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Title:
LIQUID BASED SCAVENGING OF AEROSOLS
Document Type and Number:
WIPO Patent Application WO/2011/099850
Kind Code:
A2
Abstract:
The invention provides a method for the reduction of aerosol in an aerosol comprising gas by contacting the aerosol comprising gas with a liquid, wherein the aerosol comprises an aerosol compound and wherein the aerosol compound comprises an organic compound, wherein the liquid comprises a liquid compound and wherein the liquid compound comprises an organic compound, wherein the liquid has a higher temperature than the aerosol comprising gas, wherein the temperature difference is in the range of 5-200 °C; and wherein the liquid has a temperature which is lower than the dew point of the aerosol comprising gas, wherein difference between the dew point temperature of the aerosol comprising gas and the temperature of the liquid is in the range of 5-200 °C.

Inventors:
BOS ALEXANDER (NL)
ZWART ROBIN WILLEM RUDOLF (NL)
Application Number:
PCT/NL2011/050091
Publication Date:
August 18, 2011
Filing Date:
February 09, 2011
Export Citation:
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Assignee:
STICHTING ENERGIE (NL)
BOS ALEXANDER (NL)
ZWART ROBIN WILLEM RUDOLF (NL)
International Classes:
C10K1/08; B01D53/14; C10K1/16
Domestic Patent References:
WO2001036567A12001-05-25
WO2003018723A12003-03-06
WO2008010717A22008-01-24
WO2009039603A12009-04-02
Foreign References:
US5772734A1998-06-30
DE3525241A11987-01-15
US4892718A1990-01-09
US4308243A1981-12-29
EP0464285A11992-01-08
Attorney, Agent or Firm:
VAN WESTENBRUGGE, Andre (JS The Hague, NL)
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Claims:
Claims

1. A method for the reduction of aerosol in an aerosol comprising gas, wherein the method comprises contacting the aerosol comprising gas with a liquid, wherein a. the aerosol comprises an aerosol compound ;

b. the liquid comprises a liquid compound and wherein the liquid comprises a liquid condensate of the aerosol;

c. the liquid has a higher temperature than the aerosol comprising gas, and wherein the temperature difference is in the range of 5-200 °C; and d. the liquid has a temperature which is lower than the dew point of the aerosol comprising gas, wherein difference between the dew point temperature of the aerosol comprising gas and the temperature of the liquid is in the range of 5-200 °C.

2. The method according to any claim 1, wherein the temperature difference between the liquid and the aerosol comprising gas is in the range of 5-30 °C.

3. The method according to any one of claims 1-2, wherein difference between the dew point temperature of the aerosol comprising gas and the temperature of the liquid is in the range of 5-30 °C.

4. The method according to any one of the preceding claims, wherein the aerosol compound comprises an organic compound.

5. The method according to claim 4, wherein the liquid compound comprises an

organic compound.

6. The method according to any one of claims 1-5, wherein the aerosol compound and the liquid compound are polar.

7. The method according to any one of claims 1-5, wherein the aerosol compound and the liquid compound are apolar.

8. The method according to any one of the preceding claims, wherein the liquid is an organic liquid.

9. The method according to any one of the preceding claims, wherein the aerosol comprising gas comprises (an at least partially cleaned) off-gas of a torrefaction process.

10. The method according to any one of the preceding claims, wherein the aerosol comprising gas comprises (an at least partially cleaned) off-gas of a gasification process.

11. The method according to any one of the preceding claims, wherein the aerosol compound comprises an inorganic compound.

12. The method according to claim 11, wherein the liquid compound comprises an inorganic compound.

13. The method according to any one of claims 11-12, wherein one or more of the aerosol compound and the inorganic liquid compound comprises an inorganic salt.

14. The method according to any one of claims 11-13, wherein the liquid is an

inorganic liquid.

15. The method according to any one of the preceding claims, where the aerosol

comprising gas is contacted with both an inorganic liquid and an organic liquid.

16. The method according to any one of the preceding claims, wherein contacting is performed in a reactor with counter flow of the aerosol comprising gas and the liquid.

17. The method according to any one of the preceding claims, wherein contacting is performed in a reactor, and wherein the liquid is sprayed or atomized in the reactor.

18. The method according to any one of the preceding claims, wherein contacting is performed in a reactor containing a bed.

19. The method according to any one of the preceding claims, wherein contacting is performed in a reactor, and wherein the aerosol comprising gas is injected in the liquid.

