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Ideal Gas Mixtures

P1 + P2 +P3 + … + Pn = Pt

The total pressure of a gas system is the sum of all the individual partial pressures of the different gas components in the system

Watch the following video on partial pressure  and Dalton’s Law

http://www.youtube.com/watch?v=w2UXUwNGAeY

V1 + V2 + V3 + … + Vn = Vt

The total volume of a gas system is the sum of the individual partial volume of the different gas components in the system

Visit the following site on partial volume and Amagat’s Law

http://www.sciencehq.com/chemistry/amagat-law.html

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Standard Temperature and Pressure

Standard Temperature  = 273K (kelvin)

Standard Pressure = 1 atm (101.3kPa)

Watch http://www.youtube.com/watch?v=w2UXUwNGAeY for more info on STP and examples

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The Ideal Gas Equation of State

PV = nRT

P = Pressure

V = Volume

n = moles

R = Gas constant

T = Temperature

For more info watch

http://www.youtube.com/watch?v=yn7kmeD47Zc

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Material Balance on combustion Reactors

Material balances are important first step when designing a new process or analysing an existing one. They are almost always prerequisite to all other calculations in the solution of process engineering problems.

For tutorials please visit

http://www.sophia.org/concepts/chemical-reaction-types-combustion

http://www.knowmia.com/watch/lesson/7012

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Theoretical and Excess Air

Stoichiometric or Theoretical Combustion is the ideal combustion process where fuel is burned completely.

With unburned components in the exhaust gas, such as C, H2, CO, the combustion process is uncompleted and not stoichiometric.

The combustion process can be expressed as:

[C + H (fuel)] + [O2 + N2 (Air)] -> (Combustion Process) -> [CO2 + H2O + N2 (Heat)]

To determine the excess air or excess fuel for a combustion system we starts with the stoichiometric air-fuel ratio. The stoichiometric ratio is the perfect ideal fuel ratio where the chemical mixing proportion is correct. When burned all fuel and air is consumed without any excess left over.

Process heating equipment are rarely run that way. “On-ratio” combustion used in boilers and high temperature process furnaces usually incorporates a modest amount of excess air – about 10 to 20% more than what is needed to burn the fuel completely.

If an insufficient amount of air is supplied to the burner, unburned fuel, soot, smoke, and carbon monoxide exhausts from the boiler – resulting in heat transfer surface fouling, pollution, lower combustion efficiency, flame instability and a potential for explosion.

To avoid inefficient and unsafe conditions boilers normally operate at an excess air level. This excess air level also provides protection from insufficient oxygen conditions caused by variations in fuel composition and “operating slops” in the fuel-air control system. Typical values of excess air are indicated for various fuels in the table below.

  • if air content is higher than the stoichiometric ratio – the mixture is said to be fuel-lean
  • if air content is less than the stoichiometric ratio – the mixture is fuel-rich

For tutorials please visit:

http://www.sophia.org/concepts/chemical-reaction-types-combustion

http://www.knowmia.com/watch/lesson/7012

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Combustion Chemistry

A combustion reaction is a type of chemical reactions where a compound and an oxidant is reacted to produce  heat and a new product.

This is an example of a combustion reaction
CH4 + 2 O2 → CO2 + 2 H2O + heat

 

Combustion

For tutorials please visit:

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Purging

A purge stream are usually referred to as an outlet on a Chemical plant enable the accumulating gasses that are useless to the process to be removed. Usually inert gasses are removed with this outlet. In many other cases, the gasses are burned so it may be more environmental friendly and safe.

Purge by definition of Scribd: “When a process uses a recycle loop, there can often be a build-up of some undesired material within the system. By using a purge, a fraction of the recycle loop material is removed. This purge fraction is generally only a few per cent of the recycle flow rate.”

You can also visit the page for mass balance examples:

http://www.scribd.com/doc/62923088/Chemical-Calculations-for-Chemical-Engineering-PROBLEMS-in-MATERIAL-BALANCE-RECYCLE-ByPASS-PURGE

Watch the YouTube video of purge streams: https://www.youtube.com/watch?v=47tPvx3lOKc

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Product separation and recycle

Something interesting: Separation of a multiple compound and recycling fractions in a plant are very important as it saves costs, lower waste and makes the products cheaper. Therefore we must know how to do these things. Technology improves every year to optimize and increase the amounts of used matter to be recycled. Aluminium costs 90% cheaper to recycle instead of extracting it from bauxite.
YouTube recycling:

https://www.youtube.com/watch?v=_GP3JuiX5BY

In chemical plant we also have to recycle some of the product that has not formed into the desirable chemical. To find the efficiency of a process the total conversion of the reactant must be calculated. This will also help to find the fraction that will needed to be recycled.
Conversion = (reactant input – reactant present in output)/(initial reactant input)
The concept is very basic once you have understood it. In most problems in your current handbook the percentage conversion and percentage recycle are given. The recycle stream usually will complicate your problem.
Watch this YouTube video of a mass balance where a recycle stream is present in a mass balance problem:

https://www.youtube.com/watch?v=bF19fAoRpVo

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Extent of reaction

What is the extent of reaction? The extend of reaction are the coefficient called “Xi” (ξ). This sign is added to the coefficients of a molecular balanced equation.

Example:

If the combustion of propane is used in a mass balance problem the extent of reaction would be:

Equation: C3H8 + 5O2 = 4H20 + 3C02

For propane: 1ξ

For oxygen: 5ξ

For Water: 4ξ

For carbon dioxide: 3ξ

See the following clip on YouTube where the extent of reaction are used in mass balances: https://www.youtube.com/watch?v=jyso8NSytWw

Another problem for practise: http://www.youtube.com/watch?v=YusSU0jlOUk

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Atomic Species balances

At atomic species balances the independent atomic species are also used to calculate the degree of freedom.

What is atomic balance: An atomic balance is one in which we balance each individual atomic species rather than each independent. See page: http://pillars.che.pitt.edu/student/slide.cgi?course_id=12&slide_id=57.0

YouTube video where atomic species are used: https://www.youtube.com/watch?v=NDm4FRt2fyM