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THERMOECONOMIC ANALYSIS OF THE ENVIRONMENTAL IMPACT OF
CONDENSING BOILERS
Rita Avram, University Ovidius of Constantza
Tudor Baracu, University Ovidius of Constantza
Enrico Sciubba, University of Rome 1 La SapienzaEden Mamut, Center for Advanced Engineering Sciences, UOC
Abstract
The thermodynamic analysis and optimisation methods are classical subjects with very well
developed methods [4], [5]. These methods have been developed starting from three main
laws in thermodynamics:
Mass conservation law.
Energy conservation law or the 1stlaw of thermodynamics.
Process irreversibility law or the 2ndlaw of thermodynamics.
The operation costs of industrial processes can be defined as being in proportion to the mass
and energy expenses. In this way it is obvious that we can define the operation expenses as
proportional with exergy destruction. Exergy destruction can be divided into the part
corresponding to the reversible process and the part related to the irreversibility of the
process. So, the operation costs depend linear of irreversibility of the process (curve V of
figure 1). The investment costs are dependent also of irreversibility of the industrial processes.
The investment costs are very high for a reversible process and decrease exponentially with
the irreversibility of the process (curve C in figure 3). The total costs as a sum of investment
and operation costs has always a minimum.
Figure 1Total costs as a function of process irreversibility
This method of fixing the technical parameters by using economical categories is called
thermoeconomic analysis and optimisation.
The thermoeconomic analysis of environmental impact of industrial sistems, can be
considered that has been first time done by Odum and his school [7]. Odum have introducedfirst time the global energy accounting in complex systems, addressing the question of
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valuing inputs which were considered non-energetic, as solar radiation, land surface,
crops, fisheries and labour. The approach of Odum and his school is based on the definition of
a cumulative energetic index (later called embodied energy or eMergy).
Another method was developed in the 70s to asses the environmental impact of a given
process or technology. The method is called Life Cycle Analysis and was aimed at thecalculation of the net energy output of a given energy conversion device. The word net here
have the meaning that the balance is computed over the entire useful life of the system, and
that the total amount of energy and materials, used in the fabrication process, in the
maintenance, and in the decommissioning or disposing of the device is subtracted from the
gross overall energy generation. LCA has been extended to include items as labour,
environmental damage and recycles.
In the last period it has been developed an exergetic approach to the calculation of
environmental costs [8]: the general idea is that of establishing exergy as the only proper
measure of environmental impact. The environmental costs (in the monetary sense) can be
included in Thermoeconomic analyses by extending the control volume beyond the plantunder consideration, to include a portion of the biosphere, named immediate surroundings.
The analysis has to be extended by assuming the fact that emissions of this extended control
volume have parameters equal to those of the general environment (zero impact) or to the
legal pollution limits.
The paper is presenting the results of research carried out under a cooperation between the
Center for Advanced Engineering Sciences of University Ovidius Constantza and the
Department of Mechanical Engineering of University of Rome 1 la Sapienza to develop an
analysis tool for the environmental impact of condensing boilers. The research project has
been co sponsored by Celsius 2000 Ltd, a Romanian manufacturer of hydronic condensing
boilers.
References
[1] E. Mamut (1999), Thermodynamic Analysis and Optimisation, Int. Summer School on 2nd
Law Based Analysis and Design, Constantza, Romania.
[2] D. Dommann (1990), Die Fernwarme und Fernkalteversorgung, Verlang ModerneIndustrie, Berlin, Germany.
[3] B.T. Larsen, P.F. Pederson, P.D. Pedersen (1990), Experience Gained from Two Funded
Energy Efficiency demonstration programmes in Norway, Caddet Newsletter, no. 1, TheNederlands.
[4] Y. El Sayed, (1999), Short Course in Thermoeconomics, Int. Summer School on 2ndLaw
Based Analysis and Design, Constantza, Romania.
[5] A. Bejan, E. Mamut, (1999), Thermodynamic Optimization of Complex Energy Systems,
Kluwer Acad. Pub., The Nederlands.
[6] W. Fratzscher, (1999), Exergy and Possible Applications, Revue Generale de Thermique,
36 no.9, Elsevier Pub., France
[7] H.T. Odum, (!996)Environmental Accounting, J. Wiley & Sons, U.S.A.
[8] E. Sciubba, (1999) Extended Exergy Accounting Towards an Exergetic Theory of
Value, ECOS 99, Tokyo, Japan.