Energy and economic analysis of traditional versus introduced crops cultivation in the mountains of the Indian Himalayas: A case study

This study analyzed the energy and economics associated with cultivation of traditional and introduced crops in the mountains of the Central Himalaya, India. The production cost in terms of energy for introduced crops such as tomato (Lycopersicon esculentum) and bell pepper (Capsicum annuum) cultivation was 90,358–320,516 MJ ha⁻¹ as compared to between 19,814 and 42,380 MJ ha⁻¹ for traditional crops within Himalayan agroecosystems. For the introduced crops, high energy and monetary input was associated with human labor, forest resources, chemical fertilizer and pesticides. However, energy threshold/projection for farmyard manure in traditional crop cultivation was 80–90% of the total energy cost, thus traditional crop cultivation was more efficient in energy and economics. During the study, the farm productivity of introduced crops cultivation declined with increasing years of cultivation. Consequently, the energy output from the system has been declining at the rate of −y20,598 to y20,748 MJ ha⁻¹ yr⁻¹ for tomato and y12,072 to y15,056 MJ ha⁻¹ yr⁻¹ for bell pepper under irrigated and rain-fed land use in the mountains, respectively. The comparative analysis on this paradigm shift indicates that more research is needed to support sustainable crop cultivation in the fragile Himalayan environment.     

Harvesting operations and energetics of tall grasses for biomass energy production: A case study

The U.S.A. imports about 50% of its energy needs while Florida imports about 85%. Among the renewable energy sources available, biomass appears promising especially in the southeast which includes Florida because of a favorable environment for production and the available methods to convert biomass to energy. Optimal production of biomass requires the identification and management of high yielding persistent perennial cultivars. Elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spontaneum L.) are two tall grasses that meet these requirements. To optimize the supply of convertible biomass, suitable methods of harvesting the crop must be available. The purpose of this research was to study the feasibility and energetics of harvesting, drying, and baling tall grasses with conventional farm machinery.

A Mathews rotary scythe and a New Holland 849 Auto Wrap large round baler were determined to provide a practical harvesting system for baled biomass averaging 15–27 Mg ha⁻¹. The rotary scythe can be used for harvesting and fluffing or turning a windrow over to expedite drying. This harvesting system requires about 3 kg diesel fuel Mg⁻¹ dry biomass (DB), 25 min of time Mg⁻¹ DB, and a cost of about $10 to 12 Mg⁻¹ DB. Energy requirements of harvesting operations would be about 300–375 MJ Mg⁻¹ DB, and primary energy requirements for production and harvesting are about 1100–1500 MJ Mg⁻¹ DB. For each unit of fossil fuel invested in the total production and harvesting system, 12–15 units would be returned in biomass.     

Biomass equations for determining fractions of European aspen growing on abandoned farmland and some practical implications

A study was conducted in order to construct functions for aboveground biomass of fractions of young European aspens (Populus tremula L.). The constructed functions were designed to be used for predicting the amount of biofuel produced from small areas. Biomass production was estimated in 11 stands of European aspen growing on abandoned farmland. The stands were located in Sweden at latitudes ranging from 65° to 60° N, and their total age varied from 5 to 24 years. A modified “mean tree technique” was used to estimate biomass production; i.e. depending on the plot area size, the number of sampled trees was chosen. The mean total dry weight above stump level for aspen stands was 78 tonnes ha⁻¹ with a range of 14–162 d.w. ha⁻¹. Mean annual increment for the stands was 5.56 tonnes ha⁻¹ year⁻¹ (2.86–9.15). Aspens growing on silt soils produced more than on fine sand soils. In addition to estimating conventional dry weights of trees and tree components, specific leaf area, total surface area and LAI, among other measures, were estimated. The mean LAI was 2.58 and the specific leaf area was 9.4 m² kg⁻¹. Some practical implications are given.     

