Marek A. Wójtowicz

Modeling the evolution of volatile species during tobacco pyrolysis

Abstract A great need exists for comprehensive biomass-pyrolysis models that could predict yields and evolution patterns of selected volatile products as a function of feedstock characteristics and process conditions. Low heating rate data obtained from a thermogravimetric analyzer (TGA), coupled with Fourier transform infrared analysis of evolving products (TG-FTIR), were used to perform kinetic analysis of tobacco pyrolysis. The results were utilized to create input to a biomass-pyrolysis model based on first-order kinetic expressions with a Gaussian distribution of activation energies. Pyrolysis simulations were carried out for high heating rate conditions, and predicted product yields were compared with literature data.

Modeling of biomass pyrolysis kinetics

Over the next decade there will be a renewed emphasis on the use of biomass as a fuel and the cofiring of coal and biomass materials. In view of the tremendous diversity of biomass feedstocks, a great need exists for a robust, comprehensive model that could be utilized to predict the composition and properties of pyrolysis products as a function of feedstock characteristics and process conditions. The objective of this work was to adapt an existing coal pyrolysis model, the Functional Group-Depolymerization, Vaporization Crosslinking (FG-DVC) model, and make it suitable for the pyrolysis of biomass. The soundness of this approach is based on numerous similarities between biomass and coal. However, there are important differences, which preclude direct application of the coal model. This work involved: (1) selection of a set of materials representing the main types of biomass, (2) development of a classification scheme, (3) development of a modeling approach based on an extension of a coal pyrolysis model, (4) calibration of the model for a set of standard materials against pyrolysis data taken over a range of heating rates, and (5) validation of the model against pyrolysis data taken under higher heating rate conditions. A streamlined version of the FG-DVC coal pyrolysis model was successfully developed for whole biomass samples and demonstrated to have predictive capability when extrapolated to high heating rate conditions (103 °C/sec). Improvements will be needed in the model to properly account for mineral effects and secondary reactions, and the model has not yet been tested under the very high heating rates that may exist in some combustion devices (104–105 °C/sec).

Control of nitric oxide, nitrous oxide, and ammonia emissions using microwave plasmas

The subject of this paper is mitigation of the undesirable side-effects of selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR): ammonia slip, residual NO(x), and N(2)O emissions. The use of microwave-plasma discharge within the flue gas was explored as a potential pollution-control method. The key issues addressed were: (1) N(2)O, NH(3), and NO removal efficiencies; and (2) sustaining a stable plasma at atmospheric, or close to atmospheric, pressure. In non-oxidizing atmospheres, removal efficiencies were always close to 100% for all species. In the presence of oxygen, however, appreciable amounts of nitric oxide and ammonia were formed. Methods leading to preventing these undesirable effects were examined. In a number of runs, stable plasma operation was attained at pressures close to atmospheric.

Some aspects of the thermal annealing process in a phenol-formaldehyde resin char

Abstract It is well known that chars and carbons lose reactivity as a function of the severity of their heat treatment in inert environments. In this study, phenol-formaldehyde resins of low impurity contents were prepared and heat treated at heat treatment temperatures (HTT) ranging from 1273 K to 1673 K. The low-temperature oxygen reactivity of the chars was then measured, both in the oxygen chemisorption regime (423 K, 101 kPa O2) and the oxygen gasification regime (573–673 K, 0.5 to 101 kPa O2). The oxygen gasification reactivity varied with heat treatment by an order of magnitude. It was concluded that this was not entirely attributable to changes in total surface area with heat treatment. The variation of the reactivity to active surface ares (ASA) ratio with burnoff was small in 1273 K char and large in 1673 K char. The kinetics of annealing were explored, and it was found that a single firstorder deactivation reaction model was unable to describe the variation of either reactivity or ASA with HTT. A first-order distributed activation energy model was found to fit the data reasonably, and implied that the deactivation reactions that are of relevance under these conditions have a preexponential factor of between 1013 and 1014 s−1, and activation energies in excess of 450 kJ/mole.

