WASTE TO ENERGY IN POWER PLANTS; INCREASING THERMAL EFFICIENCY
AND DECREASING ENVIRONMENT DEFECTS
Mohsen Sharifpur
Department of Mechanical Engineering
Eastern Mediterranean University
G.Magosa, North Cyprus, Mersin 10, Turkey
E-mail: mohsen.sharifpur@emu.edu.tr
ABSTRACT
The international energy outlook 2007 gives a clear picture of
energy growth expectation over the next two decades. The
word net energy consumption, 2004-2030, will increase about
85 percent. On the other hand more than 80 percent of today
and near future energy production should supply from oil,
natural gas, coal and nuclear power plants. However the overall
thermal efficiency of all power plants in the world is less than
50%, as a result for production of 30364 billion kilowatt-hours
in 2030, it should use about twice of the energy resources and
transfer about 30000 billion kilowatt-hours to environment as
waste energy. This subject has five important defects, consist
of; increasing global warming, green house effect, air pollution,
wasting natural resources and final cost of the electricity.
Hence researches on waste to energy in power plants should be
remarkable. In present study, it is developed the idea of using
“boiling condenser”(BC) for steam power plants (coal, heavy
oil, gas-fired steam turbine and nuclear power plants) and also
it is offered a new idea of “exhaust gas energy
converter”(EGEC) for gas power plants. In this manner, not
only at least 15% of unused energy in the power plants could
be employed, but also the consistency with environment is
more appreciable.
gas in the electricity generation sector worldwide exceeds the
growth in renewable energy consumption. The capital costs of
new power plants using renewable fuels remain relatively high
in comparison with those for plants fired with coal or natural
gas. However the biomass type of renewable energy has
advantage of that is renewable energy, but final fuel production
(Biofuels) is almost same as natural gas.
Fig. 1 Word electricity generation capacity by fuel type [4]
Keywords: Increasing thermal efficiency, Power plants, BC,
EGEC, Environment defects
1. INTRODUCTION
It can conclude from efficiency comparison of various power
generation technologies [1-3] that the average thermal
efficiency of existing power plants in the world, consist of
steam power plants (coal, heavy oil, gas-fired steam turbine and
nuclear power plants), diesel engines, gas turbine and
combined-cycle is less than 50 %. In order to inform about
today and projection of near future variety of power plans, it
should look at Fig. 1 (by the IEO2007 reference case) [4],
which shows the world energy generation by fuel type 20042030. The renewable share of world electricity generation falls
slightly in the projection, from 19 percent in 2004 to 16 percent
in 2030, as growth in the consumption of both coal and natural
Thus, it can conclude that more than 80 % of today and neat
future electricity generation should produce from oil, natural
gas, coal and nuclear power plants. This means, for production
of 30364 billion kilowatt-hours electricity in 2030, it should
use about twice of the energy resources and transfer about
30000 billion kilowatt-hours to environment as waste energy.
This subject has five important defects, consist of; increasing
global warming, green house effect, air pollution, wasting
natural resources and final cost of the electricity. Hence
researches on waste to energy in power plants for increasing
thermal efficiency should be remarkable.
A lot of work is done for increasing the efficiency of power
plants in last decades. The important ones are improving feed
water heaters, regeneration systems [5], modification of
combined-cycles [6, 7]. Adrian Bejan among the others [8]
explored alternatives to the usual thermodynamic optimization
formulation, where the thermodynamic performance of a
system is improved subject to physical size constraints (e.g.,
entropy generation minimization). Kopac and Hilalci [9]
investigate about effect of ambient temperature on the
efficiency of a power plant. Also, Elzinaty [10] worked on
using waste heat for some new purposes, same as desalination.
In present study, it is developed the idea of using boiling
condenser (BC) [11] for steam power plants (coal, heavy oil,
gas-fired steam turbine and nuclear power plants) and also it is
offered a new idea of “exhaust gas energy converter” (EGEC)
for gas power plants. In this manner, not only at least 15% of
unused energy in the power plants could be employed, but also
the consistency with environment is more appreciable.
However, in this day and age, a lot of efforts are doing for
reducing the CO2 emission of power plants in the world. But,
usually capturing the CO2 in power generation plants makes
reduction of the thermal efficiency about 8 % [12]. Thus by
using BC or EGEC it could rectify the efficiency reduction
caused by pollution devices.
Hence, as a heat exchanger, the steam transfers its latent heat to
the working fluid during the path within coming down. Thus,
while the condensation happens inside the tubes (for steam),
boiling occurs outside of the tube bundles for the working
fluid, i.e. inside the channels between the tubes. There are some
recirculation pumps those circulate the working fluid among
the tube bundles with an accurate control system. Therefore by
changing the operating conditions of recirculation pumps, it
can control the amount of exchanged heat between steam and
the working fluid. The upper parts of the tube bundles are not
inside the working fluid, and then it helps to dry (or make
superheat) the vapor of the working fluid along the path. This
part is the same as chimney in the BWR but heated one.
