Working of compressors and expanders and importance of Moeler Diagram

Moiler diagram and working of compressors and expanders.

This diagram plays an important role in calculations of outlet conditions like Temperature, Pressure (generally an input), Enthalpy and Entropy of compressors and expanders.

Which inturn helps in calculating work performed by the compressor..

Please note compressors and expanders works in Isentropic flash conditions means Entropy is constant both PH(Pressure Enthalpy) and (Pressure Entropy) Calculations will be done on this object.

Some other objects and corresponding flashes.
Headers- RhoU Flash
Drums-Pressure Internal Energy flash.
Exchangers - PT Flash.
Valves/Pipes - Isenthalpic -  with knowledge of this by knowing outside pressure of valve it is possible to calculate temperature and velocity through valve

To be continued.. 

Basics of Fluid Mechanics and how it is helpful in simulation(Part1)

Topic1:
Basic Equations:
Lets start with a continuity equation which is A1V1=A2V2 , if area(A) is small the velocity(V) will be more, application would be gardening pipe..

There is an extension of this equation is Bernoulis Equation most famous energy balance equation.

P1+Rho1*g*h1+1/2Rho1*V1^2 = P2 + Rho2*g*h2+1/2Rho2*V2^2

1st term is pressure energy term , 2nd term is potential energy term and third is kinetic energy term.
Pressure in Pascals,
Density in Kg/m3,
Velocity in m/s,
h1 in meters,
g is 9.8m/s^2.
This equation can be modified in to simple cases i.e many terms will get cancel according to the given problem..

One example is if inlet and outlet of a pipe is in a same height then Potential energy term will cancel out.
P1+1/2Rho1*V1^2 = P2 +1/2Rho2*V2^2

Second Example is Leak from a tank: V1(Velocity of tank) =0 because the fluid wont move and only the V2 is in motion.
P1+Rho1*g*h1 = P2 + Rho2*g*h2+1/2Rho2*V2^2
If the tank is open to atmosphere then pressure terms will get cancel.
Lets do a simple example,
Inlet conditions of water flowing in a pipe with a conditions of 1.2 m/s and having 130 Kpa and its height is 2m and the outlet of the pipe is at 4m height and the outlet velocity is 7m/s. Calculate Outlet pressure.

It is at certain height and the velocity is more so we can say the outlet pressure will be less

130000+1000(9.8)(2)+1/2(1000)(1.2)^2 = P2 + 1000(9.8)(4)+1/2(1000)(7)^2

On substituting we will get P2 = 86.62 Kpa which is lower than the inlet pressure.

Continuity and Bernouli equations are basic equations that are used in calculating Flow meters velocities (Venturi / Orifice meter).

How to find pressure drop if U tube Manometer is installed and we know reading of Manometer.
Delp=delrho*g*h this is similar to rho*g*h

Here h is the Manometer reading.
In general, fluid in U tube Manometer will be Mercury, density of Mercury is 13600kg/m3.
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Topic2
Pumps: The objective of pump is to trasfer liquid from source to a destination.

This may be filling a tank at higher level or circulating a liquid. In both the cases pressure is required to make this work.. This is generally referred as HEAD.

HEAD = STATIC HEAD + FRICTION HEAD.

Head(feet)/2.31 = Pressure(Psi).

Please Note: Supplier/vendor terminology is HEAD and users terminology is pressure.

STATIC HEAD is the vertical distance that the liquid has to be lifted.
FRICTION HEAD is due to the fittings and size of the pipe.

The centrifugal pumps which generally creates energy due to rotation of impellers - the created energy is converted in to fluid pressure.

Pump power is P = delp*Q/eff

Q in m3/sec
P in Watts = kgm2s-3
Pressure in Pa = kg/m. s2
Eff is efficiency.

DelH = delp/rho

In steady state simulation inlet stream conditions will be given(pressure, temperature, flow  and composition) and we can provide outlet pressure or pressure rise or pressure ratio and efficiency in pump Unitop, the simulator will predict required power. This is the basic equation.

In dynamic simulation we generally provide curves, head vs flow and efficiency vs flow/power vs flow. And when pump is running at its design conditions we verify the power / efficiency.


Pump Curves:
There are 4 types of curves related to pump,
1) Head vs Flow,
2) Efficiency vs Flow
3) Power vs Flow
4) NPSH Required vs Flow

Pump Curves data extraction in OTS modelling is one of the most important work to get a proper discharge pressures of the pump.

In general there will be controller (Indirect action ) arrangement at the minimum circulation line, unless the flow develops the pump will be in minimum circulation. If flow starts developing the forward flow controller will start opening The forward controllers has to kept in auto which is a direct action controller.

