Patent Description:
In recent years, with increasingly serious environmental problems, an emission reduction technology in industrial production has also been continuously developed, and the treatment of emissions of air pollutants becomes one important issue. With the transformation of the conventional desulfurization, denitrification, and dust removal of most coal-fired power plants being completed, air pollutants of thermal power have officially entered an ultra-clean emission stage. In the future, an incremental market for the air pollution control industry will mainly come from the ultra-low emission transformation of coal-fired power plants and the treatment of flue gas of non-electricity industry. The treatment of air pollutants in the non-electricity industry comprises the treatment of various kinds of industrial flue gases which involve steel, cement, metallurgy, etc. The steel industry has entered an ultra-low emission transformation stage. The steel industry comprises five procedures: sintering, coking, iron making, steel making, and steel rolling. The emission of NOx during a sintering procedure accounts for half of the total emission in main procedures of the steel industry. Therefore, the control of nitrogen oxides (NOx) in flue gas during the sintering procedure of the steel industry is the focus of the steel companies on NOx reduction.

At present, denitrification technologies of sintering flue gas mainly comprise activated carbon adsorption, oxidative denitrification, and selective catalytic reduction (SCR), etc. Activated carbon used in the activated carbon adsorption is expensive, has a limited adsorption capacity, requires frequent regeneration, consumes a large amount of water, and is prone to secondary pollution. In addition, the loss of raw materials during a regeneration process is large, so that investment costs and operation costs are high. The oxidative denitrification means to oxidize insoluble NO into easily soluble NO<NUM> by use of an oxidant and then absorb NO<NUM> with water or an alkaline solution. However, a common oxidant, O<NUM>, for oxidative denitrification tends to be prepared at a high cost, and the efficiency of the subsequent absorption is greatly affected by flue gas conditions and thus unstable. At present, the SCR technology is widely applied to denitrification in power plants. However, the operating temperature of the SCR technology is much higher than that of the sintering flue gas, so the sintering flue gas needs to be heated, resulting in higher costs. Studies on the improvement of this technology have also been widely reported.

<CIT> has disclosed a desulfurization, denitrification, and white smoke elimination system for low-temperature flue gas, including a wet desulfurization tower, a gas-gas heat exchanger, and a denitrification reactor. Wet flue gas after wet desulfurization enters the gas-gas heat exchanger after being mixed with hot gas and preheated, is heated and mixed with hot gas to increase its temperature, and then enters the denitrification reactor to remove nitrogen oxides. Flue gas after denitrification is cooled by the gas-gas heat exchanger and discharged through a chimney. Although thermal loads required for denitrification reaction are reduced to a certain extent, hot gas is still needed to supplement a heat source. <CIT> has disclosed a fired heater device for a desulfurization and denitrification system of flue gas. The device is equipped with a burner and a blender on flue and heats low-temperature flue gas by burning fuels to enable the flue gas to reach an optimal catalytic temperature of a denitrification catalyst. However, the device also needs to use the fuels and has relatively high costs.

Each of <CIT> and <CIT> shows a system for the purification of flue gas from a sintering furnce, comprising a desulfurization device, a catalytic carbon monoxide oxidation device, and a catalytic dentrification device.

In addition, CO produced due to the incomplete combustion of carbonaceous substances will also harm human bodies and the environment, and the sintering procedure of the steel industry also produces a relatively large amount of CO. However, the above flue gas treatment process cannot treat CO in the flue gas. The heat of combustion of CO is <NUM> kJ/mol, so that CO has a high calorific value and a high utilization value. The content of CO in the sintering flue gas is generally high. For example, a sintering machine of <NUM><NUM> produces <NUM> million m<NUM>/h of flue gas, and a maximum concentration of CO can reach <NUM>/m<NUM>. If CO can be used reasonably, CO can provide heat for reheating the flue gas, so that the temperature of the flue gas can reach a range of activity of the denitrification catalyst.

In summary, in addition to desulfurization and denitrification, the removal of CO is also necessary for the treatment of the sintering flue gas, so as to achieve higher purification efficiency and reduce treatment costs as much as possible.

