How is desulfurized coal made? What is the desulfurization process?

Generally, the circulating fluidized bed boiler is at a working temperature of 850-950, at which the limestone can fully undergo roasting reaction, so that the calcium carbonate is decomposed into calcium oxide, and the calcium oxide is salted with the sulfur dioxide produced by coal combustion to generate calcium sulfate, which is discharged in solid form to achieve the purpose of desulfurization.

Limestone Roasting Reaction Equation:

CaCO3 = Cao + CO2 - caloric Q

Desulfurization Reaction Equation:

CAO+SO2+1 2O2=CASO4+Calorific Q, therefore, the circulating fluidized bed boiler can achieve efficient and cheap desulfurization in the furnace, and the general desulfurization rate is more than 90%. At the same time, due to the low combustion temperature in the furnace, the NOx generated in the circulating fluidized bed boiler is mainly composed of fuel NOX, that is, the N in the fuel is converted into NOX. However, the amount of thermal NOx, that is, the amount of NOx converted into N in the air, is very small. At the same time, the circulating fluidized bed boiler adopts the method of graded air supply, that is, the primary air is fed from under the air distribution plate, and the secondary air is fed from the dense phase zone at the bottom of the furnace in three layers, which can effectively inhibit the generation of NOx. As a result, pollutant emissions in circulating fluidized bed boilers are low.

When the boiler is running, the bed material in the furnace is mainly composed of ash in the coal, unreacted limestone, limestone desulfurization reaction products, etc., these bed materials are in a fluidized state under the action of the primary air sent from the air distribution plate and the secondary air sent from the air distribution plate, and some particles are entrained by the flue gas in the furnace and move upward, and a part of the solid particles will fall along the side wall of the furnace at different heights of the furnace to form the internal circulation of the material; The rest of the solid particles are entrained by the flue gas into the separator for gas-solid two-phase separation, and the vast majority of the particles are separated and sent back to the furnace through the return valve to form the external circulation of the material. In this way, the fuel and limestone can be reciprocated and reciprocated in the furnace for many times, so the circulating fluidized bed boiler has a high combustion efficiency and low limestone consumption.

At present, the desulfurization technology of coal chemical industry generally adopts MDEA in small and medium-sized enterprises, NHD in medium-sized enterprises, and low-temperature methanol washing in large enterprises. At present, large-scale coal chemical industry basically adopts airflow bed gasification, with high vaporization temperature and very little organic sulfur, and the sulfur-resistant shift is used for transformation, and the desulfurization before the transformation is adopted, and most of the low-temperature methanol washing is used after transformation.

1. The comprehensive technology of low-temperature methanol elution and sulfurization and decarburization is the most mature, advanced and reliable, but the investment is large, and it is generally used in large-scale coal chemical plants.

2. NHD is a physical absorption desulfurization and decarburization process suitable for China's national conditions, although the technical indicators are not as good as low-temperature methanol washing, but the investment is low, and the overall energy consumption is lower than the traditional hot potash alkali decarburization, which is the first choice for small and medium-sized enterprises to carry out technological transformation, and new medium-sized coal chemical plants can also be considered.

3. MDEA has the lowest one-time investment, but the energy consumption is high, and it is not recommended for new projects.

4. The above three processes all refer to pressure gasification or desulfurization and decarburization under medium pressure, if it is a traditional intermittent gasification of atmospheric pressure fixed layer, atmospheric pressure tannin gum desulfurization + shift gas desulfurization + PSA decarburization is a better choice.

1. The coal desulfurization technology before combustion is mainly coal washing and desulfurization, that is, the coal is purified before combustion to remove part of the sulfur and ash in the raw coal. It is divided into physical method, chemical method and microbial method. 1. Physical Law:

It mainly refers to gravity beneficiation, which uses the density difference between organic matter and pyrite in coal to separate them. The influencing factors of this method mainly include the crushing particle size of coal and the state of sulfur. The main methods include jigging coal preparation, heavy medium coal preparation, wind coal preparation, etc.

2. Chemical method: it can be divided into physical chemical method and pure chemical method. The physicochemical method is flotation; Chemical methods include alkali desulfurization, gas desulfurization, pyrolysis and hydrogenation desulfurization, oxidation desulfurization, etc.

3. Microbial method: a new bioengineering technology applied to the coal industry on the basis of bacterial leaching of metals, which can remove organic sulfur and inorganic sulfur from coal. China's current coal washing rate is low, about 20, while the United States is 42, the United Kingdom is 94 9, France is 88 7, and Japan is 98 2.

