BFP in a Thermal Power Plant

Its good To think of new ideas, But just thinking how about filling cold boiler when there is no steam and so no turbine rotation?

Sir, During steam blowing we could take steam pressure upto 10kg without the use of BFP (By directly filling the drum using a small motor in the DM plant). So can a similar thing happen here? Like, using a relatively higher rating motor in DM plant to take steam pressure to around 50kg/Sq.cm and then bringing BFP into picture (because by that time the BFP would be rotating at around 1000rpm).

Theoretically what you are saying is doable, But you just can not rule out the conventional wisdom, Think it 10 times before reaching on any conclusion, why motor is being used instead of direct coupling? You have not given some of information like how is that 3.7MW motor is operated, spatially at the starts, is it fed by external power? thats the where key is, I guess there must be some external power used for that, Filling boiler with some makeshift arrangement at the start of plant is not advisable, Things has to work always without delays and breakdown,

Thermal power plants are being made for decades, So why not to look on some history? and try find out if it had been done ever or not,and why it is discarded? or if it is already done in some part of world? And then come up with the list of advantage and disadvantage,after that you can come up with an agenda to overcome to those disadvantage points,isn't it we are taught?

Yes, it is possible, just like how the gas turbine works, compressor & turbine share the same shaft, however if the Boiler Feed Pump as you mentioned, is coupled that way you will not have a place to play with flow variables.There is a delay lag between the feeding and the steam conversion, how can you then handle that coupling the BFP to the turbine? you see, its IMPRACTICAL. unlike the case of a gas turbine where the medium(gas) flow is in simultaneous process along the equipment.

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How many boiler feed pumps are there? Is there one for each turbine?

If so, I can envision a solution where you do a number of things:

• keep one or two BFP pumps electrically driven to deal with startup conditions and other needs for control mentioned by others in the thread
• have another pump on each (or almost each) turbine to provide the bulk of the BFP requirement
• have the output of the pumps manifolded together, and the input to the boilers fed from the manifold (sort of a communist solution: from each (pump) according to its abilities, to each (boiler) according to its needs)
• you might need control valves of some sort on the input to each boiler, and possibly on the output of each pump, to achieve the proper flow of water to each boiler without overloading any pump

Or you might have another arrangement without the same manifold as described--just use the electric pumps to start a boiler / turbine pair (are they paired) and switch to the shaft driven BFP when at "full operating speed". (Some sort of manifolding would still be required, so that one or two (the 2nd being a spare) electric pump could feed any of the boilers.

Whether this would result in any savings in initial capital cost or future operating costs is (as my professors used to say) left as an exercise for the reader.

<BFP's can be directly coupled to the turbine shaft so that the need for motor is eliminated?> You are not asking if the pump is directly connected to THE tubine generator ? is that right. Yes, boiler feed pumps can be steam driven turbine pumps with multi nozzels for dialing in the loads, as new arrangements are made necessary. In these plants steaming is never (almost never) shut down, so the need for a cold iron start is seldom, but yes as others have mentioned in this thread an electric driven backup BFP is needed also. http://www.clydeunion.com/sites/clydeunion.com/files/uploadedfiles/TWL_Brochure_PDF.pdf Warmest Regards, Ray

Sir, I was asking if there can be a possibility of connecting the shaft of BFP to TG shaft via some oil coupling. If that is not possible please let me know the reason. Thank you sir.

Sir, Tell me i'm getting this wrong .... you want to run the Boiler appurtenance via a secondary source (electric turbine's shaft) that is unrelated to the boiler load (feed water level)? You must be asking if it is a mechanical possibility, regardless if it is wise and standard practice. Does that sum it up? Let me share with you two words of wisdom ; Low water, and lack of purge. These are the two things that can kill you in boiler operations

"shaft via some oil coupling" you mean by hydraulics?

On the face of it an electric motor is a prime mover and can be replaced with any other type prime mover, but for a designer things are not that simple.

Practical limitations are that the BFP must have exceptionally high starting torque, that means you have to closely match the torque-speed characteristics curves of the BFP to that of the prime mover.

The pump manufacturer has selected a particular design motor for the coupling, you cannot even replace that motor at random with another make even with the same Kw rating since deviations in characteristics, efficacy and torque development by each widely differ and failure would be imminent.

