Chemical and pharmaceutical waste disposal with thermal plasma pyrolysis-melting
الموضوعات : Journal of Theoretical and Applied Physics
Shahrooz Saviz
1
,
Davoud Dorranian
2
,
Amir Hossein Sari
3
1 - Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran
2 - Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran
3 - Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran
الکلمات المفتاحية: Plasma Reactor, Plasma torch, Gasification, Covid-19 wastes, slag,
ملخص المقالة :
Thermal plasma treatment is considered as a suitable alternative for the treatment of highly-hazardous wastes such as industrial, radioactive and medical waste. Therefore, a Plasma-Gasification-Melting (PGM) system for treatment of Chemical and Pharmaceutical Wastes (CPW) with a capacity of 1 ton/day is developed using a melting and gasification furnace equipped with two non-transferred thermal plasma torches. In this article, the whole method of chemical and pharmaceutical waste disposal is presented along with exhaust gas analysis, and slag and energy balance approach for improving the relevant technology process. It is successfully demonstrated that the thermal plasma process converts chemical and pharmaceutical wastes into harmless slag. Also, the associated emission level of air pollutants is shown to be very low. The synthetic gas produced can be used as a source of energy. (11.7 Nm3 / hr for CO and 16.4 Nm3 / hr for H2). The total power consumption of the system is 120 k W including 90 kW for thermal plasma torch and 30 kW for utilities with natural gas flow rate of 1.3 Nm3/hr.
Chemical and pharmaceutical waste disposal with thermal plasma pyrolysis-melting
Shahrooz saviza,1, Davoud Dorranianb, Amirhossein Saric
a Plasma Physics research center, Science and research Branch, Tehran, Iran
b Plasma Physics research center, Science and research Branch, Tehran, Iran
c Plasma Physics research center, Science and research Branch, Tehran, Iran
Abstract
Thermal plasma treatment is considered as a suitable alternative for the treatment of highly-hazardous wastes such as industrial, radioactive and medical waste. Therefore, a Plasma-Gasification-Melting (PGM) system for treatment of Chemical and Pharmaceutical Wastes (CPW) with a capacity of 1 ton/day is developed using a melting and gasification furnace equipped with two non-transferred thermal plasma torches. In this article, the whole method of chemical and pharmaceutical waste disposal is presented along with exhaust gas analysis, and slag and energy balance approach for improving the relevant technology process. It is successfully demonstrated that the thermal plasma process converts chemical and pharmaceutical wastes into harmless slag. Also, the associated emission level of air pollutants is shown to be very low. The synthetic gas produced can be used as a source of energy. (11.7 Nm3 / hr for CO and 16.4 Nm3 / hr for H2). The total power consumption of the system is 120 k W including 90 kW for thermal plasma torch and 30 kW for utilities with natural gas flow rate of 1.3 Nm3/hr.
Keywords: Plasma torch, Gasification, Slag, Plasma Reactor, Covid-19 wastes.
1. Introduction
Hazardous wastes such as pathology, chemical and pharmaceutical and radioactive wastes pose many hazards to human health and living organisms [1-6]. There is currently no balance between the production of hazardous waste and the methods of its disposal [7-8]. The diversity of hazardous wastes is increasing though no specific methods have yet been proposed for their disposal. The most recent example is the Covid-19 virus. The horrific number of patients infected with the virus and the daily increase in the number of hospitalized patients have led to a dramatic increase in hazardous waste. Any medications, equipment, vaccines etc. that are relevant to patients with Covid-19 can be a potential source of hazardous waste contaminated with the covid-19 virus. In third world countries, due to the lack of separation of corona patients' waste from other hazardous wastes, it is more likely for all wastes to be infected with this virus. One type of hazardous waste that is difficult to dispose of is chemical and pharmaceutical waste. This waste cannot be decontaminated by methods such as autoclaving. Therefore, one of the possible methods to eliminate them is the application of thermal methods. The presence of chemicals, outdated drugs, and a variety of attenuated viruses and large volumes of minerals in vial containers require high temperature systems. Fossil fuels are not able to create adequately high temperature for melting minerals, thus large amounts of ash remain and many chemicals are left unchanged inside the ash. The new method of using thermal plasma solves the temperature problem [9-13]. Plasma torches [14] can produce temperatures of up to 15,000 °C. In this method, plasma furnaces reach a temperature of about 1800 degrees Celsius. Therefore, all minerals are removed from the furnace in the form of melt. The volume of waste is significantly reduced and the remaining melt is completely safe. On the other hand, organic matter is released as a synthetic gas from the top of the furnace and can be used to generate energy.
