1-How do you decide
Right hand side & Left hand side of a Boiler?
Boiler front is decided based on boiler outlet duct.
If you stand by facing towards
boiler out let duct, then the most front part of you is deemed as Boiler front
, next to that is boiler rear & LHS & RHS side of you is deemed as
Boiler left hand side & right hand side.
2-Why in Some HP boilers drums are aligned at an angle 2 to 40 towards
right or left?
Drum slanting side depends on the
connection of CBD line. If CBD line is connected at LHS side of the drum then
the drum is slanted towards LHS side that is it is made down by an angle 2 to 40.
This is because to avoid the blow down of excess water throughout the
drum length & for such drums CBD line is extended for only for short
distance only .And also it is been ensured that all the sludge will collect at
slant position only.
3-How it is been decided that RHS or LHS safety valve of steam drum is
set at higher pressure?
It is decided based on the
slanting angle of steam, drums & CBD line connection.
If drum is aligned horizontally
then you can set any side of the Safety valve at higher pressure as there is
uniform spreading of sludge in drum.
Whereas if drum is slanted (made
down)towards right or left from where CBD line is connected then it is needed
to set that side safety valve at higher pressure to avoid carryover of sludge
into the safety valve if t blows first. Such sludge will deposit on safety
valves disc & seat which again leads into leakages & wrong operation
related issues. So safety valve of such location is always set at higher
pressure.
4-Why thickness of steam drum dish end is somewhat lesser than other
area
Because dish end has spherical
shape, so there develop hoop or circumferential stresses & on the other
part of the drum longitudinal stress.
For Hoop stresses
σc = Pd/2tη
Thickness t = Pd/(2 ησ)
& For longitudinal stresses
σl = Pd/4tη
Thickness t = Pd/(4 ησ)
Where P = Pressure acting & d
is internal diameter of the drum
Based on above relations
thickness for spherical part of the drum that is dish end, the thickness is
lesser than other part of the drum.
5-Why the start up vent is used in Boilers?
Start up vent is used for
- To provide minimum steam flow
from the boiler during start up, shutdown & sudden load cut off
- It is used to manual relieve of
excess pressure
- Used to give excess flow for
temperature rising during start up or partial loads
- Used to take excess load on
boilers during peak load test
6-Why the super heater safety valve is set at lower pressure than drum
safety valve
If drum safety valves set at
lower pressure, then there will be very less or no steam flow to super heaters.
In order to save super heater
coils from starvation due to no flow of steam during steam blow from drum
safety valves, the super heater safety valves are always set at lower pressure
than drum safety.
7-Why LHS/RHS water wall panels expand more (towards down) than front
& rear water wall panels?
Side water panels are usually
straight hence expansion readings show more value where as front & rear water wall panel
will have bends.
8-Why pressure gauges fitted at boiler firing floors show more pressure
than actual (that of fitted at steam drum EL.level)
Pressure gauges show 2 to 3
kg/cm2 higher pressure due to addition of hydraulic head in PG impulse line
laid from actual location to firing floor
9-Why there is a pressure difference between main steam line pressure
& drum pressure?
Main steam line pressure shows
lower pressure than drum pressure due to pressure loss in super heater coils.
And this pressure difference increases as the number of super heater coils &
steam flow increase.
10-Why do high pressure Boilers have higher efficiency & lower fuel
consumption?
Because:
1-High pressure boilers have higher
saturation temperature
2-High pressure boilers have
higher feed water temperature at economiser inlet
3-High pressure boiler have lower
enthalpy of evaporation (latent heat)will be less
H = Hf + Hfg + Cps x (Tsup-Tsat)
-
Where,
Hf = Enthalpy of liquid at
operating pressure
Hfg = Latent heat
Tsup = Suepr heated steam
temperature
Tsat = Saturated temperature of
steam
Example:What amount of heat
would be required to produce 5000 kg of steam at a pressure of 65 kg/cm2 and temperature 485 °C from water at temperature 175
°C?
Steam
pressure P = 65 kg/cm2
Steam
temperature Tsup = 485 °C
At
above parameters, saturated temperature Ts = 282.7
°C
hf =
298.82 kcal/kg, hfg = 364.47 kcal/kg
Now,
enthalpy of 1 kg of superheated steam
Hsup= hf + hfg + Cps (Tsup - Ts)
hsup
= 298.82 + 364.47
+ 0.5 X (485
- 282.7)
hsup
= 764.44 kcal/kg
Amount
of heat already associated with 1 kg of water =
1 X 1 X (175 – 0) X 175
kcal/kg
Therefore
net heat to be supplied per kg is 764.44 – 175 = 589.44 kcal/kg
11-Why there is more CO in flue gas?
More CO
in flue gas is due to improper combustion, that is due to
- Less
excess air
- In
adequate turbulent
- Lower
furnace/bed temperature
- Higher
FC in fuel
12-Why Does boiler furnace pressure
fluctuate?
- Interrupted fuel flow
- Leakage in boiler pressure parts
- Furnace combustion controller not
working properly
- Malfunctioning of fans pneumatic
dampers
- Higher moisture in fuel
13-Why there is more NOX in flue
gas?
- Higher NOx is due to
- Higher bed temperature or furnace
temperature
- Higher excess air
- More N2 in fuel
14-Why there is no Temperature gauge (TG) is fitted on steam drum of any Boiler?
In steam dream
the phase of water is at saturated state, so no any necessary of providing TG.
However temperature gauges are provided at drum inlet feed water line &
drum outlet saturated line.
In some drums
whose thickness is > 100 mm, there you may find thermo couples for measuring
skit temperature. So in order to avoid weakening of steam drums due to
making number of drill holes for unnecessary instruments, the TG is not
generally provided for drums.
For example
if drum PG showing pressure 110 kg/cm2, then its temperature will
be around 320 deg c. (Refer steam table for saturation temperature). And
generally not used in any calculation or performance analysis, if required one
can refer steam tables for saturated water
The temperature
gauge or thermo couple provided at the drum outlet lines is used during plant
start up.
can you please explain the flow path of steam in turbine vacuum ejector system with real images and show different parts like after cooler inter cooler in a single condenser arrangement.
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