facility. However, different from the nearshore facilities, where the
costs on biomass transportation from the sea to the onshore processing facility are known (~30% of the macroalgae costs [47]), the
real monetary transportation costs from the open ocean offshore
biorefineries can be only estimated. A more realistic approach is to
estimate the energy expenses required for transportation that will
limit the distance of an offshore cultivation site from the processing
facility.
The maximum economic distance from the processing facility
of an offshore cultivation area is calculated using Eq. 28:
D t ¼
ε
P n
p¼1 E p
2E t
ð28Þ
where D t (km) is the maximum economic transportation distance,
and ε is the ratio of the energy embedded in the final products that
can be used for transportation of the feedstock to keep the process
economically viable. Here, we assume that the transportation vessel
makes only one direction with cargo and is empty on its way back.
To exemplify the estimation of transportation energy constraints of the offshore cultivation, following Ref. [48], we assumed
that the transportation will be done with Aframax ship tanker.
The tanker capacity is 100,000 tons and the average fuel consumption (between full and empty cargo) is 25.4 gal km
À1
(4019.55 MJ km
À1 ) of heavy ship oil. Previous extensive studies
in the bioethanol industry showed that for profitability and positive
net energy balance, the energetic cost of transportation should be
at ~1.8% of the total energy embedded in the final products,
distributed equally between biomass transportation and final products distribution [49]. Therefore, we constrained the total energy
expenditures (ε) on transportation on 0.9% of the energy embedded in the potential products of the transported macroalgae biomass. The recent work on offshore cultivation analysis of Ulva
species showed that the D t of the farm varies from 115 to
690 km, depending on the moisture content of the macroalgae
during transportation.
5 Environmental Risks and Sustainability
Large-scale macroalgae cultivation can be responsible for positive
and negative impact on coastal and marine ecosystems [50]. Therefore, the balance is necessary to attain in between food, chemicals,
and fuel production and its environmental cost [51]. Although
scale-up reduces production costs of macroalgae, the offshore cultivation is challenging because of the harsh environment and also
could possess risks to the environment. Risk management framework should be developed for each individual case to address these
factors.
Design and Analysis of Offshore Macroalgae Biorefineries
21
costs on biomass transportation from the sea to the onshore processing facility are known (~30% of the macroalgae costs [47]), the
real monetary transportation costs from the open ocean offshore
biorefineries can be only estimated. A more realistic approach is to
estimate the energy expenses required for transportation that will
limit the distance of an offshore cultivation site from the processing
facility.
The maximum economic distance from the processing facility
of an offshore cultivation area is calculated using Eq. 28:
D t ¼
ε
P n
p¼1 E p
2E t
ð28Þ
where D t (km) is the maximum economic transportation distance,
and ε is the ratio of the energy embedded in the final products that
can be used for transportation of the feedstock to keep the process
economically viable. Here, we assume that the transportation vessel
makes only one direction with cargo and is empty on its way back.
To exemplify the estimation of transportation energy constraints of the offshore cultivation, following Ref. [48], we assumed
that the transportation will be done with Aframax ship tanker.
The tanker capacity is 100,000 tons and the average fuel consumption (between full and empty cargo) is 25.4 gal km
À1
(4019.55 MJ km
À1 ) of heavy ship oil. Previous extensive studies
in the bioethanol industry showed that for profitability and positive
net energy balance, the energetic cost of transportation should be
at ~1.8% of the total energy embedded in the final products,
distributed equally between biomass transportation and final products distribution [49]. Therefore, we constrained the total energy
expenditures (ε) on transportation on 0.9% of the energy embedded in the potential products of the transported macroalgae biomass. The recent work on offshore cultivation analysis of Ulva
species showed that the D t of the farm varies from 115 to
690 km, depending on the moisture content of the macroalgae
during transportation.
5 Environmental Risks and Sustainability
Large-scale macroalgae cultivation can be responsible for positive
and negative impact on coastal and marine ecosystems [50]. Therefore, the balance is necessary to attain in between food, chemicals,
and fuel production and its environmental cost [51]. Although
scale-up reduces production costs of macroalgae, the offshore cultivation is challenging because of the harsh environment and also
could possess risks to the environment. Risk management framework should be developed for each individual case to address these
factors.
Design and Analysis of Offshore Macroalgae Biorefineries
21