The on-going COVID-19 pandemic highlights the severe health risks posed by deep submicron sized airborne viruses and particulates in the spread of infectious diseases. There is an urgent need for the development of efficient, durable and reusable filters for this size range. Here we report the realization of efficient particulate filters using nanowire-based low-density metal foams which combine extremely large surface areas with excellent mechanical properties. The metal foams exhibit outstanding filtration efficiencies (>96.6%) in the PM0.3 regime, with potentials for further improvement. Their mechanical stability and light weight, chemical and radiation resistance, ease of cleaning and reuse, and recyclability further make such metal foams promising filters for combating COVID-19 and other types of airborne particulates.

The magnetic properties of cobalt metal nanowires grown by electrodeposition in porous membranes depend largely on the synthesis conditions. Here, we focus on the role of electrolyte additives on the...

This paper presents key lessons learned from hundreds of field missions for assessing the condition of HRSGs at sites around the world. These involved field inspections, root cause of failure analyses and performance assessments on HRSGs of nearly every design, fuel type and operating mode. Statistics on degradation and failure risk areas are presented. Analysis techniques used in both preparing for field work and in assessing field examination results are also discussed. Trends in the evolution of the principal damage mechanisms over the years are examined, and predictions of future problem areas are considered with a view to guiding asset management actions. The impact on HRSG integrity of changes in unit designs, such as the move to flexible operation in response to the increasing contribution from renewables, is also assessed, and likely future trends are outlined. The use of qualitative and quantitative risk-based methods is also discussed and compared to the use of condition-based inspection methods as a basis for a fleet wide management strategy. A case study including a large IPP with several generating assets in its portfolio is presented and the most cost-effective method with respect to current corporate strategy is discussed. Recommendations for fleet management strategies are made.

Reducing the minimum load at which a unit can reliably operate is one method to manage changes in market demands and avoid inherent concerns over frequent on and off cycling. For this reason, it is now becoming common practice for plants to develop new lower minimum load levels that are well below conventional targets provided when the unit was first commissioned. For many plants, the criteria for successful operation were not based on optimizing minimum load levels. In fact, most conventional steam plants were commissioned during an era when full base load operation was expected throughout the life of the plant. Base load availability was the key driver not parameters that promoted unit flexibility. As a result, there are opportunities for plants to lower minimum load levels, but it is important for owners to understand the trade-offs and risks that come with such operation. TG Advisers (Turbine - Generator) and Tetra Engineering (Boiler) partnered on an analytical assessment and process simulation for a US site with four vintage boilers and steam turbines, the boilers having been converted from coal to gas-firing some years earlier. The boilers were modeled at different load points using boiler and power plant process simulation software. Key issues analyzed were superheat steam temperature, stability of natural circulation, and maintenance of minimum flow velocities. Secondary factors included cold end condensation and the potential for accumulation of dissolved solids in the circuit. Utilizing the results of Tetra’s boiler model, TGA completed off-design modeling and calculations for the steam turbine and balance of plant equipment. Examples of primary interest was the impact of the predicted steam conditions and superheat, resulting thermal transient cycles, and LP blading concerns influenced by moisture content and back pressure control. Finally, balance of plant equipment was reviewed to ensure acceptable operating points for key equipment such as boiler feed pumps, feedwater heaters, and hood spray systems. Following computer simulations, a plant testing plan was developed, and plant testing was completed. The paper will review analytical predictions and actual plant testing as well as overall lessons learned from the project. Through these analytical and testing efforts the minimum load was reduced from the current practice of 65 MW to 31 MW.