Runaway Reaction
What is Runaway Reaction
Runaway Reactions are any reaction systems which displays acceleration in rate of reaction at certain conditions so great that they are very difficult or impossible to control. The accompanying characteristics of such reactions are that they occur with very rapid increase of temperature or pressure.
In general it can be said that runaway reactions are highly exothermic reactions. Exothermic reactions are those which give off heat as the reaction progresses. If the heat removal system is not able to remove as much heat as the reaction is producing then temperature of the reaction mixture starts increasing. If the rapid increase of temperature or pressure is not controlled properly then it can cause damage to the equipment, surroundings and Human lives.
Risk Assessment and Evaluation of Hazards
Any chemical reaction which has a possibility to runaway under certain conditions should be studied very well and the knowledge of the reaction and reaction mechanism should be properly used to assess the risks involved in the process to deal with the hazards to control it by designing adequate control systems and heat removal systems or to not allow such a condition to ever happen by designing adequate operational procedures and proper training schemes.
Proper knowledge of the chemistry and thermochemistry of the reaction goes into the evaluation of the hazard. The things which should be tackled are if runaway occurs then is it possible whether the reactants or products or intermediates gets decomposed and what is the rate and quantity of the gas and heat released during the runaway.
The rate of reaction increases with increasing volume of reaction mixture. The rate of heat removal decreases with decrease in surface area. Hence if the volume to surface area ratio increases then the rate of reaction increases and the difficulty to remove heat also increases. Hence this point should be noted while scaling the reaction.
Full scale testing of the runaway not only requires a lot of money but is very dangerous hence preliminary calculations are done by researching the literature for theoretical calculations and simulations are also performed. Lab scale calorie metric studies at very controlled conditions are done and proper vent sizes are estimated.
Risk assessment involves defining process, plants and the operating conditions, identification of hazards and then assessing the adequate methods to deal with them, choosing appropriate safety and protective measures and maintaining the measures all the time during the operation of the plant. Risk assessment is started from the initial stage of planning and carried till the plant becomes operational.
Safety, Protective and Control measures
Safety measures are decided by referring to the risk assessment studies. The measures can be inherent in nature which eliminates the hazard, process control can be used which prevents the hazard from occurring and also protective measures can be employed which limits the consequence of runaway hazard.
As much as possible it should be tried to reduce or eliminate the possibility of the runaway hazard. It can be done by substituting the reactants with safer alternatives, if it can’t be done then care should be taken that very low quantity of reaction mixture stays in the reactor which can be done by using a continuous process instead of a batch process, Semi batch process can be used if using a continuous process is not possible because it is better to control the heat liberation in exothermic reaction by controlling the quantity of one of the reactants.
Process control procedures should be installed in order to prevent the runaway from occurring by using proper and reliable control systems, actuators, sensors and automatic systems to take actions when they predict the occurrence of such a hazard.
Protective measures are to be used at the time the hazard is occurring. Plant should be designed to contain the pressure generated during the runaway, emergency relief valves should be there to vent the gases produced to a safer place, the reaction should be stopped by either using a reaction inhibitor, quenching by crash cooling or by directly dumping the reaction mixture in to the quenching liquid itself.
https://youtu.be/C561PCq5E1g
Unit Operation and Unit Process
Unit Operation and Unit Process :- The entire chemical engineering can be classified into two groups; unit operations or unit processes. The concept of unit operations was introduced in 1915 by Dr. Arthur D. Little. The concept of unit processes was introduced in 1923 by P.H. Groggin.
Unit Operations
A unit operation is defined as a process which does not involve any chemical reaction. Unit operations only deal with physical changes of the materials involved in the process. They are equipments which cause the materials to undergo physical changes.
The physical changes are carried out for variety of purposes. Generally unit operations steps are carried out before subjecting the materials to chemical reactions so that chemical reactions happen smoothly.
The physical changes can imply phase changes such as; evaporation, condensation, crystallization etc. Thus Distillation is a unit operation step because condensation and evaporation happens inside the column. Evaporators, and crystallisers are also unit operations equipment.
Unit operation equipments are also responsible for mechanical operations which involves size reduction, physical separations, mixing, and grinding. The mass transfer, heat transfer process all may happen together. Chemical reaction doesn’t happen.
The unit operations are classified in the following manner:
Fluid flow operations: Pumping, compression, and fluidisation.
Mechanical operations: Size reduction, size enlargement, mixing, agitation, blending, filtration, classification-separation, etc.
Mass transfer: Distillation, evaporation, crystallization, leaching, absorption, adsorption, extraction, etc.
Heat transfer: When materials are handled the heat transfer can take place by any fundamental mechanism; conduction, convection, or radiation. Usually two fundamental mechanisms occur simultaneously.
Unit Process
Chemical reaction is at the heart of the unit processes. A chemical reactor is an equipment which falls under the category of unit processes. Literal chemical change takes place inside the equipment wherein the the chemical structure of the material changes and it transforms and forms an entirely new material.
