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Part
Content
One
Some of general information about chemical engineering Topics
Two
(PROCESS VALVES) course
Three
Questions asked by the page and their correct answers
Four
Questions asked by our fans and answers by our page
Five
Questions asked by our fans and answers by others
I am a Chemical
Engineer
• We discuss Chemical Engineering
and provide some information and
news.
• We would like to think of our page
as an exchange page of experience
and information.
https://www.facebook.com/IamCheEng
Slogan
Connecting chemical engineers.
Vision
Improving the chemical Engineering
skills to meet the work environment &
to decrease the gap between study
and work.
Mission
Gathering information about any
chemical engineering fields.
How about a career where the opportunities are endless? Trying not to
sound like an advertisement, I'd like to describe some of the more
common careers pursued with a Chemical Engineering degree. Firstly, if
you're considering studying Chemical Engineering, but you're a little
timid because of the horror stories that you hear, you actually may want to
think about it some more! I've actually heard someone say, "How hard can
it be?" Really hard, but really rewarding too! True, the material involved
in far from easy and some of the concepts take hours (and in some cases
years!) to master, but isn't having this degree worth the effort? I think that
you'll find that it will be. I guess what I'm saying is, if you're serious
about wanting to be a Chemical Engineer, go for it and don't be afraid to
fail (as long as you've done your best). If you're not sure what you want to
do, take some preliminary courses first and then ask some of the current
students what they think so far and compare you're academic merit to
theirs.
Now, once you've got the degree, the fun really starts. I suggest taking the
Fundamentals of Engineering Exam (FE Exam) shortly before or after
graduation. The after 4 or 5 years of industrial work, you can take the
Professional Engineering Exam (PE Exam) and become a Certified
Professional Engineer. Always a good idea to take these exams,
remember, if you don't someone else will and they'll probably get your
job! Speaking of jobs, what kind of work can you do with a Chemical
Engineering degree?
"I love designing equipment, optimizing processes, and performing
financial analyses on these processes."
--DESIGN ENGINEER
"I like to analyze existing processes and suggest changes needed to
increase profitability"
--PROCESS ENGINEER
"I really like designing and performing experiments to test theories and
check the economic impact of plant changes on a small scale"
"I'm a people person and I don't like being trapped in one place all of the
time"
--FIELD ENGINEER OR TECHNICAL SALES PERSONNEL
"I want to be a physician"
--MEDICAL SCHOOLS REALLY LIKE CHEMICAL ENGINEERS
"I'm out of school, I'm tired of engineering and I never want to do it
again"
--YOU GRADUATED WITH ONE OF THE MOST DIFFICULT
UNDERGRADUATE DEGREES THAT THERE IS. MAYBE YOU'D
RATHER LOOK INTO BECOMING A FORENSIC CHEMIST OR
AN ENVIRONMENTAL CONSULTANT. WHATEVER YOU
DECIDE TO DO, YOU HAVE A QUALITY EDUCATION THAT NO
ONE CAN TAKE FROM YOU.
A Chemical Engineering degree may not be a free ride through life,
but it does provide a solid base to start a wide variety of careers and
after all, wasn't that you're objective to begin with?
Below you'll find an interview that was completed many years ago (circa
2000) that high schools students have used to help them make their
decision regarding chemical engineering.
Interview with a Chemical Engineer
Many students find their way to
The Chemical Engineers’ Resource Page
in search of a chemical engineer to interview for career research. We
applaud these students and are happy to help in their quest to learn more
about chemical engineering. The following are 17 of the most commonly
asked questions.
Why Become a Chemical Engineer? and Interview
with a Chemical Engineer BY
Christopher Haslego
Owner and Chief Webmaster
www.cheresources.com
NO
1.
How did you come to choose this career? Why did
it appeal to you?
Actually, as with many college students, I changed my major course of study
during my freshman year. I began college as a computer science major. I
quickly found that computer science just was not for me. I explored the
campus and found a course of study that combined technical thinking with a
topic that had always interested me…..chemistry. As I learned more about
chemical engineering, I just knew it was for me.
2. What kind of training or education did this career require
and what college or university did you attend?
The training included a 5 year (sometimes 4 depending on the university that
you attend) academic cirriculum. I attended West Virginia University in
Morgantown, WV. My classes included 4 units of Calculus, at least 6 of
chemistry, some general engineering which included computer programming,
thermodynamics, transport analysis, fluid dynamics, heat transfer, material
and energy balance (2 classes), process control, chemical reaction
engineering, separation technology, and chemical process design just to name
some of the more important classes. However, at a university type setting,
you'll also be required to take classes known as core requirements to make
you a "well rounded individual". Mine included Theatre, Spanish,
Criminology, Political Science, Geology, and Physiology....you get the
picture. You can go to WVU's chemical engineering page at
www.cemr.wvu/~wwwche/ and look under the "Undergraduate program" to
see a complete cirriculum there.
3. Are there any other skills beyond formal training that
someone needs to do this job?
Your college training is just the beginning of your education. When you land
your first job, you’ll learn how the “real” world works. There are numerous
skills that chemical engineers entering a chemical plant environment just do
not know. You will learn many aspects of the business world, details of the
equipment and process that you work with, and other “political” issues of the
workplace. While the training that you receive in college is extremely
important, I’d say that most people would agree hat on-the-job training is
where they learned the skills that made them a good engineer. These are all
reasons why it’s so hard to land that first job without any experience. In
short, many people will know more than you and will be more productive
much faster.
4. How long is a typical work day? What time does
your day end?
