AU2002210608A1

AU2002210608A1 - Method and device for taking slurry samples from a process flow

Info

Publication number: AU2002210608A1
Application number: AU2002210608A
Authority: AU
Inventors: Christian Von Alfthan
Original assignee: Outotec Oyj
Current assignee: Metso Corp
Priority date: 2000-10-26
Filing date: 2001-10-23
Publication date: 2002-07-11
Anticipated expiration: 2021-10-23

Description

METHOD AND DEVICE FOR TAKING SLURRY SAMPLES FROM A PROCESS FLOW

The present invention relates to a method and device for taking slurry samples containing solids from large process flows, when a two-step sampling is applied.

From slurries flowing in large process flows, there are usually extracted samples for analysis, because owing to the large volume, the slurry as a whole cannot be measured. Among the employed analysers, there are for instance X- ray fluorescence analysers and particle size analysers. An important quality factor for a sample is a representative sample, which varies within the range 10 l/min - 1000 l/min. In addition, the sampler must not be blocked by slurry or by impurities contained in the flow.

Various samplers of different types are developed for sampling. In the environmental pressure, free-flowing slurries are generally sampled by vertical sample cutters, that cut a small slice of the process flow. The moving sample cutters move throughout the whole flow and take a representative sample, even if the sample flow is not homogeneous. Fixed cutter samplers cut a representative sample, if the flow is homogeneous in the horizontal direction. They also allow non-homogeneity in the vertical direction. The input aperture for the cutter flow must be sufficiently large in order to prevent accidental large particles or impurities from blocking the aperture too easily. Advantageously the minimum width for the aperture is 8 mm, but there is often needed a width of 20 mm or even larger.

A sample obtained from large flows, which sample is taken by letting the slurry flow freely to the sample cutter, is too large for the analyser. A constriction of the sample flow in the sample line reduces the flowing speed at the cutter orifice, which leads to separation, and consequently the obtained sample is not representative. In that case a good solution is to take the sample in two steps For example, there is first taken a primary sample having a speed of 5,000 l/min, and from said primary sample there is taken a secondary sample, which is suitable for the analyser. One of the problems is, however, that the primary sample cannot be directly returned to the main process flow.

The object of the present invention is to eliminate some of the drawbacks of the prior art and to realize an improved method and device for taking slurry samples from process flows flowing under environmental pressure, in which method and device the primary and secondary samplers are interconnected. The essential novel features of the invention are apparent from the appended claims.

According to the invention, in the process flow to be analysed, there is installed a sampling device that provides for primary and secondary sampling by the same device, at flowing conditions that are advantageous for sampling. At the primary sampler, the cross-section of the device is designed so that the speed of the flow entering the sampler is essentially the same as that of the process flow to be analysed. In a device according to the invention, the secondary sampler is advantageously connected to the primary sampler, so that the secondary sample can be taken from a slurry flow flowing either in the primary sampler or in a conduit piece connected to the primary sampler. The secondary sampler is placed inside the primary sampler or outside thereof, in the immediate vicinity of the outlet opening of the primary sampler, at a point where the cross-section of the primary sample flow is enlarged, and consequently the flow speed is reduced, so that the flow entering the secondary sampler has a speed that is suitable for the analyser at such an orifice of the secondary sampler where blocking can essentially be avoided. Thus, according to the invention, the speed of the flow entering the primary sampler is essentially equal to that of the process flow to be analysed, but higher than the speed of the flow located around the secondary sampler. In the sampling device according to the invention, there is advantageously used a flow-through type primary sampler, in which case the flow entering the primary sampler from one direction is conducted out of the primary sampler at the end that is opposite to the input direction. Advantageously the primary sampler is installed in the main process flow essentially in the flowing direction. As such, the primary sampler can be manufactured of one piece, in which case the sample flow flowing therethrough is discharged from the sampler directly back to the main process flow. The primary sampler can also be manufactured of at least two pieces, in which case, for discharging the sample flow passing through the sampler, the sampler itself is provided with one or several conduit pieces that guide the sample flow out of the primary sampler and back to the process flow.

For the secondary sampling according to the invention, inside the primary sampler, near the outlet opening of the primary sampler, or in a conduit piece connected to the outlet side of the primary sampler flow, there is installed a secondary sampler. The secondary sampler can also be installed outside the primary sampler or outside the conduit piece connected to the primary sampler, in the immediate vicinity of the outlet opening of the slurry flowing from the primary sampler. The employed secondary sampler can be any known sampler, such as a suction ladle sampler. The secondary sampler can be installed for instance in an inclined position with respect to the process flowing direction, so that the outlet opening of the sampler is located higher than the inlet opening of the sampler flow. Further, the secondary sampler can also be installed so that the outlet opening of the sampler is lower than the inlet opening of the sampler flow. Moreover, the secondary sampler can be installed in a slant position with respect to the process flowing direction, in which case the inlet and outlet openings of the secondary sampler flow are located at essentially the same height with respect to the process flowing direction.

