Pyrolysis process utilizing pyrolytic oil recycle

A pyrolysis process and system produces a solid residue and a clean, enriched fuel gas. In the process, the pyrolytic oil and filter cake are recycled in such a manner as to produce products of optimal value, and to minimize the need for servicing and downtime of the system. Recycling of water recovered in the process may also be employed to achieve enrichment of the gaseous product. The process may be carried out in such a manner as to produce a non-polluting wastewater stream that can be discharged directly from the system.

BACKGROUND OF THE INVENTION 
It is well known that organic, and in particular cellulosic, materials can 
be pyrolyzed to produce valuable solid residue products, including 
charcoal and activated carbon, as well as gaseous and liquid fuels. 
Exemplary of the prior art that describes such processes is Bowen U.S. 
Pat. No. 4,145,256; a pyrolysis process specifically adapted for the 
production of highly activated carbon is disclosed in Bowen and Purdy 
Application for U.S. patent Ser. No. 84,294, filed on Oct. 12, 1979, and 
now issued as U.S. Pat. No. 4,230,602 on Oct. 28, 1980. 
In such a process, and depending upon the conditions of operation and the 
volumes of gases introduced (e.g., air and steam) and generated, there 
will normally be a significant amount of particulate solids entrained in 
the offgas stream. Since the desired liquid and gaseous products are 
obtained from the offgas stream, and since it is necessary that such 
products be relatively free from such contamination, it is important that 
these particles be removed. This is, of course, a well-recognized problem, 
which has in the past been dealt with in a number of ways. 
For example, the gas stream may be passed from the reactor into a cyclone 
separator for the purpose of removing the solid particles, and then 
treated in a condenser and demister. However, because pyrolysis offgases 
contain significant amount of tars and oils, in addition to the 
particulate solids, condensation on the walls of any such equipment is 
considerable, and becomes excessive after relatively short periods of 
operation. The deposits of condensates and solids must be removed 
periodically to allow satisfactory operation, necessitating not only 
significant and frequent periods of downtime for servicing of the system, 
but also representing an arduous, unpleasant and hazardous task that must 
be performed manually. 
As an alternative to such a "dry" offgas treatment, water scrubbing has 
also been employed. However, as conventionally practiced that approach 
also suffers from serious disadvantages, outstanding among which are the 
need to treat the wastewater to make it environmentally acceptable and to 
recover from it as much as possible of the valuable organic constituents, 
such recovery being inhibited to a considerable extent because as much as 
60 percent of the condensed organics are in solution. Thus, the separation 
requires the provision of a wastewater treatment plant, which represents 
not only a large capital expenditure but also an inconvenient and 
expensive added operation. 
In view of such disadvantages, it has been suggested that the gas stream be 
cleansed by scrubbing it with the pyrolytic oil. Doing so may obviously 
avoid the introduction of, and hence the need to treat, water, and it 
inherently enables the recovery of at least some of the oil. Furthermore, 
since the oil itself functions as a natural solvent for condensible 
fractions of the offgas stream, those fractions of the deposits are 
readily dissolved, thereby removing them and washing the particles from 
the interior walls of the system, thus continuously maintaining proper 
operating conditions without need for regular manual cleaning. 
Notwithstanding the advantages of such a procedure, as far as is known 
there has not heretofore been such an implementation of it as will permit 
practical operation on a continuous basis. Moreover, it is not believed 
that there has to date been developed such a system or method, which 
utilizes pyrolytic oil scrubbing for the production of products of optimal 
value, and especially enriched gases. 
Accordingly, it is a principal object of the present invention to provide a 
novel, continuous process, and a novel system for carrying out the same, 
for pyrolyzing a cellulosic material so as to produce pyrolytic oil, a 
solid residue, and a cleansed, enriched gaseous product. 
It is a more specific object of the invention to provide such a process and 
system in which the pyrolytic oil produced is utilized as the scrubbing 
medium to remove particulate solids from the gas stream, to thereby avoid 
problems attendant to the use of dry and conventional water-scrubbing 
cleansing techniques. 
Another object of the invention is to provide a process and a system of the 
foregoing nature, in which the characteristics of the recycled pryolytic 
oil stream may automatically be controlled, to either permit or prevent 
dehydration of the oil, so as to ensure optimal operation and the 
attainment of the foregoing objects. 
Yet another object is to provide such a novel method and system wherein a 
portion of the water vapor condensed from the gaseous product may be 
discharged directly, as a non-polluting wastewater stream. 
A further object of the invention is to provide a process and system having 
such features and advantages, which is also convenient, efficient and 
relatively simple and inexpensive to carry out and to use. 
SUMMARY OF THE INVENTION 
It has now been found that certain of the foregoing and related objects of 
the invention are readily attained in a continuous process for producing a 
solid residue and a clean, enriched gaseous product from a cellulosic 
material that pyrolyzes to a solid residue and a gaseous mixture, which 
gaseous mixture comprises condensible and noncondensible fractions, the 
condensible fraction comprising condensible organic vapors and water 
vapor. The process comprises the continuous pyrolysis of such a material 
as a moving packed bed, in which bed the temperature varies and passes 
through a maximum value of about 760.degree. to 1150.degree. Celsius at an 
intermediate level. The products include a solid residue and a gaseous 
mixture; the gaseous mixture has entrained in it a significant amount of 
fine particles of the residue, and it is at a temperature of about 
110.degree. to 400.degree. Celsius. Pyrolytic oil is injected into the 
gaseous mixture to scrub the residue particles from it and to effect 
condensation of a portion of the condensible fraction thereof, thereby 
enabling recovery of a relatively clean gaseous product and a pyrolytic 
oil mixture containing the residue particles. The resultant pyrolytic oil 
mixture is filtered to separate it into an oil portion and a filter cake, 
with the latter containing pyrolytic oil and residue particles in a weight 
ratio of about 1 to 10:1. The filter cake is recycled for treatment by 
introducing it into the bed; introduction will generally be at a level at 
which the temperature is at least about 260.degree. Celsius, preferably it 
will be above the aforesaid "intermediate" level, and most desirably the 
filter cake will be introduced at a subsurface level that is at least 
about two feet beneath the surface, since these conditions promote 
cracking of the oils, as will normally be highly desirable. The oil 
portion of the pyrolytic oil mixture is recycled to provide the injected 
pyrolytic oil used for scrubbing. Similarly, a substantial amount of the 
organic vapors and the water vapor present in the gaseous mixture after 
scrubbing is condensed and recovered, and at least part of the condensate 
is recycled by injecting it into the residue at the bottom of the bed, to 
effectively quench the same. The recycling steps are controlled, with 
respect to the rate of introduction of the cellulosic feed material, so as 
to produce both an enriched gaseous product and also a net yield of 
pyrolytic oil, the latter amounting to at least three percent, based upon 
the weight of dry feed. 
