Back-up Fuel Requirement 1

[CKent]

Is there a standard requirement for determining the quantity of back-up fuel required in a power plant?

We are planning to build a 500 MW STG plant that will run on HFO380 as main fuel with ALCO as back-up.

We have identified the fuel requirement per day to be about 3500 m3 per day and planned to build storage tank farm with a 100,000 m3 capacity.

However, we are undecided whether to come up with the same capacity which we feel will be too big.

Is it a practice to determine the back-up requirement considering the 45 days fuel supply requirement?

 

[ccfowler]

Your planning and evaluation should reflect the specific needs of your system and not some arbitrary time period.

- REALISTIC hourly, daily, weekly, monthly, ... load profiles
- TRUE (not some nonsense idealized) heat rate under all of the varying loading conditions
- REALISTIC allowances for start-up & shut-down fuel requirements
- REALISTIC evaluation of seasonal (or other) availability of fuel for re-supply
- REALISTIC evaluation of likely future variations in the above evaluation data. (Likely progressive increases or decreases in load profiles, likely changes in fuel availability, ....)

Depending on the specific situation, a 45 day supply may be reasonable, but a much longer period may actually be needed. Needing a 3 to 6 month supply would not be the least bit surprising. What would be the realistic consequences of running out of fuel? One bad out-of-fuel episode could easily outweigh any seemingly attractive initial savings.

Depending on the specific system and cycle design, maximum efficiency (minimum heat rate) may be experienced at full load, 70% load, or whatever load, and maximum and minimum load fuel consumption rates could be punishingly great.

The most important thing to keep in mind is REALISTIC evaluation of the specific situation. What if the unit must be operated in some partially-disabled mode for an extended time (for example, by-passing a failed feedwater heater during repairs, less than optimal combustion due to control or burner problems, ...)? Under partially-disabled operation, it may be possible to maintain adequate generation but at drastically increased fuel consumption rates. It would be wise to make allowances for realistic amounts of such operation.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[rmw]

Wow, CCFowler - what excellent advice. Especially the part about running at less than optimum heat rate conditions. Star for you.

CKent, read and re-read his post carefully.

rmw

 

[ccfowler]

CKent,

Another consideration that you may want to consider is unusual operation of the plant for an extended time. For example, I have known of mid-range units being operated at full load continuously for several months without ever backing off for a moment for any reason other than emergency equipment repairs. (Normal, scheduled repairs would simply be posponed until the urgent power need passed.) The units were not intended for this operating mode, and their sorry heat rate peaked at somewhere around 70% to 75% of full load. The seemingly outrageous costs (and staffing problems) were endured because the alternatives were even worse. Situations like that can happen, and you may need to make provisions to have sufficient fuel on hand (or suitably assured replenishment arrangements) to deal with such unusual needs.

Also, you may need to pay some serious attention to the plant's actual auxiliary power and steam requirements under varying load or seasonal conditions. It is not unusual for these to be inadequately considered in planning work. It is a rare power plant that is not its own best customer. (Where else do you find multi-thousand horsepower motors scattered around a facility?)



Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[EdStainless]

Another aspect is the seasonality of demand and fuel supply.
I know of plants that are used the most in the winter, and have the greatest risk of supply upset in the winter. By the first of Oct they have enough fuel (primary and backup) on hand to run for seven months.
They burn some of it off over the summer and then restock as fall approaches.

If this plant is critical to the system then 45 day be not be nearly enough fuel on hand.

You need to consider both the storage capacity of your primary fuel and your backup.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[davefitz]

If the primary fuel is supplied by pipeline , then it might be prudent to size the backup fuel tanks for the number of days it would take to repair a failed pipeline , assuming the worst case pipeline failure occurred. Perhaps a 3 day supply would be prudent.

 

[abeltio]

At one plant, we had a similar situation and the answer was:

with a reliable and redundant source of oil (a refinery)
the most critical condition was: failure of one of the two main tanks (not the daily tanks) and went out of service

the reserve tank was sized to maintain operation for 3 days (what took to fill up the remaining main tank) + 3 days for operation/settling/margin/heating = 6 days, considering full load operation (max case scenario).

if the oil supply has uncertainty, the reserve capacity will need to consider the logistics involved in supplying the oil.

saludos
a.

saludos.
a.