WO2013171081A1

WO2013171081A1 - Hydrothermal carbonization method for the coalification of carbohydrate-containing biomass

Info

Publication number: WO2013171081A1
Application number: PCT/EP2013/059341
Authority: WO
Inventors: Ingo Bauer; Rudolf BÖNSCH
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2012-05-18
Filing date: 2013-05-06
Publication date: 2013-11-21
Anticipated expiration: 2014-11-18
Also published as: DE102012104309A1

Description

Hydrothermal Carbonization Method for the Coalification of Carbohydrate- Containing Biomass

Field of the Invention

This invention relates to a hydrothermal carbonization method for the coalification of carbohydrate-containing biomass as feedstock.

Prior art

When carrying out hydrothermal carbonization methods, also referred to as HTC methods, carbohydrate-containing biomass is dispersed in water and exposed to elevated process temperatures between for example 180 and 350 °C in the presence of a catalyst, such as citric acid, in an autoclave for a defined period which mostly is a few hours, wherein the water is maintained in the liquid phase by building up a corresponding excess pressure. This results in a coalification of the biomass, in which the feedstock biomass is converted into a product consisting of coal or its precursors peat, humus or lignite, cf. the specialist article "Zauberkohle aus dem Dampfkochtopf", Max Planck Forschung 2/2006, pages 20-25, and WO 2008/1 13309. The degree of coalification generally increases with the duration of the conversion, as it is also the case in the naturally occurring coalification of biomass.

After the conversion by means of methods known per se, the method product of the HTC method, the so-called HTC coal, is mechanically separated from the water phase and thermally dried. When the separation of the product is effected by a simple filtration step, for example by vacuum or pressure filtration by forming a filter cake, the residual moisture to be removed by thermal drying generally is between 50 and 70 wt-% based on the weight of the product after the mechanical separation from the water phase. If the thermal drying expenditure is to be reduced, an additional equipment expenditure becomes necessary for the further dehydration of the product. For this purpose, mechanical pressing methods usually are recommendable, as they are technically realized e.g. by means of chamber filter presses.

The water left in the product of a hydrothermal carbonization method chiefly is bound to the product by adsorption or absorption; the height of the water content in the product, i.e. the residual moisture, therefore substantially depends on the size of the specific surface of the product.

In our own experiments we have observed that the use of feedstocks rich in lignin, such as wood, wood barks, leads to an HTC product with relatively low residual moisture (50 - 55 wt-%) after the product separation by means of vacuum filtration. After the product separation by means of vacuum filtration, the use of feedstocks poor in lignin (fermentation residues, stillage, feedstocks rich in starch such as cereal grains), on the other hand, leads to a product with relatively high residual moisture (60 - 70 wt-%). This fits in with the observation that in the HTC process wood pieces substantially retain their shape, whereas cereal grains disintegrate to a mostly powdery product.

What is disadvantageous in a high residual moisture of the HTC product on the one hand is the high equipment expenditure required for drying, e.g. the use of a chamber filter press, or the high energetic expenditure for drying by evaporation and on the other hand the resulting increased amount of dissolved inorganic impurities, such as alkali and alkaline earth ions, transferred to the product from the bound water content.

During the HTC process, these impurities can pass over from the biomass into the water phase. The amount of these impurities left on the product after drying leads to an increased formation of ash and to the lowering of the ash melting temperature when using the HTC product as feed material, for example in combustion and gasification processes, which in turn promotes slagging effects in the plants used for this purpose and can lead to disadvantageous consequences for the refractory brickwork or linings used in the plants. Therefore, it has been the object to provide an improved HTC method, which supplies a product with lower residual moisture and at the same time a reduced content of impurities, so that drying requires less energy and equipment expenditure. Description of the Invention

This object is solved by a method which comprises the features of claim 1 . Preferred aspects of the method according to the invention can be found in the sub-claims. Methods for the hydrothermal carbonization for the purpose of coalifying carbohydrate-containing biomass as feedstock comprise the following typical method steps:

(a) mixing the feedstock with water by forming a dispersion,

(b) optionally adding auxiliary substances and catalysts,

(c) reacting the dispersion under HTC conditions,

(d) obtaining a moist, carbonaceous HTC product by separating the obtained solids from the water phase by means of a mechanical separation method.

The method according to the invention in addition is characterized in that the fat or oil content of the feedstock is at least 6 wt-% of the dry matter, preferably at least 10 wt-% of the dry matter of the feedstock or is adjusted to these minimum values.

The addition of fats or oils to the biomass or the aqueous dispersion of the biomass to be treated by the HTC method surprisingly effects a distinct reduction of the residual moisture of the HTC product and hence a distinct reduction of the energetic and technical drying expenditure. The probable cause for the reduced residual moisture of the HTC product is the adsorption or absorption of the added oil or fat on its outer and/or inner surface, whereby the absorption capacity of the solid HTC product for water and thus its moisture content is reduced. This is astonishing, as under the method conditions, in particular at the high temperatures existing then, no significant absorption or adsorption has been expected.

Particular Aspects of the Invention

A particular aspect of the method provides that the adjustment of the fat or oil content of the feedstock is effected by adding fats and/or oils in a corresponding quantity. The addition of the oil or fat practically is effected along with filling the feedstocks into the autoclave or before closing the autoclave. It is, however, also possible to add or admix the oil or fat to the dispersion at the end of the HTC process, after opening the autoclave.

