CN104896470A - Pulverized coal fired boiler with ultralow nitric oxide emission - Google Patents

Abstract

A pulverized coal boiler with ultra-low nitrogen oxide emissions belongs to the field of environmental protection technology for coal-fired power generation. The burner is a boiler burner with a reducing agent generator, which can generate CO as a reducing agent, so that NO and CO can undergo a reduction reaction to achieve flue gas denitrification; Burner LNB deep air classification to reduce the original production of NO, and use the overfired air OFA to adjust the molar ratio of reducing agent CO to NO; the heating surface of the water wall, panel heating surface and convection heating surface in the furnace are attached along the flow direction of the flue gas A catalyst layer or an independent catalyst layer is set in the tail flue; the system of the present invention has a simple structure and stable operation, and can complete the denitrification reaction without using an amino reducing agent. The denitrification efficiency is high, and the denitrification cost is significantly reduced. boiler.

Description

A pulverized coal boiler with ultra-low nitrogen oxide emission

technical field

The invention belongs to the technical field of coal-fired power generation and environmental protection, and in particular relates to a pulverized coal boiler with ultra-low emission of nitrogen oxides.

Background technique

With the country's increasing emphasis on environmental protection, the control of pollutant emissions from thermal power plants is becoming more and more stringent. According to the "Coal Power Energy Conservation and Emission Reduction Upgrading and Transformation Action Plan (2014-2020)", the NO _x emission of new coal-fired power generation units in the central and eastern regions must reach the emission limit of gas-fired units (50mg/m ³ ), and the ultra-low emission will be The development trend of coal-fired power stations in the future.

At present, the denitrification method of pulverized coal boiler mainly adopts low nitrogen combustion technology combined with selective catalytic reduction denitrification technology (SCR) or selective non-catalytic reduction denitrification technology (SNCR). Selective non-catalytic reduction denitrification technology (SNCR) does not require the use of catalysts, requires few changes to the boiler body, and is low in cost. However, due to the poor mixing uniformity of the reducing agent and NO in the pulverized coal boiler, the reaction time is short, and the denitrification efficiency is only 30-40%. Only circulating fluidized bed boilers can achieve 70-80% denitrification efficiency, so its use is greatly restricted.

Selective catalytic reduction denitration technology (SCR) is currently the mainstream denitrification technology for pulverized coal boilers, with a market share of more than 95%, and the denitrification efficiency can generally reach 80-90%, but there are some problems in its use:

(1) It is necessary to arrange a catalyst layer in the flue at the tail of the boiler. The reconstruction project is difficult to construct, and the catalyst layer has body resistance, which affects the operating economy of the unit;

(2) The catalyst has a service life, and needs to be replaced regularly after deactivation, resulting in high follow-up costs, and it is difficult to regenerate and dispose of the deactivated denitrification catalyst, which is likely to cause environmental pollution;

(3) When ammonia is used as the reducing agent, it is easy to escape ammonia, because the catalyst will be oxidized to generate sulfur trioxide, which will react with ammonia and adhere to the heating surface;

(4) The denitrification reaction requires the use of an amino reducing agent, which has high operating costs and potential safety issues, and the amino reducing agent itself needs to consume a lot of energy in the production process, and also pollutes the environment.

Contents of the invention

In order to solve the problems existing in the above-mentioned prior art, the object of the present invention is to provide a pulverized coal boiler with ultra-low nitrogen oxide emissions, which has a simple structure and stable operation, and can complete the denitrification reaction without using an amino reducing agent, and has high denitrification efficiency, It does not increase operating costs, and can be used for the renovation of existing pulverized coal boilers, and can also be used for the design of new pulverized coal boilers.

In order to achieve the above object, the present invention adopts following technical scheme:

A pulverized coal boiler with ultra-low nitrogen oxide emissions, comprising a furnace 1, a boiler burner 2, and a water wall heating surface 3, a panel heating surface 4 and a convection heating surface 5 arranged in the furnace 1;

The boiler burner 2 is a boiler burner with a reducing agent generating device, which can generate the reducing agent CO, so that NO and CO undergo a reduction reaction under the catalysis of the catalyst carried by the boiler itself, and realize flue gas denitrification; It can promote the oxidation reaction of CO and O ₂ in the flue gas to generate CO ₂ , thereby reducing the incomplete combustion heat loss of the boiler, improving the thermal efficiency of the boiler and controlling the CO emission within the allowable range; the reduction of NO and CO in the flue gas The main reaction equation of the reaction is 2CO+2NO→N ₂ +2CO ₂ , and the effective reaction temperature range is 80°C to 1400°C.

