CN114904381B

CN114904381B - A cement production system and its gas treatment method

Info

Publication number: CN114904381B
Application number: CN202210507175.6A
Authority: CN
Inventors: 王昊
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2022-05-10
Filing date: 2022-05-10
Publication date: 2023-05-23
Anticipated expiration: 2042-05-10
Also published as: CN114904381A

Abstract

The invention provides a cement production system and a gas treatment method thereof. The cement production system comprises a cement decomposition and high-temperature denitration unit, a raw material mill, a dust removal unit, a low-temperature denitration unit and a wet treatment unit which are sequentially connected with each other in a gas mode. The gas treatment method comprises the following steps: in each production cycle, according to the running state of a raw mill, the exhaust gas of a cement decomposition and high-temperature denitration unit sequentially passes through or does not pass through the raw mill to carry out heat exchange, passes through a dust removal unit to carry out dust removal and passes through a low-temperature denitration unit to carry out selective catalytic reduction denitration treatment, and then the treated exhaust gas is subjected to wet absorption by a wet treatment unit according to a preset rule to obtain recovered slurry; and recycling the recovered slurry as a denitration reducing agent to a cement decomposition and high-temperature denitration unit or a low-temperature denitration unit. Prolonging the service life of the low-temperature catalytic catalyst, ensuring the denitration efficiency, reducing the ammonia escape, and effectively reducing the consumption of the denitration reducing agent so as to reduce the denitration cost.

Description

Cement production system and gas treatment method thereof

Technical Field

The invention relates to the technical field of gas treatment, in particular to a cement production system and a gas treatment method thereof.

Background

A large amount of nitrogen oxides (NOx) are generated during high temperature calcination, fuel coal combustion, raw meal decomposition, etc. in cement production. With increasingly stringent environmental requirements, emission limits for nitrogen oxides (NOx) are becoming lower. In order to meet the requirement of emission limit, when the exhaust gas containing nitrogen oxides is subjected to denitration, the injection amount of a denitration reducing agent (such as ammonia water, urea, melamine and other nitrogen-containing substances) is larger and larger, so that not only is the cost increased, but also the ammonia escape problem is increased. The ammonia escape not only can pollute the atmosphere and influence the health of human bodies, but also increases the consumption of the denitration reducing agent and increases the cost. In addition, when the traditional cement kiln performs exhaust denitration, the denitration catalyst is arranged at a high-temperature and high-dust section before raw material grinding, so that the service life of the catalyst is extremely short, and meanwhile, the catalyst is easy to be blocked by dust to cause production stoppage.

Disclosure of Invention

In view of the above problems, the present invention provides a cement production system and a gas treatment method thereof that overcome or at least partially solve the above problems.

An object of the present invention is to provide a gas treatment method of a cement production system which effectively reduces consumption of a denitration reducing agent to thereby reduce denitration costs.

A further object of the present invention is to reduce the operating costs of the overall system while ensuring the denitration effect by rationally setting the start-up times of the raw mill and wet processing unit in each production cycle.

It is yet a further object of the present invention to improve the stability of the recovered slurry.

It is yet a further object of the present invention to increase the service life of the denitration catalyst.

It is yet a further object of the present invention to reduce the risk of catalyst plugging.

It is yet a further object of the present invention to desulphurize flue gas.

Another object of the present invention is to provide a cement production system which can realize the above gas treatment method.

In particular, according to an aspect of an embodiment of the present invention, there is provided a gas treatment method of a cement production system including a cement decomposition and high temperature denitration unit, a raw meal mill, a dust removal unit, a low temperature denitration unit, and a wet treatment unit, which are sequentially gas-connected, the gas treatment method comprising:

in each production cycle, according to the running state of the raw mill, enabling the exhaust gas of the cement decomposition and high-temperature denitration unit to sequentially pass through or not pass through the raw mill for heat exchange, pass through the dust removal unit for dust removal and pass through the low-temperature denitration unit for selective catalytic reduction denitration treatment, and then enabling the treated exhaust gas to pass through the wet treatment unit for wet absorption according to a preset rule to obtain recovered slurry;

and recycling the recovered slurry as a denitration reducing agent to the cement decomposition and high-temperature denitration unit or the low-temperature denitration unit.

