Analyzing the performance of cyclones and scrubbers as air pollution control methods for household solid waste incinerator

Household solid waste processing through incinerators may pose environmental problems, as gas emissions from combustion are released. Air Pollution Control Devices (APCD), such as cyclones and cyclone scrubbers, are frequently utilized to mitigate these issues. This study aims to evaluate the efficacy of cyclones and cyclone scrubbers as APCD for incinerators. To conduct the study, gas emissions for the parameters SO2, NOx, and CO were measured from the combustion of mixed waste in an incinerator with a fixed waste composition. Data were collected every 5 minutes within 45 minutes of combustion at the inlet and outlet of each APCD. The results indicate that using a cyclone can eliminate 37% of NOx and 91% of CO emissions. In contrast, a cyclone scrubber can remove 53% of NOx and 96% of CO emissions. Notably, the gas analyzer failed to recognize the SO2 parameter. Implementing a cyclone can reduce gas emissions from incinerator combustion, and combining a scrubber within the cyclone can increase its effectiveness in reducing these emissions.


Introduction
For many years, waste has posed a challenge for numerous countries, Indonesia included.As the population grows, so does the amount of waste generated, making efficient waste processing crucial.To address this issue, the incinerator has emerged as a valuable tool for quickly reducing waste.Incinerators can transform waste into ashes by utilizing a solid waste destruction system that burns waste at high temperatures (ranging from 600-1000 o C).Research has revealed that incinerator usage may reduce solid waste mass by up to 89%.
Incinerators pose a significant disadvantage as they have the potential to release harmful pollutants into the air, which can lead to a decline in air quality.These pollutants encompass particulates, acid gases, nitrogen oxides, carbon monoxide, organic compounds, sulfur, and other unidentified substances, all of which can cause detrimental implications on the environment and public health.For instance, they can contribute to global warming, lead to acidification, and negatively impact the wellbeing of both humans and animals [1].Given these negative consequences, it is imperative to have an air pollution control device (APCD) to prevent the discharge of contaminated air into the environment.A cyclone is a common type of APCD unit which uses centrifugal force and low pressure due to rotation to separate materials based on density and size.To increase the cyclone's collection efficiency for smaller particles and to reduce the emissions from combustion, a scrubber was added to the cyclone.The performance of the scrubber unit depends largely on the quality of the water used.To prevent water contamination, a filtration tank is required at the outlet of the scrubber [2].
The products of the combustion reaction consist primarily of carbon dioxide, water vapor, and heat energy.However, the combustion of certain fuels can result in other byproducts, such as carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), and ash.The efficiency of cyclones and cyclone scrubbers in reducing these byproducts is influenced by several factors, such as cyclone diameter, gas viscosity, particle density, and inlet velocity [3].
Emission tests were conducted in incinerators that process household waste and the combustion produced emissions of SO2, NOx, and CO, which had to be decreased before release into the atmosphere.It could be achieved by diverting gas emissions to the cyclone or cyclone scrubber before they exited the chimney and entered the environment.Therefore, this research was conducted to identify the effectiveness of the performance of cyclones and cyclone scrubbers in reducing gas emissions so that they are safe for the environment.

Methods
Mixed waste was burned in an incinerator combustion chamber to conduct the research.The waste composition was based on the household waste from Patumbak District, Deli Serdang Regency, North Sumatra, one of the sub-districts in North Sumatra Province.Table 1 shows the household solid waste compositions used in this study [4].To experiment, every APCD was subjected to identical treatment, involving 17.5 kg of waste in the combustion chamber.Emission was sampled at each APCD's inlet and outlet points, focusing on SO2, NOx, and CO gas emissions as test parameters.Data on emissions were collected every 5 minutes during a 45 minutes burning period.A gas analyzer was used to test the emissions and provide realtime results.The emission test methods are summarized in Table 2.

Table 2. Emissions test method Gas Emissions
Test Method SO2 Portable Pump-Suction Gas Detector NOx Gas Analyzer E 4500-3 CO Gas Analyzer E 4500-3 The data obtained will also be compared with the quality standards based on the Regulation of the Minister of Environment and Forestry No. 70 of 2016 about Quality Standards for Emissions of Businesses and/or Thermal-Waste Treatment Activities.To find out the percentage of the removal efficiency that the test results show, can be calculated using the equation 1: Where Cin and Cout are emission concentrations at the APCD inlet and outlet.

Results and discussion
The gas parameters at the APCD inlet show high emission levels.It is due to the excessive initial combustion load that leaves no space for oxygen and fuel (waste) to mix (turbulence) in the combustion chamber.However, the emission concentration that drops as the combustion continues until it ends.The oxygen supply, waste composition and the temperature of the combustion chamber greatly affect the emission formation [5].
The sampling of the gas emission test at the APPU inlet and outlet is illustrated in Figure 2. The comparison of the test data obtained and the quality standards shows that the emission concentration that enters the environment is under the quality standard or environmentally safe [6].The SO2 parameter was not identified in the measurement results.It was caused by several factors: the emission test equipment's inability to identify concentrations lower than 0.3 mg/Nm 3 and a small amount of sulfur compounds in the burned waste.Burning sulfur content in the waste creates SO2 gas [6].The test results and the comparison with the quality standards are presented in Table 3.As shown in Table 3, there is a decrease in emission gas allowance that each APCD shows, which may indicate the use of a cyclone and cyclone scrubber to get rid of emission gas from the combustion chamber.The removal efficiency calculation indicates that the cyclone scrubber is more efficient in removing emission gas than the cyclone.The NOx parameter reaches 53% and the CO parameter reaches 96%.It is affected by adding a scrubber that facilitates contact between water (absorbent) and emission gas.The gas that enters the cyclone scrubber will be sprayed with water so that the gas will be bound to the water substance to create a gas-in-liquid solution, while the light gas will move up and out towards the chimney [8].Using clean water in the scrubber is three times better for removing gas emissions [9].The efficiency results change significantly due to the unstable gas emission input during measurement.The results of efficiency calculations are presented in Table 4.The concentration of NOx emissions at the inlet changes due to the fuel's evaporation of nitrogen and the oxidation of nitrogen in the charcoal in the final minutes of combustion.The concentration of CO emissions at the inlet changes due to a volatile fuel and the oxygen supply during combustion [10].The emission reduction for each parameter in the cyclone is not clear yet.However, the emission reduction in the cyclone scrubber is confirmed due to the water absorbent that can reduce gas emissions from combustion. Figure 3 shows the reduced concentration of each parameter in each APCD.

Conclusions
This study demonstrates the significant potential of implementing cyclone and cyclone scrubber as air pollution control devices to reduce incinerator emissions.The results revealed a notable decrease in the concentration of NOx and CO gases following the combustion process.In addition, the addition of a scrubber utilizing water as an absorbent demonstrated remarkable performance, surpassing the effectiveness of the cyclone alone.The cyclone scrubber achieved an impressive removal efficiency of 53% for NOx and 96% for CO gases.These findings highlight the practical benefits of these technologies for mitigating incinerator emissions, highlighting their significance for air pollution control and environmental sustainability efforts.

Table 1 .
Solid waste composition 3Legend:: boundary of study Figure1.Flow chart process for incinerator

Table 3 .
Result of emission testing *Not detected by the device