The 1 oxide
Such as ammonia oxidation to nitric acid, oxidation of toluene to benzoic acid production, such as the oxidation of ethylene to ethylene oxide.
( 1) oxidation of fire hazard
The oxidation reaction heat is required, but the reaction is exothermic, especially catalytic gas phase reactions, are generally in 250 ~ 600 degrees high temperatures, the heat of reaction if not promptly removed, will make the temperature rises rapidly even explosion.
In some oxidation, such as ammonia, ethylene and methanol vapor in the air oxidation, the material ratio close to the lower limit of explosion, if the ratio imbalance, improper temperature control, easy to burst into flames.
The oxidation of most of the material is flammable and explosive substances. Such as ethylene oxide ethylene oxide, ethylene is a flammable gas, explosion limit is 2.7% ~ 34%, spontaneous ignition point of 450 DEG C; toluene oxidation of benzoic acid, toluene is a flammable liquid, vapor to form explosive mixture with air, explosion limit is 1.2% ~ 7%; methanol oxidation of formaldehyde, methanol is flammable liquid, its vapor and air explosion limit is 6% ~ 36.5%.
The oxidizing agent having a lot of fire hazards. Such as potassium chlorate, potassium permanganate, chromium anhydride belong to the oxidizing agent, such as the case of high temperature or impact, friction and organic acids, contact, can cause fire explosion; organic peroxides are of not only strong oxidizing, and most of them are flammable materials, some are particularly sensitive to temperature, when the temperature is explosion.
The oxidation products are also has a fire hazard. Such as ethylene oxide is a flammable gas; nitric acid is corrosive materials, but also is a strong oxidizing agent; containing 36.7% formaldehyde aqueous solution is a flammable liquid, the steam explosion limit is 7.7% ~ 73%. In addition, some of the oxidation process may also generate a greater risk of peroxides, such as the oxidation of acetaldehyde to acetic acid production process with peracetic acid generation, peracetic acid is an organic peroxide, nature of extreme instability, due to high temperature, friction or impact will decomposition or burning.
( 2) the oxidation process of fire prevention measures
The oxidation process such as air or oxygen as the oxidant, reaction of the ratio of materials ( flammable gas and air mixing ratio ) should be strictly controlled in the explosive range. Air enters the reactor before, should go through a gas purifying device, removing the dust in the air, moisture, grease and the decrease of catalyst activity or poisoned impurities, in order to maintain the catalyst activity, reduce the risk of fire and explosion.
The oxidation reaction of the contactor has two kinds of horizontal and vertical, filled with catalyst. The general use of vertical, because this form of convenient loading and unloading catalyst, and safety. In the catalytic oxidation process, the exothermic reaction, should control the suitable temperature, flow rate, temperature, pressure and prevent explosion gas mixture in the range of.
The in order to prevent contact in case of explosion or fire endanger personal safety and equipment, in the reactor and pipeline shall be installed to prevent the spread of flame arrester, tempering, prevent, make fire does not affect the other systems. In order to prevent contact explosion, contactor should have pressure relief device, and try to use automatic control or regulation as well as alarm interlock device.
The use of nitric acid, potassium permanganate as oxidant, to strictly control the feeding speed, prevent more, wrongs, the solid oxidant should be crushed after use, preferably in the form of solution, use, or intermittent stirring reaction, strict control of reaction temperature, must not exceed by oxidizing substance spontaneous ignition point.
The use of an oxidizing agent to oxidize inorganic matter, such as the use of potassium chlorate oxidation iron blue pigments, should control the drying temperature does not exceed its burning temperature, the drying prior to the application of water washing products, the oxidizing agent is thoroughly cleanse, to prevent incomplete reaction of potassium chlorate by dry material fire. Some oxidation of organic compounds, especially in the high temperature oxidation, in the equipment and piping may be produced within Jiao Zhuang, should be promptly removed, to prevent the spontaneous combustion.
The oxidation reaction using the raw materials and products, in accordance with the relevant provisions on the administration of dangerous goods, take corresponding prevention measures, such as quarantine, away from fire, avoid high temperature and sunlight, preventing friction and impact. If the flammable liquid or gas, should install the guide in addition to electrostatic grounding device.
When the equipment system should set up nitrogen, water vapor extinguishing device, so as to be able to put out a fire in time.
2 reduction
Such as nitrobenzene in hydrochloric acid solution by iron powder reduction to aniline, o-nitroanisole in alkaline aqueous solution by zinc reduction into o-anisidine, using insurance powder, potassium borohydride, lithium aluminium hydride reducing agent for reducing etc..
Reduction of process hazard analysis and fire protection requirements:
( 1) using either a nascent reduction, or catalyst the hydrogen activation after reduction, has the presence of hydrogen ( hydrogen explosion limit is 4% - 75%), especially catalytic hydrogenation reduction, mostly in the heated, pressurized conditions, if the wrong operation or for equipment defect with hydrogen leakage, easy and air form explosive mixtures, such as meeting with fire that will explode. Therefore, in the course of the operation to strictly control the temperature, pressure and flow; workshop electrical equipment must conform to the explosion-proof requirements. Wire and cable junction box should not be in the workshop top laying installation; building ventilation is better, should adopt the light roof, roof or a set, in order to make hydrogen to escape; reaction of hydrogen produced in the exhaust pipe is available workshop roof, and higher than the roof above 2m, after the flame arrester discharge; pressure response of the equipment shall be equipped with safety valve, produced in the reaction pressure of equipment to install the bursting disc; the installation of hydrogen detection and alarm device.
