Sustainable development of the Kamojang geothermal field

Geothermal electricity production in Indonesia began with the operation of a 0.25 MW_e pilot project in Kamojang geothermal field, in 1978. Commercial operation started in 1983, with the commissioning of the 30 MW_e Unit-1 power plant. In 1987, an additional capacity of 110 MW_e was provided by the Unit-2 and Unit-3 power plants. The addition of the 60 MWe Unit-4 power plant in 2008 increased the total generating capacity to 200 MW_e. The 27 years of commercial operation have led to a slight decline in reservoir pressure and temperature within the active production sector. The most recent significant change in the field conditions and performance occurred following the 2008 increase in generating capacity from 140 to 200 MWe. The production decline of individual wells has been relatively low, at an average of 3%/yr. However, the increased rate of steam withdrawal might negatively affect long-term sustainability of energy production at Kamojang unless suitable field management strategies are implemented. In order to stabilize the steam flow, it has been necessary to drill about three make-up wells every 2–3 years. The unbalanced mass extraction, where less than 30% of the produced steam mass can be injected, is a serious concern for long-term reservoir management in Kamojang. The field operator (Pertamina) plans to increase the Kamojang generating capacity from 200 to 230 MWe (Unit 5) and optimize the long-term performance of the Kamojang geothermal resource. The response of the reservoir during the previous three decades is being used to guide reservoir development for the planned increase in production capacity.     

Characteristics and management of the Sumikawa geothermal reservoir, northeastern Japan

The subsurface temperature gradually increases southward in the Sumikawa geothermal field and decreases sharply toward the north. The geothermal reservoir contains a two-phase zone between the cap rock and hot water zone. The target for production was designated in the deep zone, in the high temperature southern area. The production and reinjection areas have been separated to recover thermal energy efficiently during the recycling of reinjection fluid; the wells have been spaced as far apart as possible to reduce well interference. To improve productivity and injectivity, cold-water well stimulation was applied, and this experiment reduced the number of wells required for 50 MW_e power generation.     

Economic feasibility assessment of rice straw utilization for electricity generating through combustion in Thailand

The economic feasibility of biomass based combustion projects of various capacities to generate electricity from rice straw is evaluated for Thailand. For an assumed lifespan of 20 years, rice straw-fueled combustion facilities would generate Net Present Values (NPV) of −3.15, 0.94, 2.96, 9.33, and 18.79 million USD for projected 5, 8, 10, 15, and 20 MW_e plants, respectively. Examining the effects of scale on the cost of generated electricity (COE) over the considered range of capacities indicates that COE varies from 0.0676 USD/kWh at 20 MW_e to 0.0899 USD/kWh at 5 MW_e. By scaling up the power plants, the variations of the financial parameters, namely NPV values, become less sensitive to the critical variables. As an example, if the fuel price, selling price of electricity, and the plant factor change by +36% (31.0 USD/t), −16% (0.0758 USD/kWh), and −14% (5650 h/yr), respectively, the largest scale project is still appealing for investment. Nevertheless, to ensure a secure fuel supply, smaller scale power plants, i.e., 8 and 10 MW_e may be more practicable. A further sensitivity analysis is discussed in terms of the financial feasibility of the projects (i.e., NPV ? 0), and the investment appraisal condition (here, Internal Rate of Return or IRR ? 11%).     

Sustainability analysis of the Ahuachapán geothermal field: management and modeling

The Ahuachapán geothermal field (AGF) is located in north western El Salvador. To date, 53 wells (20 producers and 8 injectors) have been drilled in the Ahuachapán geothermal field and the adjacent Chipilapa area. Over the past 33 years, 550 Mtonnes have been extracted from the reservoir, and the reservoir pressure has declined by more than 15 bars. By 1985, the large pressure drawdown due to over-exploitation of the resource reduced the power generation capacity to only 45 MW_e. Several activities were carried out in the period 1997–2005 as part of “stabilization” and “optimization” projects to increase the electric energy generation to 85 MW_e, with a total mass extraction of 850 kg/s.     

