MAHAGENCO Presentation on 210 MW Boiler Construction
Presented by Uddhao G. Manapure K-57, Batch Koradi Training Centre Koradi
1. INTRODUCTION
Boiler is any closed vessel exceeding 22.75 liters in capacity used for steam generation under pressure. First boiler was developed in 1725 and its working pressure was 6 to 10 kg/cm2 and was called Wagon Boiler
There are mainly two types of Boilers 1. Fire Tube Boiler 2. Water tube Boiler The boiler used for generation of power is somewhat different in construction than the boilers used in other industrial applications. The boiler used for power generation is constructed by the four walls called water walls. These walls are made up of long tubes called water wall tubes through which water flows and the combustion of fuel takes place inside the boiler. The flue gases so formed passes through two passes of the boiler. 1. First Pass 2. Second Pass
Boiler used in Thermal Power Plant are again subdivided into 1. Natural Circulation 2. Forced Circulation - operating pressure approaches
to critical pressure
According to working pressure 1. Sub critical Pressure Boiler: - working press. Range 130 to 180 kg/cm2 2. Critical Pressure Boiler: - pressure 221.2 kg/cm2 3. Supercritical pressure Boiler or Once Through Boiler: - working pressure 240 kg/cm2
Boiler design Considerations:Following factors are taken into consideration: Lowest capital cost, easy in construction, simplicity safety, good working condition, easy in maintenance. Availability of auxiliaries Efficient operation, effective for heat transfer well insulate of casings, ability to deliver pure steam with effective drum internals, to genrate steam of full capacity.
1.1 Boiler Construction :Main parts of Boiler used in Thermal power plant 1) Boiler Drum 2) Down corners 3) Water wall 4) Furnace Superheater 5) Primary Superheater 6) Platen superheater 7) Final Superheater 8) Reheater 9) Economizer 10) Burners 11) Ignitors 12) Windbox 13) Soot Blowers The flue gas formed by combustion of a fuel in the furnace passes through two passes I) II)
First Pass Second Pass
First pass consist of 1) 2) 3) 4)
Furnace water wall Platen super heater Reheater Water wall screen tubes
Second pass consist of 1) Final super heater 2) LTSH 3) Economizer After second pass flue gases flows through air preheater where it gives heat to air then passes through ESP & blown out to atmosphere through chimney.
1.1.1.Boiler Drum :1) Drum is a pressure vessel 2) It is made of special carbon steel plate Material of SA-299 grade A1 Or SA- 515 Grade 70 Plates thickness having 132 mm 3) The function of Boiler Drum is to separate water & steam from the mixture generated in the furnace wall. 4) It also provides a water storage for preventing the starvation of tubes.
Parts :1) Turbo separator 2) Screen dryer 3) Feed pipe 4) Baffle Plate 5) Drum level gauge (lower) 6) Riser tube (Water walls Tubes) i.e 6 x 23 rows on drum 7) Chemical dosing pipe 8) Main hole & main hole cover 9) Safety Valve 10) Sampling line 11) Vents Technical specification of 210 MW boiler drum is given below. Length 15700 mm Weight 123 Tonnes Internal Diameter 1676 mm Outside Diameter 1942 mm Thickness of Metal 132 mm Material Carbon Steel SA 515 Gr. 70 or S.A. 299 A1 Pressure in Drum 149.7 Kg. /cm2 (LMW Unit) 168 Kg. /cm2 (KWU Unit) Total Number of Turboseprater in each row 50 Location :Boiler drum is located at height of 53 Mtr. from a ground level. The main supporting structure of a boiler consist of 18 main column & 12 auxilary column. The main columns supported the main boiler components.
1.1.2 Down comers 1)
There are 6 to 8 down comer from drum and are jointed to ring headers to provide water to water walls.
2)
The Two down comers joined to Platen water wall header.
3)
platter water wall header are not provided to every boiler. Rear Bottom Ringheader
Left
Right
Front 1) 2) 3) 4) 5)
Two down comer – to front side of Bottom Ringheader Two down comer - to rear side of Bottom Ringheader One down comer – to left side of Bottom Ringheader One down corner – To right side of Bottom Ringheader Two down comer – Tow water wall platen inletheader.
1.1.3 Water walls 1) Water wall tubes also called as riser tubes. 2) furance made up of 4 water walls I) front water wall II) LHS water wall III) IV)
I)
rear water wall RHS water wall
Front water wall :-
Connection’s made up of water tubes from the front portion of Bottom Ringheader to front top header are shown. 1) Platen water walls :There are four platen water walls located at the top of the combustion chamber to increase the heating surface without increasing the volume of the boiler furnace. 2) L.H.S. water walls :The left side water wall connections from Bottom Ringheader to left top headers as shown.
