July 28, 2008

Distillation, Absorption & LLE - 3-in-1 Software - Available for Free

ChemSep is a program for performing multicomponent separation process calculations. ChemSep is designed for use in courses on thermodynamics and/or separation processes and features an easy to use interface for Windows, equilibrium and rate-based column models, integrated graphics (with GNUplot), and export capabilities (e.g. to Excel, Word, and html).

ChemSep integrates flash, the classic equilibrium stage column model and a nonequilibrium or rate-based column model in one easy to use program. ChemSep-Lite (a version with some limitations) is available free - Download from Original Site.

Following are the case studies presented on ChemSep site.

You can either download above PDF or can download ChemSep simulation files also from ChemSep Site which can be used with ChemSep Lite.

ChemSep is CAPE open Compliant that means you can use these simulation files with other programs e.g. ASPEN. It is also integrated with Sulzer's Column Rating tool SULCOL.

Download ChemSep Guide Book Here.

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July 22, 2008

Guaranteed Energy Saving in Vacuum System

Steam Ejectors are the widely used equipments for vacuum generation till the recent developments of liquid ring & dry pumps. Also, the reason for preferable use of ejectors was availability of steam at different levels, low maintenance, non availability of other systems etc. with major one being the only system suitable for very high vacuum.

However, the major disadvantage of using ejectors is - higher steam consumption. As we go for higher vacuum, the steam consumption goes up exponentially & since the cost of fuel is going up like a rocket in the recent past, the alternative solutions are more benefitial.

Here is a proven method which is used by us for sometime & is working fine.

Related References

The option is to use dry vacuum pumps which are capable of running dry e.g. Screw or Scroll. The picture of a typical pump from M/s. Kinny is given above. Here are the two main parts as photographed from an actual installation.

The other advantage of these pumps is to recover process fluids. These pumps discharge non-condensables & vapor load at ambient pressure so the benefit is that you can boil your fluid at low temperature under vacuum & can recover them at atmospheric pressure with probably cooling water.

Thus it can be used for multipurpose depending your system. I am using them for both. In one of my process I have to remove methanol under vacuum So I used dry screw pump there & then recovered methanol at the downstream with cooling water condensation. Boiling was done using low temperature hot water at 80°C. However, the vapor load should be low in such cases.

This example is given for a 1 torr vacuum in the system. Kindly do some financial calculation before making any decision in your plant.

Calculate following.

  • Steam Running Cost Including boiler efficiency

  • Cooling water cost.

  • Cooling water Pumping cost

  • Condensate Pumping cost

  • Any other direct & indirect cost

Now the installation cost for steam ejectors was ~Rs.12 Lac while the cost of vacuum pump was only Rs. 16 Lac, but the saving was Rs. 10 Lac/year which paid back my investment in less than 6 months.

So now you need to assess your current systems & implement this sure shot energy saving plan.

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July 16, 2008

High Efficiency Boiler Fans - Amazing Potential of Energy Saving

The fans help burn the fuels efficiently and complete combustion. The combustion air requirement from under the grate is met by supply air from forced draft fans (FD fans), and the combustion product from furnace is exhausted by induced draft fan (ID fan). The secondary air fan (SA fan) supplies air over the grate to create turbulence over fuel.

For spreading fuel over the grate, and the burning fuel in suspension the pneumatic spreader is used, and pneumatic spreader fan (PS fan) plays important role in spreading and burning fuel efficiently. The balanced drought system, thus, is very essential for economic operations of boiler

Related References

For a particular specified duty, there is only one diameter of impeller at specified speed, which can give best efficiency, provided optimised inlet diameter and good blading is provided. Low lead edge angle and long smooth passage of air from inlet to outlet of impeller, without separation of flow in two blades will provide highest possible efficiencies. It is therefore work of the designer to:
  • Establish best diameter of wheel that is capable of highest efficiency possible at specified speed and duty.
  • Establish optimum impeller inlet diameter at specified duty and speed.
  • Select blade angles and number of blades to convert dynamic energy into static energy, without separation of flow and avoiding shock conversions.

The performance curves of laboratory tested high efficiency fan are presented below.

The features are:
  • maximum efficiency is 88%.
  • Optimal operating range is between 50 to 75% of free delivery.
  • Maximum BHP occurs at highest efficiency point, making it possible to use small motors.
  • Maximum noise level occurs at minimum efficiency.

