cb gf web in aug 2016, controls r2 8.23.16 final

BOILER FEED

WATER CONTROL

Presented by Cleaver Brooks’ Steve Connor

and Grundfos’ Jim Swetye

TODAY’S AGENDA

• Again address high pressure boilers (FT & IWT) in the 100 – 1200 HP range

• Where the water level is measured in these boilers

• The ways in which the pressure in the boiler and system is controlled

• Maintaining a reliable and safe level of water in the boiler is critical

• Ways in which the boiler water level is controlled

• Matching this control with (4) distinct pumping strategies

• A couple pump selection exercises

• Summary

• Q&A

2

FIRETUBE

Watertube (IWT)

Integral burner

Gun burner

Maximizing Efficiency with Hydronic Boilers

3

BOILER SIZES AND

FEED PUMP SIZES

Boiler HP

Range

Boiler

Pressure

Range

Typical Feed

Pump Type

Typical

Max. Feed

Pump

Flow

Range

Typical

Max. Feed

Pump

Head

Where

Used?

100 to

1200

150 to 500

psi

Vertical

inline

multistage;

regenerative

turbines

10 to 125

gpm1250 feet

General

industry;

institutional;

universities;

some

commercial

buildings

4

WATERTUBE OR IWT

Maximizing Efficiency with Hydronic Boilers

5

THE WATERTUBE

BOILER

• Opposite of Firetube

• Water in the Tubes

• Natural and Forced Circulation

• Large Furnace

• Upper & Lower Drums or Headers

Upper Steam Drum

Lower Mud Drum

Furnace

Outlet nozzle location

6

STEAM QUALITY

Steam disengaging area

Water level

IWT Upper Steam drum

Steam outlet

7

THE FIRETUBE

BOILER

8

Steam space

Water level

Steam outlet

9

HEATING SURFACE

Safe water level

2000 Deg. F

900 Deg. F

Steam

10

Operating High Limit Modulating

16

TYPICAL

STEAM SYSTEM

T

T

T

T

T

LegendSteamCond

Vapor

H P Cond Return

D A TankD A Tank

Feed PumpBoiler

Strainer

Trap Trap

TrapTT

TT

DA Tank

TT

TT

TTT

Legend

Trap

HP SteamPRV

LP Steam

Trap

LP Condensate Return

Motive

Force

Flash

Modulating Control or Transducer

17

18

PLANT MASTER

18

PLC BASED

BOILER CONTROLS

19

LOW WATER CUTOFF

& PUMP CONTROL

20

Bowl

Float

Armature

Switching head

LOW WATER CUTOFF

& PUMP CONTROL

21

Pump switch

LWCO Switch

22

At 0”= 2”

Section I, High pressure boilers

is first visible point in GG = 2”

above tubes…

23

Magnetostrictive Technology

Retrofitable!

24

MAGNETOSTRICTIVE

BOILER LEVEL CONTROL

TECHNOLOGY

Sensing rod

Titanium float

Sensor head

Display box

25

PLC Platform

Modulating feed water valve

Pump

Loop Controller(s)

26

VFD Controller

Magnetostrictive level control

27

THREE ELEMENT

FEED WATER CONTROL

28

BOILER FEED PUMP

CONTROL METHODS

1. On/Off control and fixed speed pumps

2. Feed control valve and fixed speed pumps

3. Feed control valve and variable speed pumps

4. Variable speed pumps only (no control valve)

Method# Name

30

Deaerator

Feed pumps Burner Boiler

Control box

METHOD #1 –

On/off control with fixed speed pump

31

Advantages:

• Inexpensive

• Simple to install

• No bypass

• No feed valve

Disadvantages:

• Mechanical stress on the boiler

• Pumps are liable to cavitate at start-up

• Large number of Starts-Stops can

stress pumps

• Variations in steam production

• Boiler water swell and carry-over

METHOD #1 –

On/off control with fixed speed pump

32

Deaerator

Feed pumps Burner

Boiler

Bypass

Feed valve

METHOD #2 –

Feed valve with fixed speed pumps

33

Advantages:

• Minimize risk of boiler water

swell/carry-over

• Feed is adjusted according to

steam consumption

• Steam quality higher due to

more constant water level

Disadvantages:

• Bypass is required

• Feed valves are expensive

• Pressure loss across the feed

valve requires larger sized

pumps

METHOD #2 –

Feed valve with fixed speed pumps

34

Deaerator

Feed pumps

Boiler

Recirculation line

Feed valve

Transducer

METHOD #3 –

Feed valve with variable speed pumps with recirculation line

Level Sensor

35

Advantages:

