Ammonia as energy carrier of the renewable energy; thermodynamic consideration

Transcription

1 Ammonia as energy carrier of the renewable energy; thermodynamic consideration Ken-ichi AIKA Research Office of Energy carrier, Department of Green Innovation Japan Science and Technology Agency (JST) URL: http// At present ammonia is mostly formed through reforming of natural gas (CH4) ton per day plant is said to consume about 35 GJ of natural gas to produce 1 ton ammonia (22.5 GJ of enthalpy). About 50% of extra energy is wasted. If 1 ton ammonia is produced through water electrolysis, 22.5 GJ of electricity is necessary theoretically. Here again, extra electric energy must be wasted. The author discusses roughly how the efficiency depends upon the process size and the renewable energy cost.

2 Back ground Cost of renewable energy varies over the world. The sun belt area and windy area can supply economic energy. (Example; 3cent/kWh thorough wind at Patagonia) The cost is high at the populated area. (Example; 13cent/kWh through waste woods, 22cent/kWh through wind in Japan) [Thus renewable energy must be stored and transported to industrialized countries such as Japan: Energy carrier project] Renewable energy is turned to H2 then to NH3 (or methyl cyclohexane) and carried to industrial area, and used.

3 MEXT (JST-ALCA Specially important project) Energy carrier: Organization Governing board MEXT METI Academia Private sector Industries NEDO, JST Total system scenario design Program officer (PO) Total manager Senior director Fellow (Technical analysis) Fellow (Patent) NH3 production team High temp energy gathering New IS process NH3 utilization team NH3 decomp & separation NH3 fuel cell Organic hydride team Electrolysis synthesis Hydrogenation/dehydro. Process engineering team H2 purification separation Results Comments METI NEDO Advanced NH3 process NH3 combustion Organic hydride fuel cell Information exchange Basic R&D program 3

4 Image of NH3 production and use Solar heat production Heat collection H 2 O IS H2 production H 2 Heat storage Media Usage N 2 Liq. transfer Energy storage H 2 e H 2 H 2 H2 production e Small scale synthesis Fuel SOFC Kojima, Hiroshima U. modified

5 Importance of sharing the basic concept: NH3 production is divided to 2; inevitable part (thermodynamics) and manageable part (excess energy) A rough and simple estimation (to compete with the present resources) 2000t/d plant:400m$? NH3 sell price: 0.30$/kg, 300$/tNH3? Maintenance free operation, 30years: (300day/y)? Total selling: 9000d*300$/t*2000t/d=5400M$? Plant cost is below 10%: Running cost is exclusively important. Running cost owes energy (material). The energy is divided to two; thermodynamic and excess energy.

6 Thermodynamics of NH3 synthesis Synthesis from CH4, H2O, and air 7/16 CH 4 + 5/8 H 2 O + 1/8 O 2 + 1/2 N 2 7/16 CO kj (0.4 GJ/t-NH3: 1.8% of NH3 combustion) NH3 combustion + 3/4 O 2 1/2 N 2 + 3/2 H 2 O(l) kj 22.5 GJ/t-NH3 About 1.5 times energy (CH4), 34.5 GJ/t-NH3, is used for 1000 t/d plant. Synthesis from H2O electrolysis and air 3/2 H 2 O + 1/2 N 2 + 3/4 O kj (106.3Wh/mol) ½ N 2 + 3/2 H 2 ΔH= kj (2.7 GJ/t-NH3)

7 Comparison of NH3 source, CH4 or Electricity (or IS method) Energy loss 11 GJ How can we control? 22 GJ Electricity Or IS method 22 GJ CH4 NH3 H2O NH3 Modern process Future process (model)

8 Only excess energy part is manageable for NH3 plant (either CH4 process or renewable energy process) Extra heat for H2 production NH3 synthesis Combustion heat of NH3 Process size 7 GJ/tNH3 4 GJ/tNH3 22 GJ/tNH tnh3/d 33 GJ/tNH3 CH4 process is fully developed. This is the target for the renewable energy process at the natural gas production area. Key is energy cost at renewable energy production site.

9 Electric power cost having the same energy of CH4 with 56 cent/kg C tax or CO2 treatment CH4 with 112 cent/kg 6.8 cent/kwh 35GJ/tNH3 plant 3.4 cent/kwh Plant efficiency Renewable energy cost 1000 t plant Present Future

10 Another problem: process size Solar energy density is low. The size of facility is limited. Assumption: manageable cost is related with -0.8 power of process size. Is the smaller process possible?

11 Wind farm Demark; 20x1MW (can be turned to 12 t-nh3 / d) with 25% effectiveness Wind > Electric power > Electrolysis of H2O > H2 > NH3 > Transported

12 Abdavi [Shrms 1] 100MW, Heated liquid media gathers C heat for steam. 60 t-nh3/d (assuming 25% efectiveness)

13 Scale effect NH3 plant (either for CH4 process or renewable energy process) Extra heat = k (process size )-0.8 Extra heat for 22 GJ/tNH3 H2 production NH3 synthesis 7 GJ/tNH3 4 GJ/tNH3 11 GJ/tNH3 Combustion heat of NH3 22 GJ/tNH3 22 GJ/tNH3 Process size 1000 tnh3/d 10 tmh3/d 33 GJ/tNH3 55 GJ/tNH3

14 Extra heat = k (process size )-0.8 Electric hydrolysis case 7 Electric power cost competitive to CH4 source of 112 cent/kg Electric power cost competitive to CH4 source of 56 cent/kg Process size order; weak size effect 3 10 t/day E cost: cent/kwh E cost: cent/kwh E used: 10GJ/tNH3

15 Solar or wind NH3 is economically possible under solar energy cost of 3-7cent/kWh if: The ammonia process (at the renewable energy site where N2 and H2 is separately produced) is developed competitive to the present natural gas process. (Remote area for fertilizer or industrial area as energy storage are already feasible.) More favorable; Renewable energy conversion technology is improved, and the cost get less. Fossil fuel is restricted further.

16 Image of NH3 production and use Solar heat production Heat collection H 2 O IS H2 production H 2 Heat storage Media Usage N 2 Liq. transfer Energy storage H 2 e H 2 H 2 H2 production e Small scale synthesis Fuel SOFC Kojima, Hiroshima U. modified