Desulfurization and denitration process, desulfurization and denitration process flow introduction

             Desulfurization and denitration process, desulfurization and denitration process flow introduction

Flue gas desulfurization and denitration technologies include pafp, ACFP, pyrolusite method, electron beam ammonia method, pulse corona method, gypsum wet method, catalytic oxidation method, microbial degradation method and other technologies.
1. Wet flue gas desulfurization technology:
Advantages: the wet flue gas desulfurization technology is a gas-liquid reaction, with fast reaction speed and high desulfurization efficiency, generally higher than 90%. The technology is mature and widely applicable. Wet desulfurization technology is relatively mature, and its production and operation are safe and reliable. It has always occupied a leading position in many desulfurization technologies.
Classification: common wet flue gas desulfurization technologies include limestone gypsum method, indirect limestone gypsum method, lemon absorption method, etc.
2. Dry flue gas desulfurization technology:
Advantages: the dry flue gas desulfurization technology is a gas reaction. Compared with the wet desulfurization system, the equipment is simple, the floor area is small, the investment and operation cost are low, the operation is convenient, the energy consumption is low, the products are easy to dispose, and there is no sewage treatment system.
Disadvantages: however, the reaction speed is slow and the desulfurization rate is low. The advanced one can reach 60-80%. However, at present, the desulfurization efficiency of this method is low, the utilization rate of absorbent is low, the phenomenon of wear and scaling is serious, it is difficult to maintain the equipment, the stability and reliability of equipment operation are not high, and the service life is short, which limits the application of this method.
Classification: the commonly used dry flue gas desulfurization technologies include activated carbon adsorption method, electron beam radiation method, charged dry absorbent injection method, metal oxide desulfurization method, etc.
A typical dry desulfurization system injects desulfurizer (such as limestone, dolomite or hydrated lime) directly into the furnace. Taking limestone as an example, when calcined at high temperature, the desulfurizer calcines to form porous calcium oxide particles, which react with SO2 in the flue gas to produce calcium sulfate to achieve the purpose of desulfurization.
Flue gas desulfurization and denitration technology is a boiler flue gas purification technology applied to the chemical industry where multiple nitrogen oxides and sulfur oxides are generated. Nitrogen oxides and sulfur oxides are one of the main sources of air pollution. Therefore, the application of this technology has many benefits for ambient air purification.
Desulfurization and denitration adopt two-stage process of oxidation absorption tower and basic absorption tower. The oxidation absorption tower uses oxidant hcio3 to oxidize no, SO2 and toxic metals, while the basic absorption tower uses Na2S and NaOH as absorbents to absorb the residual alkaline gas as a follow-up process. The removal rate of this process is more than 95%.
Chloric acid is a strong acid, which is stronger than sulfuric acid. 99% of the chloric acid solution with a concentration of 35% can be dissociated. Chloric acid is a strong oxidant, and the oxidation potential is controlled by the pH of the liquid phase. Under the condition of acid medium, the oxidizability of chloric acid is stronger than that of perchloric acid (hcio4).
According to the formation mechanism of nitrogen oxides in cement kilns, there are two kinds of technical measures for reducing nitrogen and emission in Cement Kilns:
One is to treat from the source. Control the generation of NOx during calcination. Its technical measures: adopt low nitrogen burner; Segmented combustion in calciner and pipeline to control combustion temperature; Change the batching scheme and use mineralizer to reduce the clinker firing temperature.
The other is from the end of governance. Technical measures for controlling NOx emission in flue gas:
"Staged combustion +sncr" has been piloted in China; Selective non catalytic reduction (SNCR) has been piloted in China; ③ Selective catalytic reduction (SCR) has only three lines of experiments in Europe; Sncr/scr combined denitration technology, domestic cement denitration has no successful experience; Biological denitration technology.
In short, cement denitration in China is still in the exploration and demonstration stage, and has not been scientifically summarized. Whether various design process and technical routes and equipment and facilities are scientific and reasonable, and the denitration efficiency, operation cost, cement energy consumption, and the amount of secondary pollutant emissions will be tested by practice.
Introduction of desulfurization and Denitration Process Flow
Limestone method can only desulfurize but not denitrify
Limestone desulfurization principle:
Limestone or lime is used as desulfurization absorbent. Limestone is crushed and ground into powder and mixed with water to form absorption slurry. When lime is used as absorbent, lime powder is digested and added with water to make absorbent slurry. In the absorption tower, the absorption slurry is mixed with the flue gas in contact, and the sulfur dioxide in the flue gas is removed by chemical reaction with the calcium carbonate in the slurry and the aerated oxidizing air. The final reaction product is gypsum.
Boiler desulfurization and Denitration Process

1、 Brief introduction of Denitration Process
1、
Introduction to Denitration Process
Nitrogen oxide (NOx) is a gas produced by the oxidation of nitrogen in the combustion process. It not only stimulates human respiratory system, damages animals and plants, destroys the ozone layer, but also is one of the main substances that cause greenhouse effect, acid rain and photochemical reaction
。 All over the world, NOx emission limits are becoming more stringent, and thermal power plants, waste incineration plants and cement plants, as the main sources of NOx emissions, have received special attention for their emission reduction.
