Disposal of Sewage Sludge and Municipal Refuse by the Occidental

15 Disposal of Sewage Sludge and Municipal Refuse by the

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Occidental Flash Pyrolysis Process EUGENE J. CONE

1

Occidental Research Corporation, 1855 Carrion Road, La Verne, CA 91750

For the last several years, Occidental Research Corporation has been interested in the production of synthetic oil and/or gas by pyrolysis of "waste" organic materials. Within the last two years, this interest has extended to disposal of sewage sludge and sewage sludge/municipal solid waste mixtures by pyrolysis. The emphasis of the current work has been on defining and optimizing product yields (i.e., controlling the mix of liquid, gas, or char products) and on controlling their composition. System variables being investigated include temperature, pressure, and residence time. Objectives 1.

2. 3. 4.

Specific objectives of the research program are as follows: Demonstrate in small pilot scale equipment that pyrolysis of sewage sludge can be accomplished by the Occidental Research Corporation Flash PyrolysisTM process as practiced with municipal solid waste at El Cajon, San Diego, with only minor modification to existing equipment. Define any interaction or "nonlinear" effects caused by copyrolysis of sewage sludge/municipal solid waste as compared to separate pyrolysis of the materials. Define variables controlling product mix (liquid, gas, char). Optimize product quality.

Experimental Apparatus The pyrolysis system used in the experiments reported here was based on transport of sewage sludge or municipal solid waste through an electrically heated one inch nominal diameter pipe. Typical solids feed rates were 2 kg/hr, and typical carrier gas rates were 6.6 standard cubic meters per hour. 1

Current Address: Envirotech, One Davis Drive, Belmont, CA 94002 0-8412-0434-9/78/47-076-287$05.00/0 © 1978 American Chemical Society Jones and Radding; Solid Wastes and Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

288

SOLID

WASTES

A N D RESIDUES

The system components consisted of a modified screw feeder, a 7 m long U-shaped section of e l e c t r i c a l l y heated pipe, two cyclones, a glass fiber packed f i l t e r , a liquid product conden sing section, and a gas flow sampling and metering section. Schematics of the system are shown in Figures 1 and 2. Products leaving the system were passed through a thermal oxidizer to eliminate any possible a i r pollution. Two different liquid recovery systems have been used in our pyrolysis experiments. The f i r s t (Figure 1) consisted of two externally cooled "knockout pots", and the second (Figure 2) used direct contact spray quenching with an immiscible hydro carbon l i q u i d , followed by phase separation and product recovery. This second method of product recovery models the technology now in use at Occidental's municipal solid waste demonstration plant at El Cajon, in San Diego County, California; however, all data actually discussed here were taken with the f i r s t system. Discussion of Experimental Results The two feed materials used in these experiments were finely shredded municipal refuse as obtained from the "front end" of the Occidental Resource Recovery system, (1,2) and sewage sludge as obtained from the San E l i j o , CA sewage treatment plant. The municipal refuse was usually reground in a hammer mill before pyrolysis so as to increase ease of handling in the small scale equipment used. The sewage sludge was a i r dried and then ground in the same m i l l . Typical particle size distribution for the pyrolysis feed materials are as shown in Table I. TABLE I PYROLYSIS FEED-PARTICLE SIZE DISTRIBUTION Screen Opening, μίτι

Municipal Solid Waste - Percent Throuqh Screen

Sewage Sludge - Percent Through Screen

841

96.8

297

90.4

77.0

149

82.4

54.4

105

77.2

50.6

75

66.4

36.2

45

44.0

26.8

37

36.6

20.2

100

Jones and Radding; Solid Wastes and Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 1. Pyrolysis pilot plant initial design Jones and Radding; Solid Wastes and Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 2. Pyrolysis pilot plant with improved product collection system Jones and Radding; Solid Wastes and Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

15.

