Analysis And Summary of Problems in The Engineering Application of Ozone Advanced Oxidation Technology

Analysis and Summary of Problems in the Engineering Application of Ozone Advanced Oxidation Technology

With the continuous improvement of national standards for wastewater discharge, ozone advanced oxidation technology has been widely applied. However, there are some confusing and perplexing issues in the engineering application of this technology that need to be clarified and resolved urgently. This paper focuses on the analysis of four aspects: the gas source of the ozone generator, commonly used design parameters, the circulating cooling water system, and the instrument setup, providing references for the design and construction of ozone advanced oxidation technology.

01 Technical Overview

Ozone advanced oxidation technology is currently widely used in the upgrading and renovation of municipal wastewater treatment plants and the deep treatment of high-concentration and refractory industrial wastewater. Its essence is to generate hydroxyl radicals (·OH) with stronger oxidizing power and lower selectivity, which have a redox potential 35% higher than that of ozone and can degrade various stable and poorly biodegradable pollutants in wastewater. However, there are several key issues to be addressed during the design stage, such as how to select the appropriate gas source and understand the power consumption and cost parameters of the ozone generator. These issues all require in-depth analysis and resolution.

In engineering applications, this technology not only needs to consider its treatment effect but also comprehensively take into account factors such as cost and safety. Different gas sources will affect the power consumption, cost, and ozone concentration of the ozone generator; when setting up instruments, it is necessary to fully consider the potential hazards of ozone and oxygen leakage, promptly identify and eliminate potential risks to ensure safe production. Therefore, a comprehensive understanding of all aspects of ozone advanced oxidation technology in engineering applications is crucial for improving the efficiency and quality of the project.

02 Gas Source Analysis

The gas sources for ozone generators mainly include air source, oxygen-enriched source, and liquid oxygen source. The air source uses an on-site air purification system to treat air and obtain clean and dry air as the gas source; the oxygen-enriched source is prepared by an on-site oxygen generation system; the liquid oxygen source vaporizes liquid oxygen into gaseous oxygen. The oxygen-enriched source and the liquid oxygen source are collectively referred to as oxygen sources.

Different gas sources have different characteristics, such as differences in generator power consumption, gas source power consumption, and annual electricity costs. When choosing a gas source, multiple factors need to be comprehensively considered to ensure high efficiency and stable quality of the product.

Generally, air source generators are suitable for small-scale ozone generation (≤10kg/h) and situations where ozone concentration requirements are not high, and are less used in actual engineering; liquid oxygen source generators are suitable for medium and small-scale ozone generation (≤20kg/h) and areas where liquid oxygen is easily purchased; oxygen-enriched source generators are suitable for various scales or situations where liquid oxygen purchase is inconvenient, liquid oxygen station installation is restricted, but ozone concentration requirements are high.

Among them, PSA oxygen generation is often used for medium and small-scale ozone generation (≤20kg/h), and VPSA oxygen generation is often used for large-scale ozone generation (>20kg/h). By analyzing the characteristics and applicable scenarios of different gas sources, we can more reasonably select the gas source and improve the operating efficiency of the ozone generator.

03 Common Parameters

In the engineering application of advanced oxidation technology with ozone, the common parameters of ozone generators mainly involve ozone generation capacity, power consumption and cost, ozone concentration, and parameter conversion. The power consumption of ozone generators varies with different gas sources. By referring to relevant standards and combining the data provided by various generator suppliers, we can summarize the power consumption and various costs of ozone generators for three types of gas sources. In the early stage of a project, these data can be used to estimate power consumption and cost indicators. For example, there are significant differences in power consumption and cost among air source, liquid oxygen source, and enriched oxygen source, which is of great significance for cost control and benefit assessment of the project.

The ozone concentration at the outlet of the ozone generator also varies with different gas sources. By summarizing the ozone concentration at the outlet of the three types of gas source generators, we can refer to the relevant data in the early stage of the project to estimate indicators such as ozone dosage. In addition, there are parameter conversions between liquid oxygen, oxygen, and ozone, as well as conversions of ozone concentration in different measurement units. For instance, the mass ratio of oxygen to ozone, the conversion between mass fraction and volume fraction of ozone at the outlet of different gas source generators, etc. Mastering these conversion relationships can help complete the design tasks at different stages of the engineering project more efficiently.