The sampling device according to the invention is applied to substantially large process flows, where the flowing speed is advantageously within the range 2 - 5 meters per second. In that case the process flow contains kinetic energy that can be utilized in order to create a counterforce for the friction of the flow contained in the primary sampler. Thus the flowing speed in the primary sampler or in a conduit piece connected to the primary sampler is lower than the speed of the process flow outside the primary sampler. However, the flowing speed at the inlet opening of the primary sampler can be maintained at an essentially same level as that of the process flow by making the cross- section of the inlet opening smaller than the cross-section of the housing of the primary sampler. Thus the slurry flow at the orifice of the primary sampler is made to correspond to the slurry flow in the main process flow surrounding the sampling device according to the invention. Hence, the sample flow entering the primary sampler has essentially the same qualities as the main process flow. By maintaining the speed of the slurry flow at the secondary sampler smaller than the speed of the main process flow, the wearing strain directed to the device is also reduced, which as such increases the working age of the device and reduces repair and maintenance costs.

The invention is explained in more detail below, with reference to the appended drawings, where

Fig. 1 shows a preferred embodiment of the invention, seen in a schematical side-view illustration, and

Fig. 2 shows the preferred embodiment of Fig. 1 , seen in a schematical top- view illustration.

According to the drawings, the sampling device according to the invention is placed in the main process flow to be analysed, the flowing direction whereof is described by means of an arrow marked with the reference number 1. A primary sample taken from the main process flow 1 is conducted to a primary sampler 2 via an inlet opening 8 that is provided in the primary sampler 2, arranged first in the direction of the main process flow 1 In the vicinity of the inlet opening 8, there is installed at least one flow guide 9 in order to improve the horizontal homogeneity of the sample flow in preparation for the secondary sampling. By means of a conduit piece 3 connected to the primary sampler 2, the cross-section of the primary sample flow is increased, so that the speed of the primary sample proceeding in the inlet opening 8 is advantageously made essentially equal to the speed of the main process flow. The primary sample flow coming from the conduit piece 3 is conducted onto a sieve 4, which is installed essentially near to the orifice of the secondary sampler 5 in order to prevent any oversized particles and/or impurities possibly contained in the primary sample flow from entering the sampler 5. Part of the primary sample flow is directed to the secondary sampler 5, the outlet orifice whereof is placed outside the main process flow 1. From the secondary sampler 5, the secondary sample flow is conducted, via a conduit piece 6, to the analyser to be analysed, whereas the rest of the primary sample flow is conducted, through the outlet opening of the sampling device, back to the main process flow.

Claims

1. A method for taking samples for analysis from slurry flows containing solids, in which method a two-step sampling is applied; in the first step, there is applied primary sampling, and in the second step, secondary sampling, characterized in that the speed of the flow entering the primary sampler (2) is essentially equal to the speed of the process flow (1), but higher than the speed of the flow in the surroundings of the secondary sampler (5).

2. A method according to claim 1 , characterized in that the speed of the flow entering the primary sampler (2) is adjusted by utilizing the kinetic energy contained in the process flow (1).

3. A method according to claim 1 or 2, characterized in that the speed of the flow entering the primary sampler (2) can be adjusted by adjusting the cross- section of the flow.

4. A device for realizing the method according to claim 1 , characterized in that the primary sampler (2) and the secondary sampler (5) are connected to each other in order to create advantageous flowing conditions.

5. A device according to claim 4, characterized in that the primary sampler (2) represents the flow-through type, and that the secondary sampler (5) is installed in the outlet side thereof.

6. A device according to claim 4 or 5, characterized in that the secondary sampler (5) is installed inside the primary sampler (2) or inside a conduit piece connected to the primary sampler (2).

7. A device according to claim 4 or 5, characterized in that the secondary sampler (5) is installed outside the primary sampler (2), in the immediate vicinity of the outlet opening of the flow from the primary sampler (2).

8. A device according to any of the preceding claims 4 - 7, characterized in that the secondary sampler (5) is installed in a direction deviant from the direction (1) of the main process flow.

9. A device according to any of the preceding claims 4 - 7, characterized in that the secondary sampler (5) is installed in a conduit piece (3) connected to the primary sampler (2) in a direction that is deviant from the direction (1) of the main process flow.

10. A device according to any of the preceding claims 4 - 7, characterized in that the secondary sampler (5) is installed in an inclined position with respect to the direction of main process flow (1).

11. A device according to any of the preceding claims 4 - 7, characterized in that the secondary sampler (5) is installed in a slant position with respect to the direction of the main process flow (1).

12. A device according to any of the preceding claims 4 - 11 , characterized in that in front of the secondary sampler (5), there is installed a sieve (4).

13. A device according to any of the preceding claims 4 - 12, characterized in that in front of the secondary sampler (5), there is installed a flow guide (9).