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Coupled biomass (lignin) gasification and iron ore reduction: A novel approach for biomass conversion and application
Accepted Manuscript Coupled biomass (lignin) gasification and iron ore reduction: a novel approach for biomass conversion and application
Rufei Wei, Shanghuan Feng, Hongming Long, Jiaxin Li, Zhongshun Yuan, Daqiang Cang, Chunbao (Charles) Xu PII:
S0360-5442(17)31456-1
DOI:
10.1016/j.energy.2017.08.080
Reference:
EGY 11449
To appear in:
Energy
Received Date:
21 January 2017
Revised Date:
31 May 2017
Accepted Date:
16 August 2017
Please cite this article as: Rufei Wei, Shanghuan Feng, Hongming Long, Jiaxin Li, Zhongshun Yuan, Daqiang Cang, Chunbao (Charles) Xu, Coupled biomass (lignin) gasification and iron ore reduction: a novel approach for biomass conversion and application, Energy (2017), doi: 10.1016/j. energy.2017.08.080
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ACCEPTED MANUSCRIPT
Coupled biomass gasification and iron ore reduction (CBGIOR) process
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Coupled biomass (lignin) gasification and iron ore reduction: a novel
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approach for biomass conversion and application
3 4 5 6
Rufei Weia, Shanghuan Fengb, Hongming Longa*, Jiaxin Lia, Zhongshun Yuanb, Daqiang Cangc,
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Chunbao (Charles) Xua,b*
8 9
a
School of Metallurgical Engineering, Anhui University of Technology, Ma’anshan, Anhui 243002,
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China;
11
b
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Biochemical Engineering, Western University, Ontario N6GA5B9, Canada;
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c
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Beijing 100083, China.
Institute for Chemicals and Fuels from Alternative Resources (ICFAR), Department of Chemical and
School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing,
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Corresponding authors: [email protected] (C. Xu), [email protected] (H. Long)
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Abstract
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Aiming at a novel application of biomass, coupled biomass gasification and iron ore reduction
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was investigated and demonstrated in this work through pyrolysis/gasification of iron ore–lignin
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pellets (ILP) at 1093 ～1333 K. The solid, liquid and gaseous products were analyzed by XRD,
32
SEM, chemical analysis, GC-MS, GC and TG-FTIR. Direct reduction iron (DRI) and gaseous
33
products (CO, H2 and CH4) were produced in the process. The metallization degree of the iron
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ore and CO content of the gaseous products increased with increasing the reaction temperature,
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as expected. The gas yield from the experiments with ILP was much higher than that from the
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tests with lignin pellets (LP) at 1173 ～1333 K, owing mainly to the iron ore reduction
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producing a larger amount of CO. Whereas, the yields of oil and char in the ILP reduction
38
process were found to be much lower than those from the tests with lignin alone, due to the
39
conversion of oil and char products into gaseous products catalyzed by the iron oxide and
40
metallic iron. Thus, in pyrolysis/gasification of ILP the presence of lignin provided reducing
41
agents for reduction of iron oxide, whereas the presence of iron oxide/metallic iron provided an
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oxidant/catalyst for biomass gasification.
43 44
Keywords: Biomass; Lignin; Direct reduction iron; Reduction; Pyrolysis/Gasification; Carbon
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monoxide.
46 47 48 49 50 51 52 53 54 2
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1 Introduction
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Biomass is one of the most important energy sources in near future amongst the renewable
57
energies. Biomass can be converted into various energy and solid, liquid and gaseous fuel
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products via three main processes, i.e., physical conversion, chemical or thermochemical
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conversion, and biochemical conversion[1, 2]. Biomass gasification is an important
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thermochemical conversion process, generating gaseous products (including H2, CO. CO2 and
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CH4, et al.) with a high calorific value. However, there are still some problems in biomass
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gasification, including high tar content in the product, and low calorific value of gaseous
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products, etc. In order to solve these problems, adding catalyst[3], raising temperature[4],
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employing plasma gasification or supercritical water gasification[5, 6] have been proposed.
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Although raising temperature can effectively reduce the tar yield, it results in increased costs.
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However, if biomass gasification is coupled with other applications, such as reduction of metal
67
oxides/ores to produce valuable direct reduction iron (DRI) products, the economics of high-
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temperature gasification of the biomass, would be greatly improved.
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On the other hand, with increased concerns over greenhouse gas emissions and depletion of
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fossil energy, seeking alternative energy sources is an efficacious way to address these problems
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fundamentally for iron and steel industry [7-10]. As a novel application, biomass has
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demonstrated to be an effective reducing agent for iron oxides reduction in ironmaking
73
processes. Raw biomass [10, 11], biomass-derived char [12], syngas [9] and tar [8] can all be
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used as reducing agents. Iron ore - biomass pellets, consisting of biomass powder, iron ore
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powder and a small amount of binder materials, were produced with a pelletizer or briquetting
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press, which represent a new kind of raw materials for ironmaking [9, 13]. Wood sawdust,
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bamboo char, pine sawdust, coconut shell char and rice husk char were ever used in the iron ore-
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biomass pellets [12-14], producing DRI at temperatures of 1000-1300 C. In addition, high
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quality pig iron could also be produced at various temperatures for a short residence time in the
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smelting reduction of magnetite using biomass as a reducing agent [11]. Other metal ores, such
81
as manganese oxide ore, were also reduced at low temperatures by biomass straw as both a 3
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reductant and fuel [13]. However, the previous studies were mainly focused on the quality of
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metallic iron, but ignoring the biomass conversion in the reduction process.
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At present, the gasification agents for biomass gasification are oxygen (air, oxygen-enriched
85
air and pure oxygen)[2], carbon monoxide[6] and water vapor[15]. In fact, iron oxide can also be
86
used as a gasification agent, because it can provide oxygen [16, 17]. Iron ore has been used as an
87
oxygen carrier for chemical looping gasification of biomass char [17]. However, the previous
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studies [7, 11, 13, 18] referring to the mixture of biomass and iron ore were mainly focused on
89
reduction of iron oxide by biomass, while ignoring the biomass gasification by iron oxide. This
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work presents the coupled biomass gasification and iron ore reduction, and investigates the gas
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conversion of lignin and the reduction characteristics of iron ore by biomass in the process with
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iron ore–biomass pellets heated to high temperatures, contributing new knowledge to the
93
utilization of biomass energy.
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2 Materials and methods
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2.1 Materials
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The biomass materials used in the experiments were organosolv lignin, supplied by a
97
company in British Columbia, Canada, and derived from mixture of softwood and hardwood.
98
Iron ore powder was provided by an iron ore plant in Hebei province, China. The chemical
99
compositions of the lignin and iron ore are given in Tables 1 and 2, respectively. Before
100
experiments, these materials were dried in an oven in air at 358 K for 1 h, and then were mixed
101
sufficiently and stored in a desiccator for the planned tests.
102 103
2.2 Experimental and procedure
104
In this work, iron ore–lignin pellets (ILP) were made using a cold press with mixtures of
105
organosolv lignin powder and iron oxide powder under a uniaxial pressure of 20 MPa in a tablet
106
mold (20 mm inner diameter and 50 mm high). In this work, the mass ratio between organosolv 4
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lignin powder and iron oxide powder in ILP was maintained at 1:2 (wt/wt), unless specified
108
otherwise. Lignin pellets (LP) with lignin powder only were also prepared by the same method
109
as that for making ILP. In all tests with either ILP or LP, the amount of lignin used was ensured
110
the same.
111
The pyrolysis/gasification experiments of ILP and LP were carried on the experimental
112
apparatus schematically shown in Fig. 1. An electric furnace, with the maximum working
113
temperature of 1473 K, was used for heating. In a typical experiment, N2 was introduced to the
114
reactor at the rate of 25 mL/min, and the reactor was heated to a preset temperature (1093, 1173,
115
1253 and 1333 K), soaking for 10 min after the preset temperature was reached. In each test, the
116
mass of LP used was 5 g and 10 g for ILP. The sample was put into a basket, and inserted
117
quickly to the reactor center to allow fast heating of the sample. The evolved gases during the
118
sample heating (15 min) were collected into a gas bag through a filter and cold trap. After 15 min
119
of experiment, the furnace was turned off, and the sample was pushed out of the furnace center
120
to the N2 inlet side for cooling. The sample was removed from the reactor after it cooled down to
121
room temperature. After injecting a fixed volume of air into the gas bag as internal standard for
122
gas volume determine, the composition of the gas in the bag was analyzed using a Micro-GC-
123
TCD (Agilent 3000).
124
After the test, the solid residue was taken out of the basket, and the oil product formed by
125
pyrolysis/gasification of the lignin, condensing on the inner wall of the reactor outlet and gas
126
sampling lines, was washed using acetone, and kept for further analysis. To ensure
127
reproducibility of the test results, each test was repeated for three times, and the relative errors
128
for the product yields were controlled to be within 10%. If the relative errors were bigger than
129
10%, one more repetition test would be conducted.
130 131 132
2.3 Products characterization For LP, the yield (Y) of solid, gas and liquid products in mass percentage was defined as: 5
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𝑚𝑠𝑜𝑙𝑖𝑑 𝑟𝑒𝑠𝑖𝑑𝑢𝑒
133
𝑌char =
134
𝑌gas = 𝑚
135
𝑌oil = 100% ‒ 𝑌char ‒ 𝑌gas
𝑚𝑙𝑖𝑔𝑛𝑖𝑛 𝑚𝑔𝑎𝑠 𝑙𝑖𝑔𝑛𝑖𝑛
(1)
× 100%
× 100%
(2) (3)
136
where Ychar, Ygas, and Yoil denote the yield (% wt/wt) of char, gas and crude bio-oil (with water),
137
respectively; msolid resideu, mgas and mlignin denote the dry mass (g) of solid residue, gas and lignin,
138
respectively. The ash content in the lignin is negligibly low (Table 1), so all solid residue can be
139
considered as char. The dry mass (g) of a gas was approximately estimated based on its
140
composition analyzed by micro-GC, using the following the equation while assuming the volume
141
increase of the inlet gas flow during the process was negligible:
142
𝑃
𝑚𝑔𝑎𝑠 = 𝑅𝑇 × 𝐿 × t × 𝑤 × M
(4)
143
Where P, T, L, t, w and M are the experimental pressure, temperature, gas flow, gas collection
144
time, gas composition by micro-GC and molar mass of the gas species. R is the gas constant.
145
Similarly for ILP, the yield (Y) of respective product in mass percentage was defined as: 𝑚𝑠𝑜𝑙𝑖𝑑 𝑟𝑒𝑠𝑖𝑑𝑢𝑒 ‒ (𝑚𝑖𝑟𝑜𝑛 ‒ 𝑜𝑟𝑒 ‒ 𝑚𝑜 ‒ 𝑙𝑜𝑠𝑠)
146
𝑌char =
147
𝑌gas = 𝑚
148
𝑌oil = 100% ‒ 𝑌char ‒ 𝑌gas
𝑚𝑙𝑖𝑔𝑛𝑖𝑛 + 𝑚𝑜 ‒ 𝑙𝑜𝑠𝑠 𝑚𝑔𝑎𝑠 𝑙𝑖𝑔𝑛𝑖𝑛 + 𝑚𝑜 ‒ 𝑙𝑜𝑠𝑠
× 100%
× 100%
(5) (6) (7)
149
where msolid residue, miron-ore and mo-lose denotes the dry mass (g) of solid residue after reduction,
150
iron ore before reaction, and oxygen loss of iron ore in the reduction process, respectively. It
151
shall be noted that the oxygen in gas product is from both lignin and iron ore during the
152
reduction process, and the mass of oxygen loss for iron ore can be calculated in terms of the
153
reduction degree of iron ore.
