September 25, 2007

Acetic Acid Failure - Part II

This is with reference to my earlier post on the topic.

After analysis, we found that the selection of worng type of pipe is causing typical failure problem.

The background details of this failure are posted in my previous article on this topic. After failure of this exchanger & associated piping downstream of it, we carried out physical inspection & boroscopy of tubes. MOC was also tested for any supplier / manufacturing defect. Following are the results.

  1. First we checked the MOC from a third party lab & got it tested for SS-316L. So that everybody is cleared about the doubt on its inferiority. This is the first reaction normally when any material failure occurs.

  2. Then we did boroscopy of tubes & found the following pics.

  3. Now this led us to the direction of Erosion caused phenomenon or some surface / Localized / crevice boiling related phenomenon which might have been the reason for this.

  4. For confirmation we checked the pipe line downstream of this exchanger & found following.

  5. a. The failure was starting at welding joints where welding slag was creating rough surfaces, Crevices and sufficient localized drop in pressure to help vaporization of liquid e.g. water, acetic acid, or toluene.

    b. The marks of erosion were higher on bottom side than on the top portion of the horizontal pipe.

    c. The marks were appearing upto a certain length but not in the whole pipe.

    d. Apart from exchanger failure, pipe failure has occured three times and in all cases it started from welding point upto a finite length.

  6. Based on this we decided not only to calculate but analysed the mixture for its IBP in the lab. It was calculated to be 120°C whereas lab measured it ~123°C at Atmospheric condition.

  7. The pressure in the system was supposed to be ~3 bar, but to increase the plant capacity operator has fully opened a valve on the reactor inlet which was downstream of this exchanger. So the pressure in the system was having a back pressure only equal to system pressure drop.

  8. This led to a situation where minor pressure drop can cause vapor formation.

  9. So whenever, there was a crevice or rough surface found in the flow path probably one of the component was getting vaproized causing higher velocity of flow.

  10. The toal flow was around 5-6000 Kg/Hr out of which only 100 Kg/hr vaporization was sufficient to reach an erosion velocity of ~8 m/sec.

  11. Therefore, the starting point was some errosion and then crevice corrosion in the area where SS grainular structure is destroyed.

  12. This is supporting the fact that there was no corrsion / erosion in the entire system except this section.

After this we are planning to install Seamless socket welded pipes to avoid such failures in future.

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September 18, 2007

New Hot Gas Expander from GE

GE Oil & Gas has received GE ecomagination certification for hot gas expander technology that works with a waste gas recovery system to help refineries significantly reduce their energy costs while also lowering emissions.

The hot gas expander for GE’s Power Recovery Air Train features GE’s latest technology and meets the rigid standards of ecomagination, the GE corporate initiative to address challenges such as the need for cleaner, more efficient sources of energy, reduced emissions and abundant sources of clean water.

“Energy accounts for about 50% of the total operating costs for a refinery,” said Jeff Nagel, vice president-global services for GE Oil & Gas. “Wasting flue gas, which is largely air and is a by-product of the refinery processes, means wasting a tremendous opportunity to reduce energy costs and the carbon footprint of the entire refining industry. A Power Recovery Air Train equipped with a GE expander can maximize the use of this waste gas to produce the additional power a refinery needs to operate.”

An average-sized GE expander for power recovery system is designed to recover 18 megawatts of power, thus avoiding the use of the same amount of energy from the grid, which can save a refinery operator nearly $9M electricity costs each year. The technology also avoids the emissions of 244,000 metric tons of CO2 each year – the equivalent of removing 44,000 U.S. passenger cars from the roads for a year.

Compared to a system without the new GE expander, an 18-megawatt Power Recovery Train with the new expander is designed to recover more than 148,000 megawatt-hours of electricity from waste energy every year, or the amount used by 13,900 U.S. households.

Previously, power recovery air trains were equipped with older expander technology that was unable to meet customer requirements for four to five years of uninterrupted run time. Benefiting from improvements in materials and aerodynamics achieved over the past decade, the latest GE expander can withstand heavy crude oil corrosion and erosion to deliver improved reliability and availability and meet the four to five year performance standard. “This capability sets our waste gas recovery solution apart from others available in the industry,” Nagel noted.

“With our ecomagination program, we strive to introduce and modify technologies that will be better for the environment. It's good for nature, for people and for business,” said Claudi Santiago, a GE senior vice president and president and CEO of GE Oil & Gas.

SOURCE: GE Oil & Gas

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September 17, 2007

Forum Update

Thanks to Mr. Milt Beychok for his postings & initiative.
Now we have ~16 Posts and 6 users in our Forum.

Request you to make it successful & welcome your suggestions for improvement.

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September 08, 2007

Useful Videos

I have launched a page called "Videos" for useful visuals on different chemical aspects or sometimes for some FUN also.

So Enjoy them.

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September 05, 2007

How to measure pump performance without flowmeters?

We all face a very common problem of how to measure the performance of an inefficient pump in absence of flow meters particularly in case of cooling water pumps where usually there is no flow meter.

Based on my past experience in energy audit for last several years I found that we know the pump is not upto the mark based on its physical apperance of corrosion, leakages, sound etc. but how to prove it based on data that too when it is delivering the design head when you measure discharge & suction pressures. This is very confusing.

Read the simple method to verify the performance. You only need the performance curve originally supplied by the manufacturer.

This is a very common problem that all of process engineers face. How to estimate the performance sufficient enough to make a decision on improvement measures be it overhauling, replacement etc.

The confusing thing is that we are able to see the problems physically, the corrosion, leakages, sound, extra power consumption BUT still feel doubtful as pressure gauge is showing a good reading near to design value on the discharge side.

If we consider this discharge head & plot it on curve to find out the flow rate it is also similar or near to design value giving a good efficiency on mathematics. This is the point where most of us fails. So what to do?

My simple approach is to start measuring from shut off head.

  1. First Read the curve for Q & H and put it in Excel table.

  2. Use simple X-Y plot to draw this H Vs Q curve.

  3. Try to fit this data in a cubical equation, which is sufficient mostly with R-sqaured = 0.999 or better generally.

  4. Calculate H value for each Q in the same table based on curve fit equation & check for any significant deviation.

  5. If deviation is found fine tune your fit data either by dividing flow rate or by multiplying using a common factor which should be incorporated in the final equation. This is a problem related to Excel as it gives large numbers in exponential form after truncation. Otherwise, if you are using any other data fit software you don't need to do it.

  6. Now start your experiment.

  7. Measure shut off head & power at this condition.

  8. Measure discharge pressure at several flow rate values by opening the discharge valve slowly. Also record the power for each point. You should consider ~4-5 points including 100% full open condition.

  9. At least two points are absolutely necessary with shut off & 100% opening.

  10. Plot these points along with original design data.

  11. Calculate flow rate from the curve based on equation derived above but considering shift in shut off head.

  12. This flow rate value is the MAXIMUM possible value of flow which your pump can give in the given operating condition.

  13. Actual flow rate will be further less depending on the corrosion, leakages etc.

  14. However, you can judge the performance which may be sufficient enough to decide the replacement or modification in the system.

  15. This will also give you an idea about your system requirement - static head and dynamic head both. Thus you can also decide if a pump with lower head is suitable or not.

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