BASIC DESIGN - KNOWLEDGE - BOILER

We have experienced a lot of basic engineering errors, their justification, then Rectification and Alteration, Later Replacement and finally Failure in the same pattern in the Coal & Biomass fired Boilers

BOILER DESIGN SELECTION & CALCULATION SEQUENCE

  1. BOILER GENERAL CONFIGURATION SELECTION
    1. Steam Circuit
      1. Radiant Super Heater
      2. Inter stage Attemperator
      3. Convective Super heater
    2. Water Circuit
      1. Deaerator
      2. Boiler Feed Water Pump
      3. HP Heater
      4. Economiser
      5. Steam Drum
    3. Primary Air Circuit
      1. FD Fan / PA Fan
      2. SCAPH
      3. Air Pre-Heater & Air Pre-Heater Bypass
      4. Wind box / Air inlet Hopper / Stoker
    4. Secondary Air Circuit
      1. SA Fan
      2. SCAPH
      3. Air Pre-Heater & Air Pre-Heater Bypass
      4. Furnace - Over Fire Air / Spreading Air
    5. Flue Gas Circuit
      1. Furnace
      2. Radiant Superheater
      3. Connective Super heater
      4. Boiler Bank / Evaporator / Screen Tube
      5. Economiser
      6. Air Pre-Heater
      7. ESP / Bag Filter / Wet Scrubber / MDC
      8. ID Fan
      9. Chimney

If calculation goes wrong, then this improper ratio of Steam & Water mixture leads to Flow Assist Corrosion failure (FAC failure)

Uneven heat / gas flow distribution leads to imbalance in superheater and leads to tube failure, Header Sagging & Distortion

If superheater pressure drop is very low, it means steam distribution is not proper. A correct pressure drop ensures good distribution of steam to individual tubes

Feed water temperature at Economiser outlet should be 20 to 30 degC below from saturation temperature of boiler drum water

Restrict the difference between steam temperature before & after (inlet and outlet) Attemperator water spray to below 30 degC

According to various experiments, best suitable range of ESP Inlet Flue Gas temperature is 150 deg C to 165 Deg C. ESP Inlet Flue gas volume will change w.r.t. Inlet Flue Gas temperature. An increase in Inlet flue gas temperatures than design is directly proportional to the ESP inlet gas flow rate and migration velocity and reduces dust particle contact time, hence reduced ESP collection efficiency and performance.

Read Example on Boiler Efficiency Calculation described in details in  attachment.