FI92109C - Method for determining the combustion properties of residual liquor formed in the production of cellulose - Google Patents

Description

92109

Method for determining the combustion properties of a waste liquid formed in the manufacture of cellulose

The invention relates to a method for determining the combustion properties of waste liquor of varying physical and chemical properties formed in cellulose production, in which method the waste liquor is determined before it is fed to a recovery boiler.

In cellulose cooking, the wood raw material is usually boiled in a strongly alkaline solution, whereby the lignin, which binds the cellulose fibers together, separates. The effluent formed during cooking, commonly referred to as black liquor, thus comprises lignin, its decomposition products as well as the decomposition products of the carbohydrate material, i.e. cellulose and broth celluloses, as well as various extractants. The composition of the black liquor varies quite a lot depending on the type of wood raw material used and thus its chemical and physical properties vary greatly.

Black liquor contains quite a variety of ingredients that are economically significant and profitable to recover. In addition, the black liquor contains 25 materials that can be burned and thus recover energy that would otherwise have to be obtained. The black liquor is utilized by first evaporating the water out of it and then burning it, typically at a dry matter content of 60-70% in a recovery boiler. In this case, these inorganic salts in the black liquor are recovered so that they can be re-used after the treatment steps suitable for the cooking solution. As the price of energy is constantly rising, efforts have been made to carry out combustion as efficiently as possible. In this case, the aim is both to achieve the best possible energy efficiency, the most efficient 2 92109 possible chemical regeneration and, in addition, low waste emissions. However, the problem with the incineration crop is that the different properties of black liquor greatly affect its combustion, and the variation in the physical and chemical properties of the liquor also causes the combustion of the liquor to require different conditions and yield measures. Similarly, variation in dry matter content greatly affects combustion properties. In the past, the problem has been avoided by the fact that the cooking process of the cellulose 10 and, consequently, the physical and chemical properties of the black liquor have been kept as constant as possible. In this case, it was possible to carry out the combustion at relatively fixed setpoints, which were reached on the basis of test runs. However, the application of this procedure-15 most often requires the use of only one chip grade and the production of a certain type of the same cellulose pulp grade, whereby the process variations remain small and the resulting black liquor is relatively uniform. However, it is quite typical in the present conditions to use different types of chips depending on the situation, to produce cellulosic pulps with different properties, to use a closed loop to avoid wastewater, etc., as a result of which

Various emission parameters are used in the combustion of black liquor, such as pareunet, which describes the properties of black liquor, parameters describing the operation of the process, and various production and emission values. In general, an attempt has been made to measure the combustion behavior of black liquor 30 by applying various methods based on the activation energies of the lipids as determined by the DTA technique and the putative relationships between them and the combustibility of the liquors. However, the results obtained in this respect are not 35 good enough and the combustion cannot be efficiently controlled on the basis of these. The combustibility of the lye has also been studied by burning the lye droplets in a laboratory furnace with air in place while the combustion event is being recorded by a video camera11a. By examining in this way, it has been found that the combustion of 5 black liquors in a recovery boiler can be divided into four separate successive stages, each of which is clearly dependent on the composition of the lye to be burned. Step one is a relatively long drying step in which water evaporates from the pi-sar. After the dough, the drop suddenly flashes into the flame, whereby the pyrolysis gases released in the so-called pyrolysis stage, i.e. the second stage, burn within a relatively short time. At this point, the drop usually also swells strongly. Thereafter, the porous coke residue, which has swelled several times compared to the original droplet, begins to return to its surface. The duration of this third stage varies very strongly between different types of lyes. Finally, in the fourth combustion step, the inorganic residue is oxidized according to generally known reactions. These various combustion steps are generally known per se and will not be explained in more detail for this reason. However, from the point of view of the combustion of the lye, it would be particularly necessary to know the properties of the lye to be fed with respect to these combustion stages, so that the combustion can be controlled as well as possible. However, this has not been possible in any way with the currently known weathering techniques.

