DE102008055981A1 - Method for reducing pollutant emissions e.g. carbon-monoxide emissions, of surface burner in combustion system, involves arranging or folding burner surface such that fluid is partially or completely passed through porous surfaces - Google Patents

Abstract

The method involves arranging or folding a burner surface such that fluid e.g. air, fuel/air mixture, cold fire product and exhaust gas, is partially or completely passed through porous surfaces. The porous surfaces are provided in perforated plates, fleeces, knitted fabrics, meshworks, laminations, sintered metals, or foams. Flow-guided or surface-stabilized fuel grading and/or air grading takes place in an area of reaction- or equilibrium zone. Oxygen from the exhaust gas for oxidation of carbon-monoxide is supplied. An independent claim is also included for a device for reducing pollutant emissions of a surface burner.

Description

The object of the patent is the arrangement of surfaces of a surface burner, which can be operated with and without fuel or air staging and has the aim to reduce the carbon monoxide and nitrogen oxide emissions. The combustion system can be operated with both liquid and gaseous fuels. Especially with modulating burner systems, the conflict of objectives is to achieve low carbon monoxide and nitrogen oxide emissions. The concept of the arrangement, which exemplifies in 1 is shown, that an overflow of the combustion exhaust gases in or after the combustion zone (reaction zone) is achieved by folding the burner surface.

ever according to power and air ratio is located at a certain distance to the burner surface the Reaction zone, in which almost all the chemically bound energy of the fuel is converted into thermal energy (heat). This zone, depending on the surface structure forming several small conical flames or a flame carpet is connected with a visible flame lights and gives the thermal Energy primarily by heat radiation and convection to the burner surface and environment. Then follows the equilibrium zone, where there is no increase in temperature, but secondary reactions such as the oxidation of carbon monoxide take place to carbon dioxide. This process is in contrast for nitric oxide formation, which takes place directly in the flame front, relatively slow and can be several centimeters depending on the flow conditions be.

The general aim of combustion is to emit low pollutants. The challenge lies in high surface loads to achieve low nitrogen oxide emissions. By conduction and radiant heat transport, the porous surface is heated by the burning gas mixture and the flame is cooled. Due to the much higher emissivity of the solid surface to the exhaust gas can be given correspondingly more energy to the environment. For a further reduction of nitrogen oxide emissions, grading concepts such as fuel or air grading can be implemented. The basic idea is a partial conversion of the fuel in each individual stage, without reaching the adiabatic flame temperature, so that the complete fuel conversion is achieved at generally low flame temperatures and thus a locally more uniform heat release takes place. Due to the special arrangement of the burner surfaces optimum mixing in the individual stages can be achieved with favorable flow. The first partial conversion of the fuel / air mixture takes place directly on the burner surfaces, while the next stages flow-controlled ( 2 ) or surface stabilized who can. Alternatively, the mixture formation can be influenced so that both areas of the burner can be operated individually stepped.

at low area loads It is the task to maximize carbon monoxide emissions as much as possible reduce. The minimum of carbon monoxide formation is slightly above stoichiometric Area because enough Oxygen for oxidizing carbon monoxide from the intermediate reactions to disposal stands. In addition to the required oxygen is the temperature level in the post-reaction zone of crucial importance. Here may the Reactions will not be quenched. With ideal mixture of fuel and oxidizer, it will suggest an increase in carbon monoxide emissions stoichiometry because of the likelihood of oxidizing carbon monoxide through locally lacking oxygen is not given. In the "high" hyperstoichiometry become the "slow" reactions of oxidizing by the low combustion temperatures in the reaction zone inhibited and optionally quenched.

reason for the Increases in carbon monoxide at low power are both previously described effects. At low power, the mixture formation increasingly worse and the probability that locally sufficient Oxygen for oxidation exists, decreases. As a second effect are the higher ones to name specific losses, which are equivalent to the temperature effect with higher air numbers are because here also the temperatures in the post-reaction zone fall off sharply and prevent oxidation on. The design helps by its arrangement to diminish both effects, so that lower Carbon monoxide emissions are the result. By the overflow of the Burnt exhaust gases increase the likelihood that the available one Oxygen in the exhaust gas can be used for oxidizing and at the same time the specific losses are reduced by the type of flow guidance.

Claims (9)

A method for reducing the pollutant emissions of a surface burner, characterized in that the porous surfaces are completely or partially overflowed by the arrangement or folding of fluids. Method according to claim 1, characterized in that that the fluids are air, fuel / air mixtures, cold flame products, Exhaust gases or a mixture of the aforementioned fluids are. A method according to claim 1 and claim 2, characterized characterized in that the porous surface wholly or partly on perforated plates, nonwovens, crocheted, braided, Laminations, sintered metals or solid foams (pore burner) consists. A method according to claim 1 to claim 3, characterized characterized in that a flow-controlled or surface stabilized Fuel and / or air grading in the region of the reaction or equilibrium zone he follows. Device for reducing pollutant emissions a surface burner, characterized in that completely by the arrangement or folding or partially the porous one Surfaces through Fluids are overflowed. Device according to claim 5, characterized in that that the fluids are air, fuel / air mixtures, cold flame products, Exhaust gases or a mixture of the aforementioned fluids are. Apparatus according to claim 5 and claim 6, characterized characterized in that the porous surface wholly or partly on perforated plates, nonwovens, crocheted, braided, Laminations, sintered metals or solid foams (pore burner) consists. Apparatus according to claim 5 to claim 7, characterized characterized in that a flow-controlled or surface stabilized Fuel and / or air grading in the region of the reaction or equilibrium zone he follows. Apparatus according to claim 5 to claim 8, characterized in that the burner arrangement according to 1 or a combination of these arrangements.