Take into reference the torque-speed characteristics of the pump and refer to any hydraulics prime mover system characteristics you will immediately drop that idea yourself.

The generator turbine speed has to be varied in an unpredictable fashion in order to initially synchronize the generator and later to maintain stability when large sections of system become faulty or a large load is taken in, the boiler liquid requirements have to e maintained without fail hence direct coupling with shaft where speed torque characteristics cannot match BFP requirements is not acceptable.

Re: The generator turbine speed has to be varied in an unpredictable fashion in order to initially synchronize the generator and later to maintain stability when large sections of system become faulty or a large load is taken in, the boiler liquid requirements have to e maintained without fail hence direct coupling with shaft where speed torque characteristics cannot match BFP requirements is not acceptable.

Yes, the speed has to vary unpredictably (well, at least in some sense), but, I'm not a generator person, but I don't think the speed variations are very big. You have to keep the speed somewhere close to synchronous speed (to deliver approximately 60 Hz.)--what would the speed variation range be--maybe 5% at under all but extreme conditions?

Sir/Sir's, We have 2 BFP's installed in our plant(one during normal operation and one as a backup). My idea was, why cant we couple one bfp to the turbine shaft so that during smooth and normal operation of the turbine and in case of a rapid change in turbine load we can switch over to the emergency one which runs on motor. I was specifically interested in such a kind of concept because of the following reason. We are generating 135MW and of that 135 MW, 3.7 MW would be consumed by the feed pump alone. So over a long period of time; if we are able to save this 3.7 MW by running the BFP through any other possible means, it would lead to a good economical result. So I just wanted to check the feasibility of such a concept. Thanks to all for their valuable comments.

Dear MSCS, Thank you for returning to informing us that you are reading what we take the time to write.... Sometimes a question gets asked and the Original poster (OP) never returns to thank anyone, or to explain in anyway if it was helpful. There are a great many ways in which you can achieve substantial cost savings in a thermo plant. One important and often overlooked one, is to put a good steam trap program in place to prevent any unnecessary losses and train the operating personnel on the value of stopping/changing leaky traps. Good luck in your endeavors. Warmest Regards, Ray

Thank you Mr. Ray. Good luck to you 2..

You are practically saving nothing, if the motor is running it is consuming 3.7 MW electrical and in case of direct shaft coupling the turbine still has to cater this load mechanically (only prime mover type has changed!).

There are host of safeties and interlocks associated, direct coupling to turbine means you have to re-assess and redesign the automation logic and watchdog arrangements. Can you do that conveniently?

GE has done this for many years through a varible hydraulic coupling. Do your research and you will find examples. Very easy to do. You still have to have at least one electric driven one as a backup.

What I suggest for cases like this is recovering heat from flue gases and driving an Organic Rankine Cycle system to drive the BFPs. ORCs are most often used to generate electricity from sources such as waste heat, but they're also frequently used to drive mechanical loads such as blowers, etc.; and there's plenty of waste heat available in a boiler's flue gas to drive a 3.7 MW load. Contact me for details: Do not post email addresses -Admin DZ

Dear Mr.MSCS,

The Answer for your Question is - YES.

Yes, you can couple the pump to a small turbine speed of 2900 R.P.M, to the Pump of 2900 R.P.M.- called TURBO FEED PUMP. This can be done but will result in a low over-all thermal efficiency of the system of turbine coupled to the pump.

This Turbine can be designed to work at a back-pressure and send the exhaust steam to De-Aerator. But the sp.Steam Consumption per HP.Hr or kWHr for this system will be very high, your data indicates Power for Feed Pump is 2.74% ( 3.7/135 = 0.0274 or 2.74%) and in the case of turbine coupled pump it can be about 3.5% - thus loss of Efficiency.

If the same steam is used at the main turbine the output will be high, thus higher efficiency is achieved - since the steam is sent to condenser which has a vaccuum and abs. pressure of the condenser will be 0.1 kg/cm^2 and at lower pressure, the power out put or HEAT DROP per Kg. of Steam will be more - Refer MOLLIER CHART.

You have not indicated the Boiler Pressure. This small Turbine - no.of stages will be less and hence less efficient.

Thanks,

DHAYANANDHAN.S