EP1646588A1

EP1646588A1 - Apparatus and method for performing deep well wet oxidation

Info

Publication number: EP1646588A1
Application number: EP03816379A
Authority: EP
Inventors: Marco Jan Hendrik Patrick Fleurke
Original assignee: Vartech BV
Current assignee: Vartech BV
Priority date: 2003-03-20
Filing date: 2003-03-20
Publication date: 2006-04-19
Also published as: WO2004083128A1; AU2003304008A1

Abstract

The present invention relates to an apparatus for performing a deep well wet oxidation treatment of a fluid waste stream, the apparatus at least omprising: a deep well reaction vessel which is suspended in a subterranean hole; a first pipe for feeding the fluid waste stream into the reaction vessel, the first pipe being suspended in said reaction vessel and thereby defining a down going flow through the first pipe and an up going flow through a passage defined by the first pipe and the reaction vessel; a heat exchanger in heat exchange relation to the reaction vessel; and oxidant feeding means for feeding an oxidant to the first pipe nearby a reaction zone in which during use of the apparatus the wet oxidation of the fluid waste stream can take place; wherein the outlet of the oxidant feeding means is comprised in the wall of the first pipe.

Description

Title: Apparatus and method for performing deep well wet oxidation

The present invention relates to an apparatus for performing deep well wet oxidation treatment of waste and other combustible materials in an aqueous stream such as organic solvents, municipal sludge, toxic or contaminated products and the like. Various wet oxidation treatment processes are disclosed in the prior art. In general, the temperature of combustible material dissolved and/or suspended in water in the presence of oxygen is increased to produce a wet oxidation reaction wherein complex organic materials are converted into water, carbon dioxide, dilute organic acids and a small amount of sterile, inert ash. The combustion reaction is exothermic and can be carried out in a reaction apparatus having a continuous heat exchanger such that the heat evolved by the combustion reaction can be used to heat an influent waste stream to the desired temperature. This provides an energy-efficient system. The prior art has also proposed utilizing wet oxidation processes of this type in a continuous vertical heat exchange column which may be supported in a subterranean well (i.e. deep well*¹ ) . The chemical reaction occurs within a vertical reaction vessel that generally extends downwardly into the ground to a depth of from 600 - 2000 m, usually 1200 m. The fluid to be treated is pumped into an influent tube or pipe, i.e. the Mown comer*' with other reactants for the chemical reaction. A fluid head creates pressure and heat is added which facilitates the reaction. The temperature and pressure are greatest in the lower regions of the pipe where the reaction occurs. Following the reaction, the fluid continues its continuous flow upwardly through an annulus, i.e. the up co er' , where the effluent may be processed further.

A key to the commercial success of such deep well vertical pipe reaction systems is their energy realized by applying the natural principles of gravity and thermodynamics to create the heat and pressure required to sustain the wet oxidation reaction.

Wet oxidation of the fluid waste stream occurs in the aqueous phase when sufficient oxygen, heat and pressure are present in the system. The wet oxidation reaction is an exothermic reaction which is capable of autogenic operation after the lower portion or reaction zone of the vertical pipes are preheated to the appropriate temperature for oxidation of the waste stream.

The efficiency of this system is also seen in the fact that the pumps injecting the fluid waste stream theoretically only need to be large enough to overcome the wall friction and any differential head between the influent and effluent pipes. The vertical pipes are designed to provide sufficient residence time of the fluid waste stream in the reaction zone to complete the oxidation reactions.

To maintain the efficiency of the subterranean system, it is vital that the walls of the pipes remain substantially free of inorganic scale and that no other accumulations or plugging occur. Scale build-up on the walls of the pipes increases the wall friction and reduces the available cross-sectional area through which the fluid waste stream may flow, thereby increasing the load on the pump circulating the fluid waste stream.

Scale build-up on the walls of the vertical tubes also reduces the efficiency of the counterflow heat exchange between the influent and the effluent through the walls of the pipes separating the two flows. Similarly, scale accumulations on the wall of the pipe adjacent the heat exchange medium reduces the efficiency of preheating the reaction zone.

