The data set encompasses the data generated through the 8 experimental runs on the 25 kWth calcium looping pilot plant at Cranfield University arranged into 8 functional Excel spreadsheets. The operational data are gathered by the acquisition with Labview software (the composition of the gas from the calciner and carbonator; temperatures of the electrical furnaces on the preheating lines and around the calciner; temperatures of the gas in the preheating lines and in the calciner) and Pico software (temperatures in the carbonator and lower loop seal and pressures in the calciner and in the carbonator). Moreover, the data from the experimental diary (inputs of gasses and solids into the rig) and the data from the post-processing of the extracted solids are included. All the data are combined into comprehensible charts that describe and explain the experimental runs together with the mass and energetic model of the system during steady state operations.