Method of controlling hydrocarbon release rate by maintaining target oxygen concentration in discharge gases

In a hydrocarbon release rate controlling method, a first chamber is provided capable of receiving successive batches of feed materials for thermal processing having widely varying energy content, heating is produced in the first chamber to cause pyrolyzing of the feed materials into fluid materials, a second chamber is provided communicating with the first chamber and capable of receiving the fluid materials from the first chamber and communicating the fluid materials to a discharge location, heating is produced in the second chamber to cause oxidizing of the fluid materials into discharge gases reaching the discharge location, a jacketed vessel is provided defining a channel surrounding the first and second chambers containing a flow of coolant fluid through the channel, separate variable flows of primary and secondary air are respectively produced into and through the first and second chambers, the temperatures in the first and second chambers are sensed, the temperature of the coolant in the channel of the jacketed vessel is sensed, the concentration of a preselected gas in the discharge gases is sensed, and, in response to the temperatures sensed in the first and second chambers and jacketed vessel channel coolant and in response to the concentration of the preselected gas sensed in the discharge gases, the primary and secondary flows of air into the first and second chambers are controlled so as to proportion and vary the respective amounts thereof and thereby maintain the concentration of the preselected gas in the discharge gases at a preset target level corresponding with the generation of harmless discharge gases and production of carbon-free residue ash.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to controlled processing of 
materials and, more particularly, is concerned with a method of 
controlling hydrocarbon release rate by maintaining target oxygen 
concentration in discharge gases so as to thereby convert successive 
batches of materials of widely varying energy content into substantially 
harmless gases and carbon-free residue ash. 
2. Description of the Prior Art 
The problem of disposal of waste matter involves a material processing 
challenge that is becoming increasingly acute. The primary material 
processing methods of waste disposal have been burning in incinerators and 
burial in landfills. These two material processing methods have severe 
disadvantages. Burning of waste liberates particulate matter and fumes 
which contribute to pollution of the air. Burial of wastes contributes to 
the contamination of ground water. A third material processing method is 
recycling of waste. Although increasing amounts of waste are being 
recycled, which alleviates the problems of the two primary material 
processing methods, presently available recycling methods do not provide a 
complete solution to the waste disposal problem. 
The problem of disposal of biomedical waste materials is even more acute. 
The term "biomedical waste materials" is used herein in a generic sense to 
encompass all waste generated by medical hospitals, laboratories and 
clinics which may contain hazardous, toxic or infectious matter whose 
disposal is governed by more stringent regulations than those covering 
other waste. It was reported in The Wall Street Journal in 1989 that about 
13,000 tons a day of biomedical waste, as much as 20% of it infectious, is 
generated by around 6,800 U.S. hospitals. 
Hospitals and other generators of biomedical waste materials have employed 
three main material processing methods of waste handling and disposal: (1) 
on-site incineration with only the residue transferred to landfills; (2) 
on-site steam autoclaving and followed by later transfer of the waste to 
landfills; and (3) transfer of the waste by licensed hazardous waste 
haulers to off-site incinerators and landfills. Of these three main 
material processing methods, theoretically at least, on-site disposal is 
the preferred one. 
However, many hospital incinerators, being predominantly located in urban 
areas, emit pollutants at a relatively high rate which adversely affect 
large populations of people. In the emissions of hospital incinerators, 
the Environmental Protection Agency (EPA) has identified harmful 
substances, including metals such as arsenic, cadmium and lead; dioxins 
and furans; organic compounds like ethylene, acid gases and carbon 
monoxide; and soot, viruses, and pathogens. Emissions of these 
incinerators may pose a public health threat as large as that from 
landfills. 
Conventional incinerators most commonly are designed to operate above a 
certain temperature, such as 1200.degree.-1400.degree. F., to comply with 
requirements of the permit laws of many states. The reason for this 
requirement is that conventional thinking has been that operation of 
incinerators at such elevated temperatures will substantially eliminate 
the release of most harmful substances. This may have been true where the 
materials being consumed by the incinerator were assumed to be fairly 
uniform in terms of energy content and thus burned more or less evenly. 
However, this is the exception and not the normal situation today, 
particularly in the case of biomedical waste materials which can range 
from wet paper towels and steel surgery tools to plastic syringes and 
containers of saline solution. The thermal processing of these materials 
by temperature control alone will ordinarily result in the inability to 
control the hydrocarbon release rate and the repeated emission of 
un-burned hydrocarbons, typically visible as periodic puffs of black 
smoke, which is unacceptable under most current environmental regulations. 