The idea underlying the invention likewise comprises the use of feedstocks with increased oil or fat content. These feedstocks can be used in the method according to the invention alone or as admixture to feedstocks containing less oil or fat. For example, one or more further carbohydrate-based feedstocks richer in oil can be admixed to a first feedstock poor in oil or fat, in order to adjust the fat or

011 content of the feedstock according to the invention. It is advantageous that in this way the one or more further feedstocks can be converted to the HTC product, the so-called HTC coal.

Typically, the method according to the invention is carried out such that in method step 1 (c) the temperature is between 180 and 350 °C, preferably between 200 and 300 °C, the pressure is between 1 and 100 bar, absolute, preferably between 60 and 90 bar, absolute, and the duration of the treatment is between 5 min and

12 h, preferably between 1 h and 3 h, and that an HTC catalyst is added. As HTC catalyst citric acid can be used, for example. The temperature and residence time for the HTC process is chosen in dependence on the type of biomass used and on the desired quality of the HTC product. The skilled person will adapt the method conditions by routine experiments with regard to the specific type of feedstock, so as to obtain the HTC product in an optimum way.

The separation of the solid HTC product, the so-called HTC coal, is effected by using a mechanical separation method, for example the filtration, sedimentation, centrifugation or decantation individually or in any combination. The selection of the suitable separation method chiefly depends on the nature of the HTC product.

Advantageously, oils or fats of animal or vegetable origin are used, since the same generally contain less harmful substances than mineral oils and therefore create less problems with respect to the release of pollutants during the subsequent use of the HTC product.

In principle, it is possible to carry out the HTC method according to the invention either intermittently or continuously. The intermittent or discontinuous operation is preferred, since with regard to the multitude of possible carbohydrate-containing feedstocks which can differ distinctly in terms of their specific properties, a greater flexibility exists for adjusting optimum method conditions (e.g. temperature, duration of treatment) than this is possible in a continuous method. However, in case larger amounts of largely homogeneous biomass must be processed, the continuous operation can be more advantageous, since set-up times for example for filling and draining the reaction tank then are eliminated.

Exemplary embodiments and numerical examples

Further developments, advantages and possible applications of the invention can also be taken from the following description of exemplary embodiments and numerical examples. All features described and/or illustrated form the invention per se or in any combination, independent of their inclusion in the claims or their back-reference.

Numerical example: The following batch was charged into a stirred autoclave:

30 g of unground grain maize

- water content 10 wt-%, dry matter (DM) 27 g

- inherent content of fats/oils 2.6 wt-%, based on dry matter, corresponding to 0.7 g per 30 g of grain maize

- 0.5 g of citric acid as catalyst

The determination of the fat or oil content of the feedstocks was effected according to the method EN ISO 1 1085:2010 (method A).

This mixture was filled up to 100 g with distilled water. The amounts of soybean oil indicated in the following table were added before carrying out the hydrothermal carbonization. After the HTC conversion in the autoclave at 300 °C and 80 bar (absolute) for a period of 2 hours, a solid, moist product of fine-grained to lumpy consistency was obtained by sucking off on a nutsch filter. The weight loss thereof was determined gravimetrically after drying in the drying cabinet at 100 °C (12 hours). From the ratio of the weights before and after drying, the water content of the HTC product separated by the filtration step was calculated.

The effect underlying the invention will be noticed from a total content of fats or oils of about 6 wt-%, particularly clearly from a total content of fats or oils of about 10 wt-%, based on the dry matter of the feedstock. The HTC products obtained in experiments 3, 4 and 5 each had a lumpy, rubber-like consistency.

Comparative example:

In experiment 1 no soybean oil was added. Under otherwise identical experimental conditions, a solid HTC product of largely powdery consistency was obtained. Its water content was more than twice the water content of the HTC products, which where obtained when carrying out the method according to the invention (experiments 3, 4 and 5).

Claims

1 . A hydrothermal carbonization method (HTC method) for the coalification of carbohydrate-containing biomass as feedstock, comprising the following method steps:

(a) mixing the feedstock with water by forming a dispersion,

(b) optionally adding auxiliary substances and catalysts,

(c) reacting the dispersion under HTC conditions,

(d) obtaining a moist, carbonaceous HTC product by separating the obtained solids from the water phase by means of a mechanical separation method,

characterized in that

the fat or oil content of the feedstock is at least 6 wt-% of the dry matter, preferably at least 10 wt-% of the dry matter of the feedstock, or is adjusted to these minimum values.

2. The method according to claim 1 ,

characterized in that

the adjustment of the fat or oil content of the feedstock is effected by adding fats and/or oils in a corresponding quantity.

3. The method according to claim 2,

characterized in that

the added fats or oils are present as pure substances or bound to or contained in at least one further feedstock whose fat or oil content is higher than that of the first feedstock.

4. The method according to any of the preceding claims,

characterized in that

in method step 1 (c) the temperature is between 180 and 350 °C, preferably between 200 and 300 °C, the pressure is between 1 and 100 bar, absolute, preferably between 60 and 90 bar, absolute, and the duration of the treatment is between 5 min and 12 h, preferably between 1 h and 3 h, and that an HTC catalyst is added.

5. The method according to any of the preceding claims,

characterized in that

citric acid is used as HTC catalyst.

6. The method according to any of the preceding claims,

characterized in that

as mechanical separation method the filtration, sedimentation, centrifugation or decantation is used individually or in any combination.

7. The method according to any of the preceding claims,

characterized in that

the used fats and/or oils are of animal or vegetable origin.

8. The method according to any of the preceding claims,

characterized in that

the method is carried out intermittently or continuously.