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RENEWABLES

Detailed block flow diagrams of the Bio- lene that have not been fully removed or now ready for small scale and multipurpo-
SNG production starting from biomass decomposed in the previous steps should se commercial applications.
gasification, biogas upgrading, and power also be reduced down to acceptable le- Stein and Ray (2016) provided a techni-
to gas including the explained sections are vels for the downstream catalytic metha- cal and economical assessment of an
reported in Figure 3 a, b, and c, respec- nation (typically less than 5 ppm vol). industrial scale biomass gasification and
tively. SNG plant, using woody materials as
The first pathway to produce a clean gas feedstock, demonstrating that the inte-
that can be converted into Bio-SNG is the gration between biomass gasification and
biomass gasification. SNG can be pro- VESTA technology VESTA catalytic methanation is feasible for
duced from biomass by using different integration for Bio-SNG both small scale and large scale bio based
plant configurations, which depend on units. The plant configuration chosen was
the selected gasification technology with production selected by Stein and Ray (2016) accor-
an impact on the downstream syngas Today, more than ever, the bio based ding to the following basis. The main input
conditioning and cleaning steps (Dome- sector starting is seeing the interest and data are relevant to the woody material
nichini et al., 2016). Gasification techno- investment of the main European Com- feedstock and the outlet thermal power
logies can be oxygen-blown or air-blown munity states’ members. Considering of produced SNG of approximately 200
and have applications for various wood these current incentives, a number of stu- MWh, which correspond to a product
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and waste based fuels. Feedstock prepa- dies proved that the biomass gasification flowrate of 21,000 Nm /h. The adopted
ration and gasification (e.g., with oxygen followed by a suitable polishing step and biomass gasification technology was the
coming from an Air Separation Unit), tar the clean gas methanation is a viable and Continuously Fluidized Bed, which is pres-
removal, gas cooling and clean-up, and economically attractive solution to produ- surized and oxygen blown. The final clean-
clean syngas methanation are the main ce Bio-SNG. The aim of this Section is to up is based on catalytic reforming for tar
sections involved in the general process prove that biogas upgrading is as feasible removal and physical solvent washing of
scheme proposed in Figure 3 a. Exam- and efficient as the Power to Gas appli- H S, followed by VESTA clean syngas me-
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ples of biomass gasification are reported cation and biomass gasification to gene- thanation and chemical solvent washing
also in Mancuso (2015), Domenichini et al. rate a clean syngas and a subsequent for the CO removal.
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(2016), and Stein and Ray (2016). Bio-SNG that can be integrated into the Considering a middle term forecast for the
existing natural gas networks for transpor- natural gas price of 8-10 $/MMBtu the
Biogas upgrading through tation and heating purposes. biomass gasification plant can be econo-
the VESTA process for Main technologies are available and matu- mically attractive with an incentive in line
re for commercial application for the three
with what currently applies in Northern
“SNG production is proved renewable process schemes in Figures 3 Europe, or alternatively considering a mo-
to be technically feasible a, b, and c. netization for the low level heat integration
Starting from the available data in litera- (e.g., district heating). Biogas upgrading
ture and from previous studies, a techni- and Power to Gas alternatives will allow
Biogas upgrading is the second pathway cal assessment of the VESTA integration the widest use of Bio-SNG to provide an
to produce Bio-SNG that deals with the with biogas upgrading for the Bio-SNG alternative for transport, industrial, and
integrated SNG production from biogas production was performed and the main domestic demands in all the green eco-
and renewable hydrogen (i.e. from elec- results collected. nomies.
trolytic cells). Likewise the first pathway,
the syngas conditioning and cleaning
steps can vary depending upon feed gas Previous studies A case study:
composition. Figure 3b shows the block The paper of Chandel and Williams (2009) Biogas upgrading with
flow diagram of biogas upgrading and identified the conditions under which SNG
SNG production from purified biogas and production is economically viable by focu- VESTA technology
renewable hydrogen, which includes the sing on the process scheme of the coal- The case study presented in this paper
following sections: biogas clean-up (deep to-SNG. The three pathways proposed addresses the biogas upgrading integra-
desulphurisation, dehalogenation, and in this paper have advantages because ted with Wood’s VESTA technology. The
compression), clean syngas methanation, biomass is carbon-neutral, and above all, process scheme that is the core of this
CO removal system, and SNG drying. CO capture would generate null carbon case study is provided in Figure 3b.
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Power to gas applications typically pro- emissions. Likewise any other methana- The syngas coming to the methanation
duce CO rich gases that can be adapt tion process, inlet syngas must be purified section has no specific limitation of un-
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for the Bio-SNG production. Figure 3c before entering the methanation section desirable compounds, since adequate
shows the block flow diagram of this pro- and the purification step is defined accor- treatment can be included in the SNG
cess scheme , which deals with the CO ding the impurities to be removed in the unit scope. The selected plant configura-
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rich gas conversion to Green-SNG by specific application. For instance, one of tion deals with 3 MWh of biogas and 550
using renewable hydrogen and the subse- the issues associated with biomass gasifi- Nm /h of hydrogen as feedstocks and an
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quent drying section. cation is tar formation. Tar can be removed outlet thermal power of produced SNG of
The purification of synthesis gas essen- through specific processes downstream 4.4 MWh. These additional basis relevant
tially consists of acid gas removal (H S, of the gasifier, such as water scrubbing, oil to the integrated scheme have been ap-
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COS, HCN, NH , etc.) which can be obtai- scrubbing, thermal cracking, catalytic cra- plied for the case study:
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ned through either physical or chemical cking (Domenichini et al., 2012). All the re- • Renewable hydrogen generation in-
absorption. Additionally, residual compo- quired technologies for the polishing steps volves electrolyzes
nents like benzene, toluene or naphtha- and the subsequent methanation are by • Final clean-up is mainly based on ei-
28 Impiantistica Italiana - Novembre-Dicembre 2018