Fire hazard analysis of distillation units

According to the operating pressure, can be divided into atmospheric distillation, vacuum distillation (for high boiling point, difficult to volatilize or high temperature distillation can cause decomposition, explosion, polymerization and other heat sensitive substances mixture, decompression can reduce the boiling point of materials, thereby reducing the distillation temperature, increase safety, such as nitrotoluene decomposition explosion at high temperature, styrene easy to polymerize at high temperature; also can be used for highly toxic materials distillation to prevent leakage into the air), pressurized distillation (for atmospheric pressure gas system).

1. Method of distillation

(1) According to the continuity of production, it can be divided into continuous distillation and intermittent distillation.

(2) According to the operation mode, it can be divided into no reflux and reflux distillation; among them, no reflux is divided into simple distillation and equilibrium distillation, and reflux distillation is called distillation; distillation can be divided into general distillation and azeotropic distillation, extractive distillation, steam distillation and so on.

2. Composition of distillation

A complete distillation system is generally composed of a distillation tower, reboiler, condensing cooler, reflux tube, material pump, product storage tank, etc., or maybe a combination of two or more of them. Simple distillation system is usually composed of a distillation kettle and its heating device, condensing cooler and receiving tank. The heating device of kettle distillation has the jacket type outside the kettle, the inner coil type of the kettle, and some materials also adopt the direct fire heating type or electric heating type outside the kettle.

3. Brief process flow

Take the atmospheric and vacuum equipment in petroleum refining as an example to carry on the risk analysis. According to the characteristics of the production process, The technology uses atmospheric and vacuum distillation, The fractionator has two side lines, The first line (about 157℃) is distilled and heated to 90℃ by pump and feedstock, Combined with the second line, cooled to 45℃, As a fuel oil 2^#(heavy diesel) outlet device; The second line (about 259℃) was distilled and heat transferred to 94℃ by pump and feedstock, Combined with the front line, cooled to 45℃, As a fuel oil 2^#(heavy diesel) outlet device. stripping tower (I): stripping tray 10 layers, operating temperature 175℃, Operating pressure 0.1 MPa; stripping tower (II):6-layer stripping tray, Operating temperature 260℃, Operating pressure 0.1 MPa.

4. Analysis of the fire and explosion hazard of atmospheric and vacuum distillation units

• materials and products are fire and explosion hazards

 Most of the raw materials, intermediates and products in the process of atmospheric and vacuum distillation of petroleum refining belong to fire dangerous goods, in which crude oil and light oil are flammable, explosive, easy to evaporate, and have flammable gas, which will explode when the source of fire occurs.

• danger of electric desalination dehydration

 In the process of electric desalination and dehydration, there is high temperature hot oil, electric device with high voltage electric field, if the desalination tank is not filled with raw oil or air, start high voltage power supply; Or high-voltage electrical insulation or high electric field strength insulation breakdown, will lead to fire and explosion.

 The overpressure of the electric desalination dehydration tank and the untimely unloading of the safety valve lead to the leakage of the pipeline and flange connection of the desalination dehydration tank, the loss of the raw material oil, and the fire and explosion accident caused by the ignition source.

 The crude oil is operated in the electric desalination tank with a temperature of 130~145℃ and a pressure of 0.9~1.2 MPa. In addition, the runaway interface in the tank can easily cause oil with water or water with oil, bring fluctuations to production and threaten safety. The composition of crude oil is complex. If the water content of the inlet device is too large, it is easy to cause dehydration of the electric desalination tank, and a large amount of water enters the heat transfer system and tower, which can cause overpressure oil leakage of the equipment and take off the safety valve of the atmospheric pressure tower when it is serious.

• Fire hazard in distilled parts

operation temperature of the system is high, the high temperature is above 400℃, the medium is flammable and explosive. If the equipment failure or aging, or human factors such as illegal operation, misoperation caused by leakage, open fire or high heat fire and explosion risk. In addition, the cold exchange equipment in the device has a pressure difference between the tube side and the shell side. Once the phenomenon of high pressure channeling and low pressure occurs, the low pressure part will crack, resulting in material leakage, thus causing fire and explosion accidents.