Optionally, the operating state of the raw mill includes an on state and an off state; and is also provided with

In each production cycle, when the running state of the raw mill is the on state, the exhaust gas of the cement decomposing and high-temperature denitration unit is subjected to heat exchange through the raw mill, and when the running state of the raw mill is the off state, the exhaust gas of the cement decomposing and high-temperature denitration unit is not subjected to heat exchange through the raw mill.

Optionally, the preset rules include turning on the wet processing unit regardless of whether the operating state of the raw mill is the on state; and is also provided with

The step of subjecting the treated exhaust gas to wet absorption by the wet treatment unit according to a preset rule to obtain recovered slurry comprises the following steps:

and whether the operation state of the raw mill is the opening state or not, the treated exhaust gas is subjected to wet absorption by the wet treatment unit to obtain the recovered slurry.

Optionally, the preset rule includes turning off the wet processing unit when the operation state of the raw mill is the on state, and turning on the wet processing unit when the operation state of the raw mill is the off state; and is also provided with

when the running state of the raw mill is the opening state, closing the wet processing unit to ensure that the treated exhaust gas does not pass through the wet processing unit;

and when the running state of the raw mill is the closed state, starting the wet treatment unit, and enabling the treated exhaust gas to be subjected to wet absorption by the wet treatment unit to obtain the recovered slurry.

Optionally, the low temperature denitration unit is configured such that when the operation state of the raw mill is the on state, a denitration catalyst in the low temperature denitration unit adsorbs and stores ammonia carried in the exhaust gas in the selective catalytic reduction denitration process, and then when the operation state of the raw mill is the off state, the ammonia stored in the denitration catalyst is allowed to react with nitrogen oxides;

preferably, the denitration catalyst of the low-temperature denitration unit is a sulfur-resistant catalyst.

Optionally, in each of the production cycles, the raw mill is in the on state for a time period greater than or equal to 70% and less than 100%;

preferably, the raw mill is in the on state for 80% of the time during each of the production cycles.

Optionally, the substance contained in the recovered slurry includes at least an ammonium salt, and the molar amount of the ammonium salt is 50% or more of the total molar amount of all the ammonia substances contained in the recovered slurry, based on the amino group.

Optionally, the absorption liquid used in the wet processing unit comprises at least one of: water, dilute sulfuric acid and dilute sulfurous acid; and is also provided with

The ammonium salt comprises at least one of the following: ammonium sulfate, ammonium bisulfate, ammonium sulfite, and ammonium bisulfate.

According to another aspect of embodiments of the present invention, there is also provided a cement production system comprising a cement decomposition and high temperature denitration unit, a raw meal mill, a dust removal unit, a low temperature denitration unit, and a wet processing unit connected in series, wherein, in each production cycle,

the cement decomposition and high-temperature denitration unit is configured to decompose the pretreated cement raw material and perform selective non-catalytic reduction denitration treatment on nitrogen oxides in the air flow;

the raw mill is configured to perform or not perform heat exchange with the exhaust gas of the cement-decomposing and high-temperature denitration unit according to the operation state of the raw mill;

the dust removing unit is configured to remove dust from the exhaust gas on which the heat exchange has been performed or on which the heat exchange has not been performed;

the low-temperature denitration unit is configured to perform selective catalytic reduction denitration treatment on the exhaust gas after dust removal;

the wet processing unit is configured to perform wet absorption on the exhaust gas subjected to the selective catalytic reduction denitration treatment according to a preset rule to obtain recovered slurry, and return the recovered slurry to the cement decomposition and high-temperature denitration unit or the low-temperature denitration unit as a denitration reducing agent.

The raw mill is further configured to:

and when the running state of the raw mill is the closed state, the heat exchange is not performed with the exhaust gas.

Optionally, the preset rules include that the wet processing unit is turned on regardless of whether the running state of the raw mill is the on state; and is also provided with

The wet processing unit is further configured to:

and whether the operation state of the raw mill is the opening state or not is kept open, and the exhaust gas after the selective catalytic reduction denitration treatment is subjected to wet absorption to obtain the recovered slurry.

