PL246789B1 - Pellets made of a mixture of straw and dry sewage sludge, with improved mechanical strength - Google Patents

Abstract

The subject of the application is a pellet made of a mixture of straw and dry sewage sludge, with improved mechanical strength, characterized in that the mixture of straw and dry sewage sludge containing dry sewage sludge and straw in a mass ratio of dry sewage sludge to straw of 1:99 to 1:4, contains an additive improving mechanical strength, which is torrefacted sawdust from coniferous wood in an amount of 0.5 to 2% (m/m), calculated on the mass of the pellet, which torrefacted product was obtained by carrying out the process at a temperature of 230°C, for 80 minutes, in a flow of 12 l/h of inert gas.

Description

Description of the invention

FIELD OF TECHNOLOGY

The subject of the invention is a pellet made of a mixture of straw and dry sewage sludge, with improved mechanical strength.

STATE OF TECHNOLOGY

Unprocessed plant biomass is characterized by a relatively low bulk density, which makes it difficult to transport, store and use in practice. Hence, it is necessary to densify it, e.g. in the form of pellets or briquettes. They are produced from dry, crushed biomass under high pressure and at elevated temperature, usually without the addition of a binder. During agglomeration, the forces and temperature that occur cause the densification of a significant amount of raw material in a small volume. This results in a decrease in water content, an increase in the concentration of mass and energy, and significantly improves the comfort of distribution and use of this biofuel.

The quality of pellets, determined by several physical properties such as bulk density, calorific value, mechanical strength, moisture content and calorific value, depends on the quality of the raw material and the parameters of their production. One of the most important parameters concerning pellets is mechanical strength.

Mechanical strength means the ability of the concentrated biofuel to remain intact during technological operations and transportation, therefore it is one of the most important quality parameters for both the manufacturer and the customer.

In order to obtain the appropriate mechanical strength, it may be necessary to use binding substances - so-called binders - in the pellet production process. Usually, substances of organic origin - plant or animal - are used as binders, so that their addition does not reduce the biomass content in the fuel. Binders are added to biomass in the range of 0.5% to 5.0% by mass.

Polish patent application P.395378 presents a fuel pellet produced from dried sewage sludge.

Polish patent description PL214121 describes a method for obtaining fuel in the form of pellets using animal meat and bone meal and feathers, with the addition of bran, straw, oil cakes and oil plant meals and using animal and vegetable fats as binders.

Polish patent description PL215280 presents a method for obtaining fuel pellets from biomass, in which a post-fermentation substrate obtained as a result of the biogas process is used as a binder.

The authors of Polish patent application P.421069 describe a method for obtaining pellets from sawdust with rye bran.

Polish patent application P.427593 discloses a method for obtaining fuel in the form of pellets consisting of wood chips, sewage sludge and grass straw in various weight ratios.

Polish patent application P.380210 discloses a method for producing pellets from bran from mills, malt houses or distilleries.

Patent description JP2019172766 presents a method for obtaining pellets from bamboo biomass, in which sewage sludge is used as a binder.

The authors of the invention TWI639693 described a method of obtaining thickened fuel from food residues and organic deposits bound with a binder, which may be selected from one or a combination of the following substances: kitchen waste, sweet potato flour, corn starch, rice, oatmeal.

Patent description EP2865736 describes a solid fuel obtained from a mixture of biodegradable municipal waste and/or industrial fibrous materials from natural textiles and fibres, and/or industrial waste of cellulosic products, phytomass from cultivation, preferably straw, waste from hydroponic cultivation, dust from grinding all types of cereals and/or dried fruits and/or dried flowers and/or dried vegetables after the expiry date and/or pomace and other waste from plant production and/or tobacco waste and/or cork waste.

Patent description KR101539224 discloses a solid fuel consisting of biomass and organic sludge from a sewage treatment plant. In order to improve the mechanical properties of the fuel, a binder was used, which may be: a saccharified waste solution, a seaweed extract concentrate, a chitosan solution, corn starch and a mixture thereof and is used in an amount of 0.1 to 2.0% by weight based on the total weight of the fuel mixture.

Patent application US20110197501 discloses a composition of solid fuel consisting of coal dust and biomass, for the production of which a binder was used, being a substance selected from: lignin, lignin and asphalt emulsion, wheat starch, lignosulfonate, tall oil, coal tar, polyvinyl alcohol, phenolic resin, paper sludge, molasses, lime, guar gum, a polymeric material and a mixture thereof.

