TW201315943A - Combustion system with low nitrogen oxides emission - Google Patents

Abstract

The invention relates to a combustion system with low nitrogen oxides emission comprising a coal powdered system and a boiler burning device. The combustion system combines a main burning zone using LNB, a reburning zone and a burnout zone using over fire air (OFA). The main burning zone is an oxygen insufficient zone, and receives about 77 to 82wt% fuel from a dynamic classifier connecting to the exit of a coal grinder and air from a forced draft fan. The reburning area is also an oxygen insufficient zone, and receives about 18 to 23wt% fuel from a dynamic classifier connecting to the exit of a coal grinder. The NOx emission can be reduced by a staged combustion. The burnout zone may have sufficient residual air from OFA hole to achieve complete burning and reduce NOx emission concentration of flue gas.

Description

Combustion system that reduces nitrogen oxide emissions

The present invention relates to combustion systems, and more particularly to a combustion system that reduces nitrogen oxide emissions.

Electricity demand has always been the most important resource for domestic industries, especially for large enterprises such as petrochemical industry and paper industry. Most of them are equipped with steam and electricity symbiosis plants. In addition to providing electricity, steam can also be used as a heat source. In order to save fuel costs, most domestic steam and electricity symbiosis plants are mainly coal-fired boilers. Boilers will produce air pollutants such as sulfur oxides and nitrogen oxides; nitrogen oxides may involve the formation of acid rain and ground ozone, and energy conservation and emission reduction are the top priorities in the world.

Currently, NOx emission control technologies include low NOx burners (LNB), staged combustion, reburning, flue gas reflux (FGR), and selective catalyst reduction (SCR). And selective non-catalytic reduction (SNCR), etc., can be used to reduce nitrogen oxide emissions.

The LNB is a two-stage burner. The first section supplies about 80% of the theoretical air volume. The heat generated during combustion converts the nitrogen in the fuel or coal. Due to lack of oxygen, the nitrogen in the fuel cannot form nitrogen oxides. The fuel or coal and the remaining air burn at a slower rate in the second stage to lower the flame temperature, thereby reducing the chance of nitrogen in the air producing NOx.

Staged Combustion allows the burner to operate under fuel-rich conditions, with Over Fired Air (OFA) placed above the burner to deliver the remaining air to reduce nitrogen oxide formation.

Reburning is supplied as a fuel segment. The first stage supplies about 80% of the fuel, the second stage supplies about 10-20%, and the third stage supplies about 10% of the remaining fuel and enough air to reduce nitrogen oxides.

At present, there are quite a lot of commercial nitrogen oxide control technologies. However, different equipment must select the most favorable control technology and make the greatest possible reduction in emissions under the premise of meeting emission standards. Therefore, how to select and combine the most favorable control technologies to achieve the maximum possible reduction in emissions is still a challenge.

In view of the above, the present inventors have made great efforts to improve and solve the above-mentioned shortcomings, and have finally made a proposal to rationally and effectively improve the above-mentioned defects.

It is an object of the present invention to provide a combustion system that reduces nitrogen oxide emissions.

In order to achieve the above object, the present invention is a combustion system for reducing nitrogen oxide emissions, the combustion system comprising: a coal-carbon milling system and a boiler combustion device having a combination of a main combustion zone (using LNB) and a reburning zone (Reburning) And the burning zone (using the upper air (OFA)) and other technologies; the main combustion zone is an anoxic zone, and the coal mill outlet power filter provides about 77~82wt% of fuel to the main burner and the air supplied by the blower; The reburning zone is also an anoxic zone. The coal mill outlet power filter provides 18~23wt% of fuel to the reburning burner. The phased combustion reduces NOx emissions, and the air hole in the burning zone provides enough excess air. To achieve complete reduction in smoke NOx emission concentration.

The combustion system of the present invention is equipped with a low NOx burner, a reburner and an air hole on the fire, which can reduce the emission of nitrogen oxides through a clever arrangement.

The detailed description and technical content of the present invention are set forth in the accompanying drawings.

Please refer to the first figure, which is a schematic diagram of a combustion system according to an embodiment of the present invention. The combustion system 1 includes a combustion device 10, a main burner 12 reburner 14, and a fire air hole 16. The combustion unit 10 furnace 102 has a main combustion zone 104, a reburning zone 106, and a combustion zone 108.

