JPS6394802A - Method and device for cooling concrete - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Roasted” (“L”) The present invention relates to a method and apparatus for cooling fresh concrete.

-3= When placing concrete, the forming temperature of concrete is an important factor. Particularly in mass concrete structures, this temperature directly affects the workability of the cleat (the degree of ease with which the concrete can be formed), the occurrence of cracking due to shrinkage, and the final strength. It is well known that the lower the concrete forming temperature, the more effective it is against these conditions.

Traditionally, methods to reduce the humidity of concrete have included the use of cold water, ice, and liquid nitrogen, as well as combinations thereof. Cooling with liquid nitrogen, which is effective in these methods, uses a liquid nitrogen lance in a drum-type mixer to inject liquid nitrogen into the mixer to cool the concrete, and is actually used in Aus1~Laria, the United States, etc. However, most of this is injected into mixers, etc., which is not convenient for mixing concrete near sites where large amounts of concrete are required, and the sites where ready-mixed concrete is manufactured and concrete are placed are often separated. Furthermore, when liquid nitrogen is injected from a lance into the concrete being mixed, the liquid nitrogen vaporizes before being injected into the concrete, and its cooling energy is not utilized effectively. That is, in the concrete cooling method using liquid nitrogen, the problem is how to effectively utilize the cold energy of the liquid nitrogen from an economical point of view.

Broadly speaking, they are cooling methods within the mixer and effective use of cold energy in the exhaust gas. Therefore, in order to improve the efficiency within the mixer, it is important to inject liquid nitrogen close to the material to be cooled. Conventionally, due to the pressure drop that occurs while passing from the liquid nitrogen storage tank to the supply equipment, control equipment piping, and heat intrusion from the outside, some of the liquid nitrogen becomes gaseous.As a result, the liquid nitrogen becomes a gas-liquid mixture, and a certain amount of liquid nitrogen is As a result, the volume becomes larger. Therefore, the injection speed from the nozzle increases, collides with the material to be cooled, forms a mist, and some of the material is already cooled and exchanges heat with the vaporized nitrogen gas, resulting in the temperature of the nitrogen gas that becomes exhaust gas. decrease. As a result, the liquid nitrogen gas cannot effectively use cold energy, especially latent heat of vaporization.

In view of the above-mentioned points, the present invention provides a method and apparatus for supplying concrete with thermal efficiency by reducing the degree of concretion in the mixer as desired near the concrete placement site. The purpose is to

In order to achieve the above objectives, the present invention uses a two-axis forced mixing mixer and directly injects only liquid nitrogen separated into gas and liquid into the mixed concrete. We are now able to supply high quality ready-mixed concrete. Although the two-shaft forced kneading mixer operates in batch mode, the time required for batching can be shortened by effective use of cold and heat and other controls, so by repeating batch processing it is possible to supply labor as desired. so that it can be done efficiently.

In addition, in order to carry out the above method, the mounting position and angle of the liquid nitrogen injection nozzle relative to the mixer, and the control means, etc., were devised to improve efficiency, and safety measures were also taken into consideration when managing the retention of H. , improved effectiveness.

The present invention will be described below with reference to the accompanying drawings.

Support 1 In FIG. 1, a schematic explanatory diagram showing the general concept of the present invention is shown.

A plurality of nozzles 4 are inserted from the side of the two-shaft forced mixer 1.
The liquid nitrogen separated by the gas-liquid separator 5 is supplied to the concrete in the crosstalk via a control valve (CV) 2 and a shutoff valve (PV) 3. In order to inject liquid nitrogen directly into the concrete being mixed, the mounting position of the nozzle 4 with respect to the drum of the mixer 1 is, for example, as shown in FIG.
, 1b Attach within an angle of 45° to the plane containing the axis of the mosquito. This arrangement allows substantially only liquid nitrogen to be injected into the concrete being mixed at a position very close to the top of the mixer. The third enlarged view of the nozzle 4 part
It is shown in the figure. A metal nozzle support tube 7 is welded to the drum 6 so that its tip does not come into contact with the blade rotating inside the drum 1. A nozzle tip 8 is attached to the support tube, and liquid nitrogen is injected into the tip 8. A supply lance 9 is connected. The nozzle tip 8 is preferably made of fluorinated ethylene, (for example, Teflon, trade name), nylon, or the like. In addition, by considering the fitting area between the chip and the support tube 7 to be as small as possible, in addition to the chip having low heat conductivity, low temperature effects on the welded part of the support tube 7 to the drum 6 due to low temperature than liquid nitrogen. It is desirable to reduce the For example, an annular groove such as 8b may be provided on the outer surface of the chip.

