Principles and technical requirements for fire and explosion protection

According to the principle of material burning, the basic principle of preventing fires and explosions during production is based on two essential conditions for the burning of substances. On the one hand, it is impossible to form a combustion system, prevent and limit the direct interaction between fire and explosion hazards, combustion aids and fire sources; on the other hand, eliminate all fire sources that can cause fire and prevent flames and explosions. Expansion.

(1) Control and eliminate fire sources

Burning fire, reaction heat, power supply, maintenance fire, mechanical friction heat, impacting Mars, and smoking fires are common causes of ignition and explosion of inflammable and explosive materials. Control the use of such fire sources, strictly enforce various rules and regulations, is very important for fire and explosion protection.

1, open fire

Open flame refers to heating fire, maintenance fire and other fire sources in the production process.

(1) Heating with fire

When heating a flammable body, avoid using an open flame and use steam or other heat carrier. If an open flame must be used, the equipment should be tightly closed and the combustion chamber should be constructed or isolated separately from the equipment. In order to prevent the leakage of flammable substances into the combustion chamber, the equipment shall be periodically tested for water pressure and air pressure.

The arrangement of open flame heating equipment in the installation shall be kept away from the storage area of ​​the process equipment that may leak flammable liquids and vapours, and shall be placed in the side wind direction or upwind direction of the equipment emitting flammable materials.

(2) Maintenance fire

Maintenance fires mainly refer to welding, torches, and fires. In workshops where there is a risk of fire and explosion, the welding and cutting operations should be avoided as much as possible, and the equipment or pipe sections that need to be repaired should be unloaded to a safe place for repair.

The place where the welding work is carried out must maintain a certain safe distance from the pipeline of the flammable and explosive production equipment.

When welding equipment and pipelines for transportation and containing flammable materials, the system should be thoroughly cleaned, purged and replaced with inert gas, and dynamically welded before passing the gas analysis.

The concentration of combustible gas should meet the following criteria:

The flammable gas or vapor with a lower explosion limit of more than 4% by volume should be less than 0.5%.

The combustible gas or vapor with a lower explosion limit of less than 4% should have a concentration of less than 0.2%.

When the system to be repaired is connected to other equipment, the connected pipes should be removed, disconnected or blocked by metal blinds to prevent flammable materials from entering the inspection system and burning or exploding during the fire.

The welding wire should be replaced or repaired in time. It is not possible to use the metal parts of the inflammable and explosive production equipment as the welding ground wire to prevent high temperature or electric spark in the place where the circuit is in poor contact.

Always check the smelting equipment to prevent the flue bonfire and the crucible from leaking. Do not overfill the material, prevent spillage, and strictly control the heating temperature. When cooking in the production area, you should pay attention to the choice of the location.

The torch is a lightweight heating device. The use of blowtorch in a workshop with explosion hazard should be carried out in accordance with the hot fire system. When using the blowtorch in other locations, the combustibles at the operating site should be cleaned up.

(3) Management system for hot work in the fire-fighting area and management system for hot work tickets

All work that can produce sparks, such as electric welding, gas welding, gas cutting, grinding wheel grinding, electric drill drilling, blowtorch work, impact work, etc., are all hot work. It is necessary to apply for hot work tickets for hot work.

According to the dangerous degree of hot work, combined with the actual situation of our factory, the hot work is divided into two levels: dangerous hot work and general hot work.

Dangerous hot work: included in warehouses (including flammable and explosive warehouses), in oil depots, on oil tanks, on oil pipes, on oil transformers, on SF6 circuit breakers, on each bearing of the unit, in the wind tunnel of the generator, in the battery room Dangerous cable trenches, hot fires in dark wells, etc. The hot work ticket is approved by the company's safety controller, and the maintenance team leader and safety officer are on duty.

General hot work: hot work other than dangerous hot work. The hot work ticket is approved by the person in charge of the maintenance team, and the maintenance team security officer is on duty.

1) Use of hot work tickets: The hot work tickets have a specified range of use and effective use period. Several hot items cannot be combined with a hot work ticket.

2) Remove the hot fire: If it is not necessary to fire at the present, the moving parts should be removed and moved to the fixed hot fire area for hot work.

3) Preparation before the fire: Before the hot work, the combustible materials around the hot fire area must be removed, and sufficient non-combustible materials should be used to isolate the surrounding equipment, pipes, holes, etc.; The measure of whereabouts.

4) Hot fire procedure: Before the hot work, the hot work unit fills in the hot work ticket and can only perform the hot work after approval. The fire executives will start work only after seeing the approved hot work tickets and security measures.

5) Hot fire monitoring: When there is a hot work, there must be someone to be supervised. The guardian and the number of people are prescribed above.

2, friction and impact

The friction of the rotating parts of the bearing in the machine, the mutual impact of the irons or the impact of the iron tools on the concrete floor may cause sparks. When the pipe or the iron container is cracked, the material may also ignite due to friction.

Add oil to the bearings in a timely manner, maintain good lubrication, and often remove adhering flammable dirt.

In order to prevent metal parts from colliding with the material into the device, a magnetic separator can be installed on these devices. When there is no separator, the breakdown of hazardous materials (calcium carbide) should be protected by an inert gas.

When transporting metal containers containing flammable gases or flammable liquids, do not throw them to prevent collision with each other to avoid accidents caused by sparks or container bursts. Shoes with nails are not allowed to enter the inflammable and explosive workshops. In the particularly dangerous explosion-proof workshops, the ground should be laid with soft materials that do not generate sparks.

3, other use of fire

High temperature surfaces should prevent flammable materials from coming into contact with high temperature equipment and pipe surfaces. The discharge of combustibles should be kept away from hot surfaces, and the hot surfaces should be insulated. Do not bake clothes and other combustible items on high temperature pipes and equipment. Oil rags, oil-cotton yarns, etc. are prone to spontaneous combustion and cause fires. They should be packed in metal drums and boxes, placed in a safe place and disposed of in time. Smoking is prone to fire, and the temperature of the cigarette can reach 800, C, and can often be hidden for a long time. Therefore, it is necessary to strengthen publicity and education and fire management in this area, and prohibit smoking in factories and warehouses where there is a risk of fire and explosion.

4, electrical sparks

Electric sparks are an important source of ignition for flammable gases, combustible vapors, and combustible explosions of combustible dust and air explosive mixtures. In places with explosion or flammable hazards, if the electrical equipment does not meet the requirements of the explosion-proof regulations, the sparks, arcs and dangerous temperatures generated by the electrical equipment may cause fire and explosion accidents.

(2) Control of hazardous materials

1. Take measures according to the physical and chemical properties of the materials

In the production process, it is necessary to understand the chemical properties of various substances, and according to different properties, take corresponding measures to prevent fire and explosion and prevent the spread of fire.

For oils with self-ignition ability, substances that can spontaneously ignite in air, substances that burn and explode in water, etc., air should be isolated, waterproof or moisture-proof, or ventilation, heat dissipation, cooling, etc. should be taken to prevent spontaneous combustion and explosion of substances.

Flammable, combustible gas and liquid vapor should be based on their relative density with air, and the corresponding sewage method should be adopted. According to the boiling point and saturated vapor pressure of the material, the pressure resistance, storage temperature and heat preservation and cooling measures of the container should be considered.

The liquid has fluidity, so it is necessary to take into account the problem of liquid dispersion and fire spread after the container is broken. The water-insoluble combustion liquid can be burned on the surface of the water to prevent the fire from spreading from high to low with the water flow. Necessary protective dykes.

2, system sealing and negative pressure operation

In order to prevent the vapor, flammable dust and air from forming an explosive mixture, the equipment should be sealed. For production and equipment under negative pressure, air should be prevented from inhaling. In order to ensure the airtightness of the equipment, the flange system should be used as little as possible for the dangerous goods system, but it is convenient to install and maintain. Pipes carrying dangerous gases and liquids should be seamless.

Negative pressure operation prevents toxic or explosive gases in the system from escaping out of the unit. However, under negative pressure operation, it is necessary to prevent poor airtightness of the equipment, especially when the valve is opened, outside air enters the system through the aperture.

3, ventilation replacement

When using ventilation measures, attention should be paid to the air in the production plant. If it contains flammable and explosive gases, it should not be recycled. In a room with flammable gas, the exhaust device and the air supply device should have separate fan rooms. If the fan room is located in the factory, there should be isolation measures. Ventilation equipment that excludes or transports air and other gases at temperatures above 800C, using non-combustible materials. Exhaust systems that eliminate dust from burning explosions should use a dust collector that does not generate sparks. When the dust is in contact with water to generate explosive gas, the wet dust removal system should not be used.

