Research PaperDynamic simulation of liquefied petroleum gas vaporisation for burners
Introduction
Liquefied petroleum gas (LPG) is mainly composed of propane (C3H8) and n-butane (C4H10) with some propylene (C3H6), butylene (C4H8), and other minor compositions of hydrocarbons. LPG is in gaseous form at ambient temperatures and pressures. Due to a dramatic reduction in the volume after being liquefied, LPG is commonly stored and transported in liquid form in pressurised steel cylinders. This makes LPG a popular domestic fuel in rural and remote areas, even in some urban regions away from natural gas transmission networks [1]. For instance, Chinese total LPG consumption for householders was 21.73 million tons in 2014 [2].
The common way for domestic and commercial burners to use LPG is to supply liquid LPG in commercially available cylinders without thermal insulation and then to use it in gaseous form. The liquid-to-vapour phase change occurring within the cylinder is called spontaneous (or natural) vaporisation in which process the heat for vaporisation comes from the liquid itself and/or from the surroundings and components with lower boiling points vaporise easier and earlier. The properties of both the liquid and the vapour vary continuously with the change in LPG compositions over time. The minimum inlet pressure of a gas regulator automatically modulates high-pressure gas to a safe pre-determined limit for gas burners, so the cylinder cannot be completely emptied and the remaining liquid is called as the residue. It means that if the vapour pressure in the cylinder is less than the required minimum value, the natural vaporisation process will be completed.
To estimate the physical properties of LPG and the residue amount, it is necessary to know the composition [3]. The chromatography method is usually applied to determine the composition of LPG after analysing its sample [4], [5], [6], [7]. However, it is hard to adopt this method to continuously determine the composition that changes instantaneously through the vaporisation process. Some mathematical models were developed to predict the dynamic behaviours of LPG spontaneous vaporisation in the cylinder [3], [8], [9]. However, such models are typically valid for specific and rigorous assumptions. The LPG within the cylinder was assumed to be ideal [3], [8], [9]. Furthermore, Yan [8] assumed that the change in LPG composition did not alter the values of some thermodynamic properties and the ratio of the pressure to the temperature of LPG kept constant. Tian and Jiang [3] treated the mass fraction of each component as an equivalent of its mole fraction and assumed that the LPG temperature remained unchanged throughout the vaporisation [3]. These above mentioned assumptions are in conflict with the practical natural vaporisation and may cause some limitations of the models.
This work emphasises the need to account for the non-ideal behaviour of both the liquid and the vapour phases in the pressurized steel cylinder and the importance of variable physical properties in investigating the real LPG spontaneous vaporisation process. The main objective of this study is to present a comprehensive model and explore the detailed transient characteristics of LPG natural vaporisation process for gas burners, which can provide a basis for designing or retrofitting burners to get good combustion performance and predicting the residue amount. First, a dynamic model is established which prediction accuracy is validated by using the previous experimental data. Further, the transient behaviours of LPG vaporisation are obtained and analysed, with special emphasis on variation of combustion properties of vapour LPG. Finally, the effects of initial composition, surrounding temperature and discharge rate on the natural vaporisation and the residue amount are discussed based on the simulation results.
Section snippets
Description
As shown in Fig. 1, when the user opens the reducing valve to use LPG, the vapour flows out. Then the vapour pressure in the cylinder reduces and the equilibrium no longer exists. The liquid LPG has to vaporise immediately to mitigate the drop in the pressure and to regain a vapour-liquid equilibrium (VLE) condition. Due to no temperature difference, the latent heat of vaporisation is only from the liquid itself at the beginning. The liquid temperature thus decreases, which generates the
Model validation
In this study, the presented model was validated with the experimental data obtained by the chromatography method [11] under the same operating conditions listed in Table 2. For ‘ysp118-I type’ cylinders generally used as a group in commercial sectors, the minimum inlet pressure of the regulator is 0.17 MPa [11], [13].
As shown in Fig. 4, Fig. 5, more than 89% and 78% of the calculation results are with the ±4% bandwidth of experimental results for compositions in vapour and liquid phases,
Concluding remarks
The transient behaviours of LPG spontaneous vaporisation in the cylinder were clearly studied by the presented general model. Some conclusions are obtained by this investigation.
- (1)
The proposed model is proved to be applicable for determining real-time compositions and physical properties of LPG throughout the discharge process.
- (2)
From the beginning to the end of the natural vaporisation, the WI of vapour LPG increases by 8.0%. The WI obtained by the proposed graphical design procedure can ensure
Acknowledgements
This work was done while Guo-Hua Shi was visiting at the University of Melbourne. The visit was supported by the program of China Scholarships Council [No. 201606735054]. The authors appreciate the support from the Natural Science Foundation of Hebei Province, China [E2016502027], the Fundamental Research Funds for the Central Universities, China [2017MS124] and the Scientific Research Project of Education Department of Hebei Province, China [Z2015119]. The authors also gratefully acknowledge
References (23)
- et al.
Natural gas pricing reform in China: Getting closer to a market system?
Energ. Policy
(2015) - et al.
Accurate measurement method for the residues in liquefied petroleum gas (LPG)
Fuel
(2005) Fire investigation and ignitable liquid residue analysis—a review: 2001–2007
Forensic. Sci. Int.
(2008)- et al.
From natural gas to hydrogen via the Wobbe index: The role of standardized gateways in sustainable infrastructure transitions
Int. J. Hydrogen. Energ
(2007) - et al.
Combustion stability and thermal efficiency in a porous media burner for LPG cooking in the food industry using Al2O3 particles coming from grinding wastes
Appl. Therm. Eng.
(2015) - et al.
Estimation of combustion air requirement and heating value of fuel gas mixtures from flame spectra
Appl. Therm. Eng.
(2016) - et al.
Performance of an evaporator for a LPG powered vehicle
Appl. Therm. Eng.
(2004) - et al.
Replacing conventional fuels in USA, Europe, and UK with plastic pyrolysis gases–Part I: Experiments and graphical interchangeability methods
Energ. Convers. Manag.
(2016) - National Bureau of Statistics of the People’s Republic of China, China statistical yearbook 2016, Chinese Statistics...
- et al.
Simulation of the LPG component changes during the spontaneous vaporization
J. Fuel Chem. Technol.
(2003)
Determination of composition of liquefied petroleum gas by capillary gas chromatography
J. Instrum. Anal.
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