22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Evaluation of operating conditions for syngas formation in a cogeneration
system with arc plasma gasifier of coal and biomass waste
A.A. Halinouski1, A.V. Gorbunov1, G. Petraconi Filho1, A.M. Essiptchouk1, A.R. Marquesi1 and H.S. Maciel2
1
2
Technological Institute of Aeronautics (ITA), São José dos Campos, SP, Brazil
Institute for Research and Development – IP&D/UNIVAP, São José dos Campos, SP, Brazil
Abstract: Production of syngas by reaction of coal and bagasse with air and steam was
studied in plasma reactor. Application of obtaining syngas for combined heat and power
production was investigated. Energy balance of the process was analysed.
Keywords: plasma gasification, energy balance, syngas, coal, biomass
1. Introduction
Thermal plasma gasification technologies are last two
decades in the commercialization stage for such feedstock
class, as industrial wastes, MSW, ash residues, and also
for such promising large group, as low grade coals [1-2]
and biomass [3], that can be used to produce a high
calorific syngas (high heating value HHV ≥ 10-15 MJ/kg)
at low operating cost. Plasma gasification process of
syngas production consists of the following steps:
feedstock pre-treatment (drying, milling), gasification in
plasma reactor, cleaning and cooling of syngas (Fig. 1).
grades of coal belong mainly to subbituminous class. As a
result of our comparative analysis the coal of Recreio
mines (Rio Grande do Sul (RS)) [4] was used for our next
assessment because of most typical composition, which is
near to others large scale commercial coals of Santa
Catarina and RS states. This variant of low cost coal have
the HHV (dry base, db) = 22.46 MJ/kg [4]). As a second
kind of feedstock for our study such industrial scale
biomass waste was chosen as sugar cane bagasse with the
composition CH 1.61 O 0.7 and HHV (db) = 18.88 MJ/kg [5].
The initial chemical composition for the bagasse is the
same as from typical biofuels producing facilities as well
as from commercial sugar mills [5]. The elemental
composition of both type of the feedstock is presented in
Table 1
Table 1. The composition of the feedstock
Fig.1. Principal schematic process of syngas producing
based on the thermal plasma gasification.
The objective of our research is the assessment and
comparison of this process potential for the competitive
variants of these low grade coal and biomass wastes (for
the example of Brazilian industry origin these) based on
detailed parametric analysis of the plasma gasification
with using thermodynamic and chemical kinetic
simulation methods.
Herewith as one of the most interesting and industrially
prospective cases for the parametrical analysis can be
investigated such variant of biomass waste feedstock as
sugar cane bagasse.
2. Composition of feedstock used for the modelling
There are a few reports with chemical analysis in some
details for Brazilian industrial coals. Brazilian industrial
P-III-9-14
Coal, wt. %.
Bagasse, wt. %.
Moisture
12.59
25
C
56.2
46.85
H
3.61
6.29
O
10.77
43.72
N
1.01
-
S
0.57
-
Ash
27.8
3.2
LHV(db) (MJ/kg)
21.67
17.5
3. Thermodynamic modeling and parametric analysis
for the gasification process at the conditions of
different plasma oxidants
The series of thermodynamic calculations had allowed
to fulfill the parametrical analysis of steam plasma
gasification in a comparison with air assisted one. As a
result of calculations the comparison effects of the
temperature, pressure and ratio of flow rates of gasifying
agent to feedstock on syngas composition as well as on
gasification efficiency parameters (gasification degree of
organic part of feedstock (GD), low heating value of
syngas (LHV sg , as well as energy and exergy efficiencies
of gasifier (i.e. 1st and 2nd thermodynamic law
efficiencies) were determined. The energy efficiency
1
relates the low heating value LHV sg of gas produced from
1 kg of feedstock m sg , with the low heating value of
feedstock LHV f and the necessary power of plasma torch
to maintain the reactions P pl :
EnE =
msg LHVsg
6.3 % CO 2 , 6.7 % H 2 O and 2.5 % CH 4 at the temperature
1250K. This calculated composition is near to the
experimental data for steam-nitrogen plasma gasification
of low grade coal feedstock (Russian lignite [2]): 51.1
vol. % H 2 , 34.1 % CO and 14.8 % N 2 .
(1)
LHVf + Ppl
Then the electric energy efficiency EnE cc of
cogeneration system was established based on the
simplified model of F. Rutberg et al. [6] for this system
with plasma gasifier and gas turbine:
EnE cc = η cc EnE
(2)
where η cc is the efficiency of combined cycle (≈ 0.63 for
the composition of syngas under consideration in this
study).
Additionally such useful parameter as electric energy
yield EY was calculated for this system with plasma
gasifier and gas turbine using the simple expression which
takes into account that part of the generated electricity is
used for gasification of feedstock:
EY =
EnE el ( LHV f + Ppl ) − Ppl htorch
LHV f
,
(3)
where η torch is the averaged thermal efficiency of the torch
(≈ 0.9 for transferred arc torches). This energy yield
coefficient describes which part of chemical energy of the
feedstock will be available in form of net electric energy.
To calculate P pl value the thermodynamically obtained
data were used for the difference of total enthalpy of
reactive mixture (i.e. converted to syngas initial feedstock
and gasifying agent) at varied gasification temperature
and similar enthalpy of this mixture at the constant initial
temperature (300 K). For calculation of initial enthalpy
the modified for the coal and bagasse procedure [7] with
taking into account the summarized values of the heat of
formation of reagents was used.
