Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
1998-06-12
2001-01-09
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S761000
Reexamination Certificate
active
06171509
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to the inhibition of plugging in supercritical water reaction systems. More particularly, the invention relates to the inhibition of plugging in components upstream from a supercritical water reactor.
2. Description of the Related Art
Materials that are reacted in supercritical waste oxidization (“SCWO”) systems typically operate at relatively high pressures and high temperatures (e.g., at least about 700° F. and 3200 psia (about 370° C. and 220 bar)). Other systems may operate in the vicinity of supercritical conditions for water (i.e., at least about 500° F. and about 2000 psia (about 260° C. and 138 bar). Inorganic salts tend to have a low solubility within supercritical water. At a constant pressure, the solubility of salts typically increases as the temperature of the water increases. As the temperature approaches within about 10° F. (about 5° C.) of the supercritical temperature of water, the solubility of inorganic salts tends to drop to low values. Concurrently, the solubility of organic compounds, normally relatively insoluble in water, increases. This increase in solubility tends to assist the oxidation of the organic compounds.
Oxidizable matter that is reacted or oxidized in SCWO systems may cause solids or char to form within the reactor due to the low insolubility of the oxidation products within supercritical water. Alternately, the streams themselves (especially hazardous waste streams) may contain salts or solids, which tend to be insoluble at supercritical conditions. The presence of salts or solids in the reaction zone of the reactor tends to cause problems. For instance, if significant amounts of salts or solids are generated, the salts or solids may either partially or fully plug the reactor, thereby reducing reactor efficiency and/or causing expensive reactor shut-downs for maintenance purposes. Given the particularly high temperatures and pressures at which these systems operate, the replacement and/or maintenance of equipment in such systems tends to be expensive. Therefore, plugging in these systems tends to be a particularly difficult problem to address.
The plugging problem may be accentuated if additives are mixed with the stream to be treated. For instance, additives may be mixed with a given stream to raise or lower its pH (e.g., for the purpose of reducing corrosion) or to neutralize corrosive elements in the stream. These additives, or compounds produced from the additives, may in turn cause plugging in the system. By way of example, if a stream has a low pH, a practitioner may wish to add sodium hydroxide (NaOH) to the stream to raise the pH. If the waste stream contains chlorinated compounds oxidation of these compounds will typically produce hydrochloric acid (HCl). To inhibit the corrosion due to HCl, as well as other acidic compounds, NaOH is typically added to neutralize these acidic products. The reaction of NaOH with HCl typically produces the salt sodium chloride (NaCl). The formed salt may cause plugging of the reactor. Thus the additives available to control stream pH, and/or system corrosion, have necessarily been limited by practical considerations related to system plugging.
During at least one treatment procedure water is heated to supercritical conditions before entering the reactor, typically before oxidants are added. For salt containing waste streams, the rise to supercritical conditions may cause precipitation to occur prior to reaching the reactor. Thus plugging of the system may occur within the heater and conduits upstream from the reactor. While a number of reactor designs are known to prevent plugging of the waste stream within the reactor, little has been done to prevent plugging in the heater or conduits leading to the reactor. It is therefore desirable to devise a method and system for preventing the precipitation of salts within the system upstream from the reactor due to the rise to supercritical conditions. Such a method may help prevent the plugging of the system.
