Fluid treatment method

The subterranean treatment apparatus and methods disclosed herein are useful for treating various waste streams, including municipal and industrial streams. The disclosed apparatus and methods are particularly useful in determining and controlling the temperature of the reaction zone in a deep well reaction apparatus while avoiding fouling of thermocouples and permitting easy service and replacement. In the disclosed embodiment, a fluid quiescent zone is created in the heat exchanger of the treatment apparatus located within the reaction zone and the temperature is used to control the system by operation of the heat exchanger or control of the C.O.D. of the influent.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to improved subterranean fluid treatment apparatus 
and methods for treatment of various materials, including municipal and 
industrial waste streams. More particularly, the present invention relates 
to downhole or deep well reaction apparatus and methods for reactive 
treatment of fluid waste streams, including municipal sludge and 
industrial waste. 
2. Description of the Prior Art 
Above ground wet oxidation systems have been in use for several years for 
the treatment of municipal sludge received from a sewage treatment process 
with limited success. The above ground wet oxidation systems use high 
pressure and heat to initiate the wet oxidation reaction, however, the 
apparatus is not energy efficient and results in only partial oxidation of 
the sludge; see, for example, U.S. Pat. Nos. 2,665,249 and 2,932,613. 
Further, because the extreme pressures must be generated by a piston, the 
apparatus is subject to failure. The above ground wet oxidation processes 
have not, therefore, replaced the traditional methods of treatment of 
municipal sludge, which includes aerobic and anaerobic treatment, 
settling, dewatering, drying, incineration, etc. 
Various downhole or deep well fluid treatment systems have been proposed by 
the prior art, however, the first successful deep well reaction apparatus 
was built by the assignee of the present application based upon the 
disclosure in U.S. Pat. No. 4,272,383 of Dr. McGrew, entitled "Method and 
Apparatus for Effecting Subsurface, Controlled, Accelerated Chemical 
Reactions", which is assigned to the assignee of the present invention. A 
downnole fluid treatment system generally includes a plurality of nested 
pipes which extend vertically into the ground a predetermined depth to 
establish the desired pressure for treatment of the waste at the reaction 
temperature. The fluid to be treated is pumped into the vertical reaction 
pipes to form a hydrostatic column of fluid exerting a pressure sufficient 
to cause an accelerated reaction rate when the fluid is heated to the 
reaction temperature. Earlier prior art patents, including U.S. Pat. Nos. 
3,449,247, 3,606,999 and 3,853,759, proposed various deep well reaction 
systems, however, these systems were never built or tested. 
The above referenced patent of Dr. McGrew and the otner referenced prior 
art recognized that it is theoretically possible to substantially fully 
oxidize municipal and industrial wastes, including municipal sludge, at a 
deptn of approximately one mile, provided the concentration of the 
oxidizable material in the municipal sludge is balanced against the oxygen 
injected into the system. In the actual application of this concept in wet 
oxidation of municipal sludge, for example, considerable difficulties have 
been experienced in maintaining the reaction at the desired temperature 
and pressure to achieve maximum or optimum reduction of the chemical 
oxidation demand (C.O.D.) of the fluid waste stream. The temperature of 
the "reaction zone" located adjacent the lower extent of the reaction 
vessel must be continuously monitored to determine when the system becomes 
autogenic. Heat must be added to the influent to initiate the reaction. 
When the reaction becomes autogenic, heat is removed from the system to 
maintain the temperature of the reaction zone at the desired reaction 
temperature. The above referenced patent of McGrew proposes a heat 
exchanger located within the nested tube reaction apparatus for adding or 
removing heat. This was an important breakthrough, however, temperature 
sensing means located within the reaction vessel become fouled or 
otherwise failed making temperature measurement difficult. Thermocouples 
permanently attached to the pipes within the reaction vessel, required 
removal of over 5000 feet of reaction apparatus to replace the 
thermocouples which also became fouled in a relatively short period of 
time. Further, additional means to control the temperature of the 
reactants in the reaction vessel have been found desirable. 