• Minimize the risk of water

sink & swell/carry-over

• Feed adjusted according to

steam consumption

• Energy savings on pump

operation

• Steam quality higher due to

more constant water level

Disadvantages:

• Bypass is required

• Feed valve is expensive

• Pressure loss across feed valve requires

larger sized pumps

• Stopping pump at closed valve requires

signal from pressure transducer

METHOD #3 –

Feed valve with variable speed pumps with recirculation line

36

RE-CIRCULATION

FLOW WITH AUTO VALVE

Re-circulation

common manifold

Re-circulation lines

Auto Valve in

recirculation line

Service line with

normally closed

shutoff valve

37

Deaerator

Feed pumps

Boiler

Sensor

METHOD #4 –

Variable speed pumps less feed valve

38

Advantages:

• Feed is adjusted according

to steam consumption

• Even steam production

• Faster reaction with

changed speed

• Energy savings on pump

operation

• No bypass line

• No feed valve and

associated pressure loss

• Minimize risk of

swell/carry-over

Disadvantages:

• Requires precise and qualified

start-up

• Non-return valve required

• Minimum frequency must be

defined to ensure pump can

always overcome the pressure in

boiler – pump MUST stop when

steam consumption is zero

METHOD #4 –

Variable speed pumps less feed valve

39

SUMMARY OF

CONTROL METHODS

Method

#Name

Pump

Speed

Type

Duty

Uses

feed

valve?

Is orifice flow

recirculation by-pass

line required?

1 On/Off control and fixed speed pumps Fixed Intermittent No No

2 Feed control valve and fixed speed pumps Fixed Continuous Yes Yes

3 Feed control valve and variable speed pumps Variable Continuous Yes Yes

4 Variable speed pumps only (no control valve) Variable Continuous No No

40

CHECKLIST –

Boiler feed pump selection process

Step Action

1 Determine control method to be used

2 Calculate BASE flow rate

3 Add for by-pass flow if required

4 Sum of base flow and by-pass flow is the total flow required

5 Calculate BASE pumping head

6 Add for all suction piping head components

7 Add for all discharge piping system head components (including feed valve if required)

8 Sum of all head components = total pumping head

9 Determine deaerator tank water temperature

10 Perform NPSHa calculation

11 Make preliminary pump selection

12 Check NPSHr versus NPSHa

13 Assure material compatibility - chemical and temperature

14 Make final pump selection

41

BOILER FEED PUMPS:

USEFUL FORMULAS

1. Base flow calculation equation

Boiler maximum capacity horsepower X 0.069 X C = Base flow rate

C = 1.50 for On/Off intermittent operation

C = 1.15 for continuous feed operation

2. Determine BASE head for feed pump

Formula based on Safety Valve setting:

Pump head in feet = Maximum pressure X 2.31 X 1.03 ÷ Liquid Specific Gravity

3. Head components on suction side of piping system

Pressure above atmospheric on deaerator converted to feet of head = feet

Elevation difference between minimum deaerator water level and pump inlet = feet

Suction pipe friction loss = feet

Suction fitting friction loss = feet

Suction line valves and strainer friction loss = feet

Total = feet

4. Head components on discharge side of piping system

Friction loss through discharge piping = feet

Friction loss through discharge fittings = feet

Friction loss through feed valve = feet

Elevation of boiler maximum water level above pump = feet

Total = feet

5. NPSHa equation

± Elevation** + Absolute pressure – Vapor Pressure – Suction Line Friction = NPSHa

(Feet) (psi X 2.31 = Feet) (psi X 2.31 = Feet) (Feet) (Feet)

** Elevation of deaerator tank minimum water level above pump’s first impeller

42

SPECIFICATION

FOR EXERCISE

a) Control method is variable speed pump with

bypass recirculation and feed valve

b) Boiler maximum capacity = 250 HP

c) Boiler safety valve setting – 125 psig

d) Pressure safety factor = 3% above boiler’s safety

valve setting

e) Boiler operating pressure – 100 psig

f) Continuous Boiler Blowdown flow - Required

g) Bypass recirculation flow – Required

h) Altitude – Sea level

i) Pressure in deaerator tank above atmospheric

pressure = 5 psi (14.7 + 5 = 19.7 psi absolute)