20. Use of a liquid condensate of an aerosol for scavenging aerosol in an aerosol

comprising gas, wherein the aerosol in the aerosol comprising gas and the aerosol in the liquid condensate are the same.

21. Use according to claim 20, wherein the liquid condensate comprises a plurality of aerosols and wherein the aerosol comprising gas comprises a plurality of aerosols and wherein one or more of the aerosols in the aerosol comprising gas and the aerosols in the liquid condensate are the same.

Description:
Liquid based scavenging of aerosols

Field of the invention

The invention relates to a method for the reduction of aerosols in an aerosol comprising gas, such as in gas generated during for instance gasification of an organic feedstock like biomass or waste, or in gas generated during for instance torrefaction of such feedstock.

Background of the invention

An aerosol is a suspension of fine solid particles and/or liquid droplets in a gas.

Examples of aerosols are for instance smoke, oceanic haze, air pollution, and smog.

Aerosol formation in industrial processes is undesired because the presence of aerosol in a gas may lead to efficiency reduction of the process and/or may make downstream purification compulsory. Hence, once the aerosol particles are present, it is often desired to reduce the aerosol content. Some of the industrial processes described below also relate to aerosol reduction.

WO 0136567 describes a method for removing particulate matter and aerosols from a gas stream generated by gasification prior to the gas stream being used as fuel in an internal combustion device or as synthesis gas for subsequent processing. The method consists of first cooling the gas stream, then oil scrubbing it to further cool it and to remove particulates and some tars, and finally passing the gas stream through one or more vortex chambers to remove additional tars. Each vortex chamber employs a high-speed fan that forces the tar droplets against the interior wall of the vortex chamber where the tar coalesces and is removed.

WO2003018723 describes a method and device for cleaning synthesis gas obtained during gasification of biomass. The synthesis gas is passed through a saturation device and an absorption device, both of which are fed with oil. In this way the synthesis gas is scrubbed with oil and tar is substantially removed therefrom. The tar-containing oil which is released in this process is subjected to a cleaning step, as a result of which oil with a high percentage of tar and oil with a relatively low percentage of tar are formed. The first oil can be returned to the gasification, and the remaining oil can be reused. According to WO2003018723 dust, soot, ash and other particles may be scrubbed out. WO2008010717 describes a method for purifying a combustible gas that is contaminated with contaminants, such as tar and/or dust particles, comprises feeding oil to the contaminated gas. The oil evaporates through contact with the contaminated gas. The evaporated oil is condensed on a quantity of the contaminants in such a manner that said contaminants grow in size to form particles of increased size in the gas. An electric field between electrodes is applied, by means of which said particles of increased size are electrically charged and removed from the gas. The condensation of the oil takes place at a temperature above the water dew point of the contaminated gas. This water dew point is preferably between 50-100 °C, in particular between 50-80 °C.

WO2009039603 describes a system and method for removing liquid mist and aerosol entrained in a process carrier gas stream in e.g. a fast pyrolysis process with a settling tank for collection of liquids, the settling tank containing liquid extracted from the gas stream, a liquid separator connected to the tank for further separating liquids from the stream, a downward tilting drain connected to the separator to permit the gas stream and the separated liquid to exit the separator and flow into a riser connected to the settling tank such that it can discharge the collected liquid to the tank and simultaneously provide an exit to the treated gas flow.

US5772734 describes a membrane hybrid process for treating organic-containing gas streams to remove or recover the organic. The process combines absorbent scrubbing, gas stripping, condensation, and membrane separation, and is particularly useful in treating high- volume, low-organic-concentration streams. The process may be operated such that the only products are a clean air stream suitable for venting to the atmosphere, and a small-volume, condensed liquid organic stream suitable to reuse or disposal.

DE3525241 (US4892718) describes a process for removing carbonyl sulphide, carbon disulphide and mercaptan, possibly in addition to hydrogen sulphide, and a process is described for removing sulphur oxides and/or nitrogen oxides from gases containing these compounds in a process step by scrubbing the gases to be purified at atmospheric or elevated pressure and temperatures between 20 and 200 DEG C with a solution. The process according to this document is characterised in that a solution is used of salts of scandium, of yttrium, of lanthanides, of actinides or mixtures thereof in water and/or in organic solvents. US4308243 describes a method for treating residue gases proceeding from units applying the Claus reaction for the removal of sulphur and having been subjected to a conversion of the sulphur compounds into sulphuretted hydrogen. This method consists in that, prior to absorption of the sulphuretted hydrogen by a selective solvent in aqueous solution, the gases to be treated are cooled to a temperature so selected as to condense the water contained in the gases to form an aqueous effluent which is thereafter injected into the circuit of the selective solvent.

