Method of pyrolyzing organic material using a two-bed pyrolysis system

An improvement in a method of pyrolysis wherein an organic material, such as city waste, is pyrolyzed using a two-bed type pyrolysis system including a fluidized bed type pyrolysis reactor and a combustion reactor and wherein energy is recovered from burning the pyrolysis gases produced is disclosed. The improvement comprises recovering the heat of a combustion exhaust gas which is generated when the energy of the pyrolysis gas is recovered, heating a fluid medium with the recovered heat, and heating the organic material to be pyrolyzed with the heated fluid heat medium to dry the organic material before it is pyrolyzed.

BACKGROUND OF THE INVENTION 
This invention relates in general to methods of pyrolysis and, more 
particularly, to a pyrolysis method in which an organic material, such as 
biomass or city waste, is pyrolyzed in a two-bed type pyrolysis system 
which includes a fluidized bed type pyrolysis reactor and a combustion 
reactor to obtain a high-energy fuel gas as the pyrolysis gas. 
Methods have been proposed for the gasification of municipal waste and 
biomass to produce high energy fuel gas. However, biomass and municipal 
waste generally have a high water content and when such material is fed to 
a pyrolysis apparatus a large amount of heat is required for pyrolysis 
thereof since much heat is consumed in the vaporization of the water. 
For example, in a partial oxidation type pyrolysis method in which an 
organic material is pyrolyzed utilizing heat generated through the burning 
of part of the material, it is necessary to supply large amounts of air to 
the material, to oxidize and burn the same. Accordingly, the recovered 
fuel gas contains N.sub.2 from the air and CO.sub.2 remaining in the 
reaction zone after the material has been combusted, thereby resulting in 
the fuel gas having a relatively low calorific value. 
In a two-bed type pyrolysis operation, a heat medium is heated with the 
heat generated by the combustion of char and tar which are by-products of 
the pyrolysis of a material. The heat medium is circulated between a 
fluidized bed type pyrolysis reactor and a combustion to thereby obtain 
the heat required for pyrolyzing the material. In such two-bed type 
pyrolysis operations, it is necessary that a large amount of recovered 
fuel gas in addition to char and oil be burned in order to supply 
sufficient heat to the material. Therefore, this pyrolyzing method also 
has a relatively low gas recovery rate. 
The fuel gas recovered in pyrolyzing methods is utilized as a power source. 
Thus, the fuel gas is burned such, for example, as by a gasoline or a gas 
turbine or the like. However, the combustion exhaust gas is merely 
discharged to the ambient atmosphere or, since it has a high temperature, 
can be used to heat water. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a 
pyrolysis method which is free from the drawbacks of the conventional 
pyrolysis methods discussed above. Another object of the present invention 
is to provide a pyrolysis method which improves the quality and recovery 
rate of the fuel gas in a pyrolysis system by reducing the water content 
of an organic material before it is pyrolyzed. 
Still another object of the present invention is to provide a new and 
improved pyrolysis method whereby a wider range of materials can be 
pyrolyzed than in the use of conventional techniques. 
Briefly, in accordance with the present invention these and other objects 
are attained by providing an improvement in a pyrolysis method wherein an 
organic material, such as municipal waste, is pyrolyzed using a two-bed 
pyrolysis system including a fluidized bed type pyrolysis reactor and a 
combustion reactor and wherein energy is recovered from burning the 
pyrolysis gases produced. The improvement comprises (a) recovering the 
heat of a combustion exhaust gas which is generated in the energy 
recovery, (b) heating a fluid heat medium with the recovered heat, and (c) 
heating the organic material to be pyrolyzed with the heated fluid heat 
medium, thereby drying the organic material before it is pyrolyzed. 
According to another feature of the present invention, heat is recovered 
from the combustion exhaust gas discharged from the combustion reactor and 
used as necessary to heat the fluid heat medium. 
In the pyrolysis method of the present invention, the organic material is 
heated either directly or indirectly by the fluid heat medium. 
The heat recovery is carried out utilizing a boiler or a heat exchanger. 
The fluid heat medium may be constituted by steam, air, oil or the like. 
In one preferred embodiment of the present invention, the organic material 
to be pyrolyzed is divided into a component having a high water content 
and a component having a low water content, and only the high water 
content component is pre-heated by the fluid heat medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings wherein like reference characters designate 
identical or corresponding parts throughout the several views, and more 
particularly to FIG. 1, a two-bed type pyrolysis apparatus is generally 
designated 1. Such two-bed type pyrolysis apparatus are known in the art 
and, for example, reference is made to U.S. Pat. No. 3,853,498 issued Dec. 
