Enhancing the Performance of a Hazardous Waste Incineration Facility through the Usage of a Dedicated Application
The operational aspect also seems to be important here and has not been widely described in the literature so far. This article presents a tool which is a new approach to this issue—a desktop application supporting waste incineration plant operators by selecting components (different types of waste) for individual portions of the feed mixture. In the next stage, one can consider coupling the described tool with other models. Possible extension of the application can be a module for energy and mass calculations.
2. Materials and Methods
An important area of optimization of the performance of the incineration plant with a rotary kiln is the appropriate composition of subsequent portions of the feed material. This situation applies especially to incineration facilities for hazardous waste that handle diverse types of waste. These wastes are characterized by different fuel properties, which complicates the process of their thermal transformation and contributes to operational problems.
2.1. Selected Issues of Conducting the Thermal Process in a Rotary Kiln
Selecting the appropriate batch of the input material is a tedious task. Proficiency, knowledge and effective collaboration of employees of an incineration facility are essential prerequisites for this task. However, despite meeting all of the necessary conditions, unforeseen issues may arise that can impact the functionality of the entire system. These complications are associated with the characteristics of specific waste types, which exert a substantial adverse influence on the overall functioning of the facility. It is important to ensure that the input material remains consistent in terms of physicochemical and fuel properties during a thermal process. Furthermore, these properties are required to fulfill the necessary criteria, enabling the process to be conducted in compliance with the relevant legislation.
The parameters of the input material that are particularly taken into account are:
calorific value and elemental composition,
content of chlorine and other halogens,
content of alkaline salts and other compounds of this nature,
pH, flammability and reactivity.
Improper selection of the batch of feed material can result in a range of consequences. They can include a short-term increase in the emission of a specific gas, a temporary halt in the movement of material within the kiln, or even the requirement to halt the entire installation for necessary repairs and renovations. Three of the most common problematic situations can be distinguished here:
usage of the kiln lining,
emissions exceeding standards,
temporary retention of the material in the kiln.
In the basic chemical approach to the phenomena related to the degradation of the lining in a rotary kiln, it can be described by the following reactions.
R-COOH + 2NaOH → RH + Na2CO3 + H2O↑
R-CH2-OH + NaOH → R-CH2-ONa +H2O↑
Al2O3 + 2NaOH → 2NaAlO2 + H2O↑
xR-CH2-Cl + (2x + 3)O2→ (x + 1)CO2 + (x + 2)/2H2O + x/2Cl2↑
R-CH2-CH2-Cl → R-CH=CH2 + HCl↑
Al2O3 + 6HCl → 2AlCl3 + 3H2O↑
Reactions (1)–(3) take place at high temperatures, corresponding to the operating regime of a rotary kiln. Reactions (1) and (2) are characterized by the combination of examples of compounds potentially present in hazardous waste—carboxylic acids and alcohols—with basic compounds, here: sodium. These reactions produce solid sodium salts that can form a layer of material in the furnace. As the thickness of this layer increases, a temporary agglomeration of the charge material takes place in the furnace. Reaction (3) is a probable illustration of the reaction of alkaline compounds with the lining material, here defined as aluminum oxide—the basic building block of fireclay bricks in a furnace in a waste incineration plant. Aluminum and its compounds are characterized by amphoteric properties, hence the possibility of forming a basic salt. The resulting product, compared to durable ceramic aluminum (III) oxide, is characterized by susceptibility to crumbling, which increases susceptibility to chipping.
In the case of equations with acidic compounds, here: chlorine, the first two Reactions (4) and (5)—describe the breakdown of an organic compound containing chlorine. The first one (4) is combustion taking place in an oxygen-rich atmosphere, which produces chlorine gas. In the case of interaction with the lining, chlorine gas is not considered as a factor that reacts with aluminum oxide, but gaseous components containing chlorine e.g., HCl, are important. It is produced in a situation of oxygen deficiency, which may occur in the rotary kiln chamber of a hazardous waste incinerator. The formation of hydrogen chloride is described by Reaction (5). Then it can react with amphoteric aluminum oxide, which is a component of fireclay brick, to form a salt—aluminum chloride. This salt, like NaAlO2, is susceptible to crushing. This is related to the chemical structure of the compound—the ionic bonds present there. For comparison, aluminum oxide is described as a durable compound due to its strong interatomic bonds—polar covalent. Therefore, after the formation of salts with chlorine, the brick will tend to chip—erode.
