Compact regenerative incinerator

A compact regenerative incinerator for incinerating an effluent includes a single vessel with two compartments separated by a partition. Each compartment includes an opening and a combustion chamber, and these are separated by a thermal storage medium. The incinerator also has a bypass system, which includes a bypass opening in the vessel and a bypass thermal storage medium separating the opening from the combustion chambers. Valving, which includes one or more flushed control valves, directs the effluent to flow into one of the compartment openings and directs the products of incineration to flow out of the other. The valving is also adapted to direct the effluent into the bypass opening while reversing the flow direction in the incinerator. A controller monitors effluent concentration, its temperature and that of the products of incineration, as well as rates of temperature change, and uses the resulting information to reverse the flow direction at times which optimize efficacy for differing levels of delivery of effluent. A purging system recirculates a portion of the products of incineration during purging, and pressure is regulated so that the purging occurs within a set period of time.

BACKGROUND OF THE INVENTION 
The present invention is related to regenerative incinerator systems, 
particularly to those for use in incinerating effluents containing 
volatile hydrocarbons. 
Various industrial processes, such as wood treatment, web offset printing, 
adhesive tape manufacturing and other coating operations, generate 
effluents containing volatile organic compounds, which may be toxic, 
photochemically reactive, or present an offensive odor, and whose 
concentrations may vary over time. Regenerative incinerators have been 
used to incinerate these waste vapors. Known regenerative incinerator 
designs include arrangements of cylindrical vessels containing a loosely 
packed material that serves as a thermal energy storage and transfer 
medium for gasses passing through it during the incineration process. 
Typical regenerative incinerators employ multiple vessels which are 
interconnected by way of ducts, which form a part of the combustion 
chamber. Such systems may be costly to fabricate and operate, as well as 
require large amounts of floor area to accommodate the multiple vessels. 
SUMMARY OF THE INVENTION 
In general, the invention features an improved method and apparatus for 
incinerating an effluent, such as gases containing vapors of volatile 
hydrocarbons. The compact regenerative incinerator includes a single 
vessel with an internal partition separating the vessel into two 
compartments. Each compartment includes an opening and a combustion 
chamber, and these are separated by a primary thermal storage medium. The 
combustion chambers preferably are interconnected through a swirl tube 
extending through a passage in the partition. The incinerator also has a 
bypass system, which includes an opening in the vessel and a bypass 
thermal storage medium separating the opening from the combustion 
chambers. Valving directs the effluent to flow into one of the openings 
and directs the products of incineration to flow out of the other. The 
valving is also adapted to direct the effluent into the bypass system 
while reversing the flow direction in the incinerator. 
The incinerator preferably includes a controller to monitor effluent 
concentration, its temperature and that of the products of incineration, 
as well as rates of temperature change, and to use the resulting 
information to establish the time at which to reverse the flow direction. 
This may be done so as to optimize the efficacy of the incinerator for 
differing levels of delivery of effluent, and may be based on a computer 
model of the incinerator. 
A purging system may be connected to the valving, and operate to 
recirculate a portion of the expelled products of incineration and direct 
them to purge one of the thermal recovery media and its associated 
combustion chamber prior to the reversing. An exhaust pressure balance 
damper regulates the pressure so as to perform purging within a set period 
of time. A portion of the products of incineration are recirculated to the 
exhaust fan before purging, so as to allow the fan to accelerate. 
Essentially identical burners for each combustion chamber may be fired in 
parallel and burn at essentially identical energy input levels, and a 
real-time average temperature may be used in controlling the burners. 
Liquid, ambient air, or other means may cool the exhaust fan if the 
temperature exceeds a predetermined value. The incinerator may include one 
or more flushed control valves. 
The single vessel design of the invention has a significant impact on 
installed cost of the incinerator, due to reduced material and labor costs 
in its fabrication, and the small amount of floor space required for its 
installation. This, in turn, permits flexibility in the site selection 
process. The control valves which manage flow through the incinerator are 
located in one cluster either adjacent to the vessel or directly below it, 
to simplify connection to the effluent source, and to further reduce 
required floor space. Because the vessel has a low surface area, heat loss 
to the surroundings is reduced, for a system having a given flow rate 
capacity. Further, the resulting low number of external connection points 
reduces the potential for leakage. 
The incinerator may accept effluent containing vapors at varying 
concentrations and flow rates, which may arise from one or more 
independent processes, while maintaining a high degree of thermal 
effectiveness. The split combustion chamber with swirl tube and parallel 
burners ensures that the effluent being treated uniformly reaches the 
proper incineration temperature and is held for the time duration required 
for thorough incineration of the effluent. The design of the swirl tube is 
such that the effluent is accelerated in speed and induced to swirl, 
resulting in a high amount of turbulence, which promotes more complete 
oxidation of the volatile organic compounds by stripping the products of 
combustion from the unburned hydrocarbons and allowing those hydrocarbons 
access to oxygen. The parallel burners allow for reduced gas consumption 
and prevent excessive amplitude of the individual chamber burning firing 
rates. The bypass system, purging system and double valves prevent leakage 
of untreated effluent from the incinerator, particularly during flow 
reversal. A second flush operation during valve changeover further 
improves leakage prevention The secondary mass of thermal storage medium 
adds heat to effluent brought into the vessel by way of the bypass system, 
preventing cooling of the effluent and improving clean up efficiency. An 
exhaust duct back-pressure valve allows for consistent and timely purging 
during flow reversal A "tee" damper allows for stabilization of the fan 
flow before flow reversal to prevent a reduction in flow of effluent 
during flushing. The exhaust fan is protected from excessive temperature, 
which might otherwise cause damage.

