Drying pyrolysis process

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. 

Figure 1. Schematic of drying-pyrolysis process pilot plant...

In this study, to make a comparison with drying-pyrolysis process, the experiments on direct feed processes, i.e., direct pyrolysis process and incineration process, were conducted. In these processes, the dewatered cake was directly fed into the furnace. The plant was operated at steady state for at least 5 or 6 hours in all runs. 

Performance of Drying-Pyrolysis Process Indirect steam drying operation was available to all kinds of dewatered cakes tested and its efficiency (overall heat transfer coefficient U) varied with the kinds of cakes. 

Exhaust Gases Table IV shows the analytical results of exhaust gas from drying-pyrolysis process and from direct pyrolysis process and incineration process on cake A, 3 to 83 % of S in the fed cake remains in the residue, 17 to 51 % of S converts... 

Table V. Behaviour of nitrogen oxide in exhaust gas of drying-pyrolysis process, ...

Table VII. Comparison of drying-pyrolysis process, direct...

A pilot plant study was carried out on "drying-pyrolysis" process in order to put the sludge pyrolysis process with multiple hearth furnace to a practical use. Additional studies were carried out on direct pyrolysis process and incineration process in order to compare these three thermal processings. The samples in this study were 5 dewatered cakes obtained from various sewage treatment plants and from various dewatering methods. The pilot plant for the experiments of this study consisted of a four-shaft indirect steam dryer with a total heating area of 10.1 m, a four hearth furnace with a total hearth area of 1.63 and its incidental facilities. 

The two direct feed processes (direct pyrolysis process and incineration process)were experimented, and the result of comparison with drying-pyrolysis process was obtained. 

This result suggests that pyrolysis processes, particulary drying-pyrolysis process can solve the problems of secondary pollution by Cr 6 or NOx and of large energy consumption for... 

As a conclusion from the above summaries, this study achieved the purposes. Namely, drying-pyrolysis process was proved to be the most cost effective and environmentally acceptable process of the three processes and its technical feasibility was verified. Moreover, direct pyrolysis process was ascertained to be slightly inferior to drying-pyrolysis process in economical point, but to be the process which can improve conventional incineration process. 

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