Apparatus for recovering energy from pyrolyzable, carbonaceous waste materials of varying composition

An apparatus for recovering energy from pyrolyzable, carbonaceous waste materials, for example household refuse, comprising a rotary tube reactor (4) adapted to be charged with the waste materials and producing, as products, a (low temperature) carbonization gas and a pyrolytic coke at a reaction temperature of above 200.degree. C.; a fluidized bed or swirling layer gasifier adapted to be supplied with an oxygen-containing gasifying agent, the pyrolytic coke and, optionally, waste materials and from which exit a hot gas having a temperature of between 400.degree. and 1000.degree. C. and an inert ash. Further, the system includes cleaning stages (8, 20) for the carbonization gas, connected subsequent to the rotary tube reactor and the gasifier (14), and further a combustion device (24) for the cleaned gases, as a part of a boiler system.

The present invention relates to an apparatus for recovering energy from 
pyrolyzable, carbonaceous waste materials of varying composition, 
comprising 
at least one rotary tube reactor adapted to be charged with the waste 
materials and producing as products, a low temperature carbonization gas 
and a pyrolytic coke at a reaction temperature of above 200.degree. C.; 
a cleaning stage for the carbonization gas, said stage being connected 
subsequent to the rotary tube reactor; 
and a combustion device for the cleaned carbonization gas. 
Pyrolizable waste materials, such as, for example, industrial or household 
refuse, are employed in continuous processes for the generation of 
pyrolytic gas. The apparatus for a system of this kind includes a heated 
rotary tube as the pyrolysis reactor. The material is transported by the 
combined action of rotation and inclination of the rotary tube. The 
recovered pyrolytic gas is not free from solid materials. Thus, a 
pyrolytic gas cleaning step must be performed subsequent to the reactor 
(compare periodical CAV, Chemische Apparate und Verfahren, 1981, p. 128). 
In the conventional apparatus, it appeared inevitable that the reactor has 
connected subsequent thereto (downstream thereoff) a pyrolytic gas 
purification or cleaning unit operating with cooling and recondensation of 
the gases to form pyrolytic oil. Normally, this pyrolytic gas had to be 
heated again in order that it could be burnt. Add to this that 
inhomogenous waste materials, i.e. even such materials of varying 
composition, e.g. the household refuse produced in large quantities, 
result in a quality and composition of the pyrolytic oil which can hardly 
be determined. 
Accordingly, it is the object of the invention to provide an apparatus of 
the kind as outlined above, in which even the use of waste materials of 
varying composition and which, further may even be highly inhomogenous in 
nature, permits to recover energy without pyrolytic oil difficult to 
handle being produced in the apparatus. 
In the above apparatus, this object is solved in accordance with the 
present invention in that in addition to the series-connected installation 
of a first branch (rotary tube reactor, carbonization gas purification 
stage), a second installation branch is connected to precede the 
combustion device, said second branch including a fluidized bed or 
swirling layer gasifier which has supplied thereto 
an oxygen-containing gasifying agent, 
the pyrolytic coke 
and, optionally, waste materials, and from which exit 
a hot gas having temperature of between 400.degree. and 1000.degree. to be 
used for combustion in the combustion device, 
and an inert ash 
and that the second branch further includes a cleaning or purification 
stage for the hot gas from the fluidized bed or swirling layer gasifier. 
In pyrolytic systems operating with a secondary medium, e.g. with a 
swirling layer of fluidized bed, the problem of contamination of the 
secondary medium by the various waste materials which are processed is 
well known. Purification or cleaning and reprocessing of the secondary 
medium is costly and requires much energy. 
It is therefore another object of the invention to provide an apparatus in 
which the swirling layer or fluidized bed gasifier is adapted to operate 
even without a secondary medium. Such mode of operation is practicable 
if--as indicated above--pyrolytic coke from the rotary tube (or kiln) 
reactor is employed as the medium to be gasified. 
Normally, the cleaning stages are operated without cooling or condensation; 
these stages are merely hot-gas dust separators from which the gas exits 
without separation of the relatively high-boiling components (e.g. 
phenols) resulting from the pyrolysis. 