When you need additional head use pumps in series and when you need additional flow use pumps in parallel arrangement.
Affinity Laws:
Volume Proportional to Speed
Head Proportional to Speed2
Power Proportional to Speed3

Small change in Speed can give significant change to the parameters.
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Topic3:
FRICTION HEAD -> Calculated based on Darcy Equation.

Darcy friction factor =4f

Hf= fd* L/D * V^2/2g

Hf-> Friction Head in Meters.
f ->fanning friction factor,
D->Pipe Diameter,
L->Length of the pipe.
V->Mean velocity of fluid.

Head loss due to fittings is calculated based on K Method.

H_fittings = K V2/2g

Example the K value for 90degree elbow having R/D=1.5 is 0.45. This is a long radius elbow.
Note: "K "value will be different for different fittings. In general these will be saved in softwares.
If fluid velocity is 4m/s
Then head loss due to fittings is 0.367m

Now the total head loss is Ht=H_fittings + Hf
For Laminar flow f = 16/Re
For Turbulent and e/d(Relative pipe Roughness)<0.001 we have f = 0.0079/Re^1/4
For greater values of e/d(Relative pipe Roughness) we need to use Moody Chart.

How to read Moody chart: 
https://www.youtube.com/watch?v=tISdp_394Bw


Steps involved in calculating Hf/Pressure Drop in a pipe is
1) Calculate Reynolds number-> Decide the region->if Re<2000 it is laminar or else Turbulent.
Ignore transition region.
2) Use the proper correlation/Moody chart for calculating f(friction factor)
and substitute all the value in Darcy Equation. to get the values like Hf and also Pressure Drop(Rho*g*Hf).Power required etc.

Simulators clearly mention the pressure drop is calculated based on Darcy friction factor.. Beggs and Brill is one of the Equation. As per these experiments they have divided in to 3 flow regimes, defined as segregated, intermittent and distributed flow - the term liquid hold up will vary based on three flow regimes. 

There Will be 3 terms in pressure drop calculations in a pipe..  friction, elevation and acceleration term. 



The drawbacks for this equation is.. it won't predict properly for high pressure gas condensate systems. As it is derived based on water - Air system. 

I think most important part is how Moody chart is converted to equation format.- Answer for this is there are many equations in literature to find the f in turbulent flow region one of them is
Colebrook - White Equation

https://en.m.wikipedia.org/wiki/Darcy_friction_factor_formulae


Reynolds Number = Intertial Force/Viscous Force = Rho*d*V/Viscosity

Rho in Kg/m3
d in Meters
V in m/s --> If flow rate is given divide it by cross section area to get in m/s
Viscosity in kg/m-s which is equivalent to N-s/m2 =Pa.s

1c.p = 1 Mpa.s = 0.001 Pa.s=0.001N-s/m2 =0.001kg/m-s.


Power units 1 Watt = 1 J/Sec = Kg m^2 s^-2
1 Hp= 736 Watts.
Valve coefficient Cv=q*(sg/delp) 0.5

Reviewed by Prof KV Rao

Group contribution method joback

Hi everyone this blog is about how pure components properties are calculated using the group contribution methods available.

There is nothing much to explain because Wikipedia covered about joback method to calculate the 11 properties and also given example for acetone.

The 11 properties are, Boiling point, critical temperature, critical pressure, critical volume, melting point, hformation, gformation, heat capacity, heat of fusion and dynamic viscosity

I am writing this blog,  is just for my practice for another compound namely methylchloride (CH3CL),  so CH3- is a paraffinic group and CL is a chlorine derivative. Here CH3 is one group and CL is another group. So we want to know how these two groups contribute to form a compound.

To begin with,  as explained in Wikipedia collect all the individual /group properties like critical properties tc, pc, vc, tm, hform, gform, and as per correlation just sum it and substitute in equation. In software's this groups data will be saved in databases.

 I have also compared with standard software as well. For my surprise I could able to match the compound  properties even in decimal level.


The advantage here is the correlations are very simple all we need to do is summation of individual group properties and substitute in correlations. All properties are calculated at standard conditions 1bar and 25degC.

Joback is an extension of lyderson who found relationship between boiling point and critical point. 

Diameter Calculation of Sieve Tray Column

This blog is about, the diameter calculations of a sieve tray column. Software's can give diameter for each stage but to verify on our own,the below Sinnot Procedure will help you in comparing the results. We may not get the exact match becasue software equations might be much more detailed. The below procedure help a student on how text book methods are used for comparing the results and where exactly the basic knowledge will help in sizing a distillation column.

