Thermodynamic Assessment of Waste Heat Operated Combined Compression–Absorption Refrigeration System

Abstract

An industrial waste heat operated combined refrigeration cycle is proposed, which integrates the Rankine cycle and compression–absorption refrigeration cycle. This combined cycle produces higher coefficient of performance than the conventional refrigeration cycle. An analysis through energy and exergy is performed to guide the thermodynamic improvement for this cycle, and a comprehensive parametric study is conducted to investigate the effects of exhaust gas inlet temperature, pinch point, and gas composition on energetic and exergetic COP and exergy destruction in each component of the combined refrigeration cycle. The results show that the exhaust gas inlet temperature and pinch point have significant effects on exergy destruction in most of the components of the cycle. Effects of increasing the exhaust gas temperature and pinch point were found negligible for exergy destruction in solution pump and throttling valve. Both energetic and exergetic COPs increases with the increase in exhaust gas temperature and decreases with the increase in pinch point and oxygen content of the gas. Modeling the exhaust gas as an air underestimates the energetic performance and overestimates the exergetic performance of the combined refrigeration cycle. This study contributes important information to the role of operating variables influence on the thermodynamic performance of low temperature source combined compression–absorption refrigeration system.

Nomenclature

c _p :

Specific heat (kJ kg⁻¹ K⁻¹)

$\dot{E}$ :

Exergy transfer rate (kW)

h :

Specific enthalpy (kJ kg⁻¹)

HRSG :

Heat recovery steam generator

$\dot{m}$ :

Mass flow rate (kg s⁻¹)

M :

Molar mass (kg kmol⁻¹)

P :

Pressure (bar)

PP :

Pinch point (K)

$\dot{Q}$ :

Rate of heat transfer (kW)

R :

Universal gas constant (kJ kmol⁻¹ K⁻¹)

s :

Specific entropy (kJ kg⁻¹ K⁻¹)

ST:

Steam turbine

T :

Temperature (K)

$\overset{.}{W}$ :

Rate of work output (kW)

η _I :

Energy efficiency (or first law efficiency)

η _ex :

The second law efficiency or exergetic efficiency

η _p :

Pump isentropic efficiency

η _t :

Turbine isentropic efficiency

0:

Environmental

f:

Solution circulation ratio

g:

Exhaust gas

GEN:

Generator

p:

Pump

r:

Refrigerant

s:

Steam

t:

Turbine

w:

Water