The debate about climate change and awareness of global warming is increasing, with greater numbers of people now convinced that this is one of the most challenging issues of modern times. The shipping industry has obviously always been a polluting business, due to the requirement of moving massive floating structures around the globe.
Ship owners are becoming increasingly aware of their responsibilities and are looking into alternatives to conventional ship designs – not only because regulations are forcing them to do so, but also because of their own sustainability policies. In recent years, this has resulted in a new focus on minimising emissions and improving the energy efficiency of vessels.
Waste heat recovery
One of the solutions to reduce emissions and improve efficiency is to reuse heat from exhaust gases, otherwise known as waste heat recovery. This process not only reduces emissions, but also brings a financial benefit to businesses through improved energy efficiency. In this specific case, exhaust gases are evaporating water to (superheated) steam, resulting in a significant power recovery from the exhaust heat.
Initially the hot well is filled with make-up water. In the hot well, the water may be heated by steam injection. From the hot well, water is supplied to the steam drum by the feed pumps. The steam drum consists of a layer of hot water and steam. The water is circulated by pumps through the evaporator part of the economizers. Some goes back to the steam drum as wet steam and the rest as water. The pressure in the steam drum will feed the super-heater part of the economizers and also the conventional network of heat consumers. The super-heated system will drive the steam turbine that is connected to the generator creating electricity. Downstream of the turbine, the vacuum condenser ensures, by seawater cooling, that the pressure in the condensate is as low as possible (near to absolute vacuum) to create the highest generator output. This condensate will be pumped back to the hot well where it may be heated by the hot water loop of the engines. For the network of conventional heat consumers, a back-up oil-fired steam boiler is installed.