SUMMARY OF THE INVENTION 
The present invention provides a method of controlling hydrocarbon release 
rate in thermal processing of materials which is designed to overcome the 
aforementioned problems of conventional incineration. The hydrocarbon 
release rate is controlled in a manner which converts successive batches 
of materials, particularly biomedical waste materials, of widely varying 
energy content into substantially harmless gases and carbon-free residue 
ash. The residue ash is a sterile, inert inorganic powder, which is 
non-hazardous, non-leachable and capable of disposal as ordinary trash. 
Accordingly, the present invention is directed to a method of controlling 
the hydrocarbon release rate in the thermal processing and conversion of 
materials of widely varying energy content in a batch processing cycle. 
The hydrocarbon release rate controlling method comprises the steps of: 
(a) providing a first chamber capable of receiving successive batches of 
feed materials for thermal processing and having widely varying energy 
content; (b) producing heating in the first chamber to cause pyrolyzing of 
the feed materials into fluid materials; (c) providing a second chamber 
communicating with the first chamber and capable of receiving the fluid 
materials from the first chamber and communicating the fluid materials to 
a discharge location; (d) producing heating in the second chamber to cause 
oxidizing of the fluid materials into discharge gases reaching the 
discharge location; (e) providing a jacketed vessel defining a channel 
surrounding the first and second chambers containing a flow of coolant 
fluid through the channel; (f) producing separate variable flows of 
primary and secondary air respectively into and through the first and 
second chambers; (g) sensing the temperatures in the first and second 
chambers; (h) sensing the temperature of the coolant in the channel of the 
jacketed vessel; (i) sensing the concentration of a preselected gas in the 
discharge gases; and (j) in response to the temperatures sensed in the 
first and second chambers and jacketed vessel channel coolant and in 
response to the concentration of the preselected gas sensed in the 
discharge gases, controlling primary and secondary flows of air into the 
first and second chambers so as to proportion and vary the respective 
amounts thereof and thereby maintain concentration of the preselected gas 
in the discharge gases at a preset target corresponding to the generation 
of substantially harmless discharge gases and production of substantially 
carbon-free residue ash. The preselected gas is preferably oxygen. 
More particularly, the controlling of the primary and secondary air flows 
includes comparing the sensed concentration of the preselected gas to the 
preset target thereof, and changing the proportion of primary air flow to 
secondary air flow if the sensed concentration of the preselected gas is 
either higher or lower than the preset target thereof. The changing of the 
proportion of primary and secondary air flows occurs at a higher rate if 
the sensed concentration of the preselected gas is lower than the preset 
target, whereas the changing of the proportion of primary and secondary 
air flows occurs at a lower rate if the sensed concentration of the 
preselected gas is higher than the preset target. 
Also, the controlling of the primary and secondary air flows includes 
comparing the sensed concentration of the preselected gas to the preset 
target thereof, and changing the speed of a fan to change the amount of 
primary and secondary air flows if the sensed concentration of the 
preselected gas is higher or lower than the preset target thereof. The 
changing of the speed of the fan occurs at a higher rate if the sensed 
concentration of the preselected gas is lower than the preset target 
thereof, whereas the changing of the speed of the fan occurs at a lower 
rate if the sensed concentration of the preselected gas is higher than the 
preset target thereof. 
The hydrocarbon release rate controlling method also includes the step of 
providing a heated refractory mass having an exterior surface forming the 
base of the first chamber and exposed to feed materials received therein 
such that the feed materials in close proximity to the exterior surface 
are heated and oxidized by the refractory mass. In the preferred 
embodiment, the refractory mass is heated by an arrangement of passages 
defining at least a portion of the second chamber and communicating with 
the first chamber such that the refractory mass is surrounded by the 
jacketed vessel and maintained in a heated condition at an elevated 
temperature by the heating produced in the first chamber and by the 
pyrolyzing and oxidizing of materials in the respective first and second 
chambers. The heated condition of the refractory mass, in turn, causes 
heating and oxidizing of materials in close proximity to the exterior 
surface of the refractory mass. The hydrocarbon release rate controlling 
method further includes the step of initiating a slow-start sequence for a 
predetermined period of time after the receipt of a new batch of material 
into the first chamber during which the desired target level of 
concentration of the preselected gas is temporarily increased so that the 
hydrocarbon release rate is temporarily reduced for the duration of the 
predetermined period of time. Also, the hydrocarbon release rate 
controlling method includes the step of ending a batch processing cycle by 
diverting substantially all air flow into the first chamber to cause 
oxidation of any remaining feed materials in the first chamber and thereby 
reduce such materials to substantially carbon-free residue ash. 
