Chemical Process Selection, Design and Operation
Adequate and flexible initial design is essential for the promotion of a chemical plant organic product or inorganic product.
In older days it was classified as inorganic chemical technology and organic chemical technology. Subsequently the oxford university made it as chemical works organization and management.
Some factors that must be considered in planning a plant are discussed in this section. The Process Engineer is an expert in the current aspects of chemical process design. Practical experience is a must if the senior design engineer is able to foresee and solve the problems of production, such as maintenance, safety and obeying the government, environmental by loss and control.
Experience consultants either individuals or professional consulting firms are able to advise, design and for erection of chemical plants.
Chemical Process Control and Instrumentation
Automatic and Instrument control chemical processes are common and essential. Instruments should not be chosen simply to record a variables, of the process. But their function is to assure consistent quality by sensing controls, recording and maintaining desired operating conditions. Instruments are the essential tool for modern processes. They are classified as
1. Indicating Instruments 2. Recording Instruments 3. Controlling Instruments
Two types of Instruments are currently used as analogue and digital.
Analogue Instruments such as pressure spring thermometers and Bourden Gauges shows results by mechanical moments of some type of device which is directly proportional to the quantity measured.
On the other hand, digital devices are converts the quantity measured into a signal and electric circuits converts the signal to read the numerical values forward by control. Now the computers can monitor and regulate outputs from both the analogue and digital devices according to a prearranged program, also general conventional digital inputs are required. Chemical analytical control has been used in day to day factory procedures for analysis of incoming raw material or outgoing products. Thus quality chemicals are produced more in these days reliably their when human analysed control were used.
The latest advancement are the chromatography system, many spectroscopy have been automated an install of on-line basis for the process to run continuously without the problems encountered manually before.
Role of Chemical Engineers
Engineers are trained primarily to work in chemical industries. some of
the vital role of the chemical engineers are as follows;
Chemical Process Economics
Engineer are totally different from Scientist by their customers of cost of production and profit generator. Therefore the objective of engineer should be to deliver safely the best product or most efficient service at lower cost to the employer and the public who consumes the product.
Yield and conversion are the chemical prospects from the basis for the material balances which is useful for cost determination.
Materials and their quantities from the standard practices are tabulated in the flow charts, energy given are observed for the chemical reactions and energy is frequently a major cost in chemical plants but it often possible by altering the process procedures by using modern separation technologies like “RO” and “Advanced Separation Processes” to produce high quality chemicals with low energy consumption.
The location of the chemical plant is decided ourselves by the availability of raw materials, transportation, market and power. Now the environmental constituents, water supply, availability of efficient labor, cost of land and waste disposal facilities form the criteria for the plant location.
Construction of Plant
For small and large companies construction engineering organizations are available that will built a plant and participate in its design. Some large chemical companies have their own civil construction department and starts their own plants.
The advancement of this is the worker who is going to operate the equipment can be more intimately corrected to the constructions and be familiar themselves for the future alternatives, expansion or modifications.
In built-in plants the top engineers are chartered engineers qualified for the development activities. They have been trained and suitably examined to guarantee technical competency and owe personal responsibility. They are now called as functional consultants and registered firm for dealing with legal aspects with proper training.
Research and Development
adequate and skilled research with patent protection is necessary for future profits. In the chemical process industries one of the outstanding tactics is rapidly changing processes, new raw materials and new markets. Research creates these changes and the factory will have a competitive progress. This research brings about development and the adoption of ideas, concepts, methodologies form the production of the industry. The results and benefits of research establishes the developing coutry on the road of progress and raise the level of life of common man.
Chemical Engineer in coming years
The latest research and development have classified the following new industries;
chemical process industry had its growth from pre scientific chemical
industries followed by scientific chemical industry. The growth with
restrains, green challenge to chemical industry and the modern
separations process involved in the indian chemical industry seen
The Research is divided into three categories like Fundamental Research, Exploratory Research and Process Research.
The largest tonnage inorganic chemicals is H2SO4. It is consumed by industry in the manufacture of other products. Thereby it reaches the public knowledge vary scarely. Large quantities are consumed by petroleum and metal industries. The important organic chemical include alcohols, dyes, dye intermediates used to produce other chemicals. Ethyl alcohol was initially produced by bio chemical fermentation before the second world war.
But now it is produced primarily from petroleum on the latest discovery of natural gas. The important petroleum products are gasoline, lubricants, petrochemicals, other fuels and miscellaneous chemicals. Since the second world war petrochemicals have assumed a commander role in the economy. The largest petrochemical ammonia is produced by reaction of H2 from natural gas or petroleum with N2 available in the Air.
This Ammonia reacts with CO2 to produce Urea in a fertilizer plant. Normally there are five different units in the fertilizer manufacture from coal based mines.
