Development of the Kiener Pyrolysis System for

Environmental Protection, Energy Recovery and Recycling

F. NOWAK

Galgenberg, West Germany

ABSTRACT

The unique feature of this process is the highly efficient combination of refuse volatilization in an air-free atmosphere and cracking of the produced gases. The system is capable of processing domestic, commercial and industrial refuse, and s.ewage sludge.

The gas recovered by this process is used as a fuel for gas turbines and gas engines. The produced gas could also be used in the chemical industry as a feed stock to produce materials such as plastics. Metals and other inorganics which do not undergo chemical changes in the process can be recovered from the residue for recycling.

A pilot plant has been in operation for some time. The first phase ot the program, the scienti­fic and technical evaluation of the system by a research group at Stuttgart University, has been completed. The second phase, optimizing of the chemical processes in the fully automated

660 lb/hr (300 kg/h) pilot plant, is presently underway. The experiments are being conducted under actual working conditions and will be completed by the end of 1977. The third and last phase is the construction of a demonstration

plant with a refuse throughput capacity of 3 tons/hr. This plant will be constructed and placed in operation during 1978.

29

INTRODUCTION

Pyrolysis or destructive distillation as a process has been mastered and applied in industry for many years. The most widely known application of pyrolysis is the production of city gas and coke from coal.

In the past, pyrolysis was mainly employed for the conversion of organic materials with a high-energy content such as wood, peat, coal and oil shale. The complex chemical and physical

•

reactions governing the process, however, are in general the same for materials such as rubber, plastics, paper, textiles, oils, fats and cellulose­containing materials. Most of these materials are composed of large molecules. Heat treatment breaks up the large molecules and pyrolysis of the materials mentioned results in a char with a low hydrogen content and a hydrogen-rich gas. The controlling factors for the chemical reac­tions are temperature, particle size, mixing and residence time of the materials in the pyrolysis unit. In the pyrolysis system developed by Mr. Kiener and described herein, the volatile fraction of the organic content of the domestic, com­merical and industrial refuse is completely gasified. The recovered gas is further processed

and can be used as a fuel for gas turbines and motors, or as a feed stock in the chemical industry

w

o

GAS

CRACK

ING

a REA

CTION

UN

IT

Gas T

�.-I

OO"C

Exha

ust Ga

s T

emp

. -

600°C

Temp.

450

-'!J:Xf'C

GAS

GAS

SCRUBBER

Air

FIG

.1

for the production of materials such as plastics. The main feature of the "Kiener Pyrolysis

System" is the efficient combination of gasifica­tion and gas cracking, each of which can be fully automated and optimized.

The process was patented in the United States on June 7, 1977 under Patent No. 4028068.

PILOT PLANT CONSTRUCTION DETAILS

AND OPERATION

The pilot plant described in this paper was constructed in 1974. It can process approximately 440 lb/hr (200 kg/hr) of refuse with a moisture content of 20 percent. Extremely wet refuse will reduce its capacity to about 330 lb/hr (150 kg/h). Fig. 1 shows a schematic of the pilot plant.

A rotating drum sloping along its longitudinal axis serves as the pyrolysis and gas producing unit. Special vanes of gas-tight construction are welded to the inside wall of this drum. These vanes serve as heat exchanger for the indirect heating of the drum contents with exhaust gases from a gas turbine or gas motor, or oil or gas burners. The vanes not only maximize heat transfer but they also have the function of mixing and transporting the materials in the drum. Gas-tight locks on both ends of the drum permit continuous charging and discharging of the drum. Pressure inside the drum is kept between ± 2 mm water column. The drum contents are heated to a temperature of 750 to 950 F (400 to 500C) in an air-free atmosphere. Even the most difficult materials are completely pyrolysed at these temperatures. The heavy hydro­carbons like tar, phenol and oil are completely volatalized. The residue which can be further processed consists of char, ash, coal residue, metals and glass. The drum is normally charged with shredded refuse. Shredding of the refuse to a maximum particle size of 3 to 4 in. (8 to 10 cm) is sufficient.