In the prior art several methods of removing scale build-up in deep well wet oxidation systems are known. However, an important disadvantage of the known methods of removing scale is that the wet oxidation reaction can not be continued while removing the scale. Furthermore, in case that mechanical removal of the scale is used, components of the deep well wet oxidation apparatus, in particular oxygen feeding means and thermocoupling tubes and the like, may be damaged as they are suspended as a separate feeding pipe in the fluid waste stream thereby allowing contact between mechanical scale removal means and the oxygen feeding means, thermocoupling tubings and the like. The person skilled in the art will readily understand that this is not desired.

It is an object of the present invention to avoid the above and other problems and to provide an efficient and cost effective apparatus for performing a deep well wet oxidation treatment.

It is a further object of the present invention to provide an apparatus for performing a deep well wet oxidation treatment allowing scale to be removed by any mechanical means, such as Vortec® tools, a rotocavitator, etc.

To this end the present invention provides an apparatus for performing a deep well wet oxidation treatment of a fluid waste stream, the apparatus at least comprising:

- a deep well reaction vessel which is suspended in a subterranean hole;

- a first pipe for feeding the fluid waste stream into the reaction vessel, the first pipe being suspended in said reaction vessel and thereby defining a down going flow through the first pipe and an up going flow through a passage defined by the first pipe and the reaction vessel;

- a heat exchanger in heat exchange relation to the reaction vessel; and - oxidant feeding means for feeding an oxidant to the first pipe nearby a reaction zone in which during use of the apparatus the wet oxidation of the fluid waste stream can take place; wherein the outlet of the oxidant feeding means is comprised in the wall of the first pipe. Herewith scale can be effectively removed. An important advantage of the apparatus of the present invention is that mechanical scale removing means may be used, while the risk that components of the deep well wet oxidation apparatus, in particular oxygen feeding means, thermocoupling tubings and the like, are damaged is minimized.

The person skilled will readily understand what is meant with Meep well wet oxidation treatment' and knows how to select the proper conditions to allow wet oxidation to take place in the selected reaction zone. Generally the deep well reaction vessel will have a depth between 600 - 2000 m below ground surface, more usually a depth of about 1200 m.

The fluid waste stream may be any fluid (usually aqueous) waste stream containing organic compounds, municipal sludge, etc.

The person skilled in the art will readily understand that, while the down going flow is defined to flow through the first pipe and while the up going flow is defined to flow through a passage (e.g. annulus) defined by the first pipe and the reaction vessel, the direction of the flow can also be reversed according to the present invention, if desired. According to the present invention, the oxidant may be any oxidant suitable for performing a wet oxidation. Usually the oxidant will be an oxygen containing fluid such as air, in particular oxygen rich gas, more preferably substantially pure oxygen gas. The exact position of the reaction zone in the reaction vessel will depend on circumstances such as the depth of the reaction vessel, the type of fluid waste stream, the pressure and temperature in the reaction vessel, and the like. The person skilled in the art will understand what is meant by "nearby a reaction zone". As the exact position of the reaction zone may vary with the circumstances, the position of the feeding of the oxidant to the reaction zone may also vary. Preferably, the oxidant will be fed just upstream of the reaction zone, thereby avoiding that the oxidant already reacts with the fluid waste stream under pressure and temperature conditions that are not suitable for efficient wet oxidation.

It has been shown that for a reaction vessel having a depth of about 1200 m, with a reaction zone at 180 - 340°C and 10 - 100 bar, suitable wet oxidation results may be obtained by adding the oxidant at a depth of 150 - 800 m, preferably 180 - 500 m, more preferably 200 - 300 m.

In this respect, the person skilled in the art will readily understand that the selected temperature and pressure may depend on the fluid waste stream to be treated in order to obtain an objected COD (Chemical Oxygen Demand) reduction of the fluid waste stream. The layout of the reaction vessel and the heat transfer ratios define the depth at which the oxidant will be injected and the total depth of the reaction vessel.