NiSb2 as negative electrode for Li-ion batteries: An original conversion reaction

The study of the electrochemical reaction mechanism of lithium with NiSb₂ intermetallic material is reported here. The nickel diantimonide prepared by classic ceramic route is proposed as possible candidate for anodic applications in Li-ion batteries. The electrochemical characterisation of NiSb₂ versus Li⁺/Li⁰ shows a reversible uptake of 5 lithium per formula unit, which leads to reversible capacities of 500 mAh g⁻¹ at an average potential of 0.9 V. From ex situ XRD and ¹²¹Sb Mössbauer measurements it was shown that during the first discharge the orthorhombic NiSb₂ phase undergoes a pure conversion process (NiSb₂ + 6 Li⁺ + 6e⁻ → Ni⁰ + 2Li₃Sb). During the charge process that follows, the lithium extraction from the composite electrode takes place through an original conversion process, leading to the formation of the high pressure NiSb₂ polymorph. This highly reversible mechanism makes it possible to sustain 100% of the specific capacity after 15 cycles.     

Combustion and NOx emission characteristics of a retrofitted down-fired 660 MWe utility boiler at different loads

Industrial experiments were performed for a retrofitted 660 MW_e full-scale down-fired boiler. Measurements of ignition of the primary air/fuel mixture flow, the gas temperature distribution of the furnace and the gas components in the furnace were conducted at loads of 660, 550 and 330 MW_e. With decreasing load, the gas temperature decreases and the ignition position of the primary coal/air flow becomes farther along the axis of the fuel-rich pipe in the burner region under the arches. The furnace temperature also decreases with decreasing load, as does the difference between the temperatures in the burning region and the lower position of the burnout region. With decreasing load, the exhaust gas temperature decreases from 129.8 °C to 114.3 °C, while NO_x emissions decrease from 2448 to 1610 mg/m³. All three loads result in low carbon content in fly ash and great boiler thermal efficiency higher than 92%. Compared with the case of 660 MW_e before retrofit, the exhaust gas temperature decreased from 136 to 129.8 °C, the carbon content in the fly ash decreased from 9.55% to 2.43% and the boiler efficiency increased from 84.54% to 93.66%.     

Electrolytic Sn/Li2O coatings for thin-film lithium ion battery anodes

Sn/Li₂O composite coatings on stainless steel substrate, as anodes of thin-film lithium battery are carried out in SnCl₂ and LiNO₃ mixed solutions by using cathodic electrochemical synthesis and subsequently annealed at 200 °C. Through cathodic polarization tests, three major regions are verified: (I) O₂ + 4H⁺ + 4e⁻ → 2H₂O (∼0.25 to −0.5 V), (II) 2H⁺ + 2e⁻ → H₂, Sn²⁺ + 2e⁻ → Sn, and NO₃⁻ + H₂O + 2e⁻ → NO₂⁻ + 2OH⁻ (−0.5 to −1.34 V), and (III) 2H₂O + 2e⁻ → H₂ + 2OH⁻ (−1.34 to −2 V vs. Ag/AgCl). The coated specimens are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and charge/discharge tests. The nano-sized Sn particles embedded in Li₂O matrix are obtained at the lower part of region II such as −1.2 V, while the micro-sized Sn with little Li₂O at the upper part, such as −0.7 V. Charge/discharge cycle tests elucidated that Sn/Li₂O composite film showed better cycle performance than Sn or SnO₂ film, due to the retarding effects of amorphous Li₂O on the further aggregation of Sn particles. On the other hand, the one tested for cut-off voltage at 0.9 V (vs. Li/Li⁺) is better than those at 1.2 and 1.5 V since the incomplete de-alloy at lower cut-off voltage may inhibit the coarsening of Sn particles, revealing capacity 587 mAh g⁻¹ after 50 cycle, and capacity retention ratio C50/C2 81.6%, higher than 63.5% and 49.1% at 1.2 and 1.5 V (vs. Li/Li⁺), respectively.     