In preferred embodiments of the foregoing process, the feed of cellulosic 
material will comprise wood waste, the temperature at the intermediate 
level of the bed will be about 875.degree. to 1000.degree. Celsius, the 
gaseous mixture will have a temperature of about 120.degree. to 
370.degree. (and most desirably about 135.degree. to 200.degree.) Celsius, 
the viscosity of the recycled oil (i.e., the oil as introduced into the 
scubber) will be maintained at a value of about 20 to 175 centipoise, its 
temperature will be about 10.degree. to 45.degree. Celsius, and the 
residue will be quenched to a temperature of about 100.degree. Celsius. 
The process may include the additional steps of monitoring the recycled 
oil to determine its temperature and viscosity, automatically maintaining 
the viscosity of the oil at 5 to 265 centipoise, by adjusting the rate of 
flow thereof, and simultaneously maintaining the temperature of the 
recycled oil at about 20.degree. to 40.degree. Celsius. Other steps of the 
process may involve demisting of the gaseous mixture exiting from the oil 
scrubber/condenser, to remove the aerosol fractions therefrom for 
filtration along with the pyrolytic oil mixture, and monitoring of the 
water from the condensation and recovery operations, to determine the 
organic content thereof and to thereby enable adjustment of the rate of 
flow of the recycled oil so as to achieve a preselected value of organic 
substances therein. 
In especially preferred embodiments of the invention, the water recovered 
in the initial water vapor condensation and recovery step will be fully 
utilized in the process, with substantially no portion thereof being 
removed therefrom as a wastewater stream. Generally, the recovered 
condensate will be received in a holding vessel, and recycle will 
conveniently be controlled by maintaining a preselected level therein. 
Most desirably, a further portion of the recovered condensate will be 
recycled by introducing it into the pyrolytic oil separated in the 
filtering operation. 
In those embodiments in which recovered water is recycled, especially by 
introduction into the scrubbing oil stream, it will be particularly 
advantageous to effect a second water condensation subsequent to the 
first, to remove a major proportion of the water vapor contained in the 
gaseous mixture. The condensate from the second water condensation will 
usually be substantially free from contamination, and therefore suitable 
for discharge directly from the system. Thus, the process may be used to 
produce a solid residue, a relatively dry, purified gaseous product, and a 
relatively clean wastewater stream. 
The process may beneficially be carried out with the pyrolytic scrubbing 
oil recycled at a rate such that substantial hydration of the gaseous 
mixture, and a corresponding partial dehydration of the recycled oil, 
occurs. Alternatively, the recycling rate of oil may be such as to 
substantially avoid its dehydration. In either case, the temperature of 
the oil mixture after scrubbing will be about 40.degree. to 75.degree. 
Celsius; however, the preferred temperature for the dehydrated oil is 
55.degree. to 68.degree. Celsius, whereas the preferred value for the 
second case, in which substantial dehydration of the oil is avoided, is 
about 45.degree. to 52.degree. Celsius. 
Additional objects of the invention are readily attained in a system for 
carrying out the continuous pyrolysis of a cellulosic feedstock of the 
nature previously described. The system employs a reactor for continuously 
effecting pyrolysis of the feed as a descending packed bed, the reactor 
having inlets for feed, filter cake, reaction air and char-quenching 
water, and having outlets for offgases and the char or other solid residue 
product. Oil scrubber/condenser means is connected to the offgas outlet of 
the reactor, and at least initial water condenser means is provided in the 
offgas stream of the oil scrubber/condenser means. The system also 
includes means for recycling condensate from the water condenser means to 
the quench water inlet of the reactor, filter means in the liquid stream 
from the oil scrubber/condenser, means for recycling filter cake from the 
filter means to the filter cake inlet of the reactor, means for recycling 
pyrolytic oil from the filter means to the oil scrubber/condenser means, 
and means for controlling the rates of recycle of the condensed water, 
filter cake and pyrolytic oil. Hence, the system is adapted for the 
production of an enriched gaseous product and pyrolytic oil from such a 
cellulosic feed material. 
In preferred embodiments of the system, the filter cake feed inlet of the 
reactor is spaced downwardly from the top thereof, so as to permit 
introduction at a level below the normal upper surface of the bed 
established therein. More specifically, the reactor may include means for 
distributing the feed material and for maintaining the upper surface of 
the bed at a predetermined level, with the feed inlet being disposed for 
introduction of the filter cake feed material at a level at least about 
two feet therebelow. 
The system may additionally include a demister in the offgas stream between 
the oil scrubber/condenser means and the initial water condenser means, 
with the liquid outlet from the demister being connected to the filter 
means. It may have means for injecting the condensate from the water 
condenser means into the stream of pyrolytic oil recycled to the oil 
scrubber/condenser means, and a holding vessel to receive the condensate 
and to supply water to the reactor and to the recycled pyrolytic oil 
stream may be provided. The system may additionally include a second or 
final water condenser connected to the first or initial water condenser, 
to receive and further dry the clean offgas exiting therefrom, and the 
final condenser may advantageously be of a direct water-contact type 
(i.e., a water scrubber/condenser). Finally, a thermal energy transfer 
device, through which the stream of recycled pyrolytic oil passes, may be 
employed to enable control of the temperature thereof.

DETAILED DESCRIPTION OF THE ILLUSTRATED AND PREFERRED EMBODIMENTS 
Turning now in detail to FIG. 1 of the appended drawings, the system 
illustrated comprises a pyrolysis reactor 10, an oil scrubber/condenser 
12, a demister 14, a first water condenser 48, a water surge reservoir 62, 
a second water condenser 64, a filter 16, an oil surge reservoir 18, and a 
heater/cooler 20. The reactor 10 is of the vertical, moving, packed-bed 
type described in detail in the above-identified Bowen patent and Bowen 
and Purdy application, the relevant portions of which are hereby 
incorporated by reference; the nature of reactor 10 will be evident, and 
further description is not believed to be necessary here. The feedstock is 
introduced through line 22 and is deposited upon the upper surface of the 
bed, and the reactor 10 will normally be provided with a leveling device 
to uniformly distribute the fresh feed material. During its descent 
through the reactor, the feedstock is pyrolyzed. The solid residue 
produced is quenched and discharged from the bottom through line 24, and 
the generated gases (including water vapor from quenching and also from 
reaction of the cellulosic feed material) flow upwardly through the bed; 
the resultant gaseous product is withdrawn through conduit 26. 