Following are the tips for maintaing good fan system.
  • Use correct belt tensions as per manufacturers recommendations only. This will not only increase life of belts, it as well saves energy. Use of belt tension meter is recommended.
  • Excess tightening of adaptor sleeve also heats up bearings causing more wear, and more power consumption. Use of filler gauges while tightening adaptor sleeve is recommended.
  • Fill grease into bearing with correct quantity and quality recommended. It is general observation that plummer blocks are filled with grease fully which overheats bearings.

Now try to see the nos & utility of these considerations which are posted on this "Chemical Professionals' Blog. The example is given just for Cement Industry which may be the largest user of fans & blowers.

The World Cement production capacity is ~2250 Million TPA. The average power consumption in cement industry for fans is ~75 kWh/Te of Cement produced. Which means the total power consumption in fans in cement industry alone is ~ 168750 Million Units per year.

If we assume current efficiency of 80% (Best possible) & replace it with high efficiency fan of 88% than there will be a reduction of 10% in the power consumption. Thus we can save ~16875 Million Units per year.

At an average price of 12 Cents/unit it becomes ~2000 Million USD saving per year.....WOW.......

Wait Wait.........More savings are available

For each unit of power there is an average carbon credit of 0.01 Te, which means you can save another 1650 Million USD / year at minimum 10$/Te of credit rate.

So total potential is ~$3650 Million / year just by single change across the world. Avoid Global Warming as a BONUS.......

Enjoy Reading.......your favorite Blog - Chemical Professionals

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July 10, 2008

Save Power or Increase Capacity of your Air Compressors.

Have you ever noticed that most of the package air compressor units face a typical problem of higher air temperature from interstage coolers? Yes. Go & Check it. You might be having very high approach to equilibrium in case of these inter stage coolers. Why?

The simple reason is that they have a basic design flaw of using a cross flow exchanger in place of true counter current exchanger. These cross flow exchangers have low pressure drop compared to counter current & therefore save on compressor sizing if its a turnkey package unit.

So What?

Till date there is no guideline or formula in any of the heat transfer books for what should be the flow configuration in a given exchanger. This can come either from FE to some extent or by CFD analysis only.

Related References

As said above, there is no guideline or formula which can tell you that whether water flow should be from top or from bottom but this depends on common sense & logical thinking of design engineers.

One good example is as below.
It was a interstage cooler of air compressor in which air is in cross flow pattern and coolign water flow was in two pass in the tubes. So basically one side was counter current & one was co-current but not in real sense. The Sketch is given below.

We were facing the problem of high temperature in this exchanger since commissioning. Based on my previous experience I decided to inspect it for the same flaw ( Actually I got it from experience from a lube oil cooler of big size compressor of 14 MW load - Yes you got it right it was form Fertilizer unit)

On inspection we found above configuration. In this case air exit temperature can not go below CW outlet temperature. So if exchanger is designed for 33° to 43°C CW temperatures then air temperature will always be expected to go beyond 43 + 5° (Expected approach OR ATE) = 48°C. While in true counter current it can be 33 + 5° = 38°C. So there is a huge possible gap in air cooling from 38 to 48°C.

In our case the air temperature were further high at 52°C.

Therefore, based on my previous experience I suggested to swap the CW connections to make it like

In this case, after changing the CW connection, we were able to bring down the air temperatures by 6 - 9°C in different exchangers raising the capacity of air compressor by 10% or so due to cummulative effect in 3 stages.

So, try to identify the configuration of CW inlet & outlet viz-a-viz process inlet & outlet & then you can improve the cooling just by making them right.

Hope you will find some of them in your plant as well.

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July 04, 2008

Pump Efficiency - Quick Way to Calculate

Pump efficiency have always been a problem to determine, especially when no pump information is available. Here is a small equation which can be used to estimate an approximate value without power measurement.

I see this equation more useful for getting the flow information which is generally not available while head & power can be measured.

The formula is useful to make decisions for improvements in pumping system.

The equation is

Eff = 80 - 0.2855 * F + 0.000378 * F * G - 0.000000238 * F * G^2 + 0.000539 * F^2 - 0.0000000639 * (F^2) * G + 0.0000000004 * (F^2) * (G^2)

Where F = Developed head in Feet - F should be 50 to 300 feet
G = Flow in GPM - G should be 100 to 1000 GPM

So if you know flow & head, you can calculate approx efficiency & then can confirm this with power consumption. OR if you dont know flow then use iteration method to calculate flow based on actual power consumption.

Thus it is very useful for all process engineers who need to improve their pumping system. This formula can definitely guide them in making proper decision on replacing or repairing the pumps.

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