NZ248884A - Hydrolysis and/or drying of biological material with steam - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £48884 - 6 OCT W NEW ZEALAND PATENTS ACT, 1953 COMPLETE SPECIFICATION No.: 248884 Date: 7 October 1993 "Multi Effect Hydrolysing/Drying System for Biological Materials" We, CONVERTECH GROUP LIMITED, a duly incorporated New Zealand company of 32 John Street, Rangiora, New Zealand hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a multi effect hydrolysing/drying system for biological materials and related means and methods.

In our New Zealand Patent Specification No. 229080 (European equivalent Application No. 90304922.9 and Australian equivalent Application No. 55013/90) there is disclosed a process for preparing a hydrolysed lignocellulosic material, the full content of which is hereby incorporated by way of reference.

The present invention relates to an improved procedure in relation to such procedures, methods, etc. which provide several options for an operator of such plant or which provides plant and methods of operation thereof which enables, not only the performance in some configurations of such processes, but also improved processes.

One aspect worthy of attention is the role certain water soluble elemental contents such as sodium and potassium have in providing an unwanted glass-like material or vitreous lava when certain biological materials are burnt, eg. sodium and potassium appear to have some role in the formation of such materials. In this respect, I refer to publication "Alkali Deposits in Biomass Power Plant Boilers" by TR Miles presented to the Strategic Benefits of Biomass and Waste Fuels Conference sponsored by Electric Power Research Institute, March 30-April 1 1993, L'enfant Plaza Hotel, Washington, D.C, "Operating Experience with Ash Deposition and Biomass Combustion Systems" by Thomas R Miles presented to the Biomass Combustion Conference, Reno, Nevada, January 29, 1992.

The present invention, therefore, is directed to processes and related products and related plant which provide some options or at least provides the public with a useful choice.

In a first aspect the invention comprises a combustion process comprising I) subjecting a lignocellulosic and/or cellulosic material to entrainment in steam at elevated temperature(s) and pressure(s) to achieve at least partial hydrolysis, II) prior to step (I), or subsequent thereto, or both, subjecting the materials to washing at an elevated temperature, HI) taking the washed and at least partially hydrolysed material into a second entrainment system having a steam environment at elevated temperature(s) and pressure(s) to reduce the water content thereof, IV) subjecting the at least partly dried, washed and at least partially hydrolysed material of step (III) while still in a steam environment of elevated temperature(s) and pressure(s) to either a powder forming or gasification or pyrolysis or solvolysis process, and V) feeding the powder or gas produced by step (IV) from its pressurised step (IV) environment into a combustion chamber and combusting the powder or gas therein.

Preferably a washing step takes place both before and after step (II).

Preferably the washing between steps (I) and (III) is at a pressure at least as high as about the lower of the end pressure of step (I) and the initial pressure of step (III).

Preferably step (I) involves a series of different steam/solid entrainment systems the operating pressures of which progress serially upwardly.

Preferably the pressure or end pressure of step (I) is at about 35 bar and the steam is at at least saturation temperature.

Preferably at least some volatiles produced in step (I) are removed from the ongoing solids stream to step (ID). 248£61 Preferably step (HQ is at an elevated pressure and the steam environment is at at least saturation temperature.

Preferably the steam environment in step (ID) has as some stage between 15°C to 30°C of super heat.

Preferably step (m) involves a series of different steam/solid entrainment systems.

Preferably step (m) is operated at a pressure of greater than about 20 bar.

Preferably a powder is produced by step (TV).

Preferably a milling procedure to produce the powder is operated under the steam atmosphere at a pressure of from about 20 to about 30 bar.

Preferably the solids in step (IV) are reduced to a particle size of less than 50 microns across.

Preferably wet milling is used.

Preferably step (IV) involves a gasification or pyrolysis or solvolysis process.

Preferably pyrolysis of the solids material occurs in a steam environment at a temperature in the range of about 200°C to about 1000°C.

