CEM techniques and X-ray analytical microscope analysis for evaluating the combustion emissions and char of CCA- and ACQ-treated woods after QUV degradation

Two types of preservative-treated woods, CCA-(chromated copper arsenate) and ACQ-(ammoniacal copper quats) treated specimens, and Taiwania cryptomerioides Hay (Taiwania), as a control specimen, were used in this study. They underwent an accelerated weathering test that consisted of QUV degradation for 0, 104, 200, 400, and 800 h. The emission gas concentrations of O2 and CO2, the emission contents (CO, SO2 and NOx) and the temperature of the emission, gases during the combustion of the specimen were measured using Continuous Emission Monitoring (CEM) techniques. X-ray Analytical Microscope (X-ray) Analysis and Elemental Analysis (EA) were used to examine certain residual elements of the char as well as particles from each specimen before combustion. The objectives of this study were to investigate the pollutants from both preservative-treated woods, compare them with those of Taiwania, and assess them as a reference of emission quantity for air pollution. When the specimens that had been subjected to QUV degradation were combusted, the emission gas temperatures of all specimens rose rapidly to about 210-235degC, then increased slowly up to 260-270degC and then lowered back down to a steady temperature in the 210-220degC, shown as a plateau curve. The concentration of O2 decreased linearly from 20.7% to about 16.4-17.5%, and the concentration of CO2 increased from 0.2% to about 2.3-3.4%. Both O2 and CO2 had a close relationship during the combustion. The highest emission quantities of CO and NOx for the CCA-treated specimens were about 264.5-354.0 and 7.7-13.0 ppm, and for the ACQ-treated specimens the ranges were 131.5-281.5 and 23.5-29.5 ppm, respectively. SO2 was not found in the emission gases during combustion of either of the preserved specimens. The result of the X-rays indicated that for the CCA-treated specimens, the main metal elements Cr, As, and Cu decreased from 0.0676 to 0.0320%, 0.0090 to 0.0079% and 0.0187 to 0.0089% respectively, but Cu for the ACQ-treated specimen decreased from 0.1198 to 0.0010%. The result of the EA indicated that prior to combustion, the amount of N (0.30%) is higher for the ACQ-treated woods than that for the CCA ones; therefore, the NOsub(x) gases during combustion were higher for the ACQ-treated woods.