WO2011029129A1

WO2011029129A1 - Mobile system for drying and pyrolysis of lignocellulosic materials by interrupted combustion

Info

Publication number: WO2011029129A1
Application number: PCT/AU2010/000935
Authority: WO
Inventors: Alwyn Stanley Joyce; James Alexander Joyce
Original assignee: Black Is Green Pty Ltd
Priority date: 2009-09-08
Filing date: 2010-07-24
Publication date: 2011-03-17
Also published as: WO2011029129A9

Abstract

This invention describes a process for the drying and pyrolysis of a wide choice of lignocellulosic materials using a device which is sufficiently compact, lightweight and robust to allow transport and operation while in motion. The process involves a pre- heated continuous feed of lignocellulosic materials and time/temperature-controlled pyrolysis by interrupted combustion within a wholly or largely self-fuelled pyrolysis vessel which is suitable for mounting on a self-propelled vehicle or on a trailer and from which char, pyrolysis oil and pyrolysis gas can be recovered.

Description

MOBILE SYSTEM FOR DRYING AND PYROLYSIS

OF LIGNOCELLULOSIC MATERIALS BY INTERRUPTED COMBUSTION

The present invention relates generally to the drying and pyrolysis of a wide choice of lignocellulosic materials within a device which is sufficiently compact, lightweight and robust to allow its transport on a self-propelled vehicle or on a trailer and to allow its operation when in motion as well as when stationary.

There is a long history to the art of pyrolysis of lignocellulosic materials of diverse type, but industrial application has been hindered by the fact that most pyrolysis devices are large and constructed at a fixed location or small and of quite limited output. Many existing pyrolysis processes also operate only by batch processing, rather than by continuous feed.

The aim of the current invention is to provide the combination of mobility, continuous throughput and rapid pyrolysis. Such attributes open the way to economical, on-site, on-demand servicing of industries such as agriculture, forestry and general greenwaste.

The accompanying drawings (Figures 1 to 4) illustrate a preferred drying and pyrolysis unit that may be utilised in the present invention.

The first stage of the process is to provide a continuous feed of suitably cut, granulated or chipped lignocellulosic materials sourced, for example, from crop waste, plantation prunings or green waste. The feed mechanism can be configured to provide an initial drying stage, using hot exhaust gas from the pyrolysis unit.

The pyrolysis unit is a vertical metal cylinder fitted with multiple fixed or removable decks, variously slotted, perforated and/or screened, and with a rotating central shaft which carries arms from which hang rakes of varied type.

The chamber above the top deck (designated as Deck 1 in Figure 1) is intended to be primarily a drying chamber, but if relatively dry lignocellulosic feed material is introduced then there may also be some charring occurring within this chamber. One or more chambers formed by decks below the top deck (such as that designated as Deck 2 in Figure 1) continue the drying process, but with increasing amounts of charring. The penultimate chamber (designated as Deck 3 in Figure 1) is intended to complete the charring process and the bottom chamber (designated as Deck 4 in Figure 1) serves as a final collection chamber for char prior to its discharge from the pyrolysis vessel.

The floor of the bottom deck is typically neither slotted nor perforated because it acts as a collection surface for char which is raked for discharge typically through a lateral port (Figure 4). An upper deck or a set of multiple, similar- purpose decks has a floor characterised by concentric slots (Figure 1) which are used in conjunction with suitable rake tines to harvest and remove promptly to a lower level any adequately charred and consequently brittle lignocellulosic material. These upper decks also have a bulk transfer opening (Figure 1) which is designed to permit bulky, uncharred or incompletely charred lignocellulosic material to drop to a lower deck level after at least one complete revolution of the rakes. The deck floor immediately above the bottom deck (Figure 3) may be slotted or perforated, but has no bulk transfer hole because this deck serves as the final charring chamber, from which feed material can transfer only after final charring has rendered it sufficiently brittle to be broken by the rakes and harvested by dropping through the deck slots or perforations. The continuous harvesting downwards of brittle, charred material into a chamber essentially devoid of oxygen is the process which serves to interrupt the combustion of the lignocellulosic feed material, thereby preventing its continued combustion to an ash product.

