Measuring process exhaust air, supply air and burner gas at thermal post-combustion installations for waste air purification

Thermal post-combustion after chemical installations

Process data

Measuring task:
Measuring flow rate of inflowing, solvent-containing exhaust air to manage combustion processes in a combustion plant

Measuring points:
Supply point of exhaust air, Supply point of natural gas, Supply of air in TNV (RTO), exhaust air after the TNV

Measuring range:
Typically 5 … 15 m/s

process pressure:
Slight underpressure, overpressure

process environment:
Typically ATEX zone 2
Sometimes SIL 2 required


Thermal post-combustion is an exhaust air and exhaust gas cleaning process. Air hygienically it’s an optimal process because exhaust air/exhaust gases except for sulfur, halogen or other thermally non-decomposable foreign substances are turned into the non-hazardous substances water (H2O) or carbon dioxide (CO2). The process is perfectly suited for VOC laden gases starting at 1g/Nm³ at a VOC precipitator efficiency over 99.8 %. That way required limit values can be adhered to.

Fast start and stop allow the use under highly fluctuating process conditions.
Special flow sensors can measure inflow of exhaus gases to the post-combustion plant and therefore regulate the process, guaranteeing optimal combustion.

Your advantage

Our vortex sensor has no moving parts. It is available in stainless steel, titanium or Hastelloy. Optimal use for solvent-containing exhaust air (VOC) in the RTO process.

Longevity and minimal maintenance effort result in low operating expences in the combustion plant. 

Tried and tested
Höntzsch vortex sensors are used in many, partly quite challenging applications and deliver reliable measuring results.

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Thermal post-combustion – managed process for exhaust air purification

Process exhaust gases have tob e cleaned wherever they can cause damage for humans and the environment. Especially volatile organic compounds (VOC) have to be transformed. Natural VOCs occur during natural putrefaction and degradation processes.

VOCs arise in incomplete combustions (from traffic) or industrial processes. They’re used for exhaust air purification escpecially in surface technology, paint and glue production, print, textile and furniture industry as well as in the pharmaceutical, chemical and ceramic industry.

Energy saving in regenerative post-combustion (RNV/RTO)

Thermal or thermal regenerative post-combustion is the process of cleaning industrial exhaust gases. Contaminated air is lead to a combustion chamber and burned in temperatures between 700 °C and 1,200 °C.

It requires a lot of energy to heat the combustion chamber to the required temperatures. To reuse the energy, the cleaned hot exhaust air is released through a recuperator. There it releases part of its energy to the inflowing exhaust gas which therefore enters the combustion chamber already preheated.

Operating the combustion chamber requires fuel, usually natural gas and oxygen. Oxygen is added through ambient air.

The use of primary energy in the oxidation process depends strongly on the amount and the heating value of the substance. The combustion process has to be regulated in relation to the amount of exhaust air. Inflow of exhaust gas has to be measured first, then natural gas and supply air.  Those are the most important values for managing the entire process.

Measuring points of solvent-containing exhaust gases (VOC)

Different measuring points require diefferent measuring techniques. The most challenging is the exhaust gas supply. The measured gas here can be highly VOC contaminated and therefore very aggressive towards the sensor material. In some parts it’s purposely enhanced with VOCs so it can be used more efficiently in the post-combustion plant. It can also contain particles that stick to the sensor and therefore influence the measuring results. Our Höntzsch vortex sensor is the preferred measuring instrument since it delivers reliable measuring results even in particle-laden VOC gases.

Fuel gas, usually natural gas however can be measured with our thermal flow sensor. The sensor directly delivers standard flow rate and mass flow rate. Optionally, measuring values can be transferred via M-Bus or Wifi.

The third common measuring point within the thermal post-compustion plant is the supply for the combustion process. Many operators demand SIL 2 certified sensors. 

Höntzsch vortex sensors are available SIL 2 certified.