In this paper, the system of chemical and pharmaceutical waste disposal with thermal plasma technology is analyzed. In the second part, the generalities of the process in the system and its configuration are examined. In the third part, the output results and system performance are examined and, finally, the conclusion is presented in the fourth part.
2. Experimental Section
2.1. Process overview and plasma reactor configuration
The process of design and construction of the disposal plant for thermal-plasma-based and chemical and pharmaceutical waste was implemented in three six-month periods. In the first six months, the whole plant was designed by professional consulate teams led by PPRC specialists. Second period was dedicated to technical works on construction of the plant and the third period was devoted to tests and optimizations. During the optimization period, attempts were made to improve the operation process of the plant. Some of the main activities performed during this period include normal operation of the plant, decreasing the amount of pollutants in the exhaust gas, reducing the operational cost and upgrading of the feeding system.
The schematic setup of the constructed thermal plasma-based medical waste disposal plant is presented in Fig. 1.
[1] * correspondence author
Email address: Shahrooz.saviz@srbiau.ac.ir (Shahrooz saviz)
The components of the plasma disposal system are shown in Figure 1. As seen, the system consists of three main sections for PGM process on CPW: 1- waste feeding system 2- Long shaft furnace with two non-transfer plasma torches 3- Exhaust gas purification system including afterburner system and water scrubber.
2.2. Specification of CPW
The CPWs are taken from Farhikhtegan Hospital, Tehran, Iran. The physical properties of CPW in terms of weight percentage of different compounds are given in Table 1.
Table 1. Physical composition of the CPW
| Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
Vial of medicine (glass) (%) | 49.3 | 42.2 | 50.2 | 39.7 | 43.2 |
Plastic (%) | 28.4 | 32.6 | 26.1 | 30.4 | 28.7 |
Paper (%) | 2.2 | 1.9 | 2.9 | 1.7 | 2.1 |
Metal (%) | 1.1 | 1.3 | 0.4 | 0.6 | 0.8 |
Residues of pharmaceutical powders (%) | 9.2 | 8.8 | 5.1 | 11.2 | 10.8 |
Residues of drug solutions (%) | 8.4 | 7.9 | 10.2 | 12.2 | 10.3 |
Others (%) | 1.4 | 5.3 | 5.1 | 4.2 | 4.1 |
One of the important parameters in examining the mass and energy balance of a reactor is lower heating value (LHV) of the waste. Equation 1 is related to the calculation of this parameter. The Lower Heating Value (LHV) of the CPW is obtained from the following equation:
(1)
The definitions and mean values of the coefficients in Equation 1. are as follows:
A: Heating value of the combustible materials=18400,
B: Heat loss due to water in the waste=2636,
C: Heat loss due to glass in the waste=628,
D: Heat loss due to metals in the waste=544,
E (): Average heat loss due to other inorganic materials in the waste=450,
: Weight percentage of combustible materials,
: Water weight percentage,
: Glass weight percentage,
: Metals weight percentage.
: Weight percentage of other inorganic materials.
The percentages of combustible and non-combustible materials are given in Table 2. Using Eq. 1 and the given weight percentages of combustible and non-combustible materials as well as the coefficients A, B, C, D and E, the LHVs of the waste are calculated for five samples as given in table 2.
