JP7496325B2 - Waste plastic evaluation method, waste plastic evaluation system - Google Patents

Description

The present invention relates to a method and system for evaluating waste plastics. In particular, the present invention relates to a method and system for evaluating waste plastics from the perspective of whether they are suitable for use as cement fuel.

In addition to China's restrictions on imports of waste plastics (hereafter sometimes abbreviated as "waste plastics"), various countries are accelerating their restrictions on the acceptance of waste plastics due to the impact of amendments to the Basel Convention on the export of waste plastics, and it is expected that the amount of waste plastic processed in Japan will further increase in the future.

On the other hand, waste plastics have a calorific value that allows them to be used as a fuel for firing. Therefore, the use of waste plastics as an alternative fuel (auxiliary fuel) to pulverized coal, which is the main fuel used to fire cement clinker in cement kilns (rotary kilns), is being considered. From the perspective of fuel recycling, combustible solid waste such as waste plastics has traditionally been used as fuel for cement kilns in the bottom section and calciner, where it has little impact on the quality of cement clinker and the manufacturing process. However, as the amount of combustible solid waste used in the bottom section and calciner has approached saturation, the use of combustible solid waste in the main burners installed in the front section of the kiln is being considered.

However, when combustible solid waste such as waste plastics is used as auxiliary fuel in the main burner of a cement kiln, the combustible solid waste ejected from the main burner may land on the cement clinker inside the cement kiln and continue to burn on its surface (hereinafter referred to as "landing combustion"). When this landing combustion occurs, the cement clinker around the point where the combustible solid waste lands is reduced and burned, causing changes in the color of the cement clinker, etc., which is undesirable.

For example, in the following Patent Document 1, in consideration of the above-mentioned problems, a technology is disclosed for burning combustible solid waste such as waste plastic in a floating state.

JP 2013-237571 A Japanese Patent Application Laid-Open No. 4-227781

As mentioned above, in a situation where the use of waste plastics is expected to expand, there is a possibility that unknown waste plastics that have not been used in factories to date will be accepted as cement fuel. For this reason, from the standpoint of combustibility, it is preferable to establish in advance criteria for determining whether the target waste plastics can be fed into the kiln front section, and the conditions for feeding them, etc. However, at present, no criteria have been established for determining whether the target waste plastics can be fed into the kiln front section.

One of the indicators for determining whether waste plastic can be fed into the kiln front is the particle size of the waste plastic. It is generally believed that waste plastic with a large particle size is more likely to not burn completely in the air current inside the cement kiln and to experience the above-mentioned ground combustion. For this reason, a method can be considered for determining whether waste plastic can be fed into the kiln front only when the particle size of the waste plastic is smaller than a standard value.

However, after careful consideration by the inventors, it was confirmed that the burnout time varies depending on the waste plastic even if the particle size is roughly the same. For this reason, if the particle size is used as a criterion to determine whether or not to accept the waste plastic at the front of the kiln, some waste plastic may cause ground combustion, which may reduce the quality of the cement clinker. The fact that the burnout time varies depending on the waste plastic even if the particle size is roughly the same will be described later in the section "Form for carrying out the invention" with reference to Figure 6.

Another method would be to use a combustion test device to directly measure the flammability of the waste plastic to be accepted. However, such testing equipment can only measure small samples of a few grams at most. In particular, waste plastics are often heterogeneous in composition, and under these circumstances, it is difficult from the standpoint of reliability to use the flammability results of the sample as a representative value for the flammability results of the waste plastic to be accepted. Another method that could be considered to ensure reliability is to conduct repeated combustion tests, but this method is labor-intensive and requires a lot of time to determine whether or not to accept the waste plastic.

Means for evaluating the combustibility of coal are known, using indices such as carbon content, the atomic ratio of H to C, and the atomic ratio of O to C (see Patent Document 2). In particular, it is generally known that the combustibility of coal is closely correlated with fixed carbon and fuel ratio (= fixed carbon/volatile matter), and it is possible to estimate the combustibility from these values. However, as a result of the inventor's intensive research, when the combustibility of waste plastic was evaluated using the same indices, no high correlation was obtained, and it was confirmed that this is not practical. This point will be described later in the section "Form for carrying out the invention" with reference to FIG. 7.

In view of the above problems, the present invention aims to provide a method and system that can evaluate the combustibility of waste plastics in a simple manner.

