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#BoilerManual #FluidCirculation #Section2 #Page41

9. Spray attemperators inject a fine mist of high purity water to control steam temperature.

10. Gas recirculation is used to control final reheat steam temperatures. There is a spray attemperator in the "hot reheat line", but under normal operating conditions, its use should not be necessary. {I have noted that 33% = 1,400,000 at 2500 psig; Full Load = 4, 200,000 at 3000 psig, econ included. The psig = "pressure per square inch gauge".}

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#BoilerManual #FluidCirculation #Section2 #Page40

Answers for fluid circulation

1. The answer is "B". When you heat water that is converting to steam, the heat produces more steam rather than raising the water temperature.

2. At 3206 psi, water and steam have the same densities. This is known as the critical pressure.

3. The answer to question three is False[/]. The need to match fluid flow and firing rate is [i]criticalat all load levels to avoid overheat conditions.

4. Before a UP boiler is fired, the flow in the furnace circuit must be at least 33% of the full load flow.

5. Internal corrosion can be minimized by controlling the pH of the feedwater and by limiting the amounts of oxygen and carbon dioxide in the feedwater.

6. The first fluid flow path is through the neck of the cyclone. Passes two through six are within the barrel of the cyclone. The seventh pass is through the re-entrant throat.

7. The two purposes are interrelated. First, the mix system keeps fluid temperatures within 80 F of the average temperature of a particular flow path.

8. The connecting tubing from the primary to the secondary superheater crisscrosses to prevent flue gas temperature imbalances from carrying over to the steam.

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#BoilerManual #FluidCirculation #Section2 #Page39

8. Why is steam flow from the primary superheater outlet crisscrossed on its way to the secondary superheater inlet?

9. What is the function of spray attemperators?

10. How do you control final reheat steam temperature?

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#BoilerManual #FluidCirculation #Section2 #Page38

Questions for fluid circulation

1. To which of the following water/steam stages can you apply heat without a rise in temperature occurring?
.....A. water up to its saturation point
.....B. saturation point to saturated steam
.....C. saturated steam to superheater steam
.....D. none of the above.

2. What term is used when water and steam reach 3206 psi?

3. True or false.
.....The need to match fluid flow and firing rate is necessary only at
.....high load levels.

4. What should the minimum flow in the furnace circuits be before a UP boiler is fired?

5. How can you control internal corrosion on economizer tubes?

6. Name the seven fluid flow paths within each cyclone.

7. What are the two (2) main purposes of the mix system?

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#BoilerManual #FluidCirculation #Section2 #Page37

slightly superheated upon entering the roof inlet header. At this point, steam temperature begins to rise again (and becomes more superheated) as it passes through the roof tubes and convection pass enclosures. Superheated steam at about 695 F enters the primary superheater where its temperature is increased to about 765 F. Between the primary and secondary superheater, the superheated steam is attemperated, thus reducing its temperature and enthalpy below that of the PSH.

By the time steam exits the SSH, it has been brought up to the desired steam temperature of 1005 F. Due to pressure losses throughout the system, the steam pressure leaving the SSH is 2620 psi.

Temperature and pressure are expended in doing work on the HP turbine. Low pressure steam leaving the turbine enters the reheater at 547 psi and 622 F. Lost pressure cannot be regained in the reheater. However, energy in the form of temperature and enthalpy can be regained. Superheated steam leaves the reheater and enters the intermediate and low pressure stages of the turbine at 1005 F and 519 psi. This completes the boiler fluid cycle at full load.

This concludes the section on fluid circulation through the UP boiler. You should now be familiar with the fluid flow paths in addition to the effects of pressure and temperature on the state of the fluid. You should also be aware of the impact that you, as the operator, have on determining the operating efficiency of your unit.

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#BoilerManual #FluidCirculation #Section2 #Page36

Fluid Cycle at Full Load

Full load flow and pressure are maintained by feed pumps at approximately 4.2 mlb/hr and 3000 psi respectively. Referring to Figure 27, feedwater enters the economizer at about 481 F, at this point it is saturated water.