Evolution of the Wairakei geothermal reservoir during 50 years of production

The Wairakei geothermal field has been under production for more than 50 years. Exploration wells show that the high-temperature and very permeable, productive resource extends over about 12 km² within a greater area of about 25 km² that shows various effects of thermal activity. Up to 2006, 3 km³ of fluid and 2750 PJ of energy had been extracted at an average rate of 5250 t/h and enthalpy of 1130 kJ/kg. Significant production started in 1955 and up to 1978 there was no injection of cooled geothermal fluids. During the first decade of operation a pressure drawdown of up to 20 bars (2 MPa) developed and spread evenly across the reservoir, even though fluid extraction was focused within an area of 1 km² close to the northeastern field boundary. This pressure reduction resulted in widespread boiling and formation of segregated steam zones at the top of the reservoir together with inflow of cooler fluids into its northeastern part via the original natural outflow channels. From 1975 to 1997 pressures in the deep liquid reservoir stabilized at 23–25 bars (2.3–2.5 MPa) below the original pressure, with little change up to the time injection commenced in 1998. This natural pressure support indicates that prior to injection there was substantial recharge, 80% of which is assessed as high-temperature deep inflow. Since 1998 about 30% of the extracted fluids have been injected and reservoir pressures have increased by 3–4 bars (0.3–0.4 MPa). To date, significant returns of injected fluids have not been detected in the production areas. Over the 50 years of operation, temperatures in the main production areas have declined from 250 to 220 °C while deeper production zones toward the western boundary of the reservoir have remained at about 250 °C. A series of deeper makeup wells to maintain future production have been drilled in the high-temperature recharge area. An increasing fraction of injection, both in-field and out-field is planned over the next few years.     

Aluto-langano geothermal field, ethiopian rift valley: physical characteristics and the effects of gas on well performance

This study, which focuses on the Aluto-Langano geothermal field, is part of the ongoing investigations of the geothermal systems in the Ethiopian Rift Valley. Aluto-Langano is a water-dominated gas-rich geothermal field, with a maximum temperature close to 360°C, in the Lakes District region of the Ethiopian Rift Valley. The upflow zone for the system lies along a deep, young NNE trending fault and is characterized by boiling. As a result, the deep upflow zone loses some water as steam and produces a cooler saline shallow aquifer. The high partial pressure of carbon dioxide (about 30 bar in the reservoir) depresses the water table and restricts boiling to deeper levels. The main aquifer for the system is in the Tertiary ignimbrite, which lies below 1400 m. The capacity of the existing wells is close to 7 MW_c; the energy potential of the area is estimated to be between 3000 and 6000 MW_t yr km⁻³, or 10–20 MW_c km⁻³ for over 30 years.     

Reservoir characteristics and development plan of the Oguni geothermal field, Kyushu, Japan

Geothermal power development at the Oguni field, central Kyushu, is planned to begin in the year 2001 with a double flash system generating 20 MW_e. The Oguni reservoir has been delineated by systematic geothermal surveys, well tests and reservoir engineering studies. The fractured reservoir is horizontally layered and divided into northern and southern portions. Both of them have NaCl dominant fluids ranging from 200 to 240°C. The northern reservoir covers a large area including the Takenoyu Fault Zone and has a relatively high permeability (kh≈80–230 darcy-m). By contrast, the southern reservoir covers a relatively small area and has limited transmissivity. The southern reservoir has a higher pressure (1 MPa) than the northern reservoir, indicating little connectivity between them. Based on numerical calculations, as well as the surface topography and environmental aspects, the production and reinjection zones have been separated, and a large part of the necessary fluid will be produced from the northern reservoir along the Takenoyu Fault and a small part will be taken from the southern reservoir. The separated water will be reinjected into the northernmost part of the northern reservoir, in order to prevent a cold sweep problem for production.     

