生物质燃烧产生的SO2主要来源于燃料中有机硫的氧化和硫酸盐的热分解，与生物质燃料品种有关。目前，为降低SO2的排放指标，生物质发电厂可采用的脱硫技术包括：炉内脱硫、半干法脱硫（SDA、CFB）、干法脱硫（SDS）以及湿法脱硫等。
The SO2 generated by biomass combustion mainly comes from the oxidation of organic sulfur in the fuel and the thermal decomposition of sulfate, which is related to the variety of biomass fuel. At present, in order to reduce the emission indicators of SO2, the desulfurization technologies that biomass power plants can adopt include: furnace desulfurization, semi dry desulfurization (SDA, CFB), dry desulfurization (SDS), and wet desulfurization.
3.1炉内石灰石脱硫
3.1 Limestone desulfurization in the furnace
炉内石灰石脱硫技术是通过向炉内直接添加石灰石粉来控制SO2的排放。投入炉内的石灰石在850℃左右条件下发生锻烧反应生成氧化钙，然后氧化钙、SO2和氧气经过一些列化学反应，终生成硫酸钙，化学反应式为：
The limestone desulfurization technology in the furnace controls SO2 emissions by directly adding limestone powder to the furnace. The limestone put into the furnace undergoes calcination reaction at about 850 ℃ to generate Calcium oxide, and then Calcium oxide, SO2 and oxygen undergo a series of chemical reactions to finally generate calcium sulfate. The chemical reaction formula is:
CaCO3→CaO+CO2 （煅烧反应）
CaCO3 → CaO+CO2 (calcination reaction)
CaO+SO2+1/2O2→CaSO4 （固硫反应）
CaO+SO2+1/2O2 → CaSO4 (sulfur fixation reaction)
国内燃煤流化床锅炉炉内脱硫效率一般达60%，生物质循环流化床锅炉炉内喷钙脱硫的效率比传统燃煤循环流化床锅炉低，大约在50%左右。甚更低，要获得更高的脱硫效率，需考虑炉后脱硫。
The desulfurization efficiency of coal-fired fluidized bed boilers in China is generally up to 60%, while the efficiency of calcium injection desulfurization in biomass circulating fluidized bed boilers is lower than that of traditional coal-fired circulating fluidized bed boilers, which is about 50%. Even lower, in order to achieve higher desulfurization efficiency, it is necessary to consider desulfurization after the furnace.
3.2 SDA旋转喷雾半干法脱硫
3.2 SDA rotary spray semi dry desulfurization
半干法脱硫常用的工艺为SDA旋转喷雾半干法。SDA法的工艺流程为：石灰制备系统将熟石灰制备成一定浓度的Ca(OH)2浆液，该浆液经过旋转雾化器喷入半干式反应塔中，形成极小的雾滴，喷入100~150℃锅炉出口烟气中，烟气与石灰浆液雾滴充分接触发生物理、化学反应，气体中的SO2等酸性其他被吸收净化。同时，部分与氧气发生氧化反应，使CaSO3转化为CaSO4。反应式为：
The most commonly used process for semi dry desulfurization is SDA rotary spray semi dry process. The process flow of the SDA method is as follows: the lime preparation system prepares hydrated lime into a certain concentration of Ca (OH) 2 slurry. The slurry is sprayed into a semi dry reaction tower through a rotary atomizer to form extremely small droplets, which are sprayed into the flue gas at the outlet of the 100-150 ℃ boiler. The flue gas and lime slurry droplets come into full contact and undergo physical and chemical reactions, and acidic substances such as SO2 in the gas are absorbed and purified. At the same time, some undergo oxidation reaction with oxygen, converting CaSO3 into CaSO4. The reaction formula is:
SO2+ Ca(OH)2→CaSO3+ H2O
SO2+Ca (OH) 2 → CaSO3+H2O
SO2+ 1/2O2+ Ca(OH)2→CaSO4+ H2O
SO2+1/2O2+Ca (OH) 2 → CaSO4+H2O
SO3+Ca(OH)2→CaSO4+ H2O
SO3+Ca (OH) 2 → CaSO4+H2O
2HCl+Ca(OH)2→CaCl2+ H2O
2HCl+Ca (OH) 2 → CaCl2+H2O
2HF+Ca(OH)2→CaF2+ H2O
2HF+Ca (OH) 2 → CaF2+H2O
SDA脱硫工艺特点：脱硫效率高达98%以上；SDA工艺系统结构简单，调节灵活，可控性好；湿法脱硫的机理，干法的特点；无废水产生，系统不需防腐处理。
SDA desulfurization process features: desulfurization efficiency can reach over 98%; The SDA process system has a simple structure, flexible adjustment, and good controllability; The mechanism of wet desulfurization and the characteristics of dry method; No wastewater is generated, and the system does not require anti-corrosion treatment.
