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Abstract

The present invention is directed to a method for essentially complete oxidation of a concentrated liquor containing oxidizable organic matter. Each step of the method is performed under substantially superatmospheric pressure. Initially, the liquor is preheated to a temperature higher than about 10° C. below the boiling point of water at the substantially superatmospheric pressure. A feed formed of the concentrated liquor is then essentially completely oxidized at a temperature of at least 800° C. in the presence of a gas comprising at least sixty percent by volume of oxygen to form a suspension of a hot gas and a molten slag. The molten slag is separated from the hot gas before the slag is dissolved in water to form a brine. The separated hot gas is then cooled to a temperature below 250° C. by quenching with an aqueous liquid. Finally, the aqueous liquid is separated from the hot gas.

Description

[0001] 1. Field of the Invention[0002] The present invention relates generally to a method of oxidizing waste liquors and, more particularly, to a method for mineralisation by oxidation at substantially superatmospheric pressure of essentially all organic matter present in a concentrated liquor that has been obtained by evaporation of waste liquors.[0003] 2. Description of the Related Art[0004] Today, industries are striving to minimise environmental impact. A part of this impact is the discharge of contaminated effluent to waterways and the emission of polluted gases to the ambient air.[0005] Industry effluent often contains organic substances in low concentrations and inorganic ions, derived from raw materials and from chemicals introduced to the process. The organic matter is sedimented or degraded in the receiving water systems, thus consuming the oxygen in the water. Part of the organic matter is taken in by living organisms. Some of these substances may accumulate in living ti...

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Benefits of technology

[0028] According to a preferred embodiment of the present invention, the molten slag is allowed to flow down through constriction, such as a small passage to an agitated slag dissolving vessel, wherein water is introduced in such quantities that the steam generated will suffice to prevent hot gas from entering the dissolving vessel through the passage.

Problems solved by technology

The organic matter is sedimented or degraded in the receiving water systems, thus consuming the oxygen in the water.

Some of the substances are poisonous.

The inorganic matter, however, may also include small quantities of metal ions, which are considered harmful.

Some chloro-organic substances contained in the flue gases are considered an environmental hazard even in very low concentrations.

However, pulp mill bleach plant effluent are so diluted that they are currently not evaporated nor combusted, even if such a method is known, e.g., as disclosed in Finnish Patent No. 85293.

However, with very low concentrations of the inorganic matter, a complete precipitation can not be achieved and the separation of the precipitated matter from large quantities of liquid is difficult.

As a result, the heat transfer surfaces of the evaporation equipment become fouled, and the evaporation capacity is reduced.

With this ballast, a considerable amount of energy is needed to increase the temperature above 800.degree. C.

Of course, the fossil fuel also requires combustion air, which further increases the amount of inert nitrogen passed through the combustion chamber and the subsequent flue gas duct.

As a result, the combustion chamber becomes very big, and the devices needed for cleaning and transporting the gas become large and also expensive.

For this reason, the treatment of dilute effluent by evaporation and incineration has not become a common practice in the process industry.

However, they deal with methods to gasify organic matter in reducing conditions and not with complete oxidation of this matter.

The preferred oxygen content of the pressurized gas is close to 100 percent, by volume, but the pressurised gas can be contaminated with other gases, e.g., nitrogen, carbon monoxide, or carbon dioxide.

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