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Introduction to the High-Temperature Dry Heat Sterilization Process for Medical Waste
The high-temperature dry heat sterilization technique for medical waste is generally recognized as the most reliable method for high-temperature dry heat sterilization. This technique involves using an organic heat transfer medium heated by high-temperature thermal oil in a cooking pot, which can reach temperatures of approximately 180°C. This method replaces traditional steam sterilization (which operates under conditions of 220 kPa and 134°C for about 45-60 minutes).
Due to the high sterilization temperature of around 180°C in the cooking pot, dry heat has a significant specific heat capacity and strong penetration power. Additionally, it releases a large amount of latent heat during condensation, which aids in denaturing proteins. The high-temperature dry heat cooking pot operates under vacuum conditions of -100 Pa to -50 Pa and at high temperatures of 180-200°C. It is also equipped with a synchronous stirring device to mix medical waste, maintaining this process for 20-30 minutes, effectively killing harmful microorganisms. This includes heat-resistant biological indicators compliant with healthcare industry standards—such as thermophilic Bacillus spores—as well as the notoriously difficult-to-inactivate prion associated with bovine spongiform encephalopathy (BSE).
The high-temperature dry heat sterilization process for medical waste is a simple, reliable, economical, and rapid treatment method that does not generate wastewater and avoids secondary pollution. It has been widely adopted in developed countries like those in Europe and America.
Sterilization methods refer to techniques used to kill or remove all microorganisms, including bacteria, fungi, viruses, and others. Microorganisms are present wherever there is life and reproduce rapidly. Bacterial spores have strong heat resistance and are difficult to kill. The function of the protein molecules that make up cells depends on their specific structure. When subjected to high temperatures, the hydrogen bonds within the protein molecules break, affecting the rearrangement of the molecular spatial configuration, which ultimately leads to the death of microorganisms. The design of the high-temperature dry heat sterilization system was developed with the prion of bovine spongiform encephalopathy, which is the most challenging to kill, as the hypothetical target.
The technological characteristics of the high-temperature dry heat sterilization process for medical waste disposal are as follows:
(1) Clean and sanitary: The sterilization process does not involve any toxic chemicals or substances, aside from the misting of disinfectant. There are no harmful dioxins produced in the exhaust emissions; the exhaust is treated through dust spraying, UV light decomposition purifiers, and activated carbon adsorption devices, which eliminate bacteria and absorb odors before the exhaust is released, meeting national standards.
(2) The sterilization effect meets the LOG6 standard; the sterilization effectiveness can be ensured for different types of medical waste by adjusting operational parameters.
(3) Fully automated control: The process utilizes PLC control technology, making it simple and safe to operate.
(4) Fewer operators are required, facilitating convenient and reliable management. The sterilization process operates in a closed environment, ensuring safety management. Operational parameters can be recorded and printed at any time, providing a basis for operational analysis and reliability tracing.
(5) Safe and reliable with low operating costs; the primary raw materials during operation are water and electricity, with costs lower than incineration treatment technology.
(6) Flexible operation mode, suitable for actual operating conditions, allowing for intermittent operation.
2. Advantages of the high-temperature dry heat sterilization technology disposal process for medical waste.
The main technical and economic advantages are shown in Table 2-1:
The advantages and disadvantages of the high-temperature dry heat sterilization technology for medical waste disposal and the high-temperature steam sterilization disposal process are presented in the table below.
