VOCs exhaust gas bypass is not according to the design requirements or normal operating procedures complete through the VOCs exhaust gas treatment facilities all units, directly to the atmosphere emission channel. The setting of VOCs exhaust gas bypass is mainly for the consideration of safety production, and the exhaust gas bypass is reserved before the VOCs exhaust gas treatment facilities for the accident discharge in emergency state. In recent years, the ecological environment department has put forward a series of management requirements for VOCs exhaust gas bypass.
1. Requirements for VOCs exhaust gas bypass management

In June 2020, the Ministry of Ecology and Environment issued the Notice on Issuing the Key Measures for the Treatment of Volatile Organic Compounds in 2020 (Air Environment [2020] No. 33), which proposed to improve the waste gas collection rate in accordance with the principle of "all receivable". If the bypass of the exhaust gas emission system must be retained due to production safety and other reasons, the list of retained bypass shall be reported to the local ecological environment department. The bypass shall be kept closed in non-emergency cases, and supervision shall be strengthened by means of seal, installation of automatic monitoring facilities and flow meter, etc. After it is opened, the report shall be made to the local ecological environment department in time and ledger records shall be made.

When the VOCs waste gas treatment system fails or is overhauled, the corresponding production process equipment should stop running and be put into use synchronously after the maintenance is completed; If production process equipment cannot be stopped or cannot be stopped in time due to safety and other factors, waste gas emergency treatment facilities should be set up or other alternative measures should be taken.

In August 2021, the Ministry of Ecology and Environment put forward the outstanding problems existing in VOCs exhaust gas bypass in the Notice on Accelerating the Solution of Outstanding Problems in the current treatment of Volatile Organic Compounds (Ring Atmosphere (2021) No. 65), and clarified the focus of on-site investigation and inspection of exhaust gas bypass and its treatment requirements.

The notice pointed out that there are many VOCs exhaust gas bypass production facilities and treatment facilities, the number of bypass pipelines is hidden, the bypass is not incorporated into daily supervision, bypass flue and valve air leakage is serious, some enterprises on the grounds of safety through the emergency outlet of end treatment facilities, direct discharge pipeline in the middle process of treatment facilities, coke oven hot spare chimney direct discharge, steal discharge, etc. Some enterprises forged the bypass management ledger or falsified the bypass opening parameters of the central control system.

Notice put forward waste gas bypass on-site inspection focus, to the top of the production workshop, the top of the production device, spare chimneys, abandoned chimneys, emergency discharge, treatment facilities (including the exhaust gas disposal function of the boiler, furnace, etc.) as the focus, check can not through the treatment facilities direct emission of organic waste gas bypass, one by one register; Check the records of the enterprise bypass management ledger, bypass installation flowmeter, automatic monitoring equipment, bypass seal, bypass valve opening mode, bypass opening signal parameter preservation of the central control system, bypass backup treatment facilities construction, etc., and establish the check list of organic exhaust gas bypass; Portable equipment was used to detect the by-pass exhaust emission on site.

Notice clear VOCs exhaust gas bypass treatment requirements, the production system and treatment facilities of the bypass system assessment, in addition to ensure the safety of production must be retained emergency bypass, should be taken to completely remove, cut off, physical isolation and other ways to ban the bypass (including the production workshop, production plant construction of direct discharge pipeline, etc.). In principle, no emergency bypass shall be set up in the production workshop of solvent using industries such as industrial coating, packaging and printing. For emergency bypasses that really need to be retained, the enterprise should report to the local ecological environment department, keep them closed and sealed in non-emergency cases, strengthen supervision by installing automatic monitoring equipment and flow meters, and keep historical records. After opening, the enterprise should report to the local ecological environment department in time and make ledger records. Valve corrosion, damage should be replaced in time, encourage the selection of leakage rate is less than 0.5% of the valve; For enterprises with central control system, induction valves are encouraged to be set in the bypass, and signals such as valve opening status and opening degree are connected to the central control system. Historical records shall be kept for at least 5 years. On the premise of ensuring safety, treatment of bypass exhaust gas is encouraged to prevent direct discharge.

2, VOCs exhaust gas bypass setting principle

VOCs treatment facilities exhaust gas bypass can be mainly divided into two categories, because of safety production and other reasons set up emergency bypass and non-emergency bypass, under what circumstances the bypass should be retained, under what circumstances should be firmly banned?

Exhaust gas bypass is usually provided in the treatment of VOCs by thermal oxidation and its combination technology, which mainly includes thermal combustion (TO), thermal storage combustion (RTO), catalytic combustion (CO), thermal storage catalytic combustion (RCO) and adsorption method + various combustion technologies (exhaust gas should not be provided with exhaust gas bypass before entering the adsorption device). In addition, common VOCs treatment facilities should not be set up bypass, mainly including adsorption method, absorption method, condensation method, biological method and so on.

3. Illegal risk of direct exhaust of VOCs exhaust gas bypass

According to the relevant report of the field inspector of the Ministry of Ecology and Environment, some enterprises regard the VOCs exhaust gas bypass as a "convenient door", through which they can directly discharge or steal the exhaust of VOCs exhaust gas. How do laws and regulations punish this practice of evading environmental supervision and discharging pollutants?

Law of the People's Republic of China on Prevention and Control of Air Pollution

Article 20 Enterprises, public institutions and other producers and business operators that discharge pollutants into the atmosphere shall, in accordance with laws and regulations and the provisions of the competent environmental protection department under The State Council, set up discharge outlets for atmospheric pollutants. It is prohibited to discharge air pollutants by means of evading supervision, such as discharges, tampering or falsifying monitoring data, temporary suspension of production for the purpose of evading on-site inspection, opening emergency discharge channels in non-emergency situations, and abnormal operation of air pollution prevention and control facilities.

Article 99 Whoever, in violation of the provisions of this Law, commits any of the following acts shall be ordered by the competent environmental protection department of the people's government at or above the county level to make corrections or restrict production or stop production for rectification, and shall also be fined not less than 100,000 yuan but not more than one million yuan; (1) Discharge of atmospheric pollutants without obtaining a pollutant discharge permit according to law; (2) Discharging atmospheric pollutants in excess of the standards for the discharge of atmospheric pollutants or in excess of the total emission control targets for major atmospheric pollutants; (3) Discharge of atmospheric pollutants by means of evading supervision and control.