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Exhaust Air Purification

The Regenerative Thermal Oxidation (RTO) Process

RTO from Eisenmann
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RTO from Eisenmann

RTO from Eisenmann

Eisenmann’s regenerative thermal oxidizers feature uncomplicated, robust technology with low operating costs. The space-saving single reactor system treats exhaust air flows from 10,000 to 120,000 Nm³/h, depending on size. For larger air quantities, multiple reactors are deployed in parallel.


Advantages of Eisenmann’s RTOs

  • Space-saving single reactor configuration
  • Continuous air distribution instead of diverter valves
  • No need for compressed air
  • Low operating and maintenance costs; low-wear and easy to maintain 
  • Can be used on exhaust air flows with a high or low concentration of pollutants
  • Burn out mode suitable for exhaust air flows that cause fouling

  

The RTO contains a heat exchanger mass consisting of a packing of ceramic honeycomb elements. This is divided into sections – each part alternately serves the cooling phase, while the other serves the heating phase. The exhaust air flows through the RTO’s heat exchanger mass from bottom to top, which heats it up to oxidation temperature – approximately 800 °C. The hot purified gases then flow downwards through the other part of the heat exchanger mass, giving it their heat.

  

Rotating Distributor Replaces Valves

Regenerative thermal oxidation (RTO)
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Regenerative thermal oxidation (RTO)

Regenerative thermal oxidation (RTO)

 Eisenmann’s patented air distribution system uses a rotating distributor to ensure a steady, alternating flow through the different sections of the heat exchanger in the regenerative thermal oxidizer (RTO). This eliminates the need for complicated valve or damper systems. The air flow remains constant, and there are no volume fluctuations caused by valve switching, as in the conventional three-tower RTO. 

The Thermal Oxidation process

Thermal oxidizers from Eisenmann
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Thermal oxidizers from Eisenmann

Thermal oxidizers from Eisenmann

 Eisenmann’s thermal oxidizers have proven to be robust, reliable and universal all-rounders. More than 1,200 pre-assembled and tested thermal oxidizers have been dispatched from our plant in Böblingen to satisfied customers around the world.

Thermal oxidation achieves gas purities well under the required 20 mg C/Nm³. Another advantage of this process is the low CO and NOx levels in the purified gas. 

How a Thermal Oxidizer Works

  

In a thermal oxidizer, the exhaust air needing treatment is first pre-heated in an integrated heat exchanger using exhaust air that has already been treated. Subsequently, the pollutants in the exhaust air are oxidized at a temperature of 750 °C in the thermal oxidizer’s combustion chamber. The quantity of additional fuel required depends on the amount of pollutants in the exhaust air and the temperatures achieved in the pre-heating stage.

Further heat recovery systems can be installed downstream. Effective arrangements include heating circulating air or fresh air, supplying hot or warm water, heating heat transfer oil and steam generation.

ECO-friendly and energy-efficient: thermal oxidation systems with downstream catalysts

Fitting a thermal oxidation system with a downstream oxidation catalyst cuts fuel consumption and lower carbon monoxide concentrations in the treated gas.

In practice, the oxidation combustionchamber often operates at temperatures that are far higher than those used by other manufacturing processes (such as drying systems). In other words the energy demand from the production is well below the possible energy recovery of the thermal oxidation system. To overcome this problem, the combustion chamber would need to operate on lower temperature. But this would lead to non-compliance with statutory emission thresholds as complete combustion of the volatile organic compounds (VOC) and other pollutants would not be achieved.

Thermal oxidation system with downstream catalysts
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Thermal oxidation system with downstream catalysts

A catalyst: lower temperature, better oxidation
Eisenmann addresses this dilemma by optionally installing an oxidation catalyst from Clariant. Positioned downstream from the combustion chamber, the oxidation catalyst reduces carbon monoxide concentrations in the treated gas to under 10 mg/Nm³. At the same time, the temperature in the combustion chamber can be lowered to 550 °C. This slashes the volume of admixed natural gas needed by up to 40 %.

Advantages at a glance

  • Lower combustion-chamber temperature allows waste heat to be utilized by other processes
  • Significantly lower carbon monoxide concentrations in treated gas (< 10 mg/Nm³)
  • Rapid return on investment through lower energy costs (payback in < 3 years)
  • EnviCat® VOC Catalysts reduce the energy consumption of thermal units as much as 40 %

The Adsorption Process ā€“ Cleans and Concentrates

ADW technology from Eisenmann
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ADW technology from Eisenmann

ADW technology from Eisenmann

In contrast to thermal oxidation processes, adsorption does not involve chemical transformation of pollutants or a significant increase in temperature. Adsorption makes use of the propensity of certain compounds (e.g. activated carbon or zeolite) to attract and adhere gas or vapor to their surface.

The adsorbed pollutants then need to be removed. To this end, adsorption is always followed by desorption. The resulting desorption flow is up to 20 times more concentrated and accordingly has a much smaller volume. This means it can be treated much more cost-effectively.

 

Large Quantities of Air, but Few Pollutants- ADW

Eisenmann adsorption wheel
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Eisenmann adsorption wheel

Eisenmann adsorption wheel

The Eisenmann adsorption wheel consists of chambers concentrically positioned around a shaft containing activated carbon or zeolite as adsorption material. The exhaust air is directed from above through the adsorption material. While doing so, the solvent molecules settle on the adsorption material. Desorption takes place in a separate section of the rotating wheel. Hot air is passed across the adsorption material in the opposite direction, and the settled pollutants are driven out. 

The desorption flow from the adsorption wheel can be fed to a regenerative or a thermal oxidizer. Here, the concentrated desorption flow is treated, with results well under limit values. If there is no surplus energy from production available to heat the desorption flow, recuperative thermal oxidation with a heat recovery system is an ideal option. 

Combustion Chamber Technology

Combustion chambers from Eisenmann
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Combustion chambers from Eisenmann

Combustion chambers from Eisenmann

Heavily polluted exhaust and halogen contamination can increase the risk of corrosion in exhaust air purification plants. In such cases, an Eisenmann combustion chamber is the perfect solution.

Eisenmann combustion chambers are also highly suitable for the safe treatment of explosive exhaust gases, especially from the chemical, pharmaceutical and petrochemical industries. Beside the safe compliance with Clean Air Standards, surplus energy can be recycled to the production process.

Combustion Chambers: Efficient Use of Waste Heat

Combustion chamber technology
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Combustion chamber technology

Combustion chamber technology

Waste heat from combustion chambers systems can be effectively used – depending on operating conditions - to heat thermal oil and/or hot water, to generate steam or provide energy for the combustion process.

A further advantage of combustion chambers is that they can be used on exhaust gases in areas at high risk of explosion (Ex zones 0, 1 and 2, under European legislation).

Dust caused by the combustion process is seperated by appropriate equipment downstream the combustion chamber (filters, scrubbers, ESP).

Additional treatment of exhaust gas, using washing columns or catalysts, is necessary where gaseous pollutants such as SO2, HCl or NOx are formed during the combustion. Please contact us for more information about our references or possible applications.

Contact

Contact person

Name

Aidin  Yousefnejad

Firm

Eisenmann Anlagenbau GmbH & Co. KG

Environmental Technology

Telephone

work T
+49 7031 78-3217
fax F
+49 7031 78-223217
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