Combined hydrothermal carbonization and gasification of biomass with carbon capture B. Erlach * , B. Harder, G. Tsatsaronis Technische Universität Berlin, Institute for Energy Engineering, Marchstr 18, 10587 Berlin, Germany article info Article history: Received 31 August 2011 Received in revised form 20 January 2012 Accepted 22 January 2012 Available online 20 February 2012 Keywords: Hydrothermal carbonization Biocoal Biomass upgrading Gasification BECCS Exergy analysis abstract Bio-energy with carbon capture and storage (BECCS) can result in negative net carbon emissions and may therefore provide an important technology option for meeting current greenhouse gas stabilization targets. To this end, syngas from biomass gasification combined with pre-combustion carbon capture can be used to produce either biofuels or electricity. Pre-treating the biomass with hydrothermal carbon- ization (HTC) produces a coal-like substance, biocoal, which is potentially better suited for entrained flow gasification than raw biomass. This paper compares HTC followed by entrained flow gasification of the biocoal with fluidized bed gasification of raw wood, both with carbon capture and storage (CCS). Simulation studies undertaken with Aspen Plus are interpreted using exergy analysis. Syngas production is more efficient from biocoal than from raw wood but the conversion losses in the HTC process outweigh the efficiency gains in the gasification. Carbon losses through gaseous and dissolved byproducts in the HTC also limit the capture rate. A CCS-IGCC with fluidized bed gasification using raw wood results in an electrical efficiency of 28.6% (HHV) and a carbon capture rate of 84.5%, while the conversion chain of HTC and a CCS-IGCC with entrained flow gasification yields an electrical efficiency of 27.7% and a capture rate of 72.7%. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Syngas from biomass gasification is widely discussed as an intermediate feedstock for the production of electricity and second- generation biofuels e and increasingly now for bio-energy with carbon capture and storage (BECCS) [1,2]. BECCS may lead to negative carbon emissions if the biomass is grown sustainably. Several studies have found that such negative emissions technol- ogies might be essential for achieving stabilization targets of below 450 ppm CO 2 [3,4]. For coal gasification, with and without CCS, the preferred technology is pressurized oxygen-blown entrained flow gasifica- tion. The advantages of entrained flow gasification are a high syngas quality with high H 2 and CO concentrations and low tar and hydrocarbon content, as well as a short residence time resulting in compact gasifier equipment. Several large-scale coal-fed entrained flow gasifiers with a capacity of several hundred MW th are in operation, but none with carbon capture. For biomass, however, pressurized entrained flow gasification is infeasible because of problems related to the feeding system. The gasifier requires feedstock at small particle size (0.1 mm for coal). Laboratory-scale tests with pulverized wood indicated that a pneumatic feeding system is not suitable for wood powder, due to the high cohesion between the fibrous particles [5]. Fluidized bed gasifiers accept a particle size of up to 70 mm [6] and are therefore better suited for biomass. Typical plant input capacities range up to 50 MW th [6]. However, the syngas contains tar and CH 4 and is therefore less suited for carbon capture. The foregoing observations indicate three options for biomass gasification with CCS: 1. adopt fluidized bed gasification and condition the syngas so that is meets the requirements of the shift reactor and CO 2 removal unit, 2. develop a dedicated biomass feeding system for entrained flow gasifiers, 3. pre-treat the biomass to make it suitable for fine milling and use in the conventional pneumatic transport machinery employed in entrained flow gasifiers. Research on a dedicated biomass feeding system using screw feeders and piston compressors is presented in Ref. [5]. This system requires particles no smaller than 1 mm, but since biomass * Corresponding author. Tel.: þ49 30 314 28 449; fax: þ49 30 314 21 683. E-mail address: erlach@iet.tu-berlin.de (B. Erlach). Contents lists available at SciVerse ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2012.01.057 Energy 45 (2012) 329e338