Applied Energy 119 (2014) 351–362 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Modelling of a chemisorption refrigeration and power cogeneration system ⇑ Huashan Bao , Yaodong Wang, Anthony Paul Roskilly 1 Sir Joseph Swan Centre for Energy Research, Newcastle University, Newcastle upon Tyne NE1 7RU, UK highlights An adsorption cogeneration was proposed and simulated for cooling and electricity. A dynamic model was built and studied to demonstrate the variability of the system. A dynamic model included the complex coupling of thermodynamic and chemical kinetic. Mutual constrains between main components and optimisation methods were discussed. The highest theoretical COP and exergy efficiency of cogeneration is 0.57 and 0.62. article info abstract Article history: The present work for the first time explores the possibility of a small-scale cogeneration unit by combin- Received 3 June 2013 ing solid–gas chemisorption refrigeration cycle and a scroll expander. The innovation in this work is the Received in revised form 5 December 2013 capability of producing refrigeration and electricity continuously and simultaneously without aggravat- Accepted 6 January 2014 ing the energy scarcity and environmental impact. Individual modelling for each component, which has been validated by experimental data, was firstly investigated in order to identify the proper operation condition for the cogeneration mode achieving 1000 W power output. Subsequently, with the integrated Keywords: modelling of two components the cogeneration performance was studied to demonstrate the viability of Cogeneration this concept. However, because of the mutual constraint between the chemisorption and the expansion Chemisorption Scroll expander when they link in series, the power output of the cogeneration mode was only around one third of the Numerical modelling original expectation under the same condition identified in the individual modelling. Methods of improv- Power generation ing the global performance including the selection of reactive mediums were also discussed and would be Refrigeration of referable value for the future practical investigation. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction fuel demand, to cut greenhouse gas emissions by 80% comparing to the level of 1990 by 2050 [3] and also to minimise the transmis- The Digest of United Kingdom Energy Statistics (DUKES) has sion and distribution losses, the domestic small-scale, distributed estimated that over 80% and 30% of the demand for coal and natu- electric generators are required to assist households to reduce ral gas, respectively, have been from major power producers over the carbon footprint of their homes. the last decade, which meanwhile is responsible for about one- There is increasing number of the domestic small-scale electric quarter of total CO2 emission in UK [1]. The dominated final elec- power generation systems (66 kW) around the world employing tricity consumer in UK has been always the residential sector, renewable energy resources, like wind turbines, solar panels, hydro the consumption of which increased by 58% between 1970 and turbines, geothermal heat, etc. [4]. Among those the cogeneration 2011 [1]. More than 7% of total electricity generation has been lost or tri-generation system (such as CCHP, combined cooling, heat through the transmission and distribution system in UK, and sur- and power) which yields multi-product to meet the daily demand prisingly this figure is higher than that of other major European of the average household are fairly attractive due to the further countries those have even lower population density, such as Spain, strengthened energy utilisation efficiency. For cogeneration of France and Germany [2]. Therefore, with the pressure to reduce cooling and electricity or even CCHP, thermally driven refrigeration like absorption/adsorption is always one of the important technical ⇑ Corresponding author. Tel.: +44 001912464849. strategies, where the ammonia as the working medium has been E-mail addresses: [email protected] (H. Bao), [email protected] extensively engaged with thanks to its desirable characteristics (Y. Wang), [email protected] (A.P. Roskilly). of superior thermodynamic qualities, zero ODP and zero GWP. 1 Tel.: +44 191 208 5869; fax: +44 191 208 8533. 