CONE

Occidental Flash Pyrolysis Process

291

Clearly the sewage sludge particles used in these experi ments tend to be larger than the corresponding municipal solid waste particles. Thus, the median sewage sludge particle is about 100 ym whereas the median municipal solid waste particle is about 50 ym. This should tend to make the sewage sludge used here more d i f f i c u l t to pyrolyze, but the exact magnitude of the effect has not been determined. Typical feed compositions are as shown in Table II. TABLE II PYROLYSIS FEED COMPOSITION Weight Percent

Municipal Solid Waste

Sewage Sludge

C

41.9

29.9

H

6.3

5.0

Ν

0.5

2.5

S

0.3

1.0

Cl

0.4

0.1

Ash

12.4

44.0

H0

4.0

6.0

38.2

18.4

2

0 (by difference)

Note that the significant difference in ash content between municipal solid waste and sewage sludge makes i t necessary to compare product yields in terms of moisture and ash free (MAF) materials. Figure 3 shows a plot of o i l y i e l d as a function of tempera ture for pyrolysis of sewage sludge and municipal solid waste. Data i s , of course, on a MAF basis for both feed and products. Note that the o i l yield for sewage sludge is about 10% lower than that for municipal solid waste at 900°F, but essentially the same over the rest of the temperature range investigated. Figures 4 and 5 show similar plots for gas and char yields, respectively. Gas yield for sewage sludge is about the same at 900°F and about 10% lower over the rest of the temperature range. Char y i e l d for sewage sludge is about 10% higher over most of the pyrolysis temperature range, but only about 4% higher at 1600°F. Composition of pyrolytic o i l is shown in Table III. Again, data is on an MAF basis. Note that the sewage sludge o i l formed


292

SOLID WASTES AND

RESIDUES

Ο SEWAGE SLUDGE • 50

MSW

r

TEMPERATURE,*F

Figure 3.

Yield of oil vs. temperature for pyrolysis of sewage sludge and municipal solid waste (MSW) (data based on MAF oil and feed)


CONE


Figure 4. Yield of gas vs. temperature for pyrolysis of sewage sludge and municipal solid waste (MSW) (data based on MAF feed)


294

Figure 5.

SOLID

WASTES

AND

RESIDUES

Yield of MAF char vs. temperature for pyrolysis of sewage sludge and municipal solid waste (MSW) (data based on MAF feed and char)



78.0 10.3

1600

6.5

64.2

7.6

60.7

1400

7.0

52.4

60.1

6.6

54.3

900

1200

6.8

C

Pyrolysis Temperature, °F

3.1

0.3

18

7.8 12.6

65.0

17080

7.6 11.9

70.5 1.0

1.5

7.9 12.5

69.7

1.9

1.3

1.4

8.4 11.9

66.3

17

11394

1.3

0.2

2.0

0.8

9.5

28 26 31 32 27

14736 13206 13635 13588 12579

0.2

0.1 0.1 0.3

0.3

36 13211 1.1

9.4

0.1

0.2

0.5

6.6

29

14501

35

0.1

0.6

6.4

24

13372

Run No.

13114

0.2

0.7

5.7

7.1

69.9

0.4

19

8.4

66.4

11243

0.1

0.8

9.5

69.2

8.6

9.9

Oil From Sewage Sludge HHV H Ν S Cl (BTU/lb)

62.6

65.7

6

5

C

7

1.0

0.2

1.3

8684

9286

Run No.

10781

0.2

0.1

0.7

0.2

0.1

0.6

Oil From Municipal Solid Waste HHV (BTU/lb) S Cl H J L

TABLE III PYROLYTIC OIL PROPERTIES (MAF OIL)

296

SOLID

Ο Ο VO

Ο Ο

O Ο

ο ο i—

σ>

00

00

CO OsJ

CVJ Γ

ο

ο

ΙΟ

LO

CVJ

00 CVJ

CO

^-

LO

CVJ

CVJ CO

CT>

CO r—

ρ— CO

ο CVJ

ο r—

ο ο

αϊ ο.

«s*

CT»

CO

LO

CVJ

r—

r— r—

r— CO

CO CO

CV1 ι—

Γ—

m

ο ο

cvi

ο

ο ο CVJ

•"3

CO ι—ι CO

Ο

ο Cd >-

0Û < 5C|

CO

cvj

ο ο

c

ΟΟ r— r—

CVJ

CT>

LO

CT»

ο

«3-

cvj

00 CVJ

LO

LO

Ο CO

LO ι—

cr>

vo

ο

CVJ

ο

CO

CVJ

ο

vo CO

CO

«vt-

ΟΟ

oo

oô

ο

ο

00 CVJ

00

ο ο en

CVJ

CO

>-J Q_

ο

00

Γ

00

Ο

ο

AND

CO

Ο

Ο

WASTES

CO

ο

LO CO

ο

Ο CO

ο ο

2

r—

CO

:

>> fO r - S-

IL.

