A student technical seminar on the use of condensing economisers used in thermal power industry and the need to increase their use for lesser carbon footprint.

1. Submitted By
Appalla Aditya Shiva
12881A0306
CONDENSING
ECONOMISERS

2. CONTENTS:
•Industrial Waste Heat Sources & Sinks.
•Operating Principle of a Condensing Economiser.
•Indirect Contact Condensing Economisers.
•Direct Contact Condensing Economisers.
•How Much Heat is Recovered?
•Applications of Condensing Economisers.
•Case Study – Transparent Energy Systems Pvt. Ltd., Pune, India.
•Myths surrounding Condensing Economisers.
•Key Considerations.
•Market Barriers.
•Future Scope in India.
•List of References.

3. Industrial Waste Heat Sources & Sinks
SOURCES:
■High Temperature Sources
(Incinerators, furnaces & kilns):
650 - 1600°C.
■Medium Temperature Sources
(Ovens, crackers, turbine
exhausts): 230 - 650°C.
■Low Temperature Sources
(Condensates, dies, bearings etc.):
30 - 230°C.
SINKS:
■Heat exchangers.
■Fans.
■Fins.
What is Common: FLUE GASES

4. OPERATING PRINCIPLE OF A
CONDENSING ECONOMISER:
Condensing Economisers
are heat exchangers used
in boilers that recover heat
from flue gases to heat the
feed water and condense
flue gas to moisture.
Also known as FEEDWATER
ECONOMISERS.

5. INDIRECT CONTACT
CONDENSING ECONOMISERS:
In principle, a shell & tube heat
exchanger. Counter flow action
between the feed water and flue
gases takes place to condense the
flue gases.
Max. fluid heating temp.: 95°C.
Min. stack gas cooling temp.: 25°C

6. ■ Provides energy savings upto
15%.
■ Can heat process water upto
100°C, without contamination.
■ Provides water savings of upto
4,00,000 litres per year.
■ Reduces GHG emissions on site
by approximately 53 kgs/kWh.
■ Water condensate absorbs CO2 at
a rate of 1 kg/hr.
■ Required condensate needs to
be treated.
■ Must be designed to withstand
corrosion.
■ Very low heat transfer
coefficient (~ 32 W/m2
).
Merits: Limitations:

7. DIRECT CONTACT
CONDENSING ECONOMISERS:
Similar to a condenser used to cool
steam. Recovers latent heat of the
gas by spraying the feed water
directly on the incoming plume.
Max. fluid heating temp.: 60°C
Min. stack gas cooling temp.: 25°C.

8. ■ Non fouling heat exchanger
surface.
■ High heat transfer coefficient
b/w 2500 – 3150 W/m2
.
■ Provides energy savings by
upto 10% in comparison to
conventional economisers.
■ Produces dilute condensate in
comparison to that of indirect
one.
■ Saves make up water in plant
by upto 4%.
■ Reduces GHG emissions
onsite by 55 kgs/kWh.
■ Can heat the feed water only
upto 60°C.
■ Requires significantly low
temperature feed water to
enter the economiser.
■ Process water condensate
must be treated to remove the
combustion products first and
then flue gas condensate.
■ Mist eliminator is necessary to
prevent carryover of small
droplets.
Merits: Limitations:

9. HOW MUCH HEAT IS RECOVERED?
If the boiler exhaust gases are leaving the furnace at 900°C at the rate of
2100 m3
/hr and are condensed to 90°C, then the total heat recovered by
condensing in the economiser is:
Q = m ∙ Cpf ∙ ∆T
where Cpf = Specific heat of flue gases = 1000.59 kJ/kg – K, and m = V × ρ,
where ρ = Density of flue gases = 1.19 kg/m3
.
Q = V × ρ ∙ Cpf ∙ ∆T = (2100/3600) × 1.19 × 1000.59 × (900 – 90) = 562.61kW
For a plant operating all day, the Q recovered is 13.2 MW.
For the plant operating for 325 – 340 Days a year, the Q recovered is 4.5
GW.

