Charles M. Kinoshita

Removal of inorganic constituents of biomass feedstocks by mechanical dewatering and leaching

Inorganic constituents of ash in biomass fuels are responsible for equipment failure and operating difficulties in thermochemical energy conversion facilities. Alkali metals, in the presence of chlorine and sulfur, are the leading contributors to this problem. Banagrass, a herbaceous species being considered for use as a dedicated energy crop, contains high levels of potassium and chlorine. Some inorganic elements are water soluble and the opportunity exists to remove them by mechanical dewatering and leaching as part of the feedstock preparation process. Laboratory-scale equipment, representative of processes employed in the commercial extraction of sugar from cane, was used to prepare banagrass fuel treatments that included two degrees of comminution (coarse and fine) and two dewatering schemes (mechanical dewatering only, and a multi-step process consisting of initial mechanical dewatering followed by a water rinse and second dewatering). The treatment that included fine comminution and multi-step dewatering resulted in a fuel with substantial reductions in ash (45%), K (90%), Cl (98%), S (55%), Na (68%), P (72%) and Mg (68%). The coarse comminution and multi-step dewatering scheme also resulted in reductions, but generally with 10–20% more of the initial constituent mass retained in the fuel. These two treatments produced fuels containing 0.11 and 0.23 kg (Na2O + K2O) GJ−1, respectively, with corresponding ash fusion temperature estimates of 1250 and 1075°C. By comparison, bagasse, the fibrous by-product of sugar cane, contains 0.06 kg (Na2O + K2O) GJ−1 and has an estimated ash fusion temperature of roughly 1500°C. Banagrass subjected to the most severe treatment, fine comminution with multi-step dewatering, should produce a boiler fuel with characteristics similar to those of bagasse.

Production of hydrogen from bio-oil using CaO as a CO2 sorbent

Abstract Steam reforming of bio-oil into transportation-fuel-grade hydrogen using CaO as a CO2 sorbent is modelled using the ASPEN PLUS process simulator. The simulations predict that (1) operating the absorbing (reforming) reactor at 600–850°C and the desorbing (regeneration) reactor at ∼800°C and near ambient pressure is optimal; (2) the gas exiting the absorbing reactor contains >95% H 2 (dry gas, molar basis) versus only 67% theoretically producible without the aid of sorbents; (3) hydrogen yield from the sorbent-aided system is comparable to that predicted for catalytic steam reforming of bio-oil without the use of sorbents, ∼0.07– 0.08 kg H 2 per kg of bio-oil.

Entropy Generation in Multicomponent Reacting Flows

A comprehensive equation to determine the rate of local entropy generation in multicomponent, reacting, laminar fluid flow involving heat and mass transfer is formulated based on species-average velocity in a multicomponent continuum. The entropy-generation equation developed in this study suggests that species diffusion induces a diffusive-viscous effect, heretofore not reported in the literature, which could contribute significantly to entropy generation in multicomponent fluid systems, and that entropy generation in a multicomponent system exceeds that in a single-component fluid system having similar velocity and temperature distributions because a greater number of irreversible processes, such as species diffusion, chemical reaction, and the Soret and Dufour effects, are involved. Under appropriate conditions, if the diffusive-viscous effect is neglected, the entropy-generation equation of this study reduces to those reported in the literature for simpler fluid systems based on mean flow.

Fuel characteristics of processed, high-fiber sugarcane

A study of treatment methods to improve the fuel characteristics of sugarcane variety B52298 was conducted. Two parent materials, whole cane (WC) and stripped cane (SC), were included in the study. The whole cane material was subjected to three treatments: (1) no treatment, WC-U; (2) a single milling, WC-M; and (3) an initial milling followed by leaching and a secondary milling, WC-MLM. Treatments (1) through (3) are in order of increasing severity. The stripped cane material was subjected to treatment (3) and designated as SC-MLM. Regardless of parent material, milling produced moisture contents of ∼50% wet basis and fiber bulk densities of ∼97 kg m−3 in the treated fuels and produced a shift in particle distributions toward smaller sizes. Geometric mean diameters (by weight) of the WC-U, WC-M, WC-MLM, and SC-MLM materials were 2.3, 1.8, 1.3, and 1.3 mm, respectively. Ash generated from the fuel was reduced by roughly 1% (absolute) for each milling operation, resulting in reductions of ∼2% for the WC-MLM and SC-MLM treatments. Ash reduction was primarily due to the removal of K, Cl, and S by the treatment operations. Ash removal, in addition to reductions in the O content of the treated fuels, contributed to an increase in the energy content of the fuels from ∼17.6 MJ kg−1 in the parent materials to 18.4 and 19.2 MJ kg−1 for the WC-MLM and SC-MLM treatments, respectively. K, Cl, S, and N concentrations were all reduced in the fuel by the treatments. K comprised ∼1.3% of the parent materials and Cl accounted for 0.65% and 0.83% of dry matter for the whole cane and stripped cane parent materials, respectively. Reductions in K concentration relative to the parent materials for the WC-M, WC-MLM, and SC-MLM treatments were 50%, 86%, and 91%, respectively. Cl was reduced 62% by the WC-M treatment relative to the unprocessed whole cane, and removal was essentially complete for the two leached treatments. Sulfur in the two parent materials accounted for ∼0.22% of plant dry matter. Compared to the parent materials, the WC-M, WC-MLM, and SC-MLM treatments removed 36%, 82%, and 86% of the S, respectively. Nitrogen concentrations in the stripped cane and whole cane parent materials were 0.48% and 0.37%, respectively. Nitrogen reduction by the WC-M, WC-MLM, and SC-MLM treatments was 12%, 27%, and 57%, respectively. Ash deformation temperatures (oxidizing atmosphere) increased in the treated fuels compared to parent materials. Ash from the WC-MLM treatment did not attain the initial stage of deformation at the maximum test temperature, 1482 °C. Ash of the WC-M and SC-MLM treatments became fluid at ∼1350 °C. Experimentally determined fluid temperatures for the more severely treated fuels compared well with values predicted by a ternary phase diagram for the SiO2–K2O–CaO system. Slagging and fouling indices were computed for each of the fuel treatments. Values for WC-U and WC-M exceeded a benchmark of 0.34 kg (K2O+Na2O) GJ−1 and would be expected to cause ash deposition in boiler use. Values for the WC-MLM and SC-MLM treatments were 0.13 and 0.08 kg (K2O+Na2O) GJ−1, respectively, and are good candidates for boiler fuels. Concomitant reductions in S and Cl for these two fuels further reduce the likelihood of ash deposition, as well as improve environmental performance by reducing criteria and acid gas pollutant emissions. Mass balances for K and Cl were conducted for the treatment operations. Closure for the balances ranged from 112% to 122% over all treatments, and was viewed as validating the consistency of the results.

