Method for direct gasification of solid waste materials

Direct gasification of a high BTU content fuel gas from a hydrocarbon content solid waste material W which may include some glass content is effected by preheating heat carrier solids HCS in a flash calciner to a temperature capable of thermally cracking the hydrocarbon content of the solid waste material W directly into the high BTU content fuel gas. The HCS are separated from the products of combustion and fed into a gas sealed refractory lined horizontal axis rotary kiln retort concurrently with the solid waste W. Momentary contact and mixing of the solid waste W with the HCS in the rotary kiln in the absence of oxygen is sufficient to directly thermally crack the solid waste material into the high BTU gas product. Separated HCS are returned to the flash calciner for reheating. A trommel, coupled directly to the output of the rotary kiln retort and having a trommel screen with mesh openings smaller than glass agglomerates, but sized larger than the HCS, permits separation of the HCS and discharging of glass agglomerates from the downstream end of the trommel screen to prevent shut down of the direct gasification unit. Direct gasification of steel industry waste water treatment plant sludge, automobile shredded refuse ASR, municipal solid waste MSW and refuse derived fuel RDF and oil mill scale is effectively achieved, irrespective of glass content contaminant.

This invention relates to a method and apparatus for direct gasification of 
solid waste by heating solid waste materials continuously in the absence 
of air to high temperature to directly produce a high BTU gas, and more 
particularly to a method and apparatus which utilizes a rotary retort and 
a flash calciner for significantly improving the efficiency of the direct 
gasification process. 
BACKGROUND OF THE INVENTION 
Our society generates a tremendous amount of hydrocarbon and 
carbohydrate-based waste. Some wastes are easily segregated and recycled, 
while others are not. A variety of waste based on available technology 
cannot be economically recycled into a usable, saleable, clean, high BTU 
content gas. 
The United States generates over 200,000,000 tons per year of municipal 
solid waste (MSW). This waste contains many different types of carboneous 
materials like hydrocarbon based, carbohydrate and cellulose-based 
materials. 
MSW typically contains on a dry basis the following percentage of 
components: 
______________________________________ 
Volatile Matter 79.56% 
Fixed Carbon 9.98% 
Ash 20.46% 
C 45.52% 
H 5.75% 
N 0.29% 
O 37.79% 
S 0.19% 
______________________________________ 
EQU Cl 0.43-1.54% 
Some municipalities have installed plants that separate the burnable 
fraction from metals and other non-burnables. The burnable material is 
commonly called Refuse Derived Fuel (RDF). It contains leather, rubber, 
plastics, paper, yard waste, etc. 
The United States scraps about 10,000,000 automobiles per year. A large 
portion of the automobiles are shredded. After shredding, the non-metal 
portion is separated from the metallics in air classifiers or like means. 
Such material is commonly called "fluff" or Automobile Shredder Residue 
(ASR). Such material is light and fluffy. Over 1.5 million tons of ASR per 
year are generated. Currently, ASR is being land filled, using up very 
valuable space. 
It is almost impossible to economically separate the plastics using solvent 
extraction or other chemical or mechanical methods from the fluff. The 
fluff normally includes polyurethanes, leather, vinyls, glass, nylons and 
other thermal and heat-setting plastics. 
Automobile and truck tires continue to be a disposal problem throughout the 
United States. In addition to the 200 million tires discarded in this 
country every year, there exist another one billion tires in piles. 
The steel industry uses large quantities of oil in the production of sheet 
and strip steel products. A large percentage of rolling oils, lubricating 
oils, and hydraulic oils eventually are removed in the waste water 
treatment plant in the form of a high oil content sludge. A typical large, 
integrated steel mill generates between 50,000 and 100,000 tons per year. 
The major steel industry mills have an on-site plant to treat and separate 
their waste water coming from the finishing part of the mill. The sludge 
typically contains: 
______________________________________ 
Oil 5-15% Dry Basis 
Solids 95-85% Dry Basis 
Water 30-60% 
______________________________________ 
Such oil containing sludge is stockpiled openly to the atmosphere such that 
acid rain leaches out the oil and other heavy metals. A typical steel mill 
may stockpile between 300,000 to 800,000 tons of the waste water treatment 
plant sludge. 
Some of the oil from the rolling operation in a typical steel mill ends up 
in mill scale. Mill scale is also stockpiled outside where the oil may 
leach into the ground. Mill scale typically contains: 
______________________________________ 
Oil 1-15% 
Iron Oxide 60-75% 
______________________________________ 
One U.S. mill is currently trying a detergent process to wash out the oil. 
The oily wash water goes to the waste water treatment plant, where some of 
the oil accumulates in the sludge. 
Over the past several decades, there have been attempts to volatize 
hydrocarbons from such solid waste. Such processes have included indirect 
retort processes. Heat Carrier Solids (HCS) have been used to remove 
hydrocarbons from solids. In the 1970's, Tosco used aluminum oxide balls 
to recover oil from oil shale. 
U.S. Pat. No. 3,008,894 issued Nov. 14, 1961 to W. J. Culbertson, Jr. is 
exemplary of oil recovery from oil shale. 