I begin work at 8:00 A.M. and I generally finish between 5 and 6 P.M. I
should mention that I now work in an office environment. I began my career
in a chemical plant, but the hours where the same. The problem was that it
was not uncommon to receive calls on weekends or late at night if problems
occurred at the plant. I work this schedule five days a week (Monday
through Friday).
5. What is the starting salary or hourly wage for this job? Is
there overtime pay?
The starting salary is usually around $45,000 per year but can be as low as
$38,000 or as high as $50,000 per year. Most chemical engineers work on a
fixed salary every two weeks or month. This means that they do not earn
extra money for working more than 40 hours per week. Most employers are
liberal with salary employees. For example, you may work 50 hours one
weeks, and only 35 the next. Usually, I’d say that the yearly average works
out to be near 40 hours per week, but some people prefer to (or are required
to) work more.
6. How can you advance your career as a chemical engineer?
The best way for anyone to advance in their career is to separate themselves
from other employees. Stand out, do something great! In general, the best
ways to do this are to earn money for the company by finding ways to
manufacture products cheaper, find unique solutions to complicated
problems, or increase the efficiency of the way that you and others work.
All of these will help the company that you work for perform better. It will
also help you succeed.
7. How much paid vacation time do you receive?
I receive two weeks paid vacation, two “float” holidays, and two personal
days. That’s a total of 14 paid days off per year. During my fifth year of
service with my company, I’ll receive an additional 5 days per year and
there are further increases the longer that you’re with the company.
Although some companies place restrictions on the number of paid sick
days that one can receive, mine does not. We have a simple policy, “if
you’re sick, don’t come to work” (this is not very common and people
appreciate it and it is seldom, if ever, abused).
8. Do you have a retirement plan? What is included?
My company offer its employees a standard retirement package called a
401K. This allows employees to put money into an account (without being
taxed) to save for retirement. My company automatically contributes 3% of
my salary to this account and I can add up to 14% of my annual salary (up
to $10,000 per year) into the account. My company, additionally, matches
50% of the first 6% that I contribute. Essentially, if I save 6% of my salary,
my company puts in 6% of my salary. Don’t overlook the importance of
saving for retirement when you begin your career. Young workers often
begin saving too late and may delay their retirement. This money is later
taxed when it is withdrawn after you retire.
9. Does the job have medical or dental benefits? Is it full
coverage or is there a deductible or co-payment?
I have both medical and dental benefits. With the cost of healthcare, very
few companies offer “full” coverage. I pay (very little) for these insurance
plans and my employer pays the remaining amount. Most dental work is
covered at 80% (check-ups and an annual x-ray are covered at 100%). I
have a small co-pay for hospital and doctor visits, but under normal
circumstances I have to visit my Primary Care Physician (PCP) and
coordinate my care with her. To avoid the circus that healthcare has
become….try to stay healthy :)
10. What are three things that you enjoy about your job?
I enjoy most everything about my job! I work as a design engineer for a
company that supplies heat transfer equipment to the chemical industry. I
also do some marketing and sales work as well. I guess I enjoy the
following the most:
a. The independent work environment (no one looking over my shoulder)
b. Knowing that I’m directly responsible for helping my company to
succeed
c. Being able to travel anywhere in the US at any time that I choose
11. What are some things that you do not enjoy?
I spend a lot of time on the phone, which really is not my favorite thing to
be doing, but it’s important nonetheless. Sometimes, it can be hard to
accomplish goals because of the “official” channels that you have to work
through…this can be frustrating.
12. How long have you been working in this occupation?
How long do you expect to remain in this field? If you are
going to make a change, why?
I’ve been in my current position for two years now. I also working for
another company for a year. I made the change because I really did not feel
comfortable with my last employers. They did not encourage “forward”
thinking at all. Creativity was not encouraged for fear that an idea may not
work. This is not a good environment for a young engineer. I made the
change and I’ve glad that I did ever since. My current employer goes out of
their way to encourage new ideas and we’re a better company because of it.
13. How much of a demand do you see for this occupation in
the future?
When I graduated from college in 1998, there was a great demand for
chemical engineers. Naturally demand goes up and down depending on the
economy and how many people graduate each year. Generally, I’d say that
there is always a need for good chemical engineers. Chemical engineers can
perform many different functions. Probably why you don’t hear of many
chemical engineers who are out of work.
14. What high school classes are good for preparing to become
a chemical engineer?
This is an easy question. While the classes are free, take as much math and
science as you possibly can. They will only prepare you better for college
and give you an advantage over your peers who will probably be very
intelligent.
15. What advice would you give to someone considering this
occupation?
Be ready to work hard to get through college. Don’t get discouraged. If at
all possible, DO AN INTERNSHIP, DO AN INTERSHIP, DO AN
INTERSHIP. An internship will give you an opportunity to get some
experience before you graduate. The field is very rewarding and you most
likely will never have to worry about finding a job for the rest of your life.
Instead, you’ll only worry will be finding a job that you enjoy.
16. Where are job for chemical engineers available (rural,
urban)?
Most chemical plants are found in rural areas, so to begin you’re career, you
may find yourself in a remote area. After you gain some valuable
experience, you may consider a bit of a career change and may be able to
land a good job in a more urban area (this is pretty much what I did). My
first job was in rural South Carolina and now I reside in beautiful
Richmond, VA.
17. Did you specialize in any topic in particular?
In school, I emphasized polymers (plastics) in my studies. This helped get
me my first job in a polymer plant. Now I concentrate on heat transfer (one
topic in chemical engineering).