Projected Impact of Deep Ocean Carbon Dioxide Discharge on Atmospheric CO2 Concentrations

An evaluation of oceanic containment strategies for anthropogenic carbon dioxide is presented. Energy conservation is also addressed through an input hydrocarbon-fuel consumption function. The effectiveness of the proposed countermeasures is determined from atmospheric CO2 concentration predictions. A previous box model with a diffusive deep ocean is adapted and applied to the concept of fractional CO2 injection in 500 m deep waters. Next, the contributions of oceanic calcium carbonate sediment dissolution, and of deep seawater renewal, are included. Numerical results show that for CO2 direct removal measures to be effective, large fractions of anthropogenic carbon dioxide have to be processed. This point favors fuel pre-processing concepts. The global model also indicates that energy conservation, i.e. a hydrocarbon-fuel consumption slowdown, remains the most effective way to mitigate the greenhouse effect, because it offers mankind a substantial time delay to implement new energy production alternatives.

Chemical equilibrium computations for gasification of biomass to produce methanol

Gasification of biomass into synthesis gas is the first step in producing methanol from biomass. Catalytic conversion of the gas produced by the gasifier into methanol is strongly affected by the composition of the product gas. It is thus important to know what the gas composition would be under different gasification conditions and to be able to identify those conditions that would be optimal for methanol production. A computer program is developed to determine the equilibrium composition of biomass gasification products under various conditions. The theoretical influence of temperature, pressure, moisture, and equivalence ratio on gasification is analyzed. The equilibrium computations are used to define appropriate gasification conditions for methanol production and related gasification parameters. By judiciously adjusting certain gasification parameters, it appears that one can optimize the gas generated from biomass for subsequent synthesis into methanol. Energy balances and theoretical methanol yield...

Measurements of gas phase carbon in steam explosion of biomass

Abstract Banagrass, a fast growing tropical grass with potential use as a feedstock for energy, fuel, and chemical production, was tested in a pilot-scale steam exploder equipped with a gas sampling system. Known quantities of argon injected into the reactor with process steam served as a trace gas and permitted quantification of biomass-derived gases. A total of 77 tests were performed over a uniform matrix of temperature and log 10 Reaction Ordinate, R 0 = t exp ( t − 100) 14.75 where t is time in minutes and T is temperature in degree Celsius. The main carbon-containing species in the biomass-derived gases was CO 2 . Gas-phase carbon ranged from 0.5% to 2.4%, averaging 1.1% of feedstock carbon. Gas phase carbon increased with increasing severity, reaching a maximum at ∼205°C.

A strategy to reduce CO2 emissions from hydrocarbon-fueled power plants by precombustion reforming and deep ocean discharge of CO2

Abstract A process to reduce atmospheric CO 2 emissions from hydrocarbon-fueled power plants is proposed. The fuel is reformed into a mixture of hydrogen and CO 2 before combustion takes place. These gases are subsequently separated by preferential absorption or by differential phase changes. Thereafter, hydrogen replaces the original fuel for power generation. The liquefied CO 2 is discharged into the deep ocean. Water depths of about 500 m appear to be favorable from logistic and thermoeconomic standpoints. Calculations for a 500 MW methane power plant, retrofitted with the proposed system, indicate moderate power and cost penalties. The relative impact of a widespread implementation of this global warming countermeasure is assessed, and the advantages of moderate hydrocarbon consumption trends, as well as of high CO 2 discharge fractions are highlighted. This latter point may indicate the need for sweeping changes, such as the establishment of hydrogen-based economies if global warming is to be avoided.

Cycle analyses of 5 and 20 MWe biomass gasifier-based electric power stations in Hawaii

Thermodynamic cycle analyses of biomass gasifier-based electric power stations at two scales, nominally 5 and 20 MWe (net electric power output), were performed to assess process performance and viability. Various configurations (Rankine, simple, steam-injected gas turbine, and combined cycles) of a 5 MW stand-alone power station were modeled and a 20 MW biomass-based integrated gasifier combined-cycle cogeneration facility at a sugar factory was simulated. Information gained from these analyses will be applied to determine whether biomass gasification based electricity production is practicable in Hawaii and other sugar producing locales.