Similar processes use fine particle HCS to recover oil from oil-bearing 
solids. In these processes, the objective is to produce a distillate 
liquid that can either become feed stock for an oil refinery or other 
oil-based product. 
Another method employed in the past for heating solids indirectly is 
through a metallic or ceramic shell, such as an indirectly-fired heated 
retort. A limitation to this approach is the amount of heat that can be 
transferred through the thickness of the metallic or ceramic shell. 
More recently, Battelle of Columbus, Ohio has effected gasification of wood 
chips and RDF in a biomass gasification process, producing medium-BTU 
product gas. U.S. Pat. No. 4,828,581 exemplifies the Battelle approach, 
utilizing two circulating fluid bed reactors, one of which is a 
gasification reactor in which the biomass is converted into a medium BTU 
gas and residual char, and a second, is a combustion reactor that burns 
the residual char to provide heat for the direct gasification of the 
biomass. Heat transfer between the reactors is accomplished by circulating 
sand (HCS) between the gasifier and the combustor. 
While the Battelle process effects direct gasification of wood chips and 
RDF, such process and apparatus requires the use of steam or nitrogen to 
maintain two fluidized beds, increasing the process cost by the 
fluidization, while additionally requiring extraneous energy and 
extraneous fluid to support the particles in the fluidizing bed reactors. 
The energy cost of the system is quite high, and the fluidized bed 
combustor also requires a source of compressed air, both of which may not 
be readily available on the situs of the gasification apparatus. 
It therefore a primary object of this invention to provide an indirect 
retort process for treatment of shredded MSW and like waste, with 
increased thermal efficiency in an apparatus and process which is highly 
simple, and which is applicable for direct gas conversion of a variety of 
hydrocarbon content waste that to date cannot either be technically or 
economically recycled into a usable, saleable clean and high BTU content 
gas. 
It is a further object of this invention to provide a method and apparatus 
for the direct gasification of municipal and like waste, which 
automatically removes acids and particulates from materials in the gas 
phase, which eliminates the need for fluidized beds or like lifting 
devices in the direct gasification of the waste, and in heating the Heat 
Carrying Solids (HCS) prior to contact with the treatable waste. 
These and other objects of the present invention will be more clearly 
understood by reference to the following description and to the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In general, the process and apparatus of the present invention is based on 
the concept of heating hydrocarbon content waste materials continuously in 
the absence of air to high temperature to produce a high BTU gas. The 
temperature selected is that temperature which thermally cracks the 
hydrocarbon Organic materials to carbon and gas. This is accomplished by 
adding and storing the process heat requirement in Heat Carrying Solids 
(HCS). The type of HCS may vary; for example the HCS may be iron oxide, 
aluminum oxide, refractory inert, fine mesh sand, or retorted residue from 
the starting waste material. 
FIG. 1, illustrating a solid waste direct gasification apparatus practicing 
the method of the invention and forming a preferred embodiment, is a flow 
diagram. A typical operation involves the treatment of a steel mill waste 
water treatment plant sludge or waste W containing for example 60% water, 
15% hydrocarbons and 25% solids. To effect the desired heat transfer from 
the HCS, 10 pounds of solids are required for each pound of sludge heated 
to 1200.degree. F. In the embodiment of FIG. 1, the HCS may be one half 
inch diameter balls, or a fine mesh sand or granular type material. As 
will be seen hereinafter, for purposes of illustration, makeup HCS in the 
form of mill scale is supplied as needed to the circulating HCS to 
maintain the desired heat transfer to ensure that the waste water 
treatment plant sludge is heated to the desired 1200.degree. F. to 
1400.degree. F. in the absence of oxygen to effect by pyrolysis, the 
direct gasification of the hydrocarbon content of the waste W. 
FIG. 3 is a schematic block diagram of the direct gasification of a 
hydrocarbon containing solid waste material utilizing the apparatus and 
process parameters as set forth in the flow diagram of FIG. 1, with the 
retorted solids (RS) and the HCS separated in the disengage chamber 
recirculated to the fired heater of the flash calciner. The block diagram 
of FIG. 3 illustrates in a sequence from right to left, the timing and 
entry of the fuel and air to the fired heater of a flash furnace 14, along 
with the heat carrying solids (HCS), the removal of the exhaust gas from a 
mixing reactor 18 for heat recovery and for separation of particulates, 
and the initial provision of both fuel and air to the fired heater 14. 
With the recirculation of the separated HCS and retort residue from a 
downstream disengage chamber 20, which is preferably a cyclone separator 
back to the fired heater, the carbon content of the retorted solids may 
constitute sufficient fuel to heat the incoming HCS to the desired 
1800.degree. F. temperature, prior to mixing of the HCS with the 
hydrocarbon based feed stock in the rotary kiln mixing reactor 18. The 
block diagram also shows the high BTU gas product after separation from 
the HCS and retorted solids in the disengage chamber 20 further subjected 
to a water spray in a condenser/scrubber 22. The gas leaving cyclone 
separator 20 is subject to particulate separation at a bag house 30 
downstream of the condenser/scrubber 22. 
