WO2009133341A2

WO2009133341A2 - Gasifier improvements

Info

Publication number: WO2009133341A2
Application number: PCT/GB2009/000991
Authority: WO
Inventors: Peter Hadden Stein
Original assignee: Peter Hadden Stein
Priority date: 2008-04-29
Filing date: 2009-04-15
Publication date: 2009-11-05
Also published as: WO2009133341A3; GB0807716D0

Abstract

An improved gasifier in which fuel is heated to produce gas and char. A static outer refractory lined vessel is heated by hot gases. Within the static vessel is a rotary cylindrical retort. The rotary vessel is provided with vanes attached to the ends and the circumference of the vessel. The shape of the vanes is such as to form a longitudinal cavity when the circumference of the retort is cut away between the vanes to allow the heating gases to penetrate towards the axis of the retort. An L-shaped extension to the inner surface of the vanes provides a restricted passage for the distribution of fuel. Gas and char exit via an axial unit, and both feed and exit are sealed by specially designed seals.

Description

GASIFIER IMPROVEMENTS

The present invention relates to an apparatus for the gasification of any carbonaceous or other material of significant calorific value to produce a high quality gas preferably to fuel a reciprocating gas engine for the generation of electricity

Rotary gasification systems have been known for very many years. However, there are inherent problems in the conventional designs in that the retort is usually heated by burners impinging directly upon the retort causing "hotspots", gas produced in the retort being burned to heat it or extraneous fuel being introduced. The apparatus the subject hereof provides significant improvements to the long established technology, with the advantage of allowing a modular and adaptable system to be custom built to suit the composition and quantity of the waste supply. A wide range of fuels can be processed including, but not limited to, forestry waste, municipal waste, food waste including factory processing waste, sewage, animal waste, rubber tyres and mixtures thereof.

Fuel of an appropriate size is fed into the sealed retort and gasified at about 800⁰C. The retort consists of a substantially horizontal, cylindrical reactor which rotates slowly within an insulated static vessel. The waste material is indirectly heated the retort in an oxygen-free atmosphere by the exhaust gas from a secondary converter introduced into the outer vessel. . The gas produced, after cooling and cleaning, can be used to generate "green" electricity via a gas engine or gas turbine. Thermal energy produced also has profitable uses including the use of a steam turbine to increase electricity output.

Features of the design are the extension of the rotating vessel beyond the ends of the stationary outer vessel, its insulated ends and external roller support, and provision of an innovatory internal vane arrangement which allows homogeneous distribution of the feed material over an increased surface area of the retort whilst providing access for the heating gas to the increased surface area extending into the retort vessel interior. This exposes it quickly to the heat without the need for rapid tumbling and agitation that is used in competing processes. Furthermore "hot and cold spots" are avoided, thus increasing the plant's ability to produce gas of a consistently good quality. The vanes are not necessarily of the same size, shape or cross section along the axis of the retort, and there can be advantages in variation. It is also possible to construct the vanes with a curved cross section. It can also be advantageous to provide one or more intermediate plate divisions to slow the passage of fuel and ensure its dispersion to the hotter outer surfaces of the retort and to provide support and stiffening of the vanes.

As a result of the internal configuration, the design is also an improvement on the conventional rotating reactor design because, inter alia, it permits the use of a more compact unit. A slight increase in diameter allows the use of a shorter vessel. Thermal analysis and test results confirm that the system provides the correct rate of heating needed to generate good quality gas. Refractory insulation acts as a good heat sink and gives the required temperature stability. The design is robust and has the advantage that, whilst innovative, it draws on proven engineering principles.

The gasifier takes any carbonaceous material, wood, plastic etc preferably with a size less than 16mm. Gas quality is initially determined by the overall temperature and subsequently by the gas temperature and gas residence time in the gasifier. By a process of rapid heating in the absence of air in the rotary retort, the feed fuel is gasified to produce significant quantities of gas fuel.

A purpose designed feeding mechanism is provided which ensures a positive seal between the gasifier and atmosphere, removes entrained air from the fuel and positively feeds the fuel to the gasifier.

The transition time of the fuel from initial entry to ash removal is determined by the retort design, the angle of inclination and the speed of rotation. The angle of inclination can be adjusted manually. The gasifier is designed to heat up the fuel as quickly as possible to the pyrolysis temperature in order for maximum efficiency.

Internal vanes are attached to the ends and inner surface of the rotating vessel and constructed in such a way that the fuel introduced falls initially on to the inner surface of the vanes, i.e. the surface nearest to the longitudinal axis of the gasifier, from where it falls progressively through the restricting gaps between the vanes to reach the outer chambers formed between the and the vessel circumferential wall. The cutaway section of the circumferential wall gives direct heating of the larger part of the vanes to improve heat flow to the fuel and hence its gasification with particular effect on larger fuel quantities.

The gas produced leaves the vessel via an axial vent tube which also contains a scrolling device to remove the char residues, with seals provided between the gasifier and the atmosphere to prevent ingress of air.

