Hydraulic energy dissipator for wet oxidation process

This invention relates to a process and apparatus for dissipating the energy of a wet oxidation mixture after that stream traverses a pressure control valve. The depressurized stream is discharged into a phase separator vessel containing a gas phase and a liquid phase. The pressure control valve is positioned to discharge the oxidation mixture at a selected orientation below the surface level of the liquid phase in the vessel. This dissipates the energy of the mixture and prevents erosion of the phase separator vessel. The apparatus of the invention includes the separator vessel with gas and liquid phase exits, a control device for maintaining the liquid phase at the selected level in the vessel, a pressure control valve positioned at an aperture in the vessel for discharging the mixture below the surface level of the liquid phase in the vessel, and sealing device between the control valve and the separator vessel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process and apparatus for dissipating the 
energy of a pressurized stream as that stream traverses a pressure control 
valve, and more particularly, to dissipating the energy of a wet oxidation 
mixture after that stream traverses a pressure control valve. 
2. Description of Related Art 
Wet oxidation is a well known process for treatment of aqueous wastewaters. 
The process involves heating a mixture of the wastewater plus an 
oxygen-containing gas to elevated temperature and pressure to effect 
oxidation of oxidizable substances contained in the wastewater. All wet 
oxidation systems include one or more pressure control valves to regulate 
the flow of liquid, solids and gases from the high pressure part of the 
system to the low pressure part of the system. Depending on the 
composition of the process stream and the temperature and pressure of the 
flowing stream, the pressure control valve discharge can be highly 
abrasive to the piping and receiving vessel on the low pressure side. The 
process stream velocity is commonly at or close to sonic velocity due to 
the high pressure drop across the pressure control valve. There will be 
steam flashing at the control valve outlet if the process stream 
temperature is close to the vapor pressure of water. The wet oxidation 
system process stream commonly contains significant concentrations of 
suspended solids. The combination of suspended solids, flashing steam, and 
high velocity makes the pressure control valve effluent extremely 
abrasive. 
Presently, a specially designed pressure control valve and receiving pot 
combination are employed to minimize the effects of abrasion on the low 
pressure side of the system. The receiving pot is typically small in 
diameter and includes special wear resistant materials that can stand up 
to highly abrasive conditions for long periods of time. The total process 
stream sweeps through the receiving pot and on to a standard phase 
separator vessel. It is difficult to determine the correct size for a 
receiving pot and there are still applications where the current pot 
design fails due to unknown and/or uncontrollable process factors. 
Ledding, in U.S. Pat. No. 3,150,105, discloses a blow down tank or other 
suitable decompression vessel which receives the cooled regenerated carbon 
slurry from a wet oxidation reactor. No further description of the blow 
down tank is provided. 
In U.S. Pat. No. 3,994,702, Schweimanns et al. disclose a flooded slucing 
chamber for ash removal from a pressurized gasification chamber. 
Meidl et al., in U.S. Pat. No. 4,620,563 disclose a blowdown pot with an 
inlet pressure control valve through which the pot receives unwanted 
residue e.g., ash from a high pressure chemical reactor. This reactor 
residue can be continuously or semi-continuously blown out from the high 
pressure, high temperature chemical reactor into the relatively low 
pressure blowdown pot which includes means for maintaining a liquid level 
therein, thus minimizing steam flashing and vessel wear. 
In U.S. Pat. No. 5,011,114, Depuydt et al. disclose a pressure control 
valve with a valve seat and support assembly which extends beyond the 
valve body to prevent erosion by the blowdown slurry. The apparatus also 
includes a displacement-compensating seal between the valve and receiving 
vessel to allow for thermal expansion and contraction during the blowdown 
cycle while maintaining the integrity of the seal. 
In general, these references disclose methods and/or apparatus for handling 
only a fraction of the total process stream passing through a wet 
oxidation treatment system. The receiving pot presently in use is 
susceptible to failure due to abrasion wear. Applicants have devised a 
process and an apparatus to overcome the shortcomings of the process and 
apparatus presently in use. 
SUMMARY OF THE INVENTION 
The invention is a process for use in a wet oxidation system where 
wastewater and oxygen-containing gas are combined to form a wet oxidation 
mixture which is pressurized and heated within a pressure vessel to effect 
wet oxidation treatment. The mixture then flows from said pressure vessel, 
through cooling means to cool said mixture, then to a pressure control 
valve which maintains the system at a selected operating pressure. The 
improvement comprises depressurizing and discharging said cooled oxidation 
mixture through said pressure control valve into a phase separator vessel 
of selected length to diameter ratio, said vessel containing a gas phase 
and a liquid phase. The pressure control valve is positioned to discharge 
said oxidation mixture at a selected orientation below the surface level 
of said liquid phase within said vessel, thereby dissipating the energy of 
the oxidation mixture therein and preventing erosion of said phase 
separator vessel. 