2. USING BOILING CONDENSER (BC)
Boiling condenser (BC) is a new design heat exchanger [11]
that could be replaced with typical condensers in the steam
power plants (coal, heavy oil, gas-fired steam turbine and
nuclear power plants). In the Fig. 2, it is shown a BC with its
cycle. A boiling condenser is almost the same as the core of a
boiling water reactor (BWR) [13]. Inside a BC consists of some
vertical channels which inside the channels are parallel vertical
tube bundles. Steam from the power plant turbine exit could
enter to the tube bundles of BC (from upward to down).
Outside of the tube bundles (between tube bundle and the
channel) are almost filled of a proper subcooled working fluid.
The BC cycle is working with this working fluid.
Fig. 2 Boiling condenser and its cycle
Fig. 3 Schematic diagram of Catalagzi power plant in Turkey
Fig. 3 shows the Schematic diagram of 154 MW Catalagzi
power plants in Turkey [9]. The fuel used in this power plant is
low calorific value coal middling with particle size below 0.5
mm. In the Fig. 4 is shown the power output of modified
Catalagzi power plant by utilizing BC, is increased to 186 MW.
Fig.4 Using BC with some changes to the main cycle
The working fluid for BC cycle is chosen R-141b. For
comparison of this modified power plant with old one, there are
taken the nodes of 5, 14, 31 and 32 as the reference points (i.e.
the properties are the same in these points for both). The results
confirm that the BC recovers at least 15.2 % of the condenser
waste energy of the power plant and the overall thermal
efficiency of the power plant increases at least %7.5.
3. EXHAUST GAS ENERGY CONVERTER (EGEC)
ability to reuse in the cycle as regeneration. This is due to
increasing temperature after compressor (i.e. the temperature of
points 10, 2 and 4 are close to each other). But, it can get some
parts of this waste energy by using a proper working fluid in an
exact thermodynamics cycle (EGEC) which could operate
between the exhaust gas temperature (or intercooler
temperature) and environment temperature. The power plant
(Fig. 5) with applied EGEC is shown schematically in Fig. 7. In
this manner some part of waste heat could be converted to
work.
Usually a significant amount of energy wastes to environment
from the exhaust gas (gas turbine exit) of gas power plants. The
Exhaust Gas Energy Converter (EGEC) could be an exact
thermodynamics cycle, with proper working fluid for
recovering some fraction of waste heat from an exhaust gas. It
includes boiling heat exchanger, turbine, condenser and a pump
with an accurate control system.
Fig. 7 A typical gas turbine with EGEC unit
It is possible to use the combine form of BC and EGEC in a
combined power plant. Fig. 8 shows the application of BC and
EGEC to a typical combined power plant, schematically.
Fig. 5 A typical gas turbine with regeneration
Fig. 5 shows a typical gas turbine with regeneration, intercooler
and reheater. The T-s diagram of the cycle is shown in Fig. 6.
Fig.6 The T-s diagram of the gas turbine cycle
From the T-s diagram, it is clear that the exhaust gas energy
(qout) and also the removal heat from intercooler do not have
Fig. 7 A typical combined power plant with EGEC and BC
4. RESULTS AND DISCUSSION
As it is shown in table 1, the net power of the Catalagzi power
plant [9] is 154.144 MW, but after applying BC (theoretically
[11]) increases to 186.255 MW (i.e. the net power out increases
20.83 %). The result confirms that the BC recovers at least 15.2
% of condensers waste energy of the power plant and the
overall thermal efficiency of the power plant increases at least
%7.5.
Table 1 compassion of two power plants (with and without BC)
Power plant Without BC 35.76 Power plant With BC 43.21 Wnet −total (KW) 154144 186268 Wnet − BC (KW) ― 40151 Wnet − Steam (KW) (KW) Q&
154144 146117 211272 175017 Fuel Energy (KW) Advantage versus Global warming (KW) 431063 ― 431063 32124 ηThermal (%) Condenser
However, it must consider that this result notwithstanding some
limitations (same as getting nodes of 5, 14, 31 and 32 as the
reference points for BC application), the thermal efficiency has
had 7.5% increases.
Table 2 the thermal efficiency of the EGEC cycle
Working Fluid of the EGEC Cycle = R-141b
Texh‐gas = 120 °C, Tamb‐ave =20°C, Ttur‐ 141= 110 °C, Tpump‐ 141 = 31.7°C P tur‐ 141= 0.8 Mpa, P con‐ 141= 0.1 Mpa Texh‐gas = 135 °C, Tamb‐ave =20°C, Ttur‐ 141= 125 °C, Tpump‐ 141 = 28.74°C P tur‐ 141= 1 Mpa, P con‐ 141= 0.09 Mpa Texh‐gas = 160 °C, Tamb‐ave =20°C, Ttur‐ 141= 150 °C, Tpump‐ 141 = 31.7°C P tur‐ 141= 1.7 Mpa, P con‐ 141= 0.1 Mpa Texh‐gas = 175 °C, Tamb‐ave =20°C, Ttur‐ 141= 165 °C, Tpump‐ 141 = 31.7°C P tur‐ 141= 2.1 Mpa, P con‐ 141= 0.1 Mpa ηThermal (%) 15.05 16.94 19.21 20.15 Thus for using BC in a new design power plant, it is possible to
find more efficiency by finding exact turbine exit condition (for
steam cycle) and exact working fluid (for BC cycle). Using BC
and its cycle has capability to be utilized for all of the Steam
power plants (coal, heavy oil, gas-fired steam turbine and
nuclear power plants). This recovering heat of condenser (15%)
is due to the latent heat of steam which is too much at low
pressure (turbine exit), and then in the BC cycle, it is possible
to transfer this heat to boiling another working fluid.