In use of the apparatus according to the present invention, the suitable conditions of temperature and pressure are created in the reaction vessel to define a reaction zone wherein wet oxidation can take place. Then a fluid waste stream is fed into the first pipe (the Mown comer'' ) being suspended in the deep well reaction vessel thereby defining a down going flow through the first pipe. The wet oxidation reaction of the fluid waste stream takes place in the selected reaction zone by adding an oxidant such as gaseous oxygen to the fluid waste stream. The oxidation reaction is exothermic, and the heat evolved by the reaction can be used to heat the influent fluid waste stream or can be collected for other use. In the wet oxidation reaction, organic materials are, amongst others, converted into water, carbon dioxide, dilute organic acids and ash. Then the reacted effluent waste stream is further transported in an up going flow through a passage (the up comer' ) defined by the first pipe and the reaction vessel. Finally the effluent may be further processed. According to the present invention it is preferred that the outlet of the oxidant feeding means is placed nearby the reaction zone.

Herewith it can be avoided that the oxidant already reacts with the fluid waste stream under pressure and temperature conditions that are not suitable for efficient wet oxidation. Preferably the outlet of the oxidant feeding means is placed just upstream of the reaction zone.

In a structurally simple and elegant embodiment of the apparatus according to the present invention, the oxidant feeding means comprise a second pipe, which second pipe extends at least partially along the first pipe.

In a particular preferred embodiment, the second pipe extends along the first pipe in a substantially concentric manner, preferably over a range from the inlet of the first pipe to nearby the outlet of the second pipe.

Further it is preferred that the first pipe is at least partially thermally isolated. Herewith it can be avoided that a heated down going stream through the first pipe (down comer) loses heat before reaching the selected reaction zone. In this respect it is preferred that the first pipe is thermally isolated substantially over a range from the inlet of the first pipe to nearby the outlet of the oxidant feeding means .

Preferably the first pipe can be thermally isolated by feeding an isolating fluid, preferably gaseous nitrogen, through the second pipe.

Further it is preferred that the inner diameter of the first pipe is substantially constant, at least over a range from the inlet of the first pipe to the reaction zone, preferably also including the reaction zone. Herewith the scale in the first pipe can be easily removed by mechanical means, while the risk that components are damaged is minimized, in particular when no further feeding means or sensors are suspended in the first pipe. The person skilled in the art will understand that the heat exchanger may be provided at any suitable position. However, according to the present invention, the heat exchanger is preferably positioned outside of and also substantially parallel to the reaction vessel, in the subterranean hole. Herewith, the first pipe can be cleaned without affecting the heat exchanger.

Preferably the heat exchanger comprises a third pipe and a fourth pipe, the fourth pipe at least partially concentrically extending along the third pipe, wherein the heat exchanger can be thermally controlled by flowing an isolating fluid such as nitrogen gas (or 'any other suitable fluid) between the third and fourth pipe.

In a further aspect the present invention relates to a method for performing a deep well wet oxidation treatment of a fluid waste stream, the method comprising the steps of: - flowing a fluid waste stream in a down going flow to a selected depth below the ground surface in a reaction vessel suspended in a subterranean hole to form a hydrostatic column of fluid exerting a selected pressure for performing a wet oxidation reaction in a selected reaction zone in the reaction vessel; - providing a selected temperature to the fluid waste stream suitable for performing a wet oxidation reaction in the selected reaction zone;

- adding an oxidant to the fluid waste stream nearby the reaction zone; - performing the wet oxidation reaction in the selected reaction zone;

- controlling the temperature of the reaction zone by adding heat to the fluid in the reaction zone if the temperature of the fluid in the reaction zone is below a selected temperature and removing heat from the fluid in the reaction zone if the fluid in the reaction zone is above a selected temperature; and

- flowing the reacted fluid waste stream further, back up to substantially ground surface.

The person skilled in the art will know how to select a suitable flow rate for the fluid waste stream in the down going flow.

