Table of Content
- LPG Usage Areas and Features
- LPG Storage Tanks And Tank Accessories
- Typical Spherical LPG Tank Operations
- Over Pressure Protection İn LPG Tanks
- Firefighting Tactics and Leak Prevent
- January 4, 1966, Feyzin Refinery Bleve
LPG Usage Areas and Features
Developing technology and rising living standards have made energy one of our most important needs. In this context, Liquid Petroleum Gas (LPG), one of the important energy sources, has been among our most basic needs in today's conditions. LPG, which in all areas of our lives, consumes both cylinder gas and autogas.
LPG consists of a mixture of butane and propane gases. LPG is produced by processing petroleum in refineries or from natural gas deposits. LPG in the gas phase under normal conditions. But it is stored under pressure and in the form of liquid.
LPG, which is liquefied for transportation and storage, is consumed in the gas phase. It has flammable and combustible properties. It is very slightly soluble in water. It is colorless and odorless. For this reason, it is odorization with mercaptans or sulfur compounds so that it can be detected in case of gas leakage. The presence of 2% to 9% in the air is a sufficient mixing ratio for the risk of explosion. For this reason, both storage and transfer should with strict safety codes and rules.
LPG Storage Tanks And Tank Accessories
In the filling facilities and terminals, LPG is stored in liquefied form under pressure in specially designed cylindrical and spherical tanks. LPG is stored in tanks in three ways propane, butane, or mix. Propane has the highest vapor pressure and propane storage tanks are designed to resistant higher pressures.
Read More, Storage and Handling Safety in LPG Plants
Typical Spherical LPG Tank Operations
A typical Spherical LPG tank can be built from 1000 m3 to 5000 m3 volume and has multiple nozzles and connection points. Of these, the most valve open-close operations are in the liquid, gas phase inlets and drain lines. For this reason, these areas critical zones for operational safety. Past disasters have shown us how important these areas and even drainage operations.
Over Pressure Protection İn LPG Tanks
Safety valves are used to protect the tank from explosion when the LPG tank's vapor pressure increases above the design pressure for any reason. The selection of safety valves should be made according to engineering calculations and API standards and should be tested by expert inspectors at least once every five years.
Safety valves are the silent guards of the tanks and are the most important safety equipment on the tank.
Firefighting Tactics and Leak Prevent
Leakage prevent system
There should be zero tolerance for leakage in LPG storage tanks. In this context, all inlet and outlet nozzles of the tanks should be equipped with remotely operable emergency shut-off valves in case of leaks. LPG leaks or other emergencies may happen in tanks or pipelines. Thanks to this emergency shut-off system, control of LPG spread out of the tank is prevented in case of emergency. It is recommended to test this emergency shut-off system with regular periods.
In addition, attention should be attention to zones where LPG can be collected in case of leakage, such as storm drains and sewers around LPG tanks.
Fire fighting Systems in LPG tanks
The most important active fire protection system in LPG tanks is the sprinkler system on the spherical LPG tank. All important details are written at NFPA 58 and API 2510&API2510A, For example, How many liters of water should be applied per square meter of the tank shells per minute, how much water reserve you should have for fire fighting, fire pump flow rates, etc. Firefighting systems should be designed in accordance with this standard, otherwise, you can not win this dangerous war.
Emergency action plan in LPG Tank fires; The first action to take in LPG tank fire time is to stop the source of the burning LPG, otherwise, it is not possible to extinguish LPG fires. In this type of fire, emergency shut-off valves play a most important role. If the source of the LPG leak in the fire is stopped and the LPG in the pipeline runs out, the fire will continue for some time but the fire will stop when the LPG runs out. In the meantime, if the fire zone is wetted with the water, unwanted scenarios may not occur. Because fire intensity will decrease as LPG and oxygen in the amount of air will decrease due to the evaporation of water. LPG fires can occur as jet fire, UVCE, and BLEVE. Of course, the worst of these three fires can be BLEVE. Terminals and facilities should plan the largest portion of the fire fighting plan with barriers that can prevent BLEVE.
Bleve
The phenomenon known as Boiling Liquid Expanding Vapor Explosion BLEVE is when the liquid in a tank reaches a temperature well above its boiling point, rupturing the tank it is in. If we talk about how it can happen, in fire conditions, and high-temperature exposure of the tank shell, the liquid LPG in the tank will heat up and increase the internal vapor pressure and the Tank shell temperature increase causes a decrease in the strength of the tank shell metal. High internal pressure and a decrease in the strength of the steel will cause a rupture in the tank for a short time.
