How does biomass boiler perform desulfurization and denitrification?

2019-09-04

If you have some problems in the process of using biomass boilers in peacetime, you must solve them in time. If these problems are not answered for a long time, you should have a lot of influence on everyone’s work, so I hope everyone will not ignore them. It is. How should we go for desulfurization and denitrification of biomass boilers?

1. Does the biomass boiler need desulfurization and off-selling?

The characteristics of the biomass boiler flue gas. After investigation, testing and analysis of the biomass boiler flue gas, the biomass boiler flue gas has the following characteristics:

  1. Furnace temperature difference is large, biomass boiler mainly has grate furnace and circulating fluidized bed furnace, each furnace type is divided into medium temperature medium pressure furnace, sub-high temperature sub-high pressure furnace, high temperature and high pressure furnace, furnace temperature is 700~760 . (], 880~950. (], 850~1100 °C;
  2. The content of hydrogen in biomass is high, and the water content in flue gas is also high, <p(H20) can reach 15%~30%; and the flue gas of coal-fired boiler will not exceed 10%;
  3. The content of alkali metal containing soot is higher, up to 8%;
  4. Sulfur dioxide, nitrogen oxides have low concentration and large fluctuations. When burning pure biomass, the concentration of sulfur dioxide and nitrogen oxides fluctuates between 100 and 250 mg/m3, such as doping template, wood, bark, sulfur dioxide and nitrogen in flue gas. The oxide concentration fluctuates between 250 and 600 mg/m3, and the instantaneous level can reach more than 1 g/m3.

2. Technical scheme for desulfurization and denitrification for biomass boilers

Low nitrogen combustion technology

Low-nitrogen combustion technology belongs to control combustion technology. By adjusting the oxygen content in the combustion air and reducing the production of nitrogen oxides, all low-nitrogen combustion technologies must enable the boiler to have a stable combustion process, otherwise the transformation effect will not be obvious or the combustion will not occur. Stable problem. For biomass boilers, common flue gas recycling technology.

There are two processes for flue gas recycling technology:

  1. The flue gas behind the induced draft fan is directly led to the inlet of the primary fan. The program does not need to be modified once, and the recirculating flue gas does not need an exhaust fan. It saves electricity and energy, and the transformation is simple. The concentration of nitrogen oxides can be reduced by 20% to 40%.
  2. The flue gas behind the induced draft fan is directly led to the primary and secondary air chambers of the furnace. In this scheme, the primary fan needs to be operated under load reduction, and the recirculated flue gas also needs to be equipped with a high-temperature exhaust fan, and the wind pressure is equivalent to that of the primary fan. The program increases the operating power consumption, and the transformation is relatively complicated, and the nitrogen oxide mass fraction can be reduced by 25% to 50%.

Flue gas recirculation technology will also increase the concentration of sulfur dioxide pollutants in the flue gas and increase the water content, but reduce the total amount of flue gas emissions. The process flow of flue gas recycling technology is shown in Figure 1. Scheme 1 Scheme 2 Figure 1 Flue Gas Recycling Technology Process

SNCR technology

SNCR is a selective non-catalytic reduction technology. SNCR technology is suitable for boilers with a flue gas outlet temperature of 800?1100 °C. Below this temperature, the denitration efficiency is low, and the mixing effect of ammonia and flue gas has a great influence on the denitration efficiency. (such as the cyclone inlet area mixing effect is better).

If the mixing is insufficient and the reaction time is not enough, to achieve the same denitration efficiency, the operating cost will increase, and the ammonia escape of the exhaust gas will also exceed the standard. In addition, the S03 content in biomass boiler flue gas is often high, and in the low temperature zone below 280 °C, there are problems such as clogging and corrosion of sulfate. The SNCR denitration efficiency is also related to the initial concentration of nitrogen oxides in the flue gas. The SNCR denitration efficiency of the biomass boiler is 20% to 50%.

〇3 oxidation technology

NO% oxidation is oxidized by a strong oxidant and finally converted into nitric acid or nitrate. The commonly used oxidants are hydroxyl radicals H0_, 03, H202, Mn04_, C102, Cl2; among them, 03 is a commonly used oxidant, and the reaction rate is fast, in the case of flue gas. When fully mixed, the oxidation rate is over 90%, and the operation is stable, and the industrial application performance is high. 03 Oxidative denitration suitable temperature is 50 ~ 180 ° C, and no requirement for S02 concentration, can be installed in the low temperature flue gas section, after NO% oxidation, it is necessary to increase the alkaline substance absorption system to absorb the oxidized nitrogen oxides.

  1. Desulfurization technology scheme Biomass boiler flue gas belongs to low S02 concentration flue gas. The commonly used methods include decalcification technology such as calcium injection in the furnace, calcium injection in the circulating fluidized bed outside the furnace (calcium injection outside the furnace), and wet method outside the furnace. Various schemes can meet emission index requirements, and cost control is the key. The double-alkali method, ammonia method and magnesium method in wet desulfurization have lower operating costs, and the ammonia method directly produces ammonium sulfate fertilizer, which can be collected with the dust collector. The ash is mixed into a compound fertilizer and returned to the farmland; and the mixed salt treatment produced by the double alkali method and the magnesium method has a difficulty.
  2. Desulfurization and denitrification integration technology 2.3.1 Wet desulfurization and denitrification integration technology adopts 〇3 denitration scheme, wet desulfurization uses ammonia water as desulfurization absorbent, and after absorption and oxidation of pollutants, it produces agricultural fertilizers such as ammonium nitrate and ammonium sulfate.
  3. Semi-dry desulfurization and denitrification integration technology adopts 〇3 denitration scheme, dry desulfurization uses the external circulating fluidized bed to spray calcium. After the pollutants are absorbed and oxidized, the products are calcium nitrate, calcium nitrite and sulfuric acid respectively. Calcium, calcium sulfite, desulfurization and denitrification products enter the bag filter with the flue gas and are finally discharged into the ash system. Semi-dry method: low-nitrogen combustion, SNCR, and internal and external calcium injection technology are only applicable to areas where the requirements of flue gas emission are not high. 〇3 oxidation, double alkali method, ammonia method, and magnesium method are applicable to all areas.

The technical options for different emission indicators, the original pollutant concentration, and the smoke emission index requirements, can choose technical solutions with feasible technology and low operating costs. Biomass boiler users can choose the appropriate desulfurization according to this table according to the characteristics of biomass boiler flue gas, combined with biomass fuel to choose the appropriate denitrification scheme.

The above contents are all detailed introductions on the desulfurization and denitrification of biomass boiler. I believe that everyone has received a lot of help after reading them, hoping to use it better.

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