No. | Item | High-Temperature Dry Heat Sterilization Technology for Medical Waste Disposal | High-Temperature Steam Sterilization Disposal Process for Medical Waste |
1 | Technical Principle | Utilizes pre-crushing to break medical waste into small pieces, increasing the heat exposure area, allowing high-temperature dry heat to quickly transfer to the waste for sterilization. The waste is thoroughly stirred to fully absorb the heat and is subjected to a micro-negative pressure vacuum, which rapidly kills pathogenic bacteria. | Uses high-temperature steam to transfer heat through radiation to the medical waste, killing pathogenic bacteria. |
2 | Technical Reliability | Meets national medical waste sterilization and disposal requirements | Meets national medical waste sterilization and disposal requirements |
3 | Technical Maturity | Achieved localization, with mature and reliable technology and high equipment utilization | Achieved localization, older process |
4 | Sterilization Cycle Time | 20-30 minutes, saving a lot of time | 45-60 minutes in the sterilization cabinet, longer time, total process takes about 90 minutes |
5 | Sterilization Effect | Stable sterilization rate achieving LOG6, 99.99% | Unstable sterilization effect, achieving LOG4, 99.99% |
6 | Equipment Requirements | Sealed, high-temperature resistant, negative pressure operation, stirring, insulation | Sealed, high-temperature and high-pressure resistant, negative pressure operation, insulation |
7 | Weight Before and After Disposal | Drying reduces weight by 25-30% | Increased moisture increases weight |
8 | Residue Recovery and Utilization | Residue itself has drying properties, high calorific value, can be sent to waste incineration plants for treatment or landfills | Residue becomes heavier due to increased moisture, lower calorific value, can only be sent to landfill sites for disposal |
9 | Applicable Scope | Suitable for medical waste disposal of all sizes, can operate continuously or intermittently, low operating costs | Suitable for small and medium-sized medical waste disposal, continuous or intermittent operation, high operating costs |
10 | Equipment Investment | Highly integrated equipment, moderate investment | Many scattered equipment, moderate investment |
11 | Technical Advantages and Disadvantages | High degree of automation, equipment can automatically detect issues, low labor intensity, simple operation, short processing cycle, efficient, saves a lot of energy costs. No secondary pollution to the environment, products can be recovered as fuel. | High degree of automation, equipment can automatically detect issues, high labor intensity, complex operation, long processing cycle, low efficiency, high energy consumption. Generates waste gas and wastewater, products can be recovered as fuel. |
12 | Operating Method | Can operate intermittently or continuously, easy production adjustment | Can operate intermittently or continuously, easy production adjustment |
13 | Worker Operating Environment | Good operating environment | Relatively poor operating environment |
14 | Operational Requirements | High degree of automation, low labor intensity | High degree of automation, but requires dense loading and may have discharge issues, high labor intensity |
15 | Pollutant Emission | Very low VOCs emissions | Odor emissions, generates wastewater which needs heating and sterilization, leading to secondary pollution requiring environmental treatment |
16 | Land Occupation | Relatively moderate | Large land area |
17 | Operating Costs | Relatively simple operation, high equipment reliability, heat transfer oil is reused, low energy consumption, low operating costs | Relatively complex operation, lower equipment reliability, no heat recovery from high-temperature steam, high energy consumption, high operating costs |
Table 2-1
In summary, for a disposal scale of less than 10 tons per day for this project, the use of high-temperature dry heat sterilization technology is reasonable and feasible.
3. Determination of the Technical Scheme
For a centralized treatment capacity of around 10 tons of medical waste per day, it is preferred to use high-temperature dry heat sterilization technology for disposal.
Based on an understanding of the high-temperature dry heat sterilization technology for medical waste treatment, and considering the overall technical and economic advantages, as well as the project's actual situation and the local economic development level: the disposal scale is relatively moderate, and the operating costs should not be excessively high. Additionally, considering that medical waste disposal involves many factors, especially in terms of management, the adaptation period for the collection and transportation of medical waste may be relatively long, making a batch operational mode more suitable.
In summary, for the proposed new project with a scale of 10 tons per day, it is reasonable and feasible to recommend the use of high-temperature dry heat sterilization technology for medical waste disposal.
4.Process Flow
4.1 Process Flow Diagram
The main process flow for the high-temperature dry heat sterilization technology used in this project for medical waste disposal is as follows:
Medical Waste → Collection → Transportation → Unloading and Weighing → Storage or Temporary Storage → Feeding → Shredding → Sterilization → Discharge → Landfilling or Sending to Municipal Waste Incineration Plant for Incineration.
4.2 Design of High-Temperature Dry Heat Sterilization Device for Medical Waste Treatment System
4.2.1 Introduction to High-Temperature Dry Heat Sterilization Technology
The sterilization method for medical waste is generally recognized as most reliable when using high-temperature dry heat sterilization technology. Due to the high cooking temperature within the sterilization pot, which can reach above 180-200°C, this process has a high specific heat and strong penetration. Additionally, the process releases a significant amount of latent heat during condensation, making it easier to denature proteins. Under vacuum conditions, with a micro negative pressure of -100Pa to -50Pa and at temperatures of 180-200°C, the negative pressure operation is maintained for 20-30 minutes, effectively killing all microorganisms, including the heat-resistant biological indicators recognized by the healthcare industry—thermophilic spore-forming bacteria—as well as the most resistant pathogens, such as prions associated with bovine spongiform encephalopathy.
High-temperature dry heat sterilization technology is a simple, reliable, economical, and rapid method for medical waste disposal, which has minimal environmental impact and is widely adopted in developed countries such as those in Europe and North America. The technology is mature and trustworthy.
Currently, the main procedure for the high-temperature dry heat sterilization technology involves first shredding the medical waste, followed by the high-temperature dry heat sterilization process.
4.3 The treatment process of medical waste through crushing followed by high-temperature dry heat sterilization technology.
