COMBUSTION OF SOLID LIGNIN-RICH RESIDUES … Meeting of the Italian Section of the Combustion...

XXXVIII Meeting of the Italian Section of the Combustion Institute

COMBUSTION OF SOLID LIGNIN-RICH

RESIDUES FROM BIOETHANOL PRODUCTION

IN FLUIDIZED BED REACTORS

R. Solimene*, A. Cammarota*, R. Chirone*, P. Leoni**, N. Rossi**, P.

Salatino*** [email protected]

*Istituto di Ricerche sulla Combustione - Consiglio Nazionale delle Ricerche, Piazzale V.

Tecchio 80, 80125 Napoli, Italy

** Enel Ingegneria e Ricerca S.p.A, Via Andrea Pisano 120, 56122 Pisa, Italy

*** Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale -

Università degli Studi di Napoli Federico II, Piazzale V. Tecchio 80, 80125 Napoli, Italy

Introduction

The deployment and the exploitation of alternative fuels became more and more

relevant to reduce the emissions of greenhouse gases and to limit the dependence

on countries supplying fossil fuels. In this perspective, the Community legislation

regulated, with the 209/28 EC Directive, the minimum amount of biofuel at 10%v

for automotive fuels by 2020. OECD estimates predict that the production of

second-generation bioethanol, i.e. ethanol produced from lignocellulosic biomass

and scraps of agricultural crops will be of 155 billion liters by 2020. The

composition of lignocellulosic biomass is typically: cellulose (35-45%),

hemicellulose (25-30%) and lignin (25-30%). The cellulose and hemicellulose are

made of fermentable sugars, while the lignin is a polymer consisting of several

units of not fermentable phenylpropane. The residues of bioethanol production,

typically the solid residues after ethanol distillation and separation, are

characterized by high lignin content. These residues can be used in part to

energetically support the process of bioethanol production (about 40%), while 60%

of them are process wastes. The high lignin content residues can be exploited for

the production of some chemicals [1], as well as in thermochemical processes like

combustion [2-3], co-combustion, gasification, pyrolysis [4].

The aim of this work was to investigate the co-combustion of high lignin content

residues (in the following simply called lignin), coming from a second-generation

bioethanol production plant, with coal in fluidized beds. To this end, the

experimental investigation was carried out with the aid of different experimental

apparatus, at lab and pilot-scale, and of different diagnostic and experimental

protocols. In particular, it was investigated: 1) the combustion and the attrition of a

single lignin particle in lab-scale fluidized bed reactors, 2) the co-combustion of

different mixtures coal-lignin in a pilot-scale bubbling fluidized bed combustor

(200kWth).


Experimental

A stainless steel atmospheric bubbling fluidized bed combustor 41 mm ID and 1 m

operated at 1123K was used for lab-scale devolatilization/attrition and combustion

experiments (Fig. 1). Three different configurations of the reactor were used for the

experimental tests. In the first configuration (Fig. 1A), used for particle

fragmentation experiments, the top section of the fluidization column was left open

to the atmosphere. A stainless steel circular basket could be inserted from the top in

order to retrieve fragmented and un-fragmented particles from the bed. In the

second configuration (Fig. 1B), used for fines elutriation rate experiments, a two-

exit head was fitted to the top flange of the fluidization column. By operating a

valve it was possible to convey flue gases alternately to two removable filters made

of porous alumina. The third

configuration (Fig. 1C), used

for single particle

combustion/devolatilization

experiments, also consisted in

leaving open the top section of

the fluidization column. A

stainless steel probe was

inserted from the top of the

column in order to convey a

fraction of the exit gases

directly to the gas analyzers.

The analysis of the time-

resolved CO2 concentration

was used to characterize the

devolatilization process varying

the initial size of the fuel

particle and considering wet

and pre-dried fuel. The details

of the experimental apparatus

and procedures are reported

elsewhere [5-6].

The pilot-scale 200kWth FBC

schematically shown in Fig. 2

was used to carry out an

experimental campaign of co-

combustion of lignin with coal.

