Thermal Conversion of Solid Wastes and Biomass - American

41

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on July 14, 2016 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch041

PUROX System Demonstration Test on Simulated Japanese Refuse T. MASUDA Showa Denko K.K., Environmental Systems Department,27-17, Hamamatsu-cho 1-Chome, Minato-Ku, Tokyo 105, Japan T. F. FISHER Union Carbide Corporation, Linde Division, Tonawanda, NY 14150

The PUROX System, developed by Union Carbide Corporation of the U.S., pyrolyzes refuse by use of oxygen. It additionally purifies and recovers the pyrolysis gas and collects the inorganic residue in the form of slag. The wastewater generated during gas purification is discharged after treatment. There are several papers (1, 2, 3, 4) published on the details of the system. Figure 1 shows the schematic flow of a typical PUROX System. Showa Denko K.K. has imported the technology of the system and modified it to establish a process that meets conditions peculiar to the Japanese market, which are as follows: Refuse Composition Since Japanese refuse contains a higher proportion of household garbage, its moisture content is higher than that of its U.S. counterpart. Additionally, its plastic content has been increasing in recent years. A comparison of Japanese and U.S. refuse is given in Table I. TABLE I . COMPARISON OF JAPANESE AND U.S. REFUSE Japanese Refuse" L.M.R. H.M.R. S.M.R. Combustibles wt.% Ash Moisture Lower H.V. kJ/kg (kcal/kg) Higher H.V. kJ/kg (kcal/kg) 11

25.5 6.0 68.5 3,050 (730) 5,190 (1,240)

31.9 13.8 54.3 5,360 (1,280) 7,200 (1,720)

40.0 20.0 40.0 7,540 (1,800) 9,170 (2,190)

U.S. Refuse

49.5 19.5 31.0 8,080 (1,930) 9,630 (2,300)

U t i l i z a t i o n of Recovered Gas The p o t e n t i a l f o r u t i l i z i n g the recovered gas i s extremely l i m i t e d due to the d i s t a n c e of plant l o c a t i o n s See a b b r e v i a t i o n s

0-8412-0565-5/80/47-130-573$05.00/0 © 1980 American Chemical Society

Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


As Received Refuse

Figure 1.

Ferrous Metal

Front End

Wastewater

Wastewater Treatment

Schematicflowof a typical PUROX system

Residue

Converter

Particulates

Gas Cleaning System


Product Gas

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41.

MASUDA

AND

FISHER

PUROX

System Demonstration Test

575

from places of p o s s i b l e use and the r e s t r a i n t s imposed by laws and r e g u l a t i o n s i n c l u d i n g the gas u t i l i t y indus t r y law. Wastewater Treatment Since the sewer system i s p o o r l y developed at many l o c a t i o n s and the competent government agencies f o r sewage treatment are d i f f e r e n t from those f o r r e f u s e treatment, the wastewater has to be brought below the r e l e v a n t e f f l u e n t standards w i t h i n the r e f u s e treatment p l a n t . The cost f o r such wastewater treatment i s sub s t a n t i a l , one reason being the greater amount of waste water generated due to the higher moisture content of the r e f u s e . To meet the abovementioned l o c a l c o n d i t i o n s , Showa Denko has e s t a b l i s h e d a process whereby the p y r o l y s i s gas i s d i r e c t l y com busted and the generated heat i s u t i l i z e d f o r evaporation and o x i d a t i o n of the wastewater from the r e f u s e p i t ( h e r e i n a f t e r c a l l e d the Dry P r o c e s s ) . The schematic flow of the Dry Process PUROX System i s as shown i n F i g u r e 2. Simulation Test Using the PUROX System p i l o t p l a n t of Union Carbide l o c a t e d at Tonawanda, New York, U. S. Α., Showa Denko conducted a demon s t r a t i o n t e s t on simulated Japanese r e f u s e from June through August, 1978, a f t e r making some m o d i f i c a t i o n s of the p l a n t . An o v e r a l l view of the p i l o t plant appears i n Figure 3. The purpose of the demonstration was to achieve the f o l l o w i n g three objectives. 1) To conduct t e s t s on simulated Japanese r e f u s e and thereby c o l l e c t a d d i t i o n a l data to supplement those obtained on U.S. r e f u s e , i n order to o b t a i n the t e c h n i c a l approval of the M i n i s t r y of Health and Welfare (MHW) of Japan f o r the PUROX System, 2) To analyze i n accordance with procedures provided i n the Japanese I n d u s t r i a l Standard or those e s t a b l i s h e d by the Environment Agency and MHW of Japan, i n order to evaluate outgoing streams on the b a s i s of Japanese n a t i o n a l e n v i ronmental standards and emission and e f f l u e n t standards, 3) To o b t a i n engineering data necessary f o r the design of the components of the Dry Process, namely, the gas combustor, waste heat b o i l e r , and e l e c t r o s t a t i c p r e c i p i t a t o r . The r e f u s e used f o r the t e s t was shredded r e f u s e from St. Catharines, Canada. Glass, p l a s t i c s , s i l a g e , f r u i t s and vege t a b l e s , and water were added to them to simulate Japanese r e f u s e . Refuse of high, intermediate, standard, and low moisture were prepared to simulate t y p i c a l Japanese r e f u s e . The r e f u s e mixing r a t i o f o r the four simulated r e f u s e are given i n Table I I . The q u a l i t y of the simulated Japanese r e f u s e t e s t e d as w e l l as that of Japanese r e f u s e are shown i n Figure 4.



