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Chloride removal from a biomass gasification product stream by a fixed bed of self-prepared sorbent material

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Title:Chloride removal from a biomass gasification product stream by a fixed bed of self-prepared sorbent material
Authors:Foley, Michael J.
Keywords:chloride removal
Date Issued:Dec 2011
Publisher:[Honolulu] : [University of Hawaii at Manoa], [December 2011]
Abstract:Biomass gasification is a carbon neutral technology for producing fuel gas or synthesis gas (syngas) from biomass materials. Contaminants must be removed from the product gas before it is delivered to downstream devices such as gas turbines, solid oxide fuel cells (SOFC) or catalysts for liquid chemical/fuel synthesis. Contaminants of concern, present in the product gas, include tar components, alkali metals, sulfur, trace elements and chlorine. Chlorine-containing molecules present in biomass fuels volatize under gasification conditions and cause serious corrosion and deposition damage in downstream process components. This hinders the feasibility of industrializing biomass gasification as a renewable energy production technology. An extensive literature review identified gas treatment using a solid sorbent material loaded in a fixed-bed reactor as a practical means of chloride removal from a gasification system at elevated temperature. Coal ash, a solid byproduct of coal power plants, has been found to perform well as a chloride sorbent due to its structure and chemical composition. No previous experimental studies have employed coal ash as a sorbent material in a biomass gasification process.
Coal ash was obtained from the Hawaiian Commercial & Sugar Company (HC&S) coal/biomass-fired boiler and from the AES Hawaii Power Plant and was used as the parent material in a variety of sorbent preparations. Preparation techniques, including various binder materials and hydration processes, were explored to manufacture the raw material into durable pellets or granules with a high affinity for chloride. The prepared materials were tested in a lab-scale experiment to identify sorbent preparations that provided the highest chloride adsorption capacity. A commercially available chloride sorbent, BASF CL-760, was also tested to provide a basis for comparison. The two sorbents prepared by hydrating AES fly ash and bed material (limestone) provided the highest chloride adsorption capacity of the manufactured sorbents when subjected to a 400°C gas stream containing ~650 ppmw Cl-and an average GHSV of about 1500 hr-1. The AES fly ash and bed material sorbents provided an average adsorption capacity of 2.1% and 4.0% (g Cl-per g used sorbent), respectively. The CL-760 was found to have an average chloride adsorption capacity of 2.4% when subjected to the same conditions.
The hydrated AES fly ash and bed material sorbents were subsequently tested in a bench-scale fluidized-bed biomass gasifier. Each sorbent was loaded into a fix-bed operating at ~400°C. The gas flow through the bed was varied over the duration of the tests so that the chloride adsorption performance of the sorbents at increasing gas hourly space velocities (GHSV) could be evaluated. The hydrated AES fly ash sorbent was tested at GHSVs ranging from 8,909 hr-1 to 52,111 hr-1. The hydrated AES bed material sorbent was tested at GHSVs ranging from 3,237 hr-1 to 13,266 hr-1. Both sorbents were found to be most effective at removing chloride at the lowest GHSVs. At a GHSV of 8,909 hr-1, the hydrated AES fly ash sorbent reduced the chloride concentration in the dry product gas from ~300 ppmv to ~50 ppmv, an 83% reduction. At a GHSV of 3,237 hr-1, the hydrated AES bed material sorbent reduced the dry product gas chloride concentration from ~300 ppmv to ~10 ppmv, a reduction of about 97%. Pre-and post-sample analysis data were used to perform mass balance calculations that showed that between 85.8% and 99.2% of the chlorine input to the system could be accounted for in the test results. The analyses confirmed that the self-prepared sorbent materials are effective at the removal of chloride from a biomass gasification product gas stream.
Description:M.S. University of Hawaii at Manoa 2011.
Includes bibliographical references.
Appears in Collections: M.S. - Civil Engineering

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