Thai English

Development of Plasma Pyrolysis-Gasification for Disposal of Medical Waste

September 2, 2019.

 

1. Introduction

 

 

Fig. 1 Illegal disposal of infectious waste in public areas. [1]

 

        “Nakhon Si Thammarat people are frightened, someone illegally discarded infected waste” was the headline of the Daily News newspaper on May 4, 2015 [1]. It reflects the serious problems of Thai society in the incorrectl disposal of infectious waste. Due to many limitations such as hospital liability weakness of law enforcement, lack of awareness of social problems, not enough waste incinerator and lacking appropriate technology, etc. Infected waste is waste generated from hospitals and health science research centers. Currently, Thailand has a hospital which consists of hospitals, public health center, community health centers, both public and private clinics. There are more than 37,000 places with more than 140,000 beds. On average, infectious waste occurs 0.5 - 0.8 kilograms per bed per day. In 2012, there were 4.2 billion tons or 40 million kilograms of infectious waste at the time. That number of infectious waste incinerators is insufficient. Nationwide, there are 13 kilns of local government organizations and 4 private incinerators, although about half of the hospitals have their own internal furnaces, such as La Ngu Hospital, Satun Province, but not enough [2]. Causing the dumping of infectious waste in public places or dumping with general community garbage or burned in a non-standard kiln. Infectious waste is a dangerous waste contaminated with many serious pathogens that can spread to the community, such as diarrhea, helminthiasis, cholera, dysentery, tetanus, hepatitis, and AIDS, etc. In addition, infectious waste includes blood bags, cotton gauze, wipe syringes, saline bottles, radioactive substances, antibiotics, cytotoxic drugs, dangerous chemicals, sharp objects, carcasses, a piece of meat, which would cause pollution to the environment, such as groundwater contamination, contamination in public water sources, contamination in the food chain or the occurrence of dangerous gases such as dioxin, furan, if the infected waste is burned together with community waste, in a non-standard incinerator with a temperature below 800 oC [3].

 

        Plasma pyrolysis-gasification technology is an effective infectious waste disposal technology, both economically and environmentally. Because the plasma has a temperature higher than 1,200 oC and has high intensity UV radiation. The high temperature of the plasma will cause gasification or pyrolysis of plastic waste components, cotton balls, glass bottles, fabric, biodegradable, forming a fuel gas such as hydrogen, carbon monoxide, and methane. At the same time, heat and UV radiation will completely destroy all germs, both normal germs and heat-resistant germs, by the temperature of the plasma at the cathode area of about 20,000 K and at the anode area of about 7,000 K and at the waste area of about 1,500 K.  Plasma pyrolysis-gasification technology is an appropriate technology to be developed in Thailand, to solve the crisis due to improperly infected garbage disposal. The plasma technology has hygienic waste management features as follows;

 

1. high temperature and UV rays can break down all waste components and completely destroy various germs,

2. very quick to increase and reduce the temperature, less than milliseconds,

3. compact, which can be developed for use with a community hospital of a bed number less than 100 beds or a hospital center with more than 1,000 beds,

4. no fly ash and bottom ash, so no trapping and removal problems,

5. no harmful gases such as dioxins, sulfur, NOx or SOx.

 

2. Thermal plasmas or hot plasmas

 

 

Fig. 2 State of matter at various temperatures. When the temperature rises, the solid changes to liquid, gas, and plasma.

 

        Plasma is the fourth state of matter which occurs when the gas has a very high temperature, as shown in Figure 2. As the temperature of the gas is increased, the particles will have more kinetic energy. Severe collisions between particles can overcome the internal bonding between electrons and nuclei, electrons are split from atoms, causing ionization to be positive ions and free electrons with negative charges. In addition, recombination between the ion and electrons cause the formation of electromagnetic waves or photon particles. As a result, plasma is a state of matter that consists of many particles, including ions, electrons, atoms, molecules, radicals, and photons. The major interaction in plasma is the force acting on the charge particles due to the electromagnetic field. Plasma behave differently from matter in the state of the gas, which has no charged particles. Plasma that contains electrons and ions, which are in thermal equilibrium state, known as thermal plasma. In general, thermal plasma or hot plasma that is currently in use has temperatures between 1,500 - 5,500 oC [4,5].

