Rice Straw Smoke Generation System for Controlled Human Inhalation Exposures

A unique burner system was designed for the purposes of exposing human subjects to rice straw smoke under highly controlled conditions. The system burns individual straws and has produced particle concentrations up to 900 w g m m 3 in a temperature- and humidity-controlled exposure chamber. Burner operation is fully automatic and programmable. Ignition is by radiant heating in a manner similar to the field. Particle concentration is controlled by the firing interval between straws and by the ratio of burner outlet flow mixing with the main purified air supplied to the exposure chamber. Steady-state particle concentrations are achieved within 5 min from start. Repeatability of particle concentration is excellent at the two exposure levels used, 200 and 500 w g m m 3 . Measurements of particle size distributions suggest that approximately 80% of mass is in the size fraction below 1 w m. Although particle concentrations are controlled at target levels with good precision, emission factors are higher than achieved with similar material in wind tunnel and field experiments. Further characterization of particulate matter is needed to determine if higher emission factors are associated with changes in particle composition and morphology that may influence exposure results.     

Development of a bioprocess combined with membrane technology for the treatment and recycling of textile effluent

A mixed culture of dye-decolorising Pseudomonas spp. was immobilised on polyurethane foam, and used in a bench-scale continuous culture bioreactor to treat textile effluent for colour removal. The provision of soluble wheat starch (0.2% w/v) to the culture medium promoted growth of biomass and enhanced decolorisation of effluent in the bioreactor. The bioprocess was further combined with membrane filtration technology to improve the quality of treated effluent. The treated effluent showed 90, 82 and 60% reduction in COD, BOD₅ and toxicity levels, respectively, and had potential for re-use in dyeing processes. The colour difference of the cotton fabrics dyed using the treated effluent samples compared to those dyed using normal supply water was found to be industrially acceptable. The described process could improve treatment efficiency and allow water recycling within the textile factory.     

Deterministic and stochastic Petri net models of protection schemes

The authors establish the relevance of Petri net modeling to protection studies. They illustrate how the different Petri net models capture the information that is of importance to both qualitative and quantitative evaluation of protection schemes. The marked Petri nets allow one to evaluate the qualitative performance measures of conservativeness, safeness, and properness. Time Petri nets are able to represent the timing parameters of protection schemes, and serve as a tool for the establishment of relationships between these parameters, in order that the coordination between primary and backup protection is ensured. An alternative means of representing timing information is the timed Petri net, which is useful in the computation of the cycle times of the operational cycles of protection schemes. Stochastic Petri nets adequately represent the stochastic nature of protection. Their advantage over simulation techniques as a means of computing the mean sojourn time and the steady-state probability of occupancy of each state of the protection scheme is demonstrated     

Salt recovery from agricultural drainage water using a liquid film solar-assisted concentrator – Simulation and model validation

Salt management in irrigated agriculture is critical to the economies of the San Joaquin Valley of California and many other areas around the world. Purified salts can be recovered as marketable products through fractional crystallization following concentration of final stage drainage water from integrated on-farm drainage management systems. To obtain recovered salt and use as a commercial product, new systems which can perform with higher efficiency and lower environmental impact than solar evaporation basins or solar ponds that have previously been used for the final stage are in need of development. For this purpose, a number of solar-assisted brine concentration concepts have been explored, including an open liquid film-type using a tilted evaporation surface described here. Model performance was conceptually evaluated and then experimentally verified.A transient model was developed from energy and component mass balances and employed constitutive heat and mass transfer relationships from various other sources for simulating concentration of agricultural drainage water using a liquid film solar-assisted concentrator.Measured maximum evaporation rate and productivity were between 1.3 and 1.5 kg m⁻² h⁻¹, and 80 kg m⁻² over a 7 day experimental period respectively which was about a third better performance compared with a shallow basin horizontal concentrator. Measurements were in good agreement with model predictions: within 2 °C at the peak and 4 °C at the lowest evaporation, and 0.2 kg m⁻² h⁻¹ for evaporation rates during the peak evaporation periods of the day when compared with independent data sets. Cumulative evaporation rates were from 75 to 85 kg m⁻² for the tilted concentrator model and 60 to 65 kg m⁻² for the horizontal concentrator model after 7 days. The tilted concentrator yielded productivity and efficiency that were 33% higher than the horizontal concentrator according to the experimental result for the same period and location.     

