Investigations on disposal of low-calorific landfill gases by a small scale fluidised bubbling bed combustion plant

Abstract

Poor landfill gases cannot be used to drive gas engines or be burnt in gas flares. This follows why the combustion flame front velocity for poor gases becomes very low. From this moment the non-flammable poor landfill gases are polluting the environment. An energetical utilisation of very poor landfill gases is of ecological interest and is also an important contribution for climate protection. A feasible solution must be found. In our University lab we are using a Fluidised Bubbling Bed Combustion (SFBC) plant with 200 kW completed by heat exchangers for pre-heating the combustion air as well the combustion gas. In the past this SFBC-principle had successfully been applied to a thermal utilization of very different wastes. Using this principle we are able to recover the energy content of very poor landfill gases down to a concentration below the lower explosion limit. The fluidised red hot inertia bed material at a temperature of 850°C is an excellent ignition source to run the process at constant parameters within legal limits. Therefore we have very low pollutant emission levels. Using a developed mathematical SFBC-model we theoretically investigated the lowest possibly methane concentration limits under given pre-conditions as well as fluidised bed temperature level, fluidisation air and fuel gas temperatures, necessary oxygen concentration level. Following to these model investigations we realized their experi-mental verification in our 200 kW lab SFBC testing plant in a wide-spread plant load range. These lab tests had very successful results. The possible SFBC operation conditions have been estimated. Based on these results we engineered by the help of industrial partners a real SFBC plant installed on a closed landfill in Mecklenburg – Western Pomerania, 65 km far from our University lab. Using these plant we dispose there real very poor landfill gas. The landfill gas is poor enough to avoid a further operation of a common gas flare. The automatically operated SFBC process is running at 850 °C without any technical interruptions since one year. At the moment the maintenance rate is 3 weeks. The plant is supervised by data remote control. The contribution will compare the lab test results with the results of the real existing plant. If the poor landfill gas flow is strong enough the SFBC produces enough energy e.g. to drive a steam cycle or a gas turbine externally fired by the SFBC that generates electrical power. In this case the necessary power equipment has to be added to the SFBC plant.