In view of the problem in the existing art, an object of the present invention is to provide an apparatus and a method for purifying CO and NOx in sintering flue gas. In the present invention, the flue gas is sequentially subjected to desulfurization, CO removal, and denitrification. The desulfurization can reduce a toxic effect of SO<NUM> in the flue gas on a denitrification catalyst, and the flue gas is re-heated during the CO removal to make the flue gas reach the temperature required for a denitrification reaction, which can reduce CO emissions and reheating costs. The preceding process achieves cascade purification of the flue gas, and meanwhile, the apparatus is simple in structure and convenient in operation.

To achieve this object, the present invention adopts technical solutions below. In one aspect, the present application provides an apparatus for purifying CO and NOx in sintering flue gas according to claim <NUM>.

In the present invention the apparatus for purifying flue gas comprises the desulfurization unit, the CO combustion unit, and the denitrification unit in sequence, that is, desulfurization, CO removal, and denitrification are performed in sequence. The SCR reactor is disposed after the desulfurization unit to reduce a toxic effect of SO<NUM> on a catalyst and improve a service life of a SCR denitrification catalyst; the CO combustion unit is disposed before the denitrification unit, which can not only remove CO in the flue gas but also reheat the flue gas by use of its high calorific value to make the flue gas entering the subsequent SCR reactor reach a temperature range of activity of a denitrification catalyst and improve the treatment efficiency of the flue gas. Moreover, the apparatus in the present invention has a simple structure, convenient operations, and low investment and operation costs.

The followings are preferred technical solutions of the present invention, and not to be construed as limitations to the technical solutions provided by the present application. Through the following technical solutions, the objects and the beneficial effects of the present application can be better implemented and achieved.

As a preferred technical solution of the present invention, the desulfurization unit comprises a desulfurizer supply device, a spraying device, and a desulfurization tower, where the desulfurizer supply device is connected to the spraying device, and the spraying device is disposed inside the desulfurization tower and at the top of the desulfurization tower.

In the present invention, the desulfurization treatment adopts a semi-dry method which optionally comprises any one of a method of a circulating fluidized bed, a method of a dense flow absorber, or a rotary spray drying method. The operations of the desulfurization unit, such as the supply of the desulfurizer and liquid spraying, are controlled by a PLC control system.

As a preferred technical solution of the present invention, the CO catalytic combustor comprises a housing, a catalyst, a heat preservation layer, and a heat storage body, where the heat preservation layer is coated at an outer side of the housing, the catalyst and the heat storage body are disposed inside the housing, and the heat storage body is disposed around the catalyst.

Preferably, a material of the heat storage body is ceramics.

Preferably, the catalyst is a precious metal catalyst, preferably a palladium-based catalyst.

In the present invention, in the presence of the catalyst, CO can combust at a relatively low temperature to heat the flue gas after the desulfurization; and the CO catalytic combustor is provided with the heat preservation layer and the heat storage body, which can prevent heat released by the combustion of CO from being dissipated in large amounts and make full use of the heat to heat the flue gas.

Preferably, the SCR reactor comprises an ammonia injection grid and a bed of a denitrification catalyst, where the ammonia injection grid is disposed at the inlet of flue gas of the SCR reactor.

Preferably, the denitrification catalyst comprises a honeycomb catalyst and/or a plate catalyst.

Preferably, the denitrification catalyst comprises a vanadium-tungsten-titanium catalyst.

Preferably, a hot blast stove is further provided between the CO catalytic combustor and the SCR reactor.

In the present invention, since the initial temperature of the apparatus is relatively low during the ignition of a furnace, and the temperature of the SCR denitrification cannot be reached by relying on the heat provided by the catalytic combustion of CO, the hot blast stove is disposed to heat the flue gas. After the apparatus operates stably, the hot blast stove may be turned off. In this way, the denitrification can also be achieved when the furnace is started and stopped.

In the present invention, the apparatus further comprises a dust removal unit comprising a first dust removal means and a second dust removal means, where a gas outlet of the first dust removal means is connected to a gas inlet of the desulfurization unit, a gas inlet of the second dust removal means is connected to a gas outlet of the desulfurization unit, and a gas outlet of the second dust removal means is connected to a gas inlet of the CO combustion unit.