The block diagram evidences the simplicity yet effectiveness of the 
invention and emphasizes the basic process steps of the invention and the 
apparatus practicing that process. The direct gasification of the 
hydrocarbon based waste feed stock is achieved utilizing minimal energy 
input with effective use of the carbon content of the retorted solids as 
part or all of the fuel for reheating the heat carrying solids HCS at the 
fired heater of the flash calciner. 
Turning to FIG. 1, the principal components of the direct gasification 
system or apparatus 10 consist of a surge bin or Sins 12 for incoming 
waste water treatment plant sludge W, flash furnace 14 including a flash 
calciner 16, the rotary kiln 18, the cyclone separator 20 for separating 
the usable, saleable, clean and high BTU content gas G, a 
condenser/scrubber 22 for condensing and removal of condensable liquids 
from the separated gas G, the bag house or dust collector 30, a combustion 
air preheater 26, a combustion air heater 28, and a containment free stack 
32. 
Additional components for the system 10 will be identified in the following 
description, which describes the process or method steps to produce the 
high BTU fuel gas G, which may be advantageously delivered directly to a 
coke oven or blast furnace (not shown) at a steel plant site, where the 
solid waste direct gasification apparatus is preferably located. 
Fresh high hydrocarbon containing steel mill waste water treatment plant 
sludge indicated by the arrow W is maintained in one or more surge bins 12 
overlying a waste feed inlet system 38 and preferably continuously fed at 
a predefined flow rate onto the upper run of the endless conveyor belt 38a 
under the control of a metering or outlet valve 12a of the surge bin 12. 
The waste W drops into an inlet hopper 46a of a feed screw 46 which 
discharges into the inlet end 18a of the rotary kiln 18. 
The rotary kiln 18 may be a commercial, refractorily lined rotary kiln 
incinerator such as that manufactured by the Fuller Co. of Bethlehem, Pa. 
or the Finch Environmental Corporation of West Pittston, Pa. 
In the process of this invention, the HCS, which is continuously circulated 
within a loop including the flash calciner 16 of flash furnace 14, rotary 
kiln 18, cyclone separator 20 and a portion of heater discharge duct 66 of 
the flash calciner 16, effects the direct contact heating of the high 
hydrocarbon content waste material W in the rotary kiln 18. 
The flash calciner 16 comprises a swirl-type furnace in which fuel is 
combusted in intimate contact with particulate material. In the 
illustrated apparatus, fuel is initially supplied to the air heater 28 via 
a fuel supply line, which preferably is bleed line 48 from gas product 
line 50 on the discharge side of the bag house 30. Bleed line 48 is 
coupled to a fuel nozzle 52 which forms one element of air heater 28. A 
combustion air supply line 54 opens to combustion chamber C of the air 
heater at 28, proximate to the outlet of fuel nozzle 52 where ignition is 
effected. The products of combustion of the fuel and air mixture are 
discharged from the combustion chamber and flow to the flash calciner 16. 
The accumulated HCS are fed into the products of combustion at the junction 
55 of a retorted solids discharge duct 56 and air heater discharge duct 66 
under control of a valve 60 within duct 56. Within the flash calciner 16, 
the turbulent swirling mixture of combustion gases and retorted solids, 
principally HCS, along with any supplemental fuel supplied to supplemental 
fuel nozzle 62 from bleed line 48 via supplemental fuel feed line 68 is 
further combusted. The turbulent swirling mixture of combustion gases, 
fuel and HCS produces a highly uniform temperature profile throughout the 
flash furnace 14. 
A cyclone separator 70 at the outlet of the flash calciner 16 separates the 
combustion gas from the now heated HCS. Useful to the gasification process 
is the feature of the flash calciner 16, that conventional flame 
temperatures associated with combustion are never attained as the intimate 
contact with the HCS absorbs the excess heat instantaneously. As such, the 
hot HCS at approximately 1850.degree. F., separated from the combustion 
gases by centrifugal force, fall by gravity into the bottom of the cyclone 
separator. The hot HCS pass through control valves 72 and are delivered by 
an oblique discharge duct 74 directly into the inlet end 18a of the rotary 
kiln. 