Concrete is fed into the mixer 1 from storage hoppers 10 (sand), 11 (gravel), and 12 (cement) for sand, gravel, and cement through a meter 13 and a feed chute 14 in a batch manner. Also, water goes from pipe 15 to remixer 1
supplied to

The concrete that has been crossed is the lower opening 1 of the mixer 1.
6 and is discharged into a hopper 17 below, and the hopper 17 is moved to a required location to supply concrete. The raw material for the higher batch is supplied from the hopper 10111.12 to the mixer 1 along with water in the same manner as described above, and the next patch cycle is started.

The liquid nitrogen is supplied into the mixer 1 by arranging it toward the middle of each stirring shaft and the mixer drum 6 on the side of the drum within 45 degrees from the horizontal plane, as shown in Fig. 2, to avoid mortar clogging of the nozzles. This is an effective arrangement because it avoids this and also supplies liquid nitrogen into the concrete where the lines are mixed. By smoothing the finish of the nozzle 8 made of resin, mortar adhesion can be prevented or peeling can be facilitated. In the production of concrete, cement, sand, and water are first added to the mixer to make mortar, and then gravel is added. The supply control of liquid nitrogen will be explained later, but normally it is not supplied at the initial stage of making mortar. Even if mortar adheres to the nozzle 8 during mortar operation, the nozzle 8 is easily peeled off. Also, if the nozzle becomes clogged, keep liquid nitrogen flowing at all times.

Alternatively, it is also possible to provide a means for detecting clogging as well as a mechanism for removing the clogging. FIG. 4 shows an overview of the clogging detection and removal mechanism.

When the mortar closes the outlet of the nozzle 8 as indicated by pll, a pressure switch 20 leading to the lance 9 senses the closing pressure, which activates the solenoid valve 21 to move the piston of the air cylinder 22.

The piston moves a link mechanism 25 with 24 as a fulcrum,
Apply the discharge part 23 at the tip to the clogged mortar "p"
′ into the drum. Excessive drum 6 of discharge section 23
It is desirable to provide a stop 26 on the link to avoid inward protrusion. Note that this removal operation is controlled so that it is performed only when nitrogen injection is stopped.

With this consideration, batch operations can be repeated continuously without interrupting concrete production. Although the preferred position of the nozzle is shown in Fig. 2, the nozzle can be placed at the bottom of the drum 6, for example, in order to supply liquid nitrogen more directly into the concrete. requires a means to control the opening and closing of the nozzle opening.

Although the positioning of the nozzles 4 has been described with reference to FIG. 2, it is advantageous to arrange a plurality of nozzles 4 on both sides of the drum 6 and in the axial direction in order to supply liquid nitrogen to the concrete generally uniformly. An example of the arrangement is shown in FIG. As shown in the figure, a plurality of nozzles 4 are arranged on both sides of the drum 6. As shown in the illustrated example, the positions are preferably different axial positions on both sides. The large arrow 4a in the figure schematically indicates the direction in which the concrete behaves depending on the direction of the stirring blades 30 attached to the stirring @ 1a, 1b. shows.

Furthermore, in order to supply liquid nitrogen more uniformly, if the shape of the tip 8 of the nozzle 4 is such that the liquid spreads in the axial direction in a fan shape at the tip as shown by 4b, the uniformity of mixing of liquid nitrogen is improved. do.

An example of such a chip is shown in Figures 6A and 6B. FIG. 6A is a side view, and FIG. 6B is a plan view of one end of the nozzle tip 11. The connection part with the lance 9 has a cylindrical shape with a diameter, and the tip part has a modified elliptical shape with a width. Of course, the direction of the width is parallel to the axial direction of the drum 6 during installation.

In order to further utilize the residual cold energy in the nitrogen gas that has been used as cold energy in the device considered above, an exhaust fan 31 and a duct 32 are installed in the exhaust system from the mixer 1. Cold heat is effectively used by introducing exhaust gas into the gravel supply line or hopper 10.11, exchanging heat with the material to be cooled, and reducing the temperature of the nitrogen gas discharged outside the system to room temperature. It will be like that. Among the materials to be cooled, cooling of gravel is particularly effective. The gravel used for concrete is large, with some having a diameter of 150 mm, and it is difficult to cool the center of the gravel in a mixer in a short time, but if it is pre-cooled before entering the mixer, it can be shortened. [time] can be cooled, and
Changes in concrete humidity after cooling are reduced, allowing for accurate temperature control.

Also, since gravel is similar to sand, there is no decrease in void ratio due to moisture.
Since exhaust gas can be sent at a constant pressure, the capacity of the exhaust fan can be selected appropriately.

The capacity of the exhaust fan is to draw in extra outside air from the openings such as the cooled material inlet on the top of the mixer, and to prevent freezing inside the exhaust duct and exhaust fan, the average temperature of the exhaust gas will be above O'C. Let's call it Jlffi.

