The reasons for the increase in exhaust gas temperature of gas-fired boiler and relevant solutions

Eight main reasons for the increase in exhaust gas temperature of gas-fired boiler:

1. Ash accumulation on the heating surface. The scaling and ash deposition on the water-cooled wall of the furnace and the ash deposition of the superheater, convention tube bundles, economizer and preheater can increase the thermal resistance of the flue gas, weaken the heat transfer, lessen the cooling effect of the flue gas and increase the exhaust gas temperature of the gas-fired boiler.

2. Too high excess air coefficient. Under normal circumstances, as the furnace outlet excess air coefficient increases, the exhaust gas temperature of the gas-fired boiler rises.

3. Too high air leakage coefficient. The air leakage refers to the air leakage in the furnace and flue gas duct, which is one of the main reasons why the boiler exhaust gas temperature rises. This factor is inevitable. Therefore, the allowable air leakage coefficient for a certain heating surface is specified. When the air leakage coefficient increases, the exhaust gas temperature of the gas-fired boiler rises.

4. High feed water temperature. The heat transfer temperature difference between the flue gas temperature and the water temperature is small, which correspondingly increases the exhaust gas temperature of the gas-fired boiler.

5. The increase of moisture in the fuel. It can increase the amount and specific heat of the flue gas, which increases the exhaust gas temperature of the gas-fired boiler.

6. The increase of boiler’s work load. The work load increases, and the flue gas amount, steam quantity, feed water quantity, air quantity also increase proportionally. However, due to the increase of furnace outlet flue gas temperature, the exhaust gas temperature of the gas-fired boiler rises.

7. Poor fuel quality. When the low calorific value gas fuel is used, the furnace temperature decreases, the radiation heat transfer in the furnace reduces and the flue gas amount increases due to the non-combustible components in the low-calorific value fuel, which increases the exhaust gas temperature of the gas-fired boiler.

8. The secondary combustion in the flue gas duct at the boiler end. The exhaust gas temperature abnormally increases.

Methods to decrease the exhaust gas temperature of gas-fired boiler:

1. Economizer

Increase the heat exchange area of the boiler economizer. For example, adopting the economizer whose actual internal area is 1-2 times larger than the ordinary can effectively reduce the flow rate of flue gas, improve the heat exchange efficiency and lower the exhaust gas temperature.

2. Air preheater

An air preheater is installed with the connected pipe behind the economizer, which can effectively increase the air temperature for supporting the combustion, improve the fuel ignition conditions and make the boiler combustion better.

3. Condenser

The condenser is usually installed next to the economizer. Before being exhausted from the boiler, the flue gas first passes the condenser. The latent heat in the high-temperature flue gas releases heat under the condensation work and the heat released will be put into use again by the boiler. In this way, the exhaust gas temperature will decrease and the boiler thermal efficiency will increase.

4. Two-way combustion system adjustment

The boiler design specifications have a certain adaptability to the fuel, and different media have different influences on the outside during the combustion process. Adjusting and coordinating the economizer and air preheater can control the boiler exhaust gas temperature within a certain range, which can sufficiently utilize the heat energy and ensure the integrity of the equipment structure and function.

With more than 30 years of boiler manufacturing experience, ZOZEN Boiler has formed more than 400 varieties and specifications of gas-fired boilers, biomass-fired boilers, coal-fired boilers and thermal oil heaters which are widely used in the chemical, food, wine, heating, paper-making, printing and dyeing, rubber and other industries. Especially, ZOZEN gas-fired boilers can make the exhaust gas temperature lower than 60℃, which can effectively improve the thermal efficiency and save the boiler operating cost for customers. If you have more questions about the exhaust gas temperature standards of gas-fired boiler, welcome to consult ZOZEN Boiler.