Accumulation, transfers and dissipation of energy in chir pine forests

Energy stored and net energy fixed at four sites of natural chir pine forest were assessed. Of the total energy stored by the vegetation (3836.6 GJ ha⁻¹) 98.7% was in trees, 0.4% in shrubs and 0.9% in the herb layer. Net energy fixed by the vegetation was 318.5 GJ ha⁻¹ yr⁻¹ of which the shares of tree, shrub and herb layers were 84.7% 0.9% and 14.4%, respectively. The energy capture efficiency (photosynthetic radiation) of the vegetation was 1.07% (0.91% in trees, 0.01% in shrubs and 0.15% in herbs). Of the total transfer of energy to the forest floor through litter fall (142.7 GJ ha⁻¹ yr⁻¹ leaf litter and woody litter accounted for 68.4% and 31.6%, respectively. Energy stored in the above-ground biomass of the trees from 2877 ha or in the net annual above-ground production from 39,903 ha is sufficient to operate a 50 MW generating station for one year. Total biomass and net production from 1 ha of natural chir pine forest is sufficient to meet the energy need of an average household of western Himalaya for 61.1 and 4.4 years, respectively.     

Effect of fertilization on the biomass production of coppiced mixed birch and willow stands on a cut-away peatland

This investigation deals with the biomass production of coppiced mixed birch and willow stands growing on a peat cut-away area at Aitoneva, Kihniö (62°12′N, 23°18′E), Finland. The 16-year-old stands were harvested and left to coppice for 14 years, fertilization experiment (control, PK and wood ash fertilization) with three replications was established after the clear cutting. The mother stands before clear cutting (11,000 stems per hectare on average) were dominated by silver birch (69% of the stem number). After clear cutting the number of stems rose 7-fold to 75 500 stems ha⁻¹. Now the stands were dominated by Betula pubescens with 46% out of the total stem number, the share of B. pendula being only 25% and with Salix spp 29%. At the age of 14 years self-thinning had decreased the stem number to 12,800 stems ha⁻¹. The leafless biomass production of the coppiced stands on the control plots was lower than that of the seed originated mother stands had been during the previous rotation. However, with fertilization the 14-year-old coppiced stands reached the same total production as the 16-year-old mother stands had reached. The foliar phosphorus concentrations showed a severe phosphorus deficiency on the controls. Fertilization increased biomass of the stands considerably. After 14 growing seasons the above-ground leafless dry-mass of the fertilized stands was 61.8 (PK-fertilization) and 61.4 t ha⁻¹ (Ash) and that of the control stands 37.6 t ha⁻¹. A single PK fertilizer application had increased the standing biomass by 24 t ha⁻¹ (64%). Even though fertilization increased biomass production it did not increase nutrient concentrations of wood and bark, but rather decreased them. Fertilization decreased the nitrogen concentrations of leafless above-ground biomass.     

Fermentation properties of agro-residues, leaf biomass and urban market garbage in a solid phase biogas fermenter

The decomposition and gas production pattern of eight unprocessed biomass feedstocks representing annual weeds, leaf litter, agro residues and market wastes were monitored in this laboratory study. Solid phase fermentation was effected with a weekly fed biomass bed sprinkled twice daily with recycled fermentor liquid to initiate and sustain biogas production from the decomposing biomass bed. Fermentors were fed from the top with gradually increasing feed rates to determine maximum feed rates sustainable. Feed rates of 1 g total solids (TS) l⁻¹d⁻¹ was possible which lead to pseudo steady state gas production rates between 0.26–0.98 l l⁻¹ d⁻¹ at specific gas yields of 0.18–0.44 l g⁻¹ TS at 35–75% volatile solids (VS) destruction. Feedstocks such as paper mulberry (Broussenetia), Parthenium, Synedrella and urban garbage lost >50% VS in 30 d while paddy straw, bagasse and sugarcane trash exhibited lower VS loss (≥35%) in this period. During decomposition, bulky biomass feedstocks underwent compaction and obviated the need for a pretreatment step. Bulk densities rose manifold to reach between 150–350 g l⁻¹ within 20 d. A higher decomposition rate, process optimization and use of pre-compacted feedstocks have the potential to increase the feed rates (0.96–1.93 g TS l⁻¹d⁻¹), quantity of feedstock held in the reactor as well as gas production rates. The current gas production rates and space economy in these fermentors compare well with Indian cattle dung fermentors (0.3–0.5 l l⁻¹ d⁻¹) and is attractive.     

