Energy and Exergy Analyses of an Integrated Solar Based Hydrogen Production and Liquefaction System

Abstract

The present paper concerns studies on energy and exergy analyses of a new integrated system with heliostat field, Cu–Cl cycle, Isobutane cycle, and Linde–Hampson system. The present system is capable of producing liquefied hydrogen for easier storage than hydrogen gas. A parametric study is conducted to investigate the effects of variation in solar light intensity, ambient temperature, and flow rate of makeup water required by the Cu–Cl cycle on hydrogen production rate, hydrogen liquefaction rate, and overall energy and exergy efficiencies. The results show that an increase in solar light intensity has positive effect on hydrogen production rate and hydrogen liquefaction rate as they increase from 205 to 492.5 L/s, and 43 to 103 L/s, respectively. The overall energy and exergy efficiencies are observed to be increasing from 4.1 % to 7.3 %, and 4.9 % to 8.2 %, respectively with increase in solar light intensity from 600 to 750 W/m². The rise in ambient temperature from 290 to 330 K affects the performance of the system in the positive manner. The increase in supplied rate of makeup water to the Cu–Cl cycle from 0.05 to 0.15 L/s results in increase in the overall exergy efficiency of the integrated system from 8.2 % to 9.6 %.

Nomenclature

A:

Area

C :

Concentration ratio

d:

Diameter, m

$\overset{.}{ Ex}$ :

Exergy destruction rate, kW

f :

Fraction

Fr:

View factor

h:

Specific enthalpy, kJ/kg; Heat transfer coefficient, W/m² K

hw:

Hot water

HHV:

Higher heating value

I :

Solar light intensity, W/m²

$\dot{m}$ :

Mass flow rate, kg/s

M:

Molecular weight, kg/mol

mf :

Mass fraction

P:

Pressure, kPa

$\dot{Q}$ :

Heat flow rate, kW

T:

Temperature, K

s:

Specific entropy, kJ/kg K

w:

Specific work, kJ/kg

$\dot{W}$ :

Work rate, kW

η:

Efficiency

ε:

Receiver surface emissivity

σ :

Stefan-Boltzmann constant, W/m² K⁴

ρ:

Density, kg/m³

∂:

Thickness, m

λ:

Thermal conductivity, W/m K

abs:

Absorbed

avg:

Average

ch:

Chemical

cond:

Conduction

conv:

Convection

convr:

Conversion

comp:

Compressor

elec:

Electrolyzer

em:

Emissive

en:

Energy

ex:

Exergy

fc :

Forced convection

H:

Heliostat

H₂ :

Hydrogen

HE:

Heat exchanger

i:

Inner

iso:

Isobutane

insi:

Inner side of receiver

insu:

Insulation

i:

i^th state

k:

k^th state

liq:

Liquid

m:

m^th state

ms:

Molten salt

nc:

Natural convection

o:

Outer

ov:

Overall

p:

Pump

ph:

Physical

rec:

Receiver

ref:

Reflection

S:

Solar

surf:

Surface

sys:

System

th:

Thermal

turb:

Turbine

w:

Wall surface

0:

Ambient state