Flox - Model DGV100 - Thermal Oxidizer for Landfill Gas
Methane concentrations in landfill gases typically de-cline significantly when suction of gas in landfills iscontinued in due form after closure of the landfill. Thedesired or undesired aerobisation of the landfill is thereason for this decline. In practical operation this of-ten leads to compromises in landfill gas management,as state of the art appliances (engines, flares) are lim-ited to relatively high minimum CH4 concentrations inthe landfill gas. This leads to an incomplete gas col-lection and undesired emissions from the landfillbody. This is no longer necessary with the e-flox DGVprocess. This process allows the save and completeextraction of landfill gases and the continuous trans-formation of the landfill to aerobic digestion until theend of the active landfill gas management.
Functional Description:
FLOX®-burners with ceramic recuperators for heat recovery are the core elements of the process, installed in a well insulated combustion chamber. After startup of the system a central start-up burner heats up the furnace to minimum 850°C, typically using LPG. Reaching this temperature threshold, the plant switches from flame to FLOX®-mode. With landfill gas concentrations above 6 Vol% no supplementary fuel is required, this mode is characterised as autothermal operation. A complete oxidation of the gas, unaffected by issues like flame stability etc. is a major benefit of the Flameless Oxidation (FLOX®') technology. Landfill gas and air a preheated by means of the hot flue gas leaving the combustion chamber, using ceramic recuperators integrated in the burners. This allows to maintain hight combustion temperatures despite of decreasing methane concentrations. Two limiting factors have to be taken into account for the layout of the plant: The maximum landfill gas flow is defined by the size and the number of the burners, the maximum thermal load is defined by the maximum amount of cooling air, which itself is subject to the plant layout. Thus, the major size definition is the flow of the landfill gas to be treated. The thermal load can be adapted to the specific needs of the project and has only a minor effect on investment costs. The plant can be operated in a wide range of operating conditions. The minimum load is defined by the minimum CHU-concentration in the landfill gas required to maintain the operating temperature of the furnace. This is the so called autothermal ChU concentration, which is typically at 6 Vol% CH4 in C02. This value decreases when the Nc-concentration in the landfill gas rises with progressing aerobisation of the landfill.
C150 FLOX^-burner with ceramic recuperator:
The recuperators are made of corrosion and thermo-shock resistant high performance ceramic material SiSiC. This material is good for combustion temperatures of up to 1250°C and corrosion resistant against H2S and halogens in the landfill gas. H2S concentration is supposed to decline when the landfill is converted to aerobic digestion. This will allow at some point to use metallic recuperators which convert the system to autothermal operating conditions of down to 2 % CH4.
Plant Control:
The plant is controlled with a modular PLC controller. The furnace controller ensures the optimum operating conditions, using the furnace temperature and the oxygen concentration in the flue gas as input values. Remote control of the plant from a supervising process control system is possible via digital input/output signals or the optional ProfiNet interface. A visualisa-
Principle
Fire without flame - efficient, clean and stable
FLOX® stands for » FLameless OXidation « und describes the combustion technology which was discovered by Dr.-Ing. Joachim A.Wünning in the early 90's. Since this time it was continuously improved and is today the basis of all our burners.
The following figure shows the temperature distribution in a furnace operated in FLOX® mode.
Fuel and combustion air react in a homogeneous reaction volume downstream of the burner nozzles, whereas in traditional flame combustion the reaction takes place in a highly intensive reaction zone attached to the burner nozzles. The ignition is induced by the recirculation of hot combustion gases.
This results in lowest NOx emissions, even when high air preheating is applied. Furthermore, it allows to burn low calorific value gases without any problems on flame stability. Due to this
homogeneous distributed reaction the temperature stress caused by peak temperatures is low and average temperatures can be increased significantly without changing the materials of the boiler.
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