Furthermore, the person skilled in the art will know how to select the conditions of temperature and pressure in the selected reaction zone at the selected depth. The controlling of the temperature in the reaction vessel before, during and after the wet oxidation may be obtained in any suitable manner, e.g. using a heat exchanger. The exact position of such a heat exchanger is not crucial as long as the objected effect is achieved.

After a part of the fluid waste stream has undergone wet oxidation this part will flow further, back up to substantially ground surface. Here, the reacted fluid waste stream may be processed further, if desired. According to a preferred embodiment of the method according to the present invention, the fluid waste stream is flown through a first pipe being suspended in the reaction vessel. In this case, the first pipe and reaction vessel define a down going flow through the first pipe and an up going flow through a passage (e.g. annulus) defined by the first pipe and the reaction vessel. The oxidant is flown through a second pipe, the second pipe extending along the first pipe in a substantially concentric manner.

The selected pressure in the reaction zone may be any pressure suitable for performing a wet oxidation reaction in the reaction zone. However, usually the selected pressure in the reaction zone is between 10 - 100, preferably 25 - 85, most preferably 40 - 60 bar. It has been shown that herewith an efficient wet oxidation may take place in the reaction zone.

The selected temperature in the reaction zone may be any pressure suitable for performing a wet oxidation reaction in the reaction zone. Usually, the selected temperature in the reaction zone is between 180 - 340°C, preferably 250 - 300°C, most preferably 270 - 280°C.

According to a particular preferred embodiment of the method according to the present invention, the fluid waste stream is only fed in the reaction vessel after the reaction zone has obtained a suitable temperature allowing efficient wet oxidation to take place. If an unheated waste stream is fed in the down comer, this may result in an ineffective oxidation. Furthermore, plugging of the down comer may occur. Therefore, preferably the selected temperature in the reaction zone is obtained by flowing a heated heating fluid through the down comer. This heating fluid may be any suitable fluid for heating up the selected reaction zone. Preferably, water is used as the heating fluid. After the reaction zone has reached the desired temperature, the fluid waste stream is fed.

Advantageously, the oxidant is added to the reaction zone after the selected temperature and pressure have been obtained in the reaction zone. This results in an efficient wet oxidation in the reaction zone.

Hereinafter the present invention will be illustrated in more detail by a drawing. Herein shows:

Figure 1 a schematic cross-sectional view of the apparatus according to the present invention; and

Figures 2 - 5 schematic cross-sectional views of different phases in the wet oxidation of a fluid waste stream using the apparatus according to Fig. 1.

Figure 1 shows a schematic cross-sectional view of the apparatus according to the present invention for performing a deep well oxidation treatment of a fluid waste stream such as sewage sludge. The apparatus 1 comprises a deep well reaction vessel 2 (length: 1208 m; internal diameter 34,6 cm), which vessel 2 is suspended in a subterranean hole 3 (length: 1250 m; internal diameter: 55,9 cm) in the ground 19. The vessel 2 may e.g. be made from stainless steel. The subterranean hole is 3 filled with a heat transfer fluid (HTF) 16. The HTF 16 may be any suitable fluid medium, such as non-corrosive oils or demineralized water.

The reaction vessel 2 is - in the shown embodiment through the HTF 16 (internal diameter: 10,2 cm) - in heat exchanging contact with a heat exchanger 4. The heat exchanger 4 is positioned outside the reaction vessel 2, but in the subterranean hole 3. The heat exchanger 4 extends substantially parallel to the reaction vessel 2. The heat exchanger 4 is in the shown embodiment in the form of an open ended pipe 17 which can be thermally controlled by a surrounding concentric pipe 18. Between the pipe 17 and the pipe 18 of the heat exchanger 4 an isolating fluid such as nitrogen gas may flow.

The apparatus 1 further comprises a first pipe 5 (the Mown comer'; length: 1187 m; internal diameter: 18 cm) for feeding the fluid waste stream into the reaction vessel 2. The first pipe 5 is suspended in the reaction vessel 2. Together, the reaction vessel 2 and the first pipe 5 define during use a down going flow through the first pipe 5 and an up going flow through the annulus 6 defined by the first pipe 5 and reaction vessel 2. In Fig. 1, the down going and up going flowing flows are indicated with arrows .