These and other features and advantages and attainments of the present 
invention will become apparent to those skilled in the art upon a reading 
of the following detailed description when taken in conjunction with the 
drawings wherein there is shown and described illustrative embodiments of 
the invention.

DETAILED DESCRIPTION OF THE INVENTION 
In the following description, like reference characters designate like or 
corresponding parts throughout the several views. Also in the following 
description, it is to be understood that such terms as "forward", 
"rearward", "left", "right", "upwardly", "downwardly", and the like, are 
words of convenience and are not to be construed as limiting terms. 
Material Processing Apparatus--In General 
Referring now to the drawings, and particularly to FIGS. 1, 2, 7, 13 and 
14, there is illustrated an exemplary apparatus, generally designated 10, 
for controlled thermal processing of materials, and in particular for 
controlled disposal of biomedical waste materials, which is operated in 
accordance with the hydrocarbon release rate controlling method of the 
present invention. The material processing apparatus 10 basically includes 
a coolant jacketed vessel 12 defining a first pyrolysis chamber 14 and a 
second oxidation chamber 16. The apparatus 10 also includes one or more 
first heater units 18 having a plurality of elongated rod-like electric 
heating elements 20 mounted in the vessel 12 and being operable to 
electrically generate heat for pyrolyzing materials in the first chamber 
14, and one or more second heater units 22 having a plurality of electric 
heating elements 24 mounted in the vessel 12 and being operable to 
electrically generate heat for oxidizing materials in the second chamber 
16. 
The apparatus 10 further includes an air flow generating means, preferably 
an induction fan 26 and a fan speed controller 27, connected in flow 
communication with the first and second chambers 14, 16, and first and 
second airflow inlet valves 28, 30 connected to the jacketed vessel 12. 
The apparatus also includes an air intake proportioning valve 31 connected 
in flow communication with the first and second air inlet valves 28, 30. 
The induction fan 26, proportioning valve 31, and first and second inlet 
valves 28, 30 function to produce separate primary and secondary variable 
flows of air respectively into and through the first and second chambers 
14, 16. One suitable embodiment of the fan speed controller 27 is a 
commercially-available unit identified as GPD 503 marketed by Magnetek of 
New Berlin, Wis. One suitable embodiment of the valves 28, 30 is disclosed 
in U.S. Pat No. 4,635,899, the disclosure of which is incorporated herein 
by reference thereto. One suitable embodiment of the proportioning valve 
31 is a pair of conventional air intake butterfly valves controlled by a 
standard proportioning motor marketed by the Honeywell Corporation. The 
respective amounts of air in the primary and secondary flows drawn through 
the first and second chambers 14, 16 by operation of the induction fan 26 
are proportioned by the operation of proportioning valve 31 to separately 
adjust the ratio of the amounts of air flow routed to the first and second 
air inlet valves 28, 30. The respective amounts of air drawn in the 
primary and secondary flows are correspondingly varied by varying the 
speed of operation of the induction fan 26. 
Still further at least three temperature sensors 32, 34, 36, such as 
conventional thermocouples, are mounted on the vessel 12 for sensing the 
temperatures in the first and second chambers 14, 16 and in the coolant 
circulating about a channel 38 defined by the jacketed vessel 12 about the 
first and second chambers 14, 16. Additionally, a gas sensor 40 is mounted 
on a discharge outlet 42 of the vessel 12 for sensing the concentration of 
a predetermined gas, for example oxygen, in the discharge gases. Also, a 
computer-based central control system 44 (FIG. 14) is incorporated in the 
apparatus 10 for controlling and directing the overall operation of the 
apparatus 10 in accordance with the hydrocarbon release rate controlling 
method of the present invention. One suitable computer which can be 
employed by the control system 44 is identified as PC-55 marketed by the 
Westinghouse Electric Corporation of Pittsburgh, Pa. 
Further, as seen in FIGS. 7 and 12-14, the apparatus 10 includes a heat 
exchanger 46 connected in flow communication between the second chamber 16 
and the discharge outlet 42. The heat exchanger 46 functions to remove 
heat from and thereby cool the coolant flowing through the channel 38 
defined by jacketed vessel 12. As pointed out in FIG. 13, the heat removed 
by the heat exchanger 46 can be employed in other applications in the 
facility housing the material processing apparatus 10. 
For many applications, the material processing apparatus 10 can be provided 
in the form of a single unit where all components of the apparatus are 
contained within the one unit. However, in order to accommodate space and 
installation requirements, there are other applications where the material 
processing apparatus 10 needs to be provided in the form of two separate 
first and second units 48, 50, as shown in FIGS. 1-12. Referring to FIGS. 
