WO2020133574A1

WO2020133574A1 - Method for removing, recycling, and reusing nitrogen oxide in combustion exhaust

Info

Publication number: WO2020133574A1
Application number: PCT/CN2019/070792
Authority: WO
Inventors: 沈美庆; 王军; 沈谷蓉; 王建强
Original assignee: 天津大学
Priority date: 2018-12-27
Filing date: 2019-01-08
Publication date: 2020-07-02
Also published as: CN109621627B; CN109621627A

Abstract

Provided is a method for removing, recycling, and reusing a nitrogen oxide in combustion exhaust, comprising the following steps: A. allowing combustion exhaust containing a nitrogen oxide to come into contact with an adsorbent at a temperature less than 150 °C to adsorb the nitrogen oxide, where the adsorbent comprises an activated component loaded on a molecular sieve carrier, the activated component comprises a precious metal, a rare earth metal, or a transitional metal, and, in terms of elemental content, the activated component accounts for 0.1-20 wt% of the total mass of the adsorbent; and, B. introducing high-temperature air of over 250 °C into the adsorbent to allow the adsorbed nitrogen oxide to be detached and introduced with the high-temperature air into a combustion chamber to serve as combustion air. This is applicable in various coal-fired, gas-fired, and oil-fired boilers and vehicle engines, not only removes NOx pollution, but also uses NOx as a combustion oxidant, and implements the utilization of a pollutant as a resource.

Description

Method for eliminating and recycling nitrogen oxide in combustion exhaust gas

Technical field

The invention relates to the technical field of pollution control and resource reuse of nitrogen oxides in combustion exhaust gas, in particular to a method for recycling nitrogen oxides in combustion exhaust gas generated in the combustion process of coal combustion/oil/natural gas.

Background technique

There are a large number of combustion devices and power plants fueled by coal, oil, and natural gas in industry, such as boilers and blast furnaces in coal-fired/oil/gas power plants, building materials (cement, glass, ceramics, etc.), steel, and other industries, and Motor vehicle engines, etc. Combustion will emit a large amount of nitrogen oxides (NOx), causing great harm to the ecological environment and human health. How to eliminate these NOx pollution is the direction of industrial denitrification technology.

At this stage, pollution control of nitrogen oxides generally adopts ammonia selective catalytic reduction technology (NH ₃ -SCR). NH ₃ -SCR technology has the most mature mainstream denitration technology with high denitration efficiency. NH ₃ -SCR technology uses NH ₃ /urea as reducing material to react with nitrogen oxides to produce nitrogen and water under the action of catalytic materials. Therefore, the core components of NH ₃ -SCR technology include catalytic materials, urea injection systems (urea tanks, nozzles, urea metering units, control systems, etc.), nitrogen oxide sensors, etc.; the entire system is complex, the cost of equipment and raw materials is high, and catalysis Materials need higher temperature (greater than 200℃) to work. It is difficult to meet the demand for zero emissions of nitrogen oxides in industries such as motor vehicles, coal/oil/gas power plants, building materials (cement, glass, ceramics, etc.), steel and other industries.

Although NOx is a pollutant, it is also a valuable oxidant resource from another perspective, for example, it can be used as a liquid oxidant for rockets. The large amount of NH ₃ consumed in the NH ₃ -SCR technology is also a valuable industrial raw material. It is a pity that NOx and NH _3, both of which have valuable value, react and generate nitrogen with no industrial value.

Therefore, it is of great significance to find a method for recycling nitrogen oxides in combustion exhaust gas with simple process, low cost, and low temperature (no more than 150℃) activity.

Summary of the invention

In order to solve the above problems, the present invention is proposed.

The present invention provides a method for eliminating and recycling nitrogen oxides in combustion exhaust gas, which includes the following steps:

A. The combustion exhaust gas containing nitrogen oxides is contacted with an adsorbent at a temperature of less than 150°C to adsorb nitrogen oxides therein; wherein the adsorbent includes an active component supported on a molecular sieve carrier, and the active component is selected From precious metals, rare earth metals or transition metals, and in terms of elemental content, the active component accounts for 0.1-20 wt% of the total mass of the adsorbent; then,

B. Pass high-temperature air greater than 250°C into the adsorbent to desorb the adsorbed nitrogen oxides and send it to the combustion chamber as combustion-supporting air with the high-temperature air.

The combustion exhaust gas includes various coal-fired/oil/natural gas boilers and engine exhaust gases, such as motor vehicles, coal-fired power plants, gas turbines, cement, glass, ceramics, iron and steel, etc. after dedusting and desulfurization. Exhaust gas.

