It is safe to say that everyone’s goal in process control is to increase reliability of their process measurements. Facilities spend endless resources to identify and displace problematic points, also know as “bad actors”. One common problem area in a refinery is reliably measuring the heavy residual hydrocarbons from the “bottoms” of the distillation towers in their crude unit. Typically, these applications are Vaccum Distillation (VDU) Feed & Delayed Coker (DCU) Feed; also known as furnace pass flow.
These flow measurements most commonly incorporate orifice and wedge meter installations using a differential pressure (DP) transmitter, requiring a flow restriction to be placed inline. This restriction creates pressure drop and is susceptible to clogging due to the high viscosity of the heavy oil residual, therefore steam purging is incorporated to alleviate buildup. Cost of regular maintenance for DP transmitters, along with downtime required for purging decreases the unit output capacities.
A growing solution for this application is the use of ultrasonic flow meters with waveguide transducers. Here we look at a few major benefits of implementing the ultrasonic technology.
- Unobstructed Flow Path
- Traditional Orifice and Wedge Meter installations (shown below) employ differential pressure technique, requiring a flow restriction to be placed inline. This restriction creates pressure drop and is susceptible to clogging due to the high viscosity of the heavy oil residual and can require personnel exposure time in the unit. In addition, the amount of purging that is required to prevent clogging increases maintenance costs and decreases the unit output capacities.
- Bundle Wave Technology
- Typical wetted ultrasonic meters require transducers to be located inside the process, exposing them to the extreme temperatures and requiring isolation capability in order to service the instrument. BWT allows the transducer to be removed from the process, outside of the harsh environment. This prevents maintenance issues related to thermal shock when using solid state buffers and allows the instrument to be fully serviced under process conditions.
- SIL Rated System
- Typical systems incorporate redundancy for operational control and safety shutdown systems and are capable of being SIL certified by design (SIL 2 or SIL 3 depending on configuration), with the ability to incorporate redundant sensors and electronics in a single packaged solution for Operations and Safety Shutdown. Providing safety and reliability without the operational expense of maintaining DP measurements.
In conclusion, ultrasonic flow meter technology when coupled with waveguide transducers provides the safest, most reliable solution to difficult flow applications with high temperatures and high viscosity liquids. Implementing this solution, a facility can lower maintenance costs while increasing safety, measurement reliability and overall plant efficiently.