Cogeneration

[neweng1]

Hi
I am an electrical guy but need some assistance for pricing a project. I have been asked to price a 2 MW project using
coogen each using 750 KW gensets. Now manufacturer is asking me all weird questions. As a mechanical engineer, could you kindly advise me what I need to know to tell a manufacturer. I would appreciate a word.
Thanks

 

[byrdj]

what's the questions?

 

[Ashereng]

Water analysis!!! Do it twice. That's right. Twice. Use two different companies to do the sampling, and use two different labs.

I was on a job where they somehow missed the iron content in the water - leading to the water treatment not being designed to remove iron - leading to no steam because we would foul the tubes.

Otherwise, what type of weird questions?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[neweng1]

thanks, like temperature, heat exchanger stuff, steam turbine type. OK Let me cut to the chase.
If I have to compare a 750 KW diesel gen and a 750 KW Co-gen plant, how can I compare in terms of investment.

Thanks

 

[Ashereng]

Hmmm. I don't know.

Co-gen is usually cheaper because you already have excess steam that you are wasting. Hence, a co-gen to turn it to electricity for use/sale into grid.

Diesel is a fuel with a cost, and it's going up.

Why is a manufacturer asking you these types of questions?



"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[JStephen]

It sounds like you need more information than you'll be able to get online- find an ME used to dealing with similar situations.

The only cogen plant I've dealt with (and that in an indirect way) was a generating plant using waste heat for hothouses- just the opposite of Ashereng's situation.

 

[neweng1]

Hi Guys,
I am back with the exact situation. We will be using three 800 KW Diesel generators and tapping the heat from exhaust and jacket and later on for heating and cooling. Please advise me so that as an electrical guy I can understand that
what I need in terms of mechanical equipments.
How does it work, what do we use like hot water tank,heat exchanger or what else. I beleive I need a kind of block diagram to proceed ahead with this. I would appreciate a word from you guys.

Thanks

 

[CESSNA1]

NEWENG1: Get the duty cycle for the engines. Are all 3 going to put out 800Kw 24/7? I doubt it. Waste heat is directly related to engine power. Cogen or waste heat systems like this work best when the load is relatively constant throughout the day and week. If you have widely fluctuating loads you may wind up with a sub par ssytem and unhappy customers. You are going to need heat exchangers, pumps, valves, supplemental energy, and coolant. If any part of the system interfaces with a potable water system you will need non-toxic coolant.

I was involved with a diesel waste heat ssytem many years ago and the engine manufacturer outright lied about the amount of waste heat rejected by the engine. Make sure the data you get from anybody is valid. Water cooled manifolds for the engine may be available. They will increase the amount of waste heat.

Good Luck
Regards
Dave

 

[neweng1]

Thanks CESSNA1
This is what I was looking for. I would be grateful, if you could spare a moment and let me know what extra components we need like heat exchangers etc. In my company there are lot of mechanical engineers but unfortunately
no body gave me such to the point observation like you did. Could you please advise me, if we need these exchaners and hot water tank seprately for each generator. I have just a dilemna , if you could help me getting out it.
What I need in terms of mechanical components and what will be the price. One more favor, if you could advise me a company that can give us a complete package and the prcining and space requirements.

Thanks

 

[UWH]

neweng1,

designing a heat recovery system is not easy, and there are different ways to do it - including two main difference: low temperature and high temperature (steam). Sounds like you may be dealing with the more simple low temperature situation:

typically you need a radiator (usually remote-mounted) designed to handle the full heat rejection to the jacketwater (and aftercooler) some engines run the jacketwater and aftercooler on separate circuits. If so you'll need a 2-circuit rad.

if the radiator is remote-mounted you will possibly need an expansion tank on the engine as well as one on the radiator.

additionally, you may need an extra circulating pump and controls if the engine jacketwater pump cannot create the required flow through all the engine-side heat recovery components.

You run a heat exchanger (usually shell-and-tube style) in parallel with the radiator and use a 3-way, thermostatic, load-balancing valve to regulate the temperature of water going to your heat recovery system.

mechanical "AMOT" valves are perfect for this purpose (they use a wax reservoir inside them to control diversion of the coolant flow and do not need electrical power) but they have to be specified at the correct temperature.

you will require a separate heat recovery device to extract heat from the exhaust, with a bypass valve around it.

... and a lot of piping and valves.

Major radiator suppliers and your engine dealers (if they are any good) can assist with all this.

Hope this helps.

 

[UWH]

Oh yeah, and separate cooling systems for each engine is a strongly preferable system. If the cooling circuits (at least on the engine side) are interconnected you can and will run into problems if one of the engines is running or not pulling the same load as the others.

 

[CESSNA1]

NEWENG1: Do a web search on waste heat systems there are companies out there that do this work. I cannot understand why the ME's at your company do not work with you.

Regards
Dave

 

[EMSOGI]

Dear all,
I have to make a comparative analysis between two condensing solutions for a 400MW power plant:
- Water condenser with cooling tower
- Air cooled condenser
The analysis should take into account all the aspects:
- Power Plant Efficiency
- Investment costs
- Equipment differences
- Utilities consumptions (costs)
- Water availability
- Environmental impact (CT Plume)
- Any other pertinent aspect that can drive the choice

Does anyone of you have experience of such analysis? Could you suggest any references for similar studies?

Thanks in advance and Regards

lottol