There are pending several applications for patent relating to improvements 
in deep well reaction apparatus assigned to the assignee of the present 
application, the disclosures of which are incorporated herein by 
reference. For example, U.S. patent application Ser. No. 755,880, filed 
July 7, 1985, discloses the use of an insulated tubular in the heat 
exchanger for concentrating the heat adjacent the lower extent of the 
reaction vessel and limiting heat loss during removal of the heat. U.S. 
patent application Ser. Nos. 943,409, filed Dec. 19, 1986 and filed Mar. 
24, 1986 disclose methods of inhibiting scale build-up and methods for 
cleaning the system to limit downtime. U.S. patent application Ser. No. 
017,659 filed Mar. 24, 1987 discloses a method of continuous treatment in 
a downhole reaction apparatus wherein boiling is initiated in the upcomer 
to maintain the system at elevated temperatures. 
The need, however, remains for improvements in determining and controlling 
the temperature of the reaction zone while avoiding fouling of 
thermocouples and permitting easy replacement of thermocouples when 
damaged or inoperative. 
SUMMARY OF THE INVENTION 
As described above, the basic components of a deep well reaction apparatus 
includes a plurality of nested pipes which extend vertically into the 
ground a predetermined depth to establish the desired pressure for 
treatment of waste streams at elevated reaction temperatures. In the 
preferred embodiments, the pipes are nested in telescopic heat transfer 
relation, wherein the influent, which includes the reactants, flows 
downwardly, preferably in the inner pipe, and the effluent, which includes 
the reaction products, flows upwardly, preferably in the outer pipe. This 
is the preferred circulation of the influent and effluent where a heat 
exchanger is located within the nested tubes, such that the hot heat 
transfer fluid is in heat transfer relation with the downflowing influent. 
To avoid fouling, the temperature sensing means in one disclosed embodiment 
is preferably located in the heat exchanger rather than the reaction 
vessel because the heat exchange fluid is inert to thermocouples. The 
temperature of the flowing heat exchanger fluid is not, however, a 
reliable indicator of the temperature of the reaction vessel. Further, the 
temperature of the heat transfer fluid is increased or decreased to adjust 
the temperature of the reaction vessel. In a preferred embodiment of this 
invention, a fluid quiescent zone is created at the end of the heat 
exchanger within the reaction zone by spacing the central tube of the heat 
exchanger from the closed end of the outer tube a distance sufficient to 
stagnate the fluid flow and create a "quiescent zone". The temperature of 
the heat exchange fluid in this quiescent zone has been found to be a 
reliable indicator of the temperature of the reaction zone and therefore a 
temperature sensing means, such as a conventional thermocouple, is located 
within the quiescent zone, substantially eliminating thermocouple fouling 
problems and reducing the requirement for replacement of the sensing 
means. 
Where the temperature sensing means, such as a thermocouple, is located 
within the reaction vessel, the thermocouple must be protected by a 
thermowell. The thermowell comprises a pipe having an open end which 
telescopically receives the thermocouple. As described above, the prior 
art teaches permanent attachment of the temperature sensing means to the 
nested pipes of the reaction vessel. Thus, the temperature sensing means 
cannot be removed from the system without pulling the pipes of the 
reaction vessel. The method of this invention solves this problem by 
releasably affixing the thermowell to one of the pipes, lowering the pipe 
into the ground for installation in the apparatus and then flowing a fluid 
into the apparatus which preferentially attacks the clamping means and 
releases the thermowell tube for later service. In the most preferred 
method of locating the thermocouple within the reaction vessel, the 
thermowell tube is releasably attached to a surface of one of the reaction 
vessel pipes by metal clamps, the pipe is lowered into position and an 
acid is used to remove the clamps and free the thermowell for service and 
replacement. 
Having provided a reliable means for continuously monitoring the 
temperature of the reaction zone, it is now possible to more accurately 
maintain the temperature of the reaction at the desired temperature. 