The combustion of the lye is affected by, among other things, the droplet size of the lye, which is affected by both the viscosity of the lye and the surface tension. The droplet size, in turn, determines the heat-receiving surface of the liquor and thus the drying time and the end point of the drying phase from the liquor inlet to the inlet. The expansion property of the dry matter affects the trajectory of the dry matter particle generated from the black liquor in the fire-35 nest and thus the pyrolysis site in the boiler 4 92109 as well as the combustion of the coke residue. Furthermore, the slight swelling of the lye droplets appears to have a significant effect on the increase in the height of the heap at the bottom of the recovery boiler. In addition, the expansion property describes the flammability properties of the liquor, because the expansion increases the area of the reactive surface of the oxygen and thus improves the flammability. Correspondingly, a change in the effluent of the liquor changes the trajectory of the droplets in the recovery boiler and, in excess, may cause the droplets to travel to the tops of the boiler. Coke with a high-expansion lye burns 10 times faster than coke with a low-expansion liquor, which is due, at least in part, to a larger reaction area. Furthermore, the burning rate of coke is a factor that perhaps most significantly determines the flammability of black liquor in a recovery boiler.

15 The chemical properties of black liquors have been determined by various chromatographic analysis methods, in which, inter alia, in connection with the determination of cellulose fiber and other cellulosic material in connection with wood processing, infr it is possible to get the so-called With DRIFT technology, the reflection spectrum corresponding to IR radiation. FTIR is quite accurate and fast in its method of analysis, and despite the fact that it cannot currently be applied to online measurement, the sample preparation it requires is easy and fast to do. It is known from DE 35 04 486 to measure the progress of cooking cellulose by measuring the cooking solution according to the FTIR method. However, the application according to this publication is in no way related to the combustion properties of black liquor or their definition.

The object of the present invention is to provide a method for determining the combustion properties of waste liquor produced in the manufacture of cellulose by measuring it as easily and simply as possible. The method according to the invention is characterized in that the infrared spectrum is measured from the sample, that two spectral peaks are selected from the spectral peaks occurring at different frequencies of the infrared spectrum for each measurable burning characteristic, and that the combustion of each spectrum is determined.

Surprisingly, it has been found that in measurements performed by the FTIR technique, there are essentially linear dependencies between the ratios of the intensities of certain spectral peaks of the infrared spectral peaks and certain combustion properties of the blackhead. The essential idea of the invention is that the black liquor fed to the boiler is measured by IR or FTIR technology and its certain combustion properties are determined by means of preselected infrared spectrum frequency peak intensity ratios, whereby the boiler combustion conditions can be determined by. It is essential for a preferred embodiment of the invention that the sample 20 taken from the black liquor is measured by the FTIR method and the relative drying time, pyrolysis and coke burning time as well as the specific expansion of the liquor can be determined on the basis of the intensities of certain predetermined peaks. According to 25 key figures.

The invention is described in more detail in the accompanying examples and the accompanying drawings, in which Figure 1 shows the relative composition of the dry matter of pine sulphate black liquor as a function of cooking time, Figure 2 shows the I1505 ratio of intensities as a function of the relative pyrolysis 35 måntysulfaattimustalipeålle, 4 is a 6 92109 Figure spectral peaks I1595 and I17J5 a function of the intensity ratio of coke relatively burning time mantysulfaattimustalipealle, shown in Figure 5 the spectral I14S6 / I1505 in-5 intensity ratio as a function of the relative ominaispaisunnan mantysulfaattimustalipealle, shown in Figure 6 koivusulfaattimustalipean relative composition of dry matter as a function of cooking time, Figure 7 shows the ratio of the intensities of spectral peaks I1350 and I1U7 10 to drying as a function of time for the birch sulphate blackhead, Fig. 8 shows the ratio of the intensities of the spectral peaks I1350 and IU17 as a function of the relative pyrolysis time for the birch sulphate blackhead and Fig. 9 shows the ratio of the intensities of the spectral peaks I1350 and I1S50 as a function of the specific expansion.

