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Volume 46 (1992)
- Issue 6 Pages 359-
- Issue 5 Pages 293-
- Issue 4 Pages 212-
- Issue 3 Pages 135-
- Issue 2 Pages 71-
- Issue 1 Pages 3-
Volume 46, Issue 4
Displaying 1-9 of 9 articles from this issue
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Ken TOYOKURA1992 Volume 46 Issue 4 Pages 212-215
Published: 1992
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSDownload PDF (4575K) -
Masayoshi MURAKAMI1992 Volume 46 Issue 4 Pages 216-221
Published: 1992
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESS1) Now, salt makers in Japan are generally using crystallizers with outside heater, which have two types, down-flow and up-flow, classified by brine flow in the evaporating chamber. 2) The down-flow type crystallizers are used usually, and recently the up-flow types are increasing owing to large-size products. 3) The size of products depend on the brine velocity in crystallizer. According to decreasing of velocity, crystals grow larger in the up-flow type crystallizer, and become smaller in the down-flow type. 4) I consider that crystals grow principally in the evaporating chamber, and so the size of products (salt) depend on the vertical velocity of brine in the evaporating chamber and the terminal velocity of salt particles. 5) The largest product is obtained when brine velocity is equal to the terminal velocity.View full abstractDownload PDF (3849K) -
Michihiko NAKAMURA, Tomio SHIMOMURA, Tosiaki KUNIYA1992 Volume 46 Issue 4 Pages 222-228
Published: 1992
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSThe crystal size distribution (CSD) of sodium chloride produced by industrial crystallizers usually oscillates up and down, even under the constant operational conditions. And further, agglomerative crystals and/or crystals with rough surface are often obtained. In order to get information for the control of CSD and to examine the formation condition of agglomerative crystals with the aid of an electron microscope, industrial operations have been carried out under various conditions. As the result, it was found that the oscillating phenomena of CSD can be prevented, by making the operational variations as small as possible, such as feed rates of raw brine and steam and brine density, and by setting the variations of the suspension density in crystallizer to be less than 10% through the manipulation of a withdrawing salt-leg. The agglomerative crystals are produced at the initial stage of the operation and decrease in its steady state. The agglomeration, however, increases with increase in the variations of brine feed rate, brine density and suspension density, which arises from the increase in nucleation, followed by the formation of fine crystals. The Rosin-Rammler's representative size of the crystals obtained in this experiment was 800-1,000 μm. By using a design chart, the rates of nucleation and growth were evaluated to be 6E+7-9E+7N/m3/h and 0.04-0.09mm/h, respectively.View full abstractDownload PDF (4495K) -
Mitsuru SAKUMA, Takashi YAMAKAWA, Masahiro ISHIKAWA, Toshihiro YAMANIS ...1992 Volume 46 Issue 4 Pages 229-239
Published: 1992
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSThe nucleation mechanism of salts was studied through crystallization tests of salts with an average crystal size of 1.1mm using the perfect mixed bed type crystallizer, and with that of 2.0mm using the cone shape type crystallizer. Average values of crystal growth and nucleation rate obtained from the diagram chart, approximately agreed with those estimated from Hatch's equation. We determined that it was possible to do stable operations preventing the cycling by feeding such information as concentration of slurry in a crystallizer, size distribution of crystals (amount of steam) and concentration of slurry in evaporated crystallizer and size distribution of crystals to the computer and calculating and adding the amount of seed crystal in evaporated crystallizer. And it became clear that condensed crystals mutually linked together were forming in a very high state of supersaturation when the evaporated crystallizer was started up. The rotation rate of the circulating pump affects considerably the nucleation rate in a crystallizer. When the rotation rate was over 13.2m/s, it caused rapid nucleation. And as the concentration of slurry in the crystallizer became higher, the nucleation was dominated by the impeller of the pump. We determined the existence of the most suitable concentration of slurry. But the nucleation rate in crystallizer, when changes in the amount of steam occur, lead to a stable production by controlling the supplying amount of seed crystal.View full abstractDownload PDF (6966K) -
Leo EHARA, Tadashi TANABE, Atsushi OTSUBO1992 Volume 46 Issue 4 Pages 240-244
Published: 1992
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSAs the results of the heating study, it was found that large-size crystals are obtained at high production rate, by the reduction of circulating feed rate to evaporator and the increase in circulating feed rate to crystallizer. Under fixed feed rates, the effective nucleation rate showed a minimum at a particular production rate, suggesting that clusters (precursor of nucleus) are generated during the dissolution of fine crystals in evaporator and that the clusters, as well as secondary nuclei, are easily incorporated into growing crystals in crystallizer.View full abstractDownload PDF (3034K) -
