Gross Calorific Value Effects


Thread Starter


Respected Members,

We are the provider of natural gas to the power plants. The power plant have a GE gas turbines with combined cycle. According to our agreement we provide the natural gas with value of GCV between 900 to 950 BTU/SCF.

Now the customer identify that our GCV is increased and the new value of GCV is 1100 BTU/SCf and he claim that they face operational problems as well as damage the hot gas path parts of the gas turbine.

I want to know how and why higher GCV effect the Gas turbine parts?

Respected Members,

Good day. Its urgent please I am unaware about GE turbines. What is the design value of natural gas CV of GE turbine?

GE supplies a fuel system that is designed for the heating value defined by the purchaser. They basically match the fuel nozzles to the specified gas. You would likely need to contact GE to see what changes (if any) are required to use your gas. It is possible control settings can be made to accommodate this gas, but it is more likely that fuel nozzle tips will need to change. You have to get the answer from GE. It is extremely likely there will be a cost associated for this service.

>Good day. Its urgent please I am unaware about GE turbines.
>What is the design value of natural gas CV of GE turbine?

I don't believe there IS a single design value of natural gas Calorific Value for GE-design heavy duty gas turbines. It's my understanding that when a potential purchaser is negotiating for the configuration and purchase of a GE-design heavy duty gas turbine they are asked to provide the characteristics of the fuel(s) that will be burned at the site. This is used when sizing fuel nozzle orifices, fuel valves and calculating operating parameters.

I believe that calorific value is much more important for GE-design heavy duty gas turbines with DLN (Dry Low NOx) combustors than units with conventional combustors (diffusion flame combustors). DLN combustors are much more ... sensitive than diffusion flame combustors ever were. If the unit is in combined cycle operation, and starts and stops relatively frequently, and it is not always operated at Base Load (in other words, it is operated for long periods at less than rated load), I would think a higher calorific value fuel could possibly be more problematic.

But, really, this is not a topic that you can take to a court of law or arbitration based on what you learn from a free World Wide Web forum. You should be asking for a report and documentation from the Customer that they obtained from the OEM with specific details of the problem and how a higher-than-expected calorific value of fuel could cause problems.

You might also search the World Wide Web for a copy of GE publication GER-3620, as it has a lot of information about different fuels and operating conditions and maintenance intervals. There may be other GE publications related to fuels and combustion and effects--there are a LOT of GE publications.... I believe several publications have been written in the last few decades about fuels, but you are probably looking for the most recent ones, and ones related to the type of GE-design heavy duty gas turbine involved in this matter. I wish I could help you identify the proper publications, but, as I said there are LOTS of GE publications and I don't think anyone in GE knows exactly how many there are, which ones would be applicable, and where to obtain them (they are NOT located in one, convenient and easily accessible place--at least not publicly on the World Wide Web).

I can understand this would be an urgent matter, but, as I said you need to be working with the Customer and your legal department to obtain information. You might also ask the Customer if they can arrange a meeting with the OEM to discuss this in detail with everyone--including you and/or your organization.

Often, unfortunately, many things are said about gas turbine damage which over time turn out to be only marginally true or less than completely true (sometimes much less). The costs involved can be huge, and the lost revenue from generation (sometimes the steam is more valuable than the electricity if the unit is supplying steam to a nearby facility (say a refinery or other process plant) can also be huge. And, a LOT of people say things they thought they understood without really understanding them before they "repeat" what they think they heard (but didn't really understand).

If there is a contract to provide a specific range of calorific value of fuel, is there a clause for what happens if the fuel is out of the specified range? Are there penalties? Is there a clause that the supplier must notify the purchaser if the calorific value is not within the specified range? There can be all kinds of possibilities, but it's probably best to obtain advice from a qualified individual or firm who can ask the proper questions and work with a legal department or lawyer to understand the contract and help everyone to obtain the best and most correct information possible.
At the time of specification of the gas turbine, the fuel control system will be set up to a specified CV (range). If the CV gets too high, it can cause a control problem with gas fuel control valves and how they will react.

Control problems for sure, damage to hot gas parts, I would doubt it.
If you are going to stay at the higher CV, then the control system can be recalibrated to adjust to that CV value.
You need to consult the turbine manufacturer directly.

The higher caloric value of the gas generally means less gas needed for a given power developed, so you have better efficiency near the design rating.
Mr d,

what about this?

For lower LHV gas fuel, more mass of fuel must be put into the engine, and thus it produces MORE power.

For higher LHV gas fuel, less mass of fuel must be put into the engine, and thus it produces LESS power.

>The higher caloric value of the gas generally means less gas
>needed for a given power developed, so you have better
>efficiency near the design rating.


What I believed that higher calorific value of fuel will generate more heat in gas turbine during combustion and will produced more torque on shaft and electric power. Therefore, control system is expected to response and limit the fuel flow.

I think there is no any system that looks at the fuel control valve open position feedback only to regulate the power/energy flow. As long as machine combustion temperature remain within specification how higher calorific value could increase the hot gas path maintenance interval?

When a GE-design heavy duty gas turbine is being started (during initial firing attempt to establish flame) the fuel control valve is directed to open to some position and the resulting firing and exhaust temperature "is what it is". (Of course if the exhaust temperature is TOO high, exhaust temperature control will try to limit the temperature.)

On a GE-design heavy duty gas turbine, shortly after flame is established, the fuel control valve is again directed to move to some position and the resulting firing and exhaust temperature "is what it is". (Again, if the exhaust temperature is TOO high, exhaust temperature control will try to limit the fuel to reduce the temperature.)

On most newer GE-design gas turbine control systems, once flame has been established and warm-up is complete the fuel is ramped up to maintain a desired acceleration rate (most units, anyway; I believe some F-class units use the starting means (the LCI or Static Starter (Variable Frequency Drive) to control actual acceleration rate up to near rated speed).

Once the unit is synchronized and loading starts, the control system (including the fuel control valves (including the SRV (Stop-Ratio Valve)) are designed for a fairly specific range of calorific values. The control system is configured for a certain range of calorific values, and if the calorific value exceeds that range then at Part Load it is conceivable the resulting firing temperature (the <b><i>ACTUAL</b></i> firing temperature--<b>NOT</b> the <b>calculated</b> firing temperature) of the hot combustion gases in the combustors and entering the first stage turbine nozzles could be higher than design for a particular valve position and air flow (IGV angle) and could result in damage to nozzles, liners, transition pieces, etc., for lower loads and air flows.

You are correct, though, that once the maximum allowable exhaust temperature is reached the control system would react to limit further exhaust temperature increases--and with a higher calorific value fuel gas that could occur at some load other than rated. And, that could present operational problems--especially for complicated units operating in combined cycle mode with very stringent requirements for temperatures and loads.

Of course, I'm referring primarily to GE-design heavy duty gas turbines with DLN combustion systems, which are just a little touchy when it comes to fuel heating values. But, I believe most of the physical "damage" could be caused by starting and warm-up and low load operation. I once worked on an F-class unit which experienced lack of purge air during starting and acceleration and with only one fired start and about five minutes of operation at FSNL two fuel nozzles in each of the 14 combustors were damaged and required replacement. It doesn't take much for DLN combustion hardware to get damaged.

But, really, we are all just speculating here--some based on past experience which may or may not be relevant, and others just speculating based on assumptions and "feelings." I doubt we'll hear back from the original poster about this.

As for torque control by a GE-design heavy duty gas turbine, I've never seen torque be directly monitored or controlled--except in special monitoring circumstances with special equipment installed just for data-gathering--and even then, the information wasn't used for controlling the fuel or the load.