Summary of the invention

Disadvantage(s) of prior art methods to remove aerosols from aerosol comprising gasses may be that they are complicated, expensive or not efficient.

Hence, it is an aspect of the invention to provide an alternative method for aerosol abatement, which preferably further at least partly obviates one or more of above-described drawbacks. The present invention provides a relative simple method with unexpected good results.

In a first aspect, the invention provides a method for the reduction of aerosol in an aerosol comprising gas (herein further also indicates as "gas"), wherein the aerosol comprises an aerosol compound, wherein the method comprises contacting the aerosol comprising gas with a liquid (herein also indicated as aerosol scavenging liquid), which liquid has a higher temperature than the aerosol comprising gas, and wherein the liquid comprises a liquid compound, and especially wherein the liquid comprises a liquid condensate of the aerosol.

It appears that best results are obtained when the liquid has a higher temperature than the gas. When the temperature of the liquid is higher than the temperature of the gas, a substantially higher reduction in the aerosol content is achieved than in the other way around. The higher temperature may facilitate evaporation of aerosol compound(s), which may then be absorbed by the liquid, and removed in this way from the gas. When contacting the gas with a liquid at lower temperature, an aerosol haze may be visible, which disappears when the temperature of the liquid is increased to a temperature higher than the gas.

Herein, the phrase "reduction of aerosol(s) in an aerosol comprising gas" and similar phrases are used to indicate that the total content of aerosols in the gas is reduced. Hence, instead of "reduction of aerosols in an aerosol comprising gas" also the "aerosol abatement" or "reduction of aerosol content" may be used. As mentioned above, the terms "aerosol" or "aerosols" or "aerosol particles" refer to fine solid particles and/or liquid droplets in a gas (i.e. the aerosol comprising gas). Herein, it especially refers to liquid particles in a gas. The aerosol content can for instance be measured with (surface) filter measurements, for instance according to NEN-ISO 9096.

The aerosol, especially when referring to organic feedstock related thermal processes, such as biomass gasification or biomass torrefaction, will essentially be based on organic compounds, such as oils and/or tars. Hence, in an embodiment, the aerosol compound comprises an organic compound. The term "an organic compound" may also relate to a plurality of organic compounds. The aerosol may comprise a plurality of organic compounds. This implies that the particles in the aerosol may comprise one or more organic compounds. Examples of characteristic organic compounds that may be found in aerosol particles after gasification are mainly non- polar 2-3 rings and possibly 4-7 rings, poly aromatic hydrocarbons like acenaphthene, phenanthrene, chrysene and perylene, and after torrefaction are mainly polar phenolic and/or acetic hydrocarbons like acetic acid, acetate, phenol and methanol. Gas after pyrolysis may for instance comprise polar phenolic hydrocarbons. Gas from drying will comprise water and particulate matter.

Organic gasification aerosols particularly comprise heavier tar components for example one or more of benzo(a)-anthracene, chrysene, benzo(b)-fluoranthene, benzo(k)-fluoranthene, benzo(e)-pyrene, benzo(a)-pyrene, perylene, indeno(123-cd)- perylene, dibenzo(ah)-anthracene, benzo(ghi) -perylene and coronene, though could also consist out of some lighter organic components like ethylbenzene, m/p-xylene, o- xylene+styrene, phenol, o-cresol, indene, m/p-cresol, naphthalene, quinoline, isoquinoline, 2-methyl-naphthalene, 1 -methyl-naphthalene, biphenyl, ethyl- naphthalene, acenaphtylene, acenaphtehene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene.

Organic torrefaction aerosols may particularly comprise one or more components with a calorific value significantly higher than the original feedstock, typically between 30 and 35 MJ/kg, and may have an elemental composition similar to the elemental composition of lignins. They may have a high solubility in ethanol or glycerol and lightly less high solubility in water or hydrocarbon liquids such as diesel. However, the aerosol may also be based on inorganic compounds, such as particles including one or more selected from the group comprising KC1, KOH, and K 2 0. Therefore, in an embodiment the aerosol compound comprises an inorganic compound. Such inorganic compounds may be released in processes such as gasification of biomass at high temperatures. The term "an inorganic compound" may also relate to a plurality of inorganic compounds. The aerosol may comprise a plurality of inorganic compounds. This implies that the particles in the aerosol may comprise one or more inorganic compounds. Examples of inorganic compounds that may also be involved in the formation of aerosols are for instance KC1, KOH, K 2 0, etc. In an embodiment, the aerosol compound comprises an inorganic salt.