10. APPLICATIONS:
•Thermal Power Plants.
•Breweries and wineries.
•Chemical & Pharmaceutical Plants.
•Textile Processing Plants and tanneries.
•Greenhouses.
•Commercial Laundry.
•Pulp and Paper Mills.
•District Heating Plants.
•Air Conditioning Plants.

11. CASE STUDY: Transparent Energy
Systems Pvt. Ltd., Pune, India.
First company in India to
manufacture a natural gas fired
condensing boiler economiser unit.
Cools flue gases below its dew
point temperature to 47°C. Also
makes the flue gas condensate
alkaline.
Achieves a thermal efficiency of
94% on the basis of Higher
Heating Value of the fuel & 103%
on the basis of Lower Heating
Value of the fuel.

12. MYTHS SURROUNDING CONDENSING ECONOMISERS:
Myth 1: They are only efficient when fully condensing.
Response: Not true. They need not fully condense. Seasonal condensation also
yields same results (proved by Energy Savings Trust, London, UK).
Myth 2: They are expensive.
Response: They were expensive when first introduced. But with the new
equipment, they have become cheap.
Myth 3: The plume is a nuisance.
Response: Plume is an indication of the proper functioning of the system. Care
must be taken to not let out the plume near residential areas.
Myth 4: The condensate is a problem and creates difficulties in installation.
Response: Condensate has a pH anywhere between 3 – 5, which is the same
as tomato juice. This condensate can be handled by a separate drain to treat it.

13. KEY CONSIDERATIONS:
•Establishing how much heat is available.
•Is there sufficient heat sink available?
•Ensure that entering temperature of the heat sink is below flue gas dew point
to cause condensation.
•Evaluate impact on the existing system including blow down, flash steam,
deaerator, water treatment etc.
•Fuel used.
•Space for component installation including stacks, plume impingement unit
etc.
•Cost savings, installed cost, payback period and payback rate.
•Direct or Indirect?
- site specific.
- customer preference and cost.
- application and heat sink temperature.

14. MARKET BARRIERS:
•Not an “off-the-shelf” technology. Each application is an engineered
solution. Requires good understanding of the technology and its
applications.
•Needs a suitable and large heat sink. Small heat sinks capture only upto
25% of the latent heat.
•Steam is a necessary evil in the industry and the project will face a lot of
challenges in getting approved.
•Initial units installed in the 1980’s and 1990’s has sulphur induced
corrosion which is a stigma carried even today. This is not an issue with
natural gas fired boilers.

15. FUTURE SCOPE IN INDIA:
The USA, UK, Europe, Canada, Australia and New Zealand have already
installed various plants of sizeable capacities to reduce CO2 emissions and
increase energy savings.
India has entered the fray with a few manufacturers and application in local
industries.
Govt. of India has begun to work out possible changes in thermal power
plants in accordance with its scheme of rural electrification. NTPC, Kawas
is one such project.
A 4 MW waste heat recovery unit has been set up by G. R. Sponge &
Power Limited in Chhattisgarh in 2007 and ratified by the UN.

16. List of References:
•‘Condensing Boiler Economisers’, Global Energy Partners LLC, California,
2009.
•‘Steam Tip Sheets #26a & 26b’, Advanced Manufacturing Office, U.S.
Department of Energy, January, 2012.
•Zaidi, Aqeel, ‘Maximizing Boiler Heat Recovery Using Condensing
Economisers’, Enbridge Gas Distribution, Toronto, Canada, February 2008.
•‘Indian Company puts its new Boiler to the Field Test’, Transparent Energy
Systems Pvt. Ltd., Pune, India, Todays Boiler, 2013.
•‘Boiler Stack Gas Heat Recovery’, Defense Technical Information Center,
Naval Civil Engineering Laboratory, September 1987.
•‘Domestic Condensing Boilers – The Benefits and The Myths’, Energy
Savings Trust, London, UK, November, 2003.

17. Thank You!