Effect of coppicing height on the regeneration and productivity of certain firewood shrubs in alkaline soils of North Indian plains

Four shrubs, viz. Hibiscus tiliaceus, Leucaena leucocephala, Vitex negundo and Sesbania sesban, were evaluated for their performance as firewood crops in coppiced stands of varying cutting heights (15, 30 and 45 cm) in repeated annual harvests (4) on alkaline soils of the North Indian plains. The dry wood yield of Leucaena and Sesbania ranged between 22.9–42.6 and 9.9–18.0 tonnes ha⁻¹ year⁻¹, respectively. Leucaena showed progressive increases in yield from coppiced stumps up to the 4th harvest while Sesbania showed a reduction after the third harvest mainly due to the high degeneration (60%) of coppiced stumps. Degeneration was low (<10%) in Leucaena and Vitex. The coppicing heights generally did not show any significant effect on the growth and productivity. The number of coppice shoots per stump increased with stump height and production of coppice shoots was maximum in Vitex and minimum in Leucaena. The average diameter of coppice shoots tended to decrease with increasing coppicing height of the stumps.     

Energy feedstock characteristics of willow and hybrid poplar clones at harvest age

Woody biomass feedstock produced from willow and hybrid poplar can be converted into bioenergy via thermochemical and biochemical processes. Variation in key properties that relate to the quality of biomass feedstock and determine its value for energy conversion were determined at rotation age (3 years), in 30 willow and seven hybrid poplar clones, grown in a short-rotation intensive culture (SRIC) system in central NY. Substantial clonal variation in the concentrations of nitrogen (2.9–5.0 gkg⁻¹), phosphorus (0.4–0.8 gkg⁻¹) potassium (1.2–2.4 gkg⁻¹), sodium (0.09–0.20 gkg⁻¹), calcium (3.9–8.9 gkg⁻¹), magnesium (0.2–0.6 gkg⁻¹), ash (13.2–27.2 gkg⁻¹) and bark percentage (3.6–8.1%) was found in stem (bark+wood) samples. A lower amount of variation was documented for specific gravity (0.33–0.48 gcm⁻³) and percent moisture (49–56%). Bark had a higher concentration of inorganic elements and ash, relative to wood. Willow clones as a group had a higher specific gravity, bark percentage and calcium concentration relative to hybrid poplar clones, which had a higher potassium concentration. The two groups were similar in terms of the concentrations of other elements and ash. Clonal variation in these characteristics present opportunities for manipulating feedstock quality through selection, breeding and plantation management.     

Agronomic characteristics of US 72-1153 energycane for biomass

Biomass production and plant quality vary between plant species and morphological components of a plant. The purpose of this two-part experiment was (1) to study the influence of energycane [Saccharum sp. (L.) ‘US 72-1153’] harvest treatments (6) on dry biomass yield and (2) monitor changes in quantity and quality of plant components with increased plant height. Treatments for Part 1 determined the influence of plant height when harvested at 1.2, 2.5, and 3.7 m, mature stage in October (4.9 m, in flower), mature stage in December (4.9 m, in flower), and additional treatment harvested in October, which received half the total N (168 kg ha⁻¹) on dry biomass yield from 1986 to 1989. Part 2 treatments were to monitor changes in quantity and quality (crude protein and in vitro organic matter digestion) of plant components (green leaf, dead leaf, and stem) at 0.6 m plant height increments to a final height of 4.3 m during 1986 and 1987. Treatments from both parts of the study received 25 kg P ha⁻¹ and 93 kg K ha⁻¹ in one application and 336 kg N ha⁻¹ yr⁻¹ in single or split applications applied prior to growth of each harvest. Plants repeatedly harvested at the 1.2 m height (Part 1) and mature stage produced a 4-year average yield of 10 and 48 Mg ha⁻¹ yr⁻¹ dry biomass, respectively and decreased in dry biomass yield 89% (1.2 m harvest) and 53% (mature harvest) between years 1 and 4. The stem (1986 and 1987) and dead leaf (1986) plant components increased quadratically as plant height increased, and green leaf decreased from 70% (0.6 m) to 17% (4.3 m height). The crude protein concentration decreased 51% (green leaf) and 81% (stem) and in-vitro organic matter digestion decreased 54, 32, and 34% for dead leaf, green leaf, and stem, respectively as plant height increased from 0.6 to 4.3 m. These data indicate that harvest management is an important factor for energycane biomass yield, ratoon-crop success and plant quality if biomass is used as a methane source.     