Referring to FIGS. 1-3, the compact regenerative incinerator of the 
invention 10 includes a cylindrically shaped insulated vessel 12, which is 
positioned vertically, and a cluster 14, which includes ductwork and 
valving and is located generally below and adjacent to the vessel, for 
controlling the direction of passage of the effluent 18 through the 
incinerator. A typical vessel may have an overall height of about 27 feet 
and an outer diameter of about 15 feet. A ladder 26, platform 24, and 
rungs 30 allow access to hatches 28, which allow for inspection and 
loading of the thermal storage media. 
An incinerator inlet duct 16 is connected to receive the effluent 18, which 
may include volatile organic compounds, from a process. Among the many 
compounds which may be incinerated are, for example, petroleum distillate, 
toluene, xylene, heptane, and methyl-ethyl ketone (MEK). The inlet duct 16 
is connected to two bottom vessel openings 32, 33 via first and second 
duplex inlet valves 34, 36. An exhaust duct 38 is connected to the two 
openings in the bottom of the vessel by first and second duplex exhaust 
valves 40, 42. An exhaust fan 20 is connected to the exhaust duct to expel 
treated effluent into an exhaust stack 22 for release into the atmosphere 
The output of the exhaust fan is also connected to an exhaust 
recirculation duct 44, which is connected to the inlet duct and further 
ducts (see FIG. 4), to provide a pressurized flow of treated gas for 
recirculation, sealing of closed valves and flushing of the thermal 
storage media prior to changes in flow direction. A bypass duct 46 is 
connected to the inlet duct via a bypass valve 74 and leads to a third 
opening 48 in the vessel wall. Two burners 50, 51 are also mounted in the 
vessel wall, and the vessel is mounted on stilts 52. 
Referring to FIG. 4, which schematically shows valves positioned for 
effluent flow into and upward through a first chamber of the incinerator 
and downward through and out of a second chamber, the exhaust 
recirculation duct 44 is also connected to a flush control valve 62, to a 
recirculation damper 64, and to slave flush valves 54, 56, 58, 60, 66 of 
inlet, exhaust, and first and second chamber flush valves 34, 36, 40, 42, 
70, 72. The flush control valve 62 is connected to a three-way valve 68 
(or "tee" damper), which is in turn connected to the exhaust duct 38 and 
the first and second chamber flush valves 70, 72. First and second chamber 
flush ducts lead to the two bottom vessel openings 32, 33. Make-up valves 
76, 78 are also provided to admit air into the bypass duct 46 and the 
exhaust duct 38. 
Referring to FIGS. 10-12, a flushed duplex valve, for example the first 
flushed duplex inlet valve 34, includes a pair of main blades 130, 132 
mounted on main shafts 138, 136, and a slave flushing valve blade 134 
mounted on a slave shaft 140. The main shafts are linked to the slave 
shaft by a linkage 142 (see FIG. 12), which opens the slave flush valve 
after the main valves are closed. 
Referring to FIGS. 1, 4, and 7-9, the vessel 12 is generally cylindrical in 
shape, with a rounded top 80 and bottom 82. A vertical dwarf partition 84 
bisects the vessel from its bottom to an elevation some distance below the 
top of the vessel, splitting the vessel into two chambers of equal size 
81, 83. This partition 84 is welded to the lower end of the vessel to 
provided an air-tight seal between the chambers. Primary grid-work 94, 96, 
forming a lower horizontal grating, is attached to the lower portion of 
the vessel, a short distance above its bottom, and to the partition 84 by 
brackets 98. The primary grid-work is made of a heat resistant steel such 
as a type 304 stainless steel, and supports first and second primary 
thermal storage media 100, 102, which may comprise a porous mass about 
eight feet deep of metal, ceramic, or any other material that is stable at 
the incineration temperature. Preferred thermal storage media are 
Flexisaddle chemical stoneware available from Koch Engineering of Akron, 
Ohio, with two-inch size utilized on the bottom twelve inches and one-inch 
size utilized for the remainder of the beds of media 100, 102. Secondary 
grid-work 104, 106 is similarly horizontally mounted in the vessel and is 
positioned near the top end of the partition to support a collective 
secondary thermal storage medium made up of first and second secondary 
thermal storage media 108, 110, which are about two feet deep. The 
secondary media may be of the same type as employed for the primary media, 
with the bottom six inches of the secondary beds formed of the two-inch 
size. Of course, other primary and secondary bed depths could be used, 
depending on the requirements of the particular system. The space between 
the top of the primary thermal storage media and the upper grating 
(secondary grid-work 104, 106) forms the combustion zone of the 
incinerator 10, which is separated into first and second combustion 
chambers 90, 92. The spaces below the first and second primary storage 
media, respectively, form first and second thermal recovery chambers 86, 
88. 