At present, the main effective methods to reduce NOx emissions from power plant boilers in the world can be roughly divided into the following four types:
(1) Low nitrogen combustion technology, which controls the generation of nitrogen oxides in the combustion process, is mainly applicable to large coal-fired boilers, etc; Low NOx combustion technology can only reduce
30 ~ 50% of NOx emission value. To further reduce NOx emission, flue gas denitration technology must be adopted.
(2) Selective catalytic reduction (SCR, selective
Catalytic
Reduction), mainly used in large coal-fired boilers, is currently the most widely used flue gas denitration technology in China;
(3) Selective non catalytic reduction (SNCR, selective
Non-Catalytic
Reduction), which is mainly used in medium and small boilers such as waste incineration plants. The technology is mature, but its efficiency is lower than that of SCR method; Small investment and short construction period.
(4) Selective catalytic reduction (SCR) + selective non catalytic reduction (SNCR) technology is mainly used for low NOx emissions and site constraints of large coal-fired boilers, and is also relatively suitable for old boiler reconstruction projects.
Xincheng company will adopt selective non catalytic reduction (SNCR) technology to reduce NOx emissions from power plant boilers. Therefore, SNCR denitration method of power plant is introduced as follows:
2. Introduction of selective non catalytic reduction (SNCR) technology
1）
Brief introduction of SNCR denitration
SNCR denitration technology is a relatively mature commercial NOx control and treatment technology. SNCR denitration method is mainly to spray reductant into the containing
In the combustion products of NOx, reduction reaction occurs to remove NOx and generate nitrogen and water. SNCR denitration can achieve a NOx removal rate of more than 90% in laboratory tests. In the application of large boilers,
During the short-term demonstration period, the denitration efficiency can reach 75%. SNCR denitration technology was applied in some fuel oil and gas-fired power plants in Japan in the mid-1970s. 80
In the late S, some coal-fired power plants in EU countries also began the industrial application of SNCR denitration technology. In the early 1990s, the United States began to apply SNCR denitration technology. At present, the world's coal-fired power plants SNCR
The total installed capacity of denitration process is above 2gw.
The denitration agent selected for SNCR denitration system of the project is ammonia water. Dilute the ammonia water into a certain proportion of dilute ammonia water, and send it to the spray gun in front of the furnace with a transfer pump.
2）
Working principle of SNCR
Selective non catalytic reduction (SNCR) denitration process is to use NHX based reductants (such as ammonia
Ammonia or urea, etc.) is injected into the area with furnace temperature of 850 ℃ -1150 ℃, and the reductant is injected through the spray gun installed in the platen superheater area. The reductant is rapidly thermally decomposed into NH3 and other by-products, and then NH3
It is generated by SNCR reaction with NOx in flue gas
N2 and H2O.
3) SNCR system composition
This scheme adopts a typical SNCR denitration process, and its system is mainly composed of six parts: ammonia unloading module (reductant preparation module), reductant storage module, concentration adjustment (dilution) module, metering and distribution module, injection module and SNCR control module.
4) SNCR process flow
The typical process flow of SNCR is: reductant - > boiler / kiln (reactor) - > dust removal and desulfurization device - > induced draft fan - > chimney. The reducing agent is mainly ammonia (urea solution), 20% ammonia solution (or urea solution made by adding preparation module) is sent to the static mixer through the transmission chemical pump, and is quantitatively mixed with the softened water sent by the dilution water module. It is accurately distributed to each spray gun through the metering and distribution device, and then injected into the furnace through the spray gun to realize the denitration reaction. As shown in the following figure:
5) SNCR reaction process
1. NH3 as reducing agent:
4NO+4NH3+O2—>4N2+6H2O
2NO+4NH3+2O2—>3N2+6H2O
6NO2+8NH3—>7N2+12H2O
2. Urea as reducing agent:
CO(NH2)2+2NO→2N2+CO2+2H2O
CO（NH2）2+H2O—>2NH3+CO2
4NO+4NH3+O2—>4N2+6H2O
2NO+4NH3+2O2—>3N2+6H2O
6NO2+8NH3—>7N2+12H2O
6) SNCR technical features
 SNCR technical features:
1. The denitration efficiency can reach 75%.
2. Ammonia escape is 8-12ppm high.
3. The system is simple and saves investment.
4. Without catalyst, the operation cost is saved.
5. The floor area is small.
 SNCR technology has low investment cost, short construction cycle and medium denitration efficiency, which is more suitable for developing countries lacking funds and the transformation of existing small and medium-sized boilers. The disadvantage of this technology is that the removal efficiency of NOx is not high, and ammonia escape is relatively high. Therefore, the use of SNCR technology in multiple bands is limited. However, for the transformation of small and medium-sized units or old units, because of its advantages in economic performance, it is still attractive.
