FR3137382A1 - Surface type salt separator scraped by a sliding scraping plate to a resolubilization zone of the precipitated salts, Associated biomass gasification installation. - Google Patents

Abstract

Surface type salt separator scraped by a sliding scraping plate to a resolubilization zone of the precipitated salts, Associated biomass gasification installation. The invention relates to a separator of salts contained in a solution which is carried under supercritical conditions, with at least one scraping plate whose sliding will generate continuous friction. All the phases which can appear within the solution, some of which are potentially clogging because they stick to the walls, in particular the salts contained are eliminated because they are ablated by friction. The stroke of the scraping plate allows it to be brought into a salt resolubilization zone, that is to say in an area of the interior chamber of the enclosure or in the tube where the temperature is lower at the salt precipitation temperature. Figure for the abstract: fig. 3

Description

Scraped surface type salt separator by a sliding scraper plate to a resolubilization zone of the precipitated salts, Associated biomass gasification installation.

The present invention relates generally to salt separators and more particularly to those intended to be implemented in a thermochemical conversion installation of a carbonaceous material feedstock, in particular under supercritical fluid, for the production of a gaseous mixture.

By “carbonaceous material charge” is meant here and within the scope of the invention any material containing a quantity of carbon, in particular any carbonaceous material from residues.

It can therefore be biomass, i.e. any inhomogeneous material of plant origin containing carbon, such as lignocellulosic biomass, forest or agricultural residues (straw), which can be almost dry or soaked in water like household waste or waste resulting from water treatment such as sewage treatment plant sludge.

It can also be a fossil fuel, such as coal.

It may also be combustible waste of industrial origin, in particular from the food industry, containing carbon, such as plastic materials or used tires, used oils, organic solvents

It can also be a combination of biomass and fossil fuel.

By "supercritical fluid" is meant here and in the context of the invention, the usual meaning, namely a pressure and a temperature beyond which the fluid is in a supercritical state. Its behavior becomes intermediate between the liquid state and the gaseous state: its density is that of a liquid, but its low viscosity is similar to that of a gas.

Thus, by "supercritical water" is meant the usual meaning, that is, water at temperatures above 374°C under a pressure greater than 22.1 MPa.

Although described with reference to a preferred application of gasification of a carbonaceous material feedstock under supercritical water, a salt separator according to the invention can be implemented in numerous applications, and particularly in the industrial fields of agri-food, chemistry, energy, including the oil sector and the transport sector, etc. for which a separation of salts from an aqueous fluid mixture is required.

Generally, a salt separator according to the invention is suitable for the separation of salts initially present in aqueous solutions with or without organic matter.

More specifically, a salt separator according to the invention is advantageously implemented in a thermochemical conversion plant for wet carbon resources, such as supercritical water gasification.

Many existing processes allow the thermochemical conversion of a carbonaceous feedstock into liquid fuels (biofuels, biochar), solid fuels (granules), and gaseous fuels (biogas, methane, syngas, hydrogen).

Among these, the gasification of biomass and coal has been known for a long time. In general, it can be defined as a thermochemical transformation of biomass or coal by the action of heat in the presence of gasifying agents. The aim is to generate, at the end of gasification, a mixture of gases.

Thus, the gasification processes of lignocellulosic biomass make it possible to generate a gas rich in methane or hydrogen.

The separation and recovery of inorganic constituents present in the feed stream of the reactors that implement these thermochemical processes is crucial, as these constituents can lead to plant blockage, fouling and poisoning of the gasification catalyst. In addition, the recovery of salts offers the possibility of producing a fertilizer as a valuable by-product.

Numerous articles in the literature show that the separation of salts in a thermochemical conversion process is of major importance for the actual efficiency of the overall process and for the lifetime of the associated plant. However, the disadvantage of the salt separators known so far is that the salt separation is still not satisfactory or, although satisfactory, requires too high thermal or mechanical energy inputs or the salts are associated with a significant proportion of organic matter. Furthermore, clogging and deposits are a major problem in such salt separators.