The vertical partition 84 (FIGS. 7-8) includes two metal sheets 119, which 
may be made of type 304 stainless steel, with spacers 120 (FIG. 8) between 
to maintain a gap of approximately 2 inches and to provide adequate 
stiffness without corrugation, thus presenting a minimum surface area. 
These sheets 119 incorporate expansion joints 122 at each end and their 
outer surfaces are insulated with 1/2 inch of ceramic insulation, such as 
Fiberfrax.RTM., 118 which is rated for continuous service to 2300.degree. 
F. A cooling fan 182 (FIG. 4) feeds a manifold mounted across the bottom 
of the vessel and aligned with the partition 84, which serves as a 
distribution system for cooling air. The cooling air enters at the bottom 
of the partition and flows vertically at a velocity of approximately 1000 
feet per minute (FPM) until the flow is split (FIG. 9) to go around a 
swirl tube 112, at which point the velocity increases. 
The swirl tube 112 is mounted through a hole in the partition, somewhat 
below the secondary grates 104, 106. The swirl tube 112 is similar to the 
vertical partition in that it also is of a double walled construction with 
cooling air circulated between its walls. The hot side surfaces (inner and 
outer) of the swirl tube 112 are insulated with the Fiberfrax.RTM. blanket 
and a spiral baffle 116 is mounted between the walls to maintain 
separation and provide high cooling air velocity. Cooling air enters at 
the intersection of the swirl tube 112 and the vertical partition and 
flows horizontally toward the ends of the swirl tube. At the ends of the 
swirl tube, the cooling air passes through a series of holes in its outer 
wall and into a collection annulus from which the air is directed to the 
secondary thermal storage media support grid framework. 
As is shown in FIG. 7, support for the upper media grid-work 104, 106 is 
provided by brackets 98 attached to the Vertical partition 84 across the 
center of the vessel, brackets 98 attached to the sidewall of the vessel 
and beams 114 which minimize the unsupported span. The beams 114 are 
rectangular tubes, which like the partition 84 and swirl tube 112, are 
insulated with a Fiberfrax.RTM. blanket and have cooling air directed 
through them. The cooling air for these beams is the spent air from the 
swirl tube, which enters the beam tubes from the collection annulus and 
travels to the outer wall where the beams are supported. The air moves 
through the beam tubes at high velocity, and is exhausted by way of 
flexible tubes which penetrate the shell of the vessel 12. This air can be 
either vented to atmosphere through a vent valve 184, or collected via a 
cooling make-up valve 186 for use as make-up air in the process. 
As stated above, a preferred insulation for protection of metal structures 
in the high temperature section is Fiberfrax.RTM. Durablanket.RTM. ceramic 
fiber insulation. (Fiberfrax.RTM. and Durablanket.RTM. are U.S. registered 
trademarks of the Carborundum Company, of Niagara Falls N.Y.). A suitable 
specific grade selected for use is the HP-S which is high strength and has 
low shrinkage. This material has a continuous use limit of 2300.degree. F. 
and a melting point of 3200.degree. F. 
The secondary media support grid-work 104, 106 is similar to that used for 
the primary heat exchange media except that it is made of a high creep 
strength alloy, such as type 309 stainless steel, as it is subjected to 
higher temperatures. The loading for the secondary grid-work is relatively 
low and with the air cooled support structure below the grid-work 
providing a maximum free span of approximately 1/4 of the vessel diameter, 
the grid-work will support the media even at higher excursion 
temperatures. To protect the grid-work from direct flame or high infrared 
radiation, a 0.010" coating of Fiberfrax.RTM. refractory material is 
applied by spray painting or dipping. This coating has the same continuous 
use temperature limits as the insulation used on the vertical partition, 
swirl tube and grid support beams. 
Referring to FIG. 13, the vessel 12 and its associated flow control valving 
15, are monitored by sensors 200-254 associated with the functional 
components of the vessel as shown. The variables sensed by these sensors 
are presented in table 1. The sensors are connected to a 
microprocessor-based controller 170 by return lines 172, which may be a 
field buss, and the controller, in turn, is connected to the flow control 
valving 15 by control lines 174, which may also be served by the same 
buss. A multiple channel recorder is used to record temperatures and other 
system variables and to maintain operational records for the appropriate 
regulatory agencies as well as for use in trouble-shooting the system. 