Following initiation of the reaction by flowing hot heat transfer fluid 
downwardly through the heat exchanger, heat is preferably removed from the 
reaction zone by reversing the flow of the heat exchange fluid. Where a 
central insulated tubular is used in the heat exchanger, the heat may be 
efficiently removed by flowing the heat exchange fluid downwardly in the 
annular space between the center tube and the outer tube of the heat 
exchanger and circulating the heated heat exchange fluid upwardly through 
the center insulated tubular. It has been discovered that the temperature 
of the reaction zone may also be or alternatively adjusted by continually 
adjusting the C.O.D. of the influent, wherein the concentration of the 
principal reactant, for example municipal sludge, is increased where the 
temperature must be increased and the concentration of the principal 
reactant is reduced where the temperature should be reduced. This provides 
an additional means of adjusting the temperature of the reaction zone 
which may be utilized independently of a heat exchanger or as an 
additional means for adjustment of the temperature. 
It has been further discovered that the temperature gradient across a pipe 
of the reaction vessel may be accurately determined and utilized to 
determine the scale build-up on the reaction vessel wall. This is 
accomplished by determining the temperature on opposed sides of a reaction 
vessel pipe at the same depth. An increase in the temperature gradient 
indicates an increase in the scale build-up. 
Other advantages and meritorious features of this invention will be more 
fully understood from the following description of the preferred 
embodiments and methods of this invention, the appended claims, and the 
drawings, a brief description of which follows:

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND METHODS OF THIS INVENTION 
The continuous fluid treatment apparatus 20 illustrated in FIGS. 1 to 3 is 
a vertical downhole or deep well fluid reaction apparatus suitable for 
treatment of various fluid streams, including but not limited to municipal 
and industrial waste. The illustrated fluid treatment apparatus has been 
used experimentally to treat municipal sludge wherein the primary reactant 
was sewage sludge dilluted in water and the secondary reactant was oxygen 
or air. As disclosed in the above-referenced McGrew patent, the fluid 
treatment apparatus generally comprises a plurality of generally 
concentric and telescopically nested pipes which extend vertically into 
the ground. In a treatment apparatus specifically designed for wet 
oxidation of municipal sludge, for example, the pipes may extend 
approximately one mile into the ground to form a hydrostatic column of 
fluid exerting a pressure sufficient to prevent boiling of the reactants 
in the downcomer pipe. It will be understood, however, that the reaction 
vessel may also be operated at supercritical temperatures and pressures to 
further accelerate the reaction in particular applications. Or more 
preferably, the liquid effluent may be selectively boiled in the upcomer 
pipe as described in the copending U.S. patent application Ser. No. 
17,659, filed Feb. 24, 1987. Supercritical temperatures and pressures are 
not required for treatment of municipal sludge. The fluid treatment 
apparatus of this invention may also be used in various conversion 
reactions wherein a solid particulate, for example, is suspended in the 
circulating fluid. Further, the pipes are generally not continuous. Each 
pipe comprises a plurality of sections which are interconnected in serial 
alignment in a string, similar to the pipes in an oil well. In a typical 
municipal sludge wet oxidation application, the length of each pipe 
section is 40 feet long, the total length is about 5200 feet and the flow 
rate of the fluid being treated is about 80 to 400 gallons per minute. 
In the disclosed embodiment of the fluid treatment apparatus, the heat 
exchanger 22 is located at the center of the nested pipes which comprise 
the fluid treatment vessel or reaction vessel. It will be understood, 
however, that the heat exchanger, being self-contained, may be located 
alongside an upcomer pipe, preferably within the downcomer pipe, in heat 
transfer relation with the downflowing influent. ln the preferred 
embodiment, the innermost pipe 24 of the heat exchanger is an insulated 
tubular having an open end 26. As described more fully hereinbelow and in 
the above-referenced copending U.S. application Ser. No. 755,880, filed 
July 17, 1985, the insulated tubular 24 reduces radial heat transfer from 
downflowing hot heat transfer fluid in the insulated tubular to 
recirculating upwardly flowing heat transfer fluid in the annular space 
between the insulated tubular 24 and second pipe 28, as shown in FIG. 2. 
