Two-stage separation process

Details Two-stage separation process Two-stage separation process

1998-10-01

2001-02-20

Barry, Chester T. (Department: 1724)

Liquid purification or separation

Processes

Including controlling process in response to a sensed condition

C210S743000, C210S761000, C210S110000, C210S120000, C210S134000, C210S137000

Reexamination Certificate

active

06190564

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present invention is directed to a separation process for an oxidized liquid effluent mixture from a subcritical wet oxidation process and, more particularly, to a two-stage separation process for separating the oxidized liquid effluent mixture.
2. Description of the Related Art
Wet oxidation is well known for the treatment of aqueous wastewaters. The process generally involves heating a mixture of the wastewater and an oxygen-containing gas to effect oxidation of oxidizable substances contained in the wastewater. When air is used as the source of oxygen-containing gas, the wet oxidation process is generally referred to as “wet air oxidation.”
Generally, subcritical wet oxidation systems include a wet oxidation chamber followed by a single separator vessel, with a pressure control valve therebetween to maintain the oxidation chamber pressure. When the oxidation process is terminated, an oxidized effluent mixture traverses the pressure control valve to the separator vessel. The pressure drop between the wet oxidation system and the separator vessel causes the mixture to separate into an oxidized liquid effluent and a gaseous phase.
Low pressure separators generally operate at, or near, ambient pressure. If a single low pressure separator vessel follows the wet oxidation system, the oxidized liquid effluent is generally acceptable for downstream processes (such as for pumping, or for storage in tanks). However, the gaseous phase produced from a single low pressure separation vessel is disadvantageous because it is at a low pressure, and requires additional equipment and energy to transport to downstream processes. In some instances, the gaseous phase may require further treatment, and potentially the expenditure of significant amounts of energy and expense for transport to and through subsequent treatment processes. Moreover, the gaseous phase from a single low pressure separator vessel generally contains a significant amount of water vapor. The water vapor also adds expense to downstream treatment of the gaseous phase, for example, increasing the energy requirement in a high temperature afterburner. Condensation of the water vapor on the interior of equipment may also cause corrosion to the equipment that comes into contact with the gaseous phase.
High pressure separators generally operate in the range of about 50 to 100 psig. If a single high pressure separation vessel is used, the energy expenditure for moving the gas would be eliminated, as the gaseous phase would retain sufficient pressure to provide the motive force to be transported to another location. However, in this instance, the oxidized liquid effluent may not be suitable for discharge to downstream processes, because the over pressure may cause a significant amount of gases, including CO
2
, N
2
, and O
2
, to remain dissolved in the oxidized liquid effluent. When such as oxidized liquid effluent is stored in a low pressure covered collection tank, for example, the dissolved gases remaining therein will come out of solution and collect within the talk, causing operational problems. Several techniques associated with various high pressure or temperature processes, including wet oxidation, are reported below.
U.S. Pat. No. 3,150,105 discloses a blow down talk to receive cooled regenerated carbon slurry from a wet oxidation reactor.
U.S. Pat. No. 3,994,702 discloses a flooded sluicing chamber for ash removal from a pressurized gasification chamber.
U.S. Pat. No. 4,620,563 discloses 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.
U.S. Pat. No. 5,011,114 discloses a pressure control valve with a valve seat and support assembly extending beyond the valve body to prevent erosion by the blowdown slurry.
U.S. Pat. No. 5,389,264 discloses a process for dissipating the energy of a wet oxidation mixture and preventing erosion of the phase separator vessel after that stream traverses a pressure control valve.
A need remains, however, for an improved process for providing an essentially gasfree oxidized liquid effluent with a gaseous phase with a reduced water vapor concentration, from a subcritical wet oxidation system. Lastly, there is a need to reduce or eliminate the energy requirement for transporting the gaseous phase to further treatment.
SUMMARY OF THE INVENTION
The present invention is directed to a process for separating the discharge from a subcritical wet oxidation process. The process involves providing an oxidized liquid effluent mixture by reacting an aqueous waste stream containing oxidizable materials with an oxidant at a first superatmospheric pressure. A first oxidized liquid effluent and a first gaseous phase are provided by subjecting the oxidized liquid effluent mixture to a first pressure drop from the first superatmospheric pressure to a second superatmospheric pressure. A second oxidized liquid effluent and a second gaseous phase are provided by subjecting the first oxidized liquid effluent to a second pressure drop from the second superatmospheric pressure to essentially atmospheric pressure. The pressure exerted on the first gaseous phase provides energy for transporting the first gaseous phase from a first location to a second location.
In another aspect of the invention, the process involves separating the discharge from a subcritical wet oxidation process. The process involves discharging a cooled wet oxidation mixture of liquid and gases from a subcritical wet oxidation system operating at superatmospheric pressure, through a first pressure control valve to a first separator vessel maintained at a superatmospheric pressure lower than the oxidation system, to form a superatmospheric first gaseous phase and a first oxidized liquid effluent therein. The superatmospheric first gaseous phase is discharged from the first separator vessel to further treatment or to the environment. The first oxidized liquid effluent is discharged from the first separator vessel, through a first level control valve for controlling the liquid level in the first separator vessel, to a second separator vessel maintained at essentially atmospheric pressure, to form a second gaseous phase and an essentially degassed second oxidized liquid effluent therein. The second gaseous phase is discharged from the second separator vessel, and the essentially degassed second oxidized liquid effluent is discharged from the second separator vessel.


REFERENCES:
patent: 2944396 (1960-07-01), Barton
patent: 5106513 (1992-04-01), Hong
patent: 5183577 (1993-02-01), Lehmann
patent: 5230810 (1993-07-01), Clark et al.
patent: 5240619 (1993-08-01), Copa et al.
patent: 5534148 (1996-07-01), Suzuki et al.
patent: 5651897 (1997-07-01), Lehmann
patent: 5674405 (1997-10-01), Bourhis

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