The invention includes an apparatus for carrying out the above process. The 
apparatus comprises a phase separator vessel having a length to diameter 
ratio greater than about 1.0, said vessel capable of containing a gas 
phase and a liquid phase therein. The vessel has an upper exit means for 
removing said gas phase therefrom, and a lower exit means for removing 
said liquid phase therefrom. A control means for maintaining said liquid 
phase at a selected level within said vessel is present. A pressure 
control valve is positioned at an aperture on said separator vessel, said 
valve depressurizing and discharging said pressurized and heated wet 
oxidation mixture at a selected orientation below the selected level of 
said liquid phase within said vessel. Finally, there is a sealing means 
for maintaining a fluid-tight seal between said pressure control valve and 
said separator vessel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a wet oxidation mixture of wastewater and gases, which 
has been pressurized and heated to effect wet oxidation treatment, is 
cooled by flowing from a wet oxidation reactor, through cooling means, 
such as a process heat exchanger, then enters a conduit 10 controlled by a 
pressure control valve 12. The valve 12 maintains the oxidation mixture at 
the desired system operating pressure, as measured by an upstream pressure 
monitor (not shown). The pressure control valve 12 has a flange 14 which 
is fluid-tight sealingly secured to a flanged aperture 16 in a separator 
vessel 18 such that the oxidation mixture is depressurized directly from 
said valve 12, through said aperture 16, into said separator vessel, 
essentially to atmospheric pressure. The vessel 18, in this embodiment of 
the invention, has a length to diameter ratio of greater than about 1.0, 
with the longer dimension oriented vertically. Within this vessel is a 
lower liquid phase 20 with a liquid surface 22 and an upper gas phase 24. 
The valve 12 and flange 14 are positioned at the flanged aperture 16 in 
the vessel 18 so the oxidation mixture is discharged in a selected 
orientation below the surface 22 of the liquid phase to dissipate the 
energy of the oxidation mixture therein. With the vertically oriented 
separator vessel 18, the orientation of the oxidation mixture discharge 
stream is at least about 30.degree. below horizontal, providing a greater 
overall distance to the opposite wall of the vessel than just the vessel 
diameter. This orientation allows the liquid phase within the separator 
vessel 18 to more effectively dissipate the energy of the oxidation 
mixture and prevent erosion of the vessel wall by that mixture as it 
discharges. As mentioned above, the pressurized wet oxidation mixture 
commonly contains three phases, gas, liquid and suspended solids. As the 
mixture traverses the pressure control valve to a lower pressure 
environment, the expanding gases (air and steam) give the mixture very 
high velocity. This gives the more dense liquid and solids portion of the 
mixture large momentum. The discharge of the mixture below the liquid 
level in the separator vessel, into a dense liquid medium, allows the 
liquid in the separator vessel to absorb the momentum of the mixture 
before the liquid and solids contact the wall of the vessel and cause 
erosion damage. 
Within the liquid phase 20 the gases disengage from the mixture and rise to 
the upper gas phase 24. The gases flow through a demister 26 which removes 
droplets of liquid carried by the gases, and exit the separator via an 
upper gas conduit 28. The volume of the separator vessel 18 for the upper 
gas phase 24 must be sufficiently large to accommodate the volume of 
pressurized oxidation gases which expand as they reach reduced pressure 
conditions in the separator vessel. The separator vessel is generally 
operated at or near atmospheric pressure, although there may be situations 
where it is advantageous for the separator to operate at above atmospheric 
pressure. The lower liquid phase 20 exits the separator via a lower liquid 
conduit 30 controlled by a level control valve 32. A level controller 34 
controls the liquid outlet valve 32 and maintains the liquid surface level 
22 within the vessel 18 at a point between two level sensors 36. The 
surface level is well above the oxidation mixture discharge point into the 
separator vessel. The liquid within the separator vessel is preferably 
oxidized wastewater which dissipates the energy of the depressurizing 
mixture. 
Referring to FIG. 2, those components in common with FIG. 1 are shown with 
the same indica. In this embodiment the separator vessel 18 is oriented 
with the longer dimension horizontal and with the pressure control valve 
again positioned to discharge below the surface 22 of the liquid phase 20. 
In this embodiment, the greater width of the liquid phase within the 
separator vessel allows the pressure control valve discharge stream to be 
oriented between horizontal and about 30.degree. below horizontal. The 
liquid phase surface 22 is maintained above the discharge point and 
between the two level sensors 36, by the level controller 34 and control 
valve 32 as described above. This orientation likewise allows the liquid 
phase within the separator vessel 18 to dissipate the energy of the 
oxidation mixture and prevent erosion of the vessel wall by that mixture 
as it discharges. The liquid within the vessel is preferably oxidized 
effluent from the wet oxidation system. 
While the invention has been particularly shown and described with 
reference to a preferred embodiment thereof, it will be understood by 
those skilled in the art that various changes in form and details may be 
make therein without departing from the spirit and scope of the invention.