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    Dear Sir,
    How much sea water typically circulates through the closed circuit of a cooling system?Can you give us a brief of how the chemical dosing is being done?


  • #2
    Engine specific flow values depend on the size of the engine: the larger the engine, the higher the heat load and the volume of the cooling system leading to a higher flow is needed. The nominal flow values for each engine are defined in the technical data and they vary in the range of 20 m3 /h - 400 m3 /h . The nominal flow is defined for LT and HT circuits separately but the values are in many cases the same as mixed cooling systems have a combined flow at some parts of the system. In 2-circuit systems with fully separate LT and HT circuits the flow requirement for the HT pump can be significantly lower than the flow requirement for the LT pump due to the lower volume of the HT circuit compared to the LT circuit.

    The chemical parameters followed up related to the cooling water are pH and hardness.

    Nitrites are typically used as corrosion inhibitors. The required concentration of the nitrites in order to provide the highest possible protection against corrosion depends on multiple factors, such as temperature, chloride and sulphate content and pH, thus providing an additional reason for ensuring that the pH levels are within the acceptable levels. The normal pH limits are 6,5 – 8,5 for the raw water and 8 – 11 for the cooling water.
    The hardness of the water indicates the mineral content of the water. The recommended value for raw water hardness is 178 mg/l of .

    Suitable levels of calcium and magnesium compounds in the cooling water cause a thin, corrosion protective layer to form on the heat exchanging surfaces of the cooling system. If the water is soft it has the ability to dissolve oxygen and carbon dioxide from the air, thus leading to a low pH and a high corrosive effect. Too high hardness increases the deposit formation and will eventually affect the heat transferring properties of the system.


    • #3
      Hello Anish,

      Unfortunately there was an issue all these days with the forum site and i did get the change to say a big thanks for your excellent reply earlier.It is very encouraging that you motivate the young people to get a clear and better idea of what really happens at "sea". Recently i bought the whole series of your books and i am really impressed from your good job.

      Back to technical issues i would like to make a last question which i think confuses too much most of the guys working in the shipping field.There is reference from many articles talking about slow steaming that evaporation process from the Fresh water generator cannot take place when vessels are sailing lets say at 40%MCR or in general at slow steaming.None of them does not explain the reason though .Checking your guide to slow steaming procedures published from Marine insight last year there is no reference to that issue and to be honest i was quite impressed that you omitted it(Usually all topics are covered 100%).It is difficult to understand why that happens.As far as i know the outlet temperature of the jacket water should be expected with a temperature around 78-82 even if you are at slow steaming.What changes in the closed circuit which makes the evaporation process not possible to take place?Even if we make assumption that the outlet temperature of the jacket water is 65degc its difficult to understand the reason.As far as i know the water starts boiling at the vacuum even in the case the water is not hot.Also from what i know in the FWG you can expect some steam with jacket water temperature at 45degc,Theoretically speaking you could use the FWG at lower temperatures of jacket water.i can understand that you may have lower temperature at the inlet of the Main engine if you use some of the water for the condenser of the FWG especially in the case the sea water temperature is too low but again electrical or steam preheaters before the ME inlet could not be used?

      Just to note that i have asked about this issues some engineers with good experience but i did not manage to get a clear reply.Also i suspect this is the reason why some charterers supply the vessels with fresh water from shore when there is demand for ultra slow steaming.Please confirm this as well if you have any experience like this.

      I would appreciate your reply!

      Thanks again!!


      • #4
        Could you please provide more specificaiton about the cooling system?


        • #5
          Angel777 : The FWG is another waste heat recovery unit which utilises the waste heat of main engine to heat the sea water. At slow steaming there is insufficient heat from main engine
          for fresh water generation. You ca run the FWG at slow steaming if heaters for jacket water is provided in the system. The whole point of waste recovery unit is lost and additional work is needed to maintain the FWG temp.During slow steaming, if the jacket water which is at 70-80deg C is supplied to FWG for heating, the JCW temperature will further drop and again additional work is needed to be done by use of additional heaters (normally steam heaters are used, boiler fuel consumption will increase and purchasing water from shore is still cheaper than burning fuel). Please understand when companies are adopting slow steaming, the main intent behind is to reduce the fuel consumption as fuel is the biggest factor in operating cost of the ship.


          • Angel777
            Angel777 commented
            Editing a comment
            Thanks a lot Anish..

        • #6
          To get the best answer,first we need to compare the cooling system with the normal water.after that it would be easy to make out with sea water.Compare the temperature results of both the water. I am an engineer and we use Airdex services cooling systems.We too are working on these kind of projects.


          • #7
            RX Marine was established in 1996 in Mumbai, India; as a chemical manufacturing company catering exclusively to the needs of the marine industry.In a short span of 12 years the company has established itself as one of leading wholesale suppliers of a wide range of chemicals for -Marine industry internationally- and other local industries and plants .our client list bears testimony to this. The RXSOL policy has its foundation on two pillars of strength – continuous investments in research and development to deliver premium quality products and a commitment to services.
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            • #8
              Originally posted by danmain View Post
              To get the best answer,first we need to compare the cooling system with the normal water.after that it would be easy to make out with sea water.Compare the temperature results of both the water. I am an engineer and we use Airdex services cooling systems.We too are working on these kind of projects.
              Airdex cooling systems are a pretty solid product, but we're looking for an alternative. Can someone recommend a company they have had experiences with, please?


              • #9
                Can you show me some of the cooling system.