In the process of distillation, because of the boiling state, the system always presents a gas-liquid coexistence state. If the material leaks out or inhales air because of equipment rupture or operation error, or because of condensation and insufficient cooling, a large amount of steam escapes through the storage tank and other parts, explosive gas mixture can be formed.

Due to the increase of sulfur content, the properties of feedstock oil change, the ammonia injection is not changed at the top of fractionator, and the corrosion phenomenon in the top oil and gas line, top circulation line and cold exchange system HCI-H₂S-H₂O fractionator increases to varying degrees, speeding up the corrosion of equipment and causing leakage accident due to corrosion, thus causing fire and explosion accident.

• readily form explosive gas mixtures

In the process of distillation, because of the boiling state, the gas-liquid coexistence state is always present in the system. If the material leaks out or inhales air due to equipment rupture or operation error, or because of condensation and insufficient cooling, a large amount of steam escapes through the storage tank and other parts, explosive gas mixture can be formed, and explosion combustion in or out of the container will occur in the ignition source. For example, before the shutdown and maintenance of a refinery decompression tower, due to the elimination of too fast vacuum, the oil and gas in the tower is very thick, the temperature is very high, the air is inhaled by the emptying valve in large quantities, resulting in an explosion accident, and the 10-story tray in the tower is blown off.

• prone to spontaneous combustion

The spontaneous combustion point of crude oil and petroleum distillate is low, such as 255~390℃ of gasoline ,350 380℃ of diesel oil and 350℃ of crude oil, while the temperature of oil in distillation unit is between 220 and 395℃.

• Complex and dangerous distillation process

Distillation operation is a complex process. There are many auxiliary equipments in distillation column, such as feed pump, heated reboiler, gas condensate cooler, reflux tube and receiving tank, side line discharge (including multiple side line discharge), top discharge, bottom discharge system, etc. For example, the distillation control temperature is too high, it is easy to appear the danger of overpressure explosion, blanking, overheating decomposition and spontaneous combustion, and even make the operation out of control and cause explosion; if the temperature is too low, there is the danger of flooding tower. For tower distillation, the amount of gasification can be increased, and uncondensed steam can enter the receiving tank, resulting in an overpressure explosion of the tank. The increase of reflux in operation will not only reduce the operating temperature in the system, but also lead to flooding towers and be out of control. The outlet pipe of distillation equipment is condensed and blocked, which will cause the pressure in the equipment to rise and explode in fire. In high temperature distillation equipment, if cold water or other low boiling point substances enter, a large amount of gasification will occur in an instant, and an explosion fire will occur due to the sudden rise of internal pressure.

• Heating systems are dangerous

The raw material should be heated to 400℃ by heating furnace before entering the decompression tower, and the furnace temperature can reach more than 700℃. If the operation of the heating furnace is improper, the flow rate of the feedstock oil in the furnace tube is too low, the residence time is too long or the temperature is too high, it will crack and coking in the furnace tube, make the furnace tube blocked and the heat conduction poor cause local overheating, lead to the leakage of the material in the furnace tube and cause the fire and explosion accident. Improper selection of furnace tube materials and serious wear and corrosion may lead to perforation, rupture or leakage of furnace tube, resulting in leakage of material in furnace tube and fire and explosion accident.

The valve, flange, gasket and so on on the outlet line of the furnace pipe cannot appear the problem, otherwise once the leakage may occur the fire. Furnace fuel can not leak, if gas leakage to the outside and air mixed to form explosive gas, heating furnace with open fire will occur deflagration. If the furnace flamenze occurs, attention should be paid to steaming the residual gas to avoid a furnace explosion.