18. How does chemistry enter into your profession?
For example: As a chemical engineer, you may have to separate water and
benzene sometime....you had better know how the two interact chemically
before you start. Do you know if they are miscible in one another?
"Miscible" is a term used to describe two liquids that mix thoroughly....like
water and alcohol. But water and oil are "Immiscible" in that the oil "floats
on top of the water"...this is just one example of how chemistry is very
important to a chemical engineer. If you're going to be responsible for
moving, separating, and reacting chemicals...you better know about the
chemicals and how they react to one another first! Some of the chemical
knowledge will also come with experience. For example, if someone were
to ask you how to remove caffeine from coffee beans, what would you
recommend? Experience tells me that there are two basic, industrially
accepted methods. One uses a solvent known as methyl chloride and the
other uses carbon dioxide under extremely high pressure (supercritical
carbon dioxide). The use of methyl chloride is an older method and requires
additional precautions because methyl chloride is poisonous so one must be
sure that is does not contaminate the coffee. Using supercritical carbon
dioxide requires more expensive equipment, but the risk on contamination is
no longer there because carbon dioxide is not poisonous to humans. Using
carbon dioxide to decaffeinate coffee has been advertised as "natural
decaffeination".
Dosing pumps
can operate based
on the principles of dynamic pumps or
positive displacement pumps depending
on the design. Dynamic pumps produce
a variable flow suited for generating
high flow rates with low viscosity
fluids, while positive displacement
pumps produce a constant flow suited
for producing high pressures (and low
flow rates) with high viscosity fluids.
Most dosing pumps are positive
displacement pumps, which provide
steady, low flow for a variety of types of
media.Dosing pumps are used in a
variety of commercial, industrial,
municipal, and maritime applications.
Examples include agriculture and
horticulture, dairy farms, breweries and
distilleries, construction, food service
and food processing, power generation,
and oil and gas production. Dosing
pumps are also used in the aerospace
and defense, automotive, machine tool,
mining, medical, pharmaceutical,
semiconductor, and paper industries.
Bernoulli equation
In fluid dynamics,
Bernoulli's
principle states that
for an inviscid flow,
an increase in the
speed of the fluid
occurs
simultaneously with a
decrease in pressure
or a decrease in
the fluid‘s potential
energy.
Operation of
Spiral Heat Exchangers
:
The hot fluid enters at the corner of the unit and flows from the inside outward. The
cold fluid enters at the periphery and flows towards the center.Thus, true
counter-current flow is achieved.
Advantages of Spiral type:
- Efficient use of Temperature Difference.
- Low Fouling (Self Cleaning).
- High Overall Heat Transfer Coefficient.
- Easy Maintenance.
- Space Saving.
difference between steady and unsteady flow:
steady: A steady flow is one in which the conditions (velocity, pressure and
cross-section) may differ
from point to point but DO NOT change with time.
unsteady: If at any point in the fluid, the conditions change with time, the flow is
described as unsteady.
steam trap:
Mostly, steam traps are automatic valves that discharge condensate and some
non-condensable gasses. In a perfect world, they perform this task without
consuming much live steam in the system. The most important functions a steam
trap performs are the following:
1. They get rid of condensate as soon as it is formed
2. They get rid of non-condensable gasses
A Steam Trap performs two functions. First, it
is an air vent. As steam fills the pipes on
startup it must displace air, and during
equipment operation all air formed must be
vented. Secondly, it is a water outlet valve,
which allows residual water to be removed
from the steam system faster than it is formed.
Plate Heat Exchangers
have a high heat transfer rate compared to
other types of heat exchangers due to their large surface area. They are composed
of a number of thin metal plates compressed together into a ‗plate pack‘ by two
pressure plates. Within a plate heat exchanger, the fluid paths alternate between
plates allowing the two fluids to interact, but not mix, several times in a small
area. Each plate is corrugated to increase the surface area and maximize heat
transfer. Plate Heat Exchangers have a number of applications in the
pharmaceutical, petrochemical, chemical, power, industrial dairy, and food &
beverage industry.Plate heat exchangers are ideal for applications where the
fluids have relatively low viscosity with no particles. Also they are an ideal
choice where there is a close approach between product outlet temperature and
service inlet temperature. Plate heat exchangers consist of thin, corrugated plates
which are gasketted or Cu brazed. The plates are tightened into a plate pack
inside a frame, with product in alternate channels, and service fluid in between
product channels.Plate heat exchangers are small, yet efficient. It is possible to
have a Plate exchanger with the same thermal capacity of a Shell & Tube heat
exchanger five times its size. The compact design conserves space in the heat
exchanger environment, as well as material cost. Plate heat exchangers are
available in a variety of sizes and materials to suit many different applicationsand
industries.
Jet Mill
works on micronizing of
products using compressed air instead
of mechanical impacts due to which
the micro size is very fine. Micro
milled products are obtained in
microns after the material collide with
each other and reduce themselves by
attrition and collision.which consists
of grinding chamber takes the shape of
an oval loop of pipe 25 to 200 mm in
diameter and 1.2 to 2.4 m in
height .Feed enters near the bottom of
the loop through a venture injector.
Centrifugal classification of the
ground particles takes place at the
upper bend of the loop. The operating
gas enters the grinding chamber
through energizing nozzles placed in
the wall. A discharge opening in the
inner wall leads to a cyclone separator
and a bag collector of the product.
Brief on
Ammonia production
from Natural Gas -
1) Feed-stock desulphurization
This part of the process is to remove the sulfur from the feed-stock over a Zinc oxide
catalyst bed, as sulfur is poison to the catalysts used in the Subsequent processed. The
sculpture level is reduced to less than 0.1 ppm in this part of the process.
