Liquid purification or separation – Processes – Preventing – decreasing – or delaying precipitation,...
Reexamination Certificate
1999-05-06
2001-05-29
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Preventing, decreasing, or delaying precipitation,...
C210S753000, C210S754000, C210S761000, C588S253000, C588S253000, C588S253000
Reexamination Certificate
active
06238568
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to a method and system for wet oxidation. The present invention is particularly, but not exclusively, useful as a method and system for hydrothermal treatment in a reactor which minimizes build-up or plugging of precipitating salts in the reactor and other equipment.
BACKGROUND
The process of wet oxidation 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 significant development in the field of wet oxidation occurred with the issuance of U.S. Pat. No. 4,338,199, to Modell on Jul. 6, 1982. The Modell '199 patent discloses a wet oxidation process which is known as supercritical water oxidation (“SCWO”). In some implementations of the SCWO process, oxidation occurs essentially entirely at conditions which are supercritical in both temperature (>374° C.) and pressure (>about 3,200 psi or 220 bar). Importantly, the SCWO process gives rapid and complete oxidation of virtually any organic compound in a matter of seconds.
A related process, known as supercritical temperature water oxidation (“STWO”), can provide similar oxidation effectiveness for certain feedstocks, but at a lower pressure. This process is described in U.S. Pat. No. 5,106,513, issued Apr. 21, 1992 to Hong, and utilizes temperatures in the range of six hundred degrees Celsius (600° C.) and pressures between 25 bar to 220 bar.
The various processes for oxidation in an aqueous matrix 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. A somewhat related process in which an oxidant is largely or entirely excluded from the system in order to form products which are not fully oxidized is called hydrothermal reforming. The processes of hydrothermal oxidation and hydrothermal reforming will hereinafter be jointly referred to as “hydrothermal treatment.”
A common difficulty with some hydrothermal applications is precipitating of salts during processing, including salts which are normally water soluble such as sodium chloride (NaCl). The salt precipitants deposit on surfaces in the reactor and cause plugging of the reactor or other equipment. Further, the salt can cause fouling of heat transfer surfaces in the system. The build-up of salt precipitates can eventually necessitate an online or off-line cleaning of the system.
Many approaches have been tried to prevent or inhibit the salt precipitates from plugging the reactor and/or the formation of salt precipitates. Examples of prior approaches include (i) alternating reactors, (ii) a reversing flow reactor, (iii) a brine pool at the bottom of the reactor, (iv) adding inert particles to the feed material, (v) adding molten salts to the feed material, (vi) purge through a porous wall of the reactor, (vii) adding a cooler stream at the wall of the reactor, (viii) using a mechanical scraper, and/or (ix) using high velocity flow in the reactor. Unfortunately, these approaches include one or more of the following drawbacks: expensive, limited success in inhibiting salt accumulation, reduce efficiency of the system, and/or create a corrosion/materials problem.
Another common difficulty with some hydrothermal applications is the generating of reaction products which contain corrosive elements such as acids or bases. The corrosive elements damage the reactor and the system.
Many approaches have been tried to inhibit the formation of corrosive elements and/or to minimize the damage caused by the corrosive elements. Example of prior approaches include (i) neutralizing the feed material with a neutralizing agent, (ii) using a corrosion resistant liner in the reactor, (iii) using cold flow near the wall of the reactor, and/or (iv) purging through a porous wall of the reactor. Unfortunately, these approaches include one or more of the following drawbacks: expensive to manufacture and operate, limited success in minimizing damage caused by the corrosive elements, not applicable to all process streams, and/or creates salt precipitates which plug the reactor.
In light of the above, it is an object of the present invention to provide a system and method for hydrothermal treatment which continuously and reliably handles reaction medium containing or generating precipitating salts. Another object of the present invention is to provide a system and method for hydrothermal treatment of corrosive reaction medium. Still another object of the present invention is to provide a system and method for hydrothermal treatment which allow precipitating salts to be transported through the reactor without plugging. Yet another object of the present invention is to provide a system and method for accomplishing hydrothermal treatment which is easy to implement, simple to use, and relatively inexpensive to operate.
SUMMARY
A system for performing hydrothermal treatment of a feed material is provided herein. The hydrothermal treatment is typically performed in a reaction chamber of a reactor at temperatures in a range of between three hundred seventy-four degrees Celsius (374° C.) to about eight hundred degrees Celsius (800° C.) and at pressures above about 25 bars. Uniquely, an additive is mixed with the feed material to produce a reaction medium in the reaction chamber which contains phosphate.
Importantly, the present invention recognizes that phosphate assists in the transport of precipitating salts in the reactor, inhibits excessive build-up of salts in the reactor and inhibits plugging of the hydrothermal treatment system. With the present invention, the precipitating salts may initially accumulate slightly on the reactor wall. Subsequently, the salts transport through the reactor. Further, as a result of the present invention, corrosive elements in the reaction medium can be neutralized because the phosphate allows any precipitants, created by neutralization, to be transported through the reactor.
As provided herein, the additive adjusts the composition of the reaction medium so that the reaction medium contains phosphate salt. Preferrably, the phosphate salt includes a mono-basic phosphate salt such as monosodium phosphate. The adjustment to the reaction medium can be made with an additive which includes one or more (i) phosphate salts, (ii) phosphorus containing compounds, (iii) phosphoric acids, (iv) organo-phosphates, (v) neutralizing compounds, (vi) neutralizing agents, and/or (vii) a combination thereof.
The exact percentage of phosphate in the reaction medium depends upon the type of feed material utilized and the type of additive utilized. It is anticipated that a phosphate concentration of between approximately one and 100 percent of the total salts in the reaction medium will significantly inhibit build-up of precipitating salts. Preferably, the phosphate concentration in the reaction medium is between 10 and 100 percent of the total salts in the reaction medium. Depending upon the reaction medium, higher phosphate concentrations may be necessary. For example, a phosphate concentration of between approximately 50 to 100 percent of the total salts in the reaction medium may be beneficial for the transport of precipitating salts.
A suitable phosphate compound can be selected from a group which includes H
3
PO
4
, NaH
2
PO
4
, Na
2
HPO
4
, Na
3
PO
4
, (NH
4
)
3
PO
4
, (NH
4
)
2
HPO
4
, (NH
4
)H
2
PO
4
. Alternately, the phosphate compound can be selected from a group which includes KH
2
PO
4
, K
2
HPO
4
, or K
3
PO
4
.
A suitable neutralizing compound can be selected from a group which includes NaOH, NaHCO
3
, Na
2
CO
3
, KOH, KHCO
3
, K
2
CO
3
, Ca(OH)
2
, CaO, CaCO
3
, NaNO
3
, NaNO
2
, KNO
3
, KNO
2
, Ca(NO
3
)
2
, Na
3
PO
4
, Na
2
HPO
4
, KPO
4
and K
2
HPO
4
. Alternately, the neutralizing compound can be selected from a group which inclu
General Atomics
Hruskoci Peter A.
Nydegger & Associates
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