The method for evaluating waste plastics according to the present invention includes:
A step (a) of analyzing a target waste plastic, which is a waste plastic to be considered for use as cement fuel, to measure the mass ratio of fixed carbon contained in the target waste plastic and the composition ratio of all target analysis elements belonging to either one of the element groups of N, O and S, or C, N and S;
A step (b) of reading out a regression equation in which the mass ratio of fixed carbon and the composition ratio of each of the target analysis elements are explanatory variables and the burnout time of the waste plastic is an explained variable, which have been recorded in advance;
The method is characterized by having a process (c) of estimating the burn-out time of the target waste plastic by calculation by applying the value of the mass ratio of fixed carbon contained in the target waste plastic and the value of the composition ratio of the target analyzed element measured in the process (a) to the regression equation read out in the process (b).

The amount (mass ratio) of fixed carbon contained in waste plastics, and the composition ratio of each target analyte element, such as nitrogen (N), oxygen (O) and sulfur (S), or carbon (C), nitrogen (N) and sulfur (S), contained in waste plastics, can be easily measured using general analytical methods and analytical devices. For example, the mass ratio of fixed carbon (fixed carbon amount) can be easily measured by industrial analysis in accordance with JIS M 8812, and the composition ratio of each target analyte element can be easily measured, for example, using a commercially available organic element analyzer. In other words, according to the above method, the fixed carbon mass ratio and the composition ratio of the target analyte element are measured for the target waste plastic, and then information on the measurement results is applied to a regression equation obtained in advance, and the burn-out time can be estimated by calculation even if the target waste plastic is unknown.

The method for evaluating waste plastics includes a step (d) of deriving the regression equation by calculation before the step (b),
The step (d)
A step (d1) of analyzing each of a plurality of samples made of waste plastics to measure the mass ratio of fixed carbon and the composition ratio of the target analyte element contained in each of the plurality of samples;
A step (d2) of subjecting each of the plurality of samples to a combustion treatment and measuring a burnout time;
a step (d3) of performing a multiple regression analysis by computation processing, using the burnout times of the respective samples measured in the step (d2) as explained variables, and the values of the mass ratios of fixed carbon and the composition ratios of the target analytical elements contained in the respective samples measured in the step (d1) as explanatory variables, to derive the regression equation;
The method may further include a step (d4) of recording the regression equation derived in the step (d3).

As a result of the inventor's intensive research, a multiple regression analysis was performed on a large number of waste plastic samples, with the mass ratio of fixed carbon and the composition ratio of each target analytical element as explanatory variables, and the burn-off time as the explained variable, and it was confirmed that an extremely high correlation was found. In other words, by performing a multiple regression analysis on the waste plastic samples in advance in the above step (d) to create and record a regression equation, it is possible to estimate the burn-off time with high accuracy even for unknown waste plastics by simply measuring the mass ratio of fixed carbon and the composition ratio of each target analytical element such as N, O and S, or C, N and S, for the target waste plastics that are candidates for acceptance.

The target elements to be analyzed may include halogen elements such as bromine (Br) and chlorine (Cl) and phosphorus (P) in addition to N, O and S, or C, N and S.

The waste plastic evaluation method includes a step (e) of determining how to handle the target waste plastic by comparing the burnout time of the target waste plastic estimated in the step (c) with a reference time stored in advance,
The step (e) may be a step of deciding to put the target waste plastic into the front of the cement kiln if the burn-out time of the target waste plastic estimated in the step (c) is shorter than the reference time.

According to the above method, it is estimated that the burnout time of the target waste plastics is shorter than the standard time, so it is considered that there is no risk of landing and burning even if it is put in front of the cement kiln. This allows the waste plastics to be used effectively without causing a deterioration in the quality of the cement clinker.

In the above method, step (e) may be a step of determining whether to feed the target waste plastics into the bottom of a cement kiln, to crush the target waste plastics, or to postpone acceptance of the target waste plastics if the burnout time of the target waste plastics estimated in step (c) is longer than the reference time.

If the burnout time estimated in step (c) is longer than the reference time, there is a possibility that the target waste plastics will cause ground combustion if they are fed into the front of the cement kiln. Therefore, it is possible that such target waste plastics can be used as cement fuel while reducing the risk of ground combustion by feeding them into the rear of the cement kiln or by subjecting them to crushing processing. In addition, depending on the burnout time estimated in step (c), it is possible to refrain from using the target waste plastics as cement fuel and thereby suppress the impact on the quality of the cement clinker. Note that, if the burnout time is short, it is also possible to increase the screen diameter of the waste plastic crusher in the crushing process at the waste plastic receiving stage and use the coarser waste plastics as cement fuel.

In addition, the waste plastic evaluation system according to the present invention comprises:
Analytical equipment for analyzing target waste plastics, which are waste plastics to be considered for use as cement fuel, to measure the mass ratio of fixed carbon contained in the target waste plastics and the composition ratio of all target analytical elements belonging to either one of the element groups of N, O and S, or C, N and S;
A memory unit in which a regression equation is recorded in which the mass ratio of fixed carbon and the composition ratio of each of the target analysis elements are explanatory variables and the burnout time of the waste plastic is an explained variable;
The apparatus is characterized in that it is equipped with a calculation processing unit that reads out the regression equation from the memory unit, and applies the value of the mass ratio of fixed carbon contained in the target waste plastic and the value of the composition ratio of the target analyzed element measured by the analysis equipment to the regression equation, thereby estimating the burn-out time of the target waste plastic by calculation processing.