The gases generated in the pyrolysis unit are passed through a cyclonic gas cleaner in which soot and flyash is removed. The gas flow then continues to the gas cracking and generating unit which it enters at a temperature of approximately 650 F (350C). At this point, the gas temperature is raised to the cracking temperature of 2000 to 2200F (1100 to 1200 C) through the addition of air and the burning of a portion of the gas. The cracking process converts the complex bonded hydrocarbons to methane, hydrogen, carbon dioxide, carbon monoxide and minor quantities

31

of other simple bonded hydrocarbons. Of course, the nitrogen in the gas is unaffected by the crack­ing process. After cracking, the gases are passed through an incandescent layer of coal where all of the subsequent reactions take place. The result­ing gas mixture consists of hydrogen, carbon monoxide, simple hydrocarbons, carbon dioxide, nitrogen and minor quantities of steam and heavy hydrocarbons. The endothermic chemical reactions cause the gas temperature to drop to approx­imately 840F (450C), the gas exit temperature from the reactor.

Prior to wet scrubbing, the gases are passed through a second cyclonic gas cleaner to remove dust particles. The gas washer removes the remain­ing dust particles, cleans the gas of undesirable compounds and lowers its temperature to about 160 to 175 F (70 to 80C). Since raw refuse has an average moisture content of 25 percent, of which approximately 8 percent is deoxidized in the gas generator, the water vapor in the gas remains at the saturation point. The water vapor content of the gas at the above temperature, 110 to 130 gr/ft3 (250 to 300 g/m3), can be condensed through additional cooling of the gas to make it available for other purposes in the process.

After washing, the gas is cooled about 72 F (40 C) prior to its storage in a gas holder and its use in a gas turbine. The gas storage serves to balance fluctuations in gas quantity and heating value. The gas composition is fairly independent of the raw refuse mix. The heating value of the gas at a specific weight of 0.069 to 0.075 lb/fe (1.1 to 1.2 kg/m3) varies between 2250 and 3500 btu/lb (1250 and 1950 kcal/kg). The electricity produced can be introduced directly into any grid or power system.

The hot exhaust gas from the gas turbine is returned to heat the pyrolysis unit. Auxiliary fuel for this purpose is only required for a short period of time to start the process. The residual heat in the exhaust, after extraction of the process heat, can be recovered and used as a supply for a district heating system.

Blowers are required to move the gases through the process.

The fully automated plant makes it possible to optimize each step in the process. In addition, the automation makes it feasible to change the plant operation within 1 hr from processing average refuse to processing materials with a high­energy content, such as used tires, used oil and plastics.

Waste Gas Heat GAS CRACKING 8 REACTION UNIT

PYROLYSIS UNIT GAS COOLER

GAS CLEANER

Ref u�se"--__ "'.I

Heat

Residue - MaInly Innerts, Metals a Carbon GAS STORAGE Heat

GAS MOTOR

Hot Exhaust For Heating Of The Pyrolysis Unit

FIG.2

Start-up of the cold plant requires 30 min. Only 15 min are necessary for start-up after a 24 hr shutdown. Complete shutdown of the plant takes a few minutes.

ALTERNATE METHODS OF OPERATION OF

THE KIENER PYROLYSIS PROCESS

There are two basic methods of process opera­tion. The first one is designed for power produc­tion and heat recovery and the second one is recovery of raw materials. The choice between these methods is based upon economics and depends on the waste rna terial to be processed and market conditions.

OPERATION METHOD NO.1

A schematic of the process for operation method No. I, power production and heat re­covery, is shown in Fig. 2. This method of operation is especially well-suited for processing waste material with high-energy content such as used tires, plastic scrap, carpet remnants, wood,

32

and organic wastes from industry. It also can be employed for materials with a relatively low heating value such as refuse and sludge and other materials which present special problems when disposed of by incineration.

OPERATION METHOD NO.2

A schematic of operation method No. 2, re­covery of raw materials, is shown in Fig. 3. This method of operation is employed for waste materials producing easily condensable gases. The condensate can be stored during times of low demand and can be reintroduced into the process during times of high demand. The con­densate from the pyrolysis of tires is very much desired by the chemical industry.

MATERIAL AND ENERGY BALANCE FOR THE

PYROLYSIS OF DOMESTIC REFUSE

Test data of the waste material processed and of the gaseous, liquid and solid end products is

Gas For Heating Of The Pyrolysis Unit

Waste Gas - Heat

Refuse

Ifur

����==-=-=..:..:.. G UNIT

,---=. Condensate I

Heat

CONDENSATION UNIT

- Soot I

Metals

FIG.3

shown in Tables 1 through 4. This data was taken from an arbitrarily selected test run.

