The present invention relates generally to apparatuses and methods for metering and conveying dry powder or granular materials to a blender, and more particularly to an apparatus and method for accurately metering and conveying dry powder or granular materials to a blender in a substantially closed system.
In conventional oil field operations, dry powder and granular materials are transported in sacks to the well location. The sacks are then manually moved to a metering feeder mounted on a fluid blending device. The metering feeder has a hopper to collect the dry powder or granular material and to serve as a reservoir. The hopper is kept full by opening sacks of the dry powder or granular material and dumping them into the hopper. The amount of dry powder or granular material must be kept at a constant level in the hopper so as to maximize the accuracy and repeatability of the metering feeder. The accuracy and repeatability of the metering feeder is dependent on having a constant material bulk density at the screw auger.
Fluctuating levels of powder or granular material in the hopper can alter the bulk density of the material, and thus negatively affect the desired quality of the oil field service fluid. However, it is difficult to maintain a constant feed of material to the hopper when the hopper is being filled manually. Thus, the drawback of such systems is that there is a likelihood the hopper will be either overfilled in which case dry powder or granular material is spilled, or underfilled in which case the bulk density will be altered, which in turn will reduce the quality of the oil field service fluid. In the case where the dry powder or granular material is spilled, material is lost and clean up is necessary, which translates into lost revenue. This method also generates a lot of dust since the hopper is open to the outside air.
Alternate methods have been proposed, which also have drawbacks of their own. One such method is to transport the dry powder or granular material to the well location in a large bulk tank and to convey the material pneumatically or mechanically to the metering feeder on the fluid blending device. This method, however, requires the conveying device to be controlled either automatically with level sensors and control loops, or manually in order to keep the dry powder or granular material at a constant level in the metering hopper for maximum accuracy and repeatability. Vehicle roading and equipment vibrations tend to compact the powder or granular material and cause significant variations in the bulk density of the material which affects the accuracy and repeatability of the metering feeder. This process is also labor intensive, susceptible to sensor failures and likely to generate dust.