1-12, the material processing apparatus 10 includes a casing 52 having 
outer and inner spaced walls 54, 56 forming the coolant jacketed airtight 
pressure vessel 12 inside of the inner wall 56 and the channel 38 between 
the outer and inner walls 54, 56. The channel 38 surrounds the vessel 12 
and contains the flow of coolant fluid, such as water. FIG. 13 illustrates 
an example of the circulation flow path of the coolant fluid about the 
vessel channel 38 and between the first and second units 48, 50 of the 
vessel 12. As mentioned above, the vessel 12 of the apparatus 10 is 
separated into first and second units 48, 50 and has means in the form of 
a pair of tubular extensions 54A, 56A of the outer and inner walls 54, 56 
which are fastened together to interconnect the first and second units 48, 
50 in flow communication with one another. 
Referring to FIGS. 7-11, the vessel 12 defines the first pyrolysis chamber 
14 having an inlet 58 and the second oxidation chamber 16 connected in 
communication with the first pyrolysis chamber 14 and having the discharge 
outlet 42. The first chamber 14 in which the materials will be pyrolyzed 
receives the materials through the inlet 58 via operation of an automatic 
feeding system 59. The first chamber 14 of the vessel 12 for pyrolyzing 
materials is disposed in the first unit 48. The material, through 
pyrolysis, or burning in a starved oxygen atmosphere, is converted to a 
gas that exits the first chamber 14 by passing down through holes 60 in 
fire brick 62 formed in the bottom of the first chamber 14 and therefrom 
to the second chamber 16. 
The second chamber 16 receives the pyrolyzed materials from the first 
chamber 14 and, after oxidizing the pyrolyzed materials therein, 
discharges the oxidized materials therefrom through the discharge outlet 
42. The second chamber 16 has primary and secondary sections 16A, 16B for 
oxidizing materials in two successive stages. The primary section 16A is 
disposed in the first unit 48 of the vessel 12 between the first chamber 
14 and the tubular extensions 54A, 56A. The secondary section 16B is 
disposed in the second unit 50 of the vessel 12. 
The primary section 16A of the second chamber 16 contains a series of 
serpentine passages or tunnels 64, 66, 68 defined in a mass 70 of 
refractory material contained in the first unit 48. As the pyrolyzed gas 
passes down through the holes 60 in fire brick 62 formed in the bottom of 
the first chamber 14, it enters the center tunnel 64, which is plugged at 
one end, and passes therethrough in a rearward direction toward the rear 
of the first unit 48 to a rear manifold 72, then splits into two gas flows 
and reverses in direction to pass toward the front of the first unit 48 
through the opposite side tunnels 66, 68 (on the opposite sides of the 
plugged center tunnel 64) as it is being oxidized, and then to a front 
manifold 74 where the oxidized gas passes down to a lower tunnel 76, again 
reversing in direction, to pass towards and through the second unit 50. 
The refractory mass 70 has an upper exterior surface 70A which is exposed 
to the first chamber 14. The series or arrangement of serpentine passages 
64, 66, 68 formed in the refractory mass 70 define the primary section 16A 
of the second chamber 16 and provide communication with the first chamber 
14. The refractory mass 70 also is surrounded by the jacketed vessel 12 
and maintained in a heated condition at elevated temperatures by the 
heating produced in the first chamber 14 by the first heater units 18 and 
by the pyrolyzing and oxidizing of materials in the respective first and 
second chambers 14, 16. The heated condition of the refractory mass 70, in 
turn, causes heating and oxidizing of materials which come in close 
proximity to the exterior surface 70A thereof. By the provision of the 
refractory mass 70 and maintenance of its heated condition at elevated 
temperatures, the waste material in the first chamber 14 which comes in 
close proximity to or contact with the upper exterior surface 70A of the 
refractory mass 70 is being continuously heated from underneath by the 
refractory mass 70 which increases oxidation of difficult material present 
in the first chamber 14 and contributes to the substantially complete 
conversion thereof to the carbon-free residue ash. It should be noted here 
that in keeping with the principles of the present invention, other means 
for heating and maintaining the refractory mass at elevated temperatures 
can be employed, such as electrical heaters or the like (not shown) 
embedded in the refractory mass. 
The secondary section 16B of the second chamber 16 is located in the second 
unit 50. The oxidized gas from the primary section 16A of the second 
chamber 16 flows through the lower tunnel 76 in a direction toward the 
rear of the first unit 48, through the tubular extensions 54A, 54B, and 
into the secondary section 16B in the second unit 50. The secondary 
section 16B has a series of spaced air flow baffles 78 with offset 
openings 80 extending across the flow path of air through secondary 
section 16B. 