The average material balance is shown in Fig. 4. The data shows that 1.1 ton (1 t) of refuse produced on the average 900 lb (408 kg) of raw gas which includes steam. The gas quantity after gas generation and washing amounted to 2400 lb (1092 kg). It is composed of about 50 percent nitrogen, 25 percent plus hydrogen, 12.5 percent carbon monoxide, 10 percent carbon dioxide, 3 percent methane, and minor amounts of oxygen and miscellaneous hydrocarbons. Concentrations of 170 ppm hydrogen sulfide, 400 ppm ammonia and 6 ppm hydrocyanide were measured. Hydrogen chloride concentrations were not measurable. The lower heat value of the gas produced was 147 Btu/ ft3 (1308 kcal/m3).

The volume of wastewater amounted to 320

lb/ton (160 kg/ t) of refuse processed. Most of the heavy metals remained in the

residue and only insignificant quantities of heavy metals were to be found in the wash water.

33

The energy balance presented in Fig. 5 shows that the results are satisfactory despite the rela­tively low heating value of the refuse. Approxi­mately two-third of the heat content of the pro­cessed material was contained in the clean gas. The energy requirement for the pyrolysis of the waste material remained fairly constant and one can, therefore, expect that 80 percent of the 2320 Btu/lb (1290 kcal/kg) heat content of average refuse is available for use.

The above tests were conducted by the Institute for Town Planning and Water Quality of the University of Stuttgart.

Figure 6 shows that heat balance for a test run with refuse having a heating value of 4160 Btu/lb (2310 kcal/kg). The refuse composition for this test was as follows: 20 percent inerts, 28 percent frne refuse and 52 percent volatiles. The analysis of the fine refuse portion showed 55 percent volatiles after subtracting 15 percent for the non­combustible materials and 10 percent for ash. The heat balance in Fig. 6 proves that, through the

SOLIDS

ORGANIC MATTER

MINERAL MATTER

METAL

LOWER HEATING VALUE

TABLE 1 REFUSE COMPOSITION

75% by weight

32% of solids by weight

62% of solids by weight

6% of solids by weight

2320 Btu/lb (1290 kcal/kg.)

TABLE 2 ANALYSIS AND AVERAGE COMPOSITION OF THE CLEANED GAS PRODUCED IN THE

PYROLYSIS OF DOMESTIC REFUSE

2 6.7 Vol. -% NH3

400 ppm

13.0 Vol. - % H2S 170 ppm

3.0 Vol. -% S02 not measurable

0. 1 Vol. -% HCN 6 ppm

1.2 Vol. -% NO x not measurable

10.0 Vol. -% HCL not measurable

46.0 Vol. -% HF not measurable

Hg less than 0.05

Lower Heating Value 147 Btu/ft3 (1308 kcal/m3)

Specific Weight 0.07 Ib/ft3 (1.13 kg/m3)

TABLE 3 ANALYSIS OF RESIDUE FROM THE PYROLYSIS OF DOMESTIC REFUSE

Discharge from

Pyrolysis Drum

Specific Weight (Uncompacted 70 Ib/ft' (1.12 t/m3)

Combustibles 1 3% by weight

Dust from Cyclon e

56% by weight

mg/m

Lower Heating Value 1300 Btu/lb (725 kcal/kg) 4100 Btu/lb (2275 kcal/kg)

34

TABLE 4 ANALYSIS OF WASHWATER FROM PYROLYSIS OF DOMESTIC REFUSE

DRY SOLIDS

COMBUSTIBLES

pH

Ntotal

B .O . D ·s

Ptotal

NNH3

COD

TOC

CYANIDE

SULFIDE

SULFATE

CHLORIDE

EXTRACTABLE PETRO ETHER

PHENOLtotal

580 kg Residue

nclJdng� 12 � I From C)dore

I PYROLYSIS DRUM

I 1000 kg Domestic Refuse HL: 1290 kcal/ kg

I 7'3J kg Air

7000 ppm

65% by weight

"