Preferably the pyrolysis temperature is in the range of from 700°C to 1000°C.

Preferably said combustion chamber is the combustion chamber of a gas turbine engine.

Preferably the pressure or end pressure of step (ID) is at least as high as the pressure of step (IV), and the pressure of step (IV) is greater than that required for injection into said combustion chamber of said gas turbine engine.

Preferably at least part thereof is also a process or method hereafter defined.

In a further aspect the invention consists in a combustion process comprising I) subjecting a lignocellulosic and/or cellulosic material to at least partial hydrolysis in steam at elevated temperature(s) and pressure(s), II) prior to step (I), or subsequent thereto, or both, subjecting the materials to washing at an elevated temperature, m) taking the washed and at least partially hydrolysed material into a second steam environment at elevated temperature(s) and pressure(s) to reduce the water content thereof, IV) subjecting the at least partly dried, washed and at least partially hydrolysed material of step (III) while still in a steam environment of elevated temperature(s) and pressure(s) to either a powder forming or gasification or pyrolysis or solvolysis process, and V) feeding the powder or gas produced by step (IV) from its pressurised step (IV) environment into a combustion chamber and combusting the powder or gas therein.

In a still further aspect the invention consists in a process for producing an at least partially hydrolysed and at least partially diy lignocellulosic and/or cellulosic material comprising I) subjecting a lignocellulosic and/or cellulosic material to entrainment in steam at elevated temperature(s) and pressure(s) to achieve at least partial hydrolysis, II) prior to step (I), or subsequent thereto, or both, subjecting the materials to washing at an elevated temperature, III) injecting the washed and at least partially hydrolysed material into a second entrainment system having a steam environment at elevated temperature(s) and pressure(s) to reduce the water content thereof, the pressure(s) of step (III) being 2 4 4 6- * y less than that at the end of step (I) and the injection procedure being of a kind to shred the solids material; and IV) thereafter (a) harvesting the solids from step (III) or (b) combusting the solids from step (HI) in air (directly or optionally after powder forming or gasification in a steam environment), and V) optionally forming any product of step (III) harvested under step (IV)(a) to briquette formation and/or blending with oil to create a fuel slurry.

Preferably the injection procedure is of a kind involving an injection nozzle and an impingement grid and/or screen, the movement through the injection nozzle being as a result of the pressure differential between the environment of the incoming material and tlhe steam environment in said second entrainment system.

Preferably prior to harvesting or combusting the shredded at least substantially dried material of step (HI) is subjected to a milling procedure.

In another aspect the invention consists in a process for preparing a hydrolysed, substantially diy, biological material which has a reduced tendency for formation of vitreous ash products should it be burnt comprising: (I) subjecting a biological material to a steam entrainment then collection system to achieve at least partial hydrolysis; (II) taking the collected solids, at least partially hydrolysed, into a different steam entrainment then collection system to reduce the water content of the solids stream; and (III) harvesting the substantially dry, substantially hydrolysed solids from the steam system of step (II); the process being characterised in that: there is included prior to step (II) and/or step (I) at least one water based washing step at an elevated temperature.

Preferably said biological material is a lignocellulosic material.

Preferably said material is wood chips and/or bark.

Preferably said steam entrainment of step (I) involves a series of discrete systems.

Preferably said series of discrete systems have an inter-relating thermodynamic/heat exchange inter-relationship so as minimise the input of heat from outside of the overall system.

Preferably said thermodynamic/heat exchange inter-relationship in the steam entrainment system of step (I) extends also to such a relationship with the downstream steps and the environments thereof.

Preferably the steam entrainment of step (I) is at a pressure and temperature such as to provide for the biological material a saturation steam condition.

Preferably said washing step (II) is subsequent to a preliminary steaming of the biological material.

In yet another aspect the invention is a process for preparing a solids fraction low in vitreous ash forming elements selected from potassium and sodium from a biologically sourced material having such elements, said process comprising: i) subjecting the materials to steam in a high pressure steam system into which energy and/or water as required may be added while extracting volatiles from said material; ii) passing the heated solid streams from the system of step i) into an elevated temperature washing step or sequence; and iii) removing much of the washing water from said solids stream to thereby provide the solids fraction low in said elements.

