The heavy fraction remaining following the distillation of crudes is called petroleum resids. A variety of solvent-extraction processes yield deasphalted oil (DAO) from these resids. These oils serve as downstream feedstocks for catalytic crackers and hydrocrackers. Depending upon the system configuration, level monitoring of the separator, preflash, stripper and hot oil phases may include surge and flash drums, separators and strippers.
Level control is critical because interface level control of the separator feeds the flash drum, whose level feeds the stripper, etc. Application extremes include high temperatures, high pressures, and the presence of steam.