7.4

1760 ppm

450 ppm

not measurable

1600 ppm

6400 ppm

300 ppm

15.0 ppm

0.7 ppm

170.0 ppm

1500 ppm

65 ppm

370 ppm

GAS WASHING a COOLING SYSTEM

I 160 kg Wash Water

L' l25f kg Gos And Steam

I GAS CRACKING a REACTION UNIT

L�q Ash

FIG.4

35

1206 Meal in Gas and Ste.9.!!l.-- ,.2QQ Meal in Coul

PYROLYSIS DRUM_

.Jl. Meal in Ash

� Meal in Gas

1772 Meal

I )r-. �--. .. --�

........ 1-"-----1 482 Meal For Heating Of The Pyrolysis Unit

1290 MeaL Refuse

/'

) .. I� '\ 482 �'--!-1-f---' �/ For Heating Of The Pyrolysis Drum

Heat Losses 118 M"' co"'-I '--___ --'

782 Meal Excess Gas

425 Meal in Wash Water And Heat Losses

c.J2AS WASHING 8 COOLING SYSTEM

�9 Meal in Gas And Steam

�� CRACKING 8 REACTION UNIT 1706 Meal

421 Meal in Resid,."ue'--_--'

27 Meal in Cyclone Du."'st_---'

return of the heat in the exhaust gas of the gas motor, almost all of the heat contained in wet refuse can be recovered in the generated gas. Assuming an efficiency of 36 percent for the gas motor and an efficiency of 92 percent for the electric generator, the calculated power produced from 1.1 ton ( 1 t) refuse with a heating value of 4 160 Btu/lb (23 10 kcal/kg) is 860 kWh.

MATERIAL AND ENERGY BALANCE FOR

THE PYROLYSIS OF DOMESTIC REFUSE

MIXED WITH DEWATERED SLUDGE

In this test run shredded refuse was mixed with digested sludge with a water content of 65 percent. The data of this test run is presented in Tables 7 through 12.

The material balance is shown in Fig. 7. The data indicates that pyrolysis of one ton ( 1 t) of a mixture consisting of 78.5 percent domestic re­fuse and 2 1.5 percent digested sludge produced 3 1 10 lb ( 14 10 kg) of clean gas with a heating value of 147 Btu/ft3 ( 13 10 kcal/m3). With the exception of the hydrogen content, the gas

FIG.5

36

composition was similar to the gas produced from the pyrolysis of domestic refuse alone.

The quantity of heat required to maintain the pyrolysis process at a temperature of 790F (420 C) is estimated at 990 Btu/lb (550 kcal/kg) of refuse-sludge mixture. Approximately 62.5 percent of the heat content of the mixture is, therefore, available for other usage. Hydrogen fluoride and hydrogen chloride were not found in the clean gas. We are convinced that pyrolysis of sludge without the addition of refuse is pos­sible. Power production from sludge will depend on the degree of dewatering. Recovery of heat will always be insured.

CONCLUSIONS

The main benefits of the "Kiener Pyrolysis Method" are:

1. Simple and efficient flue gas cleaning, since the volume of gas produced in the pyrolysis portion of the process is approximately one sixth of the volume of gas produced by incineration, and heavy metals are not oxidized.

.. :J

� '" .. a:: " .. J: .. .0 '" c .. Vl

0 u

� 0 If)

.. :>

"'? '" .. a:: 'Q .. .2 0 >

"0 .. J: -0 U

� If) ..-..-

'" '" .3 c o

'" 0 <:> '" :> 0

.c " w c:: 0 .. J: 0

:J "0 '" .. a:: -0 U

� 0 CO N

o - -'0 0 � � U I

- � � o If) .-"? U M �

� ..- Vl

If) N

00 .s

- 0 0 <3 u �

::x::� o o� 0", c:o�

........

-

'" 0 <:> .s

. --

� 0 �

2310K c al/kg Heat Content of Refuse

r-....

�.