154
The metallization and reduction degrees of iron ore were determined by chemical analysis
155
in accordance to the ISO 11258 standard following the procedure given in reference [19] and
156
defined as:
157
M=
𝑀𝐹𝑒 𝑇𝐹𝑒
× 100%
(8) 6
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R=𝑀+
𝐹𝑒2 + 3 × 𝑇𝐹𝑒
× 100%
(9)
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where MFe is the mass (g) of metallic iron of the reduced iron ore sample after the experiment,
160
TFe is the total amount (g) of Fe in the reduced sample, and Fe2+ is the mass (g) of Fe2+ in the
161
reduced sample.
162
The residue solid samples obtained from the ILP after reduction was characterized by XRD
163
on a Mac M21X powder diffractometer, and the microstructure characterization of the residue
164
solid samples was done on an EVO18 Special Edition (Carl Zeiss, Germany) Scanning Electron
165
Microscope (SEM) operating at 25 kV. The energy spectra (EDS) for some points in the ILP
166
samples were collected during the SEM analysis to reveal the atomic compositions of the
167
samples.
168
The composition of the obtained crude bio-oil was analyzed by gas chromatography and
169
mass spectrometry (GC-MS) (Agilent Technologies, 5977A MSD with a SHRXI-5MS column:
170
30 m × 250 mm × 0.25μm). Helium was used as the carrier gas and the GC oven temperature
171
program was set as follows: hold at 85C for 2 min, heated to 280 C at a heating rate of 20
172
C/min, then hold for 5 min. The compounds in the crude bio-oil were identified with the NIST
173
library (updated in 2011).
174
Thermogravimetric analysis (TGA) was carried out on a Perkin Elmer (Pyris 1 TGA)
175
instrument coupled with a Fourier Transform Infrared Spectrometer (FT-IR). The lignin or
176
lignin-iron ore mixture (1:2 wt/wt) with particles size＜0.425 mm (20 mesh) was heated at a
177
heating rate of 50 K/min from 293 K to 1373 K under nitrogen atmosphere (20 mL/min). FT-IR
178
was performed online to qualitatively determine the composition of the gas emitted from the
179
TGA process in the wave number range of 4000-500 cm-1.
180
3 Results and discussions
181
3.1 Analysis of gaseous and liquid products
182
The yields of gaseous product (Gas), char and liquid product (Oil including water) from the 7
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reactions with ILP and LP samples are shown in Fig.2. It is obvious that the formation of these
184
products from ILP and LP are significantly different, particularly at higher temperatures. For
185
instance, when the temperature was higher than 1173 K, the gas yield from ILP involving both
186
lignin pyrolysis/gasification and iron ore reduction was much higher than that from the LP
187
involving lignin pyrolysis/gasification only, whereas the oil and char yields from ILP are much
188
lower than those from LP, suggesting catalytic effects of iron ore or reduced iron species on
189
conversion of oil and char into gaseous products[20, 21].
190
With LP, the yields of three products did not vary too much with the increases of
191
temperature, because the operating temperatures in this work are already much higher than
192
common pyrolysis temperatures (673-973 K)[1]. In contrast, the yields of three products from
193
reactions of ILP varies greatly with the increases of temperature. As shown in Fig 2a, the gas
194
yield increases while the yields of char and oil decrease with increasing the temperature,
195
indicating conversion of char and oil into gaseous products during the ILP reduction. It has been
196
commonly agreed that bio-char and bio-oil vapor formed from biomass pyrolysis could reduce
197
iron ore and transform to CO/CO2 and H2O[16]. In addition, Iron ore can be a catalyst for the
198
pyrolysis/gasification of biomass such as lignin[3], contributing to an increase in gas yield and a
199
decrease in char yield.
200
The compositions of the gas products from the experiments with ILP and LP are shown in
201
Fig.3. At a relatively low temperature, i.e., 1093 K, the gas compositions in both experiments are
202
nearly the same, likely because at this temperature the reduction of iron ore by lignin is not
203
significant, as evidenced by the metallization degree of iron ore being only 2.1% (Fig.7a). As can
204
be noted that at the temperature higher than 1173 K, the compositions (CH4 and H2) of the gas
205
products from ILP and LP are generally similar, which was likely due to the decomposition of
206
lignin occurring at relatively lower temperatures. As such, the gas compositions of CH4 and H2 at
207
these temperatures are believed to be mainly determined by the pyrolysis/gasification of lignin.
208
In contrast, the CO yield from ILP is much higher than that of LP, particularly at higher
209
temperatures. Apparently, the greater formation of CO from ILP is due to the reduction of iron 8
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ore by lignin-derived carbon at these temperatures via the following reduction/gasification
211
reactions (as evidenced by Fig 7a discussed later). CO and CO2 are produced by the reaction of
212
lignin-derived carbon with iron oxide, and the CO2 produced by the reduction could gasify the
213
lignin-derived carbon to produce more CO (as evidenced by the results in Fig. 3a).
214
C + Fe𝑥𝑂𝑦→Fe𝑥𝑂𝑦 ‒ 1 + 𝐶𝑂 + 𝐶𝑂2
(10)
215
C + 𝐶𝑂2→2𝐶𝑂
(11)
216
The GC-MS chromatograms of the oils obtained from the experiments with ILP and LP are
217
comparatively illustrated in Fig.4. On one hand, as well known only lower boiling points
218
compounds in bio-oils could be vaporized and pass the GC column, while bio-oils usually
219
contain a greater portion of high-boiling point compounds, hence not detectable by GC-MS. On
220
the other hand, in this study the oil products were of less interest compared with gaseous
221
products. Accordingly, in this work for GC-MS analysis of the bio-oils, only major detectable
222
compounds in the oils, mainly aromatics, are presented. Less condensed aromatic compounds
223
gradually disappear while increasing the reaction temperature, likely due to the cracking or
224
gasification of these less condensed compounds. For instance, biphenylene and 4-Ethylbiphenyl
225
are present in the oils obtained at 1073 and 1173 K, but disappear at higher temperatures.
226
Fluorene-9-methanol and 4H-cyclopenta phenanthrene were detected in the oils at temperatures
227
below 1253 K but they were not detected in the oils at 1333 K, irrespective of the presence iron
228
ore. In the 1333 K oils, the major compounds detected are highly condensed aromatics such as
229
fluoranthene, pyrene and benz anthracene. The presence of heavy aromatics in the oil products
230
above 1173 K is apparently a result of the pyrolysis/gasification processes for lignin. Although
231
they were present in similar concentrations in the oils obtained from the experiments with ILP
232
and LP as illustrated in Fig.4, the absolute amounts of these heavy aromatics in the oils from the
233
experiments with ILP were actually much greater than those with LP due to the much suppressed
234
oil formation in the presence of iron ore, as evidenced in Figure 2. Thus, the presence of iron
235
species (ion oxides or reduced iron) could catalyze the cracking/gasification of heavy aromatics
236
into gaseous products. 9
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3.2 Analysis of the solid residues/products
238
Fig.5 shows the XRD of the obtained solid residues/products from reduction of ILP at
239
different temperatures. It can be seen that effects of reaction temperature are significant on the
240
crystalline structure of the recovered solid residues from ILP pyrolysis/gasification. The major
241
crystalline species identified in the raw iron ore sample are Fe2O3 and Fe3O4 at room
242
temperature. For the ILP, the major iron-containing species transformed to FeO as the
243
temperature was increased to 1093 K, and further to metallic Fe when the temperature was above
244
1173 K. At 1253 K, metallic Fe becomes the only iron species in the ILP-derived solid products,
245
and the peak of metallic iron increases with increasing the reaction temperature, indicating the
246
increased extent of reduction of iron ore by lignin at a higher temperature, as expected.
247
To better understand the morphology of metallic iron and lignin after the reduction, the ILP
248
and LP samples after reduction at 1423 K and 1093 K were studied by SEM and EDS analyses.
249
It should be noted that one special experiment was carried on 1423K with ILP aiming to prepare
250
reduced ILP sample only for SEM measurement. With the ILP sample at 1333K, however, many
251
powder falling off from the polishing surface of ILP sample, making the surface not conducive to
252
SEM observation. Thus, to facilitate observation, the ILP sample after reduction at 1423 K was
253
prepared and used for SEM analyses. Fig.6 shows SEM and EDS analyses results for the ILP and
254
LP samples after reaction. As clearly shown in Fig.6a, the reduction product from ILP contains
255
two phases: the phase in gray area and the phase in black areas. The EDS of two phases, as
256
shown in Fig.6c and d, indicates that the dominant element of the gray area is iron while the
257
black area is composed mainly of carbon, silicon, calcium, aluminum and iron. Thus, the gray
258
area is metallic iron phase and the black area the carbon residue and slag phase, as similarly
259
reported in the literature with other carbon-containing pellets[22].
260
The morphology of lignin-derived char residue is shown in Fig.6b. The char appears in the
261
form of carbon film of a very thin thickness. It was commonly believed that iron oxide can be
262
reduced by carbon reducing agent through the following processes: gasification of carbon to
263
form CO that reduces iron oxide at a relatively lower temperature, followed by direct reduction 10
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of iron oxide by solid carbon at higher temperatures[23]. The formation of thin film structure
265
carbon the lignin char with a high surface area would promote the gasification and direct
266
reduction reactions of carbon, hence facilitate the reduction of iron ore.
267
3.3 Reduction degree of ILP
268
To reveal the degree of reduction of iron ore by lignin, solid residues of ILP after reaction at
269
different temperatures were analyzed by chemical titration, and the results are shown in Fig. 7.
270
At 1093 K, the reduction degree of the pellets is 23.7%, and metallization degree is 2.1%, which
271
are in a good agreement with the XRD analysis (Fig. 5). The metallization and reduction degrees
272
both increase as the temperature increases, attaining the maximum values (86.3% and 91.3%,
273
respectively) at 1333 K. The iron oxide reduction is an endothermic reaction, thus
274
thermodynamically and kinetically favorable at a higher temperature. However, when the
275
temperature reaches a certain temperature, the depleted iron oxide in the sample would
276
kinetically limit the metallization and reduction degrees, hence both degrees level off at above
277
1253 K, as evidenced in Fig. 7.
278
As shown in Fig.7b, with increasing the lignin-to-iron ore mass ratio, both the reduction and
279
metallization degrees increase as expected, although they level off at the ratio above 1:1 (wt/wt).
280
For instance, at the ratio of 1:3 (wt/wt), the metallization degree and the reduction degree are
281
only 43.3% and 60.4%, respectively, while they are as high as 89.5% and 92.1%, respectively at
282
the ratios above 1:1 (wt/wt). Theoretically, given enough amount of lignin and enough
283
temperature, the iron ore can be completely reduced (100% metallization degree). In the present
284
experiments at a temperature of 1093 - 1333 K (or 820 - 1060C), lignin would undergo fast
285
pyrolysis first, releasing vapor/gases quickly. Then the gasification reactions would take place by
286
cracking of the vapor and between the vapor/gas and the residual char, in particular catalyzed by
287
the iron ore or reduced iron. H2 and CO as well as hydrocarbon radicals generated in the
288
gasification reactions along with the residual char would serve as reducing agents accounting for
289
the reduction of iron oxide, as evidenced by the high metallization ratio in this study, i.e., about 11
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290
90% at 1333K. On the other hand, however, when the ILP pellets were put into the furnace, it
291
would quickly foam, reducing the contact with iron oxide powder, and even overflow from the
292
basket [16]. Thus, at a very high lignin-to-iron ore mass ratio, the efficiency of lignin as a
293
reducing agent would decrease, accounting for the leveled-off metallization and reduction
294
degrees, as shown in Figure 7.
