Application of activated process char for gas treatment of biomass gasification producer gases

York Neubauer and Omid-Henrik ElhamiInstitute of Energy Engineering | NWG-TCKON | Chicago | 03.11.2015

Thermo-chemical gasification

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gasification product gas:(depending on feed and conditions):• gaseous compounds

H2, CO, CH4, C2-C5, CO2, H2O, (N2)

gas contaminants:• particulate matter - ash, unreacted

carbon• condensable organic species – ‘tar’• further contaminants -

containing S, N, Cl, …

Motivation

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thermo-chemical gasification yields fuel- and synthesis gases for multiple utilization pathways

the comparably small to medium sized plants for utilizing biogeneous feedstocks are faced with rather high specific capital and operational expenditures for gas cleanup (dust, tar, N, S, Cl …)

No established standard process for process gas cleaning and conditioning available – new engineering with each new project and client requirements necessary

Either optimized gasifier operation or complex gas aftertreatment

Lack of knowledge about the ‘black box’ gasifier

Junior research group „TCKON“ @ TU Berlin

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Targeted influencing of heterogeneous reactions of gas or vapor with the solid surfaces of carbon structures during the conversion process

Selective influencing of char properties and utilizing char generated in the process

Fluorescence measurements of aromatic multi-component mixtures in hot product gases of thermochemical conversion processes / development of a robust ‘tar‘-sensor

‘Fundamental examinations and selective influencing of heterogeneous reactions in thermochemical conversion of biomass and robust, continuous on-line monitoring of the organic load of the gas phase’.

Main aims:

Biomass gasification and its gas quality challenge

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adapted from: Hofbauer H, Gas production for polygeneration plants. International Conference on PolygenerationStrategies (ICPS), Vienna, Austria (2009)

Process char: just an reaction intermediate ?

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Making use of activated carbon within gas producer process chains

adapted from Hofbauer H, Gas production for polygeneration plants. International Conference on PolygenerationStrategies (ICPS), Vienna, Austria (2009)

pyrolysis char activation

processchar

pyrolysischar

AC

General approach

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Objectives:• Creating suitable pore structures for ‘tar’-

species adsorption

• Investigations on PAH adsorption on activated process char (AC)

• Study effect of the gasification medium and the gas composition on the pore structure of char intermediates in FB gasification

• Feasibility of operating the gasifier in a mode generating useful AC for subsequent gas processing

Generating char: fixed bed and screw-type pyrolysis unit

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• reaktor di: 200 mm• bed height: 50 cm• temperature up to 700°C

Generating process-char: bubbling fluidized bed gasifier

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• reactor di: 114 mm• bed height: 60-80 cm• temperature 700-900°C• gas flow ~6 Nm³/h• fuel input 3 kg/h

Activating the char

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• reactor di: 50 or 80 mm• bed height: 3-20 cm• temperature 700-1000°C

N2

CO2

CO

H2

CH4

PAH dosing system

evaporator HPLC pump H2O

gas

preh

eate

rch

ar

activ

atio

n re

acto

r

T

online μ-GC / online GC-FID

off-gas

mass flow controllerOptional for

adsorption tests

PAH adsorption on char in the literature

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Quantitative study of PAH adsorption on activated carbon from model compounds by Mastral et al.²:

total microporosity is the main factor controlling the adsorption process

• micropore sizes higher than 0.7 nm, wherePAH molecules do not find diffusionalproblems favors the adsorption

• High development of the mesoporosity notonly drive the adsorbate molecules to themicropores but also promote the multilayerinteractions increasing the equilibriumadsorption capacity

• low surface acidity, due to both thehydrophobic nature and the lower humidityadsorption capacity of the PAH

Evolution of pore volume per gram of starting char as a function of burn-off(char obtained from olive stones) 3

2 A. M. Mastral et. al. Development of Efficient Adsorbent Materials for PAH Cleaning from AFBC Hot Gas. Energy & Fuels 18, 2004 3 F. Rodriguez-Reinoso et. al. The use of steam and CO2 as activating agents in the preparation of activated carbons. Carbon Vol. 33, No. 1, 1995

starting materials and activated char

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Proximate analysis (dry basis, %)

