This page contains a Flash digital edition of a book.
heat exchangers


››› believes this is more convenient since it does not restrict normal ship operations in port or require system upgrades. Ballast water is drawn from the tank and pasteurised using waste machinery heat, via a heat exchanger. Here it is mixed with nitrogen for deoxygenation. The ballast water is then injected into the bottom of the tank through rotary jet heads and fixed nozzles, to ensure thorough mixing. By recirculating the ballast water, the full tank volume is treated, the company says. One benefit of the system, it notes, is that it reduces corrosion in the tank. A scale model of the system has been built but no full scale installations have been made and the system is not yet type-approved.


Although heat has only a small share of the ballast water treatment market, researchers have explored its potential and reported encouraging potential if it is combined with filtration. A paper by two Malaysian academics presented at the International Conference on Marine Technology in 2012 reported that a system harnessing shipboard waste heat would provide an economic solution for ballast water treatment but, based on an analysis of waste heat available on a crude oil tanker, a complementing treatment method would be necessary to treat high volumes. They proposed a heat-filtration combination system, in which sea water would circulate as a secondary coolant to collect the heat but


Wärtsilä develops evaporator for LNG fuel LNG propulsion depends on heat exchangers. Between the bunker tanks, where the fuel is typically stored at -160°C, and the engine it has to be warmed by a heat exchanger and regasified. Such technology is not new – the same is needed before LNG cargo can be distributed along onshore pipelines – but systems for use on board a vessel to deliver gas for use in a dual-fuel diesel engine have different requirements. One company that is focusing on this is Wärtsilä. Its interest is clearly driven by the need to offer fuel delivery systems for its range of dual- fuel engines, which now include low speed units launched last November.


Sören Karlsson, who is general manager of supply management for Wärtsilä’s fuel gas systems, explained to Marine Propulsion how these heat exchangers, termed evaporators, are built and operated.


They are typically made of stainless steel, he said, since carbon steel loses its strength at cryogenic temperatures. Their construction also has to allow for shrinkage and expansion due to the large temperature differences, which would otherwise create high thermal loads. For small duty LNG evaporators, water bath


Understanding the heat exchange between a tanker’s cargo heater and the oil around it can have a big impact on capital and operating costs for the heating system, according to a paper published in December by the International Journal of Current Engineering and Technology. As a result, the paper’s introduction notes, “the study of the influence of capacity fluctuations on the heat transfer around a horizontal tubular heater is one of the most urgent tasks for transportation of high- viscosity liquids by sea.”


The paper was written by Dr Abbas Alwi Sakhir Abed, who is assistant professor in the Engineering College at Iraq’s Al-Qadisiya University. His work indicates that heat


90 I Marine Propulsion I April/May 2014


Wärtsilä’s dual-fuel system includes a shell and tube heat exchanger to regasify the LNG fuel (credit: Wärtsilä)


evaporators are typically used, which consist of a stainless steel coil immersed into a hot water bath. That heat could come from steam, electricity or a waste heat source, Mr Karlsson explained. However, a water bath evaporator can be quite large, which makes them unsuitable as evaporators for engines the size of Wärtsilä’s. Instead, the manufacturer typically uses shell and tube heat exchangers, because of their


Understanding cargo heating is an ‘urgent task’


transfer under dynamic conditions can range from 1.5 to 4 times higher than when the oil is static, when free convection prevails. The paper develops equations that can be used to predict the increase in heat transfer when influenced by fluid movement caused by the rolling characteristics of vessels. This will enable optimisation of sizing of exchangers. Initial tests were carried out in a laboratory tank to verify heat transfer rates using a cylindrical heater immersed in medical Vaseline oil. With no rolling effect, and hence free convection, the results achieved were in close correlation to those derived from numerical analyses. Further tests were then conducted with varying amplitudes of oil


oscillation being introduced.


The results indicated three aspects of heat transfer where magnitudes vary with the degree of fluid movement. The first of these is the influence of free convection under low fluid oscillations. The second is when more mixed convection is introduced as oscillations increase and the third where more strongly forced fluid movement has a dominant effect on heat transfer.


The paper proposes equations that can be more reliably used to predict heat transfer rates which, in turn, can be used to evaluate heat exchanger capacity requirements. MP


Read the paper via www.tinyurl.com/tank-heat www.mpropulsion.com


compactness. It has also, with its sub supplier, developed a design to ensure a low pressure drop and large contact surface on the LNG side in order to achieve efficient superheating of the gas. To avoid the risk of freezing, ethylene glycol is typically used as an intermediate heating medium. This extracts waste heat from the engine-cooling water systems.


would also be filtered in what they termed a filtration-cum-heat exchanger, fitted in line with the ballast system. Like the Hi Tech Marine arrangement, this proposed system would recirculate the ballast water during a voyage, passing it through the filter and the heat exchanger.


The authors estimated the operating costs but said that the pumping costs would be negligible as no changes in pumping arrangements would be needed. Capital costs would include the heat exchanger, filtration units and extra piping. They quoted figures of US$0.06-0.19 per tonne of treated water for the filtration and US$0.056-0.17 per tonne for the heat treatment system.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108