Here’s an important fact about RTO/RCO performance that even some engineers don’t fully appreciate: A unit’s thermal energy recovery efficiency alone isn’t a true indicator of its actual fuel consumption or cost.
An RTO is a counter flow regenerator during which heat energy is alternately accumulated for the length of the recovery period (exhaust flow), and then subsequently released from the heat exchange media to the process air flow during the preheat period (inlet flow). Since the preheat and recovery periods are basically the same period in each direction of flow, the energy released on the inlet flow must equal the energy recovered on the outlet flow.
That means overall efficiency also requires uniformity in the plug air flow and temperature profile through the entire heat exchange media bed. But those characteristics aren’t always considered during RTO design — thus leading to considerably reduced performance and increased operating costs.
The design of a heat exchange bed spans many possible options with regard to:
- the geometry and dimensions of the RTO/RCO unit configuration
- the RTO/RCO heat exchange media material and configuration used
- the mass flow rate conditions of the of the process exhaust
- the RTO/RCO valve cycle time duration for both preheat and recovery period
The overall performance of the RTO unit will depend on the final design. And the best RTO design for a specific process application is not easily determined. Doing so requires extensive knowledge of the application as well as the RTO.
First, one must be more specific with regards to the definition “best RTO design.” Does one want the RTO unit to have…
- …the minimum operation cost, both total electric and fuel?
- …maximum destruction removal efficiency (DRE)?
- …maximum up-time operation?
- …minimum maintenance?
- …all of the above?
In other words: Many criteria can be used to determine if the design is the “best” possible.
Since individual or particular RTO applications may have different objectives for the optimization of the design, it is essential that the RTO supplier have experience with how all the unique process conditions will impact the design requirements:
- Batch or continuous process
- Single or multiple processes
- 24-hour or shift operation
- Allowable offline or down time for RTO inspection and/or maintenance
- Site location and elevation
- Required VOC outlet concentration
- Required CO outlet concentration
- Required NOx outlet concentration
- Required availability uptime
- Ambient conditions, cold package & moisture barrier
- Process exhaust conditions
- Any other site-specific requirements
NESTEC’s staff have been installing RTOs on a variety of unique applications since the 1970s. Over the past four decades, our team members have developed a huge spectrum of smart solutions for optimizing the installations of existing RTOs and new RTOs alike.
For assistance, call or e-mail NESTEC for a free evaluation of your application and/or assistance in establishing a solution for the best and most economical approach.
Jim Nester, president: firstname.lastname@example.org
Rick Reimlinger, vice president: email@example.com
Rodney Pennington, vice president of special projects: firstname.lastname@example.org