3.3 CFB循环流化床半干法脱硫
3.3 CFB circulating fluidized bed semi dry desulfurization
循环流化床烟气脱硫工艺的原理是：脱硫剂Ca(OH)2粉末和烟气中的SO2，在有水参与的情况下，在Ca(OH)2粒子的液相表面发生反应，反应机理与SDA旋转喷雾干燥相同。其主要反应发生在100~150℃脱硫反应塔内，Ca(OH)2粉末、烟气及喷入的水分，在流化状态下充分混合，此时由于有水参与，Ca(OH)2粉末表面离子化，烟气中的酸性气体与Ca2+接触并迅速反应。
The principle of circulating fluidized bed flue gas desulfurization process is that the desulfurization agent Ca (OH) 2 powder and SO2 in flue gas react on the liquid surface of Ca (OH) 2 particles with the participation of water. The reaction mechanism is the same as SDA rotary spray drying. The main reaction occurs in a desulfurization reaction tower at 100-150 ℃. Ca (OH) 2 powder, flue gas, and injected water are fully mixed in a fluidized state. At this time, due to the participation of water, the surface of Ca (OH) 2 powder ionizes, and the acidic gas in the flue gas comes into contact with Ca2+and reacts rapidly.
由于有物料再循环系统，使得脱硫塔内参加反应的Ca(OH)2量远远大于新投加的Ca(OH)2量，即实际反应的脱硫剂与酸性气体的摩尔比远远大于表观摩尔比，从而使SO2、SO3、HCl、HF等酸性气体能被充分地吸收，实现脱硫。
Due to the presence of a material recycling system, the amount of Ca (OH) 2 participating in the reaction in the desulfurization tower is much greater than the newly added Ca (OH) 2. This means that the molar ratio of the actual reaction desulfurizer to the acidic gas is much greater than the apparent molar ratio, allowing acidic gases such as SO2, SO3, HCl, HF, etc. to be fully absorbed, achieving efficient desulfurization.
CFB主要工艺特点：烟气、物料、水在剧烈的掺混升降运动中接触时间长、混合充分，脱硫效率达到90%；不产生废水，不需要设置废水处理系统；尾部烟囱不需要防腐。
The main process characteristics of CFB include long contact time and sufficient mixing of flue gas, materials, and water during intense mixing and lifting movements, with a desulfurization efficiency of 90%; No wastewater is generated and there is no need to set up a wastewater treatment system; The tail chimney does not require anti-corrosion.
