Experimental study on the effect of pyrolysis pressure, peak temperature, and particle size on the potential stability of vine shoots-derived biochar

Published Date

1 October 2014, Vol.133:163–172, doi:10.1016/j.fuel.2014.05.019

Title 

Experimental study on the effect of pyrolysis pressure, peak temperature, and particle size on the potential stability of vine shoots-derived biochar

• Author 

• Joan J. Manyà ^,
• Miguel A. Ortigosa
• Sergio Laguarta
• José A. Manso

• Thermo-chemical Processes Group (GPT), Aragón Institute of Engineering Research (I3A), University of Zaragoza, Technological College of Huesca, crta. Cuarte s/n, E-22071 Huesca, Spain

Received 5 February 2014. Revised 2 May 2014. Accepted 8 May 2014. Available online 23 May 2014.

Highlights

• •
  A central composite design was applied to assessing the effect of selected factors.
• •
  Stability of the vine shoots-derived biochar was mainly determined by the particle size.
• •
  Using a bed of alumina represents a low-cost way to partly remove tar from the pyrolysis gas.

Abstract

This study examines the effect of three key operating factors (peak temperature, particle size and pressure) on the potential stability of the biochar produced by slow pyrolysis of vine shoots. The following response variables were considered as key indicators of the potential stability of biochar in soils: the fixed-carbon yield, the fraction of aromatic carbon, and the molar H:C and O:C ratios. Slow pyrolysis tests were conducted in a laboratory-scale fixed-bed unit and planned according to a 2-level factorial design. The behavior of the product gas yield and composition at the outlet of the secondary cracking reactor (a fixed-bed of activated alumina particles at 700 °C) was also evaluated as a function of the three factors. The results from the statistical tests revealed that the particle size is the most significant factor in determining the potential stability of biochars. Using larger particles of biomass and, in a lesser extent, operating at higher peak temperatures leads to the production of more stable materials. Unexpectedly, the absolute pressure only plays a significantly positive role in decreasing the tar content in the producer gas at the outlet of a secondary cracking reactor.

Keywords

• Biochar
• Pyrolysis
• Vine shoots
• Pressure
• Particle size

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Nomenclature

GHSV

gas hourly space velocity (h⁻¹)

m_bio

dry mass of biomass sample (kg)

m_char

mass of produced biochar (kg)

adjusted coefficient of determination

x₁

coded variable for pressure

x₂

coded variable for peak temperature

x₃

coded variable for particle size

y_char

biochar yield (kg kg⁻¹ of biomass in a dry basis)

y_FC

fixed-carbon yield (kg kg⁻¹ of biomass in a dry and ash-free basis)

y_gas

yield of producer gas (kg kg⁻¹ of biomass in a dry and N₂-free basis)

y_water

yield of water (g kg⁻¹ of biomass in a dry basis)

y_tar

yield of tar (g kg⁻¹ of biomass in a dry basis)

Greek symbols

β₀

regression coefficient for the intercept term

β₁

regression coefficient for the linear effect of pressure

β₂

regression coefficient for the linear effect of peak temperature

β₃

regression coefficient for the linear effect of particle size

β₁₂

regression coefficient for the interaction term between pressure and peak temperature

β₁₃

regression coefficient for the interaction term between pressure and particle size

β₂₃

regression coefficient for the interaction term between peak temperature and particle size

β₁₁

regression coefficient for the quadratic effect of peak temperature

ρ

Pearson’s correlation coefficient

Acronyms

BET

Brunauer Emmett Teller

CEC

cation exchange capacity

CP-MAS

cross polarization and magic angle spinning

FC

fixed carbon

GC

gas chromatography

NMR

nuclear magnetic resonance

PID

proportional integral derivative

RSM

response surface methodology

TGA

thermogravimetric analysis

XRF

X-ray fluorescence

WGS

water gas shift

 Table 1

Table 1.

Fig. 1.

 Table 2

Table 2.

 Table 3

Table 3.

 Table 4

Table 4.

Fig. 2.

Fig. 3.

Fig. 4.

 Table 5

Table 5.

Fig. 5.

• ⁎ 
  Corresponding author. Tel.: +34 974292649; fax: +34 974239302.

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