Dairy biomass (DB) is evaluated as a possible co-firing fuel with coal. Cofiring of DB offers a technique of utilizing dairy manure for power/steam generation, reducing greenhouse gas concerns, and increasing financial returns to dairy operators. The effects of cofiring coal and DB have been studied in a 30 kW (100,000 BTU/hr) burner boiler facility. Experiments were performed with Texas Lignite coal (TXL) as a base line fuel. The combustion efficiency from co-firing is also addressed in the present work. Two forms of partially composted DB fuels were investigated: low ash separated solids and high ash soil surface. Two types of coal were investigated: TXL and Wyoming Powder River Basin coal (WYO). Proximate and ultimate analyses were performed on coal and DB. DB fuels have much higher nitrogen (kg/GJ) and ash content (kg/GJ) than coal. The HHV of TXL and WYO coal as received were 14,000 and 18,000 kJ/kg, while the HHV of the LA-PC-DBSepS and the HA-PC-DB-SoilS were 13,000 and 4,000 kJ/kg. The HHV based on stoichiometric air were 3,000 kJ/kg for both coals and LA-PC-DB-SepS and 2,900 kJ/kg for HA-PC-DB-SoilS. The nitrogen and sulfur loading for TXL and WYO ranged from 0.15 to 0.48 kg/GJ and from 0.33 to 2.67 for the DB fuels. TXL began pyrolysis at 640 K and the WYO at 660 K. The HA-PC-DB-SoilSs began pyrolysis at 530 K and the LA-PC-DB-SepS at 510 K. The maximum rate of volatile release occurred at 700 K for both coals and HA-PC-DB-SoilS and 750K for LA-PC-DB-SepS. The NOx emissions for equivalence ratio (φ) varying from 0.9 to 1.2 ranged from 0.34 to 0.90 kg/GJ (0.79 to 0.16 lb/mmBTU) for pure TXL. They ranged from 0.35 to 0.7 kg/GJ (0.82 to 0.16 lb/mmBTU) for a 90:10 TXL:LA-PC-DB-SepS blend and from 0.32 to 0.5 kg/GJ (0.74 to 0.12 lb/mmBTU) for a 80:20 TXL:LA-PC-DB-SepS blend over the same range of φ. In a rich environment, DB:coal cofiring produced less NOx and CO than pure coal. This result is probably due to the fuel bound nitrogen in DB is mostly in the form of urea which reduces NOx to non-polluting gases such as nitrogen (N2).

Growing rates of manure produced from large dairies have increased concern for the environmental quality of nearby streams and watersheds. Typically the manure from the freestalls on these dairies is flushed with water to a mechanical separator. Here, flushed dairy biomass (DB) is parted into separated solids and separated liquid. The separated liquid is discharged into lagoons for treatment and eventual land application. This thesis proposes thermodynamic models for firing DB in small scale boiler systems that would eliminate land application and lagoons, which are being claimed to be the source of nutrient leaching and overloading. Fuel analysis of flushed DB from a dairy in central Texas show that it contains 93%moisture (%M), 3%ash (%A), and 4%combustibles (%Cb), while separated DB solids contain 81%M, 2%A, and 17%Cb. The dry, ash-free higher heating value of DB is approximately 20,000 kJ/kg. Using dry, ash-free results, computations can be made over ranges of %M and %A. For example, DB containing 70%M requires 9.74%Cb to vaporize all moisture and produce gaseous products of combustion at 373 K, but requires 17.82%Cb to burn in a regenerative combustor with a flame temperature of 1200 K. Separated solids that are pressed in an auger to 70%M (3%A and 27%Cb) can burn at 1200 K with exhaust temperatures of up to 1130 K and a minimum required heat exchanger effectiveness of 15%. Pressed solids can thus be fired in a boiler, where the remaining separated liquid can be used as feed water. The pressed solids only can release about 30% of the heat required to vaporize the remaining unclean feed water. However, pressed DB solids can be blended with drier fuels to vaporize almost all the unclean water. The low quality steam produced from the unclean water can be used in thermal processes on the farm. A similar system can be developed for vacuumed DB without the need to vaporize unclean feed water. As for large dairies with anaerobic digester systems already installed, directly firing the produced biogas in a small scale boiler system may be another way to similarly vaporize the remaining effluent.

