PADDLE MIXER-EXTRUSION REACTOR FOR TORREFACTION AND PYROLYSIS

This work is focused on the fundamental understanding and the development of paddle mixer reactors (or modified screw augers). This work will contribute to the effort of the thermal conversion of biomass and wastes. We developed and studied two paddle systems (i) 25-mm lab-scale (up to 1 kg/hr) and (ii) 101-mm pilot-scale (up to 100 kg/hr). Thermal behavior of the two systems was studied and it was estimated that the lab-scale system has a high heating rate of up to 530 °C/s. Residence times were thoroughly measured and were determined as a function of rotation frequency and volume fraction. We also determined the specific process energy requirements and the specific heat of the material. Extensive pyrolysis experiments were carried out with many types of biomass. It was found that solid/liquid yields were comparable to those measured in circulating fluidized bed at NREL. Modification of the pilot-scale system is required to enhance the mass flow rates and the heating rate. Fiber and plastic waste blends were thoroughly investigated in a mixture of 40% plastic and 60% fiber. Extensive torrefaction experiments were carried out and thermal and mechanical properties of the torrefied material were measured and correlated with mass loss. Degradation reaction of waste blends was modeled using a first-order reaction. Excellent fit between the experimental and modeling results was obtained. Activation energy and pre-exponential factors were determined. One major finding was that the paddle mixer significantly increased the homogeneity of the waste blend and it is further increased as the size of the material reduces. Density was measured and found that at a density of ~1200 kg/m3, the water intake was 0.7% after 30 days of immersion in water. Extensive grinding study was carried out with these torrefied waste blends and the grinding energy behavior was found similar to that of PRB coal. Heat content was measured, and it was shown that the initial heat content is ~30 MJ/kg and as the torrefaction process proceeds the value increases to ~35 MJ/kg at ~51% mass loss. Combustion experiments were carried out and showed that with the reduction of volatile matter (due to thermal degradation) the combustion time has increased

Chlorine removal from U.S. solid waste blends through torrefaction

The amount of solid waste generated annually is increasing around the world. Although the waste has a high calorific value, one major obstacle that may prevent it from becoming a feedstock for power applications is the existence of polyvinyl chloride (PVC), which causes corrosion and emission issues after combustion due to its high chlorine content. Torrefaction is known to release hydrochloric acid; thus, it has been applied in this study for the reduction of chlorine from potential waste feedstocks. Fiber-plastic (60-40%) waste blends, with different chlorine content levels, as well as PVC were used in the current study. Torrefaction was conducted at 400 °C. Chlorine and heat content were measured. Experimental results showed that organically bonded chlorine was reduced during torrefaction as a function of mass loss. The chlorine removal efficiency was only dependent on temperature and residence time, not chlorine level. The heat content of the sample increased with mass loss up to a maximum of ~34 MJ/kg at ~45% mass loss. It was also observed that at ~30% mass loss, the organic chlorine content per unit heat content reduced by ~90%, while the heat content was ~32 MJ/kg, and ~90% energy was retained

Properties of torrefied U.S. waste blends

Power generation facilities in the U.S. are looking for a potential renewable fuel that is sustainable, low-cost, complies with environmental regulation standards and is a drop-in fuel in the existing infrastructure. Although torrefied woody biomass, meets most of these requirements, its high cost, due to the use of woody biomass, prevented its commercialization. Industrial waste blends, which are also mostly renewable, are suitable feedstock for torrefaction, and can be an economically viable solution, thus may prolong the life of some of the existing coal power plants in the U.S. This paper focuses on the torrefaction dynamics of paper fiber-plastic waste blend of 60% fiber and 40% plastic and the characterization of its torrefied product as a function of extent of reaction (denoted by mass loss). Two forms of the blend are used, one is un-densified and the other is in the form of pellets with three times the density of the un-densified material. Torrefaction of these blends was conducted at 300°C in the mass loss range of 0-51%. The torrefied product was characterized by moisture content, grindability, particle size distribution, energy content, molecular functional structure, and chlorine content. It was shown that although torrefaction dynamics is of the two forms differs significantly from each other, their properties and composition depend on the mass loss. Fiber content was shown to decrease relative to plastic upon the extent of torrefaction. Further, the torrefied product demonstrates a similar grinding behavior to Powder River Basin (PRB) coal. Upon grinding the fiber was concentrated in the smaller size fractions, while the plastic was concentrated in the larger size fractions

Direct evidence of nuclear Argonaute distribution during transcriptional silencing links the actin cytoskeleton to nuclear RNAi machinery in human cells

Mammalian RNAi machinery facilitating transcriptional gene silencing (TGS) is the RNA-induced transcriptional gene silencing-like (RITS-like) complex, comprising of Argonaute (Ago) and small interfering RNA (siRNA) components. We have previously demonstrated promoter-targeted siRNA induce TGS in human immunodeficiency virus type-1 (HIV-1) and simian immunodeficiency virus (SIV), which profoundly suppresses retrovirus replication via heterochromatin formation and histone methylation. Here, we examine subcellular co-localization of Ago proteins with promoter-targeted siRNAs during TGS of SIV and HIV-1 infection. Analysis of retrovirus-infected cells revealed Ago1 co-localized with siRNA in the nucleus, while Ago2 co-localized with siRNA in the inner nuclear envelope. Mismatched and scrambled siRNAs were observed in the cytoplasm, indicating sequence specificity. This is the first report directly visualizing nuclear compartment distribution of Ago-associated siRNA and further reveals a novel nuclear trafficking mechanism for RITS-like components involving the actin cytoskeleton. These results establish a model for elucidating mammalian TGS and suggest a fundamental mechanism underlying nuclear delivery of RITS-like components

