Comments on Press Reports comparing Chinese Power equipment with BHEL supplied equipment.

I have started my career as Engineer Trainee in BHEL Haridwar in 1973. I was Erection Engineer and erected 4 out of 5 Turbines of 200 MW at Obra from 1977 to 1982.

Later on I joined NTPC Corporate Office and was involved in Performance Guarantee Tests of Steam Turbines of 200 MW of Singrauli, Korba and Ramagundam. We use to discuss the gap between the Design Heat Rate and actual Station Heat Rate extensively. Being pioneer in India in acceptance testing of Steam Turbines I claim a proficiency and expertise in this area which very few people could match.

I was transferred to Vindhyachal STPS in 1987 and worked in O&M of 6x210 MW Units. In these units I discovered the importance of CW Chlorination in maintaining good Condenser Vacuum which is primarily responsible for Turbine Heat Rate.

I left NTPC in 1996 and worked in DLF Industries, ALSTOM and NASL.

I joined Steag after the company was entrusted with O&M of 4x600 MW IPP at Jharsuguda. I was entrusted with Turbine Maintenance but was also associated with Performance Guarantee Tests of Steam Turbines due to past experience.

My experience at Jharsuguda tells me that Dongfang Steam Turbines are no way inferior to BHEL Steam Turbines and I am shocked to read the following news reports:

Business Standard: CEA shock for Chinese power equipment

The Indian Express: Bhel equipment outperforms Chinese gear on critical parameters, says study

The Financial Express: Bhel equipment outperforms Chinese gear on critical parameters, says study

The Economic Times: Chinese equipment less efficient than supplied by BHEL: Government

I am quoting below from these reports and responding:

The Financial Express: The CEA report found that the operating heat rate of Chinese power equipment works out to 2,719 kcal/kWh compared to 2,520 kcal/kWh for Bhel gear.
The load factor of Chinese equipment averaged 57.2% during the study while it stood at 71.6% for Bhel gear.
Bhel equipment also outdid Chinese hardware on secondary fuel oil consumption. The fuel oil consumption of Chinese equipment was 6.13 ml/kWh while it was just 3.06 ml/kWh for Bhel gear.

The Operating Heat Rate mainly depends upon the Loading Factor. When the Loading Factors are different the comparison is unfair. The Loading Factor does not depend upon the machines but what Load Schedule you get from the grid. The Power Grids are under the control of Government Bodies and give less schedule to Private Companies who are operating the Chinese supplied power plants. Once again the Fuel Oil consumption parameter is based on units generated (kWh) which will be less and the specific fuel oil consumption is more.

As an expert in the field I can say that the report has been prepared just to blackmail the Chinese suppliers and please the Politicians who might be seeking such report.

I am waiting for the Report to be made public and examine it thoroughly.

Important Feed back for KN series Steam Turbines of BHEL.

As per Report of BHEL the KN series Steam Turbines were introduced in 1997. As per the Report there were lot of problems initially and combined HP IP modules called K Turbine were sent back to works and LP Turbine called N turbine were also rectified at site. Thus the KN series.

Recently the combined HP IP module had to be reopened after overhauling due to suspected leakage from Balancing Leak off pipe.

By the way there is a Balance Drum on HP Rotor rear side and a steam pipe called balancing leak of is connected between IP 6th stage and the Balance Drum. There is a sliding joint in the pipe to take care of expansion of inner casing.

The space between inner and outer casing of K Turbine is filled with IP Turbine exhaust steam which is at 302 degC.

Due to leakage in the sliding joint of balancing leak off pipe high temperature steam at 465 degC (full load parameter) was heating the space between inner and outer casing during the cold start causing high HP Top, Bottom and Flange Temperatures, high expansion of HP Outer casing and Rotor expansions. The Top Bottom temperature differential was also high (37 degC).

This is an important feed back for these machines. In case the extraction steam temperature to Deaerator (which should be equal or 1 degC lower than IP Turbine exhaust temperature) is higher than IP Turbine exhaust it indicates leakage in these joints and should be attended by opening the K Turbine.

There are two pipes in lower half of the inner casing and the same has to be removed to attend the leakage.

 

Effect of Atmospheric Pressure on measurement of Condenser Vacuum.