The circulation in the heat exchanger is reversed when the reaction 
becomes autogenic, as shown in FIG. 3. The insulated tubular then 
conserves the heat of reaction for other uses by preventing heat loss. ln 
the disclosed embodiment, the insulated tubular 24 is generally concentric 
with and telescopically nested in second pipe 28 which has a closed end 30 
spaced from the open end 26 of the insulated tubular providing a closed 
heat exchanger system. The fluid to be treated is then circulated around 
or in fluid heat transfer relation with the heat exchanger 22, as now 
described. 
In the disclosed embodiment, a third pipe 32 having an open end 34 
surrounds the second pipe 28 of the heat exchanger in generally concentric 
spaced telescopic relation. A fourth pipe 36 having a closed end 38 
surrounds the third pipe 32 in spaced relation. The fluid to be treated, 
referred to as the influent, is circulated downwardly through downcomer 
pipe 32 in contact with the second pipe 28 of the heat exchanger 22. The 
treated fluid, referred to as the effluent, then flows through the open 
end 34 of the third pipe 32 and upwardly through the annular space between 
the downcomer pipe 32 and the upcomer pipe 36 in contact with the outer 
surface of the third pipe 32. As described more fully in the 
above-referenced McGrew patent, the fluid treatment apparatus creates a 
reaction zone in the lower portion of the apparatus when the reaction 
becomes autogenic, wherein the reaction is accelerated under heat and 
pressure. It will be understood, however, that the reaction apparatus of 
this invention is not limited to subcritical pressures and temperatures or 
particular reactants. For ease of explanation, however, the operation of 
the reaction apparatus will be described with regard to the subcritical 
wet oxidation treatment of sewage sludge. 
FIG. 1 illustrates schematically suitable above ground components which may 
be utilized in the fluid treatment apparatus and processes of this 
invention. The heat exchange fluid, such as oil, water-steam or any 
suitable heat transfer fluid, is stored in a reservoir tank 40. For ease 
of description, the heat transfer fluid may be referred to below as oil, 
which is preferred in many applications. The oil is heated in a heater 42, 
such as a conventional gas fired heater. The oil is pumped by pump 44 from 
reservoir 40 through line 46 to heater 42 and the rate of flow is 
controlled by valve 52. The heated oil is then transferred through line 48 
to the insulated tubular 24 of the heat exchanger 22 and the rate of flow 
is controlled by valve 50. The heat transfer fluid is then returned 
through line 74 from second pipe 28 to reservoir 40 for recirculation, as 
described. When heat is to be removed from the system, such as when the 
reaction becomes exothermic, the circulation in the heat exchanger 22 may 
be reversed, as shown in FIG. 3, wherein the heated oil is received from 
the insulated tubular 24 through line 48 and transferred through line 58 
to the oil heat exchanger 54. As will be understood, this is accomplished 
by closing valve 50 and opening valve 60. The cooled heat exchanger fluid 
is then tranferred through line 56 and punped by pump 57 to the storage 
tank 40 or line 74 through line 75 and back to pipe 28 of the heat 
exchanger. The cooled heat transfer fluid is transferred to line 74 by 
closing valves 62 and 76. 
During initiation of the reaction in the reaction vessel, heated oil is 
then supplied through line 48 into insulated tubular 24. As best shown in 
FIG. 2, the heated oil then flows downwardly through the insulated tubular 
as shown by arrow 70. The oil then flows out of the bottom open end 26 of 
the insulated tubular and the oil is recirculated upwardly through the 
annular space between the insulated tubular 24 and second pipe 28, as 
showm by arrows 72. The heat transfer fluid is then discharged from the 
top of pipe 28 through line 74 back to the reservoir 40 through valve 76. 
When the circulation in the heat exchanger 22 is reversed, as shown in 
FIG. 3, the heat transfer fluid flows downwardly through the annular space 
between second pipe 28 and the insulated tubular 24, as shown by arrows 
70A and upwardly through insulated tubular, as shown by arrow 72A. 