More specifically, various scientific articles focus on the dynamics of salt precipitation under supercritical hydrogenation conditions, which makes it possible to separate salts initially present in an aqueous solution containing organic matter.

There reproduces a salt separator as disclosed in publication [1], as it has been envisaged for the gasification of biomass with supercritical water. This separator 1 comprises as a biomass injection device, a cylindrical tube 10 with an injection orifice 11 through which the biomass is injected, and an outlet orifice 12 through which the biomass is evacuated into an inner chamber C delimited by a double-walled enclosure 2 20, 21 of which the outer one 21, thermally insulating, integrates heating elements 22 which thus heat the chamber C and the injection tube 10.

When the wet biomass is introduced into the tube 10, it is gradually brought to a temperature of approximately 450°C: precipitation occurs almost instantly as soon as the temperature reached causes a reduction in the solubility of the salts, leading to the separation of the wet biomass into various phases, in particular solids in a separation zone S within the chamber C.

In the configuration installed vertically of the separator, the biomass/water/salts and other solids mixture, this separation zone S generates a gravity separation into a brine highly loaded with salts and a solution depleted in salts. A resolubilization zone R, immediately below the separation zone S allows the resolubilization of the salts which are therefore evacuated by gravity in the form of brine through the outlet orifice 23 pierced in the bottom 24 of the separator, and this without mixing with the part of the effluents which rises in the chamber C to be evacuated through the outlet orifice 25 towards a gasification reactor, not shown.

Such gravity separators are also described in publications [2] and [3]: they are implemented for inorganic fluids and salt deposits for hydrothermal gasification. For the same application, there are also cyclonic separators.

Overall, a gravity separator works satisfactorily when the phases involved are denser than the carrier medium and according to a grain size distribution allowing gravity separation and brine-type behavior, salts which are described as type I in this case.

However, in some cases, the salts precipitate into particles so small (micro or nano-particles) that they do not sediment.

In other cases, gravitational separation is not easy, as specified in the publication [3]. Thus, the passage of the wet carbonaceous material in subcritical conditions to supercritical conditions can be accompanied by the appearance of very sticky solid phases, in the form of salts that are called type II. These type II salts can accumulate on the internal walls of the inner chamber of the separator and, if necessary, clog the injection tube 10 of the separator as shown in .

To avoid such harmful accumulation of salts II, one could consider applying known solutions, implemented in scraped surface heat exchangers. Such exchangers are particularly used in fouling processes, i.e. when the walls of the exchangers can be the site of fouling phenomena of the walls involved in heat transfers, i.e. with deposition of undesirable materials.

As examples, the scrapers used may be rotary, for example of the worm or blade type, or even oscillating piston type, for example with plates, annular or not. The actuation of the scraper, rotary or oscillating piston type, is generally operated by an electric motor.

Scrapers for heat exchangers have been particularly considered for supercritical oxidation reactors, as described in US Patents 5,100,560A, US6,054,057 A and US5,461,648 A.

US patent application 2012/214977 describes a scraper for ultrafiltration applications. Specific scrapers have also been considered for viscous fluids: https://www.hrsasia.co.in/heat-exchanger-specialists/scraped-surface-heat-exchanger/.

In the field of organic fluids, other defouling solutions have already been considered, including:

- the vibration of parts by pressure pulsation, as described in application US2008/0073063A1,

- chemical treatments, such as that of patent application CA 2119056.

All these solutions are not suitable for the problem of accumulation of type II salts on the walls, which can also possibly occur on the scrapers themselves.

There is therefore a need to find a solution which allows better control of the elimination of salts, in particular type II salts, present in a solution, in particular a solution intended to undergo a thermochemical conversion treatment such as wet biomass intended to be gasified.

The aim of the invention is to meet at least part of this need.