Phosphorus-doped glass proton exchange membranes for low temperature direct methanol fuel cells

Phosphorus-doped silicon dioxide thin films were used as ion exchange membranes in low temperature proton exchange membrane fuel cells. Phosphorus-doped silicon dioxide glass (PSG) was deposited via plasma-enhanced chemical vapor deposition (PECVD). The plasma deposition of PSG films allows for low temperature fabrication that is compatible with current microelectronic industrial processing. SiH₄, PH₃ and N₂O were used as the reactant gases. The effect of plasma deposition parameters, substrate temperature, RF power, and chamber pressure, on the ionic conductivity of the PSG films is elucidated. PSG conductivities as high as 2.54 × 10⁻⁴ S cm⁻¹ were realized, which is 250 times higher than the conductivity of pure SiO₂ films (1 × 10⁻⁶ S cm⁻¹) under identical deposition conditions. The higher conductivity films were deposited at low temperature, moderate pressure, limited reactant gas flow rate, and high RF power.     

Electrochemical properties of Li1.4Al0.4Ti1.6(PO4)3 synthesized by a co-precipitation method

Sub-micron Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) ceramic powder is synthesized by a co-precipitation method which can be applied for mass production. A pure Nasicon phase is confirmed by X-ray diffraction analysis and the primary particle size of the product is 200-500 nm. The sinterability of LATP is investigated and the relative density of 97% reached at a sintering temperature as low as 900 °C for 6 h. The bulk lithium ionic conductivity of the sintered pellet is 2.19 × 10⁻³ S cm⁻¹, and a total conductivity of 1.83 × 10⁻⁴ S cm⁻¹ is obtained.     

The conversion among reactions at Ni-based anodes in solid oxide fuel cells with low concentrations of dry methane

Dry methane with different concentrations is directly fed to solid oxide fuel cells (SOFCs) with a Ni-yttria-stabilized zirconia (Ni-YSZ) anode and a Ni-scandia-stabilized zirconia (Ni-ScSZ) anode. The anode outlet gases are measured in situ by gas chromatography (GC) to study the reactions of dry methane at different current densities. The comparison between the measured open-circuit voltages (OCVs) and theoretical values, the quantitative analysis of components under different current densities and the activation energy analysis of elementary reactions of CH₄ are investigated to identify the types of reactions occurring to methane in SOFCs. It is found that reactions of partial oxidation, CH₄ + 2O²⁻ → CO + H₂O + H₂ + 4e⁻, CH₄ + 3O²⁻ → CO + 2H₂O + 6e⁻, and complete oxidation occur to CH₄ at the Ni-based anodes in sequence while the current density increasing.     

Development program of hot dry rock geothermal resource in the Yangbajing Basin of China

Geothermal energy from hot dry rock (HDR), considered an almost inexhaustible source of “green” energy, was first developed and tested in the 1970s, leading to installations in America, Japan, Britain, France and other countries. In the present work, a liquating rock mass at a depth of 5-15 km in the Tibet Yangbajing region in China was subjected to detailed analysis. The temperature distribution of the geothermal field in the region was determined by the finite element method. The results estimate that the HDR geothermal resource of the Yangbajing region is 5.4 × 10⁹ MW a, representing a huge potential source of HDR geothermal energy for China. Based on detailed research into the continental dynamics of the environment forming the HDR geothermal field of Tibet, along with the tectonic characteristics of the southern slope of Tanggula Mountain and the Dangxiong-Yangbajing Basin, and the magnitude and orientation of the in situ stresses in the region, the design of an arrangement for extracting these HDR geothermal resources is proposed: taking the fault zone nearest the high-temperature liquating rock region as the location of an artificial reservoir, a vertical injection well could be drilled at a low point on the downdip side of the fault, and two dipping production wells drilled higher up. In this way, an artificial reservoir 3 × 10¹¹ m³ in volume would be created: 360 times the volume of the HDR geothermal reservoir in Cornwall, UK, which uses hydrofracturing. An investigation of the reservoir features, including seepage analysis of the heat exchange area, project implementation and investment analysis, indicates that a 10⁴ MW capacity power station with a projected operating life of approximately 100 years could be constructed. An analysis of a geothermal extraction system comprising one injection well and two production wells suggest that a power station of 1000 MW installed capacity could be constructed initially to provide electricity production of 8.64 × 10⁹ kWh per year.     