In the present invention, since the flue gas generally contains a large amount of dust, dust removal needs to be performed before desulfurization and denitrification. In the present application, to avoid an effect of residual dust and desulfurizer particles that may be carried after the desulfurization on the subsequent denitrification, dust removal is performed again.

Preferably, the first dust removal means is an electric precipitator.

Preferably, the second dust removal means is a bag filter.

In the present invention, the apparatus further comprises a heat exchange unit.

The heat exchange unit comprises a heat exchanger, where a cold source inlet of the heat exchanger is connected to a gas outlet of the second dust removal means, a cold source outlet of the heat exchanger is connected to a gas inlet of the CO catalytic combustor, and a heat source inlet of the heat exchanger is connected to a gas outlet of the SCR reactor.

Preferably, the apparatus further comprises a chimney, where a heat source outlet of the heat exchanger is connected to the chimney.

In the present invention, the temperature of the flue gas after desulfurization generally cannot reach the temperature of the catalytic combustion of CO, or the temperature is so low that the catalytic combustion of CO is not enough to heat the flue gas to the denitrification temperature; and the temperature of the flue gas after denitrification is generally high, and the direct discharge of the flue gas not only causes energy wastes but also easily damages a flue gas discharge apparatus. Therefore, the flue gas after denitrification may exchange heat with the flue gas after dust removals and desulfurization, so as to make full use of heat and improve the treatment efficiency of the apparatus.

In another aspect, the present invention provides a method for purifying CO and NOx in sintering flue gas by using the preceding apparatus. The method comprises: after a desulfurization treatment, the sintering flue gas enters the CO combustion unit to undergo a combustion reaction, and then undergoes a SCR denitrification treatment to obtain purified flue gas.

As a preferred technical solution of the present invention, the desulfurization treatment is semi-dry desulfurization.

Preferably, a desulfurizer for the desulfurization treatment comprises a calcium-based absorbent.

Preferably, the flue gas after the desulfurization treatment has a temperature of <NUM>-<NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, etc. However, the temperature is not limited to the listed values, and other unlisted values within this value range are also applicable.

Preferably, a first dust removal is performed before the desulfurization treatment, preferably an electric dust removal.

Preferably, a second dust removal is performed after the desulfurization treatment, preferably bag filtering.

As a preferred technical solution of the present application, the temperature of the combustion reaction is <NUM>-<NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, etc. However, the temperature is not limited to the listed values, and other unlisted values within this value range are also applicable.

In the present invention, within this temperature range, the higher the temperature of the combustion reaction, the higher the efficiency of the catalytic combustion, and the more complete the removal of CO.

Preferably, a catalyst for the combustion reaction is a precious metal catalyst, preferably a palladium-based catalyst.

Preferably, the flue gas after the combustion reaction has a temperature of <NUM>-<NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, etc. However, the temperature is not limited to the listed values, and other unlisted values within this value range are also applicable.

Preferably, a heat exchange treatment is performed before the flue gas enters the CO combustion unit.

Preferably, the flue gas after the heat exchange treatment has a temperature of <NUM>-<NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, etc. However, the temperature is not limited to the listed values, and other unlisted values within this value range are also applicable.

Preferably, a heat source for the heat exchange treatment is flue gas after the SCR denitrification treatment.

As a preferred technical solution of the present invention, the temperature of the denitrification treatment is <NUM>-<NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, etc. However, the temperature is not limited to the listed values, and other unlisted values within this value range are also applicable.

Preferably, a catalyst for the denitrification treatment comprises a honeycomb catalyst and/or a plate catalyst.

Preferably, the catalyst for the denitrification treatment comprises a vanadium-tungsten-titanium catalyst.

Preferably, the flue gas after the denitrification treatment is discharged through a chimney after the heat exchange treatment.

As a preferred technical solution of the present invention, the method comprises the following steps:.

Compared with the existing art, the present invention has beneficial effects below.

<FIG> is a structural diagram illustrating the connections of the flue gas purification apparatus according to Example <NUM> of the present invention.

Wherein, <NUM>. first dust removal means; <NUM>. desulfurization tower, <NUM>. second dust removal means; <NUM>. heat exchanger; <NUM>. CO catalytic combustor; <NUM>. hot blast stove; <NUM>. SCR reactor; <NUM>. ammonia injection grid; <NUM>: chimney.