To this end, the invention relates to a salt separator for separating salts from a solution containing them, the salt separator comprising:

- a tube comprising an injection orifice through which a solution containing one or more salts is intended to be injected, and an outlet orifice through which the solution is intended to be evacuated, at least part of the height of the internal wall of the tube being adapted to be heated to a temperature greater than or equal to the precipitation temperature of the salts,

- an enclosure delimiting an interior chamber including a separation zone for precipitated salts into which the outlet orifice of the tube opens, the enclosure comprising:

• a cover to which the tube is fixed or made entirely and through which the injection port is pierced,

• at least one side wall pierced with at least one outlet orifice through which the solution free of precipitated salts is intended to be evacuated, and

• a base pierced with at least one outlet orifice through which the precipitated salts are intended to be evacuated in the form of brine,

- at least one scraping plate, pierced to allow the solution to pass through, the scraping plate being mounted to slide at least in the tube along a stroke which on the one hand generates scraping friction directly with the heated internal wall of the tube and/or with any deposit of solid matter including precipitated salts, likely to form thereon, and on the other hand positions the scraping plate in at least one so-called resolubilization zone in the tube or in the enclosure, in which the temperature is lower than the precipitation temperature of the salts so as to allow the resolubilization of the precipitated salts, deposited on the scraping plate.

According to an advantageous configuration, the salt resolubilization zone is reached when the scraper plate is in an extreme position, outside the heated internal wall part of the tube, close to the injection port or close to the outlet port through which the precipitated salts are intended to be evacuated in the form of brine.

Advantageously, the stroke of the scraper plate is a back and forth stroke in operation.

The tube is advantageously made of a metallic material adapted to the operating conditions of temperature and pressure: it can be made of Inconel®, stainless steel or other.

For the means of heating the tube, several alternatives can be considered which can be combined with each other:

• external heating means arranged around the tube to heat its internal wall part to a temperature greater than or equal to the precipitation temperature of the salts,
• heating resistors, in the form of cartridges, intended to be supplied by an external electrical power source and integrated into the thickness of the tube to heat its internal wall part to a temperature greater than or equal to the salt precipitation temperature,
• a heat transfer fluid circuit made in the thickness of the envelope to heat its internal wall part to a temperature greater than or equal to the precipitation temperature of the salts.

The salt separator advantageously comprises mechanical means for sliding the scraping plate actuated by at least one motor and/or a pressurized drive fluid circuit.

According to an advantageous variant embodiment, the mechanical sliding means comprise a screw arranged axially inside the tube and onto which the scraping plate is screwed in order to constitute an endless screw, the plate being guided in translation by at least one guide rail which extends and is held over at least the height of the tube and, where appropriate, up to the bottom of the enclosure.

The screw may constitute a mechanical coupling shaft or be equipped at its end outside the enclosure with a Pelton or Francis type hydraulic turbine. Reference may be made to patent application EP3839405 for the implementation of a hydraulic solution for rotating the screw.

The invention also relates to a biomass gasification installation comprising:

- a salt separator as described above;

- a gasification reactor connected to the salt separator enclosure to be supplied with salt-free biomass.

According to an advantageous embodiment, the salt separator tube integrates into its thickness a part of the recovery circuit for the effluents obtained at the reactor outlet, as a heat transfer fluid circuit for heating its internal wall part to a temperature greater than or equal to the salt precipitation temperature.

According to another advantageous embodiment, the temperature of the biomass at the injection port is around 20°C lower than the salt precipitation temperature, the temperature of the biomass at the outlet port of the salt separator being around 20°C higher than the salt precipitation temperature.

Advantageously, the operating temperature of the reactor is approximately 600°C and the operating pressure of the reactor is approximately 300 bars.

Thus, the invention essentially consists in producing a separator of salts contained in a solution, preferably to be converted thermochemically, which is brought to supercritical conditions, with at least one scraping plate whose sliding will generate continuous friction. All the phases which may appear within the solution, some of which are potentially fouling because they stick to the walls, in particular the salts contained are eliminated because they are ablated by the friction.