Upon entering the oil scrubber/condenser 12, the offgas stream is scrubbed 
with oil, as will be discussed in greater detail hereinafter. Suffice to 
say here that the oil scrubbing serves the dual function of removing solid 
particles from the gas stream while also effecting condensation of 
portions of the condensible organic vapors and of the moisture contained 
therein. From the scrubber/condenser 12, the treated gas is conducted 
through line 28 into the demister 14, where any residual aerosols are 
mechanically removed, to produce a relatively clean gas, which exists from 
the demister 14 through line 30 and enters the initial water condenser 48 
and thereafter the final water condenser 64, wherein condensation of 
additional mositure is effected (as will be more fully discussed 
hereinbelow). The condensate (essentially water, but containing a 
significant amount of condensed organics) from the initial water condenser 
48 passes into the surge reservoir 62, from which it may be withdrawn as 
desired (as will also be discussed more fully hereinafter). Although not 
illustrated, it will be appreciated that an appropriate fan or blower will 
be provided in the offgas system to maintain a draft sufficient to 
withdraw the gas streams therethrough; consequently, the reactor 10 will 
normally operate at slightly below atmospheric pressure. 
Contaminated (i.e., particulate-containing) oil streams 32, 34 flow 
respectively from the oil scrubber/condenser 12 and the demister 14, and 
are combined for introduction through line 36 into a rotary vacuum filter 
16. In the filter 16, the solid residue particles are removed from the 
oil, which is then discharged through line 38 into the oil surge reservoir 
18. Part of the pyrolysis oil held in tank 18 is withdrawn through line 40 
for recirculation to the oil scrubber/condenser 12 through line 42, 
passing first through the heater/cooler 20 to adjust its temperature to an 
appropriate value, as dictated by the conditions of operation. The 
pyrolytic oil passing through line 40 may have water from the reservoir 62 
injected into it through line 60, thus providing a higher moisture content 
scrubbing medium, if so desired. Alternatively, the oil may pass 
unadulterated to the unit 20 and the oil scrubber/condenser 12; these 
alternative embodiments will also be more fully discussed hereinbelow. In 
any event, the rest of the oil is withdrawn from the surge tank 18 through 
line 44, for delivery to bulk storage as the product oil. It might be 
noted at this point that adding water to the oil permits its partial 
dehydration during scrubbing, thereby greatly increasing the cooling 
capacity of the scrubbing medium and, in turn, greatly reducing the flow 
of oil through the oil scrubber/condenser. In such a case, the oil exiting 
the oil scrubber/condenser will have a lower moisture content than that of 
the oil entering the same unit. 
Some of the recovered water may be withdrawn from the surge reservoir 62 
through line 58, with the amount thereof being that necessary to cool the 
solid residue residing at the bottom of the reactor 10 to a desirable 
temperature (e.g., about 100.degree. Celsius), thereby typically producing 
a moisture content in the residue of about four to five weight percent, on 
a wet basis. This reduces the moisture content of the product gas by an 
amount proportional to the production rate of the solid residue, thereby 
further enhancing the heating value of the product gas, and making the 
process essentially independent of any external water supply. 
Nevertheless, quench water may be added to the process from an external 
source (not shown), such as city water connected into the water line 58. 
The filter cake is removed from the filter 16 through line 46, and is 
recycled to the reactor 10 for introduction, preferably at a subsurface 
level. While relative positions are suggested in FIG. 1, no attempt has 
been made to depict therein the actual placement of the feed, filter cake 
and water recycle lines, 22, 46 and 58 with respect to the depth of the 
bed or position within the reactor. 
Regardless of whether or not the system includes the initial water 
condenser 48, it may beneficially include the final water condenser 64, so 
as to remove water vapor from the gas passing through line 50 and thereby 
produce a dried gas 66, since such moisture represents an inert fraction 
that will substantially reduce the heating value of the ultimate product. 
Such a condenser 64 is, however, especially desirable in cooperation with 
the condenser 48, since the latter will serve to remove organic 
contaminants from the gas (which are then returned to the reactor 10 and 
the scrubber 12 in the water flowing through lines 58, and normally also 
in the hydrated oil flowing in line 42), resulting in a relatively 
uncontaminated water stream from condenser 64, which may be sufficiently 
clean to permit direct discharge without undesirable or impermissible 
environmental effects. 
With final regard to FIG. 1, it will be noted that air is introduced into 
the reactor 10 through line 56 (which will, in practice, usually comprise 
grids of tubes at several levels). This will establish the maximum 
temperature zone within the pyrolysis bed, and will significantly affect 
(by virtue of location, distribution, and air flow rate) the nature of the 
process and of the products produced. While the filter cake will normally 
be introduced above the maximum temperature level (in this instance, the 
relative positions are indicated in the figure by the lines 46 and 56), 
that will not necessarily be the case. The sensible heat of the char in 
the lower portions of the bed may be entirely adequate to effect 
substantial cracking of the pyrolytic oil in the filter cake (as is 
important for maximum enrichment of the gas), and the filter cake may 
therefore be introduced low in the bed, as long as the residence time 
(prior to discharge from the reactor 10 with the solid residue product) is 
not unduly brief. 
In the water recycle process, automatic control may be achieved by setting 
the flow rate of the scrubbing oil stream 42, with the temperature of the 
oil being automatically adjusted to maintain the temperature of the 
contaminated oil stream 36 at a value compatible with partial dehydration 
of the scrubbing oil. The moisture content of the filtered oil stream 38 
may be continuously monitored by viscosity measurement (as will hereafter 
be more fully described). If the oil is dehydrating excessively, relative 
to the desired moisture content, the flow rate of the make-up water stream 
60 is incrementally increased until the desired mositure content is 
obtained; if it is hydrating, the opposite action is automatically taken 
to correct the condition. 
