NOH HeatTransfer

David Cronin-Ohio Valley Area Manager

Heat Transfer, Controls & Instrumentation, Metering.

David Cronin-Ohio Valley Area Manager

Heat Transfer, Controls & Instrumentation, Metering.

Heat Exchangers

Selection IssuesSelection Issues

• Maximum design Capacity

• Steam Supply pressure

• Materials of construction

• Space and access

• Controls/Communication

• Steam Quality

• Load TURNDOWN

• Condensate quality & system Issues

• Maintenance of ALL components

• Maximum Pressure Drop allowed

• Water Quality-TDS, hardness, chlorides

Selection IssuesSelection Issues

• Maximum design Capacity

• Steam Supply pressure

• Materials of construction

• Space and access

• Controls/Communication

• Steam Quality

• Load TURNDOWN

• Condensate quality & system Issues

• Maintenance of ALL components

Metal Wall

Scale Film

Steam

Air Film Stagnant Water

Condensate Film

Heat Transfer Q = “U” x A x DT

Water

Being

Heated

Heat Transfer

Steam Supply QualitySteam Supply Quality

• LP steam carries more Btu’s, increases efficiencies.

• LP steam is normally better quality, increasing efficiencies.

• LP steam REDUCES scaling (The lower the better).

• LP steam typically requires PRV’s to generate from HP.

• PRV’s require space and give more to maintain.

• LP steam requires large pipes.

• LP condensate is difficult to drain from HX.

• HP steam requires no PRV’s and smaller pipe.

• HP steam makes HX, conditioning, & control equipment smaller.

• Installation less expensive with HP steam.

• We can combine the benefits from both systems !

Methods of ControlMethods of Control

Constant Pressure with float & thermostatic steam trap- “Wild loop”

Constant Pressure with float & thermostatic steam trap in

conjunction with mixing valve

Constant Pressure with control of the heating surface

Control “Mass” flow of steam with discharge temperature of the

Secondary Side

Typical HX ???-Open SystemTypical HX ???-Open System

Steam and Condensate QualitySteam and Condensate Quality

• Vacuum breakers introduce air !!!!

• Reverses Heat Transfer !!!!

• Wastes steam !!!!

• Increases duty cycles of heat transfer equipment !!!!

• Increases duty cycles of Control equipment !!!!

• Barriers heat transfer, reduces heating efficiency !!!!

• Reduces equipment capability to handle load changes !!!!

• Corrodes (oxygen pitting) Heat Transfer Equipment !!!!

• Generates Carbonic Acid !!!!

• Erodes Heat Transfer Equipment !!!!

• Corrodes/erodes Condensate System !!!!

• Increases Chemical requirements !!!!

“STALL” Issues“STALL” Issues

• Poor Control !!!!

• Slow response to load changes !!!!

• Noise !!!!

• Waterhammer !!!!

• Leaking Gaskets !!!!

• Damaged / Failed Equipment !!!!

• Increased Maintenance !!!!

• Premature failure due to thermal

Cycling

Definition: The point at which the necessary pressure differential across the

trap is below the point at which condensate can be removed from the heat

exchanger.

Loss of Positive Differential PressureLoss of Positive Differential Pressure

www.SpiraxSarco.comwww.SpiraxSarco.com

APT rangeStall due to elevated return line

15 metres

1.5 bar g

1.0

bar g

Air Heater

Battery

A steam trap is

being used to drain

the system


APT rangeStall due to elevated return line

15 metres

1.5 bar g

1.0

bar g

Air Heater

Battery

A steam trap is

being used to drain

the system

Condensate backing up into

heat exchanger-loss of “A”

Condensate backing up into

heat exchanger-loss of “A”


APT range

Heat Exchanger

P2

P1

Product Temperature Input

Stall conditions


APT range

Heat Exchanger

P2

P1


Stall conditions

Temperature Control Valve Opens and

positive differential pressure is increased.Temperature Control Valve Opens and

positive differential pressure is increased.


