applications of gas turbines - gten.cagten.ca/downloads/2011presentations/11-iagt-105.pdf · 14 is...

19th SYMPOSIUM ON INDUSTRIAL

APPLICATIONS OF GAS TURBINES

Presented at the 19th Symposium on Industrial Application of Gas Turbines (IAGT)

Banff, Alberta, Canada - October 17-19, 2011

The IAGT Committee shall not be responsible for statements or opinions advanced in technical papers or in symposium or meeting discussions.

MEASURING HYDROCARBON DEW POINT,

THE ECONOMIC IMPACT

by

Jack Herring / Michell Instruments, Inc.

Outline

• Introduction

• Fuel Quality Issues

• Superheat for CGT Operation

• Hydrocarbon Dew Point

• Costs/Risks of Inadequate HCDP Data

• HCDP Measurement Methods

• Instrument Cost Saving / Risk Reduction

2

11-IAGT-105 MEASURING HYDROCARBON

DEW POINT, THE ECONOMIC IMPACT

Introduction

3



+ =

BUT WHAT IF …

… The Gas Is Wet / Dirty?


DEW POINT, THE ECONOMIC IMPACT 4

The Picture Changes



+ =

Could it be from high Hydrocarbon Dew Point?

Quality Fuel =



Clean Gas Burns Right



Clean Gas Burns Fast



High HCDP – Burns Too Long



HCDP – What Is It?



But There‟s A Pressure Issue



Drop the pressure

from 1000 psig @

70 F and you cut

the envelope –

now you have

condensate.

Superheat is

needed to

address that risk.

What Are The Real Risks?

• Excess NOX - Fines and penalties - The

majority of the NOX produced in the

combustion chamber is called 'thermal

NOX '. …The reaction rates are highly

temperature dependent, and the NOX

production rate becomes significant above

flame temperatures of about 1815 C

(3300 F).



… Risk? (cont.)

• Combustor Damage – Operating above

the design temperature damages burners

and other hot zone components..



BURNT BURNER TIP END COVER ASSEMBLY PRIOR

TO REPAIRPhotos courtesy Gas Turbine Efficiency, Ltd.

… Risk? (cont.)

• Flashback Damage – Impacts even more

components in a turbine engine.



Photos courtesy Dr. Meherwan Boyce, “Major Problems in Combined Cycle Power Plants”

Don‟t Know The Dew Points?

Add more heat

to be sure you

don‟t cut that

envelope.

What does that

cost – heating

80 instead of

50 could cost

$650,000/yr!11-IAGT-105 MEASURING HYDROCARBON


How Is HCDP Measured?

• Manual Optical Method

• EOS From GC Data

• Automatic Optical Dew Point



Manual Optical Dewscope

PROS

+ The traditional and widely

used measurement

technique

+ The de facto standard for

hydrocarbon dew point

measurement

+ Low capital investment

CONS

– Periodic spot checking

only

– ‘Subjective’, operator

dependant

measurement of

variable sensitive and

repeatability

– Labor intensive (1hr/pt)

= high overhead costs

17



EOS Accuracy = Extent of GC“Small quantities of heavy hydrocarbons above C6 raise

the dew point significantly. Using a standard analysis

can result in an artificially low dew point determination…

Extended Gas Analysis to C14 … checks for the

presence of the heavy hydrocarbons and quantifies their

amounts to the level of C14. … It is, however, the only

type of (EOS) analysis that will result in an accurate dew

point determination. … An analysis procedure for C1

through C14 is described in GPA 2286-95.”GE Publication GER-3942 “GAS FUEL CLEAN-UP SYSTEM DESIGN

CONSIDERATIONS FOR GE HEAVY-DUTY GAS TURBINES”, C. Wilkes, GE Power

Systems (emphasis added)

18



Analysis Illustration:

1020 BTU/CF Lean Gas

1020 BTU Sample C6+C6+

60/30/10 split

C9+C9+

60/30/10 split

C12+ C14

HCDP @ Cricondentherm

C -54.7 -51.3 -31.2 -22.1 -6.5 2.5

F -66.5 -60.3 -24.1 -7.8 20.3 36.5



EOS Method With GC Analysis

PROS

+ Potential to combine a number of gas quality/fiscal metering parameters into one analyzer

+ The components contributing to a high dew point level may be identified and so help to determine the reason/source.

+ Possibility to provide a theoretical phase envelope curve

CONS

- Indirect method of determining HCDP

- Accuracy is dependant on correct use of specialized reference gases

- The limit of analysis sensitivity can produce large HCDP errors

- Trained staff required to maintain proper performance

- High initial and operating costs (analyzer house, personnel and special reference gases)

20



Automatic Optical Method

• Accurate to 0.5 C

( 1.0 F)

• Readings as often as

every 5 minutes

• No operator bias

• Very low maintenance

• Proven technology

21



How Does a Sensor Work?



Dark Spot™ Sensor

Enhanced Detector Sensitivity



EOS Method Using GC Analysis

PROS

+ Direct fundamental „objective‟

measurement with high

sensitivity and repeatability

+ Stand alone operation – Built-

in verification routines

+ Its like having your own

skilled technician taking a

Bureau of Mines reading

every 10 minutes, 24/7.

CONS

– Significant initial investment

(but still significantly less than

a C9+ GC) and very low

operating costs

24



Comparing Methods

25

Method Accuracy On-line Measure/ Calculated

Manual Optical Excellent No Measured

EOS from Field GC Poor Yes Calculated

Automatic Optical Excellent Yes Measured

Method Operator

Bias

Operator

Training

Installed

Cost (~$K)

Maint./Ops.

Costs (~$K/Yr)

Manual Optical Yes High 10 10

EOS from Field GC No* High 75 7

Automatic Optical None Low 60 <1



Instrumentation ROI

1. NOX emission under better control - could save

hundreds of thousands or even millions.

2. Fewer unplanned (expensive) outages – saving

burner section rebuild could save $2,500,000

per occurrence.

3. Longer turbine life – warning of impending

flashbacks will save your CGT

4. Lower parasitic costs – knowing the dew points

could save $325,000 / yr.



Practical FAQ

• Measurement cycles can be as often as

every 5 min with an automated instrument.

• Since fuel quality changes slowly, this rate is

sufficient to take appropriate action

especially as the existing GC will be tracking

BTU and can verify changes in fuel quality.

• Critical instrumentation should have key

spares in stock but these are often available

from the vendor for immediate shipment.11-IAGT-105 MEASURING HYDROCARBON


Questions?

See me for a copy of

presentation and/or

SwRI Report.

Thanks for attending!



applications of gas turbines - gten.cagten.ca/downloads/2011presentations/11-iagt-105.pdf · 14 is...

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