COGAS plant as possible future alternative to the diesel engine for the propulsion of large ships

Abstract

Strong restrictions on emissions of engines for marine propulsion (particularly SOx, NOx) will probably be adopted in the near future. In this paper, by using specifically developed simulation techniques, a COGAS plant solution is proposed in substitution of the originally adopted prime mover (a two stroke low speed diesel engine), for the propulsion of a large container ship, whose characteristics and performance are known. Starting from the performance and cycle characteristics of an existing gas turbine, the COGAS steam cycle characteristics and related components are defined through an original design procedure. The combined cycle is compared with a Diesel engine, not only with regard to the plant performance and efficiency at design and high load off-design conditions, in both steady state and dynamic situations, but also for what concerns: engines dimensions and weights, engine room layout, overall propulsion plant weight, ship hull loading capacity, economic considerations.

Optimization of waste heat recovery from the exhaust gas of marine diesel engines

“…It is based on a calculation procedure already presented and validated by the authors in a previous study. 14 These codes have been developed to simulate the physics of cross flow water tube boilers, with steam drum, forced circulation and finned tubes.…”

Waste Heat Recovery from Marine Gas Turbines and Diesel Engines

“…Using the Nusselt number and finned pipes correlations, the convective heat exchange coefficient is determined as reported in [13]. For each heat exchanger, the heat exchange between the hot and cold fluid is determined with the procedure here summarized, described more in detail in [13].…”

“…Using the Nusselt number and finned pipes correlations, the convective heat exchange coefficient is determined as reported in [13]. By applying the steady state continuity and energy equations (see Nomenclature for the meaning of the symbols):…”

“…Using the Nusselt number and finned pipes correlations, the convective heat exchange coefficient is determined as reported in [13]. For each HRSG heat exchanger, the total heat exchange area (A), necessary for the pipes length evaluation, is determined by means of the following heat exchange balance equation:…”

Simulation and performance comparison between diesel and natural gas engines for marine applications

“…4,5 An example is the combined gas and steam turbine (COGAS) propulsion system (combined gas turbine and steam turbine electric drive system (COGES) in case of electric propulsion), whose applicability to a large container ship, as an alternative to the traditional two-stroke DE, was studied by Benvenuto and colleagues. [6][7][8] Other examples of propulsion plants with improved efficiency are those obtained by applying to traditional DE propulsion systems techniques of waste heat recovery (WHR), able to exploit part of the thermal energy contained in the exhaust gases and/or in the scavenging air coming from turbocharger (TC) compressor. [9][10][11][12] In these solutions, the increase in the overall efficiency (3%-4% in the best cases) allows a proportional reduction of the CO 2 emissions because the percentage of carbon is nearly the same in the fuel oils used in both traditional and alternative solutions.…”