Pyrolysis continued performance

There are several procedures to perform pyrolysis flash pyrolysis (pulse mode), slow gradient heating pyrolysis (continuous mode), step pyrolysis, etc. Commonly, the pyrolysis for analytical purposes is done in pulse mode. This consists of a very rapid heating of the sample from ambient temperature, targeting isothermal conditions at a temperature where the sample is completely pyrolysed. Controlled slow temperature gradients are also possible in pyrolysis, but their use in analytical pyrolysis is limited. Step pyrolysis heats the sample rapidly but in steps, each step following a plateau of constant temperature kept for a limited time period. 

Beside continuous horizontal kilns, numerous other methods for dry pyrolysis of urea have been described, eg, use of stirred batch or continuous reactors, ribbon mixers, ball mills, etc (109), heated metal surfaces such as moving belts, screws, rotating dmms, etc (110), molten tin or its alloys (111), dielectric heating (112), and fluidized beds (with performed urea cyanurate) (113). AH of these modifications yield impure CA. 

TG-FT-IR, Pyrolysis analyses were performed on the preliquefaction solids using thermogravimetric (TG) analysis with on-line analysis of the evolved products (including an infrared spectrum of the condensables) by FT-IR. The TG-FTIR method has been described previously (23-25). The Bomem TG/plus instrument was employed. A sample is continuously weighed while it is heated. A flow of helium sweeps the products into a multi-pass cell for FT-IR analysis. Quantitative analysis of up to 20 gas species is performed on line. Quantitation of the tar species is performed by comparison with the balance reading. 

Pyrolysis may be performed using continuous-mode or pulse-mode instruments. In the first instance, the material must be introduced rapidly into the furnace at a predetermined temperature, which is maintained throughout the pyrolysis. Common modem pulse-mode instruments allow very rapid sample heating within a specified time. There are three different types of pulse-mode pyrolyzers ... 

In run R13, the EP performed satisfactorily and the pyrolysis liquids recovered from this point had very different physical appearance (higher density atul viscosity and lower moisture content) compared to the liquids recovered from the scrubber. However, short-circuiting occurred again in the EP approximately after 30 minutes of operation, leading to the thought of installing a pump for the continuous removal of the collected liquids. 

The authors had already conducted the laboratory scale study and the preliminary pilot plant study, and proposed that "drying-pyrolysis process" (pyrolysis followed by indirect steam drying of dewatered sludge cake) (Fig,-i) could be one of the most economical and feasible alternatives for conventional incineration process. The authors have further conducted the feasibility study on a continuous system of "drying-pyrolysis process to evaluate the performance of the process in pilot scale, and to demonstrate its effectiveness as a thermal processing of sewage sludge. This paper presents the results of this pilot plant study. 

In addition to the thermogravimetry experiments, batch pyrolysis experiments continuously monitoring HCl formation were performed with PVC to determine the optimum temperature for HCl formation. Under conditions of maximum HCl formation, PVC was pyrolyzed with and without oxygen in a fluidized bed reactor and the formation of polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) measured. Avoiding the formation of these highly toxic compounds would be a critical element in any waste stream processing scheme. 

In the previous section, we came to the conclusion that two catalytic sites were always obtained simultaneously, but not in the same proportions, when an Fe precursor and an N precursor were present at the same time in the pyrolysis reactor. This demonstration was performed with the help of ToF SIMS analysis of either heat-treated iron acetate or CIFeTMPP adsorbed on N-enriched prepyrolyzed PTCDA . The two catalytic sites were labeled Fe-N4/C and Fe-N2/C, according to the relative abundance of their typical ions detected by ToF SIMS. While Fe-N4/C corresponds to the catalytic site proposed by van Veen and illustrated in Figure 3.5, the full coordination of Fe-N2/C, illustrated in Figure 3.19, is not completely known. Possible Fe-N2+2/C catalytic structures have been proposed by various authors > but have not yet been confirmed. In the following discussion we will continue to use the Fe-N4/C and Fe-N2/C labels to identify these catalytic sites. 

All of the pyrolysis reactions described herein were performed in continuous flow, isothermal reactor systems. One such laboratory reactor system is schematically depicted in Figure 1. Usually, these systems incorporated separate preheat zones, for hydrocarbon and diluent. Catalysts or promoters used were added along with the diluent stream. The heated portions of the preheat and reactor systems were constructed from 316 stainless steel in most cases. 

---