Influence of rotor structural dynamics representations on the electrical transient performance of FSIG and DFIG wind turbines

An assessment of the impact that the representation of rotor structural dynamics has on the electrical transient performance of fixed‐speed induction generators (FSIGs) and doubly fed induction generators (DFIGs) wind turbines is presented. A three‐mass model that takes into account not only the shaft flexibility but also the blade flexibility in the structural dynamics is developed and used to derive an effective two‐mass model of the drive train dynamics, which represents the dominant natural frequency of vibration of the rotor structure. For the purposes of this investigation, the dynamic performance of both FSIG and DFIG wind turbines is evaluated during electrical transients such as a three‐phase fault in the network. The studies are conducted in the software code Bladed, where a detailed representation of the structural dynamics is used to derive the three‐mass model and the effective two‐mass model. Simulation results which illustrate how these representations of the rotor dynamics affect the response of the wind turbine during the fault are presented and discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Energy efficiency as a resource in the ISO New England Forward Capacity Market

ISO New England, which oversees New England’s bulk electric power system and wholesale electricity markets, recently established a Forward Capacity Market (FCM) that will pay suppliers to ensure sufficient capacity is available to meet future peak loads. Under the FCM, ISO New England projects the needs of the power system 3 years in advance and then holds an annual auction to purchase the resources necessary to satisfy the future regional requirements. This market is groundbreaking in that it was the first to allow energy efficiency and other demand resources to compete directly with generators. In the first auction, held in February 2008, demand resources contributed substantially to eliminating the need for new generating capacity in the near term and to providing low-cost resources to the region’s ratepayers. Two additional successful auctions have now been held. Participating in the FCM requires a considerable and complex bid, financial assurance, and claim activities. Meeting new intensive measurement, tracking, and verification requirements adds new costs. For efficiency portfolio administrators, participation raises policy questions regarding ownership of capacity credits, appropriate disposition of revenues, increasing emphasis on peak savings, and whether traditionally short-term budget cycles should change to enable the longer-term planning necessary to bid resources several years into the future. On the other hand, revenues from the FCM can provide needed funding for additional efficiency investments. This paper describes the FCM, examines the experience and trade-offs involved in participating for efficiency programs, and reviews the benefits of such participation for the program and the region, including the positive value from increased exposure of the part that efficiency can play in our energy mix.     

A model of PV generation suitable for stability analysis

This paper describes a model of photovoltaic (PV) generation suitable for studying its interactions with the power system. Experimental results suggest that the maximum power point tracking part of the control system of the PV generator dominates the dynamic behavior of the system. These experimental results are used to develop and validate the proposed model. It is shown that the model accurately reflects the behavior of the generator following both small and fast changes in irradiance and AC grid voltage. The proposed model is designed to be integrated in a dynamic simulation program.     

Prediction of flicker produced by wind turbines

Electrical flicker is a measure of voltage variations which may cause disturbances to consumers. Flicker is caused by both generators and loads connected to the network. This paper discusses the various issues which affect electrical flicker from wind turbines, and describes the development of a software tool capable of predicting, at the design stage, the flicker which would be produced by a wind turbine, or by a wind farm of similar turbines, on a particular network. The paper describes the modelling of the physical dynamics of the wind turbine and the turbulence in the wind which drives it, the electrical dynamics of the generator, and the network itself with various types of embedded consumer loads. Measurements carried out on two different 1 MW wind turbines have been used to validate the models. Copyright © 1998 John Wiley & Sons, Ltd.     

Preparation of transmission electron microscopy cross-section specimens of crack tips using focused ion beam milling

The preparation of transmission electron microscope (TEM) thin foil specimens from metal alloys containing cracks is usually thwarted by the difficulty in preventing preferential erosion of material along the flanks and at the tips of cracks. Recent developments in focused ion beam (FIB) micromachining methods have the potential to overcome this inherent problem. In this article we describe the development of new procedures, one using FIB alone and the other using a combination of FIB with more conventional ion milling to generate TEM specimens that largely retain the microstructural information at stress corrosion cracks in austentic alloys. Examples of corrosion product phase identification and interfacial segregation are included to verify that detailed information is not destroyed by ion bombardment during specimen preparation.     

Influence of Tower Shadow and Wind Turbulence on the Performance of Power System Stabilizers for DFIG-Based Wind Farms

The aim of the paper is to demonstrate the way in which mechanical power variations, due to tower shadow and wind turbulence, influence control performance of power system stabilizer (PSS) loops for doubly-fed induction generators (DFIGs). The PSS auxiliary loops are applied on a specific DFIG control scheme, the flux magnitude and angle controller (FMAC). However, since the PSS signal is applied at the output of the basic controller, the PSS performance characteristics displayed are deemed typical for DFIG control schemes in general. The relative capabilities of PSS controllers based on stator power, rotor speed, and network frequency, when the DFIG turbine is subjected to aerodynamic torque variations, are investigated via simulation studies. A two-generator aggregate model of a wind farm is introduced, which enables the influence of tower shadow and wind turbulence on both an individual turbine and on the overall wind farm itself to be assessed.