Water passes through the economizer as temperature and heat energy increase. Entering the cyclones at about 580 F, additional temperature and heat energy are absorbed by the fluid as it passes through the cyclone circuits. Entering the furnace floor and wall tubes at about 640 F, the saturated water will continue to rise in temperature as more heat is absorbed in the high heat input areas of the furnace. At a point approximately half the way up the furnace first passes, the fluid temperature will level off to approximately 690 F, which is saturation temperature or boiling point at a pressure of about 3000 psi. The additional heat being absorbed through the remainder of the furnace passes is utilized in the conversion of saturated water (0% quality) and is

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Alt = The image of a graph has no label but it's identical to Figure 26 except the straight line is at the 3000 psi level and the parts of the boiler show slightly altered coverage of the curve sections. The Reheat curve is shorter.

#BoilerManual #FluidCirculation #Section2 #Page35

As pressure and temperature fall off in the high pressure stage of the turbine, the steam loses most of its superheat and begins to approach saturation temperature. Because of the velocities at which steam moves through the turbine, it would be quite erosive to the turbine if the steam quality dropped below 100%. However a considerable amount of heat (and consequently fuel) was used to initially convert the water into steam. Therefore, the overall plant efficiency can be increased by sending this steam back to the boiler and reheating it, so that it can be used by the turbine again.

Low pressure steam from the turbine, at a temperature of approximately 475 F enters the reheater. Steam exits the reheater at approximately 960 F and is returned to the turbine. This completes the boiler fluid cycle at 33% load.

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Alt = Labeled Fig 26 Boiler fluid cycle at minimum feedwater flow. It revisits the steam graph of Figure 7 and it's laid out similarly, and is in turn similar to Figure 3. The graph is laid out with points where the x column is labeled in terms of Temperature in degrees, incrementing every 100 degrees + from 300 to 1200; the y row is labeled in terms of Enthalpy -- Btu/lb incrementing every 200 Btus/lb from 400 to 1600).

There are no Points A, B or C are on a straight line, but there is that straight line, labeled 2500psi rather than 2000 psi; where Point C was, there is still that steam curve which goes all the way up to the upper right corner of the graph. From left to right, the graph is marked off in terms of which parts of the curve is covered by which part of the boiler.

Before that 2500 psi straight line begins, marked off from left to right is the Econ. and Cyc. from approximately 350 Btu/lb mark to 6h4 600 Btu/lb mark. From that point to the end of that straight line is marked off Furnace passes, subdivided into 1st, 2nd, 3rd for the front wall and 1st and 2nd for the side wall. The roof tubes begin at what used to be Point C, then after that along that steam curve is PSH, and then SSH which is marked as overlapping the PSH a bit. Below those markings, beginning where the SSH marking starts, is a separate curve labeled Reheater.

#BoilerManual #FluidCirculation #Section2 #Page34

BOILER FLUID CYCLE

We have now discussed, in some detail, the fluid circulation throughout the boiler, and the effects of pressure, temperature and enthalpy on the generation of steam. Let's back up and examine the specific properties and phase changes that occur in each boiler circuit at Baldwin.

Fluid Cycle at Minimum Feedwater Flow

Flow and pressure are maintained by the feed pumps at approximately 1.4 mlb/hr {million lbs/r?} and 2500 psi respectively. Referring to Figure 26, feedwater enters the economizer at about 375 F, at this point it is saturated water. As flow passes through the economizer tube banks, additional heat energy and temperature are picked up. Still in the form of saturated water, the fluid leaves the economizer and enters the cyclones at about 535 F. Temperature and heat energy increase as flow is directed through the cyclone circuits and feed into the furnace wall headers at about 625 F. Entering the furnace wall tubes and up to a point approximately 1/4 to 1/3 the way up the furnace, the fluid is still in its saturated water state (0% quality), but contains much more heat energy and is about 670 F. At this point, the fluid temperature will level off at about 670 F. The additional heat being absorbed through the remainder of the furnace passes is being expended in the conversion of saturated water (0% quality) into saturated steam (100% quality).

At this point (100% quality), the steam temperature will begin to rise again and become superheated as flow passes through the roof tubes (furnace and convection pass) and to the convection pass enclosure. Superheated steam at a temperature of about 680 F enters the primary superheater and exits at about 765 F. Between the PSH and SSH, the superheated steam is attemperated, thus reducing its temperature and enthalpy below that of the PSH outlet. By the time the steam leaves the SSH, it has been brought up to the desired temperature of 1005 F.

