Abstract:Gas in NH3The forming process is relatively complex, coal pyrolysis temperature, gasification temperature, coal gasification, coal rank and the nitrogen content of inertinite content and other factors directly affect the gasifier NH3Generation. NH3The content of gas, a furnace is greater than two and the carbonization furnace gas furnace. That of NH in gas analysis and at the same time3With CO2The reaction of NH and gas washing water4HCO3, NH4HCO3Is to bring some security risks of phenol water evaporation system, the need to take effective measures, eliminate the hazards and safety hazards from the source; gas in NH3You can replace some or all of soda ash as the desulfurization absorbent in gas wet desulfurization, thus saving the cost of desulfurization.

1Introduction

Chinese is one of the world's coal resources is one of the most rich countries, coal occupies the position in the Chinese play a decisive role in the structure of energy, Chinese energy situation determines our economic development cannot do without coal, based on the requirements of low carbon economy, vigorously develop clean coal technology in line with China's energy security strategy, coal gasification is a the use of clean coal technology, the atmospheric fixed bed gasifier gasification technology, its production scale, investment cost, construction period, in line with the majority of metallurgy and chemical industry, building materials and machinery industries such as gas, over the years has been widely used, but as in the China earlier application of clean coal technology, still in the future is the main coal gasification technology of industrial fuel gas.

The application process of producer gas, people are more concerned about the gas calorific value, cleanness and H2The content of S, and NH in gas3The design process often exist in the gas station will be ignored. The gas in NH3From the coal nitrogen, the nitrogen content in the coal is generally not high, usually between 0.3-3.5%, 1-2%, NH in producer gas3The forming process is complex, and the pyrolysis temperature, gasification temperature, coal gasification and reaction atmosphere. Some factors of coal and gas station for operation and other aspects of the impact, the gas in NH3The content is less, almost no what influence on the gas station system, but some gas stations are different, due to various factors, resulting in gas NH3The content is high, resulting in a series of positive and negative effects on the gas station system, NH system analysis of furnace gas making process3The forming factors, and the gas in NH3The influence of gas station system, it is beneficial for us to the gas station system more perfect design and reasonable application.

2The formation of ammonia gas

2.1Producer gas production

2.1.1 The principle of gas gasification furnace

The gasification furnace can be divided into two steps to understand, the first is the air through the fuel layer, C and O2An exothermic reaction occurs, with heat and reactant CO for the next reaction2Steam and air mixture; then the fuel layer, C and H2O, O2And CO2Mixed reaction endothermic and exothermic, generating gas, the main reaction equation as follows.

2C+O2=2CO+221.2kJ (1)

2CO+O2=2CO2+566.0 kJ (2)

C+O2=CO2+393.8 kJ (3)

CO2+C=2CO-172.6kJ (4)

C+2H2O=CO2+2H2-90.2 kJ (5)

C+H2O=CO+H2-131.4 kJ (6)

2.1.2 Producer gas production

Differentiate according to the structure, the gasifier is generally divided into two sections, a section of the furnace and furnace carbonization furnace, the coal gasification reaction principle is the same, but because of the different structure form, the production process in the furnace of coal gas is slightly different.

The gas production process of a furnace: by stoker coal into gas furnace furnace at the same time, the coal into the furnace, dry distillation and temperature in the first short time, and then enter the gasification reaction layer. As the gasification agent in air and water from the bottom of the steam drum into the furnace, at 1100-1200 deg.c and coal gasification reaction layer formed in the redox reaction, carbon monoxide and hydrogen as the main component of the gas, furnace gas temperature of 500-600 DEG C.

