Distribution of ash forming elements during pyrolysis of municipal - - PowerPoint PPT Presentation

Distribution of ash forming elements during pyrolysis of municipal wastewater sludge and sludge from milk processing factories

Marzena Kwapinska, D. A. Agar, J.J. Leahy

6th International Conference on Sustainable Solid Waste Management

Pyrolysis – an alternative to land spreading of sludge

• Pathogens removal
• Reduced volume
• Pyrolysis of sludge can fulfil

its own heat demand * (necessary heat for drying and pyrolysis)

• Nutrients recovery
• The potential application of all pyrolysis

products greatly depends on the presence of various contaminants.

• Release and fate of heavy metals.
• Release of contaminants NH3, HCl, HCN, H2S –

water scrubbing is compulsory

• challenges

* Salman C.A, S. Schwede, H. Li, E. Thorin, J. Yan: Integrated

concept fpr sludge pyrolysis in waste water treatment plants for biofuel production and nutrients recovery, SMICE 2018

Objectives

Investigate the potential of pyrolysis as a conversion technology for sludge

• Examine properties of dairy sludge (DS) and sewage sludge (SS)
• Pyrolysis of sludge in laboratory reactor in order to measure the amount of

pyrolysis products and determine their properties

• Investigate distribution of major (Al, Ca, Fe, K, Mg, Na, P, S, Si) and minor (As,

Ba, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Se, Ti, V and Zn) ash forming elements between solid and liquid pyrolysis products

Materials

Bench drying at ambient temperature

Dairy Sludge (DS):

• DS-1 biological sludge, 13 % solids
• DS-2 biological sludge, 32 % solids
• DS-3-DAF sludge from dissolved air

floatation, 32 % solids

Sewage Sludge (SS):

• SS-1 biological sludge, dried pellets - 91 % solids
• SS-2 biological sludge, dried granules -94 % solids
• SS-3 biological sludge, belt press cake -15 % solids

Properties

• wt. %

DS-1 DS-2 DS-3- DAF SS-1 SS-4 C 30.0 39.3 43.3 37.3 39.0 H 4.6 5.6 6.9 5.5 5.4 N 5.4 7.7 1.6 5.7 6.8 S 0.5 0.6 0.1 1.0 0.7 O 23.2 23.2 11.6 17.9 19.2

Properties of dried sludge

• high volatile matter content
• low fixed carbon content in DS-DAF-1

10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100

ash fixed C volatiles

DS-1 DS-2 DS-DAF-1 SS-1 SS-2 SS-3

• wt. %

Major ash forming elements

5000 10000 15000 20000 25000 30000 35000 40000 300000 400000 500000 600000

mg/kg of dry sludge SS1 SS2 SS4 Al Ca Fe K Mg Na P S Si

10000 20000 30000 40000 50000 60000 70000 200000 400000 600000

mg/kg of dry sludge DS-1 DS-2 DS-3-DAF Al Ca Fe K Mg Na P S Si

Dairy Sludge Sewage Sludge

• Si content was the highest among all elements for both sludge types (higher in SS (270-400 g/kg) than in DS (150-300 g/kg))
• Similar content of Na (20 - 30 g/kg), K (3 – 9 g/kg), P (12 - 18 g/kg) and S (1 - 4 g/kg) in all sludge samples
• Al and Ca content similar in all SS but significant difference in DS
• Fe and Mg content higher in SS than in DS but large differences between samples

Dairy Sludge

50 100 150 200 250 300 350 400 450 1000 1500 2000

As Ba Cd Co Cr Cu Hg Mn Ni Pb Sb Se Ti V Zn

mg/kg of dry sludge SS1 SS2 SS4

50 100 150 200 250 300 350 400 450 DS-1 DS-2 DS-3-DAF As Ba Cd Co Cr Cu Hg Mn Ni Pb Sb Se Ti V Zn

mg/kg of dry sludge

Minor ash forming elements

Sewage Sludge

• In general content of heavy metals is higher in SS (Ti, Zn, Cu, Ba and Mn four times higher than in DS also

Cr, Pb, Ni and V)

• Similar concentrations of Hg with trace amounts of Se and Sb in all sludge samples
• SS samples contained trace amounts of As, Co and Cd

Laboratory scale fixed bed pyrolysis

Temperature 700°C Residence time 10 min

• mass of char
• mass of liquid

(oil and aqueous)

• mass of gas by difference

Experimental set-up

condenser cooler quartz tube reactor

Pyrolysis of dried sludge

Mass balance

Sample Solid product,

• wt. %

Liquid,

• wt. %

Gas,

• wt. %

DS-1 30.5 37.2 32.3 DS-2 39.7 37.9 22.5 DS-3-DAF 37.5 14.7 47.8 SS-1 44.8 25.7 29.5 SS-2 40.2

• SS-4

36.5 33.2 30.3

Properties,

• wt. % db.

