Economizer
- The economizer is used to heat feed water so as to recover a part of heat which would otherwise be lost through flue gases.
- It is connected in the passage of the flue gases in between the exit from the boiler and enter to the chimney.
- By its use, economical use of fuel is achieved and also the rate of producing steam is increased.
- Figure represents Green’s economizer, which is one of the many types of economizers available.
- It consists of groups of vertical cast iron pipes, they are available upto 4 m. These groups of vertical tubes are built in sections of 4, 6, 8, 10 or 12 tubes wide fitted at their two ends to the cast iron boxes by pressing hydraulically, at the top and bottom.
- The sides of the top boxes are machined and bolted together to form an air tight roof.
- All the tubes are enclosed within the brick-work of the economizer. There are two pipes C and D outside the brick-work. Rows of top and bottom boxes are connected to these top and bottom pipes.
- The feed water is pumped to the bottom pipe D, from where it goes to bottom boxes and rises up in the groups of vertical pipes into the top boxes.
- From the top boxes it goes to the pipe G from where it passes to the water space of the boiler via the feed check valve.
- F is the control valve for inlet water. G is the control valve for exit of water from the economizer. S is a safety valve which is set 10 to 15% more pressure than the pressure at which boiler safety valve is to blow off.
- Passage of flue gases through economizer may result in collection of soot on the tubes, which will reduce the transfer of heat to water from hot gases. Hence, it is required to continuously scrape these tubes by scrapers (J) to remove the soot collected on them.
- A pair of scrapers for two adjacent tubes coupled together and move up and down simultaneously scraping the soot from the tubes.
- A pair is connected by a chain passing over the pulley.
- The movement of the scrapers is slow and their movement can be automatically, intermittently and timely reversed. The soot is collected in soot chamber L and can be removed from the soot chamber door.
- It is necessary that temperature of the feed water entering the economizer must be high enough so that moisture from the flue gases does not condense on the economizer tubes.
- Further this moisture condensation on the tubes may absorb SO2 and CO2 from the flue gases and form acids to corrode the tubes.
- Hence, if feed water temperature is less, hot water from the outlet of economizer is mixed to raise the inlet temperature of feed water.
- Economizer chamber should be leak-proof against air infiltration otherwise draught of boiler will be adversely affected.