3.4 SDS干法脱硫
3.4 SDS dry desulfurization
SDS干法脱硫可采用碱性吸收剂喷射，在锅炉出口后端合适位置增加碳酸氢钠超细粉喷射口，使其与180~250℃烟气中的SO2发生化学反应，如：
SDS dry desulfurization can be achieved by using alkaline absorbent injection, and adding a sodium bicarbonate ultrafine powder injection port at a suitable position at the rear end of the boiler outlet to chemically react with SO2 in the flue gas at 180-250 ℃, such as:
2NaHCO3+热量-----Na2CO3+ CO2+ H2O
2NaHCO3+Heat - Na2CO3+CO2+H2O
Na2CO3+ SO2+ 1/2 O2+ 热量-----Na2SO4+ CO2
Na2CO3+SO2+1/2 O2+Heat - Na2SO4+CO2
SDS工艺主要技术特点：脱硫效率可达95%以上；对烟气流量、SO2浓度等工况的变化适应性较强；脱硫剂成本较高，总体运行成本相对较高，适用于烟气含硫量低（或烟气量小），总消耗量不大，这样吸收剂增加的成本不敏感；腐蚀性轻微，基本不用采取特殊防腐措施，但需采取相应防磨措施；由于脱硫工艺不需要对烟气进行了増湿减温，排放烟气温度基本没有降低，烟气排放始终保持良好的视觉效果；系统不产生废水。由于SDS反应窗口温区（即烟气温度180~250℃），这样才能保证90%以上的脱硫效率。对于生物质锅炉采用SDS干法脱硫系统，由于生物质锅炉一般的排烟温度是较低，一般是130-150℃，为了保证较高的脱硫效率，需将锅炉烟气升温，造成运行成本的大大增加。
The main technical characteristics of the SDS process are: the desulfurization efficiency can reach over 95%; Strong adaptability to changes in flue gas flow rate, SO2 concentration, and other operating conditions; The cost of desulfurizers is relatively high, and the overall operating cost is relatively high. It is suitable for flue gas with low sulfur content (or small flue gas content), and the total consumption is not large, so the increased cost of absorbers is not sensitive; Slightly corrosive, no special anti-corrosion measures need to be taken, but corresponding anti wear measures need to be taken; Due to the fact that the desulfurization process does not require humidification and temperature reduction of the flue gas, the temperature of the discharged flue gas remains basically unchanged, and the flue gas emissions always maintain a good visual effect; The system does not produce wastewater. Due to the temperature range of the SDS reaction window (i.e. flue gas temperature of 180-250 ℃), it is necessary to ensure a desulfurization efficiency of over 90%. For biomass boilers using SDS dry desulfurization system, due to the generally low exhaust gas temperature of biomass boilers, which is generally 130-150 ℃, in order to ensure high desulfurization efficiency, it is necessary to raise the temperature of the boiler flue gas, resulting in a significant increase in operating costs.
3.5湿法脱硫
3.5 Wet desulfurization
湿法脱硫采用石灰石浆液、氢氧化钠溶液或者氨水等碱性溶液与烟气接触，吸收液通过喷嘴雾化喷入吸收塔，分散成细小的液滴并覆盖吸收塔的整个断面。液滴中的碱液与塔内烟气逆流充分接触，发生传质与吸收反应，烟气中的SO2、SO3等被碱液吸收。
Wet desulfurization uses alkaline solutions such as limestone slurry, sodium hydroxide solution or ammonia water to contact with flue gas, and the absorption liquid is sprayed into the absorption tower through high-efficiency nozzle atomization to disperse into small droplets and cover the entire section of the absorption tower. The alkali solution in the droplet fully contacts the flue gas in the tower in countercurrent, leading to mass transfer and absorption reactions. SO2, SO3, and other substances in the flue gas are absorbed by the alkali solution.
该工艺的特点是：技术比较成熟，脱硫效率高（90~98%）；适应性强，能适应高浓度SO2烟气条件；产生脱硫废水；系统复杂，几乎所有设备都需防腐；排烟温度低于烟气露点温度，烟囱需要做防腐。烟囱排烟存在烟羽问题、脱硫废水二次污染问题。
The characteristics of this process are: relatively mature technology, high desulfurization efficiency (90-98%); Strong adaptability, able to adapt to high concentration SO2 flue gas conditions; Generate desulfurization wastewater; The system is complex, and almost all Almost all needs anti-corrosion; The exhaust temperature is lower than the dew point temperature of the flue gas, and the chimney needs to be protected against corrosion. There are issues with smoke plumes and secondary pollution of desulfurization wastewater in chimney smoke exhaust.
