acs lng chemistry

Gas Turbine Fuel Flexibility

LNG, DME, MeOH, and Synthesis Gas

Introduction

Fuel Types and Properties

Fuel Flexibility

High level of concern raised by customers over gas interchangeability and fuel flexibility in general Driven by imported LNG, and declining

US natural Gas production Key products offerings could be

Monitoring and fuel system retrofits to existing SPG gas turbines

Modifications to competitors equipment Products need to accept wider range of

gas fuel quality

Fuel Spectrum

Fuel Type and Temperature

Fuel Type and Delivery

Fuel Flexibility

Stranded gas off-shore must be delivered to markets in a convenient form for shipping. Non-cryogenic liquid (Gas-to-Liquids), Fischer-

Tropsch Pressured gas (CNG or Dimethyl Ether, DME)

DME for China and Indian diesel and home markets

GE spent $20 million in R&D, BP continues to develop, as do the Japanese

Methanol LNG

Key Terminology

Wobbe Index Based on fuel gas heating value and

gas density (specific gravity) Widely used interchangeability parameter

Dew Point Boundary on a temperature/pressure

map defining the region where condensation of complex mixtures of hydrocarbons occurs

Higher Hydrocarbons

Gas Turbine Power Industry

Technology Progression

Significant Impact of Gas Turbine Since the 1960’s.

Technology shift to PreMixed Combustion in the 1990’s.

Industry StatisticsGas Turbine Sales

Power Generation Market

Year

1980 1985 1990 1995 2000 2005

Nu

mb

er o

f T

urb

ines

In

stal

led

0

100

200

300

400

500

Cu

mu

lati

ve M

We

0

50000

100000

150000

200000

250000

Data are based on gas turbines for the power generationsector. Pumping, pipeline, cogeneration, and emergencyapplications are not included in the total.

GT Industry Statistics

210,000 MWe installed in power generation (US) Rapid construction/installation times.

4,000+ gas turbines installed in pipeline and refinery operations.

16,000+ gas turbines installed worldwide 50% in Oil and Gas Operation

Industry Statistics

22% of all US natural gas consumption is now used to generate electricity (both for consumers and industrial applications)

Most efficient package utility plants in the world are combined cycle (gas turbine+steam turbine)

Gas turbine power plants comprise less than 2% of all emissions in power generation sector.

August 2003 BlackoutP

ow

er G

ener

atio

n T

ech

no

log

y

Time to Restart

Text

Text

Text

Text

Gas Turbines

Fossil Steam

Nuclear

Simple cycle gas turbines: 10 minutes to 30 minutes

Combined cycle gas turbines: 2 to 4 hours

Fossil Steam Plants4 to 8 hours

Nuclear PlantsAs long as 48 hours

Environmental Impact: NOx

NO

x, p

pm

, 15%

O2

Technology

15

30

45

60

75

90

105

110

IC-G

as

Fir

ed

IC O

il

GT

-Ga

s

GT

-Oil

PC

With SCR

No SCR

Recip Engines

Gas TurbinesNo SCR

+600

With SCR

GT+HRSG: 2.5-5 ppm

NOx

Energy Resource Base

Off-Shore Gas Reserves

Four methods of moving plentiful off-shore supplies to the end-user. LNG

Extensive investment in LNG underway. However, wide variability of off-shore supply compositions greatly complicates the usability in DLN gas turbines.

Non-cryogenic liquid (Gas-to-Liquids), Fischer-Tropsch

Pressured gas (CNG or Dimethyl Ether, DME)

Methanol

Global Gas Supply Base

EU Proposed Range

US Historical

Nig

eria

Om

anM

alay

sia

Au

stra

lia

Wo

bb

e In

dex

(H

HV

)

Approximate Reserves, TCF

1200

1250

1300

1350

1400

1450

1500

1550

Qat

ar

UA

E

Alg

eria

Tri

nid

ad

US Domestic : 1342 +/- 2%

Comparison of Off-Shore Reserves with Gas Quality

World energy reserves of hydrocarbons are approximately even divided between natural gas, oil, and coal. But if methane hydrates are added to the resource base, the global reserves in gas could represent more than 80% of the hydrocarbon resources.

