Diesel Generator vs Natural Gas Generator 5

[CuriousElectron]

Hi Guys,

Recently I was using generator vendor sizing software and after I modeled all my loads, I got two different required generator ratings. Diesel type came out at a higher rating than the natural gas type. What gives? The electrical rating of the unit should not change regardless of the fuel type.

Any ideas?
Thank you,
EE

 

[waross]

It has to do with the engines ability to accept and recover from block loading.
When a heavy load hits, the engine slows down slightly and then recovers.
An engine with more inertia may perform a little better.
A naturally aspirated engine may perform better than a turbo aspirated engine.
A PMG excited set may perform better than a self excited set.
The software is sizing according to the specified voltage drop when a motor starts.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[CuriousElectron]

Hi Guys -

I have a follow-up question. I used a vendor sizing software to size a generator and I got confusing results. It appears the software is recommending 3x150kW units or a single 350kW unit. Does this recommendation make sense to you? Why would I purchase 3 separate units which I'd have to synch/connect and maintain versus a single unit, which would be easier to integrate into the existing system..

Maybe I'm missing something here.
Any thoughts?

Thanks,
EE

 

[waross]

The three units may be an N + 1 arrangement.
The package would include a load control panel.
Apart from that, without seeing and running the software myself, I am just guessing.
Another thought;
The single set may be for a standby installation and the three units for a prime rated N + 1 installation.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Or the three unit offering may cost less because they're made in greater quantity or are considerably cheaper to transport.

Or

Perhaps you haven't demonstrated that you need all 350kW all the time.

Suggest you give this a read:

Diesel verses Ngas




Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Cost Comparison

It’s a common misconception that industrial diesel engines are considerably less expensive than comparable natural gas models. Below 150kW, natural gas engines are actually more cost effective, even without factoring in the fuel differential.

For applications where more kW are required, power producers can create parallel configurations of smaller engines to provide them with the cumulative kW needed for the operation. Parallel systems have the advantage of supporting load sharing and management, making them one of the most cost-effective and environmentally friendly options, in terms of fuel use, for variable load applications such as mini-grids.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

One little problem with the article.
The author equates wet stacking to fuel bypassing and feels that it will not be a problem with gaseous fuels.
Not so.
Wet stacking occurs under light loading when the combustion pressure is not great enough to seal the piston rings.
At light loads the engine may lose lube oil past the rings.
It is lube oil, not diesel fuel that accumulates in the exhaust system.
Gaseous engines may have a similar problem at light loads.
Wet stacking may occur with a brand new engine or an old worn out engine.
Once an engine is well broken in wet stacking is unlikely to occur until the engine is near the end of its life cycle.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Parchie]

Y'all,
IDK if it's just me but from the standpoint of having a reliable power source, diesel-fed engines are the better option. Gas lines break during quakes and or gas leaks/lost when residences get ripped during storms, etc; but you can store diesel inside containers and ride out the disasters!

 

[waross]

If you want to have fuel on hand to ride out a natural gas failure, use propane.
Easy to store and a natural gas engine may be configured as a duel fuel engine, running on either natural gas or propane.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

I understand the emergency fuel flown in following a disaster will be diesel, not propane.

 

[waross]

but you can store diesel inside containers and ride out the disasters!

or
but you can store propane inside containers and ride out the disasters!
I rode out Hurricane Mitch.
I was responsible for repairing a small island generating plant.
Five generators, total capacity 2.2 MW.
Diesel fuel and propane were generally available. Nobody was flying fuel anywhere.
Natural gas is a good solution for a department store.
Most facilities just need enough running time for an orderly shutdown of business during a major disaster.
There are problems with long term storage of diesel fuel that don't apply to propane or butane.
Hospitals are a special case. I would hope that any new hospitals will incorporate standby generator fuel issues in the major disaster response planning.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crshears]