2) Primary Reforming
The gas from the desulphuriser is mixed with process steam,
usually coming from an extraction turbine, and steam gas mixture is then heated
further to 500-600 °C in the convection section before entering the primary reformer.
Sometimes in some plants the preheated steam/gas mixture is passed through an
adiabatic pre-reformer and reheated in the convection section before entering the
primary reformer.
Brief on
Ammonia production
from Natural Gas -
The amount of process steam is given to adjust steam to carbon-molar ratio (S/C-
ratio), which should be around 3.0 for the reforming processes. The optimum ratio
depends on several factors, such as feed-stock quality, purge gas recovery, primary
reformer capacity, shift operation and the plant steam balance. In new plants, S/C
ratio may be less than 3.0.
The primary reformer consists of a large number of high-nickel chromium alloy
tubes filled with nickel-containing reforming catalyst in a big chamber (Radiant box)
with burners to provide heat.
The overall reaction is highly endothermic and additional heat is provided by
burning of gas in burners provided for the purpose, to raise the temperature to
780-830 °C at the reformer outlet.
The composition of gas leaving the reformer is given by close approach to the
following chemical equilibrium:
CH4 + H2O = CO + 3H2
CO + H2O = CO2 + H2
The heat for the primary reforming is supplied by burning natural gas or other
gaseous fuels, in the burners of a radiant box containing catalyst filled tubes.
The flue gas leaving the radiant box has temperature in excess of 900 °C, after
supplying the high level heat to the reforming process. About 50-60% of fuel‘s heat
value is directly used in the process itself. The heat content (waste heat) of the
flue-gas is recovered in the reformer convection section, for various process and steam
duties. The fuel energy required in the conventional reforming process is 40-50% of
the process feed energy.
The flue-gas leaving the convection section at 100-200 °C is one of the main sources
of emissions from the plant. These emissions are mainly CO2, NOx, with small
amounts of SO2 and CO.
3) Secondary reforming
Only 30-40% of the hydrocarbon feed is reformed in the primary reformer because
of the chemical equilibrium at the actual operating conditions. The temperature must
be raised to increase the conversion. This is done in the secondary reformer by
internal combustion of part of the gas with process air, which also provides the
nitrogen for the final synthesis gas. In the conventional reforming process the degree
of primary reforming is adjusted
Brief on
Ammonia production
from Natural Gas -
so that the air supplied to the secondary reformer meets both the heat and the
stoichiometric synthesis gas requirement.
The process air is compressed to the reforming pressure and heated further in the
primary reformer convection section to about 600 °C. The process gas is mixed with
the air in a burner and then passed over a nickel-containing secondary reformer
catalyst. The reformer outlet temperature is around 1000 °C, and up to 99% of the
hydrocarbon feed (to primary reformer) is converted, giving a residual methane
content of 0.2-0.3 (dry gas bases) in the process gas leaving the secondary reformer.
The process gas is cooled to 350-400 °C in a waste heat boiler or waste heat
boiler/super heater down stream from the secondary reformer.
4) Shift conversion (High & Low)
The process gas from the secondary reformer contains 12-15% CO (dry gas bases)
and most of the CO is converted in the shift section according to the reaction:
CO + H2O = CO2+ H2
In the high temperature shift conversion (HTS), the gas is passed through a bed of
iron oxide/Chromium oxide catalyst at around 400 °C, where the CO content is
reduced to about 3% (dry gas bases), limited by the shift equilibrium at the actual
operating temperature. There is tendency to use copper containing catalyst to
increase conversion. The gas from the HTS is cooled and passed through the low
temperature shift (LTS) converter.
The LTS is filled with a copper oxide/Zinc oxide-based catalyst and operates at
about 200-220 °C. The residual CO content is important for the efficiency of the
process. Therefore, efficiency of shift step in obtaining the highest shift conversion
is very important.
5) CO2 Removal
The process gas from the low temperature shift converter contains mainly H2, N2,
CO2, and excess process steam. The gas is cooled and most of the excess steam is
condensed before it enters the CO2 removal section. This condensate usually
contains 1500-2000 ppm of ammonia, 800-1200 ppm of methanol and minor
concentration of other chemicals. All these are stripped and in the best practices the
condensate is recycled.
The heat released during cooling/condensation is used for:
regeneration of CO2, scrubbing solution.
Brief on
Ammonia production
from Natural Gas -
The amount of heat released depends on the process steam to carbon ratio. If all this
low level heat is used for CO2 removal or absorption refrigeration, high-level heat
has can be used for feed water system. An energy-efficient process should therefore
have a CO2 removal system with low heat demand.
The CO2 is removed in a chemical or physical absorption process. The solvents used
in chemical absorption process are mainly aqueous amine solutions Mono
Ethanolamine (MEA), activated Methyl DiEthanolamines (aMDEA) or hot
potassium carbonate solutions.
Residual CO2 content are usually in the range 100-1000 ppmv, depending on the
process used. Contents of CO2 down to 50 ppmv are achievable.
6) Methanation (not in all plants)
The small residual amount of CO and CO2 in the synthesis gas, are
poisonous for the ammonia synthesis catalyst and must be removed by conversion to
CH4 in the methanator :
CO + 3H2 = CH4 + H2O
CO2 + 4H2 = CH4 + 2H2O
The reaction takes place at around 300 °C in a reactor filled with nickel containing
catalyst. Methane is an inert gas but water must be removed before entering
converter.