Optionally, the preset rule includes that the wet processing unit is turned off when the operation state of the raw mill is the on state, and the wet processing unit is turned on when the operation state of the raw mill is the off state; and is also provided with

The wet processing unit is further configured to:

when the operating state of the raw mill is the on state, the wet processing unit is turned off so as not to wet-absorb the exhaust gas;

when the running state of the raw mill is the off state, the wet processing unit is turned on and the exhaust gas is subjected to wet absorption to obtain the recovered slurry.

Optionally, the low temperature denitration unit is further configured to: the denitration catalyst in the low-temperature denitration unit adsorbs and stores ammonia carried in the exhaust gas in the selective catalytic reduction denitration treatment when the operation state of the raw mill is the on state, and then allows the ammonia stored in the denitration catalyst to react with nitrogen oxides when the operation state of the raw mill is the off state.

Optionally, the substances contained in the recovered slurry include at least ammonium salt, and the molar amount of the ammonium salt is 50% or more of the total molar amount of all the ammonia substances contained in the recovered slurry, based on the amino group;

the absorption liquid used in the wet treatment unit is at least one of the following: water, dilute sulfuric acid and dilute sulfurous acid; and is also provided with

In the cement production system and the gas treatment method thereof, the low-temperature catalytic denitration process is arranged behind the raw material mill and the dust removal unit, and the wet treatment unit is arranged behind the low-temperature catalytic denitration process, is started according to a preset rule for absorbing escaped sulfur dioxide, sulfur trioxide, sulfate, ammonia, ammonium salt and the like carried in the exhaust gas, and recycles the absorbed waste liquid as a reducing agent to high-temperature SNCR denitration or low-temperature SCR denitration. The service life of the catalyst in the low-temperature catalytic denitration process is prolonged, the denitration efficiency is ensured, the ammonia escape is reduced, and the consumption of the denitration reducing agent is effectively reduced, so that the denitration cost is reduced.

Further, in the cement production system and the gas treatment method thereof of the present invention, the operating state of the raw mill includes an on state and an off state in each production cycle. When the raw meal mill is in an on state, the raw meal therein exchanges heat with the exhaust gas from the cement-decomposing and high-temperature denitration unit, and the wet treatment unit is turned off, ammonia escapes to be adsorbed by the low-temperature denitration unit. When the raw material mill is in a closed state, the raw material therein does not exchange heat with the exhaust gas, the low-temperature denitration unit can fully react with nitrogen oxides at a higher temperature, and the wet treatment unit is started to perform wet absorption on the exhaust gas after the low-temperature catalytic denitration process to obtain recovered slurry. Thus, by reasonably setting the opening time of the raw mill and the wet processing unit in each production cycle, the running cost of the whole system can be reduced on the premise of ensuring the denitration effect.

Further, in the cement production system and the gas treatment method thereof, the recovered slurry obtained contains mainly ammonium salt, so that the slurry is more stable and secondary ammonia escape is not easy to form.

The foregoing description is only an overview of the present invention, and is intended to be implemented in accordance with the teachings of the present invention in order that the same may be more clearly understood and to make the same and other objects, features and advantages of the present invention more readily apparent.

The above, as well as additional objectives, advantages, and features of the present invention will become apparent to those skilled in the art from the following detailed description of a specific embodiment of the present invention when read in conjunction with the accompanying drawings.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to designate like parts throughout the figures. In the drawings:

FIG. 1 shows a schematic block diagram of a cement production system according to an embodiment of the invention;

FIG. 2 shows a schematic flow diagram of a gas treatment method of a cement production system according to an embodiment of the invention;

fig. 3 shows a schematic flow chart of a gas treatment method of a cement production system according to another embodiment of the present invention.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

In order to solve the technical problems, the invention provides a cement production system.

