How to determine the diameter of stainless steel welded ventilation pipeline?

The caliber size of stainless steel welded ventilation pipes is determined by calculation according to the rated air volume and recommended wind speed of the system, and at the same time, combined with the adjustment of medium characteristics, transportation distance and resistance loss, the national standard series size is finally preferred to ensure ventilation efficiency and system stability. The specific steps are as follows:

1. Clear core calculation parameters

First, we need to obtain two key data:

the rated air flow

Q

: It is determined by the treatment capacity of environmental protection treatment equipment (such as waste gas purifier and dust collector), and the unit is.

m

three

/h

(cubic meters per hour).

Recommended wind speed

v

According to the type of conveying medium, too low wind speed will easily lead to dust deposition and waste gas retention; Excessive wind speed will increase pipeline resistance and energy consumption, and will also aggravate pipeline wear.

Recommended wind speed reference for common media in environmental protection engineering;

Recommended wind speed for medium type

v

(

m/s

)

8-12 parts of dust-free common waste gas (such as spray paint waste gas and oil fume)

Waste gas containing fine dust (such as sawdust powder and cement powder) 12-15.

15-20 parts of waste gas (such as ore powder and metal chips) containing coarse dust.

High temperature flue gas (

>300

∘

C

） 10~15

2. Calculate theoretical pipe diameter with formula

Derived from the cross-sectional area formula of circular pipeline, the calculation formula is as follows:

D=

3600×π×v

4Q

Among them:

D

= pipe inner diameter (

m

)

Q

= rated air volume (

m

three

/h

)

v

= recommended wind speed (

m/s

)

Pi?

Take 3.14

For example, an environmental protection project needs to deliver air volume.

Q=18000 m

three

/h

The waste gas containing fine dust, choose the wind speed.

v=15 m/s

, then:

D=

3600×3.14×15

4×18000

=

169560

72000

≈

0.425

≈0.652 m

That is, the theoretical pipe diameter is about 652 mm.

3. Revise the pipe diameter and select the national standard series.

The calculated theoretical pipe diameter needs to be revised in combination with the actual working conditions, and then matched with the national standard size:

National standard series is preferred: the national standard diameter (DN) of circular stainless steel air duct is 300, 400, 500, 600, 700, 800mm, etc. The theoretical value of the above example is 652mm, and DN700mm (inner diameter is 700mm) can be selected nearby to avoid non-standard size increasing the cost of processing and accessories.

Long-distance transportation correction: when the transportation distance is more than ＞50m, the resistance along the transportation path will increase, so it is necessary to enlarge the calculated pipe diameter by 10%~20% (for example, DN600, DN700 is actually selected) or add a booster fan.

Correction of branch pipes: For the branch pipes after the main pipe is diverted, the pipe diameter shall be calculated according to the proportion of branch pipe air volume, so as to ensure that the branch pipe wind speed matches the main pipe wind speed and prevent dust from settling due to too low local wind speed.

4. The principle of caliber adjustment in special scenes

Negative pressure dust removal system: In order to reduce the air leakage rate of the pipeline, the diameter should not be too large (the wind speed should not be less than 12m/s) to avoid pipeline deformation under negative pressure.

High-temperature flue gas transportation: high temperature will cause the pipeline to expand with heat and contract with cold, so the expansion allowance should be reserved in caliber design, and the wind speed should not be too high to reduce heat loss.

Corrosive medium transportation: circular pipes are preferred (with uniform stress and no fouling), and the diameter selection should be combined with the wall thickness to ensure the rigidity of the pipes.