04 Cooling Water System

When an ozone generator is in operation, it generates a large amount of heat energy and requires cooling; otherwise, the ozone will decompose as it is produced due to high temperatures. Water-cooled generators have good cooling effects, stable operation, no ozone attenuation, and can work continuously for long periods. However, they have complex structures and high costs. Large generators or those used in important places are usually water-cooled. In water treatment projects, water-cooled generators are often selected, and they are equipped with suitable cooling water systems, which can not only ensure the output and efficiency of ozone but also extend the service life and stability of the generator. The most commonly used water-cooled ozone generator is the closed-loop cooling water system, which is divided into internal and external circulation systems.

The internal circulation is mainly used to cool the discharge chamber of the generator and is equipped with a plate heat exchanger, circulating water pump, buffer water tank and accessories by the generator manufacturer. The external circulation system is used to cool the heat exchanger. There are differences in the requirements for the amount and quality of circulating cooling water between the internal and external circulation cooling water systems. The selection of the external circulation cooling water source should be based on the actual situation of the project and choose an economically feasible water source. For example, industrial projects should give priority to using the external circulation cooling water provided by the cooling tower in the factory; for municipal or industrial park projects, it is necessary to first verify whether the treated water from the sewage treatment plant meets the requirements; when the ozone generation capacity is small, it is possible to consider using the factory's tap water, etc. By rationally configuring the internal and external circulation cooling water systems, the normal operation of the ozone generator can be ensured.

05 Instrument Settings

Ozone is a colorless, fishy-smelling, and toxic gas. Oxygen leakage can also pose a danger to human health and may cause fires or explosions. Therefore, monitoring ozone and oxygen leakage, and promptly identifying and eliminating potential hazards, is a crucial aspect of ensuring safe production. Additionally, the relationship between ozone concentration and water quality is not intuitive, and instruments are needed to accurately monitor and regulate it. Currently, the types of instruments that may be equipped in an ozone catalytic oxidation unit mainly include dew point meters, ozone leakage alarms, oxygen leakage alarms, ozone concentration meters, water ozone concentration meters, tail gas ozone concentration meters, and exhaust ozone concentration meters.

Different instruments have different installation locations and functions. For instance, dew point meters are typically installed at the inlet of air-source and oxygen-enriched source ozone generators to monitor dew point temperature and assess the operational status of the oxygen generation system. Ozone leakage alarms are placed in the ozone generator room to monitor the ozone concentration in the indoor air for possible leaks. Oxygen leakage alarms are installed in the oxygen-source ozone generator preparation room to monitor oxygen concentration. Water ozone concentration meters, tail gas ozone concentration meters, and exhaust ozone concentration meters can be selectively configured based on specific project requirements and investment. By rationally setting up these instruments, problems can be detected in a timely manner, ensuring the safe operation of the advanced oxidation unit with ozone.

06 Summary and Suggestions

The selection of the gas source type for an ozone generator should be determined by considering multiple factors. Generally speaking, air source generators are suitable for applications where the ozone production rate is ≤ 10 kg/h and the requirement for ozone concentration is not high; liquid oxygen source generators are suitable for applications where the ozone production rate is ≤ 20 kg/h and liquid oxygen is readily available; oxygen-enriched source generators are suitable for various scales or areas where liquid oxygen purchase is inconvenient and liquid oxygen station installation is restricted but a higher ozone concentration is required. When mastering the common parameters of ozone generators, it is necessary to flexibly apply empirical data on power consumption and cost, ozone concentration, and parameter conversion to improve the efficiency of project design.

For internal and external circulation cooling water systems, a suitable external circulation cooling water source should be selected based on the actual project conditions, and the system should be reasonably configured to ensure the normal operation of the ozone generator. In terms of instrument setup, dew point meters, ozone leakage alarms, oxygen leakage alarms, and ozone concentration meters are generally required, while other instruments can be selectively configured based on specific project needs and investment. Through these summaries and suggestions, it is hoped that this can provide useful references for the design and construction of advanced ozone oxidation technology and promote its better development in engineering applications.