Preferably said high pressure steam system is a steam/solids entrainment system. Preferably the output of step (iii) is input into a hydrolysis process as claimed in our New Zealand Patent Specification No. 229080 (European Equivalent Application No. 90304922.9 and Australian Equivalent Application No. 55013/90).

Preferably washing water removed by steps (iii) is used as a heat exchange liquid for an optional prewashing step prior to step (i) Preferably the system of step (i) is an entrainment system having heat exchange input, the entrainment system including a blower therein and a collection cyclone for the solid stream.

Preferably said heat exchange input is by means of a fluid jacket Preferably said cyclone passes into step (ii) for a sequence of more than auger or other type washer capable of first allowing washing water to act on the solids stream and them to squeeze much of the water therefrom to thereby perform steps (ii) and (iii).

Preferably the solids being squeezed by said one auger or other type washer is capable of forming a plug with said material.

Preferably the washing water to said sequence of washing augers is counter current In another aspect the invention is a process of treating a biological material having a cellulosic content and having a potassium and sodium content (the "source material") in a multi effect hydrolysis and diying sequence which comprises: a) subjecting the source material at a first elevated temperature and first elevated pressure to a steairi treatment b) taking the solids stream through a washing step [or sequence of washing steps] with water thereby removing at least some of the soluble materials therefrom including some at least of those having a potassium and/or sodium elemental content; c) transferring the solid stream from b) into at least one steam hydrolysis environment at an elevated pressure and temperature; and d) taking the at least substantially hydrolysed material from step c) into at least one drying treatment in a steam environment; and e) thereafter extracting the solids stream in a substantially dry form from step d).

Preferably steam treatment of steps (a) is with superheated steam.

Preferably said step (a) is after prewashing and/or the removal of at least some of volatiles thereof.

Preferably step (b) is a washing step of the solids stream less its volatiles content removed earlier.

In another aspect the invention is an improved hydrolysis/drying process for biological materials comprising: I) subjecting the materials to a pre-heating treatment; II) subjecting the materials to a primary hydrolysis treatment in an entrainment system at a first elevated temperature and a first elevated pressure, the environment being that of saturated steam and at a temperature of greater than 200°C for a controlled period; III) taking the at least partially hydrolysed solids stream from step II) into a combined hydrolysis/drying treatment at a second elevated pressure and a second elevated temperature substantially without flashing for a period; and IV) flashing the solids stream from treatment III) into a drying treatment at a third pressure substantially below the first and second pressures of stages I) and II) respectively, the environment being that of superheated steam; and V) extracting the solids stream from the drying treatment of step IV).

Preferably pre-treatment step (I) comprises (a) optionally a hot water prewashing step; and (b) optionally subjection to a steam environment at an elevated pressure and temperature.

Preferably such elevated temperature and pressure of said optional steam pre-treatment step is above 180°C.

Preferably said optional steam pre-treatment step has steam with superheating.

Preferably such elevated temperature and pressure of said optional steam pre-treatment step is at a pressure of about 12 bar and there is superheating in the range of 1°C tc jO°C of superheat Preferably said superheating is about 20°C.

Preferably volatiles are extracted from solids steam during said optional steam pre-treatment.

Preferably said pre-heating treatment involves a washing step or sequence of steps preferably after the optional steam treatment Preferably said washing is with water at an elevated temperature passing current through auger plug forming washers or washer.

Preferably said pre-heating treatment also includes a saturated steam treatment stage preferably after the washing step or steps that follows a first steam treatment, such saturated steam treatment preferably being at about 24 bar (about 222°C saturated).

Preferably such system is an entrainment system and including a blower and a collection cyclone for the solids stream.

