CFBC (circulating fluidization bed combustion )BOILER PRESSURE PART’S & THEIR FUNCTION:-

Today we discussed about the CFBC (circulating fluidization bed combustion ) boiler pressure parts and their uses .CFBC boiler is a Single-drum, natural circulation, top supported, and membrane wall construction. Internal Recycle Circulating Fluidized Bed, Boiler (IR-CFB), Natural Circulation, Single Drum, Top Supported, Membrane Wall Furnace, Balanced ,Draft, Outdoor Installation. Different pressure parts are listed below for cfbc boiler and mention their function also.

1.Economizer

2.Steam drum

 3.Down comers

 4.Furnace walls

 5.Divisional Wall

 6.Buckstays & Seismic stoppers

 7.RDZ zone

 8.U beam Hopper Panel

 9.SH Enclosure Panel

 10.Riser Tubes

 11.Saturated steam supply pipes

 12.Wing Wall

 13.Primary Super heater

14.Secondary Superheater

 15.Attemperator

16.Main steam piping

CFBC BOILER PRESSURE PART’S & THEIR FUNCTION:-

1.ECONOMISER:

Economizer is very important part of steam generation unit . The function of an Economiser is to absorb heat from flue gases & add this as a sensible heat to the feed water, before the water enters to the steam drum. It’s also improve the steam generation quality and also boiler efficiency as well. Economiser is located in between SSH outlet and Air Pre-heater.

Feed water flows from the bottom header to the top headers through these coils. Heated water flows out from the top header to steam drum through the connecting pipe. The economiser is provided with drain valves located on the inlet header.

Economiser top header is provided with following attachments:-

-An air vent valves which will be kept open during initial filling to remove the air

trapped between the coils. These valves need to be closed after free flow of water from the vent.

-Pressure Transmitter with twin isolation valves

-Thermocouple is provided for panel mounted temperature indicator

2.STEAM DRUM:

Steam drum is mounted on the top of the boiler it consist different part for steam purification Steam drum is a welded cylindrical vessel made of SA 516 Gr.70 material. The cylindrical portion of the vessel is made of 100 mm thick plates and the two hemispherical dish ends are 90 mm thick. Two elliptical manholes at either end of the drum provide access inside the drum during shut down inspection and maintenance purpose also. These manholes are closed tight at either end by 120 mm thick plates, bolted against the manhole rim by two holding bars. A gasket is fitted between the cover plate and the mating machined surfaces in the end shield. The cover plate swing inside the drum, for convenience during opening.

3.DOWN COMER PIPES:

There are total six main down comers from steam drum divided into two main groups(LHS & RHS),which supplies water to all Furnace wall bottom ring headers, Divisional wall, U beam hopper panel, U beam enclosure panel and Superheater enclosure panel, front wall and rear wall bottom headers. Drain lines with isolation valves  are provided for individual main down comer to remove the drain the down comers. These valve also used for the giving the header blow down of boiler during light up or shut down of boiler at 5-10 kg pressure removing the sludge from the bottom ring header.

4.FURNACE:

Boiler furnace contain tube wall panel for initially water heated purpose .The construction of the furnace is made up of totally gas sealed enclosure suitable for positive Draft operation with water cooled membrane wall panels. Furnace is provided with various openings for peephole, fuel feeding chute, fly ash recycling port; start up oil burner, secondary air ports, instruments tapping manholes and Bed ash drain ports.

5.DIVISIONAL PANEL

Divisional walls formed with top and bottom header of and panel tubes for distribution of water . Divisional wall receives water from steam drum through down common supply pipes. Flat pins/studs are provided welded to pressure parts for holding refractory castable.

6.BUCKSTAY AND SIESMIC STOPPERS

To strengthen the wall tubes, Backstays beams are provided all around the furnace wall at 10 different. The buck stay beams are supported on the angle cleats welded to the water wall panels with the help of clamping rods. Individual level backstay beams are connected at corners with flexible tie plates to accommodate thermal expansion during operation.To hold the pressure parts at their desired position and to direct the thermal expansion, seismic stoppers are provided at all around the furnace walls at 9 different elevations. Seismic stoppers are also provided at middle of the drum.

