When conveying line leaks can be a good thing
A reader says that his plant's pneumatic conveying system had been running well, but that it had developed a few leaks as a result of inadequate maintenance. During a planned shutdown, maintenance workers located all the leaks and sealed them. But when the system was started up afterward, it couldn't convey material at as high a capacity as it had before and the system line pressures were higher. What happened?
This is a dilute-phase pressure conveying system with a 6-inch conveying line. Based on the system's normal operating pressure of 12 psig and the material's saltation velocity of 4,000 fpm in this line, we multiply 4,000 fpm by 0.2006 square feet (the area inside the conveying line) to calculate the system airflow of 802 acfm. (When using saltation velocity in these calculations, remember that the saltation velocity is ideally about 10 percent lower than the material's pickup velocity.) To determine the inlet airflow to the system's air mover (a blower), we calculate 802 (14.7 + 12)/(14.7) = 1,457 scfm. For simplicity in these calculations, we'll assume that the system operates at a constant temperature.