Cogeneration-Regional experiences: D.Pawan Kumar
• Steam is a basic need of any process industry. Most industries produceand utilize steam at low
pressure for heating purposes and need power too for drives.
• The word cogeneration relates to simultaneous generation of Heat (steam) and power. Captive
power generation is different and relates to power generation for in-house needs.
• Generating steam at higher pressure and temperature in a cogeneration system, adds just 10
to 20% on the fuel costs, but economical by- product electrical energy is produced.
• In steam based cogeneration systems, back pressure turbines are deployed where high
pressure, often superheated steam from boilers is expanded in a turbine to generate power, and
back pressure exhaust steam is utilized for process requirements. Higher the inlet pressure and
temperature, higher the power output and likewise, lower the back pressure, higher the power
IILLLLUUSSTTRRAATTIIVVEE VVAARRIIAATTIIOONN OOFF COGEN POWER WWIITTHH IINNLLEETT SSTTEEAAMM
250°C Saturated 330°C 350°C
Back Pressure (g)
3 KG/cm2 3 KG/cm2 3 KG/cm2 3 KG/cm2
Exhaust Steam Dry 190°C 7 % Wet Dry 210°C Dry 210°C
IILLLLUUSSTTRRAATTIIVVEE VVAARRIIAATTIIOONN OOFF CCOOGGEENN PPOOWWEERR
WWIITTHH BBAACCKK PPRREESSSSUURREE
3 Kg/cm2 g
4 Kg/cm2 g
5 Kg/cm2 g
10 TPH, 33 KG/cm2 g 10 TPH, 33 KG/cm2 g 10 TPH, 33 KG/cm2 g
Power output from
Kg/kW steam rate
• In steam based cogeneration systems, extraction back pressure turbines are deployed where
steam requirements for process are at two or three pressure levels. Extraction condensing
turbines are deployed, where steam requirements for process are at two or three pressure levels
and, steam demands are fluctuating, necessitating condenser use to balance the steam quantity.
• The key factors influencing industrial cogeneration economics include capacity utilization,
process steam demand, pressure variations, Power demand pattern, turbine Inlet steam
parameters, turndown ratio and efficiency of boiler and turbo generator, auxiliary power
consumption, fuel and power costs prevalent, stand-alone or grid linked operations.
• With Wide variety of cogeneration schemes and innovations for process industry to choose from,
cogeneration offers a win-win situation, be it for a rice mill, paper mill, sugar unit or a cement
plant, or even for steam throttling avoidance, wherever steam/heat and power are
simultaneously needed, especially in regions strapped for grid power.
IIlllluussttrraattiivvee CCooggeenn PPootteennttiiaall iinnddiiccaattoorrss iinn SSuuggaarr PPllaannttss
( Bar / °C )
( T/T Bagasse)
( kW )
( Ton / MWh )
21/340 2.50 227.3 11 4.5
32/380 2.43 286 8.50 3.5
42/400 2.40 313 7.67 3.2
45/440 2.33 328 7.10 3.0
67/480 2.27 378 6 2.6
87/510 2.24 401 5.59 2.5
110/535 2.21 427 5.18 2.3
Sugar mill Cogeneration trends and features in the region:
Own / saved bagasse, biomass & coal used as primary fuels, during season & off season
High and extra high pressure superheated steam generated and expanded through back
1970s <1000 11/200 0.5 <50% 20
1980s >1250 21/380 1.5 <55% 15
1990s 2500 45/440 3.5 60% 8
2000s 5000 64/485 22-24 >70% <5.8
>5000 84/510 25-30 – –
>5000 105/525 ~35 _ –
>7000 110/525 ~36 80% _
pressure or double extraction cum condensing TG sets.
Boiler efficiencies range from 68-72% on bagasse & near 80% on coal.
TG efficiencies around 90%.
Steam to fuel ratio ranges from 2.4 kg/kg to 2.65 kg/kg.
Steam to power ratio ranges from 5.2 – 5.6 kg/kW during season & 3.6 – 4.0 kg/kW during off
PLF 55 – 60% during season & near 90% during off season.
Extraction steam at 8 bar used for HP heater & process requirements.
Back pressure steam at 1.5 bar used for process requirements & de-aerator.
Power generated during season used for cogen plant auxiliaries, sugar / by-product processes
& balance exported to the grid.
Power generated during off season used for cogen plant auxiliaries, by-products, colony &
balance exported to grid.
Capex needs around IC 52.5-55 million/ MW for cogen power plant & IC10-15million/ MW for
concurrent sugar factory modernization.
O&M costs 3-5%.
Incentives and long term PPAs are in place.
Going by Indian experiences, significant cogeneration potential remains to be tapped in South
Asian region’s sugar industry too, if a well conceived action plan is implemented supported by
proactive policy interventions.