TABLE 1 
______________________________________ 
DESIG- SYM- 
NATOR BOL VARIABLE SENSED 
______________________________________ 
200 BF1 BURNER FIRING RATE #1 
202 BF1 BURNER FIRING RATE #2 
204 CO CARBON MONOXIDE MONITOR 
206 FCA COOLING AIR FLOW RATE 
208 FCW COOLING WATER FLOW RATE 
210 FRI FLOW RATE OF EFFLUENT 
AT INLET 
212 OX1 OXYGEN #1 MONITOR 
214 OX2 OXYGEN #2 MONITOR 
216 PBP BACK-PRESSURE FLUSHING LOOP 
218 PCA COOLING AIR PRESSURE 
220 PDS SWIRL TUBE PRESSURE 
DIFFERENTIAL 
222 PDT TOTAL INCINERATOR PRESSURE 
DIFFERENTIAL 
224 PEE EXHAUST PRESSURE AT EXIT 
226 PEI EXHAUST PRESSURE AT INLET 
228 SCE SOLVENT CONCENTRATION AT EXIT 
230 SCI SOLVENT CONCENTRATION AT INLET 
232 TC1 TEMPERATURE COMBUSTION 
CHAMBER #1 
234 TC2 TEMPERATURE COMBUSTION 
CHAMBER #2 
236 TCA TEMPERATURE COOLING AIR 
AT INLET 
238 TCE TEMPERATURE COOLING AIR 
AT EXIT 
240 TEE TEMPERATURE EFFLUENT AT EXIT 
242 TEI TEMPERATURE EFFLUENT AT INLET 
244 TM1 TEMPERATURE OF MEDIA #1 
NEAR BOTTOM 
246 TM2 TEMPERATURE OF MEDIA #1 
NEAR TOP 
248 TM3 TEMPERATURE OF MEDIA #2 
NEAR BOTTOM 
250 TM4 TEMPERATURE OF MEDIA #2 
NEAR TOP 
252 TSM TEMPERATURE IN AREA ABOVE 
SECONDARY MEDIA 
254 ZCV VALVE POSITION INDICATOR (ALL 
CONTROL VALVES) 
______________________________________ 
In operation of the compact regenerative incinerator of the invention (see 
FIGS. 4, 13), a stream of effluent consisting typically of air and some 
quantity of volatile organic compound which cannot be directly released to 
atmosphere is drawn at a suitable flow rate (such as 120000 SCFM) from the 
inlet duct 16 via the first inlet valve 34 into the lower end of the first 
thermal energy recovery chamber 86, and passes vertically upward through 
the first primary thermal storage medium 100. During this passage, the 
temperature of the effluent is raised by means of convective heat transfer 
of thermal energy from the thermal storage media 100, with a reduction in 
the temperature of the these media. Upon exiting from the thermal storage 
media 100, the effluent is heated additionally to the desired incineration 
temperature by means of a first burner 50 firing into the first combustion 
chamber 90. At this point the majority of the effluent enters the swirl 
tube 112, which passes through the vertical partition 84 between the 
chambers 81 and 83. The partition and swirl tube assure that the effluent 
being treated uniformly reaches the proper incineration temperature and is 
held for the required time duration before entry into the second primary 
thermal storage medium 102 where the stream temperature is subsequently 
reduced. As the effluent enters the swirl tube, its velocity increases 
resulting in the stream becoming very turbulent which in turn aids in the 
complete incineration of the volatile organic compounds in the effluent. 
To assure that effective turbulence is maintained, the system flow may be 
limited to no less than thirty-three percent of the design flow rate. The 
swirl tube pressure differential is therefore continuously monitored by 
the swirl tube pressure differential sensor 220 (FIG. 13), and the 
resulting data is analyzed by the controller 170, which may direct the 
recirculation damper 64 to open and admit a sufficient quantity of 
recirculation air to maintain the minimum flow. 
A small portion of the heated effluent will bypass the swirl tube and cross 
the partition by flowing up through the first secondary thermal storage 
medium 108 positioned above the combustion chamber 90 and into the 
secondary combustion chamber 111 where it will remain for an additional 
period before flowing into the second combustion chamber 92 via the second 
secondary thermal storage medium 10. From the second primary combustion 
chamber 92, the treated effluent passes vertically downward through the 
second primary thermal storage medium 102, where heat energy is removed 
from the stream and stored in the medium for subsequent use by the 
incineration process to reduce the fuel usage. Upon exiting the second 
thermal energy recovery chamber 88, through the opening 33, the treated 
effluent passes through the second exhaust valve 42 and is exhausted to 
atmosphere via the exhaust duct 38, fan 20, and stack 22. The system 
exhaust fan 20 is located in such a position as to maintain a pressure 
within the system which is lower than atmospheric, thus preventing 
accidental release of untreated effluent. 
The flow through the thermal storage media results in a continuously 
changing level of energy potential (average temperature) with one thermal 
storage chamber cooling down as the other is increasing in temperature. At 
some point in time the flow direction must be reversed to recover the 
stored thermal energy. In the conventional regenerative system, this 
reversal occurs on a fixed time cycle basis which in turn places a 
restriction on the range of solvent loadings usable for a specific design. 
In the compact regenerative incinerator system of the invention, the 
length of time between flow reversal cycles is variable, which allows for 
adjustment of the heat recovery effectiveness corresponding to the solvent 
loading of the effluent to be treated and consequently optimization for 
these varying conditions. A typical time between reversals may be one and 
one-half to two minutes; however, the exact moment in time at which the 
reversal sequence is initiated is determined by real time analysis in the 
controller 170 of system variables such as air flow rate, solvent 
concentration of effluent, temperatures, burner firing rate, damper 
positions, and carbon monoxide and oxygen levels. 