The above system can automatically estimate the burnout time even for unknown waste plastics that have never been accepted as cement fuel, based on the fixed carbon mass ratio and the composition ratio of the target analytical elements measured by the analytical equipment. The results of this estimation can be used as an indicator for determining how to handle unknown waste plastics.

The waste plastic evaluation system includes a regression equation deriving unit,
The regression equation derivation unit includes:
A sample combustion facility that performs a combustion process on each of a plurality of samples made of waste plastic and measures the burnout time;
a sample analysis facility for analyzing each of the plurality of samples to measure the mass ratio of fixed carbon and the composition ratio of the target analyte element contained in each of the plurality of samples;
a regression equation derivation processing unit that performs multiple regression analysis by computation processing using a burnout time of each of the plurality of samples measured by the sample combustion equipment as an explained variable and a value of the mass ratio of fixed carbon contained in each of the plurality of samples and a value of the composition ratio of the target analysis element measured by the sample analysis equipment as explanatory variables to derive the regression equation,
The regression equation derivation processing unit may record the regression equation in the storage unit.

In the above, the sample analysis equipment may be a common equipment with the analysis equipment that analyzes the target waste plastic. Also, the regression equation derivation processing unit may be common with the calculation processing unit that estimates the burnout time of the target waste plastic based on the regression equation read from the memory unit.

The storage unit may be configured so that information about the regression equation can be updated.

According to the above configuration, by increasing the number of samples made of waste plastic, it is possible to update the regression equation with higher estimation accuracy in the memory unit. This makes it possible to estimate the burnout time of the target waste plastic with higher accuracy.

The storage unit stores information about a reference time related to a burnout time,
The calculation processing unit may also be configured to output result information regarding the handling method of the target waste plastic based on the comparison result between the estimated burn-out time of the target waste plastic and the reference time read out from the memory unit.

The above system can automatically output information about how to handle unknown waste plastics, such as whether they can be fed into the front of a cement kiln, even if the waste plastics have never been used as cement fuel before. This allows appropriate decisions to be made when handling the target waste plastics, regardless of the level of expertise of the cement plant workers.

According to the present invention, it is possible to evaluate the combustibility of waste plastics in a simple manner. As a result, even if a waste plastic is unknown and has never been accepted by a cement plant, it is possible to easily display a judgment index for determining whether it can be accepted or not, taking into account the presence or absence of an impact on the quality of cement clinker.

1 is a block diagram showing a schematic configuration of one embodiment of a waste plastic evaluation system of the present invention. 1 is a flowchart showing the processing steps of the waste plastic evaluation method of the present invention. FIG. 2 is a block diagram illustrating a configuration of an embodiment of a regression equation derivation unit. 13 is a flowchart showing a processing procedure for deriving a regression equation. 1 is a diagram showing a schematic configuration example of a sample combustion facility. 1 is a graph showing the results of a combustion test for each sample Sw (sample Nos. 1 to 17). 1 is a graph showing the relationship between the mass ratio of fixed carbon contained in each sample Sw and the burnout time of each sample Sw. 13 is a graph showing the relationship between the calculation results calculated from a regression equation based on a simple regression analysis in which the mass ratio of fixed carbon contained in each sample Sw is used as an explanatory variable and the actual measurement results for the burnout time for each sample Sw. 1 is a graph showing the relationship between the calculation results calculated from a regression equation based on multiple regression analysis in which the mass ratio of fixed carbon contained in each sample Sw and the composition ratios of nitrogen, oxygen, and sulfur are explanatory variables, and the actual measurement results, for the burn-out time for each sample Sw. 1 is a graph showing the relationship between the calculation results calculated from a regression equation based on multiple regression analysis in which the mass ratio of fixed carbon contained in each sample Sw and the composition ratios of carbon, nitrogen, and sulfur are explanatory variables and the actual measurement results for the burn-out time for each sample Sw.

The waste plastic evaluation system and evaluation method of the present invention relate to a system and method for evaluating the combustibility of target waste plastics. The evaluation results of the combustibility of waste plastics obtained by this evaluation system and evaluation method can be used, for example, as information for determining whether the waste plastics are suitable for use as cement fuel, or whether there are any points that need to be considered when using the waste plastics.