j) Height of deaerator tank minimum water level

above pump’s first impeller = 10 feet

k) Friction line loss through suction piping = .5 foot

l) Friction loss through suction side fittings = .5 foot

m) Friction loss through suction side valves = None

n) Friction loss through suction side strainer = 1 foot

o) Friction loss through discharge piping = 1 foot

p) Friction loss through discharge side fittings = 1

foot

q) Friction loss through feed valve – 15 psi

r) Elevation of boiler maximum water level above

pump’s discharge port = 5 feet

s) Liquid Specific Gravity = 0.955

t) Temperature of water in deaerator tank = 227

degrees F

u) Vapor pressure in deaerator tank = 19.7 psi

v) Pump materials all 316 stainless steel to resist

treatment chemicals

w) Mechanical seal to be silicon carbide/silicon

carbide/EPDM to withstand liquid temperature

43

FROM PREVIOUS

EXERCISE –

Fixed speed pumps with feed valve and recirculation line

Recirculation line

Feed valve

Boiler

Level Sensor

Feed pumps

Deaerator

44

Deaerator

Boiler

Recirculation

line

Feed valveFeed pumps

Transducer

Level Sensor

FROM CURRENT

EXERCISE – #2

Feed Valve with Variable Speed Pumps with Recirculation line

45

STEP 13 –

Preliminary pump selection

• Conditions of

Service:

• Flow = 28 gpm

• Head = 272 feet

Does this 11

stage pump

pump meet the

required flow

and head

conditions of

service?

YES

46

SUMMARY OF

PERFORMANCE CHARACTERISTICS

Advantages of control via variable speed pump versus a fixed speed pump

when using a feed valve and recirculation:

• More even steam production

• Faster reaction with changed speed consumption

• Fewer losses by variable level

• Carry over

• Reduced energy consumption and operating costs

However, the variable speed unit will be more expensive in initial purchase cost.

For this reason, you must perform a Life Cycle Cost calculation before making

your final decision on which method to use.

Exercise #

Use Feed

Valve?

Reciculation

Line? Speed Type

Duty Point

GPM Flow

Duty Point Feet

of Head Pump Size

Number of

Stages

Efficiency at

Duty Point

BHP at Duty

Point

1 Yes Yes Fixed 28 272 1.25 x 1.25 11 65% 2.96

2 Yes Yes Variable 28 272 1.25 x 1.25 11 65% 2.96

47

CURVE COMPARISON –

FIXED SPEED VS VARIABLE

SPEED

Duty point

operation at

3550 rpm

48

CURVE COMPARISON –

CONT.

Fixed speed reduced flow Variable speed reduced flow

Full speed

BHP

Reduced speed

BHP

49

Check list for boiler feed pump selection

Step Action

1 Determine cont rol method to be used


3 Add for Cont inuous Boiler Blowdown flow


5 Sum of base flow, by-pass flow, and Blowdown flow is the total flow required


7 Add for all suct ion piping head components



10 Calculate head at boiler safety vavle set t ing plus three percent


12 Perform NPSHa calculat ion

13 Make preliminary pump select ion

14 Assure that shutoff head equals or exceeds three percent above safety valve set t ing


16 Assure material compat ibilit y - chemical and temperature

17 Make final pump select ion

50

BOILER FEED PUMPS:

USEFUL FORMULAS

1.Baseflowcalculationequation

BoilermaximumcapacityhorsepowerX0.069XC=Baseflowrate

C=1.50forOn/Offintermittentoperation

C=1.15forcontinuousfeedoperation

2.DetermineBASEheadforfeedpump

FormulabasedonSafetyValvesetting:

Pumpheadinfeet=MaximumpressureX2.31X1.03÷LiquidSpecificGravity

3.Headcomponentsonsuctionsideofpipingsystem

Pressureaboveatmosphericondeaeratorconvertedtofeetofhead= feet

Elevationdifferencebetweenminimumdeaeratorwaterlevelandpumpinlet= feet

Suctionpipefrictionloss= feet

Suctionfittingfrictionloss= feet

Suctionlinevalvesandstrainerfrictionloss= feet

Total= feet

4.Headcomponentsondischargesideofpipingsystem

Frictionlossthroughdischargepiping= feet

Frictionlossthroughdischargefittings= feet

Frictionlossthroughfeedvalve= feet

Elevationofboilermaximumwaterlevelabovepump= feet

Total= feet

5.NPSHaequation

±Elevation**+Absolutepressure–VaporPressure–SuctionLineFriction=NPSHa

(Feet)(psiX2.31=Feet)(psiX2.31=Feet)(Feet)(Feet)

