Electric resistance heating devices – Heating devices – Tank or container type liquid heater
Reexamination Certificate
1998-03-30
2002-11-05
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Tank or container type liquid heater
C219S536000
Reexamination Certificate
active
06477323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system and method for recovering spent or waste sulfuric acid liquid and reprocessing it, in particular a system and method for continuously reprocessing waste sulfuric acid liquid wherein sulfuric acid liquid which has enough concentration and impurity for reuse can be provided in a stable and continuous way. The present invention also relates to a heater supporting structure for a heating device made of glass, which is used as a heating device for corrosive liquid such as sulfuric acid and nitric acid.
2. Discussion of Background
In a semiconductor fabrication process, sulfuric acid liquid has been used for cleaning of wafers and removal of photo resists.
The waste sulfuric acid which has been used in such process has been disposed after neutralized, taken over to dealers for disposal of industrial waste, or concentrated and distilled for recycling.
As such systems for reprocessing waste sulfuric acid liquid have been known a continuous system including a concentration step and a distillation step which is disclosed in U.S. Pat. No. 3,294,650, and a batch processing system for production of reprocessed sulfuric acid liquid for batteries which is disclosed-in Intreprinderea Chemida “Dudesti” Rom. RO 83,474, May 30, 1984, application Ser. No. 103,545, Feb. 27, 1981; 3pp CA 1985, 103(4) 56183z.
As conventional systems for reprocessing waste sulfuric acid liquid have been known a normal pressure type apparatus which is operated at substantially atmospheric pressure, and a reduced pressure type apparatus which is provided with a vacuum device such as a vacuum pump and is operated under reduced pressure from a few Torr (1×10
3
Pa) to tens of Torr (5×10
3
Pa). Although a continuous system is adopted in such a normal pressure type apparatus because of easy removal of each liquid, the material of a gasket usable to pipe connecting portions for each liquid is limited because the operating temperature is 330° C. or higher. If the gasket is made of e.g. metal or carbon, there is a possibility that impurities might mix. If the operation is carried out without use of the gasket for that reason, there has been created a problem in that the apparatus and pipes could be broken by occurrence of leakage of each liquid at the connecting portions and difficulty in absorption of expansion and contraction of the system and the pipes due to a temperature difference.
In the conventional apparatuses, heating vessels are of a vertical type or a horizontal type without a baffle plate. In the concentration step, it has been unstable to concentrate the liquid to a target level. In order to cope with this problem in such a reduced pressure type apparatus, there have been adapted a semi-batch system wherein the process flow is cut off so that concentrated sulfuric acid liquid from a concentrating vessel is held in an intermediate tank and is transferred into the distillation step after determining the concentration of the concentrated sulfuric acid liquid in the intermediate tank, or a system wherein switching to the distillation operation is made after finding the concentration state by estimating the concentration state based on an evaporating temperature in a batch system or by measuring the concentration of the concentrated sulfuric acid liquid which is taken out of the concentrating vessel through a branch pipe and is cooled. Such an normal pressure type apparatus has created a problem in that the apparatus and the pipes are quite likely to be broken because the evaporating temperature is remarkably raised to a specified value or higher to maintain high concentration. The normal pressure apparatus is insufficient in terms of stable and continuous operation.
As the heating vessel for concentrating or distilling corrosive liquid such as sulfuric acid or nitric acid is usually used a heating vessel made of the in terms of corrosion resistance.
As the heating source for such a heating vessel have been used hot water, steam, heat medium and electricity. The heating vessel has been heated by such a heating source from within, from outside or from within and outside. The heating from within has usually been adopted since the heating from outside creates a problem in that there is much heat loss due to radiation of heat.
When the heating is carried out from within, there has been adopted a supporting structure wherein a heater to be provided in the heating vessel is supported only by a heater inserting portion of the heating vessel in a cantilevered way.
Since there is a possibility that such a supporting structure could break the heater or the heating vessel made of glass, it is required that the heater have a length less than 1000 mm or the inside of the heating vessel be slowly heated so as to prevent the liquid in the vessel for vibrating. If there is no other way but to heat the inside of the vessel intensely, the heater and the vessel have been used being ready for breakage, which has required that the heater and the vessel are repaired or exchanged with new ones periodically.
Although it is proposed that a plurality of short heaters are arranged to cope with this problem, this proposal requires that the heating vessel must become larger, creating a problem in terms of apparatus cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the problems of the prior art.
The foregoing and other objects of the present invention have been attained by providing a system for continuously reprocessing waste sulfuric acid liquid, comprising:
an apparatus for concentration including
a heating vessel for concentration having a supply device for continuously supplying waste sulfuric acid liquid thereto, an inlet for receiving the waste sulfuric acid liquid, and a heating device, and
a condenser for cooling and condensing vaporized sulfuric acid led out of the heating vessel;
an apparatus for distillation including
a heating vessel for distillation having an inlet for continuously receiving concentrated sulfuric acid liquid, and a heating device, and
a condenser for distillation for cooling and condensing vaporized sulfuric acid led out of the heating vessel for distillation; and
a connecting pipe for continuously removing the concentrated sulfuric acid liquid through a bottom of the heating vessel for concentration and supplying the concentrated sulfuric acid liquid to the heating vessel for distillation;
wherein the heating vessel for concentration is elongated in a horizontal direction, and the heating vessel for concentration has a baffle plate provided therein so that the sulfuric acid liquid which is supplied through the inlet of the heating vessel for concentration is gradually concentrated so as to have higher concentration at an outlet of the heating vessel for concentration than concentration at the inlet of the heating vessel for concentration.
The present invention also provides a method for continuously reprocessing waste sulfuric acid liquid, comprising:
concentrating waste sulfuric acid liquid by an apparatus for concentration including
a heating vessel for concentration having a supply device for continuously supplying waste sulfuric acid liquid thereto, an inlet for receiving the waste sulfuric acid liquid, and a heating device, and
a condenser for cooling and condensing vaporized sulfuric acid let out of the heating vessel; and
distilling the concentrated waste sulfuric acid liquid by an apparatus for distillation including
a heating vessel for distillation having an inlet for continuously receiving the concentrated sulfuric acid liquid, and a heating device, and
a condenser for distillation for cooling and condensing vaporized sulfuric acid let out of the heating vessel for distillation;
wherein the heating vessel for concentration is elongated in a horizontal direction, and the heating vessel for concentration has a baffle plate provided therein so that the sulfuric acid liquid which is supplied through the inlet of the heating vessel for concentration is gradually concentr
Fukuizumi Masataka
Koizumi Kiyohito
Matoba Toru
Osuda Hiroshi
Sadakata Takayuki
Asahi Techno Glass Corporation
Campbell Thor
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Walberg Teresa
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