Advanced Vortex Combustion - AVC

 Conventional Combustion Approaches
 Ramgen's AVC
 AVC test results

Conventional Combustion Approaches

Since the mid 1970’s the emissions control from combustion processes has been a area of great public concern due to its impact on health and the environment. As a result the combustion industry has experienced rapid changes in both the regulations for controlling emissions and in the technologies used to meet them. The emissions of principal concern include carbon monoxide “CO”, unburned hydrocarbons, particulate matter, oxides of sulfur, and nitrogen monoxide and nitrogen dioxide NOx. Carbon dioxide and water vapor are not yet regarded as pollutants; however, they both contribute to global warming which is now receiving tremendous international attention.

The reduction of NOx emissions has received particular attention due to its toxicity, itself a precursor to chemical smog and acid rain, and its direct impact on the depletion of ozone in the stratosphere. Many scientists and consultants believe that NOx emissions pose more a threat to public health and the environment than the other combustion emissions, although actual consequences to be more indirect and long-term.

Since the mid 1970’s, NOx emissions from conventional combustion systems have been decreasing from levels between 90 to 250 ppmv, parts per million by dry volume at 15 % oxygen, to less than 50 ppmv, using various water and steam injection techniques.

The dry low emissions approach to control NOx emissions was introduced in the late 1980’s, in an attempt to eliminate the costly onsite requirement for water or steam injection. This introduction and its continued development has resulted in further reductions of industrial gas turbine NOx emissions to levels between 10 and 25 ppmv.

The majority of industrial gas turbines are unable to achieve NOx emissions below 10 ppmv and require the addition of expensive exhaust gas after-treatment, such as selective catalytic reduction “SCR”. The SCR technique requires the injection of highly toxic ammonia into the exhaust stream to neutralize those remaining emissions. At a minimum, this is a very costly, but it can also create environmental hazards that must also be managed, and does require the storage and handling of ammonia in densely populated regions.

NOx emissions form in the primary zone of the combustion chamber. The highest gas temperature and subsequent NOx emissions occur at the stoichiometric condition, which is the single point between too much fuel, or rich conditions, and not enough fuel, or lean conditions. A decrease in temperature reduces the NOx emissions, but increases the CO emission as the combustor approaches lean extinction.

In order to meet <10 ppmv ultra low NOx emissions requirements without a SCR, the combustor must be operated near the lean extinction limit. The lean extinction limit is that area where the combustor temperature is low and the flame is extremely weak, which then becomes very susceptible to sudden flameouts. These instabilities occur when fluctuations in the heat release rate couple with the acoustics of the combustion system to produce pressure oscillations.

Industry Norm Swirl Stabilized Combustion

The industrial gas turbine community has battled with balancing extremely low emissions, with engine flameouts and the unstable pressure fluctuations that can cause great damage to the engine since the early 1990’s.