All kinds of chemical reactions carried out in industrial equipments comes under this category. Some examples of such chemical reactions are; sulphonation, nitration, halogenation, alkylation, hydrolysis, hydrogenation, polymerization, oxidation, reduction, etc. The examples can be innumerable as there can be innumerable compounds which can be formed by reaction of two or more materials or by decomposition of the material itself. Thus classification can be similarly endless.
Most of the chemical reactions are irreversible in nature. A chemical reaction step in a process forms the heart of the process, often governing the economics of the entire process. Thus the unit processes are often subject of optimization.
Often unit operations have to be carried out before unit processes to give proper shape to the materials so that they will be able to react optimally. Also unit operations are often needed even after the chemical reaction has happened, they are needed for the purpose of separation of the primary product from the secondary or tertiary products. All the unit operation processes wherein chemical reaction is made to take place to improve the efficiency of the equipment also falls under unit processes. For example, reactive distillation, reactive extraction, reactive absorption, etc.
Process Flow Diagram (PFD)
A process flow diagram (PFD) is a graphical representation of a chemical engineering process that shows the primary process flow path. It does not show the minor details of the process, rather it focuses on the equipment used, control valves and other instruments that are present. It helps to illustrate how the major components of a process plant interact with each other to bring about the desired effect. It is also effectively used in other sectors such as business administration to understand how different sections of a company can work efficiently in order to achieve their specific targets. Frank Gilbreth Sr. was the first person to develop a flow diagram in the year 1921, when he introduced it to the American Society of Mechanical Engineers (ASME).
The most important benefit of drawing a process flow diagram is that it gives the working personnel an overall view of the entire process taking place. This in turn helps them to make necessary improvements and changes wherever needed so that it is run at its maximum potential. Once all the changes are made, the process flow diagram acts as a standard to be followed by all people involved. This avoids confusion and also helps to prevent errors.
These flow diagrams may not always show the working of the whole plant. It may be used to represent different sections of a plant. This would help to understand more in detail about each specific operation that is being carried out, such as raw material storage, reaction, separation, purification, recovery and product storage. A typical PSD will contain operational data such as temperature, pressure and mass flow rates. Relief and safety valves are usually excluded from PSD whereas the control valves are critical components. Also keep in mind that these diagrams are not dimensionally in sync with the actual plant.
PFD symbols are a set of diagrams that show how different parts of the process are interconnected to each other. The symbols also depict the instrumentation devices that are used in the process. Examples of symbols include valves, pumps, compressors, reboilers and heat exchangers. Process lines represent the path through which the materials flow and are represented by various pipe symbols. There are also signal lines which are thinner than the process lines and they represent the kind of signal provided such as electronic or pnuematic signals. The commonly used symbols are prescribed by agencies such as ISO and ANSI.
Different kinds of process flow diagrams are used depending on the level of information and details that are required. A block flow diagram would show all the units that are present in the process but with very less details. The piping and instrumentation (P&ID) diagrams are more complex and include minor details such as equipment information, utility lines, bypass lines, drains and vents. P&IDs are developed on the basis of process flow diagrams only. The complexity of the PFD also varies depending on the level of details required by the personnel. The first section of the PFD should contain the legend sheet which shows the symbols and their names. This would be helpful for any person looking into it and helps to avoid confusion.
https://youtu.be/tVbedmqfUFI ko
Fire Extinguisher Types and Uses
Fire Extinguisher Types and Uses:
Fire Extinguisher term which means cut off or alter the fire or blow down of fire which is caused due to any explosive material or gas presence or any electrical fault found. Fire extinguisher is device which is used for cut off the fire. These fire cut off equipment are comes in different variant with respect to the Fire Zones Proposed & class of Fire.
Types of Fire Extinguisher:
Extinguisher types are mentioned below as classified:
1. Water Type Fire Extinguisher:
Generally for cut off firing shall be done by the water spraying over. Water type fire extinguisher operates on the principle which is as follows when water is sprays or threw in the line of fire where combustion of any material, gas & other electrical utility system caused then it’s lower down or cools the temperature of substance that is in combustible form than its Ignition Point (Ignition Point is term which defined as the lowest temperature at which substance about to become combustible when free to air) & extinguishes the fire.
Drawbacks of Water Type Fire Extinguisher:
Water as fire extinguishers fluid not to be used in every case. Water can’t be used with oil & petrol because of the density differences across they floats over the water layer which means water sink against the fluid surface.
Water cannot be used in case of firing from electrical cabling or Control System it conduct electricity (Due to the presence of ions in the Water Solution), there is some chances of Getting Electric Shock during the Extinguish Process Which leads to Server Injuries or sudden death to Fire extinguish Person.
2. Foam Type Fire Extinguisher:
Foam Type extinguisher works on the principle in which restrict the oxygen processing to the combustible material or substance which is firing/Burning at the moment.
Foam type extinguisher contains cylinder with a small bottle arrangement for the Aluminum Sulphate Solution whereas cylinder contains sodium bicarbonate Solution (has some portion of saponin which used to produce the FOG) which is saturated (Saturated Solution is defined as the solution which contains the Solute parts in maximum concentration of the Solution, show sign of dissolving within the Solution). This equipment is used in application cases of Petrol & Oil.