In the present embodiment, the main burner 12 is provided with 77 to 82 wt% of fuel from the coal mill outlet power filter, and the air supplied by the blower is supplied to the main combustion zone 104, and the main burner 12 is arranged at the four corners of the combustion device 10. Two-layer four-corner cut circle. The reburner 14 is provided with 18 to 23 wt% of fuel from the coal mill outlet power filter, and the air supplied by the blower to the reburning zone 106. The regenerator 14 is arranged on the wall of the combustion device 10 to form a layer of two Cut into circles. The upper air holes 16 are disposed above the reburning zone 106, and are arranged on the wall of the combustion device 10 to form a tangential circle around each other. Sufficient air is provided via the upper air hole 16 to form the burn zone 108 to ensure complete combustion of the unburnt material within the combustion device 10. In this embodiment, the height ratio a:b:c of the main combustion zone 104, the reburning zone 106, and the burnt zone 108 is 1.2:1:2.5.

In the present embodiment, air and fuel are fed to the main combustion zone 104 and the reburning zone 106 via the main combustor 12 and the reburner 14, respectively. This embodiment employs a reburning technique to provide 77 to 82 wt% of fuel in the main combustion zone 104 and 18 to 23 wt% of fuel in the reburn zone 106.

In addition, the present embodiment employs a low NOx burner (LNB) and staged combustion technology. The excess combustion rate of the main combustion zone 104 of the combustion system 1 is 0.95 to 0.97, preferably 0.96, which belongs to the anoxic zone. The excess air rate of the reburning zone 106 is from 0.80 to 0.85, preferably 0.83, which is a more anoxic zone. The burn-in zone 108 has an excess air ratio of 1.10 to 1.30, preferably 1.20. In the reburning zone 106, the reburning fuel produces a large amount of hydrocarbon ions by micro-anoxic conditions, which react with the nitrogen oxides of the upstream main combustion zone 104 to reduce the nitrogen oxides to nitrogen. Achieve the effect of reducing nitrogen oxides.

The reburning technology can be widely applied to various types of boilers, and the size is not limited, and the effect of removing nitrogen oxides is determined by the temperature of the main combustion zone and the reburning zone, the residence time and the flow field type in the combustion device; In terms of residence time, the lower the temperature, the greater the effect of removing nitrogen oxides. In order to maintain optimal nitrogen oxide removal efficiency and complete combustion in the combustion device, the fuel nozzle of the reburner and the upper air nozzle Must be well designed.

The following is a comparison of the combustion system of the present embodiment with a combustion system without an LNB, a reburner, and an air hole on the fire, as shown in Table 1:

Table I

As can be seen from the data in Table 1, this embodiment combines LNB, reburner and upper air holes to reduce the carbon content of fly ash from 6% to 3% and nitrogen oxide emissions without reducing the performance efficiency of the combustion system. The concentration is from 830 to 250 mg/Nm ³ .

1. . . Combustion System

10. . . Combustion device

12. . . Main burner

14. . . Reburner

16. . . Air hole on fire

102. . . Hearth

104. . . Main combustion zone

106. . . Reburning zone

108. . . Burning area

The first figure is a schematic diagram of a combustion system for reducing nitrogen oxide emissions according to an embodiment of the present invention.

1. . . Combustion System

10. . . Combustion device

12. . . Main burner

14. . . Reburner

16. . . Air hole on fire

102. . . Hearth

104. . . Main combustion zone

106. . . Reburning zone

108. . . Burning area

Claims (7)

A combustion system that reduces nitrogen oxide emissions, including:
a combustion device having a main combustion zone, a reburning zone and a burning zone;
a main burner that supplies air and fuel to the main combustion zone;
A reburner provides air and fuel to the reburning zone; and a fire upper air is disposed above the reburning zone to provide sufficient air through at least one upper air hole to form the burning zone. The combustion system of claim 1, wherein 78 to 82 wt% of fuel is provided in the main combustion zone, and 18 to 23 wt% of fuel is provided in the reburning zone. The combustion system according to claim 1, wherein the main combustion zone has an excess air ratio of 0.95 to 0.97, the reburning zone has an excess air ratio of 0.80 to 0.85, and the burned zone has an excess air ratio of 1.10 to 1.30. The combustion system of claim 1, wherein the main burner is arranged in a four-corner tangential circle at four corners of the combustion device. The combustion system of claim 1, wherein the reburner is arranged on the wall of the combustion device in a layer of two tangential circles. The combustion system of claim 1, wherein the air on the fire is arranged on the wall of the combustion device to form a tangential circle around each other. The combustion system of claim 1, wherein the ratio of the height of the main combustion zone, the reburning zone, and the burning zone is 1.2:1:2.5.