The effect of irradiance growing on hydrogen photoevolution and on the kinetic growth in Rhodopseudomonas palustris, strain 42OL

The relationship between hydrogen generation and the age of culture was investigated under fed-batch growth conditions. The specific growth rate (μ_e) was determined during the log phase of the growth curve and the μ_eMax was 0.02643 h⁻¹. Boltzmann's sigmoidal regression model was used to determine the specific rate of hydrogen evolution (μH): the maximum was 0.04440 h⁻¹. At low irradiance (36–75 W m⁻²), an inverse relationship was found between μH and I; after increasing the irradiance further, μH reached a plateau (0.00916 h⁻¹). The maximum reactor yield of cumulative hydrogen (4.5 l) was obtained at an irradiance of 320 W m⁻², but the highest hydrogen evolution rate (17.217 ml h⁻¹) was achieved at 500 W m⁻². The light conversion efficiency reached its maximum (6.91%) at the lowest irradiance investigated (36 W m⁻²); when the irradiance increased further, it decreased progressively down to 0.36%.     

Structural,electrical and electrochemical characterizations of SrNb0.1Co0.9O3−δ as a cathode of solid oxide fuel cells operating below 600 °C

SrNb_0.1Co_0.9O_3−δ (SNC) perovskite oxide has been prepared by high-energy ball milling followed by calcination at 1100 °C. According to oxygen temperature-programmed desorption and thermogravimetry analysis results, highly charged Nb⁵⁺ successfully stabilizes the perovskite structure to avoid order-disorder phase transition. The electrical conductivity reaches 550 S cm⁻¹ at 300 °C in air and as high as 106 S cm⁻¹ under P(O₂) = 1 × 10⁻⁵ atm at 900 °C. The high electrical conductivity is beneficial in improving the charge-transfer process for the oxygen reduction reaction on the cathode. Based on the defect chemical analysis, the Nb-doping in SrCoO_3−δ perovskite facilitates the formation of Co²⁺, which increases oxygen nonstoichiometry and, subsequently, the mixed valence of [Co²⁺]/[Co³⁺] under lower oxygen partial pressure. A relatively low thermal expansion coefficient of 19.1 × 10⁻⁶ K⁻¹ in air was achieved. All above properties show SNC to be a promising cathode material in the practical application of low-temperature solid oxide fuel cells.     

Developing a statistical model to predict hydrogen production by a mixed anaerobic mesophilic culture

Optimizing the hydrogen (H₂) yield at several initial pH conditions in a mixed batch anaerobic mesophilic culture fed with glucose and linoleic acid (LA) was performed using a three factor three level Box–Benkhen design (BBD). Based on the BBD approach, a statistical model was developed to predict the H₂ yield. The variables considered for the experimental design were the LA concentration, the initial pH and the number of times glucose was added to the culture. The D-optimality method predicted a maximum H₂ yield of 3.49 mol H₂ mol glucose⁻¹ for cultures fed 1.9 g l⁻¹ LA, maintained at an initial pH of 5.15 and received 1.79 glucose additions. The response outcome (H₂ yield of 3.38 ± 0.22 mol mol glucose⁻¹) at the nearest setting of the experimental factors (2.0 g l⁻¹ LA, an initial pH of 5.0 and two glucose additions) was 3.3% less than the predicted maximum value. The model provides a useful approach for predicting H₂ production when H₂ consumers are inhibited in mixed batch anaerobic cultures.     