A boiling condenser (BC) could be an adaptor between main
power plants and environment, i.e. it can design the power
plant for maximum output efficiency but independent to
environment conditions, and then BC as an interface, could
adapt the power plant and environment. For example in
Catalagzi power plant [9], the steam at low pressure turbine
(LPT) exit has 35.5ºC, because of the average condenser inlet
and outlet, are 19ºC and 39ºC respectively.
In the case of EGEC cycle, Table 2 offered the thermal
efficiency of the EGEC cycle for some different exhaust gas
temperatures. The average ambient temperature (Tamb-ave) in a
year is assumed to be 20 ºC. For deriving this data it is used
EES software [14], by using R-141b as working fluid and also
pump and turbine efficiency of 90 %. The results confirm that
by using EGEC, not only at least 15% of unused energy from
exhaust gases of gas turbine power plants could be employed,
but also it has more consistency with environment. Table 2 is a
sample calculation of converting some part of exhaust gas
energy to work. Hence in an actual situation, with exact
information of the exhaust gas temperature, it could design
accurate EGEC cycle with proper working fluid for more
efficiency. However, it can use this system for anywhere that
needs to remove some energy of high temperature gases, same
as intercoolers.
5. CONCIUSION
Because of overall thermal efficiency of world power plants is
less than 50 %, thus for producing 30364 billion kilowatt-hours
electricity in 2030, it should use about twice of the energy
resources and transfer about 30000 billion kilowatt-hours to
environment as waste energy. In this work for reducing this
problem is developed the boiling condenser (BC) for steam
power plants (coal, heavy oil, gas-fired steam turbine and
nuclear power plants) to recover at least 15 % of the waste
energy in the condensers. Also for gas turbine power plants is
offered to use exhaust gas energy converter (EGEC) to recover
at least 15 % of the exhaust gas energy. Using BC and EGEC in
power plants have five important advantages, consist of;
decreasing global warming, green house effect, air pollution,
saving natural resources and reducing final cost of the
electricity.
6. REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
Janos M. Beer, “High efficiency electric power
generation: The environmental role”, Progress in Energy
and Combustion Science, Vol. 33, 2007, pp. 107–134.
Kiarash Dorry, “A thermodynamic and economic
design/optimization of gas turbine power plants”, Master
Thesis, Mechanical engineering department, Eastern
Mediterranean university, 2005.
Steven E.K., “Advancing Gas Turbine Technology:
Evolution and Revolution”, Power Engineering, 1995,
Vol. 99, No. 5, pp. 25-28.
EIA Report No.: DOE/EIA-0484, International Energy
Outlook2007,
http://www.eia.doe.gov/oiaf/ieo/electricity.html, 2007.
Cengel Y.A., Boles M. A., “Thermodynamics an
Engineering Approach”, McGraw-Hill, 2006.
Stefano Consonni, Paolo Silva, “Off-design performance
of integrated waste-to-energy, combined cycle plants”,
Applied Thermal Engineering, Vol. 27, 2007 pp. 712–
721
Chuang C.C., Sue D.C., “Performance effects of
combined cycle power plant with variable condenser
pressure and loading”, Energy, Vol. 30, 2005, pp. 1793–
1801
[8]
[9]
[10]
[11]
[12]
[13]
[14]
Bejan A., “Thermodynamic optimization Alternatives:
Minimization of Physical Size Subject to Fixed Power”,
International Journal of Energy Research, Vol. 23,
1999, pp. 1111-1121
Mehmet Kopac, Ayhan Hilalci, “Effect of ambient
temperature on the efficiency of the regenerative and
reheat Catalagzi power plant in Turkey, Applied Thermal
Engineering, Vol. 27, 2007, pp 1377–1385.
Rami Elzinaty, “Design of a desalination system using
waste heat of power plant”, Master Thesis, Mechanical
Engineering department, Eastern Mediterranean
university, 2003.
Mohsen Sharifpur, “Designing Boiling Condenser for
more efficiency in power plants and less environment
defects”, ASME POWER 2007, July 2007, USA.
John Davison, “Performance and costs of power plants
with capture and storage of CO2”, Energy, Vol. 32, 2007,
pp. 1163–1176.
El-Wakil M.M., “Nuclear Heat Transport”, American
Nuclear Society, 1981.
Engineering Equation Solver (EES), Educational version
distributed by McGraw-Hill, 2007.