In the starting stage of the device, the oven should be carried out to remove moisture and inspect the equipment. If the ignition temperature is not strictly operated in accordance with the rules and heating curves, it will be easy to occur equipment accidents and explosion accidents.

• equipment, pipelines vulnerable

Equipment, pipeline and so on in the long time repeated pressure and material high-speed flow, friction process, metal shell materials are prone to metal fatigue. Operation under high temperature conditions causes temperature difference stress failure and high temperature creep rupture. Tall towers and pipes are vulnerable to deformation cracks caused by additional stress such as vibration, wind, foundation sinking and external loads. Acidic in the treatment of crude oil with high sulfur content in corrosive media such as petroleum distillation

Sulfur compounds, with strong corrosion, in the pressure relief tower bottom pump outlet high temperature pipeline, atmospheric pressure tower top oil and gas volatile line, air cooler gas, liquid phase change and other parts, prone to corrosion perforation, wall thickness thinning, and then lose bearing capacity or leakage, resulting in fire.

• ignition source in the process

In order to meet the distillation requirement of oil, the temperature of the furnace chamber is very high, and the furnace is easy to become the ignition source of combustible material. Atmospheric distillation unit uses more electricity, there are distribution rooms, a large number of motors, wires, switches, control instruments, among which there is no explosion-proof or can not meet the requirements of explosion-proof grade, the generation of electric sparks or short circuit may form a source of ignition.

The high speed flow of oil in the pipeline will produce static electricity and easily accumulate, the highest electrostatic voltage can reach more than ten thousand volts, if the static electricity can not be removed in time, it may discharge to produce electric spark. During thunderstorms, if combustible gas is discharged from the top of the distillation tower, it may cause a lightning strike to catch fire. Before the equipment pipeline overhaul, the system does not carry on the thorough replacement, the cleaning, before the gas analysis qualified, carries on the fire, the overhaul operation, has the fire explosion danger.

5. Technical Measures for Fire Protection and Explosion Protection

• prevent the formation of explosive mixtures

When the electric desalination dehydrator starts, the air in the tank should be drained, and then the high voltage should be connected after filling the oil, so as to avoid the explosion of the mixture of oil and gas in the tank caused by the electric spark. High voltage electrical appliances should be regularly checked, maintenance: found poor insulation or high electric field strength should stop using, to prevent the production of electric sparks.

The distillation system should strictly carry out air tightness and wind resistance inspections to ensure its airtight. When the vacuum distillation is in normal production, the flanges and emptying valves connected with the tower should be tight to prevent the formation of explosive gas in the air suction tower. After distillation, we should pay attention to the correct elimination of vacuum. When the temperature in the tower is cooled below 200℃, the vacuum in the tower can be eliminated slowly.

• operate in strict accordance with regulations

In distillation operation, not only the operating parameters such as temperature, pressure, feed quantity, reflux and so on are strictly controlled, but also the mutual restriction and mutual influence between them should be paid attention to. Automatic control systems and safety instrument systems should be used as much as possible to reduce human errors.

When steam is heated, the opening degree of the control valve should be suitable to prevent the material from evaporating sharply, and a large amount of steam cannot be discharged to increase the pressure and cause the equipment to burst. In operation, we should always pay attention to keep the distillation system unobstructed, prevent the pipe from clogging, pressure rise, and cause danger. To avoid the low boiling and water entering the high temperature distillation system, the condensed water in the tower and its auxiliary equipment must be released before the high temperature distillation system starts, so as to prevent the sudden contact with the high temperature material from vaporizing and pressurizing and causing the spray or explosion.

• Anti-corrosion Measures

Distillation equipment and pipes should meet the requirements of safe production in material and design. Reasonable flow rate and necessary corrosion margin can be used to avoid 90℃ of quick turning elbows on the oil transfer line, select suitable corrosion resistant materials, coatings and wear-resistant liners, adopt anode protection and cathodic protection, and take process anticorrosion measures, such as sulfur containing materials to be treated before entering distillation equipment, use neutralizer and corrosion inhibitor, etc.