These system variables have different effects on the controller's 
determination of optimum time between reversals. The air volume flow rate, 
as measured by the inlet flow rate sensor 210, has the most dramatic 
effect on the time rate of change of the energy level in the thermal 
storage media 100, 102, and therefore has the largest effect on optimum 
reversal timing. A higher flow rate will reduce the time required to raise 
the first or lower the second primary thermal storage media average 
temperatures. In a fixed schedule incinerator, this increased flow rate 
would reduce the temperature differences from the entries to the exits of 
the media 100, 102 to inefficient levels before the end of a cycle. In 
high flow rate conditions, therefore, the controller 170 will operate the 
flow control valving 15 to shorten the cycle, thereby providing for 
efficient thermal exchange. 
The solvent concentration by volume in the effluent, as monitored by the 
inlet solvent concentration sensor 230, is also important, since it is 
proportionally related to the exothermic temperature rise of the effluent 
being treated. In an ideal situation, the temperature of the effluent at 
the exit of the preheat media bed, plus the exothermic temperature rise, 
would equal the control temperature required for the desired hydrocarbon 
destruction effect. When the solvent concentration rises, however, the 
oxidation process releases a larger amount of energy and quickly heats all 
exposed components, including the partition 84, swirl tube 112, beams 114, 
upper media grid-work 104, 106 and the upper media 108, 110. If this 
process were allowed to continue for too long, a dangerous 
over-temperature condition would occur. As solvent concentrations rise, 
therefore, the controller 170 will operate the flow control valving 15 to 
shorten the cycle, in order to protect or to limit the temperature to 
which the components would be exposed. 
The constraints of the system define a minimum cycle time value, however, 
below which the controller 170 will not shorten the cycle. Once this point 
is reached, recirculation air is added by opening the recirculation valve 
64 to increase the mass flow and reduce the solvent concentration and 
hence the temperature rise. Should this be insufficient, fresh make-up air 
at ambient temperature is introduced directly into the vessel 12 in place 
of the blend of recirculated air, through make-up valve 76. 
There are also concentration levels below which the energy provided by the 
effluent oxidation is insufficient to raise the temperature high enough to 
completely destroy the volatile organic compounds (VOC). At these levels, 
the burners must be fired in order to maintain the effluent in the 
combustion chambers at the required temperature for a sufficient duration. 
Multiple combustion chamber temperature sensors, such as thermocouples, 
232, 234 are placed within each combustion chamber, and these are averaged 
to control the parallel burners 50, 51. Media temperature sensors 244, 
246, 248, 250 are placed at the entry and exit of each of the thermal 
energy storage media beds to measure the dynamic rate of change of stored 
energy. This information, along with the effluent inlet and outlet 
temperatures, as measured by the inlet effluent sensor 242 and the exit 
effluent sensor 240, is used in calculating the system heat exchanger 
effectiveness on a real time basis, and in determining (based on rate of 
change) when the flow direction change is to be made. 
The amount of thermal energy (natural gas) input into the system by the 
burners is also continuously monitored by burner firing rate sensors 200, 
202 and is tracked on a real time basis by the controller 170. During any 
given operating cycle, the preheat temperature of the effluent going into 
the combustion chamber is continuously decreasing because the energy level 
of the thermal storage media is diminishing, so the burners are adjusted 
to provide the extra thermal energy required to incinerate the effluent. 
To minimize fuel usage, therefore, the cycle time between flow reversals 
is adjusted to minimize the average firing rate when the effluent 
concentration is low enough to require burner firing. 
The regenerative incinerator of the invention may thus accommodate 
concurrently changing flow rates and solvent concentrations. The 
controller 170 calculates the appropriate cycle length, burner firing 
level and, if necessary, allows for recirculation or make up air. These 
operations can be performed with the controller programmed to optimize 
heat recovery effectiveness, based on a computer model for the parameters 
of the particular system. At a high volume flow rate with a low solvent 
loading the energy recovery is thereby maximized for optimum fuel usage. 
Conversely, at low volume flows and high solvent loadings, a reduced heat 
recovery level is provided to prevent a destructive over-temperature 
situation. 
The incinerator of the invention provides a significant advantage over a 
fixed time system. This is in part because at any specific effluent flow 
rate and time between flow reversal cycles, the average heat exchanger 
effectiveness of the thermal storage media system is a fixed value. This 
means that for a fixed time system the maximum effectiveness must match 
the projected maximum solvent loading to prevent an over-temperature 
situation. A fixed time system would therefore suffer from ineffectiveness 
during that portion of its operation where the process did not operate at 
maximum loading. The incinerator of the invention, on the other hand, can 
adjust the cycle time and/or the mass flow (while possibly adding 
recirculation air or fresh make-up air) to match the exothermic energy 
release without exceeding safe operating temperature limits at high 
solvent concentrations, or using excessive natural gas at low solvent 
concentrations. 
