How to "full-process" control of VOCs emissions from industrial coatings?

In recent years, with the gradual emergence of pollution problems, China’s ambient air quality has formed a situation where PM2.

01 Status of VOCs-related Enterprises

In fact, as early as July 15 to September 22, 2020, the Ministry of Ecology and Environment organized five rounds of blue sky defense campaigns to provide precise assistance in summer VOCs pollution prevention and control, involving the Beijing-Tianjin-Hebei and surrounding areas, the Fenwei Plain, and the Soviet Union.

33,000 companies were found to have environmental problems, accounting for 28% of all companies.

02 What measures should be taken by companies involved in VOCs

In the "Recommendations of the Central Committee of the Communist Party of China on Formulating the Fourteenth Five-Year Plan for National Economic and Social Development and the Long-term Goals for 2035", it is clearly stated that "strengthen the coordinated control of multiple pollutants and coordinated regional governance, and strengthen fine particulate matter and ozone.

03 Corporate VOCs full-process governance standard case

Schematic diagram of the whole process of VOs governance

Scope of application

1.

Storage precautions

Standardize material storage space and keep containers tightly closed

2.

Precautions for transportation

1.

2.
Bulk liquid materials: filling and pipeline transportation are preferred
.

3.
VOCs process emission control

Spraying process

The company should spray in a confined space, and the generated volatile organic waste gas should be connected to waste gas collection and treatment equipment
.

The spray booth should be airtight and in a slight negative pressure to increase the exhaust gas collection rate
.

Drying process

Enterprises should dry in a confined space, and the generated volatile organic waste gas should be connected to waste gas collection and treatment equipment
.
It is strictly forbidden to dry and dry naturally in an open workshop or outdoor! It is strictly forbidden to dry in an unsealed workshop!

Local waste gas collection process

When local exhaust gas is collected, an effective air collecting hood should be used.
The unorganized discharge position of VOCs at the farthest opening surface of the air exhaust hood (air collecting hood) is to control the wind speed not less than 0.
3 m/s
.

Wind speed measurement location selection (as shown in the figure below):

If the wind speed is less than 0.
3 m/s, the collection effect is very poor.
It is recommended to add a curtain or fence around the air collecting hood
.

4.
Selection and operation and maintenance of VOCs terminal treatment equipment

Waste gas treatment facility

Option 1: The combined treatment process of filtration + activated carbon adsorption is suitable for small and micro enterprises with a small amount of spraying and a short continuous spraying time
.
The front end of the activated carbon adsorption box is equipped with filter cotton to prevent the activated carbon box from inhaling dust or suspended matter, which affects the adsorption efficiency
.
Activated carbon needs to be regenerated or replaced regularly
.

Waste gas treatment equipment should be opened before production equipment and shut down after production equipment
.

Case 2: Spray + activated carbon adsorption spray washing can reduce the temperature of exhaust gas and absorb part of the exhaust gas and dust that are easily soluble in water, which is beneficial to the adsorption of activated carbon
.
The quality and efficiency of the washing liquid and activated carbon must be checked regularly, and the waste liquid and waste activated carbon must be replaced in time to ensure the cleaning and adsorption effect
.

Waste gas treatment equipment should be opened before production equipment and shut down after production equipment
.

Case 3: Activated carbon adsorption + combustion (co)

The process has high efficiency for waste gas treatment, and is suitable for industrial coating companies that use a large amount of VOCs raw and auxiliary materials
.

Waste gas treatment equipment should be opened before production equipment and shut down after production equipment
.

Maintenance tips:

1.
When the combustion method is used to treat exhaust gas, it should generally be treated by activated carbon adsorption (concentration) before combustion

2.
Activated carbon should be checked regularly, and the activated carbon that has expired should be replaced in time

Case 4: Heat storage combustion should clean barrels, cylinders and other organic material containers in a closed system or a closed space, and connect the exhaust gas to the exhaust gas treatment facility after collection; if it cannot be sealed, local exhaust gas collection measures should be taken
.
When cleaning the reactor, the waste gas collection system should be turned on
.

Waste gas treatment equipment should be opened before production equipment and shut down after production equipment
.

Maintenance tips:

1.
Strictly abide by the operating procedures and strictly prevent explosions and other safety accidents
.

2.
When burning halogen-containing waste gas, it is easy to cause secondary pollution
.

VOCs exhaust gas pretreatment facility

Water curtain pretreatment facility: used to capture and filter the mist particles produced in the spraying process
.

Waste gas treatment equipment should be opened before production equipment and shut down after production equipment
.

Maintenance tips:

1.
Regularly clean the water curtain facilities to ensure smooth water flow

2.
Salvage paint residues regularly to prevent clogging of facilities

3.
Regularly replace the water curtain water

Spray tower: used to capture and filter the mist particles produced in the spraying process
.

Waste gas treatment equipment should be opened before production equipment and shut down after production equipment
.

Maintenance tips:

1.
Regularly dredge the pipes, clean the surface dirt, and ensure smooth water flow

2.
Salvage paint residues regularly to prevent clogging of facilities

3.
Regularly replace or replenish water for spray tower

Filter felt, filter plate, filter bag: used to capture and filter mist particles produced by spraying
.

Waste gas treatment equipment should be opened before production equipment and shut down after production equipment
.

Maintenance tips: 1.
Excessive air flow can easily cause damage to the filter device and reduce the service life of the facility.
It is easy to be blocked by paint slag, and should be replaced in time (1-2 weeks).

5.
Ledger and management requirements

VOCs raw and auxiliary materials purchase ledger

Industrial coating companies should use raw and auxiliary materials with low volatile organic content, and establish a ledger to record the purchase amount of production raw and auxiliary materials and the content of volatile organic compounds
.
The retention period of the ledger shall not be less than three years
.

Suggestion: Record one by one according to the actual purchase volume
.

Production and governance facility operation management ledger

It mainly includes the operating time of production equipment and treatment equipment, equipment operating parameters, maintenance information, consumables or pharmaceuticals, hazardous waste, solvent recovery, energy consumption and other information
.

(The following is only an example of the ledger.
The ledger that the enterprise should create includes but is not limited to the following content
.
)

6.
Exhaust cylinder setting

Sampling hole location requirements

1.
The sampling location should be preferentially selected in the vertical pipe section, and should avoid the flue elbows and parts with sharp changes in cross section
.
2.
The sampling hole should be set at a distance not less than 6 times the diameter from the downstream direction of the elbow, valve, and reducer, and not less than 3 times the diameter from the upstream direction of the above components (as shown in the figure above)
.
3.
According to relevant standards and regulations, the exhaust pipe of the downstream section of the waste gas treatment equipment must have sampling holes in accordance with the specifications; the upstream section of the treatment facility must have sampling holes if the air volume is greater than 10000m7/h and the imported VOCs concentration is greater than 200mg/m3
.

Sample hole and ladder, sampling platform, guardrail setting example