Horst-Henning Grotheer

Jet-REMPI for process control in incineration

The mobile Jet-REMPI apparatus is an optimized variant of the conventional REMPI mass spectrometry which is known for its selectivity and on-line capability. By shifting the ionization volume from the molecular regime of the sample beam as in conventional arrangements, to the vicinity of the jet, a significant sensitivity improvement was achieved without loss in the other favorable features of this technique. The laboratory set-up was converted into a mobile unit so that the technique could be field-tested. The experimental test reactor KLEAA was developed in order to simulate grate incineration under well-defined conditions. To this end selected waste samples of up to 3 kg mass are taken as fuel and are connected to the bottom end of a pre- heated cylindrical combustion chamber which is equipped with heating elements to allow for a variable temperature profile. Measurable quantities include velocities of ignition and of combustion, mass loss rate of the sample, and pollutants along with permanent gases such as CO, CO2, O2 in the exhaust gas line. The coupling of these machines served two purposes: (a) to test Jet-REMPI under realistic conditions and to study its requirements with regard to sampling techniques, (b) to better characterize and understand the non-stationary behavior of the KLEAA reactor which is operated batch-wise. For these measurements wood diluted with suitable inert material was taken as a fuel, i.e., an essentially chlorine-free situation prevailed. Samples were drawn downstream of the filter. The Jet-REMPI measurements constitute the first field measurements carried out with this method. The monitored compounds include typical products of incomplete combustion such as phenol, benzene, naphthalene, fluorene and other compounds. As a drawback it turned out that particulates cannot be tolerated in the REMPI ion source because they lead to non-resonant contributions which are recorded as noise.

Measurements in the raw gas of a full scale municipal waste incinerator using a wavelength resolved REMPI mass spectrometer.

A resonance enhanced multiphoton ionization (REMPI) mass spectrometer consisting of a tunable laser unit (Nd:YAG pump laser and OPO) and a reflectron mass spectrometer have been upgraded to cope with the difficult conditions such as vibrations, temperature fluctuations and dust, prevailing in an incinerator. On-line measurements of the raw gas have been carried out at the municipal waste incinerator in Stuttgart. Although this test series could not be completed the results are encouraging. They show that wavelength resolution can provide valuable information beyond the one obtainable by fixed frequency REMPI. Examples discussed include separation of interferants to the aniline signal and identification of phenantrene.

Low-noise ion source for the implementation of Jet-REMPI: novel on-line monitor for process control

Modern techniques for on-line process control require versatile monitoring mthods which combine high sensitivity with high selectivity. In this paper a novel REMPI-mass spectrometer is presented. In comparison to standard instruments, sensitivity is increased by shifting the ionization regime to the vicinity of thecontinuum portion (jet) of the sample beam as opposed to the more conventional ionization under molcular beam conditions. A further gain in sensitivity is achieved by increasing the ionization volume. This was made possibl eby a complete redesign of the ion source. A very low base-line level is achieved by choosing a geometry preventing secondary ionization through thecollisions of ions/electrons with surfaces. These innovations have resulted in excellent performance from our apparatus as demonstrated by the dichorotoluene and naphtalene spectra obtained under various conditions. For naphtalene we have now a detection limit of 5 ppt (more fraction) for S/N equals 1 in 20 sec. Further developments of the technique and research needs ae discussed.

DLR‐Jet REMPI – Ultrasensitive Monitor for Process Control in Thermal Processes

Process control requires sensitive and selective on-line monitors for species concentrations. This applies in particular if feeds of varying compositions are involved. Current REMPI (= Resonance Enhanced Multiphoton Ionization) mass spectrometers would be suitable instruments in terms of selectivity and on-line capability, their sensitivities, however, are generally too low. By contrast, the DLR-Jet REMPI geometry provides a major sensitivity improvement. An extended test series shows that this is achieved without paying a price in terms of selectivity. The paper provides some of these results and lists up the development steps needed to make Jet REMPI an instrument suitable for industrial use.