First, an overview

With the increasing policy of air pollution control, the enforcement of environmental protection law tends to be more stringent. At present, besides Beijing, Tianjin, Shanghai, Chongqing, Guangzhou and other first-tier cities, Guangdong, Hebei and other provinces and municipalities have issued local VOCs emission standards, including benzene, toluene and xylene. The emission standards of benzene and non methane total hydrocarbons are all stricter than those of the national standard. The improvement of standards also means that the corresponding purification and disposal technology and equipment technological level must be upgraded and improved simultaneously. It also means that the innovation of environmental protection technology, research and development and technological progress should be impelled by policies.

Over the past 20 years, VOCs treatment in China has developed from activated carbon adsorption, electrostatic capture, low temperature plasma pyrolysis and catalytic oxidation decomposition to adsorption concentration (activated carbon, molecular sieve), hot air back-blowing desorption into RTO, RCO and TNV (zeolite wheel + regenerator) of thermal incinerator (regenerator, thermal decomposition furnace). The high-end waste gas purification and disposal stage.

Practical engineering operation for more than 20 years shows that although the traditional activated carbon adsorption and purification can ensure the stable discharge of VOCs after disposal, the secondary purification and fractionation of desorption solvents have various problems in investment, operation, management and technology, and there are still wastes due to the subsequent regeneration and reuse of saturated carbon. Abandoning regenerated carbon and the two pollution of desorption and regeneration are the major problems of emissions.

Most VOCs waste gases have the characteristics of low concentration and high air volume. Using a single low temperature plasma and ultraviolet photooxygen decomposition technology, the removal rate of VOCs waste gases is only 30-40% due to the short time in the purification process (less than 1 second), and there are flammable and explosive safety risks.

RTO, RCO and TNV all belong to the purification technology of thermal incineration and oxidative decomposition VOCs. They are suitable for VOCs in a wide range of concentration, complete oxidative decomposition, high purification efficiency and easy to supervise. They have gradually become the main waste gas treatment technology options promoted by environmental protection management departments in various places. Beijing, Tianjin, Hebei, Yangtze River Delta and Pearl River Delta are economically developed areas. In the district, most environmental protection law enforcement departments have issued documents requiring that no matter what purification means are used in front of VOCs, thermal oxidation purification devices must be matched eventually.

The core of RTO, RCO and TNV oxidation purification process is to physically adsorb, intercept and concentrate VOCs in waste gas by solid phase such as activated carbon (granular carbon, cellulose carbon, honeycomb carbon), zeolite molecular sieve (5-10 times), and then desorb them by hot air back-blown desorption, and then feed them into thermal oxidation furnace at high temperature (900-1000 C) or high temperature (900-1000 C). Catalytic decomposition furnace (450 C) and thermal oxygen combustion carbonization decomposition under a certain residence time (1 - 1.5 seconds).

The applicable working conditions must be VOCs industrial enterprises with large production capacity and 24 hours of continuous operation. And can only do online disposal, not offline disposal, which is unacceptable for most of the petrochemical, chemical, medical and other industries with strict fire prevention, explosion-proof, open fire control.

In actual operation, because the device is not in long-term operation state, it needs additional fuel to heat the regenerative furnace body after each shutdown, which results in high additional energy consumption. At the same time, due to the frequent switching of the RTO valve in the work, the reliability of the RTO valve becomes worse at high temperature, which may lead to the VOCs concentrated in the system can not enter the thermal incinerator smoothly, but stay in the system pipeline. Because pressure and concentration gradually accumulate and increase, it will bring the safety risk of explosion. In addition, due to the complexity of RTO, RCO and TNV processes, the automation level of its supporting electrical appliances and control systems is also high, and the professional level of operators, managers and maintenance personnel is correspondingly high, but most factories do not meet the above conditions, which also lays a long-term security risk for future operation.

According to the statistics, at present, the domestic enterprises involved in VOCs production and emission account for 90% of the total enterprise data of 10,000-50,000 m hourly emissions. The production and emission of VOCs involve more than 120 industries of the national economy, involving more than 1000 kinds of organic solvents (such as equipment, vehicles, painting, automobiles and motorcycles). Furniture, shoe-making, printing, rubber and plastic processing, etc.), because of the different production properties of various industries and the different technological formulations, the VOCs exhaust gas components produced are extremely different, and they all have the characteristics of small daily total discharge volume (5-60Kg/day), high fluctuation of short-term concentration (100-500mg/m), short operation time, discontinuous operation, and so on. VOCs are produced in many and scattered sites, and belong to the small plant, the old plant itself is narrow, it is difficult to install large space of environmental protection purification devices and equipment.

Owing to the complex composition of VOCs pollutants, no matter the environmental protection supervision department, the production owners are confused about the technology and process selection of purification treatment. Most of the enterprises with purification treatment facilities in the past, because of the improper selection of process technology, it is difficult to operate reliably and steadily, accounting for 80% of the enterprises in Beijing, Tianjin and Hebei region. The single low-temperature plasma, photo-oxidation and activated carbon adsorption are commonly used, but the discharge can not reach the standard through on-site environmental monitoring. From the statistics of the feedback data of the three national environmental monitoring, the most prominent problem is in this respect.

The above-mentioned enterprises have been very clear that pollution control has reached the critical moment to determine the survival of enterprises. They are also eager to seek a VOCs waste gas treatment technology and equipment which can bear the funds of technological transformation, low operating costs, simple use and strong safety and reliability.

Two. Liquid membrane absorption and activated carbon absorption.