The two section of the furnace gas production process: the coal storage bunker in batches into the gasifier through the stoker, joined the gasifier of coal into the first distillation section, in the coal carbonization zone in the slow down of this experience, dry and low temperature carbonization process. First of all the coal in the water was drying out, along with the continuous downward movement of coal, the increase in temperature, distillation and distillation of coal tar. After drying and carbonization of coal char was state continues downward, into the gasification, gasification section in the oxidation - reduction reaction, the formation of CO and H2As the main component of the gas. Coal ash in coal and few unreacted ash to form continues downward, the gray knife to clear out. As the gasification agent in air and water from the bottom of the steam drum into the furnace, at 1100 to 1200 DEG C, and into the gasification is the coal char state of redox reaction, formed by CO and H2M is the main component of gas. The gas is divided into two parts to run, which is a part of the M2The lower section gas channel finally exit from the sandwich up, lower section gas export, the gas is called the lower section gas; and the other part of the gas M1In charge of gas layer into the carbonization zone upstream through gasification, and slow down the coal for direct contact, its heat transfer directly to coal gasification, dry distillation and drying process described above, while producing M dry gas part with high calorific value gas mainly alkanes3. This part of the retorting gas and gas upstream in the process of the dry distillation gas outlet by the upper formation, upper gas furnace, lower section gas temperature of 450-550 DEG C, the upper gas temperature of 80-120 DEG C.

The gas production process of carbonization furnace: by stoker coal into gas furnace furnace, adding the gasifier coal into the first distillation section, in the coal carbonization zone in the slow down of this experience, drying, carbonization process. The first coal moisture in the dry out, along with the continuous downward movement of the coal tar, the increase in temperature, and most sulfides were also carbonization, formation of hydrocarbons and light tar by gas carrying out. At the same time, as the gasification agent in air and water from the bottom of the steam drum into the furnace, at 1100-1200 deg.c and into the gasification is properties of char coal redox reaction, to form carbon monoxide and hydrogen as the main component of the gas. The gas to run into the distillation section, through gasification and slow down the coal for direct contact, its heat transfer directly to coal gasification, dry distillation, drying process described above, and part of the dry distillation gas hydrocarbon based high calorific value gas, dry gas produced this upstream gas and dry distillation process the gas outlet by gas furnace, a temperature of 250-320 DEG C.

2.2The formation of ammonia gas

Literature[1]The formation of NH coal carbonization and pyrolysis process3Coal, carbonization temperature is higher than 600 DEG C, NH3Substances appear in raw gas coal began, in the high temperature carbonization process NH3The generation of more, NH3The yield and nitrogen content in coal, the formation of 12-16% NH n3. Zhao Wei used tubular reactor for catalytic pyrolysis of coal in the range 600-900 DEG C, found in coal pyrolysis conditions of 600 DEG C, only a small amount of NH3The formation, the higher the temperature of pyrolysis, gas products in NH3The greater the amount generated[2]. Coal pyrolysis experiment of Wu Yangfang in fixed bed reactor, that can promote the NH in the presence of water vapor and methane pyrolysis atmosphere.3Generation[3]. NH3Not only in the coal pyrolysis process in the gasification process, there is also a NH3Generation, formation of nitrides in the investigation found that Zhao Wei during the gasification experiment, in coal gasification conditions, the conversion of N to NH3The amount of increase with the increase of temperature, water vapor in the atmosphere NH3The production volume was significantly higher than the experimental results of pyrolysis conditions[4].

A furnace, drying and carbonization layer by layer is thin, the coal into the furnace after high temperature carbonization, the pyrolysis of NH3At the same time in a large amount, CO2And the presence of steam gasification reaction conditions, N in coal will also have a considerable part of conversion to NH3. The two section of the furnace and the carbonization furnace drying carbonization layer and thick layer, used for distillation section coal carbonization gas temperature of 550-650 DEG C, the dry distillation process for low temperature carbonization, normal operation, coal carbonization and pyrolysis process NH3The two generation is less, and the carbonization furnace furnace coal gas NH3Mainly from the gasification process, two furnace on Shanxi Datong on a company under section gas in NH3The content of the actual calculations also illustrate this point, the lower section gas furnace NH3The content is 597mg/Nm3The upper gas, NH3The content is 619mg/Nm3We can see that, in the coal, coal pyrolysis carbonization zone NH3The amount is less than 12 mg/Nm3.

