Abstract:
An oxidative evaporation process for treating waste water or other aqueous solutions containing organics or reduced forms of inorganics is described. The process relies upon excessive amounts of pressurized oxygen gas to both oxidize the solution and to increase the solution&#39;s evaporation rate. The oxidized liquid effluent from a reactor undergoes a series of flashing steps until a saturated solution is produced which readily crystallizes upon cooling.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a process and apparatus specially applied to perform water evaporation and liquid phase oxidation reactions with forced circulating media. The operation can be conducted at elevated temperature and pressure conditions. Oxygen gas, a primary oxidant, as well as the medium for forced circulation, is supplied in excess amounts and is kept circulating under pressurized condition through the reaction systems. 
     The oxidation reactions generate heat, which is utilized to evaporate water in the reactor. By forcing the flow of oxygen gas through the reactor, the unreacted oxygen gas sweeps the vapor out of the reactor and causes a high rate of evaporation in the limited space and volume of the reactor. 
     The system thus performs both oxidation of reactive substances and evaporation of water in a controlled manner. The products of the system include steam and the oxidized salts in the forms of carbonate or other salt derivatives which are recovered in solid forms. 
     The system serves well as a new method of treating aqueous waste solutions containing organic and/or inorganic constituents. The organic and inorganic compounds are oxidized to form carbonate or sulfate and recovered as solids, and water in the feed is reclaimed as low pressure steam. 
     DESCRIPTION OF RELATED ART 
     The conventional process for evaporation refers to the single or multi-effect evaporation system. The operation of the conventional evaporation system is conducted under vacuum and low temperature. The conventional system provides no conditions for oxidative reactions to take place. Consequently, the heat required to evaporate water is solely dependent on outside sources. It is also understood that the removal of water vapor from the evaporator in the conventional system relies on vacuum pumping operations performed by means of mechanical or hydraulic devices. In contrast to those features, the process of this invention provides a positive means to perform oxidation reactions and the water vapor produced in the evaporation process is carried out of the reactor by a forced circulating gas medium. 
     Another conventional process for treating waste water streams to be referenced is known as the Wet-Air-Oxidation process. It is my understanding that in this conventional process liquid and gas are maintained in a mixed phase throughout the reactor, and that the process suppresses water evaporation in order to maintain this mixed phase. The conventional process also uses air instead of oxygen gas. Further, there is no gaseous stream discharged from the reactor in the conventional process; the end product of the process is a liquid rather than separate streams of solids and steam. These fundamental differences of the new process over the conventional process results in higher efficiency in oxygen usage and greater reduction in the liquid volume of the waste stream. 
     SUMMARY OF THE INVENTION 
     The process of this invention treats aqueous solutions containing organic compounds and/or reduced forms of inorganic compounds. The solution is heated and introduced into a reactor through which oxygen gas is circulated. The oxygen gas, which is pressurized, oxidizes reactive substances in the solution and carries evaporated water out of the reactor. Effluent from the reactor, having a higher salt concentration than the feed stream of aqueous solution, is converted into a stream of crystallized salts. 
    
    
     DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic diagram of the preferred embodiment of the process and apparatus of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The feed stream 1, an alkaline solution or being adjusted to be alkaline and containing organic and/or inorganic salts, is introduced to the Reactor 2 by mixing with the heated reactor bottoms side stream 3 to gain temperature to the level required by the process reactions. Independently, a rate controlled oxygen gas 14 is introduced at the bottom of the reactor. In the reactor, liquid and gas are maintained as separate phases, and thus the reactor may be referred to as a two-phase reactor. 
     The Reactor 2 is pressurized with the oxygen gas at a pressure sufficiently higher than the vapor pressure of water at the reacting temperature so as to maintain the reactor liquid saturated with dissolved oxygen. 
     In the Reactor 2, organic compounds are converted into carbon dioxide (CO 2 ) and water (H 2  O). CO 2  is in turn absorbed in alkaline solution to form carbonate salts and remain in the liquid phase. The inorganic salts, such as sulfide or bisulfides, are converted to sulfate which is also waterborne and remains in the solution. 
     The oxygen gas is kept circulated with the aid of the Gas Compressor 4. The circulating gas 14 will sweep out the water vapor from the Reactor 2 in an amount proportional to the rate of gas circulation. The rate of water evaporated in the reactor will thus be regulated by the rate of circulating gas. 
     The overhead stream 5, containing mainly water vapor and the excess oxygen gas, will be led to the Overhead Condensor 6 where water vapor is condensed. The condensate contains no salts and is readily disposable by conventional routes or can be recycled to the Reactor 2. The excess oxygen gas is recovered for reuse. 
     In the gas circulation loop, the make-up oxygen gas is supplied at the suction side of the compressor 4. The amount of oxygen make-up is automatically regulated by maintaining the suction pressure of the compressor constant. 
     The bottoms stream 7 is mainly a solution of oxidized inorganic salts, such as carbonates or sulfates. Their concentrations depend on the organic and inorganic content in the feed, and on the rate of oxygen gas circulated which controls the extent of water being evaporated. The bottoms stream is pumped to the Side Stream Heat Exchanger 8. 
     The Side Stream Heat Exchanger 8 is the sole source of heat supply for the entire system. Heat in the form of steam or electricity is transferred to the side stream of the reactor bottoms. The heated side stream is brought to mix with the feed stream 1 so that the influent to the Reactor 2 can be preheated. Heating the feed stream by mixing with the side stream of the reactor bottoms prevents fouling caused by polymerization or coagulation of organic compounds in the feed under high temperatures. 
     A net amount of the reactor bottoms 9 is withdrawn from the recycling side stream. The salt concentration in the reactor bottoms is further concentrated in a seres of flashing steps, by which water is recovered as low pressure steam and the dissolved salts are recovered as crystallized forms of salts. 
     Two Flash Pots 10, 13 in series are employed to achieve the recovery of salts and steam as follows. The first Flash Pot 10 provides a capacity for flashing the reactor bottoms stream and a recycled stream 11. The recycled stream 11 is the flashed liquid 12 pumped for reheating at the Overhead Condenser 6. The reheated stream 11 is then recycled to the first Flash Pot 10 until the salt concentration reaches a level tht the final flash at the second Flash Pot 13 will result in forming a saturated solution 15. 
     The latent heat of the reactor overhead vapor is thus utilized for reheating the flashed liquid from the first Flash Pot. The amount of heat required for reheating the flashed liquid, as indicated by the temperature of the recycled stream, is regulated by the rate of oxygen gas in circulation. The oxygen circulation rates in turn regulate the evaporation of water in the reactor. The water vapor generated in the reactor should provide a sufficient amount of heat for reheating the flashed liquid. 
     The steam generated from the flash pots is a low pressure steam, which is a usable energy source. The underflow from the second Flash Pot is a salt saturated solution, which forms crystals upon cooling after being discharged from the system. 
     When an inert gas, such as nitrogen, is used in lieu of oxygen, the process system can be utilized as a double effect evaporator. Water in the feed is evaporated in the reactor (the first effect evaporator) and the vapor is recovered as condensate at the Overhead Condenser. In the Overhead Condenser, the latent heat of the vapor is recovered to heat the first flash bottoms. A further evaporation of water takes place in the second Flash Pot (the second effect evaporator). 
     While the preferred embodiments of the invention have been shown, changes, additions and substitutions of equivalent steps and compounds can be made without departing from the spirit and scope of the invention.