7.RDZ ZONE

Reduced Diameter Zone is patented technique by B&W which is employed in IR CFBC boiler to reduce the erosion rate of the furnace wall panel tubes. This arrangement is provided for all the four side wall panels and division wall panels at the location, where the refractory application ends. Ceramic tiles provided to protect the tubes at RDZ.

U BEAM (IMPACT SEPARATOR) HOPPER PANEL

The U beam hopper panel is formed with Top & Bottom header and panel tubes of Part of the U beam hopper panel is made up of membrane wall and the outlet end is arranged staggered for flue gas exit. U beam hopper panel wall receives water from steam drum through down commer supply pipes.

8.PRIMARY SUPERHEATER ENCLOSURE PANEL

Both the primary and secondary superheater coil assembly are enclosed by separate enclosure panels at LHS & RHS side formed with inlet and outlet header of & Panel tubes of. SH enclosure panel wall receives water from steam drum through downcommer supply pipes.

9.RISER TUBES:

Saturated steam from furnace wall panels, U beam hopper panel, U beam enclosure panel, PSH (primary super heater ) & SSH (secondary super heater ) enclosure panels is supplied to steam drum through individual section riser tubes.

10.SATURATED STEAM SUPPLY TUBES

Dry Saturated steam from the steam drum is connected to common header through supply pipes provided from the top of steam drum. From common header steam is supplied through pipes to primary wing wall inlet collection header. Tapping with a manual isolation valve is taken from saturated steam header for steam purging in wind box during MFT condition.

11.WING WALL

Boiler is providing wing wall assembly located at boiler front wall. From wing wall inlet collection header steam is supplied to primary wing wall bottom header of through pipes. Steam from primary wing wall is connected to primary wing wall top header through pipes.

12.PRIMARY SUPER HEATER

PSH-1 is located at flue gas exit of boiler before economizer, it’s pendent type supported from Super structure through sling rods. Steam from the Secondary wing wall outlet collection header steam enters the PSH-I inlet header. From the PSH-1 inlet header, steam flows to PSH-1 outlet header through thick coils.

13.SECONDARY SUPER HEATER:

From attemperator steam is passed through the SSH inlet header steam flows to SSH outlet header  through  thick coils. SSH is located between the U Beam and PSH-2. The SH headers are supported through sling rods with rocker washers from the super structure of the boiler.

14. ATTEMPERATORS

To achieve fine control on final steam temperature attemperation is provided.

Attemperator is provided in between primary superheate-1& primary superheater -2.

15.MAIN STEAM PIPING

Super heated steam from secondary superheater outlet header is connected to common steam distribution header by the main steam piping.

Main steam piping is of pipe with the following attachments:

-Temperature Elements ,Pressure indicators  for local indication at main steam line and for local indication at firing floor.

-A Electromatic Relief valve provided with silencer.

-Super heater Safety valve (PSV) with the silencer at exhaust piping.

Pressure Transmitter

-A Temperature Gauge with tag number is also provided.

-Start up vent valve provided with isolation valve To reduce the noise level

from the steam venting to atmosphere, a silencer is provided to the start up vent line.

-Drain connection with isolation valves before the MSSV is terminated to S.H

common drain header.

-Main Steam Stop Valve (MSSV) along with a integral bypass inching type motorised

valve Drain connection after the main steam stop valve is terminated to the S.H header with a isolation valves and NRV.

– A NRV (non retrun valve ) is provided after the stop valve to prevent back flow of the steam from common header to the boiler.

-A temperature and pressure test points are provided after the NRV in the main steam line. Steam flow-measuring device, i.e. flow nozzle along with flow transmitter Tag numbers.

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