295
3.4 Roles of lignin in reduction of iron ore
296
In order to investigate the roles of lignin in the reduction of iron oxide, lignin alone and
297
lignin-iron ore mixture were studied by TGA experiments. A same amount of lignin was used in
298
these experiments. The TGA and DTG (derivative thermogravimetric analysis) curves of these
299
samples are shown in Fig.8. As can be seen from Fig. 8a, the mass loss curves of lignin alone
300
and lignin-iron ore mixture are obviously different. The mass loss curve of the lignin-iron ore
301
mixture keeps decline after 773 K, but at temperatures below this the TGA curve is similar to
302
that of lignin alone, suggesting the reduction of iron ore occurs at above 773 K. From the DTG
303
curves as shown in Fig.8b, the DTG curves of lignin alone and lignin-iron ore mixture are
304
obviously different, especially in two distinct temperature ranges, 773-973 K and 973-1373 K,
305
indicating the reduction of iron ore by lignin could take place in these two temperature ranges.
306
The mass loss rate at 973-1373 K was significantly faster than that at 773-973 K, suggesting
307
stronger reduction occurring at 973-1373 K than at 773-973 K.
308
The evolved gas from the TGA experiments were online analyzed by FTIR, and the FTIR
309
spectra of the gases at various temperatures are displayed in Fig.9. According to the FTIR
310
spectra, it can be evident that the temperature range of evolved gases is consistent with that of
311
weight loss in the TGA tests of both samples. The main species the evolved gas are CO2 (2450 ~
312
2250 cm-1, 750 ~ 600 cm -1), CO (2250 ~ 2050 cm-1), CH4 (3000 ~ 3030 cm-1), H2O (3800 ~
313
3500 cm-1, 1600 ~ 1500 cm-1) and other organic gas containing C = O (1850 ~ 1600 cm -1) and
314
C-O-C / C-C (1500 ~ 1050 cm-1) functional groups. Comparing the FTIR spectra of the gas
315
evolved from these two samples, it can be seen that in the IR absorbance of the gas evolved from 12
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316
the TGA experiments of lignin-iron ore mixture intensified at >973 K, particularly the
317
absorbance spectra of CO2, indicating that a large amount of gas formed mainly due to the
318
reduction of iron ore by CO and C derived from lignin at above 973 K.
319
The relative amounts of CO2, CH4 and CO were calculated by integration of the FTIR
320
characteristic peak of CO2, CH4 and CO at 2363 cm-1, 3017 cm-1 and 2167 cm-1, respectively,
321
and the results are shown in Fig.9c. At below 973 K, the evolution of all gas components (CO2,
322
CH4 and CO) from the lignin-iron ore mixture follows the similar trend as that of the lignin
323
alone, because at such low temperatures reduction of iron ore is not significant. However, at >
324
973 K, CO and CO2 evolved from the lignin-iron ore mixture were found to be much greater than
325
those from lignin alone, indicating that reduction of iron oxide by lignin took place preferably at
326
a high temperature, as evidenced previously in Fig.4 and 5.
327
In our previous studies on reduction of iron ore by hydrogen, the reduction started at around
328
600K and the maximum reaction rate was observed at about 830 K[16]. In this work, H2
329
appeared in the evolved gas in the experiments with either lignin alone or lignin-iron ore
330
mixture, as shown in Fig.3. Thus, iron ore could be reduced by hydrogen in the lower
331
temperature range, i.e., 773-973 K as shown in Fig.8. However, as illustrated in Fig.3, the H2
332
yield in the experiments with ILP is almost the same as that in the tests with LP. A possible
333
explanation was proposed by the authors, as presented in two equations. The formation of H2 by
334
steam gasification of carbon (char or lignin) could offset the consumption of H2 in iron ore
335
reduction, leading to a similar amount of H2 evolved from the experiments with ILP as that with
336
LP (Fig. 6).
337
H2 + Fe𝑥𝑂𝑦→Fe𝑥𝑂𝑦 ‒ 1 + 𝐻2𝑂
(12)
338
H2O + C→CO + 𝐻2
(13)
339
Zhao et al[24] studied manganese oxide ore reduction using biomass straw as a reductant.
340
They considered that the main role of reduction of manganese oxide by biomass was through CO
341
gas produced from biomass pyrolysis at the temperature lower than 873 K. In their experiments,
342
H2 should also play a role as a reductant. However, as well known the reduction of iron oxides is 13
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343
more difficult than that of manganese oxides, for instance, Strezov[18] found that the reduction
344
of iron ore using sawdust commenced at approximately 943 K, which was higher than the
345
starting temperature (773 K) for iron ore reduction in this work. This could be mainly owing to
346
the use of pure lignin in this study, producing more H2 in pyrolysis/gasification, which was
347
evidenced by a literature study of Yang et al[25] demonstrating that much more H2 was produced
348
from lignin pyrolysis than that from hemicellulose or cellulose. The formation of H2 from lignin
349
pyrolysis at a lower temperature might account for the lower starting temperature (773 K) for
350
iron ore reduction in this work. The findings on iron-ore reduction by carbon at high
351
temperatures are similar to those reported in the literature [11, 24].
352
4. Prospective of coupled biomass gasification and iron ore reduction
353
The positive results from this study show great promise of application of lignin in iron and
354
steel making industry as a reducing agent for DRI production. Apart from lignin, other kinds of
355
biomass have also been investigated and demonstrated promise to be as reducing agents for iron
356
ores in our previous work[3, 16, 20]. For better economics, iron ore reduction and biomass
357
gasification can be coupled, and the coupled biomass gasification and iron ore reduction
358
(CBGIOR) process can be conceptually shown in Fig. 10.
359
In the proposed CBGIOR process, the presence of biomass (lignin) supplies carbon and
360
hydrogen-containing reducing agents by pyrolysis/gasification for iron ore reduction, whereas
361
the iron oxide could provide oxidant and reduced iron as a catalyst to promote biomass
362
gasification, via the following reactions: 𝐹𝑒𝑥𝑂𝑦
363
Biomass → 𝐻2 + 𝐶𝑂 + 𝐶𝐹𝑖𝑥𝑒𝑑 𝑐𝑎𝑟𝑏𝑜𝑛 + 𝑂𝑡ℎ𝑒𝑟𝑠
(14)
364
𝐹𝑒𝑥𝑂𝑦 + H2→𝐻2𝑂 + 𝐹𝑒
(15)
365
𝐹𝑒𝑥𝑂𝑦 + CO→CO2 + 𝐹𝑒
366
𝐹𝑒𝑥𝑂𝑦 + C𝐹𝑖𝑥𝑒𝑑 𝑐𝑎𝑟𝑏𝑜𝑛→CO2 + 𝐶𝑂 + 𝐹𝑒
367
(16)
The overall reaction: 14
(17)
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368
𝐹𝑒𝑥𝑂𝑦
Biomass + 3𝐹𝑒𝑥𝑂𝑦 → 𝐻2𝑂 + 𝐶𝑂 + 𝐶𝑂2 + 3𝐹𝑒 + 𝑂𝑡ℎ𝑒𝑟𝑠
(18)
369
Firstly, H2 and CO are produced via the pyrolysis/gasification of biomass catalyzed by iron
370
oxide, and the iron oxide is reduced mainly by H2 at a lower temperature (before 973 K) due to
371
the higher reactivity of H2 than that of CO. When the temperature further increases (above 973
372
K), reactions 16 and 17 would occur simultaneously. The overall reaction involved in the
373
proposed CBGIOR process is reaction 18.
374
Compared with conventional biomass gasification processes and ironmaking processes, the
375
CIORBG process has several advantages, e.g., (1) it integrates biomass pyrolysis/gasification
376
and iron ore reduction in a synergistic way, co-generating syngas of a high calorific value
377
(containing CO, H2, CH4, CO2, etc.) and DRI cost-effectively; (2) it suppressed bio-oil yield with
378
greatly increased gas yield (Fig. 2), reducing the adverse effects of bio-oil on the syngas
379
production (pipe blockage and corrosion etc.); (3) owing to high reductive activity of carbon in
380
char and biomass pyrolysis vapor or gasification gases (CO/H2 gases), the iron ore reduction
381
temperature of the process (1073 K～1333 K) is much lower than the conventional blast furnace
382
processes (1173 K～1773 K) and the coal-based DRI processes (1523 K～1623 K). Future work
383
is needed on further development of the CBGIOR process, in particular with respect to
384
optimizing the biomass-iron ore blending ratio, designing suitable reactors, and minimizing the
385
formation of bio-oil and enhancing the metallization degree of iron ore, etc.
386
5. Conclusions
387
Coupled biomass gasification and iron ore reduction was investigated and demonstrated in
388
this work through pyrolysis/gasification of ILP at 1093～1333 K. The solid (char), oil and gas
389
products were analyzed by XRD, SEM, chemical analysis, GC-MS, Micro-GC and TG-FTIR.
390
Direct reduction iron (DRI) was produced in the process. The reduction and metallization
391
degrees of iron ore increased with increasing the reaction temperature as expected, reaching the
392
maximum values (86.3% and 91.3%, respectively) at 1333 K. The gas yields in the experiments
393
with ILP were much higher than those with LP at 1173 ～1333 K, owing to the much greater 15
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394
amount of CO formed in reduction of iron ore by lignin (carbon). Whereas, the bio-oil yields in
395
pyrolysis/gasification of LP were much higher than those in pyrolysis/gasification of ILP,
396
suggesting that the presence of iron ore or metallic iron could catalyze gasification of the oil into
397
gaseous products. It was found that in the pyrolysis/gasification of ILP, the iron ore could be
398
reduced by lignin-derived hydrogen first, then by CO and carbon. Meanwhile, during the
399
pyrolysis/gasification of ILP, the iron ore or metallic iron could act as an oxidant/catalyst to
400
promote biomass gasification. Based on the positive results from this study, a novel conceptual
401
process, i.e., coupled biomass gasification and iron ore reduction (CBGIOR) process was
402
proposed.
403
Acknowledgements: The authors would like to acknowledge the funding from BioFuelNet
404
Canada, a Network of Centres of Excellence, NSERC through the Discovery Grants, the
405
NSERC/FPInnovations Industrial Research Chair in Forest Biorefinery and National Natural
406
Science Foundation of China (Grant No. 51274003, 51674002 and U1660206).
407 408 409 410 411 412 413 414 415 416
References: 1. Bridgwater AV, Meier D, Radlein D. An overview of fast pyrolysis of biomass. ORG GEOCHEM. 1999. 2. Kirubakaran V, Sivaramakrishnan V, Nalini R, Sekar T, Premalatha M, Subramanian P. A review on gasification of biomass. RENEW SUST ENERG REV. 2009;13(1):179-86. 3. Hurley S, Li H, Xu C. Effects of impregnated metal ions on air/CO 2 -gasification of woody biomass. BIORESOURCE TECHNOL. 2010;101(23):9301-7. 4. Jiang G, Nowakowski DJ, Bridgwater AV. Effect of the Temperature on the Composition of Lignin Pyrolysis Products. Energy Fuels. 2010;24(8):4470-5. 16
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5. Kang S, Li X, Fan J, Chang J. Hydrothermal conversion of lignin: A review. Renewable and Sustainable Energy Reviews. 2013;27:546-58.
