1. A method of determining a moving packed bed velocity comprising: providing a standpipe having a standpipe net a standpipe outlet, a standpipe axial length from the standpipe net to the standpipe outlet, and a standpipe interior, where the stand interior is a volume between the standpipe inlet and the standpipe outlet and bounded by the standpipe; providing a moving packed bed in the standpipe, where the moving packed bed extends from the standpipe inlet to the standpipe outlet; defining a first axial length, where the first axial length is a first segment of the standpipe axial length and where the first segment originates at a first inlet point and terminates at a first outlet point, and where the first inlet point is between the standpipe inlet and the first outlet point, and defining a first section inlet, where the first section inlet is an area bounded by the standpipe and perpendicular to the first axial length at the first inlet point, and defining a first section outlet, where the first section outlet is an area bounded by the standpipe and perpendicular to the first axial length at the first outlet point, and defining a first section volume, where the first section volume is bounded by the first section inlet, the first section outlet, and a first portion of the standpipe, where the first portion of the standpipe extends from the first section inlet to the first section outlet; defining a second axial length, where the second axial length is a second segment of the standpipe axial length, and where the second segment originates at a second inlet point and terminates at a second outlet point, and where the second inlet point is between the first outlet point and the second outlet point, and defining a second section inlet, where the second section inlet is an area bounded by the standpipe and perpendicular to the second axial length at the second inlet point, and defining a second section outlet, where the second section outlet is an area bounded by the standpipe and perpendicular to the second axial length at the second outlet point, and defining second section volume, where the second section volume is bounded by the second section inlet, the second section outlet, and a second portion of the standpipe, where the second portion of the standpipe extends from the second section inlet to the second section outlet; defining a volume between the first section volume and the second section volume, where the volume between the first section volume and the second section volume is bounded by the first section outlet, the second section inlet, and a portion of the standpipe extending from the first section outlet to the second section inlet; providing a fluid flow through the first section volume, the second section volume, and the volume between the first section volume and the second section volume, where the fluid flow has a flow direction, where the flow direction is either from the first section inlet to the second section outlet or from the second section outlet to the first section inlet; providing an aeration flow to the standpipe interior, where the aeration flow fluidly communicates with the standpipe interior within the volume between the first section volume and the second section volume; measuring a first differential pressure over a first pressure length, where the first pressure length is between the first section inlet and the first section outlet and parallel to the first axial length; in the first section using the first differential pressure means; measuring a first gas velocity over a first gas length, where the first gas length is between the first section inlet and the first section outlet and parallel to the first axial length; measuring a second differential pressure over a second pressure length, where the second pressure length is between the second section inlet and the second section outlet and parallel to the second axial length; measuring a second gas velocity over a second gas length, where the second gas length is between the second section inlet and the second section outlet and parallel to the second axial length; formulating a first Ergun correlation relating the first differential pressure, the first pressure length, and the first gas velocity; formulating a second Ergun correlation relating the second differential pressure, the second pressure length, and the second gas velocity; and utilizing a numerical or mathematical method to determine the moving packed bed velocity of the moving packed bed in the standpipe, by determining the moving packed bed velocity which satisfies the first Ergun correlation and the second Ergun correlation within a desired accuracy.