7) Synthesis Gas Compression and Ammonia Synthesis
Modern ammonia plants use centrifugal compressors for synthesis gas compression,
usually driven by steam turbines, with steam being produced within the ammonia
plant from exothermic heat of reactions. The refrigeration compressor, needed for
condensation of product ammonia, is also driven by a steam turbine.
The synthesis of ammonia takes place on an iron catalyst at pressure usually in the
range of 100- 250 kg/cm2 and temperatures in the range of 350-550 °C:
N2 + 3H2 = 2NH3
Only 20-30% of synthesis gas is converted to ammonia per pass in multi bed catalyst
filled the converter due to the unfavorable equilibrium conditions. The ammonia that
is formed is separated from the product gas mixture by cooling/ condensation, and
the unreacted gas is recycled with the addition of fresh make up synthesis gas, thus
maintaining the loop pressure.
Brief on
Ammonia production
from Natural Gas -
In addition, extensive heat exchange is required due to exothermic reaction and large
temperature range in the loop.
Conventional reforming with methanation as the final purification step, produces a
synthesis gas contains inerts (Methane and argon) in quantities that don‘t dissolve in
the condensed ammonia.
The major part of these is removed by taking out a purge stream from the loop. The
size of this purge stream controls the level of inerts in the loop to about 10-15%. The
purge gas is scrubbed with water to remove ammonia before being used as fuel or
before being sent to hydrogen recovery unit.
Ammonia condensation is far from complete if cooling is with water or air and is
usually not satisfactory. Vaporizing ammonia is used as a refrigerant in most
ammonia plants, to achieve sufficiently low ammonia concentration in the recycled
gas. The ammonia vapours are liquefied by compression in the refrigeration
compressor. The process described is shown in the following Block flow diagram.
phosphate determination
A Quantitative method to determine the
amount of phosphate present in samples
such as boiler feedwater is as follows. A
measured amount of boiler water is
poured into a mixing tube and
ammonium heptamolybdate reagent is
added. The tube is then stoppered and
vigorously shaken. The next step is to
add dilute stannous chloride reagent,
which has been freshly prepared from
concentrated stannous chloride reagent
and distilled water, to the mixture in the
tube. This will produce a blue color (due
to the formation of molybdenum blue)
and the depth of the blue color indicates
the amount of phosphate in the boiler
water. The absorbance of the blue
solution can be measured with a
colorimeter and the concentration of
phosphate in the original solution can be
calculated. Alternatively, a direct (but
approximate) reading of phosphate
concentration can be obtained by using a
Lovibond comparator.
This method for phosphate
determination is known as Deniges'
method.A simple Qualitative method to
determine the presence of phosphate
ions in a sample is as follows. A small
amount of the sample is acidified with
Concentrated Nitric Acid to which a
little ammonium molybdate is added.
The presence of Phosphate Ions is
indicated by the formation of a bright
yellow precipitate layer.
Urea
is a white dry organic
compound and a crystalline substance
and has minimum of 46% Nitrogen
calculated in dry state. This has the
melting point of 132 deg F.
Urea is made by reacting carbon
dioxide (CO2) with anhydrous
ammonia (NH3) under pressure of 3000
psi and temperatures of around 350 deg
F. Water is removed during processing
and the molten matter is either
converted to prills or into granules.
Rate of Reaction:
The rate of a reaction is the speed at which a reaction happens. If a reaction has a
low rate, that means the molecules combine at a slower speed than a reaction
with a high rate.
The rate of reaction, r, is defined to be the slope of the concentration-time plot
for a species divided by the stoichiometric coefficient of that species.
Additionally, if the species is a reactant, the negative value of the slope is used,
because the slope is negative and a positive rate is desired. For the example
shown above
rate of reaction = r =-∆[A]/∆t
1. Ammonia pumping : Liquid ammonia is pumped from the multistage pump which
maintain the reaction pressure in the vertical stainless steel vessel
2. Carbon dioxide compression: ammonia plant directly boost the carbon dioxide
from the compression section as it readily form at the CO2 section of ammonia
production plant.
3. Urea synthesis tower: It is lined with film of oxides to protect form corrosion.
Catalyst bed is placed in the inner side of the autoclave structure and 180- 200 atm
pressure at temperature about 180-200 deg centigrade is maintained. Plug flow
operation take places and molten urea is removed from the top of the tower.
4. Distillation tower and Flash drum: This high pressure slurry is flashed to 1 atm
pressure and distilled to remove excess ammonia and decomposed ammonia
carbamated salts are removed and recycled.
5. Vacuum Evaporator: The solution is fed to vacuum evaporator for concentrating
the slurry.
6. Prilling Tower: It is dryer where the molten slurry is passed from top of the tower
into a bucket which rotates and sprinkles the slurry and air is passed from the bottom.
All the moisture is removed as the urea form into granules during it journey to the
bottom of the tower. This granules are sent by conveyor to the bagging section.
Vacuum distillation in petroleum refining:
Petroleum crude oil is a complex mixture of hundreds of different hydrocarbon
compounds generally having from 3 to 60 carbon atoms per molecule, although
there may be small amounts of hydrocarbons outside that range.The refining of
crude oil begins with distilling the incoming crude oil in a so-called atmospheric
distillation column operating at pressures slightly above atmospheric pressure.In
distilling the crude oil, it is important not to subject the crude oil to temperatures
above 370 to 380 °C because the high molecular weight components in the
crude oil will undergo thermal cracking and form petroleum coke at
temperatures above that.