**Elevationofdeaeratortankminimumwaterlevelabovepump’sfirstimpeller

51

SPECIFICATION

FOR EXERCISE

a) Control Method: Continuous duty variable speed pump (feed valve and recirculation line are not required)

b) Boiler maximum capacity = 250 HP

c) Boiler safety valve setting = 115 psig

d) Pressure safety factor = 3% above boiler’s safety valve setting

e) Boiler operating pressure = 100 psig

f) Continuous Boiler Blowdown flow - Required

g) Bypass recirculation flow – Not required

h) Altitude – Sea level

i) Pressure in deaerator tank above atmospheric pressure = 5 psi (14.7 + 5 = 19.7 psi absolute)

j) Height of deaerator tank minimum water level above pump’s first impeller = 10 feet

k) Friction line loss through suction piping = .5 foot

l) Friction loss through suction side fittings = .5 foot

m) Friction loss through suction side valves = None

n) Friction loss through suction side strainer = 1 feet

o) Friction loss through discharge piping = 1 foot

p) Friction loss through discharge side fittings = 1 foot

q) Pressure drop across feed valve – None – Feed valve is not required

r) Elevation of boiler maximum water level above pump’s discharge port = 5 feet

s) Liquid Specific Gravity = 0.953

t) Temperature of water in deaerator tank = 227 degrees F

u) Vapor pressure in deaerator tank = 19.7 psi

v) Pump materials all 316 stainless steel to resist treatment chemicals

w) Mechanical seal to be silicon carbide/silicon carbide/EPDM to withstand liquid temperature

52

Deaerator

Feed pumps

Boiler

Sensor

FROM CURRENT

EXERCISE – # 3:

Variable speed pumps (without feed valve

and without recirculation line)

53

STEP 1 –

• Determine control method

• A variable speed pump has been specified. Specification excludes feed

valve and recirculation line

X

Step Action


















54

STEP 2 –

Calculate the BASE feed pump flow rate

The formula for this calculation is:

• Boiler maximum capacity in horsepower X 0.069 X C

• The maximum capacity in boiler horsepower is 250

• The C factor is 1.15 for continuous duty

Therefore:

250 X 0.069 X 1.15 = 20 gpm = BASE flow rate

55

STEP 3 –

Continuous Boiler Blowdown Flow

Determination:

1. The BASE flow rate has been established at 20

gpm

2. We will on next slide need to add for bypass

flow, which can add 10 to 20 percent to the

BASE flow rate

3. Blowdown flow is to be approximately 10 percent

of flow at pump’s Best Efficiency Point

4. So the total boiler blowdown flow required is

approximately 3 gpm

56

STEP 4 –

Recirculation by-pass flow

Not required per the specification

57

STEP 5 –

Calculate total flow required

• BASE flow = 20 gpm

• Blowdown flow = 3 gpm

• Recirculation flow = 0 gpm

• Total flow required= 23 gpm

X

X

X

X

X

Step Action


















58

STEP 6 –

Calculate BASE pumping head

• Boiler operating pressure setting + 3%

Formula: BASE head in feet = Boiler operating pressure X 2.31 X 1.03 ÷ Specific Gravity

BASE head = 100 psi X 2.31 X 1.03 ÷ 0.953 = 250 feet

59

STEP 7 –

Add for suction piping system head components

From specification:

Gauge pressure on deaerator tank = 5 psi X 2.31 = - 12 feet

Water elevation above first impeller = - 10 feet

Friction loss through suction piping = + .5 feet

Friction loss through suction fittings = + .5 feet

Friction loss through suction side valves and strainer = + 1 feet

Total = - 20 feet

60

STEP 8 –

Add for discharge piping system head components

From specification:

Friction loss through discharge piping = + 1 foot

Friction loss through discharge fittings = + 1 foot

Friction loss through feed valve = + 0 feet

Elevation of boiler maximum water level above pump = + 5 feet

Total = + 7 feet

61

STEP 9 –

Sum of all head components

BASE head with safety factor = + 250 feet

Suction side piping system head = - 20 feet

Discharge side piping system head = + 7 feet

Total = + 237 feet

62

STEP 10 –

Pressure safety valve considerations

At shutoff head (dead head):

Head in feet = Pressure relief valve setting X 2.31 X 1.03 ÷ Liquid Specific Gravity

