cht bip shell besst practice - flue gas dewpoint_v2

8/12/2019 CHT BIP Shell Besst Practice - Flue Gas Dewpoint_v2

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Best Practise for Kochi BIP Energy Management

Furnace & heat exchange various

20 March 2007


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Air preheaters - why

Higher efficiencies- Can raise by 5 to 10%

Higher flame temperature

- Better combustion quality- But potential for increased NOx emissions


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Furnace efficiency as a function of stack exit temperature

Assuming 0% radiation losses, and 20C outside temperature

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0 2 4 6 8 10 12 14

Measured stack oxygen - vol% or m ol%

Furnace

efficiency

150 200 350 450 550 650 750 850 950 1050

Stack exit temperature (C)


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Air preheaters - constraints

Flue gas exit temperature too low- Dewpoint corrosion- Keep cold corner metal wall temps > dewpoint + 15C

- Consider LPS preheat preheater

Air to furnace too hot- Nox formation


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Simplified schematic


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50

Fuel Oil

C/H ratio : 6 kg / kg(10% H2O in Flue Gas)

Fuel Gas

MW = 20 kg / kmoleC/H ratio : 3,4 kg / kg(15% H2O in Flue Gas)

1000101

% mass S in Fuel Oil

ppm (vol) H2S in Fuel Gas

75

50

100

125

150

1 5 100,50,1

100

125

150

100505 500

1 5 100,5

175

AcidDew

point,C


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Heat exchanger foulingHeat exchanger fouling

Due to fouling, Heat Exchangers (HX) suffer from efficiency loss over time


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Heat exchanger cleaningHeat exchanger cleaning

Clean-out dates are clearly visible in a HX OHTC curve

Goal: find the optimal clean-out schedule for a HX with respect to cost

Clean-out dates


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VOEDING

F-201 A/

B/C

P-202

A/B

E-204

LGO

E-203

KERO

E-205

HGO

KERO

E-209AB

LGO

DAMPNAAR C-201

V-

201

P-201A/B

E-211BE-210B

E-211AE-210A

OCRLONGRESIDU

C-202

E-211CE-210C

E-206A

MCR C-201

E-206B

V-101-

A

E-207AB

LONG RES.

E-207CD

E-202A

E-202B

E-201A

TCR C-202

E-201B

TCR C-201

E-

213AB

LONG RES.

E-213CD

E-

212A

OCR C-201

E-212B

N.C. N.C.

N.

C.

N.C.

E-208AB

N.C.

MIXE

R

PROCESWAT

EREX V-

801

PROCESWATERNAAR C-801

V-101-

B

NAAR V-101-A

MIXE

R


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Heat exchanger networkHeat exchanger network

Optimisation for a single HX is straightforward

The interaction between heat exchangers in a heat exchanger network,

however, requires the use of advanced optimisation techniques.

HX_A HX_B

FhotA

ThotA_out ThotB_out

Tcold_in

Fcold

TcoldA_out TcoldB_out

FhotBThotA_in ThotB_in


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HEAT4N Optimisation

HEAT for Networks (HEAT4N) is designed to:

Determine an optimal clean-out strategy for a train of heat exchangers

by minimising the overall averaged costs ($/day).

Overall costs are defined as:

Efficiency loss costsThroughput loss costs +Product quality loss costs +

Clean-out costs +_____________________________________Overall Costs


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HEAT4N Software

HEAT4N is a user-friendly flowsheeting software package.

HEAT4N provides predictive foulingmodels for heat exchangers in anetwork

The fouling models, combined witheconomical parameters, determinethe optimal clean-out scheme for atrain of heat exchangers

Heat for Networks graphical user interface.


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HEAT4N Output Optimal clean-out scenario

The clean-out scenario provides:- Most cost-effective clean-out frequency with corresponding costs

-Average overall costs- Regret costs for postponing cleaning of a HX. This identifies bad actorsin the train.

0926.2HX21

..95,6101,3060.6HX3

01844.4HX2

27,3301400.8HX1

Cumulative Regret Costs,postponing one year [$]

Average OverallCosts [$/day]

Optimal Clean-Out period [y]

Name


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HEAT4N Output User specified clean-out scenarios

The optimal clean-out scenario might be difficult to implement. Therefore, incooperation with technologists, different clean-out scenarios are compared to findthe most cost-effective applicable clean-out scheme; i.e. comparison of costs for

different (user-specified) clean-out scenarios.

The output from the user-defined scenarios can provide decision support formaintenance optimisation

2889410.3222.6Scenario 3

365323.8216.1Scenario 2

388011.6213.9Scenario 14077-212.3Base case

Av overallcosts [$/d]

Extra bundles tobe cleaned

Increase in FIT[C]

FIT [C]Scenario


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HEAT4N Benefits

As a decision support tool HEAT4N will

Cut operational & maintenance costs

Increase profits Require absolutely no capital investment or significant changes to

your existing operational structure Allow you to establish an optimal heat exchanger cleaning schedule

for future years


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Advanced furnace controls why ?

Safety- Consistency with protective functions

Reliability

- Control scheme to avoid loss/trip of furnace

Cost- Drive oxygen down consistently to best practise =>

fuel savings


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Advanced Air/Fuel Ratio Control of

Heaters/Boilers

Dual Fuels

Double ratio cross limiting to Shell DEP Standard Minimum air/fuel ratio

Fuel gas compensation (density/composition) Oxygen trimming control

Protective controllers Integration with safeguarding and protectivecontrols


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Typical Design Inadequacies Encountered

Safeguarding implemented not in accordance with Shell standards

Critical I/O not redundant

No mechanical stops on heater/boiler air blower dampers

Air/fuel ratio control system air leading, with no limits on increase

of air in case fuel flow does not follow

No compensation for fuel gas composition

No low air/fuel ratio protection provided

Instrumentation problems Burner turndown

Advanced Air/Fuel Ratio Control of Heaters/Boilers


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D-1050Fuel Gas

Advanced A/F Ratio Control

(Fuel Oil and Fuel Gas)

PIxx

To Pilots

From Air Flow FT

To Air Flow FC SP

To FG CVvia signal

selector

To FO CVvia signal

selector

Y3

AI

xx

FT

xx

Y2

Y6

Y7

Y9

Y17Hsel

Y10

Y8

Y16Lsel

QC

Oxygen

Fuel Oil Supply

Fuel Oil Return

XSLLxx L

LL

Min Air

Max fuel

A/F Ratio

arwu

LOAD

To Burners

FCxx

I

Y5

FI

FC

Y4

I

Y1

Y22

FTFT


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Important Messages

Advanced air/fuel ratio control can producesignificant benefits, but care needs to be taken to

integrate control with safeguarding and ensureinstrumentation is working well.

ATTENTION TO DETAIL

cht bip shell besst practice - flue gas dewpoint_v2

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