FLOX‑2®: Mul­ti-stage fla­me­l­ess oxi­da­ti­on as a con­tri­bu­ti­on to the gene­ra­ti­on of CO2-neu­tral pro­cess heat

7th Ener­gy Rese­arch Pro­gram­me, BMWK, 1 May 2020 to 31 Decem­ber 2023

Project description

The pro­cess of fla­me­l­ess oxi­da­ti­on can be descri­bed by an idea­li­sed repre­sen­ta­ti­on, as shown in Figu­re 1. In step I, the com­bus­ti­on air mixes with the recir­cu­la­ted exhaust gas. The exhaust gas tem­pe­ra­tu­re is abo­ve the auto-igni­ti­on tem­pe­ra­tu­re of the air/fuel mix­tu­re, 850 °C is com­mon in tech­ni­cal appli­ca­ti­ons. In step II, the fuel is injec­ted. Due to the high exhaust gas tem­pe­ra­tu­re, the mix­tu­re is igni­ted and heat is released by the com­bus­ti­on reac­tion. This heat is made available to the pro­cess in step III.

Figu­re 1: Idea­li­sed pro­cess of fla­me­l­ess oxi­da­ti­on [from „ Hand­book of Bur­ner Tech­no­lo­gy for Indus­tri­al Fur­naces“ by J. G. Wün­ning, 2015]

Mul­ti-stage fla­me­l­ess oxi­da­ti­on is con­side­red an exten­si­on of fla­me­l­ess oxi­da­ti­on. Fur­ther­mo­re, this type of com­bus­ti­on is also available in pro­ces­ses with com­bus­ti­on cham­ber tem­pe­ra­tures below the auto-igni­ti­on tem­pe­ra­tu­re. Thus, hea­ting up in fla­me mode is no lon­ger requi­red and com­bus­ti­on can take place fla­me­l­ess even at low pro­cess tem­pe­ra­tures.
Fuel fle­xi­bi­li­ty (no fla­me sta­bi­li­sa­ti­on) and extre­me­ly low pol­lutant emis­si­ons (reduc­tion of ther­mal and fuel NO) are achie­ved with the new com­bus­ti­on pro­cess almost inde­pendent­ly of the pro­cess tem­pe­ra­tu­re.
Figu­re 2 shows an idea­li­sed repre­sen­ta­ti­on of mul­ti-stage fla­me­l­ess oxi­da­ti­on for the case of fuel-rich pri­ma­ry com­bus­ti­on. The pri­ma­ry com­bus­ti­on cham­ber is adia­ba­tic and stages I and II of the fla­me­l­ess oxi­da­ti­on take place in a fuel-rich regime. The resul­ting exhaust gas con­ta­ins the com­ple­te enthal­py of the reac­tion of the pri­ma­ry com­bus­ti­on and has a tem­pe­ra­tu­re abo­ve 850 °C. The down­stream hea­ting cham­ber is used to heat the exhaust gas. The secon­da­ry air (step III) and the hot com­bus­ti­on gases from the com­bus­ti­on cham­ber (step IV) are fed to the down­stream hea­ting cham­ber in such a way that fla­me­l­ess com­bus­ti­on also takes place the­re with the neces­sa­ry recir­cu­la­ti­on of the com­bus­ti­on gases. Heat is released in the hea­ting cham­ber (step V) after steps III and IV once com­ple­te com­bus­ti­on has been achieved.

Figu­re 2: Idea­li­sed pro­cess of mul­ti-stage fla­me­l­ess oxi­da­ti­on with fuel-rich com­bus­ti­on in stage 1

An alter­na­ti­ve is high­ly fuel-lean com­bus­ti­on in the 1st stage and a sup­p­ly of fuel in the 2nd stage.

Project goals

  • Deve­lo­p­ment of a novel com­bus­ti­on pro­cess for various pro­cess gases, inclu­ding N‑based gases, who­se com­po­si­ti­on is not per­ma­nent­ly constant.
  • low-pol­lu­ti­on com­bus­ti­on of any fuel mix­tures for the gene­ra­ti­on of high-qua­li­ty pro­cess heat
  • almost com­ple­te sup­pres­si­on of ther­mal and fuel NO for­ma­ti­on, so that the use of N‑based fuels is also pos­si­ble wit­hout cos­t­ly secon­da­ry mea­su­res for deni­tri­fi­ca­ti­on of the exhaust gases (DeNOx)
  • The appli­ca­bi­li­ty of FLOX® tech­no­lo­gy is exten­ded to pro­ces­ses with tem­pe­ra­tures below the auto-igni­ti­on tem­pe­ra­tu­re of the respec­ti­ve fuels

Project participants


Lin­da Gies­ler, M.Sc.

+49 241 80–26060


Dr.-Ing. Nico Schmitz

+49 241 80–26064



The pro­ject with the fun­ding code 03EN2044 is part of the 7th Ener­gy Rese­arch Pro­gram­me and is fun­ded by the Fede­ral Minis­try for Eco­no­mic Affairs and Cli­ma­te Action based on a reso­lu­ti­on of the Ger­man Bundestag.