The boiler burner 2 includes a low-nitrogen burner LNB and an overfired air OFA, utilizing low oxygen and deep air staged combustion to not only reduce the original production of NO, but also to produce a CO reducing agent during the combustion process, and utilize the overfired air OFA Adjust the molar ratio of reducing agent CO and NO;

The metal oxides on the surface of the water-cooled wall heating surface 3, the panel heating surface 4 and the convection heating surface 5 have been activated and have good catalytic performance, which can promote the oxidation reaction of CO and O ₂ in the flue gas to generate CO ₂ , In this way, the chemical incomplete loss q ₃ can be recovered, the thermal efficiency of the boiler can be improved and the CO emission can be controlled within the allowable range; at the same time, the reduction reaction of NO and CO in the flue gas can be promoted;

For difficult-to-combustible coals, in order to enhance the denitrification reaction efficiency, an attached catalyst layer A is installed on the water-cooled wall heating surface 3, panel heating surface 4, and convection heating surface 5 along the flue gas flow direction, or an independent catalyst layer B is installed on the tail flue. ;

The oxygen concentration in the exhaust gas of the boiler is 0-4.5%, so the heat loss of the exhaust gas is lower than that of a conventional pulverized coal boiler, and the heat loss of the boiler exhaust gas is 1%-4%;

The pulverized coal boiler minimizes the sum of the boiler exhaust heat loss q ₂ and the incomplete combustion heat loss q ₄ of the boiler by controlling the total amount of combustion oxygen and the air depth staged combustion, while the conventional pulverized coal boiler requires the exhaust heat loss q _2. The sum of the incomplete combustion heat loss q ₄ of ash and slag and the chemical incomplete combustion heat loss q ₃ is the minimum; the chemical incomplete combustion heat loss q ₃ due to the generation of CO is formed by catalytic oxidation in the furnace to form CO ₂ Can be recycled, thereby improving the thermal efficiency of the boiler.

The method for adjusting the molar ratio of the reductant CO to NO by the overfired air OFA is as follows: increasing the overfired air OFA is a separately sent hot air located at the top of the low-nitrogen burner LNB, and increasing the total air volume of the overfired air OFA can Reducing the molar ratio of reducing agent CO to NO and reducing the total air volume of overfired air OFA can increase the molar ratio of reducing agent CO to NO.

The molar ratio of the reducing agent CO to NO is (0.5-6):1.

The reducing agent CO concentration generated by the boiler burner 2 is 100-1000 ppm, the excess air coefficient in the area of the boiler burner 2 is 0.5-0.8, and the excess air coefficient at the outlet of the furnace 1 is 1.0-1.2.

The surface temperature of the attached catalyst layer A and the independent catalyst layer B is 200°C to 1000°C.

The attached catalyst layer A and the independent catalyst layer B are various mixtures of iron, copper, nickel, manganese, cobalt, titanium, aluminum or rare earth metals and their oxides, which vary according to the reaction temperature and arrangement position.

The attached catalyst layer A is attached to all or part of the outer surfaces of the water wall heating surface 3 , the panel heating surface 4 and the convection heating surface 5 in the furnace.

The attached catalyst layer A is attached by spraying, welding or surfacing, and the thickness of the attached layer is 0.1-5mm.

The independent catalyst layer B adopts plate type catalyst or honeycomb catalyst, arranged in one or more layers.

The core content of the present invention is to adjust the combustion conditions of the furnace, that is, to use the low-nitrogen burner LNB deep air classification to reduce the original production of NO, and to use the overfired air OFA to adjust the molar ratio of the reducing agent CO and NO to promote the reduction. The reaction occurs, while ensuring the denitrification efficiency similar to that of the ammonia denitrification technology, the cost of the denitrification device and the cost of denitrification are greatly reduced.

Compared with the prior art, the present invention has the following advantages:

1. Adopt deep staged combustion and other methods to achieve lower nitrogen emissions in the furnace and reduce the NOx concentration of the generated flue gas.