2940 Kcal

) j .,

2495Kcal -

-

2370Kcal

- -

2235Kcal

--..-

2235Kcal

) '-'

-0 U

::x:: 0 M U)

PYRO LYSIS DRUM

GAS C RACKING a REACTION

EAT VALUE OF GAS a M)

UNIT (H STEA

GAS W ASHING a COOLING EAT VALU E OF GAS) UNIT ( H

GAS S TOR AGE TANK

GAS M OTOR

805 Kcal Kinetic Energy

FIG.6

37

286 K9 Residue Inell,ldino Cool 703 ICIjJ Gas Ineludin; Steam

II K; Oust from C,,"'C::'O::: .. '-_--,

PYROLYSIS DRUM

785 K; Domestic Refuse

Lower Hl!Of.no Value 220'0 Keol/K;

215 Kg Digest.d SludO'

Lo .. ., Hto'ino \Iolu. 250 Keol /KO

8 8 0 K; Air

Gos 8 Sfeom 1970 Meal Coo' 170 Meal

PYROLYSIS DRUM 2350 Mco'

R.'uU a Slud;. Mi.'Uf, 1800 Meal

Heat Losses 112 Meal

Residue 8 Char 240 Meal

OuSI from C"etone 28 Meal

40 KO Cool

GAS WASHING a COOUNG SYSTEM

1620 KO Gas 6 Steam

210 K Woshwof,f

LOIII.r Heating Volu. 1 17 0 Kcal/K; Of 1310 Kcol/m3

GAS CRACKING a REACTION UNIT

3 KO Ash

FIG.7

ASh 12 Meal

ralys!s Drum Heo';no 550 Meal

GAS COOLING a WASHING SYSTEM

GAS CRACKING a REACTION UNI T 2140 Meat

FIG. 8

38

TABLE 5 AVERAGE GRAIN SIZE DISTRIBUTION IN THE RESIDUE FROM THE PYROLYSIS O F

DOMESTIC RE FUSE

DIAMETER INCHES DIAMETER (rom) % BY WEIGHT

0.2 - 0.4 5 - 10 57

0.08 - 0.2 2 - 5 7.2

0.04 - 0.08 1 - 2 4.4

0.02 - 0.04 0.05 - 1 6.3

0 - 0.02 o - 0.5 25.1

TABLE 6 AVERAGE HEAVY METAL CONTENT IN THE RE FUSE, THE RESIDUE AND THE WASH WATER

REFUSE RESIDUE WASHWATER

Fe 1600 ppm 2200 ppm 17 ppm

Cu 20 ppm 18 ppm 0.1 ppm

Ni 50 ppm 70 ppm 0.1 ppm

Co 6 ppm 6 ppm not measurable

Zn 40 ppm 120 ppm 2 ppm

Cd 2 ppm 3 ppm not measurable

Pb 15 ppm 20 ppm 0.3 ppm

Mn 30 ppm 75 ppm 1.5 ppm

Cr 45 ppm 60 ppm 0.1 ppm

TABLE 7 RE FUSE AND DIGESTER SLUDGE COMPOSITION

SOLIDS

ORGANIC MATTER

MINERAL MATTER

METALS

LOWER HEAT VALUE

LOt-1ER HEAT VALUE COMBINED

REFUSE DIGESTED SLUDGE

65% by weight 35% by weight

60% of solids by weight 40% of solids

35% of solids by weight 56% of solids

4% of solids by weight

4000 Btu/lb (2200 kcal/kg) 450 Btu/lb

3000 Btu/lb (1670 kcal/kg)

MOISTURE CONTENT OF THE REFUSE-SLUDGE MIXTURE 41.5% BY WEIGHT

39

by weight

by weight

(250 kcal /kg)

TABLE 8 ANALYSIS AND AVERAGE COMPOSITION OF THE CLEANED GAS PRODUCED IN THE PYROL YSIS OF REFUSE AND SLUDGE

13.5 Vol .-% NH3 750 ppm

11. 2 Vol .-% H2S 140 ppm

4.4 Vol.-% S02 not measurabl e

1.9 Vol.-% HCN 8 ppm

2.1 Vol .-% NO not measurabl e x

14.5 Vol.-% HCl not measurabl e

52.4 Vol -% HF not measurable

Lower Heating Value 2360 Btu/lb (1310 kcal/m')

Specific Weight 0.07 Ib/ft' (1.12 kg)

,ABLE 9 ANALYSIS OF RESIDUE FROM THE PYROLYSIS OF DOMESTIC REFUSE AND DE WATERED DIGESTED SLUDGE

Discharge From Pyrolysis Drum

Dust From Cycl one

SPECIFIC HEIGHT (Uncompacted) 70 lb/ft "3 (1.1 t/l'1 3 )