The stroke of the scraper plate allows it to be brought into a salt resolubilization zone, that is to say into an area of the inner chamber of the enclosure or in the tube where the temperature is lower than the salt precipitation temperature.

The operation of the salt separator firstly allows the solution to be converted to be heated to a temperature guaranteeing the precipitation of the salts and their separation by the friction induced by the scraping plate, the resolubilization of the salts precipitated and deposited on the plate and then to separate the solution to be converted into a flow depleted in salts which is evacuated from the separator to be directed towards a conversion reactor, in particular a gasification reactor, and into a flow loaded with salts to be extracted in the form of brine.

Other advantages and characteristics will become more apparent upon reading the detailed description, given for illustrative and non-limiting purposes, with reference to the following figures.

there is a schematic view in longitudinal section of a salt separator according to the state of the art.

there is a perspective view of a salt separator incorporating an injection device according to one embodiment of the invention.

there is a perspective view of a salt separator incorporating an injection device according to another embodiment of the invention.

there is a synoptic view of a wet biomass gasification installation integrating a salt separator according to the invention.

Detailed description

For the sake of clarity, the same elements are designated by the same numerical references according to the state of the art and according to the invention.

It is specified that throughout the application, the terms “input”, “output”, “upstream”, “downstream” are to be understood in relation to the direction of circulation of the fluid considered within a salt separator and a gasification installation according to the invention.

There relating to a salt separator according to the state of the art has already been commented on in the preamble. It will therefore not be commented on below.

In , a salt separator 1 according to an embodiment of the invention is shown. In the example illustrated, the salt separator 1 is of axisymmetric shape of revolution. In its installed configuration, it extends vertically.

This separator 1 firstly comprises a tube 10, typically made of metal, part of the height of the internal wall of the envelope of which is adapted to be heated to a temperature greater than or equal to the precipitation temperature of the salts contained in a wet biomass which one seeks to convert, advantageously in a gasification installation such as that detailed below.

The tube 10, of cylindrical shape in the illustrated example, comprises an injection orifice 11 through which the wet biomass containing salts is injected, and an outlet orifice 12 through which it is evacuated.

Heating resistors, in the form of cartridges, intended to be powered by an external power source are advantageously integrated into the thickness of the tube10 to heat its internal wall to a temperature greater than or equal to the precipitation temperature of the salts. These may be cylindrical cartridges of small diameter, typically equal to 3.15 mm, such as those marketed by the Omega company: https://www.omega.fr/subsection/cartouches-chauffantes.html.

The separator 1 also comprises an enclosure 2 around the tube 10. This enclosure 2 delimits an interior chamber C including a zone S for separating the precipitated salts into which the outlet orifice 12 of the tube 10 opens.

The cover 26 of the enclosure is pierced with the injection orifice 11.

The enclosure 2 has a double metal wall 20, 21, which is pierced with one or more outlet orifices 25 through which the biomass without the precipitated salts is intended to be evacuated.

The bottom 24 of the enclosure is pierced with an outlet orifice 23 through which the precipitated salts are intended to be evacuated in the form of brine.

A scraping plate 13 is slidably mounted in the tube 10 and in the inner chamber C of the enclosure along a stroke which on the one hand generates scraping friction directly with the heated inner wall of the tube 10 and/or with any deposit of solid material including precipitated salts, likely to form thereon, and on the other hand positions the scraping plate in at least one so-called resolubilization zone (R) in the tube or in the enclosure, in which the temperature is lower than the precipitation temperature of the salts so as to allow the resolubilization of the precipitated salts, deposited on the scraping plate.

The scraping plate 13 is pierced with one or more orifices 130 to allow the solution to pass through.

Preferably, the operation of the separator is provided so that the stroke of the scraping plate 13 performs back and forth movements at least over the entire internal wall of the heated tube 10 to scrape off any deposit of solid material including precipitated salts.