F r o n t End

Wastewater

Oxygen

Fuel

Figure 2.

Air

Fuel

/

-IL

1J

Combustor

Off-gad

Electro static Precipitator

Particulate

Waste Heat Boiler

Schematic flowsheet of the dry process PUROX system

Slag

Converter

Other Wastewater

Ferrous M a t e r i a l

As Received Refuse


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MASUDA

Figure 3.

PUROX

577


Overall view of the pilot plant

Japanese

refuse

Simulated Japanese

refuse

A - High Moisture Β - Intermediate moisture C - Standard moisture D - Low Moisture

10

20

Ash content (wt.%) Figure 4.

Quality of Japanese refuse and simulated Japanese refuse


578

THERMAL CONVERSION OF SOLID WASTES AND BIOMASS

TABLE I I .

TYPICAL REFUSE MIXING RATIO


H.M.R. Raw shredded r e f u s e (wt.%) Silage Shredded potato Polyvinylchloride Polyethylene Glass Water

17.6 0.0 58.0 0.9 1.8 1.6 20.1

S.M.R. 37.0 10.4 10.4 1.8 3.8 5.1 30.2

- 38 .2 - 10 .6 - 11 .1 - 1 .9 - 5 .2 - 30 .6

L.M.R. 46.8 3.0 9.1 2.9 5.9 9.8 21.9

- 47.6 - 3.1 -

3.0

- 10.0 - 22.0

Although the p i l o t p l a n t had a refuse treatment c a p a c i t y of 20 Mg/d, i t was u s u a l l y operated a t reduced load due t o l i m i t a t i o n s coming from the r e f u s e p r e p a r a t i o n s i t e . Also schedule c o n s t r a i n t s prevented replacement o f the desuperheater and scrubber employed to c l e a n f u e l gas i n the p i l o t p l a n t , by a waste heat b o i l e r and e l e c t r o s t a t i c p r e c i p i t a t o r , such as a r e employed i n the Dry Process PUROX System design. Consequently, dust was not r e c y c l e d . Refuse prepared a t a s e t mixing r a t i o was supplied by apron conveyor to the feeder. The feeder p e l l e t i z e d the r e f u s e and charged the p e l l e t s i n t o the converter, where i t was d r i e d , pyrol y z e d , combusted and melted to form p y r o l y s i s gas and molten s l a g . The s l a g , o r i n o r g a n i c r e s i d u e , was c o n t i n u o u s l y tapped from the converter, quenched i n the water tank and c o l l e c t e d i n the s l a g bunker. The p y r o l y s i s gas was combusted i n the combustor and discharged a f t e r scrubbing. The process flow of the p i l o t plant i s shown i n F i g u r e 5, together with a m a t e r i a l balance f o r the case of high moisture r e f u s e . A t y p i c a l energy balance i s shown i n F i g u r e 6. TABLE I I I . ANALYSIS OF PYROLYSIS GAS Japanese Refuse" L.M.R. H.M.R. S.M.R. CO dry gas v o l . % C02 H CH4 CmHn " Others H2O Nm3/Nm3 dry gas Lower H.V. kJ/Nm3 dry gas (kcal/Nm^ dry gas) 2

11

11

16.00 58.91 18.41 2.96 2.30 1.42 1.3

30.09 38.93 24.16 2.52 2.33 1.97 1.2

6,900 (1,650)

9,420 (2,250)

U.S. Refus

28.64 36.40 25.69 3.77 3.85 1.65 0.8

38 27 23 5.0 5.1 1.9 0.7

11,510 (2,750)

14,570 (3,270)

See a b b r e v i a t i o n s


MASUDA

A N D FISHER

PUROX



41.


579


Basis:

0.36 EU

Air 0.0

Combustor

Heat loss 0.09 EU

Propane 0.67

0.05 EU

Cooling

Water

1.53 EU

Off-gas

Δ

Δ

Off-gas 0.12 EU

Wastewater 1.41 EU

Scrubber

Δ

Energy balance of the pilot plant (high moisture refuse)

Residue 0.08 EU

Converter

Heat loss 0.08 EU

Figure 6.