The person skilled in the art will readily understand that, while the down going flow is defined to flow through the first pipe 5 and the up going flow is defined to flow through the annulus 6, the direction of the flows can also be reversed, if desired.

Further the apparatus 1 comprise oxidant feeding means 7 for feeding e.g. an oxidant rich gas into the first pipe 5. The oxidant feeding means are embodied in a second pipe that extends in a substantially concentric manner along the first pipe 5. The outlet 8 of the second pipe 7 is comprised in the wall of the first pipe 5. Preferably the outlet 8 of the second pipe 7 is placed nearby that part of the reaction vessel 2 forming in use the wet oxidation reaction zone 9. Figures 2 - 5 show schematic cross-sectional views of different phases in the wet oxidation of a fluid waste stream using the apparatus according to Fig. 1.

In Fig. 2 a heated heating fluid 10 such as water is fed through the first pipe 5 in order to obtain a selected temperature in the reaction zone 9 of the reaction vessel 2. Usually, the selected temperature in the reaction zone 9 is between 180 - 340°C, preferably 250 - 310°C, most preferably 270 - 280°C.

If desired, the first pipe 5 may be thermally isolated by feeding an isolating fluid 11 such as nitrogen gas through the second pipe I , in order to reduce heat loss of the heating fluid 10.

Herewith the first pipe 5 is isolated at least over a range from the inlet 12 of the first pipe 5 to the outlet 8 of the second pipe 7.

After a suitable temperature for performing a wet oxidation in the reaction zone 9 has been obtained, a fluid waste stream 13 (see Fig. 3) is fed through the same first pipe 5 thereby replacing the heating fluid 10. The suitable temperature may e.g. be determined by temperature sensors 20.

When the fluid waste stream 13 approaches the reaction zone 9, the feeding of the isolating fluid 11 through the second pipe 7 is stopped. Instead an oxidant 14 such as gaseous oxygen is fed through the second pipe 7. The oxidant 14 enters the first pipe 5 nearby, but preferably just upstream of, the reaction zone 9.

In Fig. 4 the fluid waste stream 13 reaches the reaction zone 9 and the wet oxidation of the fluid waste stream 13 begins. As the wet oxidation reaction is exothermic, the temperature of the reaction zone 9 may rise. The temperature of the reaction zone 9 may be controlled by removing heat from the fluid 13 in the reaction zone 9 if the fluid 13 in the reaction zone 9 is above a selected temperature. Instead, heat may be added if the temperature of the fluid 14 is below a selected temperature. This may for example be done using the heat exchanger 4 and HTF 16.

After the reaction zone 9 the at least partially reacted fluid waste stream 13 is transported further, through annulus 6, back up to the ground surface 15 (see Fig. 5) . The stream 13 may then further be processed.

The person skilled in the art will understand that many modifications may be made. For instance, pumps, further feeding means and sensors for e.g. temperature and pressure may be present.

Claims

C A I M S

1. Apparatus (1) for performing a deep well wet oxidation treatment of a fluid waste stream (13) , the apparatus (1) at least comprising:

- a deep well reaction vessel (2) which is suspended in a subterranean hole (3) ;

- a first pipe (5) for feeding the fluid waste stream (13) into the reaction vessel (2) , the first pipe (5) being suspended in said reaction vessel (2) and thereby defining a down going flow through the first pipe (5) and an up going flow through a passage (6) defined by the first pipe (5) and the reaction vessel (2) ;

- a heat exchanger (4) in heat exchange relation to the reaction vessel (2) ; and

- oxidant feeding means (7) for feeding an oxidant (14) to the first pipe (5) nearby a reaction zone (9) in which during use of the apparatus (1) the wet oxidation of the fluid waste stream (13) can

2. Apparatus according to claim 1, wherein the outlet (8) of the oxidant feeding means is placed nearby the reaction zone (9) .

3. Apparatus according to claim 1 or 2, wherein the outlet (8) of the oxidant feeding means is placed just upstream of the reaction zone (9) .