3Influence of furnace gas in ammonia system of gas station

3.1Influence of furnace gas in ammonia evaporation of phenol water treatment system

3.1.1 Evaporation treatment process of phenol water coal gas station

The gas station management evaporation concentration method process of phenol containing wastewater, the phenol wastewater was pretreated by sedimentation, combining multistage mechanical filtration and water dilution method, separation. The pretreated wastewater pump into the gas furnace phenol water evaporation tank, gas heat will depend on part of wastewater containing phenol waste water vaporization, part of the low boiling point of benzene, phenol is vaporized, vaporization after containing low boiling benzene, phenol steam steam into the bottom as the gasification agent application, has the temperature inside the furnace oxide layer is in commonly 1100, 1200 degrees Celsius, under this temperature, benzene phenols are cracked into carbon dioxide and water. Most of the higher boiling point of benzene, phenol was vaporized, with regular sewage discharged to the water tank, tar pool, waiting for the next phase of the final treatment.

3.1.2 Influence of furnace gas in ammonia evaporation of phenol water treatment system

The two stage gasifier of furnace gas temperature is higher, the impurity content is more, need to go through a series of purification, cooling, conveying to gas is ignited by. The end of cold gas indirect cooler equipment commonly used gas and water heat transfer, most gas stations to prevent blockage of impurities in the gas equipment, or for improving the gas cooling effect into account, in the indirect cooler, using continuous washing wastewater containing phenol, ammonia gas, CO gas in Yu Shimei2Flushing water containing ammonia and reaction of NH4HCO3, and soluble in phenol containing waste water, the reaction equation is: NH3+CO2+H2O=NH4HCO3. Literature[5,6]The use of ammonia scrubbing in flue gas CO2Do a lot of experiments, the mechanism and gas station NH4HCO3The generation of the same.

Mixed with phenolic wastewater in NH4HCO3In the process of phenol wastewater evaporation and decomposition, with increasing temperature, formed after decomposition of NH3, CO2And H2A part of O with the steam gasification agent into the furnace, the other part of the steam pipe into the blind end or relief tube, with the decrease of temperature, the reaction of NH with re4HCO3And, the condensation condensation crystallization, crystallization process and Literature[7]The similar. After crystallization of NH4HCO3White crystal accumulation, finally blocked the steam pipe, the system is not smooth, will lead to serious steam explosion overpressure in gas station system design, the need to take effective measures, eliminate the hazards and safety hazards from the source.

3.2Effect of ammonia on furnace gas wet desulfurization system

The gas wet desulfurization method used earlier is ammonia washing neutralization method, since the early 50 century abroad ADA, China has developed a modified ADA method, MSQ method, KCS method and tannin extract desulfurization technology etc.. Wet desulfurization can be summarized into physical absorption, chemical absorption and oxidation of three, which is oxidation with alkaline solution as the absorbent, and adding oxygen carrier as catalyst, the absorption of H2S, and the oxidation of elemental sulfur, oxidation by modified ADA method, HPF method and 888 ammonia extract method as the representative, general with soda ash as the desulfurization absorbent, the desulfurization technology in gas station application.

Literature[8,9]Were introduced to HPF and sulfonated cobalt phthalocyanine compounds as catalyst, NH3.H2O as absorbent by liquid phase catalytic oxidation gas wet desulfurization technology, NH3.H2O are the source of gas in NH3, the desulfurization and regeneration process is as follows (1) - (11), including (1) - (8) for the desulfurization reaction, (9) - (11) for regeneration reaction.

