Daniel Mahon Thermochemical heat storage MgSO 4 .7H 2 O Potential of - - PowerPoint PPT Presentation

Daniel Mahon Thermochemical heat storage

MgSO4.7H2O

Potential of MgSO4.7H2O High energy density –2.8GJ/m3 (778kWh/m3) [1] Relatively cheap - ~£61/1000kg [2] Sensible heat losses only 10% heat loss [1] Stores heat indefinitely Non-Toxic or Corrosive Problems with MgSO4.7H2O Cycle stability Vapour transportation / Slow hydration Rehydration conditions

MgSO4 SEM + EDX

Before any dehydration “large particles” After 1˚C/min dehydration After 10˚C/min dehydration 1˚C/min sample after rehydration

(Average particle size = 2.4µm)

MgSO4 Thermal analysis TGA

TGA cycle stability results for 1˚C/min heating rate TGA cycle stability results for 10˚C/min heating rate

MgSO4 Thermal analysis DSC

DSC cycle stability data for MgSO4 with a heating rate of 1˚C/min DSC cycle stability data for MgSO4 with a heating rate of 10˚C/min

MgSO4 Thermal analysis RGA

DSC & RGA Overlay showing unusual endothermic peaks RGA data for MgSO4 different heating rates

MgSO4 Heat rate effects (Enthalpy)

Heating Rate (℃/min) 1 5 10 Enthalpy (normalized) (J/g) (cycle 1) 1429.4 1382.1 1347.3 Enthalpy (normalized) (J/g) (cycle 2) 1268.1 1284.4 1340.3 Enthalpy (normalized) (J/g) (cycle 3) 1315.8 1244.9 1094.2 Enthalpy (normalized) (J/g) (cycle 4) 1303.7 1053.5 1275.8 Enthalpy (normalized) (J/g) (cycle 5) 1279.6 1216.4 1218.0 Enthalpy (normalized) (J/g) (cycle 6) 1413.3 1564.3 1446.3 Enthalpy (normalized) (J/g )(cycle 7) 1296.3 1217.9 1208.2 Heating Rate (℃/min) Max Temperature (℃) Enthalpy (normalized) (J/g) Average Enthalpy (J/g) Peak Temperature (℃) 1 110 1230.6 1284 87.045 5 110 1330.1 100.389 10 110 1291.5 101.764 1 150 1429.4 1386 87.323 5 150 1382.1 100.190 10 150 1347.3 114.412

Data for various heating rates and maximum dehydration temperature Data showing dehydration cycle stability with different heating rates

Zeolite Cycle stability

(Zeolite-Y ammonium SiO2.Al2O3 925 m2g)

Cycle stability of Zeolite Heating rates minimal effect on material Lack of “slow kinetics” 752J/g = Average dehydration enthalpy

• Creation of composite materials with different wt%

– for increased vapour transportation – Decreased hydration time – Higher peak temperature output

Composite analysis (Zeolite + MgSO4)

Composite analysis (Zeolite + MgSO4)

Sample No. Run No. Wt% Predicted Enthalpy J/g Experimental Enthalpy J/g Average Enthalpy J/g % difference Experimental/Predict ed Peak Temp (˚C) 1 1 35 943.8 1126.2 1126.2 19.3% 76.19 2 1 30 1026.2 72.58 3 1 30 916.4 1067.1 1046.65 14.2% 73.40 4 1 25 960.99 88.70 5 1 25 889.00 988.64 974.81 9.65% 89.18 6 1 20 918.88 86.17 7 1 20 861.60 905.16 912.02 5.86% 87.40 8 1 15 826.86 85.02 9 1 15 834.20 862.52 844.69 1.26% 85.20 200 400 600 800 1000 1200 15 wt% 20 wt% 25 wt% 30 wt% 35 wt%

Dehydration Enthalpy of composite Samples

Run 1 Run 2 Predicted

Dehydration data for several Zeolite + MgSO4 composites No sign of pore blocking

Conclusion

• MgSO4

– Good cycle stability – Little effect from high heating rates – Potential to use lower dehydration temperature

• Zeolite (Y ammonium SiO2.Al2O3 925 m2g)

– Lack of slow kinetics – Relatively large heat storage potential – Good cycle stability

• Composite materials

– Higher than expected enthalpy – No degradation from pore blocking observed

Industrial Absorbent Analysis

Minimal mass loss below 150˚C (approx. 7%)

• Low endothermic

peaks

• Low storage

potential (approx. 180J/g)

Composite analysis – Industrial Absorbent

SEM coloured images key Colour Purple Yellow Green Calcium (Ca) Magnesium (Mg) Oxygen (O)

These cube structures may be dolomite CaMg(CO3)2

Layered porous structure