Liquid purification or separation – With heater or heat exchanger – With treating fluid addition
Reexamination Certificate
2001-10-18
2004-08-10
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
With heater or heat exchanger
With treating fluid addition
C015S093100, C210S205000, C210S219000, C422S184100, C422S200000, C422S224000
Reexamination Certificate
active
06773581
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to methods and systems for using a hydrothermal reactor for the purposes of either waste destruction, energy generation, or production of chemicals. More specifically, the present invention pertains to methods and systems for the hydrothermal treatment of organics in a reactor when the organics contain or generate inorganic compounds such as salts or oxides during oxidation. The present invention is particularly, but not exclusively, useful as a method and system for using a reactor to accomplish the hydrothermal treatment of materials in a way which avoids the unwanted build-up of inorganic compounds in the reactor.
BACKGROUND OF THE INVENTION
The present invention relates generally to the conversion of a broad spectrum of materials and especially to a method for the hydrothermal treatment of organics. Of particular importance to the present invention are organics which contain inorganic compounds such as salts or oxides or which will generate these inorganic compounds under supercritical temperature and pressure conditions, or at supercritical temperatures and elevated, yet subcritical pressures.
The process of wet oxidation has been used for the treatment of aqueous streams for over thirty (30) years. In general, a wet oxidation process involves the addition of an oxidizing agent, typically air or oxygen, to an aqueous stream at elevated temperatures and pressures. The resultant “combustion” of organic or inorganic oxidizable materials occurs directly within the aqueous phase.
A wet oxidation process is typically characterized by operating pressures in the range of 30 bar to 250 bar (440 psia-3,630 psia) and operating temperatures in a range of one hundred fifty degrees Celsius to three hundred seventy degrees Celsius (150° C.-370° C.). Under these conditions, liquid and gas phases coexist for aqueous media. Since gas phase oxidation is quite slow at these temperatures, the reaction is primarily carried out in the liquid phase. To do this, the reactor operating pressure is typically maintained at or above the saturated water vapor pressure. This causes at least part of the water to be present in a liquid form. Even in the liquid phase, however, reaction times for substantial oxidation are on the order of one (1) hour. In many applications, reaction times of this length are unacceptable.
In addition to unacceptably long reaction times, the utility of conventional wet oxidation is limited by several factors. These include: the degree of oxidation attainable; an inability to adequately oxidize refractory compounds; and the lack of usefulness for power recovery due to the low temperature of the process. For these reasons, there has been considerable interest in extending wet oxidation to higher temperatures and pressures. For example, U.S. Pat. No. 2,944,396, which issued Jul. 12, 1960 to Barton et al., discloses a process wherein an additional second oxidation stage is accomplished after wet oxidation. In the Barton process, unoxidized volatile combustibles which accumulate in the vapor phase of the first stage wet oxidation reactor are sent to complete their oxidation in the second stage. This second stage is operated at temperatures above the critical temperature of water, about three hundred seventy four degrees Celsius (374° C.).
A significant development in the field occurred with the issuance of U.S. Pat. No. 4,338,199, entitled “Processing Methods for the Oxidation of Organics In Supercritical Water,” which issued to Modell on Jul. 6, 1982. Specifically, the Modell '199 patent discloses a wet oxidation process which has now come to be widely known as supercritical water oxidation (“SCWO”). As the acronym SCWO implies, in some implementations of the SCWO process, oxidation occurs essentially entirely at conditions which are supercritical in both temperature (greater than 374° C.) and pressure (greater than about 3,200 psi or 220 bar). Importantly, SCWO has been shown to give rapid and complete oxidation of virtually any organic compound in a matter of seconds at temperatures between five hundred degrees and six hundred fifty degrees Celsius (500° C.-650° C.) and at pressures around 250 bar. During this oxidation, carbon and hydrogen in the oxidized material form the conventional combustion products, namely carbon dioxide (“CO
2
”) and water. When chlorinated hydrocarbons are involved, however, they give rise to hydrochloric acid (“HCl”), which will react with available cations to form chloride salts. Due to the corrosive effect of HCl, it may be necessary to intentionally add alkali to the reactor to avoid high concentrations of hydrochloric acid in the reactor. This is especially important in the cooldown equipment following the reactor. In a different reaction, when sulfur oxidation is involved, the final product in SCWO is a sulfate anion. This is in contrast to standard, dry combustion, in which gaseous sulfur dioxide (“SO
2
”) is formed and must generally be treated before being released into the atmosphere. As in the case of chloride, alkali may be intentionally added to avoid high concentrations of corrosive sulfuric acid. Similarly, the product of phosphorus oxidation is a phosphate anion.
At typical SCWO reactor conditions, densities are around 0.1 g/cc. Thus, water molecules are considerably farther apart than they are in water at standard temperatures and pressures (STP). Also, hydrogen bonding, a short-range phenomenon, is almost entirely disrupted, and the water molecules lose the ordering that is responsible for many of the characteristic properties of water at STP. In particular, the solubility behavior of water under SCWO conditions is closer to that of high pressure steam than to water at STP. Further, at typical SCWO conditions, smaller polar and nonpolar organic compounds, having relatively high volatility, will exist as vapors and are completely miscible with supercritical water. It also happens that gases such as nitrogen (N
2
), oxygen (O
2
), and carbon dioxide (CO
2
) show similar complete miscibility in supercritical water. The loss of bulk polarity in supercritical water also significantly decreases the solubility of salts. The lack of solubility of salts in supercritical water causes the salts to precipitate as solids and deposit on process surfaces causing fouling of heat transfer surfaces and blockage of the process flow.
A process related to SCWO known as supercritical temperature water oxidation (“STWO”) can provide similar oxidation effectiveness for certain feedstocks but at lower pressure. This process has been described in U.S. Pat. No. 5,106,513, entitled “Process for Oxidation of Materials in Water at Supercritical Temperatures and Subcritical Pressures,” which issued to Hong on Apr. 21, 1992, and utilizes temperatures in the range of six hundred degrees Celsius (600° C.) and pressures between 25 bar to 220 bar. On the other hand, for the treatment of some feedstocks, the combination of temperatures in the range of four hundred degrees Celsius to five hundred degrees Celsius (400° C.-500° C.) and pressures of up to 1,000 bar (15,000 psi) have proven useful to keep certain inorganic materials from precipitating out of solution (Buelow, S. J., “Reduction of Nitrate Salts Under Hydrothermal Conditions,” Proceedings of the 12
th
International Conference on the Properties of Water and Steam, ASME, Orlando, Fla., September, 1994).
The various processes for oxidation in an aqueous matrix (e.g. SCWO and STWO) are referred to collectively as hydrothermal oxidation, if carried out at temperatures between about three hundred seventy-four degrees Celsius to eight hundred degrees Celsius (374° C.-800° C.), and pressures between about 25 bar to 1,000 bar. Similar considerations of reaction rate, solids handling, and corrosion also apply to the related process of hydrothermal reforming, in which an oxidizer is largely or entirely excluded from the system in order to form products which are not fully oxidized. The processes of hydrothermal oxidation and hydrothermal reforming will
Downey Kevin W.
Hazlebeck David A.
Isoya Toshisuke
Martinez Martin R.
Nakayama Satoshi
General Atomics
Hruskoci Peter A.
Nydegger & Associates
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