The rotary kiln 18 is refractory lined and consists of an elongated rotary 
drum rotating about a horizontal axis H, being driven at a predefined 
speed. The internal surface of the refractory lined retort 18 is 
configured, as by helical ribs, to drive the HCS material from left to 
right, i.e. from inlet end 18a to outlet end 18b of the rotary kiln. The 
rotary kiln 18, which may be a Fuller-Traylor.RTM. rotary kiln, 
facilitates the high efficiency, near instantaneous heat transfer between 
the hot particles of the HCS and the hydrocarbon material waste W. The 
interior of the rotary kiln is sealed and the atmosphere lacks oxygen to 
prevent combustion, but instead causes the direct conversion of the 
hydrocarbon content of the waste W into carbon and gas. With the 
temperature of the HCS entering the rotary kiln at near 1800.degree. F., 
this provides a .DELTA.T of 400.degree. to 600.degree. F. The temperature 
may be reduced to below 1400.degree. F. to minimize or prevent 
agglomeration of glass if the waste has significant glass content, 
depending upon whether glass is clear, green or brown glass, all having 
different melting temperatures. In a system 10 under a predescribed flow 
rate, a given weight HCS is heated in the flash calciner 16 to a 
temperature that, in turn, will heat the waste W in the rotary kiln 18 to 
a temperature adequate to effect the direct conversion of the hydrocarbons 
to carbon and gas, usually between 1200.degree. F. and 1500.degree. F. The 
reaction time is limited, otherwise, the hydrocarbon content of the waste 
material W is distilled off to produce a vapor that condenses at ambient 
conditions. Tests show that heating the waste material W to 1200.degree. 
to 1400.degree. F. converts all the convertible material to carbon and 
gas. The parameters of the rotary kiln operation are controlled, so that 
with adequate mixing of the HCS and the hydrocarbon waste material W, in 
kiln 18 the reaction time is between 0.5 to 2 minutes. Utilizing the 
rotary kiln heat transfer action, due to the tremendous surface area of 
the HCS, along with adequate mixing of the HCS during transport 
horizontally through the rotary kiln 18, produces tremendous heat transfer 
rates. For each ton of wet sludge W, there is between 1000 to 1 million 
square feet of heat transfer surface area depending upon the HCS size and 
shape. It is this high surface area ratio that produces instant heat 
transfer. 
In the illustrated embodiment, the HCS is then immediately separated 
downstream of the rotary kiln from the retorted solids RS of the waste W, 
using cyclone separator 20, with the mixture PG,13 of HCS and retorted 
solids discharging through rotary kiln outlet 18b into the disengaging 
chamber 20a of cyclone separator 20. A trommel 19 is preferably 
incorporated in the cyclone separator 20 having a mesh size capable of 
retaining agglomerated glass particles while passing the HCS and RS 
through the mesh openings. The agglomerated glass particles 21 are 
discharged from trommel 19 after separation. A gas outlet 20b opens 
tangentially to product gas G gas discharge line 76. A conical lower 
portion 20d of the cyclone separator casing 20c opens to retorted solids 
discharge line 56. Depending upon the desired makeup of the HCS, the HCS 
can be separated from the retorted solids RS of the waste via cyclone 
separator 20, as illustrated, through elutriation, or through screening. 
The separate HCS is reheated via direct contact with the products of 
combustion discharging from air heater 28 during passage through duct 66 
connecting the air heater 28 at the downstream end of the combustion 
chamber C to the flash calciner 16 and by further heating in the flash 
calciner 16. In certain cases, the retorted solids RS of the treated 
hydrocarbon content waste material W, such as mill scale or waste water 
treatment plant sludge, function adequately as the HCS. 
Schematically in the embodiment of FIG. 1, cyclone discharge duct 56 feeds 
the HCS back into duct 66 on the discharge side of the air heater 28 and 
upstream of the flash calciner 16, along with retorted solids RS of the 
waste material W in one mode of operation. Alternatively and in most 
cases, the HCS is separated from the retorted solids as indicated by the 
arrow RS, FIG. 1, which retorted solids RS are collected in a retort 
discharge hopper 34 within a discharge branch duct 78, which branches from 
duct 56. Flow of retorted solids RS to hopper 34 is controlled by a valve 
80 and which opens directly to the retorted solids hopper. 
The production gas G exiting the rotary kiln or retort 18 and separated by 
the cyclone separator 20 passes via gas discharge line 76 into the 
condenser/scrubber 22 which receives cooling water indicated by arrow CW, 
via tube 81. The cooling water in spray form condenses out any condensable 
content of the production gas flow discharging from the cyclone separator 
20. A condensate drain pipe or line 82 open to the bottom of the scrubber, 
permits passage of the condensed liquids 84 to a sewer or the like. The 
particulates are separated from the production gas in the bag house or 
dust collector 30 connected to condenser/scrubber 22 via duct 77, and the 
final gas product G of high BTU content and free of contaminants leaves 
the dust collector 30 at the top via production gas supply line 50. In the 
example of the illustrated embodiment, the production gas G is employed as 
fuel for a steel plant coke oven or blast furnace. The condensate or waste 
water 84 can be treated using conventional and pertinent waste water 
technology. 
With respect to the products of combustion within the flash calciner 16, 
those products of combustion, as indicated by the arrow PC, pass upwardly 
from the top of the cyclone separator 70, through the air preheater 26, 
via combustion gas removal duct 86 to a second bag house or dust collector 
24. Fresh air is bled into duct 86 via air bleed duct 88, controlled by 
damper 90, which opens to the atmosphere. This permits some air to mix 
with the products of combustion PC discharging from the cyclone separator 
70 prior to entering the bag house or dust collector 24. A bag house PC 
discharge duct 92 feeds to the stack 32, where the contaminant-free, clean 
gas is discharged at the top thereof, as indicated by arrow 94. I.D. fan 
44 in bag house PC discharge duct 92 ensures the removal of the products 
of Combustion PC from the cyclone separator 20 and discharge thereof into 
the bottom of the stack 32. 