Table 2. The LHV of the CPW for five tests
|
|
|
|
|
| LHV | |||
Test 1 | 30.6 | 8.4 | 49.3 | 1.1 | 10.6 | 5045.7 | |||
Test 2 | 34.5 | 7.9 | 42.2 | 1.3 | 1.41 | 5804.2 | |||
Test 3 | 29 | 10.2 | 50.2 | 0.4 | 10.2 | 4703.8 | |||
Test 4 | 32.1 | 12.2 | 39.7 | 0.6 | 15.4 | 5262.9 | |||
Test 5 | 30.8 | 10.3 | 43.2 | 0.8 | 14.9 | 5053 | |||
Average | 31.4 | 9.8 | 44.92 | 0.84 | 10.5 | 5173.9 |
Test 1 | Test 2 | Test 3 | Test 4 | Test 5 | |
SiO2 | 57.6 | 58.3 | 54.1 | 55.4 | 59.2 |
Al2O3 | 8.26 | 9.2 | 9.8 | 8.4 | 9.5 |
Na2O | 6.56 | 10.4 | 6.9 | 6.4 | 5.7 |
MgO | 0.64 | 0.52 | 0.72 | 0.51 | 0.65 |
CaO | 4.85 | 4.2 | 3.9 | 5.1 | 4.8 |
TiO2 | 0.35 | 0.21 | 0.45 | 0.12 | 0.24 |
MnO | 0.12 | 0.08 | 0.21 | 0.17 | 0.3 |
Fe2O3 | 0.38 | 0.31 | 0.28 | 0.14 | 0.25 |
Table 4. Percentage of remaining slag to the injected CPW (wt %)
| First Step | Second Step | Third Step | Forth Step | Fifth Step |
Remaining slag (wt%) | 58.5 | 61.4 | 59.4 | 57.3 | 60.4 |
Given that the slag is not toxic and does not contain hazardous substances, it can be used in various industries including road infrastructure, construction industries etc.
3.2. Liquid Byproducts
The water scrubber is located after the combustion system. Treatment is necessary for the water used for rapid gas cooling and de-acidification
3.3. Gaseous Byproducts
The most important requirement for a hazardous waste disposal system is the standard amount of exhaust gases. For this purpose, the concentration of air pollutants before the afterburner (Table 5) and in the stack (Table 6) is measured. The gas flow rate before afterburner and in the stack is about 43 Nm3/hr and 95 Nm3/hr, respectively. This flux difference is due to the presence of the afterburner system. Gas chromatography results of the CPW plasma-pyrolysis before afterburner (Table 5) indicate that the produced gases are rich in hydrogen and carbon monoxide and also contain some other compounds. The total quantity of H2 and CO in the gaseous mixture is above 66% so we expect the afterburner temperature to rise. Possible reactions which take place during the pyrolysis of CPW include:
+heat
for cellulose
for plastic
As shown in Table 1, a significant constituent of organic matter in chemical and pharmaceutical wastes is plastic. Therefore, the percentage of hydrogen is expected to be higher than carbon monoxide. This prediction is clearly seen in Table 5. As seen in this table, the concentrations of O2 before afterburner is 0.3 which is small. This shows that oxygen starvation has happened inside the furnace.
Table 5. Exhaust gas composition before afterburner chamber
Gas | CO | H2 | CO2 | N2 | CH4 | H2O | HCL | H2S | O2 |
Molar Distribution (%) | 27.2 | 38.9 | 13.94 | 6.6 | 4.8 | 8.2 | 0.04 | 0.02 | 0.3 |
In this system, our goal is not to produce energy from synthetic gas. Synthetic gas is burned in the afterburner system. Results of exhaust gas analysis after the afterburner system is given in Table 6. The results are indicative of the standard amounts of hazardous pollutants.
