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 higher the chimney, the better the smoke exhausting ability is not because the higher the air pressure is, the smaller the air pressure is. If it were really caused by this reason, then the air in the chimney would rise on its own. The air on the ground would also go up, right? Let me explain why.

Any object in the atmosphere (including the air itself) experiences buoyancy from the air. But why doesn’t the air float up? That’s because the air is also affected by gravity. Normally, the buoyancy of the air is equal to the downward force of gravity, so it remains balanced.

However, the smoke coming out of the chimney is hot air with a very high temperature. The higher the temperature, the less the weight per unit volume. The buoyancy stays the same, but the weight of the hot air decreases. So the smoke rises and goes up. When the temperature increases, the smoke spreads horizontally. If you're in a windless area—like early morning or evening—standing on a mountain in the countryside, you can see this phenomenon when farmers burn fireworks in the valley. It's quite spectacular.

That’s why chimneys need to be tall. The higher the chimney, the more hot air it holds, which increases the total buoyancy. This creates stronger pressure, improving the smoke extraction ability. Is it just about making the chimney wider instead of taller? No. If you only make the chimney wider without increasing its height, the buoyancy will still increase proportionally with the cross-sectional area, but the suction at the bottom won’t get any stronger. The pump’s lift depends on the vertical height of the pipe, not the horizontal distance.

Additionally, chimneys are sometimes tapered for architectural reasons, not for improving smoke extraction. A taller chimney isn't always better; there's an optimal height depending on the amount of smoke and the diameter of the chimney. Once the smoke output and size are fixed, going beyond a certain height makes little difference.

The height of the chimney does affect its smoke extraction capability, but the real key is not just the height—it's the shape. Making the chimney conical helps create a greater pressure difference between the inside and outside, which significantly improves the smoke extraction performance. A taller chimney also helps form a better temperature gradient, allowing the air to expand more efficiently.

Product Summary Indicators:

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;

Resistant to 30% sulfuric acid: 80°C for 15 days, normal temperature for 30 days, no change.

3. Water resistance: Soaked at room temperature for 90 days, no change.

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

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

6. Maximum service life: 13 years.

7. Construction period: 20–30 days.

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

(1) Renovation of old chimneys and new single-tube chimney lining treatment:

1. Treatment methods and procedures: Ash sweeping (not needed for new chimneys), brushing OM interface agent, applying OM putty, brushing OM-4 base material, then brushing OM-5 high-temperature acid-resistant and anti-corrosive coating. Glass cloth can be added (1–2 layers). Total thickness: 1.5–2.0 mm.

2. Construction period: 20 days (for a 210–240 m 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 base material, then apply OM-5 high-temperature acid-resistant and anti-corrosive coating. Dry film thickness: 0.5–1.0 mm (thickness chosen based on design requirements).