Preferably, system 10 uses recuperative heat exchange to preheat the 
incoming air stream to air heater 28. The compressed air supply line 54 
opens at one end to the atmosphere via air filter 42. Line 54 includes an 
air blower 25 for forced flow and compression of the air through a looped 
heat exchanger coil 96 internally of air preheater 26 and about discharge 
duct 86 carrying the products of combustion PC from the cyclone separator 
70 to stack 32. The combustion air, shown schematically by arrow A, is 
preheated to approximately 800.degree. F. within the air preheater 26. 
Assuming that the retorted solids RS separated within the cyclone 
separator 20 do not function as the HCS for the system, nor are 
recirculated with the HCS, those retorted solids may be fed commonly via 
the water jacket screw 36 to a retorted solids surge bin 98 for storage. A 
water jacket cooling screw retorted solids supply line, indicated in 
dotted lines at 100 may optionally connect the outlet of the retorted 
solids hopper 34 to the discharge duct 102. Duct 102 connects the second 
bag house or dust collector 24 to the water jacket screw 36 driven by a 
motor M. The screw 36 feeds the excess solids from the system at bug house 
or dust collector 24 and retort discharge hopper 34 into the top of the 
storage surge bin 98. Periodically, those excess solids may be removed 
under control of a shut off valve 98a at the bottom of the 20 ton surge 
bin. 
Where the hydrocarbon content waste material is essentially dry such as 
fluff or Automobile Shredder Residue (ASR), tires, municipal waste MW, or 
Refuse Dry Fuel (RDF), such hydrocarbon waste may be fed directly from a 
surge bin 12 to the inlet end 18a of the refractory line rotary kiln 18. 
Where, however, the hydrocarbon content waste is in form of waste water 
treatment plant sludge with water content from 30% to 60%, as in the 
embodiment of the invention of FIG. 1, it may be necessary to include a 
drying stage in such system. FIG. 2 illustrates a drying stage indicated 
generally at 108 to be optionally included in the system or apparatus 10 
of FIG. 1. In FIG. 2, the same elements from the system of FIG. 1 bear 
like numerical designations. In this case, some of the HCS content is 
preheated and fed to an additional equipment rotary drum dryer mixed with 
the wet sludge W' prior to feeding of dry sludge W to the rotary kiln 18 
of the system, with the flow of the HCS controlled so that the temperature 
in the drum dryer is sufficient to adequately remove the moisture and 
provide a relatively dry sludge W to the kiln. 
The major components of the drying stage 108 resides in a preheat cyclone 
separator 110, a drum dryer 112, a screen separator 114, a pug mill 116 
and a drying stage condenser 118. 
The drying stage HCS, which may be continuously fed in a continuous loop 
path including a HCS feed line or duct 120, is fed into the discharge duct 
86 for the products of combustion at the top of the flash furnace cyclone 
separator 70 of FIG. 1, for preheating prior to those products of 
combustion PC passing to the air preheater 26. To simplify the 
description, the break in the duct or line 86 as labeled, in FIG. 2, is 
between the flash calciner 16 and the bag house or dust collector 24 of 
FIG. 1. The drying stage heat carrier solids HCS mixing with and being 
carried by the hot gas from the flash calciner to the dust collector under 
the operation of the ID fan 44, FIG. 1, in the direction of arrow labeled 
PC, FIG. 2, enter preheat cyclone separator 110, where, in flowing with 
the products of combustion PC from the flash calciner 16 to the preheat 
cyclone separator, the HCS has its temperature increased to about 
1000.degree. F. After separation by centrifugal force in the preheat 
cyclone separator 110, the HCS, collecting by gravity in the bottom of 
separator 110, pass through a preheat cyclone separator solids discharge 
duct or line 122 to the inlet end 112a of the drum dryer 112, along with a 
mixture of wet sludge from the surge bin or bins 12 for the incoming feed 
of the system, FIG. 1, and illustrated schematically by the arrow 124. The 
wet sludge W' enters pug mill 116, which pug mill mixes the wet sludge W' 
with dry sludge W bled from the solids separated by screen separator 114 
downstream of the drum dryer 112. The rotary drum dryer 112 is similar in 
operation to the rotary kiln 118 in the sense that the device is a drum, 
is mounted for rotation about a horizontal axis, is driven in rotation at 
desired speed, has internally, means for driving the mixture of wet and 
dry sludge and HCS from right to left and from inlet end 112a to outlet 
end 112b and the drum dryer is sealed in the manner of the rotary kiln 18 
of FIG. 1 The outlet line or duct 126 from the pug mill merges with the 
discharge line 122 from the preheat cyclone separator at inlet end 112a of 
the drum dryer 112. The mixture of the wet and dry sludge in a preferred 
mode of operation in turn mixes with the HCS internally of drum 112 and 
direct heat transfer is effected sufficient to remove the moisture from 
the wet sludge. The temperature of the HCS along with the feed rate of wet 
sludge W' (alone) or wet sludge W' mixed with a portion of dry sludge W 
emanating from the discharge side of the screen separator 114 determines 
the amount of moisture removed from the wet sludge prior to directing the 
sludge W to the kiln 118 of FIG. 1. In that respect, on the outlet end or 
discharge side 112b of the drum drier, the solids content of the drum 
dryer passes via line 128 to the inlet of the screen separator 114. The 
screen separator 114 separates the HCS from the now dry sludge W, and the 
dry sludge W passes to the inlet 118a of the rotary kiln 18 of the 
apparatus of FIG. 1. The separated HCS content is recirculated as 
described above via line 120 to the preheat cyclone. A solids recycle line 
132 branches from the dry sludge discharge line 134 to supply a portion of 
the dry sludge W back to the pug mill 116. That line 132 is dotted to 
indicate the optional nature of the solids recycle loop, via line 132. The 
moisture content of the wet sludge W' reaching the pug mill 116 via line 
124, may not require mixing with dry sludge prior to entry into the drum 
dryer 112. For wet, sticky sludges, part of the dried solids, of 
necessity, are mixed with the wet sludge to improve the handling 
characteristics in the pug mill 116. As may be appreciated, the pug mill 
116 itself may be omitted from the system. 