Further, noting that the flow rate of the condensate stream 58 is 
determined by the rate of production and the moisture content of the solid 
residue product, and that the flow rate of the oil hydrating stream 60 is 
determined by the oil moisture content, it is seen that a simple water 
level detector in the surge reservoir 62 will be adequate to control the 
degree of cooling of the fuel gas stream 50 in the water condenser 48. In 
addition, in order to properly divide the gas stream cooling between the 
oil scrubber/condenser 12 and the water condenser 48, the organic content 
of the condensed water stream 52 may be continuously monitored. If it is 
increasing from the desired value, the flow rate of the scrubbing oil 
stream is incrementally increased and/or the oil temperature is decreased, 
thereby increasing the degree of gas stream cooling in the oil 
scrubber/condenser and demister, and concomitantly increasing the 
condensation and recovery of organics in those units; this ultimately 
results in a decrease in the organics recovered in the water condenser 48. 
If the organic content of the condensed water stream 52 is found to be 
decreasing from its desired value, the opposite action is automatically 
taken. Finally, the flow rate of the product oil stream 44 and the oil 
level in the oil surge reservoir 18 may be monitored to control the flow 
rate of pyrolytic oil recycled to the reactor 10 as filter-cake oil in 
stream 46; if desired, oil from line 44 can be added to the filter cake 
being returned to the reactor in line 46. The degree of enrichment of the 
fuel gas stream 50 is, of course, directly related to this rate. Periodic 
sampling of the fuel gas for composition and/or heating value 
determinations is used to relate the oil recycle rate to the degree of 
enrichment, which serves as a calibration and quality control procedure. 
To automatically control the process carried out without water recycle, the 
flow rate of the scrubbing oil stream 42 is again set, and the temperature 
of the scrubbing oil stream 42 is automatically adjusted to maintain the 
temperature of the contaminated oil stream 36 at a value suitable for 
minimal oil dehydration. The proper scrubbing oil flow rate is also 
similarly determined by continuously monitoring the moisture content of 
the filtered oil stream 38. If the oil is dehydrating relative to its 
desired mositure content, the scrubbing oil flow rate is incrementally 
increased and/or the oil temperature decreased, until the rate is such 
that the desired oil moisture content can be maintained. If the oil is 
hydrating, the opposite action is automatically taken to correct the 
condition. 
Exemplary of the efficacy of the present invention are the following 
specific examples. 
EXAMPLES 1, 2 & 3 
A predried mixture of hogged, or chipped, hardwood feedstock, containing 
about seven percent moisture on a wet basis, is introduced into the top of 
a vertical reactor of the type described hereinbefore, in a system of the 
sort illustrated in FIG. 1 of the drawings. Air is distributed throughout 
a volume at an intermediate zone of the bed, with the upper air tubes 
about three feet below the surface, and the solid residue is continuously 
withdrawn from the bottom of the reactor at such a rate as to maintain the 
bed depth at a substantially constant value of about eight feet. The 
reaction mass attains a maximum temperature of approximately 950.degree. 
Celsius at the intermediate zone of the bed, and the solid residue product 
is discharged at a temperature of about 100.degree. Celsius, after 
quenching with recycled water. 
The offgas from the reactor has particulate solid residue entrained in it, 
which is substantially removed therefrom in the oil scrubber/condenser, 
utilizing as the scrubbing medium the pyrolytic oil produced in the 
process, admixed with recycled water. The scrubbed gas in subsequently 
demisted, and the oil streams from the oil scrubber/condenser and demister 
are mixed and then filtered, utilizing a standard rotary filtering device 
from which the filter cake is removed on a continuous basis. The filter 
cake is recycled to the reactor, and is introduced thereinto by a ram 
device or by a tubular screw, at a level about two feet below the bed 
surface (at which point the temperature is high enough to crack a 
substantial portion of the oil contained in the filter cake, as will be 
discussed more fully hereinafter). 
The oil fraction produced by the filtration operation is discharged into 
the surge tank, from which it (with the water injected thereinto) is 
recirculated to the scrubber/condenser, with its temperature being so 
adjusted as to maintain the desired operating conditions. To do so, the 
temperature is continuously monitored, as are the viscosity and moisture 
content of the oil stream, as described. Based upon the existing 
conditions, the oil stream is either heated or cooled, as need be, and 
conditions of the system are appropriately adjusted so as to maintain 
desired values of viscosity and moisture content therein. The so 
controlled oil is continuously sprayed into the scrubber/condenser to 
effect cleaning of the offgas stream and condensation of the condensible 
fractions thereof. After passing through the demister, the clean gas is 
passed through the initial water condenser, optimally through the second, 
and recovered and evaluated for cleanliness and heating value; it is found 
to be substantially free of solid particles, and to be well suited for use 
as a gaseous fuel. 
Set forth in Table 1 below are the specific data and parameters for the 
three Examples so performed, but in which the gas is not subjected to a 
second water vapor condensation: 
TABLE ONE 
______________________________________ 
Stream Example: 1 2 3 
No. Substance Temp. Mass Flow Rate 
______________________________________ 
22 Feed 16 3,226 
3,226 
3,226 
Dry Feed 3,000 
3,000 
3,000 
Moisture 226 226 226 
56 Process 16 641 641 641 
58 Char Quench Water 
16 217 217 217 
46 Filter Cake 38 261 435 967 
Dry Solids 87 87 87 
Dry Oil 148 296 748 
Moisture 26 52 132 
24 Product Char 100 854 854 854 
Dry Char 811 811 811 
Moisture 43 43 43 
26 Offgas Stream 149 3491 3665 4197 
Particulate Solids 87 87 87 
New Pyrolysis Prod. 
Dry Cond. Oil 667 667 667 
Dry Noncond. Oil 38 38 38 
Noncond. Gas 1193 1193 1193 
Water Vapor 1332 1332 1332 
Cracked Oil Prod. 
Dry Cond. Oil 31 62 158 
Dry Noncond. Oil 16 33 83 
Noncond. Gas 117 233 590 
Water Vapor 10 20 49 
42 Scrubbing Oil 38 5875 6141 6960 
Dry Oil 4700 4913 5567 
Moisture 1175 1228 1393 
36 Contaminated Oil 66 6438 6725 7607 
Particulate Solids 87 87 87 
Dry Oil 5398 5642 6392 
Moisture 953 996 1128 
38 Filtered Oil 60 6177 6290 6640 
Dry Oil 5250 5347 5644 
Moisture 927 943 996 
40 Dehydrated Scrubbing Oil 
54 5530 5781 6550 
Dry Oil 4700 4913 5567 
Moisture 830 868 983 
44 Product Oil 54 647 509 90 
Dry Oil 550 433 77 
Moisture 97 76 13 
30 Oil Scrubbed/ 
Demisted Gas (1) 2928 3081 3550 
New Pyrolysis Prod. 
