Plasma Scrubber

Green house effect and global warming are the critical issues in this new aera. These issues have some influence not only on the environment, but also on the economy and on the national safety. The main part of relevant gases, PFCs and SF6, the GHGs (Green House Gases) defined in the Kyoto Protocol are generated from the semiconductor and optical electronics industries. In dry etching procedures these gases are accumulated and mixed with CVD gas for chamber cleaning processes. The special PFCs gases from these tools such as SF6, CF4, C2F6, C3F8, CHF3 and NF3 have to be treated before emission.

A plasma scrubber system was developed and tested as a point of use abatement system for the treatment of PFC loaded gases coming from a production line in the semiconductor industry. The system consists of an arc heated water steam plasma unit followed by a combustion chamber and a quench-scrubber-system.

For chemical destrucion of PFC material, a water plasma is favourable because both, the oxygen and the hydrogen (which are necessary to produce the desired products after the high temperature zone: CO, CO2, HF and HCl) are supplied by the heat carrier itself.  Therefore a new plasma torch system using water as plasma gas was developed and tested under the specification to achieve a long lifetime of the electrodes.

The system was developed and tested under industrial conditions at a process line in semiconductor industry factories. It was demonstrated that with this process a reduction of PFC in the exhaust gas of > 99.9% can be achieved.

The Plasma Scrubber System

Plasma cracking is a non-incineration thermal process using temperatures above 2000°C by cracking highly stable materials like fluorinated compounds into smaller molecules.

The process gas is mixed into a steam plasma jet. Through the high temperatures and the available radical the PFC is cracked and reacts with the oxygen and the hydrogen coming from the water plasma to CO2 and HF. The exhaust gases from the high temperature reactors are cooled and cleaned in a specially developed quench and water scrubber stage.

In the first stage, the gas stream is quenched down by a injected water stream. In parallel to the quench effect one gets a first cleaning of the gas stream from the acid components. Temperature of the stream can be cooled to 40°C after quenching.

After the first stage, additional cleaning stages are followed by using recycling water for gases scrubbering. For achieving the required clean gas concentration, the last fine cleaning stage is done with clean city water.


Schematic of the POU process


CFC Decomposition

Plasma cracking using the PlasmaAir water steam generator:

The steam plasma torch was developed as heat and radical source for a process of CFC decomposition. The process will be described in details.

The process gas is mixed into a steam plasma jet. Through the high temperatures and the available radical the CFC will be cracked and react with the oxygen and the hydrogen coming from the water plasma to CO2, HCl and HF. The reaction takes place in a high temperature reactor. The hydrofluoric acid can either be neutralized or recovered.

The exhaust gases from the high temperature reactors could be fed to an exhaust gas scrubber.

Applications for plasma cracking

  • Plasma cracking is favored used to dispose of small amounts of off-gases from manufacturing processes where flammable gases are not allowed for safety reasons.
  • Destruction of CFC/HCFC/HFC from fridges, foams and spent solvents.
  • Destruction of hazardous off-gases exiting manufacturing processes
  • Disposal of HFC R 23 waste gas coming from R 22 production plant.
  • Disposal of SF6, CF4 etc waste gas coming from production plant.
  • Disposal of CF4 NF3 etc Nitrogen gas coming from semiconductor industry

Plasma cracking technology benefits

  • Proven better 99,99 % DRE
  • Classed as non-incineration
  • Non-Catalytic
  • Non flammable heating gases
  • CO and dioxin emissions well below current standards

Steam Plasma Torch

PlasmaAir AG has a long expertise in developing plasma systems for different application.

The main product is a water steam plasma torch with focus on a long lifetime of the eletrodes

The Plasma Torch

Conventionaly used arc heated plasma torches work with argon as a plasma gas. For some applications Nitrogen is used. For the here described PFC reduction process an oyidiziend plasma gas is required to assure the chemical reaction process. The main problem using oxidizing gases is the short life time of the electrodes. This limts the operation time of the system. Building a exhaust gas cleaning system, a continous operating system that operates several 100 hours is required. Therefore, a new plasma torch was developed. The focus on the development was to achieve a lifetime of min. 800 hours using water steam as plasma gas.

The power level for the application was fixed between 5 and 20 kW. This is the level that is required to treat typical exhaust gas streams containing PFC coming from production processes or from processes in semiconductor industry.

Parallel to the torch the complete equipment necessary to operate the torch was developed. A special evaporator, cooling cycle and the power supply were developed and optimized for long continuous operation.

The same torch can be operated without changes with several other plasma gases. It was continously tested with water steam, air, pure oxygen and nitrogen. Instead of the Argon, hydrogen can be used to protect the cathode from erosion.

The system can be scaled up and down in power range.

Beside the application for CFC decomposition at high temperature the torch system can be used for:

  • Plasma spraying
  • Plasma pyrolysis
  • Surface treatment
  • Plasm cutting

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Steam Plasma torch in Operation

 

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Plasmaspraying using the steam plamsma torch