"Because there are a lot of governance technologies now, [enterprises are currently using more cheaply] and using less expensive ones. A few days ago, the energy saving and consumption reduction technology exchange meeting of organic waste gas combustion treatment facilities and the unveiling ceremony of the environmental safety training base of Wuxi Ecological Environment Comprehensive Administrative Law Enforcement Bureau were held in Wuxi City, Jiangsu Province.
During the meeting, Ma Yongliang, an associate researcher at the Institute of Air Pollution and Control at Tsinghua University, pointed out that although there are many technologies for the terminal treatment of volatile organic compounds (VOCs), the application rate of inefficient treatment technologies is high due to the lack of scientific guidance when enterprises choose technologies.
When choosing VOCs treatment technology, "easy to use, inexpensive, and worry-free" is the core appeal of enterprises. The problem exposed at the moment is that due to the lack of understanding, enterprises are more concerned about the factor of "inexpensive", and ignore the essence of the "easy to use" treatment process in the various process selections, which in turn leads to the use of VOCs treatment facilities and inefficient operation, which affects the treatment effect, leads to frequent excessive emissions, and becomes a shortcoming that restricts the continuous improvement of air quality.
Inefficient and ineffective facilities will become the focus of investigation and remediation
With the prevention and control of air pollution entering the deep-water area, in order to further tap the potential of emission reduction and accelerate the solution of the current outstanding problems in air pollution control of industrial enterprises, the Ministry of Ecology and Environment issued the "Work Plan for the Investigation and Remediation of Inefficient and Failed Air Pollution Control Facilities (Draft for Comments)" on November 23, 2023, in which the treatment facilities of VOCs have become the focus of investigation.
According to this document, in the future, not only will the steel, cement, coking and other industrial furnace industries, petroleum refining, petrochemical and other VOCs emission industries be comprehensively investigated, but also bricks, glass, ceramics, industrial coating, packaging and printing, organic chemicals and other VOCs emission industries, the air pollution control facilities of key gas-related pollutant discharge units will be investigated.
At present, this plan has ended the consultation stage, according to industry insiders, the official plan will be released soon.
In terms of policy deployment, the elimination of old and backward pollution control equipment is accelerating, and the requirements for the governance ability and governance level of enterprises are being tightened. What about the practical aspects?
"Enterprises use more inefficient, ineffective equipment. Ma Yongliang combined with his research experience in many cities, and found that the application rate of water curtain pretreatment, activated carbon adsorption, UV photolysis and other technologies in the industrial coating industry and their combinations is more than 50%, and the application rate of activated carbon adsorption, UV photolysis, photocatalysis and other technologies in the printing industry is more than 60%.
He introduced that photooxidation, photocatalysis, low-temperature plasma and other processes can play a certain role in deodorization, but when dealing with high-concentration VOCs waste gas, the degradation efficiency is very low, generally less than 30%, which is an inefficient treatment facility. In addition, the use of low-cost adsorbents/catalysts, the number of replacements of adsorbents/catalysts/filters is low, or the lack of replacement can all contribute to the inefficiency of the equipment.
In addition, some companies use the process of activated carbon adsorption. However, the premise of the effective process is to use a suitable and sufficient amount of activated carbon, and secondly, to ensure the regeneration of activated carbon after adsorption.
"Many enterprises' treatment equipment is now equipped with a little activated carbon, and the suitability is not considered, and many equipment has design flaws, and the exhaust gas does not even pass through the carbon layer, causing VOCs to escape. In addition, some activated carbon is not regenerated after adsorption saturation, so the adsorption balance is reached, and how much (waste gas) goes in and how much comes out, and the treatment equipment is completely meaningless. Ma Yongliang said.
In reality, there is still a mismatch between the selected process technology and the actual demand, and the process selection is improper.
"For example, the VOCs waste gas with a relatively high temperature of more than 40 °C, when the activated carbon adsorption process is used for treatment, the waste gas is directly adsorbed without cooling and pretreatment, which not only increases the resistance, but also increases the risk of fire, and the VOCs waste gas can not achieve the treatment effect at all; Ma Yongliang said.