H2S+NH3.H2O NH4HS+H2O (1)

H2S+2NH3.H2O (NH4)2S+2H2O (2)

CO2+NH3.H2O NH4HCO3(3)

NH4HCO3+NH3.H2O (NH4)2CO3+H2O (4)

NH4HS+NH4HCO3(x-1) + S (NH4)2SX+CO2+H2O (5)

NH4HS+ NH3.H2O + S (NH (x-1)4)2SX+ H2O (6)

2 NH4HS + (NH4)2CO32 + 2 (NH (x-1) S4)2SX+CO2+H2O (7)

(NH4)2S(x-1)(NH + S4)2SX(8)

NH4HS + O2S+NH3.H2O (9)

(NH4)2S + O2+H2O S+2NH3.H2O (10)

(NH4)2SX+ O2+H2O SX+2NH3.H2O (11)

Can be seen, NH of producer gas3In the gas wet desulfurization, instead of soda as desulfurization absorbent, thus saving the cost of desulfurization. The two section of the Shanxi Datong furnace of an enterprise under section gas NH3The content is 597mg/Nm3The upper gas, NH3The content is 619mg/Nm3H, mixed gas2The content of S is 600-700 mg/Nm3In addition, without adding soda ash, using only NH in gas3As the absorbent, desulfurization liquid was about 5.7, the desulfurization efficiency can reach 99%, the literature[8]The practice has proved, even if the ammonia and sulfur in coal gas is only 0.71, 4-5g/l liquid circulation desulfurization, the desulfurization efficiency can reach 99%.

The gas in NH3The content is affected by many factors, the literature[2,4]Pointed out that the coal gasification of coal rank and inertinite content and other factors directly affect the coal pyrolysis process NH3The generation, NH3The release amount decreases with the increase of coal rank, coal inertinite content higher, pyrolysis NH3More, in addition the coal nitrogen content and nitrogen element in coal are, but also directly affect the gas in NH3The generation of. If the gas in NH3The content is less, the soda ash desulfurization absorbent gas desulfurization, but the gas in NH3The existence, is conducive to maintaining the alkalinity of circulating desulfurization corresponding liquid, can also play a role in saving the cost of desulfurization.

4Conclusion

(1) gas in NH3The forming process is relatively complex, coal pyrolysis temperature, gasification temperature, coal gasification, coal rank and the nitrogen content of inertinite content and other factors directly affect the gasifier NH3Generation.

(2) the same kind of coal gasification furnace, due to a dry layer and dry layer is thinner, the coal into the furnace after high temperature carbonization, the pyrolysis of NH3A large amount of NH,3The content of gas, a furnace is greater than two and the carbonization furnace gas furnace.

(3) NH in gas3With CO2The reaction of NH and gas washing water4HCO3, NH4HCO3Is to bring some security risks of phenol water evaporation system, the need to take effective measures, eliminate the hazards and safety hazards from the source.

(4) NH of producer gas3In the gas wet desulfurization, can partially or completely replace the soda ash as the desulfurization absorbent, thus saving the cost of desulfurization.

Reference:

[1] Guo Shucai, coal chemical technology (M), Beijing: Chemical Industry Press, 2006 July

[2] Zhao Wei; Chang Liping; Feng Zhihua (J), on the formation of nitride during coal pyrolysis, Journal of fuel chemistry, 2002, 30 (5): 408-411

[3] Zhao Wei; Feng Jie; Chang Liping (J), on the generation of nitrides during coal gasification, Journal of fuel chemistry, 2002, 30 (6): 519-522

[4] Wu Yangfang; Jing Xiaoxia; Sun Hong, coal and atmosphere on coal pyrolysis in NH3And the impact of HCN on the release of J (2008), Shanxi chemical industry, 28, (1): 18-20

[5] Dong Jianxun; Zhang Yue; Zhang Yun, using ammonia as absorbent in flue gas CO2The experimental study (J), power engineering, 2007, 27 (3): 438-450

[6] Zhang Mou; Chen Hanping; He Qiao, ammonia absorption of CO in flue gas2The experimental study (J), energy and environment, 2007, 4:81-83

[7] Tang Qizheng, the production of waste ammonia ammonium bicarbonate fertilizer (J), the use of lime kiln carbon dioxide and coking plant, environmental engineering, 1991, 9 (6): 35-37

[8] Zhong Jinming; Dong Tianhe; Du Zhanwen, HPF ammonia desulfurization of coke oven gas technology development (J), fuel and chemical industry, 1997, 28 (3): 152-156