APT range

Heat Exchanger

Stall conditions

P2

P1



APT range

Heat Exchanger

Stall conditions

P2

P1


“Stall Chart”“Stall Chart”


APT range

Total back pressure

- 0.4 bar

Steam pressure (temp)

- 2 bar

Initial Temperature Product

- 30 oC

% Flow (% control valve opening)

Final Temperature product

- 80 oC

Temperature ºC

Product Temperature

200

20

40

60

80

100

120

140

160

180

0

100 90 80 70 60 50 40 30 20 10 0

14.5

11.6

0

0.7

0.5

0.05

2.6

0.3

0.2

0.1

9.0

7.0

5.2

3.8

1.7

1.0

0.4

T1

P1

T2

P2

1

3

Air Heater

Application

Pressure bar g

2

Variable inlet temperature stall chart


APT range

Total back pressure

- 0.4 bar

Steam pressure (temp)

- 2 bar

Initial Temperature Product

- 30 oC

% Flow (% control valve opening)

Final Temperature product

- 80 oC

Temperature ºC

Product Temperature

200

20

40

60

80

100

120

140

160

180

0

100 90 80 70 60 50 40 30 20 10 0

14.5

11.6

0

0.7

0.5

0.05

2.6

0.3

0.2

0.1

9.0

7.0

5.2

3.8

1.7

1.0

0.4

T1

P1

T2

P2

1

3

Air Heater

Application

Pressure bar g

2

Variable inlet temperature stall chart

Waterhammer.Waterhammer.

Typical Heat Exchanger Types UsedTypical Heat Exchanger Types Used

•Shell and Tube-most common

•Plate and Frame

•Plate and Shell

Shell & Tube Heat ExchangerShell & Tube Heat Exchanger

•Horizontal or Vertical Installations

•Lowest “U” value of the 3 types

•“Withdrawal” distance equal to length of heat exchanger

•Lowest Cost in low to medium flowrates

•Simple Design

•Steam should be installed in the shell side

•Lowest Pressure Drop on Product Side

Plate & Frame Heat ExchangerPlate & Frame Heat Exchanger

•Very High “U” Value

•Ability to increase/decrease area with process changes

•Stainless steel is standard in gasketed models

•Small Footprint and floor space

•No Withdrawal distances required

•Install new plate pack WITHOUT pipe disruptions

•Long history of use in the process industries

•History of failure in steam systems due to “Stall”

•Perception that they do not work in steam systems

Plate & ShellPlate & Shell

•Very High “U” Values

•Typically used for high flowrates

•Not susceptible to thermal cycling

•Long History in the OPC Market

•Repairable Units relatively expensive

•Sealed units can be cost effective in high flow conditions

•Higher Pressure drop on process side

Closed Loop DrainageClosed Loop Drainage

Steam Supply QualitySteam Supply Quality

• LP steam carries more Btu’s, increases efficiencies.

• LP steam is normally better quality, increasing efficiencies.

• LP steam REDUCES scaling (The lower the better).

• LP steam typically requires PRV’s to generate from HP.

• PRV’s require space and give more to maintain.

• LP steam requires large pipes.

• LP condensate is difficult to drain from HX.

• HP steam requires no PRV’s and smaller pipe.

• HP steam makes HX, conditioning, & control equipment smaller.

• Installation less expensive with HP steam.

• We can combine the benefits from both systems !

Closed Loop Drainage +Closed Loop Drainage +

HP Steam

LP Heat Transfer

Closed Loop Drainage +Closed Loop Drainage +

HP Steam

LP Heat Transfer

HX Size ???

Plate & Frame HXPlate & Frame HX

• Smaller Footprint

• Large Surface Area’s for LP Transfer.

• NO Tube Withdrawal space req’d

• Easier to maintain

• Some Flexibility with capacity

• Stainless wetted parts as standard

• Higher efficiency

• Better control Accuracy

• More responsive

Drain

Gutter !!!

Pipe size!

Trap

New

Condensate

Old

Condensate

New

HP SteamOld

LP Steam

EASI-HEAT UNITSEASI-HEAT UNITS

EASIHEAT UNITSEASIHEAT UNITS

“EASIHEAT”Maximizes Efficiency

Minimizes Install Cost

Maximizes ROI

Natural Gas Technologies Centre ReportNatural Gas Technologies Centre Report

The thermal efficiency of a Plate &

Frame averages 93.8% while that of

the shell-and-tube with automatic

pump trap (APT) averages 87.4%, a

6.4% efficiency advantage for the

Plate & Frame heat exchanger…

Summary – Heat Transfer

HP SupplyMinimizes Installation issues

LP Heat TransferMax efficiency

Min maintenance

Closed LoopCorrect condensate removal

Max Efficiency / Min Maintenance“APT”

Heat Exchangers

Hot Water Heat ExchangersHot Water Heat Exchangers

• Instantaneous variable load capability

• Eliminates hot water storage and Legionella

bacteria risk

• Accurate temperature control

• P&F construction designed for steam use

THANK YOU !!!

Questions

?????

Questions

?????

“EASIHEAT”Maximizes Efficiency

Minimizes Install Cost

Maximizes ROI

Documents

NOH HeatTransfer