From the Particulate Solids Research Institute
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Particulate solids are often required to be introduced into a flowing gas stream. If not done correctly, introduction of solids into the gas stream can lead to impingement of solids on the pipe, resulting in erosion of the pipe in the area of the solids introduction. The impingement can also cause unwanted attrition of the solids. The reason for this problem is that the momentum of the solids is often greater than the momentum of the gas. Therefore, the flow of the solids will not be &ldquostraightened out” by the gas as the solids enter the pipe, and the momentum of the solids will cause them to impinge on the wall of the pipe. This is shown in Figure 1A for vertical pipe flow and in Figure 1C for horizontal pipe flow.
As Figure 1A shows, solids enter a vertical pneumatic conveying line horizontally. If the momentum of the horizontal solids stream is great enough, the gas will not &ldquostraighten out” the solids flow and the solids will be deflected onto the wall of the pipe resulting in erosion of the pipe if the solids are abrasive. A secondary solids deflection onto the wall is also often observed. One solution to this problem is to introduce the solids into the line in the same direction that the gas is flowing, as shown in Figure 1B.
In horizontal lines, the situation is somewhat different but the result is the same â€“ erosion of the pipe wall. In this case the solids drop down vertically into the horizontal line. A pile of solids forms immediately below the solids entrance. The gas (carrying some solids from the surface of the pile) is deflected upwards and onto the pipe surface causing erosion as shown in Figure 1C. In this case adding a deflector, called a &ldquosugar scoop” because of its shape, diverts the solids into the same direction as the gas and prevents erosion of the pipe wall as shown in Figure 1D. Therefore, a good rule-of-thumb is to introduce the solids into the conveying line in the same direction as the flowing gas. This will usually prevent the problems outlined above.