The waste plastics covered by the present invention refer to plastics contained in general waste and industrial waste as defined by the Waste Management and Public Cleansing Law, and include, for example, general waste plastics such as containers and packaging discharged from homes, stores, offices, etc., and industrial waste plastics discharged in connection with business activities such as the manufacturing, processing, or distribution stages of plastic products. Industrial waste plastics also include, for example, waste tires. These waste plastics come from a wide variety of sources, and it is expected that there will be differences in their constituent components. In particular, it is difficult to immediately determine whether waste plastics that have never been accepted as fuel in a cement plant (unknown waste plastics) can be accepted as cement fuel. The waste plastic evaluation system and evaluation method of the present invention make it possible to evaluate the combustibility of such unknown waste plastics in a simple manner and provide a criterion for accepting them as cement fuel.

The waste plastic evaluation system and evaluation method according to the present invention will be described below with reference to the drawings as appropriate.

Figure 1 is a block diagram showing a schematic configuration of one embodiment of the waste plastic evaluation system according to the present invention (hereinafter, sometimes simply abbreviated as "evaluation system"). The evaluation system 1 shown in Figure 1 comprises an analysis facility 3, a calculation processing unit 5, a memory unit 7, and a regression equation derivation unit 10. Note that Figure 2 is a flow chart showing a schematic diagram of the processing procedure performed by the evaluation system 1, i.e., the waste plastic evaluation method according to the present invention. The following description will be given with reference to the step numbers in Figure 2 as appropriate.

(Step S1)
The waste plastic to be evaluated (hereinafter referred to as “target waste plastic Tw”) is analyzed by the analysis equipment 3 .

The analytical equipment 3 is equipment that performs analysis on the target waste plastics Tw to measure the mass ratio of fixed carbon contained in the target waste plastics Tw, and the composition ratio of all elements (hereinafter referred to as "target analysis elements") that belong to either one of the element groups of nitrogen (N), oxygen (O) and sulfur (S), or carbon (C), nitrogen (N) and sulfur (S). The analytical equipment 3 may be configured to include multiple devices.

As a device for analyzing the mass ratio (fixed carbon amount) of fixed carbon contained in the target waste plastics Tw, a device that uses an analysis method conforming to JIS M 8812 "Coals and cokes - Elemental analysis method" can be used. In addition, as a device for analyzing the constituent elements of the target waste plastics Tw, for example, a commercially available organic element analyzer can be used.

Even if the amount of target waste plastics Tw is extremely large, it is considered that there is no significant discrepancy in the mass ratio of fixed carbon or the ratio of constituent elements between the target waste plastics Tw brought in at the same time at a certain time, since they have a common source. For this reason, it is not necessary to perform the above analysis process on all of the target waste plastics Tw brought in, and the analysis results for a portion of the target waste plastics Tw extracted and selected can be used as the results for the entire target waste plastics Tw brought in at that time. In other words, the process related to this step S1 can be performed simply and in a short time.

This step S1 corresponds to process (a).

(Step S2)
The calculation processing unit 5 reads out information about the regression equation iF from the storage unit 7.

The memory unit 7 records information about the regression equation iF that has been created in advance in the regression equation derivation unit 10. The memory unit 7 is composed of a storage medium such as a flash memory or a hard disk. The regression equation iF is specified so that the mass ratio of fixed carbon contained in the waste plastic and the composition ratio of each target analysis element in the waste plastic are explanatory variables, and the burn-out time of the waste plastic is the explained variable.

This step S2 corresponds to process (b). The method by which the regression equation derivation unit 10 derives the regression equation iF will be described later.

(Step S3)
In the calculation processing unit 5, the analysis result of the target waste plastic Tw in the analysis equipment 3 is introduced into the regression equation iF. As a result, the burnout time d5 of the target waste plastic Tw is estimated by calculation processing.

The calculation processing unit 5 estimates the burnout time d5 of the target waste plastic Tw by calculation processing, by applying the analysis results of the target waste plastic Tw in the analysis equipment 3 to the regression equation iF read from the memory unit 7. More specifically, the calculation processing unit 5 obtains the values of the mass ratio iT1 of fixed carbon contained in the target waste plastic Tw and the composition ratio iT2 of the target analysis element from the analysis equipment 3, and applies these values to the regression equation iF read from the memory unit 7 to calculate the burnout time d5 of the target waste plastic Tw. The calculation processing unit 5 is composed of software means or dedicated hardware means capable of realizing this calculation processing.

This step S3 corresponds to process (c).

(Step S4)
In the example of Fig. 2, the method of handling the target waste plastic Tw is determined based on the burnout time d5 of the target waste plastic Tw. For example, information on the reference time τ is recorded in advance in the memory unit 7. The calculation processing unit 5 compares the reference time τ with the estimated burnout time d5 of the target waste plastic Tw and outputs information on the method of handling the target waste plastic Tw.

