Temperature emission from wood

However, it is difficult and expensive to fully reduce the presence of residual formaldehyde to the desirable trace levels for two reasons. Both are related to the fact that at room temperature and 50% RH wood contains 9.2 wt% moisture (34) First, moisture retains formaldehyde quantitatively In form of methyIenegIycoI, and second, wood moisture may cause slow hydrolysis of methylol end groups of the UF polymer (3). Unfortunately, the nature of latent residual formaldehyde is not yet fully understood. Part of it is likely in a loosely bound state in wood moisture as methyIenegIycoI. Part of it is In form of terminal methylol groups in the cured UF-resin. Thus, the emission from wood product depends on several different factors, including the nature of the resin, the nature of the wood, the nature and porosity of the product, the press time, press temperature, moisture content of the wood before and after pressing, and many... 

Since moisture equilibration, i.e. "conditioning of wood is a slow process that may require a week or longer depending on product thickness, and since temperature adaptation lags by at least an hour, the emission from wood products is not always at equilibrium. This fact has caused non-technicaI people to incorrectly distrust product performance. However, it has been found that the emission directly reflects the daily temperature cycles of outside wails (52). Thus, mobile home placed in a warm climate, indoor air levels may change by a factor of 6 or more during a This is shown in Figure 1. 

ThermoWood is not resistant to exterior weathering and the colour will gradually change to the grey that is characteristic of outdoor exposed wood. In addition, exposure in exterior conditions results in the formation of small cracks on the surface of uncoated wood. Unpigmented or low-build stain coatings do not protect the surface of the wood, but solvent-borne alkyds and water-borne acrylic paints have been found to exhibit better performance than on unmodified wood. VOC emissions from the heat-treated wood are lower compared to unmodified wood and the compositions of the emissions differ. The level of emissions is lower when the wood is treated at a higher temperature. Emissions of terpenes are reduced to very low levels, and the VOC content is dominated by furfural, hexanal and acetic acid (treated at 180 °C), and by acetic acid (treated at 230 °C). ThermoWood passes ecotoxicity tests. 

Another application could be in the treatment of the emissions from small-scale wood burners, containing pollutants such as particulate, CO, and unbumed hydrocarbons (methane, naphthalene, etc.). Jaris and co-workers [37] arc actually studying catalysts for the total combustion of such hydrocarbons. Such a catalyst might be coupled with high-temperature ceramic filters for solving at once the entire range of pollution problems entailed by the considered emissions. 

The reduction of fuel-N to molecular nitrogen in air staging is favored in the fuel rich primary combustion zone ( Fig. 3 ). Investigations on fixed bed wood furnaces have shown that a minimum of the Total Fixed Nitrogen (TFN = HCN+NH3+NO+ NO2+2N2O emission from the primary combustion zone is reached for a stoichiometric ratio of 0.7 to 0.8 and a temperature of 1100 C to 1200 °C and providing a mean residence time of 0.5 s. After the reduction zone the combustion is completed in the burnout zone by injection of the excess air. 

It is important to note here that higher temperatures probably increase emissions from phenolic panels simply by accelerating the release of that small amount of residual formaldehyde that originates from the adhesive and subsequently becomes adsorbed to the wood substance and water in the wood. Because phenolic resins are very stable chemically, any temperature-related increase in emissions would not be expected to be associated with resin degradation. Consequently, temperature would be expected to exert much less influence on emissions from panels which have been aired out than from fresh panels. Indeed, this trend is shown by the data, as discussed below. 

The monitoring and toxicological studies of formaldehyde exposure, as well as studies on the emission of this chemical from wood products generate large numbers of samples to be analyzed. Furthermore, it is necessary to monitor the emissions on a routine basis during production to ensure that the material continues to release low level of formaldehyde. In homes, particularly in mobile homes, the amount of formaldehyde release depends on the construction technoloy, ventilation, indoor temperature and relative humidity, and age, structure and porosity of building materials. It is, therefore, necessary to study the emislon of formaldehyde from wood products as a function of these parameters. 

Transient infrared spectroscopy (TIRS) is a mid-infrared technique [82] that has been developed to obtain spectra of moving solids and viscous liquids. TIRS spectra are obtained from the generation of a thin, short-lived temperature differential that is introduced by means of either a hot or cold jet of gas. When a hot jet is used, an emission spectrum is obtained from the thin, heated surface layer. This technique is known as transient infrared emission spectroscopy (TIRES). When a cold jet is used, the blackbody-like thermal emission from the bulk of the sample is selectively absorbed as it passes through the thin, cooled surface layer. The result is a transmission spectrum convoluted with the observed thermal spectroscopy. This method is known as transient infrared transmission spectroscopy (TIRTS). TIRS is ideally suited for online analysis because it is a single-ended technique that requires no sample preparation. This technique has been applied to the lignin analysis of wood chips [83]. 

Harkness, J.B.L., Fridman, A. (1999), The Technical and Economic Feasibility ofUsing Low-Temperature Plasmas to Treat Gaseous Emissions from Pulp Mills and Wood Product Plants, National Council of the Paper Industry for Air and Stream Improvement, NCASI, Research Triangle Park, NC. 

Milota (2001) compared the emissions from various North American lumber species in a small-scale kiln with those from the same wood in a commercial kiln. The laboratory kiln functioned like the mill kiln with respect to venting characteristics, temperature, and humidity, but it dried the wood faster, possibly because the load is... 

Another furnace that does not require fuel preparation is the stoker boiler, which was used by New York State Electric Gas Corporation (NYSEG) in its TDE tests. At NYSEG, the stoker boiler, which has a 1649°C (3000°E) flame temperature (as does the cyclone boiler), has routinely blended low quaUty coal, and more recently, wood chips with its standard coal to reduce fuel costs and improve combustion efficiency. In the tire-chip tests, NYSEG burned approximately 1100 t of tire chips (smaller than 5x5 cm) mixed with coal and monitored the emissions. The company determined that the emissions were similar to those from burning coal alone. In a second test-bum of 1900 t of TDE, magnetic separation equipment removed metal from the resulting ash, so that it could be recycled as a winter traction agent for roadways. 

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