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#BoilerManual #FluidCirculation #Section2 #Page33

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Alt = Labeled Figure 25 Headers and piping (top view in the penthouse). This full page image is on its side with the bottom on the right of the page and the top on the left. On the right of a plumbing depiction is a numbered list of labels 1 thru 10 but entirely too complex to be within the scope of verbal description of where they're located. The list:
1. Roof outlet
2. PSH supply
3. PSH outlet
4. PSH crossover lines
5. SSH inlet
6. SSH outlet
7. Main steam lines
8. Reheat outlet
9. Reheat steam lines
10. Economizer outlet

#BoilerManual #FluidCirculation #Section2 #Page32

Superheating Surfaces

Two PSH supply downcomers (located at the rear of the unit) feed into mix bottles and the PSH inlet header. From the PSH inlet header, the steam enters the PSH tube banks, which are enclosed within the horizontal convection pass. Flow is up through the PSH tube banks to the PSH outlet header. The fluid is mixed in the outlet header so that temperatures are equalized and then is sent through two connecting pipes, generally referred to as crossover lines. These lines extend upward outside of the unit and enter the penthouse where they crossover and feed the steam from the right half of the PSH to the left half of the SSH {Secondary SuperHeater} outlet headers. The two paths join in the mainstream line and is sent to the high pressure (HP) stage of the turbine at approximately 1005 F and at a full load pressure of approximately 2620 psi. Both pressure and temperature are reduced in the turbine.

The steam is discharged into the SSH outlet headers. The two path join in the main stream line and is sent to the high pressure (HP) stage of the turbine at approximately 1005 F and at a full load pressure of approximately 2620 psi. Both pressure and temperature are reduced in the turbine.

Low pressure steam from the turbine flows back to the reheat superheater (RSH) through the cold reheat lines and enters the RSH inlet header located beneath the convection pass enclosure header (Figure 21). It then flows through the reheat tubes (horizontal and pendant) and on to outlet headers. From the reheat outlet headers, the steam is returned to the turbine through the hot reheat lines at a full load temperature of 1005 F and a pressure of 519 psi. It then flows through the intermediate and low pressure stages of the turbine from which it is exhausted to the condenser.

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#BoilerManual #FluidCirculation #Section2 #Page31

From the convection pass floor inlet header, tubes extend into the furnace 9 feet at a 5 degree angle and bend back at a 35 degree angle to form the furnace arch (nose). Continuing on, this same circuit levels off and forms the pendant convection pass floor below the secondary superheater and outlet loop of the reheater. Finally, the path leads to the front wall convection pass intermediate header, which in turn supplies the front wall convection pass screen tubes up to the screen outlet header.

The second area supplied by the convection pass supply downcomer is the pendant convection pass side wall. From the side wall inlet headers, flow is straight up to the outlet headers in the penthouse. These sidewall tubes form the convection pass side wall enclosure.

Finally, the horizontal convection pass enclosure header is also supplied by the convection pass downcomer. As the name implies, the four enclosure walls are contained within this circuit. The front wall headers and tubes forms the lower CP front wall and flow into the intermediate header where they join the pendant CP floor tubes to supply the screen tubes. Discharge is through the screen outlet header.

The two side wall portions of the convection pass enclosure header rise above the reheater and PSH loops and continue on to and discharge into the upper side wall headers located in the penthouse.

The remaining horizontal convection pass enclosure circuit, the rear wall, travels directly up the convection pass rear wall outlet header located in the back end of the penthouse. At this point all convection pass circuits, pendant and horizontal, are lead from outlet headers through connecting tubes to the horizontal convection pass (rear wall) outlet header and then to the primary superheater (PSH) supplies.

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#BoilerManual #FluidCirculation #Section2 #Page30

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Alt = A full page but sideways illustration of pipe connections with the bottom on the right side and the top on the left. Labeled Fig. 24 Convection pass supply circuitry. When the page is turned 90 degrees, one sees a manifold of tubes on the left, connecting by two tubes the manifold on the right which has a large vertical pipe labeled Convection pass supply downcomer. The two connecting tubes connect to that. At the bottom of the downcomer are two opposite arrows originating at the downcomer and pointing away from it along a tube that connects with the rightmost manifold with 3 branches on the right and 5 branches on the left, all of which connect together again to a slightly larger tube labeled Convection pass enclosure header.