Effects of nutrient supply and soil cadmium concentration on cadmium removal by willow

This investigation studied the effect of an increased biomass production as a result of fertilization and an elevated Cd concentration in the topsoil on concentration and amount of Cd in two clones of Salix (81090 and 78183). The experiment was conducted over a three year period using 200-dm³ lysimeters filled with clay soil. A liquid fertilizer containing all essential macro- and micronutrients in balanced proportions by weight was applied at two rates according to growth. The lower rate corresponded to 0, 20 and 20 kg N ha⁻¹ during years 1, 2 and 3, respectively, while the higher rate was 30, 60 and 60 kg N ha⁻¹ for the same period. The Cd levels in the topsoil were an initial content of 0.3 mg Cd (kg dw soil)⁻¹ and 0.6 mg Cd (kg dw soil)⁻¹ after addition of CdSO₄.

Biomass production increased significantly due to fertilization. In general, this increase in biomass resulted in a higher Cd amount in the stem. However, the magnitude was small and only statistically significant in some cases, mainly because increased biomass also resulted in a lowered Cd concentration due to an effect of biological dilution. Addition of Cd to the topsoil resulted in higher Cd concentrations and total Cd amounts (concentration×biomass) in the Salix plants. In most cases the increase in total stem Cd amount was 40–80% of the increase in soil Cd concentration, although a directly proportional increase was observed occasionally. Clone 81090 had higher concentrations and total amounts of Cd in the stems than clone 78183, while clone 78183 produced more stem biomass. The leaves had the highest Cd concentrations, but the total amounts of Cd were largest in the stems.     

Quantity and quality of harvestable biomass from Populus short rotation coppice for solid fuel use—a review of the physiological basis and management influences

Woody biomass from poplar and aspen (Populus sp.) short rotation coppice (SRC) has good combustion properties compared to non wood solid bio fuels and fossil solid fuels. This review compiles and discusses relevant literature on fuel quality and yield for Central European conditions. The most problematic quality parameter of woody biomass from Populus SRC is its high water content at harvest time (55–60%). Storing unchipped material on the field during summer is an efficient tool to lower it. In order to control other quality parameters—mainly nitrogen (N), potassium (K) and heavy metal contents but also yield—one has to take into account the physiological background of SRC. Important features are species/clone, age of sprouts, growth pattern, site and nutrient cycling. Maximum mean annual increment (MAI) occurs later than in willows. Therefore rotations should be longer than in willow: at least 6–7 years for poplars and,—due to differences in growth pattern,—10 to 12 years for aspen. Both results in MAIs of 10–12 o.d.t.ha⁻¹ yr⁻¹ and reduced nutrient concentrations due to a lower share of branches and twigs in the harvested biomass. However, with elongated rotations costs rise because yet no automated (and thus cheap) harvest methods for large stem diameters were developed. Although sometimes ignored poplars are demanding concerning site characteristics. Basic requirements are good water (minimum 350 mm rainfall during growing season) and nutrient supplies, deep soils and favourable climatic conditions (average air temperature between June and September at least 14°C). Only aspen are partly suited for poorer conditions. For Populus-SRC in general weed control during establishing phase is essential.     