Preferably, the active component is selected from silver, platinum, rhodium, palladium, yttrium, lanthanum, cerium, praseodymium, neodymium, manganese, iron, cobalt, nickel or copper; the molecular sieve support is selected from BEA, MFI or CHA type Molecular sieve.

Preferably, the molecular sieve has a pore size ranging from 0.1 nm to 1 nm and a specific surface area of 500-1000 m ² /g.

The preparation method of the adsorbent can be prepared by the hydrothermal crystallization method of the active metal source (usually its soluble salts) and the mother liquid of the molecular sieve, or by the method of impregnating the molecular sieve with the active metal source. The specific preparation method can be detailed See the applicant's other patent titled "A Method for Adsorbing Nitrogen Oxides and/or Hydrocarbon Compounds During the Cold Start of Motor Vehicles", which will not be repeated here.

The adsorbent also has a certain catalytic effect. For example, it can convert a part of NO to NO _2. Therefore, the adsorbent can also be called a catalyst.

Preferably, in step A, the nitrogen oxide is saturated or nearly saturated. The near saturation means that the adsorption capacity reaches more than 70% of its saturation adsorption capacity.

Preferably, the adsorption process of step A is less than 30 seconds.

Preferably, the adsorption temperature in step A is 50-150°C.

Preferably, before step A, a step of dedusting the combustion exhaust gas is further included.

Preferably, before step A, a step of desulfurizing the combustion exhaust gas is further included.

Preferably, before step A, a step of lowering the temperature of the combustion exhaust gas through the waste heat recovery device is further included.

More preferably, the cooling medium in the waste heat recovery device is air, which is used as the high-temperature air in step B after being heated by the waste heat of the combustion exhaust gas. In this case, the combustion exhaust gas after heat exchange further radiates to a temperature lower than 150°C along the pipeline, and then enters the adsorption device to contact with the adsorbent.

Preferably, at least two sets of nitrogen oxide adsorption devices are provided, wherein the first set performs step A when the second set performs step B, and the second set performs step A when the first set performs step B, thereby achieving continuous elimination and recycling of combustion Nitrogen oxides in the exhaust.

The beneficial effects of the invention:

1. The adsorbent in the present invention can quickly adsorb NOx at a temperature of less than 150°C, and its saturated adsorption capacity can reach 30 mol/g, which can basically completely remove the NOx in the combustion exhaust gas and achieve zero NOx pollution emissions.

2. The present invention completely avoids the shortcomings related to NH ₃ -SCR technology, in particular, no need to use expensive NH ₃ to reduce NOx, and the cost of raw materials and equipment is greatly reduced. , Greatly reducing equipment investment costs and maintenance costs, and avoid the environmental pressure caused by ammonia leakage and ammonia escape.

3. The waste heat recovery device is used to preheat the ambient air, and the preheated high temperature air desorbs NOx and is supplied to the boiler combustion chamber as combustion air, which not only realizes the recovery of waste heat, but also makes full use of NOx as a strong The characteristics of oxidants have realized the reuse of NOx resources and also eliminated NOx pollution.

BRIEF DESCRIPTION

FIG. 1 is a schematic diagram of the process flow of the method of the present invention.

2 is an adsorption curve diagram of the adsorbent of the present invention adsorbing NOx in the combustion exhaust gas of the glass industry at 100°C. The abscissa is the contact time, and the ordinate is the NOx concentration in the exhaust gas in volume ppm, the same below.

Fig. 3 is a graph of NOx desorption after the adsorbent of the present invention is saturated with exhaust gas from the glass industry and then passed into high-temperature air.

4 is an adsorption curve diagram of the adsorbent of the present invention adsorbing NOx in combustion exhaust gas of the cement industry at 150°C.

Fig. 5 is a graph of the NOx desorption curve after the adsorbent of the present invention is saturated with adsorbed exhaust gas of the cement industry and then passed into high-temperature air.

Fig. 6 is an adsorption curve diagram of the adsorbent of the present invention adsorbing NOx in the combustion exhaust gas of a gas boiler at 80°C.

Fig. 7 is a graph of NOx desorption after the adsorbent of the present invention is saturated with the exhaust gas of the gas-fired boiler and then passed into high-temperature air.

Fig. 8 is an adsorption curve diagram of the adsorbent of the present invention adsorbing NOx in the combustion exhaust gas of a fuel engine at 80°C.

9 is a graph of NOx desorption after the adsorbent of the present invention is saturated with adsorbed fuel engine exhaust gas and then passed into high-temperature air.

10 is an adsorption curve diagram of the Pd/Beta adsorbent of the present invention adsorbing NOx in the combustion exhaust gas of the glass industry at 50°C.

