Search

KR-20260067137-A - METHOD FOR CONCENTRATING SODIUM HYDROXIDE SOLUTION

KR20260067137AKR 20260067137 AKR20260067137 AKR 20260067137AKR-20260067137-A

Abstract

The present invention relates to a method for concentrating an aqueous sodium hydroxide solution in a process in which a plurality of evaporators are connected in series to concentrate the aqueous sodium hydroxide solution stepwise, wherein the steam generated when the sodium hydroxide concentrate is further evaporated and concentrated in the downstream evaporator is utilized more efficiently as a heat source for the upstream evaporator.

Inventors

  • 조현준
  • 이성규

Assignees

  • 주식회사 엘지화학

Dates

Publication Date
20260512
Application Date
20241105

Claims (11)

  1. In a stepwise concentration process of an aqueous sodium hydroxide solution comprising a concentration unit in which a plurality of evaporators from the first evaporator to the nth evaporator are connected in series, A step of introducing an aqueous sodium hydroxide solution into the first evaporator and then evaporating it to obtain a primary sodium hydroxide concentrate; A step of introducing the above primary sodium hydroxide concentrate into a downstream evaporator and evaporating it to obtain a secondary sodium hydroxide concentrate, and recovering steam evaporated from the above primary sodium hydroxide concentrate; and A method for concentrating an aqueous sodium hydroxide solution, comprising the step of: introducing the steam recovered from the downstream evaporator into a mechanical steam recompression device to compress it, and supplying the compressed steam as a heat source to the upstream evaporator.
  2. In paragraph 1, A method for concentrating an aqueous sodium hydroxide solution, wherein n is an integer from 2 to 4.
  3. In paragraph 1, A method for concentrating an aqueous sodium hydroxide solution, wherein the above nth evaporator uses externally supplied steam as a heat source.
  4. In paragraph 1, A method for concentrating an aqueous sodium hydroxide solution, comprising preheating a sodium hydroxide concentrate obtained from one or more of the first to n-1 evaporators by heat-exchanging heat with a sodium hydroxide concentrate discharged from the nth evaporator, respectively, and then introducing it into a downstream evaporator of each evaporator.
  5. In paragraph 1, A method for concentrating an aqueous sodium hydroxide solution, comprising preheating a sodium hydroxide concentrate obtained from one or more of the first to n-1 evaporators by heat-exchanging with the condensate of steam used as a heat source in the nth evaporator, respectively, and then introducing it into the downstream evaporator of each evaporator.
  6. In paragraph 1, A method for concentrating an aqueous sodium hydroxide solution, comprising independently branching a portion of the sodium hydroxide concentrate obtained from one or more of the first to n-1 evaporators, preheating it by heat exchange with the sodium hydroxide concentrate discharged from the nth evaporator, and preheating the remainder by heat exchange with the condensate of the steam used as a heat source in the nth evaporator, and then feeding it into the downstream evaporator of each evaporator.
  7. In paragraph 1, The concentration of the sodium hydroxide aqueous solution introduced into the first evaporator is 26% to 34% by weight, and A method for concentrating an aqueous sodium hydroxide solution, wherein the concentration of the nth sodium hydroxide concentrate obtained from the nth evaporator is 48% to 52% by weight.
  8. In paragraph 1, The steam evaporated from the primary sodium hydroxide concentrate in the second evaporator has a temperature of 100°C to 110°C at a pressure of 0 bar to 1 bar, A method for concentrating an aqueous sodium hydroxide solution, wherein the steam is compressed through the mechanical steam recompression device and controlled to a pressure of 0.6 bar to 2.5 bar and a temperature of 130°C to 160°C.
  9. In paragraph 1, A step of introducing a (n-1)th sodium hydroxide concentrate obtained from a shear evaporator of the nth evaporator into the nth evaporator and evaporating it to obtain an nth sodium hydroxide concentrate, and recovering steam evaporated from the (n-1)th sodium hydroxide concentrate; and A method for concentrating an aqueous sodium hydroxide solution, further comprising the step of supplying the steam recovered from the nth evaporator to a mechanical steam recompression device to compress it, and supplying the compressed steam as a heat source to a shear evaporator.
  10. In paragraph 1, A method for concentrating an aqueous sodium hydroxide solution, wherein the above mechanical vapor recompression device is provided in 1 to 3 stages.
  11. In paragraph 1, A method for concentrating an aqueous sodium hydroxide solution, wherein the plurality of evaporators from the first evaporator to the nth evaporator are operated such that the upstream evaporator is operated at a relatively lower pressure and temperature compared to the downstream evaporator.

