Exploring optimal working fluids and cycle architectures for organic Rankine cycle systems using advanced computer-aided molecular design methodologies
File(s)
Accepted version
Author(s)
White, MT
Oyewunmi, OA
Haslam, A
Markides, C
Type
Conference Paper
Abstract
The combination of computer-aided molecular design
(CAMD) with an organic Rankine cycle (ORC) power-system
model presents a powerful methodology that facilitates an in-
tegrated approach to simultaneous working-fluid design and
power-system thermodynamic or thermoeconomic optimisation.
Existing CAMD-ORC models have been focussed on simple
subcritical, non-recuperated ORC systems. The current work
introduces partially evaporated or trilateral cycles, recuperated
cycles and working-fluid mixtures into the ORC power-system
model, which to the best knowledge of the authors has not been
previously attempted. A necessary feature of a CAMD-ORC
model is the use of a mixed-integer non-linear programming
(MINLP) optimiser to simultaneously optimise integer working-
fluid variables and continuous thermodynamic cycle and eco-
nomic variables. In this paper, this feature is exploited by in-
troducing binary optimisation variables to describe the cycle lay-
out, thus enabling the cycle architecture to be optimised along-
side the working fluid and system conditions. After describing
the models for the alternative cycles, the optimisation problem
is completed for a defined heat source, considering hydrocar-
bon working fluids. Two specific case studies are considered,
in which the power output from the ORC system is maximised.
These differ in the treatment of the minimum heat-source outlet
temperature, which is unconstrained in the first case study, but
constrained in the second. This is done to replicate scenarios
such as a combined heat and power (CHP) plant, or applications
where condensation of the waste-heat stream must be avoided.
In both cases it is found that a working-fluid mixture can per-
form better than a pure working fluid. Furthermore, it is found
that partially-evaporated and recuperated cycles are optimal for
the unconstrained and constrained case studies respectively.
(CAMD) with an organic Rankine cycle (ORC) power-system
model presents a powerful methodology that facilitates an in-
tegrated approach to simultaneous working-fluid design and
power-system thermodynamic or thermoeconomic optimisation.
Existing CAMD-ORC models have been focussed on simple
subcritical, non-recuperated ORC systems. The current work
introduces partially evaporated or trilateral cycles, recuperated
cycles and working-fluid mixtures into the ORC power-system
model, which to the best knowledge of the authors has not been
previously attempted. A necessary feature of a CAMD-ORC
model is the use of a mixed-integer non-linear programming
(MINLP) optimiser to simultaneously optimise integer working-
fluid variables and continuous thermodynamic cycle and eco-
nomic variables. In this paper, this feature is exploited by in-
troducing binary optimisation variables to describe the cycle lay-
out, thus enabling the cycle architecture to be optimised along-
side the working fluid and system conditions. After describing
the models for the alternative cycles, the optimisation problem
is completed for a defined heat source, considering hydrocar-
bon working fluids. Two specific case studies are considered,
in which the power output from the ORC system is maximised.
These differ in the treatment of the minimum heat-source outlet
temperature, which is unconstrained in the first case study, but
constrained in the second. This is done to replicate scenarios
such as a combined heat and power (CHP) plant, or applications
where condensation of the waste-heat stream must be avoided.
In both cases it is found that a working-fluid mixture can per-
form better than a pure working fluid. Furthermore, it is found
that partially-evaporated and recuperated cycles are optimal for
the unconstrained and constrained case studies respectively.
Date Issued
2017-07-16
Date Acceptance
2017-05-05
Publisher
ICHMT
Copyright Statement
© 2017 HEFAT
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Grant Number
EP/P004709/1
Source
13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT2017)
Publication Status
Accepted
Start Date
2017-07-16
Finish Date
2017-07-19
Coverage Spatial
Portorož, Slovenia