Carbon monoxide is monitored by the carbon monoxide sensor 204 as it is 
generally considered a good measure of the clean-up efficiency of an 
incinerator, and monitoring of the output CO is required in many 
geographical locations. Should the CO level exceed a predetermined maximum 
level, the control system will increase the minimum average temperature or 
adjust the timing cycle to reduce the average output CO concentration. 
The percentage of oxygen in the effluent stream must be maintained above 
some minimum value to assure complete combustion of the hydrocarbons. The 
oxygen level is therefore monitored by the oxygen level sensors 212, 214 
and should its value go below a preset standard, the fresh make-up air 
damper 76 is opened to allow fresh air into the system. If a low oxygen 
situation occurs, it would tend to occur while some degree of 
recirculation is being employed. In this situation, make-up air is 
introduced and the recirculation is reduced to maintain a balanced system 
flow. The timing cycle is also adjusted, to compensate for introduction of 
the cooler fresh air. 
The solvent level at the exit of the incinerator may also be directly 
measured, by an exit solvent concentration sensor 228. This provides the 
controller and operators with a direct measurement of the operating 
clean-up efficiency of the incinerator. 
To enable the control algorithm to make logical decisions concerning the 
operation of the system, the position of all control dampers or valves is 
also monitored 5 by the valve position indicators 254. For those dampers 
which are modulated somewhere between open and shut, the specific position 
is reported. Knowing the status and applying the rationale of a decision 
tree, the control algorithm can select the most effective or efficient 
course of action. 
In addition to establishing the flow reversal, the microprocessor-based 
controller 170 functions as a safety system which modulates the bypass 
valve 74, recirculation valve 64 and make-up air damper valves 76, 78 on a 
priority basis to protect the critical components from excessive 
temperature. The temperature in the area above the secondary media is 
monitored as well, to assure that effluent passing through the bypass 
system will be adequately preheated. The full control system also contains 
the normal complement of safety related devices such as a flam safeguard 
and high temperature limit switches. 
The cooling air sensors 206, 218 monitor proper operation of the cooling 
air for the air cooled portions of the system, and the cooling water 
sensor 208 similarly monitors the cooling water, which will be described 
in more detail below. The pressure at the inlet is measured with an inlet 
exhaust pressure sensor 226, and the controller 170 maintains this 
pressure at a predetermined value, generally below atmospheric pressure, 
so as to assure that adequate draw is provided from the process, which may 
include multiple sources of effluent. The pressure at the outlet is 
measured by an exit exhaust pressure sensor 224 placed after the exhaust 
back-pressure valve 43, in order to detect possible blockages or other 
exhaust flow restrictions. A total incinerator pressure differential 
sensor 222 provides a secondary, or backup, indication of flow through the 
system. 
Referring to FIGS. 4 and 5 (note timing letters in FIG. 5), the process for 
flow reversal (labelled "SHIFT" in FIG. 5) is accomplished by use of a 
precisely timed sequence of control valve position changes, which assure 
uninterrupted flow from the process while preventing the escape of 
untreated effluent to the atmosphere. In describing the actual sequence, 
which may extend over a time interval of about fifteen seconds, it is 
assumed that at the start of the cycle the untreated effluent is entering 
the first recovery chamber 86, and the treated gasses are exiting from the 
second recovery chamber 88. This state corresponds to the valve positions 
and flow arrows in FIG. 4, and to the steady state portion of phase 1 of 
the first cycle in FIG. 5. 
At initiation of the changeover (A in FIG. 5), the bypass valve 74 opens 
(A-B) to route the untreated effluent (150) through the bypass duct 46 to 
the secondary combustion chamber area 111 at the top of the incinerator 
vessel where it is heated by passage through the secondary thermal storage 
medium, 108, 110, exiting into the primary combustion chambers 90, 92. The 
bypass system is provided to maintain continuous uninterrupted flow of the 
untreated effluent into the incinerator without release of untreated 
effluent into the environment during reversal of flow direction through 
the primary thermal storage media. During bypass, the untreated effluent 
is brought from the bypass duct 46, through the secondary combustion 
chamber 111, to the main combustion chamber area 90, 92. 
During that period in time when the untreated effluent is being brought 
into the vessel 12 by way of the bypass system, it is of a significantly 
lower temperature because it has not passed through the primary thermal 
storage media. To prevent cooling of the high temperature effluent in the 
combustion chamber and the subsequent reduction in clean-up efficiency, 
the effluent brought in by way of the bypass duct 46 is made to pass 
through a secondary mass of thermal storage medium 108, 110 where its 
temperature is elevated before entering the combustion chamber. The 
quantity of thermal storage medium used in the bypass load leveling 
configuration is no greater than that required to assure the effluent 
temperature is maintained above some designated value until completion of 
the changeover cycle. It is noted that the energy level of the secondary 
thermal storage media 108, 110 is restored by normal convective heat 
transfer and by radiation from the combustion chambers 90, 92 and various 
surfaces within the vessel 12, during normal operation. Once preheated, 
the effluent from the bypass duct 46 passes into the main combustion 
chamber area 90, 92, and mixes with that which is simultaneously being 
driven from the primary thermal storage media and is in turn heated to the 
required temperature for destruction prior to being exhausted. 