Soil carbon sequestration beneath hybrid poplar plantations in the North Central United States

Hybrid poplar plantations grown on tilled agricultural lands previously in prairie, sequester significant quantities of soil carbon. Comparisons are made between hybrid poplar plantations and adjacent row crops or mowed grass. Establishing and tending plantations often results in early soil carbon loss, but soil carbon is significantly related (positive) to tree age. Increasing tree age eventually results in a net addition of soil carbon from plantations older than about 6 to 12 years of age. Soil carbon loss under trees occurred most frequently from the surface 30 cm early in the plantation history—evidence that the loss was due to mineralization. Soil carbon gain was most significant in the 30–50 cm layer and was attributed to tree root growth. Soil carbon accretion rate beneath 12- to 18-year-old poplar plantations exceeded that of adjacent agricultural crops by l.63 ± 0.16 Mg ha⁻¹ yr⁻¹. There was a significant crop × soil depth interaction for bulk density with bulk density lower beneath trees in the 0–30 cm layer and higher in the 30–50 cm layer. There was little evidence of carbon trapping of wind-blown organic detritus by tree plantations in the prairie environment.     

Miscanthus sinensis ‘giganteus’ production on several sites in Austria

In Austria it is planned to use Miscanthus sinensis ‘Giganteus’ as a renewable energy source. The influence of site, age of crop and time of harvest on yield, water content, nitrogen content and quality was investigated. In the first year the yield was 0.7 to 2 t dry matter ha⁻¹, in the second year 7.9 to 15.5 t ha⁻¹ and in the third year 17.4 to 24.5 t ha⁻¹. In February of the first year the water content was 40 to 50%, in the second year 34 to 49% and in the third year 24 to 38%. Sufficient precipitation (about 800 mm) in mild climates is required for high yields. On sites with more rain the water content of the plants was higher. Water and nitrogen content decreased significantly during the six week period from January to the end of February. In February of the first year the nitrogen content was 7.8 to 16.6 g kg⁻¹ dry matter, in the second year 3.7 to 6.2 g kg⁻¹ and in the third year 2.6 to 7.5 g kg⁻¹. The calorific value was as high as that of firewood (18 to 19 MJ kg⁻¹ ). The ash content exceeded firewood but was lower than that of straw. By the third year of cultivation 60 to 150 kg N ha⁻¹, 100 to 200 kg K20 ha⁻¹, 10 to 35 kg P₂ O₅ ha⁻¹, 10 to 25 kg MgO ha⁻¹ and 20 to 35 kg CaO ha⁻¹ had to be taken up by the harvest at the end of February.     

Comparative economic analysis of perennial, annual, and intercrops for biomass production

Herbaceous crops may be an important source of renewable energy. Production costs can be more competitive by increasing yields so that overhead costs are applied to more biomass. Most previous economic studies of energy crops have concentrated on the production of switchgrass (Panicum virgatum L.). This study analyzes the biomass yield and economic potential of several high-yielding annual and perennial crops on prime and marginal, sloping land. Crops evaluated were reed canarygrass (Phalaris arundinacea L.) harvested twice per year; switchgrass and big bluestem (Andropogon gerardii Vitman var. gerardii); alfalfa (Medicago sativa L.); and sweet sorghum, forage sorghum [both Sorghum bicolor (L.) Moench], and maize (Zea mays L.). The intercropping of the two sorghum species into reed canarygrass and alfalfa was also analyzed. All crops but alfalfa were fertilized with 0, 70, 140, or 280 kgNha⁻¹, with economic analysis performed assuming 140 kgNha⁻¹. Sorghums were most productive, with more than 16 t of dry matter ha⁻¹. Switchgrass was the highest-yielding perennial crop. Costs per ton of biomass produced were lowest for sorghum, somewhat higher for switchgrass, higher still for big bluestem, and highest for alfalfa and reed canarygrass. Yields per ton for intercropped species were higher than for perennial species but lower than for monocrop sorghum. Costs per ton for intercropped species were less than for either alfalfa or reed canarygrass, but were higher than costs per ton of monocrop sorghum. Although the sorghums had the highest yields, high potential for erosion on sloping soils may preclude their use on these soils.     