4.生物质锅炉脱硫脱硝工艺分析
4. Analysis of recommended processes for desulfurization and denitrification of biomass boilers
针对20万标方烟气，排烟120~140℃的生物质锅炉，NOx、SO2的原始排放浓度均为400 mg/Nm3，排放浓度分别为50、35 mg/Nm3。
For biomass boilers with 200000 standard cubic meters of flue gas and smoke exhaust of 120-140 ℃, the original emission concentrations of NOx and SO2 are both 400 mg/Nm3, with emission concentrations of 50 and 35 mg/Nm3, respectively.
脱硝采用SNCR+SCR联合脱硝技术，把SNCR工艺的还原剂喷入炉膛技术同SCR工艺利用逃逸氨进行催化反应的技术结合起来，进一步脱除NOx；它是把SNCR工艺的低费用的特点同SCR工艺的率进行有效结合。SNCR将烟气中NOx浓度降200 mg/Nm3，再通过SCR将NOx降50mg/Nm3；脱硫有SDA半干法、CFB半干法、钠减法湿法三种脱硫工艺可供选择。脱硫脱硝设备投资与运行费用如表4.1所示。
It is recommended to use the SNCR+SCR combined denitrification technology, which combines the technology of spraying the reducing agent of the SNCR process into the furnace with the technology of using escaped ammonia for catalytic reaction in the SCR process to further remove NOx; It effectively combines the low cost characteristics of SNCR process with the high efficiency of SCR process. SNCR reduces the NOx concentration in flue gas to 200 mg/Nm3, and then SCR reduces NOx to 50mg/Nm3; There are three desulfurization processes available for selection: SDA semi dry method, CFB semi dry method, and sodium reduction wet method. The investment and operating costs of desulfurization and denitrification equipment are shown in Table 4.1.
表4.1 设备投资与运行费用
Table 4.1 Equipment Investment and Operating Costs
图片?
Picture?
SNCR和SCR还原剂采用尿素，SNCR工艺在脱除部分NOx的同时也为后面的SCR提供所需要的氨，可以省却尿素热解喷射系统的设置。对于没有设置SNCR的系统，若需增设补氨系统，采用尿素热解工艺，设备投资费用需要另增加75万元，运行费用每年增加80万元。
The SNCR and SCR reducing agents use urea, and the SNCR process not only removes some NOx but also provides the required ammonia for subsequent SCR, which can save the setting of the urea pyrolysis injection system. For systems without SNCR, if an ammonia replenishment system needs to be added and a urea pyrolysis process is adopted, the equipment investment cost will need to be increased by 750000 yuan, and the operating cost will increase by 800000 yuan annually.
生物质锅炉可行的脱硫技术有半干法（SDA、CFB）和湿法脱硫。与半干法脱硫相比，湿法脱硫产生脱硫废水，存在二次污染问题；虽然钠碱湿法脱硫总体投资比半干法脱硫省20~30%，但运行成本每年高出半干法500万。
The feasible desulfurization technologies for biomass boilers include semi dry (SDA, CFB) and wet desulfurization. Compared with semi dry desulfurization, wet desulfurization generates desulfurization wastewater, which poses a secondary pollution problem; Although the overall investment of sodium alkali wet desulfurization is 20-30% less than that of semi dry desulfurization, the operating cost is 5 million yuan higher per year than that of semi dry desulfurization.
CFB循环流化床半干法脱硫技术与SDA相比，运行成本基本持平，但投资成本高300万，且系统相对复杂，维护不方便。
Compared with SDA, the CFB circulating fluidized bed semi dry desulfurization technology has almost the same operating cost, but the investment cost is 3 million yuan higher, and the system is relatively complex and inconvenient to maintain.
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2023-06-08
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