Liquid ammonia storage tank

Liquid ammonia is listed as a hazardous chemical due to its flammable, explosive, and toxic properties. According to Identification of Major hazard for Hazardous Chemicals (GB18218-2009), critical ammonia storage capacity of more than 10 tons constitutes a major hazard. All liquid ammonia storage tanks belong to Class III pressure vessels. We will analyze the hazardous characteristics and hazards during the production and operation of liquid ammonia storage tanks, and propose some preventive and emergency measures to avoid accidents.

Hazard analysis of the operation process of liquid ammonia storage tanks

Hazardous characteristics of ammonia

Ammonia is a colorless and transparent gas with a pungent odor, which is prone to liquid transformation into liquid ammonia. Ammonia is lighter than air and highly soluble in water. Due to the easy volatilization of liquid ammonia into ammonia gas, when ammonia gas is mixed with air in a certain proportion, it can encounter open flame energy, with a range of 15-27%. The allowable concentration in the workshop ambient air is 30mg/m3. Leakage of ammonia gas can lead to poisoning, irritation to the eyes, lung mucosa, or skin, and a risk of chemical cold burns.

Hazard analysis of production and operation process

1. Ammonia level control

If the ammonia release speed is too fast, the liquid level operation control is too low, or other instrument and control failures occur, it can cause high-pressure synthetic gas to enter the liquid ammonia storage tank, causing overpressure in the tank and a large amount of ammonia leakage, posing great harm. The control of ammonia level is crucial.

2. Storage capacity

The storage capacity of the liquid ammonia storage tank exceeds 85% of the tank volume, and the pressure exceeds the control index range or is not strictly operated according to the procedures and steps specified in the operating regulations during the liquid ammonia tank pouring operation, which may result in overpressure leakage accidents.

3. Liquid ammonia filling

Failure to overfill liquid ammonia according to regulations or bursting of the filling pipeline can lead to leakage and poisoning accidents.

Hazard analysis of equipment and facilities

1. When the design, testing, and maintenance of liquid ammonia storage tanks are missing or inadequate, and there are defects or hidden dangers in safety accessories such as level gauges, pressure gauges, and safety valves, it may lead to tank leakage accidents.

2. In summer or during high temperatures, failure to install protective facilities such as sunshades and fixed cooling spray water for liquid ammonia storage tanks as required can cause overpressure and leakage of the tanks.

3. Damage or failure of lightning protection, anti-static facilities or grounding may cause electric shock to the storage tank.

4. The failure of production process alarms, interlocks, emergency pressure relief, and flammable and toxic gas alarm devices can lead to overpressure leakage accidents or expansion of accidents in storage tanks.

Accident prevention measures

Preventive measures for production process operation

1. Strictly follow the operating procedures

Pay attention to the ammonia release operation in the synthesis position, control the cold delivery and ammonia separation liquid levels, maintain a stable liquid level control within the range of 1/3 to 2/3 indicators, and prevent the liquid level from being too low or too high.

2. Strictly control the pressure of liquid ammonia storage tanks

The storage capacity of liquid ammonia shall not exceed 85% of the storage tank volume. During normal production, the liquid ammonia storage tank should be controlled at a lower liquid level, generally within 30% of the safe filling capacity, to avoid the danger of overpressure in the storage tank caused by the expansion and pressure rise of ammonia due to environmental temperature rise during the storage process.

3. Precautions for liquid ammonia filling

Ammonia loading personnel should undergo professional safety education and training before taking up their positions. They should be familiar with the performance, characteristics, operation methods, accessory structure, working principle, hazardous characteristics of liquid ammonia, and emergency response measures of the loaded container.

Before filling, it is necessary to verify the validity of the tank physical examination verification, tank car use certificate, driver's license, escort certificate, and transportation permit. The safety accessories should be complete, sensitive, and pass the inspection; The pressure inside the tank car before filling shall not be less than 0.05 MPa; The integrity of the ammonia loading connection pipeline should be inspected.

Ammonia loading personnel should strictly follow the operating procedures for liquid ammonia storage tanks, and pay attention to not exceeding 85% of the storage tank volume when filling.

Ammonia loading personnel must wear gas mask and protective gloves for operation; Fire and gas prevention equipment should be equipped on site; During the filling period, it is not allowed to leave the site and strengthen the inspection of the tank car pressure, whether there is any leakage from the pipeline flange, etc. The tank car gas should be recycled to the system and not discharged arbitrarily. If there is any abnormal situation such as leakage, the filling should be stopped immediately and effective measures should be taken to prevent sudden accidents.

Daily inspections should be conducted on ammonia loading facilities, measures, and procedures, and records of inspections and filling should be kept.