Basic design criteria and corresponding results performance of a pilot-scale fluidized superheated atmospheric condition steam dryer

Abstract

The interest in compressed biofuels such as pellets and briquettes has increased in Sweden. In order to be compressed, the biomass must have a suitable moisture level, i.e. it has to be dried. In recent years, this has led to a considerable amount of research and development of different kinds of drying methods. Predominantly, such efforts have been made on a laboratory scale. However, when a drying method is developed on a laboratory scale, the up-scaling is problematic. This paper reports on the development and building of an pilot-scale test and demonstration plant. The requirements of the industrial partners in combination with a survey of available drying techniques led to the choice of a drying method that uses atmospheric condition superheated steam, a method in which the drying can take place either in a fluidized or in a fixed bed. Sawdust and willow wood chips were used as testing materials. A typical flow of steam in the experiments was 0.46 kg/ s with an input of wet material in the range of 150– 240 kg/ h . When sawdust was dried in a fluidized bed and the temperature after the superheater was 201°C, the moisture content was reduced from 51.9% to 19.4%. The dry material flow was 115 kg/ h , the energy efficiency 83.3% and the specific power consumption was 75 kJ/ kg . When willow wood chips were dried in a fixed bed and the temperature after the superheater was 207°C, the moisture content was reduced from 58.3% to 17.1%. The dry material flow was 66 kg/ h , the energy efficiency 76.4% and the specific power consumption was 208 kJ/ kg .