In corresponding manner and preferably, it is also contemplated that the 
gas conduits carrying the (low temperature) carbonization gas or hot gas 
are adapted to be heated such that the temperature of the gases may be 
kept above 200.degree. C. A temperature of this order is generally 
sufficient to maintain the indicated higher-boiling components in the 
gaseous form. A further simplification is obtained when the gas conduits 
of the first and second branches are joined into a mixed (composite) gas 
conduit or pipeline. 
Accordingly, the apparatus according to the invention may be operated in 
different modes of operation. Depending on the raw material (grain size, 
water contents, calorific value), it can be discriminated between the 
following categories: 
1. Drying and degassing in the rotary tube reactor with subsequent 
gasification of the pyrolytic coke in the fluidized bed or swirling layer 
gasifier; 
2. drying, degassing and gasifying in the rotary tube reactor only; 
3. drying, degassing and gasifying in the fluidized bed or swirling layer 
gasifier only; 
4. drying and degassing in the fluidized bed or swirling layer gasifier. 
In special instances (for example, in the case of high water contents), a 
flue gas return conduit may be provided for returning the flue gas into 
the rotary tube where the gas is utilized to pre-dry and heat the raw 
materials. 
The pyrolytic gas (carbonization gas) leaves the rotary tube reactor at 
temperature of above 200.degree. C., generally from between 400.degree. 
and 1000.degree. C., and this gas is first freed from dust in a gas 
cleaning stage. The ash produced is withdrawn through gas-tight conveying 
systems. Upon sufficient dust removal, the carbonization gas is fed, in 
combination or admixture with a hot gas from the swirling layer gasifier, 
to a hot gas burner as described, for instance, in the abovementioned 
publication CAV on page 122 thereof. Depending on the mixing ratio and 
oxygen-containing gasifying medium, the combustion gas upstream of the 
burner has a gas calorific value of from 600 to 6000 kcal/Nm.sup.3. The 
power to be yielded from a typical apparatus according to the invention is 
in the range of from 20 to 60,000 kW, based upon the separate 
installations. The complete system is controlled by controlled variables, 
such as oxygen contents, exhaust gas temperature, CO/CO.sub.2 ratio, 
feeding or return temperature, which may be picked up from the boiler 
system by sensors. Also, the system may be operated in a fully automatic 
manner.

A raw material bin 2 is charged through a customary waste material inlet 1 
supplied via vehicles. As waste materials, the following materials may be 
used: Industrial refuse composed, for example, of loaded fuller's earth 
with wood, cardboard, paper, plastics materials and canteen refuse; 
household refuse (summer or winter refuse), old tires, bulk garbage from 
scrap metal utilization, and the like. The waste material to be used for 
the pyrolysis in a rotary tube is taken from the raw material bin 2 
through a continuously controllable conveying system 3. The waste 
materials are fed into the rotary tube reactor through a gas-tight lock 
gate system. The material is transported or conveyed by rotation and 
inclination of the rotary tube. Air as gasifying medium is supplied to the 
rotary tube reactor 4 through air supply means 5 including a variable 
blower 5'. The rotary rube reactor may be heated separately; in many 
instances, such auxiliary heating is not required. The (low temperature) 
carbonization gas produced by partial combustion and pyrolysis has a 
temperature of, normally, between 400.degree. and 500.degree. C., but in 
any case above 200.degree. C., and a calorific value of between 1000 and 
3000 kcal/Nm.sup.3. By a discharge or outlet conduit 6 emanating from the 
inlet of the rotary tube reactor and being thermally insulated, the 
carbonization gas is maintained at a temperature of above 200.degree. C. 
and fed to a first gas cleaning or purification stage 8. The gas cleaning 
stage includes one or optionally several cyclone gas separators or 
equivalent gas cleaning assemblies, such as filters or the like, from 
which fine ash is withdrawn or discharged (ash outlet 10) or carbonaceous 
dusts are fed to a collecting point 29 through a feed pipe 9 which may 
optionally be provided with a cooling device. 
The carbonization gas from which dust or coke has been removed, passes 
through a short conduit 22' to a hot-gas mixing conduit 22 being highly 
thermally insulated or even adapted to be heated, respectively, so as to 
ensure in any case that the hot gas cannot cool to below 200.degree. C. 
during its passage to a combustion device 24/25. 