More specifically, in the example of the , the scraping plate can take, outside the heated part of the internal wall of the tube 10, a first extreme position P1 near the injection orifice 11 and a second extreme position P2 near the outlet orifice 23 through which the precipitated salts are intended to be evacuated in the form of brine. In each of these two positions P1, P2, the temperature is lower than the precipitation temperature of the salts, which makes it possible to resolubilize them.

In the example of the , the scraping plate can take, outside the heated part of the internal wall of the tube 10, a first extreme position P1 near the injection orifice 11 and a second extreme position P3 near the outlet orifice 12 of the tube 10. In each of these two positions P1, P3, the temperature is lower than the precipitation temperature of the salts, which makes it possible to resolubilize them.

In Figures 2 and 3, an advantageous variant of mechanical sliding means of the scraper plate 13 is illustrated. A screw 14 is arranged axially inside the tube 10 and the scraper plate 13 is screwed onto this screw in order to constitute an endless screw. To transform the rotation of the screw 14 into translation of the scraper plate 13, the latter is guided in translation by two guide rails 16 which extend parallel to each other and are held over the height of the tube 10 in notches provided for this purpose in the bottom 24 of the enclosure. 8, the screw constituting a mechanical coupling shaft or being provided at its end outside the enclosure with a hydraulic turbine.

Figures 2 and 3 also illustrate an advantageous variant of mechanical means for rotating the screw 14: its end outside the enclosure 2 is constituted by a hydraulic turbine of the Pelton or Francis type 15 which, under the action of a pressurized fluid F, causes the rotation of the screw 14. Reference may be made to application EP3839405 for more details.

There illustrates a wet biomass gasification installation 3 which integrates a salt separator 1 according to the invention.

On this , the different symbols relating to temperatures are as follows:

T-: precipitation temperature of salts, typically around 450°C, reduced by 20°C,

T+: salt precipitation temperature, typically around 450°C, increased by 20°C,

Tg: biomass gasification temperature, typically around 600°C.

This installation 3 includes from upstream to downstream in the direction of circulation of biomass to be gasified:

- a heat exchanger 4, which can be standard in the management of non-sticky viscous fluid and optimized for heat recovery between ambient temperature and at most temperature T-.

- a salt separator 1, connected downstream to the heat exchanger 4, which allows the transition from T- to T+ and the evacuation of biomass effluents without salts while separating the salts in the form of brine,

- a high pressure separator 5, connected downstream to the separator 1, to separate the salts precipitated in solid form from the brine water,

- a gasification reactor 6, connected downstream to the salt separator 1 to gasify the biomass without salts at temperature Tg.

Gasification reactor 6 is typically a shell-tube reactor and operates at 600°C under pressure of 300 bar.

On this , the solid lines symbolize the material flows before gasification, respectively at a cold (ambient) temperature at the inlet of exchanger 4, at a temperature close to T-/T+ at the outlet of exchanger 4, then at the required gasification temperature Tg from the outlet of separator 1.

The dotted lines represent the post-gasification material flows which exit at the reactor temperature Tg, pass into a heating circuit within the envelope 2 at this temperature Tg, in order to heat the biomass which enters the separator 1, then pass back into the heat exchanger 4 to be cooled.

As specified on this , once cooled, the effluents converted by gasification (syngas) are evacuated from installation 3 to a storage or direct exploitation process.

Other variations and improvements may be envisaged without departing from the scope of the invention.

List of cited references

[1]: “ A novel salt separator for the supercritical water gasification of biomass ”, J Reimer, G. Peng, S. Viereck, E. De Boni, J. Breinl, F. Vogel, J. of Supercritical Fluids 117 (2016 ) 113–121.

[2]: “ Continuous salt precipitation and separation from supercritical water. Part 1: Type 1 salts ”, Martin Schubert, Johann W. Regler, Frederic Vogel, J. of Supercritical Fluids 52 (2010) 99–112.

[3]: “ Continuous salt precipitation and separation from supercritical water. Part 2. Type 2 salts and mixtures of two salts ”, Martin Schubert, Johann W. Regler, Frederic Voge, J. of Supercritical Fluids 52 (2010) 113–124.

