2010 Partner Workshop_slh

8/7/2019 2010 Partner Workshop_slh

http://slidepdf.com/reader/full/2010-partner-workshopslh 1/7

2010 Alliance Workshop

The primary cause of unavailability in

our coal-fired plants is the reliability of

the boiler/steam generator.

Severe duty on both the fire side and the

water/steam side of the various heat

transfer surfaces in the boiler/steam

generator cause frequent unplanned

outages and lengthening of planned

outages to repair failures to these

critical components of the power plant.

Utilities have opportunities to increase

electrical output at existing unitswithout increasing fuel burn or carbon

footprint by focusing on the boiler system in three areas.

1. Improving Combustion and Thermal Efficiency (Storm)

2. Reducing Forced Outages and Extending Time Between Outages. (UDC / DNF)

3. Improving the Effectiveness of the Tail End Clean Up Equipment (environment)(Neundorfer)

These three areas are well known and routinely controlled by plant management. Unfortunately the

historical standard has been that the management team is acting as the final distiller of information

for use in management decisions. They combine the input they receive from the burner group, the

maintenance group, and the environmental folks. With this information plans are formulated andexecuted. This places the full responsibility for overlaps directly on management. This is

inequitable, as the management team is not expected to be expert in every field and operation in

the plant. Experience has shown us that with this model at play the overlap areas are usually

overlooked.

As providers of services to you, we (speaking as a community) have been complicit in that we have

concentrated on our individual areas of expertise, concerned but

not caught up in bridging the chasms that would maximize our

total service to you.

Historically our focus has been safety and budget driven. Cost control can only be effective if we focus the monies available in

just the right locations. The shot gun approach or the process of

spending money for the sake of using up the budget will not

provide relief from tube leaks. Less money does not necessarily

translate into lower availability.

Figure 1 Chasm Miao Keng in Chongqing Province of China



Setting Criteria for Repairs

It seems we all pray at the altar of budget and time. We utilize a

comprehensive plan supported by inspections, lab results or other

scientific results. This plan must have a financial component indicating

the return on investment in the repairs. Data driven decision making isthe only consistently effective method to support budgets. In many

cases the data is best supported by well planned and documented photography of the problem

areas as well as a statistical analysis of failures or near failures that will likely be avoided. Varying

lost generation scenarios at different times of the year usually works well at underpinning your

budget requests. Simple, concise, data supported and to the point is always more effective than the

Chicken Little The sky is falling technique. We make recommendations as to the repairs required

by strict applications of the following criteria.

<65% of MWT for replacements

<75% >65% of MWT for pad welds (if permissible)

<85% >75% of MWT for shielding



Ranking of Priorities

In outages, a boiler planner often lacks

advance knowledge of what new tasks will

arise and what specific actions will be

needed to make progress at known tasks.With when and what uncertain, boiler

planners must instead reactively prioritize

between currently eligible tasks based onwhatever information is available. The

approach is designed to make best use of

whatever priority-relevant information is

available at decision-time. Boiler plannersmust decide priority among competing

tasks. An ideal priority determination

process should use whatever information is

available, even it presents itself just before

a decision is required or after a task hasbeen awarded priority and begun

executing.

Which should be deferred, interrupted, or aborted? One approach to making such decisions is to

identify all tasks to be carried out and all the constraints on those tasks, then search for the best

possible order.

Priority #1 problem must;

Safety or loss of life issue

Certain forced outage before the next planned outage


Probable but not guaranteed forced outage before the next planned outage

Performance issue


Low grade performance issue

Long range mechanical optimization

Information or documentation issue

Figure 2 Priority Model



Lets review a single example relating to the system inspection and discovery process and how the

chasms have been treated in the past. As you will see, I site only one example due to the

complexities of this process.

During our discovery inspection process we look for the ingress of outside air that enters the boiler

from non-productive sources. We refer to this leakage of air as Tramp Air since it contributesnothing to the combustion process. It comes in around burned soot blower housings, holes in the

casing, and other locations. We mark and record these items report them to you with a very low

priority. This tramp air is not a direct risk to a forced outage therefore it is not considered essential

for repair during that specific outage. It is flagged for If time and money allow. This category

rarely gets any attention

due to the budget

pressures that exist in

most plants.

