The boiler is a 3 pass Fully Wet back shell and tube type boiler. It consists of a flue ends with reversal chamber. The flue gas turns in the reversal chamber into the second pass tubes and ends up in front smoke box. The flue gas turns again in the smoke box into third pass tubes and leaves the boiler from the outlet of the third pass to the chimney. The flue gas tube, second pass and third pass tubes are fully surrounded by water and thus provide a safe heat transfer surface. The tube diameter is chosen judiciously to prevent any chocking of the tubes by the soot being carried by the flue gas.
Two numbers of feed pumps are given out of which one will be normally working and other will be standby. There is sufficient steam space in the shell to assure a good quality steam. The normal water level is kept well above the last row of the tubes providing sufficient margin. This ensures the safety of the boiler tubes. On – off Mobery type water level controller is provided and this would control the water level between two set points. Two fusible plugs are provided for additional safety.
The boiler smoke box doors are of hinged construction, which can be opened very easily for cleaning the tubes. The shell is provided with necessary manhole for waterside cleaning and maintenance.
A boiler control panel is floor mounted and includes the necessary control equipment and starters plus mains isolation. Control pressure switches are attached to the side of the panel.
Superior Features of our Boilers:
•Compact and efficient design which requires less floor space.
•High thermal efficiency
•Three Pass Wet Back Design
•Ample furnace and combustion volume ensures complete combustion
•Adequate total heating surface
•To Reduced scale formation Heat flux is kept to bare minimum
•Square Box design minimizes Radiation losses
•Safety aspect maintain with strict quality controls
A) SCOPE OF BOILER
1. Shell and Tube Assembly
Boiler shell is constructed in suitable sections dependent upon boiler size. Following the rolling process, longitudinal and circumferential seams are machine welded and subjected to X-Ray and NDT inspection to comply with the latest standard requirements with required Manholes; Hand-holes etc. mounted on Saddles.
The boiler is of fully wet back design. The furnace tube is designed to allow adequate expansion and is located between the front tube plate and the totally submerged reversal chamber. The rear reversal chamber plate is stayed to the boiler rear tube plate with adequate number of stay bars.
Two passes of tubes of Electrical Resistance Welding.
The second pass of tubes is fitted between the boiler front tube plate and the reversal chamber front tube plate. The first tubes are expanded into both tube plates. Third pass tubes are fitted between the boiler front and rear tube plates and are expanded into position. The required number of stay tubes and stay bars are fitted in all boilers. All stay tubes are lightly expanded before being welded in the tube plates and reversal chamber.
Access doors permit as far as is practicable, the internal inspection of heating surfaces and include a main door on top of the boiler shell and one mud door is provided in the rear tube plate.
|Shell, Furnace and Tube Plates||SA 516 GR 70 / Equivalent|
|Furnace Access Tube||SA 516 GR 70 / Equivalent|
|Plain and Stay Tubes||BS 3059 ERW 320 & BS 3059 GR 360 (63.5mm x 3.66 Thk)|
|Man door Mud door Lifting Lug||A – 531 C l – 1|
|Pads||SA 516 GR 70 / Equivalent|
|Bosses||SA 516 GR 70 / Equivalent|
|Stand pipes||SA 106 Gr B|
2. Mountings and Fittings
Mountings and controls are fitted to pads and nozzles welded to boiler shell. Below are the makes of mountings and fittings on the boiler. They shall be supplied with boiler as per IBR formalities and as per the requirement of Day-to-Day Operation & Maintenance.
|1.||Safety Valves||2 Nos||Fainger/Darling make|
|2.||Main Steam Stop Valve||1 No||Rushas/Sant/Atam/Equivalent|
|3.||Isolation & Drain Valves||1 Set||Rushas/Sant/Atam/Equivalent|
|4.||Blow Down Valve||1 No||Rushas/Sant/Atam/Equivalent|
|5.||Water Level Gauge||2 Nos||Rushas/Sant/Atam/Equivalent|
|6.||Pressure Gauge||1 No||Pioneer/Waree|
|7.||Pressure switch||2 Nos||Indfoss/Danfoss|
|8.||Fusible Plug||2 Nos||Rushas/Sant/Atam/Equivalent|
|9.||Feed Check Valves||2 Nos||Precision Controls|
|10.||Water Level Controller||1 No||Malhotra/Equivalent|
|11.||Water Feed Pump||1 No||Grundfos/Equivalent|
|12.||ID Fan||1 No||Rakhoh|
3. Burner for IDO
A fully automatic high efficiency Burner capable of operating at excess air lower than 17% will be provided with boiler. The unit is with burner management systems and all the functions The Burner Control Panel is complete with Electronic Temperature Controller, Boiler Sequence Controller Ignition Transformer, Oil Pre-heater, Air Damper Motor, Flame Surveillance System and Solenoid Valves.
The firing rate will be controlled automatically by modulating damper motor in accordance with boiler load, and should maintain same efficiency throughout the modulating range.
The burner should be freely accessible for easy maintenance with minimum removal of oil pipe work and electrical wiring.
4. Insulation and Cladding
The external surface of the boiler shell and the periphery of the front Smoke Box are to be insulated with min 75mm thick mineral wool/Rockwool slabs securely fixed and clad in min 0.8 mm stainless steel so as to achieve surface temperatures of not more than 30⁰C.
5. Control panel with Electrical Cabling
It will be Self-Standing /skid mounted Cabinet. It will be Powder Coated, prewired & will consist of the following:
• Power Circuit
• Control Fuses and Contactors.
• Control Switches & Push Buttons
• Indicating Lamps.
• Main Supply – 415V/3 Phase 50Hz
• Control Supply – 240V/50Hz
• Internal Cabling will be given to Burner, Fan, Pump, Mobery, Pressure Switch, etc. Heat resistant wiring is used for wiring between water level controls and the control panel, all other wiring is in PVC covered wiring carried in flexible conduit. The panel is completely pre-wired at our factory thereby reducing pre-commissioning time at site.
B) SAFETIES PROVIDED IN BOILER
|Sr. No.||Unsafe Condition||Controller||Controlling Action|
|1.||Extra low-water level in Boiler||Level Controller||Starts the feed water pump to maintain the water level range required|
|2.||Very extra low-water level in Boiler||Fusible Plug||Melting of the fusible plug at high temperature, suddenly bringing down the pressure and quenches the fire with water|
|3.||Steam Pressure High||Pressure Switch||It trips the ID fan, FD fan to control the pressure|
|4.||Steam Pressure High||Safety Valve||Opening of safety valve to balance the pressure|