Fig. 1 shows a schematic block diagram of a cement production system 100 according to an embodiment of the invention. Referring to fig. 1, the cement production system 100 may include at least a cement decomposition and high temperature denitration unit 110, a raw mill 120, a dust removal unit 130, a low temperature denitration unit 140, and a wet processing unit 150, which are sequentially gas-connected. The sequential gas connection referred to herein is understood to mean that the gas outlet of each preceding cell is connected to the gas inlet of an adjacent following cell. Note that, in fig. 1, solid lines with arrows indicate gas passages, broken lines with arrows indicate recycling transmission passages of materials as denitration reducing agents from the wet processing unit 150 to the cement-decomposing and high-temperature denitration unit 110 or the low-temperature denitration unit 140, and dashed lines with arrows indicate raw material transmission passages from the raw material mill 120 to the cement-decomposing and high-temperature denitration unit 110.

In each production cycle, the cement decomposition and high temperature denitration unit 110 is configured to decompose pretreated cement raw meal and to perform Selective Non-catalytic reduction (SNCR) denitration treatment on nitrogen oxides in the gas stream. Specifically, reducing agents such as ammonia water, urea, melamine and other nitrogen-containing substances are sprayed in SNCR denitration treatment. The specific operation of the cement raw meal decomposition and the corresponding SNCR denitration treatment should be known to the person skilled in the art and will not be described in detail herein.

The raw mill 120 is configured to exchange heat with the exhaust gas of the cement-decomposing and high-temperature denitration unit 110 or not according to its own operation state. Specifically, the exhaust gas may be passed through a preheater in the raw meal mill 120 to preheat the raw meal. Of course, the exhaust gas may be heat exchanged with the raw meal in other ways, and the invention is not limited thereto. The raw meal after being processed in the raw meal mill 120 is transported to the cement decomposing and high temperature denitration unit 110 through a raw meal transport passage.

The dust removing unit 130 is configured to remove dust from the exhaust gas that has undergone heat exchange or has not undergone heat exchange. Specifically, the dust removing unit 130 may employ a bag-type dust remover or the like.

The low-temperature denitration unit 140 is configured to perform a selective catalytic reduction (Selective Catalytic Reduction, abbreviated as SCR) denitration process on the exhaust gas after dust removal. Specifically, a low-temperature denitration catalyst may be provided in the low-temperature denitration unit 140, and the selective catalytic reduction reaction is performed at a temperature of 120 to 200 ℃, preferably 120 to 180 ℃, for example 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃ by spraying a reducing agent. The low-temperature denitration catalyst can be a low-temperature denitration catalyst currently available on the market, and of course, other low-temperature denitration catalysts can also be used, and a catalyst with sulfur resistance is preferred, so that the invention is not limited to the low-temperature denitration catalyst.

The wet processing unit 150 is configured to perform wet absorption on the exhaust gas subjected to the selective catalytic reduction denitration treatment according to a preset rule to obtain a recovered slurry, and return the recovered slurry as a denitration reducing agent to the cement-decomposing and high-temperature denitration unit 110. Specifically, the exhaust gas is brought into contact with an absorption liquid in the wet treatment unit 150 to perform wet absorption, whereby escaped sulfur dioxide, sulfur trioxide, sulfate, ammonia, ammonium salt, and the like carried in the exhaust gas are absorbed by the absorption liquid. The absorption liquid may include water or an acidic solution (e.g., dilute sulfuric acid, dilute sulfurous acid, etc.) to enhance the absorption effect of ammonia and ammonia-based substances such as ammonium salts. The resulting recycled slurry is transported to the cement-decomposing and high-temperature-denitrating unit 110 or the low-temperature-denitrating unit 140 through a recycling transport channel.

Because the recycled slurry is rich in ammonia-based reducing substances, in some embodiments, the recycled slurry may be injected directly into the cement decomposition and high temperature denitration unit 110 (e.g., the decomposing furnace and its vicinity), to effect SNCR denitration. In other alternative embodiments, an alkaline substance (such as sodium bicarbonate, etc.) may be added to the recovered slurry to react with the ammonium salt to generate ammonia, and then the ammonia is sprayed into the cement decomposition and high temperature denitration unit 110 to implement SNCR denitration. When the recovered slurry is recycled to the low temperature denitration unit 140, the manner is similar to that of the cement decomposition and high temperature denitration unit 110, and will not be described again.

