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#BoilerManual #OptimizingCombustion #Section9 #Page15

flow is controlled by the velocity damper in each cyclone to maintain the proper fuel-air relationship. This air flow is automatically temperature compensated to provide the correct amount of air under all boiler loads. The total air flow to the cyclone is controlled by the windbox to furnace differential pressure, which is varied as a function of load to increase or decrease the forced draft fan output.

Automatic compensation for the number of cyclones in service has been incorporated along with the additional feature of an oxygen analyzer. This gas analyzer serves as an important aid to the operator in monitoring excess air for optimum firing conditions.

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Alt = Labeled Fig. 4 Comparison of sintering characteristics. This graph has its x axis marked in terms of Sintering temperature - F where it increments every 100 degrees from 1400 to 1900. Its y axis is marked Strength of sintered fly ash -- 1000 psi and increments every 4 units from 0 to 20. There are 3 lines on the graph, all originating at the 1500 degree mark just above 0 on the y axis. Topmost line is marked Coal A; middle line is Coal B, and bottom line is Coal C. Small circles mark where their upward curves intersect with each temperature vertical line up to the 1800 F mark, where both Coal B and Coal C end. Coal A ends at the 1700 F mark.

#BoilerManual #Ramping #Section8 #Page15

increased flow would drop PSH outlet temperature, so the 207 valve is driven closed a proportionate amount in an effort to maintain a constant flow and therefore temperature though the PSH. The amount of 207 valve closure is based on the ratio of 201 to 207 valve port areas. As the total 201valve port area increases, the 207 valve port area must be decreased an equal amount. The initial opening of the 201 and closing of the 207 should provide an even flow exchange. The 202 valve should not have to move significantly to maintain boiler pressure.

Between points B and C, the 201 and 207 valves should stabilize in partially open positions (the 207 valve opening will vary slightly depending on firing rate).

At point C, as the 201 valves are ramped open, the 207 will begin to close entirely. As flow to the turbine is increased, the 202 will close off gradually. Flow to the flashtank will decrease as it maintains boiler pressure. The 202 valves will close entirely with the opening of the 200 valves, taking the entire system off of the bypass.

While the 205 valve has not been shown in Figure 6C, its operation should be mentioned. The 205 valve is a non-return valve. When throttle pressure increases above flashtank pressure, shortly after point C, the 205 valve will close and all steam flow willl be through the 201 valves. Flow to the flashtank through the 202 will he distributed to the feedwater heaters, deaerator and condenser.

STEAM TEMPERATURE CONTROL DURING RAMP

So far we have discussed the bypass system valve operation and the controll of pressure and flow during the ramp. The other major area of concern is the control of steam temperatures. Steam temperature control is achieved by adjustment of the firing rate. The adjustment is

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#BoilerManual #BypassSystem #Section7 #Page15

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Alt = Labeled Fig. 4D Startup -- Steam line warming. This image is sideways with the bottom long the right edge and the top along the left edge and is best described in the main text when it refers to this image. The Secondary Suprheater is now involved.

#BoilerManual #CycloneOperation #Section6 #Page15

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Alt = Notes I made on the page: B7 STOP =Either A1 or A6 or both
A1 STOP = A6 only
A6 STOP = A1 only
This image is of a complex flow chart marked Sequece 4 with the number circled; also marked BOILER AIR FLOW DAMPER MANAGEMENT. It uses Cyclone A5 as the beginning of logic that applies to all cyclones in the sequence covered in the main text, but a label in the center of the chart reads "SAME FOR ALL CYCLONES" as it points to the points in the logic flow Cyclone successful yes/no at the top side and also to the bottom side at the point that reads "Delay timed out? yes".