2.2. Proposed Optimization Solution
The experimental determination of these values primarily focuses on ensuring the proper execution of the thermal process within the kiln, and on what influences the financial aspect of the incineration plant performance. Specifically, the goal of achieving a consistent temperature distribution in an autothermal process can be accomplished by utilizing a batch mixture that possesses a consistent calorific value. As a result of this, there is no need to provide additional fuel to the rotary kiln, thereby minimizing costs in this particular domain. Furthermore, the prolonged presence of waste with excessive levels of acidic or alkaline substances leads to accelerated lining usage and deterioration. This involves more frequent renovations, which is expensive. The installation then does not conduct a thermal process, and therefore does not generate revenues.
Moreover, the application should meet several conditions for intuitive and effective use, namely:
enable compatibility with systems used in waste incineration plants,
ensure flexibility in selecting the mixture,
ensure the stability of the solution, consistent with the adopted assumptions,
enable different modes of use.
It is assumed that the proposed solution will, among other things, accelerate the decision-making process and create a feeding schedule.
2.3. Algorithm for Selecting Components for the Mixture
The aim of choosing the elements of the waste mixture with the use of the developed application is to optimally create an input batch to the rotary kiln. The term “optimally” in this context refers to guaranteeing the preservation of specific operational parameters of the facility while minimizing any operational issues that may arise in the installation for thermal treatment of hazardous waste.
The application is limited in scope as it considers only five specific parameters, namely calorific value, pH, contents of: chlorine (Cl), alkaline salts (Na, K, Ca salts) and other halogens (F, I, Br). Each parameter is allocated a specific range of values in which the acquired outcomes are expected to be located. This information can be observed within the application window.
The algorithm presented in this work includes functionality that allows assigning weights to individual parameters. The mass composition of a mixture can be determined by calculating the weighted average, which takes into account the mass of each component. In the application, however, there are no considerations on specific, chemical reactions taking place at elevated temperatures. It is true that the implementation of information regarding these relationships is not subject to testing and might be extremely difficult to determine, but it is expected that the mixture properties may be adjusted by the installation operator. In practical use of the application, this is manifested by the possibility of assigning a weight to each parameter, through which the algorithm will determine the composition of the mixture, taking into account in particular the value of the selected parameter or parameters. Using this function is optional, but it may be helpful in emergency situations.
—mass of particular components,
n—number of components,
—reference value of the parameter,
—weight of individual components,
—weighted average of the parameter with index i, which is defined as:
—mass of the j-th component of the mixture,
—value of the parameter i for mixture component j.
The function is dependent on n-variables, where n represents the quantity of components that can be incorporated into the mixture. Then it is minimized in relation to the weight of individual components. The quality of the mixture related to specific parameters is described by the objective function. The closer the parameters of the mixture are to the reference values, the lower the value of this function will be, indicating better performance. The ant algorithm, which is one of the swarm algorithms in the field of artificial intelligence, was employed to minimize the objective function.
2.4. Functionality of the Application
The application provides flexibility of use by providing a number of functions available to the user. These are primarily:
selecting waste included in the mixture and its mass,
generating the composition of subsequent portions of input material,
updating of the mass of available waste,
assigning weights to individual waste parameters,
generating a report on the simulations performed.
Hazardous waste incineration plants usually have their own laboratory where they test the properties of the waste they receive. After loading the database with this information into the application, the user has at his disposal a list of all available waste along with their more or less precise characteristics. For the purposes of the program, waste should be defined by at least five parameters, which are the parameters taken into account in the algorithm. These are properties tested by laboratories because they are crucial for the combustion process. Based on the list of available waste and their parameters, the operator can select any waste to create a batch mixture, and also set the total mass of the batch material. This is a convenient solution that provides flexibility. It happens that some hazardous waste requires priority in directing to thermal processing, and the mass assignment facilitates adapting the portion of the feed material to the characteristics of the rotary kiln and the thermal process.
Given the high frequency of loading in a waste incineration plant throughout the day, an important feature of the application is its capability to generate multiple waste mixtures. The tool does not have any predetermined upper limits in this regard. Nevertheless, the total waste consumption can potentially serve as a constraining element. In addition, tests conducted on the mixture by simulating multiple waste selection showed stability and compliance with set parameters. In all of the obtained results, the simulated portion of the feed material is in compliance with requirements.
Updating the mass of waste used to create the batch is a key aspect that has been programmed to ensure smooth operation of the incinerator. This function allows the operator to create additional mixtures and prevents mass loss. The application automatically deducts the corresponding mass from the waste incorporated in the mixture based on the indicated results.