The aerosol is present in a gas (the aerosol comprising gas). In an embodiment, the gas comprises (an at least partially cleaned) off-gas (or product gas) of a thermal treatment of an organic feedstock. For instance, in an embodiment, the gas comprises (an at least partially cleaned) off-gas of a (biomass) torrefaction process. In another embodiment, the gas comprises (an at least partially cleaned) off-gas (or product gas) of a (biomass) gasification process. In general, off-gas of torrefaction contains useful compounds, such as (lower) hydrocarbons, but also undesired aerosol particles. Likewise, the off-gas from a gasification process may in addition to useful compounds, such as H 2 and/or CO, contain undesired aerosol particles. In another embodiment, the gas comprises (an at least partially cleaned) off-gas of a (biomass) pyrolysis process. In yet another embodiment, the gas comprises (an at least partially cleaned) off-gas of a (biomass) drying process. Off-gasses of drying and pyrolysis may also comprise useful (lower) hydrocarbons.

Drying may for instance take place at a temperature of about 100-150 °C, torrefaction at about 200-300 °C, pyrolysis at about 350-550 °C and gasification at about 650-1300 °C.

Organic feedstocks that may be used may for instance be selected from the group consisting of biomass, waste (like RDF (refuse-derived fuel) and MSW (municipal solid waste)), but also coal.

Such off-gas (or "product gas") is often subjected to a cleaning by leading the off-gas one or more times through an absorber, a scrubber, a filter, or through two or more of these. However, instead of a complicated electrostatic precipitator, ESP, such as described in WO2008010717, also a reactor may be applied wherein the method of the invention is applied. The method of the invention is relative easy and may have high efficiency, such as a reduction of over 70 % or even over 80 % in one cycle.

In the method of the invention, the gas comprising aerosol is contacted with the liquid. Contacting the gas with the liquid may be done with methods known in the art.

In an embodiment, contacting is performed in a reactor with counter flow of the gas and the liquid. In view of efficiency, counter flow may be beneficial. In an embodiment, contacting may be performed in a reactor, and the liquid is sprayed or atomized in the reactor, such as in a wet scrubber. Contacting may also be performed in a reactor containing a plurality of trays. However, contacting may also be performed in a reactor containing a bed, such as a packed bed. In yet another embodiment, contacting is performed in a reactor, and the gas is injected in the liquid ("bubbling"), such as for instance described in EP0464285.

The conditions under which the gas and the liquid are contacted and the nature of the liquid may have consequences on the efficiency of the reduction of the aerosol in the gas.

Preferably, the liquid comprises a liquid compound that has affinity to the aerosol compound. Herein, the phrase "having affinity" especially refers to having the same polarity. Compounds or fluids may have affinity when they have the same polarity.

A good affinity may for instance be obtained when the liquid compound and the aerosol compound are similar. For instance, when leading over a chromatography column, the retention indices are similar, such as for instance defined as that the difference in retention index is less than 50%, especially less than 30%, yet even more especially less than 10% of the retention index of the compound or liquid having the highest retention index. Identical compounds have of course a large affinity.

A rule for determining if compounds or fluids may have affinity is whether the mixture of components or fluids becoming one solution, e.g. that polar molecules will mix to form solutions and non-polar molecules will form solutions, but a polar and non- polar combination will not form a solution.

In a specific embodiment, wherein the aerosol compound comprises an organic compound, the liquid compound (also) comprises an organic compound. For maximizing affinity, in an embodiment, the aerosol compound and the liquid compound are polar, and in another embodiment, the aerosol compound and the liquid compound are apolar.

In a specific embodiment, the liquid is an organic liquid. An organic liquid may comprise one or more organic compounds. Assuming that the aerosol compound is polar, the organic liquid is preferably also polar. Assuming that the aerosol compound is apolar, the organic liquid is preferably also apolar.