Specifically, when the estimated burnout time d5 of the target waste plastic Tw is sufficiently shorter than the reference time τ, the calculation processing unit 5 outputs information that the target waste plastic Tw can be fed into the front of the cement kiln. On the other hand, when the estimated burnout time d5 of the target waste plastic Tw is longer than the reference time τ, depending on the magnitude of the difference, options such as feeding the target waste plastic Tw into the bottom of the cement kiln, crushing the target waste plastic Tw, or not accepting the target waste plastic Tw as cement fuel are output. As a result, even if the target waste plastic Tw is an unknown waste plastic that has not been accepted as cement fuel, it is possible to recognize by simple processing whether it can be accepted as cement fuel or what points should be noted when accepting it.

This step S4 corresponds to process (e). However, it is optional whether or not the calculation processing unit 5 performs the calculation processing corresponding to step S4.

Figure 3 is a block diagram showing a schematic configuration of one embodiment of the regression equation derivation unit 10. The regression equation derivation unit 10 shown in Figure 3 includes a sample analysis facility 13, a sample combustion facility 14, and a regression equation derivation processing unit 15. Figure 4 is a flow chart showing a schematic derivation procedure of the regression equation iF performed in the regression equation derivation unit 10. The following description will be given with reference to the step numbers in Figure 4 as appropriate.

In the regression equation derivation unit 10, processing is performed on multiple samples Sw made of waste plastic that have been prepared in advance in order to derive the regression equation iF.

(Step S11)
A plurality of samples Sw made of waste plastics are analyzed by sample analysis equipment 13. This sample analysis equipment 13 is equipment that performs analysis on each of the plurality of samples Sw to measure the mass ratio of fixed carbon and the composition ratio of the target analysis element contained in each of the plurality of samples Sw. That is, the sample analysis equipment 13 is equipment having the same function as the analysis equipment 3 shown in Fig. 1. The sample analysis equipment 13 and the analysis equipment 3 may be configured as a common equipment.

This step S11 corresponds to process (d1).

(Step S12)
A combustion process is performed on the multiple samples Sw by the sample combustion equipment 14. The sample combustion equipment 14 is configured to combust each sample Sw and measure the burnout time.

Figure 5 is a conceptual diagram showing an example of the sample combustion equipment 14. This sample combustion equipment 14 is composed of an electrically heated batch type vertical tubular furnace to simulate rapid temperature rise. In detail, the sample combustion equipment 14 includes a reaction tube 41, a heating section 42, and a measuring section 43.

The reaction tube 41 is, for example, a circular tube made of alumina, and a water-cooling jacket 45 is attached to the top and bottom of the tube. The heating section 42 is, for example, composed of a spiral silicon carbide heating element. The heating section 42 and the reaction tube 41 are integrated and can be moved in the vertical direction dV.

The measuring unit 43 is composed of, for example, a computer and an electronic balance. A hanging hook 46 made of a highly heat-resistant material is installed on the bottom of the electronic balance, and a basket containing a sample Sw made of waste plastic is attached to this hanging hook 46. The basket is made of, for example, platinum.

The sample combustion equipment 14 is provided with a gas supply port 51 for introducing an atmospheric gas into the reaction tube 41 from the bottom side, and a gas exhaust port 52 for discharging the combustion exhaust gas after the sample Sw is burned in the reaction tube 41. Furthermore, from the viewpoint of protecting the measurement unit 43 (particularly the electronic balance) from the combustion exhaust gas, an inert gas supply port 53 is provided for introducing an inert gas (e.g., nitrogen gas) to create a positive pressure inside the measurement unit 43.

First, a basket containing a sample Sw made of waste plastic is hung from the measuring unit 43 (electronic balance). Then, the temperature inside the reaction tube 41 is heated to a predetermined temperature (e.g., 1400°C) by heat from the heating unit 42, and the reaction tube 41 is quickly moved in the vertical direction dV to the position of the basket. The point at which this movement is completed is set as the combustion start time, and the combustion time of the sample Sw is measured by continuously measuring the mass measured by the measuring unit 43 (electronic balance).

The combustion time is measured by assuming that the mass at the point when the measurement value on the electronic balance becomes constant is the mass when the combustibles in the sample are completely burned, and then the time it takes for 99% of the combustibles to burn off (99% reaction time).

The sample combustion equipment 14 shown in FIG. 5 is merely an example. The sample combustion equipment 14 may have any device configuration as long as it is capable of measuring the combustion time of a sample Sw made of waste plastic in a high-temperature environment such as when cement raw materials are combusted in a cement kiln.

This step S12 corresponds to process (d2).

