Synthetic ammonia production safety technology

Ammonia (NH3) is a strong irritating gas with a special odor. The relative density is 0.5971 (air = 1), flammable, and the self-ignition point is 65112. It can form an explosive mixture with air (explosion limit of 15.7%~ 27.4%). Ammonia gas can be liquefied at room temperature (critical pressure 11.4 MPa, critical temperature 132.512), boiling point is -33.512, and freezing point is -77.712. The aqueous solution of ammonia is called ammonia and is alkaline.
The main use of ammonia is in the production of nitrogen fertilizer, but also in the production of nitric acid, soda ash, chemical fiber, plastics, rubber, medicine, dyes and explosive crystals. Liquid ammonia can be used as a refrigerant.


Production Process The raw materials used in the production of synthetic ammonia are solid fuel (coal), liquid fuel (petroleum or its products), gaseous fuel (natural gas, coke oven gas, refinery gas).

The production of synthetic ammonia is divided into three parts:

Gasification - the original (combustion) material passes through the air (oxygen) and steam, and is vaporized into water gas (half water gas). The crude feed gas is composed of hydrogen, nitrogen, carbon dioxide, carbon monoxide and a small amount of hydrogen sulfide, oxygen and dust. After being recovered by the waste heat boiler, it is stored in the gas cabinet;
Conversion purification - the raw material gas from the gas cabinet is removed by the electrostatic precipitator to the pressure of the air press, desulfurization (hydrogen sulfide removal), conversion (converting carbon monoxide to hydrogen and carbon dioxide), decarburization (absorption of carbon dioxide) Thereafter, the pressure is again pressurized into a copper washing tower (with copper acetate ammonia solution) and an alkali washing column (with a caustic soda solution) to further remove carbon monoxide and carbon dioxide in the raw material gas (the content is reduced to less than 3 parts per 100,000) to obtain pure hydrogen gas. Mixed with hydrogen;
Synthesis - The purified hydrogen-nitrogen mixed gas (H2: N2 = 3:1) is pressurized to 30 to 32 MPa by a compressor to enter a synthesis tower, and is synthesized into ammonia at a high temperature in the presence of an iron catalyst.
Production is carried out continuously under sealing, high pressure and high temperature.


Occupational hazard Ammonia production materials (flammable, explosive, toxic) and process conditions determine that it has great inherent risks. Accident statistics show that the most concentrated chemical and chemical system explosion poisoning accidents are synthetic ammonia production.
Explosion - Chemical explosions in the production of synthetic ammonia can be classified into three categories. First, high temperature and high pressure make the explosive limit of flammable gas widened. Once the gas material is peroxygen (also known as oxygen permeability), it is easy to explode in equipment and pipelines. Second, high temperature and high pressure gas materials will rapidly expand and air when leaking from equipment pipelines. Mixing to form an explosive mixture, encountering an open flame or causing a static spark caused by friction at a high velocity material and a crack (spray) port, causing fire and space explosion. Third, the rotating equipment such as a pneumatic machine operates at a high temperature to cause the lubricating oil to volatize and crack. The formation of carbon deposits in the pipeline can cause the charcoal to burn or explode.
High temperature and high pressure can accelerate the creep of the metal material of the equipment and change the metallographic structure. It will also aggravate the hydrogen corrosion and nitriding of the steel by hydrogen and nitrogen, which will aggravate the fatigue corrosion of the equipment and weaken its mechanical strength, causing physical explosion. A chemical explosion often followed by a physical explosion.
Poisoning - In the production of synthetic ammonia, large-scale accidental leakage of liquid ammonia will cause low-temperature cloud clusters to cause poisoning to a large number of people, and space explosion will occur in case of fire. The frequency and severity of poisoning of carbon monoxide and hydrogen sulfide are the highest in chemical production.
1. Carbon monoxide Carbon monoxide is a blood suffocating gas. When it enters the blood, it combines with hemoglobin to form carboxyhemoglobin, which reduces blood oxygen production capacity and causes tissue hypoxia. Acute carbon monoxide poisoning is an acute cerebral hypoxia disease caused by inhalation of more carbon monoxide, mainly based on the symptoms and signs of the central nervous system. The maximum allowable concentration of the carbon monoxide workshop in China's health standards is 30mg/m3.
2. Hydrogen Sulfide Hydrogen sulfide is a strong neurotoxic substance that has a strong stimulating effect on the mucous membrane. Its systemic toxic effect is due to its inhibition of cytochrome oxidase, blocking of the biological oxidation process, resulting in tissue hypoxia (internal asphyxia). The maximum allowable concentration of hydrogen sulfide workshop in China's health standards is 10mg/m3.
3. The toxicity of ammonia is described in “Safety of Nitric Acid Production”.
Synthetic ammonia production also has occupational hazards such as noise and corrosive liquid burns.