In general, the aerosol will comprise a plurality of (organic) aerosol compounds, i.e. the term "an aerosol compound" may also refer to a plurality of (organic) aerosol compounds. In such instance, a liquid compound or a plurality of liquid compounds may be chosen that fits well with the plurality of (organic) aerosol compounds. Hence, since the aerosol may comprise a plurality of compounds, such as a plurality of organic compounds, preferably the liquid also comprises a plurality of (organic) compounds. In this way, affinity between the liquid and the organic compounds of the aerosol may be maximized. In a specific embodiment, the liquid comprises a liquid condensate of the aerosol. Especially, the liquid condensate of the aerosol has a large affinity to the aerosol compound(s). Hence, in a preferred embodiment the liquid condensate of the aerosol is applied as liquid.

In another specific embodiment, wherein the aerosol compound comprises an inorganic compound, the liquid compound (also) comprises an inorganic compound. In a specific embodiment, the liquid is an inorganic liquid. An inorganic liquid may comprise one or more inorganic compounds, such as one or more inorganic salts. An example of an inorganic liquid is for instance a concentrated aqueous salt solution or (ionic) suspension, with one or more inorganic compounds like KC1, KOH, or K 2 0. Such inorganic liquid may of course comprise two or more of such inorganic compounds. For maximizing affinity, in an embodiment the ionicity of the liquid is adjusted to optimize solubility of the inorganic compound(s) of the aerosol. In embodiment of the method of the invention, the liquid may comprise an ionic liquid. Other terms for "ionic liquid" are for instance liquid electrolytes, ionic melts, ionic fluids, or liquid salts.

In general, the aerosol will comprise a plurality of (inorganic) aerosol compounds, i.e. the term "an aerosol compound" may refer to a plurality of (inorganic) aerosol compounds. In such instance, a liquid compound or a plurality of liquid compounds may be chosen that fits well with the plurality of (inorganic) aerosol compounds. In a specific embodiment, the liquid comprises a liquid condensate of the aerosol. Especially, the liquid condensate of the aerosol has a large affinity to the aerosol compound(s). Hence, in a preferred embodiment the liquid condensate of the aerosol is applied as liquid.

As will be clear to the person skilled in the art, an aerosol (particle) may in an embodiment comprise both one or more organic compounds and one or more inorganic compounds.

Using a condensate as liquid may facilitate removing both inorganic and organic compounds from the gas. Using condensate has further the advantage that the affinity may be relatively high. Liquid condensate can for instance be obtained by cooling the aerosol comprising gas to a temperature wherein aerosols start to form condensate. This condensate may then be applied. In another embodiment, compounds which are known to be present in the aerosol in the aerosol comprising gas are mixed to form a liquid condensate.

In another embodiment, the gas may (sequentially) be contacted with both an inorganic liquid and an organic liquid. This may be done in separate reactors or separate reactor sections. In general, this will include a sequential contacting of the gas with the respective liquids. Contacting the gas with the liquid may be performed a plurality of times (two or more cycles).

As mentioned above, it appears that best results are obtained when the liquid has a higher temperature than the gas. Further conditions under which the gas and the liquid are contacted and the nature of the liquid are elucidated below. Especially, the temperature difference is at least 2 °C, more preferably at least 5 °C. Herein, the term "temperature difference" thus relates to the temperature of the liquid minus the temperature of the gas. In a preferred embodiment, the temperature difference is in the range of 5-200 °C, especially in the range of 5-30 °C. For (off-)gasses from torrefaction, a temperature difference in the range of 5-30 °C may suffice.

It further appears that best results are obtained when the temperature of the liquid is also tuned with respect to the dew point of the aerosol comprising gas. When the temperature of the liquid is lower than the dew point from the gas, a higher reduction in the aerosol content is achieved than in the other way around. The term "dew point" refers to the temperature to which a gas must be cooled, at constant barometric pressure, for a gas compound to condense from such gas. The dew point is a saturation point. Hence, in a specific embodiment, the liquid has a temperature (when contacting with the gas) which is lower than the dew point of the aerosol. Especially, the temperature difference is in the range of 5-200 °C (here the temperature difference relates to the dew point temperature of the aerosol comprising gas minus the temperature of the liquid). In an embodiment, the temperature difference is in the range of 5-30 °C (i.e. the liquid is 5-30 °C lower in temperature than the dew point of the aerosol comprising gas). Hence, the temperature of the liquid is preferably higher (such as at least 2 °C, more especially at least 5 °C) than the temperature of the gas, but is preferably lower than the dew point of the aerosol comprising gas (such as at least 2 °C, more especially at least 5 °C). A liquid temperature lower than the dew point of the gas provides improved results with respect to aerosol removal over the situation wherein the liquid temperature is higher than the dew point of the gas.

