Abstract
The efficiency of integrated cooling air at the intake of Turbocharger and Scavenge air at the inlet of working cylinders of the main diesel engine of dry-cargo ship by transforming the waste heat into a cold by an Refrigerant Ejector Chiller (ECh) as the most simple in design and reliable in operation and by complex in design but more efficient Absorption Lithium-Bromide Chiller (ACh) was analyzed. A ship power plant of cogeneration type using the relatively low-grade heat of water of a heat supply system with a temperature of about 90 °C, that significantly complicates the problem of its conversion into cold were considered. Because of the insufficiently high efficiency of transformation of the heat of hot water (low coefficient of performance) as compared with steam, the resulting cooling capacity may not be enough for cooling intake air of the turbocharger and scavenge air, that raises the problem of the rational distribution of heat loads between the Turbocharger Intake Air cooling circuit (subsystem) and Scavenge air cooling circuit and the need to use chillers of various types. This takes into account the rational parameters of cooling processes of the scavenge air in the cogeneration high-temperature stage of scavenge air cooler, in the intermediate stage of traditional cooling air with seawater, and in the low-temperature stage for deep cooling of the scavenge air by using a chiller. A new approach is proposed to improve the efficiency of integrated cooling Intake Air of the turbocharger and Scavenge Air at the inlet of the working cylinders of the ship main engine of a transport ship, which consists in comparing the required cooling capacity and the corresponding heat needs during the trade route with the available heat of exhaust gases and scavenge air of the cogeneration power plant, determining the deficit and excess cooling capacity of heat utilizing cooling machines of various types, that allows to identify and realize the reserves of improving the efficiency of cooling intake air of the turbocharger and the scavenge air of the main diesel engine through the joint use of chillers of various types.
Highlights
The operation conditions of ship low-speed diesel engines are characterized by a significant change in the ambient temperature during the voyage and coresponding temperatures of air at the inlet of turbocharger (TC) and the scavenge air after the TC
According to the manufacturers of ship low-speed engines "MAN" and "Wartsila" [1,2,3], an increase in air temperature at the inlet of TC by 10 °С causes an increase in specific fuel consumption bе by 0.2...0.7 %, and an increase in the scavenge air temperature after scavenge-air coolers (SAC) leads to an increase in specific fuel consumption bе by approximately 0.5 % and a corresponding decrease in the efficiency ηе of engines which poses the acute problem of complex cooling of the engine cyclic air: at the inlet of TC and scavenge air at the inlet of the engine cylinders
It is necessary to analyze the efficiency of the integrated cooling of the cyclic air of the low-speed diesel engines by transforming the waste heat of exhaust gases and scavenge air into the cold, comparing the necessary cooling capacity and the corresponding heat needs during an actual voyage with the amount of available waste heat of diesel engines, the results of which reveal a deficit or excess of the available waste heat for each of the methods for cooling the air, and reserves for additional cooling of the air due to the corresponding excess waste heat
Summary
The operation conditions of ship low-speed diesel engines are characterized by a significant change in the ambient temperature during the voyage and coresponding temperatures of air at the inlet of turbocharger (TC) and the scavenge air after the TC. At high temperatures of outboard seawater the scavenge-air coolers (SAC) are not able to maintain a scavenge air temperature at the low temperature level sufficient for damping elevated air temperatures at the inlet of TC and to provide the engine operation at a stable air temperature at the intake to the working cylinders, which would ensure high fuel efficiency of the engine. It is quite expedient to utilize it with a waste heat recovery chiller to reduce the temperature of engine intake air and scavenge air at the inlet of engine cylinders. The use of low-boiling fluids (LBF) in the waste heat recovery chiller provides deep cooling of engine cyclic air
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