Synthesis and characterization of a highly stable amorphous silicon hydride as the product of a catalytic helium–hydrogen plasma reaction

A novel highly stable surface coating SiH(1/p) which comprised high-binding-energy hydride ions was synthesized by a microwave plasma reaction of a mixture of silane, hydrogen, and helium wherein it is proposed that He⁺ served as a catalyst with atomic hydrogen to form the highly stable hydride ions. Novel silicon hydride was identified by time of flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The ToF-SIMS identified the coatings as hydride by the large SiH⁺ peak in the positive spectrum and the dominant H⁻ in the negative spectrum. XPS identified the H content of the SiH coatings as hydride ions, H⁻(1/4), H⁻(1/9), and H⁻(1/11) corresponding to peaks at 11, 43, and 55 eV, respectively. The silicon hydride surface was remarkably stable to air as shown by XPS. The highly stable amorphous silicon hydride coating may advance the production of integrated circuits and microdevices by resisting the oxygen passivation of the surface and possibly altering the dielectric constant and band gap to increase device performance.

The plasma which formed SiH(1/p) showed a number of extraordinary features. Novel emission lines with energies of q·13.6 eV where q=1,2,3,4,6,7,8,9, or 11 were previously observed by extreme ultraviolet spectroscopy recorded on microwave discharges of helium with 2% hydrogen (Int. J. Hydrogen Energy 27 (3) 301–322). These lines matched H(1/p), fractional Rydberg states of atomic hydrogen where p is an integer, formed by a resonant nonradiative energy transfer to He⁺ acting as a catalyst. The average hydrogen atom temperature of the helium–hydrogen plasma was measured to be 180–210 eV versus ≈3 eV for pure hydrogen. Using water bath calorimetry, excess power was observed from the helium–hydrogen plasma compared to control krypton plasma. For example, for an input of 8.1 W, the total plasma power of the helium–hydrogen plasma measured by water bath calorimetry was 30.0 W corresponding to 21.9 W of excess power in 3 cm³. The excess power density and energy balance were high, 7.3 W/cm³ and −2.9×10⁴ kJ/molH₂, respectively. This catalytic plasma reaction may represent a new hydrogen energy source and a new field of hydrogen chemistry.     

Emission factors of wood and charcoal-fired cookstoves

In the developing countries, energy required for cooking often has the biggest share in the total national energy demand and is normally met mostly by biomass. This paper presents the results of experimental studies on emission conducted on a number of traditional and improved cookstoves collected from different Asian countries using wood and charcoal as fuel. The emission factors from this study are comparable to those reported in the literature. In the case of wood combustion, CO₂ emission factor is in the range of 1560–1620 g kg⁻¹. The emission factors for pollutants CO, CH₄, TNMOC and NO_x were in the ranges 19–136, 6–10, 6–9 and 0.05–0.2 g kg⁻¹, respectively. In the case of charcoal combustion, CO₂ emission factor is in the range of 2155–2567 g kg⁻¹. The emission factors for pollutants CO, CH₄, TNMOC were in the ranges 35–198, 6.7–7.8, 6–10 g kg⁻¹, respectively.

Comparison between wood and charcoal fired stoves shows that, CO₂ and CO emission factor values for wood are lower as compared to charcoal. CH₄ and TNMOC emission factors for wood are with the same range as compared to charcoal. Emission factors for NO_x using wood is slightly lower than charcoal. The emission of all the pollutants per unit of useful heat was found to decrease with increasing stove efficiency for both wood and charcoal fired stoves.     

Evaluation of usher wood and karkadeh stem for charcoal in Sudan

Two unusual biomass materials Hibiscus sabdarifja var. sabdariffa (karkadeh) stem and Calotropis procera (usher) wood were investigated in the laboratory as potential raw materials for charcoal making in Sudan. The materials were characterized physically and chemically and despite the low density and high bark-to-wood ratio by volume, good yields and quality of charcoal were predicted. The carbonization trials with a laboratory retort at conditions close to those of field metal kiln gave very good charcoal yields (35% for karkadeh and 38% for usher) with high energy transformation (58% and 62%, respectively). The karkadeh charcoal, except for a somewhat high ash content, was good for domestic uses (79% fixed carbon and 30.3 MJ kg⁻¹ heat value). The usher charcoal was better with respect to fixed carbon (86.5%) and gross heat value (32.4 MJ kg⁻¹ ). Both charcoals were of low density (140–160 kg m⁻³) and further assessment of their economic suitability should be carried out under field conditions. The carbonization by-products were also collected and characterized by means of gas chromatography.     