Dry Noncond. Oil 38 38 38 
Noncond. Gas 1193 1193 1193 
Water Vapor 1332 1332 1332 
Cracked Oil Prod. 
Dry Noncond. Oil 16 33 83 
Noncond. Gas 117 233 590 
Water Vapor 10 20 49 
Oil Dehydr. Water 
Vapor 222 232 265 
60 Oil Hydrating Water 
16 345 360 410 
50 Product Fuel Gas (2) 2366 2504 2923 
New Pyrolysis Prod. 
Dry Noncond. Oil 38 38 38 
Noncond. Gas 1193 1193 1193 
Cracked Oil Prod. 
Dry Noncond. Oil 16 33 83 
Noncond. Gas 117 233 590 
Water Vapor 1002 1007 1019 
______________________________________ 
In the foregoing Table, the "Stream No." refers, of course, to FIG. 1 of 
the drawings; temperatures are expressed in degrees Celsius, and the mass 
flow rates are in units of pounds per hour. The temperatures of product 
gas entering (stream 30, note "1") and exiting (stream 50, note "2") from 
the water condenser 48 vary, and are 88.degree. and 83.degree. for Example 
1, 87.degree. and 82.degree. for Example 2 and 85.degree. and 79.degree. 
for Example 3, respectively. 
As will be appreciated, the principal variant among the three Examples lies 
in the amount of pyrolytic oil recycled to the reactor. In all cases, 
however, the temperature prevailing at the point of filter cake recycle 
(about 275.degree. Celsius) is such as to crack about 79 weight percent 
(based upon the weight of the dry filter cake oil) of the pyrolytic oil to 
noncondensible gases and vapors. More particularly, in Example 1 the 
solids content of the filter cake is 33.3 weight percent; at a dry solids 
rate of 87 pounds per hour, this represents a moist oil recycle rate of 
174 pounds per hour. In Example 2 the solids content of the filter cake is 
20 weight percent and the dry solids rate is held at 87 pounds per hour, 
providing a moist oil recycle rate of 348 pounds per hour. Finally, in 
Example 3 the solids content is such that the product oil yield is at a 
minimum practical value, i.e., three weight percent. At a dry solids rate 
of 87 pounds per hour, the filter cake contains nine weight percent of 
solids and the moist oil recycle rate is at its maximum value of 880 
pounds per hour. Additional runs are carried out in which the gaseous 
products of the foregoing Examples are further dried, using a final water 
condenser. The properties of the several gaseous products, both before and 
after final drying, are discussed in greater detail hereinbelow. 
EXAMPLES 4 & 5 
The same feedstock and system is used to carry out two additional examples, 
the significant difference from the foregoing being the elimination of the 
water recycle features, with oil scrubbing being carried out with minimal 
dehydration of the oil. Thus, the water condenser 48 and surge reservoir 
62 are eliminated, with water for quenching the char being supplied from 
an external source (still at a flow rate sufficient to reduce the char to 
a discharge temperature of about 100.degree. Celsius). As between Examples 
4 and 5, they differ essentially in that the filter cake in Example 4 is 
returned to the upper surface of the bed together with the feed, thereby 
recovering the filter cake oil, whereas in Example 5 recycle is to the 
same level as in Examples 1 through 3, thereby effecting cracking a 
substantial portion of the filter cake oil. Both gases are relatively free 
from particulates; however, as will be seen, the fuel value of the gas of 
Example 5 is significantly enhanced over that of Example 4. The operating 
parameters for these two Examples are set forth in Table Two, below: 
TABLE TWO 
______________________________________ 
Example: 
4 5 
Stream No. 
Substance Temp. Mass Flow Rate 
______________________________________ 
22 Feed 16 3226 3226 
Dry Feed 3000 3000 
Moisture 226 226 
56 Process Air 16 641 641 
58 Char Quench Water 
16 217 217 
46 Filter Cake 38 261 261 
Dry Solids 87 87 
Dry Oil 148 148 
Moisture 26 26 
24 Product Char 100 854 854 
Dry Char 811 811 
Moisture 43 43 
26 Offgas Stream 149 3491 3491 
Particulate Solids 87 87 
Dry Condensible Oil 815 698 
Dry Noncond. Oil 38 54 
Noncondensible Gas 1193 1310 
Water Vapor 1358 1342 
42 Scrubbing Oil 38 44720 40568 
Dry Oil 38012 34483 
Moisture 6708 6085 
36 Contaminated Oil 
54 45766 41476 
Particulate Solids 87 87 
Dry Oil 38827 35181 
Moisture 6852 6208 
44 Product Oil 38 785 647 
Dry Oil 667 550 
Moisture 118 97 
30 Product Gas (3) 2445 2583 
Noncondensible Gas 1193 1310 
Noncondensible Oil 38 54 
Water Vapor 1214 1219 
______________________________________ 
The units of temperature and mass flow rate are, again, Celsius and pounds 
per hour, respectively. The specific value of temperature (note "3") for 
the product gas stream 30 in Example 4 is 87.degree., whereas it is 
86.degree. in Example 5. 
It will be observed that the flow rate of scrubbing oil in the latter two 
Examples is much higher than in the first three, representing one 
significant disadvantage of the operational mode of Examples 4 and 5, in 
that the equipment used in the oil subsystem must be considerably larger, 
and hence more expensive in terms of capital expenditures and operational 
costs. Moreover, if the product gas of these Examples (i.e., 4 and 5) is 
dried to enhance its higher heating value, the water recovered would be 
contaminated with organics, and would therefore present a waste disposal 
problem. Whereas the process of Example 4 produces more pyrolytic oil than 
that of Example 5 (because it is simply vaporized from the filter cake at 
the surface of the bed, and recovered in the oil stream, with little 
change in composition), the volume and (as will be seen) fuel value of the 
gaseous product produced by the latter process are both higher (due to 
cracking of the filter cake pyrolytic oil fraction within the bed), 
representing the primary advantage of the process of Example 5 over that 
of Example 4. 
From the foregoing, it will be appreciated that gas enrichment is achieved 
in the instant process through cracking of the pyrolytic oil recycled to 
the reactor, and/or by removal of recycled water from the system as 
moisture in the solid residue product, reflected as a net reduction in the 
amount of water vapor (an inert fraction detrimental to combustion 
properties) present in the offgas stream. In the preferred embodiments, 
both effects will be utilized. The degree of gas enrichment is, of course, 
directly related to the amount of pyrolytic oil recycled to the reactor, 
and consequently will be maximized when the net production of pyrolytic 
oil is at a minimum level. Although theoretically possible, cracking of 
all of the oil produced will not generally occur in the practice of the 
invention (except, perhaps, on an interim basis), due to the need to 
maintain the quality of the oil within certain limitations necessary for 
effective scrubbing and for satisfactory filtration. 