 SNCR method does not use catalyst, and uses furnace injection denitration. Ammonia reduces NOx within the narrow temperature range of 850-1150 ℃. The good mixing of injected ammonia and flue gas is an important condition to ensure that the denitration reduction reaction is fully carried out and the minimum amount of ammonia is used to achieve the best effect. If the injected ammonia is not fully reacted, the leaked ammonia will affect the heating surface at the tail of the boiler, which not only makes the flue gas fly ash easy to deposit on the heating surface, but also the ammonia in the flue gas will generate ammonia sulfate when encountering sulfur trioxide, which is easy to block the air preheater and has the risk of corrosion.
At present, in addition to further improving its efficiency and safety, foreign research on SNCR also focuses on the joint application of SNCR and other denitration technologies.
7) Process flow diagram (ammonia or urea as reductant)
Economic analysis of 3sncr process
The SNCR process takes the boiler furnace as the reactor, which can realize the denitration of flue gas through the transformation of the boiler periphery. The project construction cycle is short, and its investment cost and operation cost are relatively low compared with other denitration technologies. Therefore, it is very suitable for the transformation of existing boilers, especially for the denitration transformation of small and medium-sized boilers. On the one hand, it effectively improves the efficiency of denitration under the condition of low investment. On the other hand, it also well controls the escape of ammonia and makes contributions to the national environmental protection cause.
4. Safety protection measures such as ammonia leakage
4.1 harm of concentrated ammonia to human body and preventive measures and treatment
Ammonia water invades the human body through inhalation and ingestion. After inhalation, it is irritating to the nose, throat and lungs, causing cough, shortness of breath and asthma; It may suffocate and die due to laryngeal edema; Pulmonary edema may occur and cause death. Ammonia splashing into the eye, if no first-aid measures are taken, can cause corneal ulcer, perforation, and further cause intraocular inflammation, eventually leading to eyeball atrophy and blindness. Skin contact can cause burns. Chronic effects, repeated low concentration exposure, can cause bronchitis. Repeated skin contact can cause dermatitis, which is characterized by dry, itchy and red skin.
Protective measures: respiratory system protection. When you may be in contact with its vapor, you should wear gas masks; In case of emergency rescue or escape, it is recommended to wear self-contained breathing apparatus. Eye protection: wear chemical safety protection eyes. Wear protective clothing and chemical resistant gloves. Smoking, eating and drinking are prohibited at the work site. After work, shower and change clothes, and keep good hygiene habits.
Once the skin is contaminated with ammonia, rinse it with water or 2% vinegar for at least 15 minutes. In case of burns, seek medical treatment. If there are redness, swelling and blisters on the skin, wash it with 2% vinegar. In case of eye contact, lift the eyelids immediately and rinse with flowing water or normal saline for at least 15 minutes. Or rinse with 3% boric acid solution and seek medical attention immediately. If inhaled, leave the scene quickly to a place with fresh air and keep breathing unblocked. Give oxygen when breathing is difficult. When breathing stops, give artificial respiration immediately and seek medical advice. If nasal mucosa is strongly stimulated, 1% ephedrine solution can be dropped, and chymotrypsin should be inhaled in severe cases. Those who take it by mistake should gargle immediately, take diluted vinegar or lemon juice orally, and see a doctor.
4.2 emergency treatment of leakage
If the leakage is large, the denitration system should be shut down. Evacuate the personnel in the leakage polluted area to the safety area, prohibit irrelevant personnel from entering the polluted area, and post a notice in an obvious place to inform others of ammonia leakage in this area. It is recommended that emergency treatment personnel wear self-contained breathing apparatus and chemical protective clothing. Do not touch the leakage directly, and stop the leakage under the condition of ensuring safety. Wash with a large amount of water, and put the diluted ammonia into the wastewater system. Absorb with sand, stone or other inert materials, then add a small amount of water, adjust it to neutral, and then put it into the wastewater system. If there is a large amount of leakage, use the dike to receive it, and then collect, transfer, recycle or dispose it innocuously. Portable ammonia detector shall be used to check and confirm that the ammonia concentration in the air is lower than 20ppm.
4.3 ammonia area management requirements
a. The walls around the ammonia area are complete, and obvious warning signs such as "no fireworks" are hung. The ammonia area shall be kept clean. It is not allowed to store other inflammables and stack sundries, and it is not allowed to build temporary buildings.
b. The fire passage around the ammonia area shall be kept unblocked. No vehicle is allowed to enter the ammonia area.
c. The ammonia area must be equipped with a sufficient number of fire extinguishers, and the ammonia tank spray system should be regularly inspected and tested. Fire extinguishers should be inspected regularly and replaced in time if they are found to be invalid.
d. Personnel working in the ammonia area must hold a work license, fully master the system equipment in the ammonia area, understand the nature of ammonia and the relevant fire and explosion prevention regulations, provide safety protection devices (protective gloves, goggles, masks that can filter ammonia, protective clothing, etc.) to operators and maintain them regularly.
e. Eyewash and rapid flushing devices shall be provided on site.
f. When unloading ammonia in the ammonia area, special personnel shall be assigned to conduct on-site inspection, and any leakage, emission and leakage shall be handled immediately. It is strictly forbidden to unload ammonia in case of fire in thunderstorms and nearby areas.