7.summary of boiler perf

8/8/2019 7.Summary of Boiler Perf

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Conditions causing Poor

Performance of Boiler

Non-Optimum Reheat or Superheat

steam temperatures.

Higher than design economizer exit gas

temperature or furnace exit gas

temperature caused by poor combustion.

Higher than design Re heater or Super

heater De-Superheating spray flows.


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Fly ash Unburned Carbon or Loss on

Ignition greater than 5% for Eastern

Bituminous Coals or greater than 1% for

Western or Lignite Coals.

High Bottom Ash Loss on Ignition.

Non-Optimum utilization or distribution

of primary air, secondary air and over

fire air, if applicable.


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Increased auxiliary horsepower

consumption by coal pulverizers and fans

Reductions in capacity factors due to

excessive furnace or convection passslagging or fouling.

Excessive boiler setting air in-leakage.

Excessive air heater leakage.

Increased cycle losses with increased

sootblowing due to non-optimum

combustion.


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Excessive pulverizer spillage on vertical

spindle, roll and race and ball bearing

type pulverizers. Reductions in capacity

factors due to pulverizer or fan capacitylimitations.

Reductions in capacity factors due to

Superheater or Reheater tubeoverheating and/or coal-ash corrosion.


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Requirements For Achieving

Optimum Conditions

Furnace exit must be oxidizing,

preferably 3% excess O2.

Minimal air in-leakage between thefurnace exit and economizer exit.

Pulverizer fineness of >75% passing

200 Mesh and


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Optimum Conditions

Optimum windbox to furnace

differential, typically 100mm w.c. at

full load. Optimum Pulverizer Primary Air to

Fuel Ratio. In most cases, air to fuel

ratio of 1.8 to 1 on roll and race and

ball bearing type pulverizers, and 1.4

to 1 on attrition and ball tube

pulverizers.


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Optimum Conditions

Fuel balanced between each

pulverizers fuel lines to within 10%

deviation from the mean. Pulverized coal line dirty airflow

balanced between each pulverizers

fuel lines within 5%.

Pulverized coal line clean air

velocities balanced to 2% of the

mean.


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Optimum Conditions

Coal line minimum velocities of 17

Mps.

Burner mechanical tolerances with6mm (circular burners), burner

buckets stroked and synchronized to

within 2 (tangentially fired).

Primary airflow metered and

controlled to 3% accuracy.


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Requirements For Combustion

Optimisation Programme

Boiler testing to identify opportunities for

improved unit heat rate.

Comprehensive inspections of the boiler,

burners, pulverizers and auxiliaries to

identify and address opportunities related to

mechanical tolerances.

Technical direction of outage repairs toensure mechanical tolerances are optimized

as well as training of maintenance personnel

in achieving optimum mechanical tolerances.


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Design new or calibration of existing air

flow measurement elements to facilitate

optimum management and control of

primary air, secondary air and overfire air

(when applicable).

Curtain or boundary air incorporated into

some low NOx burner systems must also

be precisely measured and controlled.


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Modifying existing equipment

(pulverizers, boiler heating surfaces, fans,

burner components) to meet challenges of

switching fuels or changing status of unit

between cyclic and non-cyclic.

Boiler tuning and testing to achieve all

"pre-requisites" for optimum

combustion.


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Optimisation Programme "Awareness" training of boiler

operators, maintenance personnel and

engineering personnel to sustain long

term improvements achieved through

combustion optimization during day to

day operation. Usually termed a"Performance Preservation Program".


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COMBUSTION OPTIMIZATIONGUIDELINES -

SUMMARY

Secondary Air Balancing

Burner Tilt Timing

Fuel Balancing

Reduce Air-In-Leakage

Control Primary Air Flow


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Unit Generating Capacity Limitations

From Inadequate Fan Performance

Higher ambient temperatures result in less

stack draft.

ID fan capacity limitation may result in load

reduction or inability to maintain desiredexcess air levels.

Low excess air due to fan capacity limitation

can result in

Increased slagging and fouling propensity

High Flyash Loss On Ignition

Superheater and Reheater tube overheating

High boiler exit gas temperature


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Common conditions contributing to

inadequate fan capacity

Excessive inlet cone gap & overlap clearance

Excessive boiler setting air in-filtration

Pre-spinning condition at the fan inlet

Non-Optimum damper or pre-spin vane stroke

and/or synchronization

Excessive air heater leakage

High air heater pressure differential due tonon-optimum air heater soot


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Ensure the mating surfaces between sections of

the inlet box-scroll interface are tightly sealed

and the interface plate is free of holes.

A 35-50mm

differential in static

pressure between the

fan outlet and inlet is

typical.

Holes or gaps in the

interface plate will

allow circulation

between the outlet or

scroll side and the inlet

reducing fan capacity


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Non-optimum damper stroking

Dampers should bestroked with internal

position verification

of full damper

opening.

An external key

stock indicator or

scribe mark should

be present to verify

internal damper

position from the

outside.


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Test Procedure For Collecting An

ASME Fineness Sample

Sample locations are

positioned correctly with

regard to bends and

restrictions. Ideally, test

taps should be located in avertical run of piping, 10

diameters upstream and

downstream from the

nearest disturbance. Aminimum of two taps, 90

apart, is required. Taps

should not be located at

the discharge of an

exhauster.


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Traverse points collected fromequal area test grid

Traverse points are sampled

for equal time intervals. This is

necessary for calculation of

total recovered sample (A

fineness test is said to be

representative when the sum of

the samples totals between 90 -

110% of the indicated feederflows). Collection of a timed

sample allows for determination

of relative pipe-to-pipe fuel

balance.