The water-recycle embodiments are especially desirable because, as 
mentioned above, the condensible organic contaminants are removed from the 
offgas stream and thereafter returned to the reactor (either with the 
scrubbing oil portion of the filter cake or with the quench water, and 
preferably in both streams) for ready disposal. Thus, the organics so 
recovered will either be cracked in the reactor, to report ultimately as 
noncondensible components of the gas product, or they will be removed with 
the char or other solid residue, in which product a small amount of such 
organic substances will not generally be objectionable. In any event, the 
practical consequence of such recycle is that the moisture may thereafter 
be removed from the gaseous product (such as in the final water condenser 
64 of FIG. 1) and normally discharged directly, without further treatment, 
as a relatively innocuous and unpolluted wastewater stream. 
As will be appreciated, these advantages are a direct result of the 
sequential scrubbing and condensing steps, coupled with recycle of both 
pyrolytic oil and also water condensate. Most of the condensible organics 
are removed from the offgas stream during its passage through the oil 
scrubber/condenser, either to be recovered as product oil or to be 
returned with the filter cake for reprocessing (normally cracking). The 
condensible organic substances remaining in the offgas stream after oil 
scrubbing are subsequently removed in the initial water condenser, and are 
recycled either with the oil used for scrubbing of the gas or with the 
water used for quenching of the solid residue. In any event, those 
portions that are not removed from the system as moisture in the solid 
residue are reprocessed in the reactor, either by ultimate recycle with 
the oil in the filter cake or by voltilization from the hot solid product 
and passage upwardly through the bed. Since the gases exiting from the 
initial water condenser are essentially free of condensible organics, a 
second water condenser can be used to dry the gas (preferably by direct 
contact), producing a clean wastewater stream. 
The offgas streams of embodiments in which oil scrubbing and 
water-recycling practices are not followed may, of course, also be dried 
in condenser 64, thereby increasing the higher heating values of the gases 
produced. However, in those instances the resultant wastewater stream will 
generally require treatment to remove organic contaminants and to render 
it environmentally acceptable for discharge. 
As indicated, to be suitable for use in the present process the organic 
feedstock must be capable of thermal decomposition to produce a solid 
carbonaceous product and a gaseous product containing non-condensible and 
condensible fractions, including water vapor. As a practical matter, the 
feedstock should be a waste material that is readily available in ample 
supply, so as to maximize the economic factors and the benefits of the 
invention. All things considered, a most desirable material for use in the 
present process is wood waste (e.g., bark, sawdust, forest harvesting 
residues and the like) in view of the vast amounts available, the want of 
optimal end uses, and the value of products that can be produced from it. 
Other feedstocks are suitable, however, including materials such as sugar 
cane bagasse, straw, rice hulls, peanut shells and similar agricultural 
waste materials. While the feed can frequently be used as received, it may 
be desirable to predry it, to pelletize or otherwise densify it, and/or to 
reduce its particle size, depending upon the conditions of operation and 
the nature of the products to be produced. 
Of fundamental importance to the process is the composition of the 
pyrolytic oil product and, in particular, its moisture content. This is so 
because a primary function served by the oil in the process is to 
thermally contact and thereby cool the offgas stream, the mechanism of 
which is essentially and desirably evaporative. Consequently, without 
sufficient moisture the oil would soon dehydrate completely, devolatilize, 
and become overheated, causing it to deteriorate and ultimately to become 
unsuitable for use. On the other hand, and especially in connection with 
the embodiments of the invention in which water is not recycled, if the 
amount of moisture is excessive problems attendant to water scrubbing 
would tend to recur. Thus, up to 50 percent of the pyrolytic oil could be 
dissolved in the wastewater and thereby lost, the solvent characteristics 
of the oil would be diminished significantly, and wastewater treatment 
facilities would be necessary. For the foregoing reasons, the amount of 
moisture in the pyrolytic oil should be maintained at about 10 to 50, and 
preferably 15 to 25, percent, based upon the weight of the wet oil. 
Insofar as the highly volatile components of the oil are concerned (i.e., 
those that volatilize to a significant extent under the conditions of 
operation), if the content were to fall too low the solvent power of the 
oil as a scrubbing medium would become inadequate to maintain the system 
free from tarry deposits. While the volatile content of the oil also 
contributes beneficially to the maintenance of a desirably low viscosity, 
that is not a critical function, since normally that property can readily 
be corrected by the addition of water. Obviously, the solvent power of the 
oil could also be adjusted by introducing appropriate solvents from an 
independent supply, but that would be impractical as an economic matter, 
and would in fact frustrate a fundamental advantage of using the pyrolytic 
oil as the scrubbing medium. For this reason, it is essential to the 
process that a minimum amount of excess oil be produced on an ongoing 
basis; otherwise, it would soon become deficient in solvent power because 
of the constant loss of the highly volatile components that are the 
primary solvents. Thus, as a practical matter, the conditions of operation 
must be such as will result in a net production of at least three pounds 
of new oil for every one hundred pounds of dry feed processed. 
A convenient way to determine that the recycled oil contains an appropriate 
amount of volatile constituents is by measurement of its viscosity. 
Maintaining that property within certain limits, taken in light of its 
moisture content, will ensure the quality of the oil; specifically, it 
must have a viscosity of about 5 to 265, and preferably about 20 to 175, 
centipoise. The lower values (5 and 20) correspond generally to moisture 
contents of about 40 and 25 percent, respectively, in oil at a temperature 
of about 65.degree. Celsius. Conversely, at a temperature of 20.degree. 
Celsius, the higher values (265 and 175 centipoise) correspond 
respectively to moisture levels of 10 and 15 percent. By way of further 
illustration, a satisfactory oil at a temperature of 38.degree. Celsius 
and containing 15, 20 or 25 percent of water will have respective 
viscosity values of 70, 40 and 35 centipoise. All things considered, a 
moisture content of 15 percent in the oil will generally be optimal for 
operations in which water is not recovered for recycle, and a 
concentration of about 20 percent will generally be optimal in the 
alternative embodiments, as providing both a desirable viscosity (with 
suitable amounts of volatiles present) and also a desirable apparent heat 
capacity, without introducing water-scrubbing difficulties. In addition to 
maintaining a net oil production of at least three percent, control of 
conditions to avoid volatile losses in excess of about 30 (and at the very 
most 40) weight percent is also desirable to ensure satisfactory 
operation; this is accomplished primarily by avoiding excessively high 
temperatures in the several oil streams, such as by increasing flow rates 
and the like. 