Preferably there is a first hot wash step, a first steam subjection step preferably with making up of water therein, a washing and drying step or steps and then a saturated steam step prior to passage of the solid stream into the hydrolysis step of III).

Preferably the hydrolysis/drying step of III) is preferably in two parts irrespective of whether or not the step of III) is in two parts.

Preferably the hydrolysis is in an entrainment and collection system (preferably cyclone collection) for a pre-determined time at an elevated pressure of about 35 bar in saturated steam (about 242°C saturated) for a brief period of time, eg. from for example 10 seconds to 90 seconds.

Preferably there is a passage into a second hydrolysis stage from the first hydrolysis stage (preferably without flashing) and preferably at the same pressure, eg. about 35 bar, with superheating (eg. 10 to 30°C superheating) but for a small residence time, eg. 6 to 15 seconds.

Preferably the drying step of IV) is at a pressure of above atmospheric pressure but very much below that of the hydrolysis stages.

Preferably the pressure is of the order of 2 bar with a degree of superheating, (eg. about 150 °C superheated steam) with a dwell time therein for so long as is required to reduce the water content therein down to the level required for the end purpose of the materials, whether it be for burning, panel or product forming purposes or other.

Preferably the system is operated in a manner substantially as herein described.

In yet a still further aspect the invention is a method of treating a cellulosic biological material which comprises subjecting the material to a controlled hydrolysis at about 35 bar for a period of 10 seconds to 90 seconds in steam, then without any substantial pressure change and without any significant flashing, subjecting the solids stream, for a period of 15 seconds or less, to another steam environment in a saturation or a superheated condition and thereafter drying the solids stream at a pressure of about 2 bar in superheated steam of about 150°C for such time as is required to reduce the solid stream to a moisture content as might be required for the particular end purposes.

Preferably the moisture content has been reduced to about 1% by weight (moisture/product).

Preferably the controlled hydrolysis reduces the water content of the solids fraction by about 80% or more by weight Preferably the energy for the system is from a thermal input largely supplied in a counter current manner.

In another aspect the invention is plant for performing a process or method of the present inventions, In yet an even further aspect the invention is a product or heat energy generated by a process or method of any one of the present inventions.

Preferred forms of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagram showing the apparatus diagrammatically over its various stages, pre-treatment, hydrolysis and drying (the hydrolysis/drying merging at one stage in the preferred form) and showing the typical types of apparatus that might be used therein; Figures 1A and IB are, together, an enlargement of Figure 1 showing the various components thereof more clearly, Figure 2 is a diagrammatic view primarily of the solids stream showing the sequence of preferred steps of the pre-treatment process referred to with respect to Figures 1, 1A and IB; Figure 3 is a similar diagram to that of Figure 2 but carrying on therefrom showing the hydrolysis/drying steps in the preferred form of the invention (evaporation 1 being a steam system that is a merger of both a continuation of the hydrolysis stage and a commencement of the drying stage); Figure 4 is a diagram taken from Canadian Patent No. 1213711 of K Shen in relation to rice husks (also in Australian Specification No. 586191 of K C Shen); Figure 5 (in a similar manner to that shown in Figures 1, 1A and IB) there is shown an overall preferred process providing a primary atmospheric wash and preheating stage, a third preheater stage (first steam carrier stage) with volatile separation, a three stage wash from the first steam carrier stage into a second steam carrier stage (fourth preheater stage), transfer from that second steam carrier stage into a primary hydrolysis stage, and thence a feed into a main evaporation stage prior to passage into a final evaporation stage (optionally through an injection nozzle of a known kind which would provide shredding between the two evaporation stages, the position of such a shredder being denoted by the letter "X"); Figure 6 is a flow diagram showing a system in accordance with the present invention with its primary heater secondary heater hydrolyser evaporator etc leading into a powder producing system for feeding a gas turbine, such downstream system including a ball mill etc, and Figure 7 shows a variation of the system shown in Figure 6 to the extent that instead the downstream process is to generate a combustible gas by ultra pyrolysis in a steam environment to then be burned and to drive a gas turbine.