The types of rakes attached to the circulating arms differ from one deck to another, depending on the intended function of the particular deck. In Figure 1 the upper two decks are shown to be equipped with alternating tines of two types. One type consists of short, largely rigid tines which are intended to mix, spread and drag the lignocellulosic material as it dries and begins to pyrolyse from contact with hot combustion gases which have been released from deeper within the pyro lysis unit. The second type of tine is long, springy and designed to scrape along concentric slots within the deck floor. The function of these tines is not only to mix, spread and drag the lignocellulosic material, but also to break up any of the material which has become sufficiently brittle by pyrolysis to be suitable for harvesting by dropping through the slots in the deck floor. Within the penultimate deck (Deck 3 in Figure 1), intended for final charring, the rake tines are fitted with drag chains to encourage maximum breakage of brittle char so that it can be harvested through slots or perforations to the bottom deck (Deck 4 in Figure 1) where cooler temperatures and a scarcity of oxygen interrupt the combustion which would otherwise cause it to proceed to ash. Within the lowest chamber the rake arms are curved scrapers which drag across the bottom deck and sweep the brittle, crushed char towards the outer walls where it can be discharged through a port as the arms circulate.

Exhaust gas is vented via one or more flues, fitted with dampers to control the rate of flow, then a wet scrubber or an afterburner mechanism to control the quality of the emissions and a spark arrestor to control any spark hazard. There is potential to capture and use heat from the exhaust gas and to capture and use incompletely combusted pyrolysis gas.

Control over temperature, oxygen and degree of pyrolysis is achieved by adjusting the rate of input of lignocellulosic feedstock, the number of drying decks, the rate of rotation of the rakes, the rate of forced air injection and the rate of output of flue gas. Typical operating temperatures in the hottest parts of the pyrolysis vessel are 300 to 500 degrees Celsius and typical temperatures in the bottom char collection deck are less than about 130 degrees Celsius. The residence time of material passing through the pyrolysis unit is adjustable but is generally of the order of seconds to minutes. The pyrolysis process is initiated by loading lignocellulosic feedstock into the drying and pyrolysis decks, then igniting material in the penultimate deck (Deck 3 in Figure 1). The initial combustion releases enough heat to cause the release of some pyrolysis gas which then acts as fuel to continue the heating, drying and pyrolysis process. To encourage the efficient combustion of the pyrolysis gas some of the unburned gas is recirculated from middle or upper decks in the vessel to the main charring deck by return pipes (Figure 1) which exploit a venturi effect as forced air is injected into the main charring deck. For relatively dry feedstock no supplementary fuel is needed to operate the pyrolysis vessel: for relatively wet or slow pyrolysing feedstock the fuel can be assisted when necessary by one or more gas burners.

The prime intent of the process is to generate useful char, which is suitably cooled and drawn off from the bottom of the pyrolyser unit either for immediate spreading for agricultural purposes or for collection and processing for various uses elsewhere. Pyrolysis oil and surplus pyrolysis gas generated within the unit also can be collected for use.

The pyrolysis unit can be operated in a static location but it is designed to be suitable for mounting on a truck or trailer which is can be registered for road use and which is suitable for use on agricultural land. The initial drying and feeding apparatus may be mounted on the same truck or trailer, or temporarily attached for field use or it may be supported by an accompanying agricultural implement. The char discharge mechanism may also involve the use of an associated spreader implement or a pelletizing/briquetting device and/or an accompanying storage truck, trailer or bin.

Claims

What is claimed is:

Invention of a drying and vertical pyrolysis unit which is sufficiently compact, lightweight and robust to allow its transport on a vehicle or trailer and its operation while in motion.

Invention of a drying and vertical pyrolysis unit which is suitable for continuous feed and transport of a wide variety of lignocellulosic materials

Invention of a pyrolysis unit with a controllable temperature profile and a short residence time for feed materials

Invention of a pyrolysis unit which not only provides for extraction of solid, liquid and gaseous products of pyrolysis but which uses some of its own lignocellulosic feed and derived pyrolysis gas as a main or sole fuel for continued pyrolysis.