0306-2619/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2014.01.012 352 H. Bao et al. / Applied Energy 119 (2014) 351–362 Nomenclature A area (m2) [X] molar volumetric concentration (mol/m3) Ca, Cr axial, radial clearance (m) COP coefficient of performance (–) Greek letters cp heat capacity (J/kg/K) a initial angle of involute Ft force (N) d thickness (m) fa, fr axial, radial flow coefficient (–) e porosity (–) 0 fEG mass fraction (–) e pressure ratio (–) H height (m) g efficiency (-) DHr reaction heat (J/mol (NH3)) h rotation angle (rad) 2 h heat transfer coefficient (W/m /K) k thermal conductivity (W/m/K) h enthalpy (J/kg) m molar volume (m3/mol) ^ h specific enthalpy on a molar basis (J/mol) q density (kg/m3) I armature current (A) x angular velocity (rad/s) 2 Js, JL moment of inertia of scroll and load (kg m ) k expansion index (–) 2 Subscripts ks, kL friction coefficient of scroll and load (kg m /s) a axial ke coefficient of back electromotive force (V s/rad) ar armature k coefficient of torque sensitivity (N m/A) t EG expanded graphite La axial clearance length (m) b bulk Lar armature inductance (H) c constraint m mass (kg) des desorption M molar mass (kg/mol) eq equilibrium Mt driving torque (N m) ex exergy _ m mass flow rate (kg/s) f fluid n molar number (mol) i chamber number P pressure (Pa) in inlet Pit scroll pitch (m) L load Power power (W) mech mechanical Q heat (J) out outlet r basic circle radius (m) r reactant R resistance (X) ref refrigeration RC gas constant (J/mol/K) s salt R orbiting radius (m) or shaft shaft t time (s) syn synthesis t wrap thickness (m) w S2 MnCl Á2NH T temperature (K) 2 3 s6 MnCl Á6NH T load torque (N m) 2 3 L tec technical UA overall heat exchange coefficient (W/K) 3 therm thermal V volume (m ) w wall W work (W) x reaction conversion (–) Moreover, from an economic perspective, ammonia refrigeration is rectifier expands through a turbine, which is supposed to exit the the most cost effective and energy efficient method of processing turbine with a cold temperature and that is how it generates refrig- and storing frozen and unfrozen foods. Although ammonia is poi- eration. Hasan et al. [7] numerically analysed the energy and exer- sonous and flammable in high concentrations, two factors mitigate gy efficiency of this cycle, and concluded that solar thermal energy this risk: its distinctive smell is detectable at concentrations well at 77 °C could achieve an exergy efficiency higher than 0.6, the below those considered to be dangerous, and ammonia is lighter thermal efficiency of refrigeration and power generation with than air, it will rise and dissipate in the atmosphere on its leakage. 127 °C heat source were 0.01 and 0.15, respectively. As a matter Various of well-recognised organisations such as BREEAM (Build- of fact, in realistic situation the cooling capacity probably would ing Research Establishment Environmental Assessment Method, be much lower or even null as it could be attributed to the fact that UK), UNEP (The United Nations Environmental Programme), and at the exit of the turbine the rich ammonia binary mixture likely ASHRAE (American Society of Heating, Refrigerating and Air-Con- remains as wet vapour, rather than at liquid state to be vaporising ditioning Engineers, Inc.). have given decent credits to ammonia for refrigeration [8]. and been promoting a variety of programs to preserve the eco- Ammonia absorption power/cooling (APC) combined cycle nomic benefits of ammonia refrigeration while providing for the emerged later as an improved cycle by employing a throttle valve management of risks [5]. to ensure the sub-cooling state before vaporisation. However, the An absorption cogeneration cycle producing cooling and electric complex design of APC cycle undoubtedly compromises the com- power simultaneously was proposed by Goswami in 1995 [6]. pactness of the system. Meanwhile it arouses the balance matching Goswami cycle employs the binary mixture of ammonia and water issue between the power output and the cooling load [9,10]. The as the working fluid and the rich-ammonia solution from the thermal efficiency of cooling and net power reported by Liu and H. Bao et al. / Applied Energy 119 (2014) 351–362 353 Zhang [9] was numerically investigated with around 450 °C heat T (oC) source and was presented as 0.06 and 0.21, respectively, while -20 0 20 40 60 80 100 120 140 160 180200220 15.0 the exergy efficiency was around 0.58. NH3 MnCl2 28.7 This work proposes a new concept of cooling and power simul- A taneous generation—adsorption cogeneration cycle (Ad-Cogen cy- 14.5 20.1 Qdes o 16.9 cle), aimed to take full advantage of the merits of adsorption TA=170 C W out 13.7 technology over absorption to promote the cogeneration idea. Such 14.0 PA=Pequ,MnCl2 a cycle can be applied to small-scale household unit driven by solar B 10.6 C Q cond P (bar energy, alternatively it can be designed for medium or large cogen- PB=PC 13.5 o eration plant using industrial waste heat. Since adsorption gener- PC=Pequ,NH3(20 C) 7.4 6.2 ) ously provides extended utilisation domain of thermal energy, lnP (Pa) 5.1 from 50 °C to 600 °C, covering that of Goswami (80–150 °C) and 13.0 D E Q syn 3.9 APC (200–450 °C) cycles, it is convenient to select different suitable Q ref o o PE=PD=Pequ,NH3(0 C) reactive candidates for different application circumstances.