11 is a graph of NOx desorption after the Pd/Beta adsorbent of the present invention is saturated with adsorbed glass industry exhaust gas and then passed into high-temperature air.

detailed description

The following examples are given to illustrate the present invention, and these examples are not limitative.

Example 1

Take the combustion exhaust gas discharged from a coal-fired boiler used for smelting silica in a glass factory as an example.

After dedusting and desulfurization treatment, the combustion exhaust gas contains 1500 ppm NOx, 16.5% CO ₂ , 8% O ₂ , 11.5% H ₂ O, and the balance is N ₂ . A sample of the combustion exhaust gas was taken for the experiment. The amount of molecular sieve adsorption material was 0.589 g, the total gas flow rate was 900 mL/min, the adsorption temperature was 100° C., and the space velocity was 11,000 h ^-1 . The adsorbent used is Ce/Beta, which means that Ce is loaded on the Beta molecular sieve, and the composition of the remaining adsorbents is similar to this method), where the percentage content of Ce is 2wt%, and the NOx adsorption results are shown in Figure 2, where After about 41 seconds, the adsorption saturation is reached, and the saturated adsorption amount of NOx reaches 32.8 μmol/g adsorbent.

After the adsorption is saturated, the ventilation of the combustion exhaust gas is stopped, and the air is changed into the adsorbent and the temperature-programmed desorption experiment is carried out. The results are shown in Fig. 3, it can be seen that when the air temperature rises to 230°C, NOx begins to desorb The desorption on the agent reached the maximum instantaneous concentration of desorbed NOx at about 285℃.

The detailed adsorption and desorption results are listed in Table 1 below.

Industrially, after desorption, high-temperature air is passed into the combustion chamber of the coal-fired boiler as combustion air, so that the desorbed NOx acts as a combustion aid.

Example 2

Take the combustion exhaust gas discharged from a coal-fired boiler in a cement plant as an example.

After dedusting and desulfurization treatment, the combustion exhaust gas contains 1000 ppm NOx, 12.5% CO ₂ , 9.2% O ₂ , 6% H ₂ O, and the balance is N ₂ . A sample of the combustion exhaust gas was taken for experiments. The amount of molecular sieve adsorption material was 0.288 g, the total gas flow rate was 1000 mL/min, the adsorption temperature was 150° C., and the space velocity was 25,000 h ^-1 . The adsorbent used is La/Beta, where the percentage content of La is 5 wt%, and the NOx adsorption result is shown in FIG. 4, wherein the adsorption saturation is reached after about 34 seconds, and the saturated adsorption amount of NOx reaches 33.4 μmol/g adsorbent.

After the adsorption is saturated, the ventilation of the combustion exhaust gas is stopped, and the air is changed to the adsorbent and the temperature-programmed desorption experiment is carried out. The results are shown in Figure 5. It can be seen that when the air temperature rises to 220°C, NOx begins to desorb The desorption on the agent reached the maximum instantaneous concentration of desorbed NOx at about 280°C.

The detailed adsorption and desorption results are listed in Table 1 below.

Example 3

Take the combustion exhaust gas discharged from a gas boiler of a power plant as an example.

After dedusting and desulfurization treatment, the combustion exhaust gas contains 500 ppm NOx, 5% CO ₂ , 8% O ₂ , 5% H ₂ O, and the balance is N ₂ . A sample of the combustion exhaust gas was taken for experiments. The amount of molecular sieve adsorption material was 0.144 g, the total gas flow rate was 1000 mL/min, the adsorption temperature was 80° C., and the space velocity was 50,000 h ^-1 . The adsorbent used is Cu/ZSM-5, in which the percentage content of Cu is 10wt%, and the NOx adsorption result is shown in FIG. 6, wherein the adsorption saturation is reached after about 47 seconds, and the saturated adsorption amount of NOx reaches 33.6 μmol/g adsorption Agent.

After the adsorption is saturated, the ventilation of the combustion exhaust gas is stopped, and the air is changed to the adsorbent and the temperature-programmed desorption experiment is carried out. The results are shown in Fig. 7 and it can be seen that when the air temperature rises to 220°C, NOx begins to desorb The desorption on the agent reached the maximum instantaneous concentration of desorbed NOx at about 280°C.

The detailed adsorption and desorption results are listed in Table 1 below.

Industrially, after desorption, high-temperature air is passed into the combustion chamber of the gas boiler as combustion air, so that the desorbed NOx acts as a combustion aid.

Example 4

Take the combustion exhaust gas discharged from a car's fuel engine as an example.

