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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.