The fluid to be treated, such as municipal or industrial waste streams, is 
supplied to third pipe 32 and circulates downwardly around the heat 
exchanger 22 in the annular space between the second pipe 28 of the heat 
exchanger and pipe 32 sometimes referred to as the downcomer. As shown in 
FIG. 1, the fluid to be treated is stored in reservoir tank 80. The fluid 
to be treated, such as municipal sludge, is received through line 82 and 
the flow is controlled by valve 84. The fluid sludge is then delivered to 
the apparatus through line 86 and line 88. The fluid sludge is preferably 
diluted with water or liquid effluent from the municipal wastewater 
treatment plant delivered through line 90 and valve 92. The fluid sludge 
is preferably diluted to control the percentage of oxidizable material 
delivered to the fluid treatment apparatus. The effluent from the reaction 
vessel may also be used to dilute the sludge. The diluted sludge, fluid 
waste or other fluid to be treated then flows downwardly through pipe 32 
in contact with the outer wall 28 of the heat exchanger 22, as shown by 
arrows 94. As described, pipe 32 has an open end 34 and the effluent then 
flows upwardly through the annular space between the outer pipe 36 and 
pipe 32 for discharge from the fluid treatment apparatus as shown by arrow 
96. As shown in FIG. 1, the effluent is discharged from pipe 36 through 
line 98 to tank 100. Where the apparatus is used for wet oxidation of 
sewage sludge, for example, tank 100 is preferably a settling tank where 
the substantially inter ash is separated from the effluent fluid and gas. 
The ash may be drawn off through line 102 and the rate of flow is 
controlled by valve 104. 
In a wet oxidation reaction apparatus, the supernatant may be drawn off 
through line 106 and used as a diluent in the process. Gas may be removed 
through line 103. As shown in FIG. 1, the supernatant is drawn off through 
line 106 and delivered to line 86, which communicates with pipe 32. The 
rate of flow and dilution is then controlled by valve 108. The second 
reactant, which is air or oxygen in the wet oxidation of sewage sludge, 
for example, may be injected into the downflowing stream of the influent 
through line 112. The disclosed embodiment includes an air or gas 
compressor 110 and the rate of flow is controlled by valve 114. As will be 
understood, the second reactant may be alternatively delivered through 
line 86 where the reactant is a liquid, for example, premixed in storage 
tank 80. Further, in many applications, oxygen is preferred as the second 
reactant, as disclosed in copending U.S. application Ser. No. 010,060, 
filed Feb. 2, 1987. 
As described, the fluid treatment apparatus of this invention is primarily 
intended to treat fluid waste at elevated temperatures and pressures. The 
pressure is provided by the hydrostatic column of fluid in the reaction 
vessel. When the reaction is autogenic, the temperature is provided by the 
heat of reaction. During initiation of the reaction, however, heat must be 
added to the influent in the downcomer, preferably within the lower 
portion of the reaction vessel, creating a reaction zone. In a typical wet 
oxidation reaction of municipal sludge, for example, the downhole reaction 
temperature is approximately 500.degree. F. Thus, oil delivered to the 
reaction zone should be in excess of 500.degree. F. ln a typical wet 
oxidation reaction, the oil will be delivered to the inlet of the 
insulated tubular 24 at a temperature of about 700.degree. F. The oil or 
other heat transfer fluid then flows downwardly to the open end 26 of the 
insulated tubular where the heat is delivered to the second pipe 28 of the 
heat exchanger at a temperature of about 525.degree. to 550.degree. F. The 
fluid then flows upwardly through pipe 28, as shown by arrow 72 in FIG. 2, 
and the hot heat transfer fluid heats the downflowing influent in contact 
with the outer surface of pipe 28 in pipe 32. The temperature of the oil 
at the top exit of pipe 28 is then about 150.degree. F. As described, the 
fluid reaction occurs in a reaction zone where the temperature of the 
influent exceeds about 350.degree. F. 
