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Solid Flow Measurement

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Overview

The most common solid flow measurement occurs when material in the form of small particles, such as crushed material or powder, is carried by a conveyor belt system or by some other host

material. For example, if solid material is suspended in a liquid host, the combination is called a slurry, which is then pumped through pipes like a liquid. We will consider the conveyor system and

leave slurry to be treated as liquid flow.

Table of Contents

Conveyor Flow Concepts

Flow Sensor

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Conveyor Flow Concepts

For solid objects, the flow usually is described by a specification of the mass or weight per unit time that is being transported by the conveyor system. The units will be in many forms, for example,

kg/min or Ib/min. To make a measurement of flow, it is only necessary to weigh the quantity of material on some fixed length of the conveyor system. Knowing the speed of the conveyor allows

calculation of the material flow rate.

In Figure 5.35, a typical conveyor system is shown where material is drawn from a hopper and transported by the conveyor system. Assuming that the material can flow freely from the hopper, the

faster the conveyor is moved, the faster material will flow from the hopper, and the greater the material flow rate on the conveyor. In this case, flow rate can be calculated from

where = flow in kg/minQ

weight of material on section of length LW =

conveyor speed in m/minR =

L = length of weighing platform in m

Flow Sensor

In the example with which we are working in Figure 5.35, it is evident that the flow sensor is actually the assembly of conveyor, hopper opening, and weighing platform. It is the actual weighing

platform that performs the measurement from which flow rate is determined, however. We see that flow measurement becomes weight measurement. In this case, we have suggested that this we

is measured by means of a load cell, which is then a strain gauge measurement. Another popular device for weight measurement of moving systems like this is an LVDT that measures the droop

he conveyor at the point of measurement because of the material that it carries.

FIGURE 5.35 Conveyor system for illustrating solid-flow measurement.

EXAMPLE 5.17

A coal conveyor system moves at 100 ft/min. A weighing platform is 5.0 ft in length, and a particular weighing shows that 75 Ib of coal are on the platform. Find the coal delivery in Ib/hr.

Solution

We can use Equation (5.34) directly to find the flow

Then, converting to Ib/hr by multiplying by 60 min/hr,

Q= 90,000 Ib/hr

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Liquid Flow

:Document Type Prentice Hall

: Curtis D. JohnsonAuthor

: Process Control Instrumentation TechnologyBook

: 2005Copyright

: 0131194577ISBN

: NoNI Supported

: Sep 6, 2006Publish Date

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