Reaction order for low temperature oxidation of carbons

A detailed study of the reaction order and activation energy of O 2 gasification of chars has been carried out in this laboratory utilizing phenol-formaldehyde resin chars with low impurity levels. A survey of the literature on this topic suggests that the true order of reaction for low temperature oxidation of chars is fractional, with values in the range from 0.2 to 1 being observed in different studies. In this study, it was noted that there appears to be only a limited variation of reaction order (0.68±0.08) with burnoff, char heat treatment temperature or oxidation temperature (the latter in the limited range from 573 to 673 K). The oxygen partial pressure range examined was 0.5 to 101 kPa. The reaction order for the oxygen chemisorption process, on the other hand, was essentially unity on these same materials. The activation energy for gasification, likewise, was relatively invariant with heat treatment temperature, despite an order of magnitude change in overall reactivity upon heat treatment.

A Prototype Pyrolyzer for Solid Waste Resource Recovery in Space

Pyrolysis processing is one of several options for solid waste resource recovery in space. It has the advantage of being relatively simple and adaptable to a wide variety of feedstocks and it can produce several usable products from typical waste streams. The objective of this study is to produce a prototype mixed solid waste pyrolyzer for spacecraft applications. A two-stage reactor system was developed which can process about 1 kg of waste per cycle. The reactor includes a pyrolysis chamber where the waste is heated to temperatures above 600°C for primary pyrolysis. The volatile products (liquids, gases) are transported by a N2 purge gas to a second chamber which contains a catalyst bed for cracking the tars at temperatures of about 1000 °C – 1100 °C. The tars are cracked into carbon and additional gases. Most of the carbon is subsequently gasified by oxygenated volatiles (CO2, H2O) from the first stage. In a final step, the temperature of the first stage can be raised and the purge gas switched from N2 to CO2 in order to gasify the remaining char in the first stage and the remaining carbon deposits in the second stage. Alternatively, the char can be removed from the first stage and saved as a future source of CO2 or used to make activated carbon. The product gases from the pyrolyzer will be rich in CO and cannot be vented directly into the cabin. However, they can be processed in a shift reactor or sent to a high temperature fuel cell. A control system based on artificial neural networks (ANNs) is being developed for the reactor system. ANN models are well suited to describing the complicated relationships between the composition of the starting materials, the process conditions and the desired product yields.

Pyrolysis Processing for Solid Waste Resource Recovery in Space

The NASA objective of expanding the human experience into the far reaches of space will require the development of regenerable life support systems. A key element of these systems is a means for solid waste resource recovery. The objective of this work was to demonstrate the feasibility of pyrolysis processing as a method for the conversion of solid waste materials in a Controlled Ecological Life Support System (CELSS). A pyrolysis process will be useful to NASA in at least four respects: 1) it can be used as a pretreatment for a combustion process; 2) it can be used as a more efficient means of utilizing oxygen and recycling carbon and nitrogen; 3) it can be used to supply fuel gases to fuel cells for power generation; 4) it can be used as the basis for the production of chemicals and materials in space. A composite mixture was made consisting of 10% polyethylene, 15% urea, 25% cellulose, 25% wheat straw, 20% Gerepon TC-42 (space soap) and 5% methionine. Pyrolysis of the composite mixture produced light gases as the main products (CH4, H2, CO2, CO, H2O, NH3) and a reactive carbon-rich char as the main byproduct. Significant amounts of liquid products were formed under less severe pyrolysis conditions, but these were cracked almost completely to gases as the temperature was raised. A primary pyrolysis model was developed for the composite mixture based on an existing model for whole biomass materials. An artificial neural network model was also used successfully to model the changes in gas composition with the severity of pyrolysis conditions.