On the left side of that header is a long arrow pointing straight up toward what's labeled as F.W. convection pass screen tubes, but along the way, in the middle of the image, the arrow passes through a circle labeled Convection pass intermediat header, to which an arrow from the leftmost end of one of the two connecting tubes points back to it. That end of the tube is labeled Pendant convection pass inlet header. The arrow bends at a point labeled Furnace arch; it further continues to a point labeled Pendant convection pass floor, before the arrow arrives at the Convection pass intermediate header.

The leftmost manifold of tubes is joined at the bottom by the other connecting tube in a set of 2, then 3, then 3, then 2 tubes, and the larger tubes which connect them in sets at the top is labeled Pendant convection pass side wall headers.

#BoilerManual #FluidCirculation #Section2 #Page29

When the change of temperature between furnace circuits is less than 80 F and the unit is operating at the correct pumping and firing rates, a good fluid mix is said to exist. These conditions greatly reduce the risk of a tube failure in the furnace circuitry. See Figure 23 for a temperature comparison with and without the furnace mix system.

Convection Pass

The roof outlet header is joined by interconnections to the convection pass supply downcomers (one on each side of the unit). These downcomers travel down the length of the horizontal convection pass (CP) and supply three areas: the pendant CP floor inlet headers (which also forms the arch), the pendant CP side wall headers, and the horizontal convection pass enclosure headers. Let's examine each of these circuits in more detail (Figure 24).

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Alt = Labeled Fig. 23 Temperature comparison with and without the mix system. Two graphs are shown, each with the y axis incrementing in 100 degree F increments from 600 to 1000 F lines. The x axis increments are shown only on the bottom graph with the expectation that they be applied to the upper graph which aligns with it--in terms of percent of furnace height, increasingly incremented in 20% marks. top graph is labeled WITHOUT MIX; the bottom one is labeled WITH MIX.
The top graph plots out a solid line labeled Average, and a dotted line above the solid one and the area between the two lines is shaded and labeled Upset. The bottom graph depicts the same scheme but plots out a solid line across the entire graph and labels that line 2nd pass average. A shorter solid line under that is labeled 1st pass average, and where that line terminates along the x axis, the remainder of the 2nd pass average line is labeled 3rd pass average.

#BoilerManual #FluidCirculation #Section2 #Page28

for, the tube will overheat and eventually fail. Each section of boiler tubing, regardless of its location in the boiler, is designed to withstand certain maximum conditions of temperature and pressure. By allowing a furnace tube to exceed its design temperature, the tube is beyond the condition for which it was designed and is certain to fail. The recommended alarm points are as follows:

Furnace Alarm Temperatures (Full Load)

.......................................................Unit 1.........................Unit 2

Furnace first pass (F):
......Front Wall (F)...........................730................................725
......Side Wall (F).............................730................................725
......Rear Wall (F)............................710................................725

Furnace Second Pass (F):
...... Front Wall (F)...........................750................................760
...... Side Wall (F).............................750................................750

Furnace Third Pass (F):
...... Front Wall (F)..................................................................735

Convection Pass (F):......................740................................750

Furnace Screen Tubes (F):............765................................775

A problem now becomes apparent. Since temperature imbalances are present in the furnace and are not desirable, what can be done to reduce them if not eliminate them entirely? The answer lies in the mix system which is a built-in part of the furnace circuitry.

One of the most important features of the mix system is that all fluid temperatures in any circuit of the same pass will be within 80 F of the general average temperature of that pass. The 80 F maximum temperature differential for a furnace circuit can only be maintained if the unit is operated properly. That is, by employing balanced firing of cyclones, use of sootblowers, etc.

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#BoilerManual #FluidCirculation #Section2 #Page27

In the penthouse (Figure 21), the front, rear (screen tube) and side wall outlet headers are joined by connecting tubes to the roof inlet header. Roof tubes which travel from the roof inlet header form the furnace and convection pass (CP) roof enclosure. These tubes discharge into the roof outlet header located in the penthouse at the rear of the unit.

