Independent Generation of Hydrogen using Hydrogen as fuel Mohideen Ibramsha 1968 Alumni of Thiagarajar College of Engineering, Madurai, TN, India 1974 intellectual son of PhD guide Prof. V.Rajaraman & Mrs. Dharma Rajaramn, CS, EE, IIT, Kanpur, UP, India 1991 First HOD of CSE, CEC [now BSAU] Chennai, TN, India Associate Professor (Retd), Computer Science, Framingham, MA, USA Consultant R&D, M A M College of Engineering, Trichy, TN, India Advisor, HyDIGIT Pte Ltd, Singapore
This article was posted elsewhere on Monday, May 21, 2018 - 03:19 pm, and is reposted here without any change in contents.
Introduction: In https://mohideenibramsha7.wixsite.com/website/single-post/2018/08/07/Hydrogen-Economy-Now-4 we found that every CAM ALLAM Power Plant produces in excess the same amount of Hydrogen consumed when the required CH4 is reformed. Thus restricting Hydrogen production using CAM ALLAM Power Plant alone expects that the Hydrogen required for electricity generation must equal the Hydrogen required for all other uses. Such a constraint on use of Hydrogen in the Hydrogen economy should be avoided. We investigate independent production of Hydrogen using Hydrogen as fuel to produce the required steam for reforming CH4 here. Optimal Reformer: In the article, CAM ALLAM Hydrogen Generator, the link of which is given above, we supplied CH4 and H2O at 625 K (252 C) possibly with additional fuel to the reformer. The chemical equation is CH4 + 4H2O ‘gives’ CO2 + 4H2 + 2H2O. The reforming is an endothermic operation. The amount of additional fuel supplied to the reformer is not known. Being conservative, we assume that the input at the highest permitted temperature would require no additional fuel and thus we estimate the heat energy corresponding to the highest temperature of the feed. The highest temperature of the feed is 815 K (542 C). Feed amounts: We are interested in finding out that fraction of the Hydrogen produced that needs to be burnt for the reforming process. We use 16 Kg of CH4 and 72 Kg of steam as input getting 44 Kg of CO2, 8 Kg of Hydrogen and 36 Kg of water vapor. We ignore the heat energy in the output so that the Hydrogen fuel would be decidedly less than the calculated amount. Heating 16 Kg of CH4 to 815 K: We need to heat the Methane from atmospheric temperature of 300 K to 815 K. The specific heat of Methane is a function of its temperature. We use the values given at https://www.engineeringtoolbox.com/methane-d_980.html in the following table.
No Temperature range K Specific heat KJ/(Kg x K) Heat supplied KJ/Kg Cumulative heat KJ/Kg
1 300 – 325 2.226 55.650 55.650
2 325 – 350 2.293 57.325 112.975
3 350 – 375 2.365 59.125 172.100
4 375 – 400 2.442 61.050 233.150
5 400 – 450 2.525 126.250 359.400
6 450 – 500 2.703 135.150 494.550
7 500 – 550 2.889 144.450 639.000
8 550 – 600 3.074 153.700 792.700
9 600 – 650 3.256 162.800 955.500
10 650 – 700 3.432 171.600 1127.100
11 700 – 750 3.602 180.100 1307.200
12 750 – 800 3.765 188.250 1495.450
13 800 – 815 3.923 57.345 1552.795
For 16 Kg of CH4 we supply 1552.795 x 16 = 24844.72 KJ of heat. Heat for 72 Kg of steam: For calculating the heat required for supplying 72 Kg of team at 815 K, we use latent heat of evaporation at 373 K to be 2030 KJ/(Kg x K); and the specific heat of steam above 373 K as 1.996 KJ/(Kg x K) as given at https://www.engineeringtoolbox.com/water-thermal-properties-d_162.html . To calculate the heating of water from 300 K to 373 K we use the specific heat values given in the table below extracted from https://www.engineeringtoolbox.com/specific-heat-capacity-water-d_660.html . Heat for raising water temperature from 300 K to 373 K is calculated in the table below.
No Temperature K Specific heat KJ/(Kg x K0 Heat supplied KJ/Kg Cumulative heat KJ/Kg
1 273 – 283 4.2199 42.1990 42.1990
2 283 – 293 4.1955 41.9550 84.1540
3 293 – 298 4.1844 20.9220 105.9760
4 298 – 303 4.1816 20.9080 125.9840
5 303 – 313 4.1801 41.8010 167.7850
6 313 – 323 4.1796 41.7960 209.5810
7 323 – 333 4.1815 41.8150 251.3960
8 333 – 343 4.1851 41.8510 293.2470
9 343 – 353 4.1902 41.9020 335.1490
10 353 – 363 4.1969 41.9690 377.1180
11 363 – 373 4.2053 42.0530 419.1710
To 419.1710 KJ we add 2030 KJ of latent heat and 1.996 x (815 – 373) to get the heat supplied to generate 1 Kg of steam. The heat supplied to generate 1 Kg of steam is 419.171 + 2030 + 882.232 = 3331.403 KJ. To produce 72 Kg of steam, we supply 3331.403 x 72 = 239861.016 KJ. Total heat used for inputs: Adding the heat supplied to CH4 and steam, we get the total heat supplied as 264705.736 KJ. With 1 Kg of Hydrogen giving 120 MJ of heat, the Hydrogen used to heat the inputs to the reformer is 2.2059 Kg. We ignore the heat content of the output of 8 Kg of Hydrogen, 44 Kg of CO2 and 36 Kg of steam. By using properly designed heat exchanger to heat the input using the heat content of the output, the Hydrogen required to heat the input could be appreciably reduced. For simplicity, we ignore this benefit. Conclusion: In a Hydrogen economy we would use Hydrogen itself to supply CH4 and steam for the steam methane reformer. We get 5.7941 Kg of Hydrogen for every 16 Kg of CH4. In other words, for every Kg of Methane used, we get 0.3621 Kg of Hydrogen. This amount could be increased substantially by using heat exchangers to preheat the input using the heat content of the output of the reformer.