Conventional reactor assemblies operating in the vicinity of supercritical conditions for water are described in detail in the following patents or patent applications:
U.S. Pat. No. 5,403,533 to Hazlebeck et al., U.S. Pat. No. 4,141,829 to Thiel et al., U.S. Pat. No. 4,292,953 to Dickinson, U.S. Pat. No. 4,338,199 to Modell, U.S. Pat. No. 4,377,066 to Dickinson, U.S. Pat. No. 4,380,960 to Dickinson, U.S. Pat. No. 4,543,190 to Modell, U.S. Pat. No. 4,564,458 to Burleson, U.S. Pat. No. 4,593,202 to Dickinson, U.S. Pat. No. 4,594,164 to Titmas, U.S. Pat. No. 4,792,408 to Titmas, U.S. Pat. No. 4,822,394 to Zeigler et al., U.S. Pat. No. 4,822,497 to Hong et al., U.S. Pat. No. 4,861,497 to Welch et al., U.S. Pat. No. 4,891,139 to Zeigler et al., U.S. Pat. No. 4,113,446 to Modell et al., U.S. Pat. No. 5,106,513 to Hong, U.S. Pat. No. 4,898,107 to Dickinson, U.S. Pat. No. 4,983,296 to McMahon et al., U.S. Pat. No. 5,011,614 to Gresser et al., U.S. Pat. No. 5,053,142 to Sorensen et al., U.S. Pat. No. 5,057,231 to Mueller et al., U.S. Pat. No. 5,133,877 to Rofer et al., U.S. Pat. No. 5,183,577 to Lehmann, U.S. Pat. No. 5,192,453 to Keckler et al., U.S. Pat. No. 5,221,486 to Fassbender, U.S. Pat. No. 5,232,604 to Swallow et al., U.S. Pat. No. 5,232,605 to Baur et al., U.S. Pat. No. 5,240,619 to Copa et al., U.S. Pat. No. 5,250,193 to Sawicki et al., U.S. Pat. No. 5,252,224 to Modell et al., U.S. Pat. No. 4,822,497 to Hong et al., U.S. Pat. No. 5,551,472 to McBrayer et al., U.S. Pat. No. 5,755,974 to McBrayer et al., U.S. Pat. No. 5,620,606 to McBrayer et al., U.S. Pat. No. 5,582,715 to McBrayer et al., U.S. Pat. No. 5,591,415 to McBrayer et al., U.S. Pat. No. 5,552,039 to McBrayer et al., and U.S. Pat. No. 5,770,174 to Eller et al., U.S. Pat. No. 6,017,460 to McBrayer et al. The above-referenced patents and patent applications are hereby incorporated by reference.
SUMMARY OF THE INVENTION
A method for avoiding the precipitation of salts from a salt containing solution prior to the solution reaching the reactor is presented. A first waste stream, which includes a salt and oxidizable matter, is preferably introduced into a supercritical water oxidation system. The first stream is preferably conducted to a first pump. The first pump preferably brings the first stream to a pressure in the vicinity of supercritical conditions for water (i.e., at least about 2000 psia (about 138 bar)), more preferably to a pressure above about 3200 psia (about 220 bar).
After pressurization, the first stream is preferably conducted through a heat exchanger. The first stream is preferably heated by passage through the heat exchanger to a temperature and pressure such that the salts in the first stream remain substantially soluble in the first stream. The temperature of the first stream is preferably maintained below about 700° F. (about 370° C.). The first stream is preferably maintained at a pressure of at least about 3200 psia (about 220 bar). At temperatures above about 700° F. (about 370° C.), the solubility of the salts in the first stream may become lower. If the concentration of salts in the first stream is greater than the solubility limit of the heated first stream, a portion of the salts may precipitate out of the first stream. These precipitates may cause plugging of the system components. After passing through a heat exchanger the first stream is preferably conducted to a supercritical water reactor.
A second stream is preferably introduced into the system. The second stream is preferably a water stream which is substantially free of salts. The second stream may include water only. Preferably, the second stream is a water stream which includes oxidizable material. The oxidizable material preferably includes organic compounds.
The second stream is preferably passed to a second pump. The second pump preferably brings the second stream to a pressure in the vicinity of supercritical conditions for water. The stream is preferably brought to a pressure above about 3200 psia (about 220 bar).
Afte
McBrayer, Jr. Roy Nelson
Stenmark Lars Berhil
Tidlund Lars Henning
Barry Chester T.
Chematur Engineering AB
Conley & Rose & Tayon P.C.
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