Why should the chimney be raised? -Huaqiang Electronic Network

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Chimney

Why do you want to increase?

The higher the chimney,

The better the smoke exhausting ability.

"The higher the air pressure, the smaller."

These two sentences are correct, but the statement "the higher the chimney, the better the smoke exhausting ability" is not because of higher air pressure. If it were, then the air in the chimney would rise on its own, and even ground air would go up—haha! Let me explain why.

Any object in the atmosphere, including air itself, experiences buoyancy. However, air remains balanced without floating up because it's also pulled down by gravity. Normally, the buoyancy equals the downward force of the air, keeping it stable.

Smoke from a chimney is hot air with a much lower density than the surrounding air. As temperature increases, the air becomes less dense, reducing its weight per unit volume. Buoyancy remains the same, but the reduced weight allows the smoke to rise. When hot, smoke spreads horizontally. On windless days, like early morning or evening, you can see this phenomenon when watching farmers' fires in valleys—it’s quite impressive.

That’s why chimneys are built tall: the taller the chimney, the more hot air it holds, increasing total buoyancy and enhancing smoke extraction. But making it wider doesn’t have the same effect. Pressure depends on height, not cross-sectional area. The suction at the base remains the same regardless of width. This is similar to how water pumps work—the lift depends on vertical height, not horizontal distance.

Additionally, chimneys are often tapered for structural reasons, not for improving smoke extraction. There's an optimal height for a chimney based on smoke output and diameter. Once it exceeds that, extra height offers no benefit.

While chimney height does affect smoke extraction, the key factor isn't just height. It's about designing the chimney to be conical. This shape creates a stronger pressure difference between the inside and outside, improving smoke removal. A taller chimney helps create a better temperature gradient, allowing for better thermal expansion of air.

Product Summary Indicator:

1. High temperature resistance: 250°C.

2. Resistant to dilute acid (sulfuric acid, nitric acid, hydrochloric acid) at 5% concentration and 80°C: No change after 12 days.

3. Resistant to 30% sulfuric acid at 80°C: No change after 15 days; normal temperature, 30 days: no change.

4. Water resistance: Soaking at room temperature for 90 days: no change.

5. Resistance to peeling: (Quick heating to 250°C / water-cooled cycles): 50 cycles, no change.

6. Anti-aging index: Heat and humidity test for 500 hours: no change.

7. Maximum service life: 13 years.

8. Construction period: 20–30 days.

Single cylinder chimney conversion lining desulfurization (new chimney lining treatment) and acid chimney treatment for steel chimneys:

(1) Old chimney lining renovation and new single-tube chimney lining treatment:

1. Treatment methods and procedures: Ash cleaning (not needed for new chimneys), brush OM interface agent, OM putty, brush OM-4 two bottom materials, last brush OM-5 high-temperature acid-resistant coating. Glass cloth can be added (1–2 layers), total thickness 1.5–2.0 mm.

2. Construction period: 20 days (for 210–240M chimney).

(2) Anti-corrosion treatment plan for the inner side of the steel chimney:

1. Processing methods and procedures: After rust removal, brush OM-4 two bottom materials, then brush OM-5 high-temperature acid-resistant coating. Total dry film thickness: 0.5–1.0 mm (thickness chosen by design institute as needed).