1. The Effect of fuel ash composition on Corrosion potential in Biomass-fired boilers Research group – Shrinivas Lokare, David Dunaway, David Moulton, Marc Anderson, Helle Junker (Techwise, Denmark), Dale Tree, Larry Baxter ACERC 17 th Annual Conference February 20-21, 2003 University of Utah Salt Lake City, Utah Research Background The pollution control requirement have pushed the industry to opt for biofuels, including co-firing with coal, to reduce CO 2 production, a major greenhouse gas. The biofuels in boilers decrease the boiler efficiency due to high moisture content as well as unmanageable ash deposition problems. Furthermore, the high alkali and chlorine contents of some biofuels generate severe corrosion problems. Project Objectives To investigate the influence of fuel chemistry on chloride deposition on heat transfer surfaces in biomass-fired systems. Operating conditions Sampling section temperature - 800-900 o C. Sampling period = 30 minutes. Deposit collection probe surface temperature = 450-550 o C. 4-5% Oxygen in exhaust stream. Reactor design (Multi-fuel Flow Reactor) Premixed fuel burner 1.93 m Auxiliary methane Sample location Cooling water Inside diameter = 12 cm Experimental Set-up Probe Designs Straw Grain screenings Saw dust Sugar beat pulp Sunflower shells Shea nut shells Fuel matrix % w/wStraw Saw dust Grain screenings Sunflower shells Shea Nut shells SiO 2 526.434.41.16.6 Al 2 O 3 0.62.92.20.51.7 Fe 2 O 3 1.10.92.60.92.4 CaO9.245.315.8166.4 MgO1.89.83.913.17.9 Na 2 O0.33.21.9< 0.20.4 K2OK2O21.920.619.245.153.3 SO 3 42.85.111.710.4 P2O5P2O5 3.22.611.610.19.3 Cl5.60.22.81.21.4 Other0.35.30.50.30.2 Sum100 % w/wStraw Saw dust Grain screenings Sunflower shells Shea nut shells Moisture11.0 12.510.117.0 C43.944.944.747.643.6 H5.95.86.16.05.0 O38.738.134.735.432.0 N0.50.22.00.92.4 Sum100.0 Corrosion potential of biofuels Grain screenings – Magnification 450 X The corrosion is a relatively slow process, however, for the biofuels with higher alkali and chlorine content, under particular temperature and pressure conditions, alkali chlorides-metal surface interactions are found to be favored in the case of some biofuels. Effect of fuel mixing on ash chemistry Consistent with the hypothesis, the fuels blends produce lower levels of alkali chlorides deposition as compared to the pure fuel. The interactions between ash compounds in a fuel blend demonstrate feasibility to reduce corrosion potential. Results and Discussion Effect of fuel sulfur on ash deposit chemistry Straw (100%) – Magnification 200 XSaw dust (100%) – Magnification 200 XStraw – Saw dust (50%-50%) – Magnification 200 X Figure imported from Report on “Ash deposition and corrosion mechanisms”, by Baxter L.L., Sandia National Lab. K, Cl and S maps obtained from SEM analysis of 100% Sunflower shells (top) and 100% Straw (bottom) combustion tests. Magnification – 200 X Conclusions – The biofuels exhibit high corrosion potential due to its high alkali and chlorine content. However, small amount fuel sulfur can control chloride deposition on the surface through heterogeneous sulfation of chlorides, in a thermochemically controlled manner. Such requirements can be accomplished by blending different fuels with appropriate selection. The experimental data is found to be consistent with the previous thermodynamic equilibrium calculations confirming the hypothesis that alkali chlorides react with gaseous sulfur heterogeneously to form alkali sulfates. Acknowledgements – Department of Energy / EE; Techwise, Denmark; Ash Deposition and Corrosion Research group at BYU Fuel analysis (Ultimate) Fuel Ash analysis