Chapter Thirty One - Gas Turbines

Abstract

Publisher Summary Gas turbines have dominated warship propulsion for many years but their potential remains to be fully realized in the commercial shipping sector. Breakthroughs in container ships, a small gas carrier and the Baltic ferry Finnjet during the 1970s promised a deeper penetration that was then thwarted by the rise in bunker prices and the success of diesel engine designers in raising specific power outputs and enhancing heavy fuel burning capability. A new generation of marine gas turbine—superseding designs with roots in the 1960s—may eventually benefit from the massive investment in aero engine R&D over the past decade, strengthening competitiveness in commercial vessel propulsion, particularly as more stringent emission limits favour the adoption of very low sulfur-content distillate fuels. Optimizing the combination of low-power manoeuvring and high power operation is accomplished in many naval applications by using a combined diesel or gas turbine propulsion system (CODOG). Combined-cycle gas turbine and steam turbine electric (COGES) plants embrace gensets driven by gas and steam turbines. Waste heat recovery boilers exploit the gas turbine exhaust and produce superheated steam (at around 30 bar) for the steam turbine genset. Significant progress has been made in enhancing the thermal efficiency of simple-cycle gas turbines for ship propulsion over the years, R&D seeking to improve part-load economy and reduce the fuel cost penalty compared with diesel engines. Subsequent advances—design refinements, new materials and cooling techniques, and the appropriate matching of higher compressor pressure ratios—have resulted in some large simple-cycle turbines achieving efficiencies of over 40 per cent. Marine gas turbines are available only in specific sizes and ratings, unlike a given diesel engine design which can cover a wide power range with different in-line and V-cylinder configurations. A power rating at particular ambient conditions determines the internal engine temperatures and the resulting expected service life of components exposed to these temperatures. These “hot section” components include the combustor and the HP turbine blades and vanes. The life of the hot section components will determine the interval between major maintenance actions, resulting in an estimated average maintenance cost.