DS-1 DS- 2 DS-3- DAF SS-1 SS-2 Ash content 75.47 66.32 81.88 69.4 71.21 Volatile matter 4.05 6.77 14.48 3.2 16.02 Fixed carbon 20.48 26.91 3.63 27.4 12.77 C, db. 20.00 27.48 10.11 11.7 8.56 H, db. 0.40 0.31 0.55 28.68 28.11 N, db. 1.98 2.46 0.39 0.09 0.54 S, db. 0.36 0.41 0.04 1.94 2.67 O, db. 0.55 0.99 7.07 0.41 0.57

Chars – pyrogenic carbonaceous material

• 11 % of N was retained in the char

Pyrolysis char / pyrogenic solids – major elements

25 50 75 100 125 150

Mass fraction (%) DS-1 DS-2 DS-3-DAF Al Ca Fe K Mg Na P S Si

Dairy Sludge

50 100 150

Mass fraction (%) SS1 SS2 SS4 Al Ca Fe K Mg Na P S Si

Sewage Sludge

• 50 to 70 % of S was retained in the solids

Pyrolysis char / pyrogenic solids – minor elements

25 50 75 100 125 150 175 200 As Ba Cd Co Cr Cu Hg Mn Ni Pb Sb Se Ti V Zn

Mass fraction (%)

SS1 SS2 SS4

Sewage Sludge

25 50 75 100 125 150 175 200

DS-1 DS-2 DS-3-DAF As Ba Cd Co Cr Cu Hg Mn Ni Pb Sb Se Ti V Zn

Mass fraction, %

Dairy Sludge

• Cu, Cr, Mn, Ni, Pb, Ti, and Zn, most were retained in the char (pyrogenic solids) of both sludge types
• nly from 25 to 50% of Cd, Sb and Se was conserved in the char (pyrogenic solids)

50 100 150 200 As Ba Cd Co Cr Cu Hg Mn Ni Pb Sb Se Ti V Zn Mass % 50 100 150 200 Mass %

char

• il

aquoeous

Al Ca Fe K Mg Na P S Si 50 100 150 200 Al Ca Fe K Mg Na P S Si Mass %

char

• il

aqueous

50 100 150 200 As Ba Cd Co Cr Cu Hg Mn Ni Pb Sb Se Ti V Zn Mass %

Distribution of major and minor elements -

between liquid products

Dairy Sludge – DS-2 Sewage Sludge – SS-1

• Ca, Mg, Fe, P, Si, Al, Na and K

predominantly retained in pyrolysis chars (pyrogenic solids)

• substantial quantities of Al, K, Na and

Si and S were detected in pyrolysis

• il and in the aqueous fraction.
• The

heavy metals and trace elements As, Ba, Cd, Se, Sb and Pb, were also detected in the liquid products.

Conclusions

• Sewage sludge samples from different plants had similar properties while there were substantial

differences in the proximate and ultimate properties between dairy sludge samples.

• The concentration of P, K, Na and S was similar in SS and DS.
• There were significant differences in concentration of Al, Ca and Fe between samples within the

two tested groups.

• The heavy metal content was much lower in the DS in particular: Cr, Pb, Ni, V and the content
• f Ti, Zn, Cu, Ba and Mn was four times lower then that in SS.

Conclusions

• Both sludge types produced a significant quantity of pyrolysis solids from 30 to 40 % (DS) and

from 36 to 45 % (SS) of the initial residue mass.

• Distribution of major elements between pyrolysis products was similar for DS and SS, with Ca,

Mg, Fe, P, Si, Al, Na and K predominantly retained in pyrolysis chars (pyrogenic solids).

• However, substantial quantities of Al, K, Na and Si were detected in pyrolysis oil and in the

aqueous fraction.

• 50 to 70 % of S was retained in the solids with significant quantity captured in the liquid fraction.
• The heavy metals and trace elements were mainly retained in the pyrolysis chars (pyrogenic

solids) with the exception of As, Ba, Cd, Se, Sb and Pb, which were also detected in the liquid products.

“This work was supported by the Irish State through funding from the Technology Centres programme - Grant Number TC/2014/0016” And as a part of OF-PYRO project funded by the Environmental protection agency in Ireland

Thank you for you attention

Marzena.Kwapinska@ul.ie