The following examples illustrate in more detail how the ratio of the intensities of certain peaks in the FTIR spectrum and the combustion properties of mantesulfate black liquor and birch sulfate black liquor, respectively, correlate. Although only pine sulphate black liquor and birch sulphate tallow liquor have been treated in this context, it is self-evident that in a similar manner 25 methods are applicable to other cellulose cooking processes and waste liquors derived therefrom. It will also be apparent to those skilled in the art from the examples set forth below how intensity peaks corresponding to the properties of these lipids are determined and selected for application of the invention. In the examples, black liquors of varying chemical composition and physical properties have been prepared by sampling the liquor at appropriate intervals during pine and birch sulphate cooking. The samples have then been analyzed by FTIR and their combustion properties have been determined separately in each case by incineration under laboratory conditions in a known manner.

Example 1

A 2-4 mm fraction of industrial pine chips (Pinus svlvestris) was screened with rod screens. The chips were boiled in an 8-position (8 x 225 mL) oil bath digester and black liquor samples during cooking, with a yellowing time ranging from 75 minutes to 250 minutes.

Cooking conditions were as follows: 10 active alkalis 22% wood (as NaOH) sulphidity 30% liquid / wood ratio 4 L / kg temperature rise time 90 min

15 maximum lamp temperature 175 ° C

At each test point, the autoclave was removed from the oil bath after a certain cooking time and cooled in a water bath. The black liquor was separated by filtration from a mass which was washed and dried to constant weight.

Before cooking, the dry matter, extractant content (acetone and dichloromethane extraction; 8 and 8 hours) and lignin content were determined from the chips. From the cooked chips or pulps, the total dry matter yield was determined to be 1 to 25 and the chlorine number. To determine the lignin content, the chlorine number was multiplied by 0.82 to 0.90, depending on the magnitude of the chlorine number. The hydroxymono and dicarboxylic acids contained in the black liquor were analyzed by gas chromatography as their trimethyl derivatives. The formic and acetic acid contents of the samples were determined by preparing benzyl esters from these acids, respectively. In addition, the density and dry matter of the black liquor were analyzed. In the broth, it was assumed that 90% of the extractants would already be removed from the broth during the warm-up phase of the patient. The dry matter composition of black liquor is shown in Figure 1.

Combustion tests of black liquor samples were performed according to the prior art. In each case, the drying, pyrolysis and coke burn times as well as the relative expansion were determined at 5,800 ° C.

For FTIR analysis of black liquor samples, a drop of test liquor was applied to the surface of the potassium bromide powder and the mixture was shaken for three minutes in a vibrating-10 ball mill, after which the sample was smoothed. in a micro-cup (diameter 3 nun and depth 2 mm). Measurements were made in the wavelength range of 4000 to 400 1 / cm using DRIFT technique, and Kubelka-Munk transforms were calculated from the obtained transmittance spectra.

15 The analyzes and measurements presented above, as well as the calculation of the intensity of the measurement peaks, are in themselves well known to a person skilled in the art and are self-evident and will therefore not be explained in more detail here.

Figure 2 shows the ratio I1456 / I1505 as a function of relative drying time, Figure 3 the ratio Ι145β / Ι1505 as a function of relative pyrolysis time, Figure 4 the ratio I1595 / I1735 as a function of relative coke burn time and Figure 5 the ratio I1456 / I1505 as a function of specific expansion. The notation ln denotes the intensity of the spectral peak measured at frequency xx, i.e. the area of the peak 25 and 1 ^ / 1 ^, respectively, denotes the ratio of the areas of the spectral peaks obtained at frequencies xx and yy, respectively. As can be seen from the figures, there is a clear correlation in each case and the information obtained is easy to utilize in predicting lye combustion in the recovery mode. Other intensity ratios of FTIR peaks that can be considered in the determination of the combustion properties of man-30 thysulfate black liquor are e.g. Ιι45β / Ιι4ίΐ * ^ 1650 ^ 1735 '^ 1595 ^^ 1505 ^ leso ^^ isos · 92109 9

