In February 2019, the ship “X” was in distress in a certain sea area in Zhejiang. The captain of the ship suffered severe skin burns due to the explosion of the battery on board and urgently needed rescue. After receiving the report, although the maritime department sent the wounded to the hospital in time, the consequences of the severe burns have been irreparable.
Although the battery is small, its function and power are not general. Improper daily maintenance of the battery often lays a safety hazard for the occurrence of accidents. The battery we need to understand should not be as simple as a regular voltage test. Today I will take you Understand more aspects of marine lead-acid batteries, hoping to arouse the attention of more crew friends to the safe use of batteries.
1. Battery reaction mechanism
At present, the commonly used marine batteries are mainly lead-acid batteries. Lead-acid batteries are generally composed of positive and negative plates, separators, shells, electrolyte, and terminal posts. The chemical reaction of their discharge is based on the active material of the positive plate. (Lead dioxide) and the negative plate active material (sponge pure lead) are carried out under the action of the electrolyte (dilute sulfuric acid solution). During discharge, the positive plate changes from lead dioxide to lead sulfate, and the negative plate also changes from lead to lead. When charging lead sulfate, the lead sulfate on the positive plate is reduced to lead dioxide, and the lead sulfate on the negative plate is reduced to pure lead.
During the charging process, especially at the end of charging, there will be some incidental reactions in the above-mentioned reaction process, that is, the electrolysis water reaction and the evaporation of water caused by the increase in the temperature of the electrolyte. These reactions create conditions for the explosion of the battery.
Second, the main purpose of marine batteries
1. Backup power supply for radio equipment.
2. Power supply for low-voltage equipment: such as power supply for emergency lighting, alarm and signal device lights.
3. Power supply for starting the engine.
Depending on the purpose of the battery, the layout of the battery on board will be different.
1. The first type battery is mainly placed in the battery cabinet on the compass deck or in the small battery room on the driving deck. This arrangement not only satisfies the principle of being far away from living spaces but also convenient for personnel to approach, it is conducive to the maintenance of the crew, and it is closer to the electrical equipment to prevent voltage loss.
2. The second type of battery is usually a ship that is not equipped with an emergency generator, but uses a battery as an emergency power source, or is equipped with an emergency generator but does not meet the requirements to automatically start and automatically connect to the emergency switchboard when the main power fails When the requirements are met, the storage battery is used as a temporary emergency power source. Therefore, it should meet the requirements of emergency power supply and temporary emergency power supply in SOLAS and the “Rules for the Classification and Construction of Sea-going Steel Ships”, that is, it should be arranged on the highest continuous deck and should be easily accessible from the open deck, except for special circumstances. It shall not be placed in front of the collision bulkhead unless approved by the competent authority. Therefore, such batteries are usually arranged in the battery compartment on the boat deck.
3. According to the requirements of SOLAS and “Rules for the Classification and Construction of Sea-going Steel Ships” for the third type of storage battery, the starting storage battery should be arranged in a cabinet near the engine, and good ventilation should be maintained in all areas.
Third, the maintenance of the battery
1. Keep the battery room well ventilated. The cabins or cabinets where the batteries are placed on the ship are usually not very large, which will not only cause insufficient ventilation and increase in ambient temperature, resulting in a decrease in the capacity of the battery and a shortened life span; it also creates conditions for the accumulation of flammable and explosive gases. .
2. Keep the battery clean and dry. Due to the shaking and vibration of the ship during the voyage, the electrolyte in the battery may overflow, leading to corrosion or short circuit of the battery pole. Corrosion can increase the resistance of the pole joints, causing the battery to produce a larger voltage drop here, thereby affecting the normal operation of electrical equipment. In severe cases, the pole will be broken and the battery will be damaged. A short circuit will cause the battery to discharge itself and the active material of the electrode plate will fall off, thereby affecting its service life. Therefore, the battery must be kept clean, dry, and well ventilated to prevent damage.
3. Regularly measure the voltage, electrolyte height and specific gravity, and make a record. If it is lower than the specified value, add distilled water and charge it in time. Infrequently used batteries should be checked at least once a month and supplemented according to actual conditions.
1. Human protection. Wear protective glasses and acid-proof clothes. When the skin comes into contact with the electrolyte sulfuric acid, immediately rinse the skin surface with plenty of water and remove the contaminated clothes; when the eyes come into contact with sulfuric acid, immediately rinse with clean water for at least 10 minutes . See a doctor if necessary.
2. Smoke and fire are strictly prohibited in the battery room. Combustible gas may accumulate in the battery room due to battery charging. When there is a problem with ventilation, an open flame may cause an explosion.
Fourth, analysis of the cause of battery explosion
There are three main reasons for the explosion of the battery during the charging process.
1. Excessive internal pressure of the battery causes the battery shell to explode. At the end of battery charging, due to overcharging, water will decompose into hydrogen and oxygen, short circuit, severe sulfide, and rapid rise in electrolyte temperature during charging, which will also cause a large amount of water to evaporate. If there is too much time to overflow, the internal pressure of the battery will rise very high, causing the battery tank to deform first. When the internal pressure reaches a certain pressure, it will burst from the junction of the battery tank cover or other weak points. This is a physical process.
2. The battery exploded when hydrogen is exposed to an open flame. The explosion limit of the mixed gas of H2 and O2 is that H2 accounts for 4%-96% of the volume of the mixed gas, and the explosion limit of the mixed gas of H2 and air is 4%-74% of the volume of the mixed gas. If 80% of the overcharge is used to electrolyze water, and the H2 content inside the battery is within the explosive range or the hydrogen content in the air accumulates to the explosive limit, it will explode when it encounters an open flame. This is a chemical reaction.
3. The third type is because the battery vent is blocked, the battery bursts first, and the burst causes the battery to vibrate, and the pole wiring is not strong enough to produce sparks, which detonates the combustible gas and causes an explosion. This is a process of physics first and then chemistry, a chain reaction of the first two explosions.
1. Fireworks are strictly prohibited. Operators working in the battery charging area should wear anti-static overalls and install a human body static elimination device to prevent static sparks. Smoking is prohibited in the area, non-flammable metal tools should be used during work, and collisions should be avoided during the lifting of the battery.
2. Avoid overcharging and produce flammable and explosive gas. The battery charging device should be checked regularly to prevent malfunctions, and it is strictly forbidden to overcharge the battery.
3. Regularly check the battery vent holes to ensure that the battery vent holes are unobstructed. The accumulator should be able to discharge the hydrogen and water vapor produced in it in time. Regularly check the mechanical exhaust device to ensure gas flow in the area to prevent hydrogen accumulation.
Lead-acid batteries have been widely used in industry due to their mature technology, low price, and convenient use. Not only on ships, but also in life, they can be exposed to large and small batteries. Do not ignore them. I hope this article will let you More people know more about batteries to prevent accidents.