Example: Head = 115 psi X 2.31 X 1.03 ÷ 0.953 = 287 feet

X

X

X

X

X

X

X

X

X

X

Step Action


















63

STEP 11 –

Determine deaerator tank water temperature

From specification: 227°F

64

STEP 12 –

NPSHa calculation

NPSHa equation:

± Elevation + Absolute pressure – Vapor Pressure – Suction Line Friction = NPSHa

10 feet + (19.7 psi X 2.31) - (19.7 psi X 2.31) - 2 feet = NPSHa

10 feet + 46 feet - 46 feet - 2 feet = 8 feet NPSHa

65

STEP 13 –

Preliminary pump selection

• Conditions of

Service:

• Flow = 23 gpm

• Head = 237 feet

Does this 9

stage pump

pump meet the

required flow

and head

conditions of

service?

YES

66

STEP 14 –

Pressure safety valve considerations –

check requirement vs actual

67

STEP 15 –

Check NPSHa vs NPSHr

• Conditions of Service:

• Flow = 23 gpm

• Head = 237 Feet

• NPSHa = 8 Feet

• Pump meets or exceeds

flow/head requirement

• Low-NPSHr first stage = 3.5 feet

required

• NPSHr safety factor = 2 to 4 feet

• Target NPSHr = 7.5 feet

• NPSHa = 8 feet

Does NPSHa equal or exceed NPSHr?

YES

68

STEP 15 –

NPSH - Continued

• Conditions of Service: Flow = 23 gpm Head = 237 feet NPSHa = 8 Feet

• The NPSHa of 8 feet exceeds the NPSHr of 7.5 feet

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Step Action


















69

STEP 16 –

Check material compatibility

• Pump materials: 316 stainless steel

• Mechanical seal materials: Silicon carbide/silicon carbide/EPDM

70

STEP 17 –

Final pump selection

• Pump meets all specification requirements

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Step Action


















71

SUMMARY OF

PERFORMANCE CHARACTERISTICS

Exercise

#

Speed

Type

Use

Feed

Valve?

Reciculatio

n Line?

Duty Point

GPM Flow

Duty Point

Feet of

Head

Pump

Size

Number

of Stages

Efficiency at

Duty Point

BHP at

Duty

Point

1 Fixed Yes Yes 28 272 1.25 x 1.25 11 65% 2.96

2 Variable Yes Yes 28 272 1.25 x 1.25 11 65% 2.96

3 Variable No No 23 237 1.25 x 1.25 9 63% 2.18

Advantages of control via variable speed pump without feed valve and without bypass:

• Even steam production

• Faster reaction with changed speed consumption

• Fewer losses by variable level

• Carryover

• Few stages – lower initial cost

• Eliminate feed valve expense, maintenance, and head loss

• Eliminate bypass line expense and wasted flow recirculation

• Reduced energy consumption and costs

• Particularly at reduced speeds, flows, and heads

• Disadvantage: More complex to commission and start up.

72

6

1

GRUNDFOS TECHNICAL

INSTITUTE

www.grundfos.us/training

• Virtual Classroom

- Self-Paced

- Over 40 courses

- Certificates of Completion

• Webinars

- Live and Recorded

• Face-to-Face Training

73

http://www.grundfos.us/training

SUMMARY

• The low water cutoff and pump control is the most important safety device on the boiler.

• It controls the safe level of water in the boiler and shuts it down when the level drops to an unsafe

level

• The level control may include a float with switches or other electronic devices providing safe

monitoring and pump, and/or MFWV energizing.

• These electronic level controls can work in conjunction with VFD’s

• Three element feedwater control involves the interrelationship of level, steam flow, and feedwater flow

• With on/off pump control the signal comes from the LWCO and there is no MFWV or by-pass line.

• Continuous running pump strategy with MFWV includes a by-pass to assure proper operation, and it

may add to the size of the pump.

• A continuous running pump with VFD & MFWV also requires a by-pass line to compensate for no or

low flow conditions.

• With this strategy, the signal for the MFWV normally comes from the level control and a separate loop

controller is used for the VFD.

• With the Auto valve in the by-pass line, the re-circ stops when full flow conditions exist, saving pump

energy, and possibly resulting in a smaller pump size..

• .With VFD and no MFWV, the re-circ line is eliminated resulting in a smaller pump selection

• This strategy requires an expert technician for commissioning.

74

Gregg Achtenhagen

[email protected]

Jim Swetye

[email protected]

QUESTIONS?

mailto:[email protected]

cb gf web in aug 2016, controls r2 8.23.16 final

Education