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6. Zhang L, Champagne P, Charles XC. Supercritical water gasification of an aqueous by-
420
product from biomass hydrothermal liquefaction with novel Ru modified Ni catalysts.
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BIORESOURCE TECHNOL. 2011;102(17):8279-87.
422
7. Wei R, Zhang L, Cang D, Li J, Li X, Xu CC. Current status and potential of biomass
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utilization in ferrous metallurgical industry. RENEW SUST ENERG REV. 2017;68:511-24.
424
8. Gong FY, Ye TQ, Yuan LX, Tao K, Torimoto Y, Yamamoto M, et al. Direct reduction of
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iron oxides based on steam reforming of bio-oil: a highly efficient approach for production of
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DRI from bio-oil and iron ores. GREEN CHEM. 2009;11(12):2001-12.
427 428 429 430 431 432 433 434
9. Guo D, Zhu L, Guo S, Cui B, Luo S. Direct reduction of oxidized iron ore pellets using biomass syngas as the reducer. 10. Chakar FS, Ragauskas AJ. Review of current and future softwood kraft lignin process chemistry. Industrial Crops & Products. 2004;20(2):131-41. 11. Srivastava U, Kawatra SK, Eisele TC. Production of pig iron by utilizing biomass as a reducing agent. INT J MINER PROCESS. 2013;119(119):51-7. 12. Fu JX, Zhang C, Hwang WS, Liau YT, Lin YT. Exploration of biomass char for CO 2 reduction in RHF process for steel production. INT J GREENH GAS CON. 2012;8(5):143-9.
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13. Guo D, Hu M, Pu C, Xiao B, Hu Z, Liu S, et al. Kinetics and mechanisms of direct reduction
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of iron ore-biomass composite pellets with hydrogen gas. INT J HYDROGEN ENERG.
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2015;40(14):4733-40. 17
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14. Ueki Y, Yoshiie R, Naruse I, Ohno KI, Maeda T, Nishioka K, et al. Reaction behavior during heating biomass materials and iron oxide composites. FUEL. 2013;104(2):58-61.
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15. Osada M, Sato O, Watanabe M, Arai K, Shirai M. Water Density Effect on Lignin
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Gasification over Supported Noble Metal Catalysts in Supercritical Water. ENERG FUEL.
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2006;20(3):930-5.
443 444
16. Wei R. Fundamental studies of iron ore reduction by different reductants under mechanical activation. Beijing: University of Science and Technology Beijing, 2016.
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17. Huang Z, Zhang Y, Fu J, Yu L, Chen M, Liu S, et al. Chemical looping gasification of
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biomass char using iron ore as an oxygen carrier. INT J HYDROGEN ENERG.
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2016;41(40):17871-83.
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18. Strezov V. Iron ore reduction using sawdust: Experimental analysis and kinetic modelling. RENEW ENERG. 2006;31(12):1892-905. 19. ISO. Determination of reduction index, final reduction degree and metallization rate of iron ore for direct reduction furnace. 2007. 20. Wei R, Cang D, Bai Y, Huang D, Liu X. Reduction characteristics and kinetics of iron oxide by carbon in biomass. IRONMAK STEELMAK. 2016.
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21. Hurley S, Xu CC, Preto F, Shao Y, Li H, Wang J, et al. Catalytic gasification of woody
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biomass in an air-blown fluidized-bed reactor using Canadian limonite iron ore as the bed
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material. FUEL. 2012;91(1):170-6.
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22. Li J, Wei R, Long H, Wang P, Cang D. Sticking behavior of iron ore–coal pellets and its inhibition. POWDER TECHNOL. 2014;262:30-5. 18
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23. Long HM, Li JX, Wang P, Shi SQ. Reduction kinetics of carbon containing pellets made from metallurgical dust. IRONMAK STEELMAK. 2012;39(8):585-92.
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24. Zhao Y, Zhu G, Cheng Z. Thermal analysis and kinetic modeling of manganese oxide ore
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reduction using biomass straw as reductant. HYDROMETALLURGY. 2010;105(1-2):96-102.
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25. Yang H, Yan R, Chen H, Lee DH, Zheng C. Characteristics of hemicellulose, cellulose and
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lignin pyrolysis. FUEL. 2007;86(12–13):1781-8.
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Figure captions
487
Fig.1 Schematic diagram of experimental apparatus (1. N2 bottle; 2. Mass flow controller; 3.
488
Electric furnace; 4. Samples; 5. Filter and cold trap; 6. Gas analyzer (micro-GC); 7. Computer).
489
Fig.2 Yields of Gas, Char and Oil from the experiments with ILP (a) and LP (b)
490
Fig.3 Yields of H2, CO，CH4 and other gaseous products from the experiments with ILP (a) and
491
LP (b)
492
Fig.4 GC-MS chromatograms of the oil products from the experiments with ILP and LP
493
Fig.5 XRD patterns of the ILP sample after reduction at different temperatures
494
Fig.6 SEM images of the ILP sample (a) and LP sample (b) after reaction at 1423 K and 1093 K,
495
respectively, and the EDS spectra of point 1 (c) and point 2 (d) in the ILP sample.
496
Fig. 7 Reduction and metallization degrees of the ILP sample after pyrolysis/gasification at
497
different temperatures (a) and different lignin-to-iron ore mass ratios (b)
498
Fig.8 TGA (a) and DTG (b) curves of lignin alone and lignin-iron ore mixture
499
Fig. 9 FTIR of the evolved gases from of TGA experiments for lignin alone (a) and lignin-iron
500
ore mixture (b), and quantification analysis of gas species by FTIR (c)
501
Fig.10 Conceptual scheme of the coupled biomass gasification and iron ore reduction (CBGIOR)
502
process
503 504
20
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2
4
5
3
1
7
6
505 506
Fig.1 Schematic diagram of experimental apparatus (1. N2 bottle; 2. Mass flow controller; 3. Electric furnace;
507
4. Samples; 5. Filter and cold trap; 6. Gas analyzer (micro-GC); 7. Computer).
508 509 510 511 512 513 514 515
21
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a
Char
Oil
Gas
100
Yield (%)
80 60 40 20 0 1093
1173
1253
1333
Temperature (K)
516
b
Char
Oil
Gas
100
Yield (%)
80 60 40 20 0 1093
517 518
1173
1253
1333
Temperature (K)
Fig.2 Yields of Gas, Char and Oil from the experiments with ILP (a) and LP (b)
519
22
ACCEPTED MANUSCRIPT
a
0.030
H2
CH4
CO
Others
Gas yield (mol/g)
0.025 0.020 0.015 0.010 0.005 0.000 1093
1173
1253
1333
Temperature (K)
520
b
0.030
H2
CH4
CO
Others
Gas yield (mol/g)
0.025 0.020 0.015 0.010 0.005 0.000 1093
1173
1253
1333
Temperature (K)
521 522
Fig.3 Yields of H2, CO，CH4 and other gaseous products from the experiments with ILP (a) and
523
LP (b)
23
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6 5
525
7
1333 K, ILP 56 3 1253 K, LP
7
4 5
3 1253 K, ILP
1173 K, LP
1
56
3 4 3
1093K, LP
10
5
6
6 4 5
1 2 3
1093 K, ILP
7 7
4
2
1173 K, ILP
6
4
3
5
524
7
1333 K, LP
Intensity(a.u.)
4- 4H-Cyclopenta phenanthrene, 5- Fluoranthene, 6- Pyrene, 7- Benz anthracene
1- Biphenylene, 2- 4-Ethylbiphenyl, 3- Fluorene-9-methanol,
6 5
4
56
7
7 7
1 2
15
20
25
30
Reaction Time (min)
Fig.4 GC-MS chromatograms of the oil products from the experiments with ILP and LP
24
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1-Fe 2-FeO 3-Fe3O4 4-Fe2O3
1
Intensity (a.u.)
1333 K
1
1
1
1
1 1253 K 1 1173 K
2
2
2 1
2
1093 K
2
2
2
2
Raw iron ore3 10
20
30
43
4 4 40
50
1
34 60
70
80
90
526
2θ (°)
527
Fig.5 XRD patterns of the ILP sample after reduction at different temperatures
528 529 530 531 532 533 534 535 536 537
25
ACCEPTED MANUSCRIPT
1
a
b
c
d
2
538
539 540
Fig.6 SEM images of the ILP sample (a) and LP sample (b) after reaction at 1423 K and 1093 K,
541
respectively, and the EDS spectra of point 1 (c) and point 2 (d) in the ILP sample.
542 543 544 545
26
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a 100
Metallization degree Reduction degree
Degree (%)
80 60 40 20 0
Lignin : iron ore=1:2(wt/wt)
1093
1173
1253
1333
Temperature (K)
546
b 100 90
Metallization degree Reduction degree
Degree (%)
80 70 60 50 40
1253 K
1:3
547
1:2
1:1
1:0.5
Ratio of lignin/iron ore(wt/wt)
548
Fig. 7 Reduction and metallization degrees of the ILP sample after pyrolysis/gasification at
549
different temperatures (a) and different lignin-to-iron ore mass ratios (b)
27
ACCEPTED MANUSCRIPT
a
0
Mass loss (mg)
-2 -4 -6
LP
-8 -10
ILP
-12 373
573
773
973
1173
1373
Temperature (K)
550
b
0.120
Mass loss rate(a.u.)
0.125
2
0.130 0.135
ILP
1
0.140 0.145 0.150 LP
0.155 373
573
773
973
1173
1373
551
Temperature (K)
552
Fig.8 TGA (a) and DTG (b) curves of lignin alone and lignin-iron ore mixture
28
ACCEPTED MANUSCRIPT
553 without Fe2O3
c
with Fe2O3
Absorbance
CO2
CH4
CO
373
554
573
773
973 1173
Temperature(K)
555
Fig. 9 FTIR of the evolved gases from of TGA experiments for lignin alone (a) and lignin-iron
556
ore mixture (b), and quantification analysis of gas species by FTIR (c)
557 558 559
29
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560 561
Fig.10 Conceptual scheme of the coupled biomass gasification and iron ore reduction (CBGIOR)
562
process
563 564 565 566 567 568 569 570 571 572 573 574 575 576 30
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577
Tables captions
578
Table 1. Composition of lignin
579
Table 2. Chemical composition of iron ore
580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 31
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604
Table 1. Composition of lignin Ultimate analysis (% wt/wt, dry basis)
Composition ((% wt/wt, dry basis)
Composition Content
605
1
C
H
O1
N
Ash
Lignin
Cellulose
Hemicellulose
71.6
6.3
21.9
0.2
0
>95.02
n.a.3
n.a.3
By difference assuming 0 (% wt/wt S; 2 Data from the supplier; 3 Not analyzed.
606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 32
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628
Table 2. Chemical composition of iron ore Composition
TFe
FeO
SiO2
Al2O3
CaO
MgO
S
P
Content (% wt/wt, dry basis)
65.4
13.8
6.96
0.52
0.11
0.31
0.025
0.045
629
33
ACCEPTED MANUSCRIPT Highlights
Coupled biomass gasification and iron ore reduction by pyrolysis of iron ore– biomass pellets
Iron oxide/metallic iron provided an oxidant/catalyst for biomass gasification.