As will now be understood, the use of an insulated tubular conserves the 
heat of the hot oil for delivery to the reaction zone. Similarly, when the 
reaction becomes exothermic, the heated oil or other heat transfer fluid 
is delivered to the lower end of the insulated tubular 24, as shown by 
arrow 70A in FIG. 3, and the heated oil flows upwardly through the 
insulated tubular, as shown by arrow 72A in FIG. 3. Thus, the insulated 
tubular conserves the heat of reaction, which may be used for other 
purposes, including the generation of electricity, chemical reactions, 
etc. A suitable embodiment of the insulated tubular 24 is described in 
copending U.S. patent application Ser. No. 755,880, filed July 17, 1985. 
Briefly, the insulated tubular includes an inner tube 120, an outer tube 
122 and cylindrical spacer members 124 which define an annular insulating 
space 126 between the tubes. The space 126 may be filled with an inert gas 
or any suitable insulating material. 
Having described the general construction and operation of the fluid 
treatment apparatus 20 and the above ground components, as shown in FIG. 
1, it will be understood that accurate temperature monitoring of the 
reaction zone is very important to successful operation of the reaction 
vessel, which includes downcomer pipe 32 and upcomer pipe 36. Various 
means for monitoring the temperature of the reaction vessel have been 
tried, including conventional thermocouples located within the reaction 
vessel. Such thermocouples are normally affixed within the upcomer or 
downcomer pipes for measurement at various depths and control of the 
system. As described, however, the thermocouples become fouled with scale, 
influent materials and reaction products, making the thermocouples 
inoperative. Where the thermocouples are permanently affixed to the 
downcomer or upcomer pipes, the pipes must be pulled to service the 
thermocouples, keeping in mind that the pipes in a municipal sludge wet 
oxidation reaction apparatus are a mile deep. More often, an attempt is 
made to monitor the reaction by measuring the temperature of the influent 
and affluent streams and the pressure of the system at or near ground 
level, relying upon operational data to attempt to determine the actual 
reaction temperatures. This method of temperature sensing, however, is a 
poor substitute for actual reaction temperatures, particularly where 
accurate control of the reaction temperatures is desired for optimum 
control of the reaction vessel to achieve maximum C.O.D. reduction. The 
apparatus and methods of this invention are particularly adapted for 
accurate determination and control of the temperature of the reaction 
zone, while avoiding fouling of thermocouples and permitting easy 
replacement of the temperature measurement devices. 
In the preferred embodiment of this invention, the temperature sensing 
means for the reaction zone of the fluid treatment apparatus is located in 
the heat exchanger 22. As will be understood from the description of the 
heat exchanger above, heat exchange fluid is normally circulating in the 
heat exchanger and the temperature and flow of the heat exchange fluid is 
controlled to control the temperature of the reaction zone. Thus, it was 
not believed to be possible to accurately determine the temperature of the 
reaction zone from the temperature of the heat exchange fluid. It was 
discovered, however, that the temperature of the reaction zone could be 
accurately determined from the temperature of the heat exchange fluid in a 
quiescent zone 130 located at the lower extent of the heat exchanger. The 
quiescent zone 130 is created by spacing the open end 26 of the first or 
inner tube 24 of the heat exchanger from the closed end 30 of the outer or 
second pipe 28 a distance sufficient to staguate the flow. Where the 
spacing is sufficient to stagnate the flow of heat exchange fluid adjacent 
the closed end 30 of the second tube 28, a reservoir of fluid is created 
in intimate heat transfer relation with the lower extent of the reaction 
zone of the reaction vessel. The temperature of the fluid in the quiescent 
zone was found to be an accurate indicator of the temperature in the 
reaction vessel. Further, the difference between the temperature of the 
heat exchange fluid in the quiescent zone and the temperature of the 
reaction zone can be quantified for very accurate determination of the 
temperature of the reaction zone. 
In actual operation, it was found that the temprature of the hot oil in the 
quiescent zone was about 10.degree. to 20.degree. F. greater than the 
temperature of the reaction zone as the influent was heated by the heat 
exchanger prior to exothermic reaction. When the reactor becomes 
autogenic, the difference between the temperatures decreases until the 
temperature of the reaction zone exceeds the temperature of the heat 
exchange fluid in the quiescent zone by about the same differential. 