#BoilerManual #CycloneDescription #Section5 #Page15

FLUE GAS ANALYSIS

While feeder speeds and individual cyclone air flows are an indication of fuel/air ratio to each cyclone, the correct fuel/air ratio is determined from the analysis of representative flue gas samples. The gas samples must be taken at specific locations and at steady load conditions that will give an accurate indication of the total air to each cyclone. Sampling at the boiler outlet gives an average total air for the boiler unit. However, if only one cyclone is operating and no air is passing through the idle cyclones, then sampling at the boiler outlet will give an indication of total air for the operating cyclone. This reading, however, must be corrected for damper leakage, cooling air, and sealing air throughout the unit.

Excess air levels should be checked for each cyclone at several load points. If the averages are not equal, check the following items: secondary air flow calibration, feeder speed and coal level regulator settings.

Even the most sophisticated instrumentation is no substitute for visual inspection. Furnace inspections should be made on a regular basis. Not only will inspections be an aid to cyclone and unit operation, it is essential to the early detection of possible hazardous conditions.

FURNACE APPEARANCE

A clear bright fire should be maintained at the cyclone outlet. The primary furnace should be clear and free of sparklers. Sparklers or a hazy primary furnace indicates one of the following:

.....* Slag buildup at the secondary air ports - these may be removed by hand lancing.

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#BoilerManual #Lighters #Section4 #Page15

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Alt = Labeled Fig. 9 Lighters retracted.. The image is on its side such that the bottom is along the right edge of the page and the top is along its left, and it utilizes the mechanical symbols identified in the printed key on page 7. This image is identical to Fig. 5 except the solenoid conditions show what has occurred for the Oil Purge condition, with the upper bank of solenoids in the left section marked DE-ENERGIZED, and the lower bank of solenoids in the left section marked RETRACTED.

#BoilerManual #AirAndGasFlow #Section3 #Page15

restriction does not matter (as long as it does not change), this relationship has several applications in boiler operation. A bank of tubes, Figure 11, is a restriction to gas flow. If the differential across a bank of tubes is 1/2 inch of water at 50% boiler load, then the differential will be about 4 times as great, or 2 inches of water at 100% load. Remember that this is all based on a constant restriction. Slagging of the tube bank will alter the relationship, depending upon the severity. Differential pressures are useful as an operating guideline when comparing normal or expected differentials to the actual readings.

Steam flowing through a tube section behaves similarly. Figure 12 helps explain the reason for limiting the gas temperature at the superheater during low load or pressure raising periods. Below 10% steam flow, the pressure drop through the superheater is extremely low. If a tube were to have a water leg, it could block steam flow through that tube. The tube could overheat and fail. To protect the superheater tubes, the gas temperature entering this region is limited to a 1000 F until steam flow is greater than 10% of full load flow. Above 10% steam flow the pressure differential becomes large enough to insure that there is flow through all superheater tubes.

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Alt = Figure 11 Labeled Air flow across a tube bank. It does in fact show a manometer connected between the air flow inlet across an unlabeled tube bank, at the bottom of the inlet duct. The diagram on the left shows a manometer reading marked delta-P 1/2" at air flow of 50%. The diagram on the right shows a manometer reading of delta-P 2" with air flow of 100%. Each diagram depicts the section of furnace that contains a generic tube bank and is marked as such. The left diagram is marked 50% AIR FLOW; the right diagram is marked 100% AIR FLOW.

#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".

@Su_G #BoilerManual #UnitDescription #Section1 #Page15

Furnace Wall

The water wall furnace is a combustion chamber in which 14 ten foot diameter cyclone furnaces are evenly distributed along the lower section of the front and rear walls. The furnace stands approximately180 feet tall and is 60 feet wide by 33 feet deep.

The furnace walls utilize a gas-tight membrane construction (Figure 6). The lower portion of the furnace is full-studded construction (Figure 7) up to an elevation of 11 feet above the upper cyclone. Internally, the wall tubes are ribbed to maintain effective heat transfer in the high heat input areas of the furnace. This ribbed tube construction (Figure 8) ends at elevation 611' for Unit 1, and 549' for Unit 2.

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Alt = Figure 6 Membrane wall construction shows a section of 4 tubes side-by-side connected by metal sheets between them; above this section shows a cross-section of those tubes.