NESTEC’s Regenerative (RTO) and Catalytic (RCO) Oxidizers offer self-sustaining capabilities that afford minimal (pilot only) or zero auxiliary burner fuel consumption while processing Volatile Organic Compound (VOC) and Hazardous Air Pollutant (HAP) exhaust streams. The units use multiple sets of heat absorbing ceramic media beds that have proven performance of up to 96+% Thermal Energy Recovery (TER).
NESTEC RTO and RCO units are counterflow regenerators in which heat energy is accumulated for the length of the hot exhaust period (exhaust flow or energy recovery) and then released from the heat exchange media during the cold inlet counter flow period (inlet flow or preheat). Since the RTO/RCO is unable to accumulate mass flow, these periods are functionally the same interval in each direction of the flow. Therefore, the process air stream energy absorbed on the inlet flow (preheat) is equivalent to the energy released (recovered) from the air stream on the outlet flow.
NESTEC’s Thermal Energy Alignment System:
Unless the process solvent concentration (BTU Value) is high enough to self-sustain the oxidizer, or a Natural Gas Enhancement (NGE) system is included, the purification combustion chamber burner will have to provide additional energy (fuel) to maintain the desired purification temperature. Thus, additional mass (burner combustion products) must be added to the process air stream in the combustion chamber. This flow is included in the RTO/RCO exhaust, causing an unbalanced mass flow (more mass exists in the exhaust stream than in the inlet flow). This unbalanced mass flow in the heat exchange media will cause a decrease in TER and an increase in fuel consumption.
NESTEC, however, has developed a system to adjust interval times for counterflow regenerators that minimizes the effects of unbalanced mass flow and maximizes Thermal Energy Recovery.
A 95% RTO/RCO TER design is only achieved in a self-sustaining or balanced mass flow operation. See the ICAC site below for detailed calculations:
ICAC GUIDANCE METHOD FOR ESTIMATION OF GAS CONSUMPTION IN AN REGENERATIVE THERMAL OXIDIZER
Qi = Mi (hic-hi) preheat must equal o = Mo (hoc-ho) recovery
If (M0 ) does not equal (Mi ) then (hoc-ho) will change and the associated temperatures will also change causing a reduction in the TER efficiency and increase in fuel consumption.
- Qi ……. Heat energy released from the media on the RTO/RCO inlet flow
- Mi……. Mass flow on the RTO/RCO inlet
- hi………RTO/RCO inlet process enthalpy
- hic…….Combustion chamber inlet process enthalpy
- Qo ……. Heat energy absorbed from the media on the RTO/RCO outlet flow
- Mo ……Mass flow on the RTO/RCO outlet (process flow [Mi] + burner combustion products [MC])
- hoc ….Combustion chamber outlet flow enthalpy
- ho…… RTO/RCO Outlet flow enthalpy
Qc = Mc (hic- hcc) = energy required over the RTO/RCO design TER efficiency to self-sustain at the purification temperature.
Typical mass balanced operating conditions:
- Self-sustaining = VOC auto-ignition energy released is sufficient to maintain the desired purification temperature, no burner mass input, or fuel consumption.
- NGE (Natural Gas Enhancement), through mixing of NG addition in the process inlet flow sufficient to increase the VOC BTU level to maintain the purification temperature.
- Either and/or a combination of VOCs and NG enhancement sufficient to maintain the purification temperature.
Other factors, such as radiation losses, uniform air flow through the heat recovery media, cycle time, and Thermal Energy Alignment will affect the overall fuel consumption of the RTO/RCO.
Points to Remember
- Optimized thermal energy recovery (TER) and maximum efficiency can only be achieved in applications that are self-sustaining and have a mass balanced flow
- Radiation loss is an energy requirement in addition to energy required for the process air temperature rise across the RTO
- VOC energy contributions due to oxidation will have an approximate 10% loss due to latent heat loss in combustion process
- Non-uniform air flow distribution through the media can also result in significantly increased fuel consumption
NESTEC offers several energy saving features to provide reduction in operating costs, many of which can be applied to existing RTO systems.
If you want to maximize your RTO/RCO energy conservation and reduce your energy bill, contact NESTEC for a free process analysis.
Jim Nester, CEO: firstname.lastname@example.org
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