Domestic natural gas supply differs significantly from some off-shore natural gas resources. Based on Heating value (Btu), Wobbe Index,

and/or chemical composition

LNG’s cryogenic processing will remove virtually all components heavier than Butane. But high Btu components can still be present

in the final delivered gas supply, especially if they were present at the source.

US and Offshore Supplies

Gas Supply Industry

Regulated by the Federal Energy Regulatory Commission (FERC)

De-regulated the natural gas supply industry Transporters move the gas

But don’t own the molecules Suppliers supply the gas LDC’s distribute gas to end-users

Probably not same molecules that supplier provided.

Contracts, with FERC approval, govern the exchange between each party.

Gas Quality

Two key issues recently raised by the Federal Energy Regulatory Commission over pipeline tariff requirements. Hydrocarbon Dew Point Interchangeability

Each handled separately, despite obvious common features between the two.

Domestic Gas Composition

C1 - MethaneC2 - EthaneC3 - PropaneC4 - Butane - LNG C5 - Pentane - Liquid formation occurs

C6+-Hexane and GreaterPlus diluents (oxygen, carbon dioxide)

C1 - MethaneC2 - EthaneC3 - PropaneC4 - Butane - LNG C5 - Pentane - Liquid formation occurs

C6+-Hexane and GreaterPlus diluents (oxygen, carbon dioxide)

Hydrocarbon Dropout

When thermal value is greater than product value some producers may opt to reduce or cease processing

Rains within the pipeline – “liquid fall out”

Condensate can be a nuisance to the transporter and catastrophic to end-user

Condensate In Pipeline

Dew Point Curve

- 21. 6, 20

40, 900

8. 4, 20

70, 900

0

200

400

600

800

1000

1200

1400

1600

1800

- 250 - 200 - 150 - 100 - 50 0 50 100

Temp (F)

PSIA

Pi pel i ne Gas

Unpr ocessed

LNG

Wi nt er DP Cool i ng

Summer DP Cool i ng

Two Phase

Two Phase

Two Phase

Cri condentherm = - 56. 7 F

Cri condentherm = 5. 6 F

Cri condentherm = 76. 6 F

LNG will not drop hydrocarbon liquids

Pipeline Dew Point (95/96)

US Regional Hydrocarbon Dew Point

US Region

Mou

ntai

n

North

east

Pacific

South

Centra

l

South

East

Hyd

roca

rbo

n D

ew P

oin

t (F

)

-120

-100

-80

-60

-40

-20

0

20

40

60

Average (F)MaximumMinimum

Interchangeabiliy

FERC elected to treat gas interchangeability as a separate issue from Hydrocarbon Dew Point

Typical contract (tariff) parameters Heating Value Wobbe Index Inert content

Gas turbine equipment manufacturer specifications turned out to be a limiting factor on interchangeability.

US Wobbe DataUS Wobbe Index

2002/2003 Values (by State)

State

AL

AR

AZ

CA

CO

CT IA IL IN

IN/O

H/M

IK

SK

S/M

O/IL

/OH

/MI

KS

/MO

/IL/O

H/M

I/IN

KY

LA MA

MD MI

MN

MO

MS

MT

NC

NH NJ

NM NY

OH

OK

OL

PA RI

SD

TN

TX

TX

/LA

UT

WA

WI

WV

WY

Wo

bb

e In

dex

(B

tu/s

cf)

1150

1200

1250

1300

1350

1400

1450

US Average

Average MaximumMinimumUS Average Wobbe

Power Sector

Turbine Technology

Combined Cycle Power Plant

The gas turbine has unique fuel flexibility characteristics

Insensitive to parameters such as octane or cetane rating, which affects compression engines.

Corrosion is a factor, but usually only with heavy oils or liquid fuel, or with ingestion of corrosive material (e.g. seawater)

Concerns over domestic supply have usually focused on gas pre-treatment to meet equipment requirements

Superheat fuel (keep it in the gas phase) Removal of liquids and condensate

Offshore LNG introduces new complexities.

Gas Turbine Design

Combustion Systems

Fuel flexibility is directly tied to combustor design.

Two combustor designs in use today: Diffusion flame combustor design

Highest degree of fuel flexibility. Probably the “safest” combustion design system for

continuous burners All aircraft gas turbines are based on diffusion combustor design.