In the cement production system 100 of the embodiment of the present invention, the low-temperature denitration unit 140 is disposed after the raw mill 120 and the dust removal unit 130, and the wet treatment unit 150 is disposed after the low-temperature denitration unit 140, and the wet treatment unit 150 is turned on according to a preset rule for absorbing escaped sulfur dioxide, sulfur trioxide, sulfate, ammonia, ammonium salt, and the like carried in the exhaust gas, which prolongs the life of the catalyst in the low-temperature catalytic denitration process, ensures denitration efficiency, and reduces ammonia escape. In addition, the wet treatment unit 150 further recycles the recovered slurry obtained by absorption as a denitration reducing agent to a high-temperature denitration or low-temperature denitration process in cement production, thereby effectively reducing the consumption of the denitration reducing agent and further reducing the denitration cost.

In some embodiments, the material contained in the recovery slurry comprises at least an ammonium salt, and the molar amount of ammonium salt is greater than 50% of the total molar amount of all ammonia material contained in the recovery slurry, based on the amount of amino groups. In other words, the recovered slurry obtained contains mainly ammonium salts, and the slurry is more stable and is less likely to escape secondary ammonia. In contrast, in the scheme of directly absorbing ammonia in the prior art, the formed ammonia water is relatively unstable, and secondary ammonia escape is easy to form.

In some further embodiments, the absorption liquid used in the wet treatment unit 150 may include dilute sulfuric acid, dilute sulfurous acid, or the like, in order to maximize the conversion of ammonia to ammonium salts. The ammonium salt may specifically include at least one of ammonium sulfate, ammonium bisulfate, ammonium sulfite and ammonium bisulfate, depending on the components of the absorption liquid used.

In some embodiments, the operating conditions of the raw mill 120 include an on condition and an off condition during each production cycle. When the operation state of the raw mill 120 is an on state, heat exchange with the exhaust gas is performed, and when the operation state of the raw mill 120 is an off state, heat exchange with the exhaust gas is not performed.

In general, when the raw mill 120 is in an on state, since the exhaust gas exchanges heat with the raw meal, the temperature thereof is low when it reaches the low-temperature denitration unit 140, and the denitration efficiency of the low-temperature denitration catalyst is low, whereas when the raw mill 120 is in an off state, since the exhaust gas does not need to exchange heat with the raw meal, the denitration efficiency of the low-temperature denitration catalyst is high, and thus the denitration condition of the whole system is affected.

In view of the above, a preset rule for the wet processing unit 150 may be set accordingly to achieve a desired effect.

In some embodiments, the preset rules include that the wet processing unit 150 is turned on regardless of whether the operating state of the raw mill 120 is an on state, that is, whether the raw mill 120 is in an on state or an off state, the wet processing unit 150 remains on. Accordingly, the wet processing unit 150 is further configured to be turned on regardless of whether the operation state of the raw mill 120 is an on state or not and to wet absorb the exhaust gas after the selective catalytic reduction denitration treatment to obtain recovered slurry. This way, absorption of escaping ammonia can be maximally ensured on the basis of a suitable increase in the operating costs of the system.

In other embodiments, the preset rules include that the wet processing unit 150 is turned off when the operating state of the raw mill 120 is an on state, and that the wet processing unit 150 is turned on when the operating state of the raw mill 120 is an off state. Accordingly, the wet processing unit 150 is further configured to: when the operation state of the raw mill 120 is an on state, the wet processing unit 150 is turned off so as not to wet-absorb the exhaust gas; when the operating state of the raw mill 120 is the off state, the wet processing unit 150 is turned on and wet absorption of the exhaust gas is performed to obtain recovered slurry. In this way, the wet processing unit 150 can be selectively turned on, and by reasonably setting the on-times of the raw mill 120 and the wet processing unit 150 in each production cycle, the running cost of the whole system can be reduced on the premise of ensuring the denitration effect.

Further, the low temperature denitration unit 140 is also configured to adsorb and store ammonia carried in the exhaust gas in the selective catalytic reduction denitration process when the operation state of the raw mill 120 is an on state, and then allow the ammonia stored in the denitration catalyst to react with nitrogen oxides when the operation state of the raw mill is an off state.

