JPS5920569B2 - How to transport water-containing cake - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for transporting a water-containing cake.

More specifically, the present invention relates to a method for transporting a water-containing cake with a solid appearance exhibiting thixotropic properties over relatively long distances.

In various industrial fields, especially in the chemical industry, various types of solid cakes are handled. For example, in the wastewater treatment process of chemical factories, cakes discharged from various solid-liquid separators including various offshore filters are handled, so-called water-containing cakes. are very common.

Screw conveyors, belt conveyors, etc. are widely used to transport such cakes, but these conveyors have high construction and maintenance costs, and it is extremely difficult to transport a fixed amount over long distances. It is.

Another transportation method that is often used is to make the cake into a slurry of a certain concentration using a medium such as water, and then transport the slurry using a pump.

However, this method also requires a device and operation to separate the slurry into a cake and a medium, and the separated medium must be treated separately, making the operation complicated and uneconomical.

The present inventors focused on the fact that these water-containing cakes have thixotropic properties and can be turned into a sol by applying shear stress such as stirring, and as a result of intensive study, they found that the water-containing cakes can be turned into a sol by applying shear stress such as stirring. This made it possible to continuously and quantitatively transport water-containing cake over long distances simply by using a commonly used centrifugal pump.

The cake to be transported in the present invention is a cake obtained by filtering fine solid inorganic or organic substances contained in a liquid, and usually this cake has a water content of 30% by weight or more and has thixotropic properties. have

By applying shear stress to this cake using a centrifugal pump with a high-speed rotating impeller, it is possible to easily transform the cake into a sol state with uniform fluidity. It was found that a viscosity of 600 centipoise or less could be maintained by doing so, and the present inventors discovered that if a centrifugal pump was used, quantitative long-distance transport of the same state was possible.

A method of transporting and pumping a thixotropic, highly viscous substance while applying shear stress is known, but in order to pump a water-containing cake over a long distance in the form of a sol,
It is important to transform the water-containing cake into a sol state with uniform fluidity.

Otherwise, quantitative continuous operation would not be possible due to pump pulsations.

The present inventors have discovered that the impeller of a centrifugal pump is 1.
Taking into consideration the high speed rotation of 000 to 4,000 rpm, this problem was solved by sufficiently self-circulating the water-containing cake using the impeller of the pump and the pump flow.

The method of the present invention will be explained below with reference to FIG. 1, but the present invention is not restricted thereto as long as it does not deviate from its purpose.

In Figure 1, 1 is a cake tank, 2 is a cake circulation pump, 3 is a cake transport pump, 4 is a water-containing cake peeled off from a filter, etc., 5 is a water-containing cake that has been turned into a sol, and 6 is a flow meter and a control valve. shows.

The sol-like water-containing cake stored in advance in the cake hopper 1 is sucked by the head pressure into the cake circulation pump 2 installed at the bottom of the hopper, and is circulated in an agitated state to the hopper by the discharge pressure of the cake circulation pump. .

On the other hand, the block-shaped water-containing cake 5 peeled off from the filter etc. is supplied to the cake hopper directly or by a screw conveyor etc., and then mixed with the sol cake and uniformly mixed with the cake circulation pump 2 while repeating circulation stirring. Fluidized and completely solified.

This solized cake is transported by a cake transport pump 4 separately provided at the lower part of the cake hopper, with the flow rate adjusted to a constant level by a flow control valve 6.

If the cake hopper is to be started up without a solized cake in advance, a smooth start-up can be achieved by supplying a small amount of medium such as water to the cake hopper in advance and stirring if necessary.

The centrifugal pump used in the present invention may be either a turbine type pump or a pollute type pump, but in order to obtain sufficient agitation of the water-containing cake, the self-circulation rate of the centrifugal pump should be at least 3 times, preferably 5 times, the amount of cake to be transported. The above circulation amount is required, and the residence time of the cake in the cake hopper is on average 15 minutes or more, preferably 30 minutes or more, and the self-circulation amount by the centrifugal pump is 3 times or less and the cake residence time in the hopper is 15 minutes on average. Below this, the water-containing cake cannot be made into a sufficient sol state, and even if a centrifugal pump is used, long-distance transport becomes difficult.

The pump for transporting the sol cake can be a normal pump capable of transporting sludge or paste-like substances, but a centrifugal pump, like a cake circulation pump, is suitable for transporting a fixed amount over long distances. By installing a detector such as a flow meter and/or a control valve on the discharge side of the pump, quantitative transportation can be easily carried out.

When transporting a relatively short distance, it is also possible to transport the cake using only one centrifugal pump and partially performing self-circulation.

As mentioned above, the cake transportation method according to the present invention does not require larger or more complicated equipment or complicated operations, such as the normally used belt conveyor or slurrying of cake, that is, it uses a cake tank and a centrifugal pump. It can be something very simple.

Therefore, the method of the present invention not only made it possible to greatly reduce construction costs and maintenance costs, but also had the following effects.

1) Since the main part of the device is only the centrifugal pump, the device is compact, easy to handle, and has little trouble due to breakdowns.

2) It can be used in a wide range of transport amounts and lifting heights when transporting cakes.

3) Since the transportation amount can be freely adjusted and does not fluctuate, a stable supply is possible when the cake is recovered as a raw material for the production process.

4) The device can be closed, preventing cake scattering and odor generation.

Examples of neutralized wastewater cakes exhibiting thixotropic properties will be specifically described below.

Example 1 Moisture content 50 to 50 containing calcium phosphate as the main component obtained by neutralizing wastewater from a wet phosphoric acid production plant with slaked lime
Approximately 4 m3/H of filter cake weighing 60% by weight is supplied to the cake hopper shown in Fig. 1, and the cake is solified at an average residence time of approximately 30 minutes in the cake hopper with a circulation volume of 12 m3/H by the cake circulation pump. The sol cake was transported using a cake liquid transfer pump.

Table 1 shows the relationship between pump discharge pressure and transportation distance when the amount of cake transported per hour was maintained at 4 m3/H.

In addition, under the same conditions, a flow rate controller that combines an electromagnetic flowmeter and a control valve was installed at the outlet of the transport pump, and when quantitative measurements were performed, the actual flow rate range was 3.95 against the set value of 4m3/H.
~4.05 m3/H, and no pump pulsation occurred.

Note that volute pumps were used for both the cake circulation and transport pumps in FIG.

Comparative Example 1 In the same manner as in Example 1, the same water-containing cake was fed at a rate of about 4 m3/H to the apparatus shown in Fig. 1, and the circulation rate of the cake was 8 m3/H.
An attempt was made to transport the cake by converting it into a sol with an average residence time of about 5 minutes, but it was impossible to transport the cake using a pump.

[Brief explanation of the drawing]

FIG. 1 shows an example of carrying out the method of the present invention, in which 1 is a cake hopper, 2 is a cake circulation pump, 3 is a cake transport pump, 4 is a water-containing cake peeled from a filter, etc., and 5 is a cake circulation pump. The solized water-containing cake, 6 indicates a flow meter and a control valve.

Claims (1)

[Claims] 1. While circulating a water-containing cake with a solid appearance exhibiting thixotropy to the storage tank using a centrifugal pump installed at the bottom of the water-containing cake storage tank, an amount of water-containing cake that is three times or more the amount of water-containing cake supplied to the storage tank, A method for transporting a water-containing cake, characterized in that the water-containing cake is completely transferred to a sol state by increasing the residence time in a storage tank to an average of 15 minutes or more, and then transported by a centrifugal pump.