Factors considered for Boiler Engineering & Design

Factors considered for Boiler engineering/Boiler Design

1-Boiler Design code: IBR 1950 with latest all amendments

2. Ambient air temperature: Depends on the location of the plant, in India Generally 30 to 45 Degree C is considered.

3. Relative humidity for performance: (Normal: 60% to 70%, Maximum: 80% & Minimum: 20%).Generally it depends on site condition

4. Wind Velocity & direction for structure design: as per IS 875 (39 m/sec)

5. Seismic coefficient As per Is 1893 Zone-I

6. Wind velocity for insulation: generally 1 m/sec

Why & How these in Boilers??

7-Maximum Continuous Rating (MCR) required for particular process or use: It is the capacity of the Boiler in TPH or Kg/hour required.

8-Operating pressure & temperature: Operating pressure & temperature of the Boilers depends on the requirement of process of prime mover. Higher the operating parameters higher will be the Boiler efficiency & lower will be the fuel consumption. For high pressure Boilers water quality required is

9-Type of fuel: It depends on the easily availability of fuel, for example: Sugar based cogeneration Boilers are designed for bagasse fuel. Utility Boilers are designed for Briquettes & Indian/ Indonesian coal. Thermal power plant Boilers are designed for coal.

Gujarat state area Boilers are designed for natural gas fuel. Middle yeast country Boilers are designed for Oil fuel.

While designing the Boilers & combustion system fuel GCV, ash & moisture contents are considered.

Questions & Answers on Fuel consumption

10-Peek Capacity of the Boiler: It is the maximum allowable load on Boiler for short period. Generally it is kept 110% of MCR.Peak capacity is allowed 30 minutes in 8 hours.

11-Range of load variation/Steam temperature control range: It is the range of load (as % of MCR) during which Main steam temperature is maintained constant. Generally it is around 60-100%.

12-Percentage of excess air or Excess air coefficient at Boiler furnace & Boiler outlet

13-Circulation ratio

14-Feed water temperature at economiser inlet: In order to achieve desired efficiency & fuel consumption, feed water at economiser inlet is very must. Higher the feed water temperature, lower will be the fuel consumption & Vice versa.

14a-Feed water quality like pH, conductivity, TDS, Silica, hardness, Alkalinity etc

15-Steam temperature drop at Super heater coils: In order to get the desired main steam temperature at super heater outlet, need to maintain the ∆T across super heaters.

16-Flue gas temperature drop: While engineering Boilers, flue gas temperature drop at every zone (Super heaters, Bank zone, Economiser, APH etc) should be considered.

17-Combustion air temperature: FD & SA air temperatures after APH should be optimum. More air temperature leads to formation of clinker & less air temperature leads to less combustion efficiency.

18-Air & Flue gas ducts sizing: In order to avoid pressure drops in ducting proper sized ducts have to be considered. Flue gas pressure drop is very important for considering heat transfer at APH, Economiser, Bank zone & Super heaters.

Material of MS material (IS 2062) for air ducting is of 5 mm & for flue gas ducting is 6 mm

19. Fuel feeding system: Considerations of No. of fuel feeding system & their individual capacity is necessary for operating the Boilers at MCR & Peak loads at varying fuel parameters. If the fuel GCV, moisture & ash content vary then fuel consumption will also vary. So while engineering the Boilers fuel feeding capacity is considered 25 to 30% more.

Turn down ratio of fuel feeding system. Maximum moisture handling capacity of the system

20. Heat released in Furnace: This important factor for designing the furnace height, width & breadth

21. Heat released on Grate/Bed: This important factor for designing the furnace & combustion compartments, grate materials etc

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22. Flue gas velocity at various zones of Boilers: This is very important factor to be considered while designing the Boilers. Higher velocity of flue gas leads to erosion of pressure parts & ducting, lower flue gas velocity leads to poor heat transfer.

Generally for AFBC, Travelling grate, WHRB, oil fired Boilers ducting are designed for 18 m/sec velocity.

23. Percentage of combustion air flow through FD & SA. Generally from FD 60 to 70% and from SA 30 to 40%

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24. Steam pressure drop in all stages of Super heater coils

25. Velocity of feed water & saturated water at each pressure part

26. Overall heat transfer co-efficient & LMTD in super heater, economiser, Bank zones

27. APH: Overall heat transfer co-efficient & LMTD .Pitching of tubes along & across the air flow. Heating surface area

28. Pitching of super heater coils along & across the flue gas flow: Wide pitching of super heater to minimize fouling.

29. Desuperheating spray water quantity at MCR & other various loads

30. Maximum steam temperature at each super heaters

31. Maximum allowable metal temperature at each Super heaters

32. Pressure parts thermal expansion calculations & Maximum/minimum tolerances

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33. Grate or Bed area loading in mm Kcal/M2/Hr

34. Dust concentration at Boiler outlet in gram/NM3

35. Quantity of flue gas produced

36.No.of Safety valves installed Boiler safety valves QnA


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