COMBUSTIBLES

LOWER HEAT VALUE

17% by weight

1510 Btu/lb (840 kcal/kg)

67% by weight

4600 Btu/lb (2550 kcal/kg)

TABLE 10 ANALYSIS OF THE WASHWATER FROM THE PYROLYSIS OF DOMESTIC REFUSE AND DE WATERED DIGESTED SLUDGE

DRY SOLIDS 10,600 ppm

COMBUSTIBLES 7.1% by weight

pH 7.5

N total

1900 ppm Cyanide 25.0 ppm

BODS

620 ppm Sulfide 1-2 ppm

Ptotal not measurabl e Sulfate 520 ppm

NNH3 1750 ppm Chloride 1750 ppm

COD 7600 ppm Extractabl e Petro Ether: 95 ppm

TOC 2800 ppm Phenol 470 ppm total

40

TABLE 1 1 AVERAGE GRAIN SIZE DISTRIBUTION IN THE RESIDUE FROM THE

PYROLYSIS OF DOMESTIC REFUSE AND DEWATERED DIGESTED SLUDGE

DIANETER INCHES DIAMETER (mm) % BY \'lEIGHT

0.2 - 0.4 5 - 10 37

0.08 - 0.2 2 - 5 13

0.04 - 0.08 1 - 2 9

0.02 - 0.04 0.5 - 1 11

0 - 0.02 0 - 0.5 30

TABLE 12 AVERAGE HEAVY METAL CONTENT IN THE REFUSE, THE SLUDGE,

THE RESIDUE AND THE WASH WATER

Refuse Slud9:e Residue Wash Water (ppm) (ppm) (ppm) (ppm)

Fe 1140 1550 1420 20

Cu 28 240 52 0.1

Ni 32 60 80 0.1

Co 4 22 15 n.m.

Zn 70 1400 400 4

Cd 0-1 4 1-2 n.m.

Pb 17 170 35 0.2-1

Mn 30 240 25 4

Cr 40 38 60 0.1

n.m.= not measurabl e

2. The feasibility of producing electrical power and recovery of heat.

3. Feasibility of recovering raw materials. 4. Ability to process difficult organic wastes. 5. Low capital investment as compared to

incineration, especially for the medium sized plant.

PROPOSED DESIGN OF A DEMONSTRATION

PLANT

It is expected that the University of Stuttgart will complete the present pilot studies by the end of 1977.

The chemical and physical process will be optimized to increase the capacity of the pilot plant from 440 lb (200 kg) to 660 lb (300 kg)

per hour in the next step of development. Some of this work is being done concurrently with the present pilot studies.

The construction of a demonstration plant with a capacity of 2.72 ton/hr (2.47 t/h) is planned as the fmal phase of the studies. The basic construction of the plant will be completed during 1978. After testing, a second unit of the same capacity will be added. The combined capacity of the plant will serve a suburban community with a population of 120,000.

In the design of the plant, attention will be paid to all elements starting with the tipping floor, the refuse preparation, the pyrolysis unit, the gas preparation units, operating facilities and instru· mentation.

The experience gained by the author in a large incinerator will be very helpful.

Key Words: Energy, Gasification, Hydrocarbon, Pyrolysis, Refuse, Rotating Drum, Sludge

41

Discussion by

Richard B. Engdahl

Battelle Memorial Institute

Columbus, Ohio

Another paper on refuse pyrolysis. But this one is unusual in that it confines its claims to the data obtained since 1974 on a small pilot operation -440 Ib/hr. And even more unusual is that the next step planned is not a full scale operation but an optimization of the original small pilot to increase its capacity by 50 percent, to 660 Ib/hr. Then an 8-fold scale-up is to be made to a plant to process 2.72 ton/hr. This is still smaller than most waste­processing systems, but these modest steps in scale­up indicate a realistic awareness on the part of the developers that solid waste is a difficult fuel to handle for which scale-up is an art and not a well­defined process.

A unique feature of the Kiener process is that after the gases are cracked through partial com­bustion they are then passed through an incandes­cent bed of coal. Presumably this is to decompose any sticky tars and vapors that escape the cracking unit. The author does not explain whether this requires a special coal and how much is consumed.