Hence, the invention provides a method for the reduction of aerosol in an aerosol comprising gas, wherein the method comprises contacting the gas with a liquid, wherein

a. the aerosol comprises an aerosol compound and wherein the aerosol compound comprises an (in)organic compound,

b. the liquid comprises a liquid compound and wherein the liquid compound comprises an (in)organic compound,

c. the liquid has a higher temperature than the gas, and the temperature difference is in the range of 5-200 °C; and

d. the liquid has a temperature which is lower than the dew point of the aerosol, wherein difference between the dew point temperature of the aerosol comprising gas and the temperature of the liquid is in the range of 5-200 °C.

In yet another preferred aspect, the invention provides a method for the reduction of aerosol in an aerosol comprising gas, wherein the method comprises contacting the gas with a liquid, wherein

a. the aerosol comprises an aerosol compound and wherein the aerosol compound comprises an (in)organic compound,

b. the liquid comprises a liquid compound and wherein the liquid compound comprises an (in)organic compound,

c. the liquid has a higher temperature than the gas, d. the liquid compound preferably has a dew point which is lower than the dew point of the aerosol compound; and

e. the liquid comprises a liquid condensate of the aerosol.

Hence, the invention provides the use of a liquid condensate of an aerosol for scavenging aerosol in an aerosol comprising gas, wherein the aerosol in the aerosol comprising gas and the aerosol in the liquid condensate are the same. Especially, in an embodiment wherein the liquid condensate comprises a plurality of aerosols and wherein the aerosol comprising gas comprises a plurality of aerosols, one or more of the aerosols in the aerosol comprising gas and the aerosols in the liquid condensate are the same.

The term "an (in)organic compound" may refer to one or more organic compounds, or one or more inorganic compounds, a as well as to a mixture of one or more organic compounds and one or more inorganic compounds. Description of preferred embodiments

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawing. Figure 1 schematically depicts an apparatus 1 wherein the method of the invention may be applied.

Reference 6 indicates a gas, for instance off-gas of a torrefaction unit or biomass gasifier unit. Hence, reference 6 refers to a product gas. This gas 6 may have already been subject to purification, for instance in a collector (see for instance cited prior art in the background of the invention). Gas 6 may comprise aerosol. Aerosol particles may for instance have a dust nucleus with organic material around such nucleus. Typical dimension may be in the range of 1-10 » m for the dust nucleus and 5-100 » m for the whole aerosol. Actually, due to the upstream purification, aerosol formation may have been promoted. Cooling of such product gas may for instance lead to aerosol formation.

This gas 6 is fed to reactor 7. This reactor 7 may be a packed bed reactor, or a tray reactor, a scrubber, a bubbler, etc. The reactor 7 is configured to allow gas 6 enter the reactor via an inlet and allow a liquid (indicated with reference 17) enter the reactor via a (preferably another) inlet.

The reactor 7 is also configured to allow liquid (indicated with reference 11) leave the reactor via an outlet, and allow a gas (indicated with reference 8) leave the reactor via a (preferably another) outlet. Liquid 11 can be considered as liquid 17, but then enriched with aerosol compound(s). Gas 8 can be considered as gas 6, but then reduced in aerosol. Hence, reference 8 indicates a purified gas (i.e. purified product gas) and reference 11 refers to with aerosol compound polluted liquid 17.

Preferably, the liquid 17 for purifying the gas 6 as well as this gas 6 are led through the reactor 7 in counter current. In general, liquid 17 will introduced in an upper part of the reactor and flow through the reactor as a result to gravity and the gas 6 will be introduced in a lower part of the reactor 7.

Gas 6 has a gas temperature and liquid 17 has a liquid temperature. The latter is preferably higher than the former. Temperature controller 16 may be arranged to heat liquid 17 to a temperature that is preferably higher than that of the gas 6 and is preferably also lower than the dew point of gas 6. As will be clear to the person skilled in the art, the difference in temperature especially refers to respective temperatures at the inlet(s) of the reactor. Hence, when the gas 6 and liquid 17 contact, there is a temperature difference, with the latter being higher in temperature than the former.