1 EU of feed (EU = energy unit)

Cooling 0.20 EU

Limestone

Wastewater


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A N D FISHER

PUROX


581

A comparison o f the p y r o l y s i s gas obtained with Japanese standard r e f u s e and with U.S. r e f u s e (dry gas base) i s given i n Table I I I . I t i s apparent that higher percentage o f water and CO2 i n the gas are obtained i n the case o f Japanese r e f u s e and that the heating value per u n i t volume of the dry gas obtained i s lower. A comparison o f the s l a g composition i s given i n Table IV. The i g n i t i o n weight l o s s f i g u r e s , which show the percentages o f uncombusted m a t e r i a l s , f o r both the Japanese and the U.S. r e f u s e are s u b s t a n t i a l l y lower than the standard Japanese values obtained with the conventional stoker type i n c i n e r a t o r , which are below 10 wt.% f o r a furnace of l e s s than 200 Mg/d and below 7% f o r a furnace of more than 200 Mg/d. TABLE IV.

SLAG COMPOSITION

Japanese Refuse H.M.R. L.M.R. S.M.R. Si0 (wt.%) A1 0 CaO Na 0 FeO Ignition loss 2

2

2

3

51.6 6.7 21.9 5.3 7.4 0.2

59.3 7.1 10.2 7.3 8.1 0.05

56.4 4.8 18.0** 5.9 10.9 0.1

U.S.

Refuse

59.7 10.5 10.3 8.0 6.2 0.4

** Limestone added as n e u t r a l i z a t i o n agent. The s l a g l e a c h i n g t e s t r e s u l t s are given i n Table V. The analyses were conducted i n accordance with N o t i f i c a t i o n No. 13 o f the Environment Agency of Japan. For purposes of comparison, the leachate standards e s t a b l i s h e d by the Prime M i n i s t e r ' s O f f i c e of Japan are a l s o given. These r e s u l t s c l e a r l y show that the amounts of hazardous substances leached from PUROX System s l a g are much l e s s than those of the standards. The i n e r t nature o f the s l a g i s considered a t t r i b u t a b l e s to the p y r o l y s i s o f hazardous m a t e r i a l s such as organic phosphorus, cyanide, and PCB to form more s t a b l e and l e s s environmentally o b j e c t i o n a b l e substances, the temperature being as high as 1,650°C a t the bottom o f the converter, and t r a p p i n g of t r a c e metals i n the g l a s s y matrix. Refuse to which PCB and dry c e l l s and Ni-Cd c e l l s had been added was t e s t e d . I t was not p o s s i b l e , however, to observe the behavior o f PCB and heavy metals s i n c e t h e i r concentrations i n the s l a g d i d not show any marked d i f f e r e n c e . T h i s may have been due to a d d i t i o n of c e l l s that had each been cut i n t o three p i e c e s , thereby causing spotty d i s t r i b u t i o n of the heavy metals. Table VI gives the composition of s l a g when PCB was and when i t was not added. As shown i n the Table, the PCB content was below the d e t e c t i o n l i m i t i n both cases. I t i s considered that


582

THERMAL CONVERSION

OF SOLID WASTES AND

BIOMASS

PCB e i t h e r decomposes or e x i s t s i n the s l a g i n such a form as not to l e a c h out and, t h e r e f o r e , does not cause environmental problems. TABLE V.

SLAG LEACHING TEST RESULTS


Inland L a n d f i l l i n g Detection Analysis Limit Standard (mg/1) Alkyl mercury Total mercury Cadmium Lead Organic phosphorus Hexavalent chromium Arsenic Cyanide PCB

ND

0.0005

ND

ND

0.0005

ND

ND ND 0.023

0.0002 0.0025 0.005

0.005 0.3 3

ND ND 0.015

0.0002 0.0025 0.005

0.005 0.1 1

ND

0.0006

1

ND

0.01

1

ND 0.0025 ND ND

0.01 0.0007 0.002 0.0005

1.5 1.5 1 0.003

ND 0.0042 ND ND

0.01 0.0007 0.002 0.0005

0.5 0.5 1 0.003

TABLE V I .

EFFECT OF PCB ADDITION ON SLAG COMPOSITION (Standard Moisture Refuse)

composition (wt.%) Si0 A1 0 CaO Na 0 FeO leaching test (ppm) PCB - pH 6 - pH 8 2

2

2

3

L a n d f i l l i n g on the Sea Detection Analysis Limit Standard

PCB added

PCB not added

59.3 7.1 10.2 7.3 8.1

48.8 6.2 17.6 5.5 17.9

Thermal Conversion of Solid Wastes and Biomass - American

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