While the internally heated rotary kiln is a very simple pyrolysis chamber, the maintenance of a gas-tight seal is not a simple matter, particularly for large kilns. There is a suggestion that the system might be operated above or below atmospheric pressure. That would be a very formidable task in full scale equipment!

There is a repeated suggestion in the paper that the gases could power a gas turbine. With only two stages of centrifugal dust separation plus a modest gas washer, this seems highly unlikely in view of many similar unsuccessful attempts in the past. Blade erosion has thwarted all efforts so far to power gas turbines with solid fuel.

The claim is made that the capital cost would be less than for more conventional waste-to-energy systems. But no evidence is provided to support that claim except that the gas cleaning system could be smaller. It still appears to be a relatively complex system with some indication that there is a practical upper limit to the size of unit. More firm compar­isons should be developed, component for compo­nent, to show the relative costs compared to work­ing systems.

It seems inherent that in large scale the mass burning of refuse to produce steam or hot water

42

will always be the lowest cost method. But there will always be some applications where the com­plexity of refuse preparation and fuel-gas production will be justified. It is encouraging to learn of this careful development work toward a practical system for such applications.

Discussion by

Charles O. Velzy

Charles R. Velzy Associates

Armonk, New York

This interesting paper presents and describes the preliminary results of a development and testing program on a pyrolysis system to produce low Btu gas or oil condensate. As pointed out in the paper, it is intended that this system would serve com­munities with a population of up to 120,000, based on refuse generation of 2.4 lb/capita/day.

Several points of clarification and/or inter­pretation would be desirable. Thus, in the first sentence of the second from the last paragraph of the section entitled "Pilot Plant Construction Details and Operation," it would appear that the word "instrumented" would be more appropriate than "automated". In Fig. 2 it appears that the gas cooler and the gas cleaner should be interchanged (see Fig. 1) and an induced draft fan should be indicated preceding the gas storage. On Fig. 7 the heating value of the coal appears to be 4250 kcal/­kg. In Table 8 the lower heating value stated in the same terms as in Table 2 would be 147 Btu/fe. Also in Table 8, in the translation to English, the notation that mercury was not measurable was deleted. Further, it should be emphasized that the data presented in the tables is data from a specific single test run for each table, while some of the information presented in the text and shown on the figures is more general in background.

In the last paragraph in the right column under Fig. 3, the refuse composition is not clear. It appears as if the total combustible content was 63 percent, while the total noncombustible content was 37 percent, if the analysis was made on the dry basis. The definition and meaning of "fine refuse" also is not readily apparent. It would be desirable for the author to clarify this information.

It would also be desirable for the author to provide details on the wash water treatment. This is a matter of great concern in this country due to

the possibility of highly toxic materials being removed from the gas stream and appearing in the wash water. We must not trade an air pollution problem for a water pollution problem.

With respect to the analyses of the wash waters presented in Tables 4 and 10, the indicated com­bustibles are so dissimilar as to require an explana­tion. Thus, in Table 4, pyrolysis of refuse alone, combustibles were noted to be 65.0 percent by weight, while in Table 10, pyrolysis of refuse and sludge, combustibles were noted to be only 7.1 per­cent by weight. Is there perhaps an error by a factor of 10?

The information presented in Tables 6 and 12 would have been more useful if expressed in the form of mass balances. If this kind of information is available, it would be desirable to add it to the paper.

Discussion by

Eric H. Smith

Holden, Massachusetts

Mr. F. Nowak is to be commended for a very interesting paper on the pyrolysis system developed by Mr. Kiener. Pyrolysis systems are so important because the gas produced has many more possible uses than has the heat in the combustion gases from the direct burning of municipal refuse.

It would be of interest to know what kind of coal was found suitable, the manner in which this coal was used and how ash was removed.

COMPARISION*

O F GAS ANAL YSES

Sou ree of Data

Fig. 5

Refuse Coal

Meal Meal

1290 500

Fuel Gas

H2 26.7 CO 13.0 CH4 3.0 Cn

Hm 0.1 O2 1.2 CO2 10.0 N2 46.0

Fig. 8

Refuse Coal and

Sludge

Meal Meal

1800 170

Analysis

13.5 11.0

4.4 1.9 2.1

14.5 52.4

Other Gas

Analysis

(Approximate)

15.0 14.0

3.0 1.0 2.0

10.0 55.0

Note: A precise comparison would also require an

ultimate analysis of coal, refuse and sludge.

