**DESIGN DATA FOR BOILER FEED PUMS**

**Design data from site:**

Ø
Type
of liquid handled and its maximum & minimum temperatures

Ø
Water
qualities like pH & Hardness

Ø
Water
Kinematic Viscosity (cst)

Ø
Specific
gravity of water at operating temperature

Ø
Net
positive suction head required (NPSHR)& available (NPSHA)

Ø
Boiler
capacity & operating pressure

Ø
Maximum
& operating blow down rate of Boiler

Ø
Height
of Steam drum

Ø
Height
of Deaerator (Water inlet source)

Ø
Pressure
drop in Economiser

Ø
No.of
valves used in feed water discharge line & corresponding pressure drop as
per standard.

Ø
Maximum
& minimum suction pressure available at pump suction

Ø
Type
of cooling water & its maximum flow available for bearings cooling

**Pump Design Data:**

Ø
Rated
flow (M3/hr)

Ø
Rated
head (meters)

Ø
Nominal
speed & Effective speed (RPM) (NS > ES)

Ø
NPSHR
(meter)

Ø
Pump
& Motor efficiency

Ø
No.of
stages of pump

Ø
Motor
rating

Ø
Pump
suction & discharge nozzles sizes

Ø
Vapour
pressure (kg/cm2)

Ø
Pump’s
shut off head (meter)

Ø
Pump
minimum flow (25 to 30% depends on pump operating head & flow)

Ø Cooling water pressure

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**Other considerations:**

Ø
Balance
leak off water flow source (generally balance leak off water is diverted to Deaerator)

Ø
Pump
Rotation direction (Clock wise viewed from drive end)

Ø
Cooling
water flow rate (LPM)

Ø
Pump’s
suction & discharge elements hydro. Test pressures

Ø
Material
of constructions (MOC) of all pump internals

Ø
Type
of coupling used between pump & motor shaft

Ø
Type
of Shaft seal used (Mechanical seal)

Ø Protections given for pump (Protections like, bearing vibration sensors, bearing temperature sensors, pressure relief valve for balance leak off line, phase sequence relay for direction of rotation, cooling water pressure, pump over load etc)

**Boiler feed pumps Questions & Answers**

**Calculate the boiler feed pump and motor size required for a boiler
of capacity 90 TPH has steam drum working pressure 88 kg/cm2. The height of the drum is 35 meter from boiler feed
pump Centre. And the suction water to pump is taken from Deaerator which is
situated 15 meter above the pump centre.**

Given that,

Boiler capacity: 90 TPH =
90 M3/hr

Steam drum operating
pressure = 88 kg/cm2

Steam drum height from
pump centre = 35 meter

Height of Deaerator tank
from pump centre =15 meter

**Assumption:**

Boiler blow down 1%

Deaerator operating level
from floor: 2.5 meter

Pressure drop in Boiler
economizer: 2.5 kg/cm2

Pressure drop in feed
water control station: 5 kg/cm2

Pressure drop in line,
gate and globe valves and bends of feed water line: 5 Kg/cm2

Pump operating
temperature: 110 °C

Economizer out let feed
water temperature: 275 °C

Pump and motor efficiency:
65% and 95% respectively.

Total required discharge
head for pump = (Drum operating pressure + Drum height (m) + Economiser pressure
drop + Control valve pressure drop + Pressure drop in line, gate and globe
valves and bends) X 1.10 (Take 10–15% extra margin)

= (88 kg/cm2 + 35 meter + 2.5 kg/cm2 + 5 kg/cm2
+ 5 kg/cm2) X 1.1

Convert all the pressure
head into gravity head in meter from formula P = Density X g X H…by taking the
densities of fluids (water) at operating temperatures.

P = Desnity X g X H

Then, we have,

Total discharge head = (1248
m + 35 m + 33 m + 52.5 m + 52.5 m) X 1.1 = 1563 meter

Pump rated flow = (Boiler MCR
+ Blow down %) X 1.25 (Take 25–30% extra margin)

= (90 + (90 X 1/100))
X 1.25

** = 113.625=
115 M3/hr**

The Capacity of flow seems more, it is better to consider 3 pumps 2 running & 1 stand by

**Case-I:**

Select 2 Nos of
pumps 1 working & 1 standby (1W+1S)

For motor power, we have

Pump hydraulic power Ph = (Flow (m3/sec.)
X Total head (Hd - Hs) X g (m/sec2)
X density of feed water at 110 °C)/1000

= 0.0319
X (1563 - 15 - 2.5) X 9.81 X 951/1000

** = 459.94 KW**

Pump shaft power Ps = Pump hydraulic power X 100/Pump
efficiency

= 459.94 X 100/65
= 707.60 KW

Motor input power = (Pump
shaft power X 100/Motor efficiency) X 1.10

= (707.60 X 100/95) X 1.10

** =819.32
KW**

From motor selection chart
select Standard sized motor that is 825 KW

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**Case-II**

Select 3 Nos of pumps, 2 Working & 1
stand by (2W+1S)

Then, capacity of the one pump = 115/2 = 57.5
M3/hr (May take 58 m3/hr round figure)

For motor power, we have

Pump hydraulic power Ph = (Flow (m3/sec.)
X Total head (Hd - Hs) X g (m/sec2)
X density of feed water at 110 °C)/1000

= 0.01611 X
(1563 - 15 - 2.5) X 9.81 X 951/1000

= 232.28 KW

Pump shaft power Ps = Pump hydraulic power X 100/Pump
efficiency

= 232.28 X 100/65 =
357.35 KW

Motor input power = (Pump
shaft power X 100/Motor efficiency) X 1.10

= (357.35 X 100/95) X 1.10

** = 376.16
KW**

From motor selection
chart select Standard sized motor that is 375 KW

**Factors Considered for Boiler Engineering**

Comparing Case-1 &
II

Total
Installation capacity of Boiler feed pumps for case-1 = 825 X 2 = 1650 KW

Total
Operation power = 825 X 85% = 701.25 KW

Total
Installation capacity of Boiler feed pumps for case-II = 375 X 3 = 1125 KW

Total
Operation power = 375 X 2 X 85% = 637.5 KW

In
view of energy conservation considering Case-II is feasible. But in view of installation
& maintenance cost Case-I is feasible.

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