Experimental and theoretical studies on adsorbed natural gas storage system using activated carbons 2

Appendix A 185 Appendix A Determination of Regeneration Temperature for the Activated Carbons The regeneration temperature is applied to the adsorbent sample during the evacuation proc

Appendix A

185

Appendix A Determination of Regeneration

Temperature for the Activated Carbons

The regeneration temperature is applied to the adsorbent sample during the evacuation

process to desorb the pre-adsorbed adsorbate molecules The temperature has to be

reasonably higher to provide enhancement in desorption process, although the

maximum possible regeneration temperature depends on the adsorbent material

properties particularly the burn off temperature Generally the carbon materials burn

out at temperatures from (650 to 750) °C in presence of air However, the regeneration

temperature for the activated carbons is observed to be much lower because of their

porous surface structure

In this study, the regeneration temperature is determined experimentally for the

activated carbon (AC) samples used in the experiments The Computrac Max 5000

Moisture Analyzer is used for this purpose where the AC sample pre-adsorbed with

methane is heated up at different higher temperatures

Figure A.1 Computrac Max 5000 Moisture Analyzer

Sample Holder

Ceramic Oven

Display

RTD mounted

near the Heater to

measure Oven

Temperature

Appendix A

186

This moisture analyzer operates for the temperature range of (25 to 600) °C and

it takes only (2 to 3) minutes to reach the set temperature The operating range is (0.2

to 600) g with an accuracy of 0.1 mg in mass measurement Figure A.1 shows the

pictorial view of the moisture analyzer indicating the ceramic oven, sample holder,

RTD for temperature measurement, and the display

The AC samples pre-adsorbed with methane are heated up at different

temperatures ranging from (100 to 300) °C, and the adsorbate removal rates are

recorded as function of time Figure A.2 provides typical plots for the percentage of

adsorbate removed and the removal rate at temperatures 160 °C and 200 °C,

respectively for the AC sample type Maxsorb III In these plots, the “% Moisture” of

the vertical axis should be considered as “the percentage of adsorbate removal” It can

be seen that the percentage of adsorbate removal from the AC sample becomes steady

after about 20 minutes of heating at temperature 160 °C whereas it is gradually

increasing in case of temperature 200 °C These observations confirm that there is no

significant adsorbate removal in the extended period of heating at 160 °C However,

the gradual increase of the percentage in case of heating at 200 °C is not exactly due to

the adsorbate removal rather it is because of burn out of the AC sample

(a) 160 °C (b) 200 °C Figure A.2 The percentage and the rate of adsorbate removal as function of

time

% of adsorbate removal

is gradually increasing

% of adsorbate removal is constant

Appendix A

187

Figure A.3 shows the bar plot for the ratio of final mass and initial mass of the

Maxsorb III sample at different temperatures It can be seen that the changes in mass

ratio are sharp below 120 °C and they are very close (indicated by red circle) for the

temperatures (140 to 180) °C Again, the sharp changes in mass ratio (indicated by

blue circle) are observed for temperatures above 200 °C which indicates the possibility

of burn out of the AC sample at higher temperatures above 200 °C Therefore, the

regeneration temperature is estimated at temperatures (140 to 160) °C for the AC

samples and this temperature range is also maintained in other studies (Himeno et al.,

2002; Saha et al., 2007; Akkimaradi et al., 2009; Wang et al., 2010) when activated

carbons are used as adsorbents

0.9894

0.9877

0.9870

0.9867

0.9863

0.9858

0.9846

0.9840

0.9823

0.9800

0.978

0.980

0.982

0.984

0.986

0.988

0.990

0.992

mfinal

Temperature ( °C) Figure A.3 The ratios of final mass and initial mass of the Maxsorb III sample at

different higher temperatures

Appendix B

188

Appendix B Experimental Adsorption Uptake Data Table B.1 Experimental uptake data for adsorption of methane onto Maxsorb III

Pressure

(MPa)

Uptake

(kg/kg)

Pressure (MPa)

Uptake (kg/kg)

Pressure (MPa)

Uptake (kg/kg)

Pressure (MPa)

Uptake (kg/kg)

Temperature = 5 ºC Temperature=15 ºC Temperature=25 ºC Temperature=35 ºC

0.050 0.015 0.050 0.012 0.057 0.011 0.060 0.010 0.127 0.033 0.135 0.029 0.140 0.025 0.152 0.022 0.217 0.050 0.233 0.045 0.234 0.038 0.245 0.034 0.310 0.066 0.331 0.059 0.331 0.050 0.344 0.045 0.411 0.080 0.429 0.071 0.428 0.061 0.443 0.055 0.510 0.093 0.526 0.082 0.526 0.071 0.543 0.064 0.646 0.109 0.655 0.096 0.652 0.083 0.678 0.076 0.784 0.123 0.800 0.109 0.792 0.095 0.820 0.087 0.934 0.136 0.946 0.121 0.948 0.108 0.974 0.098 1.138 0.152 1.155 0.137 1.157 0.122 1.175 0.111 1.340 0.167 1.354 0.150 1.344 0.134 1.373 0.122 1.550 0.180 1.561 0.163 1.563 0.147 1.571 0.133 1.754 0.191 1.762 0.174 1.756 0.157 1.771 0.143 1.949 0.201 1.968 0.184 1.960 0.167 1.975 0.153 2.158 0.211 2.166 0.193 2.157 0.176 2.178 0.161