The rotating gasifier retort ideally extends beyond the ends of the static refractory lined shell and is refractory lined at its outer ends. Rollers at each end of the vessel support its weight, allow rotation and provide drive means. This extension and the refractory lining also serve to improve the weight distribution of the rotating vessel and facilitate the gasification of larger quantities of fuel.

The temperature of the gas will initially be determined by the temperature of the fuel when the gas is given off, and subsequently by heat gained by the gas from the shell. The gas is cleaned and any tars and oils removed are fed back into the retort for further gasification.

The residues after removal of the gas are continuously extracted from the retort and form a clean fuel for burning in a secondary converter to provide heat for the retort and in which any final residues are melted and deposited into a water cooled vessel for further use. By way of example only, specific embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure 1. is a cross-section of one version of the gasifier Figure 2 is a longitudinal section this version of the gasifier Figure 3 is a cross section of a second version of the gasifier retort Figure 4 is a partial longitudinal section at A-A of figure 3

Fuel is fed via an elaborate feed system which is not detailed in this document, to avoid the ingress of air, into the gasifier retort via tube 1 where it is heated to extract gas and leave a solid char. A static outer preferably cylindrical vessel 7 provided with a refractory lining 6 is heated by hot gases, preferably from a secondary converter in a later stage of a gasification process. Substantially coaxial and mostly within the static vessel, but extending beyond it at each end is a rotating substantially cylindrical gasification chamber sealed by seals 5 to prevent loss of gases. The ends of the rotating gasifier vessel which extend beyond the static outer vessel are provided with a refractory lining 6 to minimize heat loss. A further purpose of the outer extension and its refractory lining is to improve the weight distribution of the rotating vessel. As a result, the vessel can be supported on external rollers 4 beyond the ends of the static vessel. The rotating vessel is provided with vanes 9 and 11 attached to the ends of this vessel and to the circumference 3 of the vessel. The shape of the vanes is such as to extend from the vessel circumference 3 towards the vessel axis to L-shape 9 in cross section, with a further short extension 12 from the base leg of the L to provide a restricted passage 10 for the distribution of fuel. An additional vane 11 extends from the circumference 3 to the joint 13 of the major legs of the L. The circumference 3 of the vessel is cut away between vanes 9 and 11 to provide a substantially triangular cross section, longitudinal space 8 to permit the access of hot gas towards the interior of the vessel. Gas and char exit via an axial unit 2. Both feed and exit are sealed by seals 5a.

A variation of the construction is to curve the inner end of the vanes to join them, not in a point, but as a continuous curve as shown in figure 3. One or more baffles 17 can also be provided to improve the floe of the fuel and provide strength and support to the vanes. Such baffles also ensure that the fuel is moved to the hotter outer areas of the retort.

Whilst the apparatus has been described in detail in terms of specific embodiments thereof, it will be apparent that various changes and modifications can be made by one skilled in the art without departing from the spirit and scope thereof.

Claims

CLAIMS : An apparatus for the gasification of material with a usable calorific value comprising a slowly rotating substantially cylindrical retort largely enclosed within a static refractory insulated outer vessel heated by introduced hot gases, with a feed mechanism for substantially axial injection of suitably sized fuel designed to ensure anaerobic conditions within the said retort to produce fuel gas, and in which the rotary retort of the gasifier is provided with internal longitudinal substantially parallel vanes of a profile to distribute the fuel and maintain its position adjacent to the heated shell of the retort, with the circumference of the retort being cut away longitudinally between vanes to provide access for the hot gases to penetrate towards the axis of the vessel thus providing an increased heated surface area. : An apparatus as claimed in claim 1 in which vanes are of substantially V-shaped section when in position at the top of the retort, with the upper edges of the V attached to the inner surface of the retort and preferably all or at least part of the longitudinal section of the outer wall of the retort cut away between the upper ends of the V. : An apparatus as claimed in claim 1 in which vanes are of substantially U-shaped section when in position at the top of the retort, with the upper edges of the U attached to the inner surface of the retort and preferably all or at least part of the longitudinal section of the outer wall of the retort cut away between the upper ends of the U. : An apparatus as claimed in claims 1, 2, or 3 in which an extension to each vane is provided longitudinally for at least most of the length of the vane, attached to the part of the vane nearest to the axis of the retort and leaving a gap between its end and the adjacent vane to permit access of fuel to the heated outer walls of the retort and assist in its retention there.. : An apparatus as claimed in claim 4 in which a further extension to the vane extension is provided longitudinally for at least most of the length of the vane, attached to the unattached edge of each previous vane extension and extending away from the axis of the retort to further assist in the retention of fuel in areas adjacent to the heated walls of the retort, and prevent rapid tumbling and agitation of the fuel : An apparatus as claimed in any of the previous claims in which the ends of the rotary retort project beyond the ends of the static outer vessel and are insulated preferably by a refractory lining. : An apparatus as claimed in any of the previous claims in which ends of the rotating vessel project sufficiently far from the ends of the stationary vessel to permit the provision of rollers to support the rotating retort.