( 2) reduction of catalyst used in Reye nickel after moisture absorption in the air with spontaneous combustion danger, even in the absence of an ignition source is present, also can make hydrogen and air mixture is ignited to form fire explosion. Therefore, when they are used to activate hydrogen reduction reaction, you must first use of nitrogen replacement reactor all air, and after the determination of oxygen content after confirmed down to standard, to Walter hydrogen; after the reaction should be put within the reactor with nitrogen hydrogen gas clean, to open the hole cover material, to avoid the outside air and inside the reactor hydrogen to meet, in Reye nickel spontaneous combustion occurred in the absence of fire explosion, Redwood nickel should be stored in alcohol, palladium on carbon recovery when the application of alcohol and water thoroughly washed, filtered vacuum may not take too dry, to avoid oxidation ignition.
( 3) the solid reducing agent insurance powder, potassium borohydride, lithium aluminium hydride are flammable when wet dangerous goods, including insurance powder water heating, in the humid air can decompose precipitated sulfur, sulfur vapor heating with spontaneous combustion danger, and heated to 190 DEG C insurance powder itself also has a decomposable explosion danger; boron hydride potassium ( sodium) in the humid air to spontaneous combustion, water or acid is decomposed to release a large quantity of hydrogen, heat generated at the same time, may cause the hydrogen fire explosion accidents caused by; lithium aluminium hydride is dangerous when wet reducing agent, be sure to keep, to prevent damp. Insurance powder used for dissolving when in use, to strictly control the temperature, can be run under stirring, insurance powder in batches to be dissolved into the water, then in contact with organic material reaction; when using sodium borohydride ( k ) as reducing agent, in the process of mediation acid, alkalinity should pay special attention to, prevent acid fast, too much; when using lithium aluminium hydride as the reductant, special attention should be paid to, must be under the protection of nitrogen use, usually immersed in kerosene storage. In front of the reducing agent, oxidizing agent reacts violently with, produce a large amount of heat, having fire explosion risk, it may not be mixed with oxidant.
( 4) the reduction reaction intermediates, especially the reduction of aromatic nitro compounds reaction intermediates, there is a certain degree of fire risk, for example, in o-nitroanisole reduction neighbours anisidine process, produce azoxybenzene ether, the intermediate is heated to 150 DEG C to spontaneous combustion. Aniline in production if the control of reaction condition is not good, can generate explosive danger big cyclohexylamine. So in response to operation must strictly control the various reaction parameters and reaction conditions.
( 5) to carry out technological innovation, studies using low risk, high reduction efficiency of new reducing agent instead of the fire hazard is big reducing agent. Such as the use of sodium sulfide instead of iron powder reduction, can avoid hydrogen is generated, and can remove iron mud accumulation problem.
3 nitrification
Nitrification is usually refers to the molecules of organic compounds is introduced in the nitro group ( - NO2 ), substitution of hydrogen atoms and generation of nitro compounds reaction. Such as the production of TNT ( TNT ) nitration of toluene nitration of benzene to nitrobenzene, preparation, preparation of nitroglycerin and glycerine nitrifying.
The nitrification process fire risk is mainly:
( 1) the nitrification is an exothermic reaction, the introduction of a nitro to release 152.2 to 153 kJ / mol, so the need for cooling conditions of nitrification. In the nitration reaction, if any negligence, such as stirring, cooling water supply stop bad, feeding speed, will cause the temperature soared, mixed acid oxidation ability to strengthen, and many nitro compounds are generated, easy to cause fire and explosion accidents.
( 2) the nitrating agent with oxidation, common nitrating agent in concentrated nitric acid, nitric acid, sulfuric acid, fuming sulfuric acid, mixed acid has a stronger oxidation resistance, water absorption and corrosive. Them with oil, organic matter, especially unsaturated organic compounds that can cause contact combustion; in preparation of nitrating agent, if the temperature is too high or fall into a small amount of water, will induce large nitrate decomposition and evaporation, not only will lead to strong corrosion, can also cause explosion accident.
( 3) by nitration of substances such as benzene, toluene mostly flammable, glycerol ( glycerine, removal of ester ), cotton, not flammable, some also with toxicity, such as use or storage of improper management, very easy to cause fire.
( 4) nitration products mostly fire danger of explosion, especially the nitro compound and nitrate ester, heat, friction, impact or contact with fire, explosion or fire easily.
The 4 electrolysis
The current through the electrolyte solution or melt electrolyte, in two was caused by the chemical changes called electrolysis. Electrolysis in the industry have a wide range of roles. Many nonferrous metals ( sodium, potassium, magnesium, lead ) and rare metals ( such as zirconium, hafnium ) smelting, copper, zinc, aluminum and other refining; many of the basic chemical industry products ( hydrogen, oxygen, chlorine, caustic soda, potassium chloride, hydrogen peroxide ) preparation, as well as the plating, electric polishing, anodic oxidation, are realized by electrolysis.