Safety measures Synthetic ammonia enterprises are usually a major source of danger. Special measures should be taken in accordance with international conventions and relevant national regulations, such as safety inspections, safe operations, safety assessments, contingency plans and safety reporting systems, etc., to prevent large-scale liquid ammonia and carbon monoxide. The leak caused a social catastrophic accident.

1. Prevent chemical explosions (1) Prevent excessive oxygen (oxygen)
Whether using coal or heavy oil as a raw material, peroxygen is a key factor in causing chemical explosions in equipment pipelines. To control the oxygen content in the gas does not exceed 0.5%, when the oxygen content reaches 1%, it should be stopped immediately.
The main measure for controlling peroxidation when using coal to make gas is to separate the size of the coal before it enters the furnace, so that it burns evenly and completely without generating wind tunnels; when the furnace temperature is low, the air blowing time should be extended; The valve control is correct and sensitive, ensuring that the order of blowing the gas is correct; if the sequence of the blown gas is wrong or the steam is interrupted, the gas circulation cycle should be immediately transferred to the blown air venting stage, and the under-fired safety steam (also called the holding steam) should be turned on. Blow steam.
The main measures for controlling peroxidation when making gas with heavy oil are: the furnace temperature should be above 850 °C when feeding, the order of feeding is first steam, secondary oil, and post-oxygen; in operation, it is forbidden to bring water in the oil and strictly control the ratio of oxygen to oil. Between 8 and 0.9; an online oxygen content analysis alarm device must be installed (the alarm limit is set at or below 0.8% oxygen), and oil, oxygen, accident steam, system venting and oxygen venting must also be installed. The interlocking device is equipped with automatic over-current shutdown and automatically opens the venting interlock device to avoid over-oxygen explosion of downstream equipment (especially the washing tower);
(2) Strictly prevent material mutual enthalpy The use of coal gasification must prevent the gas from entering the blower system (usually when the blower suddenly stops and stops) to form an explosive mixture. The blower must be replaced before the start of the blower to prevent the blower and the air branch pipe and the main pipe from exploding.
When using heavy oil to make gas, if the oxygen compressor is stopped, the pressure of the oxygen pipeline will drop, and the high-temperature gas will fall into the oxygen pipeline and cause an explosion. Therefore, the oxygen pipeline should be equipped with a pressure alarm, a check valve and an automatic oxygenating device. In order to prevent the explosion of oxygen into the nitrogen system, a reliable non-return device should also be installed.
In the transformation and purification part: it is necessary to prevent the downstream gas (the hydrogen content has been greatly improved) from falling back to the upstream, so it is necessary to install necessary liquid seal, venting, and anti-reverse devices; strictly prevent desulfurization tower, decarbonization tower, copper washing tower, The caustic wash and the outlet gas are in the caustic wash tower, which can cause high-pressure machine liquid blows and even cause a vicious explosion. To this end, the gas flow rate should be carefully controlled, and the liquid level in the tower should be carefully controlled. At the same time, the liquid level meter should be sensitive and reliable, and the false liquid level should be prepared.
(3) Prevent the flammable gas material from leaking into the air and cause space explosion. The online flammable gas monitoring alarm should be installed at a reasonable point, and the leak should be detected in time to ensure the function of the liquid seal and the safety venting facility is normal.
2. Preventing physical explosions The key is to ensure the mechanical strength and sealing of equipment, pipelines (especially elbows, elbows) and joints. It must be inspected and repaired regularly. It is strictly forbidden to operate with illness. Physical explosion of storage tanks and gas cabinets will cause large-scale leakage, and large-scale (including outside the factory) should be banned from fire and evacuated.
3. Poisoning and noise control (1) The monitoring site for carbon monoxide, hydrogen sulfide and ammonia should be installed at the job site; enterprises with conditions should construct an accident ammonia absorption treatment system and set up a gas defense station. For locations where these gases may occur, monitoring must be performed, carrying portable gas detectors, and air or self-contained breathing apparatus.
(2) Noise reduction, sound insulation, noise reduction and other noise reduction measures shall be taken for the posts with excessive noise. The posts that are difficult to meet the standard shall provide protective equipment such as earmuffs, earplugs or ear protectors for the employees.
(3) The eye wash or water rinsing facility can be properly set up in the conversion and purification station.
4. Maintenance Safety During maintenance, the most concentrated time of explosion and poisoning accidents, in addition to careful security inspections, must strictly abide by the safety regulations for entering the tank into the tank, hot fire, and high-altitude operations. Unlicensed work is strictly prohibited.

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