As a result of the heat transfer from the HCS to the wet sludge W' within 
the drum dryer, the moisture within the sludge W' is driven off 
principally as 99% steam, although there may be a 1% vapor content which 
is not water based. The steam and vapor is preferably directed via a drum 
dryer steam discharge line 136 to the drying stage condenser 118. The 
water, as well as any other condensate such as oil, condenses within the 
condenser 118 and collects in the bottom of the condenser 118 for liquid 
discharge through liquid discharge duct or line 138. Line 138 may be 
connected to the scrubber condensate discharge line 84, FIG. 1. 
Non-condensable gas may optionally be removed from the condenser 118 via 
gas outlet line 140 shown in dotted form. Where that gas content is a 
combustible gas, line 140 may be fed to the branch fuel line 48, FIG. 1, 
and provide some modicum of fuel to fire the air heater 28 of the system 
of FIG. 1. 
In the preferred embodiment of the invention as exemplified by drawing 
FIGS. 1 and 2 and the process description within the specification 
employing the apparatus components operating under the method steps of the 
present invention, an effective indirect heating process results which 
effectively and cheaply directly converts hydrocarbons, carbohydrates, 
etc. into a high BTU gas and carbon. With the HCS in the form of balls or 
fine mesh sand, or like granular type material, the process readily 
transfers large quantities of heat at high temperatures between 
1200.degree. to 1400.degree. F./ Efficient low cost plants, in accordance 
with the invention, can adequately process 50 to 200 tons per hour of 
shredded MSW or other organic-based waste, using the process and apparatus 
of the preferred embodiment. Not only does the direct heat gasification 
process produce a useful commercial, high BTU gas product, from 
hydrocarbon content waste material, but such product gas G may be easily 
purified by removing particulate and acid content prior to combustion. The 
process and apparatus of the present invention as described directly 
gasifies the hydrocarbon content of the waste material to produce gas and 
carbon and not distillate oils from organic-type waste. As a byproduct, 
the direct gasification process of the present invention produces in 
addition to a high BTU fuel gas inert, solids which readily pass the EPA 
TCLP test for lead. 
Importantly, the process and apparatus of the present invention as set 
forth in detail in applicant's preferred embodiment, FIGS. 1 and 2, and as 
exemplified in the block diagram of FIG. 3 operating under the parameters 
stated herein, are highly effective in treating the waste materials set 
forth specifically within the specification. The invention has application 
to other hydrocarbon wastes, which are generated and discarded such as 
plastic wire insulation, textile-based waste such as carpet scrap, oil 
waste from oil refineries, scrap wood, etc. 
In the examples, which follow, the feed stock varies from example to 
example, however, the HCS employed in the direct gasification of the 
hydrocarbon content of waste feed stock, employs a suitable HCS, which may 
vary and be of the type set forth specifically within the specification 
above. However, the invention is not restricted to such feed stock or HCS 
and the system operating parameters as set forth specifically herein. 
The examples which follow constitute results from bench-type experiments 
and pilot plant runs involving utilization of significant amounts of both 
the hydrocarbon bearing waste solids W and heat carrying solids HCS 
preheated to temperatures on the order of 1800.degree. F., with mixing 
occurring within a horizontal cylindrical reactor or equivalent and with 
process parameters such as those set forth in the description of the 
preferred embodiment herein or simulations thereof. The analysis of the 
solid waste feed stock W and that of the direct gasification gas product G 
produced by the process with minimal contact time between the mixed 
hydrocarbon containing solid waste feed stock and the hot HCS in the 
absence of oxygen, show significant BTU content and the retorted solids RS 
have significant carbon content permitting burning of the carbon as fuel 
in the fired heater for heating the heat carrying solids HCS upon 
recirculation to the heater 14 simulating the preheat action of the flash 
calciner 16 of FIG. 1. In example 5, while the municipal solid waste MSW 
acting as the feed stock is similar to refuse derived fuel (RDF) discussed 
in the background of the invention, it contained significant, relatively 
large size metal and another non-burnable constituents such as glass. For 
purposes of comparison, such MSW would be economically unfeasible as 
hydrocarbon bearing solid waste feed stock for waste treatment and fuel 
product recovery systems utilizing fluidized bed reactors and/or fluidized 
bed furnaces for increasing the temperature of the recirculated heat 
carrying solids HCS prior to mixing, with the feed stock in the second 
fluidized bed reactor. 
