Flue Gas Heat Recovery in Cement Factory

Flue Gas Heat Recovery in Cement Factory

Flue gas heat recovery in cement factories is a critical energy-saving and emission-reduction technology that aims to recover the waste heat from cement kiln flue gas for reuse, thereby improving energy efficiency and reducing environmental impact.

Energy Consumption in Cement Production: Cement manufacturing is highly energy-intensive, with approximately 30%–40% of the total energy input lost as waste heat in flue gas emissions from kilns and coolers.

Environmental Pressure: Flue gas from cement plants contains pollutants (e.g., dust, SOx, NOx) and significant greenhouse gases (e.g., CO2). Heat recovery can simultaneously reduce energy waste and facilitate pollutant control.

Policy Drivers: Global energy conservation policies (e.g., carbon neutrality goals) and regulations push cement plants to adopt heat recovery technologies to lower carbon footprints and operational costs.

Key Flue Gas Heat Recovery Technologies

(1) Waste Heat Power Generation

Working Principle:

Use waste heat boilers to convert flue gas heat into high-pressure steam, which drives a steam turbine to generate electricity.

Applicable Flue Gas: High-temperature flue gas from kiln exhaust (300–500°C) and cooler exhaust (200–350°C).

System Configuration:

Kiln Tail Waste Heat Boiler: Recovers heat from kiln flue gas to produce medium/high-pressure steam.

Cooler Waste Heat Boiler: Recovers heat from 熟料 (clinker) cooler flue gas, often in conjunction with the kiln system for combined power generation.

Efficiency: Typically 15–25 kWh/ton cement, reducing reliance on grid electricity by 10%–15%.

(2) Heat Exchange for Preheating

Air Preheater:

Uses flue gas to preheat combustion air for kilns, raising air temperature by 100–200°C and reducing fuel consumption by 5%–10%.

Raw Material Drying:

Recovers low-temperature flue gas (100–200°C) to dry raw materials (e.g., limestone, clay), replacing traditional steam or fuel drying.

(3) SCR Denitrification with Heat Integration

Combined System:

Integrates selective catalytic reduction (SCR) for NOx removal with heat recovery. Flue gas heat preheats the reducing agent (e.g., ammonia) or maintains SCR catalyst activity, reducing energy consumption for denitrification.

(4) Low-Temperature Heat Recovery (Heat Pumps)

Applicable to Flue Gas <150°C:

Uses heat pumps to extract low-grade heat from flue gas for heating plant buildings, office areas, or domestic water, improving overall energy efficiency.

Typical Application Cases

Case 1: Waste Heat Power Generation in a 5,000 t/d Cement Plant

System: Two waste heat boilers (kiln tail and cooler) with a 9 MW steam turbine.

Performance:

Power generation: ~22 kWh/ton cement, annual power production ~40 million kWh.

Coal saving: ~8,000 tons/year, CO2 emission reduction ~20,000 tons/year.

Case 2: Raw Material Drying with Flue Gas Heat

Application: Dry raw material slurry (moisture content 20%–30%) using 150–200°C flue gas from the cooler.

Benefits: Reduces natural gas consumption for drying by 80%, with a payback period of 1–2 years.