To better illustrate the present invention and to facilitate the understanding of the technical solutions of the present invention, the present invention is further described in details below.

The examples described below are merely simple examples of the present invention, and are not intended to represent or limit the protection scope of the present invention. The protection scope of the present invention is defined by the claims.

Typical but non-limiting examples of the present invention are described below.

This example provides an apparatus for purifying CO and NOx in sintering flue gas. A structural diagram illustrating the connections of the apparatus is shown in <FIG>, and the apparatus comprises a desulfurization unit, a CO combustion unit, and a denitrification unit connected in sequence, where the CO combustion unit comprises a CO catalytic combustor <NUM>, the denitrification unit comprises a SCR reactor <NUM>, and an outlet of the CO catalytic combustor <NUM> is connected to an inlet of the SCR reactor <NUM>.

The desulfurization unit comprises a desulfurizer supply device, a spraying device, and a desulfurization tower <NUM>, where the spraying device is disposed inside the desulfurization tower <NUM> and at the top of the desulfurization tower <NUM>. The CO catalytic combustor <NUM> comprises a bed of a precious metal catalyst, a heat preservation layer, and a heat storage body; and the SCR reactor <NUM> comprises an ammonia injection grid <NUM> and a bed of a denitrification catalyst, where the ammonia injection grid <NUM> is disposed at an inlet of flue gas of the SCR reactor <NUM>.

A hot blast stove <NUM> is further provided between the CO catalytic combustor <NUM> and the SCR reactor <NUM>.

The apparatus further comprises a dust removal unit comprising a first dust removal means <NUM> and a second dust removal means <NUM>, where a gas outlet of the first dust removal means <NUM> is connected to a gas inlet of the desulfurization unit, a gas inlet of the second dust removal means <NUM> is connected to a gas outlet of the desulfurization unit, and a gas outlet of the second dust removal means <NUM> is connected to a gas inlet of the CO combustion unit. The first dust removal means <NUM> is an electric precipitator, and the second dust removal means <NUM> is a bag filter.

The apparatus further comprises a heat exchange unit comprising a heat exchanger <NUM>, where a cold source inlet of the heat exchanger <NUM> is connected to a gas outlet of the second dust removal means <NUM>, a cold source outlet of the heat exchanger <NUM> is connected to a gas inlet of the CO catalytic combustor <NUM>, and a heat source inlet of the heat exchanger <NUM> is connected to a gas outlet of the SCR reactor <NUM>.

The apparatus further comprises a chimney <NUM>, where a heat source outlet of the heat exchanger <NUM> is connected to the chimney <NUM>.

This example, which is not in accordance with the invention, provides an apparatus for purifying CO and NOx in sintering flue gas. The structure of the apparatus is referred to Example <NUM>. A difference only lies in that the apparatus does not comprise a heat exchanger <NUM>, that is, a gas outlet of a SCR reactor <NUM> is directly connected to a chimney <NUM>.

In this example, without the heat exchanger, though the flue gas after desulfurization may still reach a denitrification temperature range through the catalytic combustion of CO, a denitrification catalyst does not have optimal activity, and the heat of flue gas after denitrification is not effectively utilized, so that the operation efficiency of the apparatus is reduced.

This example provides an apparatus for purifying CO and NOx in sintering flue gas. A structure of the apparatus is referred to Example <NUM>. A difference only lies in that the apparatus does not comprise a hot blast stove <NUM>.

In this example, since the apparatus has a relatively low temperature when being started and stopped, without the hot blast stove, the temperature of SCR denitrification cannot be reached by relying on heat provided by heat exchanges of flue gases and the catalytic combustion of CO, that is, the flue gas purification process cannot be performed when the apparatus is started and stopped.

This example provides a method for purifying CO and NOx in sintering flue gas. The method is performed by using the apparatus in Example <NUM>. The flue gas is sintering flue gas produced by a sintering machine of <NUM><NUM> and has an amount of <NUM> million m<NUM>/h, where CO has a concentration of <NUM>/m<NUM>, and NOx has a concentration of <NUM>/m<NUM>.

