Energy, exergy, and sustainability analysis of an industrial nitric acid plant

ABSTRACT

In this paper, energy, exergy, and sustainability analyses are performed on the Karun petrochemical nitric acid plant in Mahshahr at varying ambient temperatures to reveal realistic optimization opportunities. All plant components have been analyzed individually by using mass, energy, and exergy balance equations. Results regarding energy, exergy, and sustainability evaluations of the equipment have been presented in the individual table. The energy analysis indicates that the system’s energy efficiency is 30.9% and introduces the absorber column as the equipment with the highest heat transfer to the environment in the entire plant (6889 kW). The exergy analysis revealed that the exergy efficiency of the entire system had variations ranging from 13.39% to 14.72%, which is inversely proportional to the increase in dead state temperatures. The maximum amount of exergy destruction is calculated for the converter (5129 kW at 45°C). In addition, exergy analysis identified the converter as the component with the most potential for improvement (2918 kW at 45°C). On the other hand, the highest sustainability index is found for the absorber column (1.616 at 15°C). Moreover, by selecting the optimal intermediate pressure for the compressors, the power consumption of the air compression system has been reduced by 185.9 kW, and its exergy efficiency has increased by 3%.

KEYWORDS:

• Energy
• exergy
• sustainability
• nitric acid plant
• optimization

Nomenclature

$b^{ch}$	=	Standard chemical exergy (kJ/kg)
el	=	Element
ex	=	Specific exergy (kJ/kg)
$EX$	=	Total exergy rate (kW)
$h$	=	Specific enthalpy (kJ/kg)
$\dot{m}$	=	mass flow rate (kg/s)
p	=	Pressure (bar)
$Q$	=	Heat (kW)
$Ql$	=	Heat loss (kW)
$\bar{R}$	=	World constant for gases (kJ/kmol K)
$s$	=	Specific entropy (kJ/kg K)
$SI$	=	Sustainability index
T	=	temperature (K)
W	=	Work (kW)
y	=	Mole fraction
${\mathrm{\Delta }}_{f}G$	=	Gibbs free energy formation (kJ/kg)
Abbreviations	=
ABS	=	Absorber column
AC	=	Air compressor
ACS	=	Air compression system
CC	=	Cooler condenser
CONV	=	convertor
EXP	=	Expander
DEA	=	Deaerator
TGH	=	Tail gas heater
superscript	=
ch	=	Chemical
ph	=	physical
Subscripts	=
0	=	Reference conditions of ambient
$D$	=	Destruction
en	=	Energy
ex	=	Exergy
F	=	Fuel
i	=	Inlet
$j$	=	$j_{th}$ element
IP	=	Improvement potential
$k_{th}$	=	$k_{th}$ component
l	=	liquid
O	=	Outlet
P	=	product
Q	=	heat
St	=	stage
Greek symbols	=
$\eta$	=	efficiency
$\varphi$	=	exergy destruction ratio
$\phi$	=	Fuel exergy consumption ratio
$\theta$	=	Product exergy consumption ratio

Disclosure statement

No potential conflict of interest was reported by the author(s).

Credit author statement

E. Abbasian Hamedani: Conceptualization, Methodology, Software, Investigation, Visualization, Data Curation, Writing – Original Draft. A. Abdalisousan: Conceptualization, Methodology, Validation, Writing – Review & Editing. A. Khoshgard: Conceptualization, Methodology, Writing – Original Draft, Validation the optimization of the air compression system. M. Nazari: Resources, Writing – Review & Editing.

Additional information

Notes on contributors

Erfan Abbasian Hamedani

Erfan Abbasian Hamedani, is a BSc student of Energy Engineering from the Science and Research Branch of Azad University.

Ashkan Abdalisousan

Dr. Ashkan Abdalisouan, is an assistant professor of energy engineering, field of interest: energy and exergy analysis, exergo-economic analysis, thermal systems, optimization, and energy systems modeling.

Ahmad Khoshgard

Dr. Ahmad Khoshgard, is an assistant professor of chemical engineering, field of interest: process integration, energy system modeling, energy and environment, and heat transfer.

Mehdi Nazari

Dr. Mehdi Nazari, is a member of Karun Petrochemical Company.