EXAMPLE 1 
In a bench-type experiment, 4,90 # (2,221 gms) of oily sludge at 61.degree. 
F. analyzing: 
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Solids 30.0% 
Oil & Grease 9.1% 
Water 60.9% 
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was added to 33.9# of mill scale (HCS) after preheating the HCS to a 
temperature of 1555.degree. F. The oily sludge solid waste W was added to 
a horizontal cylindrical reactor in 3 to 5 minute increments of about one 
pound each. The process produced 1.47# of retorted solids, 2.98# water and 
0.4# of high BTU direct gasification gas product G. The residual oil and 
grease content of the retorted solids (RS) was 800 ppm and the carbon 
content was 5.6%. The direct gasification gas product contained 995 BTU 
and analyzed: 
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Hydrogen 34.69% 
Carbon Dioxide 5.23% 
Propane 0.75% 
Propylene 10.98% 
Acetylene 0.14% 
Ethylene 18.01% 
Ethane 6.11% 
Oxygen 0.03% 
Nitrogen 0.80% 
Methane 21.64% 
Carbon Monoxide 1.62% 
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EXAMPLE 2 
In a bench-type experiment, 5.09# of automobile shredder fluff (ASR) was 
mixed with 32.1# of iron oxide HCS heated to 1350.degree. F. The process 
produced 2.69# of solids and 2.44# of gas. 
The direct gasification gas product contained 910 BTU/Ft.sup.3 and 
analyzed: 
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Hydrogen 30.47% 
Carbon Dioxide 11.69% 
Propane 0.43% 
Propylene 7.42% 
Acetylene 0.13% 
Ethylene 16.27% 
Ethane 5.88% 
Oxygen 0.27% 
Nitrogen 1.35% 
Methane 26.09% 
Carbon Monoxide 13.69% 
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The Total Lead in the retorted solids (RS) was 0.32% and the TCLP Lead was 
0.35 mg/l. The carbon content was 4.6% 
EXAMPLE 3 
In a bench-type experiment, 5.09# of shredded rubber tires solid waste W, 
whose thread portion of 1" to 3" particles contained steel, was mixed with 
iron oxide mill scale (HCS) heated to 1728.degree. F. The temperature of 
the resultant mixture was 1617.degree. F. The percentage of the materials 
produced were: 
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Oil & Grease 
Material % Weight Content % Carbon 
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Residue 27.2 1.38# 440 ppm 81.5 
Steel 22.3 1.14# 
Gas 46.5 2.32# 
Tarry 5.0 .25# 
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A tarry residual emulsion liquid was added back into the retort where it 
cracked to carbon and gas at a retort temperature of 1400.degree.. 
The retorted solids (RS) residue contained 440 ppm of oil and grease, and 
the carbon content was 81.5%. 
The direct gasification gas product contained 843 BTU/Ft.sup.3 and 
analyzed: 
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Hydrogen 20.36% 
Carbon Dioxide 8.80% 
Propane 0.19% 
Propylene 3.45% 
Acetylene 0.22% 
Ethylene 16.23% 
Ethane 4.36% 
Oxygen 0.72% 
Nitrogen 3.69% 
Methane 31.19% 
Carbon Monoxide 10.79% 
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EXAMPLE 4 
In this bench-type experiment, 5.6# of oily mill scale solid waste W 
containing 5% water and 3% oil was mixed with 19# aluminum oxide balls 
(HCS) heated to 1550.degree. F. The resultant temperature was 1410.degree. 
F. The experiment produced: 
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Oil & 
Material Gas % Weight Grease % 
% Carbon 
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Mill scale 
92 5.15# 500 pm 1.1 
Water 5 0.28# 
Gas 3 0.17# 
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The direct gasification gas product G contained 905 BTU/Ft.sup.3 and 
analyzed: 
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Hydrogen 32.67% 
Carbon Dioxide 4.18% 
Propane 1.25% 
Propylene 12.03% 
Acetylene 0.18% 
Ethylene 14.94% 
Ethane 5.61% 
Oxygen 0.06% 
Nitrogen 1.80% 
Methane 24.71% 
Carbon Monoxide 2.57% 
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EXAMPLE 5 
In this experiment, 1.20# of municipal waste MW was heated with 12# of 
aluminum oxide balls preheated 1711.degree. F. The residual temperature of 
the mixture was 1373.degree. F. after 1.5 minutes. The RDF produced 0.92# 
of gas and 0.28# of retorted solids residue. 