The differential in the temperatures of the scrubbing oil and the offgases 
must, of course, be sufficiently large to ensure that there will be 
adequate transfer of thermal energy for efficient condensation of the 
condensible fractions of the offgas stream. Moreover, the temperature of 
the oil must be low enough to avoid its excessive dehydration and 
devolatilization; otherwise, the oil will degrade and become unsuitable 
for effective scrubbing and cooling. Specifically, the oil should be at 
least 65 Celsius degrees cooler than the offgases, and preferably the 
differential will be 90 Celsius degrees or greater. On the other hand, the 
temperature of the oil must be maintained high enough to ensure facile 
pumping and spraying, and to avoid clogging of nozzles. All factors 
considered, therefore, the scrubbing oil will generally be used at a 
temperature in the range of 10.degree. to 45.degree. Celsius, with the 
preferred temperatures being from about 20.degree. to 40.degree. Celsius. 
In practice, the offgases are cooled in the oil scrubber/condenser to 
within 5 to 10 Celsius degrees of the apparent dew point; however, it is 
not advisable to allow the temperature of the oil to approach the dew 
point temperature of the offgas stream. If the oil temperature becomes too 
high, too much water will be evaporated from the oil into the gas, 
dehydrating the oil excessively and producing an undesirably wet gas. But 
again, if the exiting oil temperature is too low (e.g., less than about 
43.degree. Celsius), filtration will be difficult if not impossible, as a 
practical matter (unless of course the oil is otherwise heated), since 
blinding of the filter could occur at sufficiently low temperatures. For 
these reasons, the "dirty" oil from the scrubber/condenser will usually 
have a temperature of about 40.degree. to 75.degree. Celsius, with 
52.degree. and 66.degree. representing preferred upper values for the 
nondehydrating and hydrating cases, respectively. The oil from the 
demister will typically be at a temperature of about 90.degree. Celsius. 
In most instances, the oil from the scrubber/condenser will contain about 
15 percent of water, based upon the weight of wet oil. Thus, it will be 
appreciated that, in the embodiments in which water recycling is not 
employed the process will be controlled to avoid significant net mass 
transfer of water in the oil scrubbing operations. On the other hand, in 
the water-recycle embodiments hydration of the offgas stream does occur, 
and the scrubbing oil will normally transfer about 25 weight percent of 
its moisture content thereto (e.g., going from an initial value of 20 
percent to 15 percent after scrubbing). 
As has previously been mentioned, the filter cake will normally have an 
oil:solids ratio of about 1 to 10:1, with the practical lower solids limit 
depending upon the amount of solids carryover, the method of filtering, 
and the concentration of solids in the oil stream after scrubbing. The oil 
production and filtration capacity of the system will not normally be 
adequate to handle carryover amounts higher than 30 to 40 percent of the 
feed weight. When the pyrolytic oil is produced at a relatively low rate, 
it will be desirable for the solids carryover to be correspondingly low, 
so as to ensure that the amount of oil recycled with the filter cake does 
not create a deficit in the three percent net oil yield parameter of the 
process. Although a filter aid may be desirable in some instances, the 
filter cake can itself serve as the filtration medium, provided that a 
portion of its thickness is removed, as appropriate. 
The location at which the filter cake is introduced into the bed has a very 
significant effect upon the nature of the products ultimately attained, 
and hence upon the benefits to be derived from the practice of certain 
embodiments of the process. Thus, while it is entirely feasible to 
introduce the filter cake together with the feedstock at the top of the 
bed, so doing has little advantage in terms of improving the fuel 
products. Under the relatively low temperature conditions that prevail at 
the surface, the filter cake is subjected essentially only to evaporation, 
which serves to recover the filter cake oil but not to enhance heating 
values of the gas significantly. Nevertheless, such a practice may be 
employed in the water-recycle embodiments of the invention to obtain 
increased oil yields, with reliance being placed solely upon the water 
vapor reduction in the offgas stream to effect enrichment, but again the 
preferred embodiments utilize the combined effects of moisture removal and 
increased amounts of combustible components in the gas product. 
As indicated, introduction of the filter cake at subsurface levels of the 
bed, where higher temperatures prevail, permits fast heating and 
consequential cracking of the oil, to produce high heating value 
hydrocarbon gases, such as propane and butanes. To achieve these benefits, 
the filter cake will normally be introduced at a level at least two feet 
beneath the upper surface of the bed and, in any event, at a location 
which the temperature is at least 260.degree. Celsius. In this manner, the 
BTU value of the ultimate gas product can be raised by at least 10 
percent. 
More particularly, whereas a gaseous product having a heating value of 
about 150 to 200 BTU per cubic foot is readily attained from more 
conventional pyrolysis processes, utilizing processes of the present 
invention enable the production of gases having heating values in the 
range of 200 to 250 BTU per cubic foot. As will be appreciated by those 
skilled in the art, the generation of a gas having such a heating value is 
of great benefit, in view of the relationship that exists between the 
heating value of a gas and the volume of combustion product gases that it 
produces upon burning. In gaseous fuels of less than about 200 BTU per 
cubic foot, the mass of combustion gases generated at stoichiometric 
conditions, per unit of heat released, increases very rapidly as the 
heating value of the gas decreases; in gases having a heating value of 
about 200 BTU per cubic foot or higher, on the other hand, the ratio is 
fairly constant for most fuels. Consequently, 200 BTU per cubic foot 
represents what may be regarded as a minimum "break" point above which the 
most desirable heating gases are provided (this relationship is best seen 
from the graphic representation of FIG. 2, as will be discussed 
presently). 
Thus, with specific reference now to FIGS. 2 and 3, prime benefits of the 
present invention are readily appreciated. FIG. 2 presents a curve on 
which are plotted points representing, for several standard gaseous fuels 
and for products of the instant process, the relationship between the 
volumetric higher heating value of the gas and the mass of the products 
produced by its combustion with stoichiometric amounts of air (gas at a 
pressure of 760 millimeters of mercury and a temperature of 88.degree. 