4. Apparatus according to one or more of the preceding claims, wherein the oxidant feeding means comprise a second pipe (7) , which second pipe (7) extends at least partially along the first pipe (5) .

5. Apparatus according to claim 4, wherein the second pipe (7) extends along the first pipe (5) in a substantially concentric manner, preferably over a range from the inlet (12) of the first pipe (5) to nearby the outlet (8) of the second pipe (7) .

6. Apparatus according to one or more of the preceding claims, wherein the first pipe (5) is at least partially thermally isolated.

7. Apparatus according to claim 6, wherein the first pipe (5) is thermally isolated substantially over a range from the inlet (12) of the first pipe to nearby the outlet (8) of the oxidant feeding means .

8. Apparatus according to claim 6 or 7, wherein the first pipe (5) can be thermally isolated by feeding an isolating fluid (11) , preferably gaseous nitrogen, through the second pipe (7) .

9. Apparatus according to one or more of the preceding claims, wherein the inner diameter of the first pipe (5) is substantially constant.

10. Apparatus according to claim 9, wherein the inner diameter of the first pipe (5) is at least substantially constant over a range from the inlet (12) of the first pipe (5) to the reaction zone (9) , preferably also including the reaction zone (9) .

11. Apparatus according to one or more of the preceding claims, wherein the heat exchanger (4) is positioned outside of and substantially parallel to the reaction vessel (2) , in the subterranean hole (3) .

12. Apparatus according to claim 11, wherein the heat exchanger (4) comprises a third pipe (17) and a fourth pipe (18), the fourth pipe (18) at least partially concentrically extending along the third pipe (17) , wherein the heat exchanger (4) can be thermally controlled by flowing an isolating fluid such as nitrogen gas between the third pipe (17) and the fourth pipe (18) .

13. Method for performing a deep well wet oxidation treatment of a fluid waste stream (13) , the method comprising the steps of:

- flowing a fluid waste stream (13) in a down going flow to a selected depth below the ground surface (15) in a reaction vessel (2) suspended in a subterranean hole (3) to form a hydrostatic column of fluid exerting a selected pressure for performing a wet oxidation reaction in a selected reaction zone (9) in the reaction vessel (2) ;

- providing a selected temperature to the fluid waste stream (13) suitable for performing a wet oxidation reaction in the selected reaction zone (9) ;

- adding an oxidant (14) to the fluid waste stream (13) nearby the reaction zone (9) ;

- performing the wet oxidation reaction in the selected reaction zone (9) ; - controlling the temperature of the reaction zone (9) by adding heat to the fluid (13) in the reaction zone (9) if the temperature of the fluid (13) in the reaction zone (9) is below a selected temperature and removing heat from the fluid (13) in the reaction zone (9) if the fluid (13) in the reaction zone (9) is above a selected temperature; and

- flowing the reacted fluid waste stream (13) further, back up to substantially ground surface (15) .

14. Method according to claim 13, wherein the fluid waste stream (13) is flown through a first pipe (5) being suspended in the reaction vessel (2) , wherein the first pipe (5) and reaction vessel (2) define a down going flow through the first pipe (5) and an up going flow through a passage (6) defined by the first pipe (5) and the reaction vessel (2) , and wherein the oxidant (14) is flown through a second pipe (7), the second pipe (7) extending along the first pipe (5) in a substantially concentric manner.

15. Method according to claim 13 or 14, wherein the selected pressure in the reaction zone (9) is between 10 - 100, preferably 25 - 85, most preferably 40 - 60 bar.

16. Method according to one or more of the preceding claims 13

- 15, wherein the selected temperature in the reaction zone (9) is between 180 - 340°C, preferably 250 - 300°C, most preferably 270 - 280°C.

17. Method according to one or more of the preceding claims 13

- 16, wherein the selected temperature in the reaction zone (9) is obtained by flowing a heated heating fluid (10) .

18. Method according to one or more of the preceding claims 13

- 17, wherein the oxidant (14) is added to the reaction zone (9) after the selected temperature and pressure have been obtained in the reaction zone (9) .