Concentrated animal feeding operations such as cattle feedlots and dairies produce a large amount of manure, cattle biomass (CB), which may lead to land, water, and air pollution if waste handling systems and storage and treatment structures are not properly managed. However, the concentrated production of low quality CB at these feeding operations serves as a good feedstock for in situ gasification for syngas (CO and H2) production and subsequent use in power generation. A small scale (10 kW) countercurrent fixed bed gasifier was rebuilt to perform gasification studies under quasisteady state conditions using dairy biomass (DB) as feedstock and various air-steam mixtures as oxidizing sources. A DB-ash (from DB) blend and a DB-Wyoming coal blend were also studied for comparison purposes. In addition, chlorinated char was also produced via pure pyrolysis of DB using N2 and N2-steam gas mixtures. The chlorinated char is useful for enhanced capture of Hg in ESP of coal fired boilers. Two main parameters were investigated in the gasification studies with air-steam mixtures. One was the equivalence ratio ER (the ratio of stochiometric air to actual air) and the second was the steam to fuel ratio (S:F). Prior to the experimental studies, atom conservation with i) limited product species and ii) equilibrium modeling studies with a large number of product species were performed on the gasification of DB to determine suitable range of operating conditions (ER and S:F ratio). Results on bed temperature profile, gas composition (CO, CO2, H2, CH4, C2H6, and N2), gross heating value (HHV), and energy conversion efficiency (ECE) are presented. Both modeling and experimental results show that gasification under increased ER and S:F ratios tend to produce rich mixtures in H2 and CO2 but poor in CO. Increased ER produces gases with higher HHV but decreases the ECE due to higher tar and char production. Gasification of DB under the operating conditions 1.59<ER less than6.36 and 0.35<s:f>less than0.8 yielded gas mixtures with compositions as given below: CO (4.77 - 11.73 %), H2 (13.48 - 25.45%), CO2 (11-25.2%), CH4 (0.43-1.73 %), and C2H6 (0.2- 0.69%). In general, the bed temperature profiles had peaks that ranged between 519 and 1032 degrees C for DB gasification.

Biomass is one of the renewable and non-conventional energy sources and it includes municipal solid wastes and animal wastes in addition to agricultural residue. Concentrated animal feeding operations produce large quantities of cattle biomass which might result in land and water pollution if left untreated. Different methods are employed to extract the available energy from the cattle biomass (CB) which includes co-firing and gasification. There are two types of CB: Feedlot biomass (FB), animal waste from feedlots and dairy biomass (DB), animal waste from dairy farms. Experiments were performed in the part on gasification of both FB and DB. Earlier studies on gasification of DB with different steam-fuel ratios resulted in increased production of hydrogen. In the present study, dairy biomass was gasified in a medium with enriched oxygen percentage varying from 24% to 28%. The effect of enriched air mixture, equivalence ratio and steam-fuel ratio on the performance of gasifier was studied. Limited studies were done using a mixture of carbon dioxide and oxygen as the gasification medium and also a methodology was developed to determine the gasification efficiency based on mass and heat contents of gas. The results show that the peak temperature within the bed increases with increase in oxygen concentration in the gasification medium. Also carbon dioxide concentration in the mixture increases with corresponding decrease in carbon monoxide with increase in oxygen concentration of the incoming gasification medium. The peak temperature increased from 988°C to 1192°C as the oxygen concentration increased from 21% to 28% at ER=2.1. The upper limit on oxygen concentration is limited to 28% due to high peak temperature and resulting ash agglomeration. Higher heating value (HHV) of the gases decreases with increase in equivalence ratio. The gases produced using carbon dioxide and oxygen mixture had a higher HHV when compared to that of air and enriched air gasification. Typically the HHV of the gases increased from 2219 kJ/m³ to 3479 kJ/m³ when carbon dioxide and oxygen mixture is used for gasification instead of air at ER=4.2 in the absence of steam.