It is to be desired that no deposition of granular material occurs around an obstacle in the pneumatic conveying pipe, and at least it should not be heap up till a choking stand. These conditions depend principally upon the characteristics of granular material, the velocity of air, and the shapes of obstacle.
In this study the minimum air velocity for the pneumatic conveying line were measured in a pipe of rectangular section 100×100mm using granulated alumina of various mean diameter as test material.
First, the minimum air velocity to convey the particles on the flat bottom of the pipe was shown.
Next, perturbed motion of the particles and scooping phenomena around the plates and cylinders with various dimensions placed perpendicularly against the stream on the pipe bottom respectively were surveyed, and also the amount of deposition and scoop according to elaspe of time were mesured in the various conditions of air velocity.
Consequently, a formula to calculate the amount of material deposited around an obstacle at the saturate condition-not to heap up any more, was obtained.

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In the case of the measuring dust content in the flue gas, the gas sample should be drawn into the suction nozzle of the dust collector at the same velocity as that of the flue gas. That is well known isokinetic sampling.
Presently, there are some isokinetic samplers with the null balance type nozzles by which the isokinetic suction can be very easily performed. One of those is the static pressures balance type isokinetic sampler. It has, however, a few problems, e. g., that the construction is of a greatest complexity and a big form. Therefore, we have studied for developing a new isokinetic sampler with the reference static pressure tube according to a new principle of measuring.
The first step in the experiment was to measure inside static pressures of the suction nozzle in the isokinetic conditions.
We designed the reference static pressure tubes which had the same frontal shapes and showed the same static pressures as those of the suction nozzles.
Using the dust sampler equipped with the suction nozzle and the reference static pressure tube, the suction errors have been measured in relation to the static pressure differences and the excellent characteristics have been experimentally confirmed.

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Experiments would be done for the determination of the magnitude of rapping force required to get the desired rapping efficiency with various types of dust, whether the electrode is rapped in parallel to the plate (Shear rapping) or perpendicular to that (Normal rapping). For moderate electric-resistivity as talc, cement and fly-ash, acceleration of 1000m/sec² may be required for 90% removal of dusts from collecting electrode. But for high electric-resistivity dust as sulfur, a single impact has no effect to clean the collecting electrode, even by acceleration of 2000m/sec². In stead of a single impact rapping, vibration type device is actuated of impacts is tried.
The following results were obtained for normal electric-resistivity dust. (1) Normal rapping is more effective than shear rapping. The thick dust layer are more easily than the thin one. (2) Relation between the magnitude of rapping force and rapping efficiency is represent log-normal distribution.
For high electric-resistivity dust as sulfur, it is necessary for collecting electrode as clean as possible to provide the figure of 3500m/sec² at 90cycle for 3 second. The figure of 3500m/sec² at 90cycle for 3 second would certainly break the electrode construction. A single impact rapping and vibration one are inadequate to remove high electric-resistivity dust deposited on the collecting electrode. So we recommend the scraper mechanism to clean the electrode in such case.

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