These are all questions that often arise in small and medium-sized enterprises. He suggested that enterprises should accelerate the upgrading and transformation of treatment equipment, and at the same time, advocate small and medium-sized enterprises to comprehensively strengthen source substitution to fundamentally reduce the generation of VOCs.
The increment and speed of high-efficiency combustion facilities should be further accelerated
The reporter learned that at present, the VOCs terminal treatment technology system mainly includes destruction technology and recycling technology, and the destruction technology mainly includes high-temperature incineration technology (TO/RTO), catalytic combustion technology (CO/RCO), biological purification technology, low-temperature plasma, photocatalysis/photooxidation, etc., and the recovery technology mainly includes adsorption, absorption, condensation, membrane separation and other technologies.
"Before the 13th Five-Year Plan, there was a big gap between China's VOCs overall treatment technology and foreign countries. After ten years of development, at present, the purification materials, treatment equipment and process design have been greatly improved, and all kinds of treatment technology have gradually become mature and perfect. Luan Zhiqiang, a researcher at the Institute of Chemical Defense, took the treatment equipment as an example, and the technical performance of key equipment such as zeolite runner and RTO/RCO in China has reached or approached the level of foreign counterparts. The biological purification device has developed rapidly, and the equipment performance and application level have been rapidly improved.
However, with the continuous improvement of the requirements for fine control and in-depth treatment of VOCs pollution sources, there are also some new development trends in VOCs treatment technology.
Luan Zhiqiang believes that because solvent recovery can realize the recycling of resources and reduce carbon emissions, various solvent recovery technology is the focus of the current development of VOCs treatment technology, and there is a lot of room for development in coating, coating, printing, pharmaceutical/pesticide and other industries and processes.
Key equipment such as RTO/RCO is currently considered to be an efficient treatment facility, and adsorption technology, combustion technology and a variety of combination technologies are the mainstream technologies in the current VOCs treatment. Relevant data show that in 2022, there will be about 10,000 sets of high-efficiency combustion facilities in China, with an annual increase of about 1,000 sets.
According to industry insiders, such a set of equipment has higher investment and maintenance costs, and is more suitable for key industries and key pollutant discharge enterprises. However, when the exhaust gas concentration is slightly higher, it can also be used for secondary waste heat recovery, which greatly reduces production and operating costs.
The reporter noted that Gaomi City, Weifang, Shandong Province, had discussed and analyzed, technical research, exchanges and discussions, on the basis of RTO upgrading, the expert team tailored the installation of a waste heat recovery system for the dipping glove industry, and recycled the waste heat generated by the treatment facilities to the production line, so as to reduce production costs and enhance product competitiveness. In an enterprise in the rubber glove industry, the annual reduction of VOCs emissions reached 24.52 tons through "RTO + waste heat recovery". The waste heat recovered every year is equivalent to about 200,000 cubic meters of natural gas, which is equivalent to saving more than 200 yuan in costs a year, and the investment cost of equipment can be recovered in two years.
Relying on the "Green Island" model, centralized management of small and medium-sized pollution sources
"China is a big manufacturing country, VOCs pollution sources are small and scattered, and there are many industries involved. There are thousands to tens of thousands of small and medium-sized polluting enterprises involved in VOCs emissions in a prefecture-level city, which are limited by the input cost of efficient treatment facilities, resulting in a large number of inefficient/ineffective treatment facilities that have not been upgraded, which has become a shortcoming in China's VOCs emission reduction work. Luan Zhiqiang said.
However, at the same time, upgrading and transforming VOCs treatment facilities cannot require all enterprises to build RTOs and RCOs in a "one-size-fits-all" manner, and should put suitability first and build appropriate and efficient pollution control facilities.
Experts at the meeting believed that for the majority of small and medium-sized enterprises, the "green island" model of centralized pollution control and management, that is, the centralized management of small and medium-sized pollution sources, is the next development trend.
At present, a number of documents related to air pollution control, including the Action Plan for Continuous Improvement of Air Quality, encourage all localities to combine the characteristics of industrial clusters and build "green island" projects according to local conditions, namely central heating centers, centralized spraying centers, centralized organic solvent recovery and disposal centers, and centralized activated carbon regeneration centers. At present, relevant practical explorations have been carried out in Jiangsu Province, Zhejiang Province, Jiangxi Province, Guangdong Province and Shandong Province.