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Volume BD Analyses 
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% Gasified 76.60% 
% Residue 23.40% 
% Ash after combustion 17.60% 
% Weight reduction 82.40% 
% Volume reduction 92.00% 
Residue Bulk Density 25#/Ft.sup.3 
BTU content of retorted solids (RS) residue 
3,590 BTU/# 
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The direct gasification gas product contained 573 BTU/Ft.sup.3 and 
analyzed: 
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Hydrogen 8.85% 
Carbon Dioxide 7.44% 
Propane 0.19% 
Propylene 2.66% 
Acetylene 0.17% 
Ethylene 11.52% 
Ethane 3.32% 
Oxygen 6.78% 
Nitrogen 29.31% 
Methane 19.65% 
Carbon Monoxide 10.11% 
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A serious problem in processing materials containing glass like RDF and ASR 
is the glass content. In a fluidized or entrained bed in prior art 
practice, the glass reaches a softening point and sticks or agglomerates 
the HCS. These agglomerates grow and will eventually shut down the 
process. Attempts have been made to solve this problem by displacing the 
contaminated HCS with fresh HCS, but this is expensive and not feasible in 
Japan, where the contaminated HCS must be disposed of by burying in 
landfills, and landfill space is very costly. 
The process and apparatus of the present invention has the added capability 
of removing glass from the system. Particularly where the waste W to be 
treated takes the form of automobile shredder fluff (ASR) with significant 
glass content, the glass becomes molten, tends to agglomerate into sizable 
particles, and must be removed from the system. This is particularly true 
where the HCS is heated to relatively high temperatures in the order of 
1400.degree. F. to 1800.degree. F. prior to mixing with the feed stock W. 
The present invention solves the problem by two different ways. The 
applicant has determined that if the HCS temperature is controlled along 
with the mixture percentages of HCS to feed stock W and the extent of time 
of direct heating contact between HCS and feed stock, the glass will not 
agglomerate. Control is effected by measuring the residual mixture 
temperature of the HCS and retorted ash (carbon). The amount of ash 
particles, the chemistry and amount of glass present in the feed stock W 
will dictate the HCS temperature and thus the residual mixture temperature 
of the HCS and retorted ash. As an example of one set of conditions, where 
the HCS was limited in its heating to 1324.degree. F. and mixed with the 
residue to a residual mixture temperature of 1289.degree. F. agglomeration 
of glass was practically nil and insufficient to adversely affect the 
process. 
The invention additionally provides a solution to the problem of glass 
agglomeration by the use of a trommel 19 in applicant's FIG. 1 system. 
This permits system operation at higher temperature than that providing a 
residual mixture temperature of the HCS and retorted ash at 1289.degree. 
F. The applicant determined that at residual temperatures of 1400.degree. 
F., the glass will form agglomerates in excess of 8 mesh size. By 
selection of a HCS size which is smaller than the glass agglomerates (in 
such example by using a trommel 19 screen with 10 mesh openings), it is 
possible to separate HCS in the -10 mesh to 50 mesh size from an oversized 
agglomerate. If necessary, an elutriation step may be added to separate 
very light carbonaceous particles from the oversize particles and HCS, the 
very light carbonaceous particles forming a commercially useful fuel for 
burning on site, or for transport to off site fuel burners as a solid high 
BTU product in addition to the high BTU product gas G of the gasification 
system or apparatus of FIG. 1. If some agglomerates are the same size as 
the HCS, they will eventually agglomerate to a larger size if recirculated 
with the HCS over time, permitting the larger size agglomerates to be 
separated adequately by the screen of the trommel 19. 
The following examples identify parameters associated with the problem of 
glass agglomeration and the separation of the same. 
EXAMPLE 6 
In this pilot plant experiment, 9# of shredded RDF at 45.degree. F. was 
mixed with 50# of aluminum oxide HCS at 1334.degree. F. The residual 
mixture temperature was 1289.degree. F. There was no sign of glass 
agglomerations with the HCS. In this example, the trommel 19 was dispensed 
with, since it was unnecessary. 
EXAMPLE 7 
In this pilot plant experiment, 17# of RDF at 51.degree. F. was mixed with 
74# of aluminum oxide HCS at 1700.degree. F. The HCS mesh size was -8 mesh 
+14 mesh. The residual mixture temperature of the HCS and retorted ash was 
1425.degree. F. The mixture was screened by trommel 19 and all the glass 
agglomerates were +8 mesh with no visible agglomeration below 8 mesh 
present in the bottom 20D of the disengaging chamber or cyclone 20, 
accumulating the separated HCS and the ash (below 8 mesh). The sodium 
oxide content, a glass indicator, of the HCS was only 0.1% after nine 
runs. 
While the invention has been described in the form of a preferred 
embodiment, and although directed to a plurality of different solid waste 
materials having significant hydrocarbon content, it should be understood 
that modifications and changes can be made herein without departing from 
the invention and from the following claims: