METHOD FOR TREATMENT, APPARATUS AND USE

FIELD OF THE INVENTION

The invention relates to a method for hydrothermal treatment of organic material, the method comprising steps of: obtaining a reaction mixture comprising said organic material, and reacting said reaction mixture in supercritical or near-critical state of water.

The invention further relates to an apparatus for hydrothermal treatment of organic material, the apparatus comprising a reaction section for reacting a reaction mixture comprising said organic material and an enhancing addi- tive in supercritical or near-critical state of water.

The invention also relates to a use.

The method and apparatus of the invention can be used for treating waste, or low-value, streams of biomass and converting these to gaseous or liquid fuels or base components for further refining. BACKGROUND OF THE INVENTION

Research in the area of a hydrothermal gasification/ liquefaction process conducted at high pressure and high temperature dates back to 1978, when J. Model discovered that supercritical water, i.e. water at conditions where the temperature is above 374°C and the pressure is at least 221 bar, can be used to gasify organic matter and that tar production was minimized and even inhibited when supercritical water was used as a medium. The method has been further developed by a few research groups to include liquefaction, as well as gasification, of various wet biomass feeds in both near critical water, i.e. pressure of water in the range of 150-220 bar and temperature above 300 ⁰ C, and supercritical water.

The process has potentials to gasify waste sludge in the pulp and paper industry and to separate organic matter from inorganic. While the organic matter is gasified mainly to hydrogen, methane, carbon dioxide and carbon monoxide, the inorganic matter can be separated mechanically from the liquid phase. Gasification occurs around 450-700 ⁰ C depending on the material that is gasified, the prevailing process conditions and whether catalysts are used or not.

One of the problems associated with the process is that many biomass streams are difficult to gasify. As a solution, catalysts or additives are added to biomass streams. Catalysts and additives can enhance gasification

yields, alter the composition of the product gas or liquid products, shorten reaction times and reduce reaction temperatures.

Several studies have been conducted on the effect of different catalysts on hydrothermal treatment of biomass. Catalysts have been either het- erogeneous or homogeneous. Heterogeneous catalysts are in a different phase to the reactants, whereas homogeneous catalysts are in the same phase as the reactants. In the case of hydrothermal treatment said heterogeneous catalysts are typically solids.

In the earlier published articles, catalysts such as KOH, NaOH, K2CO3, LiOH and Na2CO3 have been used in experiments. Some of the studies have been disclosed in the following publications, each of which are hereby incorporated by reference in their entireties for all purposes:

1. Gasification of pyrocathecol in supercritical water in the presence of potassium hydroxide. A. Kruse, D. Meier, P. Rimbrecht, M. Schacht. 39, 2000, Ind. Eng. Chem. Res., pp. 4842-

4848.

2. Hydrogen production from glucose used as a model compound of biomass gasified in supercritical water. X.H. Hao, L.J. Guo, X. Mao, X.M. Zhang, X.J. Chen. 28, 2003, International Journal of Hydrogen Energy, pp. 55-64. 3. Hydrothermal gasification of biomass and organic wastes. H.Schmieder, J. Abeln, N. Boukis, E. Dinjus, A. Kruse, M. Kluth, G. Petrich, E. Sadri, M. Schacht. 17, 2000, J. of Supercrit. Fluids, pp. 145-153.

4. Influence of the heating rate and the type of catalyst on the formation of key intermediates and on the generation of gases during hydropyrolysis of glucose in supercritical water in a batch reactor. A. Sinag, A. Kruse, J. Rathert. 43, s.l. : American Chemical Society, 2004, Ind. Eng. Chem. Res., pp. 502-508.

5. Key compounds of the hydropyrolysis of glucose in supercritical water in the presence of K2CO3. A. Sinag, A. Kruse, V. Schwarzkopf. 42, s.l. : American Chemical Society, 2003, Ind. Eng. Chem. Res., pp. 3516-3521. 6. Supercritical water treatment of biomass for energy and material recovery. Y. Matsumura, M. Sasaki. 178, 2006, Combust. Sci. and Tech., pp. 509-536.

Results of the above-mentioned studies show an increase in gas yields, primarily in hydrogen gas yields, but also in methane and carbon dioxide yields. Carbon monoxide yields are decreased, often as much as below detection limits for the used gas analyzers. Also the liquid products contain less or no char and tar products.

One of the disadvantages associated with the use of catalysts is that homogeneous catalysts that are inserted together with biomass are expensive and often difficult to recover from the process, while heterogeneous catalysts, solids that remain in the reactor, suffer from deactivation, decompo- sition or contamination.

BRIEF DESCRIPTION OF THE INVENTION

It is thus an object of the present invention to provide a method and an apparatus for implementing the method so as to alleviate the above disadvantages. The objects of the invention are achieved by a method and an appa- ratus which are characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims. An idea of the method of the invention is that organic material is treated by reacting said organic material in water, the method comprising steps of: the method comprising steps of: obtaining a reaction mixture comprising said organic material and an enhancing additive, and reacting said reaction mixture in supercritical or near-critical state of water, and using black liquor as said enhancing additive for obtaining said reaction mixture.

An idea of the apparatus of the invention is that it comprises a reaction section for reacting a reaction mixture comprising said organic material and an enhancing additive in supercritical or near-critical state of water, wherein the apparatus comprises feeding means for feeding black liquor as an enhancing additive to the reaction mixture.

An idea of the use of the invention is that black liquor is used as an enhancing additive for converting organic material into reaction products in supercritical or near-critical state of water.

The invention is based on the realization that black liquor enhances hydrothermal treatment of organic material, e.g. biomass.

An advantage of the method and apparatus of the invention is that inexpensive black liquor, which is an abundant waste stream of production of pulp that needs to be treated anyway, can be used instead of costly chemicals in the reaction.

Another advantage of the method and apparatus of the invention is that black liquor addition makes the reaction mixture easier to process, because it reduces the biomass particle size and tendency of biomass fibers to bond into agglomerates. The reaction mixture has a slippery character due to

which higher dry matter contents are achievable. This leads to a decrease of excess water in the process and, thus, reduces energy needed for heating the reaction mixture.

Still another advantage of the method and apparatus of the inven- tion is that using black liquor for enhancing the hydrothermal treatment of bio- mass leads to an increased value of the product gas compared to the treatment of pure biomass, because an addition of black liquor increases significantly hydrogen production, gives higher gas yields at shorter reaction times, eliminates or reduces char and tar production, and eliminates or reduces pro- duction of carbon monoxide.

An idea of an embodiment of the invention is that the method and the apparatus are integrated with or connected to processes of a Kraft pulp mill and a paper mill. This provides the advantage that black liquor and biomass are fed in the hydrothermal treatment of biomass in a straightforward way avoiding costly transporting. Another advantage is that the Kraft pulp mill and the paper mill provide a constant supply for the reactants used in the hydro- thermal treatment. A preferred idea of the invention is that the reaction mixture comprises slush pulp or primary sludge and black liquor.

BRIEF DESCRIPTION OF THE DRAWINGS In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which

Figure 1 is a schematic representation of an apparatus and a method of the invention shown as a process flow diagram; Figure 2 is a schematic representation of a second apparatus and a method of the invention shown as a process flow diagram;

Figure 3 is a schematic representation of a third apparatus and a method of the invention shown as a process flow diagram; and

Figure 4 is a schematic representation of the gas yields from various gasification processes.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 is a schematic representation of an apparatus and a method of the invention shown as a process flow diagram.

First, organic material and black liquor are fed in mixing equipment 3 in which said materials are mixed in suitable proportion to each other. A

stream of biomass comprising said organic material and water is presented as an arrow 1 and stream of black liquor as an arrow 2 in Figure 1. Both the biomass and black liquor are fed through feeding means 11 and 12, respectively. The feeding means 11 , 12 are known as such. The feeding means 12 of black liquor may comprise a pump and a feeding pipe etc., whereas the structure of the feeding means 11 of biomass depends on the nature of said biomass. Easily flowing or running biomasses may be fed by, for instance, arrangements comprising a pumping system, whereas biomasses having high viscosity may be fed by conveyor arrangements, such as a screw conveyor etc. As a result of the mixing, a reaction mixture is achieved. Said suitable proportion of the materials depends on, inter alia, the dry matter contents of biomass and black liquor. The dry matter content of black liquor is typically 15-20 percentages by weight (weight-%).

The water content of the reaction mixture is preferably at least 70 weight-%, in an embodiment of the invention at least 80 weight-%, and in another embodiment of the invention at least 90 weight-%. The water participating in the reactions is preferably mainly the moisture i.e. water already present in wet biomass. Additional water may be fed in the mixing equipment 3 if necessary. Additional water may also be admixed to biomass prior to its feeding in the mixing equipment 3. The water content should be high enough to achieve a well-flowing mixture. Gas yields and compositions are affected by the water content.

The optimal water content of the reaction mixture depends on the characteristics of biomass. Black liquor addition makes the reaction mixture easier to process, because it reduces the particle size of biomass and tendency of its fibres to create agglomerates. The reaction mixture has a slippery and smooth character and, thus, high dry matter content may be achieved without sacrificing rheological characteristics of the reaction mixture. Therefore, the content of excess water in the reaction mixture may be decreased, which leads to lower energy requirement in the heating of the reaction mixture. It is to be noted that the mixing equipment 3 is known as such. It may be, for instance, an axial-flow impellar mixer with bottom and side scrapers. A mill might be needed for biomass preparation. A combined mixer and mill, a macerator, is also an alternative mixing equipment 3. The term "biomass" refers to virgin and waste materials of a plant, animal and/or fish origin, such as municipal waste, industrial waste or by-

products, agricultural waste or by-products (including also dung), waste or byproducts of the wood-processing industry, waste or by-products of the food industry, marine plants (such as algae) and combinations thereof. The biomass material is preferably selected from non-edible resources such as non-edible wastes and non-edible plant materials, including oils, fats and waxes. A preferred biomass material according to the present invention comprises waste and by products of the wood-processing industry such as residue, urban wood waste, lumber waste, wood chips, sawdust, straw, firewood, wood materials, paper sludge, primary and/or secondary sludge, deinking waste sludge, paper, by-products of the papermaking or timber processes, short rotation crops etc. Also peat and can be used as biomass in the process. Biomass may be a blend comprising water and organic material that has been purposely blended for using in the method and apparatus of the invention.

The term "black liquor" refers to a byproduct of a Kraft pulping proc- ess in which wood chips are delignified in alkaline solution. In the process, wood is decomposed into cellulose fibers, hemicellulose and lignin. The fibers are separated and directed to further processing. The resulting aqueous solution of lignin residues, hemicellulose and the inorganic chemicals used in the process is black liquor. The reaction mixture is then pressurized to a desired pressure, for instance in the range of 150-400 bar, by first pressurizing means 4 and fed to a reactor system 5. The first pressurizing means 4 may be, for instance, a pump. It is to be noted that the reactor system 5 is shown by a dashed line in Figure 1. The pressurizing to the desired pressure may take place in one step, for ex- ample by one pump, or stepwise, for example by several pumps connected in series.

The reactor system 5 comprises a heating section 6, a reaction section 7, a cooling section 8 and a separator unit 9. The reaction section 7 is shown by a dot-and-dash line in Figure 1. The sections 6-8 are connected in series by ducts etc.

The heating section 6 and the cooling section 8 may be, for instance, heat exchangers known per se. Also the reaction section 7 and the separator unit 9 are known per se.

Due to the tubular construction the capacity of the apparatus may easily be scaled up or down to fit various primary material streams.

The heating section 6 is, preferably, connected to the cooling section 8 so that heat energy discharging from reaction mixture cooling down in the cooling section 8 can be utilized in heating the reaction mixture in the heating section 6. Hydrothermal reactions needed for restructuring the organic material take place in the reaction section 7. However, important reactions forming intermediate products may also occur already in the heating section 6.

Said reactions in the reaction section 7 are gasification and/or liquefaction reactions which occur at high temperature and high pressure, either in supercritical water, i.e. at temperature above 374°C and pressure at least 221 bar, or near-critical water, i.e. at temperature above 300 ⁰ C and pressure above 150 bar. A heater device 10 has been arranged in the reaction section 7 for maintaining the temperature at desired level in the reaction section 7. The heater device 10 is, for instance, an electric or gas heater. The heater device 10 is capable of keeping a stable temperature through the whole reaction section 7. Temperature requirements vary, depending on, for instance, thermodynamics of the reactions, i.e. whether exothermic reactions or endothermic reactions occur.

In supercritical water organic compounds and gases become fully soluble in water, thus reactions can occur in one phase and reaction times are shortened.

Organic materials or compounds are decomposed and restructured under the influence of the hot compressed water. Typically, gasification reactions require temperatures of about 500-700 ⁰ C, whereas liquefaction reactions require temperatures about 350-500°C.

