MODELLING AND SIMULATION OF AMMONIA-WATER SEPARATION FOR APPLICATION IN ABSORPTION HEAT PUMP
MODELLING AND SIMULATION OF AMMONIA-WATER SEPARATION FOR APPLICATION IN ABSORPTION HEAT PUMP
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Date
1993-10
Authors
ADEGBOYEGA, ADETOKUNBOH SURAJUDEEN OLAWALE
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Abstract
Theoretical thermodynamic simulations (analyses) were
carried out on the "Extraction-System-Attached" (ESA) Ammonia-
Water Absorption Heat Pump cycles which were developed with the
aim of improving the thermodynamic performance achievable with
the conventional cycle. Theoretical simulation of the liquidliquid-
equilibria (LLE) of amnion i a-water-3ol vent (ternary)
systems using the tested semi-empirical model called UNIQUAC
equation was the basis for determining whether or not the
extracting solvents (of desirable physical properties) could form
two-phase ternary systems with aqueous ammonia solution. The
UNIQUAC binary parameters of ammonia-water mixtures and the
binary mixtures of the selected solvents and water or ammonia,
for use in the LLE simulation, were obtained from mutual
solubility and infinite dilution coefficient data. Capacity and
selectivity diagrams obtained from the data generated from LLE
simulation were used for further confirmation of the suitability
of the solvents for liquid-liquid-extraction process.
Five cycles were derived from the conventional absorption
system by using the extraction or stripping separation process
as substitute for the non-isothermal separation process used in
the conventional ammonia-water absorption heat pump.
Thermodynamic analysis models used for obtaining the
irreversibilities and COP of the cycles were derived from
system's parameters and working fluid properties such as
concentration of strong (XST) and weak (XWK) aqueous ammonia
solution, reflux or recirculation ratio (R), solvent-to-feed
ratio (SFR), enthalpy change. Simulation of these thermodynamic
models for two ESA-ammonia-water absorption heat pump cycles
(employing five different organic solvents in the extraction step
of the system) and the conventional ammonia-water absorption heat
pump cycle at two evaporator's temperatures indicated that better
thermodynamic performance, in term of the COP (heating and
cooling modes) and irreversibility, could be achieved by using
liquid-liquid extraction process to recover ammonia from the
strong aqua ammonia formed in the absorber during the pump's
operation. The cycles employing nitrobenzene as the extract
solvent, among the. KSA systems, gave the lowest irreversibilty
and highest COP values.
Description
A THESIS
PRESENTED TO THE POSTGRADUATE SCHOOL
AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE IN CHEMICAL
ENGINEERING
DEPARTMENT OF CHEMICAL ENGINEERING
FACULTY OF ENGINEERING
AHMADU BELLO UNIVERSITY, ZARIA
OCTOBER, 1993
Keywords
MODELLING,, `SIMULATION,, AMMONIA-WATER,, SEPARATION,, ABSORPTION