Claims (13)

Salt separator (1) for separating salts from a solution containing them, the salt separator comprising:

• a tube (10) comprising an injection orifice (11) through which a solution containing one or more salts is intended to be injected, and an outlet orifice (12) through which the solution is intended to be evacuated, at least part of the height of the internal wall of the tube being adapted to be heated to a temperature greater than or equal to the precipitation temperature of the salts,
• an enclosure (2) delimiting an interior chamber (C) including a separation zone (S) for the precipitated salts into which the outlet orifice of the tube opens, the enclosure comprising:

• a cover (26) to which the tube is fixed or made integrally and through which the injection orifice is pierced,
• at least one side wall (20, 21) pierced with at least one outlet orifice (25) through which the solution free of precipitated salts is intended to be evacuated, and
• a bottom (24) pierced with at least one outlet orifice (23) through which the precipitated salts are intended to be evacuated in the form of brine,

• at least one scraping plate (13), pierced to allow the solution to pass through, the scraping plate being slidably mounted at least in the tube along a stroke which on the one hand generates scraping friction directly with the heated internal wall of the tube and/or with any deposit of solid matter including precipitated salts, likely to form thereon, and on the other hand positions the scraping plate in at least one so-called resolubilization zone (R) in the tube or in the enclosure, in which the temperature is lower than the precipitation temperature of the salts so as to allow the resolubilization of the precipitated salts, deposited on the scraping plate.

Salt separator according to claim 1, the salt resolubilization zone being reached when the scraping plate is in an extreme position (P1, P2), outside the heated part of the internal wall of the tube, close to the injection orifice (11) or close to the outlet orifice (23) through which the precipitated salts are intended to be evacuated in the form of brine. Salt separator according to claim 1 or 2, the stroke of the scraper plate being a reciprocating stroke in operation. Salt separator according to one of the preceding claims, comprising external heating means arranged around the tube to heat its internal wall part to the temperature greater than or equal to the precipitation temperature of the salts. Salt separator according to one of the preceding claims, comprising heating resistors, in the form of cartridges (102), intended to be supplied by an external electrical power source and integrated into the thickness of the tube to heat its internal wall to a temperature greater than or equal to the precipitation temperature of the salts. Salt separator according to one of the preceding claims, comprising a heat transfer fluid circuit produced in the thickness of the tube to heat its internal wall part to a temperature greater than or equal to the salt precipitation temperature. Salt separator according to one of the preceding claims, comprising mechanical means for sliding the scraping plate actuated by at least one motor and/or a pressurized drive fluid circuit. Salt separator according to claim 7, the mechanical sliding means comprising a screw (14) arranged axially inside the tube and onto which the scraping plate is screwed in order to constitute an endless screw, the plate being guided in translation by at least one guide rail (16) which extends and is held over at least the height of the tube and, where appropriate, up to the bottom of the enclosure. Salt separator according to claim 8, the screw constituting a mechanical coupling shaft or being provided at its end outside the enclosure with a hydraulic turbine (15) of the Pelton or Francis type. Biomass gasification installation (3) comprising:

• a salt separator (1) according to one of the preceding claims;
• a gasification reactor (6) connected to the salt separator enclosure to be supplied with salt-free biomass.

Installation according to claim 10, the salt separator tube integrating in its thickness a part of the recovery circuit for the effluents obtained at the outlet of the reactor (10), as a heat transfer fluid circuit for heating its internal wall part to a temperature greater than or equal to the precipitation temperature of the salts. Installation according to claim 10 or 11, the temperature of the biomass at the injection port of the injection device being around 20°C lower than the salt precipitation temperature, the temperature of the biomass at the outlet port of the salt separator being around 20°C higher than the salt precipitation temperature. Installation according to one of claims 10 to 12, the operating temperature of the reactor being approximately 600°C and the operating pressure of the reactor being approximately 300 bars.