WET OXIDATION OF WASTE LIQUOR

OXYDATION PAR VOIE HUMIDE DES LIQUEURS PERDUES

English Abstract

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ABSTRACT OF THE DISCLOSURE
A safe method for mixing pure oxygen, or
an oxygen enriched gas, at high pressure, with waste
liquor in a wet oxidation system, such that inter-
mittent drying conditions are avoided, thereby pre-
venting possible spontaneous combustion, fire or
explosion; comprising adding the oxygen to pure water
before it is mixed with the waste liquor.

Claims

C L A I M S
The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as follows:
1. In a process for carrying out a wet oxidation
of a waste liquor with oxygen or oxygen enriched gas in a
reactor, the improvement which comprises mixing said oxygen
or oxygen enriched gas with pure water prior to adding said
oxygen or oxygen enriched gas to said waste liquor and adding
said mixture of oxygen or oxygen enriched gas and pure water
to the waste liquor before the latter is introduced into the
reactor.
2. A process according to claim 1, in which the
amount of pure water mixed with the oxygen or oxygen enriched
gas is in the proportion of between one-hundredth of a pound
and ten pounds of water per pound of oxygen.

Description

The present invention relates to a process
for the wet oxidation of waste liquor.
Pollution control by oxidation of aqueous
~ solutions or suspensions of organic waste products
: 5 with an oxygen-containing gas at high temperature
and pressure is a well-known procedure known as wet
oxidation; see for example U.S. Patent 2,665,249.
In all priox art wet oxidation processes, the oxygen-
;` containing gas i5 ad~ed directly to the aqueous
waste solution or susp.ension either before or after
;; the waste is introduced into the wet oxidation re~ :
' actor.
: In prior art w~t oxidation prooess~s,
waste liquor and compres3ed air can be directly
- 15 mixed wlth no hazard, hut if pure oxygen or an oxy-
gen enriched gas is used to supply oxygen for the
oxidation pro~ess, special precautions have to be
taken to prevent a spontan~ous combustion occurring
at the point oxygen and waste liquor are being mixed.
~. 20 The primary hazard is caused by a condition o~ inter-
- mittent wetting and drying in a section of pipe,
: leadins to the formation oE a dry film of combustible
material in direct contact with the oxygen or cxygen
bearing gas. This dry combustible film ignites-
spontaneously, leading to fire, explosion and ailure
of pressurized equipment. The wetting-drying con-
: dition may be cau~ed by an interruption in the flow
of gas or liyuid or even by normal variation in the
flow of the gas and the liquor.
Xn accordance with the present invention
there is provided a process for carrying out a wet
oxl~ation o~ a waste liquor with oxygen or oxygen
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enriched gas in a reactor, the imp~ovement which
comprises mixing said oxygen or oxygen enriched
ga~ with pure water prior to adding said oxygen
or oxygen enriched gas to said waste liquor,
In order to obviate the possibility of
spontaneous combustion, the oxygen or oxygen-con-
taining yas flows at high pressure to a point where
it is mixed with a stream of pure water which shGuld
be distilled, deionized, or potable water from which
lQ the hardness and substantially all oils, grease or
other oxidizable substances have been removed. This
~; water flows through an intake to e.g., a conven-
tional tee where it is mixed with the oxygen or
oxygen enriched gas.
The water-oxygen material now mixed then
flows through a pipe to another tee or the like
where it ls mixed with the waste liquor flowing to
th~ reactor. This may be a location in a pipe
line carrying the waste liquor to wet oxidation re-
actor, but it may also be at a point inside the
reactor itself where the oxygen is to be injected.
:~ This eliminates the possibility of the
formation of any dry deposits of combustible mate-
'! rials which may come in direct contact with high
pressure oxygen or oxygen~enriched gas.
The invention will now be described with
reference to the figure of the accompanying draw-
ing which is a diagrammatic representation of a
preferred embodiment.
A pipe 10 leads oxygen or oxygen enriched
gas through a check valve 12 and thence to e.g., a
tee 14, the other leg of which is a pipe 16 accommo-
dating the flow of pure water in the direction of
the arrow through another check valve 18 into the
tee to mix with the oxygen.
This mixture then flows through a third
check valve 20, a pipe 22 and another tee 24, one
leg of the tee accommodating the waste liquor as at
26. The water and oxygen bearing gas are mixed in
the tee 24 and thence proceed through another pipe
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or equivalent 28 to the reactor.
It is to be understood that the mlxture
of the water and oxygen or oxygen-enriched gas and
the waste liquor may actually take place inside
the reactor should this be found advantageous or
desirable.
In this invention it is emphasized that
the oxygen or oxygen-enriched gas must be mixed
wlth water before it is used in wet oxidation.
The purpose of the water injection is to eliminate
any possibility of the formation of any dry deposits
of combustible material in direct contact with the
high pressure oxygen. This is accomplished by pre-
venting any liquid containing combustible materials
from flowing into or contaminating the oxygen
supply line and by preventîng the formation of dry
spots in the areas which have been in contact with
waste liquor, and forming more positive and cleaner
seals in the check valves 12 and 20 in case of any
inte~ruption to the flow of oxygen~
The amount of water mixed with the oxygen
or oxygen-enriched ~as is also irnportant. If too
little water is used, the surface of pipes 14 and
22 may not be sufficiently wetted to prevent com-
bustion. There may also not be ~snough water to pre-
vent backflow of waste liquor into lines 22, 14 and
10. This would lead to the type of hazardous situa-
tion which this invention is intended to prevent.
On the Gther hand, if too much watar is mixed with
the oxygen or oxygen-enriched gas, the waste liquor
will be excesslvely diluted and the wet oxidation
process will be uneconomical.
The amount of water that should be mixed
with the oxygen or oxygen-enriched gas is between
one-hundredth of a pound and tan pounds of water per
pound of oxygen, preferably between one-tenth of a
pound and one pound of water per pound of oxygen.
For the purpose of the present invention,
an oxygen enriched gas is a gaseous mixture pro-
duced by adding substantial amounts of oxygen to air

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or an inert gas such that the resultant mixture
: contains at least about 25 per cent by volume o~
. oxygen.
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