I have following measurements of Condenser Vacuum for 210 MW units in two locations:

Tuticorin TPS -662 mmHg CW Inlet 33.15 degC outlet 43.3 degC
Nasik TPS -658 mmHg CW Inlet 28.3 degC outlet 36.15 degC

It appears that there is not much difference between -662 and -658 mmHg in the two measurements the difference is actually much bigger considering that Tuticorin is located at sea level and Nasik at a height of 599 metres from MSL. The barometric pressures at these locations are as follows:

Tuticorin 760 mmHg
Nasik 712 mmHg

The absolute pressure for the measurement would be:
Tuticorin -662+760 = 98 mmHg = 130 mbar
Nasik -658+712 = 54 mmHg = 72 mbar

The mercury gauges are not found in the modern plant so let me convert the values to Kg/cm2 and Kpa for understanding by the new generation of engineers:

Tuticorin -662 mmHg = -0.8998 Kg/cm2 = -88.23 Kpa
Nasik -658 mmHg = -0.89436 Kg/cm2 = -87.7 Kpa

It appears that the difference is only 0.5 Kpa but the real difference when converted to absolute pressure would be 130 - 72 = 58 mbar = 5.8 Kpa

The best way to get the atmospheric pressure of your place is to use a Barometer. In case you don't have it you can know the atmospheric pressure approximately from the altitude of the place.

-->

Altitude metres	Atmospheric Pressure mbar
50	1007.27
100	1001.29
150	995.38
200	989.48
250	983.57
300	977.67
350	971.86
400	966.08
450	960.3
500	954.54

Source of the above data.

Please note that altitude of a place town/city also varies a lot e.g. if you read Wikipedia page about Nasik it gives the altitude as 560 m and it is true that the area around Godavari River is at 560 m but the Thermal Power Station is situated at 599 m. To get the correct altitude you should use the data of your power station or you can use Google Maps on this link.

Pump assisted Siphon in CW System of Turbine.

To understand the content of this post please read Wikipedia Page on Siphon.

Once through CW systems are relatively unknown in Thermal Power Plants being constructed today but there are many old ones. Let us look at following image on Wikipedia page.

From Wikipedia

B can be the top point of Condenser Water Box and C the end of the outlet pipe.

The Siphon works on the basis of height difference hc. In CW System hc may be zero but the CW Pump Head equal to hc will simulate it.

In case of Siphon both inlet and outlet pipes are under vacuum. In CW System the outlet pipe will be under vacuum but inlet pipe may be under positive pressure or slight vacuum at Condenser inlet.

Since the Cooling Water picks up heat in the Water Box the pressure in Water Box should be higher than Vapour Pressure of Water at Outlet Temperature with some margin.

During Start up Vacuum is created by Condenser Water Box Priming Ejector or Vacuum Pump.

The Priming Ejector/Vacuum Pump needs to be run periodically to remove liberated dissolved gases from Cooling Water from Condenser Water Box.

Recently I visited one Thermal Power Station where I had to tell them the importance of running Water Box Priming Ejector periodically.

Beware! Steam Turbine Deposits of 1929 to 1936 have surfaced once again.

At one IPP in India H. P. Heater Safety Valve blew when the machine suddenly touched 103.6% of rated load. Maintenance Engineer thought that the original Safety Valve setting could have been disturbed but on checking the data in DCS it was found that the extraction pressure had actually reached the set value of Safety Valve to blow.

Now this is not a simple matter. The set pressures of Heater Safety Valves are such that the Turbine could never provide steam at that pressure i.e. the set pressure is higher than the extraction pressure under Turbine VWO (Valve Wide Open) condition. The blowing of the Safety Valve indicates restriction in the Turbine Casings.

On further analysis the Turbine First Stage Pressure was also found very high and higher than the value recorded during VWO test on Turbine. In spite of more than 6% capacity over TMCR under VWO condition established during Performance Guarantee Test the load had to be restricted at 98% of TMCR due to high First Stage Pressure. Analysis of all extraction pressures revealed restriction limited to High Pressure Turbine.

Restrictions may be caused by the deposits on Turbine Blading but Power Station Boiler Water Chemistry is very advanced since 1960's and deposits in high pressure zones are unknown.

I had to dig out a paper published in May 1936 by University of Illinois
Engineering Experiment Station. It was possible to get this paper because University of Illinois had undertaken Large-scale Digitization Project in 2007 at at Urbana-Champaign Library.


The title of the paper is The Cause and Prevention of Steam Turbine Blade Deposits and download link is here.


Prior to 1936 the Power Station Water Chemistry was evolving in USA. In fact the author of the paper was Special Research Assistant Professor of Chemical Engineering at University of Illinois.


I am taking liberty to quote from this paper:

"Purpose of Investigation.-Steam electrical generating stations

have encountered difficulty in the form of fouling of turbine blades.

This difficulty has become of major importance in many large stations,

whereas it has only meant annoyance in other stations.

There are several types of deposits which form on the turbine

blading and cause this fouling. One type is that which is apparently

caused by a deposition of solids carried in the steam from the boiler

water, and another is that caused by a chemical reaction between

chemicals in the steam and the material in the turbine blades. The

first type is the most common, and is readily distinguished from the

other in that it is largely soluble in water, and is washed off with comparative ease, whereas the other type of deposit adheres to the blades very tenaciously.

