Heating furnace gas blowback

Gas backflushing is CO emission reduction technology

1. Current situation and problems

Regenerative combustion technology has been widely used in various types of industrial furnaces. This combustion technology can make low calorific value gas such as blast furnace gas and producer gas directly used for billet heating through regenerative technology without mixing other high calorific value gas. And the regenerative combustion technology can realize the extremely low temperature emission of flue gas, realize waste heat recovery to the greatest extent, and achieve energy saving effect.

However, heating furnaces applying regenerative combustion technology generally have the following problems:

As shown in the figure, every time the reversing valve is switched, when a group (side) burner changes from the combustion state to the smoke exhausting state, the gas between the reversing valve and the regenerative burner will be drawn away by the smoke exhaust system , this area is called "public area" (marked area in the figure);

As long as it is a heating furnace that adopts regenerative combustion technology, this problem is common, because regenerative combustion is based on the frequent reversal of the reversing valve, and the regenerative body in the burner is used to store heat and achieve limit recovery. Therefore, the "common area" between the reversing valve and the burner must exist;

It will bring the following problems and potential risks:

The gas is directly discharged and cannot be used effectively, resulting in waste of energy and increase of production costs of enterprises;

The direct discharge of gas will cause air pollution, which will inevitably have an impact on the development of enterprises in today's increasingly severe environmental protection pressure;

The gas medium generally contains sulfur and other substances, which are mixed in the flue gas, which will cause corrosion and damage to the piping system, valves and other components; the instantaneous flue gas exhaust process has the possibility of mixing the high-temperature flue gas in the furnace with the gas in the burner. When the oxygen content in the flue gas is too high, it is easy to cause secondary combustion with the gas in the regenerator, resulting in melting, fracture, deformation and distortion of the honeycomb body, which eventually leads to blockage;

2. All-in-one solution

Energy saving and environmental protection have always been the direction and goal of Xuanding's unswerving efforts. In view of the common problems in industrial kilns using regenerative combustion technology, especially in the current situation of China's increasingly severe environmental protection, Xuanding's technical team has passed After a long period of theoretical research and field practice, an integrated solution with gas blowback as the main method is proposed, which can completely solve the problem of gas (public area) emissions and achieve the purpose of energy saving, emission reduction and environmental protection;

The all-in-one solution mainly starts from three aspects:

Gas blowback

Part of the flue gas discharged from the furnace is recycled back to the regenerative combustion system for backflushing, namely:

A part of the flue gas discharged from the flue gas exhaust system is extracted by the newly added fan, and transported to the reversing valve, and the gas in the public area is blown back and entered into the furnace for combustion.

or

Directly use the original smoke exhaust system (including fan) to lead the flue gas to the reversing valve, blow back the gas in the public area, and enter the furnace for combustion.

The following key points need careful consideration:

Selection of backflushing media to ensure process safety

Reasonable design of fan selection and backflushing pressure in the backflushing system to ensure the backflushing effect

Combined with the original commutation logic of regenerative combustion Fully consider safety, explosion-proof, safety interlock and other issues

Equipment sealing performance

The frequent commutation technology in the regenerative combustion technology strengthens the furnace gas circulation in the heating furnace, uniforms the temperature field of the furnace, and improves the heating quality.

The reversing valve used in this reversing technology needs to consider its sealing performance (especially after long-term use), because during normal smoke exhaust, the internal leakage of the reversing valve will also cause gas to be directly discharged from the exhaust system, resulting in energy waste and waste. environmental pollution;

In this regard, it is necessary to carry out special and targeted design of the sealing ring of the existing three-way valve;

Air-fuel ratio control

The unreasonable control of the air-fuel ratio will lead to incomplete combustion of the gas in the furnace, which will also cause a certain amount of gas in the flue gas to be directly discharged, resulting in energy waste and environmental pollution. influences;

According to the actual situation of the site, a residual oxygen analyzer can be configured for each section to detect the residual oxygen content and accordingly correct the air-fuel ratio coefficient and air-fuel ratio;

3. Production cases and effects

Production Case: Donghai Special Steel Bar Phase IV Heating Furnace (Technical Transformation + Gas Emission Reduction Transformation)

Original heating furnace: blast furnace gas double regenerative heating furnace 170 tons/hour

Three-stage control, centralized reversing, four-way reversing valve

Specific transformation content: technical transformation + backflushing four-way valve changed to three-way valve;

Modification of combustion system and control system;

Increase the backflush system;

Donghai Iron and Steel Plant No. 2 Heating Furnace (Renovation of Gas Emission Reduction)

Original heating furnace: blast furnace gas double regenerative heating furnace

150 tons/hour

Three-stage control, segmented and side-by-side, large three-way reversing valve

Specific transformation content: Combustion system, control system transformation;

Increase the backflush system;

Hebei Zongheng Iron and Steel 1# Line 1450 Heating Furnace (Gas Emission Reduction Transformation)

Original heating furnace: blast furnace gas double regenerative heating furnace

270 tons/hour

The heating furnace adopts the combination of centralized and decentralized control, and is divided into 5 combustion zones.

Specific transformation content: Combustion system, control system transformation;

Increase the backflush system;

third-party testing