Increasing the washing rate of coal is expected to significantly improve sulfur dioxide pollution from coal burning. However, physical separation can only remove 80 of the inorganic sulfur in the coal, accounting for 15 30 of the total sulfur content in the coal, which cannot meet the requirements of coal sulfur dioxide pollution control, so it can only be used as an auxiliary means of coal desulfurization. 2. Combustion of coal desulfurization technologyLimestone or dolomite is added as desulfurizer during coal combustion, calcium carbonate and magnesium carbonate are decomposed by heat to form calcium oxide and magnesium oxide, which react with sulfur dioxide in flue gas to form sulfate, which is discharged with ash.

There are two main types of desulfurization technologies used in the combustion process in China: briquette sulfur fixation and fluidized bed combustion desulfurization technology. 1. Briquette sulfur fixation technology:

After screening, different raw materials are mixed with coal in a certain proportion, mixed with pretreated binders and sulfur fixing agents after crushing, and extruded and dried by mechanical equipment to obtain finished industrial sulfur briquettes with certain strength and shape. Sulfur fixing agents mainly include limestone, marble, calcium carbide slag, etc., and the amount added depends on the sulfur content. Burning briquette can greatly reduce the concentration of sulfur dioxide, carbon monoxide and soot in flue gas, save coal, and the economic and environmental benefits are considerable, but the problems of ignition lag and improper operation caused by ignition lag and improper operation should be solved in industrial practical applications.

2. Fluidized bed combustion desulfurization technology: coal and adsorbent are added to the bed of the combustion chamber, and the bed is suspended for fluidized combustion by blasting air from the bottom of the furnace, which forms turbulent mixing conditions, prolongs the residence time, and improves the combustion efficiency. The reaction process is that sulfur in coal is burned to produce sulfur dioxide, and at the same time, limestone is calcined and decomposed into porous calcium oxide, and sulfur dioxide reaches the surface of the adsorbent and reacts, so as to achieve the desulfurization effect.

The main influencing factors of fluidized bed combustion desulfurization include calcium-sulfur ratio, calcination temperature, particle size, pore structure and type of desulfurizer. In order to improve the desulfurization efficiency, the following methods can be adopted: (1) improve the design and operating conditions of the combustion system (2) pre-calcination of desulfurizer (3) use additives, such as sodium carbonate, potassium carbonate, etc. (4) develop new desulfurizers.

There are several ways to desulfurize coal:

1. Physical method: Iron sulfide (pyrite) in coal is usually removed by gravity separation or magnetic separation, and the sulfur in this form accounts for about 2 3 of the sulfur in coal.

2. Chemical method: the coal is mixed with the aqueous solution of iron sulfate after crushing, heated to 100 130 in the reactor, and the iron sulfate reacts with pyrite to convert into ferrous sulfate and monomer sulfur, the former is recycled after oxidation, and the latter is used as a by-product.

3. Gasification method: Coal is underestimated by gasifier at a high temperature of 1000 1300 to become gas. Most of the sulfur in coal becomes hydrogen sulfide when it is gasified, and then it is removed by liquid absorption or solid adsorption.

4. Liquefaction method: The liquefaction of coal includes synthesis method, direct cracking hydrogenation method and hot melt hydrogenation method. In the liquefaction process, sulfur reacts with hydrogen to form hydrogen sulfide and escapes, thus obtaining a fuel with high calorific value, low sulfur and low ash content.

The <> desulfurization system is mainly composed of flue gas system, absorption and oxidation system, limestone lime slurry preparation system, by-product treatment system, wastewater treatment system, public system (process water, compressed air, accident slurry tank system, etc.), electrical control system and other parts.

The original flue gas discharged from the induced draft fan of the "limestone-gypsum" wet desulfurization process boiler is introduced into the desulfurization system by the booster fan, and the flue gas enters the absorption tower after heat exchange through the GGH (gas heater).

The original flue gas discharged from the boiler induced draft fan is introduced into the desulfurization system by the booster fan, and the flue gas enters the absorption tower after heat exchange through the GGH (gas heater). In the absorption tower, the original flue gas passes through the tower body from bottom to top, and the mist limestone slurry sprayed out by the spray system is mixed in counterflow, and the net flue gas after desulfurization removes the fog droplets carried by the flue gas through the mist eliminator at the upper part of the spray system, and then excludes the absorption tower into the GGH, and is discharged through the chimney after the GGH heat exchange and heating.

Desulfurization refers to the fixation of the sulfur element in coal into a solid with calcium-based and other methods to prevent the formation of SO2 during combustion. At present, desulfurization methods can generally be divided into three categories: pre-combustion desulfurization, combustion desulfurization and post-combustion desulfurization. The desulfurization before combustion is mainly fuel desulfurization, and the desulfurization during combustion is to improve the combustion technology desulfurization, and the flue gas desulfurization has dry desulfurization and wet desulfurization, and the limestone-gypsum desulfurization in the wet desulfurization is more economical.