Effect of reactor geometry on the temperature distribution of hydrogen producing solar reactors Joseph Costandy a , Nour El Ghazal a , Mohamed T. Mohamed b , Akanksha Menon b , Vidyasagar Shilapuram b , Nesrin Ozalp b, * a Texas A&M University at Qatar, Chemical Engineering Department, P.O. Box 23874, Doha, Qatar b Texas A&M University at Qatar, Mechanical Engineering Department, P.O. Box 23874, Doha, Qatar article info Article history: Received 31 October 2011 Received in revised form 18 February 2012 Accepted 23 February 2012 Available online 12 April 2012 Keywords: Solar reactor Hydrogen Methane cracking Reactor geometry Modeling Design abstract Global effects of greenhouse gas emissions associated with the current extensive use of fossil fuels are increasingly attracting research groups and industry to find a solution. In order to reduce or avoid such emissions, solar thermal cracking of natural gas has been studied by many research groups as a clean and economically viable option for hydrogen production with zero CO 2 emissions. By utilization of concentrated solar energy as the source of high temperature process heat, natural gas is decomposed into hydrogen gas and high grade carbon using a solar reactor. Our previous study shows that temperature distribution inside the solar reactor has significant effect on hydrogen production. In this paper, we expand our previous study by demonstrating that reactor geometry has a notable impact on temperature distribution inside the solar reactor and therefore it has an impact on natural gas to hydrogen conversion. Results show that there are approximately 22% and 32% losses from spherical and cylindrical reactors, respectively, while hydrogen production amount varies from 1.27 g/s to 8.95 g/s for spherical reactor, and 0.94 g/s to 8.94 g/s for cylindrical reactor geometry. Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction As the main source of energy for steam, power, and commodity production, fossil fuel consumption causes continuous emis- sion of greenhouse and toxic gases into the atmosphere. Hydrogen is a good alternative to fossil fuels for the production of steam, power, and some major commodities in the chemical and petroleum industries with zero or near to zero emissions. Currently, hydrogen is produced mainly by steam reforming of methane and is mostly used by petroleum industry for the refinement of crude oil [1]. Although it is the most economi- cally reasonable method of hydrogen production, steam reforming of methane produces large amount of emissions [2]. Because of these environmentally unfavorable emissions, researchers have been expending significant effort into alter- native hydrogen production techniques which could be as economically as viable as steam reforming of methane. One solution to these emission problems during hydrogen production is to adopt concentrated solar energy as the source of high temperature process heat to decompose methane, instead of using fossil fuel combustion as the source of high temperature [3]. For that purpose, direct solar thermal cracking of methane offers completely emission-free genera- tion of hydrogen, which occurs via the following reaction. * Corresponding author. Tel.: þ974 6686 2832; fax: þ974 4423 0066. E-mail addresses: joseph.costandy@qatar.tamu.edu (J. Costandy), nour.el_ghazal@qatar.tamu.edu (N. El Ghazal), mohamed. mohamed@qatar.tamu.edu (M.T. Mohamed), akanksha.menon@qatar.tamu.edu (A. Menon), vidyasagar.s@qatar.tamu.edu (V. Shila- puram), nesrin.ozalp@qatar.tamu.edu (N. Ozalp). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 16581 e16590 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.02.193