Study of Co-pyrolysis of Huai Nan Coal with Cotton Stalk

Tengfei Chang1,a, Chuyang Tang2,b, Ge Wang3,c, Meiyu Gu4, Yingdong Jia5

1School of Architecture and Construction, University of Science and Technology Liaoning, Liaoning

Province 114044, China

aastcy@126.com, bchuyangt@gmail.com, c249513011@qq.com

Key words: co-pyrolysis; coal; biomass; cotton stalk

Abstract. An experimental study on co-pyrolysis of biomass and coal was performed in a tubular

furnace for comparison of product (tar, water, gas and char) yields and composition. The coal

sample selected was Huai Nan bituminous coal (HN), while the biomass used was cotton stalk (CS),

and the blending ratio of biomass in mixtures was 0/100, 5/100, 10/100, 20/100, 30/100, and

50/100. The blends of coal and biomass were heated 600oC at 5

oC/min, and then kept for 15 min

during the pyrolysis. The results indicated that there exist synergetic effects in the co-pyrolysis of

biomass and coal. The tar yield was 9.33% higher than the theoretical value at the CS blending ratio

of 5/100. The maximum light oil content in tar was 9.67% higher than the theoretical value at the

CS blending ratio of 10/100.

Introduction

Energy is a vital input for social and economic development of any nation. With the advent of

industrialization and globalization, the demand for energy has increased exponentially [1]. China’s

primary energy supply was and still is heavily dependent on coal [2]. The effective and clean

conversion process using low rank coals has recently become one of the most desired technologies

to be developed worldwide, since their utilization can substantially lower the energy production cost

[3]. Reducing overhead and increasing utilization is definitely the only way in the right direction.

The pyrolysis of coal is a good method for producing liquid fuels and other chemicals, but the

yields of these products are limited because of the low hydrogen-to-carbon ratio in coal [4]. Both

coal and biomass have complex structures containing a number of different constituents. These

constituents show their inherent individual characteristics during thermal processes, and each one

contributes to the apparent thermal characteristics of the feedstock. On the other hand, when coal

and biomass are processed together in a process such as co-pyrolysis, some synergistic interactions

may take palace, leading to significant variations in the chemical properties of the products. Ryan M.

Soncini, et al [5] found co-pyrolysis of southern yellow pine with a sub-bituminous Power River

Basin coal and Mississipi lignite showed the product distributions evolved more tar, and less char,

CH4, and C2H4 than an additive pyrolysis, particularly at higher temperatures and for decreasing

coal rank. Li Zhang, et al [6] studied the synergetic effects in the co-pyrolysis of legume straw and

Dayan lignite in a free fall reactor and at N2 atmospheres and at the temperatures of 500℃, 600℃,

700℃, respectively. The results indicated that the char yields decrease and consequently the liquid

yields increase compared with the theoretical values. Jinxia Fei, et al [7] revealed that acid

pickling is beneficial to increase the tar yield and effect on the cross-linking reaction to less

resistant escaping of tar from the intra-particles of coal in the co-pyrolysis of a calcium-rich lignite

coal and a high-sulfur bituminous coal on a fixed-bed reactor. It is worth to devote attention to

hydroprocessing techniques, such as hydrotreating and hydrocracking in low-temperature tar

processing, with the primary objectives of reducing viscosity, reducing polynuclear aromatics, and

removing heteroatoms (sulfur, nitrogen, and oxygen) to produce usable fuels and chemicals.

Advanced Materials Research Vols. 953-954 (2014) pp 251-254Online available since 2014/Jun/18 at www.scientific.net© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.953-954.251

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Experimental

2.1 Preparation of biomass/coal samples

Huainan (HN) coal samples which is described as low grade, high ash, and inertinite rich were

chosen for the experiments. The biomass type used in the study was cotton stalks (CS), obtained

from farms in Zhengzhou, Henan province. The properties of samples, i.e. the ultimate and

proximate analyses, were presented in Table 1. The proximate analysis was conducted according to

GB/T 212-2008. C, H contents in the single samples where determined according to GB/T

476-2008. Nitrogen was determined using GB/T 19227-2008. Sulphur was determined according to

GB/T 214-2007. Experiments were carried out with manual blends of HN and SC. Particle size of

the sample was less than 178μm in diameter. In tubular furnace (Nasren GDL-B-II, China), five

blending weight ratios of SC/HN (5/100, 10/100, 20/100, 30/100) were employed.

Table 1 Ultimate and proximate analyses of tested samples.

