Probe For Influencing Factors Of Fresh Water Yield Of Marine Shell And Tube Fresh Water Generator Plant And System Energy Saving And Optimizating

With the increasing frequency of global trade and the increasing transport capacity of large ocean-going vessels,fresh water carried by vessels on an ocean voyage hardly often meets the requirement of use.For a long time,as the main desalination equipment of most ships,fresh water generator uses the main engine low-heat-quality cylinder liner cooling water as the heat source to heat and boil the sea water under low pressure.Water vapor rapidly condenses into droplet on the surface of the condenser,which is pumped to the freshwater tank by freshwater pump as the water for the whole ship's crew living and producing.However,due to multiple factors,the fresh water production and thermal efficiency will decrease after a period of time,resulting in utilization of waste heat of ship main engine and shortage of water for ship crew and boiler.In this paper,a shell-and-tube type fresh water generator with a daily fresh water output of 30 Tons is designed as the research object.Aiming at decline of water production capacity and thermal efficiency,the thermodynamic process of evaporator boiling heat transfer and condenser film condensation are analyzed.Study the law of the increasing of fouling layer thickness and the change of heat flux of heat exchanger tube by using a two-layer cylinder heat transfer model,the heat flux decreases with the increasing of fouling layer thickness,but the change rate of heat flux is most obvious in the formation stage of fouling layer.Aiming at the working characteristics of water ejector,analyze the influence of the cross section ratio between mixing chamber and nozzle together with the change of back pressure on the vacuum degree of the plant,to get the conclusion that the vacuum degree of system decreases with the increasing of cross section ratio and the injection coefficient decreases with the increasing of back pressure.According to the influence of non-condensable gas on heat transfer coefficient of condensation,study and expound that system leaking and gas precipitation are two main sources of non-condensable gas in the body.According to the actual operation status of the system,analyze the influence of cylinder cooling jacket water thermal load,seawater supply level,condenser tube condition and gas-liquid separator condition on the salinity of fresh water generator,to conclude that the main reasons for the high salinity of the fresh water generator are the rising of saline droplets,insufficient height of gas-liquid separation,the mixing of saline sea water and insufficient gas-liquid separation.As for the influencing factors of productivity and thermal efficiency decline of fresh water generator plant,it presents some specific modification schemes and energy-saving optimization methods.Solve the problems and shortcomings in heat transfer process,vacuum system and flow characteristics of fresh water generator plant from the aspects of evaporator scale slow down and scale removal process and optimization,modification of water ejector and centrifugal pumps,repairing of inner coating and optimization of evaporator structure.Expound and prove the feasibility of modification and optimizing scheme through testing data comparison,After optimization,the water production of the system increases by 50%,and the thermal efficiency of the system increases by 21.4%,which provides technical reference and experience to the repairing the same type of fresh water generator plant.