Biomass provided reducing agents for reduction of iron oxide.
Rufei Wei, Shanghuan Feng, Hongming Long, Jiaxin Li, Zhongshun Yuan, Daqiang Cang, Chunbao (Charles) Xu PII:
S0360-5442(17)31456-1
DOI:
10.1016/j.energy.2017.08.080
Reference:
EGY 11449
To appear in:
Energy
Received Date:
21 January 2017
Revised Date:
31 May 2017
Accepted Date:
16 August 2017
Please cite this article as: Rufei Wei, Shanghuan Feng, Hongming Long, Jiaxin Li, Zhongshun Yuan, Daqiang Cang, Chunbao (Charles) Xu, Coupled biomass (lignin) gasification and iron ore reduction: a novel approach for biomass conversion and application, Energy (2017), doi: 10.1016/j. energy.2017.08.080
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ACCEPTED MANUSCRIPT
Coupled biomass gasification and iron ore reduction (CBGIOR) process
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1
Coupled biomass (lignin) gasification and iron ore reduction: a novel
2
approach for biomass conversion and application
3 4 5 6
Rufei Weia, Shanghuan Fengb, Hongming Longa*, Jiaxin Lia, Zhongshun Yuanb, Daqiang Cangc,
7
Chunbao (Charles) Xua,b*
8 9
a
School of Metallurgical Engineering, Anhui University of Technology, Ma’anshan, Anhui 243002,
10
China;
11
b
12
Biochemical Engineering, Western University, Ontario N6GA5B9, Canada;
13
c
14
Beijing 100083, China.
Institute for Chemicals and Fuels from Alternative Resources (ICFAR), Department of Chemical and
School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing,
15 16
Corresponding authors: [email protected] (C. Xu), [email protected] (H. Long)
17 18 19 20 21 22 23 24 25 26 27 1
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28
Abstract
29
Aiming at a novel application of biomass, coupled biomass gasification and iron ore reduction
30
was investigated and demonstrated in this work through pyrolysis/gasification of iron ore–lignin
31
pellets (ILP) at 1093 ～1333 K. The solid, liquid and gaseous products were analyzed by XRD,
32
SEM, chemical analysis, GC-MS, GC and TG-FTIR. Direct reduction iron (DRI) and gaseous
33
products (CO, H2 and CH4) were produced in the process. The metallization degree of the iron
34
ore and CO content of the gaseous products increased with increasing the reaction temperature,
35
as expected. The gas yield from the experiments with ILP was much higher than that from the
36
tests with lignin pellets (LP) at 1173 ～1333 K, owing mainly to the iron ore reduction
37
producing a larger amount of CO. Whereas, the yields of oil and char in the ILP reduction
38
process were found to be much lower than those from the tests with lignin alone, due to the
39
conversion of oil and char products into gaseous products catalyzed by the iron oxide and
40
metallic iron. Thus, in pyrolysis/gasification of ILP the presence of lignin provided reducing
41
agents for reduction of iron oxide, whereas the presence of iron oxide/metallic iron provided an
42
oxidant/catalyst for biomass gasification.
43 44
Keywords: Biomass; Lignin; Direct reduction iron; Reduction; Pyrolysis/Gasification; Carbon
45
monoxide.
46 47 48 49 50 51 52 53 54 2
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1 Introduction
56
Biomass is one of the most important energy sources in near future amongst the renewable
57
energies. Biomass can be converted into various energy and solid, liquid and gaseous fuel
58
products via three main processes, i.e., physical conversion, chemical or thermochemical
59
conversion, and biochemical conversion[1, 2]. Biomass gasification is an important
60
thermochemical conversion process, generating gaseous products (including H2, CO. CO2 and
61
CH4, et al.) with a high calorific value. However, there are still some problems in biomass
62
gasification, including high tar content in the product, and low calorific value of gaseous
63
products, etc. In order to solve these problems, adding catalyst[3], raising temperature[4],
64
employing plasma gasification or supercritical water gasification[5, 6] have been proposed.
65
Although raising temperature can effectively reduce the tar yield, it results in increased costs.
66
However, if biomass gasification is coupled with other applications, such as reduction of metal
67
oxides/ores to produce valuable direct reduction iron (DRI) products, the economics of high-
68
temperature gasification of the biomass, would be greatly improved.
69
On the other hand, with increased concerns over greenhouse gas emissions and depletion of
70
fossil energy, seeking alternative energy sources is an efficacious way to address these problems
71
fundamentally for iron and steel industry [7-10]. As a novel application, biomass has
72
demonstrated to be an effective reducing agent for iron oxides reduction in ironmaking
73
processes. Raw biomass [10, 11], biomass-derived char [12], syngas [9] and tar [8] can all be
74
used as reducing agents. Iron ore - biomass pellets, consisting of biomass powder, iron ore
75
powder and a small amount of binder materials, were produced with a pelletizer or briquetting
76
press, which represent a new kind of raw materials for ironmaking [9, 13]. Wood sawdust,
77
bamboo char, pine sawdust, coconut shell char and rice husk char were ever used in the iron ore-
78
biomass pellets [12-14], producing DRI at temperatures of 1000-1300 C. In addition, high
79
quality pig iron could also be produced at various temperatures for a short residence time in the
80
smelting reduction of magnetite using biomass as a reducing agent [11]. Other metal ores, such
81
as manganese oxide ore, were also reduced at low temperatures by biomass straw as both a 3
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82
reductant and fuel [13]. However, the previous studies were mainly focused on the quality of
83
metallic iron, but ignoring the biomass conversion in the reduction process.
84
At present, the gasification agents for biomass gasification are oxygen (air, oxygen-enriched
85
air and pure oxygen)[2], carbon monoxide[6] and water vapor[15]. In fact, iron oxide can also be
86
used as a gasification agent, because it can provide oxygen [16, 17]. Iron ore has been used as an
87
oxygen carrier for chemical looping gasification of biomass char [17]. However, the previous
88
studies [7, 11, 13, 18] referring to the mixture of biomass and iron ore were mainly focused on
89
reduction of iron oxide by biomass, while ignoring the biomass gasification by iron oxide. This
90
work presents the coupled biomass gasification and iron ore reduction, and investigates the gas
91
conversion of lignin and the reduction characteristics of iron ore by biomass in the process with
92
iron ore–biomass pellets heated to high temperatures, contributing new knowledge to the
93
utilization of biomass energy.
94
2 Materials and methods
95
2.1 Materials
96
The biomass materials used in the experiments were organosolv lignin, supplied by a
97
company in British Columbia, Canada, and derived from mixture of softwood and hardwood.
98
Iron ore powder was provided by an iron ore plant in Hebei province, China. The chemical
99
compositions of the lignin and iron ore are given in Tables 1 and 2, respectively. Before
100
experiments, these materials were dried in an oven in air at 358 K for 1 h, and then were mixed
101
sufficiently and stored in a desiccator for the planned tests.
102 103
2.2 Experimental and procedure
104
In this work, iron ore–lignin pellets (ILP) were made using a cold press with mixtures of
105
organosolv lignin powder and iron oxide powder under a uniaxial pressure of 20 MPa in a tablet
106
mold (20 mm inner diameter and 50 mm high). In this work, the mass ratio between organosolv 4
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107
lignin powder and iron oxide powder in ILP was maintained at 1:2 (wt/wt), unless specified
108
otherwise. Lignin pellets (LP) with lignin powder only were also prepared by the same method
109
as that for making ILP. In all tests with either ILP or LP, the amount of lignin used was ensured
110
the same.
111
The pyrolysis/gasification experiments of ILP and LP were carried on the experimental
112
apparatus schematically shown in Fig. 1. An electric furnace, with the maximum working
113
temperature of 1473 K, was used for heating. In a typical experiment, N2 was introduced to the
114
reactor at the rate of 25 mL/min, and the reactor was heated to a preset temperature (1093, 1173,
115
1253 and 1333 K), soaking for 10 min after the preset temperature was reached. In each test, the
116
mass of LP used was 5 g and 10 g for ILP. The sample was put into a basket, and inserted
117
quickly to the reactor center to allow fast heating of the sample. The evolved gases during the
118
sample heating (15 min) were collected into a gas bag through a filter and cold trap. After 15 min
119
of experiment, the furnace was turned off, and the sample was pushed out of the furnace center
120
to the N2 inlet side for cooling. The sample was removed from the reactor after it cooled down to
121
room temperature. After injecting a fixed volume of air into the gas bag as internal standard for
122
gas volume determine, the composition of the gas in the bag was analyzed using a Micro-GC-
123
TCD (Agilent 3000).
124
After the test, the solid residue was taken out of the basket, and the oil product formed by
125
pyrolysis/gasification of the lignin, condensing on the inner wall of the reactor outlet and gas
126
sampling lines, was washed using acetone, and kept for further analysis. To ensure
127
reproducibility of the test results, each test was repeated for three times, and the relative errors
128
for the product yields were controlled to be within 10%. If the relative errors were bigger than
129
10%, one more repetition test would be conducted.
130 131 132
2.3 Products characterization For LP, the yield (Y) of solid, gas and liquid products in mass percentage was defined as: 5
ACCEPTED MANUSCRIPT
𝑚𝑠𝑜𝑙𝑖𝑑 𝑟𝑒𝑠𝑖𝑑𝑢𝑒
133
𝑌char =
134
𝑌gas = 𝑚
135
𝑌oil = 100% ‒ 𝑌char ‒ 𝑌gas
𝑚𝑙𝑖𝑔𝑛𝑖𝑛 𝑚𝑔𝑎𝑠 𝑙𝑖𝑔𝑛𝑖𝑛
(1)
× 100%
× 100%
(2) (3)
136
where Ychar, Ygas, and Yoil denote the yield (% wt/wt) of char, gas and crude bio-oil (with water),
137
respectively; msolid resideu, mgas and mlignin denote the dry mass (g) of solid residue, gas and lignin,
138
respectively. The ash content in the lignin is negligibly low (Table 1), so all solid residue can be
139
considered as char. The dry mass (g) of a gas was approximately estimated based on its
140
composition analyzed by micro-GC, using the following the equation while assuming the volume
141
increase of the inlet gas flow during the process was negligible:
142
𝑃
𝑚𝑔𝑎𝑠 = 𝑅𝑇 × 𝐿 × t × 𝑤 × M
(4)
143
Where P, T, L, t, w and M are the experimental pressure, temperature, gas flow, gas collection
144
time, gas composition by micro-GC and molar mass of the gas species. R is the gas constant.
145
Similarly for ILP, the yield (Y) of respective product in mass percentage was defined as: 𝑚𝑠𝑜𝑙𝑖𝑑 𝑟𝑒𝑠𝑖𝑑𝑢𝑒 ‒ (𝑚𝑖𝑟𝑜𝑛 ‒ 𝑜𝑟𝑒 ‒ 𝑚𝑜 ‒ 𝑙𝑜𝑠𝑠)
146
𝑌char =
147
𝑌gas = 𝑚
148
𝑌oil = 100% ‒ 𝑌char ‒ 𝑌gas
𝑚𝑙𝑖𝑔𝑛𝑖𝑛 + 𝑚𝑜 ‒ 𝑙𝑜𝑠𝑠 𝑚𝑔𝑎𝑠 𝑙𝑖𝑔𝑛𝑖𝑛 + 𝑚𝑜 ‒ 𝑙𝑜𝑠𝑠
× 100%
× 100%
(5) (6) (7)
149
where msolid residue, miron-ore and mo-lose denotes the dry mass (g) of solid residue after reduction,
150
iron ore before reaction, and oxygen loss of iron ore in the reduction process, respectively. It
151
shall be noted that the oxygen in gas product is from both lignin and iron ore during the
152
reduction process, and the mass of oxygen loss for iron ore can be calculated in terms of the
153
reduction degree of iron ore.