43

Pressumably only a small amount of coal is really necessary as the heat balance on Fig. 8 shows coal accounting for only 170 Meal com­pared with 1800 Mcal in refuse and digested sludge. It would be of interest to know why the ratio in Fig. 5 was 500 Mcal of coal to 1290 Mcal refuse.

The influence of coal apparently shows up in the Gas Analyses.

AUTHOR'S REPLY

To Richard B. Engdahl

As I pointed out in Chicago, we consider a scale­up from the 440 to 650 lb/hr pilot plant (its ca­pacity depends on refuse composition) to the proposed 5 ton/hr demonstration plant reasonable. Construction of larger units will be considered only after sufficient operating experience with the 5

ton/hr plant has been gained and after sufficient data has been accumulated for another scale-up.

Sealing of the larger kiln has been solved in design as well as in construction. The danger of large volumes of air entering the drum is eliminated since the pressure in the drum is effectively control­led at between 2-5 mm of H2 0 below atmospheric.

It will be feasible in the future to operate gas turbines with the low-grade gas produced in the process, and I had to mention this possibility in my paper. Of course, special att�ntion must be paid to the design of the gas cleaning system if in future large pyrolysis plants, gas turbines prove to be more economical than any other equipment.

We prepared a detailed cost analysis of a 5 ton/hr system and it shows that in this size in­cineration plants with energy recovery are more expensive. The higher cost of the incineration plant is due to the installed cost of the boiler, without considering the associated operating problems of this unit.

I repeat once more, and I hope nobody questions my expertise in the incineration field, that I am convinced that pyrolysis in its present stage of development is a valuable supplement to inciner­ation especially in communities with a population of approximately 100,000 people and less. Based on West German conditions, incineration is not the most economical solution for solid waste disposal for these communities. In addition, pyrolysis per­mits the processing of wastes which cannot be incinerated.

To Charles O. Velzy

The author agrees in general with several of the points of clarification made by Mr. Velzy. Thus the word "instrumented" in the context of the description of the pilot plant operation is more appropriate than the word "automated". Figure 2 should be corrected to show the gas cooler down­stream from the gas washer and a compressor should be shown upstream from the gas storage. The heating value of coal in Fig. 7 should be 4270 kcal/kg as stated. Air dried wood in lieu of coal was used in some test runs. The lower heating value as shown in Table 8 stated in the same terms as in Table 2 would be 147 Btu/fe. The German text of Table 8 shows a mercury concentration of less than 0.0 mg/m3 , and this concentration should be added to Table 8 of the English text. In general, the data in Drawings 4, 5, 7 and 8 and Tables 1 through 8 represent the results obtained in specific test runs.

The text of the last paragraph in the right column under Fig. 3 should be corrected to read "The refuse composition for this test was as follows: Fine refuse (passing a certain sieve) 28 per­cent; rocks, clay, porcelain, glass 14 percent; metal 6 percent; paper and light cardboard 30 percent; textiles 3 percent; leather, rubber and heavy card­board 3 percent; plastics 3 percent; and organic ki tchen waste 13 percent. The vola tile fraction of the above refuse represented 55 percent of the total. The remaining 45 percent is made up as follows:

44

Inert material (glass, porcelain, metals, etc.)

NoncOl:nbustible fraction in fine refuse

Remaining ash

Total:

20 percent

15 percent 10 percent

45 percent

Information on the treatment of the wash water is being collected at this time, but may not be available in time to include with this discussion.

The percentage of combustibles in Table 10 should be corrected to read 7 1 percent.

Mass balances have not been made to this date. I agree that mass balances are important and will see that they are made for future test runs.

To Eric Smith

The incandescent mass of coal serves as a catalyst and in theory, no coal is exhausted in the reaction. In actual operation, however, a small amount of coal is consumed to keep the variations in the heating value of the produced gas within specific limits. Wood, charcoal or coke are suitable catalysts. The ash is removed through a rotating grate.

Mr. Smith's assumption that the conversion of coal shows up in the gas analysis is correct. The relatively low heating value of the refuse accounts for the ratio of 500 Mcal of coal to 1290 Mcal of refuse as shown in Fig. 5. Of course, gas compo­sitions other than those shown in the tables are possible.