High temperature rate coefficient for the reaction of O(P) with H2 obtained by the resonance absorption of O and H atoms

The reaction of O(³P) with H₂ has been studied behind reflected shock waves in the temperature range of 1713–3532K at total pressures of about 1.4–2.0 bar by Atomic Resonance Absorption Spectroscopy using mixtures of N₂O and H₂ highly diluted in Ar. The O atoms were generated by the fast thermal decomposition of N₂O and the reaction with H₂ was followed by monitoring the time dependent O and H atom concentrations in the postshock reaction zone. For the experimental conditions chosen, the measured O and H atom concentrations were primarily sensitive to the well-known N₂O dissociation and to the studied reaction and hence its rate coefficient could be deduced. The measured rate coefficient data are fitted by the least-squares method to obtain the following three parameter expression: K₄=3.72×10⁶(T/K)^2.17exp(−4080K/T)cm³ mol⁻¹8⁻, which is in excellent agreement with the recent ab initio calculations for the rate coefficient of this reaction in the overlapping temperature range. The present result is also compared to the experimental results reported by earlier investigators.     

Combustion of ammonium and hydrazine azides

Steady-state combustion of ammonium azide (AA) and hydrazine azide (HA) was studied in a window constant-pressure bomb over a pressure range of 0.1–36 MPa. HA burns three to four times faster than AA over the whole pressure range. The temperature distribution in the combustion wave of AA and HA was measured using 5-μm-thick Π-shaped tungsten-rhenium tape thermocouples. The combustion temperature of both compounds is 240–430 K higher than the temperature calculated for the thermodynamically equilibrium composition of the combustion products due to the presence of large amounts of ammonia (0.97 and 0.87 mol per AA and HA mole, respectively). The burning surface is formed via dissociation of the salts into hydrazoic aicd HN₃ and the parent base. The growth of the surface temperature with pressure is determined by the dissociation enthalpy of the salts. The burning rate of these compounds is determined by heat release in the gas phase. Based on the data obtained on combustion of AA and HA, the kinetic parameters of the HN₃ decomposition reaction occurring in the gas phase were calculated (k = 10^16,26 exp(−19350/T) cm³ mol⁻¹ s⁻¹). An estimate of the burning rate of liquid HN₃ at 0.1 MPa (u = 1.9 g cm⁻² s⁻¹) is given.     

Feasibility of collecting naturally leached rice straw for thermal conversion

The practical application of field or natural leaching to rice straw was evaluated with the goal of improving biomass fuel value. Observations on three rice farms in the Sacramento Valley, California indicated that potassium, chlorine and total ash are leached from rice straw by rainfall regardless of rice variety, grain harvest method, straw arrangement, or stubble length. Leaching of sulfur by natural precipitation was not clearly established. In selected field plots leached straw was successfully collected in spring, even though biomass yields were variable (2.2–3.4 Mgha⁻¹) and equipment had to operate in difficult conditions. Total costs for collecting leached straw on an area basis ($77.07 ha⁻¹) are 31% higher compared to collecting crude straw in the fall ($58.67 ha⁻¹), due to reduced performance of machinery and addition of field curing operations. Analysis of historical rainfall data for the Sacramento Valley revealed that there is an 85% probability of receiving sufficient rainfall (250 mm or more) for substantial natural leaching of straw during the winter period. The available period for mechanized collection of rice straw after the winter period ranges from 0 to 45 days, depending on drying time needed to accomplish favorable field conditions, and planting date of the next crop. The feasibility of spring collection of rice straw could be improved if straw collection equipment were better equipped to operate under wet field conditions. The commercial implementation of natural leaching of rice straw as a strategy to improve fuel quality depends on a combination of factors that include grain harvest and straw collection practices, rainfall intensity and distribution, and field-specific factors.