The AISI 310 stainless steel

fluidization column had a

circular section (370 mm ID)

for almost all its height (5.05

m) whereas the upper part of

Figure 1. The experimental apparatus for

devolatilization/attrition characterization: A)

basket equipped configuration; B) two-exit head

configuration; C) open top configuration.


freeboard was characterized by ID of 700 mm and height of 1.85 m (total height of

6.9 m). The distributor plate is equipped with 55 bubble caps.

The fluidization column was fitted with several ports for temperature, pressure, and

gas concentration probes. Two cyclones are used for flue gas de-dusting. Flue gas

composition of flue gas sampled at the exhaust was measured by on-line gas

analyzers (ABB AO2020). The entire vessel is thermally insulated by a ceramic

wool blanket. The heat exchange is accomplished thanks to different devices

located along the

fluidization column The

FBC is equipped with a

continuous over-bed

feeding system. Fuel

particles are fed by means

of a belt-type device

which is held up by a mass

balance to measure the

fuel mass flow rate.

Particles fall down directly

on the bed surface at an

elevation from distributor

plate z = 1050 mm. The

start-up is accomplished

thanks to a propane

premixed burner. More

details are reported

elsewhere [7].

The pilot-scale

experimental investigation

regarded the study of

gaseous and particulate

emissions and of thermal

regimes during the co-

combustion of different

mixtures of coal-lignin

varying the percentage of

lignin fed with coal, the

bed temperature, the

excess air and the

fluidization velocity.

The properties of the

investigated fuels are

reported in table 1 in terms

of lower heating value and

Flue Gas

0

1

2

3

4

5

6

AIR

water out

air distributor plate

start-up

burner

water in

TC00

TC03

TC01PT01TCC01ZR01

TC05 PT05TC06PT06

TC07PT07

TC08PT08

TC09

GS01

TC12

TC11

TC10

PT12

PT11

PT10

TC14

TC13

TC15PT15

PT14

TC16PT16TC17

TC20

TC18

PT20

PT18

TC19

TC21TC22 GS03

TCW01

AMF1 AMF2

PMFEVPPR2PROPANE

AIRPR1

TC23

AMF3

EVW

WATER TANK

AMF5

AMF4

TCF TCP

TC02 PT02

TCW02

water in

VA01

FUEL FEEDER

FUEL

VS

water in from

cooling tower

water out to

cooling tower

BI01

HT

TCW04

TCW03

water pumpPM01

TCW05

PT03

HEATH

EXCHANGER

TC16PT16

GS02

FUEL

ON/OFF

VALVE

STEAM

CONDENSER

TC04 PT04

AMF: air mass flow rate controller

PMF: propane mass flow rate controller

PT: pressure trasducer

TC: termocouple

EV: electro-valve

PR: pressure trasmitter

HT: spark generator

GS: gas and particulate sampling port

BI01: integrate safe flame scanner

VA01: cooling air valve

ZR: zirconia probe tap

Figure 2. Schematic representation of FBC-370. PT:

pressure transducer. TC: thermocouple. GS: gas and

particulate sampling port. AMF: air mass flow rate

controller. PMF: propane mass flow rate controller.

EV: electro-valve. PR: pressure transmitter. ZR:

zirconia probe tap. VA01: cooling air valve. HT:

spark generator. BI01: integrated safe flame scanner.


proximate and ultimate analysis.

Wood chips were used as reference

biogenic fuel typically adopted in co-

combustion with coal. Silica sand was

used as bed material in the size ranges

0.30-0.42 and 0.8-1.2mm during the

experimental campaigns carried out

with lab-scale and pilot-scale

apparatus, respectively.

