Large Flue Gas Heat Exchanger for Incinerators

Large Flue Gas Heat Exchanger for Incinerators

Incinerators (such as garbage incinerators, industrial waste incinerators, hazardous waste incinerators, etc.) flue gas has a high temperature (800 - 1200 ℃), high dust (fly ash content of up to 50 - 200g/m³), strong corrosive (containing HCl, SO₂, HF and other acidic gases) and other characteristics, large flue gas heat exchanger's core role is:

Waste heat recovery: high-temperature flue gas heat into steam, hot water or heating combustion air, to enhance the system's energy efficiency (such as waste incineration plant waste heat power generation efficiency by 10% - 15%).

Flue gas cooling: for subsequent desulfurization, denitrification and other environmental protection equipment to create the appropriate temperature conditions (such as SCR denitrification flue gas temperature control in 300 - 400 ℃).

Pollutant control: reduce dioxin generation through temperature control (e.g. rapid cooling over the 200 - 400 ℃ temperature window).

Large flue gas heat exchanger design key points

1. Material selection: high temperature, corrosion and wear

High temperature section (> 600 ℃):

pipe / plate selection of 253MA heat-resistant stainless steel (temperature 1100 ℃) or nickel-based alloy (Inconel 625), resistance to high-temperature oxidation and Cl- corrosion;

flue gas side of the surfacing tungsten carbide wear-resistant layer (thickness of 0.5-1mm), to reduce fly ash scouring wear. The tungsten carbide wear-resistant layer on the flue gas side (thickness 0.5 - 1mm) reduces the wear of fly ash scouring.

Middle and low temperature section (≤600℃):

2205 duplex steel (Cl-stress corrosion resistance) or 316L stainless steel, with surface passivation treatment;

Acid flue gas area (such as after desulfurization) need to be considered titanium alloy (TA2) or fiberglass-reinforced plastic (FRP), to prevent dew-point corrosion.

2. Anti-blockage and soot cleaning system design

flow optimization:

tube heat exchanger using large pipe diameter (≥ 40mm) + staggered arrangement, flue gas flow rate control at 8 - 12m / s (to avoid dust deposition);

plate heat exchanger selection of 60 ° large-angle corrugated + wide runner (8 - 10mm), with the inlet deflector plate to even out the flow rate.

Cleaning program:

acoustic cleaning: in the heat exchanger flue gas side of the arrangement of acoustic generator (frequency 20 - 200Hz), regular (1 time per hour) vibration plate / tube bundle, to remove loose dust;

pulse blowing: for high dust scene (such as garbage incineration), the use of compressed air (0.6 - 0.8MPa) or steam pulse blowing, the blowing interval can be set to 4 - 8 hours;

Mechanical Cleaning: tube heat exchanger can be equipped with telescopic blowing gun Mechanical cleaning: Tube heat exchanger can be equipped with telescopic soot blowing gun, which regularly extends into the inner tube bundle for high pressure blowing (applicable to the scenario of hardened soot accumulation).

3. Thermal stress and expansion compensation

structural design:

large tube heat exchanger need to set up wave-shaped expansion joints (compensation ≥ 50mm), to cope with the temperature difference between the flue gas and the medium (such as flue gas 800 ℃ → water 200 ℃, the temperature difference of 600 ℃);

plate heat exchanger using elastic corrugated structure (corrugated height of 15 - 20mm), through the plate's own deformation to absorb the thermal stress, to avoid cracking of the welded place.

Temperature control:

start and stop the furnace to control the rate of temperature increase / decrease ≤ 3 ℃ / min, to avoid rapid cooling and heating;

flue gas side of the temperature sensor, over-temperature linkage bypass valve to divert flue gas, to prevent overheating of the heat exchanger.

4. Resistance loss and system matching

flue gas side resistance is controlled within 800 - 1200Pa, to avoid increasing the load of induced draft fan (every increase of 100Pa, the power consumption rises by 1% - 2%);

simulation (CFD) optimization of the flow path design, to reduce the local eddy currents (such as inlet gradual expansion of the pipe, the outlet gradual shrinkage of the pipe angle of ≤ 15 °).

Application Case: 1000t/d waste incinerator supporting flue gas heat exchanger

Project Background

Incinerator capacity: 1000 tons / day, flue gas volume: 60,000m³/h (standard condition), the initial temperature: 950 ° C;

Goal: recovery of waste heat to produce steam (3.8MPa, 400 ° C), while the flue gas cooled down to 200 ° C or less.

Program selection

High-temperature section: adopts tube fin heat exchanger (253MA material), fin height 12mm, tube diameter 50mm, staggered arrangement, flue gas flow rate 10m/s;

Medium-temperature section: matched with all-welded plate heat exchanger (2205 duplex steel), corrugation angle of 60 °, the flow path spacing of 8mm, configured with acoustic wave soot cleaner (frequency of 50Hz, 24 times a day operation).

Operation effect

Steam output: 35 tons / h, power generation efficiency increased by 13%, annual power generation of 18 million kWh;

Flue gas emission temperature: 180 ℃, dust emission concentration <10mg/m³.