In other words, when the raw mill 120 is in the on state, the temperature of the exhaust gas is low and the denitration efficiency of the low-temperature denitration catalyst is low. At this time, the denitration is completed by the cement-decomposing and high-temperature-denitration unit 110, and after the remaining ammonia escapes, it is adsorbed/absorbed by the low-temperature-denitration catalyst in the low-temperature-denitration unit 140, so that it can be stored in a large amount. In this way, wet treatment unit 150 need not be activated, but rather ammonia slip may be controlled by low temperature denitration catalyst adsorption/absorption.

When the raw mill 120 is in a closed state (i.e., the mill is stopped), the temperature of the exhaust gas is high, and the denitration effect of the low-temperature denitration catalyst is high, and at this time, ammonia stored in the low-temperature denitration catalyst in the previous low-temperature state is allowed to react in the catalyst. In particular, the catalyst provides, on the one hand, an oxidizing environment to oxidize sulfur dioxide to sulfite or sulfate and, on the other hand, a reaction platform such that a portion of the sulfur dioxide reacts with ammonia to form ammonium salts. The post wet treatment unit 150 is turned on and the escaped ammonium salt, ammonia, sulfur dioxide, etc. can be absorbed and recycled to the cement decomposition and high temperature denitration unit 110.

In this way, ammonia absorbed when the raw mill 120 is started is stored in the low-temperature denitration catalyst, and denitration reaction is performed while waiting for the stop of the mill, so that it is not wasted. In addition, in the state of stopping grinding, sulfur (such as sulfur dioxide, sulfur trioxide and the like) in the exhaust gas of a cement kiln system (such as a decomposing furnace) is out of standard, and desulfurization is required to be realized by increasing the ammonia injection amount, so that the ammonia consumption is high. By adding the low-temperature denitration unit 140, the low-temperature denitration catalyst can effectively lead ammonia and sulfur to react to generate ammonium salt to be carried out by exhaust gas, so that the ammonia injection amount can be reduced. Further, the ammonium salt is formed, and after the wet processing unit 150 captures it, a more stable recovered slurry can be formed.

In some embodiments, the time duty of the raw mill 120 in the on state may be greater than or equal to 70% and less than 100%, e.g., may be 75%, 80%, 85%, 90%, 95%, etc., during each production cycle. Preferably, the raw mill 120 may be on for 80% of the time during each production cycle. By reasonably setting the time duty of the raw mill 120 in the on state in each production cycle, the overall operational efficiency of the cement production system 100, including waste heat utilization efficiency, denitration efficiency, reductant recycling efficiency, etc., is ensured as much as possible.

The present invention also provides a gas treatment method of the cement production system 100 based on the same technical idea. The construction of the cement manufacturing system 100 may be as shown in fig. 1. Fig. 2 shows a schematic flow chart of a gas treatment method of the cement production system 100 according to an embodiment of the invention. Referring to fig. 2, the gas treatment method of the cement production system 100 may include at least the following steps S202 to S204.

In step S202, in each production cycle, according to the operation state of the raw mill 120, the exhaust gas of the cement decomposition and high temperature denitration unit 110 sequentially passes through or does not pass through the raw mill 120 to perform heat exchange, passes through the dust removal unit 130 to perform dust removal and passes through the low temperature denitration unit 140 to perform selective catalytic reduction denitration treatment, and then the treated exhaust gas passes through the wet treatment unit 150 to perform wet absorption according to a preset rule to obtain recovered slurry.

In step S204, the recovered slurry is recycled as a denitration reducing agent to the cement decomposition and high temperature denitration unit 110 or the low temperature denitration unit 140.

In some embodiments, the operating conditions of the raw mill 120 include an on condition and an off condition; and, in each production cycle, when the operation state of the raw mill 120 is an on state, the exhaust gas of the cement decomposing and high temperature denitration unit 110 is heat-exchanged through the raw mill 120, and when the operation state of the raw mill 120 is an off state, the exhaust gas of the cement decomposing and high temperature denitration unit 110 is not heat-exchanged through the raw mill 120.

