Introduction to Thermal Power and Boilers

Introduction

• Thermal power station growth from 1947 to 2008
  • Power generation increased by about 142x
• The thermal power plant is a significant contributor to the Indian Energy Scenario
• Generation of power in India is dominated by coal, followed by hydro, and then renewable energy sources
• The installed power generation capacity is projected to increase by 2012 by approximately 80%
• Boilers are classified by their installation and their purpose

General Classification of Boilers

• There are two main classifications of boilers:
  • Package & Field Erected
  • Fire tube/Water tube

Boiler Classification by Purpose

• Power boiler: generate steam used to power turbines for electricity generation
• Utility boiler: to provide industrial process steam for industrial applications

Fire Tube Boilers

• Combustion gases pass through tubes submerged in water within the boiler
• Fire tubes are classified by:
  • Type of back (dry or wet)
  • Fuel source( coal or oil)
  • Internal or external firing
  • Tube type (through tube, return tube)
  • Orientation (horizontal, vertical, inclined)

Sub-Classifications of Fire Tube Boilers

• Common designs include:
  • Simple Vertical Boilers
  • Two Pass Boilers
  • Scotch Marine Boilers
  • Locomotive Type Boilers

Water Tube Boilers

• Water is circulated through the tubes
• Water tube boilers are generally used in power stations and industrial processes

Classifications of Water Tube Boilers

• Classified by:
  • Circulation: natural (using buoyancy), forced (using pumps), or assisted (using both natural and forced circulation)
  • Number of drums: drumless (once-through), single drum, two drum (bi-drum), three drum (tri-drum), multi-drum

Boilers and Fuels: Solid Fuels

• Common solid fuel sources:
  • Coal
  • Bagasse
  • Biofuels (straw, fire-wood)
  • Coke breeze
  • Petroleum Coke (pet coke)
  • Washery rejects (middling)
  • Municipal garbage/manure

Boilers and Fuels: Liquid Fuels

• Common Liquid Fuel Sources:
  • Fuel Oil - L.D.O./H.F.O./L.S.H.S./H.S.D.
  • Black Liquor (Pulp Industry Waste)
  • Naphtha

Boilers and Fuels: Gaseous Fuels

• Common Gaseous Fuel Sources:
  • Coke Oven Gas
  • Blast Furnace Gas
  • Corex Gas
  • Biogas
  • Natural Gas

Solid Fuel Firing Systems

• Fuel Bed Firing:
  • Chain Grate/Renfrew & Oldbury Stoker
  • Traveling Grate Stoker (including Style 28X Stoker and Rotograte Spreader Stoker)
• Suspension Firing:
  • Fluidized Bed Firing (including Bubbling , Atmospheric, Circulating, and Pressurized Fluidizing Bed Firing)
  • Pulverized Coal Firing
    • Direct Firing (including Front Fired, Opposed Fired, Downshot Fired, Corner Fired)
    • Indirect Firing (Bin System)
    • Burners (Laminar, Turbulent, Low-NOx)
• For Bagasse Firing:
  • Horse Shoe Furnace
  • Dumping Grate Furnace
  • Rotograte Furnace

Liquid Fuel Firing Arrangement:

• Oil Firing:
  • Steam Atomized
  • Air Atomized
  • Pressure Atomized
• Black Liquor:
  • Black Liquor Guns Spraying on Furnace Walls
  • Burning of Char at Furnace Hearth

Gaseous Fuel Firing Equipment

• Spud Burners are used for high C.V. Gases
• Scroll Type Burners are used for low C.V. Gases (such as Blast Furnace Gas)

Steam Boiler Functions

• Steam Generation: Generates steam at specified rate and specific parameters (temperature, pressure, degree of superheat, and enthalpy content)
• Steam Separation, Washing, and Drying: Ensures steam purity and moisture removal
• Combustion Control: Balances heat generation and absorption rates to optimize operation
• Minimizing Heat Losses: Reduces heat losses through ash and other incombustibles to maintain efficiency