(Step S13)
In the regression equation derivation processing unit 15, a multiple regression analysis is performed by arithmetic processing, with the burnout times of the samples Sw measured in step S12 as explained variables, and the mass ratios of fixed carbon and the composition ratios of the target analytical elements contained in the samples Sw measured in step S11 as explanatory variables. As a result, a regression equation iF is created.

The regression equation derivation processing unit 15 is configured with software means or dedicated hardware means capable of realizing the process of creating this regression equation. A specific example of the regression equation iF to be created will be described later in the Examples section.

This step S13 corresponds to process (d3).

(Step S14)
The regression formula iF created by the regression formula derivation processing unit 15 is recorded in the storage unit 7. When the functional means constituting the regression formula derivation processing unit 15 is constituted by a computer, the information on the regression formula iF may be recorded in the storage unit 7 from this computer via a network line, or may be recorded in the storage unit 7 consisting of a storage area constructed in the same computer.

This step S14 corresponds to step (d4).

The present invention will be described in detail below with reference to examples. Note that the present invention is not limited to the contents of these examples.

Table 1 below shows the proximate analysis and elemental analysis values of several samples Sw made of waste plastics used in the verification. Each sample Sw was a crushed product that had passed through a crusher with a screen with a diameter of 20 to 30 mm, which can be used before the cement kiln is fired. In other words, each sample Sw has a common particle size of around 20 mm.

Table 2 shows the measurement method for each item. At least a part of this measurement process (analysis process) corresponds to step S11.

In the elemental analysis, the composition ratio of oxygen (O) was calculated, for example, by the difference method in accordance with JIS M 8813. In detail, assuming that the components of each sample Sw made of waste plastic were only oxygen (O), carbon (C), hydrogen (H), nitrogen (N), sulfur (S), and ash (non-combustibles), the oxygen content was calculated by subtracting the mass percentage of components other than oxygen from 100%.

(Combustion test)
The combustion test was performed by the method described above in step S12. That is, a combustion test was performed on each sample Sw shown in Table 1 using the sample combustion equipment 14 shown in Fig. 5, and the burnout time of each sample Sw was measured by measuring the time it took for 99% of the combustibles to burn out (99% reaction time).

Figure 6 is a graph showing the results of the combustion test for each sample Sw (sample No. 1 to 17). For each sample Sw, 4 grams were weighed out and then the combustion test was carried out. Note that in order to take into account non-uniformity and measurement variations within the same sample, the test was repeated three times for each sample.

In Figure 6, the horizontal axis indicates each sample number, and the vertical axis indicates the burning time. The plot on the graph in Figure 6 shows the average value of three measurement results, and the error bars above and below the plot show the standard deviation.

The combustion of waste plastics can be broadly divided into two stages: volatile matter combustion due to the release of volatile matter that occurs in the early stages of the combustion reaction, and char combustion due to the combustion of fixed carbon in the sample. In this combustion test, the volatile matter release time was defined as the time elapsed from the start of combustion to the point at which the rate of decrease in combustible matter per second fell below 1%. The char combustion time was calculated as the difference between the burnout time measured using the method described above and the volatile matter release time.

According to the results in Figure 6, while there is no significant difference between the volatile matter release times of each sample Sw, differences are confirmed between the char combustion times of each sample Sw. The char combustion time is affected by the amount of fixed carbon in the fuel (i.e., in each sample Sw). As a result, it is estimated that the combustion time of each sample Sw is likely to depend on the mass ratio of fixed carbon contained in each sample Sw. On the other hand, as mentioned above, since each sample Sw has a common particle size of around 20 mm, it was confirmed that differences occur in the burnout time even when the particle size is the same.

(Simple regression analysis based on the ratio of fixed carbon)
Therefore, in order to confirm the correlation between the mass ratio of fixed carbon and the burnout time (99% reaction time) for each sample Sw (sample No. 1 to 17), a simple regression analysis was performed with the burnout time as the explained variable and the mass ratio of fixed carbon [%] as the explanatory variable. The results are shown in Figures 7 and 8.

Fig. 7 is a graph showing the relationship between the mass ratio of fixed carbon contained in each sample Sw and the burnout time of each sample Sw. In Fig. 7, the horizontal axis shows the mass ratio [%] of fixed carbon contained in each sample Sw, and the vertical axis shows the burnout time of each sample Sw. In this example, as a result of the simple regression analysis, when the burnout time is y and the fixed carbon ratio is x, the regression equation y = 0.1928x + 0.7395 and the coefficient of determination ^R2 = 0.4477 were calculated.

Figure 8 is a graph in which the horizontal axis represents the burnout time calculated by applying the mass ratio [%] of fixed carbon for each sample Sw to the regression equation above, and the vertical axis represents the actually measured burnout time.

