Energy Balance across pulverizer is very critical for satisfactory operation of Steam Generator.

Hot air Heat loss Puliverizer frictional dissipation Dry pulverized coal + Air + Moisture Coal Motor Power Input

Prediction of Coal Drying For predicting the amount of coal drying which is needed from the pulverizers, the following methods were accepted. For very high rank coals (fixed carbon greater than 93 percent), an outlet temperature of 75 to 80° C appeared most valid. For low- and medium-volatile bituminous coals, an outlet temperature of 65 - 70° C appeared most valid. Bituminous B and C coals appear to have good outlet moisture an outlet temperature of 55 to 60° C is valid. For low-rank coals, subbituminous through lignite (less than 69 percent fixed carbon, all of the surface moisture and one-third of the equilibrium moisture is driven off in the mills.

Fluidized Bed Combustion A True Appropriate Technology for Effficient Solid Fuel Combustion

Liquid Fuel Combustion Systems

Oil Fired Furnace

Oil Supply System A typical oil supply system includes an oil tank, oil strainer, oil supply pump, heater and connecting pipelines to the boiler.

Design of Oil Supply Systems General considerations in the design of the oil supply system are safety, cost, convenience and emergency provision. Heating Loop: Heavy oils are economic but difficult to atomize owing its high viscosity at atmospheric temperatures. The oil is heated prior to burning. The heating loop consists of strainer, pump and heater. Classification of Heating Systems: Single unit heating loop Centralized heating loop Oil pumps are selected as several in number with smaller capacity:

Fuel + Air + Ignition ????

Flame in Stationary Fuel –Air Chamber Moving Flames are the Fires!!!

On Set of Fire in A Green Forest

Forest Fires Fire is an accident & Dangerous…. Flame is an Engineering Device…

Basic Geometry of A Furnace More Air (Secondary Air) Primary air + Fuel

Furnace Exit Hot Exhaust gases Heat Radiation & Convection Flame Burner

Burners An unique means to contain & control Fire : Flame.

Role of burners Burner Governs: Fuel Ignition Aerodynamics of Fuel air mixture Generation of combustion conditions. The performance of the burner determines whether combustion equipment will operate reliably & economically. Types of burners: Swirl types Direct or Parallel-flow types

Simple Burner Burning Velocity Flow velocity Air Fuel

Stability & Flammability Limits Burning Velocity > Flow Velocity : Flash Back Limit Burning Velocity < flow Velocity : Blow Off Limit Burning Velocity = Flow Velocity : Stable Flame. Rich Mixture Fuel Flow rate Flash Back Stable Flame Blow off Lean Mixture Air Flow rate

Burning Velocity & Residence Time Quality of Fuel & Fuel Chemistry. Air-fuel ratio Turbulence level Time to be spent by fuel particle in the furnace before it burns completely. Residence time is inversely proportional to burning velocity. Fuel particle continuously moving. The distance traveled by the fuel particle should be much larger than furnace height. Swirl motion will ensure the required residence time. Internally generated swirl : Swirl Burners. Externally generated swirl: Direct Burners.

Design of Swirl Burners Proper aerodynamics at the exit of the burner – required to ensure good ignition, stable and efficient combustion. Good load control Controlled generation of Nox. Reliable and safe operation. Compatibility with the FUEL system and furnace.

Types of Swirl Burners for solid fuels Tangential Swirl Burners

Types of Swirl Burners for solid fuels Axial Swirl Burners

Types of Swirl Burners for Liquid Fuels

Rotary Cup Oil Burner

Draught Systems Better combustion requires comfortable breathing….

Resistance to Air & Gas Flow Through Steam Generator System

Draft Required to Establish Air Flow Flue as out Air in

Natural Draft Hchimney pB = patm + rgas *g *Hchimney pA = patm + ratm *g *Hchimney Tgas Tatm B A

Natural Draft Natural draft establishes the furnace breathing by Natural Draft across the furnace, Dpnat = pA – pB Dpnat = patm + ratm *g *Hchimney - (patm + rgas *g *Hchimney) Dpnat = (ratm - rgas )*g *Hchimney Natural draft establishes the furnace breathing by Continuous exhalation of flue gas Continuous inhalation of fresh air.

Pressure Difference Generated in natural draft gas path The pressure of natural draft is D pnd = (a - g) g H where D pnd = head of natural draft, Pa a = ambient air density, kg/m3 g = gas density in the flue, kg/m3 H = height difference between the beginning and the end of the section, m The flue gas density, is g is calculated as Tg = gas temperature 0C g = gas density in the flue under the standard atmospheric condition (00C, 1 atm) Nm3/kg

Establishment of Flow The amount of flow is limited by the strength of the draft. Flow introduces a resistance and weakens the draft. Resistance to the flow is proportional to the square of velocity. At steady state flow resistance = Natural draft.

Mechanical (Artifical)Draft : Induced Draft Essential when Natural Draft cannot generate required amount of breathing Hchimney pB = pfan,s pA = patm + ratm *g *Hchimney Tatm B B A Tgas

Mechanical (Artifical)Draft : Forced Draft Hchimney pB = patm + rgas *g *Hchimney pA = pfan Tgas Tatm B A

Mechanical (Artifical)Draft : Balanced Draft Hchimney pB = pfan,s pA = pfan.b B Tatm B Tgas A

Resistance to Air & Gas Flow Through Steam Generator System

+ve -ve

Capacity of Fans Forced patm Natural Induced Power Consumed by fan : Induced Draft Fan Forced Draft Fan   Forced patm Natural Induced