Temperature =45 ºC Temperature=55 ºC Temperature=65 ºC Temperature=75 ºC

0.061 0.008 0.065 0.008 0.067 0.007 0.071 0.006 0.148 0.019 0.160 0.017 0.157 0.015 0.162 0.013 0.248 0.029 0.255 0.026 0.254 0.023 0.263 0.020 0.348 0.039 0.354 0.035 0.350 0.030 0.362 0.027 0.445 0.048 0.458 0.043 0.456 0.038 0.464 0.034 0.540 0.056 0.555 0.050 0.555 0.045 0.561 0.040 0.665 0.065 0.680 0.059 0.681 0.053 0.686 0.047 0.815 0.076 0.823 0.069 0.826 0.061 0.835 0.055 0.966 0.086 0.974 0.078 0.978 0.070 0.987 0.063 1.170 0.099 1.204 0.091 1.188 0.081 1.198 0.073 1.368 0.110 1.389 0.100 1.393 0.091 1.401 0.083 1.585 0.121 1.593 0.110 1.589 0.100 1.603 0.091 1.777 0.130 1.799 0.120 1.795 0.108 1.806 0.099 1.975 0.139 1.984 0.127 1.990 0.116 2.015 0.107

2.203 0.136 2.187 0.124 2.198 0.114

Appendix B

189

Table B.2 Experimental uptake data for adsorption of methane onto ACF

(A-20)

Pressure

(MPa)

Uptake

(kg/kg)

Pressure (MPa)

Uptake (kg/kg)

Pressure (MPa)

Uptake (kg/kg)

Pressure (MPa)

Uptake (kg/kg)

Temperature = 5 ºC Temperature=15 ºC Temperature=25 ºC Temperature=35 ºC

0.057 0.012 0.056 0.010 0.059 0.008 0.059 0.007 0.128 0.022 0.143 0.022 0.144 0.018 0.146 0.015 0.218 0.034 0.242 0.032 0.252 0.028 0.247 0.023 0.332 0.045 0.343 0.041 0.350 0.036 0.352 0.031 0.437 0.055 0.443 0.049 0.451 0.043 0.445 0.037 0.549 0.063 0.550 0.057 0.550 0.050 0.545 0.043 0.672 0.072 0.699 0.066 0.688 0.058 0.694 0.051 0.855 0.082 0.838 0.074 0.838 0.066 0.846 0.058 0.981 0.089 0.997 0.082 0.999 0.073 0.998 0.065 1.162 0.097 1.205 0.091 1.199 0.081 1.204 0.073 1.358 0.105 1.401 0.099 1.401 0.089 1.404 0.080 1.572 0.113 1.601 0.106 1.605 0.095 1.599 0.086 1.780 0.120 1.799 0.112 1.805 0.101 1.820 0.092 1.981 0.126 2.008 0.118 2.000 0.107 2.034 0.098 2.202 0.132 2.207 0.123 2.206 0.112 2.201 0.102 2.412 0.137 2.406 0.128 2.402 0.117 2.433 0.108

Temperature=45 ºC Temperature=55 ºC Temperature=65 ºC Temperature=75 ºC

0.062 0.006 0.051 0.004 0.067 0.004 0.059 0.003 0.157 0.014 0.157 0.012 0.147 0.009 0.151 0.008 0.261 0.021 0.254 0.018 0.249 0.015 0.249 0.013 0.354 0.027 0.360 0.024 0.358 0.020 0.346 0.017 0.452 0.032 0.453 0.029 0.457 0.025 0.445 0.021 0.561 0.038 0.562 0.034 0.551 0.029 0.544 0.025 0.694 0.044 0.711 0.041 0.702 0.035 0.723 0.032 0.845 0.051 0.854 0.047 0.861 0.041 0.850 0.037 1.001 0.057 1.005 0.053 1.009 0.047 1.027 0.042 1.206 0.065 1.200 0.059 1.203 0.053 1.198 0.048 1.414 0.072 1.407 0.066 1.403 0.059 1.403 0.053 1.602 0.078 1.609 0.072 1.599 0.064 1.603 0.058 1.804 0.083 1.803 0.077 1.833 0.070 1.825 0.064 2.038 0.090 1.995 0.082 2.005 0.074 2.001 0.068 2.230 0.094 2.198 0.087 2.236 0.080 2.199 0.072 2.394 0.098 2.416 0.091 2.403 0.083 2.402 0.075

Appendix B

190

Table B.3 Experimental uptake data for adsorption of methane onto

Chemviron

Pressure

(MPa)

Uptake

(kg/kg)

Pressure (MPa)

Uptake (kg/kg)