Exhaust gas has a relatively low temperature, and spot cooling of gravel may lead to errors in temperature control. Therefore, when exchanging heat with gravel, exhaust gas is dispersed to be cooled more uniformly. It is preferable to use a dispersion means so that it is supplied with the same amount of water. It is also desirable that the exhaust duct from the mixer be installed in the center of the upper part of the mixer. This is to prevent as much as possible contact between the wall surface of the upper part of the mixer and the exhaust gas, to prevent a drop in humidity on the wall surface, to prevent heat radiation from the wall surface to the outside, and to prevent problems such as low-temperature wheezing and cracking of the wall material. .

The exhaust volume of the exhaust fan is varied according to the operating pattern of the mixer, and the exhaust volume is reduced or stopped when liquid nitrogen is not being injected. The nitrogen gas separated from the gas-liquid separator 5 can also be connected to the duct 32 through a duct 33 equipped with a solenoid valve 34 for heat recovery. Furthermore, installing a branch pipe 38 from the duct 33 and spraying nitrogen gas onto the mixed concrete in the mixer also works effectively for cooling.

The concrete cooling method and apparatus according to the present invention are designed not only to effectively utilize cold energy but also to improve workability. The amount of concrete placed is determined by the number of batches per day. Therefore, in order to increase the number of batches, it is necessary to shorten the time for each batch. It is desirable to control the sequence so that the necessary liquid nitrogen determined by the required cooling temperature can be injected not only during the kneading time but also when the materials are added within a limited time. Injection of liquid nitrogen at the time of material input is particularly effective in heat exchange between the material and exhaust gas at the time of material input (dropping). This increases the contact area between the material and the exhaust gas and improves the heat transfer film on the contact surface.
0 is provided, and this control device 40 measures the temperature of the material to be cooled by placing thermometers at necessary locations and measuring the temperature of the material to be cooled so that the relationship between the required cooling temperature and the amount of liquid nitrogen can be automatically set. The amount is measured in the hopper 13, and the required amount of liquid nitrogen calculated by considering the specific heat and efficiency of each material is injected, and the temperature of the concrete after cooling is measured with the thermometer 41 and fed back to the control device. This device can be linked with the control valve 2 to adjust the injection amount. This is also due to temperature changes from morning, noon, and night.
Depending on the pre-cooled state of the material, even if the temperature of the material to be cooled changes, the jet of liquid nitrogen tJJ@ is increased or decreased to maintain a constant concrete placement temperature, and from the standpoint of effective use of liquid nitrogen. is necessary. In addition to the above, the program for the control device 40 is designed so that information such as the grain size and size of gravel can also be input, and the required batch operation time can also be determined.

The operating mode of the batch cycle is shown in FIG. In this case, "precooling" in the figure refers to the injection of liquid nitrogen by the concrete valve 2), which is activated at 07 during gravel pouring after mortar formation, in the latter stage of material input in Figure 7 (a). Applies to.

Injection of liquid nitrogen at the time of material input is particularly effective in heat exchange between the material and exhaust gas at the time of material input (dropping). This is due to increasing the contact area between the material and the exhaust gas and improving the heat transfer film on the contact surface. This control device can vary the injection time of liquid nitrogen and adjust the injection amount in stages by operating in combination with control valve 2 (CV) and shutoff valve (PV). Batch cycles can be operated based on the required cooling temperature.

An example of the heat balance according to the implementation of the present invention is shown below.

All data are from batches. The target concrete is 1TrL (2300kg).

The concrete was cooled by 7°C with input energy of 70 to 3 liquid nitrogen (7140 to calorie). This is 4186
This means that you have consumed calories.

Heat recovery using exhaust gas was 1080A: calories. Therefore, the amount of unused cooling heat was 1574 calories, which was a high efficiency.

In the method and apparatus of the present invention, it is necessary to prevent oxygen deficiency accidents since nitrogen, which is an inert gas, is handled, and from the viewpoint of safety measures, a shutoff valve 3 (PV
) and control valve 2 (CV) are in operation, and a mechanism 51 is provided to prevent entry into the mixer while liquid nitrogen is being injected, and when the mixer is stopped, the door can be opened to prevent anyone from entering the mixer. Consideration has been taken to ensure that nitrogen gas is never injected during inspection and maintenance work. For further safety, an exhaust fan can be operated during maintenance to provide constant ventilation.

Efficacy - In places where concrete is required according to the present invention,
In addition, by using a two-shaft forced mixing mixer nearby, batch operation can be continued efficiently and repeatedly, and the cooling energy of the cooling nitrogen used can be used extremely effectively, resulting in shortened work periods and significant cost savings. You can expect it.