In some embodiments, the preset rules include turning on the wet processing unit 150 regardless of whether the operating state of the raw mill 120 is an on state. Accordingly, the step of subjecting the treated exhaust gas to wet absorption by the wet treatment unit 150 according to a preset rule to obtain recovered slurry includes: the treated exhaust gas is wet absorbed by the wet treatment unit 150 to obtain recovered slurry regardless of whether the operation state of the raw mill 120 is an on state.

In other embodiments, the preset rules include turning off the wet processing unit 150 when the operating state of the raw mill 120 is an on state, and turning on the wet processing unit 150 when the operating state of the raw mill 120 is an off state. Accordingly, the step of subjecting the treated exhaust gas to wet absorption by the wet treatment unit 150 according to a preset rule to obtain recovered slurry includes: when the operation state of the raw mill 120 is an on state, the wet processing unit 150 is turned off so that the treated exhaust gas does not pass through the wet processing unit 150; when the operation state of the raw mill 120 is the off state, the wet processing unit 150 is turned on, and the treated exhaust gas is wet-absorbed by the wet processing unit 150 to obtain recovered slurry.

In some further embodiments, the low temperature denitration unit 140 is further configured such that when the operation state of the raw mill 120 is an on state, the denitration catalyst in the low temperature denitration unit 140 adsorbs and stores ammonia carried in the exhaust gas in the selective catalytic reduction denitration process, and then the ammonia stored in the denitration catalyst is allowed to react with nitrogen oxides when the operation state of the raw mill is an off state.

In some embodiments, the raw mill 120 is on for greater than or equal to 70% and less than 100% of the time during each production cycle.

Preferably, the raw mill 120 is on for 80% of the time during each production cycle.

In some embodiments, the material contained in the recovery slurry comprises at least an ammonium salt, and the molar amount of ammonium salt is greater than 50% of the total molar amount of all ammonia material contained in the recovery slurry, based on the amount of amino groups. In other words, the substance contained in the recovered slurry obtained is mainly ammonium salt.

In some further embodiments, the absorption liquid used in the wet treatment unit 150 may include, dilute sulfurous acid, or the like, in order to maximize the conversion of ammonia to ammonium salts. The ammonium salt may specifically include at least one of ammonium sulfate, ammonium bisulfate, ammonium sulfite and ammonium bisulfate, depending on the components of the absorption liquid used.

Having described various embodiments of the various stages of the gas treatment method of the cement production system 100 of the present invention, a specific implementation of the gas treatment method of the cement production system 100 of the present invention will be described in more detail below by way of one specific example.

Fig. 3 shows a schematic flow chart of a gas treatment method of a cement production system 100 according to another embodiment of the invention. In this embodiment, the raw mill 120 is on for 80% of the time during each production cycle. Referring to fig. 3, the gas treatment method of the cement production system 100 includes the following steps S302 to S316.

In step S302, it is determined whether the operation state of the raw mill 120 is an on state or an off state.

In step S304, if the operation state of the raw mill 120 is an on state, the exhaust gas of the cement decomposition and high temperature denitration unit 110 is subjected to heat exchange through the raw mill 120. After that, steps S308 to S310 are performed.

In step S306, if the operation state of the raw mill 120 is the off state, the exhaust gas of the cement decomposition and high temperature denitration unit 110 does not pass through the raw mill 120 to perform heat exchange. After that, steps S312 to S316 are performed.

In step S308, the exhaust gas is dedusted by the dedusting unit 130.

In step S310, the exhaust gas after dust removal is subjected to selective catalytic reduction denitration treatment by the low-temperature denitration unit 140.

Specifically, when the operation state of the raw mill 120 is an on state, the denitration catalyst in the low-temperature denitration unit 140 adsorbs/absorbs ammonia carried in the exhaust gas in the selective catalytic reduction denitration process to store the ammonia in the low-temperature denitration catalyst.

At this time, the wet processing unit 150 is turned off, and the exhaust gas after the selective catalytic reduction denitration treatment does not pass through the wet processing unit 150.

