acs lng chemistry
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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.