Results and discussion

Figure 3 reports the main results

obtained during the lab-scale

experimental investigation carried out

feeding single particles or batch of

lignin particles to the fluidized bed

reactors schematically shown in

figure 1. The characteristic

devolatilization time was estimated by means of the analysis of the time-resolved

CO2 profile measured during combustion of single lignin particles. Obtained data

are reported in figure 3A as a function of the initial fuel particle size for wet and

pre-dried fuel particles together with results achieved during previous experimental

campaigns carried out with different fuels. The devolatilization times of wet lignin

particles are similar to those of bituminous coal particles with the same initial size,

whereas devolatilization is much shorter if pre-dried lignin particles are considered.

The comparison of devolatilization times of lignin particles with transversal mixing

time of typical industrial-scale fluidized bed combustors highlights that: 1) the wet

fuel larger than 10mm could be fed mixed with coal directly in the combustor

chamber; 2) the dry fuel is extremely reactive and once fed to the fluidized bed it

could generated localized emissions of heat and micro- and macro-pollutants. On

the other hand, the attrition of single fuel particle during devolatilization and char

burn-out indicates the pathways of formation of carbonaceous fines produced

during combustion. Primary fragmentation experiments show that wet lignin

particles do not undergo fragmentation during devolatilization, as matter of fact the

multiplication factor (Nout/Nin, number of particles collected by basket divided the

number of particles fed to the reactor) remains equal to 1 whereas a particle

shrinkage of about 78% was observed. Instead, secondary or percolative

fragmentation is active in late stage of char burn-out, as it can observed by the

trend of multiplication factor reported in figure 3B as a function of apparent

conversion degree of char (carbon converted to CO2 and CO plus elutriated

carbon). Nout/Nin during char burn-out remains equal to 1 (particle does not break)

until carbon conversion is smaller than 70%, then it steeply increases. Figure 3C

shows the normalized carbon elutriation rate of char (carbon elutriated mass flow

Table 1. Properties of fuels.

fuel lignin Coal Wood

chips

LHV (as

received), kJ/kg

5645 25564 8568

Proximate analysis (as received), %w

moisture 60.7 10.3 45.5

volatiles 25.0 34.6 40.2

fixed carbon 8.1 49.4 10.8

ash 6.1 5.7 3.5

Ultimate analysis (dry basis), %w

carbon 47.0 79.3 51.3

hydrogen 5.4 4.8 6.0

nitrogen 1.2 1.0 1.4

sulfur 0.1 0.7 0.2

chlorine 0.0 0.0 0.0

ash 15.6 6.3 6.5

Oxygen (by diff.) 30.6 7.9 34.6


rate divided the initial carbon content of

char particles) under inert and oxidizing

conditions as a function of time.

The analysis of data highlights that more

carbon fines are elutriated under

oxidizing conditions. Probably the

carbon elutriated material is mainly

produced by secondary or percolative

fragmentation which takes place in the

late stage of char burn-out rather than

generated by surface abrasion.

Figure 4 reports the main results in terms

of normalized emissions of NO, SO2,

particulate and carbon in particulate as a

function of the O2 concentrated measured

at the exhaust obtained during the steady

state operation of the pilot-scale bubbling

fluidized bed combustor. A large part of

the investigated experimental conditions

regarded the operation using a mixture

lignin-coal at 30%w in lignin.

Experiments with coal, with a mixture at

40%w in lignin and with a mixture coal-

wood chips at 20%w in wood chips were

carried out for comparison. The analysis

of the experimental results mainly

highlight that: 1) the gaseous emissions

do not significantly change with respect

to coal or to reference biomass-coal

mixture at least until the mixture content

of lignin is 30-40%w; 2) the particulate

emissions increase with the percentage of

residues content, but, at the same, the

carbon content is significantly reduced. Bottom bed particles were analyzed at the

end of each experiments highlighting the absence of agglomerates but a significant

enrichment of metals like Fe, Mg, Na, Ca and K coming from lignin ash when the

apparatus were operated for long time and at high temperature.

References

[1] Ragauskas, A. J., Beckham, G. T., Biddy, M. J., Chandra, R., Chen, F.,

Davis, M. F., Davison, B. H., Dixon, R. A., Gilna, P., Keller, M., Langan, P.,

Naskar, A. K., Saddler, J. N., Tschaplinski, T. J., Tuskan, G. A., Wyman C.