The tendency of Urea is to form BIURETS which are used as regenerator salts in the metallurgical applications. Many plastics and synthetic detergents are produced with the help of oil refineries.
The basic physical operations of chemical engineering in a chemical process plant, that is distillation, fluid transportation, heat and mass transfer, evaporation, extraction, drying, crystallization, filtration, mixing, size separation, crushing and grinding, and conveying. In simple terms, the operation which involves physical changes are known as Unit Operation.
Classification of Unit Operations
Gases are discharged into the ambient atmosphere by stacks (referred to as chimneys in industry) of several types.
The chemical process steps involved the following;
This mainly fall into inorganic, natural products, organic chemicals and metallurgical industry.
Processes that involve making chemical changes to materials, as a result of chemical reaction taking place. For instance, in the combustion of coal, the entering and leaving materials are differ from each other chemically. Coal and Air enters, and flue gases and residues leave the combustion chamber. Combustion is therefore a unit process. Unit processes are also referred to as chemical conversions. In simple terms, the process which involves chemical changes are known as Unit Processes.
Together with unit operations (physical conversions), unit processes (chemical conversions) form the basic building blocks of a chemical manufacturing process. Most chemical processes consist of a combination of various unit operations and unit processes.
Addition of alkyl radical (CH3) with side chain final product. This alkylation process is widely used in organic chemicals and petroleum industries. The reaction is given as,
C=C-C-C + C-C-C
2. Amination by Ammonolysis:
Cl-CH2CH2Cl + 4NH3 ------->NH2CH2CH2NH2
EDC Ethylene Diamine
This reaction is used in manufacture of dye stuffs, organic chemicals and synthetic fibres.
3. Amination by Reduction:
CH3CHNO2CH3 + 3H2 ------> CH3CHNH2CH3
2 Nitro Paraffin Iso Propylamine
This unit process is also used in the manufacture of dye stuffs and organic chemicals.
4. Amino Oxidation:
CH3CH2CH3 + NH3 + 1.5 O2 -----> CH2:CHCN + H20
This reaction is used in the manufacture of plastics and synthetic fibres.
CaCO3 ---Heat---> CaO + CO2
This reaction is used in the cement industry.
CH3OH + CO -----> CH3COOH
Methanol Acetic Acid
This is used in the manufacture of organic chemicals.
This reaction is used in the organic chemical industry.
CH4 + O2 ------> CO2 + 2H2O ( Process Heating )
C6H5CHO + CH3CHO ------> C6H5CH:CHCHO + H2O
10.Cracking or Pyrolysis:
C-C-C-C-C-C-C --------> C-C-C + C=C-C-C
This reaction is used in petroleum destruction and distillation of coal.
1. Fluid - Solid Contact:
Represented by fixed bed reaction. It is most widely used in catalytic reactor used with precious metal catalyst to minimize attrition losses. The catalyst used in the form of pellets. It can represented by the following figure.
This is used in the packed column. The design of the column is determined by the breakthrough curve, equilibrium line for the given system of adsorbent and adsorbate's. The volume of the reactant coming from the top and the volume of which the product leaves the column, residence time, distribution decides the dimensions of the column. It is contrary to the fluid bed reactor where the bed is fluidized. Once the minimum fluidized velocity is reached the porosity of the bed is faster in a fixed bed reactor but varies from the fluidized bed where the porosity changes according to the height of the bed.
2. Fluid - Solid Separation: (Centrifugation)
This operation separates very finely divided solids from liquid or mixture of liquid and liquid emulsion.
3. Wet Scrubber:
It is an effective means of removing suspended particles from gas string by contact with liquid shower.
When solids are used in the place of liquid the operation is called Dry Scrubber. In the manufacture of MEK, wet scrubber is used and in other selected process industries Dry Scrubbers are used,
Scrubber just washes away the impurities and separate the product for further purification.
4. Filter Press:
It is the simplest type of pressure filtration. the two important parts of the filter press are plates & frames and fabric used in between the two are made of variety of corrosion resistant materials. In the laboratory scales asbestos cloth are used for filtration at different pressures.
The operation decides the value of specific cake resistance, filter medium resistance and compressibility of the chemical namely Kieselghur a specific compound in the nature of diatomacceous earth which are used in the application of bio-physics and cyrstallography.
5. Fluid Storage:
Tanks are widely used for storage of liquids of all types and atmospheric pressure when the liquid is highly volatile there is a floating roof which acts as lid for chemicals as and when the vapour pressure at which signifying the boiling point of liquid the roof changes its position and deserves the liquid from going out to the atmosphere.
6. Pressurized Spheres:
Pressurized spheres are used for pressurized storage of liquefied gases or high vapors. The pressure permits safe storage with no vapor losses. This is seen in the fertilizer plant where ammonia is stored in spheres.