The heat released from the high-temperature heat transfer oil is transmitted through the inner walls of the sterilization pot to the fragmented medical waste, achieving high-temperature disinfection and sterilization. This technology belongs to the high-temperature dry heat sterilization process. The medical waste is packaged in small sealed bags and is manually fed into the hopper above the conveyor belt. The conveyor belt automatically transports the medical waste into the feeding channel, where it enters a crusher that fragments the medical waste into small pieces. The fragmented medical waste then enters the sterilization pot within a complete set of high-temperature dry heat sterilization equipment. With the increased surface area of the medical waste, its contact area with the high-temperature dry heat sterilization pot also increases. Additionally, the sterilization pot is equipped with a stirring device, ensuring that the medical waste fully absorbs the high-temperature heat. This process is characterized by its distinction from commonly used high-temperature steam sterilization methods, as it replaces the typical high-temperature steam with high-temperature heat transfer oil as the heat transfer medium, thereby achieving disinfection and sterilization.
Natural gas (or high-quality diesel) burners are used to heat the heat transfer oil, enabling the high-temperature dry heat sterilization temperature to reach approximately 180-200°C. This high temperature has strong penetration capabilities, thoroughly disinfecting and sterilizing while reducing intermediate pollution, effectively deforming and rendering the medical waste harmless.
This project recommends adopting this high-temperature dry heat sterilization technology due to the following advantages:
1. The sterilization equipment for the high-temperature dry heat sterilization process is a closed integrated device that combines crushing, heating, sterilization and disinfection, and exhaust gas treatment.
2. The technology employs the most representative high-temperature dry heat (cooking) sterilization method, first dry crushing the medical waste, and then transferring the high-temperature heat released from the heat transfer oil through the walls of the sterilization pot to the fragmented medical waste. The moisture in the medical waste is vaporized by the high temperature, dehydrating and drying it in a closed high-heat dynamic environment, achieving the goal of killing pathogens.
3. The disposal process is automatically controlled by a computer, and this medical waste treatment equipment has several advantages:
It combines crushing, heating, high-temperature dry heat sterilization and disinfection, exhaust gas treatment, and activated carbon adsorption into one system, making it easy to operate and reducing workers' labor intensity.
The related equipment in the process system is highly integrated, making maintenance and repair simple and convenient.
The equipment has a small footprint and occupies little space in the facility.
The disinfection and sterilization efficiency of the high-temperature dry heat sterilization technology can reach between 99.99% and 99.9999%.
The high-temperature dry heat sterilization pot operates under negative pressure, preventing harmful gases from leaking and ensuring a good working environment.
The high-temperature dry heat sterilization technology has been further optimized based on disinfection and sterilization equipment, resulting in better sterilization effects, shorter disinfection times, and a highly integrated device that combines heating and exhaust gas treatment, achieving significant environmental benefits with a small footprint, convenient management and operation, and enhanced automation.
4.4 Brief Description of the High-Temperature Dry Heat Sterilization Process
The processing scale of this project is 10 tons per day (2 x 5 tons per day), and it is equipped with a high-temperature dry heat sterilization process line. The disposal flowchart is as follows:
Figure 4-2 Medical Waste Disposal Flowchart
The high-temperature dry heat sterilization technology disposal process for medical waste includes the treatment of hazardous and infectious medical waste using specialized enclosed box trucks for transportation.
After entering the facility, the medical waste transportation vehicles park in the unloading area of the medical waste disposal workshop, where the workshop operators use an automatic feeding system to send the medical waste to a shredder. Once shredded into small pieces, the medical waste is conveyed through a negative pressure pipeline to the high-temperature dry heat sterilization cooking pot. The pneumatic valve safety door on top of the cooking pot automatically closes, completing the preparatory work for the high-temperature dry heat sterilization process.
After the medical waste is placed in the high-temperature dry heat sterilization cooking pot and the preparatory work is completed, the equipment operators follow the operating procedures for the cooking pot and the requirements for medical waste processing to start the sterilization process. The steps involved are as follows: (A) Heating: During the heating and stirring operation, the waste temperature is raised to the sterilization temperature. (B) Disinfection: Under conditions of 180-200 degrees Celsius, the waste is constantly stirred for 20-30 minutes, effectively disinfecting and sterilizing the medical waste. (C) Negative Pressure: The pressure inside the container is maintained at a micro-negative pressure range of -100Pa to -50Pa, causing all waste to lose moisture and remain in a dry state. (D) Dehydration: Almost all residual moisture in the waste is removed. The entire process is accompanied by stirring, completing one cycle of the high-temperature dry heat sterilization process, after which the material is reloaded and enters the next cycle.
