This article deals in explaining the waste heat recovery system that is being used in large number of vessels these days, considering the benefits it is giving to the ship owners and also reducing the carbon footprints.
Consider a situation in which the only fuel that you need to burn on ship is for main engine, and not for any other machinery like Generator, Boilers. Sounds little amazing right? But seems little impossible! Well now we have systems on ships that can make that happen. That is where the Waste Heat Recovery system come under play. Although it is a complex arrangement to understand, but the picture below explains it in a very simple manner.
Waste Heat Recovery System
Here is the point wise explanation of this:
- Fuel is burnt in the engine. And the exhaust goes out of it. Although the energy from fuel released in the engine is already used by the engine, but the heat is still there in the exhaust. Now this heat in the exhaust can be used to heat the water and generate steam.
- Here we are talking of big engines which might be having more 5 units. You can imagine how much exhaust is generated in one minute.
- Now this smoke passes through a water tube boiler. The heat is taken by the water in the tubes and steam is generated. This steam is then comes to steam drum and from there it is used for different purposes.
- From steam drum the steam is passed through a set of regulator and finally reaching to steam turbine. And with this steam turbine, alternator is attached which generates electricity. But still one more thing is remaining.
- When engine runs at higher RPM, let’s say 60+, there is so much exhaust generated that it is too much to be used for steam generation. So this excessive exhaust is passed through a Gas Turbine which is attached on the same shaft as steam turbine. That was the basic info about the WHR systems works.
This system also has shaft generator and motor combination. It acts as generator when steam turbine is not generating enough electricity as per the consumers. And acts as motor when there is excess of electricity produced by the turbine. When it acts as motor, it helps the shaft of the engine to turn, thus reducing load on engine and less fuel consumption. WHR is a very intelligent system which works together. And the kind of efficiency the system has is really good. Single power and steam turbine can produce so much of electricity that it can be fed to several villages, if the setup was on land.
But to make it run, you need additional pumps, condensers, regulators and other more things. Let’s see some more info about these systems
Advantages of Waste Heat Recovery System on Ships
- Reduced carbon foot prints as only main engine is consuming fuel.
- Number of auxiliary machinery can be reduced like generators.
- Cost effective.
Disadvantages of Waste Heat Recovery System on Ships
- High Initial Investments
- Experienced Staff for Handling Systems
- Increased maintenance
- Consumes Space.
Over the years the popularity of using the waste heat recovery systems has grown a lot. Major shipping players like Maersk, MSC etc have WHR systems in most of their vessels. With pressure increasing on shipping sector for reducing the carbon footprints, these systems are greatly helping it to cut down. On the other hand, it is also cutting down the running cost of ships as less fuel oil is burned, which accounts for most part of money involved in running the ship.