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Publication Date: 2015-Mar-30

Publishing Venue

The Prior Art Database


The disclosed method solves the problem of requiring an extremely long pyrolyzer length/diameter to allow adequate transfer of heat across the cross-section of the pyrolyzer feedstock. The methoduses heat pipes to transport heat from a gaseous-phase heat exchanger box with an access door for cleanup to the pyrolyzer vessel. This prevents the syngas from coming into direct contact with the pyrolyzer vessel, providing for easy maintenance and reduced downtime. Enhanced feedstock mixing efficiency in the pyrolyzer is obtained through double-flighted screw design and placement of adjacent multiple screws out of phase with one another in a multiple-screw system.Some of the advantages include high efficiency of the pyrolyzer due to heat recovery from syngas or other sources of waste heat, avoidance ofconsumption ofsecondary fuel for accomplishing pyrolysis, feasible and more acceptable pyrolyzer dimensions.

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This publication is concerned with advanced pyrolyzer designs for effective syngas heat recovery in a multi-stage biomass gasifier. In prior art pyrolyzers, extremely long screws and related mechanical design issues posed a serious problem for the screw structure that used a single screw approach. A second problem is the effective utilization of total available heat. Typically, heat is more generated at the later stages of the gasification process, while the drying and pyrolysis stages are endothermic and require heat to be supplied. Further, acceptable pyrolyzer designs must also address the problems of effective cleaning of the heat exchanger surfaces.

The problem of excessive screw lengths required has been addressed in the prior art by various types of modifications to the screw design. Many references disclose advancements in screw systems for pyrolysis including US2008149471A1, WO2009138757A2, US4466809A, US20060143977A1, US5129995A, US20100095592A and WO2009025569A1. The modifications include use of multiple screws in various configurations,

The requirement of additional heat during the early stages of feedstock drying and pyrolysis have been previously addressed by means of auxiliary/secondary heating for drying and pyrolysis using methane burner, burning residual carbon from feedstock etc. Relatively long and thin single screw pyrolyzers were used to solve the problem of adequate transfer of heat across the cross-section of the pyrolyzer feedstock. Multi-stage screw pyrolyzers were earlier used in an attempt to achieve the required total length while reducing actual length of a given stage. In a few cases distinct waste heat sources are utilized for each stage.

The multi-screw approach is a common solution to enhanced mixing in plastic extrusion. The idea is to replace a single screw with an array of two or more screws to promote rapid movement of the material within the cross-section. In addition, the screw design, which is generally single-flighted, can be made to have double flights with varying cut depths along the screw length. Some designs also include an undercut between the two flights to allow exchange of material between the two paths. These design principles could be applied likewise to the pyrolyzer designfor effective mixing and temperature uniformity within the cross-section.

Other approaches to improving efficiency and implementation of heat utilization involve use of heat pipes to improve heat utilization and the recovery of heat from hot syngas. Heat pipes for directing heat utilization during pyrolysis have been disclosed in US patents and publications includingUS4160720A, US7087097B1.An approach involving coaxial heat pipes for shortening the pyrolysis process has been discussed by Broth et al. (in “Advances in Heat Pipes Technology”, Reay, ed., 1982).

Syngas as a sensible heat source is disclosed in EP127...