by Nonius Engineering
Semenov, PhD, Chief Engineer, Nonius Engineering Ltd.
The Nonius Engineering Company’s mission is to take hydro technical works to an absolutely new level on account of means for automation, monitoring and positioning of vessels, as well as to optimize all operating procedures both afloat and underwater. The Company’s Mission Statement is “Smart approach to works afloat and underwater”.
Everyone who owns a suction dredger or a mining one understands the importance of dredging productivity estimation. If you can properly estimate productivity you’ll be able to use your dredger in the optimal way. Having the log of productivity allows you to determine which operators are more efficient and deserve to be rewarded and which are not. Nonius Engineering Ltd. has more than 10 years of experience in this field and offers you a comparative description of different ways of monitoring and controlling productivity along and also introduces its new invention.
To calculate the dredging productivity you need to measure the amount of pumped material per certain time period. To do so you need to measure the velocity of slurry in the pipe and the amount of dry material in slurry. It is important to exclude water from your calculations because it obviously doesn’t count. So, to measure the instant performance of the dredger you need to multiply the amount of dry material by its velocity. To find out the amount of mined material you need to integrate instant performance as to dredger’s work time. Here is the list of existing types of density and velocity meters however none of them are flawless.
Doppler flow-meter: It is a general term for all the devices that measure velocity using the Doppler effect.
Time transit flow-meter: This kind of meter measures the time that takes the ultrasonic wave to go through the pipe alongside with the flow and then “upstream” and calculates the difference.
Electromagnetic flow-meter: To measure the velocity of the flow you need to measure electromotive force (voltage) targeted to the flow according to the Faraday’s law (movement of the conductor in the magnetic field).
Each kind has its own strong features and weaknesses, but none of them is perfect. The perfectly precise and yet jam-proof meter has not been invented yet. The Doppler flow-meter seems to be the most suitable for dredgers. The transit time meter doesn’t work properly when there are suspended particles. And using the electromagnetic kind means that you need to replace the part of the pipe with nonmagnetic one, which is quite fragile, not really wear-proof and yet expensive. However, the Doppler flow-meter is not precise enough, its results tend to depend on the pipe shape.
Traditional density meters
Differential manometer: It measures the pressure in two points of the vertical part of the pipe and then calculates the difference.
Radiation meter: This method uses penetrating power of gamma ray.
Coriolis meter: It measures phases of mechanical vibrations of U-pipes the flow is going through.
In spite of having some difficulties with health issues and being quite expensive, radiation meter is the most popular one.
Weighing a pipe section.
Lab density meter made by Toshiba uses spreading of the spectrum of the high-frequency signal going through slurry.
Resonance density meter, measures resonance of mechanical system, which depends on density and viscosity of the environment it goes through.
Capacitive density meter, measures specific inductive capacity depending on different material (air and vacuum has 1, clear water – 34, quartz sand – 11, mixture of water and sand has from 34 to 11, depending on percentage of sand).
These alternative methods allow you to achieve more precise results, however, they require quite serious changes applied to the pipe and also frequent replacements of several essential and high priced parts.
New solution – Nonius SlurryMeter 2.0 (SM 2.0)
This new method doesn’t require any radioactive elements or any new elements build in the pipe. On the other hand, it allows measuring velocity of the material as to a layer which means more precise results, more efficient way to monitor the amount of mined material and to analyze the density of slurry (also layer by layer). It also allows you to analyze the residual layer and also the type of mined material. This method is based on combination different hydro acoustic technologies. This new method is being patented.
Here is the diagram of the sensor complex that measures velocity and density and allows recognizing the type of material in the pipe.
Measuring velocity of the flow layer by layer allows you to calculate the average speed of the flow more accurately, which is important for evaluating the productivity. Judging by the thickness of the residual layer you can recognize the type of material in the pipe and adjust the pump output accordingly to reach the optimal productivity (Figure A). The diagram shows that the maximum density is achieved on the bottom layers, which corresponds with minimum velocity – the residual layers hardly move at all.
On the second diagram (Figure B) you can see what clear water flow data look like. The density parameter is always the same (around zero difference from water density) and the velocity, measured layer by layer, is represented by a classical diagram that you can find in every textbook on the subject.
Testing of this complex gave following results:
- The velocity measurements are more accurate (by 1.5-2%) than the mechanical swivel inside the pipe.
- The density measurements of the known type of material are as high as 3 % for silt, clay, fine sand and gravel sand.
So, the new density and velocity meter SM 2.0 uses only put-on sensors and allows you to measure the dredger productivity to the accuracy of 3% for the known type of material. Also, it automatically recognizes the material in the pipe. The new SM2.0 is not just a device, it comes in a package with a special software which was developed especially for this occasion and was tested on dozens of dredgers. You can find the examples of the software interface on the figures below. And that is only one of SM2.0 many advantages.