ο eu S- Q_

Ο

CVJ

Ο

ο ο

CVJ

Ο

CVJ

eu ο ο ω c to eu Ό

— . -ι— co (Ο

co

Ο)

Ε

Q J T

CD S- -Μ


RESIDUES

15.

297

Occidental Fhsh Pyrolysis Process

CONE

TABLE V CONCENTRATION OF MAJOR COMPONENTS IN PRODUCT GAS FROM PYROLYSIS OF MUNICIPAL SOLID WASTE Pyrolysis Temperature, °F

900

900

1200

1200

1400

1600

4.7

6.7

13.0

9.5

15.4

19.6

33.6

34.5

49.3

50.7

49.7

48.4

55.2

52.6

15.3

18.8

9.4

7.5

0.3

2.7

8.5

7.5

10.4

12.0

5.0

1.1

4.8

4.0

7.3

7.9

Gas/oil residence time (sec.)

0.5

0.5

0.5

0.3

0.3

0.3

Run number

5

6

7

Volume % H

2

CO co

2

CH

4

C H 2

4

19

17


18

298

SOLID

WASTES

A N D RESIDUES

in the 900-1200°F range is generally higher in carbon and hydrogen than the corresponding municipal solid waste o i l , and thus is apparently a high quality o i l . The nitrogen content might be considered a problem but blending with municipal refuse o i l and fuel oil can produce a composite fuel with nitrogen content below 1%. Table III also shows the higher heating value of pyrolytic o i l from municipal solid waste and sewage sludge c a l culated from the Dulong-Petit equation. As would be expected from the relatively large percent of carbon and hydrogen in the sewage sludge o i l , its higher heating value compares favorably with that of municipal solid waste o i l for oils formed at or below 1400°F. Table IV shows the concentration of the major components in the product gas from pyrolysis of sewage sludge, and Table V, similar data for municipal solid waste. Figures 6-10 present this data graphically. Examination of these tables and figures shows that, as expected, gas composition varies appreciably with pyrolysis temperature. Variation in, and absolute value of hydrogen and methane concentrations are seen to be about the same for sewage sludge and municipal solid waste over the entire temperature range investigated. Carbon monoxide concentration is seen to be about 20% lower for sewage sludge, and carbon dioxide concentration is about 15% lower in the 900-1200°F range, and several percent lower in the 1400-1600°F range. Ethylene concentration is considerably higher for sewage sludge gas, particularly at higher pyrolysis temperatures. Table VI compares the calculated average gross heating value for product gas from the two feed materials. It should be noted that these values appear higher than might be expected because of the presence of several percent C5+ in the gas stream. TABLE VI PYROLYSIS PRODUCT GAS GROSS HEATING VALUE Temperature, °F

Municipal Solid Waste (BTU/SCF)

Sewage Sludge (BTU/SCF)

900

260

410

1200

680

960

1400

670

880

1600

600

960

Tables VII and VIII show product recoveries for sewage sludge, and municipal solid waste, respectively. It is particul a r l y interesting to note that overall, carbon, hydrogen and ash material balances generally close to within tl0%.


15.

CONE


299

Ο MSW • SEWAGE SLUDGE 26

r

Figure 6.

Volume percent of H in pyrolysis product gas for pyrolysis of sewage sludge and municipal solid waste (MSW) 2


300

SOLID WASTES AND RESIDUES

Figure 7. Volume percent of CO in pyrolysis product gas for pyrolysis of sewage sludge and municipal solid waste (MSW)


CONE

Occidental Fhsh Pyrolysis Process

Figure 8. Volume percent of C0 in pyrolysis product gas for pyrolysis of sewage sludge and municipal solid waste (MSW) 2


302

SOLID

ι 0

900

1000

WASTES

AND

ι

ι

ι

ι

ι

1100

1200

1300

1400

1500

RESIDUES

1 1600

TEMPERATURE, *F

Figure 9.