In step S312, the exhaust gas is dedusted by the dedusting unit 130.

In step S314, the exhaust gas after dust removal is subjected to selective catalytic reduction denitration treatment by the low-temperature denitration unit 140.

Specifically, when the raw mill 120 is in the off state, ammonia stored in the low temperature denitration catalyst at a previous low temperature state is allowed to react in the catalyst. The catalyst provides an oxidizing environment to oxidize sulfur dioxide to sulfite or sulfate on the one hand and a reaction platform on the other hand, so that part of the sulfur dioxide reacts with ammonia to form ammonium salts.

In step S316, the wet processing unit 150 is turned on, and the treated exhaust gas is subjected to wet absorption by the wet processing unit 150 to obtain recovered slurry.

Specifically, the absorption liquid used in the wet processing unit 150 includes dilute sulfuric acid. The molar amount of the ammonium salt in the recovered slurry is 50% or more of the total molar amount of all the ammonia species contained in the recovered slurry, based on the amount of the amino group. Ammonium salts include ammonium sulfate and/or ammonium bisulfate.

In this embodiment, the recovered slurry obtained in step S316 is returned to the cement-decomposing and high-temperature denitration unit 110 to be used as a reducing agent for SNCR denitration during the operation of the cement production system 100.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

By now it should be appreciated by those skilled in the art that while a number of exemplary embodiments of the invention have been shown and described herein in detail, many other variations or modifications of the invention consistent with the principles of the invention may be directly ascertained or inferred from the present disclosure without departing from the spirit and scope of the invention. Accordingly, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims

1. A gas treatment method of a cement production system, the cement production system including a cement decomposition and high temperature denitration unit, a raw mill, a dust removal unit, a low temperature denitration unit, and a wet treatment unit connected in sequence by gas, the gas treatment method comprising:

recycling the recovered slurry as a denitration reducing agent to the cement decomposition and high-temperature denitration unit or the low-temperature denitration unit;

wherein, the running state of the raw mill comprises an opening state and a closing state; and is also provided with

In each production cycle, when the running state of the raw mill is the on state, the exhaust gas of the cement decomposing and high-temperature denitration unit is subjected to heat exchange through the raw mill, and when the running state of the raw mill is the off state, the exhaust gas of the cement decomposing and high-temperature denitration unit is not subjected to heat exchange through the raw mill;

wherein the preset rules include turning on the wet processing unit regardless of whether the running state of the raw mill is the on state; and is also provided with

whether the running state of the raw mill is the starting state or not, the treated exhaust gas is subjected to wet absorption by the wet treatment unit to obtain the recovered slurry; or alternatively

Wherein the preset rule includes turning off the wet processing unit when the operation state of the raw mill is the on state, and turning on the wet processing unit when the operation state of the raw mill is the off state; and is also provided with

2. A gas treatment method according to claim 1, wherein,

the low-temperature denitration unit is configured such that when the operation state of the raw mill is the on state, a denitration catalyst in the low-temperature denitration unit adsorbs and stores ammonia carried in the exhaust gas in the selective catalytic reduction denitration process, and then, when the operation state of the raw mill is the off state, the ammonia stored in the denitration catalyst is allowed to react with nitrogen oxides.

3. The gas treatment method according to claim 2, wherein the denitration catalyst of the low-temperature denitration unit is a sulfur-resistant catalyst.

4. A gas treatment method according to any one of claim 1 to 3, wherein,

in each of the production cycles, the raw mill is in the on state for a time period of greater than or equal to 70% and less than 100%.

5. The gas treatment method according to claim 4, wherein the raw mill is in the on state for 80% of the time in each production cycle.

6. A gas treatment method according to claim 1, wherein,

the substance contained in the recovered slurry includes at least an ammonium salt, and the molar amount of the ammonium salt is 50% or more of the total molar amount of all the ammonia substances contained in the recovered slurry, based on the amount of the amino group.

7. The gas treatment process according to claim 6, wherein the absorption liquid used in the wet treatment unit comprises at least one of: water, dilute sulfuric acid and dilute sulfurous acid; and is also provided with