FURNACE MIX SYSTEM

The furnace mix system has been incorporated to achieve more uniform fluid temperature throughout the three furnace passes. Uniform temperatures, or as close as possible to uniform, are desirable in the furnace circuitry of a Universal Pressure boiler. This, however, cannot be achieved all the time due to some physical and operational characteristics of the boiler. For example, some furnace tubes do not absorb the same amount of heat as other furnace tubes. This can be attributed to the tubes which are located closer to the cyclones and receive more heat than those located in the corners. Also, some tubes have bends in them to allow room for sootblowers, cyclones, and other equipment. By allowing for these bends, there is more length in the tube, therefore, more heat is absorbed.

Slagging is still another factor which affects even heat absorption by furnace tubes. A build-up of slag will effectively insulate a tube from absorbing its maximum amount of heat. Therefore, the more slag on a tube, the less heat can be absorbed by the tube.

Different heat absorption rates do exist in various furnace tubes and yield different temperatures. But why is this so important? Elimination of fluid temperature variations in the furnace can reduce the thermals stress between tubes. If thermal stresses are not reduced, it is quite possible that (over a period of time) a tube failure may occur.

If a furnace tube should absorb more heat than what it was designed

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#BoilerManual #FluidCirculation #Section2 #Page26

From the second pass inlet header, flow is straight up the second pass side wall and discharges into the side wall outlet headers located in the penthouse (Figure 21).

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Alt = Labeled Figure 22 Upper furnace circuitry. Simplified line drawing of the topmost part of the furnace but stopping where the Secondary SuperHeater (SSH) ends, and the Screen tubes of the SSH are pointed out where the furnace top meets the beginning of the SSH.

#BoilerManual #FluidCirculation #Section2 #Page25

FURNACE SIDE WALL TUBES

Now that we have covered the furnace front and rear walls, let's complete the furnace enclosure. Each of the furnace side walls are of similar construction (left/right). The side walls are divided into two sections, the first and second passes. The furnace side wall headers are supplied by the cyclone discharge mix bottle as are the front and rear walls. From the inlet headers, flow travels directly up the side walls to the first pass mix bottle. There is one bottle located on each side of the unit.

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Alt = Labeled Fig. 21 Fluid flow paths. Its a complex line drawing with circled numbers at various points along the lines superimposed on a line outline of a furnace, with a title in the lower right, ORDER OF FLOW 1 THRU 13. Circled 1 begins at what would be the barbed end of an inverted fish hook, the form that the complete furnace takes, with the firebox and cyclones located where the bottom of the shank would be, where the eye of the hook would be. At that end are numbers 3 and 4, but the illustration matches what is covered in the text body for details of how it goes.

#BoilerManual #FluidCirculation #Section2 #Page24

Returning to the second pass rear wall inlet header, flow is the same for both units. Flow travels up the second rear wall pass and feeds the screen inlet header. Flow is up behind the arch and through the screen tubes immediately ahead of the SSH {Secondary SuperHeater} inlet tube bank (Figure 22). The screen tubes are widely spaced tubes which support and complete the furnace rear wall circuit.

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Alt = labeled Fig. 20 Furnace wall mix construction. Depicts the pipe layout of connections between the 1st pass header (lower left side) and the 2nd pass inlet header (lower than the other header but in the center of the image). To the left between the two headers is the label "To mix and 2nd pass inlet header " betwixt two arrows; top arrow shows pointing away from the 1st pass outlet header to the label, and the other arrow points away from the label toward the 2nd pass inlet header.

#BoilerManual #FluidCirculation #Section2 #Page23

At this point, let's discuss separately the front wall circuits of units 1 and 2. Unit 1 has two front wall passes with one mix bottle. Flow from the first pass mix bottle enters the second pass circuit and finally discharges into the front wall header located in the penthouse (Figure 21). Unit 2 has three front wall passes with two mix bottles. Flow from the first pass mix bottle is subsequently through the second pass front wall tubes and mix bottle to the third pass wall tubes and discharges to the front wall header located in the penthouse.