Working: In fire case Knob is placed or constructed at the top of the cylinder, as pressing the knob release the bottle filled aluminum sulphate gets mixes with cylinder containing Solution NaHCO3 (Sodium Bicarbonate Solution).
Chemical Reaction: Al2SO4 + NaHCO3 —-> Al (OH) 3 + CO2 + Na2SO4
(Addition of Saponin reacted with carbon dioxide to produce foam appearance which cover the Combustible material for cut off of Firing by means of restriction in supply of Oxygen to the firing Substance).
3. Carbon Dioxide Fire Extinguisher:
Carbon dioxide type fire extinguisher which contains CO2 in Pure form for cut off for firing by spraying it over the combustible Substance. Pressure Gauge is not installed in the Carbon dioxide Extinguisher filling of cylinders may be checked by the Weighing Methods.
4. Dry Powder Fire Extinguisher:
Powder which is used for the Fire extinguishing Purpose mono ammonium sulphate, this is particularly used for Metal combustible Substance.
5. Wet Chemical Fire Extinguisher:
Wet Chemical fire extinguishers are a type of firefighting equipment that is specifically designed to extinguish fires caused by cooking oils and fats in commercial kitchens. The extinguishing agent used in these fire extinguishers is a solution of potassium acetate that helps to smother the fire and cool down the burning surface, preventing re ignition. Wet Chemical fire extinguishers are highly effective against Class F fires and are the preferred choice in commercial kitchens and other cooking areas. These fire extinguishers are easy to use and are equipped with a discharge hose that allows the operator to direct the fire extinguishing agent directly onto the fire. Wet Chemical fire extinguishers should be regularly checked and maintained to ensure they are in good working order and ready to use in the event of a fire.
Manual Call Point (MCP) For Fire Alarm
Manual Call Point
Manual call point (MCP) is a trigger mechanism which helps in identifying the building or an area where fire has occurred in order to direct the attention of personals to that area. It is a part of fire alarm system.
MCP is basically a switch which is installed at various locations so that it is accessible to everyone who detects a fire to use it to inform others about the same. The switch is put in a mechanical box and a transparent glass is attached to the box using sealing rings. The box is labeled so that one can identify that it is to be used when there is an emergency fire situation. A hammer or similar tool is provided to be used to break the glass.
MCP is accompanied with a visual indication tool to locate the call; for example a plastic flag. If someone breaks the glass to hit the switch then the plastic flag raises in the building thus helping in directing attention of the personals who will act against the emergency fire situation and also to alarm others to stay away from the building or the area.
A MCP unit can be combined with automation to automatically detect the fire using heat or smoke detectors and set off an alarm. MCP comes as wired installation and also as a non-wired or temporary installation. Both provide similar kind of protection and both can be automated. The temporary MCP has an added advantage that it does not require need for a specialized electrician and can be moved from one location to another. They run on batteries unlike the wired MCPs, thus they have to be checked every now and then to ensure that the batteries are working optimally.
The break-glass type of MCP is now being replaced with plastic elements because of the cost of replacing the glass in case of false fire detection. The plastic elements just have to be depressed firmly, they are easy to reset and can be used multiple times. They are also attractive since there is no danger to the person using it unlike the break-glass type MCP.
Types of Manual Call Point
(A) Button type:
The mechanism contains a button which needs to be pressed. The pressing of button raises a visual indicator and also informs about the change in loop current.
(B) Key type:
The mechanism contains a key hole instead of a button which calls on pressing. This mechanism contains key turning as a switch mechanism to alert everyone about the fire which has occurred. In case of false fire detection, the key can be used to easily reset the mechanism.
Uses of Manual Call Point
Although MCP can be used in conjunction with the automated system, they were designed to be used manually. The MCPs are installed at various locations at regular intervals so that they are easily accessible by anyone in case they spot a fire occurring. They can be installed in any type of infrastructure.
It is important to install MCPs even if an automatic fire detection system is already installed because automatic systems may be used during the day or at the night or when a process is running. Also, automatic systems have to be disabled if they have to be inspected. If a fire occurred in such scenarios the MCP will be very useful.
Types of Hazards in Industry
Types of Hazards
Types of Hazards
Hazard is defined as something which has the potential to cause harm. Danger is synonymous with hazard. Anything of such nature which has possibility to cause harm in some way, even theoretically, is considered a hazard.
Hazard can occur due to different reasons and the occurrence may have different consequences thus the hazards have been categorized to fall in different classes. The importance of segregation of hazards is to be able to identify what measures are to be taken to reduce or eliminate a risk.
Hazard is classified in six types in chemical industry; chemical hazard, biological hazard, physical hazard, safety hazard, ergonomic hazard, psychological hazard.
Types of Hazards
Chemical Hazard:
Working with chemicals is central to a job in a chemical industry. Different chemicals affect personals and environment in different ways. Some are toxic, some are flammable, some are quite corrosive, some are carcinogenic. Contact of such chemicals can do variety of harm to human body. If an accident is to occur then some chemicals are also liable to cause harm at a mass scale. If it is necessary to use a hazardous chemical then it is extremely important to train the personal properly with SOP prior to placing the person in that part.
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