APPLICATION OF SPATIAL LIGHT MODULATORS FOR GENERATION OF LASER BEAMS WITH A SPIRAL PHASE DISTRIBUTION

Subject of Research. This paper discusses numerical simulation of spiral beams. Spiral beams have been experimentally obtained with the use of liquid crystal spatial light modulators (LCD SLM). The ability of dynamical change for the laser beam parameters has been studied. Method. Spiral beams are traditionally obtained by means of static masks defining the amplitude and phase distribution of the beam. The paper deals with modernized method with the use of two LCD SLMs. Modulators form separately the amplitude and phase distribution of the laser beam. Main Results. Numerical modeling of space spiral beams with different amplitude and phase characteristics has been carried out with the use of VirtualLab 5.0 software package manufactured by LightTrans GmbH. Simulation results are compared to the results of a natural experiment. Experimental results are in good agreement with computer simulation. It is shown that LCD SLMs application gives the possibility for dynamical change of the spiral beam parameters, their structure and the dependence of rotation angle on the distance. Distribution phase inversion leads to a change in the rotation direction of the laser beam and, therefore, to a change in the direction of its orbital angular momentum. Practical Relevance. The use of spatial modulators makes it possible to change dynamically the beam parameters, including rotation direction change. The results can be applied for solution of problems related to laser manipulating of microparticles, as well as the problems of determining the phase inhomogeneities of transparent objects

Torrefied plastic-fiber fuel pellets as a replacement for fossil fuels — a case study life cycle assessment for Green Bay, Wisconsin, USA

Purpose: The commercial-scale production of torrefied plastic-fiber fuel pellets from waste plastics and waste fibers may offer a viable alternative to fossil fuel–based energy. In this study, the environmental impact of fuel pellets produced and consumed in Green Bay, Wisconsin, USA is evaluated and compared to the status quo of grid energy production from fossil fuels (i.e., coal or natural gas). Methods: A cradle-to-grave life cycle assessment was conducted using a functional unit of 1 kWh of energy produced using torrefied plastic-fiber fuel pellets versus production of energy from coal or natural gas. Regional data along with relevant manufacturing data was used to inform the inventory of the production of the torrefied fuel pellets, which are manufactured using waste fibers and waste plastics sourced from within 5 km of the torrefaction facility and consumed within 50 km of the facility. Since fuel pellets are produced from waste inputs and contain biogenic carbon sources, impacts were assessed with/without credit for biogenic carbon and with/without the burden of the torrefaction inputs. Results and discussion: The production of 1 kWh of energy using torrefied plastic-fiber fuel pellets was determined to produce between 0.303 and 0.757 kg CO2 eq emissions due to combustion and between 0.062 and 1.105 kg CO2 eq additional emissions as a result of the manufacturing process, with the ranges dependent upon the allocation method selected. Under a burden-free allocation due to waste materials used as inputs, along with a credit for biogenic carbon emissions, the system produces 0.365 kg CO2 eq per 1 kWh of energy; however, under a full-burden allocation with no credit for biogenic carbon emissions, 1.862 kg CO2 eq per 1 kWh of energy is produced. This highlights the differences between allocation scenarios and role of credits for biogenic carbon emissions when evaluating systems. Conclusions: The usage of torrefied plastic-fiber fuel pellets produced using waste plastics and fibers is a reasonable alternative to the status quo of waste disposal coupled with the production of grid energy from fossil fuels. In addition to the reduction in GHG emissions, the use of the process would also help to alleviate the environmental burden of waste plastics

Integration of Thermal Treatment and Extrusion by Compounding for Processing Various Wastes for Energy Applications

Waste generation is increasing, and a significant portion of the wastes is being landfilled. Torrefaction of such wastes to produce clean fuels is one of the potential solutions. This paper studied torrefaction of mixed fiber-plastic wastes at 300 °C in an integrated torrefaction-extrusion screw reactor with a throughput of up to 70 kg/h. The study experimentally measured the thermomechanical properties of the torrefaction-extrusion process and the pellets produced. The study presents the results for thermal dynamics, the effect of shaft configuration on residence time, specific mechanical energy (SME), heat transfer coefficient (U), specific heat (C) of mixed wastes, and mechanical and rheological properties of pellets. First, the thermal dynamics of the system were studied along the corresponding response of heaters with and without the flow of materials measured. The residence time measurement showed 20% and 40% cut flighting had about 2.3 and 3.7 times more residence time compared to a regular screw. The specific heat of the heterogeneous mix blend was measured at 1.58 kJ/(kg °C). The average overall heat transfer coefficient was measured experimentally for the reactor at 52.5 W/(m2 °C). The correlation between specific mechanical energy and mass flow showed more than 3 times decrease in specific energy consumed when the feed rate was increased from ∼10 to 50 kg/h. Thermomechanical analysis, flexural testing, and rheological testing were performed on the produced pellets to measure pellet properties