Progress 09/01/10 to 08/31/13
Outputs
Target Audience:
Nothing Reported
Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Executive Summary Farms and dairies generate by-products that contain more than 2 quadrillion Btu of energy per year. This energy is either not used at all or is used in old and inefficient processes. Better use of these under-utilized resources could replace significant amounts of the natural gas used in farms and dairies, and thereby reduces their operating costs. Particularly, the use of biogas generated from digestion of bio-waste (such as animal manure) in small, fuel cell powered distributed combined heat and power (CHP) systems present a realistic, near-term approach to achieve large energy efficiency improvements. However, the biogas contains various sulfur compounds (up to 1.5% vol.) that are potent poisons for fuel cell anode electro-catalyst; even a few ppm will rapidly deactivate the fuel cell. Sulfur also corrodes fuel cell components (such as interconnects) and other process equipment. TDA Research Inc. is developing a new, high capacity, low cost sorbent to remove all the sulfur species from biogas to meet the cleanliness requirements of the fuel cell power plants. Our sorbent bed is used as a polisher that is located downstream of a bulk desulfurization system; the purpose of our bed is to remove any residual hydrogen sulfide (H2S) and all other organic sulfur species. This will be a key technology that enables the use of biogas in distributed fuel cell CHP systems. TDA's sorbent removes all the sulfur (both inorganic and organic) including mercaptans, and di and trisulfides to ppb levels. The sorbent operates at ambient temperatures and are highly selective to sulfur even in the presence of saturated water, achieving much higher capacity than activated carbon for H2S. These sorbents also allowed us to effectively remove the large disulfide species (e.g., dimethyl disulfide) that are difficult to remove using conventional microporous sorbents while reducing the overall sulfur concentration of the biogas to less than 4 ppbv to ensure maximum protection to the fuel cell. These sorbents could also be used in Wastewater & Landfill CHP plants or facilities and also for converting biogas to pipeline quality SNG for vehicles or to sell the gas back to pipelines. In Phase II, we optimized the sorbent formulation and preparation procedures and scaled-up the sorbent preparation batch size from 0.25 L to 200 L. We carried out evaluations of the prepared sorbent formulations at bench-scale. We used their di-sulfide (one of the toughest class of sulfur compound to remove from biogas) adsorption capacity as a performance metric. The scaled-up sorbent retained its adsorption capacity and achieved a total sulfur breakthrough capacity of 8.8% wt. sulfur. Finally, we carried out a detailed engineering and cost analysis, we showed the economic viability of the new sorbent used as an expendable sulfur polishing bed for a fuel cell CHP system. For a typical 800 cow dairy, we estimated the added cost of desulfurization including capital expenditure to be less than 0.45 cents/kWh. The overall impact of the gas clean-up system on the cost of electricity (COE) is small, contributing less than 3.6% to the COE (based on a cost of the electricity in California for industrial use of 12.60 cents/kWh in July 2013).
Publications
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