Low cost, pervasive detection of radiation threats

The recent nuclear crisis at Fukushima, Japan is a stark reminder that radiation emergencies can and do happen. In addition to accidents, the potential use of radioactive materials by terrorists has raised serious concerns. While the primary concern has been with preventing these materials from entering the United States, thousands of dangerous radiological sources are already here within our borders, located in vulnerable locations in hospitals, food processing plants, and industrial sites. These sources pose a risk for use in two terrorist threats described by the Department of Health and Human Services (DHHS): the Dirty Bomb and the Silent Source. In a Dirty Bomb attack, radioactive material is dispersed using a conventional explosive. In a Silent Source attack, radioactive material is hidden in locations where people congregate (restaurants, airports, subway stations, shopping malls, etc.). Both scenarios can injure or kill people and cause significant political, social and economic disruption. This paper will describe the GammaPixTM technology, which has the potential to provide low cost, pervasive detection of, and warning against, radiation threats. The GammaPix technology is based on software analysis of the images produced by a surveillance or smartphone camera to measure the local gamma-ray radiation exposure at the device. The technology employs the inherent gamma-ray sensitivity of CCD and CMOS chips used in the digital image sensors of these devices. This paper describes the use of the technology in calibration and testing scenarios using installed video cameras and smartphone cameras.

Pyrolysis Yields from Microwave-Assisted Heating of Solid Wastes

This paper continues previous work on pyrolysis processing of solid wastes for spacecraft and planetary surface applications. A domestic microwave oven was modified for use in this work for scoping studies in which the effects of sample composition, use of central microwave absorbers, and secondary pyrolysis of liquids were studied. Experiments were done with wheat straw and various formulations of a feces simulant. The microwave absorbers examined included activated carbon and char produced from previous experiments. The addition of a separate microwave-heated secondary pyrolysis zone was also examined as a means of reducing the liquid product yields. In general, the feces simulants had similar pyrolysis yields when compared to wheat straw for the char and total gas yields, but individual gas yields were different. For example, the feces simulants produced significantly more ethylene, larger amounts of methane, and smaller amounts of carbon oxides (CO + CO2). This can be largely explained by the differences in elemental compositions. A comparison was also made of the microwave-assisted pyrolysis of feces simulants of variable moisture contents (0-60 wt. %). The higher moisture contents (40-60 wt. %) result in a delay for the onset of pyrolysis and a higher energy demand per gram of sample, as might be expected. However, at lower moisture contents, such as the 20 wt. % water for the baseline sample, it was found that the overall energy demand appeared to be lower than for the dried sample, perhaps due to the more efficient absorption of microwave energy.

A COMPACT, EFFICIENT PYROLYSIS/OXIDATION SYSTEM FOR SOLID WASTE

This paper addresses the feasibility of integrating pyrolysis, tar cracking and oxidation steps into a compact, efficient system for processing of spacecraft solid wastes. This work demonstrated that it is feasible to pyrolyze a representative spacecraft solid waste sample and crack and/or oxidize the effluent gases using in a microwave assisted, close-coupled integrated reactor system. The net result is a significant reduction (estimated at 70% lower) in the total energy requirement (per gram of sample) when compared to conventional heating and a simpler, more compact apparatus. Although a formal ESM calculation was not done for the preliminary reactor system due to its small size, by analogy to literature studies comparing microwave heating to conventional heating, a significant reduction in ESM is also expected for a full scale prototype. The need for waste processing varies greatly depending on the mission scenario. Another goal of the project was to demonstrate that a Microwave-Assisted Pyrolysis (MAP) approach can meet the short term, intermediate term, and long term objectives of NASA for closed-loop life support. Microwave-Assisted Pyrolysis can perform the near term objectives of volume reduction, stabilization, and water recovery, the intermediate term objective of recovering additional amounts of water and oxygen from waste materials, and the long term objective of a Controlled Ecological Life Support System (CELSS) and In-Situ Resource Utilization (ISRU).