How many tons of water do ships boil off to make enough steam aboard? Where do they get this amount of water and where do they dump all of it? If you are wondering how I suggest you continue reading.
What Is A Feed System?
The boiler feed water system is an important part of the steam production on board the vessel. Like the human circulatory system, feedwater is comparable to the blood which travels and carries the nutrients but in this case, heat energy around each part of the system.
Precisely, the feedwater is the media where the heat is stored, traveled, and delivered in the system. Boiler feed water can be on an Open or closed type system depending on the necessity and application.
The boiler feedwater system is heated to a very high temperature and also turns a high pressure in the form of gas/steam that is used by the consumer of the system (e.g., turbine).
The used steam goes back to the condenser where it is turned back into liquid form (water). The water is then pumped to the boiler by the feed water pump to complete the cycle.
Types Of Feed Systems
Commonly, there are two main types of feed water systems. these two types are;
- Open Feedwater system
- Closed Feedwater system
The obvious difference between the two types is that an open-type feedwater system is related or open to the atmosphere while a closed-type feedwater system is isolated from the atmosphere.
Open Feed System For Marine Auxiliary Boiler
An open feed system is commonly used by ships on their auxiliary boilers.
In this system, feedwater is pumped to the boiler where it is superheated and then fed to various consumers on ships. For instance, tank heating, oil purifiers, fuel conditioning system and etc.). the steam once used will be drawn to the condenser.
The condenser media is usually seawater, sometimes from the atmosphere. As it goes, heat exchange takes place in the condenser which turns steam into the water again. The condensed water is collected in a hotwell.
The hotwell serves as the suction tank where the boiler feedwater pump draws to fill up the boiler once again. Excess condensate water overflows from the hotwell or condensate tank back to the feedwater tank. The boiler feedwater pump can also suck from the feedwater tank.
The process continues and the cycle is called open feedwater system
Closed Feed Water Boiler System
Closed feed systems are used for very high-pressure applications. For example, a big turbine needs a big amount of steam to be moved.
The steam utilized by the turbine will go to the condenser. A condenser at a high vacuum will allow heat exchange to take place with a conservative drop in temperature. Condensate will be drawn by extraction pumps and circulated on an air ejector where the air is removed.
The condensate is heated gradually by the gland steam condenser and further as it passes to the low-pressure heater. The condensate is then thrown into the deaerator before the feed pumps. The feed pump supplied the feedwater to the high-pressure heater before it is fed to the boiler and so the cycle continues over and over.
The closed system provides a heat recovery system that makes it much more efficient than open type feedwater system.
What Is The Function Of De-aeration Of A Boiler Feed Water?
Deaeration is the process where dissolved oxygen in water is released which in turn prevents corrosion in the system. Water has the property that whenever its temperature rises the more it releases its dissolved oxygen.
In a closed feedwater system, the steam contacts the feedwater. The water and steam mix and as explained earlier are separated by air ejectors and extraction pumps.
Difference Between Open And Closed Feedwater Heater
The main difference between the closed and open type feedwater system is the condenser media where the steam is processed after it has been used by the consumer.
Particularly, in an open type feedwater system, the condenser uses resources outside the system like the seawater and the atmosphere itself.
Meanwhile, in the closed feedwater system type, the utilized steam is processed in the condenser by means of recirculation where high efficiency is achieved as the heat is recovered again and again.