Apparatus for measuring the static charge of flowable solids

#The invention relates to an apparatus for measuring the static charge developed by a flowable solid as it passes through a conduit. The apparatus comprises a receptacle for receiving a sample of a flowable solid, a conduit for conveying the flowable solid and a device for measuring the static charge of the flowable solid as it exits the conduit. A method for measuring the static charge of a flowable solid is also provided.

#A common problem in industry has been the processing and handling of flowable solids. Because of their high surface area-to-mass ratio and other factors, they have a tendency to develop electrostatic charges, particularly when they are conveyed through pipes or other conduits. The electrostatic charges cause the flowable solids to collect on contiguous surfaces. This phenomenon reduces the efficiency and accuracy of their conveyance. On occasion, charges can develop to an extent that spontaneous electrical discharges can occur. The discharges can lead to damage of equipment and storage containers as well as injury to personnel. Testing of the propensity of a flowable solid to develop a static charge as well as the nature of the charge developed can lead to the development of systems to improve the conveyance of flowable solids without the development of static charges.

#The principal cause for static charge generation when a flowable solid is conveyed through a conduit is frictional contact of dissimilar materials by a physical process known as the triboelectric effect. As the flowable solid passes through the conduit, static is generated by frictional contact between the flowable solid and the walls of the conduit. The frictional contact causes a flow of electrical charges from the walls of the conduit to or from the flowable solid.

#FIG. 1 is a diagram of an electrostatic charging device of the present invention.

#FIG. 2 is a plot of the static charge developed when a sample of silica is conveyed through a steel conduit at 138 kPa (20 Psi) and 207 kPa (30 Psi).

#FIG. 3 is a plot of the static charge developed when a sample of silica was conveyed through steel conduits of different diameters at 207 kPa.

#In its simplest form, the present invention comprises a conduit for transporting a flowable solid and a device for measuring the static charge on a flowable solid. The device for measuring the static charge is positioned at one end of the conduit such that it receives any flowable solids that exit the conduit. The conduit should be of sufficient length to promote the development of static charges on the flowable solid and the flowable solid should be conveyed at a sufficient rate to induce the development of such charges. Preferably, the flowable solid should be conveyed through the conduit at a rate that is the same as the rate that would be used for commercial operations. Similarly, the diameter of the conduit should be the same as the commercial device being evaluated. The conduit should also be constructed of the same material as the conduit used in commercial practice.

#Referring to FIG. 1, a simple device for practicing the invention is shown. The device comprises a receptacle, 11, at one end of a conduit, 12. The receptacle, 11, is separated from the conduit, 12, by means of a valve, 13, which prevents the flowable solid to be tested from prematurely flowing into the conduit, 12. The receptacle, 11, may also have a gas delivery system, 14, connected to it to provide a source of pressurized gas to convey the flowable solid through the conduit, 12. At the distal end of the conduit, 12, is located a static measuring device, 15. The static measuring device, 15, is capable of capturing the flowable solid as it exits the conduit, 12, and then measuring the static charge on the flowable solid.

#If the conduit is constructed of metal, it is important that it be electrically connected to ground. Otherwise, the solids passing through the conduit would induce an electrical charge on the conduit, which would produce a distortion of the measurements. The electrical connection to ground may be accomplished through the use of a grounding wire attached to the conduit by an alligator clip.