Formation of coke would result
in plugging the tubes in the
furnace that heats the feed
stream to the crude oil
distillation column. Plugging
would also occur in the piping
from the furnace to the
distillation column as well as in
the column itself.he constraint
imposed by limiting the column
inlet crude oil to a temperature
of less than 370 to 380 °C yields
a residual oil from the bottom of
the atmospheric distillation
column consisting entirely of
hydrocarbons that boil above
370 to 380 °C.
To further distill the residual oil
from the atmospheric distillation
column, the distillation must be
performed at absolute pressures
as low as 10 to 40 mmHg (also
referred to as Torr) so as to limit
the operating temperature to less
than 370 to 380 °C.The 10 to 40 mmHg absolute pressure in a vacuum
distillation column increases the volume of vapor formed per volume of liquid
distilled. The result is that such columns have very large diameters.
Covalent Functionalization of Graphene with Reactive
Intermediates:
Graphene, a material made exclusively of sp2 carbon atoms with its π electrons
delocalized over the entire 2D network, is somewhat chemically inert. Covalent
functionalization can enhance graphene‘s properties including opening its band gap,
tuning conductivity, and improving solubility and stability. Covalent
functionalization of pristine graphene typically requires reactive species that can
form covalent adducts with the sp2 carbon structures in graphene. In this Account,
we describe graphene functionalization reactions using reactive intermediates of
radicals, nitrenes, carbenes, and arynes. These reactive species covalently modify
graphene through free radical addition, CH insertion, or cycloaddition reactions.
Free radical additions are among the most common reaction, and these radicals can
be generated from diazonium salts and benzoyl peroxide. Electron transfer from
graphene to aryl diazonium ion or photoactivation of benzoyl peroxide yields aryl
radicals that subsequently add to graphene to form covalent adducts. Nitrenes,
electron-deficient species generated by thermal or photochemical activation of
organic azides, can functionalize graphene very efficiently. Because
perfluorophenyl nitrenes show enhanced bimolecular reactions compared with alkyl
or phenyl nitrenes, perfluorophenyl azides are especially effective. Carbenes are
used less frequently than nitrenes, but they undergo CH insertion and C═C
cycloaddition reactions with graphene. In addition, arynes can serve as a dienophile
in a Diels–Alder type reaction with graphene.
Further study is needed to understand and exploit the chemistry of graphene. The
generation of highly reactive intermediates in these reactions leads to side products
that complicate the product composition and analysis. Fundamental questions
remain about the reactivity and regioselectivity of graphene. The differences in the
basal plane and the undercoordinated edges of graphene and the zigzag versus
arm-chair configurations warrant comprehensive studies. The availability of
well-defined pristine graphene starting materials in large quantities remains a key
obstacle to the advancement of synthetic graphene chemistry.
Synthesis of carbide-derived carbon by
hydrothermal decomposition:
The removal of metal atoms from carbides has been reported at high
temperatures (300–1000 °C) and pressures (2–200 MPa). The following
reactions are possible between metal carbides and water:
x/2•MC + x•H2O → Mx/2Ox + x/2•CH4
MC + (x+1)•H2O → MOx + CO + (x+1)•H2
MC + (x+2)•H2O → MOx + CO2 + (x+2)•H2
MC + x•H2O → MOx + C + x•H2
Only the last reaction yields solid carbon. The yield of carbon-containing
gases increases with pressure (decreasing solid carbon yield) and decreases
with temperatures (increasing the carbon yield). The ability to produce a
usable porous carbon material is dependent on the solubility of the formed
metal oxide (such as SiO2) in supercritical water. Hydrothermal carbon
formation has been reported for SiC, TiC, WC, TaC, and NbC. Insolubility of
metal oxides, for example TiO2, is a significant complication for certain
metal carbides (e.g., Ti3SiC2).
Glycol dehydration units
or TEG dehydration units are the most
economical type of natural gas dehydration where dew points depressions of 60° to
120°F are required. Triethylene glycol (TEG) is the most common type of glycol use
for gas dehydration.
In the glycol dehydration process TEG is pumped to the top of a contactor tower
where it is flow countercurrent with wet gas flowing up the tower, utilizing internal
high efficiency structured packing for larger gas flows, or trays for smaller tower
sizing, for efficient gas/liquid contacting. The TEG adsorbs water from the wet gas
and is passed to the glycol regeneration unit where, very simply, adsorbed gases are
flashed off and the water is removed from the reboiler by heating the wet glycol to
around 400ºF at atmospheric conditions. The regenerated TEG is then pumped back to
the contactor tower inlet.
Water Treatment Plant:
1 Intake Crib
Raw water from a surface water lake or reservoir is drawn into the plant through
intake structures. Large debris like logs are prevented from entering and zebra
mussel control is performed at the intake.
2 & 3 Screens
Smaller debris like fish, vegetation and garbage are removed from the raw water by
protective bar and travelling screens before the water enters the low lift pumps.
4 Low Lift Pump Well
These pumps lift the water to flow through the treatment processes by gravity.
5 Pre-oxidation & Primary Disinfection
Disinfectants or other oxidants are added to disinfect or control tastes and odours.
The specific processes used are determined by the chemical and biological raw
water characteristics.
Water Treatment Plant:
6 Coagulation
Coagulants, rapidly add electrochemical charges that attract the small particles in
water to clump together as a ―floc‖. This initial charge neutralization process allows
the formed floc to agglomerate but remain suspended.
7 Flocculation
By slower mixing, turbulence causes the flocculated water to form larger floc
particles that become cohesive and increase in mass. This visible floc is kept in
suspension until large enough to settle under the influence of gravity.
