Off-design performance investigation of a low calorific gas fired two-shaft gas turbine

Research output: Chapter in Book/Report/Conference proceedingPaper in conference proceeding

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. Typical constraints to be considered due to the altered fuel composition are pressure loads, shaft torques, shaft overspeeds, centrifugal overloading of disks and blades, combustor flameout, surge and flutter limits for the turbomachinery. This poses limitations to usable fuel choices. In this study, the response of a natural gas fired simple cycle two-shaft gas turbine is investigated. A lean premixed combustor is also included in the model. Emphasis has been put on predicting the turbomachinery and combustor behavior as 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). 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. The operating point is plotted in the compressor map and the turbine maps at three distinct firing temperatures representing turndown from full load to bleed opening point. Gas generator speed and shaft power are shown. Surge margin and power turbine power is plotted. Overall efficiency is computed. The behavior of the Volvo lean premixed combustor is also discussed. Air split, primary zone equivalence ratio and temperature is plotted. Combustor loading, combustion intensity and pressure drop is graphed. Results are, as far as possible, given as non-dimensional parameter groups for easy comparison with other machines.

Details

Authors
Organisations
External organisations
  • Volvo Technology AB
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Energy Engineering
Original languageEnglish
Title of host publicationProceedings of the ASME Turbo Expo 2009
Subtitle of host publicationPower for Land, Sea and Air
Pages21-32
Number of pages12
Volume4
Publication statusPublished - 2009 Dec 1
Publication categoryResearch
Peer-reviewedYes
Event54th ASME Turbo Expo 2009 - Orlando, FL, Orlando, FL, United States
Duration: 2009 Jun 82009 Jun 12

Conference

Conference54th ASME Turbo Expo 2009
CountryUnited States
CityOrlando, FL
Period2009/06/082009/06/12