Hey Bill, question: if a site's primary fuel is natural gas and propane its backup fuel, might not the standby cost of having a large tank of propane get prohibitive, and/or commercial might not propane supply places even want the site as a customer as virtually no volume of propane would ever be delivered to the site, other than the small amount of make-up propane to replace that used in periodic testing...or are the propane supply companies in BC a little more flexible? My thought is it might be necessary to purchase the propane storage tank and handling facilities outright...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

I would buy the tank.
As a suggestion I may install a 500 gallon propane tank but try not to let the level fall below 400 gallons when testing and exercising.
I am sure that there will be a supplier willing to top up the tank for a minimum charge based on a 100 gallon delivery.
But again it depends.
In real life, how critical is the generator?
How much reserve time is required?
Can the facility be shut down in an orderly fashion?
If the outages are long term can the facility be evacuated?
How likely is a natural gas outage?
And a lot more questions.
A department store may require emergency lighting and Point Of Sale terminals for a few hours.
A hospital may require full power for several weeks or more.

If natural gas is deemed to be vulnerable another option is a duel fuel diesel/natural gas set.
This is a simple conversion and uses very little diesel in normal operation.
It may be arranged for a seamless transfer to 100% diesel in the event of a gas failure.

Something to bear in mind is that a disaster that damages buried gas lines may also damage the infrastructure so that it is difficult or impossible for trucks to deliver either diesel or propane.

Another case for natural gas is fire regulations as they apply o a fuel supply.
I remember a standby generator in the penthouse of an eight story department store.
The fire marshal would not allow a simple pumping system to deliver fuel to the generator.
The generator had a day tank, but the issue was replenishing the day tank.
The owner was unwilling to pay for a leak-proof, overflow-proof system that woulds satisfy the fire marshal.
The solution? Carry fuel in five gallon Jerry-cans up eight floors on the elevator and the up the stairs to the penthouse by hand.
Natural gas may have been easier.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

The disaster I had in mind was more of the cascadia subduction zone 9.0 variety, where everything west of I5 is "toast" according to one publication. Roads, bridges, sea ports, air ports, etc. are well toasted. The only way to get supplies in will be by helicopter, and my understanding is that transporting propane in this manner is not an option.
Link-1
Link-2

 

[waross]

In a disaster of that magnitude there may not be enough of a facility left to need fuel.
Also in such a disaster the normal rules don't apply.
But good points.
You have decide what level of disaster to design for and you can't assume that it will be alright because someone will break the rules.
Planning for a disaster of that magnitude I would probably go for a diesel engine with a natural gas kit added.
Another option is a large storage tank.
I installed a diesel generator in a facility that had been converted from bunker fuel heating to natural gas heating.
There was a very large, buried, bunker fuel storage tank that was repurposed for diesel fuel storage.
I don't remember the numbers but I am making an educated guess that they could run a month on a full tank of fuel.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Parchie]

@waross
or
but you can store propane inside containers and ride out the disasters!

I've never heard propane gas cylinders being flown over to disaster areas. Note the catch word "flown"!

 

[waross]

I have had a small amount of first hand exposure to disasters.
Hurricane Mitch.
Some excerpts:

Hurricane Mitch is the second-deadliest Atlantic hurricane on record, causing over 11,000 fatalities in Central America in 1998, including approximately 7,000 in Honduras and 3,800 in Nicaragua due to catastrophic flooding from the slow motion of the storm. It was the deadliest hurricane in Central American history, surpassing Hurricane Fifi–Orlene, which killed slightly fewer people there in 1974.

The official death toll in Honduras was popularly reported as "More than 5,000, Less than 10,000."
In mountain valleys, there was a small village every few miles.
Flooding and mud slides and flows would take everything in their path.
So many villages were lost, as well as all living things that an accurate death toll was impossible to determine.
When I say lost, I don't mean it as a polite word for dead.
I mean lost, gone, disappeared, carried away, buried in mud, NEVER FOUND. LOST!
The rains from Hurricane Mitch were two or three hundred miles from the eye.
History.com

Honduras and Nicaragua were especially hard hit by the hurricane. In Honduras, floods and mudslides brought on by heavy rainfall washed away entire villages, and the majority of the country’s crops and infrastructure were destroyed. The hurricane also took a major toll on Nicaragua. In one area alone, Posoltega, more than 2,000 people perished in a huge mudslide.