4, inert media protection

The inert gases commonly used in chemical production are nitrogen, carbon dioxide, water vapor and flue gas. Inert gases are often used as protective gases in the following areas:

(1) When pulverizing, screening, and powder transportation of flammable solid materials, inert gas is used for covering protection.

(2) Dispose of the combustible and explosive material system, and replace it with inert gas before the time to eliminate the original air in the system to prevent the formation of explosive mixtures.

(3) Connect inert gas through pipes to equipment and storage tanks that are dangerous to fire or explosion, in case of danger in case of danger.

(4) The flammable liquid is pressurized and transported by using an inert gas.

(5) In the production places with explosive dangers, the electrical appliances and instruments that cause spark hazard shall be protected by nitrogen positive pressure.

(6) Purge and replace with inert gas when the flammable and explosive system requires dynamic fire overhaul.

(7) When a material accident occurs, it is diluted with an inert gas, and in the event of a fire, it is treated with an inert gas.

Extinguishing.

(3) Control process parameters

In the production process, proper control of various process parameters to prevent over-temperature, over-pressure and material run-off is a fundamental measure to prevent fires and explosions.

1, temperature control

Different chemical reactions have their own suitable reaction temperature. Correct control of the reaction temperature is not only important for ensuring product quality and reducing consumption, but also necessary for fireproof and explosion-proof.

2, feeding control

(1) Feeding speed

For exothermic reactions, the feed rate should not exceed the heat transfer capacity of the equipment, otherwise it will cause a sudden rise in temperature and a side reaction that will cause decomposition of the material. If the feed rate is suddenly reduced, the temperature is lowered, the reactants cannot fully act and accumulate, and the reaction is intensified after the temperature rises, and the temperature and pressure may suddenly rise or cause an accident.

(2) Feeding ratio

The ratio of the reaction materials should be strictly controlled. Therefore, the concentration, content and flow rate of the reaction materials should be accurately analyzed and measured.

(3) Feeding sequence

In chemical production, it is necessary to feed in a certain order, otherwise explosion may occur. In order to prevent misoperations from reversing the feed sequence, the feed valves can be interlocked with each other.

(4) Control raw material purity

There are many chemical reactions, which often cause side reactions or over reactions due to impurities in the reaction materials, resulting in fire and explosion. Therefore, the production of raw materials, intermediate products and finished products should have a strict quality inspection system to ensure the purity of raw materials.

3, to prevent running, taking, dripping, leaking

During the production process, running, taking, dripping and leaking often lead to the diffusion of explosive media in the production site, which is one of the important reasons for fire and explosion accidents in chemical enterprises. There are several situations in which run, run, drip, and leak occur:

(1) The operation is not elaborate or mishandled, for example, the tank is full of materials during the receiving process. The separator liquid is unstable, and the wrong drain valve is opened.

(2) The joint surface of the equipment pipeline and the pump is not sealed and leaks.

In order to ensure safe production, to prevent run, run, drip, and leak, it is necessary to strengthen the sense of responsibility and technical training of operators and maintenance personnel, stabilize process operations, improve equipment integrity, and reduce leakage rate. In order to prevent misuse, different types of pipelines are painted in different colors to distinguish them, and important valves are listed, locked and so on. Valves on different pipes should be separated by a certain distance.

4, emergency parking treatment

In the event of an emergency such as power outage, gas outage or water stoppage, the device will be subjected to emergency stop treatment, which may cause an accident if not handled properly.

(1) Power outage

In order to prevent accidents caused by sudden power outages, more important reaction equipment should generally have dual-electric, interlocking self-injection devices. If the circuit fails and the interlock is not closed, the device has no power. At this time, it is necessary to report and report the cause of the power failure.

(2) Water stop

Pay attention to the water pressure and temperature changes of various parts when stopping water, and take measures to reduce production to maintain production. If the water pressure drops to zero, the feed should be stopped immediately. Note that all equipment that uses water to cool down should not overheat and overpressure.

(3) Stopping steam

After the steam stop, the temperature of the heating device drops, the steam moving equipment stops, some materials that are solid at normal temperature and liquid at the operating temperature should be properly treated according to the temperature change to prevent the pipeline from being blocked due to freezing. In addition, the valve that communicates with the material system should be closed in time to prevent the material from flowing back to the vapor line system.

(4) stop gas

When the airflow pressure returns to zero, all pneumatic instruments and valves can't move. At this time, the flow, pressure, and liquid level should be analyzed and judged according to the instrument or actual situation.