Reaction times vary from 30 seconds to 15 minutes depending of biomass, apparatus construction and heating time. Usually, only short reaction times are needed, that is not more than 2 minutes.

After the required reaction time has passed reaction products are cooled down in the cooling section 8 and depressuhzed.

The depressuhzation may occur in one step, for example by letting the reaction products flow through a valve arranged between the cooling section 8 and the separator unit 9, whereby gases and liquids separate. Alternatively, the depressurization is done in several steps. Thus corrosion caused by high velocities reaction products at depressurization can be minimized. Furthermore, certain gases can be separated from each other and collected at a

certain pressure. The depressurization in several steps may take place in the cooling section 8.

Following the cooling and depressurization the reaction mixture separates out to a gaseous and liquid phase. The liquid phase is collected from the bottom and the gaseous phase from the top part of the separator unit

9. The gaseous phase comprises mainly CO2, CO, H ₂ and CH ₄ , H ₂ being the main product. The main component of the liquid phase is water. The liquid phase comprises also inorganic material. Said inorganic material may be, for instance, sulphur compounds of sodium and potassium, carbonates and salts. If the gasification is not complete, organic substances, such as hydrocarbons, phenols and pure carbon can be found in the liquid phase.

It is to be noted and emphasized that the apparatus shown in Figure 1 is just an alternative to realize the apparatus of the invention. The apparatus may be construed differently. For example, the reaction mixture can be pre- heated close to its boiling temperature prior to pressuhzation to the reaction pressure, heating and pressurization of the reaction mixture can take place in one and the same section of the reactor system 5, for example in the reaction section 7 itself etc. The apparatus of Figure 1 is construed for a continuous processing, but, alternatively, the method of the invention can be performed as a batch process. The reaction mixture may also be fed directly to the reaction section 7 as shown by an arrow 15. In this embodiment, the heating section 6 is bypassed or it may be omitted entirely from the apparatus. When feeding the reaction mixture directly to the reaction section 7, the reaction mixture may be heated to the reaction temperature either prior to or after its feeding to the re- action section 7. Alternatively, the reaction mixture is pre-heated prior feeding to the reaction section 7 and heated further to the reaction temperature in the reaction section 7.

Black liquor addition to a hydrothermal treatment of biomass leads to a more effective conversion from biomass to gaseous products compared to a hydrothermal treatment without addition of black liquor. Thus more gas is produced, which gas can be sold or used as a source of energy. In addition to this the gas is more valuable, since the main components are hydrogen, carbon dioxide and methane. Due to the more effective conversion of the biomass into gas and liquid, a contamination of the apparatus is limited and delayed. Contaminants, such as char and tar, can cause clogging of pipework or deactivation of catalyzing effects of a reactor material. When purer products are pro-

duced, the need for cleaning or replacement of components in the reactor system 5 is decreased.

According to an embodiment of the invention the apparatus of the invention is directly connected to a pulping process of a pulp mill by a suitable pipework. A stream of black liquor is fed form the pulping process for use in the apparatus. In order to minimize energy losses and costs of the treatment, the biomass is preferably waste material produced in the pulp mill or in the vicinity of said pulp mill, e.g. waste paper of a paper mill, which is connected to the pulp mill. In addition, any other biomasses coming not from the paper mill but from another sources may be fed in the apparatus, too. The biomass can also be a biomass containing waste stream of the pulp mill, e.g. primary and/or secondary sludge. It is not necessary, of course, to locate the apparatus of the invention in the vicinity of the pulp mill or the paper mill.

Generally speaking, different kind of biomasses can be combined and fed into one and same treatment process. If the characteristics or composition of the biomass is varying considerably, the parameters of the process, such as temperature, pressure and reaction time, may be adjusted accordingly.

Figure 2 is a schematic representation of a second apparatus and a method of the invention shown as a process flow diagram.

The apparatus does not have mixing equipment where streams of biomass 1 and black liquor 2 are mixed prior to their feeding into a reactor system 5. Instead, the stream of biomass 1 and the stream of black liquor 2 are fed separately to the reactor system 5. The both streams are pressurized by pressurizing means before they are fed to the reactor system 5 and before they are forming a reaction mixture.