Premixed design Newest designs (DLN and DLE introduced in 1990’s) Premix fuel and air introduced tighter requirements on fuel

quality. These were necessary to control basic combustion process conditions:

Flashback, blowoff, combustion instabilities, emissions, etc

Still in wide use, although in limited production within the US. Steam or water injection for NOx emissions.

Water/steam operating costs are not insignificant;

Additional combustor wear associated with stress on hot parts was a key factor in prompting the industry to develop other technologies

Diffusion combustor is usually the design-of-choice if low quality fuels (gas or liquid) are the primary fuel Design choice for landfill gases, heavy and

medium grade oils, residual fuel oil, blast furnace gas, refinery gas, IGCC, crude oil—and even coal.

Diffusion Combustor

Required extensive research and development by both industry and government. Eliminated the need to inject a diluent for control

of NOx

Combustor design and controls are more complex Introduced additional requirements on fuel quality

requirements Wobbe Index variability requirements are typically

much narrower (15% vs. 5%) Limits on higher hydrocarbons to mitigate the risk of

flashback in premixed systems. Premixed designs are predominantly natural gas

Much harder to design “premixed” system with other fuels

Premixed Combustor

DLN Cross Section

DLN-3D

Combustion Chamber

Compressor

24 Hybrid Burners

Annular Combustor

Wide variety of fuel applicationsLarge, walk-in combustor chamberLow NOx Hybrid Burners

Silo (External) Combustor

Interchangeability

= Less than 100 MMcf/d Capacity

Capacity (in Million Cubic Feet per Day)

9,0006,000

12,00015,000

03,000

Interchangeability: Geography

Depending upon location on the pipeline grid, some users may experience more rapid shifts from domestic pipeline natural gas to imported LNG

Florida: 95%+ natural gas consumption is power generation, mostly gas turbines.

Interchangeability: Geography

Depending upon location on the pipeline grid, some users may experience more rapid shifts from domestic pipeline natural gas to imported LNG

Wobbe Index Modified Wobbe and/or Temperature Corrected

Gas Composition—(Ethane, Propane Butane) Which definition of natural gas is controlling?

EPA’s, Tariff, Fuel Specification?

Heating value limits Dew point

Many pipeline tariffs do not have dew point limits, yet the formation of condensates in the fuel supply can have severe consequences to equipment downstream.

Temperature

Interchangeability Parameters

Combustion Tests

Simulating LNG

NOx-Thermal NOx At lower combustion temperatures, less NOx is generated. But there is a limit to the minimum temperature.

Combustion instabilities (dynamics) become important in lean combustion systems.

NOx-Thermal NOxPressure Effect on NOx and CO Emissions in Industrial Gas Turbines

Anuj Bhargava., Donald W. Kendrick, Kent H. Casleton and Daniel J. Maloney

U.S. Department of Energy Federal Energy Technology Center

Meredith B. Colket, William A. Sowa United Technologies Research Center East Hartford, CT

Source: ASME 2000-GT-97

(with permission)

NOx-Combustor TestsWobbe Index variation, as well as combustor design can affect emissions.

Chart shows the response of two different combustor systems to changes in gas composition.

Full Scale Engine Evaluation

Heating Value Reduced

Dynamics Increased

Minor changes to the gas composition was coincident with a step change in the combustor dynamic pressure.

INFLUENCE OF VARIATIONS IN THE NATURAL GAS PROPERTIES ON THECOMBUSTION PROCESS IN TERMS OF EMISSIONS AND PULSATIONS FOR AHEAVY-DUTY GAS TURBINELars Nord and Helmer AndersonIJPGC2003-40188 (with permission)

Minor increase in NOx emissions with increase of Wobbe Index from 1335 to 1400, a range that would account for addition of LNG from offshore supplies.

Fuel Effects-NOx

Full scale engine testing confirms rig testing that, without burner modifications or engine control enhancements, increasing Wobbe Index can result in increased NOx.

Fuel Effects-COCO (and unburned hydrocarbon) emissions are affected as well, although not in the same manner as NOx.

Diffusion Combustor Model

Calculated for diffusion combustion system. Water Injection for NOx control, and fixed firing temperature.