Liquid 11 escaping from the reactor 7 may be reused, after an optional separation in a separator 13. For instance, when as liquid 17 aerosol condensate is applied, no separation may be necessary, and optional superfluous liquid may be removed as liquid 14. Would however as liquid 17 another liquid be used than aerosol condensate, in separator 13 aerosol condensate, and optionally superfluous liquid, may be removed as liquid(s) 14. Temperature controller 12 may optionally be used to cool, or heat, the liquid escaping from reactor 7. Reference 15 refers to liquid 11 from the reactor after optional separation and/or removal of superfluous liquid, that is reused again as liquid 17 in reactor 7.

Gas 8 escaping from the reactor 7, i.e. purified gas, may optionally be compressed in a compressor or blower 9. In this way, a gas 10 may be provided that may further be used, such as in synthesis processes like Fischer- Tropsch synthesis or methanation under high pressure or for (internal) recirculation at slight overpressure.

With the method of the invention gasification or torrefaction of biomass may be performed in a more reliable way. Costs may be reduced and congestion in torrefaction or gasification systems may be reduced, due to the aerosol reduction.

Hence, the invention also relates to a method of thermally treating (such as gasifying) an organic feedstock (such as biomass), subjecting the off-gas obtained to a cleaning, wherein at least part of the cleaning involves the method of the invention. In another aspect, the invention also relates to a method of thermally treating (such as torrefying) an organic feedstock (such as biomass), subjecting the off-gas obtained to a cleaning, wherein at least part of the cleaning involves the method of the invention.

In a embodiment, the gas is subjected to the method of the invention (for the reduction of aerosol in an aerosol comprising gas) a plurality of times. Subjecting the gas to a plurality of cycles may increase the reduction of aerosol in the gas.

Examples

Example 1

A gas, such as obtainable after biomass gasification, comprising a plurality of organic compounds comprising typically acenaphtalene, acenaphtene, fluroene, phenanthrene, anthracene, flupranthen, pyrene, was cooled (to 80 °C). Condensate, obtained by this cooling, is collected in a collector vessel and remaining gas (containing aerosol) is removed from this collector vessel and fed to a separate reactor, wherein it is bubbled through a liquid. The liquid is the condensate (from the above collector) that was obtained upon cooling of the gas. This condensate comprises mainly 2-3 rings and to smaller extend 4-7 rings poly aromatic hydrocarbon compounds, such as acenaphthene and phenanthrene, and to smaller extend chrysene and perylene.

In a first test, the condensate in the bubbled reactor is not heated and is at a temperature of about 20 °C; the aerosol comprising gas fed to the reactor has a temperature of approximately 40 °C. A white haze is visible over the liquid. However, when the condensate is heated (to a temperature above 50 °C, thus higher than the gas), the haze disappears.

As carrier gas N 2 is applied.

Example 2

A similar experiment as in Example 1 was performed, but with other conditions of the apparatus that generates the gas. This also leads to another composition of the gas and hence also the condensate. The gas as well as the condensate comprise almost completely 2-3 rings poly aromatic hydrocarbon compounds such as acenaphthene and phenanthrene.

The gas is cooled to about 80 °C. The temperature of the liquid in the condensate vessel is about 60 °C; the inlet temperature of the gas for the downstream bubbler reactor is about 50-55 °C, while the condensate within the bubbler reactor is at 60 °C; hence the gas is thus lower than the temperature of the liquid through which it is bubbled. Tests have been performed with condensate as liquid and with water as liquid.

With condensate, very good results are obtained. However, when water is being used as liquid, the results are strongly dependent on the flow of the carrier gas (N 2 was applied).

During the scavenging measurements with own condensate, gas analysis has been performed. It appears that the tar dew point after the cooling is in the range of about 100-115 °C. This is substantially more than the temperature of the gas at the inlet of the bubbler reactor (about 50-55 °C) and the temperature of the liquid in the reactor (see below).

However, the tar dew point of the gas over the liquid (here own condensate) in the bubble reactor is in the range of about 70-80 °C. Hence, bubbling the gas through the liquid leads to gas escaping from the liquid with a substantially reduced dew point. This shows also in an analytical way that tars from the gas are removed.