Since the coefficient of determination ^R2 of the regression equation is a value far from 1, it is understood that this regression equation has low accuracy as a model for estimating the burn-off time of waste plastics. This is also reflected in the fact that the calculated values are far from the measured values in FIG. 8. In other words, it is understood that a simple regression analysis using only the single parameter of fixed carbon is insufficient for estimating the burn-off time of waste plastics. This fact is a new finding made by the inventors through their intensive research.

(Multiple regression analysis using multiple dependent variables)
Based on the above findings, multiple regression analysis was performed on the burnout time using multiple parameters (dependent variables) that are expected to affect flammability. Table 3 shows a list of the parameters used in the multiple regression analysis.

Of the proximate analysis values shown in Table 3, the items other than fixed carbon (moisture, ash, and volatile matter) were used to calculate the composition ratio of oxygen (O) in elemental analysis.

Example 1
A multiple regression analysis was performed for each sample Sw (sample Nos. 1 to 17) with the burnout time as the explained variable and the mass ratio [%] of fixed carbon and the composition ratios of nitrogen (N), oxygen (O), and sulfur (S) as explanatory variables. That is, in this Example 1, nitrogen (N), oxygen (O), and sulfur (S) correspond to the target analytical elements. The results are shown in Table 4 and FIG. 9.

According to Table 4, the absolute value of the t-value is greater than 2 and the P-value is less than 0.05, so the t-value and P-value meet the 5% significance level. This shows that the relationship between the explanatory variable and the dependent variable can be statistically inferred.

From the results in Table 4, the burnout time y is calculated by the following formula (1), where the mass ratio [%] of fixed carbon is _x1 , the composition ratio [%] of nitrogen (N) is _x2 , the composition ratio [%] of oxygen (O) is _x3 , and the composition ratio [%] of sulfur (S) is _x4 :
y = 1.7192 + 0.1870* _x1 - 0.7404* _x2 - 0.0425* _x3 + 3.0266* _x4 ... (1)
In this example, equation (1) corresponds to the regression equation iF described above with reference to FIGS.

Figure 9 is a graph showing the burnout time calculated by applying the values of each sample Sw, namely, the mass ratio of fixed carbon [%], the composition ratio of nitrogen (N) [%], the composition ratio of oxygen (N) [%], and the composition ratio of sulfur (S) [%] to the regression equation shown in equation (1), and the burnout time actually measured is plotted on the vertical axis.

According to Fig. 9, it can be seen that the calculated values are close to the measured values when compared with the results of Fig. 8. Also, the coefficient of determination of the regression equation is ^R2 = 0.9253, which is a value very close to 1, and therefore it can be seen that the regression equation shown in Equation (1) is a very accurate model for estimating the burnout time of waste plastics.

Example 2
A multiple regression analysis was performed for each sample Sw (sample Nos. 1 to 17) with the burnout time as the explained variable and the mass ratio [%] of fixed carbon and the composition ratios of carbon (C), nitrogen (N), and sulfur (S) as explanatory variables. That is, in this Example 2, carbon (C), nitrogen (N), and sulfur (S) correspond to the target analyte elements. The results are shown in Table 5 and FIG. 10.

In Table 5, as in Table 4, the absolute value of the t-value is greater than 2 and the P-value is less than 0.05, so the t-value and P-value meet the 5% significance level. This shows that the relationship between the explanatory variable and the dependent variable can be statistically inferred.

From the results of Table 5, the burnout time y is calculated by the following formula (2), where the mass ratio [%] of fixed carbon is _x1 , the composition ratio [%] of carbon (C) is _x5 , the composition ratio [%] of nitrogen (N) is _x2 , and the composition ratio [%] of sulfur (S) is _x4 :
y = -1.7475 + 0.1816* _x1 + 0.0408* _x5 - 0.6171* _x2 + 3.4561* _x4 ... (2)
In this example, equation (2) corresponds to the regression equation iF described above with reference to FIGS.

Figure 10 is a graph showing the burnout time calculated by applying the respective values of each sample Sw to the regression equation shown in (2), i.e., the mass ratio of fixed carbon [%], the composition ratio of carbon (C) [%], the composition ratio of nitrogen (N) [%], and the composition ratio of sulfur (S) [%], on the horizontal axis, and the actually measured burnout time on the vertical axis.

Fig. 10 shows that the calculated values are close to the measured values, as in Fig. 9. Also, the coefficient of determination of the regression equation is ^R2 = 0.9036, which is a value very close to 1. This shows that the regression equation shown in formula (2) is a model for estimating the burnout time of waste plastics with extremely high accuracy, similar to the regression equation shown in formula (1).

