Management and Treatment of the Clean-up Water from the Scrubber of a Coal and Biomass Gasification Plant: an Industrial Case Study

Abstract

This work presents an industrial case-study on the possible application of an on-line treatment of the clean-up waters deriving from a wet scrubber used for the removal of pollutants from the syngas produced by a pilot plant used for test coal and biomass gasification. The wastewater is generated in a pilot-scale plant located in the south west of Sardinia and owned by ENEA and Sotacarbo. The plant platform includes a 5 MWth gasifier equipped with a wet scrubber for syngas clean up in co-current flow conditions and a flare. The plant is used for experimental campaigns with different feedstocks, mainly constituted by mixtures of coal and wood.
The wastewater contains suspended and dissolved solids, which must be removed for a possible reuse of the clean-up water in a closed loop with low make-up. Moreover, the high content of pollutants reduces the effectiveness of the cleaning process and may lead to fouling of surfaces and blocking of the recirculation pumps. Adsorption with carbon-based sorbents has been tested to remove dissolved solids from water.
Commercial activated carbon and different samples of coal were used to obtain sorption isotherms and breakthrough curves at lab scale. Based on the experimental results, a pilot-scale column has been designed and installed in a side stream of the clean-up system. The column was equipped with different carbon samples and tested during several gasification campaigns. The samples of coal do not show enough sorption capacity for a full-plant application, while good results were obtained when activated carbon was used as sorbent. Results show that the proposed approach can be used at full-scale, minimizing the use of external water sources for the gas cleaning system.