn the next part of the lab all controllers will be in automatic. A step change insteam demand will occur. The fuel flow, air flow, and steam demand will betrended1. Repeat steps 1 to 7 from Procedure section 6.1.22. From the Boiler Controls and Monitoring window click Trend Recorder.3. Click Air Flow4. Repeat the previous two steps and select Fuel Flow, Steam Demand

In the following steps you will create a step increase in steam demand



7. Continuously the Click top of Base Demand Scroll bar until Base Demand isset to 60% (an increase of 10%). This step increase in base demand will beapplied when the simulation is unpaused.



The response should look similar to that on the next page:

Click toincrease BaseDemand to60%

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6.3.3 DiscussionWith an increase in steam demand, air flow leads followed by fuel flow. This willensure adequate combustion air.

6.4.2 Procedure - Cross Limiting Logic - All Controllers in Automatic - StepDecrease in Steam DemandIn the next part of the lab you will observe the air flow, fuel flow, and steamdemand when a step decrease in demand occurs. All controllers will be inautomatic as for the previous part.

1. Repeat steps 1 to 7 from Procedure section 6.1.22. From the Boiler Controls and Monitoring window click Trend Recorder.3. Click Air Flow4. Repeat the previous two steps and select Fuel Flow, Steam Demand

In the following steps you will create a step decrease in steam demand



7. Continuously the Click bottom of Base Demand Scroll bar until Base Demandis set to 40% (a decrease of 10%). This step decrease in base demand will beapplied when the simulation is unpaused.


Steam Demand Air Flow

Fuel Flow

Click todecrease BaseDemand to40%

40

39


The response should look similar to that shown below:

6.4.3 DiscussionWith a decrease in steam demand, fuel flow leads (is decreased) followed by adecrease in air flow. This will ensure adequate combustion air.

6.5.2 Procedure - Changing the Air / Fuel RatioIn the next part of the lab, the air / fuel ratio will be increased from 1.0 to 1.1. Thefuel flow, air flow, and boiler efficiency will be plotted. In addition the processvariables window will be opened and the values of the fuel flow, air flow, andefficiency will be noted before and after the air / fuel ratio has been changed.

1. Repeat steps 1 to 7 from Procedure section 6.1.22. From the Boiler Controls and Monitoring window click Trend Recorder.3. Click Air Flow4. Repeat the previous two steps and select Fuel Flow, Boiler Efficiency5. From the Boiler Controls and Monitoring window Click Window6. Click Boiler Process Variables

The window should show the following values:

Steam Demand

Air Flow

Fuel Flow

40

7. Click From the Boiler Controls and Monitoring window Controller8. Click Air Flow9. Click the right side of the Air / Fuel Ratio increase/decrease button and set

the ratio to 1.1

10. Click Close to close the Air Flow Controller Tuning Window

The transient behaviour of the air flow, fuel flow, and boiler efficiency should looklike that shown on the next page.

Notice the rise in the air flow followed by the rise in fuel flow. The fuel flow risesas a result of the drop of steam flow and steam pressure. In the steady state thefuel flow has increased and the boiler efficiency decreased.

11. From the Boiler Controls and Monitoring window Click Window12. Click Boiler Process Variables

The window should show the following value:

Click to increaseAir / Fuel Ratio

Boiler Efficiency

Fuel Flow Air Flow

41

6.5.3 DiscussionNotice from the Boiler Process Data Window that:1) the air flow has risen from 54738 to 61683 lbs/hr2) the fuel flow has increased from 65.68 to 67.29 MMBTU/HR3) the boiler efficiency has decreased from 91.3 to 89.2 %4) the excess Oxygen has increased from 3.1 to 5.4 %

When the air/fuel ratio was increased, the excess oxygen increased. Because ofthe extra air passing through the boiler there is a transient cooling effect resulting ina drop in steam flow. The resulting drop in pressure is sensed by the masterpressure controller. This results in an increase in boiler firing rate. This increasedfiring for the same steam demand results in a drop in boiler efficiency.

If the air/fuel ratio had been decreased, the opposite effect would have occurred. Ofcourse the boiler must never be operated with less air than is required for completecombustion because of the possible build up of pockets of fuel rich mixture in thefirebox where it could present an explosion or fire hazard. In addition theseunburned hydrocarbons depositing on the inner surface of some of the boiler'scomponents such as an air preheater could also eventually present a fire hazard.