Isao OGURA, Toru KAGEYAMA, Hidekazu KANATANI1992 Volume 46 Issue 4 Pages 245-250
Published: 1992
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSSome operational conditions, especially a rotating speed of recirculating pump, were studied for the production of salt with average particle size of 650-850 μm by using the existing reverse circulating type of evaporating crystallizer. This facility was designed for the production of common salt and has been operating since 1972 successfully. At RUN-1 test the effect of the rotating speed of the recirculating pump, and at RUN-2 test the effect of the quantity of steam to be fed to the calandria (heat exchanger) were investigated respectively. Measured data were analyzed by the Rosin-Rammler Chart and the empirical operational Design Diagram developed by Toyokura et al. The factors affecting the particle size of salt and correlations between each factor were determined. The conclusion of the investigation was that the rate of nucleation depended on the rotating speed of the recirculating pump, the degree of supersaturation of the brine and the suspended salt concentration in the evaporating crystallizer. By using these results a stable production of a large particle size salt was achieved successfully at the existing evaporating crystallizer.View full abstractDownload PDF (3035K) -
Yoshihiro YAMAGUCHI, Kouichi NISHIOKA, Hiroshi TAKEMOTO1992 Volume 46 Issue 4 Pages 251-259
Published: 1992
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSIn the course of studies on the particle size control of salt crystal and its secondary seed generation, the data on the particle size were found to be much affected by the water content in sample crystals and their pretreatment conditions. Therefore, using the samples with two different levels of water content, their particle sizes were tested under various pretreatment conditions, such as the washing quantity of alcohol, the number of washings and impact strength. As the results, it was confirmed that the cohesive phenomena among crystals take place and are influenced by pretreatment conditions, resulting in serious errors in the data. At start-up stage in a large particle size salt productuion system, the clear relationships had been observed between the cohesive crystallization and the factors such as crystal growth rate, production rate and surface area of crystal. From the experiments by a commercial plant, it was found that by using the cohesive crystallization phenomena, the salt production capacity is improved effectively, namely resulting in shortening of the operational time required for desired size of crystal and in higher yields at startup stage.View full abstractDownload PDF (5300K) -
Yasuzi NISHINO, Shinichi HAYASHI, Tamaki AKITA, Norikazu MIYAUCHI, Hir ...1992 Volume 46 Issue 4 Pages 260-267
Published: 1992
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSSalt blocking during storage is an important problem to solve. As the physical property of salt crystal seems to be one of its factors to be discussed, we tried to do series of tests for improvement of salt quality from that point of view. Comparison was made as to crystal from in photos, breakage strength, crystal growth rate and crystal nucleation rate given by Toyokura's theory, keeping the liquid level of vacuum evaporator lowest, or in contrast with it a little higher than standard level. Furthermore, we tried seeds feeding for the purpose of crystal size control. In the case of high level operation, agglomeration of crystals seems to be suppressed, while the effect of crystal seeds addition is obscure.View full abstractDownload PDF (5342K) -
Issei IKEDA, Nobuyoshi OCHI, Fumihiko YAMADA, Toshinori MUKAE1992 Volume 46 Issue 4 Pages 268-274
Published: 1992
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSThe size control tests of crystals produced in industrial circulation-type crystallizers have been carried out, changing the salt production rate and the circulation flow volume, and some considerations based on a crystallization theory have been made on the test results. 1) The relation between the crystal size and the production rate. The crystal size has a tendency to increase with increase in the production rate in both flow types. In the case of reverse flow, there exists a clear relation because the growth rate for unit production rate is large. On the other hand, in the case of normal flow, the relation is not so clear because of small growth rate. 2) The relation between the crystal size and the circulation flow volume. With decrease in flow volume, the size increases effectivity in reverse flow, however, the reverse is found for normal flow, but with little change. The latter tendency is considered to be caused by the nucleation induced by bumping on liquid surface.View full abstractDownload PDF (4074K)
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