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Chemical exergy influence in the exergetic analysis of a real clinker rotary kiln

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Abstract

The most energy demanding process in the cement industry is clinker production, carried out in a rotary kiln. Thus, rotary kiln energetic and exergetic analyses are useful tools to reach cement production process improvements. Energetic analysis is based on the first law of thermodynamics and allows one to calculate the heat uses and losses. On the other hand, exergetic analysis is based on a combination of the First and Second Laws of Thermodynamics and allows quantifying process irreversibilities. Some rotary kiln exergy analyses neglect the mass flows chemical exergy in the exergetic analysis, considering only the fuel chemical exergy. In this work, chemical exergy impact on this analysis was evaluated. Pre-calcination effect was also studied. Rotary kiln classical and modern exergetic efficiency considering all the chemical exergy contributions were 55.5% and 41.8%, respectively, while considering just the fuel chemical exergy were 38.2% and 22.6%, respectively. The results showed that it is inadequate to neglect the mass flows chemical exergy, since their contribution in the exergetic analysis was relevant. Furthermore, it was observed that the method adopted in the process efficiency evaluation affects the system interpretation. Considering the modern exergetic efficiency, results showed that, the higher the pre-calcination, the higher rotary kiln efficiency.

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Fig. 1

adapted from Giannopoulos et al. (2007))

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Abbreviations

A:

Fuel mass percentage of ash in dry basis

\({c_i}\) :

Element fraction appearing in the form of the reference species.

\({c_p}\) :

Heat capacity at constant pressure (J/mol.K)

C:

Fuel mass percentage of carbon in dry basis.

\(E\) :

Energy (kJ)

\(\dot E\) :

Energy rate (kJ/h)

\(ex\) :

Specific exergy (J/mol)

\(ex_{ch}^0\) :

Specific standard chemical exergy (J/mol)

\(Ex\) :

Exergy (kJ)

\({\dot {E}}\) :

Exergy rate (kJ/h)

g:

Gravitational acceleration (m/s2)

\(g_f^0\) :

Standard Gibbs energy of formation (J/mol)

\(h\) :

Specific Enthalpy (J/mol)

\(h_f^0\) :

Specific Enthalpy of formation (J/mol)

H:

Fuel mass percentage of hydrogen in dry basis.

j:

Number of reference ions or molecules derived from one molecule of the element under consideration.

\({l_i}\) :

Number of atoms of the element in the molecule of the reference species.

\(\dot m\) :

Mass flow rate (kg/h)

\({M_0}\) :

Lithosphere molecular mass (kg/mol)

\({n_{i,0}}\) :

Lithosphere molar concentration of the ith element.

N:

Fuel mass percentage of Nitrogen in dry basis.

\({N_k}\) :

Number of molecules of additional elements present in the molecule of the reference species.

O:

Fuel mass percentage of oxygen in dry basis.

P:

Pressure (atm)

pH:

Negative logarithm of the hydrogen ion concentration.

\(\dot Q\) :

Heat transfer rate (kJ/h)

R:

Universal gas constant. (J/mol.K)

s:

Specific Entropy (J/mol.K)

S:

Coal mass percentage of sulfur in dry basis.

\(T\) :

Temperature (K)

\({u_0}\) :

Conventional standard molar concentration of the reference species in seawater.

v:

Velocity (m/s)

\(\dot W\) :

Power (W)

x:

Mass fraction.

z:

Position

\(\alpha\) :

Heat capacity at constant pressure parameter. (*)

\(\beta\) :

Heat capacity at constant pressure parameter. (*)

\(\delta\) :

Heat capacity at constant pressure parameter. (*)

\(\varepsilon\) :

Heat capacity at constant pressure parameter. (*)

\(\gamma\) :

Activity coefficient.

\({\eta_{en}}\) :

Energetic Efficiency.

\({\eta_{ex}}\) :

Exergetic Efficiency.

\(\mu\) :

Chemical potential. (J/mol)

\(\sigma\) :

Heat capacity at constant pressure parameter. (*)

\(\nu\) :

Stoichiometric coefficient.

\({\chi_i}\) :

Reference specie mole fraction in the lithosphere

*:

The heat capacity at constant pressure parameters have different units as a function of the heat capacity equation. For each equation, the parameters units are defined in such a way that the heat capacity has the unit (J/mol.K).

0:

Restricted dead state.

00:

Absolute dead state.

ch:

Chemical.

i:

Specie.

r:

Reaction.

d:

Destroyed.

el:

Element.

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Acknowledgements

The authors are grateful to CNPq—Conselho Nacional de Desenvolvimento Científico e Tecnológico, Capes—Coordenação de Aperfeiçoamento de Pessoal de Nível Superior and FAPEMIG—Fundação de Amparo à Pesquisa do Estado de Minas Gerais (TEC-APQ-00914-16) for the financial support.

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Authors and Affiliations

  1. Chemical Engineering Program, Departamento de Engenharia Química, Universidade Federal de Minas Gerais, Av. Presidente Antônio Carlos, Belo Horizonte, Minas Gerais, 662731270-901, Brazil

    Túlio Franco Anacleto, Ana Esther Gonçalves de Oliveira e Silva, Suzimara Reis da Silva, Esly Ferreira da Costa Junior & Andréa Oliveira Souza da Costa

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  1. Túlio Franco Anacleto
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  2. Ana Esther Gonçalves de Oliveira e Silva
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  3. Suzimara Reis da Silva
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  4. Esly Ferreira da Costa Junior
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  5. Andréa Oliveira Souza da Costa
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Correspondence to Andréa Oliveira Souza da Costa.

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Appendices

Appendix

See Tables 7, 8 and 9

Table 7 Thermodynamics properties standard values
Full size table
Table 8 Clinker substances chemical exergy
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Table 9 Reactions enthalpies
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Anacleto, T.F., e Silva, A.E.G.d., da Silva, S.R. et al. Chemical exergy influence in the exergetic analysis of a real clinker rotary kiln. Braz. J. Chem. Eng. 38, 197–214 (2021). https://doi.org/10.1007/s43153-020-00084-0

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  • DOI: https://doi.org/10.1007/s43153-020-00084-0

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