Scott Q. Turn

An experimental investigation of hydrogen production from biomass gasification

Abstract An experimental study of hydrogen production from biomass was conducted using a benchscale fluidized bed gasifier. Parametric experiments were performed to determine the effects of reactor temperature, equivalence ratio, and steam to biomass ratio. Experimental measurements of gas composition and yield were used to calculate the hydrogen yield potential, the capacity of the gas stream for hydrogen production by shifting carbon monoxide and steam reforming higher hydrocarbons. Over the ranges of experimental conditions examined, hydrogen yield potential proved to be most sensitive to equivalence ratio, varying from 62 g H2 kg−1 of dry, ash-free biomass at an equivalence ratio of 0.37, to 128 g H2 kg−1 of dry, ash-free biomass at an equivalence ratio of 0.0. Of the conditions tested, the highest hydrogen yield potential, 128 g H2 kg−1 of dry, ash-free biomass, was achieved at a reactor temperature of 850 °C, equivalence ratio of 0.0, and a steam to biomass ratio of 1.7. This is 78% of the theoretical maximum yield of 165 g H2 kg−1 of dry, ash-free biomass for this feedstock.

Particle concentrations, gas-particle partitioning, and species intercorrelations for polycyclic aromatic hydrocarbons (PAH) emitted during biomass burning

Abstract Eight types of agricultural and forest fuels including 4 cereal crop residues and 4 wood fuels were burned in a combustion wind tunnel to simulate the open burning of biomass. Concentrations for 19 PAH species in particulate matter were found to range between 120 and 4000 mg kg−1, representing between 1 and 70% of total PAH emission. Weakly flaming spreading fires in the cereals were observed to produce higher levels of heavier PAH than more robust fires, with greater partitioning of PAH to the particle phase. Individual species concentrations appeared well correlated within groups based primarily on molecular weight, but no single species was observed to correlate with all others to serve as an indicator of PAH emission strength. Equilibrium gas-particle partitioning did not appear to be achieved within the 3–5 s residence time prior to sampling for sampling temperatures between 32 and 87°C, and in particular for the heavier species emitted from wood fuel pile fires with higher stack gas temperatures and shorter residence times. Total PAH emission, particle-phase concentrations, and fraction of PAH on particles were more strongly influenced by burning conditions than by fuel type.

Elemental characterization of particulate matter emitted from biomass burning: Wind tunnel derived source profiles for herbaceous and wood fuels

Particulate matter emitted from wind tunnel simulations of biomass burning for five herbaceous crop residues (rice, wheat and barley straws, corn stover, and sugar cane trash) and four wood fuels (walnut and almond prunings and ponderosa pine and Douglas fir slash) was collected and analyzed for major elements and water soluble species. Primary constituents of the particulate matter were C, K, Cl, and S. Carbon accounted for roughly 50% of the herbaceous fuel PM and about 70% for the wood fuels. For the herbaceous fuels, particulate matter from rice straw in the size range below 10 μm aerodynamic diameter (PM10) had the highest concentrations of both K (24%) and Cl, (17%) and barley straw PM10 contained the highest sulfur content (4%). K, Cl, and S were present in the PM of the wood fuels at reduced levels with maximum concentrations of 6.5% (almond prunings), 3% (walnut prunings), and 2% (almond prunings), respectively. Analysis of water soluble species indicated that ionic forms of K, Cl, and S made up the majority of these elements from all fuels. Element balances showed K, Cl, S, and N to have the highest recovery factors (fraction of fuel element found in the particulate matter) in the PM of the elements analyzed. In general, chlorine was the most efficiently recovered element for the herbaceous fuels (10 to 35%), whereas sulfur recovery was greatest for the wood fuels (25 to 45%). Unique potassium to elemental carbon ratios of 0.20 and 0.95 were computed for particulate matter (PM10 K/C(e)) from herbaceous and wood fuels, respectively. Similarly, in the size class below 2.5 μm, high-temperature elemental carbon to bromine (PM2.5 C(eht)/Br) ratios of ∼7.5, 43, and 150 were found for the herbaceous fuels, orchard prunings, and forest slash, respectively. The molar ratios of particulate phase bromine to gas phase CO 2 (PM10 Br/CO 2 ) are of the same order of magnitude as gas phase CH 3 Br/CO 2 reported by others.

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.

The fate of inorganic constituents of biomass in fluidized bed gasification

Bagasse and four banagrass fuels with different inorganic fractions were gasified in a bench-scale fluidized bed at a nominal equivalence ratio of 0.3, reactor temperature of 800°C and atmospheric pressure. The gasifier output stream was characterized for permanent gas species, ammonia, condensable hydrocarbon species, char content and composition, and gas-phase inorganic species concentrations. Gas-phase concentrations of K, Na and Ca exceeded combustion turbine fuel specifications. Si, Fe, P, and Cl were also present in the gas phase. Significant amounts of inorganic fuel constituents were retained in the fluidized bed, dispersed over the surface of the bed particles.

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.

Atmospheric emissions from agricultural burning in California: Determination of burn fractions, distribution factors, and crop-specific contributions

Abstract A survey was conducted to determine the fraction of crop biomass normally burned during each season of the year in California. Information obtained from the survey was used in the development of a new procedure to calculate allowable atmospheric emissions from power generating facilities using fuel that would otherwise be burned in the field. Four crops (rice, almonds, walnuts, and wheat) were found to account for 95% of the total crop residue burned in California (excluding forestry). The new procedure uses seasonal (quarterly) determinations, rather than annual totals, to compute the allowed power plant emissions. Seasonal adjustments will probably reduce the economic incentives to use crop biomass as fuel. New power generation facilities will require enhanced pollution control, seasonal mitigation of emissions, or mitigation of non-agricultural emissions in order to comply with regulated emission levels.

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.

Characterization of food waste generators: A Hawaii case study

Information on food waste disposal and on recycling methods and recycled amounts is reported. Data were obtained from a mail and phone survey of all licensed food establishments in Hawaii conducted in 2004 and 2005. Of 8253 licensed food establishments, 5033 completed surveys. It was found that relationships exist between food establishment size (measured by the number of meals served per day or the number of employees) and the amount of food an establishment recycled; establishment type and recycling behavior; and establishment type and amount recycled. The amount of food waste recycled in the state of Hawaii was estimated to be 264,000 L/day and annual food waste generation was estimated to be 336,000 tonnes.

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.