Waste Heat Recovery from Flue Gas of Thermal Oil Heater and Heat Carrier Boiler

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In recent years, energy shortages and rising fuel costs have significantly increased operational expenses across various industries! Energy conservation and emission reduction have become key goals for corporate reform, with waste heat recovery and utilization being a top priority. However, conventional burners cannot withstand excessively high temperatures, limiting the recovery and utilization of flue gas waste heat. We have dedicated extensive efforts to developing a full range of high-temperature resistant air preheat burners: high-temperature resistant burners, air preheat fuel oil burners, air preheat gas burners, air preheat dual-fuel (oil/gas) burners, creating combustion systems focused on energy conservation and emission reduction. To date, these have been widely implemented and highly praised by users.

Industrial processes often discharge waste high-temperature flue gas exceeding 200°C. Conventional combustion systems primarily use ambient-temperature air for combustion assistance. If the temperature of combustion air can be increased, fuel consumption can be relatively reduced, significantly lowering costs. This is particularly advantageous in regions using low-pressure air-atomized combustion methods and where heavy oil quality is relatively unstable, greatly aiding corporate energy savings and cost reduction. By installing air preheaters at chimney outlets, the intake air temperature of boilers is substantially increased. This technology enhances combustion efficiency, improves combustion conditions, and can reduce chimney emission temperatures, achieving energy conservation and emission reduction (4---8%).

An air preheat burner is a type of high-temperature resistant combustion machine with an intake air temperature that can reach up to 150°C. It is a fully automated, load-adjusting forced-draft burner capable of using liquid (fuel oil) or gaseous (gas) fuels.

The air preheat burner is also an energy-saving burner that effectively conserves fuel and reduces flue gas temperatures. It extracts combustion air from the environment (ambient temperature: 20°C~30°C) and utilizes waste heat from combustion flue gas to preheat the combustion air via a heat exchanger. Preheated air mixed with fuel enhances combustion efficiency and quality, effectively saving fuel (a 100°C increase in combustion air temperature saves approximately 3.9% energy) while reducing flue gas temperatures and carbon emissions.

The working principle of an air preheat burner is similar to that of conventional fully automated forced-draft fuel oil, gas, or dual-fuel (oil/gas) burners, with the key difference being the use of waste heat from flue gas (exhaust) to preheat combustion air.

For typical air preheat burners, the combustion air temperature ranges from 50°C to 250°C, and in个别 cases, it can exceed 300°C.

As the temperature of combustion air increases, its density decreases. Therefore, the air/fuel flow ratio of an air preheat burner differs from that of a conventional forced-draft (ambient temperature) burner.

Conventional forced-draft fuel oil or gas burners extract combustion air from the environment (ambient temperature). After mixing with fuel, combustion occurs at temperatures exceeding 1000°C, used to heat the medium within thermal energy equipment. The resulting high-temperature flue gas (exhaust) is discharged into the atmosphere through chimneys, polluting the environment.

For example:

1. Steam boilers: medium temperature ~160°C; flue gas temperature ~250°C

2. Thermal oil heaters (heat medium boilers): medium temperature ~300°C; flue gas temperature ~380°C

Such equipment discharges significant amounts of thermal energy through flue gas (exhaust). Effective thermal energy recovery solutions can conserve energy.

Installing a flue gas/air heat exchanger at the flue gas outlet of such equipment reduces flue gas temperatures while increasing combustion air temperature, thereby saving fuel. However, this requires the burner to be high-temperature resistant.

Notes:

1) The combustion air required for natural gas combustion = 1.234 (kg/hr)/kW (theoretical air-fuel ratio, λ=1.0); during operation (λ=1.15), the combustion air required for natural gas combustion ≈ 1.419 (kg/hr)/kW.

2) For every 100°C increase in combustion air temperature, fuel savings of approximately 3.9% can be achieved, along with a reduction in carbon emissions (calculated based on natural gas combustion) of about 0.05 (kg/hr)/(℃-MW).