Example 2

Industrial birch chips were boiled according to Example 1, the cooking conditions being as follows: 5 active alkali 20% wood (NaOHrnå) sulphidity 30% liquid / wood ratio 4 L / kg temperature rise time 90 min

maximum temperature 165 ° C

Samples were taken at the intervals shown in Figure 6 and the chips and pulp samples were analyzed according to Example 1. Similarly, combustion tests and FTIR analyzes of black liquor samples were performed according to Example 1.

15 The co-rot of the black liquor dry matter in this case is shown in Figure 6.

Figure 7 shows the ratio Il350 / I1117 as a function of relative drying time, Figure 8 the ratio Il350 / I1117 as a function of relative pyrolysis time and Figure 9 the ratio I1350 / I1150 as a function of specific expansion. As can also be seen from the figures, in this case there is a clear correlation between the FTIR spectral information and the combustion properties of the Lipe, and the information obtained can be easily utilized in predicting the combustion of the liquor in the recovery boiler. Other intensity ratios of FTIR peaks that can be considered in the determination of the combustion-25 properties of birch sulphate black liquor are e.g. I1350 / Il461 / and ^ 1231 ^^ 1650 *

Claims (8)

10 92109 A method for determining the combustion properties of a waste liquor having the physical and chemical properties of cellulose in the manufacture of cellulose, in which method the waste liquor is measured before being fed to a recovery boiler. that from the spectral peaks occurring at different frequencies of the infrared spectrum, two spectral peaks are selected for each burning characteristic to be determined, that the ratio of the intensities of the selected spectral peaks is calculated to determine each burning characteristic. A method according to claim 1, characterized in that the linear correlation between the spectral peak intensities describing each combustion property to be determined and the numerical value describing the combustion properties is determined by taking a sample from the same 20 ice-cold part of the cellulose. on the basis of Method according to Claims 1 to 2, characterized in that the infrared spectrum is generated 25 by the FTIR method on a mixture of a waste liquid sample and a suitable inorganic substance as a reflection spectrum. Process according to one of the preceding claims, characterized in that the drying time, the relative pyrolysis time, the relative coke burn time and the specific expansion are used as the combustion properties to be determined. Method according to one of the preceding claims, characterized in that the intensity ratios of the spectral peaks are used in the determination of the combustion properties. ^ 1595 / ^ - 1735 '^ use / ^ mi' ^ ieso / ^ 1735 '11 921 09 ^ 159δ / ^ 1505 » ^ 1650 ^^ 1505 »^ 1350 ^^ 1117» ^ 1350 ^^ 1650 »^ 1350 ^^ 1461» ^ 1231 ^^ 1117 ^ 1231 ^^ 1650 * The method according to claim 5, characterized in that at least one of the intensity ratios of the spectral peaks measured by the FTIR method In5e / I1505 »^ 1595 ^ · ^ 1795» is used to determine the combustion properties of pine sulfate black liquor. ^ 1461 »^ 1650 ^ - ^ 1735» ^ 1595 ^^ 1505 3a ^ 1650 ^^ 1505 * A method according to claim 5, characterized in that at least one of the intensity ratios 1ι350 / 1ιιΐ7 »^« so / ^ ieso »^ liso / lioei» ^ 1231 / ^ 1117 3a / ^ 1650 * Method according to one of the preceding claims, characterized in that the infrared spectrum is measured from each sample, that a droplet of the same waste sample is burned in the presence of oxygen, that the numerical values of the desired combustion properties are measured during burning and that the measured infrared by determining the two spectral peaks for each combustion property, the ratio of the intensities of which correlates as closely as possible with the measured numerical values of that combustion property. 12 y 21 ϋ 9