JP2006214014A - Method for analyzing dissolved impurity in green liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To establish a method for analyzing a cause of operational abnormalities in an caustification process, resulting from foreign materials dissolved in green liquor by performing the adjustment of pH and analyzing the impurities precipitated at a prescribed pH value. <P>SOLUTION: This method of analysis is provided by performing the adjustment of pH by adding an acid to the green liquid obtained by dissolving smelt from a recovering boiler with weak liquid, precipitating the impurities in the green liquor at the prescribed pH value, performing the qualitative/quantitative analysis of dissolvable impurities selected among the dissolved impurities in the green and precipitated at the prescribed pH value so as to be able to analyze the concentration of dissolvable impurities in the clear liquor of the green liquor, and also thereby, solving problems quickly by elucidating the position of admixing the impurities regarding to the operational abnormalities such as the reduction of calcined lime purity, the clogging, etc., of a white liquor-filtering device and lime sludge-dehydrating device caused by the foreign materials dissolved in the green liquor, so as to contribute for performing a stable operation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for analyzing dissolved impurities in a green liquor obtained by dissolving a smelt from a recovery boiler with a weak liquid.

  In the kraft pulp manufacturing plant, the pulverized lignocellulosic material is cooked by a cooking liquid called white liquor in a digester, and the lignin component is dissolved in the cooking solution to separate the cellulose component. The lignin component dissolved in the cooking chemical becomes black liquor, which is extracted from the digester and then concentrated and further combusted in a recovery boiler. The inorganic chemicals in the black liquor are reduced by a recovery boiler, taken out as a smelt that is a melt, and sent to a chemical recovery process as shown in FIG.

  The smelt from the recovery boiler is mixed with a weak liquid (cleaning liquid containing soda) L5 in the smelt dissolving tank 1 shown in FIG. 1 to become a crude green liquid L1, and further in the green liquid clarifier 2 the crude green liquid L1. The clarified green liquor (hereinafter simply referred to as “green liquor”) L2 is purified by separating the legs D1 from the liquid. Reference numeral 3 is a dregs tank, and 4 is a dregs filter.

  This green liquor L2 is sent to the slaker 5 and quick lime C3 is added, and the soaking reaction and the causticizing reaction are performed in the slaker 5 and the causticizing tank 6 subsequent thereto. The emulsion L3 from which the unreacted coarse particles called grit have been removed from the reaction solution passes through the causticizing tank 6 from the slaker 5 and is sent to the white liquor clarifier 7. In the white liquor clarifier 7, calcium carbonate sludge, commonly called lime mud, in the milk L3 is separated, and the supernatant liquid is stored in the white liquor tank 8 as the clarified white liquor L4, while the lime mud is white liquor clarifier. 7 settles to the bottom.

  The lime mud M1 separated by the white liquor clarifier 7 is sent to the lime mud washer 9 and washed with washing water to separate the soda contained in the lime mud. And also in the weak liquid clarifier 10 following this lime mud washer 9, separation | separation of lime mud and a washing | cleaning liquid is performed. Thereafter, the lime mud M2 separated by the weak liquid clarification device 10 is further washed, dehydrated in the lime mud dewatering device 13, and fired by the lime firing rotary kiln 14. Reference numeral 11 is a weak liquid tank, and 12 is a lime mud tank.

  As described above, the smelt from the recovery boiler is dissolved in the weak solution in the smelt dissolving tank 1 and transferred to the causticizing process as a green solution. At this time, the green solution contains impurities. In general, the insoluble impurities are precipitated and removed by a green liquor clarifier, etc., and the concentration of residual insoluble impurities in the clarified liquid is analyzed and controlled, so that the calcined lime purity caused by impurities mixed in the causticizing process A technique for preventing an operational abnormality such as a decrease in the amount of water and clogging of a white liquor milk filtration apparatus is well known.

  By the way, the green liquid mud discharged from the bottom of the green liquid clarification tank is supplied to a continuous vacuum filtration type concentrator or a centrifugal sedimentation type concentrator, concentrated to a green liquid mud having a solid content concentration of 10 to 35%, and then pressed. A method for recovering green liquor from kraft green liquor that has been supplied to a concentrator and concentrated to green liquor with a solid content of 45 to 65% has been proposed (see Patent Document 1). The method for analyzing dissolved impurities in the liquid was investigated but was not found.

JP-A-5-171585.

  In general, it is well known that silicon, aluminum, etc. are dissolved in the green liquor, and the above-described management of the insoluble impurity concentration in the green liquor is not sufficient for managing impurities mixed in the causticizing process. is there. However, a method for analyzing impurities other than the green liquor component dissolved in the green liquor (in other words, soluble impurities) has not yet been established.