The combustion device constitutes part of a boiler system or plant. It 
includes a hot-gas burner 24 which may be formed also as a combination 
burner for other fuels, and a subsequently positioned boiler 25. 
Additionally, natural gas or heavy oil burners may be installed, in order 
to provide for continuous operation of the boiler system under all 
circumstances. The exhaust gases of the boiler system are discharged 
through a flue gas outlet 26. Further, a flue gas return conduit 27 is 
provided between the flue gas outlet and the rotary tube reactor 4, which 
conduit may be used for further energy recuperation. The flue gases may be 
used for heating the interior of the rotary tube reactor. 
Through a pyrolytic coke outlet 7 which may be used also as an ash 
(discharge) outlet, the resulting pyrolytic coke is then fed from the 
rotary tube reactor to the collecting point 29. This pyrolytic coke 
generally still contains a high proportion of latent energy which may be 
converted into a gas by further (low temperature) 
carbonization/gasification, and this gas may be burnt in the boiler system 
with the aid of the hot-gas burner 24. Further, another raw material 
supply 11 is connected to the collecting point 29. The conduits or 
pipelines leading to the collecting point 29 terminate within a metering 
bin 12 wherein the following products are collected: small-particle 
screened raw material from the raw material bin 2; optionally broken 
pyrolytic coke from the rotary tube reactor 4; and pyrolytic coke dust 
from the gas cleaning stage 8. 
The mixture from the metering bin 12 is fed into a swirling layer 
(fluidized bed) gasifier 14 through a charging system being connected in 
gas-tight fashion to a swirling layer gasifier housing. Swirling layer 
gasifiers of this type are described in various embodiments in literature. 
A prototype of a swirling layer gasifier of this type, according to 
WINKLER, is described, for example, in the periodical article "Die 
kommerziell angewandten Verfahren der Kohlevergasung" (The commercially 
applied methods of coal gasification), author: H. Staege, in "Technische 
Mitteilungen Krupp, Werkberichte, 1980, page 28. 
Owing to the admixture of the pyrolytic coke, the swirling layer reactor is 
capable of operating without the use of a secondary medium. It is only 
necessary that the swirling layer reactor is cleaned periodically. A 
gasifying agent is supplied to the swirling layer gasifier through a 
conduit 18. Also provided is an ash (discharge) outlet 19. The hot gas 
exiting from the gasifier 14 at a temperature of between 400.degree. and 
1000.degree. C. has its dust removed by a second gas purification stage 20 
which likewise operates preferably in accordance with the cyclone 
separation process, and the hot gas is passed to the hot-gas mixing 
conduit 22 in which it is mixed with the carbonization 1 gas from the 
rotary tube reactor. The gas mixture is supplied to the hot-gas burner 24. 
The hot-gas burner 24 and/or swirling layer gasifier 14 may be fed with air 
preheated by a preheating heat exchanger 16. The air is injected by a 
blower 15 through this heat exchanger 16. 
In the swirling layer gasifier 14, the material taken from the metering bin 
12 is completely pyrolyzed or gasified with the addition of air, 
oxygen-enriched air or pure oxygen introduced with water or (water) steam 
(conduit 18). 
The apparatus permits to employ even a highly inhomogeneous waste material 
without the provision of precedingly arranged crusher units of larger 
size. The coarse-particle material may be fed directly into the rotary 
tube reactor 4, whereas screened fine material is supplied to the swirling 
layer gasifier 14 in combination with the pyrolytic coke. 
Depending on the requirements of the system, it is also possible to take 
into account such parameters which have an effect on the calorific value 
(e.g. proportion or contents of inert material or water). 
Considered on the whole, there is thus provided an apparatus which is 
capable of processing even highly inhomogeneous materials and materials of 
varying composition. 
At this point, it may also be noted that the term "combustion systems" may 
embrace also internal combustion engines, gas engines or gas turbines and 
similar structures. 
Finally, it does not appear improbable that the recovered gases may be 
subjected to intermediate or further processing also in petrochemical 
plants, in order to at least partially recover their contents of organic 
substances.