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Alt = Labeled Fig. 19 Cyclone discharge -- furnace supply. Simple depiction of a cross section of the firebox part of the furnace with Cyclone discharge lines pointed out using arrows in the midsection of the drawing from both of the sides of the furnace toward the middle then pointing down the middle to what's marked as Furnace inlet headers. To either side of the central firebox, symmetrically depicted, are 2 cyclone barrels, one above the other; on the left side set of cyclones, the top one is labeled B Path with an arrow pointing rightward and the lower cyclone labeled A Path with another arrow pointing rightward. On the right side are their counterpart cyclones with the top right cyclone labeled A Path with an arrow pointing leftward and the lower cyclone labeled B Path with an arrow pointing leftward.

#BoilerManual #FluidCirculation #Section2 #Page22

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Alt = Figure 18 containing 2 parts where PART 1 depicts Unit 1 on the left side, labeled at the top as UNIT 1 FURNACE WALL CIRCUITRY. Depicted on the right side as labeled at the top is PART 2 showing Unit 2, labeled at the top as UNIT 2 FURNACE WALL CIRCUITRY. Both parts have the Roof inlet header pointed out. Both parts depict circuitry in 3 connected columns each, with each column topped by, respectively in left right order, "S.W. 2nd pass", "F.W. 2nd pass, and "R.W. screen". SW is presumed to mean "side wall"; FW = "front wall" and RW = "rear wall".
Comparing the SW column on both units, the only difference is that Unit 2's 2nd pass section is drawn to look longer than that of Unit 1; the Mix bottle between 2nd pass & 1st pass is labeled. The middle column FW is significantly different where Unit 1 shows, top down, its 2nd pass section, Mix bottle pointed out, then 1st pass section while on Unit 2, the top of the column shows a FW 3rd pass, then labeled Mix bottle, then 2nd pass which diverts to a labeled Mix bottle between it and the RW 2nd pass section in the RW column.
This central Mix bottle then also connects to both the FW and RW 1st pass sections. The two parts resume being identical on the bottom section with the furnace floor pointed out in both cases, and a central Cyclone discharge mix bottle pointed out. Plus I scribbled in the left hand margin.

#BoilerManual #FluidCirculation #Section2 #Page21

..........Note: Beginning at the neck circuit for any given cyclone, continue
.....................down through the sequence and replace the lower circuits with
.....................one(s) from above. Example: Starting at the neck for cyclone
.....................B4, flow is to the barrel circuits of B2, A1, A3, A5, A7 and out the
.....................re-entrant throat of B6.

Furnace Circulation

Furnace supplies taken from the cyclone discharge mix bottle feed three separate circuits; the front, rear, and sidewalls. These furnace circuits are subdivided into various passes in between which mix bottles are located. As with the cyclone discharge mix bottle, the purpose of these bottles is to balance the fluid temperature entering the following circuit in order to compensate for unbalanced heat inputs. Refer to Figure 18 as the furnace flow paths are described.

FURNACE FRONT AND REAR WALL TUBES

Supplied by the cyclone discharge and mix bottles (Figure 19), the lower furnace front and rear wall headers feed the furnace floor tubes. These floor tubes bend to form the slag neck and the furnace floor. From the furnace floor, flow is straight up the front and rear walls until bends are made to form the furnace wall openings at the cyclones.

Vertical flow continues until the first pass mix headers and bottles are reached (Figure 20). The front and rear furnace wall tubes are collected in the first pass outlet header and sent to a mix bottle. The mix bottle insures a uniform fluid temperature entering the second pas inlet header.

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#BoilerManual #FluidCirculation #Section2 #Page20

Let's continue on with the example; flow continues from the second circuit of the cyclone B5 to the third circuit of cyclone B3, then the fourth circuit of cyclone B1 and the fifth circuit of cyclone A2 to the sixth circuit of cyclone A4 to the last circuit, seven, in cyclone A6. Refer to Chart II for a tabulation of cyclone interconnections.

The discharge from circuit 7 of all cyclones is directed toward one of two cyclone discharge bottles. Seven cyclones of one wall discharge into a common mix bottle. The two bottles join and form a mix bottle which supplies the furnace front, rear, and side walls.