While there is an economic penalty when too much excess oxygen is supplied to aboiler, there is also an economic penalty when unburned fuel is released up thestack. In fact most industrial boilers operate at excess oxygen levels of at least 1.5%. This is to compensate for the fact that in the burner, mixing is imperfect and assuch, the excess oxygen must be held at some value above the value required forcomplete combustion (sometimes referred to as stoichiometric).

On many boilers the excess oxygen set point is programmed as a function of boilerload. i.e. At higher loads the excess oxygen can be reduced due to the bettermixing at the burners. Frequently boiler control systems make use of a carbonmonoxide measurement and controller to constrain the excess oxygen controller'soutput from decreasing the air by too much.

7 Experiment - Changing the Dynamics of the Boiler7.1 Objective:• Observe the effects of changing the dynamics (response) of a boiler.• Observe the effects of retuning the controllers to accommodate "faster" and

"slower" boilers.This exercise will be implemented by initializing the boiler to a predefined steadystate operating point. The boiler loading will then be changed by altering thesteam demand in a stepwise manner. The response will be plotted. Thedynamics of the boiler will then be changed along with the controlle r tuningconstants. The steam demand will be will be changed as for the previous set ofboiler dynamics and the plotted results will then be compared.

42

7.1.2 Procedure:1. From your Windows operating system, start the Win Boiler Sim program.

The program starts with the boiler in the cold shutdown state. The Boiler Controlsand Monitoring window is displayed on the screen as shown on the next page:


3. From the Boiler Controls and Monitoring window, click Boiler Initialize , clickSelect Steady State Operating Conditions.

4. Click Select Boiler Initialize Set and find the set of operating conditionswhere the comment is 50% Operating Point (50% steam flow, demand, andpressure).

5. From the Boiler Initialization window, click File6. Click Accept Initial Conditions and Return7. Click Yes8. From the Boiler Controls and Monitoring window click Trend Recorder.


Click to selectTrend Recordervariables Click to select

Window

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9. Click Steam Pressure10. Repeat the previous 2 steps for Steam Flow, Drum Level, Feedwater Flow,

Air Flow, Fuel Flow, Steam Demand11. On the Boiler Controls and Monitoring window, click the trend recorder Pause

command button at the bottom of the screen underneath the trend recorder.This will halt the simulation and hold all variables at their current value (thePause button will have red text saying "Paused".

12. From the Boiler Controls and Monitoring window, click Window13. Click Steam Demand Settings and increase the Base Demand settings to


look as follows:The response should look like that shown below:

Note that the dynamics settings for the above response are shown below:

Air Flow

Fuel FlowSteam Flow


Steam Pressure

44

7.1.3 DiscussionThe response shown is for a boiler with dynamics given in the Boiler Dynamicwindow shown on the previous page. If the time constants are reduced from 5seconds, the boiler will be given a faster response, perhaps mimicking a smallerboiler. A "faster" boiler will be explored in the next part of the experiment.

7.2.2 Procedure - A "Faster" BoilerIn the next part of the lab, the time constants of the boiler will be decreased ineffect making the boiler response faster. The same 5 % step change in steamdemand will be created and the response plotted and compared with that in7.1.2.

1. From your Windows operating system, start the Win Boiler Sim program.

The program starts with the boiler in the cold shutdown state. The Boiler Controlsand Monitoring window is displayed on the screen as shown page 42.


3. Click Boiler Dynamics. Continuously click the right hand arrow of the SelectBoiler Dynamics Scroll Bar and select the set of boiler dynamics shownbelow. The decrease in the time constants will result in a boiler with a fasterresponse.

45

4. From the Boiler Dynamics window, click File5. Click Accept Dynamics and Return6. Click Yes to close the Boiler Dynamics window.7. From the Boiler Controls and Monitoring window, click Boiler Initialize , click

Select Steady State Operating Conditions.8. Click Select Boiler Initialize Set and find the set of operating conditions

where the comment is 50% Operating Point (50% steam flow, demand, andpressure).

9. From the Boiler Initialization window, click File10. Click Accept Initial Conditions and Return11. Click Yes12. From the Boiler Controls and Monitoring window click Trend Recorder.13. Click Steam pressure14. Repeat the previous 2 steps for Steam Flow, Drum Level, Feedwater Flow,

Air Flow, Fuel Flow, Steam Demand15. On the Boiler Controls and Monitoring window, click the trend recorder Pause

command button at the bottom of the screen underneath the trend recorder.This will halt the simulation and hold all variables at their current value (thePause button will have red text saying "Paused".