The example report to

the right indicates aleaking soot blower

sleeve. The report

clearly mentions that

tramp air in leakage is

the concern. You will

also note that the

sample report assigns a

low priority #3 to the

problem. In all

likelihood this actionitem was canceled

permitting the problem

to continue and increase

during the planned run.

Due to reducing budgets

and time frames, many

of our customers are

only interested in

repairing priority #1

problems. In this casethe inspection team

devotes very little if any

time on P2 and

certainly nothing on

P3 items.

Figure 3 Sample inspection report of a soot blower opening. (Courtesy of UDC)



Now lets look through the overlap or chasm. If air enters the boiler and is no use for combustion

then the following sequence of events will occur occurs.

1. Additional volume of flue gas

increases the overall gas velocity.

This increase in velocity has twodramatic effects.

a. The erosion of tubing by fly

ash increases at the square of

velocity. So fly ash erosion is

increased dramatically. b. The increased gas velocity

through the pressure parts i.e.

superheater, reheater, and

economizer cause a reductionof heat absorption and a

decrease in thermal efficiency

of all of these components.

2. Additional volume of flue gas

increases the loading on all of the flue

gas equipment.

a. The ID fan is drawing

additional amps to handle the

extra flue gas capacity. In

many cases the boilers are load

limited due to lack of ID fan

capacity.

b. The air heater is operating at a

greater pressure loss reducing

its efficiency and increasing

erosion in the air heater itself.

Figure 4 Erosion on bent tube caused by fly ash erosion

(Courtesy UDC)

Figure 5 Air heater has reduced performance due to high

gas velocity



c. The electrostatic precipitator

operates on the principle of

balanced gas flow of a

specific velocity. When these

parameters are violated by

excess volume the efficiencyof the ESP is compromised.

This increases the opacity

and particulate output from

the system.

3. When oxygen enters the boiler not

contributing to the combustion

process, it increases the measureable

O concentration. The combustion

process utilizes oxygen sensors at theeconomizer outlet to calculate the

proper fuel air mixture.

a. If these readings are

incorrectly measured high then

the result is that the air flow is

reduced at the burners. This

miscalculation results in very

low oxygen concentrations.

This has been referred as

reducing conditions. This

reducing condition process

usually results in soot and high

corrosion rates on water wall

tubes.

b. This low oxygen flue gas

contributes to several failure

mechanisms such as;

1. Soot blower erosion due

to increase carbon

(soot) removal

2. Localized high heat flux,resulting in the potential

for overheat and

exacerbation of

waterside deposit corrosion.

Figure 7 Poor combustion can lead to excessive slag,

ash and soot accumulation as well as erosion to boiler

tubing. (Courtesy UDC)

Figure 8 Inside of boiler tube with heavy deposits

(Courtesy David N. French Metallurgists)

Figure 6 When gas speeds up through the ESP thecollection efficiency decreases.



3. Waterwall

fire-aide

corrosion

is caused

by

corrosiveconditions

in the

combustion

zone, which

are due to inadequate oxygen supply, high concentration of sulfur and or

increased chlorides in the fuel, improper alignment of the fuel burners, and

formation of molten ash on the waterwall tube surface.

Summary

You can clearly see that a small insignificant priority #3 item as originally considered in fact has a

deep and complex effect on many areas not remotely considered. This is truly a chasm that we

repeat outage after outage. Our Team Alliance synergy fills this gap with cooperation, knowledge,

expertise, and interaction. We assist in consideration of all the parameters and how they interact

throughout the system to provide the most reliable, efficient and environmentally friendly power

generating facility possible.

Figure 9 Severe corrosion (Courtesy David N. French Metallurgists)

2010 Partner Workshop_slh

Documents

Transcript of 2010 Partner Workshop_slh