Consistency measuring device

An on-line method for consistency (percent solids by weight) testing of slurries. An aqueous slurry is piped through two stations, one of which is a nuclear magnetic resonance instrument and the other of which is a nuclear density (gamma radiation) gauge. The electrical signal outputs from the stations are processed by a computer to furnish a real time reading of consistency.

SUMMARY OF THE INVENTION 
This invention deals generally with testing of a liquid suspension of 
solids and, more specifically, with the consistency testing of slurries. 
Virtually all methods of testing the consistency, the percent solids of a 
slurry, which are liquid solutions with solids suspended in them, involve 
either off-line hand-sampling techniques or shear-type transducers. 
Off-line hand-sampling is, by its very nature, an intermittent process 
which generally is unsatisfactory for meeting the process control needs of 
a high volume production process which can change between samples. 
Sheer-type consistency transducers are limited in the range of 
consistencies they can measure and are effected by process parameters such 
as stock flow rate, air entrainment, formula variations, and abrasiveness. 
Currently there is no available on-line consistency measurement system 
that will give an accurate and absolute consistency measurement for stocks 
where the solids are abrasive. 
The present invention solves these problems of on-line, real-time, 
measurement of slurry consistency and furnishes accurate, repeatable 
consistency measurement regardless of slurry air entrainment and formula 
variations. 
This is accomplished by independently measuring the quantities of total 
slurry mass and liquid carrier mass and then using an on-line computer to 
combine the readings and provide a consistency measurement. A nuclear 
density gauge is used to measure the total slurry mass. Since nuclear 
density gauges using gamma radiation are currently used to measure mass, 
the key to the present invention is to accurately measure the mass of the 
liquid carrier. To measure the mass of the liquid carrier, a nuclear 
magnetic resonance instrument is used. 
In basic terms, a nuclear magnetic resonance instrument operates by 
measuring the number of hydrogen atoms bonded to the molecules of the 
liquid carrier in the measuring field. This is done by passing the slurry 
through a high field strength magnet to temporarily disturb the hydrogen 
atom rotation, then the hydrogen atoms are bombarded by radio frequncy 
energy. When the radio frequency energy is cut off, the hydrogen atom 
relaxes and emits radio frequency energy of its own. The cumulative radio 
frequency field from the hydrogen atoms is detected by passing the slurry 
through a coil of wire that acts as an antenna. The radio frequency field 
strength detected by the antenna is related to the number of hydrogen 
atoms and therefore the mass of the carrier. 
The nuclear magnetic resonance instrument is tuned to the carrier and 
therefore is not effected by entrapped air or solids with hydrogen bound 
atoms, and produces proportionately less signal when there is less liquid. 
The nuclear density gauge and the nuclear magnetic resonance instrument 
together provide all the data required for a consistency measurement. The 
nuclear magnetic resonance instrument measures the quantity of carrier 
bound hydrogen atoms, thus measuring the mass of the liquid carrier only, 
while the nuclear density gauge measures the total mass of the solids plus 
the liquid carrier passing through it. 
These two measurements are then supplied to a computer which 
instantaneously calculates and displays consistency. 
The method and apparatus described herein yield an on-line real-time 
consistency measurement independent of air entrainment and product formula 
variation.

