Is There a Place for Weight-based Density Meters?
Processing industries are largely dominated by x-ray density sensors. Yet, there is a sizable desire across these industries to adopt alternatives to radioactive measurement devices. Attempts to develop alternatives have surfaced over the past decades, many of them have failed. This articles introduces a novel weight-based density meter for sludge and slurry with proven track record that demonstrate its potential to replace x-ray densitometers.
Weight-based methods, specifically those that deal with in-line measurement of weight of a fixed volume of fluid flowing through a pipe, are extremely suited for density measurement of multi-phase fluids, such as sludge and slurry:
- Weight-based density measurement is a direct method with a linear scale, which means that weight-based density meters can be accurately calibrated with just 2 data points, one of which is an empty pipe and the other – the current actual density of the fluid that is being measured. The latter could be simply equal to the density of water if calibrated with a water stream or the real-time density of sludge or slurry measured with alternative means.
- Linear scale also means that simply by the nature of the method weight-based densitometers can operate in a wide range of densities changing from 1000 kg/m3 to 2500 kg/m3 with no need to recalibrate for a narrow window of density as is needed for x-ray density methods.
- Weight-based density meters measure the integral density of the volume of fluid flowing through the density meter, which is specifically suited for sludge and slurry as these fluids have a distribution of densities within the volume.
DENCELL MUD-4 is the 4th generation of weight-based sludge and slurry densitometers developed by our team over the past 20 years. It has a proven industry track record since 2012. According to our knowledge, MUD-4 is the only weight-based method that actually works.
Why weight-based density meters are not common and how MUD-4 is different?
Many attempts to develop weight-based density meters have failed. Key issue at play is that in order to measure the weight of the density sensing pipe (the pipe that is being weighted to measure the density of fixed volume of fluid), the pipe has to be decoupled from the rest of the pipeline so that it can move freely in vertical direction. As soon as joints, such as bellows or other flexible connectors, are introduced, these joints become part of the measurement system. Changes in the temperature of the fluid or environment, or fluctuations of the pressure of the fluid in the pipeline affect the joints and result in a measurement error of a random nature that can be as high as 2.5%FS, and is impossible to compensate for.
DENCELL MUD-4 Sludge and Slurry density meter has a density sensor that is designed specifically to autocompensate for changes in pressure and temperature of the fluid flowing through the density sensing pipe.
DENCELL MUD-4 Sludge and Slurry Density Meter consists of a Density Sensing Pipe and DENCELL MUD-4 Density Sensor. The Density Sensor incapsulates a flexible joint in such a way that all forces inside the joint and compensated for automatically.
Temperature compensation is linear and is implemented via a temperature sensor integrated into the DENCELL MUD-4 Density Sensor. The output of the sensor is a compensated linear real-time density signal with the accuracy of the sensor of 1kg/m3. The accuracy of the density meter is 0.3%FS for low density fluids and 0.5%FS for dense multi-phase fluids, such as sludge and slurry.
This technology is protected with international patents.
DENCELL MUD-4 Sludge and Slurry Density Meter is ideally suited for measurement of density of multi-phase fluids in pipelines, open chutes and on equipment directly. The Density Meter has an internal diameter of 2 3/4 inches (70mm) and is connected to the pipeline or equipment via a by-pass. The following article provides more information on the installation of the DENCELL MUD-4 Sludge and Slurry Density Meter.
DENCELL MUD-4 Sludge and Slurry Density Meter comparison to other types of densitometors
Comparison of DENCELL MUD-4 Density Meter with other types of density meters is provided in the table below. This comparison is done specifically in regards to multi-phase fluids, such as sludge and slurry.
Weight-based Sludge and Slurry Density Meter DENCELL MUD-4
Pros:
- Direct density measurement method with a linear scale.
- Works in a wide range of densities.
- Insensitive to changes in temperature, pressure and velocity of the fluid.
- Can be installed on partially filled pipelines as well as open chutes or equipment directly.
- Safety. Non-radioactive density measurement technology.
Cons:
- Requires a by-pass in the majority of installations.
Please refer to the article on the installation of the DENCELL MUD-4 Sludge and Slurry Density Meter for more details.
Conclusion:
- An alternative to x-ray density meters that actually works.
X-ray Density Meters
Pros:
- Direct Installation on the pipeline irrespective of the diameter of the pipeline.
Cons:
- Can only be installed on the 100% filled pipelines.
- Works better on vertical pipelines. Accuracy is reduced on horizontal ones.
- Expensive maintenance due to safety standards and requirements maintain and periodically replace gamma ray sources of the meter .
- A large number of installations may exceed the maximum permissible levels of radiations within the plant.
Conclusion:
-
Expensive base price and maintenance.
Safety hazard for operators and staff.
Acoustic Density Meters
Pros:
- Inexpensive
- Ease of installation on a large variety of diameters of the pipelines
Cons:
- Can only be installed on the 100% filled pipelines.
- Accuracy depends on the density of the slurry. Work well with low density slurries.
- Calibration coefficients has to be adjusted to the properties of the slurry and are sensitive to changes in slurry properties, such as size distribution.
Conclusion:
- Although inexpensive and easy to install, the accuracy of acoustic density meters depends on the physical properties of the slurry being measured and will be unacceptable in changing environments.
Vibration Type Density Meters
Pros:
- Excellent accuracy on clear or homogenous fluids.
Cons:
- Accuracy deteriorates on multi-phase slurries.
- Single point measurement (in the case of a vibrating fork) leads to a low representativeness of the actual density of the slurry.
- Difficulty to protect the sensor from abrasive wear.
Conclusion:
- Vibration type density meters are rarely used to measure density of sludge and slurry.
Buoyancy Density Meters
Pros:
- Very Inexpensive.
- Can be installed on open tanks with steady flow.
Cons:
- Sensitive to turbulent flows.
- Provide a single point measurement that leads to low representativeness of the actual density of the slurry.
- Steady flows required by the buoyancy density meters result in a segregation of the slurry further decreasing the representativeness of the method.
Conclusion:
- Although inexpensive this method results in a substantial measurement error and is limited to steady flows in open tanks.
Conclusions
DENCELL MUD-4 Sludge and Slurry Density Meter is a technology that revives weight-based density measurement principle with all the benefits of the method. With the accuracy of 0.5%FS it has a unique value proposition: it is an accurate and safe alternative to x-ray density sensors that works.
DENCELL MUD-4 Sludge and Slurry Density Meter has clear advantages compared to other density sensor. It also has some limitations, in particular, the requirement to use a by-pass. Please refer to the Please refer to the article on the installation of the DENCELL MUD-4 Sludge and Slurry Density Meter to see how DENCELL MUD-4 Density Meter is installed.