Polish patents PL244102, PL244104, PL244103 and PL244101 disclose compositions of pellets consisting of dry sewage sludge and rapeseed cake, straw, wheat bran and hay, respectively. To improve the mechanical strength of the above-mentioned pellets, an additive composition was used, which contained quicklime and calcium lignosulfonate.

The aim of the present invention is to obtain pellets from a mixture of straw and dry sewage sludge with improved mechanical strength, which will be characterized by higher mechanical strength than pellets from a mixture of straw and dry sewage sludge, the mechanical strength of which has not been improved.

It has surprisingly been found that the pellets made from a mixture of straw and dry sewage sludge according to the invention have such properties, which are characterized by a higher mechanical strength than pellets whose mechanical strength has not been improved.

THE ESSENCE OF THE INVENTION

Pellets made from a mixture of straw and dry sewage sludge, with improved mechanical strength, are characterized in that the mixture of straw and dry sewage sludge containing dry sewage sludge and straw in a mass ratio of dry sewage sludge to straw of 1: 99 to 1: 4, contains an additive improving mechanical strength, which is torrefacted sawdust from coniferous wood in an amount of 0.5 to 2% (m/m), calculated on the mass of the pellet, which torrefacted product was obtained by carrying out the process at a temperature of 230°C, for 80 minutes, in a flow of 12 l/h of inert gas.

It turned out during the research that refining pellets made from a mixture of straw and dry sewage sludge with torrefacted sawdust from coniferous wood allows for improving the mechanical strength of the pellets by over 33% compared to pellets made from a mixture of straw and dry sewage sludge not containing torrefacted sawdust from coniferous wood.

The present invention is presented in embodiment examples 1 to 14, illustrating the composition, method of production and results of test tests for assessing the mechanical strength of pellets made of a mixture of straw and dry sewage sludge refined with torrefied sawdust from coniferous wood, and therefore cannot be considered as limiting the essence of the invention, since they are only of illustrative nature.

Example 1 illustrates the method of producing softwood sawdust torrefied product used in the present invention. Examples 2, 6 and 10 are comparative examples, and Examples 3-5, 7-9 and 11-14 are examples illustrating the invention.

EXAMPLES

Example 1

200 g of coniferous wood sawdust with properties given in Table 1 were weighed, then placed in a single-necked round-bottom flask, to which an inert gas was supplied by a bubbler near the bottom of the flask, while hot post-process gases were discharged through the top to a water cooler, in which the liquid phase condensed, and the gas phase was discharged to the atmosphere. The torrefaction process was carried out at a temperature of 230°C, for 80 min, in a flow rate of 12 l/h of inert gas. After the process was completed and cooled, 56.60 g of torrefied product was obtained.

PL 246789 Β1

Table 1. Characteristics of coniferous wood sawdust used for testing.

Parameter Unit Value Appearance — characteristic Total moisture content % 11.2 Calorific value kj/kg 16560 Elemental carbon content % 46.7

Example 2 - comparative example

1485 g of straw with properties given in Table 2 and 15 g of dry sewage sludge with properties given in Table 3 were weighed. Straw and dry sewage sludge were mixed and then granulated in a ZLSP-150B pelleting machine from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Table 2. Characteristics of the straw used for the tests.

Parameter Unit Value Appearance - characteristic Moisture content % 15 - 20 Ash content % 3-6 Calorific value MJ/kg 12.4 - 13.8

Table 3. Characteristics of dry sewage sludge used for testing.

Parameter Unit Value Appearance - dark gray powder Moisture content % 11.0 Ash content % 35.1 Calorific value MJ/kg 12.1

Example 3

1477.575 g of straw with properties given in Table 2, 14.925 g of dry sewage sludge with properties given in Table 3, 7.500 g of torrefacted product obtained in Example 1 were weighed. All components and torrefacted product were mixed and then granulated in a ZLSP-150B pelletizing device from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 4

1470.15 g of straw with properties given in Table 2, 14.85 g of dry sewage sludge with properties given in Table 3, 15.00 g of torrefacted product obtained in Example 1 were weighed. All components and torrefacted product were mixed and then granulated in a ZLSP-150B pelletizing device from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 5

1462.65 g of straw with properties given in Table 2, 7.35 g of dry sewage sludge with properties given in Table 3, 30.00 g of torrefacted product obtained in Example 1 were weighed. All components and torrefacted product were mixed and then granulated in a ZLSP-150B pelletizing machine from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 6 - comparative example