154
The metallization and reduction degrees of iron ore were determined by chemical analysis
155
in accordance to the ISO 11258 standard following the procedure given in reference [19] and
156
defined as:
157
M=
𝑀𝐹𝑒 𝑇𝐹𝑒
× 100%
(8) 6
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158
R=𝑀+
𝐹𝑒2 + 3 × 𝑇𝐹𝑒
× 100%
(9)
159
where MFe is the mass (g) of metallic iron of the reduced iron ore sample after the experiment,
160
TFe is the total amount (g) of Fe in the reduced sample, and Fe2+ is the mass (g) of Fe2+ in the
161
reduced sample.
162
The residue solid samples obtained from the ILP after reduction was characterized by XRD
163
on a Mac M21X powder diffractometer, and the microstructure characterization of the residue
164
solid samples was done on an EVO18 Special Edition (Carl Zeiss, Germany) Scanning Electron
165
Microscope (SEM) operating at 25 kV. The energy spectra (EDS) for some points in the ILP
166
samples were collected during the SEM analysis to reveal the atomic compositions of the
167
samples.
168
The composition of the obtained crude bio-oil was analyzed by gas chromatography and
169
mass spectrometry (GC-MS) (Agilent Technologies, 5977A MSD with a SHRXI-5MS column:
170
30 m × 250 mm × 0.25μm). Helium was used as the carrier gas and the GC oven temperature
171
program was set as follows: hold at 85C for 2 min, heated to 280 C at a heating rate of 20
172
C/min, then hold for 5 min. The compounds in the crude bio-oil were identified with the NIST
173
library (updated in 2011).
174
Thermogravimetric analysis (TGA) was carried out on a Perkin Elmer (Pyris 1 TGA)
175
instrument coupled with a Fourier Transform Infrared Spectrometer (FT-IR). The lignin or
176
lignin-iron ore mixture (1:2 wt/wt) with particles size＜0.425 mm (20 mesh) was heated at a
177
heating rate of 50 K/min from 293 K to 1373 K under nitrogen atmosphere (20 mL/min). FT-IR
178
was performed online to qualitatively determine the composition of the gas emitted from the
179
TGA process in the wave number range of 4000-500 cm-1.
180
3 Results and discussions
181
3.1 Analysis of gaseous and liquid products
182
The yields of gaseous product (Gas), char and liquid product (Oil including water) from the 7
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183
reactions with ILP and LP samples are shown in Fig.2. It is obvious that the formation of these
184
products from ILP and LP are significantly different, particularly at higher temperatures. For
185
instance, when the temperature was higher than 1173 K, the gas yield from ILP involving both
186
lignin pyrolysis/gasification and iron ore reduction was much higher than that from the LP
187
involving lignin pyrolysis/gasification only, whereas the oil and char yields from ILP are much
188
lower than those from LP, suggesting catalytic effects of iron ore or reduced iron species on
189
conversion of oil and char into gaseous products[20, 21].
190
With LP, the yields of three products did not vary too much with the increases of
191
temperature, because the operating temperatures in this work are already much higher than
192
common pyrolysis temperatures (673-973 K)[1]. In contrast, the yields of three products from
193
reactions of ILP varies greatly with the increases of temperature. As shown in Fig 2a, the gas
194
yield increases while the yields of char and oil decrease with increasing the temperature,
195
indicating conversion of char and oil into gaseous products during the ILP reduction. It has been
196
commonly agreed that bio-char and bio-oil vapor formed from biomass pyrolysis could reduce
197
iron ore and transform to CO/CO2 and H2O[16]. In addition, Iron ore can be a catalyst for the
198
pyrolysis/gasification of biomass such as lignin[3], contributing to an increase in gas yield and a
199
decrease in char yield.
200
The compositions of the gas products from the experiments with ILP and LP are shown in
201
Fig.3. At a relatively low temperature, i.e., 1093 K, the gas compositions in both experiments are
202
nearly the same, likely because at this temperature the reduction of iron ore by lignin is not
203
significant, as evidenced by the metallization degree of iron ore being only 2.1% (Fig.7a). As can
204
be noted that at the temperature higher than 1173 K, the compositions (CH4 and H2) of the gas
205
products from ILP and LP are generally similar, which was likely due to the decomposition of
206
lignin occurring at relatively lower temperatures. As such, the gas compositions of CH4 and H2 at
207
these temperatures are believed to be mainly determined by the pyrolysis/gasification of lignin.
208
In contrast, the CO yield from ILP is much higher than that of LP, particularly at higher
209
temperatures. Apparently, the greater formation of CO from ILP is due to the reduction of iron 8
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210
ore by lignin-derived carbon at these temperatures via the following reduction/gasification
211
reactions (as evidenced by Fig 7a discussed later). CO and CO2 are produced by the reaction of
212
lignin-derived carbon with iron oxide, and the CO2 produced by the reduction could gasify the
213
lignin-derived carbon to produce more CO (as evidenced by the results in Fig. 3a).
214
C + Fe𝑥𝑂𝑦→Fe𝑥𝑂𝑦 ‒ 1 + 𝐶𝑂 + 𝐶𝑂2
(10)
215
C + 𝐶𝑂2→2𝐶𝑂
(11)
216
The GC-MS chromatograms of the oils obtained from the experiments with ILP and LP are
217
comparatively illustrated in Fig.4. On one hand, as well known only lower boiling points
218
compounds in bio-oils could be vaporized and pass the GC column, while bio-oils usually
219
contain a greater portion of high-boiling point compounds, hence not detectable by GC-MS. On
220
the other hand, in this study the oil products were of less interest compared with gaseous
221
products. Accordingly, in this work for GC-MS analysis of the bio-oils, only major detectable
222
compounds in the oils, mainly aromatics, are presented. Less condensed aromatic compounds
223
gradually disappear while increasing the reaction temperature, likely due to the cracking or
224
gasification of these less condensed compounds. For instance, biphenylene and 4-Ethylbiphenyl
225
are present in the oils obtained at 1073 and 1173 K, but disappear at higher temperatures.
226
Fluorene-9-methanol and 4H-cyclopenta phenanthrene were detected in the oils at temperatures
227
below 1253 K but they were not detected in the oils at 1333 K, irrespective of the presence iron
228
ore. In the 1333 K oils, the major compounds detected are highly condensed aromatics such as
229
fluoranthene, pyrene and benz anthracene. The presence of heavy aromatics in the oil products
230
above 1173 K is apparently a result of the pyrolysis/gasification processes for lignin. Although
231
they were present in similar concentrations in the oils obtained from the experiments with ILP
232
and LP as illustrated in Fig.4, the absolute amounts of these heavy aromatics in the oils from the
233
experiments with ILP were actually much greater than those with LP due to the much suppressed
234
oil formation in the presence of iron ore, as evidenced in Figure 2. Thus, the presence of iron
235
species (ion oxides or reduced iron) could catalyze the cracking/gasification of heavy aromatics
236
into gaseous products. 9
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237
3.2 Analysis of the solid residues/products
238
Fig.5 shows the XRD of the obtained solid residues/products from reduction of ILP at
239
different temperatures. It can be seen that effects of reaction temperature are significant on the
240
crystalline structure of the recovered solid residues from ILP pyrolysis/gasification. The major
241
crystalline species identified in the raw iron ore sample are Fe2O3 and Fe3O4 at room
242
temperature. For the ILP, the major iron-containing species transformed to FeO as the
243
temperature was increased to 1093 K, and further to metallic Fe when the temperature was above
244
1173 K. At 1253 K, metallic Fe becomes the only iron species in the ILP-derived solid products,
245
and the peak of metallic iron increases with increasing the reaction temperature, indicating the
246
increased extent of reduction of iron ore by lignin at a higher temperature, as expected.
247
To better understand the morphology of metallic iron and lignin after the reduction, the ILP
248
and LP samples after reduction at 1423 K and 1093 K were studied by SEM and EDS analyses.
249
It should be noted that one special experiment was carried on 1423K with ILP aiming to prepare
250
reduced ILP sample only for SEM measurement. With the ILP sample at 1333K, however, many
251
powder falling off from the polishing surface of ILP sample, making the surface not conducive to
252
SEM observation. Thus, to facilitate observation, the ILP sample after reduction at 1423 K was
253
prepared and used for SEM analyses. Fig.6 shows SEM and EDS analyses results for the ILP and
254
LP samples after reaction. As clearly shown in Fig.6a, the reduction product from ILP contains
255
two phases: the phase in gray area and the phase in black areas. The EDS of two phases, as
256
shown in Fig.6c and d, indicates that the dominant element of the gray area is iron while the
257
black area is composed mainly of carbon, silicon, calcium, aluminum and iron. Thus, the gray
258
area is metallic iron phase and the black area the carbon residue and slag phase, as similarly
259
reported in the literature with other carbon-containing pellets[22].
260
The morphology of lignin-derived char residue is shown in Fig.6b. The char appears in the
261
form of carbon film of a very thin thickness. It was commonly believed that iron oxide can be
262
reduced by carbon reducing agent through the following processes: gasification of carbon to
263
form CO that reduces iron oxide at a relatively lower temperature, followed by direct reduction 10
ACCEPTED MANUSCRIPT
264
of iron oxide by solid carbon at higher temperatures[23]. The formation of thin film structure
265
carbon the lignin char with a high surface area would promote the gasification and direct
266
reduction reactions of carbon, hence facilitate the reduction of iron ore.
267
3.3 Reduction degree of ILP
268
To reveal the degree of reduction of iron ore by lignin, solid residues of ILP after reaction at
269
different temperatures were analyzed by chemical titration, and the results are shown in Fig. 7.
270
At 1093 K, the reduction degree of the pellets is 23.7%, and metallization degree is 2.1%, which
271
are in a good agreement with the XRD analysis (Fig. 5). The metallization and reduction degrees
272
both increase as the temperature increases, attaining the maximum values (86.3% and 91.3%,
273
respectively) at 1333 K. The iron oxide reduction is an endothermic reaction, thus
274
thermodynamically and kinetically favorable at a higher temperature. However, when the
275
temperature reaches a certain temperature, the depleted iron oxide in the sample would
276
kinetically limit the metallization and reduction degrees, hence both degrees level off at above
277
1253 K, as evidenced in Fig. 7.
278
As shown in Fig.7b, with increasing the lignin-to-iron ore mass ratio, both the reduction and
279
metallization degrees increase as expected, although they level off at the ratio above 1:1 (wt/wt).