[Brief explanation of the drawing]

Figure 1 is a schematic explanatory diagram showing the relationship between the concrete mixer and associated equipment used in the present invention, Figure 2 is an explanatory diagram of the attachment of a liquid nitrogen injection nozzle to the mixer, and Figure 3 is an illustration of the attachment of the mixer drum and nozzle. Explanatory drawing of the section, No. 4
The figure is an explanatory diagram of the nozzle tip blockage elimination mechanism, and Figure 5 is the second
The figure is a nozzle arrangement diagram as viewed from the v-■ arrow, Figures 6A and 6B are diagrams showing the shape of the nozzle tip, and Figure 7 is a graph explaining the aspect of the batch cycle according to the present invention. In the drawing, 1...Mixer 2...Control valve 3
... Shutoff valve 4 ... Nozzle 5 ... Gas-liquid separator 6 ... Drum 8 ... Nozzle tip
9...Liquid nitrogen supply lance 10...Hopper (
Sand) 11... Hopper (gravel) 12; Hopper (cement) 15: Water supply 31; Exhaust fan 32: Exhaust duct 33. 38: Nitrogen gas duct Patent applicant Osaka Sanso Kogyo Co., Ltd. = 20- Figure 5

Claims (15)

[Claims] (1) In a two-shaft forced mixing mixer for concrete,
Liquid nitrogen is injected directly into the materials being mixed (cement, sand, gravel, water, admixtures, etc.), the cold energy of the liquid nitrogen is used to cool the mixed concrete, and the vaporized nitrogen gas is mixed into the sand and the mixture. Or a concrete cooling method that effectively utilizes the cold energy of liquid nitrogen by introducing it into a material supply system such as gravel or a storage hopper, etc., and cooling the material with the residual cold energy of nitrogen gas. (2) A method for cooling concrete in the method of item 1 above, wherein the liquid nitrogen injected into the materials being mixed is gas-liquid separated. (3) A concrete cooling method in the method of item 2 above, in which nitrogen gas generated by gas-liquid separation is introduced into a material supply section for sand, gravel, etc. to cool the material. (4) A concrete cooling method in which nitrogen gas generated by gas-liquid separation is directly introduced into the mixer to recover cold heat in the method of item 2 above. (5) In order to ensure or shorten the batch cycle in the method of item 1 above, a concrete cooling method in which liquid nitrogen is injected from the time of material input and the amount of injection is adjusted in stages. (6) A concrete cooling method in which the injection amount of liquid nitrogen is calculated based on the temperature and amount of the material to be cooled in the method of item 1 above, and the concrete temperature after cooling is adjusted by feedback. (7) A two-shaft concrete forced mixing mixer; a nozzle that injects liquid nitrogen into the mixer at the side of the drum of the mixer; a supply system that supplies liquid nitrogen to the nozzle; means for using the nitrogen gas to cool the concrete material; the amount and concentration of materials input to the mixer; the amount of liquid nitrogen;
and means for controlling the concrete cooling system. (8) In the apparatus set forth in item 7 above, the injection position of the nozzle is set near the mixing section (concrete), and the spraying position is set on each stirring shaft within a range of 45° upward from the horizontal direction from the center of the mixer drum. A concrete cooling device in which multiple liquid nitrogen injection nozzles are installed in the axial direction at the curved part of the mixer drum toward the middle of the mixer drum. (9) A concrete cooling device incorporating a gas-liquid separator for separating only gas in front of the nozzle of the supply system in the device of item 7 or 8. (10) In the apparatus of item 7, the supply system includes a gas-liquid separator, and the concrete cooling device supplies only liquid nitrogen after nitrogen gas separation to the nozzle. (11) A concrete cooling device in which the separated nitrogen gas is supplied to a material supply system or a mixer in the device according to item 10. (12) In the apparatus according to any one of paragraphs 7 to 11, the nozzle minimizes heat conduction to the mixer drum;
In addition, synthetic resin (
Concrete cooling equipment that uses materials such as fluororesin and nylon resin. (13) In the apparatus of item 8, the nozzle has a shape in which the spray pattern spreads horizontally, and the concrete is disposed at different positions in the axial direction on both sides of the drum. Cooling system. (14) A concrete cooling device having a detection mechanism and a clogging removal mechanism when a nozzle is clogged with mortar while the nozzle is in operation in any of the devices described in items 7 to 12 above. (15) In any of the devices described in Items 7 to 13 above, the control means includes means for preventing the maintenance door from opening while liquid nitrogen is being injected into the mixer, and for preventing the maintenance door from opening during internal maintenance. Concrete cooling equipment that includes a means to prevent shortage.