Ultimate analysis (dry & ash free basis, %)

volatile matter ash fixed

carbon C H N O Ssamples reaction temperature

Fluid.-bedpine char 800-820°C 5,0 7,7 87,3 87,65 0,30 0,21 3,89 0,25

Fixed bedpine char 600°C 7,6 0,7 91,7 91,02 1,95 0,10 6,22 0,01

Fixed bedoak-char (“Räuchergold”)

600°C 15,1 1,5 83,4 83,05 2,89 0,32 12,06 0,18

fluidized bed gasifier char fixed bed pyrolysis char

Characterization of process chars – pore size distribution

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specific surface area

(m²/g)pore size distribution (cm³/g)

sample reaction temperature SBET

micropore< 2 nm

mesopore2 – 50 nm

total < 250 nm

fluidized bed gasifierpine chips ~800°C 170 0,038 0,063 0,16

fixed bed - oak chips

pyrolysis char 600°C 151 0,088 0,030 0,09

activated pyr.-char 46% burn off (CO2)

850°C 716 0,293 0,032 0,32

53% burn off (CO2) 850°C 766 0,312 0,040 0,34

60% burn off (CO2) 850°C 819 0,334 0,033 0,36

Adsorption tests - setup

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SiC

T

on-lineGC/FIDN2

naphthalene

activated carbonsample

test gas generation

adsorberwith charsample

on-line monitoring

PAH sublimation device

• Single PAH sublimation/evaporation• syringe pump + evaporator• ethylene pyrolysis

Alternatives: • on-line GC/FID• on-line GC/MS (for process gases)• on-line monitoring with LIF

SRI GC/FID

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PAH adsorption on untreated and activated carbon

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

0:00 1:00 2:00 3:00 4:00 5:00 6:00

naph

thal

ene

c/c 0

time (hh:mm)

SiC SchüttungPyrolysekoks (0% Abbrand)Aktivkoks (53% Abbrand)

Adsorption temperature: 150°Cmass of activated char sample: 4,0 gbed height: 2,4 (±0,1) cmnaphthalene load in gas phase: 1,5 g/Nm³

SiC bed

pyrolysis char (0% burn off)

activated char (53% burn off)

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On-line analysis and monitoring of gas-phase PAH by laser- induced fluorescence

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0,2

0,4

0,6

0,8

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275 300 325 350 375 400 425 450 475 500

fluor

esce

nce

Inte

nsity

(s

tand

ardi

zed)

Wavelength [nm]

0 E+00

1 E+04

2 E+04

3 E+04

4 E+04

5 E+04

6 E+04

7 E+04

00:00:00 00:14:24 00:28:48 00:43:12 00:57:36

Peak

Are

a [a

rb. U

nits

]

Time [hh:mm:ss]

Summary and next steps

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• Adsorption of tar species on process-chars and activated process-carbons

• On-line gas phase analysis and monitoring of PAH by applying online GC/FID and optical fluorescence monitoring devices

• Characterization and screening of further relevant woody biomass feedstocks (beech, pine, poplar, willow, …)

• Adsorption of multi-component PAH mixtures• Influence of steam in the process on the adsorption results• Tests with process gases from BFB gasifier

• Possibilities for char regeneration and PAH reforming will be examined:

• partial gasification/reactivation with steam or CO2• non thermal DBD-Plasma

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We want to acknowledge and would like to express our gratitude to the German Federal Ministry of Education and Researchfor financial support of our current work in thejunior research group ‘TCKON’ (FKZ: 03SF0442)

Acknowledgement

More information on our work …

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Continuous On-Line Tar Monitoring for Process Control by Application of Optical Emission Spectroscopy

Poster # 109 Poster # 110

NON -THERMAL PLASMA application for the enhancement of heterogeneous

gasification reactions

More information on our work …

20

Continuous On-Line Tar Monitoring for Process Control by Application of Optical Emission Spectroscopy

Poster # 109 Poster # 110

NON -THERMAL PLASMA application for the enhancement of heterogeneous

gasification reactions

Thank you for your interest and for your attention !