Core Oven Monitor and Humidity Control
Customer: Chart Energy & Chemicals
Project Scope: Chart's heat exchangers undergo a high hydro static pressure. After the test, the core needs all of the moisture to be removed. This process utilizes a very large oven that cooks the water out of the core. The oven controller keeps the inside ambient oven temperature at a constant 300°F. During this process, the operator will open a large valve and place a mirror (at room temperature) into the core exhaust path. If the mirror fogs, the core is still wet. If it is clear, then the core is deemed dry, or at least below dew point. Each heat exchanger has a "Calculated Heat Load" (CHL) and is used to estimate the amount of time needed to dry the core. This estimate, however, is very broad and can be affected greatly by the amount of water remaining in the core. Chart wanted a better method for determining how dry the core was mainly because of process time and utilized energy (being a 6M BTU oven).
Project Design: Industrial Automation was asked to design, construct, and program an oven monitor and humidity control system. The system consisted of an Allen Bradley Compact Logix L24ER controller, Flex I/O, a high resolution humidity and temperature transmitter, intake and exhaust pressure and temperature sensors, a Powerflex 525 VFD, three core probe thermocouple pickup points, and an Ignition SCADA/HMI system. The controller, along with all of the other equipment, monitors the core temperature and humidity, regulates the intake blower speed, controls the two intake and two exhaust valves for air flow and sampling, and monitors the temperature and pressure at the intake and exhaust ports. A Vaisala HMT330 series humidity and temperature transmitter is utilized for core humidity sampling. A custom capillary piping and valve system was designed to keep the Vaisala sensor isolated from the moisture laden air in the core during the initial stages of drying. After indirect humidity sampling has determined the core to be drying, the valves are then actuated, allowing direct humidity sampling.
The controller performs automatic moisture testing with operator verification, core cool down, and automatic oven shutdown. The program is customizable through the Ignition HMI. The customizable settings determine the moisture testing profile and drying mode. User security profiles allow for access to different levels of settings, making sure that only qualified technicians have access to make these upper level control modifications. The Ignition SCADA/HMI system also displays an active trend of the oven I/O devices and records all of these points for future data crunching.
Project Results: The applied control now gives the operator a visual and accurate indication of core moisture levels. The control allows for greatly reduced drying times allowing for faster production rates and oven through put. In addition, the energy savings in both manual and automatic shutdown can be quantified in the thousands of dollars.