10, 1974 and U.S. Pat. No. 4,344,373 issued Aug. 17, 1982, of which the 
instant application is a continuation in part, said patents disclosing 
such pyrolysis apparatus. Referring to FIG. 1, apparatus 1 includes a 
fluidized bed type pyrolysis reactor 1A and a combustion reactor such, for 
example, as a fluidized bed type combustion reactor 1B. In such apparatus, 
heat medium particles such, for example, as sand are calculated between 
the reactors 1A and 1B to burn the by-products, such as char and oil, in 
the combustion reactor 1B, and supply the combustion heat to the organic 
material to be pyrolyzed. 
A conventional drying machine 2 is provided for heating the organic 
material to be pyrolyzed, for example the municipal waste 3, in order to 
dry the same prior to pyrolyzation. An energy recovery device 4, such as a 
conventional gasoline engine or gas turbine, is provided which is adapted 
to burn a fuel gas 5 produced as the pyrolysis gas and recover the energy 
from it in the form of electric power. An exhaust heat recovery device 6, 
such as a conventional waste gas boiler, is provided. The exhaust heat 
recovery device 6 is adapted to be heated by the combustion exhaust gas 7 
discharged from the combustion reactor of the two-bed type pyrolysis 
apparatus 1 (the fluidized bed type combustion reactor 1B in the 
illustrated embodiment), and by a combustion exhaust gas 8 from the energy 
recovery device 4. A fluid heat medium 9 is associated with the exhaust 
heat recovery device 6, the fluid heat medium 9 being turned into steam in 
the heat recovery device 6 under the heating of combustion exhaust gases 7 
and 8. Reference numeral 10 designates a cooler of any conventional design 
and reference numeral 11 designates a blower. 
In operation, the waste 3 delivered to be pyrolyzed is first crushed to a 
predetermined particle size by conventional techniques in order to improve 
the drying efficiency, pyrolysis reaction rate and handling efficiency 
thereof. The crushed waste is then charged into the drying machine 2 and 
is heated with steam 9 (the fluid heat medium supplied from the exhaust 
heat recovery device 6) indirectly via a heating wall such, for example, 
as the wall of a heating pipe or a boiler drum, whereupon the waste 
material is dried. The vaporized water carried by the gas is drawn into 
blower 11, the vaporized water being removed as necessary in the cooler 
10, and the gas is then supplied to the fluidized bed type combustion 
reactor 1B in the two-bed type pyrolysis apparatus 1. 
The waste 3 is then pyrolyzed in the fluidized bed type pyrolysis reactor 
1A to produce a gas, char and oil. The char and oil is burned in the 
fluidized bed type combustion reactor 1B to generate the heat necessary 
for the pyrolysis of the waste. 
The recovered fuel gas 5 is introduced into the energy recovery device 4 to 
produce electric power, which may be supplied to the pyrolysis apparatus 1 
as well as other machines, surplus electric power being supplied to 
external equipment. 
The combustion exhaust gas 7 generated from the combustion of the char and 
oil in the fluidized bed type combustion reactor 1B in the pyrolysis 
apparatus 1 and the combustion exhaust gas 8 from the energy recovery 
device 4, are introduced into the exhaust heat recovery device 6 to 
generate the steam 9. The steam 9 thus generated, or a portion thereof, is 
directed as the fluid heat medium to the drying machine 2 wherein it is 
used for the preliminary drying of the waste 3 described above. 
The vaporized water, which generally carries a foul smelling component, is 
drawn from the drying machine 2 into the blower 11 and is used as a part 
of the waste-burning air in the fluidized bed type combustion reactor 1B 
where it is decomposed and thereby loses its foul odor. 
The extent of the decrease in the water content of the organic material to 
be pyrolyzed after the preliminary drying operation in the drying machine 
2 depends upon the amount of heat in the steam 9, i.e., the amount of heat 
in the combustion exhaust gases 7 and 8. The precise calorific value of 
the steam 9 can be determined by calculations of heating values. More 
particularly, an approximation is first made of the water content of the 
waste 3 after drying. The heat balance in the pyrolysis apparatus 1 is 
calculated in order to determine the calorific value of the combustion 
exhaust gas 7 and the recovery rate of the fuel gas 5. The calorific value 
of the combustion exhaust gas 8, which is produced after the fuel gas 5 
has been burned in the energy recovery device 4, is then determined. The 
amount of heat transferred to the steam 9, which serves as a fluid heat 
medium, is thereafter calculated on the basis of both the calorific value 
of the combustion exhaust gas 8 and of the calorific value of the 
combustion exhaust gas 7 generated in the fluidized bed type combustion 
reactor 1B in the two-bed type pyrolysis apparatus 1. The amount of heat 
in the steam 9 serving as the fluid heat medium is checked as to whether 
it is high enough to sufficiently dry the waste 3. When the calorific 
value of the steam 9 is not sufficiently high, the water content of the 
waste 3 after drying is reapproximated and the above calculations 
repeated. 
The pyrolysis operation is carried out on the basis of the water content of 
the waste, which is determined after trial calculations have been made in 
a repeated fashion as described above. 