Continuous autogenic operation of the reaction vessel results in a 
temperature in the reaction zone which is greater than the temperature of 
the oil in the quiescent zone. FIG. 6 illustrates a typical operation of 
the reaction vessel wherein the hot oil temperature in the quiescent zone 
is plotted against the temperature of the influent in the reaction zone. 
As shown, the reaction became autogenic, at about reference numeral 130, 
after about eight hours of operation. ln fact, the temperatures may 
repeatedly cross as the system flows into and out of autogenic operation. 
In actual operation, it was found that the temperature of the hot oil in 
the insulated tubular was greater than the temperature of the hot oil in 
the quiescent zone, which was greater than the temperature of the reaction 
zone during start-up, prior to autogenic operation of the reaction vessel. 
During autogenic operation of the vessel, the temperature of the reaction 
zone was greater than the temperature of the heat transfer fluid in the 
quiescent zone, which was greater than the temperature of the heat 
exchange fluids circulating in the heat exchanger. The difference between 
the temperature of the influent in the reaction zone and the temperature 
of the heat transfer fluid in the quiescent zone was found to be 
10.degree. to 20.degree. F. It was further found that the open end 26 of 
the first pipe 24 of the heat exchanger should be spaced from the closed 
end 30 of the second pipe a distance of at least five feet, or more 
preferably at least ten feet, to provide a quiescent zone, as described. 
Having determined that the temperature of the heat transfer fluid in the 
quiescent zone 130 was an accurate indicator of the temperature of the 
influent in the reaction zone, it was then possible to accurately and 
continuously monitor the temperature of the reaction zone and more 
accurately control the operation of the reaction vessel. As will now be 
understood, the heat transfer fluid, such as oil, water-steam, etc. will 
normally be inert to a conventional thermocouple. Thus, the problem of 
fouling of the thermocouples was substantially eliminated. The temperature 
of the heat transfer fluid in the quiescent zone 130 was accurately 
determined by a conventional thermocouple rod 140 as best shown in FIGS. 1 
to 3. 
Where the thermocouple is to be located within the reaction vessel, such as 
for determination of scale build-up, the thermocouple is preferably 
located in a thermowell 142, as shown in FIG. 4, which comprises a tube 
having an opening adjacent the temperature sensing means. As will be 
understood, the thermowell pipe protects the thermocouple rod 141 and 
further isolates the thermocouple from the flow of the influent or 
reaction products. The thermowell is preferably free to permit removal, 
repair or replacement of the thermocouple. A unique method of locating the 
thermowell 142 in the reaction vessel was then developed, as now 
described. First, the thermowell 142 was attached to one of the pipes of 
the reaction vessel, such as pipe 32, by clamps 150, as shown in FIG. 4. 
The pipe 32 was then lowered into the reaction vessel and installed by 
conventional means. The clamps 150 were then removed by circulating a 
fluid through the reaction vessel which preferentially attacked the 
attachment means, releasing the thermowell 142. The clamps were made of a 
relatively soft carbon steel which in the embodiment shown in FIG. 4 were 
attached to the outside surface of pipe 32 by spot welding at 152. The 
clamps were then removed by a nitric acid wash. Finally, the thermocouple 
141 was telescopically disposed into the thermowell 142, as shown in FIG. 
4. The thermowell and thermocouple can then be easily removed, as needed, 
for repair or service. 