(4) Adopting automatic control and safety protection devices

1. Automatic adjustment of process parameters

(1) Automatic temperature adjustment

(2) Automatic pressure regulation

(3) Automatic adjustment of flow and liquid level

2, program control

Program control is a control system that uses an automated tool to periodically switch the execution system at regular intervals according to process requirements. The program control system is mainly a signal sent by the program controller at a certain time interval to cause the actuator to operate.

3. Signal device, protection device, safety interlock

(1) Signal device

The installation signal alarm device can warn the operator to take timely measures to eliminate hidden dangers in the event of a dangerous situation. The signal sent is generally sound, light, etc. They are usually connected to the measuring instrument. When the temperature, pressure, liquid level, etc. exceed the control index, the alarm system will generate a signal.

(2) Protection device

When the protection device is in danger, it can automatically operate to eliminate abnormal conditions.

(3) Safety interlock

The so-called interlocking is to use mechanical or electrical control to turn on the various instruments and equipment in turn, and make them happen to each other, in order to achieve safe production.

(5) Limiting the spread of fires and explosions

1, isolation, open air layout

In the production process, some dangerous equipment and equipment should be partitioned, open-air installed and remotely operated.

(1) Partition isolation

In the overall design, the factory layout should be reasonably arranged, and a certain safety distance should be drawn between the device and the device, the device and the storage tank warehouse, and between the production area and the living area.

(2) Open air layout

In order to facilitate the emission of harmful gases and reduce the risk of accumulation in the plant due to equipment leakage, chemical equipment and equipment should be placed in the open air and semi-open air.

(3) Remote control

For some valves that are difficult for the workers to access or require quick opening and closing, otherwise there will be an accident, remote equipment can be used for equipment with high radiant heat.

2. Safety fire arrester

Fire-blocking equipment includes safety liquid seals, flame arresters and check valves. Its function is to prevent external flames from entering the equipment, pipes, containers, or the expansion of the flame between the equipment and the pipeline.

(6) Using explosion-proof electrical equipment

Explosion-proof electrical equipment is classified according to its structure and explosion-proof performance. Appropriate types of electrical equipment should be selected according to environmental characteristics.

1. General requirements

(1) Types and signs

Types, grades, and groups of explosion-proof electrical equipment should be clearly marked on the casing. The “K” in front of the old type of sign indicates explosion-proof electrical equipment for coal mines. The new type of sign with "E" is the factory's explosion-proof electrical equipment, and the "I" is the explosion-proof electrical equipment for coal mines.

(2) Zui high surface temperature

Explosion-proof electrical equipment Zui high surface temperature refers to the surface temperature of the outer casing, and other types of equipment refers to the temperature of the surface in contact with the explosive mixture.

When the surface of Class I equipment may accumulate dust, the high surface temperature of Zui is +1500C, and measures are taken to prevent +4500C when dust is accumulated.

The high surface temperature of class B equipment zui shall not exceed the relevant regulations. The limit temperature rise is for the ambient temperature +400C. Devices that are overloaded may refer to motors and power transformers.

In locations where there is an explosive mixture of dust or fibers, the temperature of the electrical equipment enclosure should generally not exceed 1250C. If this requirement cannot be guaranteed, it must also be 750 C lower than the auto-ignition point of the mixture or 2/3 below the auto-ignition point.

(3) Ambient temperature

The operating environment temperature of electrical equipment is generally 201C - +40'C. If the ambient temperature range is different, it must be marked on the nameplate and calculate the high surface temperature of the electrical equipment based on the high ambient temperature.

(4) Blocking

Fasteners that can be removed from the outside on electrical equipment, such as switch box covers, observation windows, machine bases, measuring hole covers, drain valves or oil drain screws, must have a latching structure. The purpose is to prevent non-professional personnel from disassembling the fasteners such as bolts necessary to maintain explosion-proof performance. The locking structure must be a fastening device that cannot be loosened or difficult to loosen using a general tool such as a screwdriver, wrench, pliers, or the like.

(5) External connection

The line entry device must have measures to prevent loosening and pull-off, and have elastic gaskets or other sealing measures. And the clearance and leakage distance of the junction box should meet the requirements. The grounding terminal should have a grounding mark to keep it continuous and reliable, and it has anti-loose and anti-rust measures.