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Traverse points are sampled for equal time

intervals. This is necessary for calculation of total

recovered sample (A fineness test is said to be

representative when the sum of the samples totalsbetween 90 - 110% of the indicated feeder flows).

Collection of a timed sample allows for

determination of relative pipe-to-pipe fuelbalance. Recovered fuel flow per pipe is

calculated using the following equation:)


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Fuel Flow lbs/Hr per burner line

=

gms sampled per pipe 1lb 60min p---------------------------- ---- -------- ---------------

Sample time in min. 453.6 1Hr.

0.0021 sft


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Procedure to collect coal samples

using the ASME Coal Sampler :

Insert the sample probe into the dustless

connector, open the ball valve, and slide the

probe in to the first port (probe completely

inserted) with the flag of probe (sample tip) inthe direction of flow. Turn the tip of the probe

into the flow, turn on and adjust the aspirating

air to achieve/maintain 10 psi, and start the

stopwatch. Sample each traverse point for 10seconds (total burner line sample time of 4

minutes, assuming a 24 point traverse grid).

Upon completion of the last traverse point, cut

off the air, and remove the probe. Repeat the


27/46

Procedure to collect coal samples

using the ASME Coal Sampler : :

After completing traverses of each test port on a

designated burner line, empty the sampling jug

and the filter canister into a labeled Ziploc bag.

Repeat the process for each burner line on the

pulverizer.

Once all burner lines on the pulverizer have been

tested, weigh the samples and calculate an

individual burner line fuel flow and sum the

results to determine (%) recovery. If thecumulative recovery is not between 90% - 110%

of the feeder indication, then repeat traverse

again increasing and/or decreasing the extraction

diff. Pr. until desired recovery is achieved.


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Coal Sieving Procedure

Remove 50 grams of coal from the sample. This

is done by using an ASTM riffler or by

rolling the sample (usually between 200 g

and 800 g).

Shake the sample through a series of 50, 100,140 and 200 Mesh U.S. Standard sieves

Record the weight of coal residue on each

screen and coal in the bottom pan (passing 200

Mesh). Great care should be taken in weighingcoal sample residue on each screen. Residue on

50 Mesh will be very small and must be

weighed accurately to yield representative data.


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Coal Sieves and Calculations

Wt of test sample

Wt.of residue on 50 mesh 1g

Wt.of residue on 100 mesh R2g



Wt.of residue in pan 5g


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Coal Sieves and Calculations

% Passing 50 mesh ( 50-R1) *100/50

% Passing 100 mesh {50-(R1+R2)} *100/50

% Passing 140 mesh {50-(R1+R2+R3)} *100/50

% Passing 200 mesh {50-(R1+R2+R3+R4)} *100/50


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VOLUMETRIC FLYASH SAMPLE

COLLECTION AND ANALYSIS

According to the ASME Test Code PTC 38

Determining the Concentration of Particulate

Matter in a Gas Stream; ideally test tap layout

should be such that sampling access ports and

traverse points are selected to permit sampling inzones of equal areas. The traverse grid should

facilitate a minimum of one traverse point for

every 9 ft of duct area. For example a 12 18

duct with a cross-sectional area of 216 ft will

require a minimum of (24) traverse points.


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VOLUMETRIC FLYASH SAMPLE

COLLECTION AND ANALYSIS

The traverse grid should be located in a straightrun of ductwork (constant cross-sectional area),

preferably a vertical run in order to minimize

stratification of the medium. In addition, the

traverse grid should be located a minimum ofeight (8) duct diameters downstream and two (2)

duct diameters upstream from the nearest flow

disturbance. Since these criteria are often

impossible to meet, test taps are generally

located in the best possible location. This isacceptable if all parties involved in the testing

agree. Adequacy of probe access, lighting, power

facilities, etc. should also be considered when

choosing a location


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Volumetric Fly ash Sample Collection

and Analysis

Example of Equal Area Sampling Grid


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Typical locations for collection of a fly ash sample


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Procedure for Sieving a Flyash

Sample


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Procedure for Burning a Fly ash

Sample for L.O.I. Determination

Equipment

A small oven capable of maintaining

temperatures between 150 - 815 C

A set of ceramic crucibles for burning the ash

A set of pincers or tongs for handling the

crucibles

A highly accurate scale(balance) for measuring

the ash samples; the scale should have areadability of 0.1 mg with a repeatability of + 0.1

mg.


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Procedure for Burning a Flyash


Label each of the crucibles.

Preheat the crucibles to 150 C for

approximately 15 minutes.

Weigh each crucible while hot(Wc).

Add one gram of the ash to be burned to

the crucible as it remains on the scale and

record the sample and crucible weight.


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Insert the crucible with the sample into

the oven and leave it for 1 hour at

between 150 - 260 C.

Remove the crucible with sample and

reweigh and record it, comparing the

weight to the initial weight. Any difference in the two is the amount

of water driven off.


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Replace the crucible w/sample in the

oven at 150 - 260 C and leave it for 30

minutes.

Remove, weigh, and record the crucible

w/sample.

Continue this process until the weightremains constant.

RECORD THIS WEIGHT(WCSD).


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Replace the crucible w/sample in the

oven and cook the sample at 815 C for

three (3) hours.


w/sample weight.

Replace the crucible w/sample and cookat 815 C for 30 minutes.


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w/sample weight.

Any difference indicates that there is still

carbon present in the ash.

Continue this procedure until the weight

remains constant(WCSFW).


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Once the weight no longer changes, the flyash

L.O.I. can be calculated using the following

equation:

WCSD = Crucible w/sample (dried) weight

WCSFW = Crucible w/sample (final weight)

WC = Crucible weight

% Flyash L.O.I.

= {[(WCSD - WC) - (WCSFW - WC) 100]}

WCSD

7.summary of boiler perf

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