HI Friends;

Hope all are fine. I am working in oil and gas field where gas turbine compressor set from solar turbines INc. are used. THe models are centaur 4500 and 4700.

In past our natural gas which is used for as a fuel have a GROSS DRY BTU(HHV) is 911.35 and NET DRY BTU (LHV) is 820.89 while gas density is 47.907 LB/1000 CU.FT at 14.73PSIA and 60 Degree Fahrenheit.

I calculate the LHV in BTU/LB as 820.89/.047907=17135.

On the above parameters the turbine start is good and achieve its idle speed in specified time. i want to know that if the LHV value decrease mean 820.89 to 715 then what happen? is the turbine ignite and accelerate well? also if HHV decrease then what parameters are changed mean for combustion and fuel flow?

IN short what effects take place on combustion and output power of the turbine if LHV and HHV decrease or increase?

Thanking U I will remain

 

Friends please help me its an urgent.
Thanks

 

Dear,

In your case the change in LCV is small. This will increase the mass flow in GT from combustor chamber onwards (for the same power output). The engine performance (power and efficiency) will slightly increas relative to higher LCV gas firing due to a little extra fuel mass flow.

If the fuel consists only of hydrocarbons with no inert gases and no oxygen atoms, output increases as LHV increases. Here the effects of Cp are greater than the effects of mass flow.

Also, as the amount of inert gases is increased, the decrease in LHV will provide an increase in output. Therefore in most cases of operation with lower heating value gas, it can be assumed that output and efficiency will be equal to or higher than that obtained on high LCV gas.

 

Hi Friend,

Actually the problem is that when we start the unit the ignition and acceleration is very slow. Before that its ignite and accelerate well.
only that value of fuel is change.

any guideline for me?
Thanks

 

I'm not familiar with the control systems on Solar units (I think they're called 'Turbotronic'?) or how they work, but, if you know (and it seems you do) that the fuel has a lower energy content than previously, then you should know that it's going to take slightly more fuel flow to achieve the same results as before, at any turbine operating condition.

Now, when there is some kind of closed-loop control that's active then the turbine control will likely adjust the fuel control valve in order to get the desired parameter to be equal to the setpoint. That might result in a fuel control valve opening that is slightly higher than it was previously.

But, if the amount of fuel that is being admitted during ignition ("firing") is just a fixed value based on the assumption that the fuel has a particular calorific value, and then the calorific value decreases, then the value has to be changed to achieve the same results.

Same thing for acceleration. If acceleration is not closed-loop control (meaning that there is an acceleration reference being compared to speed feedback) and the amounts of fuel being admitted were based on assumed calorific values, and then the calorific value decreases, then, the acceleration rate is likely going to be less than it was before.

So, in short, if the unit is operating relatively normally (with the exception of higher fuel flow-rates and increased openings of fuel valves) but is having problems with firing and acceleration, then it's likely that the firing and acceleration are open-loop control and the values need to be adjusted to compensate for the lower energy content of the fuel.

But, you should be asking these questions of the OEM to be sure that the fuel nozzles and fuel valves can handle the change in fuel energy value. And, maybe someone reading this post that's familiar with Solar turbine control programming can comment on how firing and acceleration is done in the turbine control and provide some clarification of confirmation of the above.

 

My 2 cents:

All Solar fuel control systems reference NGP, NPT, T5, and NGPor NPT control input for safety functions and operating functions. Therefore the fuel control system will adjust the FCV fuel flow according to the requirements of the algorithm (based on the above parameters). The Solar control system is forgiving of variations in BTU/LB to a point - outside the design parameters of the FCV and the total effective nozzle orifice area the FCV and fuel nozzle sizing may have to be changed.

BTW, I commissioned several SNGPL compressor packages back in prehistoric times ('70s), would these be the same packages? If so, the probably have the relay-logic, servo-hydraulic loader valve fuel system replaced by Turbotronic and EFCV.. Either way, the above simplified explanation still applies. Hope this helps.

 

HI Seniors,

i am new learner in gas turbine, i want to ask question related to the LHV. here is the statement

"Low LVH more power out of the two shaft gas turbine,because unit runs at cooler T3 (Combustion out let temperature) at given NGP T3 & T5 at T5 topping?