In step (<NUM>), according to the content of CO in the flue gas and the heat of combustion of CO of <NUM> kJ/mol, the catalytic combustion efficiency reaches <NUM>% in actual operation, it may be calculated that about <NUM> million kJ/h of heat is generated, and then a temperature increase of the flue gas is calculated.

In this example, flue gas purification can be achieved without an additional external heat supply, where the content of CO decreases to <NUM>/m<NUM>, the concentration of NOx decreases to <NUM>/m<NUM>, and the removal efficiency of CO and the removal efficiency of NOx both reach <NUM>%.

This example provides a method for purifying CO and NOx in sintering flue gas. The method is performed by using the apparatus in Example <NUM>. The flue gas has the same composition as the flue gas in Example <NUM>.

In this example, a temperature increase of the flue gas is calculated according to the combustion efficiency of CO in this case in a calculation manner which is the same as that in Example <NUM>. After the flue gas is purified, the content of CO decreases to <NUM>/m<NUM>, the removal efficiency of CO reaches <NUM>%, the concentration of NOx decreases to <NUM>/m<NUM>, and the removal efficiency of NOx reaches <NUM>%.

This example, which is not in accordance with the invention, provides a method for purifying CO and NOx in sintering flue gas. The method is performed by using the apparatus in Example <NUM>. The flue gas has the same composition as the flue gas in Example <NUM>. The method is referred to the method in Example <NUM>, and a difference only lies in that the flue gas after the dust removals and the desulfurization treatment in step (<NUM>) is directly subjected to a combustion reaction in a CO combustion unit.

In this example, the flue gas after the combustion reaction can only reach a temperature of about <NUM>. Though the flue gas also reaches the temperature of a SCR reaction, the efficiency of a denitrification catalyst is slightly lower. The removal efficiency of CO decreases to <NUM>%, and the removal efficiency of NOx also decreases to <NUM>%.

This example, which is not in accordance with the invention, provides an apparatus for purifying CO and NOx in sintering flue gas. The apparatus is referred to the apparatus in Example <NUM>, and a difference only lies in that a CO catalytic combustor <NUM> is not comprised.

When the apparatus in this comparative example is used for treating the flue gas, since only heat exchange is performed, the flue gas entering a SCR reactor cannot reach the temperature of activity of a denitrification catalyst and needs to be additionally heated, which greatly increases treatment costs. Meanwhile, CO in the flue gas has not been effectively removed and will still do harm to the environment and human bodies.

It can be seen in conjunction with the preceding examples and comparative example that the present invention adds the CO combustion unit between the desulfurization unit and the denitrification unit and uses the combustion of CO to heat the flue gas, which can not only reduce reheating costs of the flue gas but also significantly reduce the concentration of CO in the flue gas; the removal efficiency of CO can reach about <NUM>%, and the removal efficiency of NOx can reach <NUM>% or more. The cascade utilization of heat is achieved through heat exchange of flue gases, reducing heat losses. The apparatus is easy to operate, can operate stably with low energy consumption for a long term, and has strong applicability to the flue gas and a good development prospect.

Claim 1:
An apparatus for purifying CO and NOx in sintering flue gas, comprising: a desulfurization unit (<NUM>), a CO combustion unit (<NUM>), and a denitrification unit (<NUM>) connected in sequence, the CO combustion unit comprises a CO catalytic combustor, the denitrification unit comprises a SCR reactor, and an outlet of the CO catalytic combustor is connected to an inlet of the SCR reactor;
wherein the apparatus further comprising a dust removal unit comprising a first dust removal means (<NUM>) and a second dust removal means (<NUM>), a gas outlet of the first dust removal means is connected to a gas inlet of the desulfurization unit, a gas inlet of the second dust removal means is connected to a gas outlet of the desulfurization unit, and a gas outlet of the second dust removal means is connected to a gas inlet of the CO combustion unit;
wherein the apparatus further comprising a heat exchange unit (<NUM>) comprising a heat exchanger, a cold source inlet of the heat exchanger is connected to a gas outlet of the second dust removal means, a cold source outlet of the heat exchanger is connected to a gas inlet of the CO catalytic combustor, and a heat source inlet of the heat exchanger is connected to a gas outlet of the SCR reactor.