At the end of all these scenarios, BLEVE will happen. In the event of fire, the events will develop as follows, first of all, the tank shell will heat up with the effect of the direct flames. The heat on the tank shell will be transferred to liquid LPG, since the pressure of LPG with increasing temperature will increase, when the pressure in the tank reaches the opening pressure of the safety valves, the safety valves will be opened and the vapor of LPG will be discharged to the atmosphere. Therefore, the pressure in the tank will decreasing again. The liquid in the tank will evaporate quickly again because fire is continue and then the safety valve will open again. In this cycle, the vaporized LPG will cool the tank shell and inside tank, but if you can not stop the transfer of heat to tank shell will increase the internal pressure of the tank again, You can stop heat transfer to tank with two ways, first one fire should extinguish or you should cooling the tank shell with enough water. When the level of liquid that can cooling the tank by evaporation decreases or run out, The flames will heat the dry portion(parts above the liquid level) inside the tank very quickly, and the rupture in the tank shell and will result in BLEVE. The first way to prevent BLEVE in the event of a fire should be to cut off the LPG source of the burning fire. During this period, the burning tank and adjacent tanks should be cooled with enough water. This cooling will gain time to prevent BLEVE and fight fire.
The steel strength of the tank cooling with water will not decrease and will prevent the increase in the pressure inside the tank. Also, the main rule that should not be forgotten is the fire fighting with water in amount accordance with the standards for each square meter of the tank surface and enough cooling. Especially cooling the areas on the tank shell that are not in contact with liquid LPG is very important.
At the time of the fire, the liquid level in the tank should be known and monitored. Since the liquid LPG will evaporate rapidly when the safety valves are opened, the liquid level will appear as a thin line on the tank shell, it will not be difficult to see the level in the tank in daylight conditions. However, in night conditions or when there is a lot of smoke, it will not be possible to see the level in the tank from the outside. For this reason, firefighting will be more difficult. In cases where the tank surface is not sufficiently water-cooled, the time for BLEVE is running out.
Knowing this situation, you should fight the fire.
The method of injecting water
When a leak occurs in the tank, especially in the nozzle flange gasket, weld seam, or valve body, the LPG leak cannot be stopped by emergency shut-off valves. In such cases, it will be necessary to flood the tank. When water is injected into the tank, since water will down to the bottom of the tank due to the density difference, and the LPG will be displaced upwards. With this operation, the LPG leak will be replaced by a water leak. Thus, the LPG leak will be replaced by a water leak. LPG leakage will end. While designing such a system, should be attention, the water pressure should be higher than the vapor pressure of the LPG inside the tank. Also, a check valve should definitely be used in the water injection lines. Otherwise, LPG can flow to the water line and the situation may become more dangerous.
As a result, with this method, LPG leakage can be prevented and stopped when water is injected into the tank. It is one of the most basic barriers that can prevent BLEVE.
January 4, 1966, Feyzin Refinery Bleve
What went wrong?
During the 6 AM to 2 PM shift at the refinery, operators were required to take a routine sample and dreyn from each of the LPG storage tanks. The operator, due to the fact that he had only a single valve spanner, opened the valves in the incorrect order. This caused the release of a small amount of water and a small amount of LPG when he opened the lower valve. This prompted the operator to close the valve and then reopen it, leading to only a few drops emerging. The upper valve was then opened fully. This led to a very powerful jet of LPG to rush out. This release splashed up from the drain and gave frost burns to the operator on the face and forearm. As he recoiled from the flow, the operator partly pulled off the valve handle. The other operator, losing sight of the first operator, turned on the water supply to the sprays fitted to the sphere and, with the operator, attempted to reposition the valve handle and shut the valve.
They failed to do so. In addition, there was no remote operable emergency shut-off valve in the LPG drainage line, and there was no excessive flow valve on the line. As a result, a big fire started. The LPG fire continued because they could not cut the source of the LPG leak. One more mistake was added to these mistakes and they did not cool with water the burning tank because they believed that the safety valve alone could protect the tank and only needed to cool with water the neighboring tanks. However, a BLEVE occurred in the first tank caused by fire. Not long after, the other five tanks exploded. As a result of this disaster, 18 people died, 81 people were injured and 5 spherical LPG tanks exploded. The possibility of such disasters should be discussed with risk assessment at the installation stage the design of the tanks should be done correctly and the operation instructions should be explained to the operators with routine training. Past accidents are a very good guide to future safe days.
Accident Causes And Suggestions
This accident has shown us that drainage operations should be provided with correct procedures and good designs.
I find the most fundamental deficiency in this regard in valve selection. It is recommended to use a deadman valve in this type of sampling and drainage operations. Also, interlocking systems that will prevent the opening of both valves at the same time will also be an important barrier in preventing such accidents. Last, remotely controllable emergency shut-off valves should be at all inlet and outlet connections of the tanks, including dreyn line.
Reference
API Natural Gas Liquids and Liquefied Petroleum Gas Emergency Response Guide
RT 1 – Risque industriel » Mémento du maire et des élus locaux (mementodumaire.net)
API 2510 A
