Amado L. Maglinao

Predicting Fouling and Slagging Behavior of Dairy Manure (DM) and Cotton Gin Trash (CGT) During Thermal Conversion

Predictions regarding the slagging and fouling behavior of dairy manure (DM) and cotton gin trash (CGT) during thermal conversion were evaluated using different indices and measurements. The calculated values of the alkali index (AI), base-to-acid ratio (Rb/a), and bed agglomeration index (BAI) of ash samples from DM and CGT indicated that slagging and fouling were expected to occur during thermal conversion. On the other hand, the values obtained for slagging (Rs) and fouling (Rf) factors (indices used in characterizing coal samples) indicated very low slagging and fouling potential for DM and CGT. Agricultural biomass has characteristics very similar to lignite, for which the coal indices Rs and Rf are not recommended. Measurement of the compressive strengths of the DM and CGT ash pellets and scanning electron microscopy (SEM) of ashes subjected to different temperatures contributed additional information to better describe the conditions for slagging. The maximum compressive strengths of ash produced at various furnace temperatures were found to occur at 800°C for CGT and 600°C for DM. At typical combustion temperatures (1300°C to 1500°C), slagging is thus expected with the use of DM and CGT as feedstocks. Actual combustion studies must be made to validate these claims. The results of this study indicate that the use of compressive strength of the ash pellets determined at various combustion temperatures provides a better understanding of the melting behavior of ash in biomass. An investigation involving a combination of indices and physical measurements appears to be a good approach for evaluating slagging and fouling tendencies in thermal conversion of biomass.

DEVELOPMENT OF COMPUTER CONTROL SYSTEM FOR THE PILOT SCALE FLUIDIZED BED BIOMASS GASIFICATION SYSTEM

A pilot scale fluidized bed biomass gasifier developed at Texas A&M University in College Station, Texas was instrumented with thermocouples, pressure transducers and motor controllers for monitoring gasification temperature and pressure, air flow and biomass feeding rates. A process control program was also developed and employed for easier measurement and control The gasifier was then evaluated in the gasification of sorghum, cotton gin trash (CGT) and manure. The expected start-up time, operating temperature and desired fluidization were achieved without any trouble in the instrumented gasifier. The air flow rate was maintained at 1.99 kg/min and the fuel flow rate at 0.95 kg/min. The process control program considerably facilitated its operation which can now be remotely done. The gasification of sorghum, CGT and manure showed that they contained high amounts of volatile component matter and comparable yields of hydrogen, carbon monoxide and methane. Manure showed higher ash content while sorghum yielded lower amount of hydrogen. Their heating values and gas yields did not vary but were considered low ranging from only 4.09 to 4.19 MJ/m3 and from 1.8 to 2.5 m3/kg, respectively. The production of hydrogen and gas calorific values were significantly affected by biomass type but not by the operating temperature.

Operation of the TAMU Fluidized Bed Gasifier Using Different Biomass Feedstock

The fluidized bed gasifier (FBG) developed at the Texas A&M University, College Station, Texas was tested using poultry litter, wood chips and cotton gin trash (CGT) as feedstock. The FBG has a diameter of 305 mm and operates at a temperature approximately 760°C (1400°F) and a feeding rate about 70 kg/hr. The synthesis gas produced was analyzed. Preliminary tests showed that the gas quality is lower than the previous runs due to a decrease in hydrogen production.

Fluidized Bed Air Gasification Using Low Heating Value Sand-Bedded Dairy Manure and Sludge Pellets

Solid manure handling is a major environmental issue confronting animal facilities in the United States. One difficulty in using dairy manure as a fuel source is the presence of sand bedding used for lactating dairy cows. More than 30% of dairy farms use sand beds for a dry and clean environment that prevents bacterial growth [1]. In this study, dairy animal manure obtained directly from waste lagoons was used for the air gasification process. The manure was dried to reduce the moisture down to 5% and a sand separating system was designed to remove some sand bedding materials. Preliminary air gasification experiments showed that the direct use of dairy manure containing 75% ash content, that reflect high sand content, reduced the temperature of the reactor. The study is also aimed at handling unprocessed dairy manure and generating electric power for the on-site use. A high heating value manure is needed to run the gasifier and the produced synthesis gas (or syngas) is fed to an engine coupled with a generator. Some dairy manure gasification work were done using fresh dairy manure. The highest heating value from the dairy manure biomass was found to be 4.5MJ/kg in a fixed-bed gasifier [2]. Another gasification study using a fluidized-bed reactor could produce syngas heating value as high as 4.7MJ/m3 from dairy manure [3]. A bench-scale fluidized bed containing a 3-inch diameter reactor tube with a cyclone and a scrubber was used to gasify dairy manure using air at different temperatures. The sand separated dairy manure used in this study contained approximately 45% ash content. The maximum heating value of the synthesis gas was 3.8MJ/m3 at an operating temperature of 750°C. The syngas will need to be upgraded. To upgrade the synthesis gas heating value, sludge pellets of 18.7MJ/kg were mixed with the dairy manure in different ratios of 10% and 30%. The syngas heating values from mixed manure with sludge pellet were increased to 5MJ/m3 with 10% sludge, and 5.7MJ/m3 with 30% sludge. The sludge used has higher heating value resulting in higher gas HV. The cold gasification efficiency was achieved as high as 36±5% with dairy manure mixed with sludge pellet. At a higher operating temperature, higher efficiency was obtained with increased gas composition of hydrogen and carbon monoxide. This syngas may then be used for power generation as well as possible input gas for the Fisher Tropsch process for liquid biofuel production. The result of the experiments will be a cornerstone for the widespread application of low heating value animal waste for producing high heating value syngas that may be used for electric power generation as a result of various upgrading processes.Copyright