In a similar way, diameter is calculated for each stage and the largest diameter will be selected.

If you calculate for other stages the diameters will be different because properties will be different. Constructing a column with single diameter is cheaper. But how we accommodate the lesser diameter stages, is by simply blocking perforations of a tray so that total openings will reduce which is equivalent to lesser diameter.

Columns with different diameters also in use, but only thing is cost is higher.

In my next blog I will write a blog on pressure drop calculations.

   Approximate Column height is calculated as (Number of stages*Tray Spacing) + (15% of  Number of stages*Tray Spacing).

Questions:

How maximum vapor rate is decided? This is an initial guess which we need to mention for a coloumn to converge. What i have done is i have taken a vapor fraction of feed stream and multiplied with feed flow. Simulator will give slightly different answer. But for hand calculations this value is required so guess value using above procedure.

Topics you may like and will be covered in my future blogs:

Column Height/Number of stages is decided by relative volataility,lesser the value difficult will be separation and higher will be the stages/Height.

Example: C3 splitter, Separation of Xylenes.

Poynting correction factor can be ignored for low or medium pressure situations. This topic will be understood if you know gama-Phi Formulation.

References:

Guidance by Prof KV Rao

Introduction to chemical Engineering Thermodynamics by Smith, Vannes and Abbot.

Mass Transfer operations by Treybal.

Natural gas Hydrates in brief!

     So hello everyone I have been trying to learn on natural gas hydrates and problems on hydrate formation. So below content is only for academic point of view.

Hydrate formation is the major problem in offshore exploration which leads to flow blockage, loss of circulation and even abandonment of the well. This leads to lot of loss in form of dollars and time. The practical solution for preventing or delaying hydrate formations for a long pipeline subsea network is by adding inhibitors, any chemical which reduces the water potential can be used as an inhibitor but MEOH (Methyl alcohol is a universally accepted chemical inhibitor). Knowing the conditions (Pressure and Temperature) with and without inhibitors will help pipeline designing and pipeline operation. The most common hydrate forms structures (Structure I and Structure II) hydrates will be described.

This study also shows how to dehydrate a wet gas using glycols as a solvent which are generally available in offsite gas plant facilities. Dehydration is a solution for reducing the water content before it is sending to gas transportation.And Pressure has to be maintained with an objective of gas has to be in dew point conditions.

Basic substitute equations for calculating HFT.

·               1934, Hammerschmidt.

·               Makogon correlation.

·               1991, Motiee, 15 parameter T-Explicit Equation.

·               2005, Towler and Mokhatab and

·               Bahadori and Vuthaluru. Etc

In all the cases know the process pressure condition i.e. at what pressure it is transporting and then calculate the temperature.

How to describe Type1 and Type2 Hydrates.

Actually we can easily describe Type I and Type II (or Structure I and Structure II). Based on the below graph.

Graph -->Check Figure2.2

·         Less than 3.8 A it is difficult to form hydrate.

·         If the guest molecule are Ar,Kr,N2,O2 this is Type II.

·         From 4.4 A methane, H2s, Xe, ethane, propane will fall in Type I cages.

·         From 7A no Type I and Type II will form. There is another type called TypeH.

Definition of hydrates:

I am also going through the most common gas hydrate forms. According to Von Stackberg and Muller, each of the structure contains two types of cavities.

·         Structure I consists of 46 water molecules which constitute 2 small pentagonal dodechahedra cavities and six tetrdecahedral large cavities, having 2 opposite hexagonal faces and 12 pentagonal faces.

·         Structure II consists of 136 water molecules comprising  16  small pentagonal dodechahedra cavities and 8 hexadecahedra large cavities, having 4 symmetrically arranged hexagonal faces and 12 pentagonal faces.

The average cavity radiuses of 3 cavities are

3.9 A for pentagonal dodechahedra.

4.3 A for tetrdecahedral.

4.7 A for hexadecahedra.

Basically the reason why gas hydrates will form above the ice point of water is, gases will diffuse in these cavities which will alter the condition of formation of Ice. So this is the reason hydrates will form in ~10C.

References:

·         http://petrowiki.org/Predicting_hydrate_formation

·         http://www.gasprocessingnews.com/features/201508/predict-gas-hydrate-formation-temperature-with-a-simple-correlation.aspx

·         http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.623.6856&rep=rep1&type=pdf

·         Empirical expressions for gas hydrate stability law, its volume fraction and mass-density at temperatures 273.15 K to 290.15 KZhengquan Lu1, 2, * and Nabil Sultan1

·         PREDICTION OF GAS-HYDRATE FORMATION CONDITIONS IN PRODUCTION AND SURFACE FACILITIES A Thesis by SHARAREH AMERIPOUR

GAS PROCESSING PLANT OVERVIEW

Hi All,

So i have contributed to a project on one of the gas processing plant facility where gas is collected from wellheads and transported.