Differences in NOx due to fuel quality changes (Wobbe Index) are indicated.

.

NOx Mass Emission Change

For Rich and Lean Wobbe Gas Mixes

Water/Fuel Ratio

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Ch

an

ge

in

NO

x (

%)

fro

m 1

00

% M

eth

an

e

-10

-8

-6

-4

-2

0

2

4

6

8

10

100% Methane

Enriched Fuel GasWobbe Index +4%

Lean Fuel GasWobbe Index -4%

Increasing NOx

due to presence of higher hydrocarbons(propane and butane)

Decreasing NOx (and

increasing dynamics)with lean gas quality

Based on:

A Model for the Prediction of Thermal, Prompt and Fuel NOx from Combustion Turbines

J. L. Toof

Journal of Engineering for Gas Turbines and Power, Vol. 108, No. 4, 1986, pp. 340-347

US Domestic gas index has varied by only +/-2%, or1315 to 1369.

Requirements that are too broad could be difficult to manage without special equipment modifications to adapt to changes.

Requirements too narrow could leave a significant amount of gas unacceptable to US markets. Industry fuel specifications vary from +/-2% to +/-10%,

depending upon design features and equipment capabilities.

Supply Comparison

US Domestic gas index has varied by only by +/-2%, or 1315 to 1369.

Requirements that are too broad could be difficult to manage without special equipment modifications to adapt to changes.

Requirements too narrow could leave a significant amount of gas unacceptable to US markets. Industry fuel specifications vary from +/-2% to +/-10%.

Tolerance requirements for fuel quality are related to combustor design, emissions, and contract requirements.

LNG Source and Impact

Proposed

EU Range

Variability in NOx emissions of equipment in service can differ significantly among different gas turbine designs.

Even within a specific engine model, significant variation is evident.

NOx Variation and Design

Emissions for three different gas turbine models in power generation service, reported through EDR network.

Other Technical Issues

NO2 Plume (Yellow Plume) Observed at some installations in Europe and Asia

The plume issue appears to strongly relate to combustion systems using LNG.

Units on West Coast have reported plumes (AWMA 2004) Stack geometry, location, viewing position, and total

exhaust plume diameter affect the plume visibility.

NO2 emissions appear to be related to the presence of higher hydrocarbons in the exhaust gas.

NO2 plume was and is a problem for some gas turbines operating in countries that use LNG as the primary fuel.

Plume formation is not predictable from current models for fuel interchangeability.

LNG and PlumeNO2 production strongly dependent upon presence of specific hydrocarbons for reaction pathway.

An Experimental and Kinetic Evaluation of the Promotion Effect of Hydrocarbons on the NO-NO2 Conversion in a Flow Reactor

Proceedings of the Combustion Institute, Volume 27.

Hori, M., Matsunaga, N., Marinov, N., Pitz, W. and Westbrook, C., Proc. Combust.Inst. 27 (1998) 389-396

Conclusions

Diffusion Combustor Design Older power plants, and pipeline

applications, use this design. Most robust design Greatest fuel flexibility (Low/High HV

gases, liquids, etc). Increasing higher hydrocarbon

content could increase NOx, unless some control is used to mitigate against increased flame temperature.

Response to changes in gas composition may be more complex. Range of combustor configurations may respond

differently Annular Can-annular Silo Dual-fuel

System response complicated by many different designs that are connected on same distribution network.

Different OEM fuel specifications reflect unique requirements for each gas turbine DLN design, and each gas turbine model (or frame)

Premixed Designs

Finally…..

Offshore LNG destined for domestic users could differ substantially from historical norms based on the source of the gas.

Response of installed gas turbine fleet will be difficult to gage.

Increasing the allowable range of chemical properties will have some impacts.

But not all equipment is likely to respond the same way. Additional research on interchangeability is

needed What parameters make sense today?

Equipment modifications can be made available to adapt the existing fleet of gas turbines.

It will take time.

Research Opportunities

Full scale testing needed. More empirical evaluations similar to

what has been carried out.

Model studies on system response. Review and update of

interchangeability parameters No one office or agency acts as

repository.

Current energy budget has provisions for research funding spelled out.