The sterilized medical waste fragments are unloaded through the discharge outlet onto an automatic conveyor system, and then transported via medical waste trucks to nearby landfills for disposal or to waste-to-energy incineration plants for power generation.
In the high-temperature dry heat sterilization process, the steam generated during the operation of the cooking pot directly dehydrates and dries the waste. The exhaust gases produced during the process are treated by a dust spray and UV light decomposition + activated carbon adsorption unit before being discharged in compliance with standards.
Workshop operators disinfect the interior of the transportation vehicle’s box in the unloading area with disinfectant, and the wastewater generated from the rinsing is collected by a trench on the floor and processed by the workshop's wastewater treatment system. Only after rinsing and disinfection can the vehicle leave the facility.
The high-temperature dry heat sterilization technology does not produce residual liquid or wastewater, thus protecting the factory area and surrounding environment.
4. Waste Gas Treatment
Maintaining thermal energy output and the continuous rotation of the stirring and cutting arms in the cooking pot allows for further dehydration of the waste, almost achieving complete dryness. Once the high-temperature dry-heat sterilization process is complete, the heat transfer oil in the interlayer of the cooking pot continues to be supplied. The waste gas inside the sterilized cooking container is then extracted by a vacuum pump from the configured vacuum unit. After passing through dust spraying, a high-efficiency UV photolysis purification device, and an activated carbon adsorption unit, the treated waste gas is discharged, thereby achieving clean waste gas that meets national emission standards.
The smoke emission indicators of the organic heat carrier liquid-phase furnace have been adjusted to meet the enhanced local standard requirements of certain provinces. First, the organic heat carrier liquid-phase furnace utilizes low-pollution natural gas energy, and is equipped with relevant denitrification devices. Specifically, a urea injection system has been added at the high-temperature smoke outlet of the liquid-phase furnace, along with a two-layer catalyst for denitrification treatment, ensuring compliant NOx emissions.
5. Technical specifications for the dimensions of high-temperature dry heat sterilization equipment.
Due to space constraints, the dimensions of the equipment vary for different sites. The design is based on actual conditions and is provided for reference, as shown in Figure 6.2-1.
Elevation drawing of the high-temperature dry heat sterilization process equipment.
Floor plan of the high-temperature dry heat sterilization technology disposal process equipment.
6. Equipment Structure
The main body of the high-temperature dry heat sterilization equipment consists of a steel structure frame platform measuring 5500mm in length, 5000mm in width, and 4925mm in height, designed for the installation of the complete set of high-temperature dry heat sterilization equipment. The total height of the equipment is approximately 8160mm.
On the first floor, the layout includes one organic heat carrier liquid phase boiler, two high-temperature oil circulating pumps, one heat transfer oil storage tank, one heat transfer oil filling pump, two vacuum cooling devices, two cooking sterilization tanks, one discharge conveyor (standard configuration), which can be modified to two units with a 90-degree discharge if space is insufficient, one feeding conveyor, one air compressor, and two electrical control cabinets.
The second floor is arranged with one dust spraying and UV photolysis device, one disinfectant mixing device, one bifurcated stainless steel discharge channel with switchable flap doors, one assembly of electromagnetic valves for the compressed air pipeline, one manual control box for the cooking tank, and one manual control box for the disinfectant mixing tank and dust spraying UV photolysis.
On the third floor, the layout includes one crusher, one crusher control cabinet, one activated carbon device, one heat transfer oil expansion tank, one feeding inlet for the crusher, and one feeding flap door.
Photos of high-temperature dry heat sterilization technology processing equipment.
7. Equipment Composition
The main components of the equipment include: feeding belt conveyor, crusher, cooking pot device, vacuum cooling device, organic heat carrier liquid phase furnace device, UV photolysis electrostatic purifier, disinfection device, discharge machine, weighing and measuring device, air compressor, electrical control cabinet, and other equipment.
2. Medical Waste High-Temperature Cooking Disposal Solution
1. Fully Automatic Small Medical Waste Disposal Equipment
Specifically designed for the disposal of small quantities of medical waste.
The equipment operates automatically and has a disposal capacity of 50-500 kg.
It can automatically carry out high-temperature sterilization and crushing of medical waste
to achieve the harmless treatment of medical waste.
The equipment consists of multiple systems, including feeding system, intelligent high-temperature sterilization system, crushing system, steam system, etc.,
to ensure the safe handling of medical waste.
Material: 304/316L stainless steel with comprehensive corrosion-resistant design,
equipment lifespan is twice that of competitors in the industry.
Low failure rate and extremely low annual maintenance costs.
