Development of a co-firing fuel from biomass-derived binder and crushed coal

Andrew J. Friend (2013), Thesis

The focus of this work was the development of a co-firing boiler fuel for use in the coal power plant industry. This fuel, known as co-fire pellets, is a densified product comprised of crushed coal and a renewable binder derived from the liquid product of the fast pyrolysis of lignocellulosic biomass. The co-fire pellets can help meet certain state and federal regulations related to electricity production. A central composite design of experiments was used to evaluate properties of the co-fire pellets based on four factors relating to the makeup of the pellets. These factors are coal particle size, coal moisture content, binder percentage, and pellet cure time. Properties of the pellets were investigated using the following tests: higher heating value, proximate analysis, ultimate analysis, mass density, particle density, indirect tensile strength, impact resistance, and abrasion resistance. The experimental data was modeled using linear regression techniques. The pyrolyzed biomass binder fraction had the largest impact on pellet properties, while cure temperature was determined to be a nonessential treatment.

Techno-economic and life-cycle assessment of the carbon negative bio-oil co-fire fuel power production strategy

Lysle Whitmer, Ryan Smith, David Laird, Jill Euken, Mark Wright, Robert Brown (2013), Iowa Energy Center

[DIAGRAM]Corn stover fast pyrolysisSimplified process flow diagram of corn stover fast pyrolysis and bio-oil co-fire fuel (BCF) and coal combined heat and power system.

Process model results indicate that the fast pyrolysis facility converts 2000 Mg per day of corn stover into 632 Mg of bio-oil co-fire fuel (BCF), 895 Mg of light ends, and 158 Mg of biochar with the balance consisting of flue gas and ash. The BCF is subsequently mixed with 1467 Mg of bituminous coal at a 70/30 BCF to coal ratio. A steam boiler, operating at 1100 °C, raises high-pressure (28 bar) steam by combusting the fuel mixture. An economizer employs excess heat from the boiler to preheat process water for steam generation. Combustion gases flow through a series of heat  exchanger raising high-, medium- (11 bar), and low- (2 bar) pressure steam. Steam turbines expand a majority of the steam to produce electric power. In summary, 121, 40, and 15843 Mg per day of high-, medium-, and low-pressure steam are generated, and 82.9 MWe is exported as summarized in Table 6. Figure 5 shows a simplified process flow diagram of the corn stover fast pyrolysis and BCF-Coal combined heat and power system.

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