The heat exchanger 46 is also located in the second unit 50 above the 
secondary section 16B of the second chamber 16. The upper heat exchanger 
46 has the induction fan 26 connected at one end which operates to draw 
the gases from the first chamber 14 down through the fire brick 62 into 
the primary section 16A of the second chamber 16. The gases then flow 
through the tunnels 64, 66, 68 of the primary section 16A, back through 
the secondary section 16B of the second chamber 16, then up and forwardly 
through the center of the heat exchanger 46 to the center of the induction 
fan 26 which then forces the exhaust gas outwardly and rearwardly around 
and along the heat exchanger 46 for exiting through discharge outlet 42 
into a wet scrubber 82. The exhaust gas is virtually free of any pollution 
and the original material has been almost completely oxidized so that only 
a very small amount of fine minute dust or powder particles are collected 
in a particle separator (not shown). 
Referring to FIGS. 1, 7-9, and 14, there is illustrated a pair of heat 
generator assemblies 84 incorporated in the first chamber 14 of the 
apparatus 10. The heat generator assemblies 84 are mounted horizontally 
through the first chamber 14 and adjacent opposite side portions of the 
inner wall 56 of the casing 52. Each heat generator assembly 84 includes 
the first heater unit 18 and an elongated deflector structure 86 mounted 
adjacent to and along the electric heating elements 20 of the first 
heating unit 18. The first heater unit 18 is mounted to the vessel 12 and 
extends horizontally into the first chamber 14 between opposite ends 
thereof and along one of the opposite sides thereof. The first heater unit 
18 is powered by a power controller 87 which, in turn, is powered by an 
electrical power supply (not shown) and controlled by the computer-based 
control system 44 for producing heating of materials received in the first 
chamber 14 to cause pyrolyzing of the materials into gases. One suitable 
embodiment of the power controller 87 is a commercially-available unit 
identified as SSR2400C90 marketed by Omega Engineering of Stanford, Conn. 
The plurality of elongated electric heating elements 20 extend in 
generally parallel relation to one another and are constructed of 
electrically-resistive material operable for emitting heat radiation. The 
deflector structure 86 extends in circumferential relation partially about 
the electric heating elements 20 so as to deflect the heat radiation in a 
desired direction away from the electric heating elements 20 and from the 
adjacent side of the first chamber 14. 
Each of the second heater units 22 employed in the secondary section 16B of 
the second chamber 16 has substantially the same construction and 
configuration as the first heater unit 18 described above with one 
difference. The difference is that the electric heating elements 24 of the 
second heater unit 22 are distributed and spaced about the full circle 
instead of only about one-half of the circle. The second heater units 22 
are also powered by another power controller 87. 
Operation of Computer-Based Control System 
Referring to FIGS. 14-17, there is functionally illustrated the components 
of and the operative steps performed by the material processing apparatus 
10 under the monitoring and control of the computer-based central control 
system 44 for effecting optimal pyrolyzing and oxidizing of the materials 
therein to provide control of the hydrocarbon release rate in accordance 
with the present invention. FIG. 14 provides a functional block diagram of 
the material processing apparatus 10 illustrating the directions of 
interactions between the components of the apparatus 10 to maintain the 
target oxygen concentration and thereby control the hydrocarbon release 
rate. FIGS. 15A and 15B, taken together, depict a flow chart 88 of an 
exemplary sequence of software or program steps executed in the central 
control system 44 for controlling and directing the overall operation of 
the material processing apparatus 10. FIGS. 16A and 16B, taken together, 
depict another flow chart 90 of an exemplary oxygen-based control 
algorithm utilized by the software program in the central control system 
44 to carry out the proportioning of the air flow through the first and 
second chambers 14, 16 of the apparatus 10. While flow charts 88 and 90 
are believed to be substantially self-explanatory and readily understood 
by a person having ordinary skill in this art, certain of the features of 
the control system 44 with reference to the flow charts are described 
hereinafter. 