Giving the selected parameter or parameters greater weights, and thus greater importance when generating the composition of batches of feed material, may be an alternative in case of temporary problems that may occur in the installation. You can imagine a situation in which there was a temporary but significant drop in process efficiency. In such a case, the operator may temporarily increase the weight of the calorific value. The algorithm will then select ingredients in a way that favors this parameter.
The tool has ability to improve the handling of loading procedures by preserving data generated for each waste portion and creating detailed reports based on this data. Application users can obtain a report that provides guidance on the proportion of input materials within a specific time frame. By knowing the loading frequency at a given facility, the application can generate loading schedules for batches of feedstock per day, per week, etc. While wider ranges may not be particularly relevant due to the dynamic nature of waste incineration, they can still be demonstrated when necessary.
3. Results and Discussion
The results of the simulations are presented in the context of the stability and quality, and checking the functionality enabling the use of weights for the selected parameter.
3.1. Results of the Simulations—Stability of the Solution
The obtained results indicate compliance with the adopted ranges. Simulation 1 may serve as an example. In this case, the following properties of the mixture are obtained: calorific value 15.52 MJ/kg, pH 7.53, content of selected basic salts 5.7%, content of chlorine 2.1% and content of halogens 0.97%. In all conducted tests, the parameters of the acquired mixture are within the specified parameter ranges, most of them with a significant margin of error. The results obtained are stable and consistent with established guidelines.
3.2. Results of the Conducted Simulations—Introduction of Parameter Weights
As can be seen, the calorific value in this set of solutions is closer to the reference value than in solutions without the use of increased weight for one of the parameters. This can be observed on the example of the previously described Simulation 1. The values of the parameters of the mixture, oriented primarily on the calorific value, are as follows: CV = 17.08 MJ/kg, pH = 7.83, salts Na, K, Ca = 7.14%, Cl = 1.73%, halogens = 0.67%. In this case the values of the three parameters improved in regard to the reference value. In addition to the distinguished calorific value, these are the chlorine content and halogens content. In such a case, the algorithm changes the mass shares of individual wastes or changes the composition of the suggested mixture by adding another waste specified by the user or subtracting waste included in the previous simulation. The value of the parameter with increased importance is brought closer to the reference value at the expense of some of the remaining parameters. It should be noted, however, that in each case the values of the remaining parameters are within the given range of values.
The developed optimization tool is an application for selecting the portion of feed material for a rotary kiln. It is based on the analysis of selected parameters of waste. The application, enabling the selection of components for a batch of the input material, is intended to compose the mixture in a hazardous waste thermal treatment plant in a way that ensures effective use of the energy contained in the waste, maintains specific operating parameters of the installation and minimizes the occurrence of operational problems in the incineration plant. The proposed tool minimizes the impact of alkaline and acidic components on the furnace lining and limits the possibility of excess emissions. The application test was performed, which included ten simulations determining the mass of a portion of the input material (assumed 100 kg) and selecting waste to be used to create a portion of the input material. An initial weight of 1 was used for each of the parameters considered. The values of all parameters were within the norm. The ranges of values for individual parameters were as follows: calorific value 14.96–20.66 MJ/kg, pH 5.59–8.11, content of alkaline salts 1.42–7.39, content of chlorine 1.1–3.83, content of halogens 0.08–0.97. Application tests showed that the basic condition was met, which was the creation of mixtures with established properties. One of the functions of the tool is the ability to give higher weights to selected parameters, shifting the result towards this waste property. Similarly, simulations were carried out to check the stability of the solution after changing the weight of one of the parameters—the weight of the calorific value increased to 5. The remaining assumptions and types of waste in individual simulations were unchanged. In this case, the ranges of values for individual parameters were as follows: calorific value 17.08–18.69 MJ/kg, pH 5.68–8.23, content of alkaline salts 1.42–8.20, content of chlorine 1.12–4.37, content of halogens 0.08–0.96. The values of the favored parameter definitely approached the reference value. Despite this, the resulting batches of feed material still meet the initial guidelines in terms of all considered parameters. An interesting direction for further development of the application seems to be the expansion of a module for parallel emission calculations for a given batch composition. Currently, the application is limited only to the furnace space and does not take into account the products of the thermal process. It seems reasonable to also take this aspect into account when developing the application in the future. In this approach, it might be possible to couple the application with numerical calculations of the thermal process.
Disasters Expo USA, is proud to be supported by Inergency for their next upcoming edition on March 6th & 7th 2024!
The leading event mitigating the world’s most costly disasters is returning to the Miami Beach
And in case you missed it, here is our ultimate road trip playlist is the perfect mix of podcasts, and hidden gems that will keep you energized for the entire journey-