  As a result of diligent efforts, the inventor of the present application can analyze soluble impurities in the green liquor by analyzing the impurities precipitated at a predetermined pH value by adjusting the pH of the green liquor. Attention was paid to the completion of the present invention.

  The present invention has been made in view of the above points. By adjusting the pH of the green liquor and analyzing impurities precipitated at a predetermined pH value, the foreign matter dissolved in the green liquor can be removed. The purpose is to establish a cause analysis method for the abnormal operation of the causticizing process.

  In the present invention, as a first means for solving the above-mentioned problems, an acid is added to a green liquor obtained by dissolving a smelt from a recovery boiler with a weak liquid to adjust the pH, and a predetermined pH value is obtained. In (1), impurities in the green liquor are precipitated, and the concentration of soluble impurities in the green liquor clarified liquid is analyzed from the precipitates.

  By doing so, selected ones of the soluble impurities in the green liquor are deposited at a predetermined pH value. The dissolved impurity concentration in the green liquor clarified liquid can be analyzed by qualitatively and quantitatively analyzing the dissolved impurities thus deposited. As a result, clarify the place where impurities are mixed in regarding abnormalities in operation such as a decrease in calcined lime purity caused by foreign matters dissolved in the green liquor, clogging of white liquor milk filtration equipment, and lime mud dewatering equipment. It can be used to solve problems quickly and to obtain stable operations.

  In the present invention, as a second means for solving the above problems, in the method for analyzing dissolved impurities in green liquor provided with the first means, the pH adjustment is set to pH 10, pH 7, and pH 1. In such a case, precipitation of aluminum, silicon and iron is obtained at pH 10, precipitation of aluminum, silicon, potassium and iron is obtained at pH 7, and precipitation of vanadium and iron is obtained at pH 1. As a result, most of the soluble impurities are deposited.

  According to the first means of the present invention, the pH is adjusted by adding an acid to the green liquor obtained by dissolving the smelt from the recovery boiler with a weak liquor, and impurities in the green liquor are reduced at a predetermined pH value. In order to analyze the concentration of soluble impurities in the green liquor clear liquid from the precipitate, a selected one of the soluble impurities in the green liquor is precipitated at a predetermined pH value. Qualitative / quantitative analysis enables analysis of the concentration of soluble impurities in the green liquor clarified liquid, resulting in a decrease in the purity of the calcined lime caused by foreign matter dissolved in the green liquor, and the white liquor milk filtration device In the case of abnormal operation such as clogging of lime mud dewatering equipment, by clarifying where impurities are mixed, there is an effect that it is possible to solve problems quickly and to obtain stable operation.

  The method for analyzing dissolved impurities in green liquor of the present invention is to adjust the pH by adding acid (for example, hydrochloric acid) to green liquor obtained by dissolving smelt from a recovery boiler with weak liquor, Impurities in the green liquor are precipitated at pH values (for example, pH 10, pH 7, and pH 1), and the concentration of soluble impurities in the green liquor clarified liquid is analyzed from the precipitates.

  By doing so, selected ones of the soluble impurities in the green liquor are deposited at a predetermined pH value. For example, precipitation of aluminum, silicon, and iron is obtained at pH 10, precipitation of aluminum, silicon, potassium, and iron is obtained at pH 7, and precipitation of vanadium and iron is obtained at pH 1. Accordingly, precipitation of most soluble impurities can be obtained.

  The dissolved impurity concentration in the green liquor clarified liquid can be analyzed by qualitatively and quantitatively analyzing the dissolved impurities thus deposited. As a result, clarify the place where impurities are mixed in regarding abnormalities in operation such as a decrease in calcined lime purity caused by foreign matters dissolved in the green liquor, clogging of white liquor milk filtration equipment, and lime mud dewatering equipment. It can be used to solve problems quickly and to obtain stable operations.

  By the way, when the precipitation concentration at each pH of the dissolved substance in the green liquor was analyzed, the results shown in Table 1 were obtained.

  According to the above results, precipitation of aluminum, silicon and iron is obtained at pH 10, precipitation of aluminum, silicon, potassium and iron is obtained at pH 7, and precipitation of vanadium and iron is obtained at pH 1. .

It is a flowchart which shows the principal part of the generally known kraft pulp manufacturing plant.

Claims (2)

The pH is adjusted by adding acid to the green liquor obtained by dissolving the smelt from the recovery boiler with a weak liquor, and impurities in the green liquor are precipitated at a predetermined pH value. A method for analyzing dissolved impurities in green liquor, characterized by analyzing the concentration of soluble impurities in the solution. The method of analyzing dissolved impurities in green liquor according to claim 1, wherein the pH adjustment is pH 10, pH 7 and pH 1.

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