The deposition of solids carried in the steam appears to be the

major cause of difficulty. The efforts of this research have been directed entirely toward a study of this type of deposit, and no study

has been made of the other type.

The purpose of the present investigation has been to assemble

data relative to the occurrence of this type of deposit on steam turbine

blades in order to determine the cause of the difficulty and to devise

methods of preventing it."

Resume of Central Station Experience.-The following extract
from a letter serves to illustrate very clearly the difficulty caused by
this kind of turbine blade fouling.
"The operating records show the machines can only be kept in service for a matter of 3 to 4 weeks before the effective output of the machine drops about 20 per cent. The deposit is easily removed by washing, but of course this necessitates shutting down and leaving machine cool off, with a subsequent loss in the overall station efficiency as well as temporary reduction in the plant availability. The washing process adopted does not involve anything more than allowing the machine to cool down for 36 hours, and then starting up in the normal way, the condensation produced being sufficient to clear the fouling."

Although Power Station Water Chemistry is very advanced in India there is a reason to believe that Boiler Feed Water got contaminated with Cooling Water at this IPP and the conditions similar to pre 1936 in USA got created inadvertently.

Moreover when the unit was down for Annual Overhauling for more than 30 days the restriction due to high First Stage Pressure had vanished after Overhauling and there is no need to get surprised if you read the bold sentences in the above quotation from the research paper.

This post is to caution the new IPPs coming up in our country.

L. P. Turbine Bearings in separate pedestals.

The title may surprise new generation of Turbine Engineers because L. P. Turbine Bearings are mounted in separate pedestals since BHEL the indigenous supplier began manufacturing as per KWU (German) technology.

But if you look at 200/210 MW Steam Turbines manufactured by BHEL as per LMW (Russian) technology the bearing housing is just an extension of lower half of L. P. Turbine. Even the Generator front bearing is placed in L. P. Turbine casing.

Condensers are placed on springs which get compressed due to weight of water in hot well, Condenser Tubes and Water Boxes. This may bring the bearings down and there was a theory that it may affect the alignment between I. P./ L. P. Rotor and L. P./Generator Rotor. Although we did not check the rotor alignment by filling water in hot well (normal level plus additional water equivalent to water in tubes and water boxes) this was done at other power projects. When one such expert visited Obra where I was doing the erection of 200 MW Steam Turbines, I showed him that the alignment was getting affected even due to variation in ambient temperature by taking the alignment readings at 4 PM and 6 AM. This was happening because the L. P. Turbine Casing expands and contracts vertically from its foundation and the height of the bearing from foundation is considerable.

The pedestal mounted bearings have more rigidity and they are not affected by movement of L. P. Turbine Casings due to weight of water or thermal expansion.

Recently I was asked whether 4x600 MW Steam Turbines at Jharsuguda manufactured by Dongfang have bearings in separate pedestals or in the extended portion of L. P. Turbine. The answer is very simple the Steam Turbine at Jharsuguda is state of the art and the bearings are mounted in separate pedestals like BHEL KWU design. 

Required Dew point of air for Gas tightness test of Generator and of Hydrogen when unit is running.

While I was leaving Jharsuguda for Delhi TMD Engineer informed me that the Dew Point of Instrument Air in TG Hall below Generator was -7.0 degC and asked whether he can fill air to conduct Gas Tightness Test. I told him no and informed him that the Dew Point would increase to positive value at 4.0 Bar pressure required for the Gas Tightness Test. I recommended him to check how much the Dew Point will increase from Dew Point Calculator on this site. I also checked it at 4 barg air pressure and the value is 14.9 degC. Is it ok to fill this air? NO. This is winter season and the temperature of air will go below 14.9 degC resulting into moisture in Generator.

The engineer got confused because I had allowed -7.0 degC Dew Point of Hydrogen taken at atmospheric pressure when the unit was running. I told him that on running unit minimum cold gas temperature was 38 degC and the above Dew Point converted at 3.5 barg Hydrogen Pressure comes to 13.3 degC which is 24.7 degC lower than the Gas Temperature. At that time I had also instructed that in case the unit trips and the cold gas temperature goes below 38 degC the Hydrogen Pressure should be reduced to maintain the Dew Point 20 degC below the cold gas temperature.

If you are dealing with Generators remember that the Dew Point increases with Gas Pressure whether it is air or Hydrogen. The measurement of Dew Point done by Portable Dew Point meter is at atmospheric pressure and you need to convert the measured Dew Point at the Gas Pressure and this online calculator is a handy tool to convert. The converted Dew Point should be atleast 20 degC below the Gas Temperature.