Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2001-04-23
2004-03-23
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S761000, C588S253000, C588S253000, C588S253000, C588S253000, C588S253000, C588S253000, C588S253000
Reexamination Certificate
active
06709602
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to methods and systems for accomplishing hydrothermal treatment for the purposes of either waste destruction, energy generation, or the production of chemicals. More specifically, the present invention pertains to methods and systems for the hydrothermal treatment of solids having organic constituents. The present invention is particularly, but not exclusively, useful as a method and system for volatilizing a portion of a material and subsequently treating the volatilized portion hydrothermally.
BACKGROUND OF THE INVENTION
The present invention pertains to a process for converting materials at supercritical temperature and pressure conditions, or at supercritical temperatures and elevated, yet subcritical, pressures. Supercritical and subcritical are defined here with reference to the critical point of pure water, 705° F. and 218 atm. For example, U.S. Pat. No. 4,338,199, which issued on Jul. 6, 1982 to Modell, discloses a hydrothermal process known as supercritical water oxidation (SCWO) because in some implementations oxidation in the aqueous/steam matrix occurs essentially entirely at conditions supercritical in temperature and pressure. The SCWO process has been shown to give rapid and complete oxidation of virtually any organic compound in a matter of seconds at 1000-1250° F. and 250 atm.
Under SCWO conditions, carbon and hydrogen form the conventional combustion products CO
2
and H
2
O, while chlorinated hydrocarbons (CHC's) give rise to hydrochloric acid (HCl). If cations are available, they will react with the hydrochloric acid to form chloride salts. Alkali may be intentionally added to the reactor to avoid high, corrosive concentrations of hydrochloric acid in the reactor and especially in the cooldown equipment following the reactor. One advantage of the SCWO process is that the conversion of material can be accomplished without producing the environmentally harmful by-products that are produced when the same material is combusted in air. For example, the final product of sulfur oxidation in SCWO is sulfate anion, in contrast to normal combustion, wherein sulfur oxidation forms gaseous SO
2
. As in the case of chloride, alkali may be intentionally added to avoid high concentrations of sulfuric acid. Similarly, the SCWO product of phosphorus oxidation is phosphate anion.
A hydrothermal 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 issued Apr. 21, 1992 to Hong, and utilizes temperatures in the range of 1200° F. and pressures between 25 and 218 atm. Like SCWO, the overall goal of the process may be waste destruction, energy generation, or production of chemicals. For convenience, the processes of SCWO and STWO will both be referred to herein as hydrothermal oxidation (HTO).
A key advantage of the hydrothermal processes described above is the cleanliness of the liquid and gaseous effluents. In particular, the gaseous emissions are far cleaner than those obtained by the conventional practice of incineration. EPA's Maximum Achievable Control Technology (MACT) standards for hazardous waste incineration took effect on Sep. 30, 1999. Current operating facilities were given until Mar. 31, 2003 to comply with the regulations. New facilities are required to comply with the new regulations at start-up. Table 1 shows that HTO emissions meet the MACT standards with little or no post-treatment, while incinerators require extensive emissions cleanup.
TABLE 1
Comparison of Incineration and HTO
with Respect to MACT/Air Standards
Typical incinerator
HTO Inherent
Type of Emissions
emissions controls
Performance
in Effluent Gas
needed to meet new
(with no gas cleanup
Stream
MACT/Air Standards
MACT Standards
devices)
Dioxins/difurans,
<0.2
Rapid quench, powdered
<0.006
ng/DSCM (TEQ)
activated carbon (PAC)
with fabric filter
baghouse
Particulate Matter,
<34
Fabric filter baghouse or
<4
mg/DSCM
electrostatic precipitator
Toxic Metals,
<0.024 for Cd + Pb
Wet electrostatic
<0.015 for Cd + Pb
mg/DSCM
<0.097 for
precipitator
<0.015 for Sb + As + Be + Cr
Sb + As + Be + Cr
Destruction and
>99.99
Afterburner
>99.999
removal efficiency,
%
HCI, ppmv
<21
Packed tower wet
<0.4
scrubber
NOx, ppm
depends on air
Only local regulations
<1
district - can be
apply. Ammonia or urea
<100 ppm
injection may be
required.
CO, ppm
<100
Afterburner
<2
Hydrocarbons, ppm
<10
Afterburner
<0.03
A useful variation on the HTO process is that in which no oxidant, or a sub-stoichiometric amount of oxidant, is added to the reactor. In this case, rather than converting to CO
2
and H
2
O, the organic material can reform into useful organic products. This process will be referred to as hydrothermal gasification (HTG), while HTO and HTG will be jointly referred to as hydrothermal processing (HTP).
A conventional limitation of HTP has been its application to bulk solids. The pressurized nature of the process typically requires that bulk solids be ground to a fine particle size to allow pumping into a high pressure reactor. Both grinding and pumping can require specialty equipment. In particular, a different device is generally required for different materials such as wood, plastic, or friable solids. Once the material has been ground, introduction into a pressurized reactor usually requires slurrying the material at a high concentration to minimize the size of the HTP reactor and associated process equipment. Thus, expensive, high pressure slurry pumps for viscous streams are typically required. For other solids such as metals, glass or ceramics, suitable size-reduction for introduction into an HTP reactor vessel is completely impractical.
A large amount of hazardous waste is generated each year that cannot be placed in a typical landfill unless it is pre-treated. Among this hazardous waste is a large amount of mixed waste consisting of non-hazardous solids that are contaminated with hazardous constituents. The hazardous constituents in these mixed-waste streams are generally suitable for direct feeding into a HTP reactor if they can be first separated from the solid portion of the waste stream. Once the hazardous constituent is extracted from the solid portion, the solid portion is generally considered non-hazardous and can be disposed of without further treatment in a conventional landfill.
Examples of such mixed-wastes include soils, inorganic adsorbents and other solids that are contaminated with hazardous organic or radioactive materials. Another such mixed waste consists of conventional and chemical munitions as well as munition dunnage. Protective suits, munition bodies and equipment contaminated with energetics, biological or chemical warfare agents is another mixed waste in which the solids portion could be disposed of conventionally if the hazardous contamination was removed and treated. Similarly, PCB contaminated transformers, pesticide contaminated bags and containers, and medical/biohazard waste such as contaminated needles and glass containers are all mixed wastes that could be disposed of efficiently by first separating the waste into hazardous and non-hazardous components.
Another category of waste that can pose difficulty for treatment by HTP is a concentrated acid, base or salt solution contaminated with an organic material. Treatment could be facilitated if the hazardous organic constituents could be separated for HTP while the residual inorganic solution could be handled by simpler means.
In the preceding examples, the organic to be treated may be a minor constituent or contaminant, or it may constitute a major portion of the feedstock.
In light of the above, it is an object of the present invention to provide methods suitable for the purposes of treating hazardous waste
Hong Glenn T.
Johanson Niles W.
Rickman William S.
Spritzer Michael H.
General Atomics
Hruskoci Peter A.
Nydegger & Associates
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