Description

Method for Concentrating Sodium Hydroxide Solution The present invention relates to a method for concentrating an aqueous sodium hydroxide solution, and more specifically, to a method for utilizing steam generated when further evaporating and concentrating the sodium hydroxide concentrate in a downstream evaporator more efficiently as a heat source for a upstream evaporator in a process in which a plurality of evaporators are connected in series to concentrate an aqueous sodium hydroxide solution stepwise. Sodium hydroxide (NaOH) is obtained by electrolyzing sodium chloride (NaCl) to obtain an aqueous sodium hydroxide solution with a concentration of about 30% by weight, and then evaporated and concentrated until the concentration of sodium hydroxide reaches about 50% by weight, and shipped as a product. Specifically, a common method of evaporative concentration involves heating an aqueous solution of caustic soda (sodium hydroxide) in an evaporator to evaporate the water, and then separating the concentrated solution heated and concentrated in the evaporator from the evaporated water vapor. At this time, there is a need for the development of technology that can concentrate the sodium hydroxide solution more efficiently while recovering the latent heat of the steam generated in the evaporator to save energy and minimizing the amount of steam used during evaporator heating. For example, there is a method of using a plate-type heat exchanger as an evaporator to concentrate an aqueous sodium hydroxide solution. In this case, while it is possible to miniaturize the device by improving the thermal efficiency of the heat transfer surface of the plate-type heat exchanger used in the evaporator, there are limitations to the energy saving effect. FIG. 1 is a process flowchart for concentrating an aqueous sodium hydroxide solution according to one embodiment of the present invention. Figure 2 is a process flowchart for concentrating an aqueous sodium hydroxide solution according to Comparative Example 1. Figure 3 is a process flowchart for concentrating an aqueous sodium hydroxide solution according to Comparative Example 2. Terms and words used in the description and claims of the present invention shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention. In relation to the description of the drawings, similar reference numerals may be used for similar or related components. The singular form of the noun corresponding to the item may include one or more of the said item unless the relevant context clearly indicates otherwise. In the present disclosure, each of the phrases such as “A or B”, “at least one of A and B”, “at least one of A or B”, “A, B or C”, “at least one of A, B and C”, and “at least one of A, B, or C” may include any one of the items listed together in the corresponding phrase, or all possible combinations thereof. The term “and/or” includes a combination of multiple related described components or any of the multiple related described components. Terms such as "first," "second," or "first" or "second" may be used simply to distinguish a component from another component and do not limit the components in other aspects (e.g., importance or order). In addition, terms such as 'front,' 'rear,' 'top,' 'bottom,' 'side,' 'left,' 'right,' 'top,' and 'bottom' used herein are defined based on the drawings, and the shape and location of each component are not limited by these terms. Terms such as “include” or “have” are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in this disclosure, and do not preclude the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof. When it is said that one component is “connected,” “combined,” “supported,” or “in contact” with another component, this includes not only cases where the components are directly connected, combined, supported, or in contact, but also cases where they are indirectly connected, combined, supported, or in contact through a third component. When it is said that a component is located “on” another component, this includes not only cases where one component is in contact with the other, but also cases where another component exists between the two components. Furthermore, terms such as "approximately" and "substantially" as used herein are used to mean at or near the numerical values when inherent manufacturing and material tolerances are presented in the stated sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content in which precise or absolute numerical values are mentioned to aid in understanding the inven