With bypass established (B of FIG. 5), the flow of untreated effluent (152) 
into the recovery chamber 86 is stopped by closing the first inlet valve 
34, and the first flush valve 70 is opened to permit previously treated 
recirculation air to enter the chamber 86 through opening 32 and flow for 
such a time duration (B-F) as to assure that no untreated effluent remains 
within the first primary thermal storage medium 104. During the flushing 
period, which may extend over a period of about ten seconds, flow of 
treated effluent (154) continues uninterrupted from the second recovery 
chamber and the untreated gasses (150) remain directed into the vessel 
through the bypass duct 46. Once the flushing is completed, the first 
flush valve 70 closes (E-F), the exhaust valve 40 for the first recovery 
chamber opens (E-F) with the subsequent closure (F-G) of the exhaust valve 
42 for the second recovery chamber. To assure that there is no 
cross-contamination, as second exhaust valve 42 closes (F-G), its 
associated chamber flush valve 72 opens and remains open until that 
exhaust valve 42 is fully closed and the alternate valve is fully open (H, 
156). Following this short flushing, the second inlet valve 36 opens (G-H) 
allowing flow of untreated effluent into the second chamber and the bypass 
valve 74 closes, completing the flow reversal cycle (H). 
Inadvertent release of untreated effluent into the environment at any time 
the flow direction control valves change position is of prime concern. To 
minimize that potential, sequential valve movements are not executed until 
completion of the previous operation is proven by limit switch. 
Referring to FIG. 4, it is noted that at the initiation of the thermal 
storage media flow direction changeover cycle, the system experiences a 
temporary increase in flow volume rate due to the additional air brought 
into the system to dilute the untreated effluent in the thermal storage 
media. Because acceleration of both the exhaust fan and the air volume are 
limited by inertia, the system flow rate is preferably allowed to 
accelerate to the anticipated value before the changeover cycle begins to 
prevent a momentary reduction in flow into the incinerator while the fan 
accelerates. 
Upon receiving the signal that the changeover is imminent, the flush 
control valve 62 opens to a predetermined position at a rate which is less 
than the exhaust fan acceleration rate. During this period the flushing 
airstream is directed by the "Tee" damper position to the clean exhaust 
allowing the exhaust fan to accelerate. When the system volume has reached 
the desired flow rate and has stabilized, the flush damper is opened 
simultaneously with the shift in position of the three-way valve 68 and 
closure of the subservient flush valve 66. At completion of the changeover 
cycle, the dampers resume their original position to await the next cycle. 
It is noted that the flushing air stream need not come from the 
incinerator exhaust, but may come from another source. 
The changeover cycle timing is predicated on the flushing operation being 
completed within a specific time period. To make this possible the flow 
rate for the flushing gasses must be held constant regardless of what the 
effluent flow rate is. This is accomplished by monitoring the 
back-pressure in the exhaust duct with a back-pressure flushing sensor 
216, and maintaining it at a constant level with the exhaust pressure 
balance valve 43. As a result, the pressure in the flush duct is similarly 
held constant. With this arrangement the flush control damper setting can 
be established without concern for total system flow rate or the amount of 
air being consumed by the primary damper sealing system. 
The temperature management system for the compact regenerative incinerator 
system of the invention includes mounting of separate burners, such as a 
Kinemax natural gas-fueled burner available from Maxon Corporation of 
Muncie, Indiana, in the walls of the vessel 12 so as to fire into each of 
the primary combustion chambers to provide the additional heat energy 
needed to achieve the desired minimum incineration temperature. Although 
these burner assemblies 0 and 51 are physically located to fire into 
separate chambers 90 and 92, they are preferably fired in parallel as if 
they were a single burner. To assure an equal firing rate from each 
burner, the natural gas and combustion air piping 160, 162, 163 to each 
burner 50, 51 is exactly the same length, being of the same size and 
having the same number of elbows. This allows for utilization of a single 
gas train 164 to supply both burners with the required fuel and air 
mixture. For safe operation, the flame of both burners is monitored 
simultaneously by a single, dual input, flame safeguard unit which will 
alarm if any abnormal condition appears at either burner. In one 
embodiment of the invention, the design operating temperature is 
1500.degree. F. and one can expect temperature excursions which could 
potentially reach 1800.degree. F. 
The temperature sensors 232, 234 in each of the primary combustion chambers 
90, 92 monitor the temperature therein. Since dwell time at temperature is 
a key factor in the effective destruction of volatile organic compounds, 
the resulting signal is sent to the controller 170, which, in turn, 
calculates the real time temperature average and adjusts the burner firing 
rate accordingly. This arrangement is advantageous because it accurately 
maintains the desired average temperature, which is generally dictated by 
environmental quality regulations, while at the same time accounting for 
the heat energy released by the effluent being treated. This operating 
configuration will minimize the potential for excessive amplitude of the 
individual chamber burner firing rates, while firing the burners less 
frequently and with greater uniformity and ultimately reducing the natural 
gas consumption over time. 
