Frequently Asked Questions

FAQ

Presented by:

V.Rajagopal

GEECO, Trichy, India

The measured Gas outlet temperature is to corrected for measured flows, temperatures and leakage and then compare with guaranteed Tgo.

Whether the measured gas outlet temp. is to be compared with guaranteed Tgo?

More Gas inlet flow

Less Leakage

High Gas inlet temperature

Less Air inlet Flow

High Air inlet temperature

Less X-Ratio

Gas outlet temperature will be more with

Gas Side efficiency.

X Ratio

Air Side efficiency.

What are the parameters to be monitored for checking the efficiency of Air Preheater?

(Tgi-Tgo Unc)

Gas Side Efficiency = --------------------

(Tgi-Tai)

(Tao-Tai)

Air Side Efficiency = ---------------

(Tgi-Tai)

W

ao x C

pa (T

gi-T

go Unc

) Gas Side Efficiency

X - Ratio = --------------- = ----------------------- = -------------------------------

Wgi x C

pg (T

ao-T

ai) Air Side Efficiency

Is it Possible to replace existing APH

to Higher size (Maxtra)?

It is possible in most of the cases

What is the grid size for accurately measuring the gas and air temperatures?

Complete mixing is expected after 6 to 8 times length of hydraulic diameter.

Hydraulic Diameter,

for rectangular duct

= 2ab/(a+b)

What is the approximate length of gas outlet duct for complete mixing of gas to get uniform

temperature?

b

a

Usage of 4 Bisector air preheaters in place of 2 Trisector air preheaters?

Using 4 bi-sector air preheaters ( 2 for Py. and 2 for Sy.) is useful for better efficiency, since gas qty. to Py. can be controlled by the damper.

Total leakage will be more in 4 bisector than with

2 tri-sectors

Layout is complicated with 4 bisectors

Capital investment is more in 4 bisectors

Maintenance is easier with 2 trisector

What is the effect of increasing the height of air preheater

It will increase the heat transfer area.

Improved efficiency.

It will increase the pressure drop.

What is the effect of increasing the diameter of air preheater

It will increase the heat transfer area.

Improved efficiency.

It will decrease the pressure drop.

No

Providing sacrificing basket will reduce the performance of Air Preheater

Using lesser thickness will increase the heat transfer area.

- Will slightly decrease pressure drop

Recommended:

Sacrificing element: 0.8/0.6mm

Hot End: 0.5mm, instead of 0.6/0.8mm

Hot Intermediate: 0.5mm , instead of 0.6/0.8mm

Cold End: 0.8mm , instead of 1.2/1.0 mm

Can we use Lesser thickness for elements ?

Element manufacturing has to go with

accuracy.

Always go with reputed manufacturers.

By accepting profiles from un reputed

manufacturers, money is not gained; money

is lost by the way of loosing efficiency.

Is any method of element manufacturing acceptable?

If the element profiles are manufactured

within the tolerance, then Gas out temp. will

not vary more than ± 3°C

What is the formula for calculating leakage?

%ge Leakage = -----------------------------

%ge Leakage = -------------------------------------------------------

For, O2 out = 5.0%, O

2 in = 3.5% Leakage = 8.44%

%ge Leakage = -------------------------------------------------------------

%ge CO2 out

For, CO2 out = 13.8%, CO2 in = 15.8% Leakage = 13%

(Gas Out – Gas In)

Gas In

0.9*(%ge O2 out %ge O

2 in)*100

(21 -- %ge O2

out)

0.9*(%ge CO2 in - %ge CO2 out)*100

%ge Leak

6 8 10 12 14 16 18 22 26

Tgo, ⁰ C

147 145 143 141 139 138 136 133 130

What is the effect of Leakage on Gas outlet temperature?

The leakage is reduced by at least 2.0%.

eg: from 8.5% to 6.5%

What is the effect of Double sealing?

The distance between soot blower nozzle

tip to element surface should be 300mm

What should be the distance between soot blower nozzle tip to element surface?

Deposit of unburnt Carbon particles in Air

Preheater elements leads to fire.

Causes:

• Inadequate atomization of oil

• Improper combustion

• Ignitor leak

• Fire occurrence is more during startup with

oil firing. Frequent soot blowing is required

during startup.

Why fire occurs?

Thermocouple fire detection works reliably better

compared to IRDS. Response is slower than IRDS. Less

cost.

IRDS is highly sensitive. It detects fire even before the

start of the fire itself. That is why, it is called ‘Hot Spot

Detector’. Making the system to work continuously is

difficult. More costlier.

Fire Sensing Device: Thermocouple type or Infra Red (IRDS)?

DC Motor

AC Motor

Small Steam Turbine

Other than air motor any other drive is used as auxiliary drive?

Yes. No Problem.

Whether Electric Motor and Auxiliary Drive can run simultaneously?

Run the air motor once in a week for 30

minutes to keep fit for running during

emergency. During running ensure the flow of

lubricating oil 6 – 7 drops per min.

Keep moisture trap in air line.

Air Motor does not come up during emergency?

Yes.

Whether drive pinion can be reversed?

Support brg is designed to have the L1 life of

100,000 hrs. or 13 years of operation. That

means the chance for failure within this period

is 1%

Usage of lower size brgs. will reduce the life

of brgs.

What is the life of support brg.?

Thank You