280
For instance, at the ratio of 1:3 (wt/wt), the metallization degree and the reduction degree are
281
only 43.3% and 60.4%, respectively, while they are as high as 89.5% and 92.1%, respectively at
282
the ratios above 1:1 (wt/wt). Theoretically, given enough amount of lignin and enough
283
temperature, the iron ore can be completely reduced (100% metallization degree). In the present
284
experiments at a temperature of 1093 - 1333 K (or 820 - 1060C), lignin would undergo fast
285
pyrolysis first, releasing vapor/gases quickly. Then the gasification reactions would take place by
286
cracking of the vapor and between the vapor/gas and the residual char, in particular catalyzed by
287
the iron ore or reduced iron. H2 and CO as well as hydrocarbon radicals generated in the
288
gasification reactions along with the residual char would serve as reducing agents accounting for
289
the reduction of iron oxide, as evidenced by the high metallization ratio in this study, i.e., about 11
ACCEPTED MANUSCRIPT
290
90% at 1333K. On the other hand, however, when the ILP pellets were put into the furnace, it
291
would quickly foam, reducing the contact with iron oxide powder, and even overflow from the
292
basket [16]. Thus, at a very high lignin-to-iron ore mass ratio, the efficiency of lignin as a
293
reducing agent would decrease, accounting for the leveled-off metallization and reduction
294
degrees, as shown in Figure 7.
295
3.4 Roles of lignin in reduction of iron ore
296
In order to investigate the roles of lignin in the reduction of iron oxide, lignin alone and
297
lignin-iron ore mixture were studied by TGA experiments. A same amount of lignin was used in
298
these experiments. The TGA and DTG (derivative thermogravimetric analysis) curves of these
299
samples are shown in Fig.8. As can be seen from Fig. 8a, the mass loss curves of lignin alone
300
and lignin-iron ore mixture are obviously different. The mass loss curve of the lignin-iron ore
301
mixture keeps decline after 773 K, but at temperatures below this the TGA curve is similar to
302
that of lignin alone, suggesting the reduction of iron ore occurs at above 773 K. From the DTG
303
curves as shown in Fig.8b, the DTG curves of lignin alone and lignin-iron ore mixture are
304
obviously different, especially in two distinct temperature ranges, 773-973 K and 973-1373 K,
305
indicating the reduction of iron ore by lignin could take place in these two temperature ranges.
306
The mass loss rate at 973-1373 K was significantly faster than that at 773-973 K, suggesting
307
stronger reduction occurring at 973-1373 K than at 773-973 K.
308
The evolved gas from the TGA experiments were online analyzed by FTIR, and the FTIR
309
spectra of the gases at various temperatures are displayed in Fig.9. According to the FTIR
310
spectra, it can be evident that the temperature range of evolved gases is consistent with that of
311
weight loss in the TGA tests of both samples. The main species the evolved gas are CO2 (2450 ~
312
2250 cm-1, 750 ~ 600 cm -1), CO (2250 ~ 2050 cm-1), CH4 (3000 ~ 3030 cm-1), H2O (3800 ~
313
3500 cm-1, 1600 ~ 1500 cm-1) and other organic gas containing C = O (1850 ~ 1600 cm -1) and
314
C-O-C / C-C (1500 ~ 1050 cm-1) functional groups. Comparing the FTIR spectra of the gas
315
evolved from these two samples, it can be seen that in the IR absorbance of the gas evolved from 12
ACCEPTED MANUSCRIPT
316
the TGA experiments of lignin-iron ore mixture intensified at >973 K, particularly the
317
absorbance spectra of CO2, indicating that a large amount of gas formed mainly due to the
318
reduction of iron ore by CO and C derived from lignin at above 973 K.
319
The relative amounts of CO2, CH4 and CO were calculated by integration of the FTIR
320
characteristic peak of CO2, CH4 and CO at 2363 cm-1, 3017 cm-1 and 2167 cm-1, respectively,
321
and the results are shown in Fig.9c. At below 973 K, the evolution of all gas components (CO2,
322
CH4 and CO) from the lignin-iron ore mixture follows the similar trend as that of the lignin
323
alone, because at such low temperatures reduction of iron ore is not significant. However, at >
324
973 K, CO and CO2 evolved from the lignin-iron ore mixture were found to be much greater than
325
those from lignin alone, indicating that reduction of iron oxide by lignin took place preferably at
326
a high temperature, as evidenced previously in Fig.4 and 5.
327
In our previous studies on reduction of iron ore by hydrogen, the reduction started at around
328
600K and the maximum reaction rate was observed at about 830 K[16]. In this work, H2
329
appeared in the evolved gas in the experiments with either lignin alone or lignin-iron ore
330
mixture, as shown in Fig.3. Thus, iron ore could be reduced by hydrogen in the lower
331
temperature range, i.e., 773-973 K as shown in Fig.8. However, as illustrated in Fig.3, the H2
332
yield in the experiments with ILP is almost the same as that in the tests with LP. A possible
333
explanation was proposed by the authors, as presented in two equations. The formation of H2 by
334
steam gasification of carbon (char or lignin) could offset the consumption of H2 in iron ore
335
reduction, leading to a similar amount of H2 evolved from the experiments with ILP as that with
336
LP (Fig. 6).
337
H2 + Fe𝑥𝑂𝑦→Fe𝑥𝑂𝑦 ‒ 1 + 𝐻2𝑂
(12)
338
H2O + C→CO + 𝐻2
(13)
339
Zhao et al[24] studied manganese oxide ore reduction using biomass straw as a reductant.
340
They considered that the main role of reduction of manganese oxide by biomass was through CO
341
gas produced from biomass pyrolysis at the temperature lower than 873 K. In their experiments,
342
H2 should also play a role as a reductant. However, as well known the reduction of iron oxides is 13
ACCEPTED MANUSCRIPT
343
more difficult than that of manganese oxides, for instance, Strezov[18] found that the reduction
344
of iron ore using sawdust commenced at approximately 943 K, which was higher than the
345
starting temperature (773 K) for iron ore reduction in this work. This could be mainly owing to
346
the use of pure lignin in this study, producing more H2 in pyrolysis/gasification, which was
347
evidenced by a literature study of Yang et al[25] demonstrating that much more H2 was produced
348
from lignin pyrolysis than that from hemicellulose or cellulose. The formation of H2 from lignin
349
pyrolysis at a lower temperature might account for the lower starting temperature (773 K) for
350
iron ore reduction in this work. The findings on iron-ore reduction by carbon at high
351
temperatures are similar to those reported in the literature [11, 24].
352
4. Prospective of coupled biomass gasification and iron ore reduction
353
The positive results from this study show great promise of application of lignin in iron and
354
steel making industry as a reducing agent for DRI production. Apart from lignin, other kinds of
355
biomass have also been investigated and demonstrated promise to be as reducing agents for iron
356
ores in our previous work[3, 16, 20]. For better economics, iron ore reduction and biomass
357
gasification can be coupled, and the coupled biomass gasification and iron ore reduction
358
(CBGIOR) process can be conceptually shown in Fig. 10.
359
In the proposed CBGIOR process, the presence of biomass (lignin) supplies carbon and
360
hydrogen-containing reducing agents by pyrolysis/gasification for iron ore reduction, whereas
361
the iron oxide could provide oxidant and reduced iron as a catalyst to promote biomass
362
gasification, via the following reactions: 𝐹𝑒𝑥𝑂𝑦
363
Biomass → 𝐻2 + 𝐶𝑂 + 𝐶𝐹𝑖𝑥𝑒𝑑 𝑐𝑎𝑟𝑏𝑜𝑛 + 𝑂𝑡ℎ𝑒𝑟𝑠
(14)
364
𝐹𝑒𝑥𝑂𝑦 + H2→𝐻2𝑂 + 𝐹𝑒
(15)
365
𝐹𝑒𝑥𝑂𝑦 + CO→CO2 + 𝐹𝑒
366
𝐹𝑒𝑥𝑂𝑦 + C𝐹𝑖𝑥𝑒𝑑 𝑐𝑎𝑟𝑏𝑜𝑛→CO2 + 𝐶𝑂 + 𝐹𝑒
367
(16)
The overall reaction: 14
(17)
ACCEPTED MANUSCRIPT
368
𝐹𝑒𝑥𝑂𝑦
Biomass + 3𝐹𝑒𝑥𝑂𝑦 → 𝐻2𝑂 + 𝐶𝑂 + 𝐶𝑂2 + 3𝐹𝑒 + 𝑂𝑡ℎ𝑒𝑟𝑠
(18)
369
Firstly, H2 and CO are produced via the pyrolysis/gasification of biomass catalyzed by iron
370
oxide, and the iron oxide is reduced mainly by H2 at a lower temperature (before 973 K) due to
371
the higher reactivity of H2 than that of CO. When the temperature further increases (above 973
372
K), reactions 16 and 17 would occur simultaneously. The overall reaction involved in the
373
proposed CBGIOR process is reaction 18.
374
Compared with conventional biomass gasification processes and ironmaking processes, the
375
CIORBG process has several advantages, e.g., (1) it integrates biomass pyrolysis/gasification
376
and iron ore reduction in a synergistic way, co-generating syngas of a high calorific value
377
(containing CO, H2, CH4, CO2, etc.) and DRI cost-effectively; (2) it suppressed bio-oil yield with
378
greatly increased gas yield (Fig. 2), reducing the adverse effects of bio-oil on the syngas
379
production (pipe blockage and corrosion etc.); (3) owing to high reductive activity of carbon in
380
char and biomass pyrolysis vapor or gasification gases (CO/H2 gases), the iron ore reduction
381
temperature of the process (1073 K～1333 K) is much lower than the conventional blast furnace
382
processes (1173 K～1773 K) and the coal-based DRI processes (1523 K～1623 K). Future work
383
is needed on further development of the CBGIOR process, in particular with respect to
384
optimizing the biomass-iron ore blending ratio, designing suitable reactors, and minimizing the
385
formation of bio-oil and enhancing the metallization degree of iron ore, etc.
386
5. Conclusions
387
Coupled biomass gasification and iron ore reduction was investigated and demonstrated in
388
this work through pyrolysis/gasification of ILP at 1093～1333 K. The solid (char), oil and gas
389
products were analyzed by XRD, SEM, chemical analysis, GC-MS, Micro-GC and TG-FTIR.
390
Direct reduction iron (DRI) was produced in the process. The reduction and metallization
391
degrees of iron ore increased with increasing the reaction temperature as expected, reaching the
392
maximum values (86.3% and 91.3%, respectively) at 1333 K. The gas yields in the experiments
393
with ILP were much higher than those with LP at 1173 ～1333 K, owing to the much greater 15
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amount of CO formed in reduction of iron ore by lignin (carbon). Whereas, the bio-oil yields in
395
pyrolysis/gasification of LP were much higher than those in pyrolysis/gasification of ILP,
396
suggesting that the presence of iron ore or metallic iron could catalyze gasification of the oil into
397
gaseous products. It was found that in the pyrolysis/gasification of ILP, the iron ore could be
398
reduced by lignin-derived hydrogen first, then by CO and carbon. Meanwhile, during the
399
pyrolysis/gasification of ILP, the iron ore or metallic iron could act as an oxidant/catalyst to
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promote biomass gasification. Based on the positive results from this study, a novel conceptual
401
process, i.e., coupled biomass gasification and iron ore reduction (CBGIOR) process was
402
proposed.
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Acknowledgements: The authors would like to acknowledge the funding from BioFuelNet
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Canada, a Network of Centres of Excellence, NSERC through the Discovery Grants, the
405
NSERC/FPInnovations Industrial Research Chair in Forest Biorefinery and National Natural
406
Science Foundation of China (Grant No. 51274003, 51674002 and U1660206).