1350 g of straw with properties given in Table 2 and 150 g of dry sewage sludge with properties given in Table 3 were weighed. Straw and dry sewage sludge were mixed and then granulated in a ZLSP-150B pelleting machine from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 7

1343.25 g of straw with properties given in Table 2, 149.25 g of dry sewage sludge with properties given in Table 3, 7.50 g of torrefacted product obtained in Example 1 were weighed. All components and torrefacted product were mixed and then granulated in a ZLSP-150B pelletizing machine from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 8

1336.50 g of straw with properties given in Table 2, 148.50 g of dry sewage sludge with properties given in Table 3, 15.00 g of torrefacted product obtained in Example 1 were weighed. All components and torrefacted product were mixed and then granulated in a ZLSP-150B pelletizing device from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 9

1323.00 g of straw with properties given in Table 2, 147.00 g of dry sewage sludge with properties given in Table 3, 30.00 g of torrefacted product obtained in Example 1 were weighed. All components and torrefacted product were mixed and then granulated in a ZLSP-150B pelletizing device from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 10 - comparative example

1200 g of straw with properties given in Table 2 and 350 g of dry sewage sludge with properties given in Table 3 were weighed. Straw and dry sewage sludge were mixed and then granulated in a ZLSP-150B pelleting machine from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 1 1

1194.00 g of straw with properties from Table 2, 298.50 g of dry sewage sludge with properties from Table 3, 7.50 g of torrefacted product obtained in Example 1 were weighed. All components and torrefacted product were mixed and then granulated in a ZLSP-150B pelletizing device from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 12

1188.00 g of straw with properties given in Table 2, 297.00 g of dry sewage sludge with properties given in Table 3, 15.00 g of torrefacted product obtained in Example 1 were weighed. All components and torrefacted product were mixed and then granulated in a ZLSP-150B pelletizing device from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 13

1176.00 g of straw with properties given in Table 2, 294.00 g of dry sewage sludge with properties given in Table 3, 30.00 g of torrefacted product obtained in Example 1 were weighed. All components and torrefacted product were mixed and then granulated in a ZLSP-150B pelletizing device from Haven Polska Sp. z o.o. using a matrix with a mesh diameter of 6 mm.

Example 14

The mechanical strength of products from examples 2 to 13 was tested. The tests were performed according to PN-EN ISO 17831-1:2016-02 (Solid biofuels - Determination of mechanical strength of pellets and briquettes - Part 1: Pellets) in the "PELTEST" apparatus manufactured by TESTCHEM. The test consisted of placing approximately 500 g of tested pellets sieved on a 3.15 mm sieve in a steel cuboid rotating at 50 rpm, after 10 minutes separating the crushed pellets again on the same sieve and weighing the residue on the sieve. The following equation is used to calculate the strength of the tested pellet sample.

DU=(mA/mE)-100 where:

DU - mechanical strength, %

PL 246789 Β1 mA - sample mass after the test, g mE - sample mass before the test, g

The obtained results of mechanical strength tests are presented in Table 4.

Table 4. Mechanical resistance according to PN-EN ISO 17831-1:2016-02.

Tested sample Mechanical strength [%] Product from example 2 (comparative example) 77.51 Product from example 3 92.83 Product from example 4 93.53 Product from example 5 93.96 Product from example 6 (comparative example) 70.56 Product from example 7 94.10 Product from example 8 93.47 Product from example 9 92.70 Product from example 10 (comparative example) 79.86 Product from example 11 96.29 Product from example 12 91,91 Product from example 13 85.19

The above examples present the composition of pellets from a mixture of straw and dry sewage sludge with improved strength according to the invention and demonstrate the effectiveness of improving its mechanical strength in test trials, proving its industrial applicability.

The results of tests of the mechanical strength of pellets from a mixture of straw and dry sewage sludge with improved strength according to the invention were compared with the results of tests of pellets from a mixture of straw and dry sewage sludge not containing torrefacted material.

Claims (1)

1. Pellets made of a mixture of straw and dry sewage sludge, with improved mechanical strength, characterized in that the mixture of straw and dry sewage sludge containing dry sewage sludge and straw in a mass ratio of sewage sludge to straw of 1: 99 to 1: 4, contains an additive improving mechanical strength, which is torrefacted sawdust from coniferous wood in an amount of 0.5 to 2% (m/m), calculated on the mass of the pellet, which torrefacted product was obtained by carrying out the process at a temperature of 230°C, for 80 minutes, in a flow of 12 l/h of inert gas.