4. Results
Through preliminary thermodynamic calculating the
optimum regimes (regimes with higher value of EnE) of
the gasification were established: a) for the case with air
plasma – ER (equivalence ratio) = 0.1 for the biomass
feedstock and ER = 0.4 for the coal feedstock; b) for the
case with steam plasma – optimal SBR = 0.2 and optimal
SCR = 0.5.)
As the example in Fig.2 the calculated optimal syngas
composition is presented, which can be produced (on the
thermodynamic estimation with TERRA code) especially
under the steam plasma gasification of low grade and low
cost Brazilian coal and related feedstock. This mixture
contains as main components 50.7 vol. % H 2 , 33.2 % CO,
2
Fig. 2. Chemical composition of syngas and main
mineral products vs. temperature for the optimal
thermodynamic conditions of thermal plasma steam
gasifier with coal feedstock at the reagents ratio SCR =
0.55
Pressure P = 0.1 MPa.
Then the electric energy efficiency EnE cc of
cogeneration system and electric energy yield EY for
optimal regimes of gasification were established (Table
2).
Table 2. The main characteristics of the gasification
process of various type of feedstock.
Feedstock
Coal
Bagasse
Plasma gas
air
steam
air
steam
EnE
0.79
0.81
0.83
0.87
EnE cc
0.49
0.51
0.52
0.54
EY
0.41
0.17
0.33
0.33
Additionally the kinetic calculation for the estimation of
optimal conditions of the gasification process was carried
out, based on the two main stages of the process:
pyrolysis (i.e. devolatilization) of the initial coal or
biomass feedstock and following oxidation (i.e.
gasification of char residue, primary syngas and tars
products formed during the pyrolysis) stage. It was shown
that the heterogeneous oxidation reactions of the residual
char are critical for total rate of the gasification process
with steam or other oxidants (air, CO 2 ) under the
conditions of plasma gasifiers at such temperature range
as 1000–1600 K and operating pressure 0.1 MPa.
Figure 3 demonstrates energy balance of the process of
the air- and steam-plasma gasification of the analyzed
feedstock in a modern system for producing electricity
(without taking into account the heat losses under
assumption of thermodynamic equilibrium at 1250 K).
P-III-9-14
22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
a
Net energy = 7.82 MJ kg-1
b
Net energy = 3.31 MJ kg-1
c
Net energy = 4.29 MJ kg-1
d
Net energy = 5.73 MJ kg-1
Fig. 3. Comparison of energy balances of the electric and heat energy generation from coal in the case of use of the air
plasma (a) and steam plasma (b); from biomass (bagasse) in the case of using the air plasma (c) and steam plasma (d).
5. Conclusions
1. Thermodynamic equilibrium modeling and
parametric analysis based on thermochemical approach
was performed for the gasification process with coal and
biomass waste feedstock at the conditions of different
plasma oxidants at the variation of other operating
parameters. As a result, it was found that the maximum
level of energy (cold gas) efficiency in the case of using
steam is near 90%, while for the case of air equal to 85%.
2. The electric energy efficiency EnE cc of the combined
cycle, which have estimated in our study based on the
simplified model of cogeneration system with plasma
gasifier and gas turbine, was established to be: a) for the
case with air plasma - with biomass feedstock is 0.52 and
with coal feedstock is 0.49; b) for the case with steam
plasma - with biomass – 0.54 (at zero moisture content of
the bagasse) and with coal - 0.51.
3. The kinetic estimation for the analyzed gasification
process was shown that the heterogeneous oxidation
reactions of the residual char are critical for total rate of
the gasification process with steam or other oxidants
under the conditions of plasma gasifiers at such
temperature range as 1000–1600 K and ambient pressure.
[3] M. Hrabovsky, M. Konrad, V. Kopecky, et al.
Gasification of biomass in water/gas–stabilized plasma
for syngas production. Czechoslovak Journal of Physics,
V. 56 (2006), 2, pp. B1199-B1206.
[4] W. Kalkreuth, A. Borrego, “Exploring the possibilities
of using Brazilian subbituminous coals for blast furnace
pulverized fuel injection,” Fuel, V. 84, pp. 763-772, Apr.
2005.
[5] L. F. Pellegrini, and S. de Oliveira Jr. “Exergy
analysis of sugarcane bagasse gasification”. Energy, vol.
32, pp. 314–327, 2007.
[6] Ph.G. Rutberg, A.N. Bratsev, V.A. Kuznetsov, V.E.
Popov, A.A. Ufimtsev, S.V. Shtengel’, “On efficiency of
plasma gasification of wood residues”, Biomass and
Bioenergy, Vol. 35, Issue 1, 2011, pp. 495-504.
[7] R. K. Balan, “Thermodynamical analysis of flame
treatment of municipal solid wastes”. PhD Thesis (in
Russian), Issyk–Kul’ State University, Karakol,
Kyrgyzstan, pp.150, 2010.
6. Acknowledgement
This work was supported by CAPES and FAPESP
foundations of Brazil.
7. References
[1] I. B. Matveev, S.I. Serbin. “New approaches to the
partial and complete plasma coal gasification,” in Proc.
6th Int. Workshop and Exhib. on Plasma Ass. Comb.,
Heilbronn, 2010, pp. 38–40.
[2] M. Gorokhovski, E. I. Karpenko, F. C. Lockwood, et
al. “Plasma technologies for solid fuels: Experiment and
theory,” J. Energy Inst., vol. 78, no. 4, pp. 157–171, Dec.
2005.
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