Basically, the material processing apparatus 10 operates through one cycle 
to thermally process, that is, to pyrolyze and oxidize, a predetermined 
batch of material, such as biomedical waste material, typically of widely 
varying energy values or contents. The central control system 44 functions 
to operate and regulate the material processing apparatus 10 during each 
batch processing cycle by controlling the operation of the first and 
second heater units 18, 22, the position of the air intake proportioning 
valve 31 and the speed of the induction fan 26. The central control system 
44, under control and direction of a software program stored in its 
internal memory, repetitively and at high speed, receives inputs, 
processes the inputs and generates outputs. The inputs received by the 
central control system 44 from the various temperature and gas sensors 32, 
34, 36, 40 contain information about the current states of the pyrolysis 
process occurring in the first chamber 16 and of the oxidation process 
occurring in the primary and secondary sections 16A, 16B of the second 
chamber 16. Proportional, Integral, Derivative (PID) control algorithms 
for regulating induction fan speed and proportioning valve position are 
contained in the software program. These algorithms are employed by the 
central control system 44 to process the inputted information by 
integrating the information into a logical sequence of decision steps and 
then generating an appropriate set of output instructions to ensure that 
the pyrolysis and oxidation processes and thus the hydrocarbon release 
rate continue at an optimum level. 
More particularly, the control system 44 is responsive to the temperatures 
sensed in the first and second chambers 14, 16 by temperature sensors 32, 
34 and in the coolant circulating through the channel 38 of the jacketed 
vessel 12 by temperature sensor 36. The control system 44 also is 
responsive to the proportion, or concentration, of a preselected gas, such 
as oxygen, sensed in the discharge gases by the gas sensor 40. The control 
system 44, in response to these various temperatures sensed and to the 
concentration of oxygen sensed, functions to control the position of the 
air intake proportioning valve 31 so as to adjust the ratio of, or 
proportion, the amount of primary air flow to the amount of secondary air 
flow through the first and second inlet valves into the first and second 
chambers 14, 16. Also, the control system 44, in response to these various 
temperatures sensed and to the concentration of oxygen sensed, functions 
to control the operation of the induction fan 26 via the fan speed 
controller 27 so as to adjust the amounts (but not the proportion) of 
primary and secondary air flows into the first and second chambers 14, 16. 
Referring to the flow chart 88 of FIGS. 15A and 15B, at initiation of a new 
batch processing cycle, the central control system 44 will first determine 
from the inputted information if the conditions existing in the first and 
second chambers 14, 16 are such as to allow the apparatus 10 to operate 
(as per diamond 92) and to allow adding of the new batch to the first 
chamber 14 of the apparatus 10 (as per diamond 94). If the answer to 
diamond 92 is "yes", then the components of the apparatus 10 are set into 
operation to cause an initial heating or warm-up of the chambers 14, 16. 
If the answer to diamond 94 is "yes", then the new batch is loaded into 
the first chamber 14 and a slow-start sequence is initiated during which 
the desired target level of oxygen concentration is temporarily increased 
and the hydrocarbon release rate is temporarily reduced. The slow-start 
sequence is employed to assure a stable operation of the apparatus 10 
during the start of a new cycle upon receipt of the new batch of feed 
material in the first chamber 14. Since it is not known what the energy 
content of the newly-introduced batch of feed material is, that is, 
whether it contains a large proportion of highly volatile material or not, 
the slow-start sequence will ensure that uncontrolled release of unburned 
hydrocarbons does not occur during this part of the new batch processing 
cycle. In essence, therefore, when the control system 44 is executing the 
slow-start sequence, it raises the target oxygen concentrations for a 
preset period of time as illustrated in the graph seen in FIG. 18. 
The overall objective is to control the hydrocarbon release rate so as to 
ensure avoidance of emission of harmful substances and to ensure that the 
residue ash is virtually carbon-free. During the pyrolyzing and oxidizing 
processing cycle of the apparatus 10, the required temperatures and 
correct primary and secondary air flows must be maintained in the first 
and second chambers 14, 16 in order to obtain these desired ultimate 
results. The inputs of oxygen concentration compared to a desired target 
(for example 6%) as per diamond 96 of the flow chart 90 of FIGS. 16A and 
16B and of temperatures in the first and second chambers 14, 16 compared 
to desired targets (for example, 300.degree. F. and 2000.degree. F.) as 
per blocks 98, 100 of flow chart 88 of FIGS. 15A and 15B are received and 
processed by the central control system 44 to control the position of the 
proportioning valve 31 to set the primary and secondary air flows and to 
control the speed of the induction fan 26 in order to maintain the 
pyrolyzing and oxidizing processes and thus the hydrocarbon release rate 
at optimum levels. For example, if the level of oxygen concentration 
sensed in the discharge outlet 42 is too high, then that means that 
insufficient pyrolysis is occurring in the first chamber 14. To rectify 
this condition, the ratio of the primary and secondary air inflows is 
changed by regulating the air intake proportioning valve 31 to increase 
the amount of air flow entering the first chamber 14 and to decrease the 
amount of air flow entering the second chamber 16. If the level of oxygen 
concentration sensed is still too high, then that means that the amount of 
air in both the primary and secondary flows needs to be decreased by 
slowing down the speed of the induction fan 26. If the elevated oxygen 
concentration condition were to persist, the excess air inflow will cool 
down the chambers below the target levels. The first and second heater 
units 18, 22 are employed to preheat the chambers 14, 16 and to ignite the 
oxidation process and also to raise the temperatures of the chambers 
whenever their temperatures decrease below the preset targets. 