........................................................CHART I
...........................Cyclone Circuit Interconnections (Example)

............................................................Flow Path..........................Cyclone
.................Circuit................Cyclone No................Location

..........1. Neck.......................................B7........................................Lower
..........2. Barrel......................................B5........................................Lower
..........3. Barrel......................................B3........................................Lower
..........4. Barrel......................................B1........................................Lower
..........5. Barrel......................................A2........................................Upper
..........6. Barrel......................................A4........................................Upper
..........7. Re-entrant Throat...................A6........................................Upper

........................................................CHART II

.................Circuit................Path A...............Path B

..........1. Neck.......................................A7.............................A6
..........2. Barrel......................................B6.............................B7
..........3. Barrel......................................B4.............................B5
..........4. Barrel......................................B2.............................B3
..........5. Barrel......................................A1.............................B1
..........6. Barrel......................................A3.............................A2
..........7. Re-entrant Throat..................A5............................A4

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#BoilerManual #FluidCirculation #Section2 #Page19

Note that the flow does not follow the ordered number of cyclones. However, there is a very important pattern which should be kept in mind not only for operational purpose, but also for functional reasons.There are 14 separate flow paths, one beginning with each cyclone. Flow is arranged such that feedwater entering the first circuit of one cyclone discharges after the seventh circuit of the seventh cyclone through which it flowed.

A further distinction is made by the fact that the fourteen cyclones are grouped into two separate flow paths (A&B). Path A cyclones include the four lower cyclones of the furnace front wall together with the three upper cyclones of the furnace rear wall. Path B is just the opposite, as illustrated in figure 17.

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Alt = Figure 17 labeled "Cyclone flow paths (A & B)" depicts a row of cyclones along the upper edge labeled REAR WALL, with an arrow in the upper left pointing rightward labeled FLOW B with each cyclone along that edge labeled in descending order B7 thru B1. Opposite the row of B cyclones closer to the bottom is a corresponding row of cyclones labeled, in descending order, A7 thru A1, and labeled FRONT WALL. An arrow at the lower left pointing rightward is labeled PATH A. Lines are drawn in complicated manner to illustrate how the flow relates to each cyclone and each cyclone to each other.

#BoilerManual #FluidCirculation #Section2 #Page18

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Alt = Labeled Fig 16 Cyclone flow schematic. The image is displayed on the page sideways with the top of it along the left edge and the bottom aligned with the right. The top edge label reads "From cyclone supply downcomers (rear walls)" referring to a solid line across the top as a pipe. Arrows descend from this line to each of 7 oblongs labeled, in descending order, B7 thru B1, representing cyclone positions. Similarly along the bottom are 7 oblongs labeled, in descending order, A7 thru A1 representing another row of cyclone positions but A6, A4, and A2 are also marked "U". A note at the bottom left: "U - Upper Cyclones". Between the two rows are 3 circles aligned top down with the middle circle being larger than the other two, labeled "Cyclone discharge mix bottle", and then an arrow pointing away from that labeled "To furnace walls".

#BoilerManual #FluidCirculation #Section2 #Page17

Flow enters each cyclone at the lower neck (inlet) header. From the upper neck (outlet) header, each cyclone supplies a separate circuit of another cyclone, which in turn supplies another. Figure 16 helps to illustrate this point. Notice that the natural progression is for the flow to be directed sequentially from front to rear through the cyclone circuits.

Let's follow an example of this typical flow path by referring to Chart I. Beginning with cyclone B7, feedwater enters the lower neck header, flows through the neck tubes, and discharges into the upper neck header. This competes the first circuit. Flow is directed to the second circuit (first barrel) of an adjacent cyclone B5.

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Alt = Labeled Figure 15 Cyclone circuitry -- (re-entrant throat). A complex drawing of the tubing skeleton of a cyclone with the neck facing forward at an angle. Across the top, lef to right, are pointed out the Re-entrant throat outlet header, Plane of the furnace wall tubes and re-entrant throat outlet header. Surrounding the neck in the middle is pointed out the Re-entrant throat. Across the bottom, left to right, is pointed out the Re-entrant throat inlet header, the Furnace sidewall tubes, the Cycloe inlet header (above which is the Slag tap. Then Re-entrant throat inlet header.