Table 6. Exhaust gas composition at the stack
Gas | SOx (ppm) | NOx (ppm) | CO (ppm) | Cl2 (ppm) | NH3 (ppm) | HCl (ppm) | F (ppm) | H2S (ppm) | Dust (mg/Nm3) |
Molar Distribution (%) | 0.1±0.1 | 9.8±2.2 | 7.9±2.8 | 0.03±0.02 | 1.3±0.5 | 0.3 | 0.9±0.3 | 0.02±0.01 | 11.1±1.3 |
4. Conclusions
Thermal plasma technology is the best and most complete method for disposing of chemical and pharmaceutical wastes. In this method, both organic and inorganic wastes are paralyzed, gasified and melted to ensure their complete elimination and the least environmental pollution. The exhaust gas from the furnace is full of energy and can be recycled to increase the energy efficiency of the system. Also, with the provision of the combustion system, the amounts of dangerous exhaust gases are within the standard range.
Statements and Declarations
The authors did not receive support from any organization for the submitted work.
The authors have no relevant financial or non-financial interest to disclose.
References
(1) Chartier Y, Emmanuel J, Pieper U et al (2014) Safe management of wastes from health-care activities: a practical guide, 2nd edn. Nonserial Publications, WHO Press, Geneva.
(2) Komilis DP (2016) Issues on medical waste management research. Waste Manag 48:1–2. https:// doi.org/10.1016/j.wasman.2015.12.020.
(3) World Health Organization (2020) Health-care waste. https://www.who.int/en/news-room/fact/sheets/detail/health-care-waste. Accessed 10 Mar 2020.
(4) Xie, Y. and Zhu, J., 2013. Leaching toxicity and heavy metal bioavailability of medical waste incineration fly ash. Journal of Material Cycles and Waste Management, 15(4), pp.440-448.
(5) Homayouni, Z. and Pishvaee, M.S., 2020. A bi-objective robust optimization model for hazardous hospital waste collection and disposal network design problem. Journal of Material Cycles and Waste Management, 22(6), pp.1965-1984.
(6) Barua, U. and Hossain, D., 2021. A review of the medical waste management system at Covid-19 situation in Bangladesh. Journal of Material Cycles and Waste Management, 23(6), pp.2087-2100.
(7) Windfeld ES, Brooks MS-L (2015) Medical waste management—a review. J Environ Manag 163:98–108. https://doi.org/10.1016/j.jenvman.2015.08.013.
(8) Fang S, Jiang L, Li P, Bai J, Chang C (2020) Study on pyrolysis products characteristics of medical waste and fractional condensation of the pyrolysis oil. Energy 195:116969. https://doi. org/10.1016/j.energy.2020.116969.
(9) Nema SK, Ganeshprasad KS (2002) Plasma pyrolysis of medical waste. Curr Sci 83(3):271–278.
(10) Fiedler J, Lietz E, Bendix D, Hebecker D (2004) Experimental and numerical investigations of a plasma reactor for the thermal destruction of medical waste using a model substance. J Phys D Appl Phys 37(7):1031. https://doi.org/10.1088/0022-3727/37/7/013
(11) Byun Y, Cho M, Hwang S-M, Chung J (2012) Thermal plasma gasifcation of municipal solid waste (MSW). In: Yun Y (ed) Gasifcation for practical applications. InTech, London. https://doi. org/10.5772/48537.
(12) Huang J, Guo W, Xu P (2005) Thermodynamic study of water-steam plasma pyrolysis of medical waste for recovery of CO and H2. Plasma Sci Technol 7(6):3148. https://doi. org/10.1088/1009-0630/7/6/018.
(13) Xiaowei Cai, Changming Du, (2021) Thermal Plasma Treatment of Medical Waste (Review), Plasma Chemistry and Plasma Processing, 41, pages1–46. https://doi.org/10.1007/s11090-020-10119-6.
(14) Zhukov MF, Zasypkina IM (2007) Thermal plasma torches: design, characteristics, application. Cambridge International Science Publishing, Cambridge