Such as salt water electrolytic production of sodium hydroxide, hydrogen, chlorine, hydrogen production by water electrolysis. Salt water electrolysis process hazard analysis and fire points:
( 1) saline shall ensure that the quality of brine containing impurities such as iron, capable of generating second cathode and hydrogen; saline into ammonium salt, under suitable conditions ( pH < 4.5 ), ammonium and chlorine can generate ammonium chloride, chloride in concentrated solution of ammonium chloride can also generate yellow oily three chloride nitrogen.
-- 4HCl+NCl3 3C12+NH4Cl
Three nitrogen trichloride is an explosive substance, with many organic contact or heated to 90 DEG C and collision, which occurred in violent explosive decomposition. Decomposition of the explosive type as follows:
-- N2+3C12 2NCl3
Therefore brine mixing must strictly control the quality, especially in iron, calcium, magnesium and inorganic ammonium content. General requirements Mg2 < 2mg / L, Ca2 < 6mg / L, SO42 < 5mg / L. As far as possible should take Brine Purity automatic analysis device, so that you can observe the brine composition changes, any regulation of sodium carbonate, caustic soda, barium chloride or the amount of acrylic acid amine.
( 2) saline added height should be appropriate in operation to the electrolytic cell anode indoor add salt, such as salt water level is too low, the hydrogen is possible through the cathode net into the anode chamber of mixed with chlorine; if the electrolytic brine installed too full, under the pressure of water will rise, therefore,
( 3) prevent hydrogen mixed with chlorine hydrogen is highly flammable gas, chlorine gas is oxidized to highly toxic gas, once the two mixed gases explosion extremely easily, when chlorine gas containing hydrogen volume reached more than 5%, it may at any time in illumination or heating conditions of explosion. Cause of hydrogen and chlorine gas mixture is the main reason: the anode chamber of saline liquid level too low; electrolyzer hydrogen gas outlet plug, causing the cathode chamber pressure; the adsorption quality of diaphragm electrolyzer; asbestos fiber quality is not good, mounted in the electrolytic tank is damaged caused by the diaphragm, diaphragm partial loss or send electricity before injecting a saline volume general diaphragm washed out, and a cathode chamber pressure is equal to or more than the anode chamber pressure, may make the hydrogen into the anode chamber, which may cause increased the amount of hydrogen content in chlorine gas. The electrolytic tank to conduct a comprehensive inspection, the single groove of hydrogen in chlorine concentration control in 2% following, duct of hydrogen in chlorine concentration control in 0.4% the following.
( 4) strictly electrolysis equipment installation requirements due to the presence of hydrogen in electrolytic process, the fire explosion risk, so the electrolyzer should be installed in the natural ventilation good single buildings, plant should have sufficient explosion-proof pressure relief area.
( 5) to master the correct emergency treatment method in production when a sudden power failure or other causes of sudden stop, high pressure valve cannot be closed immediately, lest the electrolytic chlorine reflux and the explosion. In the electrolytic tank after the installation of vent pipe, to timely decompression, and in the high-pressure valve mounted one-way valve, in order to effectively prevent the running of chlorine, avoid environment pollution and to bring fire risk.
5 polymerization
A plurality of molecular binding to a larger comprising the same and high molecular weight compounds for polymerization reaction process.
Such as vinyl chloride polymerization production of PVC polymerization of butadiene, polybutadiene rubber and styrene-butadiene rubber production.
The polymerization reaction can be divided according to type of addition polymerization and condensation polymerization of two categories; according to the polymerization can be divided into bulk polymerization, suspension polymerization, solution polymerization and emulsion polymerization, condensation polymerization of five kinds of.
( 1) bulk polymerization
Bulk polymerization is in no other medium conditions ( such as the high pressure polymerization of ethylene, formaldehyde polymerization ), by immersion in the coolant pipe type polymerization kettle ( or in a polymerization vessel located in the coil, tube cooling ) of a polymerization method. The polymerization method is often due to polymerization heat is difficult to disperse the risk caused by conduction. For example, in high-pressure polyethylene production, each 1 kilograms of ethylene polymerization will emit 3.8MJ heat, if they failed to remove heat, each of 1% ethylene polymerization, can make the kettle temperature increased 12 ~ 13 degrees, to be elevated to a certain temperature, it will make ethylene decomposition, strongly exothermic, have critical poly risk. Once there is violence, blockage of equipment, pressure surge, extremely easy to explode.
( 2) the solution polymerization
Solution polymerization is a choice of solvent, make Dan Tirong into a homogeneous system, adding catalyst and initiator, generating polymer polymerization method. The polymerization method on polymerization and separation process, inflammable volatile and generates electrostatic spark.
( 3) suspension polymerization
Suspension polymerization using water as dispersion medium is the polymerization method. It is the use of organic dispersing agent or inorganic dispersant, the water insoluble liquid monomer, together with soluble in the monomer initiator after strong mixing, breaking Cheng Xiaozhu