Having provided a means for accurate monitoring of the temperature of the 
influent stream in the reaction zone, it was then possible to more 
accurately control the temperature of the reaction zone. As described 
above, the adjustment of the temperature of the reaction zone was 
previously accomplished solely with the heat exchanger 22. When the 
temperature of the reaction zone was to be increased, as during initiation 
of the wet oxidation reaction, hot oil was circulated downwardly through 
the insulated tubular 24, as shown by arrow 70 and upwardly through the 
annular space between the insulated tubular 24 and the second tube 28, as 
shown by arrows 72, in heat fluid transfer with the influent in the 
downcomer pipe 32. When the temperature was to be decreased, the 
circulation was reversed, as shown in FIG. 3, wherein cooled oil received 
from heat exchanger 54 was circulated downwardly through the annular space 
between the insulated tubular 24 and the second pipe 28, as shown by arrow 
70A and upwardly through the insulated tubular, as shown by arrow 72A of 
FIG. 3. Further or alternative adjustment of the reaction zone temprature 
was, however, found to be desirable. This adjustment was made by adjusting 
the C.O.D. of the influent. When the temperature was to be increased, the 
concentration of the primary reactant, which was sewage sludge, was 
increased in the carrier fluid, which was water. When the temperature was 
to be decreased, the concentration of the sewage sludge in water was 
decreased. This was found to be a very accurate means of controlling the 
temperature of the reaction zone. In fact, in some applications, it may be 
possible to eliminate the heat exchanger and control the temperature of 
the reaction zone by controlling the C.O.D. of the influent. 
The thermowell 142 may also be used to measure the pressure at the bottom 
of the thermowell simultaneously with the temperature. A source of gas 
under pressure, such as pump 156 is connected by pressure line 158 to the 
top of the thermowell 142 as shown in FIG. 1. The gas is then pumped under 
pressure into the thermowell until it just bubbles out of the open end 144 
of the thermowell. The pumping pressure corrected for the weight of the 
fluid in the thermowell, is then the pressure of the fluid at the depth of 
the open end 144 of the thermowell. ln FIG. 1, a temperature gauge and 
control 160 is connected to the thermocouple to determine the temperature 
of the reaction zone which may also be connected to valves 50 and 60 to 
control the circulation of the heat transfer fluid for heating or cooling 
the reaction zone, as described above. As will be understood, the method 
of locating the thermowell in the fluid treatment apparatus and method of 
determining pressure may also be used in the reaction vessel. 
FIG. 5 illustrates an apparatus and method for determining the scale 
build-up on reactor vessel wall 32. Temperature sensing means are located 
on opposite sides of pipe 32, within the reaction vessel. In the disclosed 
embodiment, the temperature sensing means are thermocouples 160 and 162 
located on opposite sides of wall 32. In the preferred embodiment, the 
thermocouples 160 and 162 are thermocouple bundles, wherein each 
thermocouple of the bundle measures the temperature at a predetermined 
depth. As described above, the thermocouples 160 and 162 located within 
the reaction vessel are preferably located within thermowells 164 and 166, 
respectively. The thermowells may either be filled with a liquid or a gas 
may be pumped into the thermowells for determination of pressure, as 
described hereinabove. The thermocouples therefore determine the 
temperature on opposite sides of wall 32 at preselected depths within the 
reaction vessel. 
The preferred method of determining scale build-up on reaction vessel wall 
32 comprises measuring the temperature differential on opposite sides of 
wall 32 at the same depth at timed intervals. An increase in the 
temperature differential indicates scale build-up on the reaction vessel 
wall. It is therefore possible to determine when the reaction vessel must 
be cleaned of scale by determining the temperature differential on a 
periodic basis. Several prior patents and pending applications for United 
States patent have been referred to herein which disclose further details 
of the preferred reaction apparatus and methods and the disclosures of 
such patents and pending applications are incorporated herein by 
reference. Further details will be understood by those skilled in the art. 
For example, the deep well reaction apparatus 20 may be installed in a 
conventional cased well. The materials, dimensions, etc. will depend upon 
the particular application for the deep well reaction apparatus and 
methods. The thermowell tube 142 is preferably formed of a material 
similar to the material used for the reaction vessel pipes, which is a 
corrosion resistant steel having elevated temperature service capability. 
Further, modifications may be made to the disclosed embodiment of the 
reaction vessel and heat exchanger without departing from the purview of 
the appended claims. For example, as described above, the downcomer pipe 
32 and heat exchanger 24 may be located side by side within the reaction 
vessel, increasing the capacity of the reaction vessel in a predetermined 
diameter well casing. Having described the fluid treatment apparatus and 
methods of this invention.