8 Sedimentation
Flocculated water is applied to large volume tanks where the flow speed slows
down and the dense floc settles. Settled floc is removed and treated as a waste
product that is discharged to the sewer system.
9 Media Gravity Filtration
Relatively floc free, settled water flows through a media filter by gravity. Filter
media are made from layers of anthracite or granular activated carbon and sand.
Gravel or synthetic materials support the media. Physical straining removes the
remaining floc. Filters are periodically backwashed to clean off accumulated floc
and other trapped impurities.
10 Clear Well
Filtered water in the clear well is used to backwash filters and kept in storage to
ensure that disinfectants are in contact with the water long enough to inactivate
disease causing organisms.
11 Secondary Disinfection
Supplemental chlorine is added to maintain disinfection concentrations while the
water is pumped through the distribution system. The purpose is to ensure
minimum residual disinfectant levels at the farthest points of the system.
12 Fluoridation
A process where silicofluoride compounds are added to treated drinking water to
artificially raise the fluoride concentration to within a specified range; for example
between 0.5 to 0.8 mg/L (ppm). Fluoridation is an optional public health dental
policy.
Water Treatment Plant:
13 High Lift Pump Well
Treat drinking water is pumped through large pressure pumps to other pumping
stations, reservoirs or points of supply within the local distribution system.
14a & 14b Elevated Water Storage Towers and Ground Level Reservoirs
Water distributed to water towers and storage reservoirs ensures stable water
pressure. An adequate supply of water is maintained to meet peak water demands or
emergencies such as fires, water main breaks, power outages and pump failures.
Distribution System
Distribution systems are comprised of large pipes known as trunk mains to deliver
drinking water. Smaller diameter branch mains feed individual streets. Service
connections to branch mains deliver water into residences. Pumping stations are
used to increase pressure and to maintain adequate supply flows.
A
steam ejector
is a type
of pump that uses the Venturi effect of
a converging-diverging nozzle to convert
the pressure energy of a motive fluid
to velocity energy which creates a low
pressure zone that draws in and entrains
a suction fluid. After passing through the
throat of the injector, the mixed fluid
expands and the velocity is reduced
which results in recompressing the
mixed fluids by converting velocity
energy back into pressure energy. The
motive fluid may be a liquid, steam or
any other gas. The entrained suction
fluid may be a gas, a liquid, a slurry, or a
dust-laden gas stream.
Heat is transferred by one of these three modes - conduction, convection and
radiation.
1) Conduction
is the method of transferring heat by contacting directly with
other objects. The mechanisms involved in conduction are the transfer of free
electrons and energy passing between molecules of contacting objects by lattice
vibration. Good conductors of heat are silver copper, iron and steel. Air and papers
are poor heat conductors.
2) Convection
is the method of transferring Heat by convection current
formed by up and down movement of fluids particles. This occurs because the
decrease in density as the result of the increase in temperature. For example, forced
current convection by heater rise hot air balloons.
3) Radiation
occurs when heat is transferred in empty space by
electromagnetic wave. For example, the sun warms the Earth through the radiation
of EM wave.
Taking the arrangement of atoms and frequency of particle collisions into account,
conduction therefore is faster than convection. Newton's law of cooling and Stefan-
Boltzman Law are related to heat transfer.
why protons will not repulse each other in nucleous?
It's just that the mass deficit creates the nuclear binding energy (or nuclear glue)
BLOWERS
Blowers develop little higher pressure in comparison to fans. They are used for
pressure below 1.65 Psi. The centrifugal blower produces energy in the air stream
by the centrifugal force and a velocity to the gas by the blades. The scroll shaped
volute diffuses the air and creates an increase in the static pressure by reducing the
gas velocity.
FANS
The performance of a centrifugal fan varies with change in conditions like
temperature, speed and density of the gas being handled. Corrections must be
applied to manufacturing standards with respect to operating conditions.
through residual strong interaction (strong force) that overcomes the coulomb
We can see the electrostatic force
force that's trying to push the nucleus
apart and keeps it together. The
electrostatic repulsion between
protons doesn't just disappear when
nucleons are fused together to make
heavier atomic nuclei.
pushing atomic nuclei apart as we look at the top of the periodic table. When
we synthesize heavier and heavier elements in the physics lab, they are more
and more reluctant to "stay together" and stabilize. And we finally reach a point
where we just can't force a super heavy nucleus to even begin to stick together.
Not even for the tiniest fraction of a second.
A non-Newtonian fluid
is a fluid whose flow properties differ in any
way from those of Newtonian fluids. Most commonly the viscosity (resistance
to deformation or other forces) of non-Newtonian fluids is dependent on shear
rate or shear rate history. However, there are some non-Newtonian fluids with
shear-independent viscosity, that nonetheless exhibit normal stress-differences
or other non-Newtonian behaviour. Many salt solutions and molten polymers are
non-Newtonian fluids, as are many commonly found substances such as
ketchup, custard, toothpaste, starch suspensions, paint, blood, and shampoo.
In
a Newtonian fluid
, the relation between the shear stress and the
shear rate is linear, passing through the origin, the constant of proportionality
being the coefficient of viscosity. In a non-Newtonian fluid, the relation between
the shear stress and the shear rate is different, and can even be time-dependent.
Therefore, a constant coefficient of viscosity cannot be defined.
Centrifugal pump:
Centrifugal pumps are used to
transport fluids by the
conversion of rotational
kinetic energy to the
hydrodynamic energy of the
fluid flow. The rotational
energy typically comes from
an engine or electric motor.