The fan speed control algorithm and air flow proportioning algorithm also 
establish the rates at which corrective actions are taken in order to 
ensure that the pyrolysis and oxidation processes continue at an optimum 
level to ensure proper control of the hydrocarbon release rate. The rates 
at which the necessary corrective changes occur are higher when too little 
concentration of oxygen is sensed in the discharge gases than when too 
much concentration of oxygen is sensed. This is because too little 
concentration of oxygen indicates a more serious situation such being that 
inadequate oxidation is occurring and, therefore, potentially 
pollution-causing gases are being exhausted by the apparatus 10. 
Therefore, for example, the rate at which changes in fan speed and 
proportioning of primary and secondary air flows occur when an oxygen 
concentration deficit condition is sensed can be twice the rate at which 
the same changes occur when an oxygen concentration surplus condition is 
sensed. 
Interdependent control of the fan speed and the proportioning valve 
position based on oxygen concentration in the discharge gases is one of 
the key aspects for controlling the hydrocarbon release rate and thus the 
processing of materials in the processing apparatus 10. Using two separate 
PID algorithms, the fan speed and valve position are varied as the oxygen 
concentration in the discharge gases varies. Preferably, the target oxygen 
concentration level for the fan control PID algorithm is preset at 1% 
lower than the target oxygen concentration level for the proportioning 
valve PID algorithm. Thus, if the proportioning valve position is below 
100% air flow to the pyrolysis chamber 14, the speed of the fan is not 
permitted to be decreased by the fan control PID algorithm. Programming 
the control system 44 in such manner will ensure that maximum throughput 
is encouraged while maintaining stable operating conditions. The following 
examples will assist in gaining an understanding of how the two PID 
control algorithms relate to each other where the oxygen concentration 
target for the fan PID algorithm is set at 6% and for the proportioning 
valve PID algorithm is set at 7%: 
a) if the oxygen concentration level is sensed at 5%, then the fan speed 
will be increased and the proportioning valve position will be adjusted to 
decrease the air to the pyrolysis chamber 14. 
b) if the oxygen concentration level is sensed at 6.5%, then the fan speed 
will be increased and the proportioning valve position will be adjusted to 
increase air to the pyrolysis chamber 14. 
c) if the oxygen concentration level is sensed at 8%, then the fan speed 
will hold until the proportioning valve position is adjusted to increase 
air 100% to the pyrolysis chamber 14 and then the fan speed will decrease. 
Underlying the present invention is recognition by the inventors herein 
that the direct correlation or correspondence between the hydrocarbon 
release rate and the concentration of a preselected gas, preferably 
oxygen, in the discharge gases can be used to control the hydrocarbon 
release rate during operation of the apparatus 10. For the apparatus 10 to 
be able to accommodate feed materials of widely varying energy contents as 
is needed in most waste disposal applications, and certainly with respect 
to biomedical waste materials, the apparatus 10 must be operated with a 
hydrocarbon release rate that avoids generation and emission of unburned 
hydrocarbons. However, it is not possible to determine in advance the 
energy value or content of the batches of material which are fed into the 
apparatus 10 in order to be able to adjust the operation of the apparatus 
10 to arrive at the desired hydrocarbon release rate. The inventors herein 
recognized that due to the direct correspondence between the oxygen 
concentration in the discharge gases and the hydrocarbon release rate, if 
only the oxygen concentration is controlled and maintained at a desired 
target then automatically the hydrocarbon release rate is controlled and 
maintained at the desired optimum level. The inputs to the control system 
44 which are processed to control and maintain the oxygen concentration at 
the desired target include the temperatures in the first and second 
chambers 14, 16 and in the jacketed vessel channel coolant and the 
concentration of the preselected gas sensed in the discharge gases. These 
inputs are processed by the software program in the control system 44 to 
generate outputs which control the primary and secondary flows of air into 
the first and second chambers 14, 16 so as to proportion and to vary the 
respective amounts thereof and thereby adjust the hydrocarbon release rate 
occurring in the apparatus 10 so as to maintain the oxygen concentration 
in the discharge gases at the desired preset target which will correspond 
to the generation of substantially harmless discharge gases and production 
of substantially carbon-free residue ash. 