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References: 1. Bridgwater AV, Meier D, Radlein D. An overview of fast pyrolysis of biomass. ORG GEOCHEM. 1999. 2. Kirubakaran V, Sivaramakrishnan V, Nalini R, Sekar T, Premalatha M, Subramanian P. A review on gasification of biomass. RENEW SUST ENERG REV. 2009;13(1):179-86. 3. Hurley S, Li H, Xu C. Effects of impregnated metal ions on air/CO 2 -gasification of woody biomass. BIORESOURCE TECHNOL. 2010;101(23):9301-7. 4. Jiang G, Nowakowski DJ, Bridgwater AV. Effect of the Temperature on the Composition of Lignin Pyrolysis Products. Energy Fuels. 2010;24(8):4470-5. 16
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5. Kang S, Li X, Fan J, Chang J. Hydrothermal conversion of lignin: A review. Renewable and Sustainable Energy Reviews. 2013;27:546-58.
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6. Zhang L, Champagne P, Charles XC. Supercritical water gasification of an aqueous by-
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product from biomass hydrothermal liquefaction with novel Ru modified Ni catalysts.
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BIORESOURCE TECHNOL. 2011;102(17):8279-87.
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7. Wei R, Zhang L, Cang D, Li J, Li X, Xu CC. Current status and potential of biomass
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utilization in ferrous metallurgical industry. RENEW SUST ENERG REV. 2017;68:511-24.
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8. Gong FY, Ye TQ, Yuan LX, Tao K, Torimoto Y, Yamamoto M, et al. Direct reduction of
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iron oxides based on steam reforming of bio-oil: a highly efficient approach for production of
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DRI from bio-oil and iron ores. GREEN CHEM. 2009;11(12):2001-12.
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9. Guo D, Zhu L, Guo S, Cui B, Luo S. Direct reduction of oxidized iron ore pellets using biomass syngas as the reducer. 10. Chakar FS, Ragauskas AJ. Review of current and future softwood kraft lignin process chemistry. Industrial Crops & Products. 2004;20(2):131-41. 11. Srivastava U, Kawatra SK, Eisele TC. Production of pig iron by utilizing biomass as a reducing agent. INT J MINER PROCESS. 2013;119(119):51-7. 12. Fu JX, Zhang C, Hwang WS, Liau YT, Lin YT. Exploration of biomass char for CO 2 reduction in RHF process for steel production. INT J GREENH GAS CON. 2012;8(5):143-9.
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13. Guo D, Hu M, Pu C, Xiao B, Hu Z, Liu S, et al. Kinetics and mechanisms of direct reduction
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of iron ore-biomass composite pellets with hydrogen gas. INT J HYDROGEN ENERG.
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15. Osada M, Sato O, Watanabe M, Arai K, Shirai M. Water Density Effect on Lignin
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Gasification over Supported Noble Metal Catalysts in Supercritical Water. ENERG FUEL.
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16. Wei R. Fundamental studies of iron ore reduction by different reductants under mechanical activation. Beijing: University of Science and Technology Beijing, 2016.
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17. Huang Z, Zhang Y, Fu J, Yu L, Chen M, Liu S, et al. Chemical looping gasification of
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biomass char using iron ore as an oxygen carrier. INT J HYDROGEN ENERG.
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18. Strezov V. Iron ore reduction using sawdust: Experimental analysis and kinetic modelling. RENEW ENERG. 2006;31(12):1892-905. 19. ISO. Determination of reduction index, final reduction degree and metallization rate of iron ore for direct reduction furnace. 2007. 20. Wei R, Cang D, Bai Y, Huang D, Liu X. Reduction characteristics and kinetics of iron oxide by carbon in biomass. IRONMAK STEELMAK. 2016.
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21. Hurley S, Xu CC, Preto F, Shao Y, Li H, Wang J, et al. Catalytic gasification of woody
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biomass in an air-blown fluidized-bed reactor using Canadian limonite iron ore as the bed
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material. FUEL. 2012;91(1):170-6.
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22. Li J, Wei R, Long H, Wang P, Cang D. Sticking behavior of iron ore–coal pellets and its inhibition. POWDER TECHNOL. 2014;262:30-5. 18
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24. Zhao Y, Zhu G, Cheng Z. Thermal analysis and kinetic modeling of manganese oxide ore
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reduction using biomass straw as reductant. HYDROMETALLURGY. 2010;105(1-2):96-102.
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25. Yang H, Yan R, Chen H, Lee DH, Zheng C. Characteristics of hemicellulose, cellulose and
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lignin pyrolysis. FUEL. 2007;86(12–13):1781-8.
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Figure captions
487
Fig.1 Schematic diagram of experimental apparatus (1. N2 bottle; 2. Mass flow controller; 3.
488
Electric furnace; 4. Samples; 5. Filter and cold trap; 6. Gas analyzer (micro-GC); 7. Computer).
489
Fig.2 Yields of Gas, Char and Oil from the experiments with ILP (a) and LP (b)
490
Fig.3 Yields of H2, CO，CH4 and other gaseous products from the experiments with ILP (a) and
491
LP (b)
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Fig.4 GC-MS chromatograms of the oil products from the experiments with ILP and LP
493
Fig.5 XRD patterns of the ILP sample after reduction at different temperatures
494
Fig.6 SEM images of the ILP sample (a) and LP sample (b) after reaction at 1423 K and 1093 K,
495
respectively, and the EDS spectra of point 1 (c) and point 2 (d) in the ILP sample.
496
Fig. 7 Reduction and metallization degrees of the ILP sample after pyrolysis/gasification at
497
different temperatures (a) and different lignin-to-iron ore mass ratios (b)
498
Fig.8 TGA (a) and DTG (b) curves of lignin alone and lignin-iron ore mixture
499
Fig. 9 FTIR of the evolved gases from of TGA experiments for lignin alone (a) and lignin-iron
500
ore mixture (b), and quantification analysis of gas species by FTIR (c)
501
Fig.10 Conceptual scheme of the coupled biomass gasification and iron ore reduction (CBGIOR)
502
process
503 504
20
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2
4
5
3
1
7
6
505 506
Fig.1 Schematic diagram of experimental apparatus (1. N2 bottle; 2. Mass flow controller; 3. Electric furnace;
507
4. Samples; 5. Filter and cold trap; 6. Gas analyzer (micro-GC); 7. Computer).
508 509 510 511 512 513 514 515
21
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a
Char
Oil
Gas
100
Yield (%)
80 60 40 20 0 1093
1173
1253
1333
Temperature (K)
516
b
Char
Oil
Gas
100
Yield (%)
80 60 40 20 0 1093
517 518
1173
1253
1333
Temperature (K)
Fig.2 Yields of Gas, Char and Oil from the experiments with ILP (a) and LP (b)
519
22
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a
0.030
H2
CH4
CO
Others
Gas yield (mol/g)
0.025 0.020 0.015 0.010 0.005 0.000 1093
1173
1253
1333
Temperature (K)
520
b
0.030
H2
CH4
CO
Others
Gas yield (mol/g)
0.025 0.020 0.015 0.010 0.005 0.000 1093
1173
1253
1333
Temperature (K)
521 522
Fig.3 Yields of H2, CO，CH4 and other gaseous products from the experiments with ILP (a) and
523
LP (b)
23
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6 5
525
7
1333 K, ILP 56 3 1253 K, LP
7
4 5
3 1253 K, ILP
1173 K, LP
1
56
3 4 3
1093K, LP
10
5
6
6 4 5
1 2 3
1093 K, ILP
7 7
4
2
1173 K, ILP
6
4
3
5
524
7
1333 K, LP
Intensity(a.u.)
4- 4H-Cyclopenta phenanthrene, 5- Fluoranthene, 6- Pyrene, 7- Benz anthracene
1- Biphenylene, 2- 4-Ethylbiphenyl, 3- Fluorene-9-methanol,
6 5
4
56
7
7 7
1 2
15
20
25
30
Reaction Time (min)
Fig.4 GC-MS chromatograms of the oil products from the experiments with ILP and LP
24
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1-Fe 2-FeO 3-Fe3O4 4-Fe2O3
1
Intensity (a.u.)
1333 K
1
1
1
1
1 1253 K 1 1173 K
2
2
2 1
2
1093 K
2
2
2
2
Raw iron ore3 10
20
30
43
4 4 40
50
1
34 60
70
80
90
526
2θ (°)
527
Fig.5 XRD patterns of the ILP sample after reduction at different temperatures
528 529 530 531 532 533 534 535 536 537
25
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1
a
b
c
d
2
538
539 540
Fig.6 SEM images of the ILP sample (a) and LP sample (b) after reaction at 1423 K and 1093 K,
541
respectively, and the EDS spectra of point 1 (c) and point 2 (d) in the ILP sample.
542 543 544 545
26
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a 100
Metallization degree Reduction degree
Degree (%)
80 60 40 20 0
Lignin : iron ore=1:2(wt/wt)
1093
1173
1253
1333
Temperature (K)
546
b 100 90
Metallization degree Reduction degree
Degree (%)
80 70 60 50 40
1253 K
1:3
547
1:2
1:1
1:0.5
Ratio of lignin/iron ore(wt/wt)
548
Fig. 7 Reduction and metallization degrees of the ILP sample after pyrolysis/gasification at
549
different temperatures (a) and different lignin-to-iron ore mass ratios (b)
27
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a
0
Mass loss (mg)
-2 -4 -6
LP
-8 -10
ILP
-12 373
573
773
973
1173
1373
Temperature (K)
550
b
0.120
Mass loss rate(a.u.)
0.125
2
0.130 0.135
ILP
1
0.140 0.145 0.150 LP
0.155 373
573
773
973
1173
1373
551
Temperature (K)
552
Fig.8 TGA (a) and DTG (b) curves of lignin alone and lignin-iron ore mixture
28
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553 without Fe2O3
c
with Fe2O3
Absorbance
CO2
CH4
CO
373
554
573
773
973 1173
Temperature(K)
555
Fig. 9 FTIR of the evolved gases from of TGA experiments for lignin alone (a) and lignin-iron
556
ore mixture (b), and quantification analysis of gas species by FTIR (c)
557 558 559
29
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560 561
Fig.10 Conceptual scheme of the coupled biomass gasification and iron ore reduction (CBGIOR)
562
process
563 564 565 566 567 568 569 570 571 572 573 574 575 576 30
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577
Tables captions
578
Table 1. Composition of lignin
579
Table 2. Chemical composition of iron ore
580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 31
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604
Table 1. Composition of lignin Ultimate analysis (% wt/wt, dry basis)
Composition ((% wt/wt, dry basis)
Composition Content
605
1
C
H
O1
N
Ash
Lignin
Cellulose
Hemicellulose
71.6
6.3
21.9
0.2
0
>95.02
n.a.3
n.a.3
By difference assuming 0 (% wt/wt S; 2 Data from the supplier; 3 Not analyzed.
606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 32
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628
Table 2. Chemical composition of iron ore Composition
TFe
FeO
SiO2
Al2O3
CaO
MgO
S
P
Content (% wt/wt, dry basis)
65.4
13.8
6.96
0.52
0.11
0.31
0.025
0.045
629
33
ACCEPTED MANUSCRIPT Highlights
Coupled biomass gasification and iron ore reduction by pyrolysis of iron ore– biomass pellets
Iron oxide/metallic iron provided an oxidant/catalyst for biomass gasification.
Biomass provided reducing agents for reduction of iron oxide.