Biological materials such as those typically containing lignocellulosic or cellulosic materials such as wood based materials, straw, rice husks or the like are all capable of being used in a process described in our earlier mentioned patent specifications. Such materials can also be used in much the same way in the processes, plant and apparatus of the present invention.

The present invention provides certain enhancements over the prior art process of our earlier patent specifications.

In the aforementioned publications in relation to ash forming components, the fuii content of which is hereby here incorporated by way of reference, T R Miles discloses that high levels of alkali in annual crop biomass fuels create serious fouling of convection surfaces and slagging of fluid beds and grates in combustion boilers. As a consequence, only minimal percentages, 5 to 15%, by weight of these fuels can be fired in combination with other fuels notwithstanding the need for frequent cleaning of the systems. He additionally states that such deposits seriously limit the potential recoverable energy from agricultural residues in particular. High alkali content of these fuels forms an eutectic with silica lowering the ash softening point to as little as 750°C from 1050°C for stem wood ash. The problem occurs even with low percentages of agricultural residues fired with stem wood. The present invention, when operated, at least in its preferred mode, overcomes such difficulties to at least an extent and provides an option such that the system can, if desired, be operated to deal with such agricultural residues (organic material) with or without cellulosic content and/or, optionally, can be operated to provide with certain input materials, (eg. wood, straw and/or rice husks) a hydrolysed substantially dry solid stream capable of being pressed as disclosed in our aforementioned patent specification into useful products.

Reference herein to "volatiles" that might usefully be extracted from organic materials such as agricultural wastes are described by Erven F Kurth the Institute of Paper Chemistry, Appleton, Wisconsin "WOOD CHEMISTRY (Browne) Chapter 12 The Extraneous Components of Wood" as being both essential oils and volatile acids. He describes the distinction between the two groups as being purely arbitrary for in many instances an essential oil may also contain appreciable amounts of acids. Acids and formats are normally constituents of the "holocellulose" and the presence of the free acids in several woods is known. For most parts essential oils possess strong and fragrant odours. They differ from the fixed or fatty oils by being entirely volatile.

Erven F Kurth describes the essential oils as generally being characterised by a great variability in composition and properties. This fact, together with their availability attributes to the marked technological value of these oils and to the purely scientific interest of others. Examples include camphor oil from the camphor woods and pine oil from the pine heart wood. He describes essential oils as being obtained from both living and felled soft woods and hard woods.

Depending, therefore, on the source agriculture materials, wood, etc, there will be a variety of different volatiles capable of being extracted to enhance the washability of the solid stream while at the same time removing from further down in the system any difficulty arising from the presence of such easily removed volatiles and/or the ability to recover such volatiles.

The preferred process of the present invention will now be described with reference to Figures 2 and 3. Figure 2 deals with a pre-treatment stage which preferably elevates the temperature of the solid stream while at the same time, in the preferred form, washes, from the solid stream, water soluble values which are frequently high in unwanted alkali metals (potassium and sodium), preferably after removal of some of the volatiles.

Figure 2 shows a pre-wash step, a first steaming step (preferably with entrainment and collection in a cyclone), a series of washing steps and then a second steaming step prior to onfeed of the solids stream into the hydrolysis/drying flow referred to with reference to Figure 3.

Preferably the pre-wash is with hot water, preferably sourced directly or indirectly from extracted superheated vapour from evaporation stage 2 referred to in Figure 3. Such superheated vapour can either be condensed or used to heat the water for such pre-washing. Preferably, however, the pre-washing is in a column as shown in Figures 1 and 1A with the column or other form being jacketed and maintained at an elevated temperature by the solids laden water resulting from the washing steps.

Water used for the pre-wash is preferably taken by auger into the steam 1 system where optional water can, if required, be added to make up for that steam being lost along with solids being passed to the wash step as well as being extracted with the volatiles.