16. From the Boiler Controls and Monitoring window, click Window17. Click Steam Demand Settings and increase the Base Demand settings to


look as follows:

Notice that the maximum transient is slightly less than for the previous (slower)set of boiler dynamics.

Air Flow

Fuel FlowSteam Flow


Steam Pressure

46

Slower Boiler / Faster Boiler Comparison - Tuning Constants the Same

In the next exercise, the dynamics will stay as for the previous transient, exceptthat the controllers will be tuned to take advantage of the faster boiler response.

20. Repeat steps 7 through 14 of Procedure section 7.2.221. From the Boiler Controls and Monitoring window click Controller22. Click Fuel Flow23. Set Proportional to 15%, Integral to 30 sec, Derivative to 0. Do this by clicking

the appropriate increase / decrease button. Click Close to close the Fuel GasController tuning window.

24. From the Boiler Controls and Monitoring window click Controller25. Click Air Flow26. Set Proportional to 15%, Integral to 30 sec, Derivative to 0. Do this by clicking

the appropriate increase / decrease button. Click Close to close the Air FlowController tuning window.

27. From the Boiler Controls and Monitoring window click Controller28. Click Feedwater29. Set Proportional to 40%, Integral to 25 Sec, Derivative to 0. Do this by clicking

the appropriate increase / decrease button. Click Close to close theFeedwater Flow Controller tuning window.

30. From the Boiler Controls and Monitoring window Click Controller31. Click Drum Level

Faster Dynamics

Slower Dynamics

47

32. Set Proportional at 150%, Integral at 40 Sec, Derivative at 0. Do this byclicking the appropriate increase / decrease button. Click Close to close theDrum Level Controller tuning window.

33. From the Boiler Controls and Monitoring window click Controller. ClickPressure

34. Set Proportional to 80%, Integral to 45 Sec, Derivative to 7. Do this by clickingthe appropriate increase / decrease button. Click Close to close the PressureController tuning window.


36. Click Steam Demand Settings and increase the Base Demand settings to55%

37. Click Close to close the Variable Demand Generator window.38. Click Unpause to restart the simulation and observe the transient. It should

look as follows:

7.2.3 DiscussionThe transient response of the "faster" boiler has been improved significantly byretuning the boiler controllers. The gains of the controllers were increased andthe integral times decreased. Derivative was increased for the pressurecontroller. Tuning boilers must be done on an individual basis. The constantsused are a function of the dynamics of a boiler. The performance can besignificantly improved when controllers are properly tuned. Notice the drop insteam pressure of about 7% for the retuned boiler, whereas a drop in steampressure of about 12% occurred when using original tuning constants with the"faster boiler". The retuned boiler displays a decaying oscillatory response.

Air Flow Fuel FlowSteam Flow

Feedwater Flow

Drum LevelSteam Pressure

48

Comparison of Boiler Responses - Original Tuning and Retuned

8 Suggestions for Additional Experiments

Win Boiler Sim is equipped with many features that will allow you to experimentwith Boiler Control. The following are a few suggestions:

1. Try running the boiler at different operating conditions. These can beselected from the Boiler Initialize window. You may also want to create someadditional sets of steady state operating conditions. This procedure isdescribed in section 4 of the user's manual.

2. Try using square wave, triangle wave, and sine wave steam demand signalswith or without random drift.

3. Try optimizing the tuning for various different sets of boiler dynamics and seehow the boiler behaves for the various types of steam demand signalsdescribed in the previous step. Remember to tune the fuel gas and air flowfirst, then the feedwater, followed by the drum level, and finally the steampressure controller. This is essentially a cascade feedforward control system.The secondary loops are always optimally tuned first.

4. Run the boiler, and observe the operation using the Dynamic Graphicwindow.

5. Study the Drum Level Control and Air / Fuel Control windows to determinewhat the control system is doing for various operating conditions. Observing

Retuned Controllers

Original Tuning ofControllers

49

the various numerical values from the text box gives the user a goodunderstanding of what the control system is doing.

6. Try initiating various alarm and shutdown conditions. This could be done bymanually shutting down the fan and /or feedwater pump, or manually closingcontrol valves.

7. Try igniting the pilot with the air flow set higher than 40% during startup.8. Try to determine how the boiler efficiency changes as the boiler is operated at

different loads.9. Try experimenting with the shrink swell factors to see how the boiler drum

transient performance is affected.10. Try decreasing the air to fuel ratio by a small amount, say .02, .03, .04, .05,

and observe the effect on the boiler efficiency.

Documents

Lab Manual