• Inspection and maintenance of reinforcing devices

It is found that the equipment breakage should be repaired in time, the instruments, instruments, equipment containers, pipelines and so on should be replaced regularly, and the equipment running with disease, overdue service and overload operation should be resolutely eliminated.

Heating furnaces must be strengthened maintenance, each overhaul must measure the thickness of the pipe wall, cleaning furnace coke removal. If the furnace is old and the pipe is denuded seriously, it should be updated.

• Installation of safety devices and fire fighting facilities

Desalination dehydration tank should be installed blackout, stop pump, oil leakage alarm device, and pay attention to check its use.

Distillation equipment should have a complete temperature, pressure, and flow meter device. Vacuum distillation pumps should be equipped with a one-way valve to prevent the sudden stop of air into the equipment. Pressure distillation equipment should be provided with a safe discharge device. Heating furnaces should be equipped with explosion doors, so that explosions can be a timely pressure relief. The system should be equipped with emergency emptying pipes and other safety devices to ensure the rapid discharge of materials in the reactor and prevent explosion accidents. The exhaust pipe of the system shall be connected to the torch system, and the fire arrester shall be installed on the pipe.

The electrical equipment of the atmospheric and vacuum distillation unit must be explosion-proof and well grounded. Fixed flammable gas leakage monitoring alarm should be installed in the installation area and tank area to detect oil and gas leakage in time.

The heating furnace, distillation tower and stripping tower should be equipped with steam fire extinguishing facilities, and the foam fire extinguishing system should be installed in the device. The control valve should be located in a convenient place to ensure that the device can quickly and timely control its spread and expansion once the fire occurs.

• Strengthening Fire and Explosion-proof Safety Management

There are more pressure vessels in the pretreatment device, and there is the danger of overpressure explosions. When the pressure vessel overpressure ruptures, the energy released by the expansion of gas or high temperature material causes the vessel to crack further and causes the vessel debris to fly around at a higher speed, resulting in casualties or property losses. At the same time, flammable and explosive materials or high temperature materials leaking from container explosions will cause fire and explosion in case of ignition source.

Formulate sound rules and regulations for fire safety production, responsibility system, electricity and fire use system, and effective and perfect emergency handling rules, establish and formulate strong fire safety supervision, inspection and inspection, system, timely detection of hidden dangers of accidents, control unsafe factors.

Distillation, if the equipment failure or aging, or human factors such as illegal operation, misoperation caused by leakage, open fire or high heat fire and explosion risk. In serious cases, explosive gas mixture can be formed if the material leaks out or inhales air due to equipment rupture or operation error, or if a large amount of steam escapes through the storage tank due to insufficient condensation and cooling, and explosion combustion in or out of the container will occur in case of ignition source. Therefore, distillation of the selected equipment is due to careful consideration.

Shenzhen CESP Co.,Ltd. focus on the field of special industrial lighting is a design, development, production and sales of high-tech enterprises, complete management team for the domestic power, metallurgy, railway, large industrial and mining enterprises, marine ships and other lighting areas to provide professional lighting solutions, but also for international well-known enterprises to provide advanced technical support and product supporting services.

CES-EX-SF is an increased safety and dustproof explosion-proof lamp, Has ATEX IECEX Certification standards, Is a low installation height of indoor lighting waterproof grade IP66 explosion-proof lamps. During use, the maximum temperature of this explosion-proof lamp is about T80℃, It does not cause explosions or ignition of other equipment. Which he can use in a general environment of -20 C ~40 C, The shell is a flame retardant, f1- UV resistant PC shell, Can withstand four J of shock, Very suitable for distillation environment. His luminous angle is about 100, Is a light efficiency in 120~140 lm/W of high-quality lamps, With a variety of shell shapes, Such as rectangle, square, oval, etc, If you need it, You can contact us for further consultation, Or you have an explosion - proof lighting problem, You can also contact to provide you with a solution.