In June, the 150 kWth CLC (Chemical Looping Combustion) pilot plant at SINTEF in Trondheim achieved its first successful operation in full CLC mode, with very good results. Methane was used as fuel and copper oxide based particles were used as oxygen carrier. At a fuel power of 100 kW, methane conversion of up to 98% was obtained. This was achieved at a rather low specific fuel reactor oxygen carrier inventory of 100 – 120 kg/MW.
The pilot plant has been built and tested through the Centre for Environment-Friendly Energy Research «BIGCCS» while the oxygen carriers have been provided through the EU FP7 project «SUCCESS». When the tests agreed in these projects are finalised this autumn the pilot plant will be supplemented with a biomass fuel feeding system and made ready for tests within the Nordic Energy Research funded project «Negative CO2«. In addition, new projects and partners will be sought for further CLC development, using both the pilot plant and the oxygen carrier know-how developed within SINTEF during the last years.
The CLC pilot plant consists of two interconnected circulating fluidized bed reactors (Figure 1) interconnected through two particle loop seals that works as gas locks to ensure that only the particles get transferred between the reactors. In addition, particles are also transferred from the fuel reactor to the air reactor through the lifter, which is fed from the bottom of the fuel reactor. The air and fuel reactors are 6 m high of which the first 1 m is a conical bottom section. Reactor internal diameters are 230 mm and 154 mm, respectively. The system has feeding and extraction screws, which makes it possible to refill and extract oxygen carrier particles during operation. Heat-up to CLC operating temperatures (850 – 950°C) is done with pre-heated air plus fuel that are introduced into the particle beds in both reactors. During CLC operation, fuel is introduced to the fuel reactor and air to the air reactor in amounts so that the overall excess air is about 20%. The oxygen carriers are sequentially oxidized in the air reactor and reduced in the fuel reactor, thereby providing the oxygen needed in the fuel reactor. The system is originally designed for operation on methane as fuel gas at a maximum fuel power of 150 kW and with steam as fluidisation gas. However, at the test site (which is provisional) there is no steam boiler installed so CO2 or N2 are used as fluidisation gas. The system has two gas analysers measuring the CO, CO2, CH4 and O2 concentration in the exhaust from each of the two reactors.
The test was performed in a one day experiment comprising heat-up sequence, operation in CLC mode and shut-down sequence. The oxygen carrier material was a copper oxide based material impregnated on a γ-alumina support. Particle density was low compared to the reactor design value causing a limitation on the maximum fuel power. At about 100 kW, the performance was very good, especially during the last hour were constant operating conditions were maintained for which the system showed stable performance with high degree of methane conversion, up to about 98% in this period. Exhaust CH4 concentration was below 1 vol-% and the CO concentration was close to zero. Figure 2 shows reactor temperatures, fuel feed and air pre-heat temperature for the period with full CLC mode. At 16:20 the fluidisation gas was shifted from CO2 to N2. The air pre-heat is the only additional heating of the system so the reactor system was in close to auto-thermal operation.