Example 3

A torrefaction unit was applied, wherein biomass was torrefied at a temperature in the range of 250-300 °C. Off-gas of the torrefaction unit was cooled in a cooler to about 100 °C. Off-gas of the torrefaction unit typically comprise mainly polar phenolic and/or acetic hydrocarbons like acetic acid, acetate, phenol and methanol. Condensate is collected in a condensate collector. Gas over the condensate in the condensate collector is fed to a reactor comprising a liquid, and the gas is bubbled through the liquid. The inlet temperature of the gas (which contains aerosols) was about 90-95°C; the temperature of the liquid in the reactor was about 100 °C.

Three liquids were tested: (1) condensate, (2) glycerol and (3) biodiesel. To determine the amount aerosol, surface filter measurements were applied, which were applied before the cooler, after the cooler end after the reactor. The following results were obtained: 0.06 g/m n 3 (m n 3 = normal cubic meters; 0 °C and 1 atmosphere) before the cooler, 2.96 g/ m n 3 after the cooler, and 0.54 g/ m n 3 after the reactor when using own condensate, 1.20 g/ m n 3 after the reactor when using glycerol and 1.19 g/ m n 3 after the reactor when using biodiesel. This shows the superiority of own condensate but also indicates that liquids other than own condensate that have an affinity with the aerosol compound can be applied as well.

Further embodiments

The invention especially provides the following non-limiting number of embodiments, wherein for the sake of understanding number have been included:

1) A method for the reduction of aerosol in an aerosol comprising gas, wherein the method comprises contacting the aerosol comprising gas with a liquid, wherein a. the aerosol comprises an aerosol compound and wherein the aerosol compound comprises an organic compound

b. the liquid comprises a liquid compound and wherein the liquid compound comprises an organic compound,

c. the liquid has a higher temperature than the aerosol comprising gas, and wherein the temperature difference is in the range of 5-200 °C; and d. the liquid has a temperature which is lower than the dew point of the aerosol comprising gas, wherein difference between the dew point temperature of the aerosol comprising gas and the temperature of the liquid is in the range of 5-200 °C.

2) The method according to embodiment 1, wherein the temperature difference between the liquid and the aerosol comprising gas is in the range of 5-30 °C.

3) The method according to any one of the preceding embodiments 1-2, wherein difference between the dew point temperature of the aerosol comprising gas and the temperature of the liquid is in the range of 5-30 °C.

4) The method according to any one of the preceding embodiments 1-3, wherein the aerosol compound comprises an organic compound.

5) The method according to embodiment 4, wherein the liquid compound comprises an organic compound.

6) The method according to embodiment 5, wherein the aerosol compound and the liquid compound are polar.

7) The method according to embodiment 5, wherein the aerosol compound and the liquid compound are apolar.

8)The method according to any one of embodiments 5-7, wherein the liquid is an organic liquid. 9) The method according to any one of the preceding embodiments 1-8, wherein the aerosol comprising gas comprises (an at least partially cleaned) off-gas of a torref action process.

10) The method according to any one of the preceding embodiments 1-9, wherein the aerosol comprising gas comprises (an at least partially cleaned) off-gas of a gasification process.

11) The method according to any one of the preceding embodiments 1-10, wherein the aerosol compound comprises an inorganic compound.

12) The method according to embodiment 11, wherein the liquid compound comprises an inorganic compound.

13) The method according to any one of embodiments 11-12, wherein one or more of the aerosol compound and the inorganic liquid compound comprises an inorganic salt.

14) The method according to any one of embodiments 11-13, wherein the liquid is an inorganic liquid.

15) The method according to any one of embodiments 1-14, wherein the liquid comprises a liquid condensate of the aerosol.

16) The method according to any one of embodiments 1-14, where the aerosol comprising gas is contacted with both an inorganic liquid and an organic liquid. 17) The method according to any one of the preceding embodiments 1-16, wherein contacting is performed in a reactor with counter flow of the aerosol comprising gas and the liquid.

18) The method according to any one of the preceding embodiments 1-17, wherein contacting is performed in a reactor, and wherein the liquid is sprayed or atomized in the reactor.

19) The method according to any one of the preceding embodiments 1-18, wherein contacting is performed in a reactor containing a bed.

20) The method according to any one of the preceding embodiments 1-19, wherein contacting is performed in a reactor, and wherein the aerosol comprising gas is injected in the liquid.

The term "substantially" herein, such as in "substantially all emission" or in "substantially consists", will be understood by the person skilled in the art. The term "substantially" may also include embodiments with "entirely", "completely", "all", etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term "substantially" may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term "comprise" includes also embodiments wherein the term "comprises" means "consists of.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.