In order to transmit heat from the steam 9 to the waste 3 in an effective 
manner, it is preferable that the drying machine 2 be constructed in a 
rotatable fashion in the same manner as conventional dryers of this type, 
or that the drying machine 2 be provided with a paddle to agitate the 
waste 3 in order to promote effective and uniform drying thereof. 
Referring now to the embodiment of the method illustrated in FIG. 2, the 
same or corresponding elements as in the first embodiment are designated 
by the same reference numerals. In this second embodiment, a heat 
exchanger is employed as the exhaust heat recovery device 15 and air 16 is 
employed as the fluid heat medium. The heated air 16 comes into direct 
contact with the waste 3 in the drying machine 17 so that the waste 3 is 
directly heated and dried. In order to improve the heat transfer rate, it 
is preferable that a drying machine 17 be constructed in a rotatable 
fashion or provided with a paddle to agitate the waste 3 as mentioned 
above. 
The air, whose temperature has decreased in the drying machine 17, is 
discharged therefrom with water vapor and a foul smelling component. A 
portion of the air is supplied as waste-burning air by a blower 18 to the 
fluidized bed type combustion reactor 1B in the two-bed type pyrolysis 
apparatus 1 which has the same construction as the apparatus 1 utilized in 
the first embodiment, and the foul smelling components are decomposed 
therein. Fresh air is added to the remaining part of the air discharged 
from the drying machine 17 and the resulting air is pressurized by a 
blower 19 to be returned to the exhaust heat recovery device 15. When 
fresh air is added to the portion of the air as discussed above which is 
discharged from the drying machine 17, the air from the drying machine is 
subjected to heat exchange in a cooler 20 in order to condense the 
vaporized water. The resulting water is removed and the fresh air then 
pre-heated. This will minimize any heat loss and remove the water in the 
drying air thereby increasing the drying efficiency. 
Moreover, in the second embodiment of the invention illustrated in FIG. 2, 
oil may be used in lieu of air 16, the oil being heated in the heat 
exchanger which constitutes the exhaust heat recovery device 15 so that 
the resulting hot oil is used as the fluid heat medium. In this case, the 
indirect-heating type drying machine 2 employed in the first embodiment 
may be used in lieu of the drying machine 17 to heat the waste 3 
indirectly. 
Turning now to FIG. 3, a third embodiment of the present invention is 
illustrated which is provided with exhaust heat recovery devices 25 and 26 
constituted by separate heat exchangers for the combustion exhaust gases 7 
and 8 respectively. Elements of this embodiment which are identical with 
corresponding elements of the embodiment illustrated in FIGS. 1 and 2 are 
designated by the same reference numerals and have the same function as 
described above. 
FIG. 4 is a flow chart of a fourth embodiment of the present invention 
wherein the waste 3 is initially subjected to a separation step by means 
of a conventional separator 30 which crushes and sieves the waste 3. 
In this connection, municipal waste generally consists of garbage, waste 
paper, and plastic scrap. The garbage will have the highest water content 
and is generally crumbly. Accordingly, the municipal waste is crushed, the 
greater part of the garbage is broken into smaller sized particles. 
Therefore, the crushed municipal waste can be separated by a sieve into 
garbage 31, the greater part of which consists of refuse from kitchens and 
has a high water content, and waste paper and plastic scrap 32, which have 
a low water content. When the garbage 31 which has been separated from the 
municipal waste is alone introduced, for example, into an indirect heating 
type drying machine 33, it can be dried with less calorific power than the 
municipal waste in an unseparated state. Therefore, when the results of 
the calculations of calorific values discussed above indicate that 
calorific values which are sufficiently high to dry the municipal waste to 
reduce the water content thereof to a predetermined level cannot possibly 
by obtained, it is preferable to preliminarily separate the municipal 
waste as indicated in the fourth embodiment of the invention. When 
calculations of calorific values indicate that the municipal waste can be 
dried sufficiently with the heat of one of the combustion exhaust gases 7 
or 8, either of them may be utilized, and, especially the combustion 
exhaust gas 8 from the energy recovery device 4 can be advantageously 
utilized. The elements of the system illustrated in FIG. 4 which are 
identical to elements found in the embodiments illustrated in FIGS. 1-3 
are designated by the same reference numerals and function in the same 
manner. 
The present invention thus provides a pyrolysis method which permits a 
reduction in the water content prior to the organic material being 
pyrolyzed by effectively utilizing the heat of a combustion exhaust gas 
and thereby improving the recovery percentage in quality of gas, the 
recovery percentage of energy, and an expansion of the range of materials 
which can be pyrolyzed. The pyrolysis method of the present invention 
therefor has extremely great practical energy-recovering effects. 
Obviously numerous modifications and variations of the present invention 
are possible in the light of the above teachings. It is therefor to be 
understood that within the scope of the claims appended hereto, the 
invention may be practiced otherwise than as specifically disclosed 
herein.