The simpler way to retrieve a product from storage respecting the flow rate value (set point) needed by your process, is to use a feeder. Depending on the maximum flow rate value and the granular size of the concerned product the most common types of feeder are belt feeder, screw feeder or Loss in Weight feeder.
Depending on the accuracy your application requires, these feeders could be based on weighing or volumetric principle. From 300 mm up to 2 m wide belt for flow rates from a few kg/h up to 1 000 t/h, with center to center distance from 800 mm up to 10 m, painted or stainless steel for food industry, the feeder you need is existing into PM range or can be designed to fully match your project needs.