The pressure of the biomass is raised up to the desired level in a second pump 13, whereas a third pump 14 takes care of pressurization of black liquor. The pumps 13, 14 are, for instance, high-pressure pumps known per se.

The pressurized streams of biomass 1 and black liquor 2 are fed to the heating section 6, where they mix and form a reaction mixture. Thereafter, the reaction mixture is heated and reacted in the heating section 6 and the reaction section 7 in the same way as described earlier in this description. Also cooling in the cooling section 8 and depressuhzation in the separator unit 9 take place in the same way as described earlier. The reaction section 7 com-

prises also a heater device 10, which is not shown in Figure 2. Generally, the structure of the reaction section 7 may be continuous tubular reactor or batch or semi-batch reactor. It may also be a fluidized bed reactor.

Figure 3 is a schematic representation of a third apparatus and a method of the invention shown as a process flow diagram. The streams of biomass 1 and black liquor 2 are pressurized by a second pump 13 and a third pump 14, respectively, and fed directly to the reaction section 7, where they mix and form a reaction mixture. The pressure of the reaction mixture may, if necessary, be raised up further in the reaction section 7. The streams of biomass 1 and black liquor 2 may be heated to the reaction temperature either prior to or after their feeding to the reaction section 7. Alternatively, the streams of biomass 1 and black liquor 2 are pre-heated prior the feeding to the reaction section 7 and heated further to the reaction temperature in the reaction section 7. Still another possibility is to heat the re- action mixture formed in the reaction section 7 in the reaction section 7 to the appropriate reaction temperature.

Cooling in the cooling section 8 and depressuhzation take place in the same way as described earlier.

The embodiment of the invention shown in Figure 3 may be applied primarily in batch processes, but it may be applied in continuous processes, too. When being applied to a batch process, the cooling section 8 is not an essential component of the apparatus, because the cooling step can take place in the reaction section 7.

Figure 4 is a schematic representation of the gas yields from various supercritical water gasification processes. To be precise, Figure 4 shows results achieved from black liquor enhanced supercritical water gasification of paper sludge compared with results from gasification of paper sludge with NaOH, K2CO3 and KOH as catalysts. Also a result of a gasification of pure paper sludge is shown, marked as "none". The gasification took place at temperature of 600 ⁰ C and pressure of

240-250 bar. The ratio of inorganic material to organic material was 0.4-0.47.

It is to be noted here that the ratio of inorganic material to organic material is preferably in the range of 0.01 - 0.5, more preferably 0.05 - 0.35. The term "inorganic material" refers to inorganic material in black liquor and the term "organic material" refers to the sum of organic materials of black liquor and biomass. The ratio is calculated as a ratio of dry matter contents ex-

pressed as weight-%.

The results are shown as moles of gas produced per weight of dry organic material of the biomass. The organic material in black liquor has been added to the organic material in the paper sludge and the total sum of organic material has thus been calculated for the mix.

As can be seen, the addition of black liquor enhances production of hydrogen when compared to conventionally used alkali catalysts. Also the production of CO was decreased below the detection limit of a gas analyser.

The gas yields are increased with increased amount of added black liquor. However, at the same time the amount of organic material is increased which again results in decreasing gas yields due to higher dry matter of the reaction products. This can be compensated by adding water to the mix.

Practical experiments have proved that the content of H ₂ can be as much as 60-70% of the gas. Without wishing to be bound by any theory, it is believed that the reason why black liquor can be used instead of alkali catalysts in the supercritical water gasification process is the high concentration of sodium and hydroxide ions in black liquor.

The method of the invention is highly profitable due to increased gasification yields as well as high dry matter content. Therefore, the process can be utilized in gasification of biomass slurries, the gasification or incineration of which is not profitable by means of known technology. The product gas can be utilized directly as fuel or as raw material for fuel synthesis (DME, Fischer Tropsch, a.s.o.). Black liquor is abundant in the pulp industry and due to its toxicity to most of organisms it must be treated in some way. Usually it is burned in recovery boiler and the resulting smelt is treated further to recover the inorganic chemicals in it. In the method according to the invention the biomass is converted to highly usable gases and/or liquids and the organic material in black liquor is also gasified or liquefied to gaseous or liquid fuels or base components for further upgrading. The method of the invention is therefore, an alternative for treatment of black liquor itself.

The inorganic material in the liquid phase can be recovered in a similar way as when black liquor is burned in a recovery boiler. It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The in-

vention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.