2, various types of equipment explosion-proof requirements

(1) Increased safety type

Refers to electrical equipment that generates arcs, sparks, or high temperatures that may ignite explosive mixtures under normal operating conditions, and measures to improve safety to avoid electrical equipment that exhibits these phenomena under normal and approved overload conditions. The outer casing of the insulated live part shall be protected by IP44, and the outer casing of the exposed live parts shall be protected by IP54. The connecting piece of the cable or wire should be securely connected to the cable or wire, and the wiring is convenient. At the same time, the cable or wire should be prevented from loosening, falling off, twisting, and maintaining good contact pressure.

(2) Flameproof type

Means enclosing a component that may ignite an explosive mixture in a rugged enclosure that withstands the explosive pressure of an internal explosion and prevents electrical equipment from being blasted to the outside through the upper slot. The outer casing of the explosion-proof device is made of steel. Made of cast steel, aluminum alloy, gray cast iron and other materials.

Explosion-proof electrical equipment can be wired directly through the explosion-proof junction box (or plug seat). The connection should have facilities to prevent the tensile force from damaging the terminals. The joint surface of the connecting device should be of sufficient length. If the cable is enclosed in the main casing, the length outside the casing shall not be less than 3 m.

(3) Oil-filled type

Refers to electrical equipment in which all or some of the live parts are immersed in the insulating oil so that they do not attract explosive mixtures above or above the fuel surface. There should be venting holes on the outer casing of oil-filled electrical equipment. There should be no debris in the hole; the amount of oil must be sufficient, the depth below the low oil surface should not be less than 25mm, the oil level indication must be clear; the oil quality must be good; the oil surface temperature TI -T4 group shall not exceed 1000C, T5 group shall not exceed 80'C, and T6 group shall not exceed 70'C. Oil-filled equipment should be installed horizontally, and its inclination should not exceed 50; it must not be moved during operation, and the mechanical connection must not be loose.

(4) Positive pressure type

Refers to an electrical device that has a protective outer casing filled with a protective gas that maintains a higher pressure than the external explosive mixture gas to prevent external explosive mixtures from entering the casing. According to its inflatable structure, it can be divided into three forms: ventilation, aeration, and airtight. The shielding gas can be air, nitrogen or other non-flammable gas. The degree of protection of the enclosure must not be lower than IP44. There must be no venting corners in the enclosure that affect safety. When normal, the wind pressure or full air pressure at the air outlet shall not be lower than 0.2 kPa; when the pressure is lower than 0.1KPa or the pressure at the pressure is less than 0.055kPa, an alarm signal or power must be cut off.

Such equipment shall have an interlocking device to protect the air before operation, and the total amount of inflation shall not be less than 5 times the volume of the equipment gas. The ventilation time (s) before operation can be calculated as follows:

t二K(V+a)/Q

Where K is a volume multiple, K) 5

V-device gas volume (m,)

A-pipe gas volume (m,)

Q-gas flow rate (m3/s).

(5) Intrinsically safe

Under the specified test conditions, the thermal effect of the spark generated under normal operation or the specified fault condition cannot ignite the circuit of the specified explosive mixture, which is called the intrinsically safe circuit. The electrical equipment of the intrinsically safe circuit is called the intrinsically safe explosion-proof electrical equipment. .

Intrinsically safe circuits should have a safety barrier. The safety barrier is composed of a current limiting component (metal film resistor, nonlinear resistor, etc.), a voltage limiting component (diode, Zener diode, etc.) and a special protection component (fast fuse, etc.), and the transistors in the circuit need to be doubled. The distance between the intrinsically safe circuit terminals and the non-intrinsically safe circuit terminals shall not be less than 50 mm. The secondary circuit of the power transformer of the intrinsically safe circuit must maintain good electrical isolation from the primary circuit.

(6) Sand filling type

Refers to the filling of the fine-grained material in the outer casing so that under the specified conditions, the arc, flame, shell wall and particulate material generated in the casing may not ignite the electrical equipment of the external explosive mixture at a dangerous temperature. The outer casing shall have sufficient mechanical strength, and the degree of protection shall not be less than IP440. The fine-grain filling material shall fill all the voids in the outer casing; the particle diameter shall be 0.25 to 1.6 mm. When filling, the water content of the fine-grained material shall not exceed 0.1%.

(7) Non-sparking type

Refers to the absence of arcing, sparking, or explosion-proof electrical equipment that can ignite the surface temperature or hot spots of surrounding explosive mixtures under normal operating conditions.