Proximate

analysis, wt.% SC HN

Ultimate

analysis, wt.%(daf) SC HN

Volatile matter(daf) 78.88 42.12 C 48.11 83.12

Fixed carbon(daf) 21.12 57.88 H 6.02 6.07

Ash(d) 4.13 26.34 N 0.98 1.54

Moisture(ad) 2.31 2.18 S 0.19 0.66

2.2 Experimental apparatus and methods

Fig. 1 shows a schematic diagram of the tubular furnace for the pyrolysis of biomass/coal. The

tubular furnace made of cast copper and five electric heaters of 1 kW were installed inside the

furnace to heat the quartz reactor tube to the desired temperature. A thermocouple was installed in

the furnace to measure the heating temperature. Sample (10g) was fed into the reactor tube,

thereafter the reactor was pushed into the furnace and heated to 600℃ at a rate of 5℃/min, and then

kept for 15 min. The volatile passed through the reactor from the solid particles and was cooled in

Erlenmeyer flask in series to collect the condensable components. The gaseous production passed

through the bypass of reducing bend and was collected by a gas bag. The gas compositions were

analyzed by GC (Shangfen GC126, China).

The water content of liquid product was determined according to GB/T 2288-2008. The light oil

was separated from tar by using rotary evaporator at 60 ℃ and determined according to ASTM D91

and ASTM D2317. Light oil compositions were analyzed by GS-MS (Micromass LCTTM,

England).

1. Furnace; 2. Reactor tube; 3. Asbestos wool 4. Samples; 5. Heat controller; 6 Temperature display; 7.

Thermocouple; 8. Temperature recorder; 9. Temperature regulation; 10. Power; 11. Heater lamp; 12. Buzzer; 13.

Cold trap; 14. Refrigerator; 15. U-tube; 16. Gas bag.

Fig. 1 Schematic diagram of the tubular furnace for the pyrolysis of biomass/coal

252 Advanced Energy Technology

Results and discussion

The samples of CS/HN are heated to 600℃ at a rate of 5℃/min, and then kept for 15 min in the

tubular furnace. The product yields from the pyrolysis of SC/HN blend as a function of SC/HN

blending ratio are shown in Fig.2. With increasing the ratio of CS, char yields decrease but volatile

matter yields increase. Water yield increases dramatically, compared with tar yield.

0/100 5/100 10/100 20/100 30/100 40/100 50/100

40

60

80

100

Pyro

lysis

pro

duct,w

t% (

d)

CS/HN, wt

Gas yield

Water yield

Tar yield

Char yield

Fig. 5 Pyrolysis product distribution

The light oil contents are lower with the increase of SC ratio in samples. The peak of light oil yield

is observed at 10/100. The maximum value of tar yield is 17.46% at 10/100. The maximum

difference of tar yields is 1.49% with a blending ratio of 5/100. With a further increasing blending

ratio of CS/HN, the experimental yields are lower than the theoretical values at the ratio of 20/100.

Under the higher blending ratio of SC, the yields of light oil are lower and get close to the values of

theoretical values. The light oil yield has maximum increases by 1.75%, compared with the

theoretical values. The maximum value of tar yield occurs at the ratio of 5/100 and the light oil

yield is at 10/100. The free radicals and hydrogen-donors are generated by CS to decompose coal

when the blending ratio below 10/100 since the recombination reaction is favored with higher coal

blending ratio. This may be due to that the right amount of CS is needed to offer enough of

hydrogen donors and play a hydrogenation role on mild coal pyrolysis conditions. With the increase

of CS ratio in samples, the free radical reaction of hydroxyl radical has higher speed and more water

is created in the pyrolysis processes. The increase of water yield could verify the postulate.

Advanced Materials Research Vols. 953-954 253

0/100 5/100 10/100 20/100 30/100 50/100

0

5

10

15

20

Tar

yie

ld (

wt%

(d

af)

)

CS/HN

Tar yield

Theoretical tar yield

Light oil yield

Theoretical light oil yield

Water yield

Theoretical water yield

Fig.3 Comparatives of the pyrolysis productions with the theoretical values

Conclusions

Experimental results showed that product distributions displayed non-linear effects under the

conditions studied. For the co-pyrolysis of HN and CS, the synergy to produce more tar was

appeared at the CS blending ratio of 5/100 and 10/100. The tar yield which was 17.46wt% reached

a maximum at the CS blending ratio of 5/100 and it was 9.33% higher than the theoretical value.

The maximum light oil content in tar was 77.38% at the CS blending ratio of 10/100 and 9.67%

higher than the theoretical value.

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[4] R. Cypres, W. Mingels, J. P. Lardinois. Feasibility study of the hydropyrolysis of coal.

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[5] Ryan M. Soncini, Nicholas C. Means, Nathan T. Weiland. Co-pyrolysis of low rank coals and

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[6] Li Zhang, Shaoping Xu, Wei Zhao, et al. Co-pyrolysis of biomass and coal in a free fall reactor.

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254 Advanced Energy Technology

Advanced Energy Technology 10.4028/www.scientific.net/AMR.953-954 Study of Co-Pyrolysis of Huai Nan Coal with Cotton Stalk 10.4028/www.scientific.net/AMR.953-954.251