Kinetics of oxygen reduction reaction on Corich core-Ptrich shell/C electrocatalysts

The nanostructured Co_{rich core}-Pt_{rich shell}/C electrocatalysts were prepared by combining the thermal decomposition and the chemical reduction methods. The particle size of homemade Co_{rich core}-Pt_{rich shell}/C analyzed by TEM was significantly greater than that of Pt grain size calculated from the XRD data due to the existence of Co in core. The mass activity and specific activity of oxygen reduction reaction (ORR) at the overpotential (η) of 0.1 V were 6.69 A g⁻¹ and 1.51 × 10⁻⁵ A cm⁻² for Pt/C, and 10.22 A g⁻¹ and 2.73 × 10⁻⁵ A cm⁻² for Co_{rich core}-Pt_{rich shell}/C in 0.5 M HClO₄ aqueous solution at 25 °C. The Tafel slopes of ORR on Pt/C and Co_{rich core}-Pt_{rich shell}/C electrocatalysts were obtained as 64 and 67 mV dec⁻¹ at a lower η (50–100 mV), and 116 and 110 mV dec⁻¹ at a higher η (120–200 mV). The exchange current densities of ORR on Pt/C and Co_{rich core}-Pt_{rich shell}/C evaluated based on the higher Tafel slope regions were 6.76 × 10⁻⁵ and 9.21 × 10⁻⁵ A cm⁻², respectively. The experimental results indicated that the ORR on Co_{rich core}-Pt_{rich shell}/C electrocatalyst in 0.5 M HClO₄ aqueous solution was a four electron transfer mechanism and first order with respect to the dissolved oxygen.     

Gallium (III) sulfide as an active material in lithium secondary batteries

In an attempt to identify an active material for use in lithium secondary batteries with high energy density, we investigated the electrochemical properties of gallium (III) sulfide (Ga₂S₃) at 30 °C. Ga₂S₃ shows two sloping plateaus in the potential range between 0.01 V and 2.0 V vs. (Li/Li⁺). The specific capacity of the Ga₂S₃ electrode in the first delithiation is ca. 920 mAh g⁻¹, which corresponds to 81% of the theoretical capacity (assuming a 10-electron reaction). The capacity in the 10th cycle is 63% of the initial capacity. Ex situ X-ray diffraction and X-ray absorption fine structure analyses revealed that the reaction of the Ga₂S₃ electrode proceeds in two steps: Ga₂S₃ + 6Li⁺ + 6e⁻ ? 2Ga + 3Li₂S and Ga + xLi⁺ + xe⁻ ? Li_xGa.     

Li2MSiO4 (M = Fe and/or Mn) cathode materials

Two iso-structural end members of the family of orthosilicates, i.e. Li₂MSiO₄ (M = Mn and Fe) and their solid solutions, were prepared and electrochemically characterized for potential use in Li-ion batteries. Due to the low specific conductivity (∼5 × 10⁻¹⁶ S cm⁻¹ for Li₂MnSiO₄ and ∼6 × 10⁻¹⁴ S cm⁻¹ for Li₂FeSiO₄ at room temperature), small particles in an intimate contact with a conducting phase (i.e. carbon) are needed. Li₂MSiO₄/C composites (M = Mn and/or Fe) prepared by the Pechini synthesis generally leads to 30–50 nm large particles embedded in a carbon matrix. The amount of carbon in the composite is close to 10 wt.% for the Li₂FeSiO₄/C composite and slightly more than 5 wt.% for the Li₂MnSiO₄/C composite. In situ XRD experiment confirms a structural collapse of Li₂MnSiO₄ and the observed structural stability is completely different for Li₂FeSiO₄, which undergoes a fully reversible two-phase transition. Solid solutions between Li₂MnSiO₄ and Li₂FeSiO₄ in principle lead to higher capacities (>1e⁻ per transition metal is feasible). For a long-term operation the cut-off voltage should be properly chosen. Electrochemical characterisation and in situ XRD experiments suggest the use of cut-off voltage close to 4.2 V.