Effect of selected additions on de novo synthesis of polychlorinated dioxins and furans

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans are generally considered the most dangerous chemical substances known to man. Although they have never been the product of purposeful human activity, yet they are formed in many chemical and virtually all thermal processes. Research on the occurrence of dioxins in the environment, their release into the environment, ways of formation and methods of reducing their emissions lasts since the late seventies of the last century. Currently, we know three basic pathways of dioxins formation in thermal processes, the most important of them being the so called de novo synthesis which occurs outside the combustion zone at 200-400°C in the presence of catalysts (eg copper) and oxygen from the products of incomplete combustion including carbon black and chlorine or chlorinated compounds. It is well known that some metals like copper catalyze the de novo synthesis, while others decompose dioxins and furans formed previously. The formation of dioxins resulting from the de novo synthesis was studied through analysis of the effect of the type of metal on the course of the de novo synthesis. The influence of the addition of sulfur, nitrogen and alkali metals on this synthesis was also examined because some reports in the literature refer to inhibitory effect of these elements.

The Analysis about Harmful Emissions of Micro Combustor Based on Porous Medium

According to the changes of the mixed gas flux ,porosity and burner structure,we measured the contents of CO, HC and Nitrogen Oxides in the harmful emissions of the methane burned in the micro combustor.In the micro scale, because the structure size of the burner is small, the combustion space and time is limited, CO and HC emissions are the products of incomplete combustion, nitrogen oxide are the products in local high temperature and oxygen enriched conditions.

Environmentally-Benign Conversion of Biomass Residues to Electricity

As petroleum resources are finite, it is imperative to use them wisely in energy conversion applications and look for alternative options as an energy source. Biomass is one of the renewable energy sources that can be used to partially replace fossil fuels. Biomass-based fuels can be produced domestically and may thus reduce dependency on fuel imports. Due to their abundant supply, and given that to an appreciable extent they are considered to be carbon-neutral, their use for power generation is of technological interest. However, whereas biomasses can be directly burned in furnaces, such a conventional direct combustion technique is ill-controlled and typically produces considerable amounts of health-hazardous airborne compounds [1,2]. Thus, an alternative technology is described herein to further address our increasing energy needs and, at the same time, utilize our biomass streams in an environmentally-benign manner. More specifically, a multi-step process/device is outlined to accept biomass, of various types and shapes, and generate an easily-identifiable form of energy as a final product. To achieve low emissions of products of incomplete combustion, the biomass is gasified pyrolyticaly, mixed with air, ignited and, finally, burned in nominally premixed low-emission flames. Combustion is thus indirect, since the biomass is not directly burned, instead its gaseous pyrolyzates are burned upon mixing with air. Thereby, combustion is well-controlled and can be complete. A demonstration device has been constructed to convert the internal energy of plastics into clean thermal energy and, eventually to electricity.

The Investigation on Application of Oxygen-Enriched Combustion in Cement Rotary Kiln

The investigation on application of oxygen-enriched combustion in cement rotary kiln shows that flame temperature in rotary kiln can be increased, which improves the utilization of coal and thermal efficiency of rotary kiln. And the fuel consumption and the cost of production can be reduced. In this situation, the objective of increasing production, improving quality and saving energy can be achieved. In the meanwhile, the requirement of air can be reduced in oxygen-enriched combustion. Thus the generation of flue gas and the products of incomplete combustion, which usually are CO, can be reduced. And then the exhaust gas loss and the generation and emission of CO2 and NOx can be accordingly reduced, which enhances to achieve the objective of reduction of pollutants and promote the environmental benefit greatly.

Comparison of Products of Incomplete Combustion of Waste Polystyrene and Styrene in Diffusion Flames and Ethyl Benzene in Fuel-Rich Premixed Flames

This study examined the effects of the mode of combustion of waste polystyrene (PS) on the emissions of products of incomplete combustion (PIC). Typically, combustion of PS in furnaces takes place with diffusion flames forming around devolatilizing chunks (pieces, shreds, pellets, etc.) of the solid polymer. In such flames a broad range of local fuel/air equivalence ratios exist, at any given instant of time. The inner side of a diffusion flame is fuel-rich and the outer side is fuel-lean, making it impossible to assess local conditions. Results are typically reported on the basis of a global equivalence ratio, φglobal, which is calculated based on the total amounts of fuel and air consumed in combustion. To examine the effects of local equivalence ratios, φ, on pollutant emissions, premixed flame combustion is necessary. In this investigation emissions from batch combustion of solid PS pellets in fixed beds, placed inside a horizontal furnace, are compared with emissions from steady-state steady-flow combustion of PS particle clouds (aerosols), inside a vertical furnace. Sampling was conducted at the exits of the furnaces. In addition, effluents from both diffusion and premixed flames of PS precursors are also compared. Liquid styrene is the monomer precursor of polystyrene; it is also the most abundant pyrolyzate. It was burned in batches inside the horizontal furnace. However, because of its unstable, often explosive combustion ethyl-benzene was chosen for the premixed combustion experiments. This choice was based on work conducted elsewhere, which showed that in flames the conversion of ethyl-benzene to styrene is extensive and extremely fast. Ethyl-benzene was pre-vaporized in nitrogen, mixed with oxygen and nitrogen, and burned in a flat flame burner. Fuel-rich conditions (φ = 2.5) were implemented to enhance the product yield. Product sampling was conducted in the luminous region of the premixed flame.