regenerative thermal oxidizers

DEC IMPIANTI S.p.A. is a private corporation, focused on engineering and supply of turn key sustainable industrial VOC and HAP emission control systems for the flexible packaging, chemical, petrochemical and pharmaceutical industries. Backed with 75+ years of global experience, thanks to products of the highest quality, patented and/or innovative processes, with thousands of systems in operation, we are facing the global challenges, focusing on innovative sustainable technologies and research.

Whenever you have to face a non-recoverable stream of VOCs, a XTO™ • thermal oxidizer could be the solution. Sometimes the VOC stream composition may result too complex to be recovered or the quantity of solvents is not interesting to go for a SRU™ • solvent recovery units.

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DEC.RTO™ • regenerative thermal oxidizers

DEC.RTO™ refers to a specific configuration of a thermal oxidizer system (XTO™): in an RTO, multiple towers or chambers are used to achieve efficient and effective air pollution control.

Typically two or more towers are utilized in parallel: the exhaust gas flow is alternated between these towers, allowing for continuous operation. While one tower is used for the oxidation and removal of pollutants, the other tower(s) are undergoing a regeneration cycle to prepare for the next exhaust gas flow.

  • Inlet Phase: The contaminated air stream enters the RTO through an inlet duct, and a damper directs the flow into one of the ceramic honeycomb beds.
  • Preheating Phase: The incoming air passes through the heated ceramic channels (honeycomb), where the thermal energy from the hot exhaust gases is transferred to the incoming air stream. This preheating step helps in reducing the energy consumption of the system.
  • Combustion Phase: The preheated air stream enters the combustion chamber, where it is further heated to the required temperature (typically between 815°C and 980°C). In the presence of oxygen, the VOCs and other pollutants in the air stream undergo combustion, converting them into carbon dioxide (CO2) and water vapor (H2O).
  • Exhaust Phase: The hot, purified air stream exits the combustion chamber and passes through the outlet duct. At the same time, a damper directs the flow into another ceramic honeycomb bed.
  • Thermal Energy Recovery: The incoming air stream absorbs the thermal energy stored in the ceramic honeycomb bed, which helps in preheating the next batch of contaminated air. This heat exchange process is crucial for the high energy efficiency of RTOs.
  • This alternating process allows for energy recovery within the system. The hot exhaust gases leaving the combustion chamber are passed through a ceramic heat exchanger, known as the regenerator, in the tower undergoing the regeneration cycle. The regenerator absorbs the heat from the exhaust gases and stores it. During the next cycle, the stored heat is transferred to the incoming cold exhaust gases, reducing the energy consumption of the system.

    The use of multiple towers in an RTO system provides several advantages, including improved operational efficiency, reduced energy consumption, and continuous operation. It allows for a consistent and reliable treatment of industrial exhaust gases while optimizing the use of energy resources.

    DEC.RTO™ • oxidation reaction

    The oxidation reaction is:

    VOCs (CxHyOz) + O2 + thermal energy = CO2 + H2O + (HEAT)

    The heat is usually recovered to pre-heat the SLA stream, in order to save on "thermal energy" (provided through gas CH4 - methane); if producing extra heat through oxidation of solvents, an energy recovery system shall be foreseen (typical applications are ranging from heating up air for dryers, steam production, heat tranfer fluid heating, water heating - industrial or sanitary, etc.).

    DEC.RTO™ • advantages

    In a regenerative thermal oxidizer (RTO) with multiple towers, the VOCs are oxidized in the combustion chamber. The hot gas released from the combustion chamber contains thermal energy. This thermal energy is accumulated through the ceramic media bed in one tower. The hot gas then cools down as it exchanges thermal energy with the ceramic media. The cooled gas is then discharged through the stack.

    The process of accumulating and exchanging thermal energy in the ceramic media bed is called regenerative: this process allows the RTO to operate at a high efficiency, while also reducing the amount of energy required to heat the incoming gas.

    Thanks to the specifically designed switching valves, the flow is alternatively reversed: thermal energy is recovered and the flow, in the following cycle, is pre-heated; this cycle is efficiently reducing the auxiliary fuel requirement, with self-sustaining operation (with no auxiliary fuel usage) even at low concentrations, thus representing an operational cost reduction.

    RTOs with multiple towers can operate at a higher efficiency than direct thermal oxidizers (DTO™): the regenerative process allows the RTO to recover heat from the outgoing gas, which can then be used to heat the incoming gas.

    thermal oxidation | incinerators • GHG and by-products

    An oxidizer is handling the transformation of the pollutant(s) into different products, with a reduced environmental impact. However, it is important to consider the resulting GHG emissions, when selecting a VOC oxidizer; the amount of GHGs generated by a thermal oxidizer depends on the type of VOCs being treated, its quantity, the needed quantity of fuel to be added for sustianing the oxidation reaction and the selected oxidizer process configuration.

    VOCs (CxHyOz) + O2 + thermal energy = CO2 + H2O + (HEAT)

    Any oxidizer will have to deal with all or most of the following issues:

  • VOCs emission (= non complete oxidation);
  • CO2 emission (= GHG, possible taxation);
  • CO emission (= GHG, non complete oxidation);
  • NOx emission (= nitrogen oxides, as a result of N2 presence);
  • N2O emission (= nitrous oxide);
  • Dioxin emission (as a result of possible chlorinated compounds );
  • High temperature emission (as a result of non complete thermal energy recovery).
  • These emissions contribute to climate change and should be taken into account when assessing the overall environmental impact of the system.

    As mentioned earlier, oxidizers typically require a significant amount of energy to operate: if this energy comes from non-renewable or carbon-intensive sources, it will dramatically contribute to environmental degradation and offset any of the potential benefits of VOC emission reduction.

    thermal oxidation | incinerators • greenwashing

    Greenwashing will occur when a company promotes an oxidizer as an environmentally friendly or sustainable technology for VOC emissions control, while neglecting to address other significant negative aspects of its environmental impact, such as greenhouse gas (GHG) emissions and harmful by-products.

    Greenwashing can happen when a company portrays an oxidizer as a comprehensive and eco-friendly solution to VOC emissions, creating the perception that it is a sustainable option without considering the complete environmental picture. While oxidizers can help reduce VOC emissions, they can have negative consequences that should not be overlooked.

    To avoid greenwashing, companies shall provide transparent and comprehensive information about the environmental impact of their VOC emission control systems: this includes addressing greenhouse gas (GHG) emissions, harmful by-products, and the energy efficiency of the system. By doing so, companies can ensure that consumers have an accurate understanding of the technology's environmental implications and make informed decisions.

    the concept of greenwashing comes into play when a company portrays an oxidizer as environmentally friendly or sustainable technology, even though it is not green and environmentally friendly as claimed: in the context of oxidizing VOCs, greenwashing can occur when the use of an oxidizer is advertised as a comprehensive and eco-friendly solution to VOC emissions, while ignoring other significant negative aspects of environmental impact, such as GHG and by-products.

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