Honduras
Main article: Effects of Hurricane Mitch in Honduras

While offshore northern Honduras, Hurricane Mitch passed over Guanaja island.[4] High waves eroded northern coastlines and damaged lagoons.[19] Most of the Bay Islands had damage to their water facilities.[20] Two days of winds exceeding 200 km/h (120 mph) destroyed nearly all of the plants and trees on Guanaja, uprooting or knocking down almost the entire mangrove forest.[21] It is estimated that the hurricane produced waves of 44 ft (13 m) in height.[22]

I was scheduled to fly out of Guanaja at noon on Saturday. The weather was so bad that the Saturday flight didn't get out until Sunday afternoon.
On Monday Mitch hit.
Most hurricanes move on in a few hours.
Mitch circled and hit the Island of Guanaja three times in three days.
Our power company had about 5000 subscribers.
We lost all but three of our poles.
Those three weren't trusted and were replaced as well.
Our generators were saturated with salt water.
I opened the connection box on one generator.
There was a white salty high water mark inside the JB.
Meggered, zero.
Tested with an Ohmmeter. Just a few Ohms of insulation resistance.
I reversed the meter leads and got a different reading.
Tried a voltage measurement from the windings to ground.
I read a small voltage.
The copper windings and the iron core, along with the insulation saturated with salty water were forming a rudimentary battery.

When I flew back in the following Sunday, I think it was, the pine trees on the North West side of the Island were stripped of needles and black.
When I left the un-cut grass beside the runway was two to three feet high.
When I flew back in a week later the grass was a few inches high.
The winds had actually stripped the grass.
On the South East side of the Island the deciduous trees were a mess. The ends of all the branches were broken off where the branches were about 5/8" to 3/4" thick.

“The country was left like a window broken in a thousand pieces. Small and big bridges were destroyed, landslides obstructed roads, and even highways with strong pavement sunk into rivers,” writes Aníbal Serrano of the Fundación en Acción Comunitaria de Honduras, Sulaco, Yoro.

Hurricane Mitch struck Central America in late October 1998, leaving more than 11,000 people dead, destroying hundreds of thousands of homes and causing more than $5 billion in damages. It was the deadliest hurricane to hit the Western Hemisphere in more than 200 years.

Several fishing boat owners on the Island of Guanaja had small weather stations.
All reported gusts to 245 MPH. No greater speeds were reported before all of the anemometers were blown away.

What's the point?
Nobody was delivering any kind of fuel by air.
You used what you had or did without.
Not just fuel, everything.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crshears]

Mitch was a bitch, for sure; in 1995 my wife and I took a two-week sailing cruise aboard the SS Fantôme to mark our fifteenth wedding anniversary...and the vessel was lost with all 29 hands aboard in the waters off Guanaja during hurricane Mitch while frantically engaged in a futile attempt to evade its path [ the story is well told in "The Ship And The Storm" ].

Seeing how devastated some of the Caribbean islands are at present due to hurricane damage seems to strongly suggest that such destruction is becoming statistically probable to likely rather than the quite rare it used to be...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

Natural gas versus diesel.
We have covered most of the factors.
Annual cost of fuel?
Is this standby or prime power?
If standby how many hours a year are anticipated?
Are we planning for a power outage or for a disaster?
At what level of disaster will we attempt to evacuate rather than cower in place.
(Considering that the facility may no longer have windows or a roof, cower may be a better word choice than shelter.) grin
How long will the set run on the fuel on hand?
Is that enough to cover the needs that we anticipate?
How will we be able to refuel during a disaster?
While we have differed as to degree, all the points raised are valid.
If I have offended anyone please accept my apology.
All of the point mentions may be well to consider for anyone planning a standby set for anything more than the occasional nuisance power failure.
Thank you all for your ideas.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[CuriousElectron]

Quick update - it turns out the software suggested using 3 units because there is a limitation on the maximum rating of natural gas that be used..Diesel single units have higher ratings