VOC exhaust gas from paint spray booth: how to calculate the emissions?

The coating industry is one of the important sources of VOC exhaust gas.

1.

1.

The largest model of a certain automobile spraying line, the input parameter is 4500mm×1950mm×1500mm(L×W×H), the production cycle is 30JPH, the inner panel spraying method is manual spraying, and the outer panel spraying method is robot automatic spraying, painting The parameters are shown in Table 1, and the size and air volume of the spray booth are shown in Table 1:

2.

Paint consumption = dry film quality / solid content / paint utilization rate = dry film density × spraying area × dry film thickness / solid content / paint utilization rate

3.

VOC generation = paint consumption × organic solvent content

VOC generated by spraying operation is the spraying room, leveling room, and drying room

VOC generation amount of overspray mist = paint consumption × (1-paint utilization rate) × organic solvent content

The amount of VOC produced by the spray paint mist of the intermediate coating = the inner panel paint consumption × (1-paint utilization rate) × organic solvent content + outer panel paint consumption × (1-paint utilization rate) × organic solvent content = 37.

In the same way, the amount of VOC produced by paint spray mist in other sections can be obtained, see Table 5 for details:

The content of each component of the organic solvent in the paint: non-methane total hydrocarbons are calculated at 60% of the total VOC, xylene is calculated at 10% of the total VOC, and the remaining esters, ketones, ethers, etc.

After the paint spray booth exhaust gas and overspray mist are flocculated by the Venturi-type water circulation system, the organic solvents such as non-methane total hydrocarbons can absorb 2% (wrapped in the paint residue), and esters, ketones, ethers, and alcohol compounds can be absorbed 13% (partly dissolved in water, partly wrapped in paint slag), the calculated data is shown in Table 7:

The VOC emission limit requirements of exhaust cylinders in Jiangsu DB32/2862-2016 "Surface Coating (Automobile Manufacturing) Emission Standards for Volatile Organic Compounds" are shown in Table 8:

It can be seen from Table 7 that the VOC emission of the centralized exhaust cylinder is 35.

2.

1.

Newly-built automobile production plants are generally located in various economic development zones, and the local ambient air quality functions are classified as Class II

The exhaust gas of the paint spraying room and the leveling room is diluted with high air volume, so the exhaust gas concentration is not high.

Q=Qa+(Qa+1-Qa)(h-ha)(/ha+1-ha)
.

In the formula, Q is the maximum allowable discharge rate of a certain exhaust cylinder; Qa is the maximum value in the list limit lower than a certain exhaust cylinder; Qa+1 is the list limit higher than a certain exhaust cylinder The smallest value in the value; h is the geometric height of a certain exhaust tube; ha is the largest value in the list limit lower than a certain exhaust tube; ha+1 is a higher value than a certain exhaust tube The smallest value in the list limit
.

According to this formula, the height of the exhaust cylinder determined by the xylene emission rate 304=7+(5.
9-7)(h-20)(/30-20) is h=20.
143m, and the final h is set to 21m.
If The estimated emission rate of a certain exhaust cylinder is higher than the limit requirements in the list, and the height of the exhaust cylinder should be calculated by extrapolation
.
For details, please refer to the extrapolation calculation method specified in Appendix B of GB16297-1996
.

For the design of the 30JPH paint shop, the domestic mainstream factory building is a two-story, partial three-story (air-conditioning platform) steel frame structure.
According to the "Building Design Fire Protection Code", the definition of single-story and multi-story buildings: residential buildings and building heights below 27m Public buildings and industrial buildings that do not exceed 24m (or have exceeded 24m, but are single-storey), so automotive industrial buildings generally do not exceed 24m.
According to the content described in 7.
1 in Appendix 1 of GB16297-1996, the exhaust cylinder must be higher than the surrounding Buildings within a radius of 200m are more than 5m, so the height of the centralized exhaust duct is tentatively set at 30m.

2.
Confirmation of the size of the centralized exhaust cylinder

According to GB50019-2015 "Industrial Building Heating Ventilation and Air Conditioning Design Code", the wind speed of brick and concrete air ducts is generally 4~12m/s.
According to experience, the general wind speed is 8m/s, and the centralized exhaust pipe Inner diameter area: the cross-sectional area of ​​the middle paint exhaust duct is 4.
0m2, the cross-sectional area of ​​the top paint exhaust duct is 3.
2m2, and the cross-sectional area of ​​the varnish exhaust duct is 4.
3m.
Comprehensive considerations, the size of the centralized exhaust cylinder is shown in Figure 1.
, Note: The size and form of the chimney need to be confirmed according to the actual production layout.
This is only a schematic diagram
.

3.
Confirmation of sampling port location and quantity

According to the requirements of GB/T16157-1996 "Sampling Methods for Particulates and Gaseous Pollutants in Exhaust from Stationary Pollution Sources", the block and measurement points of the rectangular (square) flue are shown in Table 12:

Under conventional design, the exhaust gas treatment device is generally installed on the upper part of the exhaust fan room or on the green belt, and the center of the pipeline from the runner or other exhaust gas treatment device to the chimney is about 15m.

According to HJ75-2017 "Technical Specification for Continuous Monitoring of Flue Gas (SO2, NOx, Particulate Matter) Emissions from Stationary Pollution Sources", 7.
2 requirements: "Gaseous pollutants CEMS should be set at a distance ≥ 2 times the flue path downstream of elbows, valves, and reducing pipes.
The diameter, and the distance from the upstream direction of the above components ≥ 0.
5 times the flue diameter", the equivalent diameter calculation formula D=2AB(/A+B), where A and B are side lengths
.

Exhaust cylinder of varnish paint A=3.
5m, B=3m, calculated D=9m, so the online monitoring equipment should be arranged at least 17m, the height of the sampling platform from the sampling port is 2~3m, and the sampling platform should be set at least 15.
7m high position, according to HJ75-2017 7.
7 "When the sampling platform is set at a position above the ground ≥2m, there should be an inclined ladder (or Z-shaped ladder, spiral ladder) leading to the platform, and the width should be ≥0.
9m" , As far as possible, set the sampling platform below 20m.
Generally, the height of the sampling platform can be positioned at 19.
5m, the height of the sampling port can be positioned at 20.
7m, and the Z-shaped ladder leading to the platform can be set
.