Platform for H2 production from waste biomass with inherent negative emissions

Abstract

C3H8O3 is the main byproduct of biodiesel production, accounting for 10wt% of the final products[1]. This work proposes a system for converting this waste C3H8O3 made from biomass into H2 or other syngas-derived chemicals.
This is carried out using a chemical looping reactor which provides the heat required to reform the glycerol while having inherent CO2 capture. This is achieved using dynamically operated packed bed reactors. The heat required to drive the reforming process is produced from the indirect oxyfuel combustion of biogas or offgas from downstream processes through the use of a chemical intermediate as represented in Figure 1[2]. This produces first N2 and then a mixture of CO2 and H2O which are easily separated for CO2 sequestration. As the C3H8O3 is from a biological source this gives the system the potential for negative emissions.
Then the reforming stage occurs, where the C3H8O3, H2O and CO2 are fed to the reactor producing syngas and cooling the bed to the initial solid temperature.

Figure 1. Schematic of chemical looping reforming

Figure 2. 500g setup used for the experiments
To test the potential of this system, 500 g packed bed of oxygen carrier were cyclically reduced, oxidized and used to carry out reforming experiments (Figure 2). This 500g reactor consists of a high temperature resistant stainless steel tube with inner diameter 35 mm and length of 1050 mm. A 6.3 mm ID multiple point thermocouple, with 10 measurement points is used to obtain the unsteady axial temperature profile. Determining how the axial temperature profile changes, in combination with outlet gas analysis during each of the three sections is vital for scale up and determining the effectiveness of the system.
Various conditions for the reforming were tested, at a pressure of 1 bar and initial temperatures ranging from 600-900°C. The temperature rise during oxidation at 1 and 5 bar with a starting temperature of 600°C at different points in the bed is shown in Figure 3 and this can be compared to the temperature change during reduction using biogas at the same conditions. This highlights how the temperature profile can be determined at various conditions and that the bed is successfully heated during oxidation, has minimal changes during reduction so can store heat to drive the reforming of C3H8O3.


Figure 3. Thermocouples’ recording temperature during oxidation for 1 bar (solid lines) and 5 bar (dashed lines), 10% O2, 600°C initial bed temperature and 10NLPM flowrate

Keywords: Glycerol, Neative emmisions, Reforming, Hyrdogen