7. Gas-Liquid Contact: (Absorption)
The best example is Absorption. It is used for taking a soluble gas in a solvent liquid and producing a solution plus an exit gas. Hydrogen Sulphide is removed from hydrocarbon by the absorption process.
It is classified into physiorption and chemisorption according to the process applied. The former one is almost a physical change or physical transformation while a later represents a chemical reaction which is a irreversible one. the common effluent treatment plants of varies nature lied textile effluents, sewage treatment, ETP plants in chemical industry, removal of hazardous solid wastes, etc are dealt with adsorption method and the adsorbent is regenerated over a period of time and used again and again.
9. Heat Exchangers:
The various cooling towers of natural draft and forced draft are example of industrially applied H.Es. These are common facilities in the thermal power stations and in chemical industries the application of shell & tube heat exchangers are widely used. this is an excellent application of heat transfer from one medium to the other.
Dialysis is used to separate metals in solution having widely different molecular weight. for example caustic from sugar solution or cellulose.
This involves crushing, grinding, pelletizing and prilling. Pelletizing is used in pharmaceutical industries and prilling used the manufacture of Urea.
Modern chemical processes are offer extremely complex operations involving 100s of pieces of equipment. without a systematic approach it would be impossible to analyses an existing process or to design equipment process. The typical chemical process is analyzed with the following interdependent considerations like,
- Mass & Energy Balance
- Thermo chemistry
- Unit Operations
- Plant Equipment
- Ancillary Equipment
- Process Plant Diagram
- Instrumentation Control
which deals with net profit before taxation profit after taxation dividend paid to the public and share holders. Once the process as been developed and completed attention can be made to access the various liabilities, resource and assets.
Alternatives and the remaining choices can be ranked in the order of desirability. They are as follows;
- Effectiveness for reducing waste
- Technical Risk
- Extended of current views in the facility
- Industrial Precedent
- Capital and Operating cost incurred
- Effect of the Quality of the product
- Impact of Plant Operations
- Required time for Implementation
- Other aspects important in the particular situation according to the industrial
Conservation of Energy:
dE = Q - W This is a steady state batch process.
dH = Q - Ws Thia is for flow process.
Q--> Heat energy transfered across system boundary.
W-->Work energy transfered across system boundary.
Ws->Mechanical work energy transfered across system boundary.
E--> Internal energy of the system.
dE, dH--> Changes in Internal Energy & Enthalpy during the process.
we are already classified the various unit operations and below is a particular basic column of mass transfer equipment.
It is classified into Batch and Continuous Fractionation.
a. Batch Fractionation:
Used for intermittent operation and handling of small volume of feed and products.
b. Continuous Fractionation:
These are used for high volume continous seperation of complex mistures such as petroleum fractions connected to appropriate pumps, re-boilers, condensers, scrubbers, strippers and finally automatic controls.
2. Drying of Solids:
Spray Dryer , Rotary Dryer & Tunnel Dryer are some example of these types.
Open pan evaporators and multiple effect evaporators as used in sugar and salt industries for example. Among these halogen family we have technology to separate chlorine and fluride but production of bromine from the 'sea brine'is almost not put into practice as the bromine chemicals is highly corrosive and necessary precaution has to be laid out for practical purpose.
5. Fluid Handling Equipments:
6. Fluid - Solid Contacting:
7. Fluid - Solid Separation:
8. Fluid Storage:
9. Gas - Liquid Contact:
13.Size Reduction & Enlargement:
15.Solid - Solid Separation:
The Reactor is the heart of the chemical process. The design of an industrial chemical reactor must satisfy the requirements in four main areas.
1. Chemical Factors:
This involve the kinetics of the reaction weather it's first order or second order and based on this chemical reaction engineering is built on the design must provide sufficient residence time to proceed the reaction for the required degree of reaction and conversion to product.
2. Mass Transfer Factors:
The reaction rate of homogeneous reaction may be controlled by the rate of diffusion of reactants rather than the chemical kinetics of Langmuir isotherm and Frendlich isotherm.
3. Heat Transfer Factors:
These describes weather the reaction is exothermic or endothermic. In Exothermic, heat is released outside and In Endothermic, heat is absorbed by reactants. The value of heat of reaction is necessary to operate the chemical reactor.
4. Safety Factors:
This involve the confinement of any hazardous reactant and products as well as the control of reaction and process conditions.
Based on these factors the Reactor Types as follows;
a. Mode of Operation - Batch or Continuous
b. Phases Types - Homogeneous or Heterogeneous
c. Reactor Geometry - Flow Pattern & Process of contacting the phases.
The five major classes of Reactor;
iv.Packed Bed (Fixed)
v. Fludised Bed
Compounds like pigments, dye stuffs, pharmaceuticals and polymers are manufactured by Batch Processes.The Latest Heat Exchangers are Direct or Contact Exchangers In addition to Double Pipe Exchanger, Shell & Tube Exchanger and Plated Frame Exchanger.
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