Use of the parallel burner system is considered an acceptable arrangement 
by most insurance underwriters and governmental agencies. In situations 
where local codes may require that each burner be equipped with its own 
gas train, flame safeguard and temperature control, the temperature sensor 
mounted in the chamber into which the burner is firing would provide a 
control signal through the controller. With this configuration, the 
desired reaction temperature is assured before effluent passes to the 
other chamber. 
Referring to the valve structures of FIGS. 10-12, the control valve system 
for management of the operation of the incinerator must form a tight and 
complete seal to prevent flow of untreated effluent directly to the system 
exhaust. This is mandated by the fact that the valves must seal against 
the pressure drop across the entire incinerator system because both the 
duct 16 transporting the untreated effluent to the incinerator and the 
duct 38 carrying the treated effluent to the exhaust fan 20 are connected 
at a common point where they enter the base of the vessel 12. To assure 
that there is no leakage, the five valve systems 34, 36, 40, 42, 71, which 
control the flow direction into and out of the energy recovery chambers 
employ a flushed duplex design. 
When the main blades 130, 132 of these valves are closed, the linkage 142 
opens the slave flushing valve blade 134 to tangentially introduce 
pressurized flushing air, of a pressure higher than that exerted on the 
main blades, into the space between the main valve blades when they are in 
the closed position. The linkage that performs this function is a 
spring-loaded progressive linkage, which first closes the first main 
blade, then the second, and once these are closed, opens the slave blade. 
In the closed position, each main valve blade 130, 132 will seat against a 
gasket surface 137 to minimize potential for leakage, and any leakage will 
cause flushing air to be leaked, as opposed to untreated effluent. No 
other control valves require the flushed duplex design since leakage at 
those locations cannot result in the release of untreated effluent. It is 
noted that the flush valve system 71 includes a subservient flush valve 66 
as do the other duplex valves, but these valves 70, 72, 66 are controlled 
independently by the controller, rather than linked by a linkage. 
The system exhaust fan 20 is limited by its construction to a temperature 
generally below the potential achievable within the vessel 12. The system 
exhaust temperature is continuously monitored and in the event that the 
temperature exceeds an established limit, a protection system uses a 
multiple level priority structure to evaluate and determine the course of 
action. Potential courses of action include but are not limited to those 
available for heat exchanger effectiveness control--e.g., direct addition 
of ambient air to the exhaust stream to reduce the temperature, or the use 
of evaporative cooling system, which consists of a number of water spray 
nozzles 180 mounted on a manifold which in turn is placed in the exhaust 
duct 38 before the fan inlet or in the area directly below the thermal 
storage media. Temperature of the exhaust air is reduced by absorption of 
the thermal energy in the process of phase change from liquid water to 
water vapor. With a latent heat of vaporization of approximately 1000 BTU 
per pound of water, the cooling potential is very high. It should be noted 
that if the spray nozzles are placed under the thermal storage media 
chambers, a separate manifold would be employed for each chamber. The 
evaporative cooling system is useful in protecting the valving and exhaust 
fan from over-temperature damage but should not be operated during the 
inlet cycle, since that has the potential of cooling the effluent at a 
rate which may exceed the burner recovery rate. This, in turn, could 
result in incomplete incineration of the effluent. 
The evaporative cooling is an important safety feature, as it allows for 
cooling of the fan without stopping it, while providing time for orderly 
system shutdown. Stopping of the fan during operation of the incinerator 
could lead to an excessive or dangerous solvent concentration at the 
source of the effluent. 
FIG. 6A shows the temperature profile of the first primary thermal storage 
medium 100, for a typical cycle from the top to the bottom at one foot 
intervals. As would be expected, the temperature of the media layer 
closest to the combustion chamber is the highest. This overall temperature 
profile shifts downward in temperature by a few tens of degrees as the 
medium preheats the effluent (left portion of FIG. 6A, corresponding to 
phase I of FIG. 5) and increases by the same amount while heat is being 
recovered (right portion of FIG. 6A, corresponding to phase 2 of FIG. 5). 
Referring to the media exit temperature profiles of B, the intent of the 
secondary thermal storage media 108, 110 is only to provide preheating 
during the short duration of the flushing cycle when untreated effluent is 
being brought into the vessel 112 through the bypass duct 46. Because this 
layer is of a much smaller mass than that of the primary thermal storage 
media 100, 102, the decay in air temperature exiting the media is 
considerably faster than for the full size bed and extended running in the 
bypass mode will impact the overall heat exchanger effectiveness. This is 
clear from the rather evident difference between the slope of the air 
temperature out curves for the primary flow (dotted line) and that of the 
secondary flow. Based on the sixty second time line for the primary media, 
the average heat exchanger effectiveness is 92.7%. The same average is 
matched over an eighteen second time span in the secondary media, which 
happens to coincide with the time for flushing and valve switching, with a 
couple of seconds to spare. 
Other embodiments are within the following claims.