Engine Heat rate degradation during ramping

[Heinzmannj]

Hello,
I am looking for data that provides information on the degradation to an engine's heat rate during ramping up or down. In particular I am looking at micrgrid systems with a limited number of generators operating with a higher penetration level of intermittant renewables. I am quantifying the fuel savings that could occur if a battery system was integrated into the system to provide the shock absorber that system would need.
For example if I had a 5 MW system with a 1 MW PV system and the system was loaded 70% what would the heat rate degradation be as the 1 MW PV output was pulsed due to intermittant cloud cover.

Thanks

 

[MikeHalloran]

Most clouds don't have real sharp edges.

So I'd expect the engine's governor to deal with transient loads by adjusting the fuel rate.

Not that I pretend to understand what you're asking. Can you use more and shorter words?





Mike Halloran
Pembroke Pines, FL, USA

 

[rmw]

Well, to answer in a short word, yes, a battery system could add torque to the system so as to unload the prime movers, but what provided the fuel to charge the batteries in the first place or replenish them after they do their service? Hybrid cars work on just that principal. The battery driven motor provides the acceleration in excess of what the wimpy engine will provide (and usually lots of it, torque that is), but ultimately the engine has to burn fuel to replenish the battery. So what have you accomplished?

rmw

 

[Heinzmannj]

Thanks for the posts,
No doubt that all of the energy will come from either the PV system, or the engines. The idea, somewhat similiar to a hybrid vehicle, is to allow the combustion technology to operate at optimal conditions for the maximum amount of time and therefore the most efficent heat rate, the batteries then provide the additional torque when required and recharging done on the lull of load or higher alternative generation.
An empirical test could be to run with the engine connected to a load bank at a steady state for a period of time, then for the same period of time adjust the loads up and down simulating the clouds across the PV. The differnec in fuel burned is the differnce in the heat rate. The savings would be the differnec between the steady state heat rate and the volatile heat rate monus round trip efficency of the battery system.
Frequency control for power quality would also be a valued factor.
Spinning reserve for the temporary dips in solar generation would also add to the systems value.




So the question still stands, what is the % heat rate degradation of an engine during dynamic operation? Based on experiance I believe it is higher than 5% but no higher than 25%.

 

[MikeHalloran]

I am aware of a line of microgrid generators that run at variable speed, and use an internal battery bank to deal with both load dumps and load steps, because it takes finite time for the gas turbine to spool up and down. I could probably sell you a couple if you'd like.

But I still don't grok your question. You seem to be saying that there is some huge inefficiency associated with the actual torque changes that occur during a load transient.
.. which couldn't integrate over a very long time unless the governor is broken.

Tell me again how to measure "heat rate degradation", in some _other_ words, or with equations and definitions.





Mike Halloran
Pembroke Pines, FL, USA

 

[ccfowler]

Heinzmannj,

Without specifying much more about the specific types of power generating equipment, sizes, transmission system characteristics, ..., this is necessarily an almost absurd discussion involving the comparison of apples, oranges, tomatoes, radishes, celery, etc.

One thing to be very careful about is failing to fully consider the effects of parasitic losses and periodic replacement costs where batteries are involved. There will be potentially significant losses in the battery charging system, losses within the batteries, and losses in the inverter system. Beyond this, don't forget to consider the very substantial capital costs associated with the battery system plus the time and usage degradation of batttery performance and the need for periodic battery replacement.

My first guess is that by wisely choosing the sizes and types of reciprocating engines and turbines (steam, gas, or combined cycle), the performance and costs of the system will be most reliably optimized without the involvement of any kind of battery system. If this is really for a truly isolated system, the power levels and the fluctuations of the power levels both short term (seconds to minutes) and longer term (hours, days, or months) combined with the required reliability will quite thoroughly limit your realistic options.

For example, what will be the implications of likely reliability shortfalls in your proposed system?

- Life or health threats
- Expensive damage to process equipment
- Relatively brief, minor loss of production
- Minor inconveniences

What about potential needs to allow for future load growth?

Non-economic issues are likely to be the controlling considerations for your system.

 

[Heinzmannj]

Thanks CC Fowler,
In my original post the system size was described as a 5 MW system with a 1 MW PV system and the system was loaded 70% what would the heat rate degradation be as the 1 MW PV output was pulsed due to intermittant cloud cover.
The system consistes of 2.2MW and 1 MW diesel gens and a 1.2 MW photo voltaic system. With diesel at $2/ gallon the annual fuel costs are close to 6 million dollars per year at $2 per gallon of diesel. These large variable operating costs attract alternative solutions.

No doubt trying to maintain control of fear over the concern of the risk of volatile energy costs is the highest non economic emotion that is being considered. But even then the fear of not being in control of your destiny often ellicits the highest demostrated economic value - Consider the huge dollars spent on large SUVs and Trucks 9over the past several years by people whose greates risk is foraging at Trader Joes.

 

[ccfowler]

Heinzmannj,

Your more specific information is very helpful. First, in general, diesel engines usually have quite good part-load efficiency, so very likely, there will be only a very modest efficiency burden for operation at part load.

Any additional fuel usage during ramping is only momentary, so the amount of fuel involved is necessarily relatively small.

In this relatively small system, the fact that a substantial amount of the power is provided by diesel engines answers the important question of how readily load swings can be handled. Diesels can handle nearly instantaneous load changes very readily (although there may be a physical penalty if instantaneous load on the engine exceeds its normal design limits).

It will be very important to determine the efficiency characteristics of the batteries, the charging system, and the inverter system under the full range of operating conditions that may reasonably be expected. There will be subatantial parasitic losses in all of these systems, and these characteristics must be thoroughly understood before a useful evaluation can be accomplished. These losses will present a significant burden in terms of additional diesel fuel consumed or additional capital-intensive PV system capacity that will be required for which no useful load will ever be served.

It should be relatively easy to get useful data on the part load characteristics of the engines and generators.

Given this additional information on your system, I am even more inclined to doubt that a battery system will actually make economic sense.