E., “Lignin Valorization: Improving Lignin Processing in the Biorefinery”,

dp, mm

0.1 1 10

t D9

5, s

1

10

100

1000

South African coal

Polish coal

M. d. sewage sludge

Recycled polyethylene

Polyethylene

Polypropylene

Wood pellet

Straw pellet

M. d. sewage sludge

Wood chips

Lignin

wet sewage sludge 1

wet sewage sludge 2

Dry lignin

tmix

A)

zc

0.0 0.2 0.4 0.6 0.8 1.0

No

ut/N

in

0

10

20

30

B)

C)

Figure 3. Attrition/devolatilization

results.


Science 344: 1246843 (2014).

[2] Eriksson, G., Kjellström, B., “Assessment of combined heat and power

(CHP) integrated with wood-based ethanol production”, Applied Energy 87:

3632–3641 (2010).

[3] Ren, Q., Li, S., Wang, D., Bao, S., Lu Q., “Combustion and Agglomeration

Characteristics of the Residue from Corn Stalk-Based Cellulosic Ethanol”,

Chemical Engineering &. Technology 38: 253–258 (2015).

[4] De Wild, P. J., Huijgen, W. J. J., Gosselink R. J.A., “Lignin pyrolysis for

profitable lignocellulosic biorefineries”, Biofuels, Bioproducts and

Biorefining 8 (5): 645–657 (2014).

[5] Solimene, R., Urciuolo, M., Cammarota, A., Chirone, R., Salatino, P.,

Damonte, G., Donati, C., Puglisi, G., “Devolatilization and ash comminution

of two different sewage sludges under fluidized bed combustion conditions”,

Experimental and Thermal Fluid Science 34: 387–395 (2010).

[6] Scala, F., Salatino, P., Chirone, R., “Fluidized Bed Combustion of a Biomass

Char (Robinia pseudoacacia)”, Energy & fuels 14: 781-790 (2000).

[7] Aprea, G., Cammarota, A., Chirone, R., Salatino, P., Solimene, R.,

“Hydrodynamic characterization of the biomass combustion in a pilot scale

fluidized bed combustor”, Chemical Engineering Transactions 32: 1519-

1524 (2013).

doi: 10.4405/38proci2015.VI4

exhaust O2 concentration, %

v

2 4 6 8 10

exh

au

st

NO

co

ncen

trati

on

@ 6

%v O

2,

pp

m

100

150

200

250

300

350

Colombian coal; Tbed = 850°C; Ug (@Tbed) = 1.0 m/s



Colombian coal + 30% lignin; Tbed=850°C; Ug (@Tbed) = 1.0 m/s

Colombian coal + 30% lignin; Tbed = 860°C; Ug (@Tbed) = 1.26 m/s




Colombian coal + 20% wood chips; Tbed=850°C; Ug (@Tbed) = 1.0 m/s


v

2 4 6 8 10

part

icu

late

co

ncen

trati

on

@

6%

v O

2,

g/N

m3

0

2

4

6

8

10

Colombian coal; Tbed=850°C; Ug (@Tbed) = 1.0 m/s










v

2 4 6 8 10

exh

au

st

SO

2 c

on

cen

trati

on

@ 6

%v O

2,

pp

m

250

300

350

400

450Colombian coal; Tbed=850°C; Ug (@Tbed) = 1.0 m/s


Colombian coal; Tletto=912°C; Ug (Tletto) = 1.33 m/s








v

2 4 6 8 10

Part

icu

late

carb

on

co

nc

en

trati

on

, m

g/N

m3

0

500

1000

1500










Figure 4. Normalized particulate and gaseous emissions as a function of outlet

oxygen concentration measured during different experiments carried out with the

pilot-scale bubbling fluidized bed combustor.

COMBUSTION OF SOLID LIGNIN-RICH RESIDUES … Meeting of the Italian Section of the Combustion...

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