The steam 1 step is a pre-heater stage in the form of an entrainment system powered by an appropriate blower with the water level being made up by optional water injection and with the solids stream being extracted into the first of preferably three washing steps from a cyclone. Heated by the thermal fluid heated by steam taken out of evaporation stage 1, the steam in the steam 1 system is at an elevated pressure of about 12bar with superheating. Saturation temperature at about 12bar is about 180°C and the amount of superheating is preferably of the order of 10 or 20°C.

The volatile components are purged with a vapour stream to be condensed for separation. The hot wet solids are then auger fed through a series of preferably three washing steps into which water at an elevated temperature (preferably of or above the solids stream being washed) is provided prior to the water then being squeezed as a plug is formed prior to the auger passing the squeezed materials into the next auger region of the subsequent washer.

The triple counter-flow washer with a squeeze out in each stage preferably has the pressurised hot water sourced from the condensate from a secondary thermal fluid heater and supplemented by make up water introduced from a heat exchanger. The heating of such materials can be sourced as appropriate preferably from within the system such that a single thermal fluid heater only is required so that much of the thermodynamic advantages from the prior art process of our aforementioned patent specifications is maintained.

The wash water obtained from the washes is circulated at system pressure to heat the input of solids as it enters at atmospheric pressure into the pre-wash stage. The water is then processed to provide for utilisation of the solubles.

The steam 2 system is preferably also an entrainment system with a blower and a solids collection cyclone passing via an appropriate pressure lock or solids stream transfer device to an auger for subsequent passage from there into the controlled hydrolysis stage referred to in Figure 3. The system referred to as steam 2 is heated by thermal fluid from the secondary fluid heater to about 24bar and contains steam at a saturated temperature of about 222v 14 The recirculating vapour is composed primarily of saturated steam.

The increase of pressure is preferably, therefore, of the order of from atmospheric at outset to 12bar at the steam 1 system to about 24bar at the steam 2 system and then onto about 35bar at each of the controlled hydrolysis and evaporation 1 systems referred to with reference to Figure 3.

The primary hydrolysis stage (the controlled hydrolysis) is heated by thermal fluid from the fired primary fluid heater to the pressure of, for example, 35bar (242° saturated). The extent of the hydrolysis is controlled by the timer unit which retains the solids in the system for a suitable accurately defined period for the particular solids stream determinable only by reference to the characteristic of the overall system and the input solids stream and the rate thereof. The recirculating vapour is composed of saturated steam.

In most applications with agricultural wastes (including timber chips, etc.), controlled hydrolysis, if performed at 35bar, would take a period of time of no longer than from 10 seconds to 90 seconds prior to being passed, preferably without flashing, into the system labelled evaporation 1. This again is an entrainment system with a blower and collection cyclone. Here, heated by thermal fluid from the fired primary fluid heater and maintained at the same pressure as the preceding stage (the controlled hydrolysis), the temperature is raised to give the driving force for the evaporation of the majority of the moisture entrained in the solids. During the falling rate drying period (see Figure 4) hydrolysis continues at the same rate as in saturated conditions. In the constant rate period the temperature rises so that the hydrolysis rate increases. Residence at the falling rate is shortened by the transfer of the solids to the next state. Preferably such transfer is within a period of 6 seconds or less to avoid damage to the material, eg. by overcooking.

The passage through a pressure lock and auger into evaporation stage 2 is into a lower pressure system, preferably with a pressure of about 2bar (150° C superheated) which is heated by the thermal fluid from the secondary fluid heater and, of course, the input of energy brought in with the solids stream. Pressure has been reduced to provide 30 °C of superheat for final removal of moisture. The product emerges to atmosphere as hot dry washed and hydrolysed fibre, etc. after a dwell time at evaporation stage 2 for such period of time as is required for the particular purpose.

Desired end point (eg. after evaporation 2 system) moisture contents are preferably down to about 1% by weight (moisture/product).

The evaporation 1 system optimally (on a wet basis) lowers moisture by about 80% or about 90%, ie. solids going into evaporation 2 system have only about 20% or 10% of the moisture entering the evaporation 2 system.

