Nitrogen, Sulfur, and Chlorine Transformations during the Pyrolysis of Straw

Abstract

Transformation of nitrogen, sulfur, and chlorine during straw pyrolysis at temperatures from 35 to 1450 °C was investigated by using the coupled thermogravimetry−differential scanning calorimetry−mass spectrometry (TG-DSC-MS) techniques and compared with that of coal. The characteristics of the residual solid char from the straw were analyzed using x-ray diffraction (XRD). Results show that all the nitrogen species (HCN, NH3, HNCO, and CH3CN), chloric species (HCl and Cl2), and sulfur species (SO2, H2S and COS) began to release from straw from 200 °C, compared with 350 °C for the case of coal. Most of the gaseous species from the straw were released in the form of a sharp peak, compared with the coal which has a much wider peak. NH3 and HNCO were the primary nitrogen species for both straw and coal; however for the straw the amount of NH3 released was much higher than that of HNCO. Sulfur species from the straw pyrolysis are sparse, and there was only a little COS released. During coal pyrolysis no COS was detected at all and H2S was mainly formed at 500 °C∼600 °C. SO2 was released in three stages (300−500 °C, 500−600 °C and 1200−1450 °C), and the largest SO2 emission was found at high temperatures due to the decomposition of sulfate. The major chloric species from the pyrolysis of both straw and coal was HCl, and the ion current intensity of Cl2 was very low. There was a critical temperature of around 800 °C, beyond which most of the chlorine would be released.

Kinetics investigation on the reduction of NO using straw char based on physicochemical characterization

“…The element profile of chlorine and potassium in the straw char (Fig. 2) reveals a similar result with our previous investigation on straw ash (Wang et al, 2010a). When char-preparation temperature increases from 873 to 1073 K, the content of both chlorine and potassium decreases, and with the temperature increases from 1073 to 1273 K, the content of potassium dose not change remarkably while the content of chlorine keeps decreasing until its disappearance at 1273 K. Fig.…”

“…However, previous results have shown that there are still some obvious differences in the physicochemical characteristics and the reactivity of NO with biomass char and coal char (Dong et al, 2009b;Sahu et al, 2010;Vassilev et al, 2010;Wang et al, 2010a;Yin et al, 2009). Dong et al (2007Dong et al ( , 2009a determined the kinetics parameters for the reaction of NO and char in a fixed bed at 973-1173 K, which proposed the reaction order and the apparent activation energy to be, for straw-char, 0.66 and 114.40 kJ mol À1 , respectively, and for coal-char, 0.76 and 94.79 kJ mol À1 , respectively.…”

The ash deposition mechanism in boilers burning Zhundong coal with high contents of sodium and calcium: A study from ash evaporating to condensing

“…The elemental composition of ash at different temperatures is shown in Figure 7 The release of chlorine in Zhundong coal was very similar with our previous investigation for biomass fuel, in which all chlorine was also released at around 800 o C [19]. A previous XAFS study showed that all the chlorine in brown coal was likely to be associated with sodium [3].…”

Isocyanic acid in the atmosphere and its possible link to smoke-related health effects

“…HNCO has also been observed as a by-product of urea-selective catalytic reduction systems that are being instituted to control NO x (nitric oxide and nitrogen dioxide) emissions from diesel engines (21). A number of studies show that biomass combustion and pyrolysis produce HNCO from amide or polyamide functionalities (18,22,23) f−HN-CðOÞ-g. Reduced nitrogen coproducts include HCN, CH 3 CN, and NH 3 , and the oxidized nitrogen coproducts include N 2 O, NO, HNO 2 , NO 2 , and HNO 3 .…”