2. Using CO instead of _NH3 as the denitrification reducing agent avoids the safety hazard of ammonia source, the system is simple, CO is a combustion product, and the operating cost is low.

3. When the method of attaching the catalyst layer is adopted, it is not necessary to set up an independent catalyst bed, which greatly reduces the cost of furnace renovation and efficiently utilizes the limited furnace space.

4. The catalyst uses cheap metals and their oxides, which greatly reduces the cost of the catalyst.

5. The catalyst does not contain heavy metals, and there is no disposal problem after being discarded.

Description of drawings

Fig. 1 is a schematic layout diagram of Example 1 of the present invention.

Fig. 2 is a schematic layout diagram of Example 2 of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

The pulverized coal boiler with ultra-low nitrogen oxide emission as shown in Figure 1 includes a furnace 1, a boiler burner 2 with a reducing agent generator, and a water-cooled wall heating surface 3 and a panel heating surface 4 installed in the furnace 1 And convection heating surface 5. During the operation of the boiler, the low-nitrogen burner LNB deep air classification is used, the excess air coefficient of combustion is 0.6, the original production of NO is 120ppm, the molar ratio of CO and NO is adjusted to 2.5 by using the overfired air OFA, and the concentration of CO production is 300ppm. The regional temperature is 1100°C. In order to improve the efficiency of the denitration reaction, a 1mm-thick attached catalyst layer A is deposited on the screen-type heating surface 4. The surface temperature of the screen-type heating surface 4 is 750°C, and the main components of the attached catalyst layer are Fe ₂ O ₃ and CuO . After the denitration reaction, the NO emission concentration is reduced to 20ppm, and the denitration efficiency is 83%.

Example 2

As shown in Figure 2, the pulverized coal boiler with ultra-low nitrogen oxide emissions is equipped with an independent independent catalyst layer B to improve the denitrification efficiency. The independent catalyst layer B adopts honeycomb catalysts and is arranged in one layer. The main component of the attached catalyst layer is Fe ₂ O ₃ and oxides of rare earth elements. After the denitration reaction, the NO emission concentration is reduced to 10ppm, and the denitration efficiency is increased to 92%.

Example 3

In the pulverized coal boiler with ultra-low nitrogen oxide emissions in this embodiment, the excess air coefficient of the low-nitrogen burner LNB combustion is 0.8, the original production amount of NO is 200ppm, and the molar ratio of CO and NO is adjusted to 3 by using the overfired air OFA, corresponding to The CO generation concentration is 600ppm, and the combustion zone temperature is 1200°C. On the panel heating surface 4 and the convection heating surface 5, a catalyst layer A with a thickness of 1.5mm is welded and attached. The surface temperature of the panel heating surface 4 is 800°C, and the surface temperature of the convection heating surface 5 is 600°C. The main components of the catalyst layer are Fe ₂ O ₃ and CuO. After the denitration reaction, the NO emission concentration is reduced to 50ppm, and the denitration efficiency is 75%.

Example 4

In the pulverized coal boiler with ultra-low nitrogen oxide emission in this embodiment, the original production amount of NO is 100ppm, the molar ratio of CO to NO is 2, and the corresponding CO production concentration is 200ppm. On the convective heating surface 5, a 0.5 mm-thick adhesion catalyst layer A was applied by spraying. After the denitration reaction, the NO emission concentration is reduced to 40ppm, and the denitration efficiency is 60%.

Example 5

In the pulverized coal boiler with ultra-low nitrogen oxide emissions in this embodiment, a 0.5mm adhered catalyst layer A is sprayed on the panel heating surface 4, and its main components are Fe ₂ O ₃ and CuO. On the convection heating surface 5, a 1 mm adhered catalyst layer A, whose main components are Fe ₂ O ₃ and Ni, was sprayed.