3) R.H.S. Water walls:The right side water wall connections from the right portion of bottom ring headers to the right top header as shown. 4) The rear water wall :Connection’s from bottom ring headers to rear top headers as shown.
About 60% rear water wall tubes form goose neck and are connected to the rear top most header. A goose neck helps in maintaining a better distribution of the flue gas steam in the transition zone i.e. In between first & second pass.
And about 30% of rear water wall tubes go straight to the top rear header which is exactly above the rear portion of the Ringheader.
About 10% of the water wall tube from rear side rear side bottom Ringheader are connected to the extended water wall inlet headers located below the goose neck.
From the extended water wall inlet headers water gooses to righ & Left top headers
Riser tube connection from boiler top header to drum are shown there are 6 x 23 rows of riser tube connection’s on the drum as shown, in fig
The fig. shows the complete assembly of a) Water walls from bottom ring headers to top headers. b) Riser tube connections from top header’s to drum as shown in fig.
1.1.4 Furnace : The tall rectangular raident type furnace or used in modern design of pulverized fuel boiler. Height of modern boiler is increased to lower gas temp & reduced sagging. Furnace is of two passes In front pass combustion of fuel takes place & hence this is the most hot zone of the boiler called is firing zones. The temp of firing zone is about 12000c to 14000c this type of furnace is called water cooled furnace After second pass flue gases passess through Air Preheater where it gives heat to air then passes through ESP and blown out to atmosphere through chimney.
Steam from drum comes to LTSH, It has two stages i) Upper bank & Lower bank Each bank has 134 assemblies of pitch 102 mm Material of the tubes are SA 209 T, SA 210 Gr. A, SA 213 T11 Size of the tubes is 44.5 x 4.5 mm Temprerature with standing range 4500c to 4800c
Steam from LTSH comes to platen superheater It is situated in furnace vertically. It has 29 assemblies having pitch of 457 mm Material of the tube is alloy steel SA 213 T11 SA 213 T22 Size of the tubes are 51 x 7.1 mm & 51 x 8.6 mm
1.1.7 3) Final superheaters:
It is situated vertically behind reheater having 119 assemblies at a pitch of 114 mm Size of tubes 51 x 7.6 mm Final superheater tubes are made up of SA 213 T22 alloy steel This material can with stand temperature upto 5800c
1.1.8 REHEATER :
Reheater is located behind the platen superheater. It is Two parts front & rear Front reheater has 59 assemblies at a pitch of 229 mm & Rear Reheater has 89 assemblies at a pitch of 152mm Material of Tubes SA 213 T1 alloy steel. Tube size 54 x 3.6 mm Tube material can withstand temp. upto 5500c.
1.1.9 :- Economizer :
It is located between LTSH & Air Preheaters in second pass of furnace. Feed water after HP Heater passes through economizer. After this it is goes to drum. Economizer is in two banks, lower banks & upear Bank It has 270 assemblies at a pitch of 102mm Material of tubes SA 210 Gr A1 Size of tubes 44.5 x 4.5 mm Tubes material can withstand tamp. Upto 450 0c
1.1.10 Burners & Igniters:
Coal is used as primary fuel & oil is used as a secondary fuel during start up of boilers & for flame stability at loads & other transient operating conditions. Burner is to automise fuel, penetrate & mixed with proper proportions for complete combustion. Burner are stituated at 3 elevation’s called AB,CD & EF At every there are four burners. Fo/LSHS can be fired at all elevations but LDO can be taken at AB elevation’s only startup of boiler. For every burner weather LDO/FO there is one igniter to ignite the burner. Now igniter’s are being changed from HSD/LDO to HEA (High energy arc igniters, purly electrical)
1.1.11 wind box :
The wind box is situated at 11mtr level of boiler it is in two parts. One is in LHS & other is in RHS of Boiler. There are thirteen compartments in it on each corners out of which 1) 3 for oil burners 2) 6 for coal mills. 3) 4 for auxiliary air. These compartment are connected to burner tilt mechanism which is operated +/-30 as per require according to final temp of steam. The secondary air after Airpreheater come to windbox and is given to furnace along with fuel for complete combustion.
1.1.12 Soot blowers :
About 78 soot blowers are provide at different zones to remove the accumulated soot on boiler tubes for effective heat transfer.
There are situated on the furnace & are 56 in no’s These are driven by electric motors. Super heated steam is blown through them to clean the disignated area of the water wall. Two soot blower’s are located on air heater’s to clean the basket’s of A.H. Steam from PRDS is taken for this purpose.
LRSB :
Long retractable soot blower’s are 20 in nos. These are used to clean S.H. & R.H. & are located in 2nd pass of the furnace.
