Logic diagram for system capability
A logic diagram, based on the use of test data, for determining the capability of an existing pneumatic conveying system is presented in Figure 15.4.
Specify bounding conditions
With an existing system, the pipeline will form part of the established system, and so length, geometry and bore will all be fixed. An air supply will also be available, but it may be possible to alter the balance of flow rate and pressure should this be necessary.
Material conveying characteristics
Conveying characteristics for the material form the starting point in this process, as they did for the original system design considered earlier.
Scale conveying characteristics
With a clearly defined pipeline length, bore and geometry, the available conveying data for the material can be scaled directly to that of the plant pipeline.
Specify air requirements
All the information relating to the conveying of the material will be found within the scaled conveying characteristics. Air requirements will need to be established first as these have a direct influence on the material flow rate. With an existing system the pres- sure capability will be known and so if allowances are made for pressure drops associated with material feeding, air separation, etc, as discussed in relation to other design proced- ures, a value for the conveying line pressure drop can be obtained. With a 20 per cent allowance on minimum conveying air velocity, the value of air flow rate necessary can be obtained from the conveying characteristics. If the corresponding air flow rate does not match the capability of the air mover, the characteristics of the air mover will have to be consulted in order to check on the possibility of making any necessary changes.
Specify material flow rate
Once the air requirements have been specified satisfactorily, so that both the pressure and flow rate requirements are within the capabilities of the air mover, the correspond- ing material flow rate can be obtained directly from the conveying characteristics.