Abstract
In this paper, a model for a single stage plasma gasification system for marine vessels characterized by significant waste production is proposed. The main objective of the model is to investigate the effects of different feedstock compositions on key parameters, such as electrical power produced and heat recovered. The different types of waste generated onboard are described along with their environmental impacts. Specific attention is given to solid wastes, sewage sludge and plastic wastes as potential feedstock. Their average generation, proximate and ultimate analysis are defined, as input to the process model. The process assumptions used in the simulation model are illustrated. The system model is divided into five units: the pre-treatment unit; the gasification unit; the syngas cleaning unit; the energy conversion unit; and the heat recovery unit. Four operational scenarios are investigated to consider several variations of composition of the main feedstock. From the results of the simulations, the system model shows good feedstock flexibility, and the possibility of operating in net electricity gain conditions. The cold gas efficiency of the process is also assessed and its maximum value is obtained for the highest concentrations of sewage sludge (33.3%) and plastic (16.7%). Other parameters investigated are the combustion temperature, sorbent consumption in the cleaning process, feedstock and syngas lower heating value LHV.
Highlights
Introduction and MotivationShips are complex systems, and their complexity varies depending on the purpose of the vessel, the itinerary they follow, their capacity in terms of number of passenger or transportable goods [1,2].Marine vessels can be classified based on their purpose and types of ships [3]
The effects of higher gasification temperatures on municipal solid waste plasma gasification were investigated by Indrawan et al (2019) through a model developed on Aspen Plus: using air as plasma medium, temperatures from 1500 to 4000 ◦ C were studied and the gasifier performances were compared; the main conclusions are that H2 and CO concentrations increase with temperature, and the same for the syngas lower heating value (LHV), while CO2 concentration and the plasma gas efficiency are negatively affected [35]
The results obtained from the simulations, which were performed according to the four scenarios earlier described, are presented
Summary
Their complexity varies depending on the purpose of the vessel, the itinerary they follow, their capacity in terms of number of passenger or transportable goods [1,2]. For the scope of this work, only solid wastes (including plastic) and sewage are investigated as potential feedstock: solid wastes are a very heterogeneous collection of wastes, which are, according to the IMO (International Maritime Organization), further classified in domestic wastes (paper, glass, metals, cardboard, fabric, wood, etc.), food wastes, plastic wastes, operational wastes (ropes, cans, machineries, various scraps, etc.), incinerator ashes and kitchen oils/greases [12], while black waters, produced by the flushing of toilets and from medical facilities, are generally composed of water, urines, feces and other small human fluids and solids [13]. This information will be essential during the modeling phase, as the model will require as input the mass flow rate of the feedstock and its composition in terms of proximate and ultimate analysis. The scope of this research work is to lay the fundamental modeling basis for future works, expected to go further in detail on the design process of the system
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