In Figure 5 there is shown a flow diagram by reference to diagrammatic apparatus associated with the flow diagram of a system that employs a primary atmospheric prewash and preheater for the solids inlet. The prewash gives rise to solubles laden water which is then subjected to water treatment for separation of solubles and other substances thus allowing water cleansed of unwanted content to be re-injected into the process and/or to allow surplus water to be disposed of in a suitable manner.

The primary atmospheric wash and preheater system preferably uses a three stage counter current washer.

The first steam carrier stage (third preheater stage) is the first steam entrainment system and includes a blower, a water injection system and a solids collection cyclone leading to a three stage counter current washer for the solids stream which is to transfer the solids from the first entrainment system into the second entrainment system (fourth preheater stage - second steam carrier stage).

The first steam carrier stage is heated by thermal fluid from the secondary fluid heater to 12bar (188 °C saturated) plus 10° C of superheat Volatile components are purged with a vapour stream to be condensed for separation. The hot, wet solids are washed in a triple counterflow washer with a squeeze-out in each stage. The pressurised hot water is sourced from the condensate from the secondary thermal fluid heater and supplemented by make up water introduced from a heat exchanger. The wash water containing soluble extractives is circulated at system pressure to heat the input of solids as it enters at atmospheric pressure. Water is finally processed to provide for utilisation of the solubles. The separation process with the downstream of the volatile condensate collection results in water condensate being returned to the reservoir while volatile oils separated therefrom are taken off as by-products or become a fuel.

The three stage counter current washer preferably carries one third of the solids in each compartment separated by the squeeze-out plug. The dilution in each stage by use of condensate only is one part dry solids to two parts water. Reserve dilution can be at any level by use of a water bank but the purge rate is fixed by the incoming condensate. Squeeze-out is 1:1.

The fourth preheater stage (the second steam carrier stage) is heated by thermal fluid from the secondary fluid heater to 24bar (222°C saturated). The recirculating vapour is composed of saturated steam.

The primary hydrolysis stage receives the solids from the fourth preheater stage (second steam carrier stage) via a solids transfer device previously described or optionally as disclosed in our Patents Specification No. PCT/NZ94/00097 (equivalent New Zealand Patent Application 248895).

The primary hydrolysis stage is heated by thermal fluid from fired primary fluid heater to 35bar (242°C saturated). The extent of the hydrolysis is controlled by the timer unit which retains the solids in the system for a suitable accurately defined period. The recirculating vapour is composed of saturated steam.

From the primary hydrolysis stage the first of the two evaporation stages occurs with solids transfer between-each by appropriate solids transfer device. The main or first evaporative stage is heated by thermal fluid from fired primary fluid heater and maintained at the same pressure as the preceding stage, ie; the 35bar of the primary hydrolysis stage. The temperature is raised in this stage to give the "driving force" for the evaporation of the majority of the moisture entrained in the solids. During constant rate drying period hydrolysis continues its same rate as in saturated conditions. In the falling rate period the temperature rises so that the hydrolysis rate is increased. Residence at the falling rate is shortened by transfer of the solids to the next stage, optionally, via an injection nozzle and screen capable of shredding the solids owing to the rapid pressure drop between the main evaporative stage and the final evaporative stage.

The final evaporative stage receives either through a pressure lock (or another solids transfer device) or an injection nozzle of the mason type (or any other suitable type) the solids from the preceding stage. The final evaporation stage is heated by the thermal fluid from the secondary fluid heater to 2bar (150°C superheated). Pressure is reduced to provide 30°C superheat for final removal of moisture. The product merges to atmosphere (if desired) as hot, dry, washed and hydrolysed fibre.

The present invention recognises however, that at least at the main evaporative i> ^ge at least partially dry at least partially hydrolysed lignocellulosic material is contained in a high pressure steam system thus making it possible to perform on such a pressurised system, in such a steam atmosphere (which will not support combustion),