Research Papers: Gas Turbines: Aircraft Engine

Evaluation of Gas Turbine Outboard Bleed Air on Overall Engine Efficiency and CO2e Emission in Natural Gas Compressor Stations

[+] Author and Article Information
K. K. Botros

NOVA Research & Technology Center
2928 16th Street NE,
Calgary, AB T2E 7K7, Canada
e-mail: botrosk@novachem.com

B. Sloof

TransCanada Pipelines Limited
450 1st Street SW,
Calgary, AB T2P 5H1, Canada

Contributed by the Aircraft Engine Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 28, 2013; final manuscript received July 2, 2013; published online August 30, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(10), 101201 (Aug 30, 2013) (7 pages) Paper No: GTP-13-1207; doi: 10.1115/1.4025007 History: Received June 28, 2013; Revised July 02, 2013

Gas turbine (GT) engines employed in natural gas compressor stations operate in different modes depending on the power, turbine inlet temperature, and shaft speeds. These modes apply different sequencing of bleed valve opening on the air compressor side of the engine. Improper selection of the GT and the driven centrifugal gas compressor operating conditions can lead to larger bleed losses due to wider bleed valve openings. The bleed loss inevitably manifests itself in the form of higher overall heat rate of the GT and greater engine emission. It is, therefore, imperative to determine and understand the engine and process conditions that drive the GT to operate in these different modes. The ultimate objective is to operate the engine away from the inefficient modes by adjusting the driven gas compressor parameters as well as the overall station operating conditions (i.e., load sharing, control set points, etc.). This paper describes a methodology to couple the operating conditions of the gas compressor to the modes of GT bleed valve opening (and the subsequent air bleed rates) leading to identification of the operating parameters for optimal performance (i.e., best overall efficiency and minimum CO2e emission). A predictive tool is developed to quantify the overall efficiency loss as a result of the different bleed opening modes and map out the condition on the gas compressor characteristics. One year's worth of operating data taken from two different compressor stations on TransCanada Pipelines' Alberta system were used to demonstrate the methodology. The first station employs a GE-LM1600 gas turbine driving a Cooper Rolls-RFBB-30 centrifugal compressor. The second station employs a GE-LM-2500+ gas turbine driving NP PCL-800/N compressor. The analysis conclusively indicates that there are operating regions on the gas compressor maps where losses due to bleed valves are reduced and, hence, CO2 emissions are lowered, which presents an opportunity for operation optimization.

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Fig. 2

GE-LM2500+ firing schedule and relationship to bleed valve minimum and maximum opening

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Fig. 1

GE-LM1600 VBV schedule diagram

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Fig. 12

Contours of corresponding excess fuel consumption and related charges of combined fuel and emissions (GE-LM2500+ gas turbine case)

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Fig. 13

Contours of corresponding excess fuel consumption and related charges of combined fuel and emissions overlaid on gas compressor characteristic map (GE-LM2500+ gas turbine case)

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Fig. 9

Example of engine F_TFLCYC values in relation to maximum and minimum flame temperatures (GE-LM2500+ gas turbine case)

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Fig. 10

Contours of bleed air rates during one year operation of the example GE-LM2500+ gas turbine case

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Fig. 11

Contours of engine heat rates, with and without bleed air (GE-LM2500+ gas turbine case)

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Fig. 3

Excess energy loss due to compressor bleed (GE-LM1600)

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Fig. 4

Excess CO2e emission in tonnes/day due to compressor bleed (GE-LM1600)

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Fig. 5

Total additional cost incurred due to compressor bleed ($/day) (GE-LM1600)

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Fig. 6

Corrected N1 (rpm) corresponding to the different operating zones on the compressor characteristics (GE-LM1600)

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Fig. 7

Engine heat rate map in presence of bleed (GE-LM1600)

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Fig. 8

Hypothetical engine heat rate map in absence of bleed (GE-LM1600)



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