Claims (9)

1. a pulverized-coal fired boiler for ultralow discharged nitrous oxides, comprises burner hearth (1), boiler-burner (2) and is arranged on water wall surface (3), curtain wall (4) and the convection heating surface (5) in burner hearth (1);

It is characterized in that: described boiler-burner (2) is the boiler-burner with reducing agent generating means, reducing agent CO can be generated, make NO and CO boiler itself with the catalytic action of catalyst issue raw reduction reaction, realize denitrating flue gas, catalyst can promote CO and the O in flue gas simultaneously ₂there is oxidation reaction and generate CO ₂, thus reduce the imperfect combustion heat loss of fuel gas of boiler, improve boiler thermal output and make CO emission control in allowed band; The key reaction equation that reduction reaction occurs NO and CO in flue gas is 2CO+2NO → N2+2CO2, and effecting reaction temperature range is 80 DEG C ~ 1400 DEG C;

Described boiler-burner (2) comprises low NO LNB and burnout degree OFA, hypoxemia and air deeply staged combustion is utilized not only to reduce the original growing amount of NO, and produce CO reducing agent in combustion, and burnout degree OFA is utilized to regulate the mol ratio of reducing agent CO and NO;

The metal oxide on described water wall surface (3), curtain wall (4) and convection heating surface (5) surface is through activation process;

For unburnable coal, for strengthening denitration reaction efficiency, attached catalyst layer (A) being set along on the water wall surface (3) in flue gas flow direction, curtain wall (4) and convection heating surface (5) or individual catalyst layer (B) is set at back-end ductwork;

In described boiler exhaust gas, oxygen concentration is 0 ~ 4.5%;

Described pulverized-coal fired boiler, by control combustion total oxygen demand and air deeply staged combustion, makes boiler exhaust gas heat loss q ₂and the imperfect combustion heat loss q of lime-ash ₄sum is minimum, and conventional pulverized-coal boiler requires heat loss due to exhaust gas q ₂, lime-ash is imperfect combustion heat loss q ₄and heat loss due to unburned gas q ₃sum is minimum; The heat loss due to unburned gas q formed owing to producing CO ₃then form CO by the catalytic oxidation in stove ₂reclaimed, thus improved boiler thermal output.

2. the pulverized-coal fired boiler of a kind of ultralow discharged nitrous oxides according to claim 1, it is characterized in that: the method for the mol ratio of described burnout degree OFA adjustment reducing agent CO and NO is: increasing burnout degree OFA is one hot blast sent into separately being positioned at low NO LNB top, the total blast volume increasing burnout degree OFA can reduce the mol ratio of reducing agent CO and NO, and the total blast volume reducing burnout degree OFA can increase the mol ratio of reducing agent CO and NO.

3. the pulverized-coal fired boiler of a kind of ultralow discharged nitrous oxides according to claim 2, is characterized in that: the mol ratio of described reducing agent CO and NO is (0.5 ~ 6): 1.

4. the pulverized-coal fired boiler of a kind of ultralow discharged nitrous oxides according to claim 1, it is characterized in that: the reducing agent CO concentration that described boiler-burner (2) generates is 100 ~ 1000ppm, the excess air coefficient in boiler-burner (2) region is 0.5 ~ 0.8, and burner hearth (1) outlet excess air coefficient is 1.0 ~ 1.2.

5. the pulverized-coal fired boiler of a kind of ultralow discharged nitrous oxides according to claim 1, is characterized in that: the surface temperature of described attached catalyst layer (A) and individual catalyst layer (B) is 200 DEG C ~ 1000 DEG C.

6. the pulverized-coal fired boiler of a kind of ultralow discharged nitrous oxides according to claim 1, it is characterized in that: described attached catalyst layer (A) and individual catalyst layer (B) are iron, the multiple mixture of copper, nickel, manganese, cobalt, titanium, aluminium or rare earth metal and oxide thereof, different according to the change of reaction temperature and position.

7. the pulverized-coal fired boiler of a kind of ultralow discharged nitrous oxides according to claim 1, is characterized in that: described attached catalyst layer (A) is attached to whole outer surface or the partial outer face of water wall surface in stove (3), curtain wall (4) and convection heating surface (5).

8. the pulverized-coal fired boiler of a kind of ultralow discharged nitrous oxides according to claim 1, is characterized in that: described attached catalyst layer (A) adopts spraying, deposition or built-up welding mode to adhere to, and adhesion layer thickness is 0.1 ~ 5mm.

9. the pulverized-coal fired boiler of a kind of ultralow discharged nitrous oxides according to claim 1, is characterized in that: described individual catalyst layer (B) adopts board-like catalysis or honeycomb catalyst, arranges one or more layers.