Pressure (MPa)

Uptake (kg/kg)

Pressure (MPa)

Uptake (kg/kg)

Temperature = 5 ºC Temperature=15 ºC Temperature=25 ºC Temperature=35 ºC

0.048 0.017 0.059 0.016 0.052 0.012 0.066 0.011 0.146 0.033 0.148 0.028 0.152 0.024 0.169 0.022 0.268 0.045 0.262 0.039 0.272 0.035 0.290 0.031 0.390 0.054 0.382 0.048 0.391 0.042 0.394 0.037 0.516 0.061 0.494 0.054 0.530 0.049 0.514 0.043 0.672 0.068 0.641 0.060 0.691 0.056 0.680 0.050 0.826 0.073 0.800 0.066 0.851 0.061 0.859 0.055 0.987 0.078 0.953 0.070 0.996 0.065 0.977 0.059 1.184 0.083 1.189 0.076 1.180 0.069 1.182 0.063 1.386 0.087 1.405 0.080 1.393 0.073 1.356 0.068 1.607 0.089 1.678 0.084 1.572 0.077 1.600 0.072 1.795 0.092 1.886 0.087 1.780 0.079 1.831 0.074 2.035 0.094 2.103 0.089 1.976 0.082 2.052 0.078 2.269 0.094 2.333 0.091 2.164 0.084 2.272 0.081 2.535 0.095 2.552 0.092 2.361 0.085 2.548 0.084

Temperature =45 ºC Temperature=55 ºC Temperature=65 ºC Temperature=75 ºC

0.060 0.009 0.069 0.008 0.064 0.006 0.072 0.006 0.157 0.018 0.178 0.017 0.177 0.015 0.180 0.013 0.292 0.028 0.264 0.022 0.288 0.021 0.285 0.018 0.413 0.034 0.394 0.029 0.388 0.025 0.385 0.022 0.527 0.039 0.503 0.033 0.508 0.030 0.504 0.027 0.684 0.045 0.664 0.042 0.668 0.035 0.632 0.031 0.875 0.051 0.836 0.047 0.814 0.039 0.775 0.037 1.066 0.056 0.998 0.051 0.998 0.043 0.950 0.041 1.276 0.060 1.230 0.055 1.227 0.049 1.193 0.046 1.462 0.063 1.438 0.058 1.565 0.055 1.410 0.050 1.705 0.067 1.688 0.063 1.857 0.060 1.647 0.053 1.925 0.071 1.906 0.066 2.136 0.063 1.882 0.057 2.141 0.073 2.127 0.068 2.399 0.066 2.132 0.060 2.374 0.075 2.343 0.071 2.614 0.068 2.356 0.062

Appendix C

191

Appendix C Drawings and Dimensions of the Cryostat

The detail drawings and dimensions of the cryostat, which was built to maintain constant low temperature of the adsorption cell, are given below

Flange: ISO NW16KF

130φ 

All dimensions are in mm

Appendix C

192

Appendix D

193

Appendix D Drawings and Dimensions of the Storage

Cylinder and AC Bed Heat Exchanger

All dimensions are in mm Design Pressure 40 bar.g Design Temperature 90 °C

Figure D.1 Drawings and dimensions of the Storage Cylinder

Appendix D

194

y

z x

Figure D.2 Drawings and dimensions of the AC Bed Heat Exchanger

Appendix E

195

Appendix E Details of Leak Test of the Storage

Cylinder and AC Bed Heat Exchanger

The below is the Pressure Test Certificate provided by the manufacturer for the

Storage Cylinder and the AC Bed Heat Exchanger

Appendix E

196

The storage cylinder was tested in our laboratory for pressure keeping the heat

exchanger inside the cylinder before activated carbon was packed After the end covers

bolted with the flanges, the cylinder was filled with water and pressurized up to 40 bar

using the hydraulic pump A slight pressure drop was observed after long hours which

could be due to the room temperature fluctuations and also because of the sieving

effect of water through the asbestos gaskets Figure E.1 shows the pressure test

arrangement for the storage cylinder

Figure E.1 Pressure test arrangement for the Storage Cylinder

Figure E.2 Pressure test arrangement for the AC Bed Heat Exchanger

Appendix E

197

Similarly, the AC bed heat exchanger was also tested for pressure in the

laboratory after the activated carbon was packed The heat exchanger was internally

pressurized up to 6 bar using the hydraulic pump and no pressure drop was observed

for more than 12 hours Figure E.2 shows the pressure test arrangement for the AC bed

heat exchanger

To determine the leak rate, the storage cylinder assembly was pressurized with

pure helium gas with the AC bed heat exchanger inside the cylinder The pressure

readings were recorded with time and the pressure versus time plot is shown in Figure

E.3 which shows a slight pressure drop of about 0.1 bar in 16 hours Since the charge

and discharge processes are continued only for three hours, this leaking rate is

considered negligible However, it is taken into consideration in the simulation of the

cyclic processes for the ANG storage system

Figure E.3 Leak test report of the Storage Cylinder charged with pure helium