Volume percent of CH in pyrolysis product gas for pyrolysis of sewage sludge and municipal solid waste (MSW) k


Figure 10. Volume percent of C H in pyrolysis product gas for pyrolysis of sewage sludge and municipal solid waste (MSW) 2

h



Pyrolysis temperature, °F Weight % MAF o i l based on MAF feed Weight % gas based on MAF feed Weight % MAF char based on MAF feed Water of pyrolysis--% Weight % dry o i l based on as used feed Weight % gas based on as used feed Weight % dry char based on as used feed Weight % water based on as used feed Run number Nominal gas/oil residence time (sec.) % Overall recovery % C recovery % H recovery % Ash recovery 900 43 .4 10 .7 32 .6 7 .0 20 .2 5 .0 62 .1 8 .3 29 2 95 .7 104 .9 97 .1 97 .0

900

36.3

6.9

40.8 5.3

18.5

3.5

60.7

8.5 24

2 91.2 89.1 86.6 92.4

0.3 92.6 86.4 95.7 91.1

11.4 35

65.9

2.6

12.8

39.1 16.0

6.4

32.3

900

0.3 88.0 87.4 83.7 96.0

6.2 28

51.4

11.1

19.3

17.8 3.2

21.7

37.5

1200

0.3 91.9 98.6 99.6 90.0

9.5 36

59.1

10.3

13.0

27.2 11.6

24.8

29.8

1200

0.,3 89.,1 94.,2 93.,0 98..6

10.,0 26

49.,2

31. 1

8.,9

14. 1 7.,9

40.,8

17.,2

1400

0.5 96.5 100.1 109.7 94.2

10.3 31

60.8

16.2

9.3

23.1 12.6

40.4

23.0

1400

TABLE VII PYROLYTIC PRODUCT RECOVERY FOR SEWAGE SLUDGE PRYOLYSIS

0 .5 97 .6 104 .0 98 .3 95 .7

9 .3 32

59 .5

17 .6

11 .2

29 .9 3 .5

46 .2

29 .2

1400

2 91.3 92.1 108.6 91.8

10.0 34

55.7

21.9

3.7

16.6 11.8

53.5

8.9

1400

0.3 92.5 90.3 99.9 97.4

9.9 27

47.4

30.7

4.5

11.6 8.4

59.3

8.6

1600


8.8 31.5 14.5 29.9 7.3

11.4 27.5 14.4 39.5 9.6

Weight % gas based on MAF feed

Weight % MAF char based on MAF feed

Water of pyrolysis--MAF feed

Weight % dry o i l based on as used feed

96.8

% H Recovery

105.8

97.6

% C recovery

% Ash Recovery

98.0

0.5

Nominal gas/oil residence time (sec.)

% Overall recovery

5

16.1

Weight % water based on as used feed

Run number

33.1

Weight % dry char based on as used feed

72.0

98.9

96.5

98.3

0.5

6

16.1

35.1

47.6

46.1

Weight % MAF o i l based on MAF feed

Weight % gas based on as used feed

900

900

Pyrolysis temperature, °F

15.9

14.1

102.0

96.3

98.4

95.9

0.5

7

15.8

20.5

29.6

99.9

105.4

99.3

96.3

0.3

19

93.6

103.7

99.0

98.9

0.3

17

19.1

18.2

19.9 19.0

47.3

14.4

15.1

10.4

57.0

17.0

1400

24.1

33.4

11.1

13.2

29.9

28.9

39.9

35.8 35.4

1200

1200

TABLE VIII PYROLYTIC PRODUCT RECOVERY FOR MUNICIPAL SOLID WASTE PYROLYSIS

306

SOLID

W A S T E S A N D RESIDUES

The conclusion from a l l the above is that copyrolysis of sewage sludge and municipal solid waste seems quite possible. The sludge pryolyzes quite readily during Flash P y r o l y s i s ™ to give apparently reasonable products. No special problems in the pyrolysis of sewage sludge are apparent at this time. Abstract Air-dried and ground municipal sewage sludge, and municipal solid waste have been pyrolyzed in a 2 kg/hr pilot plant. An e l e c t r i c a l l y heated vertical flow transport reactor with short residence time was used. Temperatures in the range 755-1144 Κ (900-1600°F) were investigated. O i l , gas, and char yields and composition varied appreciably with pyrolysis temperature. The results presented here suggest that the Occidental Flash P y r o l y s i s ™ process can be applied successfully to the codisposal of municipal sewage sludge with municipal refuse. Literature Cited 1. 2.

APRIL

Levy, S.J., "San Diego County Demonstrates Pyrolysis of Solid Waste," SW-80d. 2, U.S. Environmental Protection Agency, (1975). Preston, G.T., "Resource Recovery and Flash Pyrolysis of Municipal Refuse," Institute of Gas Technology Symposium "Clean Fuels from Biomass, Sewage, Urban Refuse and Agricultural Wastes," Orland, Florida, (1976). 7,

1978.


Disposal of Sewage Sludge and Municipal Refuse by the Occidental

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