Steam gasification of coal at low-medium (600-800 °C) temperature with simultaneous CO2 capture in a bubbling fluidized bed at atmospheric pressure.: 2. Results and recommendations for scaling up

A gasification gas with an H-2 content as high as 80 vol %, dry basis has been obtained by gasification of coal with pure steam at 600-800 degrees C. The gasifier used was an atmospheric and bubbling fluidized bed operating with CaO in the bed as the CO2 sorbent. The research was carried out at a small pilot plant scale with continuous feeding of coal and batch mode introduction of the CaO. The gas composition and gas quality (tar content) is given for the following variables of operation: (a) type of in-bed sorbent used, (b) the amount of CaO in the bed related to the amount of coal fed, (c) temperature in the gasifier bed, (d) weight hourly space velocity (h(-1)) of the coal in the gasifier, and (e) time(-on-stream). To capture CaO at atmospheric pressure, the gasification with in-bed CaO had to be carried out at low-medium (600-800 degrees C) gasification temperatures. For this reason, the tar content in the gasification gas was high (up to 52 g/Nm(3)), which lowered the value of the H-2-rich gasification raw gas. It is demonstrated that a gas rich in H-2 (80 Vol % H2, dry basis), and with very low CO2 and tar contents, can be obtained only if the coal gasification, at atmospheric pressure and with pure steam, is carried out at [CaO/coal] ratios above 10-15.