Liquid purification or separation – Gravitational separator – Superposed compartments or baffles – e.g. – parallel plate type
Reexamination Certificate
2000-06-02
2002-10-29
Upton, Christopher (Department: 1724)
Liquid purification or separation
Gravitational separator
Superposed compartments or baffles, e.g., parallel plate type
C210S532100, C210S540000
Reexamination Certificate
active
06471073
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a liquid extracting apparatus suitable for an application to a filtrate tank and an absorber tank of a wet type flue gas desulfurization system, for example.
BACKGROUND ART
In recent years, as a flue gas desulfurization technique for mainly removing sulfur oxides such as sulfur dioxide from the flue gas produced in a thermal power plant etc., a wet type limestone-gypsum process of tank oxidation system has been used widely in which absorbent slurry in which calcium compounds such as limestone is suspended is sent from an absorber tank at the bottom of an absorber to a gas-liquid contact section at the upper part of the absorber to be brought into air-liquid contact with flue gas while being circulated, and oxidizing air is blown compulsorily into the absorber tank to oxidize the slurry having been brought into air-liquid contact in the absorber tank, by which gypsum is produced as a by-product.
In this flue gas desulfurization system, some of the slurry in the absorber tank is extracted to effect solid-liquid separation in order to recover gypsum. A filtrate produced by this solid-liquid separation is generally sent once to a filtrate tank, and thereafter some is returned to the absorber tank, and the remaining is treated as desulfurized waste water. This waste water treatment is performed to prevent harmful impurities such as chlorine in the flue gas from accumulating while being dissolved in the liquid content circulating in the flue gas desulfurization system. Depending on the capacity etc. of a waste water treatment system, a certain limitation is sometimes imposed on the suspended solid concentration (so-called SS concentration) of the waste water.
According to the performance of the solid-liquid separator for effecting the solid-liquid separation, the suspended solid concentration of the filtrate sometimes exceeds this limit. In this case, it is necessary to extract a liquid content with a relatively low suspended solid concentration from the filtrate in the filtrate tank and to send the same to a waste water treatment system as the desulfurized waste water.
Also, in the above-described flue gas desulfurization system, in order to achieve stable operation, it is necessary to regulate the slurry extraction amount etc. for recovering gypsum to keep the amount of slurry (liquid level) in the absorber tank in a certain range, and on the other hand it is also necessary to keep the slurry concentration (suspended solid concentration mainly consisting of gypsum) in the absorber tank in a certain range (normally, 20 to 30%).
The reason for this is as follows: If the slurry concentration is too high, a trouble such as clogging of a pipe or a pump in a circulation system for sending slurry to the upper part of the absorber and in a line for extracting slurry from the absorber tank is liable to occur, leading to difficulty in operation. If the slurry concentration is too low, so-called gypsum seed crystal in the slurry decreases, and most of the gypsum yielded successively by a reaction in the absorber tank caused by the absorption of sulfur dioxide deposits in a state such as to adhere to the surface of the equipment component, for example, to the inside wall surface of the absorber tank, which gypsum turns to scale to cause a trouble such as clogging of a pipe. Also, if the slurry concentration is low, a load for the treatment in which the extracted slurry is separated into solid and liquid to recover gypsum increases, which is disadvantageous in terms of operation cost.
The amount of sulfur dioxide in the flue gas always varies depending on the power generation load, etc. Therefore, the supply amount of absorbent (limestone, etc.) charged into the absorber tank must always be regulated to the necessary minimum amount according to the inlet sulfur dioxide amount thus varying. Also, a fixed amount of cleaning water for an air sparger or the like for blowing oxidizing air always flows into the absorber tank.
Therefore, for example, in a state in which the amount of sulfur dioxide in the flue gas is small (low-load state), the amount of solid content charged into the tank or produced in the tank is small. On the other hand, since a fixed amount of the aforementioned cleaning water always flows in, the concentration of slurry in the tank tends to decrease. In particular, when a wet cooling type dust removing section is provided on the upstream side of the absorber (in the case of soot separation system), the flue gas flowing into the absorber has almost been saturated by water vapor, so that the amount of water which evaporates in the absorber and is brought away by the flue gas is very small, and therefore, there is a high possibility of the concentration of slurry in the tank decreasing beyond the aforementioned certain range during the operation.
Even when the system is stopped (desulfurization is stopped), the cleaning water is usually caused to flow continuously. In this case, therefore, even if the soot separation system is not used, the concentration of slurry in the tank decreases beyond the aforementioned certain range.
Thereupon, in such a case, it is necessary to positively extract only the liquid content with a low suspended solid concentration from the absorber tank.
Conventionally, however, there is no simple and effective means for extracting the liquid content with a low suspended solid concentration from the filtrate tank or the absorber tank.
As a conventionally known apparatus of this type, a liquid extracting apparatus (an extractor for extracting clean liquid from suspension) has been disclosed in Japanese Utility Model Provisional Publication No. 60-159350 (No. 159350/1985). This apparatus is configured so that a cylinder whose lower end only is open and which is provided with a grating in the lower end opening is arranged so as to be submerged in suspension (slurry), and a suction pipe for a pump is connected to the closed upper end of the cylinder. The pump is operated to extract the liquid at a slow speed (for example, 1 m/h to 10 m/h) not higher than a predetermined flow velocity via the cylinder, by which the precipitation and separation of solid content in the cylinder are caused, thereby removing the liquid content with a low suspended solid concentration.
However, the liquid extracting apparatus disclosed in the above-described Publication has the following problems to be solved.
When the flow rate of the liquid content to be extracted is high or when the target suspended solid concentration in the liquid content to be extracted is low, in order to satisfy the condition at which the extraction speed is not higher than the predetermined flow velocity, the inside diameter of the cylinder must be increased, or a large number of cylinders must be provided. In this case, it is difficult to effectively extract only the liquid content with a low suspended solid concentration, or the construction of apparatus is complicated and expensive.
Specifically, if the inside diameter of the cylinder is merely increased, the aspect ratio (the ratio of inside diameter to length) of the cylinder increases inevitably, so that the influence of movement of the liquid in the tank (outside the cylinder) is liable to spread to the inner part of the cylinder. Therefore, the turbulence of flow of the liquid occurs excessively in the cylinder, so that even if the aforementioned condition is satisfied in terms of the average flow velocity, a portion where the upward flow is fast is produced partially, whereby the precipitation and separation are not attained effectively. As a result, the liquid content with a sufficiently low suspended solid concentration cannot be extracted.
Also, if an attempt is made to accommodate a high flow rate by merely providing a large number of cylinders, an increase in cost for installing a number of cylinders poses a problem. In particular, since the upper end of cylinder is closed, the manufacturing cost of the cylinder itself is high, so that if a number of cylinders are disposed in a state so as to be
Ochi Eiji
Okamoto Yoshihiro
Okino Susumu
Takashina Toru
Tatani Atsushi
Mitsubishi Heavy Industries Ltd.
Upton Christopher
LandOfFree
Liquid extracting apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid extracting apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid extracting apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2996035