DETAILED DESCRIPTION OF THE INVENTION 
The preferred embodiment of the invention is shown in the FIGURE in which 
consistency measuring apparatus 10 includes pipeline 12, through which 
flows slurry 14, and adjacent to which are installed nuclear magnetic 
resonance instrument 16 and nuclear density gauge 18. 
Slurry 14 is a mixture of liquid and solids, a mixture in which the solids 
are largely insoluble and merely carried along by the liquid. Mud is 
generally considered a slurry, but much more valuable slurries are used in 
numerous industrial processes. While any liquid carrier can be used, water 
is probably the most common liquid carrier. 
Since most industrial processes require close control of the constituents 
which make up a slurry, one particular measurement has become very 
important. It is consistency, which is the ratio, expressed in percent, of 
the weight of the solids in the slurry to the total weight of the slurry. 
The present invention is capable of measuring the consistency of a slurry, 
and does so regardless of whether the liquid carrier has gas entrapped 
within it, because the invention independently measures the liquid weight 
rather than calculating the weight based on the assumption that all the 
volume which is not solid is liquid. 
Moreover, the measurement range of the present invention far exceeds most 
measurement systems previously available because it measures the liquid 
quantity by a method which has no inherent saturation characteristic. 
The present invention measures the liquid quantity with nuclear magnetic 
resonance instrument 16. As previously described, nuclear magnetic 
resonance instrument 16 actually measures the quantity of hydrogen bonded 
with other elements to form the liquid carrier in the system and therefore 
measures the weight of liquid carrier. It furnishes a simple, time 
varying, electrical signal to computer 20 by means of cable 22, and 
computer 20 converts the electrical signal into a weight based on 
previously programmed information. 
The present invention does not make any claims in regard to nuclear 
magnetic resonance instruments. Such devices are well known and 
established in other fields. The most widely known of which is medical 
technology. In diagnostic medicine, nuclear magnetic resonance, also 
called magnetic resonance imaging or MRI, uses very high resolution 
equipment and elaborate display apparatus to visually display the function 
of human organs. While the present invention could make use of the 
elaborate medical instruments, it needs neither the high resolution, the 
elaborate display, nor the resolution between many materials. 
Consistency testing apparatus 10 which needs to distinguish only the 
presence or absence of a single liquid material, requires only low 
resolution nuclear magnetic resonance instrument 16 and only a single 
output 22 of an electrical signal varying with time. Such a signal is 
available from the simplest nuclear magnetic resonance systems and 
generates an electrical signal which is related to the quantity of a 
specific substance, in this invention the liquid carrier, within the field 
of view. If the substance is flowing through the field of view, the 
electrical signal then varys according to variations in the quantity of 
material flowing past the pickup coil of instrument 16. Most important, if 
a bubble of air passes through the field of view, the quantity of liquid 
carrier is reduced and the electrical signal is reduced proportionally. 
Nuclear magnetic resonance instrument 16 therefore furnishes the computer 
20 an electrical signal which is always related to the weight of the 
liquid carrier, since it essentially measures the quantity of hydrogen 
passing through it. 
With the liquid carrier weight accurately determined, it is only necessary 
to measure the total slurry weight in order to determine the consistency. 
The total slurry weight is measured by conventional nuclear density gauge 
18. As is well established in the art, nuclear density gauge 18 uses 
cesium 137 source 24 to irradiate a section of pipeline 12 and ionization 
chamber 26 to measure the gamma radiation passing through pipeline 12. As 
the density of the total slurry varys the amount of radiation reaching 
ionization chamber 26 varys inversely, since more dense material causes 
more attenuation of the radiation. Nuclear density gauge 18 therefore 
furnishes an accurate measurement of the weight of slurry 14, the combined 
weight of the liquid carrier and the solids in slurry 14. 
Nuclear density gauge 18 furnishes the information to computer 20 by means 
of cable 28, and computer 20, having available electrical signals related 
to the total weight of slurry 14 and the weight of one constituent, the 
liquid, of the two components of slurry 14, can easily be programmed to 
yield the percentage by weight of the other constituent, the solid 
materials. 
Although the gamma ray attenuation measurement furnished by nuclear density 
gauge 18 and the hydrogen quantity measurement furnished by nuclear 
magnetic resonance instrument 16 could, along with the physical parameters 
of the materials, be used to calculate the consistency, a higher level of 
confidence in calibration is attained by relating the readings to 
empirical measurements. Therefore, sampling valve 30 is attached to 
pipeline 12. Thus, when consistency measuring apparatus 10 is first placed 
in operation or when different materials are first run in the system, a 
range of empirical measurements can be made by selecting samples and 
comparing them to the electrical signals available as they pass through 
the system. The use of empirical measurements is made easier by the fact 
that the relationship of the electrical signals to consistency is 
logarithmic. It is therefore only necessary to test a limited number of 
samples to secure an accurate calibration. 
It is to be understood that the form of this invention as shown is merely a 
preferred embodiment. Various changes may be made in the function and 
arrangement of parts; equivalent means may be substitued for those 
illustrated and described; and certain features may be used independently 
from others without departing from the spirit and scope of the invention 
as defined in the following claims. For instance, slurries other than 
those with water as a liquid carrier could be measured.