Page 48 - Industrial Plant 2015

3.2 Post-combustion processes
Post combustion technologies foresee the CO2 capture
downstream the combustion section. In this case,
carbon dioxide is contained in the flue gases from the
steam reforming furnace together with other products
and inerts from combustion.
As indicated in table 1, the CO2 present in the steam
reformer flue gas has a very low partial pressure (about
0.2 bara) and the flue gas actual volumetric flow is 20
times or more the raw syngas volumetric flow (m3/h).
These two factors and the presence in the flue gas of
components like oxygen, sulphur, NOx, dust, makes
the CO2 removal from this stream generally more
complicated and expensive. Nevertheless its quantity
is very high (table 1) and its capture is being considered
an environmental and economical challenge.
Main technologies include:
• amines (MEA, MDEA, “hindered” amines);
• chilled ammonia;
• membranes.
The basic principles of CO2 removal from flue gas are
the same as from raw hydrogen, but the experience is
so far limited. The environmental concern related to the
GHG emissions is determining a growing interest for
this application in many industries, for example in the
power sector.
In practical terms a CO2 removal of 85 - 90% is an
acceptable target, and the CO2 is also in this case
obtained at high purity and low pressure.
No pre-investment is needed in case of retrofit of a
traditional plant, however additional ducting and ID fan
addition/replacement shall be considered when the
unit is added to the SMR plant.
Licensors active in these technologies are: Axens,
Fluor, GTC, MHI, MTR etc.
4. Case study
In this section the economic impact of adding a CO2
removal unit to a SMR based hydrogen plant is
analysed.
The conclusions below reported are taken from the
preliminary results of the study (under development)
prepared by Amec Foster Wheeler Italiana for IEA GHG
Techno-economic Evaluation of H2 Production with
CO2 capture.
In the mentioned study, pre-combustion and post-
combustion CO2 removal options are considered. Both
technologies are amine based and the results have
been gathered using in-house simulations and available
technical documentation. Different technical solutions
may of course lead to different results, especially
considering the different level of maturity of the
technologies involved.
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The selected hydrogen production is 100,000 Nm3/h
(from natural gas). For the economic and technical
evaluations, the units considered in the study include:
• SMR hydrogen plant;
• CO2 removal plant (if present);
• cogen plant.
The cogen plant produces the electricity and LP steam
required to fulfil the hydrogen unit and CO2 removal
system requirements.
The CO2 removal efficiency from raw H2 and from flue
gas is considered 100% (rounded off) and 90%,
respectively. The pure CO2 stream is then compressed
to 110 bara for sequestration, EOR or other utilisation
(out of the scope of the study).
The economics of the alternatives are evaluated
through the “abatement cost” concept.
Abatement cost (AC) is defined as the incremental cost
of a low-emission technology compared to the
reference case, measured as € per ton CO2 abated
emission (ICCA, 2009):
A_C_=__(F_u_ll_c_os_t_o_f _C_O_2 e_f_fic_ie_n_t _al_te_rn_a_tiv_e_) _-_(F_u_ll_c_os_t_o_f _re_fe_r_en_c_e_s_ol_ut_io_n)
(CO2 emissions from reference solution) – (CO2 emissions from alternative)
The full cost of the alternatives includes investment
cost (calculated over 25 years at 8% discount rate),
operating costs and possible cost (energy) savings
generated by the use of the alternatives. Other
economic data:
• natural gas price = 16.8 - 50.4 €/GJ
• electric power price = 70 €/MWh
The results are summarized in table 3.
The two AC values per each CO2 capture case refer
respectively to the low and high values assumed for the
natural gas.
The “abatement cost” so calculated, compared with
the EU-ETS (European Trading System) carbon trading
price is an indicator of the profitability of the initiative.
This allowance is currently very low (ranging 5-10 €/ton
CO2) therefore providing the industry with little incentive
to invest in low-polluting technologies.
In order to encourage companies in investing in low
emissions technologies it is necessary to strengthen
the EU-ETS, thus making carbon capture systems
integration more attractive options to consider.
5. Conclusions
The analyses performed in this study lead to the
following conclusions:
• CO2 emissions from SR hydrogen plants are
significant and have the potential to impact the
economics of hydrogen production;