 

3. DC plasma torch

 

                        

                            (a)                                                                                  (b)

 

Fig. 3 (a) Thermal plasma generator using DC plasma torch. (b) Plasma jet ejected from DC plasma torch, having temperature of more than 1,200 oC.

 

        The developed DC plasma torch system has the characteristics shown in Figure 3 (a), which have the main components: a 5 kW DC power supply and a DC plasma torch. When compressing air into the torch using an air pump and supplying voltage to torch approximately 100 - 200 V, it will break down the air into hot plasma. And causes a plasma current of about 20-60 A, with the power of the plasma as shown in Figure 4, which has a maximum power of about 5,800 W.

 

 

Fig. 4 Input power and plasma power during the discharges.

 

        The major problem of the DC plasma torch is the corrosion of the torch head, caused by a positive ion collision or sputtering, resulting in a limited lifespan of the torch head. The corrosion of the torch head is shown in Figure 5. It was found that after 10 minutes of discharging, corrosion will occur and a hole will be formed at the center of the torch head area.

 

     

(a)                                                      (b)

 

Fig. 5 Torch head (a) before the discharge and (b) after discharge for 1 minute.

 

4. Conclusion

 

       Thermal plasma technology is capable of generating more than 1,200 oC. In developed countries, plasma pyrolysis-gasification technology is used to eliminate infectious and dangerous waste, which will be able to destroy germs and various toxins and obtain non-toxic gas and stable slag production. The objective of this research project is to develop a thermal plasma generator with a temperature higher than 1,200 oC by using a DC plasma torch, which can work continuously and to develop knowledge of thermal plasma for use in constructing clean technology prototype machines for the disposal of infectious and dangerous waste from hospitals. In the 2nd year of operation has been successful in development DC power supply is more than 20 kW, and has developed a DC plasma torch head with a corrosion rate of 1.5 - 5.7 mg / C [6-8], which is the rate of corrosion that is similar to the commercial ones. The plasma torch can generate hot plasma with temperatures above 1,200 oC. In the 3rd year, we will develop a DC plasma torch that can generate hot plasma with a power greater than 25 kW and fabricate a plasma furnace, consisting of waste incinerator and thermal insulation to test the burning of infectious waste from hospitals.

 

References

 

  1. หนังสือพิมพ์เดลินิวส์ ออนไลน์ วันที่ 4 พฤษภาคม 2558 (In Thai)

  2. หนังสือพิมพ์ไทยรัฐออนไลน์ วันที่ 20 มิถุนายน 2557 (In Thai)

  3. จันทนา มณีอินทร์, “การจัดการมูลฝอยติดเชื้อขององค์กรปกครองส่วนท้องถิ่น”, วิทยานิพนธ์ปริญญาโท สถาบันบัณฑิตพัฒนบริหารศาสตร์ 2556  (In Thai)

  4. Umberto Arena, “Process and technological aspects of municipal solid waste gasification: A review”, Waste Management 32 (2012) 625–639.

  5. Ajay Kumar, David D. Jones and Milford A. Hanna, “Thermochemical biomass gasification:  A review of the current status of the technology”, Energies 2009, 2, 556-581; doi:10.3390/en20300556

  6.  R. N. Szente, R. J. Munz and M. G. Drouet, “Electrode erosion in plasma torch”, Plasma Chem Plasma Process (1992) 12: 327.

  7. Plasma Energy Corp, 1988.

  8.  Westinghouse, 1979.

 

Reported by

 

Assoc. Prof. Dr. Mudtorlep Nisoa*, Dhammanoon Srinoum, Ridvee Taleh and Watcharin Kongsawat

Center of Excellence in Plasmas and Electromagnetic Waves,

Walailak University, Tha Sala District, Nakhon Si Thammarat-80161, Thailand

E-mail: mnisoa@yahoo.com*