More particularly, if the hydrocarbon release rate begins to exceed the 
optimum level, this will result in the occurrence of an oxygen 
concentration in the discharge gases lower than the desired preset target. 
This deficiency will be detected by the oxygen sensor 40 in the heat 
recovery exhaust and transmitted to the control system 44. The control 
system 44 will then adjust the proportioning valve 31 to reduce the air 
flow into the pyrolysis or first chamber 14 and increase it to the primary 
section 16A of the oxidation or second chamber 16. As less oxygen is let 
into the first chamber 14, heat generation by pyrolysis reaction in this 
chamber is reduced. Since the first chamber 14 is surrounded by the 
coolant jacketed vessel 12, the surface of the waste materials therein 
will be cooled and thereby lower the hydrocarbon release rate to the 
optimum level. On the other hand, if the hydrocarbon release rate begins 
to go below the optimum level, this will result in the occurrence of an 
oxygen concentration in the exhaust which is greater than the desired 
target. The control system 44 will detect this condition via the oxygen 
sensor 40 and begin to adjust the proportioning valve 31 so that more air 
is fed into the first or pyrolysis chamber 14 and less air is fed into the 
primary section 16A of the second or oxidation chamber 16, increasing heat 
generation in the first chamber 14 and thereby increasing the hydrocarbon 
release rate back to the optimum level. It is seen, therefore, that the 
control system 44 is continuously adjusting the proportioning valve 31 to 
tend toward the optimum hydrocarbon release rate as evidenced by the 
sensed oxygen concentration being at or near the desired target. 
To maximize the throughput of the apparatus 10, the target oxygen 
concentration for the induction fan speed algorithm is modified with the 
change of pyrolysis and oxidation temperatures, as shown in FIGS. 17 and 
18. Essentially, the control system 44 encourages a maximum induction fan 
speed provided the oxidation temperature is at an adequate level. After 
the apparatus 10 begins processing a new batch of waste material or 
excessive low energy value or content waste materials are fed into the 
apparatus 10, the control system 44 will reduce the induction fan speed if 
it needs to maintain adequate oxidation chamber temperature. If the 
temperature in the pyrolysis or first chamber 14 drops below a 
predetermined minimum value, then the control system 44 turns on the 
heating elements 18 provided that the temperature in the oxidation chamber 
16 is adequate. As mentioned earlier, in order to encourage pyrolysis and 
oxidation of the heavier hydrocarbons in the first chamber 14, the 
refractory mass 70 forming the base of the pyrolysis chamber 14 is 
constantly heated by the gases flow through the tunnels therein defining 
the primary section 16A of the oxidation chamber 16. By heating this area 
and cooling the top and sides of the pyrolysis chamber 14 with the coolant 
jacketed vessel 12, pyrolysis and oxidation of the low volatility material 
is encouraged while runaway gasification of the volatile material is 
discouraged. 
Further, as the material in the pyrolysis chamber 14 is consumed, the 
control system 44 automatically adds more and more air to the pyrolysis 
chamber 14 to maintain the hydrocarbon release rate at the optimum level 
where the oxygen concentration sensed in the discharge gases will be at 
the desired target until the chamber 14 is provided with 100% of the total 
intake of air flow rate. This means that at the end of each batch 
processing cycle, the pyrolysis chamber 14 is, in effect, flooded with 
oxygen and actually functions as an oxidation chamber to thereby cause 
substantially complete oxidation of any carbon in the residue material 
remaining in the first chamber 14 and thus reduction to carbon-free 
residue ash. 
The use of oxygen as the concentration target gas in the discharge gases to 
provide the means to proportion and regulate primary and secondary air 
flows is preferred but not essential to the proper functioning of the 
apparatus 10. The concentrations of other gases such as carbon dioxide, 
instead of oxygen, could be sensed and measured. Further, although the 
present invention has been explained and illustrated in association with 
an induction fan 26 for drawing the air flows through the first and second 
units 48, 50 of apparatus 10, it should be appreciated by those skilled in 
the art that the invention is equally applicable to such a thermal process 
having forced air flows rather than induced. 
It is thought that the present invention and many of its attendant 
advantages will be understood from the foregoing description and it will 
be apparent that various changes may be made in the form, construction and 
arrangement of the parts thereof without departing from the spirit and 
scope of the invention or sacrificing all of its material advantages, the 
forms hereinbefore described being merely preferred or exemplary 
embodiments thereof.