The fluid enters the pump
impeller along or near to the
rotating axis and is
accelerated by the impeller,
flowing radially outward into
a diffuser or volute chamber
(casing), from where it exits.
it works by:The transfer of energy from the mechanical rotation of the impeller
to the motion and pressure of the fluid is usually described in terms of
centrifugal force, especially in older sources written before the modern concept
of centrifugal force as a fictitious force in a rotating reference frame was well
articulated. The concept of centrifugal force is not actually required to describe
the action of the centrifugal pump.
The outlet pressure is a reflection of the pressure that applies the centripetal force
that curves the path of the water to move circularly inside the pump. On the other
hand, the statement that the "outward force generated within the wheel is to be
understood as being produced entirely by the medium of centrifugal force" is
best understood in terms of centrifugal force as a fictional force in the frame of
reference of the rotating impeller; the actual forces on the water are inward, or
centripetal, since that is the direction of force need to make the water move in
circles. This force is supplied by a pressure gradient that is set up by the rotation,
where the pressure at the outside, at the wall of the volute, can be taken as a
reactive centrifugal force. This was typical of nineteenth and early twentieth
century writings, mixing the concepts of centrifugal force in informal
heating value:
The amount of heat produced from the complete combustion of a unit of fuel.
The higher (or gross) heating value is that when all products of combustion are
cooled to the pre-combustion temperature, water vapor formed during
combustion is condensed, and necessary corrections have been made - Source.
Hydrogen production most used techniques..
take a break
When ALBERT EINSTEIN met
CHARLIE CHAPLIN
Einstein said
, What I admire most about
your art, is its universality. You do not say
a word, and yet the world understands
you.
“ It’s true,”
replied Chaplin
, But your fame
is even greater The world admires you,
INTRODUCTION
Where Pipework is a means of transporting solids, liquids and gases valves are
incorporated in the Pipework to facilitate the starting, stopping and diverting of the
transportation. Valves are also situated in linework such as steam lines, air lines and
water lines, which serve plants and installations with the utilities they require in their
operations.
GENERAL PRINCIPLES
Consider the different type of liquids and gases that flow around plant pipeline. High
pressure, Low pressure, Corrosive, Non-Corrosive, Low and High Viscosities and
Volatilities. If we understand this, then we can see why so may different types and sizes
of valves are in use.
Valves are manufactured from Forged Steel, Alloys, Cast Steel, Cast Iron, Brass,
Plastics etc, the properties of which limit or determine the service for which they are
designed.
Most manufactures have certain standards developed for the design, manufacture and
testing of all types of valves. The basic dimensional standards such as face to face
length, flange and bolt circle dimensions etc, are those of the API or American Petroleum
Institute and this has made it possible to interchange various manufacturers valves.
VALVE CLASSIFICATION
The various types of valve can be sub-divided into the following groups.
-
Isolation Valves (Ball, Plug, Butterfly, Gate)
-
Regulating Valves (Globe, Needle and Diaphragm)
-
Check Valves or Non – Return Valves
DESIGN FEATURES OF VALVES
VALVE COMPONENT FUNCTION
Handwheel Provides a means of operating the valve gate
or disc to open and close the valve, the direction of rotation is indicated on the handwheel, this is normally clockwise to close and anti-clockwise to open. In smaller valves of bronze or brass type the handwheel is made of alloy and is easily broken, this is to protect the spindle etc from damage if any great pressure is exerted. The handwheel may be attached to the bush in the yoke or directly to the valve or spindle.
Yoke This is the joining piece between the two
pillars, sometimes know as the bridge or the collar. The yoke may be removable or cast with the pillar and bonnet. It provides even pressure on pillars when handwheel is operated.
Pillars Brace between bonnet and yoke. They may be the removable type held in position with nuts,or the permanent type which are cast with valve bonnet. Stem and Spindle Provides a means of operating the gate or disc
to open and close the valve. The gate or disc being attached to the stem which passes through the bonnet via the stuffing box. The upper or external part of the stem may be threaded and is know as the spindle, this part is operated by the handwheel. Spindle may be rotated or just raised and lowered, depending on the type of stem operation, these will be discussed later. Spindle has square thread for greater strength.
The Gland may be held in position and adjusted by two nuts and bolts, if so adjustments must be made evenly to prevent gland binding on the stem and to ensure packing is pulled down evenly. On smaller valves the gland is held in position with one nut through which the stem passes, this nut screws direct onto the outside of the stuffing box. Stuffing Box Provides a means of passing the valve stem through the
bonnet to operate the shut off mechanism and prevent any leakage of fluid when packing is added. It is normally incorporated in the bonnet construction, in smaller valves it can be a separate part screwed onto the bonnet.
Body Provides a means of channelling the liquid or
gas, from the inlet to outlet port, via the shut off mechanism, which is normally in the shape of a disc. The body is actually the valve casing, to which connections are made to pipelines, etc, the ports may be of the flanged, screwed or welded type.
Bonnet Valve cover, this enables the internals of the
valve to be removed for servicing, it may be a flange type, this is normal for valves above 2”. For smaller valves it may be a screw type, in this case it is in the form of a large nut. At extremes in temperature high/low extended bonnet valves are used.
Seat Forms a seal with the gate or disc to prevent
fluid flow when valve is closed. There may be one or two seats in a valve, depending on the type of shut off mechanism, It is in the shape of a ring and screwed into the body, enabling valve seats to be renewed when badly scored. The face is a machine surface to form a good seal with the gate or disc. In smaller cheap valves, the valve seat may be part of the body and not removable, but in larger and more expensive valves seats are always removable.
