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Re-sizing of a natural gas fired two-shaft gas turbine for low calorific gas operation

Eriksson, Pontus ; Jonshagen, Klas LU ; Klingmann, Jens LU and Genrup, Magnus LU (2009) 54th ASME Turbo Expo 2009 4. p.539-550
Abstract

Gas turbine systems are predominantly designed to be fuelled with gaseous fuels within a limited Wobbe index range (typically HHV=45-55 MJ/Nm3 or 1200-1480 Btu/scf). When low calorific fuel gases are fired, the engine will be forced to operate outside its design envelope. The added mass flow will typically raise the cycle pressure ratio and in two-shaft designs also raise the gas generator shaft speed. In this study, the response of a natural gas fired simple cycle two-shaft gas turbine operating at full firing temperature is investigated. A model based on the Volvo Aero Corp. VT4400 gas turbine (originally Dresser Rand DR990) characterized by one compressor and two expander maps is considered. The free turbine is operated at... (More)

Gas turbine systems are predominantly designed to be fuelled with gaseous fuels within a limited Wobbe index range (typically HHV=45-55 MJ/Nm3 or 1200-1480 Btu/scf). When low calorific fuel gases are fired, the engine will be forced to operate outside its design envelope. The added mass flow will typically raise the cycle pressure ratio and in two-shaft designs also raise the gas generator shaft speed. In this study, the response of a natural gas fired simple cycle two-shaft gas turbine operating at full firing temperature is investigated. A model based on the Volvo Aero Corp. VT4400 gas turbine (originally Dresser Rand DR990) characterized by one compressor and two expander maps is considered. The free turbine is operated at fixed physical speed. Different amounts of N2 or CO2 are added to the fuel path. These two inerts are typically found in large quantities in medium and low calorific fuels. The fuels lower heating value is thus gradually changed from 50 MJ/kg (21.5 kBtu/lb) to 5MJ/kg (2.15 kBtu/lb). Emphasis has been put on predicting the compressor behavior in different resizing scenarios. The full 'firing temperature' operating point in the compressor map is tracked as the compressor size is reduced up to 7.5%, high pressure turbine size is increased up to 20%, low pressure turbine size is changed ±7.5% or up to 10% of steam (c.f. design point compressor air mass flow) is injected between the turbines. Different re-matching schemes are discussed where one turbomachinery component size is fixed and the two other component sizes are changed such that the compressor design point is restored. Finally a re-optimized turbine flow path is computed in a fixed compressor size scenario. Results are, as far as possible, given as non-dimensional parameter groups for easy comparison with other machines.

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author
; ; and
organization
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
host publication
Proceedings of the ASME Turbo Expo 2009 : Power for Land, Sea and Air - Power for Land, Sea and Air
volume
4
article number
GT2009-60386
pages
12 pages
conference name
54th ASME Turbo Expo 2009
conference location
Orlando, FL, United States
conference dates
2009-06-08 - 2009-06-12
external identifiers
  • scopus:77953186267
ISBN
9780791848852
DOI
10.1115/GT2009-60386
language
English
LU publication?
yes
id
374d163f-bc4f-4671-8b36-4c287174b0ef
date added to LUP
2018-10-18 12:41:39
date last changed
2021-06-23 06:20:38
@inproceedings{374d163f-bc4f-4671-8b36-4c287174b0ef,
  abstract     = {<p>Gas turbine systems are predominantly designed to be fuelled with gaseous fuels within a limited Wobbe index range (typically HHV=45-55 MJ/Nm<sup>3</sup> or 1200-1480 Btu/scf). When low calorific fuel gases are fired, the engine will be forced to operate outside its design envelope. The added mass flow will typically raise the cycle pressure ratio and in two-shaft designs also raise the gas generator shaft speed. In this study, the response of a natural gas fired simple cycle two-shaft gas turbine operating at full firing temperature is investigated. A model based on the Volvo Aero Corp. VT4400 gas turbine (originally Dresser Rand DR990) characterized by one compressor and two expander maps is considered. The free turbine is operated at fixed physical speed. Different amounts of N<sub>2</sub> or CO<sub>2</sub> are added to the fuel path. These two inerts are typically found in large quantities in medium and low calorific fuels. The fuels lower heating value is thus gradually changed from 50 MJ/kg (21.5 kBtu/lb) to 5MJ/kg (2.15 kBtu/lb). Emphasis has been put on predicting the compressor behavior in different resizing scenarios. The full 'firing temperature' operating point in the compressor map is tracked as the compressor size is reduced up to 7.5%, high pressure turbine size is increased up to 20%, low pressure turbine size is changed ±7.5% or up to 10% of steam (c.f. design point compressor air mass flow) is injected between the turbines. Different re-matching schemes are discussed where one turbomachinery component size is fixed and the two other component sizes are changed such that the compressor design point is restored. Finally a re-optimized turbine flow path is computed in a fixed compressor size scenario. Results are, as far as possible, given as non-dimensional parameter groups for easy comparison with other machines.</p>},
  author       = {Eriksson, Pontus and Jonshagen, Klas and Klingmann, Jens and Genrup, Magnus},
  booktitle    = {Proceedings of the ASME Turbo Expo 2009 : Power for Land, Sea and Air},
  isbn         = {9780791848852},
  language     = {eng},
  month        = {12},
  pages        = {539--550},
  title        = {Re-sizing of a natural gas fired two-shaft gas turbine for low calorific gas operation},
  url          = {http://dx.doi.org/10.1115/GT2009-60386},
  doi          = {10.1115/GT2009-60386},
  volume       = {4},
  year         = {2009},
}