35 Exergy and Environmental Analysis of a Bio-Hydrogen Supply …
533
35.3.2 Hydrogen Production from Sewage Sludge
The authors investigated the inventory data and exergy efficiency using Aspen Plus
(Aspen plus Ver 9.1). In this model, the sewage sludge is converted into hydrogen
immediately next to a household (on-site) using two-step PSA. Thus, it is expected
that this system can mitigate environmental impacts because of the lack of transportation of feedstock and hydrogen. The whole system involves three processes:
production, reforming, and two-step PSA. Inventory data with a functional unit 1.00
Nm
3 -hydrogen was investigated. Thus, we used this data assuming a linear relationship between the hydrogen amount and other inventory data. Because it is reported
that CO 2 emitted from hydrogen purification using two-step PSA can be recovered
due to its use in agriculture, CO 2 recovery was considered in this study (Kondo et al.
2018). However, the amount of CO 2 recovered from this process is smaller than
that recovered from the woody biomass process according to our simulation results
(5.47 kg-CO 2 /kg-H 2 ).
35.3.3 Hydrogen Storage Using Hydrogen Compression
Here, the inventory data and exergy efficiency of hydrogen compression or expansion
were calculated. After hydrogen production using two-step PSA, the hydrogen was
at 0.4000 MPa (Kondo et al. 2018). Thus, hydrogen needed to be compressed or
expanded for transportation or storage in each type of mobility. In the hydrogen
paths including hydrogen production from woody biomass, the transportation from
the plant to a hydrogen refueling station was included. The distance from the plant
to the hydrogen refueling station was assumed to be 27.50 km, which is the same
distance as that required for woody biomass transportation (Kondo et al. 2018).
Before hydrogen transportation from a woody biomass plant, hydrogen was
compressed from 0.4000 MPa to 20.00 MPa; after transportation, hydrogen was
compressed or expanded to the filling pressure for each type of mobility (Car:
70.00 MPa, bicycle: 3.00 MPa, Forklift: 35.00 MPa) (TOYOTA, “The MIRAI
Life Cycle Assessment for communication”Available: http://www.gronabilister.se/
toyota-mirai-lca.pdf?cms_fileid=9b81589a2a7ae33e34936c3de80b4c51; “Fuel cell
forklift catalog” 2010) (Kovaˇ c and Paranos 2019). Also, it was assumed that hydrogen
is cooled or warmed before transportation (298.15 K) and use for a type of mobility
(233.15 K) (Technova Co., Ltd. 2019). On the other hand, in the case of hydrogen
paths with sewage sludge hydrogen production, hydrogen was directly compressed
from 0.4000 MPa to the filling pressure for each type of mobility because hydrogen
was produced on-site.
533
35.3.2 Hydrogen Production from Sewage Sludge
The authors investigated the inventory data and exergy efficiency using Aspen Plus
(Aspen plus Ver 9.1). In this model, the sewage sludge is converted into hydrogen
immediately next to a household (on-site) using two-step PSA. Thus, it is expected
that this system can mitigate environmental impacts because of the lack of transportation of feedstock and hydrogen. The whole system involves three processes:
production, reforming, and two-step PSA. Inventory data with a functional unit 1.00
Nm
3 -hydrogen was investigated. Thus, we used this data assuming a linear relationship between the hydrogen amount and other inventory data. Because it is reported
that CO 2 emitted from hydrogen purification using two-step PSA can be recovered
due to its use in agriculture, CO 2 recovery was considered in this study (Kondo et al.
2018). However, the amount of CO 2 recovered from this process is smaller than
that recovered from the woody biomass process according to our simulation results
(5.47 kg-CO 2 /kg-H 2 ).
35.3.3 Hydrogen Storage Using Hydrogen Compression
Here, the inventory data and exergy efficiency of hydrogen compression or expansion
were calculated. After hydrogen production using two-step PSA, the hydrogen was
at 0.4000 MPa (Kondo et al. 2018). Thus, hydrogen needed to be compressed or
expanded for transportation or storage in each type of mobility. In the hydrogen
paths including hydrogen production from woody biomass, the transportation from
the plant to a hydrogen refueling station was included. The distance from the plant
to the hydrogen refueling station was assumed to be 27.50 km, which is the same
distance as that required for woody biomass transportation (Kondo et al. 2018).
Before hydrogen transportation from a woody biomass plant, hydrogen was
compressed from 0.4000 MPa to 20.00 MPa; after transportation, hydrogen was
compressed or expanded to the filling pressure for each type of mobility (Car:
70.00 MPa, bicycle: 3.00 MPa, Forklift: 35.00 MPa) (TOYOTA, “The MIRAI
Life Cycle Assessment for communication”Available: http://www.gronabilister.se/
toyota-mirai-lca.pdf?cms_fileid=9b81589a2a7ae33e34936c3de80b4c51; “Fuel cell
forklift catalog” 2010) (Kovaˇ c and Paranos 2019). Also, it was assumed that hydrogen
is cooled or warmed before transportation (298.15 K) and use for a type of mobility
(233.15 K) (Technova Co., Ltd. 2019). On the other hand, in the case of hydrogen
paths with sewage sludge hydrogen production, hydrogen was directly compressed
from 0.4000 MPa to the filling pressure for each type of mobility because hydrogen
was produced on-site.