Y. ZENGJUN, CTCI Beijing, China
Since petrochemical plant control buildings are usually designed to be blast-resistant without external windows, convection ventilation cannot be carried out, leading to poor air circulation. As a result, there are higher requirements for indoor air quality, and it is necessary to optimize the heating, ventilation and air conditioning (HVAC) system design scheme to improve air quality. Simultaneously, this optimization also helps to achieve energy conservation and emissions reduction that aligns with the dual carbon goals proposed in countries such as China, which aims to achieve peak carbon levels by 2030 and carbon neutrality by 2060.
The current HVAC system design scheme of a petrochemical plant’s controls building. Petrochemical production is highly risky, with the control building playing a key role as the core of petrochemical production. To ensure the smooth plant-building process and the safety of personnel in the control building, the building is usually designed to be blast-resistant and should meet the requirements of China’s Guojia Biaozhun (GB) GB50779-2022 standard, "Standard for blast resistant design of buildings in petrochemical engineering.” Requirements for temperature, humidity and air quality in the control building’s rooms—according to GB50779-2022—are shown in TABLE 1.1
To meet the requirements of temperature, humidity and air quality in the control room, a constant temperature and humidity air conditioner is placed in the control building, while a chemical filter is set up at the fresh air entrance of the control building.
Design optimization scheme of a control building’s HVAC system. According to GB50779, there are concentration limits of PM10, acid gas and alkaline gas for indoor air quality. A fresh air chemical filter is usually implemented with several functional sections, including a primary filter section (G3 or G4), a medium-effect filter section (F7 or F8) and two chemical filtration sections. The chemical filtration sections have fillers containing chemicals, such as potassium hydroxide or potassium permanganate, which can remove acid gas and alkaline gas from the fresh air to make it meet the requirements of GB50779.
However, the filtration efficiency of PM2.5 is < 65% with the combination of a primary filter section (G3 or G4) and a medium-effect filter section (F7 or F8).2 Moreover, under the current design, the pathogenic bacteria in the fresh air cannot be effectively killed, and the fresh air volume cannot be adjusted when the number of people in a room changes. To solve these problems, the HVAC system in the control building of the petrochemical plant was optimized. A sub-high efficiency filter section (H10) and a sterilization section were added to the fresh air chemical filter, which can effectively reduce the harm of PM2.5 and pathogenic bacteria in the indoor environment. Meanwhile, as the number of people in the room changes, the fresh air volume can vary by using the artificial intelligence (AI)-based people-counting video algorithm, successfully saving energy.
FIG. 1 is a flowchart of the optimization scheme of the control building’s HVAC system. The red portion in the figure is the design optimization part based on the current HVAC system. A sub-high efficiency filter section (H10) and a sterilization section were added to the fresh air chemical filter. A camera was added to the entrance and exit of the control building, and the video signal was transmitted to the people-counting module.
Adding a sub-high efficiency filter section (H10) and sterilization section in the fresh air chemical filter. The content of PM2.5 and pathogenic bacteria in fresh air, which can be effectively treated by efficient filtration and sterilization to control indoor air quality, is garnering increasing attention. This is especially true for closed buildings, such as blast-resistant control buildings of petrochemical plants.
To reduce PM2.5 content in the room, the sub-high efficiency filtration (H10) is set after the primary and medium-effect filtration sections, with the combination providing > 93% of PM2.5 removal efficiency.2
Conversely, the sterilization section adopts non-thermal plasma technology, which is widely used in air sterilization and has a very good sterilization effect.3 Non-thermal plasma (NTP) can operate at normal temperature and pressure, and has the characteristics of low running resistance, broad-spectrum sterilization and fast inactivation speed. Under the action of an electric field, the reactive species generated by NTP—primarily including singlet oxygen (1O2 ), superoxide radical (O2- ) and hydroxyl radical (-OH)—has a high redox potential to disrupt the cell membrane of bacteria during the inactivation process, leading to protein leakage and the breakdown of lipids and nucleic acids, ultimately resulting in complete bacterial inactivation to achieve the purpose of sterilization.4
Meanwhile, the sterilization section contains an independent control key. The control key can start the sterilization section if needed when there is a risk of pollution in the outdoor air.
Adjusting the fresh air volume through the AI-based people-counting video algorithm. The fresh air volume from the HVAC system of the control building was served based on the maximum number of people in the building (≤ 50 m3/hr/person) to maintain the positive pressure in the room.
In the post-epidemic era, a high proportion of fresh air is used to ensure indoor air quality and comfort. However, because fresh air must be treated by a chemical filter before it can be sent into the room, the treatment cost is high. Additionally, energy is wasted when fresh air is supplied at a volume to accommodate the maximum number of people in the control building where people are constantly entering and exiting.
To solve this problem, a camera was set up at the entrance and exit of the control building, adopting the AI-based people-counting video algorithm to count the number of people in the indoor environment in real time through three modules:
Image pre-processing module
Image-marking module
People-counting module.5
As a result, the air volume of the fan in the chemical filter can be adjusted according to the actual number of people in the control building. Doing this not only helps meet the fresh air demand of indoor personnel, but also saves the cost of fresh air treatment, contributing to a positive energy-saving effect.
Takeaway. Based on the special needs of the "post-pandemic era" and the principles of safety and saving energy, this article has explored ways to optimize the design scheme of an HVAC system in a petrochemical plant control building. By adding the sub-high efficiency filter section (H10) and sterilization section to the fresh air chemical filter, air entering the room was effectively treated through efficient filtration and sterilization, and the harm of PM2.5 and pathogenic bacteria to the indoor air environment is reduced.
Furthermore, with the use of an AI-based people-counting video algorithm, the fresh air volume can be adjusted through real-time statistics based on the number of people in the control building, effectively ensuring indoor air quality and saving energy. In the future, the fresh air filter section and sterilization section can be selected in correspondence to different outdoor air environments. In addition, with the improvement of image processing control accuracy, it is possible to create a suitable, safe, comfortable and energy-efficient indoor environment. HP
LITERATURE CITED
Ministry of Housing and Urban-Rural Development of the People’s Republic of China, “GB50779-2022: Standard for blast-resistant design of buildings in petrochemical engineering,” September 8, 2022, online: https://www.codeofchina.com/standard/GBT50779-2022.html
Wang, X., “The PM2.5 filtration performance and comprehensive assessment of air filter used in fresh air unit,” Chongqing University, 2016.
Long, Y. and L. Na, “Evaluation on the bactericidal efficiency of low-temperature machine to microbiological aerosol,” Chinese Journal of Disinfection, 2017.
Yang, J., et al., “Study on mechanism and influencing factors of inactivation of bacterial aerosol by non-thermal plasma,” China Environmental Science, 2024.
Zengjun, Y., “A method of automatic people counting used in air conditioning energy saving,” International Conference on Computer Engineering and Technology, 2010.
Yang ZENGJUN is a Senior Engineer and a member of the CPCEA HVAC professional committee. He is a registered utility engineer, a registered constructor and consulting engineer, and is primarily engaged in HVAC designs for petrochemical plants.