From the above, it can be seen that the burn-off time of unknown waste plastics can be accurately estimated by the regression formula iF obtained by performing multiple regression analysis on each sample Sw made of waste plastic, with the mass ratio of fixed carbon and the composition ratio of each target analyte element (N, O and S, or C, N and S) as explanatory variables and the burn-off time as the explained variable. This regression formula iF is created through the processes of steps S11 to S13 as described above, and then recorded in the memory unit 7.

In other words, according to the evaluation system and evaluation method of the present invention, the mass ratio of fixed carbon and the composition ratio of each target analysis element, such as N, O and S, or C, N and S, contained in the waste plastic to be evaluated (target waste plastic Tw) are measured, and then the previously created regression equation iF is read out, and the measured value is applied to the regression equation iF, thereby making it possible to accurately estimate the burn-out time d5 of the target waste plastic Tw.

1: Evaluation system 3: Analysis equipment 5: Calculation processing unit 7: Memory unit 10: Regression equation derivation unit 13: Sample analysis equipment 14: Sample combustion equipment 15: Regression equation derivation processing unit 41: Reaction tube 42: Heating unit 43: Measurement unit 45: Water-cooled jacket 46: Suspension hook 51: Gas supply port 52: Gas exhaust port 53: Inert gas supply port Sw: Sample Tw: Target waste plastic d5: Burn-out time iF: Regression equation iT1: Mass ratio of fixed carbon iT2: Constituent ratio of target analysis element

Claims (7)

A step (a) of analyzing a target waste plastic, which is a waste plastic to be considered for use as cement fuel, to measure the mass ratio of fixed carbon contained in the target waste plastic and the composition ratio of all target analysis elements belonging to either one of the element groups of N, O and S, or C, N and S;
A step (b) of reading out a regression equation in which the mass ratio of fixed carbon and the composition ratio of each of the target analysis elements are explanatory variables and the burnout time of the waste plastic is an explained variable, which have been recorded in advance;
A method for evaluating waste plastics, comprising a step (c) of estimating the burn-out time of the target waste plastics by calculation by applying the value of the mass ratio of fixed carbon contained in the target waste plastics and the value of the composition ratio of the target analyzed element measured in the step (a) to the regression equation read out in the step (b). The method includes a step (d) of deriving the regression equation by calculation before the step (b),
The step (d)
A step (d1) of analyzing each of a plurality of samples made of waste plastics to measure the mass ratio of fixed carbon and the composition ratio of the target analyte element contained in each of the plurality of samples;
A step (d2) of subjecting each of the plurality of samples to a combustion treatment and measuring a burnout time;
a step (d3) of performing a multiple regression analysis by computation processing, using the burnout times of the respective samples measured in the step (d2) as explained variables, and the values of the mass ratios of fixed carbon and the composition ratios of the target analytical elements contained in the respective samples measured in the step (d1) as explanatory variables, to derive the regression equation;
The method for evaluating waste plastics according to claim 1, further comprising a step (d4) of recording the regression equation derived in the step (d3). A step (e) of determining how to handle the target waste plastic by comparing the burnout time of the target waste plastic estimated in the step (c) with a pre-stored reference time,
The method for evaluating waste plastics described in claim 1 or 2, characterized in that the step (e) is a step of deciding to put the target waste plastics into the front of a cement kiln if the burn-out time of the target waste plastics estimated in the step (c) is shorter than the reference time. The waste plastic evaluation method according to claim 3, characterized in that, in the step (e), if the burnout time of the target waste plastic estimated in the step (c) is longer than the reference time, it is decided to either feed the target waste plastic into the bottom of a cement kiln, crush the target waste plastic, or not accept the target waste plastic. Analytical equipment for analyzing target waste plastics, which are waste plastics to be considered for use as cement fuel, to measure the mass ratio of fixed carbon contained in the target waste plastics and the composition ratio of all target analytical elements belonging to either one of the element groups of N, O and S, or C, N and S;
A memory unit in which a regression equation is recorded in which the mass ratio of fixed carbon and the composition ratio of each of the target analysis elements are explanatory variables and the burnout time of the waste plastic is an explained variable;
A waste plastic evaluation system characterized by comprising a calculation processing unit that reads out the regression equation from the memory unit, and applies the value of the mass ratio of fixed carbon contained in the target waste plastic and the value of the composition ratio of the target analyzed element measured by the analysis equipment to the regression equation to estimate the burn-out time of the target waste plastic by calculation. The waste plastic evaluation system according to claim 5, characterized in that the memory unit is configured so that information relating to the regression equation can be updated. The storage unit stores information about a reference time related to a burnout time,
The waste plastic evaluation system described in claim 5 or 6, characterized in that the calculation processing unit outputs result information regarding the handling method of the target waste plastic based on the comparison result between the estimated burn-out time of the target waste plastic and the reference time read out from the memory unit.

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