After dedusting and desulfurization treatment, the combustion exhaust gas contains 200 ppm NOx, 5% CO ₂ , 10% O ₂ , 5% H ₂ O, and the balance is N ₂ . A sample of the combustion exhaust gas was taken for experiments. The amount of molecular sieve adsorption material was 0.144 g, the total gas flow rate was 1000 mL/min, the adsorption temperature was 80° C., and the space velocity was 50,000 h ^-1 . The adsorbent used is Co/SSZ-13, where the percentage content of Co is 20wt%, and the NOx adsorption result is shown in FIG. 8, wherein the adsorption saturation is reached after 121 seconds, and the saturated adsorption amount of NOx reaches 29.8μmol/g adsorption Agent.

After the adsorption is saturated, the ventilation of the combustion exhaust gas is stopped, and the air is changed to the adsorbent and the temperature-programmed desorption experiment is carried out. The results are shown in Fig. 9 and it can be seen that when the air temperature rises to 230°C, NOx begins to desorb The desorption on the agent reached the maximum instantaneous concentration of desorbed NOx at about 283℃.

The detailed adsorption and desorption results are listed in Table 1 below.

Industrially, after desorption, high-temperature air is passed into the combustion chamber of the fuel engine as combustion air, so that the desorbed NOx acts as a combustion aid.

Example 5

After dedusting and desulfurization treatment, the combustion exhaust gas contains 1500 ppm NOx, 16.5% CO ₂ , 8% O ₂ , 11.5% H ₂ O, and the balance is N ₂ . A sample of the combustion exhaust gas was taken for experiment. The amount of molecular sieve adsorption material was 0.589 g, the total gas flow rate was 900 mL/min, the adsorption temperature was 50° C., and the space velocity was 11,000 h ^-1 . The adsorbent used is PdCe/Beta, which means that Pd and Ce are supported on the Beta molecular sieve, and the composition of the rest of the adsorbents is similar to this method, where the percentage content of Pd is 0.1wt% and the percentage content of Ce is 2wt% The results of NOx adsorption are shown in Fig. 10, where the adsorption saturation is reached after about 42 seconds, and the saturated adsorption amount of NOx reaches 40.4 μmol/g adsorbent.

After the adsorption is saturated, the ventilation of the combustion exhaust gas is stopped, and the air is changed into the adsorbent and the temperature-programmed desorption experiment is carried out. The results are shown in Fig. 11 and it can be seen that when the air temperature rises to 220°C, NOx begins to desorb The desorption on the agent reached the maximum instantaneous concentration of desorbed NOx at about 285℃.

The detailed adsorption and desorption results are listed in Table 1 below.

Table 1

Claims

A method for eliminating and recycling nitrogen oxides in combustion exhaust gas, characterized in that it includes the following steps:

A. The combustion exhaust gas containing nitrogen oxides is contacted with an adsorbent at a temperature of less than 150°C to adsorb nitrogen oxides therein; wherein the adsorbent includes an active component supported on a molecular sieve carrier, the active component It is selected from precious metals, rare earth metals or transition metals, and based on the element content, the active component accounts for 0.1-20wt% of the total mass of the adsorbent; then,

B. Pass high-temperature air greater than 250°C into the adsorbent to desorb the adsorbed nitrogen oxides and send it to the combustion chamber as combustion-supporting air with the high-temperature air.
The method according to claim 1, wherein the active component is selected from silver, platinum, rhodium, palladium, yttrium, lanthanum, cerium, praseodymium, neodymium, manganese, iron, cobalt, nickel or copper; The molecular sieve carrier is selected from BEA, MFI or CHA type molecular sieves.
The method according to claim 1, characterized in that, in step A, the nitrogen oxide is saturated with adsorption/or near saturation.
The method according to claim 4, wherein the adsorption temperature in step A is 50-150°C, and the adsorption process is less than 30 seconds.
The method according to claim 1, characterized in that before step A, the method further comprises the step of cooling the combustion exhaust gas through a waste heat recovery device.
The method according to claim 7, wherein the cooling medium in the waste heat recovery device is air, and the air is heated by the waste heat of the combustion exhaust gas and used as the high-temperature air in step B.
The method according to claim 1, wherein at least two sets of nitrogen oxide adsorption devices are provided, wherein the first set performs step A when the second set performs step B, and the second set performs step B when the first set performs step B A, so as to achieve continuous elimination and recovery of nitrogen oxides in the combustion exhaust gas.
The method according to claim 1, wherein the molecular sieve has a pore size ranging from 0.1 nm to 1 nm and a specific surface area of 500-1000 m 2 /g.