We have got three wellheads,HP Section,IP Section,LP Section, HP Compressor section,LP Compressor section, TEG Gas dehydration,TEG regeneration,Gas metering station,crude metering station and other utilities like fuel gas system,cooling water system,Waste heat recovery system etc.

ESD flow sheeting was done,Graphics were prepared for FOD and mimicked DCS as this was an in house project.


Modelling challenges:
Separation of gas and liquids in separators.
Vapor fractions.
Water-TEG interactions.
Hot oil properties which is used in regeneration section.

Most interesting part is taking a start up when ESD is activated.

We tried three ways of pressurising the system.
1) Using gas trunkline system. Which act like a source and sink.
2) Using fuel gas system- note here we have to completely change the model as reverse line has to be defined for doing this which was not considered during modeling phase.
3) Creating a hose connection near HP separator for Fuel gas.

The process looks easy but taking a startup with ESD activated is not that easy.

There will be many facilities available in offsite gas plant like desalter, Amine treating and regeneration systems, there will be compressor train in transportation line.Then Liquification.

For example:
All these things need to be done because the shutdown valves at 3 wellheads will not open until the downstream to get some pressure.
Reversible line has to be defined here as well to sense the pressure.

Lead and Lag KPI Indicators

Lead and Lag KPI Indicators.


This is one of the interesting topic for strategic thinkers. I found this skill set in operation mangers,Data Analysts profiles. I feel that this knowledge is necessary to improve our day to day activities as well.

Lag is nothing but "outputs".Which is easy to measure.

E.g1: CEOs talk in the form of outputs like the target for 2017 Quarter 1 should be say 10Bn$.
E.g2: Production has to be increased to 1000 MTPD(Metric Ton per day)
E.g3: Gasoline and Diesel production has to be increased.
E.g4: Reduce Solvent cost.

Ideally these Lag parameters are easy to identify and easy to say.

Lead is "manipulators/Influence rs" to get that desired "outputs" Which is very difficult to measure.

Identifying these manipulators are very difficult. In a nutshell for the same examples listed above will have many ways to achieve the targets. and you know it is very difficult too.

Lets try for identifying Lead manipulators/influencers to get the desired outputs.

E.g1: Increase hiring the skilled resources. - But do they really work after hiring?
E.g2: Increase imports of raw materials. - Does our capacity handles it?
E.g3: Increase the efficiency of desalter. - Does this is the only indicator?
E.g4: Decrease the solvent flow and invest on construction of new regeneration plant. - Does it really feasible in cost point of view.

The above one is the first set of Lead indicators if we dig down further there will be very few that actually improves the outputs.

It also depends on how much investments has to be spent to get the desired outputs. Few may not interest in actually investing in new things and improve using the available resources or available Facilities.

If we drill down the management pyramid the objectives of top to bottom level will differ to get the desired output.

"Operations Management" the new focus in service sector to improve efficiency

Operations Management can be defined as the conversion of inputs 6Ms in to productions of outputs through a transformation process.
Output may be goods produced or services rendered.
If output is goods then it is called production.
6Ms are like men,machines,materials,money,methods and management.


Operation management is a visible face of any company:
This function actually produce the goods and services, it typically involves the greatest bulk of the companies employees and is responsible for a large portion of the firms assets. it has a major impact on the "quality" of goods and cost of production.

It plays a vital role in achieving a firms strategic plans or goals.

Operation management or Production is a primary business function along with marketing and finance,HRD, and material management.


Example to understand better:

HDFC Bank cuts 4,581 jobs in third quarter because of improved efficiency

The bank, which reported its slowest profit growth ever at 15% for the December quarter, saw total headcount reduce to 90,421 as against 95,002 in 30 September 2016

http://www.livemint.com/Industry/ufExTeD1KbYtGjmsj0RWrN/HDFC-Bank-cuts-4581-jobs-in-third-quarter-because-of-improv.html

Another link where operation managers in HDFC are focusing more on M called"Machines"
http://trak.in/tags/business/2017/01/30/hdfc-bank-automation-humanoid-ira/

Scope of Operation management or Production management:
Designing and controlling.

• Activities related to designing or formulation of the production system.
• Activities related to analyzing and controlling of production operation after the production system has been activated.