pga ano c2plus turbine control
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C2+ Measurement Solutions for Turbine ControlUsing an X-STREAM EnhancedAnalyzer
Application Note Power
BackgroundIndustrial power markets covering multiple energy sources
require rapid control in order to optimize plant performance and
prevent costly turbine damage. Lower emission requirements
and varying fuel sources due to the increase in unconventional
natural gas sources, such as shale, have created a higher priority on
maintaining turbine efciency. Although the plants gas sources are
predominantly made up of methane, extensive variations in higher
hydrocarbons (C2+) typically exist. In fact, in some cases, over
18 % variation has been recorded with uctuations from 10% to
16 % within one minute. In addition, turbines have to be more
exible and need to present the above criteria over a wide range of
loads because gas turbine power plants are often used only for peakloads.
SolutionWith a 0100 % CH
4NDIR bench measuring 7.85 m, and a 025 %
C2H
6NDIR bench measuring 6.6 m, we designed a solution which
provides a high selectivity for CH4against C
2H
6, C
3H
8and C
4H
10as
well as CO2.
The C2H
6bench measures C
2H
6, C
3H
8and C
4H
10with response
factors of 1.0, 1.0, 1.1 and gives a low response from CH4, internally
corrected by cross compensation. Best accuracy is achieved in
Natural Gas mixtures with CH4as a major component, C2+ up to
20 %, and low water content.
Combination with Other MeasurementsSince CO
2content also varies in fuel sources, this measurement may
be combined with the hydrocarbon values for better control and
caloric value calculations. Carbon dioxide measurement utilizing
optical non-dispersive infrared (NDIR) technology can also be added
to the X-STREAM Enhancedanalyzer conguration.
A calculation of the Wobbe Index is also possible utilizing a
calculated relative density from the concentration values or by
utilizing an external density signal. Caloric value calculationsmight require integration of additional channels. As with the
BTU calculation, this is not for custody transfer but aids in rapid
adjustments to operations if uctuations occur.
ApplicationMethane and higher hydrocarbons like ethane and propane
behave differently during combustion. Par ticularly for combined
cycle turbines with lower emissions, variability of fuel sources
presents challenges for control and optimization. Although a gas
chromatograph can provide all needed measurements, speed of
response is sometimes not sufcient for such control.
A process gas analyzer (PGA) with a specic conguration of optical
benches and lters provides continuous measurement and the rapid
response necessary. In addition, an approximate caloric value
(BTU) can be provided as long as the higher hydrocarbons are low in
content. If this is not the case, the BTU value will be underestimated
but never overestimated. Such values cannot be used for custody
transfer but may be adequate to prevent turbine damage and
optimize performance. If the variation of C2+ in the fuel sources are
known, the error can be greatly minimized.
X-STREAM XE
Component Formula Concentration
Methane CH4
7090 %
Ethane C2H
6
020 %Propane C3H8Butane C
4H
10
Carbon Dioxide CO2
08 %
Oxygen O2 00.2 %
Nitrogen N2
05 %
Hydrogen Sulphide H2S 05 %
Rare Gases Ar, He, Ne, Xe Trace
Table 1 - Typical Gas Composition in Natural Gas Power Plants
Typical Power Plant Turbine
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Power
PGA_ANO_Power_C2+_Turbine_Control
System ConfigurationMethane (C1) and Ethane plus (C2+) measurements for natural gas
power applications often take place in hazardous areas. Therefore an
X-STREAM Enhancedameproof analyzer by Rosemount Analytical
(Figure 1) is recommended.
Analyzer CalibrationZeroing and Spanning calibration of all X-STREAM Enhancedanalyzer
measurement cells execute manually or automatically through
calibration solenoid valves.
Sample ConditioningFigure 2 below shows a ow diagram of the recommended analyzer
system. Sample extraction, transport, and conditioning occurs
using Rosemount Analytical Sample System Modules which include
a anged sample probe, heated pressure reduction station, sample
ltration, and sample ow control.
Figure 1 - X-STREAM EnhancedFlameproof Gas Analyzer
Figure 2 - Sample System Flow Diagram
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The contents of this publication are presented for information purposes only, and while effort has beenmade to ensure their accuracy, they are not to be construed as warranties or guarantees, express or implied,regarding the products or services described herein or their use or applicability. All sales are governed by outerms and conditions, which are available on request. We reserve the right to modify or improve the designsor specications of our products at any time without notice.
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