#BoilerManual #FluidCirculation #Section2 #Page16

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Alt = Labeled "Figure 14A Cyclone circuits". Two side view mechanical drawings of a cyclone are depicted on the left side of the image in top down order, with the Neck part facing right. A third drawing of a cyclone is a cross section view, on the right side of the image. The top left cyclone drawing points out Re-entrant throat inlet/outlet headers at the upper left; Neck outlet header at the upper right of the cyclone; in top down order below the Neck outlet header are indicated the Barrel outlet header, the Secondary air inlet, and Intermediate header. On the bottom left of the cyclone is the indication of the other Re-entrant throat inlet/outlet headers.

#BoilerManual #FluidCirculation #Section2 #Page15

Each cyclone is divided into seven (7) circuits, the front neck circuit, five barrel circuits, and the re-entrant throat circuit.

In order to explain the fluid circulation through thte cyclones, let's first identify the seven fluid circuits and their location within the cyclone setting, (Figures 14 and 15).

Circuit........Identification
.........1.........Neck - Inlet/outlet headers
.........2-6......Barrel - inlet/intermediate/outlet headers. The barrel is subdivided into five separate circuits.
.........7.........Re-entrant throat - inlet/outlet headers.

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Alt = Labeled "Figure 14 Cyclone circuitry (neck and barrel)." A poor photocopy of a photo of a rendering of a cyclone chamber which has the shape of a sideways barrel with a flat square flange on the right end; the left end is mostly closed except for a round opening on the left, and plumbing on the top and bottom. Bottom pipe labels read, in left to right order, "Neck inlet header", "Main barrel (5 subcircuits)", and "Barrel inlet header". Labeled on the righthand flange area, in order top down, are "Re-entrant throat"and "Slag tap". opposite these, on the left side of the barrel, is labeled "Neck". At the top leftmost is the label "Barrel intermediate header"; at the top rightmost is labeled "Barrel outlet header".

#BoilerManual #FluidCirculation #Section2 #Page14

Cyclone circulation

The cyclone furnace, in the form of a horizontal cylinder is compeletely water-cooled by connection to the main boiler circulation.

The fluid leaving the economizer outlet header is divided equally into the downcomers, one on each side of the unit (Figure 13). Each downcomer supplies seven cyclones, four on one wall and three on the opposing wall. There are 14 cyclones on the unit with seven (7) on the front wall and seven (7) on the rear wall. The cyclone flow paths are interconnected between the front and rear walls as follows: The lower four cyclones on one wall are connected with the upper three cyclones on the opposing wall.

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Alt = Labeled "Figure 13 Cyclone supply downcomer". Simplified drawing of a boiler furnace with the economizer outlet header pointed out and the line shown between that and where the cyclone location is illustrated, labeled "Cyclone supply downcomer".

#BoilerManual #FluidCirculation #Section2 #Page13

A starting permissive of the boiler feed pump requires that the valve stem be in the closed position before the pump can be started. It stays in the closed position until the feed pump trips. If a false feed pump trip signal should occur, the stem will attempt to move to the open position, but the pressure differential keeps the valve closed. The valve is always mounted in the vertical position so that the weight of the valve plug opens the valve.

The economizer outlet header feeds two cyclone supply downcomers (one on each side of the unit) which travel a substantial length of the unit and terminate in downcomer bottles. Each downcomer supplies seven separate cyclones.

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Alt = Figure 12 labeled Natural circulation valve; image of a mechanical drawing of the valve. Labeled are the Power driven stem at the bottom; Plug in normal operating position with higher pressure on the economizer side, which is labeled on the right side of the drawing. At the top is labeled the Natural circulation flow direction with a down-pointing arrow.

#BoilerManual #FluidCirculation #Section2 #Page12

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Alt = image of a detailed drawing of the Economizer section with the Cyclone supply downcomer, natural circulation line and the Feedwater inlet pointed out at the very bottom. Just above that is labeled Economizer. Looking further up, the Reheater is labeled, and just above that is the PSH {Primary Super Heater}. Above those are pointed out the Convection pass downcomer and the Stringer tubes. At the very top, the Economizer outlet header is pointed out. The Figure is titled Economizer circuitry.