Boiler Feed Water System Diagram and Explanation - What is the Open Feed System?
What is a Feed System?
These four components comprises of a cyclic process that starts from the formation of high pressure, highly compressed steam by the boiler. The high temperature steam goes to the turbine, where it operates the turbine and comes out in the form of exhausted low energy steam. This low energy steam goes to the condenser, where it gets converted to water. The feed pump pumps this water back to the boiler and the cycle repeats itself.
Apart from these four main parts, the system also includes a drain tank that collect the condensate from the condenser and provides a suction head to the feed pump for transferring the water back to the boiler. There is one more feed pump attached to the system , which helps in recuperating the loss of feed water by storing surplus feed from the drain tank.
In case of a feed system in an auxiliary boiler, as found on diesel propulsion ships, the drain tank or the hot well is open to the atmosphere. While in a high pressurized system, no part of the system is open to the atmosphere. A feed system, is nothing but a cyclic process that takes place between the turbine and the boiler. This cyclic process facilitates the exhausted steam to return to the boiler in the form of feed water. The feed system consists of four main parts:
- boiler
- turbine
- condenser
- feed pump
Types of Feed Systems
There are basically two main types of feed systems :
- Open feed System
- Closed feed system
Open Feed System
A open feed system is found in a system with an auxiliary boiler, which is generally on a ship with a diesel engine. In an open feed system, steam from various systems comes to the condenser and gets converted into water. This condenser is continuously circulated with sea water and operates under certain atmospheric pressure or slight vacuum. The condensate, under the effect of gravity goes to the hot well and feed filter tank. If the condenser is under vacuum, extraction pump is used to transfer the condensate to the hot well.
Apart from the condenser,the hot well also receives water from the drains of contaminated systems such as fuel oil heating system, oil tank heating, drain cooler, observation tank etc. The water from all these drains passes through a filter or internal baffles in order to separate any kind of oil presence. The water is then passed through a second stage filtration process which contains charcoal or cloth filters. In case the hot well overflows, the water goes to the feed water tank, which supplies feed water to the system whenever there is a dearth. A de-aerated type heater is used in the feed water line in order to remove any dissolved oxygen from the water. This is basically done to prevent corrosion of the boiler. The system also consists of a feed regulator which controls and maintains the level of water in boiler drum.
Image Credits
Introduction of Marine Engineering 2nd Edition by D.A Taylor