Celsius). The curve of FIG. 3 sets forth the relationship between the 
higher heating values of the same gases and the higher heating value of 
the mixtures thereof with air in stoichiometric proportions. In the 
graphs, the products designated "DRY" are the same as those bearing like 
numbers, but dried by water vapor condensation, as in condenser 64 of FIG. 
1 (i.e., the offgas flowing in line 66). These two graphs, taken together, 
are highly indicative of the degree of interchangability of two fuels in a 
given application, and of the disadvantages inherent in the use of low-BTU 
gaseous fuels. 
Taking "Texas" natural gas as a standard, despite significant variation in 
the volumetric higher heating values of other typical fuel gases (e.g., 
methane, coke-oven gas, water gas), it can been seen that there is 
practically no difference in either the volumetric higher heating values 
of their stoichiometric air mixtures, or in the mass of products that are 
generated, per million BTU, by combustion of such gases. Consequently, 
from the standpoint of energy content these gases could be interchanged 
with natural gas without signifi- cantly affecting the power output or the 
thermal efficiency of the heat device (e.g., package boiler, drying kiln, 
internal combustion engines, etc.). 
By-product gases (e.g., those of the present invention) are, however, of 
quite a different nature. The presence of inert gases, such as carbon 
dioxide, nitrogen and water vapor, significantly impact both of the 
foregoing properties. A stoichiometric mixture of blast-furnace gas and 
air, for example, has only 57 percent of the volumetric energy content of 
that of natural gas and air, and it produces almost twice (i.e., 1.86 
times) the mass of combustion products per unit of fuel energy. 
Substituting one of these gases for natural gas will, therefore, 
significantly decrease the power output and thermal efficiency of the heat 
device. 
Hence, on the basis of the foregoing criteria, FIGS. 2 and 3 show that the 
gases produced in accordance with Examples 1, 2 and 3, and subsequently 
dried by water condensation, constitute the most desirable substitutes (in 
the order of increasing value from Dry Gas 1 to Dry Gas 3, reflecting the 
increasing pyrolytic oil recycle rates thereof) for conventional fuel 
gases, of any of the gaseous by-products. Of a value equal to that of Dry 
Gas 1 is Dry Gas 5 (although displaced on the curve for the sake of 
clarity, and albeit that a significant wastewater disposal problem would 
be attendant to its production), which is the product produced without 
water recycle but with the filter cake injected at a subsurface level of 
the bed. Dry Gas 5 is readily compared to the gaseous product produced in 
the same way, but with introduction of the filter cake at the top of the 
bed (Dry Gas 4), which has lower fuel gas and stoichiometric-air mixture 
higher heating values, and (as would be expected) generates a 
significantly greater mass of combustion products on a per BTU basis. The 
value of the remaining products can readily be perceived by reference to 
the two graphs. In general, it can be seen that the products of water 
recycle and deep bed injection of the filter cake are superior to those 
produced using only deep bed injection, and that the least valuable fuel 
gases are obtained when neither effect is employed. 
The quantity and mix of products that can be recovered from the pyrolysis 
reaction depend upon numerous factors, including oil recycle rate, 
location of filter cake injection, and the temperature that is maintained 
in the offgas stream (recognizing, of course, that the measures necessary 
to control that temperature will, in turn, depend upon several factors, 
such as the nature and form of the feedstock, its moisture content, the 
air-to-feed ratio used, rates of production, and the like). In terms of 
composition, the offgas will normally comprise nitrogen, carbon dioxide, 
carbon monoxide, hydrogen, methane and higher hydrocarbons, as well as 
water vapor and vaporized tars and oils. The oil cracking reactions 
typically produce about 76 weight percent of noncondensible gases and 
vapors, including fairly large amounts of carbon monoxide and carbon 
dioxide, with lesser amounts of hydrogen, methane, ethane, propane and 
butane. 
It is of considerable importance that the oil scrubbed product gas 
temperature be maintained at least five, and preferably eight or more, 
degrees Celsius above its apparent dew point, so as to avoid excessive 
mositure condensation in the oil scrubber. Moreover, as the temperature of 
the offgas approaches its dew point value, most of the condensible 
organics will be condensed out. In the context of the foregoing, the broad 
range of initial offgas temperatures within which operation will generally 
be satisfactory is about 110.degree. to 400.degree. celsius; typically, 
the process will be carried out with an offgas temperature of about 
120.degree. to 370.degree. Celsius, and most desirably it will be about 
135.degree. to 200.degree. Celsius. As outer practical limits, the 
temperature of the offgas should not be so high as to inhibit production 
of pyrolytic oil; on the other hand, it must not be so low as to cause the 
bed to bridge or "lock up" due to the condensation of oil, tar, and water 
in the relatively cool upper regions thereof. As has been mentioned 
previously, such control of gas temperature will normally be achieved by 
variations in the air-to-feed ratio, bed depth, and the like. 
In more specific terms, the air-to-feed ratio employed will generally be in 
the range of about 0.15 to 1.5 pounds of air per pound of dry feed, 
depending upon many factors, including the products desired, the moisture 
content and bulk density of the feedstock, etc. For example, the higher 
ratios will favor low yields of char or other solid residue, whereas 
values at the lower end of the range will be advantageous from the 
standpoint of minimizing particulate carryover and maximizing the 
production of solid residue, should that be desirable. In this regard, it 
should be appreciated that, although char will often be the desired solid 
residue produced, other such products may be more desirable in certain 
instances, and processes for the production thereof are fully within the 
scope of the present invention. 
Thus, it can be seen that the present invention provides a novel, 
continuous process, and a novel system for carrying out the same, for 
pyrolyzing a cellulosic material so as to produce pyrolytic oil, a solid 
residue, and a cleansed, enriched gaseous product. In accordance 
therewith, the pyrolytic oil produced is utilized as the scrubbing medium 
to remove particulate solids from the gas stream, thereby avoiding 
problems attendant to the use of dry and water-scrubbing cleansing 
techniques. By subjecting the offgases to sequential oil scrubbing and 
water vapor condensation steps, with recycle of effluents, organic 
contaminants may either be utilized advantageously or disposed of 
innocuously, and a considerable amount of water vapor remaining may be 
condensed to produce a clean wastewater stream that is substantially free 
of pollutants. The invention also provides a process and a system of the 
foregoing nature, in which the characteristics of the recycled pyrolytic 
oil stream may automatically be controlled, to either permit or prevent 
dehydration of the oil, so as to ensure optimal operation and the 
attainment of the objects of the invention. In addition to all the 
foregoing, the process and system of the invention are convenient, 
efficient and relatively simple and inexpensive to carry out and to use.